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…		…
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
…		…
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	42	}
…		…
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
84	=head2 FEATURES	98	=head2 FEATURES
85		99
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
96		111
97	It also is quite fast (see this	112	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	114	for example).
100		115
…		…
103	Libev is very configurable. In this manual the default (and most common)	118	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	119	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	120	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	121	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	122	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	123	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	124	this argument.
110		125
111	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
112		127
113	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
117	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
118	it, you should treat it as some floating point value. Unlike the name	133	on it, you should treat it as some floating point value. Unlike the name
119	component C<stamp> might indicate, it is also used for time differences	134	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	135	throughout libev.
121		136
122	=head1 ERROR HANDLING	137	=head1 ERROR HANDLING
123		138
…		…
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	229	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
215	recommended ones.	230	recommended ones.
216		231
217	See the description of C<ev_embed> watchers for more info.	232	See the description of C<ev_embed> watchers for more info.
218		233
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
220		235
221	Sets the allocation function to use (the prototype is similar - the	236	Sets the allocation function to use (the prototype is similar - the
222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	237	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
223	used to allocate and free memory (no surprises here). If it returns zero	238	used to allocate and free memory (no surprises here). If it returns zero
224	when memory needs to be allocated (C<size != 0>), the library might abort	239	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	265	}
251		266
252	...	267	...
253	ev_set_allocator (persistent_realloc);	268	ev_set_allocator (persistent_realloc);
254		269
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
256		271
257	Set the callback function to call on a retryable system call error (such	272	Set the callback function to call on a retryable system call error (such
258	as failed select, poll, epoll_wait). The message is a printable string	273	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	274	indicating the system call or subsystem causing the problem. If this
260	callback is set, then libev will expect it to remedy the situation, no	275	callback is set, then libev will expect it to remedy the situation, no
…		…
276		291
277	=back	292	=back
278		293
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		295
281	An event loop is described by a C<struct ev_loop *>. The library knows two	296	An event loop is described by a C<struct ev_loop *> (the C<struct>
282	types of such loops, the I<default> loop, which supports signals and child	297	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	298	I<function>).
		299
		300	The library knows two types of such loops, the I<default> loop, which
		301	supports signals and child events, and dynamically created loops which do
		302	not.
284		303
285	=over 4	304	=over 4
286		305
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		307
…		…
294	If you don't know what event loop to use, use the one returned from this	313	If you don't know what event loop to use, use the one returned from this
295	function.	314	function.
296		315
297	Note that this function is I<not> thread-safe, so if you want to use it	316	Note that this function is I<not> thread-safe, so if you want to use it
298	from multiple threads, you have to lock (note also that this is unlikely,	317	from multiple threads, you have to lock (note also that this is unlikely,
299	as loops cannot bes hared easily between threads anyway).	318	as loops cannot be shared easily between threads anyway).
300		319
301	The default loop is the only loop that can handle C<ev_signal> and	320	The default loop is the only loop that can handle C<ev_signal> and
302	C<ev_child> watchers, and to do this, it always registers a handler	321	C<ev_child> watchers, and to do this, it always registers a handler
303	for C<SIGCHLD>. If this is a problem for your application you can either	322	for C<SIGCHLD>. If this is a problem for your application you can either
304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	323	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
344	flag.	363	flag.
345		364
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	366	environment variable.
348		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	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
		372	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.
		374
		375	=item C<EVFLAG_NOSIGNALFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
		382
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		384
351	This is your standard select(2) backend. Not I<completely> standard, as	385	This is your standard select(2) backend. Not I<completely> standard, as
352	libev tries to roll its own fd_set with no limits on the number of fds,	386	libev tries to roll its own fd_set with no limits on the number of fds,
353	but if that fails, expect a fairly low limit on the number of fds when	387	but if that fails, expect a fairly low limit on the number of fds when
…		…
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		415
382	For few fds, this backend is a bit little slower than poll and select,	416	For few fds, this backend is a bit little slower than poll and select,
383	but it scales phenomenally better. While poll and select usually scale	417	but it scales phenomenally better. While poll and select usually scale
384	like O(total_fds) where n is the total number of fds (or the highest fd),	418	like O(total_fds) where n is the total number of fds (or the highest fd),
385	epoll scales either O(1) or O(active_fds). The epoll design has a number	419	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	420
387	cases and requiring a system call per fd change, no fork support and bad	421	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	422	of the more advanced event mechanisms: mere annoyances include silently
		423	dropping file descriptors, requiring a system call per change per file
		424	descriptor (and unnecessary guessing of parameters), problems with dup and
		425	so on. The biggest issue is fork races, however - if a program forks then
		426	I<both> parent and child process have to recreate the epoll set, which can
		427	take considerable time (one syscall per file descriptor) and is of course
		428	hard to detect.
		429
		430	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		431	of course I<doesn't>, and epoll just loves to report events for totally
		432	I<different> file descriptors (even already closed ones, so one cannot
		433	even remove them from the set) than registered in the set (especially
		434	on SMP systems). Libev tries to counter these spurious notifications by
		435	employing an additional generation counter and comparing that against the
		436	events to filter out spurious ones, recreating the set when required.
389		437
390	While stopping, setting and starting an I/O watcher in the same iteration	438	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	439	will result in some caching, there is still a system call per such
392	(because the fd could point to a different file description now), so its	440	incident (because the same I<file descriptor> could point to a different
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	441	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	442	file descriptors might not work very well if you register events for both
395		443	file descriptors.
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399		444
400	Best performance from this backend is achieved by not unregistering all	445	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	446	watchers for a file descriptor until it has been closed, if possible,
402	i.e. keep at least one watcher active per fd at all times. Stopping and	447	i.e. keep at least one watcher active per fd at all times. Stopping and
403	starting a watcher (without re-setting it) also usually doesn't cause	448	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	449	extra overhead. A fork can both result in spurious notifications as well
		450	as in libev having to destroy and recreate the epoll object, which can
		451	take considerable time and thus should be avoided.
		452
		453	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		454	faster than epoll for maybe up to a hundred file descriptors, depending on
		455	the usage. So sad.
405		456
406	While nominally embeddable in other event loops, this feature is broken in	457	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	458	all kernel versions tested so far.
408		459
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	460	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	461	C<EVBACKEND_POLL>.
411		462
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	463	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		464
414	Kqueue deserves special mention, as at the time of this writing, it was	465	Kqueue deserves special mention, as at the time of this writing, it
415	broken on all BSDs except NetBSD (usually it doesn't work reliably with	466	was broken on all BSDs except NetBSD (usually it doesn't work reliably
416	anything but sockets and pipes, except on Darwin, where of course it's	467	with anything but sockets and pipes, except on Darwin, where of course
417	completely useless). For this reason it's not being "auto-detected" unless	468	it's completely useless). Unlike epoll, however, whose brokenness
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	469	is by design, these kqueue bugs can (and eventually will) be fixed
419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	470	without API changes to existing programs. For this reason it's not being
		471	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		472	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		473	system like NetBSD.
420		474
421	You still can embed kqueue into a normal poll or select backend and use it	475	You still can embed kqueue into a normal poll or select backend and use it
422	only for sockets (after having made sure that sockets work with kqueue on	476	only for sockets (after having made sure that sockets work with kqueue on
423	the target platform). See C<ev_embed> watchers for more info.	477	the target platform). See C<ev_embed> watchers for more info.
424		478
425	It scales in the same way as the epoll backend, but the interface to the	479	It scales in the same way as the epoll backend, but the interface to the
426	kernel is more efficient (which says nothing about its actual speed, of	480	kernel is more efficient (which says nothing about its actual speed, of
427	course). While stopping, setting and starting an I/O watcher does never	481	course). While stopping, setting and starting an I/O watcher does never
428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	482	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
429	two event changes per incident. Support for C<fork ()> is very bad and it	483	two event changes per incident. Support for C<fork ()> is very bad (but
430	drops fds silently in similarly hard-to-detect cases.	484	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		485	cases
431		486
432	This backend usually performs well under most conditions.	487	This backend usually performs well under most conditions.
433		488
434	While nominally embeddable in other event loops, this doesn't work	489	While nominally embeddable in other event loops, this doesn't work
435	everywhere, so you might need to test for this. And since it is broken	490	everywhere, so you might need to test for this. And since it is broken
436	almost everywhere, you should only use it when you have a lot of sockets	491	almost everywhere, you should only use it when you have a lot of sockets
437	(for which it usually works), by embedding it into another event loop	492	(for which it usually works), by embedding it into another event loop
438	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,	493	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
439	using it only for sockets.	494	also broken on OS X)) and, did I mention it, using it only for sockets.
440		495
441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	496	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
442	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	497	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
443	C<NOTE_EOF>.	498	C<NOTE_EOF>.
444		499
…		…
464	might perform better.	519	might perform better.
465		520
466	On the positive side, with the exception of the spurious readiness	521	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	522	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	523	in all tests and is fully embeddable, which is a rare feat among the
469	OS-specific backends.	524	OS-specific backends (I vastly prefer correctness over speed hacks).
470		525
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	526	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	527	C<EVBACKEND_POLL>.
473		528
474	=item C<EVBACKEND_ALL>	529	=item C<EVBACKEND_ALL>
…		…
479		534
480	It is definitely not recommended to use this flag.	535	It is definitely not recommended to use this flag.
481		536
482	=back	537	=back
483		538
484	If one or more of these are or'ed into the flags value, then only these	539	If one or more of the backend flags are or'ed into the flags value,
485	backends will be tried (in the reverse order as listed here). If none are	540	then only these backends will be tried (in the reverse order as listed
486	specified, all backends in C<ev_recommended_backends ()> will be tried.	541	here). If none are specified, all backends in C<ev_recommended_backends
		542	()> will be tried.
487		543
488	Example: This is the most typical usage.	544	Example: This is the most typical usage.
489		545
490	if (!ev_default_loop (0))	546	if (!ev_default_loop (0))
491	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	547	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	583	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	584	calling this function, or cope with the fact afterwards (which is usually
529	the easiest thing, you can just ignore the watchers and/or C<free ()> them	585	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	586	for example).
531		587
532	Note that certain global state, such as signal state, will not be freed by	588	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	589	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	590	as signal and child watchers) would need to be stopped manually.
535		591
536	In general it is not advisable to call this function except in the	592	In general it is not advisable to call this function except in the
537	rare occasion where you really need to free e.g. the signal handling	593	rare occasion where you really need to free e.g. the signal handling
538	pipe fds. If you need dynamically allocated loops it is better to use	594	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	595	C<ev_loop_new> and C<ev_loop_destroy>.
540		596
541	=item ev_loop_destroy (loop)	597	=item ev_loop_destroy (loop)
542		598
543	Like C<ev_default_destroy>, but destroys an event loop created by an	599	Like C<ev_default_destroy>, but destroys an event loop created by an
544	earlier call to C<ev_loop_new>.	600	earlier call to C<ev_loop_new>.
…		…
582		638
583	This value can sometimes be useful as a generation counter of sorts (it	639	This value can sometimes be useful as a generation counter of sorts (it
584	"ticks" the number of loop iterations), as it roughly corresponds with	640	"ticks" the number of loop iterations), as it roughly corresponds with
585	C<ev_prepare> and C<ev_check> calls.	641	C<ev_prepare> and C<ev_check> calls.
586		642
		643	=item unsigned int ev_loop_depth (loop)
		644
		645	Returns the number of times C<ev_loop> was entered minus the number of
		646	times C<ev_loop> was exited, in other words, the recursion depth.
		647
		648	Outside C<ev_loop>, this number is zero. In a callback, this number is
		649	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		650	in which case it is higher.
		651
		652	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		653	etc.), doesn't count as exit.
		654
587	=item unsigned int ev_backend (loop)	655	=item unsigned int ev_backend (loop)
588		656
589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	657	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
590	use.	658	use.
591		659
…		…
605		673
606	This function is rarely useful, but when some event callback runs for a	674	This function is rarely useful, but when some event callback runs for a
607	very long time without entering the event loop, updating libev's idea of	675	very long time without entering the event loop, updating libev's idea of
608	the current time is a good idea.	676	the current time is a good idea.
609		677
610	See also "The special problem of time updates" in the C<ev_timer> section.	678	See also L<The special problem of time updates> in the C<ev_timer> section.
		679
		680	=item ev_suspend (loop)
		681
		682	=item ev_resume (loop)
		683
		684	These two functions suspend and resume a loop, for use when the loop is
		685	not used for a while and timeouts should not be processed.
		686
		687	A typical use case would be an interactive program such as a game: When
		688	the user presses C<^Z> to suspend the game and resumes it an hour later it
		689	would be best to handle timeouts as if no time had actually passed while
		690	the program was suspended. This can be achieved by calling C<ev_suspend>
		691	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		692	C<ev_resume> directly afterwards to resume timer processing.
		693
		694	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		695	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		696	will be rescheduled (that is, they will lose any events that would have
		697	occured while suspended).
		698
		699	After calling C<ev_suspend> you B<must not> call I<any> function on the
		700	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		701	without a previous call to C<ev_suspend>.
		702
		703	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		704	event loop time (see C<ev_now_update>).
611		705
612	=item ev_loop (loop, int flags)	706	=item ev_loop (loop, int flags)
613		707
614	Finally, this is it, the event handler. This function usually is called	708	Finally, this is it, the event handler. This function usually is called
615	after you initialised all your watchers and you want to start handling	709	after you have initialised all your watchers and you want to start
616	events.	710	handling events.
617		711
618	If the flags argument is specified as C<0>, it will not return until	712	If the flags argument is specified as C<0>, it will not return until
619	either no event watchers are active anymore or C<ev_unloop> was called.	713	either no event watchers are active anymore or C<ev_unloop> was called.
620		714
621	Please note that an explicit C<ev_unloop> is usually better than	715	Please note that an explicit C<ev_unloop> is usually better than
…		…
631	the loop.	725	the loop.
632		726
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	727	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
634	necessary) and will handle those and any already outstanding ones. It	728	necessary) and will handle those and any already outstanding ones. It
635	will block your process until at least one new event arrives (which could	729	will block your process until at least one new event arrives (which could
636	be an event internal to libev itself, so there is no guarentee that a	730	be an event internal to libev itself, so there is no guarantee that a
637	user-registered callback will be called), and will return after one	731	user-registered callback will be called), and will return after one
638	iteration of the loop.	732	iteration of the loop.
639		733
640	This is useful if you are waiting for some external event in conjunction	734	This is useful if you are waiting for some external event in conjunction
641	with something not expressible using other libev watchers (i.e. "roll your	735	with something not expressible using other libev watchers (i.e. "roll your
…		…
685	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	779	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	780	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
687		781
688	This "unloop state" will be cleared when entering C<ev_loop> again.	782	This "unloop state" will be cleared when entering C<ev_loop> again.
689		783
		784	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		785
690	=item ev_ref (loop)	786	=item ev_ref (loop)
691		787
692	=item ev_unref (loop)	788	=item ev_unref (loop)
693		789
694	Ref/unref can be used to add or remove a reference count on the event	790	Ref/unref can be used to add or remove a reference count on the event
…		…
697		793
698	If you have a watcher you never unregister that should not keep C<ev_loop>	794	If you have a watcher you never unregister that should not keep C<ev_loop>
699	from returning, call ev_unref() after starting, and ev_ref() before	795	from returning, call ev_unref() after starting, and ev_ref() before
700	stopping it.	796	stopping it.
701		797
702	As an example, libev itself uses this for its internal signal pipe: It is	798	As an example, libev itself uses this for its internal signal pipe: It
703	not visible to the libev user and should not keep C<ev_loop> from exiting	799	is not visible to the libev user and should not keep C<ev_loop> from
704	if no event watchers registered by it are active. It is also an excellent	800	exiting if no event watchers registered by it are active. It is also an
705	way to do this for generic recurring timers or from within third-party	801	excellent way to do this for generic recurring timers or from within
706	libraries. Just remember to I<unref after start> and I<ref before stop>	802	third-party libraries. Just remember to I<unref after start> and I<ref
707	(but only if the watcher wasn't active before, or was active before,	803	before stop> (but only if the watcher wasn't active before, or was active
708	respectively).	804	before, respectively. Note also that libev might stop watchers itself
		805	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		806	in the callback).
709		807
710	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	808	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
711	running when nothing else is active.	809	running when nothing else is active.
712		810
713	struct ev_signal exitsig;	811	ev_signal exitsig;
714	ev_signal_init (&exitsig, sig_cb, SIGINT);	812	ev_signal_init (&exitsig, sig_cb, SIGINT);
715	ev_signal_start (loop, &exitsig);	813	ev_signal_start (loop, &exitsig);
716	evf_unref (loop);	814	evf_unref (loop);
717		815
718	Example: For some weird reason, unregister the above signal handler again.	816	Example: For some weird reason, unregister the above signal handler again.
…		…
742		840
743	By setting a higher I<io collect interval> you allow libev to spend more	841	By setting a higher I<io collect interval> you allow libev to spend more
744	time collecting I/O events, so you can handle more events per iteration,	842	time collecting I/O events, so you can handle more events per iteration,
745	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	843	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
746	C<ev_timer>) will be not affected. Setting this to a non-null value will	844	C<ev_timer>) will be not affected. Setting this to a non-null value will
747	introduce an additional C<ev_sleep ()> call into most loop iterations.	845	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		846	sleep time ensures that libev will not poll for I/O events more often then
		847	once per this interval, on average.
748		848
749	Likewise, by setting a higher I<timeout collect interval> you allow libev	849	Likewise, by setting a higher I<timeout collect interval> you allow libev
750	to spend more time collecting timeouts, at the expense of increased	850	to spend more time collecting timeouts, at the expense of increased
751	latency/jitter/inexactness (the watcher callback will be called	851	latency/jitter/inexactness (the watcher callback will be called
752	later). C<ev_io> watchers will not be affected. Setting this to a non-null	852	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
754		854
755	Many (busy) programs can usually benefit by setting the I/O collect	855	Many (busy) programs can usually benefit by setting the I/O collect
756	interval to a value near C<0.1> or so, which is often enough for	856	interval to a value near C<0.1> or so, which is often enough for
757	interactive servers (of course not for games), likewise for timeouts. It	857	interactive servers (of course not for games), likewise for timeouts. It
758	usually doesn't make much sense to set it to a lower value than C<0.01>,	858	usually doesn't make much sense to set it to a lower value than C<0.01>,
759	as this approaches the timing granularity of most systems.	859	as this approaches the timing granularity of most systems. Note that if
		860	you do transactions with the outside world and you can't increase the
		861	parallelity, then this setting will limit your transaction rate (if you
		862	need to poll once per transaction and the I/O collect interval is 0.01,
		863	then you can't do more than 100 transations per second).
760		864
761	Setting the I<timeout collect interval> can improve the opportunity for	865	Setting the I<timeout collect interval> can improve the opportunity for
762	saving power, as the program will "bundle" timer callback invocations that	866	saving power, as the program will "bundle" timer callback invocations that
763	are "near" in time together, by delaying some, thus reducing the number of	867	are "near" in time together, by delaying some, thus reducing the number of
764	times the process sleeps and wakes up again. Another useful technique to	868	times the process sleeps and wakes up again. Another useful technique to
765	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	869	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
766	they fire on, say, one-second boundaries only.	870	they fire on, say, one-second boundaries only.
767		871
		872	Example: we only need 0.1s timeout granularity, and we wish not to poll
		873	more often than 100 times per second:
		874
		875	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		876	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		877
		878	=item ev_invoke_pending (loop)
		879
		880	This call will simply invoke all pending watchers while resetting their
		881	pending state. Normally, C<ev_loop> does this automatically when required,
		882	but when overriding the invoke callback this call comes handy.
		883
		884	=item int ev_pending_count (loop)
		885
		886	Returns the number of pending watchers - zero indicates that no watchers
		887	are pending.
		888
		889	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		890
		891	This overrides the invoke pending functionality of the loop: Instead of
		892	invoking all pending watchers when there are any, C<ev_loop> will call
		893	this callback instead. This is useful, for example, when you want to
		894	invoke the actual watchers inside another context (another thread etc.).
		895
		896	If you want to reset the callback, use C<ev_invoke_pending> as new
		897	callback.
		898
		899	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		900
		901	Sometimes you want to share the same loop between multiple threads. This
		902	can be done relatively simply by putting mutex_lock/unlock calls around
		903	each call to a libev function.
		904
		905	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		906	wait for it to return. One way around this is to wake up the loop via
		907	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		908	and I<acquire> callbacks on the loop.
		909
		910	When set, then C<release> will be called just before the thread is
		911	suspended waiting for new events, and C<acquire> is called just
		912	afterwards.
		913
		914	Ideally, C<release> will just call your mutex_unlock function, and
		915	C<acquire> will just call the mutex_lock function again.
		916
		917	While event loop modifications are allowed between invocations of
		918	C<release> and C<acquire> (that's their only purpose after all), no
		919	modifications done will affect the event loop, i.e. adding watchers will
		920	have no effect on the set of file descriptors being watched, or the time
		921	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		922	to take note of any changes you made.
		923
		924	In theory, threads executing C<ev_loop> will be async-cancel safe between
		925	invocations of C<release> and C<acquire>.
		926
		927	See also the locking example in the C<THREADS> section later in this
		928	document.
		929
		930	=item ev_set_userdata (loop, void *data)
		931
		932	=item ev_userdata (loop)
		933
		934	Set and retrieve a single C<void *> associated with a loop. When
		935	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		936	C<0.>
		937
		938	These two functions can be used to associate arbitrary data with a loop,
		939	and are intended solely for the C<invoke_pending_cb>, C<release> and
		940	C<acquire> callbacks described above, but of course can be (ab-)used for
		941	any other purpose as well.
		942
768	=item ev_loop_verify (loop)	943	=item ev_loop_verify (loop)
769		944
770	This function only does something when C<EV_VERIFY> support has been	945	This function only does something when C<EV_VERIFY> support has been
771	compiled in. which is the default for non-minimal builds. It tries to go	946	compiled in, which is the default for non-minimal builds. It tries to go
772	through all internal structures and checks them for validity. If anything	947	through all internal structures and checks them for validity. If anything
773	is found to be inconsistent, it will print an error message to standard	948	is found to be inconsistent, it will print an error message to standard
774	error and call C<abort ()>.	949	error and call C<abort ()>.
775		950
776	This can be used to catch bugs inside libev itself: under normal	951	This can be used to catch bugs inside libev itself: under normal
…		…
780	=back	955	=back
781		956
782		957
783	=head1 ANATOMY OF A WATCHER	958	=head1 ANATOMY OF A WATCHER
784		959
		960	In the following description, uppercase C<TYPE> in names stands for the
		961	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		962	watchers and C<ev_io_start> for I/O watchers.
		963
785	A watcher is a structure that you create and register to record your	964	A watcher is a structure that you create and register to record your
786	interest in some event. For instance, if you want to wait for STDIN to	965	interest in some event. For instance, if you want to wait for STDIN to
787	become readable, you would create an C<ev_io> watcher for that:	966	become readable, you would create an C<ev_io> watcher for that:
788		967
789	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	968	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
790	{	969	{
791	ev_io_stop (w);	970	ev_io_stop (w);
792	ev_unloop (loop, EVUNLOOP_ALL);	971	ev_unloop (loop, EVUNLOOP_ALL);
793	}	972	}
794		973
795	struct ev_loop *loop = ev_default_loop (0);	974	struct ev_loop *loop = ev_default_loop (0);
		975
796	struct ev_io stdin_watcher;	976	ev_io stdin_watcher;
		977
797	ev_init (&stdin_watcher, my_cb);	978	ev_init (&stdin_watcher, my_cb);
798	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	979	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
799	ev_io_start (loop, &stdin_watcher);	980	ev_io_start (loop, &stdin_watcher);
		981
800	ev_loop (loop, 0);	982	ev_loop (loop, 0);
801		983
802	As you can see, you are responsible for allocating the memory for your	984	As you can see, you are responsible for allocating the memory for your
803	watcher structures (and it is usually a bad idea to do this on the stack,	985	watcher structures (and it is I<usually> a bad idea to do this on the
804	although this can sometimes be quite valid).	986	stack).
		987
		988	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		989	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
805		990
806	Each watcher structure must be initialised by a call to C<ev_init	991	Each watcher structure must be initialised by a call to C<ev_init
807	(watcher *, callback)>, which expects a callback to be provided. This	992	(watcher *, callback)>, which expects a callback to be provided. This
808	callback gets invoked each time the event occurs (or, in the case of I/O	993	callback gets invoked each time the event occurs (or, in the case of I/O
809	watchers, each time the event loop detects that the file descriptor given	994	watchers, each time the event loop detects that the file descriptor given
810	is readable and/or writable).	995	is readable and/or writable).
811		996
812	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	997	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
813	with arguments specific to this watcher type. There is also a macro	998	macro to configure it, with arguments specific to the watcher type. There
814	to combine initialisation and setting in one call: C<< ev_<type>_init	999	is also a macro to combine initialisation and setting in one call: C<<
815	(watcher *, callback, ...) >>.	1000	ev_TYPE_init (watcher *, callback, ...) >>.
816		1001
817	To make the watcher actually watch out for events, you have to start it	1002	To make the watcher actually watch out for events, you have to start it
818	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1003	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
819	*) >>), and you can stop watching for events at any time by calling the	1004	*) >>), and you can stop watching for events at any time by calling the
820	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1005	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
821		1006
822	As long as your watcher is active (has been started but not stopped) you	1007	As long as your watcher is active (has been started but not stopped) you
823	must not touch the values stored in it. Most specifically you must never	1008	must not touch the values stored in it. Most specifically you must never
824	reinitialise it or call its C<set> macro.	1009	reinitialise it or call its C<ev_TYPE_set> macro.
825		1010
826	Each and every callback receives the event loop pointer as first, the	1011	Each and every callback receives the event loop pointer as first, the
827	registered watcher structure as second, and a bitset of received events as	1012	registered watcher structure as second, and a bitset of received events as
828	third argument.	1013	third argument.
829		1014
…		…
887		1072
888	=item C<EV_ASYNC>	1073	=item C<EV_ASYNC>
889		1074
890	The given async watcher has been asynchronously notified (see C<ev_async>).	1075	The given async watcher has been asynchronously notified (see C<ev_async>).
891		1076
		1077	=item C<EV_CUSTOM>
		1078
		1079	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1080	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1081
892	=item C<EV_ERROR>	1082	=item C<EV_ERROR>
893		1083
894	An unspecified error has occurred, the watcher has been stopped. This might	1084	An unspecified error has occurred, the watcher has been stopped. This might
895	happen because the watcher could not be properly started because libev	1085	happen because the watcher could not be properly started because libev
896	ran out of memory, a file descriptor was found to be closed or any other	1086	ran out of memory, a file descriptor was found to be closed or any other
		1087	problem. Libev considers these application bugs.
		1088
897	problem. You best act on it by reporting the problem and somehow coping	1089	You best act on it by reporting the problem and somehow coping with the
898	with the watcher being stopped.	1090	watcher being stopped. Note that well-written programs should not receive
		1091	an error ever, so when your watcher receives it, this usually indicates a
		1092	bug in your program.
899		1093
900	Libev will usually signal a few "dummy" events together with an error, for	1094	Libev will usually signal a few "dummy" events together with an error, for
901	example it might indicate that a fd is readable or writable, and if your	1095	example it might indicate that a fd is readable or writable, and if your
902	callbacks is well-written it can just attempt the operation and cope with	1096	callbacks is well-written it can just attempt the operation and cope with
903	the error from read() or write(). This will not work in multi-threaded	1097	the error from read() or write(). This will not work in multi-threaded
…		…
906		1100
907	=back	1101	=back
908		1102
909	=head2 GENERIC WATCHER FUNCTIONS	1103	=head2 GENERIC WATCHER FUNCTIONS
910		1104
911	In the following description, C<TYPE> stands for the watcher type,
912	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
913
914	=over 4	1105	=over 4
915		1106
916	=item C<ev_init> (ev_TYPE *watcher, callback)	1107	=item C<ev_init> (ev_TYPE *watcher, callback)
917		1108
918	This macro initialises the generic portion of a watcher. The contents	1109	This macro initialises the generic portion of a watcher. The contents
…		…
923	which rolls both calls into one.	1114	which rolls both calls into one.
924		1115
925	You can reinitialise a watcher at any time as long as it has been stopped	1116	You can reinitialise a watcher at any time as long as it has been stopped
926	(or never started) and there are no pending events outstanding.	1117	(or never started) and there are no pending events outstanding.
927		1118
928	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1119	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
929	int revents)>.	1120	int revents)>.
930		1121
931	Example: Initialise an C<ev_io> watcher in two steps.	1122	Example: Initialise an C<ev_io> watcher in two steps.
932		1123
933	ev_io w;	1124	ev_io w;
…		…
967		1158
968	ev_io_start (EV_DEFAULT_UC, &w);	1159	ev_io_start (EV_DEFAULT_UC, &w);
969		1160
970	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1161	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
971		1162
972	Stops the given watcher again (if active) and clears the pending	1163	Stops the given watcher if active, and clears the pending status (whether
		1164	the watcher was active or not).
		1165
973	status. It is possible that stopped watchers are pending (for example,	1166	It is possible that stopped watchers are pending - for example,
974	non-repeating timers are being stopped when they become pending), but	1167	non-repeating timers are being stopped when they become pending - but
975	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1168	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
976	you want to free or reuse the memory used by the watcher it is therefore a	1169	pending. If you want to free or reuse the memory used by the watcher it is
977	good idea to always call its C<ev_TYPE_stop> function.	1170	therefore a good idea to always call its C<ev_TYPE_stop> function.
978		1171
979	=item bool ev_is_active (ev_TYPE *watcher)	1172	=item bool ev_is_active (ev_TYPE *watcher)
980		1173
981	Returns a true value iff the watcher is active (i.e. it has been started	1174	Returns a true value iff the watcher is active (i.e. it has been started
982	and not yet been stopped). As long as a watcher is active you must not modify	1175	and not yet been stopped). As long as a watcher is active you must not modify
…		…
1008	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1201	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1009	(default: C<-2>). Pending watchers with higher priority will be invoked	1202	(default: C<-2>). Pending watchers with higher priority will be invoked
1010	before watchers with lower priority, but priority will not keep watchers	1203	before watchers with lower priority, but priority will not keep watchers
1011	from being executed (except for C<ev_idle> watchers).	1204	from being executed (except for C<ev_idle> watchers).
1012		1205
1013	This means that priorities are I<only> used for ordering callback
1014	invocation after new events have been received. This is useful, for
1015	example, to reduce latency after idling, or more often, to bind two
1016	watchers on the same event and make sure one is called first.
1017
1018	If you need to suppress invocation when higher priority events are pending	1206	If you need to suppress invocation when higher priority events are pending
1019	you need to look at C<ev_idle> watchers, which provide this functionality.	1207	you need to look at C<ev_idle> watchers, which provide this functionality.
1020		1208
1021	You I<must not> change the priority of a watcher as long as it is active or	1209	You I<must not> change the priority of a watcher as long as it is active or
1022	pending.	1210	pending.
1023		1211
		1212	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1213	fine, as long as you do not mind that the priority value you query might
		1214	or might not have been clamped to the valid range.
		1215
1024	The default priority used by watchers when no priority has been set is	1216	The default priority used by watchers when no priority has been set is
1025	always C<0>, which is supposed to not be too high and not be too low :).	1217	always C<0>, which is supposed to not be too high and not be too low :).
1026		1218
1027	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1219	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1028	fine, as long as you do not mind that the priority value you query might	1220	priorities.
1029	or might not have been adjusted to be within valid range.
1030		1221
1031	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1222	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1032		1223
1033	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1224	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1034	C<loop> nor C<revents> need to be valid as long as the watcher callback	1225	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1056	member, you can also "subclass" the watcher type and provide your own	1247	member, you can also "subclass" the watcher type and provide your own
1057	data:	1248	data:
1058		1249
1059	struct my_io	1250	struct my_io
1060	{	1251	{
1061	struct ev_io io;	1252	ev_io io;
1062	int otherfd;	1253	int otherfd;
1063	void *somedata;	1254	void *somedata;
1064	struct whatever *mostinteresting;	1255	struct whatever *mostinteresting;
1065	};	1256	};
1066		1257
…		…
1069	ev_io_init (&w.io, my_cb, fd, EV_READ);	1260	ev_io_init (&w.io, my_cb, fd, EV_READ);
1070		1261
1071	And since your callback will be called with a pointer to the watcher, you	1262	And since your callback will be called with a pointer to the watcher, you
1072	can cast it back to your own type:	1263	can cast it back to your own type:
1073		1264
1074	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1265	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1075	{	1266	{
1076	struct my_io *w = (struct my_io *)w_;	1267	struct my_io *w = (struct my_io *)w_;
1077	...	1268	...
1078	}	1269	}
1079		1270
…		…
1097	programmers):	1288	programmers):
1098		1289
1099	#include <stddef.h>	1290	#include <stddef.h>
1100		1291
1101	static void	1292	static void
1102	t1_cb (EV_P_ struct ev_timer *w, int revents)	1293	t1_cb (EV_P_ ev_timer *w, int revents)
1103	{	1294	{
1104	struct my_biggy big = (struct my_biggy *	1295	struct my_biggy big = (struct my_biggy *)
1105	(((char *)w) - offsetof (struct my_biggy, t1));	1296	(((char *)w) - offsetof (struct my_biggy, t1));
1106	}	1297	}
1107		1298
1108	static void	1299	static void
1109	t2_cb (EV_P_ struct ev_timer *w, int revents)	1300	t2_cb (EV_P_ ev_timer *w, int revents)
1110	{	1301	{
1111	struct my_biggy big = (struct my_biggy *	1302	struct my_biggy big = (struct my_biggy *)
1112	(((char *)w) - offsetof (struct my_biggy, t2));	1303	(((char *)w) - offsetof (struct my_biggy, t2));
1113	}	1304	}
		1305
		1306	=head2 WATCHER PRIORITY MODELS
		1307
		1308	Many event loops support I<watcher priorities>, which are usually small
		1309	integers that influence the ordering of event callback invocation
		1310	between watchers in some way, all else being equal.
		1311
		1312	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1313	description for the more technical details such as the actual priority
		1314	range.
		1315
		1316	There are two common ways how these these priorities are being interpreted
		1317	by event loops:
		1318
		1319	In the more common lock-out model, higher priorities "lock out" invocation
		1320	of lower priority watchers, which means as long as higher priority
		1321	watchers receive events, lower priority watchers are not being invoked.
		1322
		1323	The less common only-for-ordering model uses priorities solely to order
		1324	callback invocation within a single event loop iteration: Higher priority
		1325	watchers are invoked before lower priority ones, but they all get invoked
		1326	before polling for new events.
		1327
		1328	Libev uses the second (only-for-ordering) model for all its watchers
		1329	except for idle watchers (which use the lock-out model).
		1330
		1331	The rationale behind this is that implementing the lock-out model for
		1332	watchers is not well supported by most kernel interfaces, and most event
		1333	libraries will just poll for the same events again and again as long as
		1334	their callbacks have not been executed, which is very inefficient in the
		1335	common case of one high-priority watcher locking out a mass of lower
		1336	priority ones.
		1337
		1338	Static (ordering) priorities are most useful when you have two or more
		1339	watchers handling the same resource: a typical usage example is having an
		1340	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1341	timeouts. Under load, data might be received while the program handles
		1342	other jobs, but since timers normally get invoked first, the timeout
		1343	handler will be executed before checking for data. In that case, giving
		1344	the timer a lower priority than the I/O watcher ensures that I/O will be
		1345	handled first even under adverse conditions (which is usually, but not
		1346	always, what you want).
		1347
		1348	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1349	will only be executed when no same or higher priority watchers have
		1350	received events, they can be used to implement the "lock-out" model when
		1351	required.
		1352
		1353	For example, to emulate how many other event libraries handle priorities,
		1354	you can associate an C<ev_idle> watcher to each such watcher, and in
		1355	the normal watcher callback, you just start the idle watcher. The real
		1356	processing is done in the idle watcher callback. This causes libev to
		1357	continously poll and process kernel event data for the watcher, but when
		1358	the lock-out case is known to be rare (which in turn is rare :), this is
		1359	workable.
		1360
		1361	Usually, however, the lock-out model implemented that way will perform
		1362	miserably under the type of load it was designed to handle. In that case,
		1363	it might be preferable to stop the real watcher before starting the
		1364	idle watcher, so the kernel will not have to process the event in case
		1365	the actual processing will be delayed for considerable time.
		1366
		1367	Here is an example of an I/O watcher that should run at a strictly lower
		1368	priority than the default, and which should only process data when no
		1369	other events are pending:
		1370
		1371	ev_idle idle; // actual processing watcher
		1372	ev_io io; // actual event watcher
		1373
		1374	static void
		1375	io_cb (EV_P_ ev_io *w, int revents)
		1376	{
		1377	// stop the I/O watcher, we received the event, but
		1378	// are not yet ready to handle it.
		1379	ev_io_stop (EV_A_ w);
		1380
		1381	// start the idle watcher to ahndle the actual event.
		1382	// it will not be executed as long as other watchers
		1383	// with the default priority are receiving events.
		1384	ev_idle_start (EV_A_ &idle);
		1385	}
		1386
		1387	static void
		1388	idle_cb (EV_P_ ev_idle *w, int revents)
		1389	{
		1390	// actual processing
		1391	read (STDIN_FILENO, ...);
		1392
		1393	// have to start the I/O watcher again, as
		1394	// we have handled the event
		1395	ev_io_start (EV_P_ &io);
		1396	}
		1397
		1398	// initialisation
		1399	ev_idle_init (&idle, idle_cb);
		1400	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1401	ev_io_start (EV_DEFAULT_ &io);
		1402
		1403	In the "real" world, it might also be beneficial to start a timer, so that
		1404	low-priority connections can not be locked out forever under load. This
		1405	enables your program to keep a lower latency for important connections
		1406	during short periods of high load, while not completely locking out less
		1407	important ones.
1114		1408
1115		1409
1116	=head1 WATCHER TYPES	1410	=head1 WATCHER TYPES
1117		1411
1118	This section describes each watcher in detail, but will not repeat	1412	This section describes each watcher in detail, but will not repeat
…		…
1144	descriptors to non-blocking mode is also usually a good idea (but not	1438	descriptors to non-blocking mode is also usually a good idea (but not
1145	required if you know what you are doing).	1439	required if you know what you are doing).
1146		1440
1147	If you cannot use non-blocking mode, then force the use of a	1441	If you cannot use non-blocking mode, then force the use of a
1148	known-to-be-good backend (at the time of this writing, this includes only	1442	known-to-be-good backend (at the time of this writing, this includes only
1149	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1443	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1444	descriptors for which non-blocking operation makes no sense (such as
		1445	files) - libev doesn't guarentee any specific behaviour in that case.
1150		1446
1151	Another thing you have to watch out for is that it is quite easy to	1447	Another thing you have to watch out for is that it is quite easy to
1152	receive "spurious" readiness notifications, that is your callback might	1448	receive "spurious" readiness notifications, that is your callback might
1153	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1449	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1154	because there is no data. Not only are some backends known to create a	1450	because there is no data. Not only are some backends known to create a
…		…
1249	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1545	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1250	readable, but only once. Since it is likely line-buffered, you could	1546	readable, but only once. Since it is likely line-buffered, you could
1251	attempt to read a whole line in the callback.	1547	attempt to read a whole line in the callback.
1252		1548
1253	static void	1549	static void
1254	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1550	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1255	{	1551	{
1256	ev_io_stop (loop, w);	1552	ev_io_stop (loop, w);
1257	.. read from stdin here (or from w->fd) and handle any I/O errors	1553	.. read from stdin here (or from w->fd) and handle any I/O errors
1258	}	1554	}
1259		1555
1260	...	1556	...
1261	struct ev_loop *loop = ev_default_init (0);	1557	struct ev_loop *loop = ev_default_init (0);
1262	struct ev_io stdin_readable;	1558	ev_io stdin_readable;
1263	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1559	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1264	ev_io_start (loop, &stdin_readable);	1560	ev_io_start (loop, &stdin_readable);
1265	ev_loop (loop, 0);	1561	ev_loop (loop, 0);
1266		1562
1267		1563
…		…
1275	year, it will still time out after (roughly) one hour. "Roughly" because	1571	year, it will still time out after (roughly) one hour. "Roughly" because
1276	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1572	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1277	monotonic clock option helps a lot here).	1573	monotonic clock option helps a lot here).
1278		1574
1279	The callback is guaranteed to be invoked only I<after> its timeout has	1575	The callback is guaranteed to be invoked only I<after> its timeout has
1280	passed, but if multiple timers become ready during the same loop iteration	1576	passed (not I<at>, so on systems with very low-resolution clocks this
1281	then order of execution is undefined.	1577	might introduce a small delay). If multiple timers become ready during the
		1578	same loop iteration then the ones with earlier time-out values are invoked
		1579	before ones of the same priority with later time-out values (but this is
		1580	no longer true when a callback calls C<ev_loop> recursively).
		1581
		1582	=head3 Be smart about timeouts
		1583
		1584	Many real-world problems involve some kind of timeout, usually for error
		1585	recovery. A typical example is an HTTP request - if the other side hangs,
		1586	you want to raise some error after a while.
		1587
		1588	What follows are some ways to handle this problem, from obvious and
		1589	inefficient to smart and efficient.
		1590
		1591	In the following, a 60 second activity timeout is assumed - a timeout that
		1592	gets reset to 60 seconds each time there is activity (e.g. each time some
		1593	data or other life sign was received).
		1594
		1595	=over 4
		1596
		1597	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1598
		1599	This is the most obvious, but not the most simple way: In the beginning,
		1600	start the watcher:
		1601
		1602	ev_timer_init (timer, callback, 60., 0.);
		1603	ev_timer_start (loop, timer);
		1604
		1605	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1606	and start it again:
		1607
		1608	ev_timer_stop (loop, timer);
		1609	ev_timer_set (timer, 60., 0.);
		1610	ev_timer_start (loop, timer);
		1611
		1612	This is relatively simple to implement, but means that each time there is
		1613	some activity, libev will first have to remove the timer from its internal
		1614	data structure and then add it again. Libev tries to be fast, but it's
		1615	still not a constant-time operation.
		1616
		1617	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1618
		1619	This is the easiest way, and involves using C<ev_timer_again> instead of
		1620	C<ev_timer_start>.
		1621
		1622	To implement this, configure an C<ev_timer> with a C<repeat> value
		1623	of C<60> and then call C<ev_timer_again> at start and each time you
		1624	successfully read or write some data. If you go into an idle state where
		1625	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1626	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1627
		1628	That means you can ignore both the C<ev_timer_start> function and the
		1629	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1630	member and C<ev_timer_again>.
		1631
		1632	At start:
		1633
		1634	ev_init (timer, callback);
		1635	timer->repeat = 60.;
		1636	ev_timer_again (loop, timer);
		1637
		1638	Each time there is some activity:
		1639
		1640	ev_timer_again (loop, timer);
		1641
		1642	It is even possible to change the time-out on the fly, regardless of
		1643	whether the watcher is active or not:
		1644
		1645	timer->repeat = 30.;
		1646	ev_timer_again (loop, timer);
		1647
		1648	This is slightly more efficient then stopping/starting the timer each time
		1649	you want to modify its timeout value, as libev does not have to completely
		1650	remove and re-insert the timer from/into its internal data structure.
		1651
		1652	It is, however, even simpler than the "obvious" way to do it.
		1653
		1654	=item 3. Let the timer time out, but then re-arm it as required.
		1655
		1656	This method is more tricky, but usually most efficient: Most timeouts are
		1657	relatively long compared to the intervals between other activity - in
		1658	our example, within 60 seconds, there are usually many I/O events with
		1659	associated activity resets.
		1660
		1661	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1662	but remember the time of last activity, and check for a real timeout only
		1663	within the callback:
		1664
		1665	ev_tstamp last_activity; // time of last activity
		1666
		1667	static void
		1668	callback (EV_P_ ev_timer *w, int revents)
		1669	{
		1670	ev_tstamp now = ev_now (EV_A);
		1671	ev_tstamp timeout = last_activity + 60.;
		1672
		1673	// if last_activity + 60. is older than now, we did time out
		1674	if (timeout < now)
		1675	{
		1676	// timeout occured, take action
		1677	}
		1678	else
		1679	{
		1680	// callback was invoked, but there was some activity, re-arm
		1681	// the watcher to fire in last_activity + 60, which is
		1682	// guaranteed to be in the future, so "again" is positive:
		1683	w->repeat = timeout - now;
		1684	ev_timer_again (EV_A_ w);
		1685	}
		1686	}
		1687
		1688	To summarise the callback: first calculate the real timeout (defined
		1689	as "60 seconds after the last activity"), then check if that time has
		1690	been reached, which means something I<did>, in fact, time out. Otherwise
		1691	the callback was invoked too early (C<timeout> is in the future), so
		1692	re-schedule the timer to fire at that future time, to see if maybe we have
		1693	a timeout then.
		1694
		1695	Note how C<ev_timer_again> is used, taking advantage of the
		1696	C<ev_timer_again> optimisation when the timer is already running.
		1697
		1698	This scheme causes more callback invocations (about one every 60 seconds
		1699	minus half the average time between activity), but virtually no calls to
		1700	libev to change the timeout.
		1701
		1702	To start the timer, simply initialise the watcher and set C<last_activity>
		1703	to the current time (meaning we just have some activity :), then call the
		1704	callback, which will "do the right thing" and start the timer:
		1705
		1706	ev_init (timer, callback);
		1707	last_activity = ev_now (loop);
		1708	callback (loop, timer, EV_TIMEOUT);
		1709
		1710	And when there is some activity, simply store the current time in
		1711	C<last_activity>, no libev calls at all:
		1712
		1713	last_actiivty = ev_now (loop);
		1714
		1715	This technique is slightly more complex, but in most cases where the
		1716	time-out is unlikely to be triggered, much more efficient.
		1717
		1718	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1719	callback :) - just change the timeout and invoke the callback, which will
		1720	fix things for you.
		1721
		1722	=item 4. Wee, just use a double-linked list for your timeouts.
		1723
		1724	If there is not one request, but many thousands (millions...), all
		1725	employing some kind of timeout with the same timeout value, then one can
		1726	do even better:
		1727
		1728	When starting the timeout, calculate the timeout value and put the timeout
		1729	at the I<end> of the list.
		1730
		1731	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1732	the list is expected to fire (for example, using the technique #3).
		1733
		1734	When there is some activity, remove the timer from the list, recalculate
		1735	the timeout, append it to the end of the list again, and make sure to
		1736	update the C<ev_timer> if it was taken from the beginning of the list.
		1737
		1738	This way, one can manage an unlimited number of timeouts in O(1) time for
		1739	starting, stopping and updating the timers, at the expense of a major
		1740	complication, and having to use a constant timeout. The constant timeout
		1741	ensures that the list stays sorted.
		1742
		1743	=back
		1744
		1745	So which method the best?
		1746
		1747	Method #2 is a simple no-brain-required solution that is adequate in most
		1748	situations. Method #3 requires a bit more thinking, but handles many cases
		1749	better, and isn't very complicated either. In most case, choosing either
		1750	one is fine, with #3 being better in typical situations.
		1751
		1752	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1753	rather complicated, but extremely efficient, something that really pays
		1754	off after the first million or so of active timers, i.e. it's usually
		1755	overkill :)
1282		1756
1283	=head3 The special problem of time updates	1757	=head3 The special problem of time updates
1284		1758
1285	Establishing the current time is a costly operation (it usually takes at	1759	Establishing the current time is a costly operation (it usually takes at
1286	least two system calls): EV therefore updates its idea of the current	1760	least two system calls): EV therefore updates its idea of the current
…		…
1298		1772
1299	If the event loop is suspended for a long time, you can also force an	1773	If the event loop is suspended for a long time, you can also force an
1300	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1774	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1301	()>.	1775	()>.
1302		1776
		1777	=head3 The special problems of suspended animation
		1778
		1779	When you leave the server world it is quite customary to hit machines that
		1780	can suspend/hibernate - what happens to the clocks during such a suspend?
		1781
		1782	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1783	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1784	to run until the system is suspended, but they will not advance while the
		1785	system is suspended. That means, on resume, it will be as if the program
		1786	was frozen for a few seconds, but the suspend time will not be counted
		1787	towards C<ev_timer> when a monotonic clock source is used. The real time
		1788	clock advanced as expected, but if it is used as sole clocksource, then a
		1789	long suspend would be detected as a time jump by libev, and timers would
		1790	be adjusted accordingly.
		1791
		1792	I would not be surprised to see different behaviour in different between
		1793	operating systems, OS versions or even different hardware.
		1794
		1795	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1796	time jump in the monotonic clocks and the realtime clock. If the program
		1797	is suspended for a very long time, and monotonic clock sources are in use,
		1798	then you can expect C<ev_timer>s to expire as the full suspension time
		1799	will be counted towards the timers. When no monotonic clock source is in
		1800	use, then libev will again assume a timejump and adjust accordingly.
		1801
		1802	It might be beneficial for this latter case to call C<ev_suspend>
		1803	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1804	deterministic behaviour in this case (you can do nothing against
		1805	C<SIGSTOP>).
		1806
1303	=head3 Watcher-Specific Functions and Data Members	1807	=head3 Watcher-Specific Functions and Data Members
1304		1808
1305	=over 4	1809	=over 4
1306		1810
1307	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1811	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1330	If the timer is started but non-repeating, stop it (as if it timed out).	1834	If the timer is started but non-repeating, stop it (as if it timed out).
1331		1835
1332	If the timer is repeating, either start it if necessary (with the	1836	If the timer is repeating, either start it if necessary (with the
1333	C<repeat> value), or reset the running timer to the C<repeat> value.	1837	C<repeat> value), or reset the running timer to the C<repeat> value.
1334		1838
1335	This sounds a bit complicated, but here is a useful and typical	1839	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1336	example: Imagine you have a TCP connection and you want a so-called idle	1840	usage example.
1337	timeout, that is, you want to be called when there have been, say, 60
1338	seconds of inactivity on the socket. The easiest way to do this is to
1339	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1340	C<ev_timer_again> each time you successfully read or write some data. If
1341	you go into an idle state where you do not expect data to travel on the
1342	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1343	automatically restart it if need be.
1344		1841
1345	That means you can ignore the C<after> value and C<ev_timer_start>	1842	=item ev_timer_remaining (loop, ev_timer *)
1346	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1347		1843
1348	ev_timer_init (timer, callback, 0., 5.);	1844	Returns the remaining time until a timer fires. If the timer is active,
1349	ev_timer_again (loop, timer);	1845	then this time is relative to the current event loop time, otherwise it's
1350	...	1846	the timeout value currently configured.
1351	timer->again = 17.;
1352	ev_timer_again (loop, timer);
1353	...
1354	timer->again = 10.;
1355	ev_timer_again (loop, timer);
1356		1847
1357	This is more slightly efficient then stopping/starting the timer each time	1848	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1358	you want to modify its timeout value.	1849	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
1359		1850	will return C<4>. When the timer expires and is restarted, it will return
1360	Note, however, that it is often even more efficient to remember the	1851	roughly C<7> (likely slightly less as callback invocation takes some time,
1361	time of the last activity and let the timer time-out naturally. In the	1852	too), and so on.
1362	callback, you then check whether the time-out is real, or, if there was
1363	some activity, you reschedule the watcher to time-out in "last_activity +
1364	timeout - ev_now ()" seconds.
1365		1853
1366	=item ev_tstamp repeat [read-write]	1854	=item ev_tstamp repeat [read-write]
1367		1855
1368	The current C<repeat> value. Will be used each time the watcher times out	1856	The current C<repeat> value. Will be used each time the watcher times out
1369	or C<ev_timer_again> is called, and determines the next timeout (if any),	1857	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1374	=head3 Examples	1862	=head3 Examples
1375		1863
1376	Example: Create a timer that fires after 60 seconds.	1864	Example: Create a timer that fires after 60 seconds.
1377		1865
1378	static void	1866	static void
1379	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1867	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1380	{	1868	{
1381	.. one minute over, w is actually stopped right here	1869	.. one minute over, w is actually stopped right here
1382	}	1870	}
1383		1871
1384	struct ev_timer mytimer;	1872	ev_timer mytimer;
1385	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1873	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1386	ev_timer_start (loop, &mytimer);	1874	ev_timer_start (loop, &mytimer);
1387		1875
1388	Example: Create a timeout timer that times out after 10 seconds of	1876	Example: Create a timeout timer that times out after 10 seconds of
1389	inactivity.	1877	inactivity.
1390		1878
1391	static void	1879	static void
1392	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1880	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1393	{	1881	{
1394	.. ten seconds without any activity	1882	.. ten seconds without any activity
1395	}	1883	}
1396		1884
1397	struct ev_timer mytimer;	1885	ev_timer mytimer;
1398	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1886	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1399	ev_timer_again (&mytimer); /* start timer */	1887	ev_timer_again (&mytimer); /* start timer */
1400	ev_loop (loop, 0);	1888	ev_loop (loop, 0);
1401		1889
1402	// and in some piece of code that gets executed on any "activity":	1890	// and in some piece of code that gets executed on any "activity":
…		…
1407	=head2 C<ev_periodic> - to cron or not to cron?	1895	=head2 C<ev_periodic> - to cron or not to cron?
1408		1896
1409	Periodic watchers are also timers of a kind, but they are very versatile	1897	Periodic watchers are also timers of a kind, but they are very versatile
1410	(and unfortunately a bit complex).	1898	(and unfortunately a bit complex).
1411		1899
1412	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1900	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1413	but on wall clock time (absolute time). You can tell a periodic watcher	1901	relative time, the physical time that passes) but on wall clock time
1414	to trigger after some specific point in time. For example, if you tell a	1902	(absolute time, the thing you can read on your calender or clock). The
1415	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1903	difference is that wall clock time can run faster or slower than real
1416	+ 10.>, that is, an absolute time not a delay) and then reset your system	1904	time, and time jumps are not uncommon (e.g. when you adjust your
1417	clock to January of the previous year, then it will take more than year	1905	wrist-watch).
1418	to trigger the event (unlike an C<ev_timer>, which would still trigger
1419	roughly 10 seconds later as it uses a relative timeout).
1420		1906
		1907	You can tell a periodic watcher to trigger after some specific point
		1908	in time: for example, if you tell a periodic watcher to trigger "in 10
		1909	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1910	not a delay) and then reset your system clock to January of the previous
		1911	year, then it will take a year or more to trigger the event (unlike an
		1912	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1913	it, as it uses a relative timeout).
		1914
1421	C<ev_periodic>s can also be used to implement vastly more complex timers,	1915	C<ev_periodic> watchers can also be used to implement vastly more complex
1422	such as triggering an event on each "midnight, local time", or other	1916	timers, such as triggering an event on each "midnight, local time", or
1423	complicated rules.	1917	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1918	those cannot react to time jumps.
1424		1919
1425	As with timers, the callback is guaranteed to be invoked only when the	1920	As with timers, the callback is guaranteed to be invoked only when the
1426	time (C<at>) has passed, but if multiple periodic timers become ready	1921	point in time where it is supposed to trigger has passed. If multiple
1427	during the same loop iteration, then order of execution is undefined.	1922	timers become ready during the same loop iteration then the ones with
		1923	earlier time-out values are invoked before ones with later time-out values
		1924	(but this is no longer true when a callback calls C<ev_loop> recursively).
1428		1925
1429	=head3 Watcher-Specific Functions and Data Members	1926	=head3 Watcher-Specific Functions and Data Members
1430		1927
1431	=over 4	1928	=over 4
1432		1929
1433	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1930	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1434		1931
1435	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1932	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1436		1933
1437	Lots of arguments, lets sort it out... There are basically three modes of	1934	Lots of arguments, let's sort it out... There are basically three modes of
1438	operation, and we will explain them from simplest to most complex:	1935	operation, and we will explain them from simplest to most complex:
1439		1936
1440	=over 4	1937	=over 4
1441		1938
1442	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1939	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1443		1940
1444	In this configuration the watcher triggers an event after the wall clock	1941	In this configuration the watcher triggers an event after the wall clock
1445	time C<at> has passed. It will not repeat and will not adjust when a time	1942	time C<offset> has passed. It will not repeat and will not adjust when a
1446	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1943	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1447	only run when the system clock reaches or surpasses this time.	1944	will be stopped and invoked when the system clock reaches or surpasses
		1945	this point in time.
1448		1946
1449	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1947	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1450		1948
1451	In this mode the watcher will always be scheduled to time out at the next	1949	In this mode the watcher will always be scheduled to time out at the next
1452	C<at + N * interval> time (for some integer N, which can also be negative)	1950	C<offset + N * interval> time (for some integer N, which can also be
1453	and then repeat, regardless of any time jumps.	1951	negative) and then repeat, regardless of any time jumps. The C<offset>
		1952	argument is merely an offset into the C<interval> periods.
1454		1953
1455	This can be used to create timers that do not drift with respect to the	1954	This can be used to create timers that do not drift with respect to the
1456	system clock, for example, here is a C<ev_periodic> that triggers each	1955	system clock, for example, here is an C<ev_periodic> that triggers each
1457	hour, on the hour:	1956	hour, on the hour (with respect to UTC):
1458		1957
1459	ev_periodic_set (&periodic, 0., 3600., 0);	1958	ev_periodic_set (&periodic, 0., 3600., 0);
1460		1959
1461	This doesn't mean there will always be 3600 seconds in between triggers,	1960	This doesn't mean there will always be 3600 seconds in between triggers,
1462	but only that the callback will be called when the system time shows a	1961	but only that the callback will be called when the system time shows a
1463	full hour (UTC), or more correctly, when the system time is evenly divisible	1962	full hour (UTC), or more correctly, when the system time is evenly divisible
1464	by 3600.	1963	by 3600.
1465		1964
1466	Another way to think about it (for the mathematically inclined) is that	1965	Another way to think about it (for the mathematically inclined) is that
1467	C<ev_periodic> will try to run the callback in this mode at the next possible	1966	C<ev_periodic> will try to run the callback in this mode at the next possible
1468	time where C<time = at (mod interval)>, regardless of any time jumps.	1967	time where C<time = offset (mod interval)>, regardless of any time jumps.
1469		1968
1470	For numerical stability it is preferable that the C<at> value is near	1969	For numerical stability it is preferable that the C<offset> value is near
1471	C<ev_now ()> (the current time), but there is no range requirement for	1970	C<ev_now ()> (the current time), but there is no range requirement for
1472	this value, and in fact is often specified as zero.	1971	this value, and in fact is often specified as zero.
1473		1972
1474	Note also that there is an upper limit to how often a timer can fire (CPU	1973	Note also that there is an upper limit to how often a timer can fire (CPU
1475	speed for example), so if C<interval> is very small then timing stability	1974	speed for example), so if C<interval> is very small then timing stability
1476	will of course deteriorate. Libev itself tries to be exact to be about one	1975	will of course deteriorate. Libev itself tries to be exact to be about one
1477	millisecond (if the OS supports it and the machine is fast enough).	1976	millisecond (if the OS supports it and the machine is fast enough).
1478		1977
1479	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1978	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1480		1979
1481	In this mode the values for C<interval> and C<at> are both being	1980	In this mode the values for C<interval> and C<offset> are both being
1482	ignored. Instead, each time the periodic watcher gets scheduled, the	1981	ignored. Instead, each time the periodic watcher gets scheduled, the
1483	reschedule callback will be called with the watcher as first, and the	1982	reschedule callback will be called with the watcher as first, and the
1484	current time as second argument.	1983	current time as second argument.
1485		1984
1486	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1985	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1487	ever, or make ANY event loop modifications whatsoever>.	1986	or make ANY other event loop modifications whatsoever, unless explicitly
		1987	allowed by documentation here>.
1488		1988
1489	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1989	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1490	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1990	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1491	only event loop modification you are allowed to do).	1991	only event loop modification you are allowed to do).
1492		1992
1493	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1993	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1494	*w, ev_tstamp now)>, e.g.:	1994	*w, ev_tstamp now)>, e.g.:
1495		1995
		1996	static ev_tstamp
1496	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1997	my_rescheduler (ev_periodic *w, ev_tstamp now)
1497	{	1998	{
1498	return now + 60.;	1999	return now + 60.;
1499	}	2000	}
1500		2001
1501	It must return the next time to trigger, based on the passed time value	2002	It must return the next time to trigger, based on the passed time value
…		…
1521	a different time than the last time it was called (e.g. in a crond like	2022	a different time than the last time it was called (e.g. in a crond like
1522	program when the crontabs have changed).	2023	program when the crontabs have changed).
1523		2024
1524	=item ev_tstamp ev_periodic_at (ev_periodic *)	2025	=item ev_tstamp ev_periodic_at (ev_periodic *)
1525		2026
1526	When active, returns the absolute time that the watcher is supposed to	2027	When active, returns the absolute time that the watcher is supposed
1527	trigger next.	2028	to trigger next. This is not the same as the C<offset> argument to
		2029	C<ev_periodic_set>, but indeed works even in interval and manual
		2030	rescheduling modes.
1528		2031
1529	=item ev_tstamp offset [read-write]	2032	=item ev_tstamp offset [read-write]
1530		2033
1531	When repeating, this contains the offset value, otherwise this is the	2034	When repeating, this contains the offset value, otherwise this is the
1532	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2035	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2036	although libev might modify this value for better numerical stability).
1533		2037
1534	Can be modified any time, but changes only take effect when the periodic	2038	Can be modified any time, but changes only take effect when the periodic
1535	timer fires or C<ev_periodic_again> is being called.	2039	timer fires or C<ev_periodic_again> is being called.
1536		2040
1537	=item ev_tstamp interval [read-write]	2041	=item ev_tstamp interval [read-write]
1538		2042
1539	The current interval value. Can be modified any time, but changes only	2043	The current interval value. Can be modified any time, but changes only
1540	take effect when the periodic timer fires or C<ev_periodic_again> is being	2044	take effect when the periodic timer fires or C<ev_periodic_again> is being
1541	called.	2045	called.
1542		2046
1543	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2047	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1544		2048
1545	The current reschedule callback, or C<0>, if this functionality is	2049	The current reschedule callback, or C<0>, if this functionality is
1546	switched off. Can be changed any time, but changes only take effect when	2050	switched off. Can be changed any time, but changes only take effect when
1547	the periodic timer fires or C<ev_periodic_again> is being called.	2051	the periodic timer fires or C<ev_periodic_again> is being called.
1548		2052
…		…
1553	Example: Call a callback every hour, or, more precisely, whenever the	2057	Example: Call a callback every hour, or, more precisely, whenever the
1554	system time is divisible by 3600. The callback invocation times have	2058	system time is divisible by 3600. The callback invocation times have
1555	potentially a lot of jitter, but good long-term stability.	2059	potentially a lot of jitter, but good long-term stability.
1556		2060
1557	static void	2061	static void
1558	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2062	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1559	{	2063	{
1560	... its now a full hour (UTC, or TAI or whatever your clock follows)	2064	... its now a full hour (UTC, or TAI or whatever your clock follows)
1561	}	2065	}
1562		2066
1563	struct ev_periodic hourly_tick;	2067	ev_periodic hourly_tick;
1564	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2068	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1565	ev_periodic_start (loop, &hourly_tick);	2069	ev_periodic_start (loop, &hourly_tick);
1566		2070
1567	Example: The same as above, but use a reschedule callback to do it:	2071	Example: The same as above, but use a reschedule callback to do it:
1568		2072
1569	#include <math.h>	2073	#include <math.h>
1570		2074
1571	static ev_tstamp	2075	static ev_tstamp
1572	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2076	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1573	{	2077	{
1574	return now + (3600. - fmod (now, 3600.));	2078	return now + (3600. - fmod (now, 3600.));
1575	}	2079	}
1576		2080
1577	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2081	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1578		2082
1579	Example: Call a callback every hour, starting now:	2083	Example: Call a callback every hour, starting now:
1580		2084
1581	struct ev_periodic hourly_tick;	2085	ev_periodic hourly_tick;
1582	ev_periodic_init (&hourly_tick, clock_cb,	2086	ev_periodic_init (&hourly_tick, clock_cb,
1583	fmod (ev_now (loop), 3600.), 3600., 0);	2087	fmod (ev_now (loop), 3600.), 3600., 0);
1584	ev_periodic_start (loop, &hourly_tick);	2088	ev_periodic_start (loop, &hourly_tick);
1585		2089
1586		2090
…		…
1589	Signal watchers will trigger an event when the process receives a specific	2093	Signal watchers will trigger an event when the process receives a specific
1590	signal one or more times. Even though signals are very asynchronous, libev	2094	signal one or more times. Even though signals are very asynchronous, libev
1591	will try it's best to deliver signals synchronously, i.e. as part of the	2095	will try it's best to deliver signals synchronously, i.e. as part of the
1592	normal event processing, like any other event.	2096	normal event processing, like any other event.
1593		2097
1594	If you want signals asynchronously, just use C<sigaction> as you would	2098	If you want signals to be delivered truly asynchronously, just use
1595	do without libev and forget about sharing the signal. You can even use	2099	C<sigaction> as you would do without libev and forget about sharing
1596	C<ev_async> from a signal handler to synchronously wake up an event loop.	2100	the signal. You can even use C<ev_async> from a signal handler to
		2101	synchronously wake up an event loop.
1597		2102
1598	You can configure as many watchers as you like per signal. Only when the	2103	You can configure as many watchers as you like for the same signal, but
		2104	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2105	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2106	C<SIGINT> in both the default loop and another loop at the same time. At
		2107	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2108
1599	first watcher gets started will libev actually register a signal handler	2109	When the first watcher gets started will libev actually register something
1600	with the kernel (thus it coexists with your own signal handlers as long as	2110	with the kernel (thus it coexists with your own signal handlers as long as
1601	you don't register any with libev for the same signal). Similarly, when	2111	you don't register any with libev for the same signal).
1602	the last signal watcher for a signal is stopped, libev will reset the
1603	signal handler to SIG_DFL (regardless of what it was set to before).
1604		2112
1605	If possible and supported, libev will install its handlers with	2113	If possible and supported, libev will install its handlers with
1606	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2114	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1607	interrupted. If you have a problem with system calls getting interrupted by	2115	not be unduly interrupted. If you have a problem with system calls getting
1608	signals you can block all signals in an C<ev_check> watcher and unblock	2116	interrupted by signals you can block all signals in an C<ev_check> watcher
1609	them in an C<ev_prepare> watcher.	2117	and unblock them in an C<ev_prepare> watcher.
		2118
		2119	=head3 The special problem of inheritance over execve
		2120
		2121	Both the signal mask (C<sigprocmask>) and the signal disposition
		2122	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2123	stopping it again), that is, libev might or might not block the signal,
		2124	and might or might not set or restore the installed signal handler.
		2125
		2126	While this does not matter for the signal disposition (libev never
		2127	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2128	C<execve>), this matters for the signal mask: many programs do not expect
		2129	certain signals to be blocked.
		2130
		2131	This means that before calling C<exec> (from the child) you should reset
		2132	the signal mask to whatever "default" you expect (all clear is a good
		2133	choice usually).
		2134
		2135	The simplest way to ensure that the signal mask is reset in the child is
		2136	to install a fork handler with C<pthread_atfork> that resets it. That will
		2137	catch fork calls done by libraries (such as the libc) as well.
		2138
		2139	In current versions of libev, you can also ensure that the signal mask is
		2140	not blocking any signals (except temporarily, so thread users watch out)
		2141	by specifying the C<EVFLAG_NOSIGNALFD> when creating the event loop. This
		2142	is not guaranteed for future versions, however.
1610		2143
1611	=head3 Watcher-Specific Functions and Data Members	2144	=head3 Watcher-Specific Functions and Data Members
1612		2145
1613	=over 4	2146	=over 4
1614		2147
…		…
1625		2158
1626	=back	2159	=back
1627		2160
1628	=head3 Examples	2161	=head3 Examples
1629		2162
1630	Example: Try to exit cleanly on SIGINT and SIGTERM.	2163	Example: Try to exit cleanly on SIGINT.
1631		2164
1632	static void	2165	static void
1633	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2166	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1634	{	2167	{
1635	ev_unloop (loop, EVUNLOOP_ALL);	2168	ev_unloop (loop, EVUNLOOP_ALL);
1636	}	2169	}
1637		2170
1638	struct ev_signal signal_watcher;	2171	ev_signal signal_watcher;
1639	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2172	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1640	ev_signal_start (loop, &sigint_cb);	2173	ev_signal_start (loop, &signal_watcher);
1641		2174
1642		2175
1643	=head2 C<ev_child> - watch out for process status changes	2176	=head2 C<ev_child> - watch out for process status changes
1644		2177
1645	Child watchers trigger when your process receives a SIGCHLD in response to	2178	Child watchers trigger when your process receives a SIGCHLD in response to
1646	some child status changes (most typically when a child of yours dies or	2179	some child status changes (most typically when a child of yours dies or
1647	exits). It is permissible to install a child watcher I<after> the child	2180	exits). It is permissible to install a child watcher I<after> the child
1648	has been forked (which implies it might have already exited), as long	2181	has been forked (which implies it might have already exited), as long
1649	as the event loop isn't entered (or is continued from a watcher), i.e.,	2182	as the event loop isn't entered (or is continued from a watcher), i.e.,
1650	forking and then immediately registering a watcher for the child is fine,	2183	forking and then immediately registering a watcher for the child is fine,
1651	but forking and registering a watcher a few event loop iterations later is	2184	but forking and registering a watcher a few event loop iterations later or
1652	not.	2185	in the next callback invocation is not.
1653		2186
1654	Only the default event loop is capable of handling signals, and therefore	2187	Only the default event loop is capable of handling signals, and therefore
1655	you can only register child watchers in the default event loop.	2188	you can only register child watchers in the default event loop.
1656		2189
		2190	Due to some design glitches inside libev, child watchers will always be
		2191	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2192	libev)
		2193
1657	=head3 Process Interaction	2194	=head3 Process Interaction
1658		2195
1659	Libev grabs C<SIGCHLD> as soon as the default event loop is	2196	Libev grabs C<SIGCHLD> as soon as the default event loop is
1660	initialised. This is necessary to guarantee proper behaviour even if	2197	initialised. This is necessary to guarantee proper behaviour even if the
1661	the first child watcher is started after the child exits. The occurrence	2198	first child watcher is started after the child exits. The occurrence
1662	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2199	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1663	synchronously as part of the event loop processing. Libev always reaps all	2200	synchronously as part of the event loop processing. Libev always reaps all
1664	children, even ones not watched.	2201	children, even ones not watched.
1665		2202
1666	=head3 Overriding the Built-In Processing	2203	=head3 Overriding the Built-In Processing
…		…
1676	=head3 Stopping the Child Watcher	2213	=head3 Stopping the Child Watcher
1677		2214
1678	Currently, the child watcher never gets stopped, even when the	2215	Currently, the child watcher never gets stopped, even when the
1679	child terminates, so normally one needs to stop the watcher in the	2216	child terminates, so normally one needs to stop the watcher in the
1680	callback. Future versions of libev might stop the watcher automatically	2217	callback. Future versions of libev might stop the watcher automatically
1681	when a child exit is detected.	2218	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2219	problem).
1682		2220
1683	=head3 Watcher-Specific Functions and Data Members	2221	=head3 Watcher-Specific Functions and Data Members
1684		2222
1685	=over 4	2223	=over 4
1686		2224
…		…
1718	its completion.	2256	its completion.
1719		2257
1720	ev_child cw;	2258	ev_child cw;
1721		2259
1722	static void	2260	static void
1723	child_cb (EV_P_ struct ev_child *w, int revents)	2261	child_cb (EV_P_ ev_child *w, int revents)
1724	{	2262	{
1725	ev_child_stop (EV_A_ w);	2263	ev_child_stop (EV_A_ w);
1726	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2264	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1727	}	2265	}
1728		2266
…		…
1743		2281
1744		2282
1745	=head2 C<ev_stat> - did the file attributes just change?	2283	=head2 C<ev_stat> - did the file attributes just change?
1746		2284
1747	This watches a file system path for attribute changes. That is, it calls	2285	This watches a file system path for attribute changes. That is, it calls
1748	C<stat> regularly (or when the OS says it changed) and sees if it changed	2286	C<stat> on that path in regular intervals (or when the OS says it changed)
1749	compared to the last time, invoking the callback if it did.	2287	and sees if it changed compared to the last time, invoking the callback if
		2288	it did.
1750		2289
1751	The path does not need to exist: changing from "path exists" to "path does	2290	The path does not need to exist: changing from "path exists" to "path does
1752	not exist" is a status change like any other. The condition "path does	2291	not exist" is a status change like any other. The condition "path does not
1753	not exist" is signified by the C<st_nlink> field being zero (which is	2292	exist" (or more correctly "path cannot be stat'ed") is signified by the
1754	otherwise always forced to be at least one) and all the other fields of	2293	C<st_nlink> field being zero (which is otherwise always forced to be at
1755	the stat buffer having unspecified contents.	2294	least one) and all the other fields of the stat buffer having unspecified
		2295	contents.
1756		2296
1757	The path I<should> be absolute and I<must not> end in a slash. If it is	2297	The path I<must not> end in a slash or contain special components such as
		2298	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1758	relative and your working directory changes, the behaviour is undefined.	2299	your working directory changes, then the behaviour is undefined.
1759		2300
1760	Since there is no standard kernel interface to do this, the portable	2301	Since there is no portable change notification interface available, the
1761	implementation simply calls C<stat (2)> regularly on the path to see if	2302	portable implementation simply calls C<stat(2)> regularly on the path
1762	it changed somehow. You can specify a recommended polling interval for	2303	to see if it changed somehow. You can specify a recommended polling
1763	this case. If you specify a polling interval of C<0> (highly recommended!)	2304	interval for this case. If you specify a polling interval of C<0> (highly
1764	then a I<suitable, unspecified default> value will be used (which	2305	recommended!) then a I<suitable, unspecified default> value will be used
1765	you can expect to be around five seconds, although this might change	2306	(which you can expect to be around five seconds, although this might
1766	dynamically). Libev will also impose a minimum interval which is currently	2307	change dynamically). Libev will also impose a minimum interval which is
1767	around C<0.1>, but thats usually overkill.	2308	currently around C<0.1>, but that's usually overkill.
1768		2309
1769	This watcher type is not meant for massive numbers of stat watchers,	2310	This watcher type is not meant for massive numbers of stat watchers,
1770	as even with OS-supported change notifications, this can be	2311	as even with OS-supported change notifications, this can be
1771	resource-intensive.	2312	resource-intensive.
1772		2313
1773	At the time of this writing, the only OS-specific interface implemented	2314	At the time of this writing, the only OS-specific interface implemented
1774	is the Linux inotify interface (implementing kqueue support is left as	2315	is the Linux inotify interface (implementing kqueue support is left as an
1775	an exercise for the reader. Note, however, that the author sees no way	2316	exercise for the reader. Note, however, that the author sees no way of
1776	of implementing C<ev_stat> semantics with kqueue).	2317	implementing C<ev_stat> semantics with kqueue, except as a hint).
1777		2318
1778	=head3 ABI Issues (Largefile Support)	2319	=head3 ABI Issues (Largefile Support)
1779		2320
1780	Libev by default (unless the user overrides this) uses the default	2321	Libev by default (unless the user overrides this) uses the default
1781	compilation environment, which means that on systems with large file	2322	compilation environment, which means that on systems with large file
1782	support disabled by default, you get the 32 bit version of the stat	2323	support disabled by default, you get the 32 bit version of the stat
1783	structure. When using the library from programs that change the ABI to	2324	structure. When using the library from programs that change the ABI to
1784	use 64 bit file offsets the programs will fail. In that case you have to	2325	use 64 bit file offsets the programs will fail. In that case you have to
1785	compile libev with the same flags to get binary compatibility. This is	2326	compile libev with the same flags to get binary compatibility. This is
1786	obviously the case with any flags that change the ABI, but the problem is	2327	obviously the case with any flags that change the ABI, but the problem is
1787	most noticeably disabled with ev_stat and large file support.	2328	most noticeably displayed with ev_stat and large file support.
1788		2329
1789	The solution for this is to lobby your distribution maker to make large	2330	The solution for this is to lobby your distribution maker to make large
1790	file interfaces available by default (as e.g. FreeBSD does) and not	2331	file interfaces available by default (as e.g. FreeBSD does) and not
1791	optional. Libev cannot simply switch on large file support because it has	2332	optional. Libev cannot simply switch on large file support because it has
1792	to exchange stat structures with application programs compiled using the	2333	to exchange stat structures with application programs compiled using the
1793	default compilation environment.	2334	default compilation environment.
1794		2335
1795	=head3 Inotify and Kqueue	2336	=head3 Inotify and Kqueue
1796		2337
1797	When C<inotify (7)> support has been compiled into libev (generally only	2338	When C<inotify (7)> support has been compiled into libev and present at
1798	available with Linux) and present at runtime, it will be used to speed up	2339	runtime, it will be used to speed up change detection where possible. The
1799	change detection where possible. The inotify descriptor will be created lazily	2340	inotify descriptor will be created lazily when the first C<ev_stat>
1800	when the first C<ev_stat> watcher is being started.	2341	watcher is being started.
1801		2342
1802	Inotify presence does not change the semantics of C<ev_stat> watchers	2343	Inotify presence does not change the semantics of C<ev_stat> watchers
1803	except that changes might be detected earlier, and in some cases, to avoid	2344	except that changes might be detected earlier, and in some cases, to avoid
1804	making regular C<stat> calls. Even in the presence of inotify support	2345	making regular C<stat> calls. Even in the presence of inotify support
1805	there are many cases where libev has to resort to regular C<stat> polling,	2346	there are many cases where libev has to resort to regular C<stat> polling,
1806	but as long as the path exists, libev usually gets away without polling.	2347	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2348	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2349	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2350	xfs are fully working) libev usually gets away without polling.
1807		2351
1808	There is no support for kqueue, as apparently it cannot be used to	2352	There is no support for kqueue, as apparently it cannot be used to
1809	implement this functionality, due to the requirement of having a file	2353	implement this functionality, due to the requirement of having a file
1810	descriptor open on the object at all times, and detecting renames, unlinks	2354	descriptor open on the object at all times, and detecting renames, unlinks
1811	etc. is difficult.	2355	etc. is difficult.
1812		2356
		2357	=head3 C<stat ()> is a synchronous operation
		2358
		2359	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2360	the process. The exception are C<ev_stat> watchers - those call C<stat
		2361	()>, which is a synchronous operation.
		2362
		2363	For local paths, this usually doesn't matter: unless the system is very
		2364	busy or the intervals between stat's are large, a stat call will be fast,
		2365	as the path data is usually in memory already (except when starting the
		2366	watcher).
		2367
		2368	For networked file systems, calling C<stat ()> can block an indefinite
		2369	time due to network issues, and even under good conditions, a stat call
		2370	often takes multiple milliseconds.
		2371
		2372	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2373	paths, although this is fully supported by libev.
		2374
1813	=head3 The special problem of stat time resolution	2375	=head3 The special problem of stat time resolution
1814		2376
1815	The C<stat ()> system call only supports full-second resolution portably, and	2377	The C<stat ()> system call only supports full-second resolution portably,
1816	even on systems where the resolution is higher, most file systems still	2378	and even on systems where the resolution is higher, most file systems
1817	only support whole seconds.	2379	still only support whole seconds.
1818		2380
1819	That means that, if the time is the only thing that changes, you can	2381	That means that, if the time is the only thing that changes, you can
1820	easily miss updates: on the first update, C<ev_stat> detects a change and	2382	easily miss updates: on the first update, C<ev_stat> detects a change and
1821	calls your callback, which does something. When there is another update	2383	calls your callback, which does something. When there is another update
1822	within the same second, C<ev_stat> will be unable to detect unless the	2384	within the same second, C<ev_stat> will be unable to detect unless the
…		…
1965		2527
1966	=head3 Watcher-Specific Functions and Data Members	2528	=head3 Watcher-Specific Functions and Data Members
1967		2529
1968	=over 4	2530	=over 4
1969		2531
1970	=item ev_idle_init (ev_signal *, callback)	2532	=item ev_idle_init (ev_idle *, callback)
1971		2533
1972	Initialises and configures the idle watcher - it has no parameters of any	2534	Initialises and configures the idle watcher - it has no parameters of any
1973	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2535	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1974	believe me.	2536	believe me.
1975		2537
…		…
1979		2541
1980	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2542	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1981	callback, free it. Also, use no error checking, as usual.	2543	callback, free it. Also, use no error checking, as usual.
1982		2544
1983	static void	2545	static void
1984	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2546	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1985	{	2547	{
1986	free (w);	2548	free (w);
1987	// now do something you wanted to do when the program has	2549	// now do something you wanted to do when the program has
1988	// no longer anything immediate to do.	2550	// no longer anything immediate to do.
1989	}	2551	}
1990		2552
1991	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2553	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1992	ev_idle_init (idle_watcher, idle_cb);	2554	ev_idle_init (idle_watcher, idle_cb);
1993	ev_idle_start (loop, idle_cb);	2555	ev_idle_start (loop, idle_watcher);
1994		2556
1995		2557
1996	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2558	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1997		2559
1998	Prepare and check watchers are usually (but not always) used in pairs:	2560	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2077		2639
2078	static ev_io iow [nfd];	2640	static ev_io iow [nfd];
2079	static ev_timer tw;	2641	static ev_timer tw;
2080		2642
2081	static void	2643	static void
2082	io_cb (ev_loop *loop, ev_io *w, int revents)	2644	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2083	{	2645	{
2084	}	2646	}
2085		2647
2086	// create io watchers for each fd and a timer before blocking	2648	// create io watchers for each fd and a timer before blocking
2087	static void	2649	static void
2088	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2650	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2089	{	2651	{
2090	int timeout = 3600000;	2652	int timeout = 3600000;
2091	struct pollfd fds [nfd];	2653	struct pollfd fds [nfd];
2092	// actual code will need to loop here and realloc etc.	2654	// actual code will need to loop here and realloc etc.
2093	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2655	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2094		2656
2095	/* the callback is illegal, but won't be called as we stop during check */	2657	/* the callback is illegal, but won't be called as we stop during check */
2096	ev_timer_init (&tw, 0, timeout * 1e-3);	2658	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2097	ev_timer_start (loop, &tw);	2659	ev_timer_start (loop, &tw);
2098		2660
2099	// create one ev_io per pollfd	2661	// create one ev_io per pollfd
2100	for (int i = 0; i < nfd; ++i)	2662	for (int i = 0; i < nfd; ++i)
2101	{	2663	{
…		…
2108	}	2670	}
2109	}	2671	}
2110		2672
2111	// stop all watchers after blocking	2673	// stop all watchers after blocking
2112	static void	2674	static void
2113	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2675	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2114	{	2676	{
2115	ev_timer_stop (loop, &tw);	2677	ev_timer_stop (loop, &tw);
2116		2678
2117	for (int i = 0; i < nfd; ++i)	2679	for (int i = 0; i < nfd; ++i)
2118	{	2680	{
…		…
2214	some fds have to be watched and handled very quickly (with low latency),	2776	some fds have to be watched and handled very quickly (with low latency),
2215	and even priorities and idle watchers might have too much overhead. In	2777	and even priorities and idle watchers might have too much overhead. In
2216	this case you would put all the high priority stuff in one loop and all	2778	this case you would put all the high priority stuff in one loop and all
2217	the rest in a second one, and embed the second one in the first.	2779	the rest in a second one, and embed the second one in the first.
2218		2780
2219	As long as the watcher is active, the callback will be invoked every time	2781	As long as the watcher is active, the callback will be invoked every
2220	there might be events pending in the embedded loop. The callback must then	2782	time there might be events pending in the embedded loop. The callback
2221	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2783	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2222	their callbacks (you could also start an idle watcher to give the embedded	2784	sweep and invoke their callbacks (the callback doesn't need to invoke the
2223	loop strictly lower priority for example). You can also set the callback	2785	C<ev_embed_sweep> function directly, it could also start an idle watcher
2224	to C<0>, in which case the embed watcher will automatically execute the	2786	to give the embedded loop strictly lower priority for example).
2225	embedded loop sweep.
2226		2787
2227	As long as the watcher is started it will automatically handle events. The	2788	You can also set the callback to C<0>, in which case the embed watcher
2228	callback will be invoked whenever some events have been handled. You can	2789	will automatically execute the embedded loop sweep whenever necessary.
2229	set the callback to C<0> to avoid having to specify one if you are not
2230	interested in that.
2231		2790
2232	Also, there have not currently been made special provisions for forking:	2791	Fork detection will be handled transparently while the C<ev_embed> watcher
2233	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2792	is active, i.e., the embedded loop will automatically be forked when the
2234	but you will also have to stop and restart any C<ev_embed> watchers	2793	embedding loop forks. In other cases, the user is responsible for calling
2235	yourself - but you can use a fork watcher to handle this automatically,	2794	C<ev_loop_fork> on the embedded loop.
2236	and future versions of libev might do just that.
2237		2795
2238	Unfortunately, not all backends are embeddable, only the ones returned by	2796	Unfortunately, not all backends are embeddable: only the ones returned by
2239	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2797	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2240	portable one.	2798	portable one.
2241		2799
2242	So when you want to use this feature you will always have to be prepared	2800	So when you want to use this feature you will always have to be prepared
2243	that you cannot get an embeddable loop. The recommended way to get around	2801	that you cannot get an embeddable loop. The recommended way to get around
2244	this is to have a separate variables for your embeddable loop, try to	2802	this is to have a separate variables for your embeddable loop, try to
2245	create it, and if that fails, use the normal loop for everything.	2803	create it, and if that fails, use the normal loop for everything.
		2804
		2805	=head3 C<ev_embed> and fork
		2806
		2807	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2808	automatically be applied to the embedded loop as well, so no special
		2809	fork handling is required in that case. When the watcher is not running,
		2810	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2811	as applicable.
2246		2812
2247	=head3 Watcher-Specific Functions and Data Members	2813	=head3 Watcher-Specific Functions and Data Members
2248		2814
2249	=over 4	2815	=over 4
2250		2816
…		…
2278	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2844	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2279	used).	2845	used).
2280		2846
2281	struct ev_loop *loop_hi = ev_default_init (0);	2847	struct ev_loop *loop_hi = ev_default_init (0);
2282	struct ev_loop *loop_lo = 0;	2848	struct ev_loop *loop_lo = 0;
2283	struct ev_embed embed;	2849	ev_embed embed;
2284		2850
2285	// see if there is a chance of getting one that works	2851	// see if there is a chance of getting one that works
2286	// (remember that a flags value of 0 means autodetection)	2852	// (remember that a flags value of 0 means autodetection)
2287	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2853	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2288	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2854	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2302	kqueue implementation). Store the kqueue/socket-only event loop in	2868	kqueue implementation). Store the kqueue/socket-only event loop in
2303	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2869	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2304		2870
2305	struct ev_loop *loop = ev_default_init (0);	2871	struct ev_loop *loop = ev_default_init (0);
2306	struct ev_loop *loop_socket = 0;	2872	struct ev_loop *loop_socket = 0;
2307	struct ev_embed embed;	2873	ev_embed embed;
2308		2874
2309	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2875	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2310	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2876	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2311	{	2877	{
2312	ev_embed_init (&embed, 0, loop_socket);	2878	ev_embed_init (&embed, 0, loop_socket);
…		…
2327	event loop blocks next and before C<ev_check> watchers are being called,	2893	event loop blocks next and before C<ev_check> watchers are being called,
2328	and only in the child after the fork. If whoever good citizen calling	2894	and only in the child after the fork. If whoever good citizen calling
2329	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2895	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2330	handlers will be invoked, too, of course.	2896	handlers will be invoked, too, of course.
2331		2897
		2898	=head3 The special problem of life after fork - how is it possible?
		2899
		2900	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2901	up/change the process environment, followed by a call to C<exec()>. This
		2902	sequence should be handled by libev without any problems.
		2903
		2904	This changes when the application actually wants to do event handling
		2905	in the child, or both parent in child, in effect "continuing" after the
		2906	fork.
		2907
		2908	The default mode of operation (for libev, with application help to detect
		2909	forks) is to duplicate all the state in the child, as would be expected
		2910	when I<either> the parent I<or> the child process continues.
		2911
		2912	When both processes want to continue using libev, then this is usually the
		2913	wrong result. In that case, usually one process (typically the parent) is
		2914	supposed to continue with all watchers in place as before, while the other
		2915	process typically wants to start fresh, i.e. without any active watchers.
		2916
		2917	The cleanest and most efficient way to achieve that with libev is to
		2918	simply create a new event loop, which of course will be "empty", and
		2919	use that for new watchers. This has the advantage of not touching more
		2920	memory than necessary, and thus avoiding the copy-on-write, and the
		2921	disadvantage of having to use multiple event loops (which do not support
		2922	signal watchers).
		2923
		2924	When this is not possible, or you want to use the default loop for
		2925	other reasons, then in the process that wants to start "fresh", call
		2926	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2927	the default loop will "orphan" (not stop) all registered watchers, so you
		2928	have to be careful not to execute code that modifies those watchers. Note
		2929	also that in that case, you have to re-register any signal watchers.
		2930
2332	=head3 Watcher-Specific Functions and Data Members	2931	=head3 Watcher-Specific Functions and Data Members
2333		2932
2334	=over 4	2933	=over 4
2335		2934
2336	=item ev_fork_init (ev_signal *, callback)	2935	=item ev_fork_init (ev_signal *, callback)
…		…
2368	is that the author does not know of a simple (or any) algorithm for a	2967	is that the author does not know of a simple (or any) algorithm for a
2369	multiple-writer-single-reader queue that works in all cases and doesn't	2968	multiple-writer-single-reader queue that works in all cases and doesn't
2370	need elaborate support such as pthreads.	2969	need elaborate support such as pthreads.
2371		2970
2372	That means that if you want to queue data, you have to provide your own	2971	That means that if you want to queue data, you have to provide your own
2373	queue. But at least I can tell you would implement locking around your	2972	queue. But at least I can tell you how to implement locking around your
2374	queue:	2973	queue:
2375		2974
2376	=over 4	2975	=over 4
2377		2976
2378	=item queueing from a signal handler context	2977	=item queueing from a signal handler context
2379		2978
2380	To implement race-free queueing, you simply add to the queue in the signal	2979	To implement race-free queueing, you simply add to the queue in the signal
2381	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2980	handler but you block the signal handler in the watcher callback. Here is
2382	some fictitious SIGUSR1 handler:	2981	an example that does that for some fictitious SIGUSR1 handler:
2383		2982
2384	static ev_async mysig;	2983	static ev_async mysig;
2385		2984
2386	static void	2985	static void
2387	sigusr1_handler (void)	2986	sigusr1_handler (void)
…		…
2453	=over 4	3052	=over 4
2454		3053
2455	=item ev_async_init (ev_async *, callback)	3054	=item ev_async_init (ev_async *, callback)
2456		3055
2457	Initialises and configures the async watcher - it has no parameters of any	3056	Initialises and configures the async watcher - it has no parameters of any
2458	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3057	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2459	believe me.	3058	trust me.
2460		3059
2461	=item ev_async_send (loop, ev_async *)	3060	=item ev_async_send (loop, ev_async *)
2462		3061
2463	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3062	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2464	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3063	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2465	C<ev_feed_event>, this call is safe to do in other threads, signal or	3064	C<ev_feed_event>, this call is safe to do from other threads, signal or
2466	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3065	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2467	section below on what exactly this means).	3066	section below on what exactly this means).
2468		3067
		3068	Note that, as with other watchers in libev, multiple events might get
		3069	compressed into a single callback invocation (another way to look at this
		3070	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3071	reset when the event loop detects that).
		3072
2469	This call incurs the overhead of a system call only once per loop iteration,	3073	This call incurs the overhead of a system call only once per event loop
2470	so while the overhead might be noticeable, it doesn't apply to repeated	3074	iteration, so while the overhead might be noticeable, it doesn't apply to
2471	calls to C<ev_async_send>.	3075	repeated calls to C<ev_async_send> for the same event loop.
2472		3076
2473	=item bool = ev_async_pending (ev_async *)	3077	=item bool = ev_async_pending (ev_async *)
2474		3078
2475	Returns a non-zero value when C<ev_async_send> has been called on the	3079	Returns a non-zero value when C<ev_async_send> has been called on the
2476	watcher but the event has not yet been processed (or even noted) by the	3080	watcher but the event has not yet been processed (or even noted) by the
…		…
2479	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3083	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2480	the loop iterates next and checks for the watcher to have become active,	3084	the loop iterates next and checks for the watcher to have become active,
2481	it will reset the flag again. C<ev_async_pending> can be used to very	3085	it will reset the flag again. C<ev_async_pending> can be used to very
2482	quickly check whether invoking the loop might be a good idea.	3086	quickly check whether invoking the loop might be a good idea.
2483		3087
2484	Not that this does I<not> check whether the watcher itself is pending, only	3088	Not that this does I<not> check whether the watcher itself is pending,
2485	whether it has been requested to make this watcher pending.	3089	only whether it has been requested to make this watcher pending: there
		3090	is a time window between the event loop checking and resetting the async
		3091	notification, and the callback being invoked.
2486		3092
2487	=back	3093	=back
2488		3094
2489		3095
2490	=head1 OTHER FUNCTIONS	3096	=head1 OTHER FUNCTIONS
…		…
2494	=over 4	3100	=over 4
2495		3101
2496	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3102	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2497		3103
2498	This function combines a simple timer and an I/O watcher, calls your	3104	This function combines a simple timer and an I/O watcher, calls your
2499	callback on whichever event happens first and automatically stop both	3105	callback on whichever event happens first and automatically stops both
2500	watchers. This is useful if you want to wait for a single event on an fd	3106	watchers. This is useful if you want to wait for a single event on an fd
2501	or timeout without having to allocate/configure/start/stop/free one or	3107	or timeout without having to allocate/configure/start/stop/free one or
2502	more watchers yourself.	3108	more watchers yourself.
2503		3109
2504	If C<fd> is less than 0, then no I/O watcher will be started and events	3110	If C<fd> is less than 0, then no I/O watcher will be started and the
2505	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3111	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2506	C<events> set will be created and started.	3112	the given C<fd> and C<events> set will be created and started.
2507		3113
2508	If C<timeout> is less than 0, then no timeout watcher will be	3114	If C<timeout> is less than 0, then no timeout watcher will be
2509	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3115	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2510	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3116	repeat = 0) will be started. C<0> is a valid timeout.
2511	dubious value.
2512		3117
2513	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3118	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2514	passed an C<revents> set like normal event callbacks (a combination of	3119	passed an C<revents> set like normal event callbacks (a combination of
2515	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3120	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2516	value passed to C<ev_once>:	3121	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3122	a timeout and an io event at the same time - you probably should give io
		3123	events precedence.
		3124
		3125	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2517		3126
2518	static void stdin_ready (int revents, void *arg)	3127	static void stdin_ready (int revents, void *arg)
2519	{	3128	{
		3129	if (revents & EV_READ)
		3130	/* stdin might have data for us, joy! */;
2520	if (revents & EV_TIMEOUT)	3131	else if (revents & EV_TIMEOUT)
2521	/* doh, nothing entered */;	3132	/* doh, nothing entered */;
2522	else if (revents & EV_READ)
2523	/* stdin might have data for us, joy! */;
2524	}	3133	}
2525		3134
2526	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3135	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2527		3136
2528	=item ev_feed_event (ev_loop *, watcher *, int revents)	3137	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2529		3138
2530	Feeds the given event set into the event loop, as if the specified event	3139	Feeds the given event set into the event loop, as if the specified event
2531	had happened for the specified watcher (which must be a pointer to an	3140	had happened for the specified watcher (which must be a pointer to an
2532	initialised but not necessarily started event watcher).	3141	initialised but not necessarily started event watcher).
2533		3142
2534	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3143	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2535		3144
2536	Feed an event on the given fd, as if a file descriptor backend detected	3145	Feed an event on the given fd, as if a file descriptor backend detected
2537	the given events it.	3146	the given events it.
2538		3147
2539	=item ev_feed_signal_event (ev_loop *loop, int signum)	3148	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2540		3149
2541	Feed an event as if the given signal occurred (C<loop> must be the default	3150	Feed an event as if the given signal occurred (C<loop> must be the default
2542	loop!).	3151	loop!).
2543		3152
2544	=back	3153	=back
…		…
2666		3275
2667	myclass obj;	3276	myclass obj;
2668	ev::io iow;	3277	ev::io iow;
2669	iow.set <myclass, &myclass::io_cb> (&obj);	3278	iow.set <myclass, &myclass::io_cb> (&obj);
2670		3279
		3280	=item w->set (object *)
		3281
		3282	This is an B<experimental> feature that might go away in a future version.
		3283
		3284	This is a variation of a method callback - leaving out the method to call
		3285	will default the method to C<operator ()>, which makes it possible to use
		3286	functor objects without having to manually specify the C<operator ()> all
		3287	the time. Incidentally, you can then also leave out the template argument
		3288	list.
		3289
		3290	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3291	int revents)>.
		3292
		3293	See the method-C<set> above for more details.
		3294
		3295	Example: use a functor object as callback.
		3296
		3297	struct myfunctor
		3298	{
		3299	void operator() (ev::io &w, int revents)
		3300	{
		3301	...
		3302	}
		3303	}
		3304
		3305	myfunctor f;
		3306
		3307	ev::io w;
		3308	w.set (&f);
		3309
2671	=item w->set<function> (void *data = 0)	3310	=item w->set<function> (void *data = 0)
2672		3311
2673	Also sets a callback, but uses a static method or plain function as	3312	Also sets a callback, but uses a static method or plain function as
2674	callback. The optional C<data> argument will be stored in the watcher's	3313	callback. The optional C<data> argument will be stored in the watcher's
2675	C<data> member and is free for you to use.	3314	C<data> member and is free for you to use.
2676		3315
2677	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3316	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2678		3317
2679	See the method-C<set> above for more details.	3318	See the method-C<set> above for more details.
2680		3319
2681	Example:	3320	Example: Use a plain function as callback.
2682		3321
2683	static void io_cb (ev::io &w, int revents) { }	3322	static void io_cb (ev::io &w, int revents) { }
2684	iow.set <io_cb> ();	3323	iow.set <io_cb> ();
2685		3324
2686	=item w->set (struct ev_loop *)	3325	=item w->set (struct ev_loop *)
…		…
2724	Example: Define a class with an IO and idle watcher, start one of them in	3363	Example: Define a class with an IO and idle watcher, start one of them in
2725	the constructor.	3364	the constructor.
2726		3365
2727	class myclass	3366	class myclass
2728	{	3367	{
2729	ev::io io; void io_cb (ev::io &w, int revents);	3368	ev::io io ; void io_cb (ev::io &w, int revents);
2730	ev:idle idle void idle_cb (ev::idle &w, int revents);	3369	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2731		3370
2732	myclass (int fd)	3371	myclass (int fd)
2733	{	3372	{
2734	io .set <myclass, &myclass::io_cb > (this);	3373	io .set <myclass, &myclass::io_cb > (this);
2735	idle.set <myclass, &myclass::idle_cb> (this);	3374	idle.set <myclass, &myclass::idle_cb> (this);
…		…
2751	=item Perl	3390	=item Perl
2752		3391
2753	The EV module implements the full libev API and is actually used to test	3392	The EV module implements the full libev API and is actually used to test
2754	libev. EV is developed together with libev. Apart from the EV core module,	3393	libev. EV is developed together with libev. Apart from the EV core module,
2755	there are additional modules that implement libev-compatible interfaces	3394	there are additional modules that implement libev-compatible interfaces
2756	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3395	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2757	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3396	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3397	and C<EV::Glib>).
2758		3398
2759	It can be found and installed via CPAN, its homepage is at	3399	It can be found and installed via CPAN, its homepage is at
2760	L<http://software.schmorp.de/pkg/EV>.	3400	L<http://software.schmorp.de/pkg/EV>.
2761		3401
2762	=item Python	3402	=item Python
2763		3403
2764	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3404	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2765	seems to be quite complete and well-documented. Note, however, that the	3405	seems to be quite complete and well-documented.
2766	patch they require for libev is outright dangerous as it breaks the ABI
2767	for everybody else, and therefore, should never be applied in an installed
2768	libev (if python requires an incompatible ABI then it needs to embed
2769	libev).
2770		3406
2771	=item Ruby	3407	=item Ruby
2772		3408
2773	Tony Arcieri has written a ruby extension that offers access to a subset	3409	Tony Arcieri has written a ruby extension that offers access to a subset
2774	of the libev API and adds file handle abstractions, asynchronous DNS and	3410	of the libev API and adds file handle abstractions, asynchronous DNS and
2775	more on top of it. It can be found via gem servers. Its homepage is at	3411	more on top of it. It can be found via gem servers. Its homepage is at
2776	L<http://rev.rubyforge.org/>.	3412	L<http://rev.rubyforge.org/>.
2777		3413
		3414	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3415	makes rev work even on mingw.
		3416
		3417	=item Haskell
		3418
		3419	A haskell binding to libev is available at
		3420	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3421
2778	=item D	3422	=item D
2779		3423
2780	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3424	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2781	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3425	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3426
		3427	=item Ocaml
		3428
		3429	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3430	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3431
		3432	=item Lua
		3433
		3434	Brian Maher has written a partial interface to libev
		3435	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3436	L<http://github.com/brimworks/lua-ev>.
2782		3437
2783	=back	3438	=back
2784		3439
2785		3440
2786	=head1 MACRO MAGIC	3441	=head1 MACRO MAGIC
…		…
2887		3542
2888	#define EV_STANDALONE 1	3543	#define EV_STANDALONE 1
2889	#include "ev.h"	3544	#include "ev.h"
2890		3545
2891	Both header files and implementation files can be compiled with a C++	3546	Both header files and implementation files can be compiled with a C++
2892	compiler (at least, thats a stated goal, and breakage will be treated	3547	compiler (at least, that's a stated goal, and breakage will be treated
2893	as a bug).	3548	as a bug).
2894		3549
2895	You need the following files in your source tree, or in a directory	3550	You need the following files in your source tree, or in a directory
2896	in your include path (e.g. in libev/ when using -Ilibev):	3551	in your include path (e.g. in libev/ when using -Ilibev):
2897		3552
…		…
2941		3596
2942	=head2 PREPROCESSOR SYMBOLS/MACROS	3597	=head2 PREPROCESSOR SYMBOLS/MACROS
2943		3598
2944	Libev can be configured via a variety of preprocessor symbols you have to	3599	Libev can be configured via a variety of preprocessor symbols you have to
2945	define before including any of its files. The default in the absence of	3600	define before including any of its files. The default in the absence of
2946	autoconf is noted for every option.	3601	autoconf is documented for every option.
2947		3602
2948	=over 4	3603	=over 4
2949		3604
2950	=item EV_STANDALONE	3605	=item EV_STANDALONE
2951		3606
…		…
2953	keeps libev from including F<config.h>, and it also defines dummy	3608	keeps libev from including F<config.h>, and it also defines dummy
2954	implementations for some libevent functions (such as logging, which is not	3609	implementations for some libevent functions (such as logging, which is not
2955	supported). It will also not define any of the structs usually found in	3610	supported). It will also not define any of the structs usually found in
2956	F<event.h> that are not directly supported by the libev core alone.	3611	F<event.h> that are not directly supported by the libev core alone.
2957		3612
		3613	In standalone mode, libev will still try to automatically deduce the
		3614	configuration, but has to be more conservative.
		3615
2958	=item EV_USE_MONOTONIC	3616	=item EV_USE_MONOTONIC
2959		3617
2960	If defined to be C<1>, libev will try to detect the availability of the	3618	If defined to be C<1>, libev will try to detect the availability of the
2961	monotonic clock option at both compile time and runtime. Otherwise no use	3619	monotonic clock option at both compile time and runtime. Otherwise no
2962	of the monotonic clock option will be attempted. If you enable this, you	3620	use of the monotonic clock option will be attempted. If you enable this,
2963	usually have to link against librt or something similar. Enabling it when	3621	you usually have to link against librt or something similar. Enabling it
2964	the functionality isn't available is safe, though, although you have	3622	when the functionality isn't available is safe, though, although you have
2965	to make sure you link against any libraries where the C<clock_gettime>	3623	to make sure you link against any libraries where the C<clock_gettime>
2966	function is hiding in (often F<-lrt>).	3624	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2967		3625
2968	=item EV_USE_REALTIME	3626	=item EV_USE_REALTIME
2969		3627
2970	If defined to be C<1>, libev will try to detect the availability of the	3628	If defined to be C<1>, libev will try to detect the availability of the
2971	real-time clock option at compile time (and assume its availability at	3629	real-time clock option at compile time (and assume its availability
2972	runtime if successful). Otherwise no use of the real-time clock option will	3630	at runtime if successful). Otherwise no use of the real-time clock
2973	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3631	option will be attempted. This effectively replaces C<gettimeofday>
2974	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3632	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2975	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3633	correctness. See the note about libraries in the description of
		3634	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3635	C<EV_USE_CLOCK_SYSCALL>.
		3636
		3637	=item EV_USE_CLOCK_SYSCALL
		3638
		3639	If defined to be C<1>, libev will try to use a direct syscall instead
		3640	of calling the system-provided C<clock_gettime> function. This option
		3641	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3642	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3643	programs needlessly. Using a direct syscall is slightly slower (in
		3644	theory), because no optimised vdso implementation can be used, but avoids
		3645	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3646	higher, as it simplifies linking (no need for C<-lrt>).
2976		3647
2977	=item EV_USE_NANOSLEEP	3648	=item EV_USE_NANOSLEEP
2978		3649
2979	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3650	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2980	and will use it for delays. Otherwise it will use C<select ()>.	3651	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2996		3667
2997	=item EV_SELECT_USE_FD_SET	3668	=item EV_SELECT_USE_FD_SET
2998		3669
2999	If defined to C<1>, then the select backend will use the system C<fd_set>	3670	If defined to C<1>, then the select backend will use the system C<fd_set>
3000	structure. This is useful if libev doesn't compile due to a missing	3671	structure. This is useful if libev doesn't compile due to a missing
3001	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3672	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3002	exotic systems. This usually limits the range of file descriptors to some	3673	on exotic systems. This usually limits the range of file descriptors to
3003	low limit such as 1024 or might have other limitations (winsocket only	3674	some low limit such as 1024 or might have other limitations (winsocket
3004	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3675	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3005	influence the size of the C<fd_set> used.	3676	configures the maximum size of the C<fd_set>.
3006		3677
3007	=item EV_SELECT_IS_WINSOCKET	3678	=item EV_SELECT_IS_WINSOCKET
3008		3679
3009	When defined to C<1>, the select backend will assume that	3680	When defined to C<1>, the select backend will assume that
3010	select/socket/connect etc. don't understand file descriptors but	3681	select/socket/connect etc. don't understand file descriptors but
…		…
3012	be used is the winsock select). This means that it will call	3683	be used is the winsock select). This means that it will call
3013	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3684	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3014	it is assumed that all these functions actually work on fds, even	3685	it is assumed that all these functions actually work on fds, even
3015	on win32. Should not be defined on non-win32 platforms.	3686	on win32. Should not be defined on non-win32 platforms.
3016		3687
3017	=item EV_FD_TO_WIN32_HANDLE	3688	=item EV_FD_TO_WIN32_HANDLE(fd)
3018		3689
3019	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3690	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3020	file descriptors to socket handles. When not defining this symbol (the	3691	file descriptors to socket handles. When not defining this symbol (the
3021	default), then libev will call C<_get_osfhandle>, which is usually	3692	default), then libev will call C<_get_osfhandle>, which is usually
3022	correct. In some cases, programs use their own file descriptor management,	3693	correct. In some cases, programs use their own file descriptor management,
3023	in which case they can provide this function to map fds to socket handles.	3694	in which case they can provide this function to map fds to socket handles.
		3695
		3696	=item EV_WIN32_HANDLE_TO_FD(handle)
		3697
		3698	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3699	using the standard C<_open_osfhandle> function. For programs implementing
		3700	their own fd to handle mapping, overwriting this function makes it easier
		3701	to do so. This can be done by defining this macro to an appropriate value.
		3702
		3703	=item EV_WIN32_CLOSE_FD(fd)
		3704
		3705	If programs implement their own fd to handle mapping on win32, then this
		3706	macro can be used to override the C<close> function, useful to unregister
		3707	file descriptors again. Note that the replacement function has to close
		3708	the underlying OS handle.
3024		3709
3025	=item EV_USE_POLL	3710	=item EV_USE_POLL
3026		3711
3027	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3712	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3028	backend. Otherwise it will be enabled on non-win32 platforms. It	3713	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3121	When doing priority-based operations, libev usually has to linearly search	3806	When doing priority-based operations, libev usually has to linearly search
3122	all the priorities, so having many of them (hundreds) uses a lot of space	3807	all the priorities, so having many of them (hundreds) uses a lot of space
3123	and time, so using the defaults of five priorities (-2 .. +2) is usually	3808	and time, so using the defaults of five priorities (-2 .. +2) is usually
3124	fine.	3809	fine.
3125		3810
3126	If your embedding application does not need any priorities, defining these both to	3811	If your embedding application does not need any priorities, defining these
3127	C<0> will save some memory and CPU.	3812	both to C<0> will save some memory and CPU.
3128		3813
3129	=item EV_PERIODIC_ENABLE	3814	=item EV_PERIODIC_ENABLE
3130		3815
3131	If undefined or defined to be C<1>, then periodic timers are supported. If	3816	If undefined or defined to be C<1>, then periodic timers are supported. If
3132	defined to be C<0>, then they are not. Disabling them saves a few kB of	3817	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
3139	code.	3824	code.
3140		3825
3141	=item EV_EMBED_ENABLE	3826	=item EV_EMBED_ENABLE
3142		3827
3143	If undefined or defined to be C<1>, then embed watchers are supported. If	3828	If undefined or defined to be C<1>, then embed watchers are supported. If
3144	defined to be C<0>, then they are not.	3829	defined to be C<0>, then they are not. Embed watchers rely on most other
		3830	watcher types, which therefore must not be disabled.
3145		3831
3146	=item EV_STAT_ENABLE	3832	=item EV_STAT_ENABLE
3147		3833
3148	If undefined or defined to be C<1>, then stat watchers are supported. If	3834	If undefined or defined to be C<1>, then stat watchers are supported. If
3149	defined to be C<0>, then they are not.	3835	defined to be C<0>, then they are not.
…		…
3159	defined to be C<0>, then they are not.	3845	defined to be C<0>, then they are not.
3160		3846
3161	=item EV_MINIMAL	3847	=item EV_MINIMAL
3162		3848
3163	If you need to shave off some kilobytes of code at the expense of some	3849	If you need to shave off some kilobytes of code at the expense of some
3164	speed, define this symbol to C<1>. Currently this is used to override some	3850	speed (but with the full API), define this symbol to C<1>. Currently this
3165	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3851	is used to override some inlining decisions, saves roughly 30% code size
3166	much smaller 2-heap for timer management over the default 4-heap.	3852	on amd64. It also selects a much smaller 2-heap for timer management over
		3853	the default 4-heap.
		3854
		3855	You can save even more by disabling watcher types you do not need
		3856	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3857	(C<-DNDEBUG>) will usually reduce code size a lot.
		3858
		3859	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3860	provide a bare-bones event library. See C<ev.h> for details on what parts
		3861	of the API are still available, and do not complain if this subset changes
		3862	over time.
		3863
		3864	=item EV_NSIG
		3865
		3866	The highest supported signal number, +1 (or, the number of
		3867	signals): Normally, libev tries to deduce the maximum number of signals
		3868	automatically, but sometimes this fails, in which case it can be
		3869	specified. Also, using a lower number than detected (C<32> should be
		3870	good for about any system in existance) can save some memory, as libev
		3871	statically allocates some 12-24 bytes per signal number.
3167		3872
3168	=item EV_PID_HASHSIZE	3873	=item EV_PID_HASHSIZE
3169		3874
3170	C<ev_child> watchers use a small hash table to distribute workload by	3875	C<ev_child> watchers use a small hash table to distribute workload by
3171	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3876	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3181	two).	3886	two).
3182		3887
3183	=item EV_USE_4HEAP	3888	=item EV_USE_4HEAP
3184		3889
3185	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3890	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3186	timer and periodics heap, libev uses a 4-heap when this symbol is defined	3891	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3187	to C<1>. The 4-heap uses more complicated (longer) code but has	3892	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3188	noticeably faster performance with many (thousands) of watchers.	3893	faster performance with many (thousands) of watchers.
3189		3894
3190	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3895	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3191	(disabled).	3896	(disabled).
3192		3897
3193	=item EV_HEAP_CACHE_AT	3898	=item EV_HEAP_CACHE_AT
3194		3899
3195	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3900	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3196	timer and periodics heap, libev can cache the timestamp (I<at>) within	3901	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3197	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	3902	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3198	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	3903	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3199	but avoids random read accesses on heap changes. This improves performance	3904	but avoids random read accesses on heap changes. This improves performance
3200	noticeably with with many (hundreds) of watchers.	3905	noticeably with many (hundreds) of watchers.
3201		3906
3202	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3907	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3203	(disabled).	3908	(disabled).
3204		3909
3205	=item EV_VERIFY	3910	=item EV_VERIFY
…		…
3211	called once per loop, which can slow down libev. If set to C<3>, then the	3916	called once per loop, which can slow down libev. If set to C<3>, then the
3212	verification code will be called very frequently, which will slow down	3917	verification code will be called very frequently, which will slow down
3213	libev considerably.	3918	libev considerably.
3214		3919
3215	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	3920	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
3216	C<0.>	3921	C<0>.
3217		3922
3218	=item EV_COMMON	3923	=item EV_COMMON
3219		3924
3220	By default, all watchers have a C<void *data> member. By redefining	3925	By default, all watchers have a C<void *data> member. By redefining
3221	this macro to a something else you can include more and other types of	3926	this macro to a something else you can include more and other types of
…		…
3238	and the way callbacks are invoked and set. Must expand to a struct member	3943	and the way callbacks are invoked and set. Must expand to a struct member
3239	definition and a statement, respectively. See the F<ev.h> header file for	3944	definition and a statement, respectively. See the F<ev.h> header file for
3240	their default definitions. One possible use for overriding these is to	3945	their default definitions. One possible use for overriding these is to
3241	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3946	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3242	method calls instead of plain function calls in C++.	3947	method calls instead of plain function calls in C++.
		3948
		3949	=back
3243		3950
3244	=head2 EXPORTED API SYMBOLS	3951	=head2 EXPORTED API SYMBOLS
3245		3952
3246	If you need to re-export the API (e.g. via a DLL) and you need a list of	3953	If you need to re-export the API (e.g. via a DLL) and you need a list of
3247	exported symbols, you can use the provided F<Symbol.*> files which list	3954	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3294	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4001	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3295		4002
3296	#include "ev_cpp.h"	4003	#include "ev_cpp.h"
3297	#include "ev.c"	4004	#include "ev.c"
3298		4005
		4006	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3299		4007
3300	=head1 THREADS AND COROUTINES	4008	=head2 THREADS AND COROUTINES
3301		4009
3302	=head2 THREADS	4010	=head3 THREADS
3303		4011
3304	Libev itself is thread-safe (unless the opposite is specifically	4012	All libev functions are reentrant and thread-safe unless explicitly
3305	documented for a function), but it uses no locking itself. This means that	4013	documented otherwise, but libev implements no locking itself. This means
3306	you can use as many loops as you want in parallel, as long as only one	4014	that you can use as many loops as you want in parallel, as long as there
3307	thread ever calls into one libev function with the same loop parameter:	4015	are no concurrent calls into any libev function with the same loop
		4016	parameter (C<ev_default_*> calls have an implicit default loop parameter,
3308	libev guarentees that different event loops share no data structures that	4017	of course): libev guarantees that different event loops share no data
3309	need locking.	4018	structures that need any locking.
3310		4019
3311	Or to put it differently: calls with different loop parameters can be done	4020	Or to put it differently: calls with different loop parameters can be done
3312	concurrently from multiple threads, calls with the same loop parameter	4021	concurrently from multiple threads, calls with the same loop parameter
3313	must be done serially (but can be done from different threads, as long as	4022	must be done serially (but can be done from different threads, as long as
3314	only one thread ever is inside a call at any point in time, e.g. by using	4023	only one thread ever is inside a call at any point in time, e.g. by using
3315	a mutex per loop).	4024	a mutex per loop).
3316		4025
3317	Specifically to support threads (and signal handlers), libev implements	4026	Specifically to support threads (and signal handlers), libev implements
3318	so-called C<ev_async> watchers, which allow some limited form of	4027	so-called C<ev_async> watchers, which allow some limited form of
3319	concurrency on the same event loop.	4028	concurrency on the same event loop, namely waking it up "from the
		4029	outside".
3320		4030
3321	If you want to know which design (one loop, locking, or multiple loops	4031	If you want to know which design (one loop, locking, or multiple loops
3322	without or something else still) is best for your problem, then I cannot	4032	without or something else still) is best for your problem, then I cannot
3323	help you. I can give some generic advice however:	4033	help you, but here is some generic advice:
3324		4034
3325	=over 4	4035	=over 4
3326		4036
3327	=item * most applications have a main thread: use the default libev loop	4037	=item * most applications have a main thread: use the default libev loop
3328	in that thread, or create a separate thread running only the default loop.	4038	in that thread, or create a separate thread running only the default loop.
…		…
3352	default loop and triggering an C<ev_async> watcher from the default loop	4062	default loop and triggering an C<ev_async> watcher from the default loop
3353	watcher callback into the event loop interested in the signal.	4063	watcher callback into the event loop interested in the signal.
3354		4064
3355	=back	4065	=back
3356		4066
		4067	=head4 THREAD LOCKING EXAMPLE
		4068
		4069	Here is a fictitious example of how to run an event loop in a different
		4070	thread than where callbacks are being invoked and watchers are
		4071	created/added/removed.
		4072
		4073	For a real-world example, see the C<EV::Loop::Async> perl module,
		4074	which uses exactly this technique (which is suited for many high-level
		4075	languages).
		4076
		4077	The example uses a pthread mutex to protect the loop data, a condition
		4078	variable to wait for callback invocations, an async watcher to notify the
		4079	event loop thread and an unspecified mechanism to wake up the main thread.
		4080
		4081	First, you need to associate some data with the event loop:
		4082
		4083	typedef struct {
		4084	mutex_t lock; /* global loop lock */
		4085	ev_async async_w;
		4086	thread_t tid;
		4087	cond_t invoke_cv;
		4088	} userdata;
		4089
		4090	void prepare_loop (EV_P)
		4091	{
		4092	// for simplicity, we use a static userdata struct.
		4093	static userdata u;
		4094
		4095	ev_async_init (&u->async_w, async_cb);
		4096	ev_async_start (EV_A_ &u->async_w);
		4097
		4098	pthread_mutex_init (&u->lock, 0);
		4099	pthread_cond_init (&u->invoke_cv, 0);
		4100
		4101	// now associate this with the loop
		4102	ev_set_userdata (EV_A_ u);
		4103	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4104	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4105
		4106	// then create the thread running ev_loop
		4107	pthread_create (&u->tid, 0, l_run, EV_A);
		4108	}
		4109
		4110	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4111	solely to wake up the event loop so it takes notice of any new watchers
		4112	that might have been added:
		4113
		4114	static void
		4115	async_cb (EV_P_ ev_async *w, int revents)
		4116	{
		4117	// just used for the side effects
		4118	}
		4119
		4120	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4121	protecting the loop data, respectively.
		4122
		4123	static void
		4124	l_release (EV_P)
		4125	{
		4126	userdata *u = ev_userdata (EV_A);
		4127	pthread_mutex_unlock (&u->lock);
		4128	}
		4129
		4130	static void
		4131	l_acquire (EV_P)
		4132	{
		4133	userdata *u = ev_userdata (EV_A);
		4134	pthread_mutex_lock (&u->lock);
		4135	}
		4136
		4137	The event loop thread first acquires the mutex, and then jumps straight
		4138	into C<ev_loop>:
		4139
		4140	void *
		4141	l_run (void *thr_arg)
		4142	{
		4143	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4144
		4145	l_acquire (EV_A);
		4146	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4147	ev_loop (EV_A_ 0);
		4148	l_release (EV_A);
		4149
		4150	return 0;
		4151	}
		4152
		4153	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4154	signal the main thread via some unspecified mechanism (signals? pipe
		4155	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4156	have been called (in a while loop because a) spurious wakeups are possible
		4157	and b) skipping inter-thread-communication when there are no pending
		4158	watchers is very beneficial):
		4159
		4160	static void
		4161	l_invoke (EV_P)
		4162	{
		4163	userdata *u = ev_userdata (EV_A);
		4164
		4165	while (ev_pending_count (EV_A))
		4166	{
		4167	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4168	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4169	}
		4170	}
		4171
		4172	Now, whenever the main thread gets told to invoke pending watchers, it
		4173	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4174	thread to continue:
		4175
		4176	static void
		4177	real_invoke_pending (EV_P)
		4178	{
		4179	userdata *u = ev_userdata (EV_A);
		4180
		4181	pthread_mutex_lock (&u->lock);
		4182	ev_invoke_pending (EV_A);
		4183	pthread_cond_signal (&u->invoke_cv);
		4184	pthread_mutex_unlock (&u->lock);
		4185	}
		4186
		4187	Whenever you want to start/stop a watcher or do other modifications to an
		4188	event loop, you will now have to lock:
		4189
		4190	ev_timer timeout_watcher;
		4191	userdata *u = ev_userdata (EV_A);
		4192
		4193	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4194
		4195	pthread_mutex_lock (&u->lock);
		4196	ev_timer_start (EV_A_ &timeout_watcher);
		4197	ev_async_send (EV_A_ &u->async_w);
		4198	pthread_mutex_unlock (&u->lock);
		4199
		4200	Note that sending the C<ev_async> watcher is required because otherwise
		4201	an event loop currently blocking in the kernel will have no knowledge
		4202	about the newly added timer. By waking up the loop it will pick up any new
		4203	watchers in the next event loop iteration.
		4204
3357	=head2 COROUTINES	4205	=head3 COROUTINES
3358		4206
3359	Libev is much more accommodating to coroutines ("cooperative threads"):	4207	Libev is very accommodating to coroutines ("cooperative threads"):
3360	libev fully supports nesting calls to it's functions from different	4208	libev fully supports nesting calls to its functions from different
3361	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4209	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3362	different coroutines and switch freely between both coroutines running the	4210	different coroutines, and switch freely between both coroutines running
3363	loop, as long as you don't confuse yourself). The only exception is that	4211	the loop, as long as you don't confuse yourself). The only exception is
3364	you must not do this from C<ev_periodic> reschedule callbacks.	4212	that you must not do this from C<ev_periodic> reschedule callbacks.
3365		4213
3366	Care has been taken to ensure that libev does not keep local state inside	4214	Care has been taken to ensure that libev does not keep local state inside
3367	C<ev_loop>, and other calls do not usually allow coroutine switches.	4215	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4216	they do not call any callbacks.
3368		4217
		4218	=head2 COMPILER WARNINGS
3369		4219
3370	=head1 COMPLEXITIES	4220	Depending on your compiler and compiler settings, you might get no or a
		4221	lot of warnings when compiling libev code. Some people are apparently
		4222	scared by this.
3371		4223
3372	In this section the complexities of (many of) the algorithms used inside	4224	However, these are unavoidable for many reasons. For one, each compiler
3373	libev will be explained. For complexity discussions about backends see the	4225	has different warnings, and each user has different tastes regarding
3374	documentation for C<ev_default_init>.	4226	warning options. "Warn-free" code therefore cannot be a goal except when
		4227	targeting a specific compiler and compiler-version.
3375		4228
3376	All of the following are about amortised time: If an array needs to be	4229	Another reason is that some compiler warnings require elaborate
3377	extended, libev needs to realloc and move the whole array, but this	4230	workarounds, or other changes to the code that make it less clear and less
3378	happens asymptotically never with higher number of elements, so O(1) might	4231	maintainable.
3379	mean it might do a lengthy realloc operation in rare cases, but on average
3380	it is much faster and asymptotically approaches constant time.
3381		4232
3382	=over 4	4233	And of course, some compiler warnings are just plain stupid, or simply
		4234	wrong (because they don't actually warn about the condition their message
		4235	seems to warn about). For example, certain older gcc versions had some
		4236	warnings that resulted an extreme number of false positives. These have
		4237	been fixed, but some people still insist on making code warn-free with
		4238	such buggy versions.
3383		4239
3384	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4240	While libev is written to generate as few warnings as possible,
		4241	"warn-free" code is not a goal, and it is recommended not to build libev
		4242	with any compiler warnings enabled unless you are prepared to cope with
		4243	them (e.g. by ignoring them). Remember that warnings are just that:
		4244	warnings, not errors, or proof of bugs.
3385		4245
3386	This means that, when you have a watcher that triggers in one hour and
3387	there are 100 watchers that would trigger before that then inserting will
3388	have to skip roughly seven (C<ld 100>) of these watchers.
3389		4246
3390	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4247	=head2 VALGRIND
3391		4248
3392	That means that changing a timer costs less than removing/adding them	4249	Valgrind has a special section here because it is a popular tool that is
3393	as only the relative motion in the event queue has to be paid for.	4250	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3394		4251
3395	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4252	If you think you found a bug (memory leak, uninitialised data access etc.)
		4253	in libev, then check twice: If valgrind reports something like:
3396		4254
3397	These just add the watcher into an array or at the head of a list.	4255	==2274== definitely lost: 0 bytes in 0 blocks.
		4256	==2274== possibly lost: 0 bytes in 0 blocks.
		4257	==2274== still reachable: 256 bytes in 1 blocks.
3398		4258
3399	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4259	Then there is no memory leak, just as memory accounted to global variables
		4260	is not a memleak - the memory is still being referenced, and didn't leak.
3400		4261
3401	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4262	Similarly, under some circumstances, valgrind might report kernel bugs
		4263	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4264	although an acceptable workaround has been found here), or it might be
		4265	confused.
3402		4266
3403	These watchers are stored in lists then need to be walked to find the	4267	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3404	correct watcher to remove. The lists are usually short (you don't usually	4268	make it into some kind of religion.
3405	have many watchers waiting for the same fd or signal).
3406		4269
3407	=item Finding the next timer in each loop iteration: O(1)	4270	If you are unsure about something, feel free to contact the mailing list
		4271	with the full valgrind report and an explanation on why you think this
		4272	is a bug in libev (best check the archives, too :). However, don't be
		4273	annoyed when you get a brisk "this is no bug" answer and take the chance
		4274	of learning how to interpret valgrind properly.
3408		4275
3409	By virtue of using a binary or 4-heap, the next timer is always found at a	4276	If you need, for some reason, empty reports from valgrind for your project
3410	fixed position in the storage array.	4277	I suggest using suppression lists.
3411		4278
3412	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3413		4279
3414	A change means an I/O watcher gets started or stopped, which requires	4280	=head1 PORTABILITY NOTES
3415	libev to recalculate its status (and possibly tell the kernel, depending
3416	on backend and whether C<ev_io_set> was used).
3417		4281
3418	=item Activating one watcher (putting it into the pending state): O(1)
3419
3420	=item Priority handling: O(number_of_priorities)
3421
3422	Priorities are implemented by allocating some space for each
3423	priority. When doing priority-based operations, libev usually has to
3424	linearly search all the priorities, but starting/stopping and activating
3425	watchers becomes O(1) w.r.t. priority handling.
3426
3427	=item Sending an ev_async: O(1)
3428
3429	=item Processing ev_async_send: O(number_of_async_watchers)
3430
3431	=item Processing signals: O(max_signal_number)
3432
3433	Sending involves a system call I<iff> there were no other C<ev_async_send>
3434	calls in the current loop iteration. Checking for async and signal events
3435	involves iterating over all running async watchers or all signal numbers.
3436
3437	=back
3438
3439
3440	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4282	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3441		4283
3442	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4284	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3443	requires, and its I/O model is fundamentally incompatible with the POSIX	4285	requires, and its I/O model is fundamentally incompatible with the POSIX
3444	model. Libev still offers limited functionality on this platform in	4286	model. Libev still offers limited functionality on this platform in
3445	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4287	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3452	way (note also that glib is the slowest event library known to man).	4294	way (note also that glib is the slowest event library known to man).
3453		4295
3454	There is no supported compilation method available on windows except	4296	There is no supported compilation method available on windows except
3455	embedding it into other applications.	4297	embedding it into other applications.
3456		4298
		4299	Sensible signal handling is officially unsupported by Microsoft - libev
		4300	tries its best, but under most conditions, signals will simply not work.
		4301
3457	Not a libev limitation but worth mentioning: windows apparently doesn't	4302	Not a libev limitation but worth mentioning: windows apparently doesn't
3458	accept large writes: instead of resulting in a partial write, windows will	4303	accept large writes: instead of resulting in a partial write, windows will
3459	either accept everything or return C<ENOBUFS> if the buffer is too large,	4304	either accept everything or return C<ENOBUFS> if the buffer is too large,
3460	so make sure you only write small amounts into your sockets (less than a	4305	so make sure you only write small amounts into your sockets (less than a
3461	megabyte seems safe, but thsi apparently depends on the amount of memory	4306	megabyte seems safe, but this apparently depends on the amount of memory
3462	available).	4307	available).
3463		4308
3464	Due to the many, low, and arbitrary limits on the win32 platform and	4309	Due to the many, low, and arbitrary limits on the win32 platform and
3465	the abysmal performance of winsockets, using a large number of sockets	4310	the abysmal performance of winsockets, using a large number of sockets
3466	is not recommended (and not reasonable). If your program needs to use	4311	is not recommended (and not reasonable). If your program needs to use
3467	more than a hundred or so sockets, then likely it needs to use a totally	4312	more than a hundred or so sockets, then likely it needs to use a totally
3468	different implementation for windows, as libev offers the POSIX readiness	4313	different implementation for windows, as libev offers the POSIX readiness
3469	notification model, which cannot be implemented efficiently on windows	4314	notification model, which cannot be implemented efficiently on windows
3470	(Microsoft monopoly games).	4315	(due to Microsoft monopoly games).
3471		4316
3472	A typical way to use libev under windows is to embed it (see the embedding	4317	A typical way to use libev under windows is to embed it (see the embedding
3473	section for details) and use the following F<evwrap.h> header file instead	4318	section for details) and use the following F<evwrap.h> header file instead
3474	of F<ev.h>:	4319	of F<ev.h>:
3475		4320
…		…
3477	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	4322	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3478		4323
3479	#include "ev.h"	4324	#include "ev.h"
3480		4325
3481	And compile the following F<evwrap.c> file into your project (make sure	4326	And compile the following F<evwrap.c> file into your project (make sure
3482	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	4327	you do I<not> compile the F<ev.c> or any other embedded source files!):
3483		4328
3484	#include "evwrap.h"	4329	#include "evwrap.h"
3485	#include "ev.c"	4330	#include "ev.c"
3486		4331
3487	=over 4	4332	=over 4
…		…
3511		4356
3512	Early versions of winsocket's select only supported waiting for a maximum	4357	Early versions of winsocket's select only supported waiting for a maximum
3513	of C<64> handles (probably owning to the fact that all windows kernels	4358	of C<64> handles (probably owning to the fact that all windows kernels
3514	can only wait for C<64> things at the same time internally; Microsoft	4359	can only wait for C<64> things at the same time internally; Microsoft
3515	recommends spawning a chain of threads and wait for 63 handles and the	4360	recommends spawning a chain of threads and wait for 63 handles and the
3516	previous thread in each. Great).	4361	previous thread in each. Sounds great!).
3517		4362
3518	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4363	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3519	to some high number (e.g. C<2048>) before compiling the winsocket select	4364	to some high number (e.g. C<2048>) before compiling the winsocket select
3520	call (which might be in libev or elsewhere, for example, perl does its own	4365	call (which might be in libev or elsewhere, for example, perl and many
3521	select emulation on windows).	4366	other interpreters do their own select emulation on windows).
3522		4367
3523	Another limit is the number of file descriptors in the Microsoft runtime	4368	Another limit is the number of file descriptors in the Microsoft runtime
3524	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4369	libraries, which by default is C<64> (there must be a hidden I<64>
3525	or something like this inside Microsoft). You can increase this by calling	4370	fetish or something like this inside Microsoft). You can increase this
3526	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4371	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3527	arbitrary limit), but is broken in many versions of the Microsoft runtime	4372	(another arbitrary limit), but is broken in many versions of the Microsoft
3528	libraries.
3529
3530	This might get you to about C<512> or C<2048> sockets (depending on	4373	runtime libraries. This might get you to about C<512> or C<2048> sockets
3531	windows version and/or the phase of the moon). To get more, you need to	4374	(depending on windows version and/or the phase of the moon). To get more,
3532	wrap all I/O functions and provide your own fd management, but the cost of	4375	you need to wrap all I/O functions and provide your own fd management, but
3533	calling select (O(n²)) will likely make this unworkable.	4376	the cost of calling select (O(n²)) will likely make this unworkable.
3534		4377
3535	=back	4378	=back
3536		4379
3537
3538	=head1 PORTABILITY REQUIREMENTS	4380	=head2 PORTABILITY REQUIREMENTS
3539		4381
3540	In addition to a working ISO-C implementation, libev relies on a few	4382	In addition to a working ISO-C implementation and of course the
3541	additional extensions:	4383	backend-specific APIs, libev relies on a few additional extensions:
3542		4384
3543	=over 4	4385	=over 4
3544		4386
3545	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4387	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3546	calling conventions regardless of C<ev_watcher_type *>.	4388	calling conventions regardless of C<ev_watcher_type *>.
…		…
3552	calls them using an C<ev_watcher *> internally.	4394	calls them using an C<ev_watcher *> internally.
3553		4395
3554	=item C<sig_atomic_t volatile> must be thread-atomic as well	4396	=item C<sig_atomic_t volatile> must be thread-atomic as well
3555		4397
3556	The type C<sig_atomic_t volatile> (or whatever is defined as	4398	The type C<sig_atomic_t volatile> (or whatever is defined as
3557	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4399	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3558	threads. This is not part of the specification for C<sig_atomic_t>, but is	4400	threads. This is not part of the specification for C<sig_atomic_t>, but is
3559	believed to be sufficiently portable.	4401	believed to be sufficiently portable.
3560		4402
3561	=item C<sigprocmask> must work in a threaded environment	4403	=item C<sigprocmask> must work in a threaded environment
3562		4404
…		…
3571	except the initial one, and run the default loop in the initial thread as	4413	except the initial one, and run the default loop in the initial thread as
3572	well.	4414	well.
3573		4415
3574	=item C<long> must be large enough for common memory allocation sizes	4416	=item C<long> must be large enough for common memory allocation sizes
3575		4417
3576	To improve portability and simplify using libev, libev uses C<long>	4418	To improve portability and simplify its API, libev uses C<long> internally
3577	internally instead of C<size_t> when allocating its data structures. On	4419	instead of C<size_t> when allocating its data structures. On non-POSIX
3578	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4420	systems (Microsoft...) this might be unexpectedly low, but is still at
3579	is still at least 31 bits everywhere, which is enough for hundreds of	4421	least 31 bits everywhere, which is enough for hundreds of millions of
3580	millions of watchers.	4422	watchers.
3581		4423
3582	=item C<double> must hold a time value in seconds with enough accuracy	4424	=item C<double> must hold a time value in seconds with enough accuracy
3583		4425
3584	The type C<double> is used to represent timestamps. It is required to	4426	The type C<double> is used to represent timestamps. It is required to
3585	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4427	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3586	enough for at least into the year 4000. This requirement is fulfilled by	4428	enough for at least into the year 4000. This requirement is fulfilled by
3587	implementations implementing IEEE 754 (basically all existing ones).	4429	implementations implementing IEEE 754, which is basically all existing
		4430	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4431	2200.
3588		4432
3589	=back	4433	=back
3590		4434
3591	If you know of other additional requirements drop me a note.	4435	If you know of other additional requirements drop me a note.
3592		4436
3593		4437
3594	=head1 COMPILER WARNINGS	4438	=head1 ALGORITHMIC COMPLEXITIES
3595		4439
3596	Depending on your compiler and compiler settings, you might get no or a	4440	In this section the complexities of (many of) the algorithms used inside
3597	lot of warnings when compiling libev code. Some people are apparently	4441	libev will be documented. For complexity discussions about backends see
3598	scared by this.	4442	the documentation for C<ev_default_init>.
3599		4443
3600	However, these are unavoidable for many reasons. For one, each compiler	4444	All of the following are about amortised time: If an array needs to be
3601	has different warnings, and each user has different tastes regarding	4445	extended, libev needs to realloc and move the whole array, but this
3602	warning options. "Warn-free" code therefore cannot be a goal except when	4446	happens asymptotically rarer with higher number of elements, so O(1) might
3603	targeting a specific compiler and compiler-version.	4447	mean that libev does a lengthy realloc operation in rare cases, but on
		4448	average it is much faster and asymptotically approaches constant time.
3604		4449
3605	Another reason is that some compiler warnings require elaborate	4450	=over 4
3606	workarounds, or other changes to the code that make it less clear and less
3607	maintainable.
3608		4451
3609	And of course, some compiler warnings are just plain stupid, or simply	4452	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3610	wrong (because they don't actually warn about the condition their message
3611	seems to warn about).
3612		4453
3613	While libev is written to generate as few warnings as possible,	4454	This means that, when you have a watcher that triggers in one hour and
3614	"warn-free" code is not a goal, and it is recommended not to build libev	4455	there are 100 watchers that would trigger before that, then inserting will
3615	with any compiler warnings enabled unless you are prepared to cope with	4456	have to skip roughly seven (C<ld 100>) of these watchers.
3616	them (e.g. by ignoring them). Remember that warnings are just that:
3617	warnings, not errors, or proof of bugs.
3618		4457
		4458	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3619		4459
3620	=head1 VALGRIND	4460	That means that changing a timer costs less than removing/adding them,
		4461	as only the relative motion in the event queue has to be paid for.
3621		4462
3622	Valgrind has a special section here because it is a popular tool that is	4463	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3623	highly useful, but valgrind reports are very hard to interpret.
3624		4464
3625	If you think you found a bug (memory leak, uninitialised data access etc.)	4465	These just add the watcher into an array or at the head of a list.
3626	in libev, then check twice: If valgrind reports something like:
3627		4466
3628	==2274== definitely lost: 0 bytes in 0 blocks.	4467	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3629	==2274== possibly lost: 0 bytes in 0 blocks.
3630	==2274== still reachable: 256 bytes in 1 blocks.
3631		4468
3632	Then there is no memory leak. Similarly, under some circumstances,	4469	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3633	valgrind might report kernel bugs as if it were a bug in libev, or it
3634	might be confused (it is a very good tool, but only a tool).
3635		4470
3636	If you are unsure about something, feel free to contact the mailing list	4471	These watchers are stored in lists, so they need to be walked to find the
3637	with the full valgrind report and an explanation on why you think this is	4472	correct watcher to remove. The lists are usually short (you don't usually
3638	a bug in libev. However, don't be annoyed when you get a brisk "this is	4473	have many watchers waiting for the same fd or signal: one is typical, two
3639	no bug" answer and take the chance of learning how to interpret valgrind	4474	is rare).
3640	properly.
3641		4475
3642	If you need, for some reason, empty reports from valgrind for your project	4476	=item Finding the next timer in each loop iteration: O(1)
3643	I suggest using suppression lists.
3644		4477
		4478	By virtue of using a binary or 4-heap, the next timer is always found at a
		4479	fixed position in the storage array.
		4480
		4481	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4482
		4483	A change means an I/O watcher gets started or stopped, which requires
		4484	libev to recalculate its status (and possibly tell the kernel, depending
		4485	on backend and whether C<ev_io_set> was used).
		4486
		4487	=item Activating one watcher (putting it into the pending state): O(1)
		4488
		4489	=item Priority handling: O(number_of_priorities)
		4490
		4491	Priorities are implemented by allocating some space for each
		4492	priority. When doing priority-based operations, libev usually has to
		4493	linearly search all the priorities, but starting/stopping and activating
		4494	watchers becomes O(1) with respect to priority handling.
		4495
		4496	=item Sending an ev_async: O(1)
		4497
		4498	=item Processing ev_async_send: O(number_of_async_watchers)
		4499
		4500	=item Processing signals: O(max_signal_number)
		4501
		4502	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4503	calls in the current loop iteration. Checking for async and signal events
		4504	involves iterating over all running async watchers or all signal numbers.
		4505
		4506	=back
		4507
		4508
		4509	=head1 GLOSSARY
		4510
		4511	=over 4
		4512
		4513	=item active
		4514
		4515	A watcher is active as long as it has been started (has been attached to
		4516	an event loop) but not yet stopped (disassociated from the event loop).
		4517
		4518	=item application
		4519
		4520	In this document, an application is whatever is using libev.
		4521
		4522	=item callback
		4523
		4524	The address of a function that is called when some event has been
		4525	detected. Callbacks are being passed the event loop, the watcher that
		4526	received the event, and the actual event bitset.
		4527
		4528	=item callback invocation
		4529
		4530	The act of calling the callback associated with a watcher.
		4531
		4532	=item event
		4533
		4534	A change of state of some external event, such as data now being available
		4535	for reading on a file descriptor, time having passed or simply not having
		4536	any other events happening anymore.
		4537
		4538	In libev, events are represented as single bits (such as C<EV_READ> or
		4539	C<EV_TIMEOUT>).
		4540
		4541	=item event library
		4542
		4543	A software package implementing an event model and loop.
		4544
		4545	=item event loop
		4546
		4547	An entity that handles and processes external events and converts them
		4548	into callback invocations.
		4549
		4550	=item event model
		4551
		4552	The model used to describe how an event loop handles and processes
		4553	watchers and events.
		4554
		4555	=item pending
		4556
		4557	A watcher is pending as soon as the corresponding event has been detected,
		4558	and stops being pending as soon as the watcher will be invoked or its
		4559	pending status is explicitly cleared by the application.
		4560
		4561	A watcher can be pending, but not active. Stopping a watcher also clears
		4562	its pending status.
		4563
		4564	=item real time
		4565
		4566	The physical time that is observed. It is apparently strictly monotonic :)
		4567
		4568	=item wall-clock time
		4569
		4570	The time and date as shown on clocks. Unlike real time, it can actually
		4571	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4572	clock.
		4573
		4574	=item watcher
		4575
		4576	A data structure that describes interest in certain events. Watchers need
		4577	to be started (attached to an event loop) before they can receive events.
		4578
		4579	=item watcher invocation
		4580
		4581	The act of calling the callback associated with a watcher.
		4582
		4583	=back
3645		4584
3646	=head1 AUTHOR	4585	=head1 AUTHOR
3647		4586
3648	Marc Lehmann <libev@schmorp.de>.	4587	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3649		4588

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