ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.174 by root, Mon Aug 18 23:23:45 2008 UTC vs.
Revision 1.238 by root, Sat Apr 18 12:10:41 2009 UTC

…		…
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
…		…
103	Libev is very configurable. In this manual the default (and most common)	117	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	118	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	119	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	120	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	121	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	122	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	123	this argument.
110		124
111	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
112		126
113	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	129	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	130	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	131	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	132	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	133	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	134	throughout libev.
121		135
122	=head1 ERROR HANDLING	136	=head1 ERROR HANDLING
123		137
…		…
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
215	recommended ones.	229	recommended ones.
216		230
217	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
218		232
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
220		234
221	Sets the allocation function to use (the prototype is similar - the	235	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	236	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	237	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	238	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	264	}
251		265
252	...	266	...
253	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
254		268
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
256		270
257	Set the callback function to call on a retryable system call error (such	271	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	272	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	273	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	274	callback is set, then libev will expect it to remedy the situation, no
…		…
276		290
277	=back	291	=back
278		292
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		294
281	An event loop is described by a C<struct ev_loop *>. The library knows two	295	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	296	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	297	I<function>).
		298
		299	The library knows two types of such loops, the I<default> loop, which
		300	supports signals and child events, and dynamically created loops which do
		301	not.
284		302
285	=over 4	303	=over 4
286		304
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		306
…		…
294	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
295	function.	313	function.
296		314
297	Note that this function is I<not> thread-safe, so if you want to use it	315	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,	316	from multiple threads, you have to lock (note also that this is unlikely,
299	as loops cannot bes hared easily between threads anyway).	317	as loops cannot be shared easily between threads anyway).
300		318
301	The default loop is the only loop that can handle C<ev_signal> and	319	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	320	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	321	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	322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
359	writing a server, you should C<accept ()> in a loop to accept as many	377	writing a server, you should C<accept ()> in a loop to accept as many
360	connections as possible during one iteration. You might also want to have	378	connections as possible during one iteration. You might also want to have
361	a look at C<ev_set_io_collect_interval ()> to increase the amount of	379	a look at C<ev_set_io_collect_interval ()> to increase the amount of
362	readiness notifications you get per iteration.	380	readiness notifications you get per iteration.
363		381
		382	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		383	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		384	C<exceptfds> set on that platform).
		385
364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	386	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
365		387
366	And this is your standard poll(2) backend. It's more complicated	388	And this is your standard poll(2) backend. It's more complicated
367	than select, but handles sparse fds better and has no artificial	389	than select, but handles sparse fds better and has no artificial
368	limit on the number of fds you can use (except it will slow down	390	limit on the number of fds you can use (except it will slow down
369	considerably with a lot of inactive fds). It scales similarly to select,	391	considerably with a lot of inactive fds). It scales similarly to select,
370	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	392	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
371	performance tips.	393	performance tips.
372		394
		395	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		396	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		397
373	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
374		399
375	For few fds, this backend is a bit little slower than poll and select,	400	For few fds, this backend is a bit little slower than poll and select,
376	but it scales phenomenally better. While poll and select usually scale	401	but it scales phenomenally better. While poll and select usually scale
377	like O(total_fds) where n is the total number of fds (or the highest fd),	402	like O(total_fds) where n is the total number of fds (or the highest fd),
378	epoll scales either O(1) or O(active_fds). The epoll design has a number	403	epoll scales either O(1) or O(active_fds).
379	of shortcomings, such as silently dropping events in some hard-to-detect	404
380	cases and requiring a system call per fd change, no fork support and bad	405	The epoll mechanism deserves honorable mention as the most misdesigned
381	support for dup.	406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
382		421
383	While stopping, setting and starting an I/O watcher in the same iteration	422	While stopping, setting and starting an I/O watcher in the same iteration
384	will result in some caching, there is still a system call per such incident	423	will result in some caching, there is still a system call per such
385	(because the fd could point to a different file description now), so its	424	incident (because the same I<file descriptor> could point to a different
386	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
387	very well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
388		427	file descriptors.
389	Please note that epoll sometimes generates spurious notifications, so you
390	need to use non-blocking I/O or other means to avoid blocking when no data
391	(or space) is available.
392		428
393	Best performance from this backend is achieved by not unregistering all	429	Best performance from this backend is achieved by not unregistering all
394	watchers for a file descriptor until it has been closed, if possible, i.e.	430	watchers for a file descriptor until it has been closed, if possible,
395	keep at least one watcher active per fd at all times.	431	i.e. keep at least one watcher active per fd at all times. Stopping and
		432	starting a watcher (without re-setting it) also usually doesn't cause
		433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
396		440
397	While nominally embeddable in other event loops, this feature is broken in	441	While nominally embeddable in other event loops, this feature is broken in
398	all kernel versions tested so far.	442	all kernel versions tested so far.
		443
		444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		445	C<EVBACKEND_POLL>.
399		446
400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
401		448
402	Kqueue deserves special mention, as at the time of this writing, it	449	Kqueue deserves special mention, as at the time of this writing, it
403	was broken on all BSDs except NetBSD (usually it doesn't work reliably	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
404	with anything but sockets and pipes, except on Darwin, where of course	451	with anything but sockets and pipes, except on Darwin, where of course
405	it's completely useless). For this reason it's not being "auto-detected"	452	it's completely useless). Unlike epoll, however, whose brokenness
		453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
406	unless you explicitly specify it explicitly in the flags (i.e. using	455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
407	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
408	system like NetBSD.	457	system like NetBSD.
409		458
410	You still can embed kqueue into a normal poll or select backend and use it	459	You still can embed kqueue into a normal poll or select backend and use it
411	only for sockets (after having made sure that sockets work with kqueue on	460	only for sockets (after having made sure that sockets work with kqueue on
…		…
413		462
414	It scales in the same way as the epoll backend, but the interface to the	463	It scales in the same way as the epoll backend, but the interface to the
415	kernel is more efficient (which says nothing about its actual speed, of	464	kernel is more efficient (which says nothing about its actual speed, of
416	course). While stopping, setting and starting an I/O watcher does never	465	course). While stopping, setting and starting an I/O watcher does never
417	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
418	two event changes per incident, support for C<fork ()> is very bad and it	467	two event changes per incident. Support for C<fork ()> is very bad (but
419	drops fds silently in similarly hard-to-detect cases.	468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
420		470
421	This backend usually performs well under most conditions.	471	This backend usually performs well under most conditions.
422		472
423	While nominally embeddable in other event loops, this doesn't work	473	While nominally embeddable in other event loops, this doesn't work
424	everywhere, so you might need to test for this. And since it is broken	474	everywhere, so you might need to test for this. And since it is broken
425	almost everywhere, you should only use it when you have a lot of sockets	475	almost everywhere, you should only use it when you have a lot of sockets
426	(for which it usually works), by embedding it into another event loop	476	(for which it usually works), by embedding it into another event loop
427	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
428	sockets.	478	also broken on OS X)) and, did I mention it, using it only for sockets.
		479
		480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		482	C<NOTE_EOF>.
429		483
430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
431		485
432	This is not implemented yet (and might never be, unless you send me an	486	This is not implemented yet (and might never be, unless you send me an
433	implementation). According to reports, C</dev/poll> only supports sockets	487	implementation). According to reports, C</dev/poll> only supports sockets
…		…
446	While this backend scales well, it requires one system call per active	500	While this backend scales well, it requires one system call per active
447	file descriptor per loop iteration. For small and medium numbers of file	501	file descriptor per loop iteration. For small and medium numbers of file
448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
449	might perform better.	503	might perform better.
450		504
451	On the positive side, ignoring the spurious readiness notifications, this	505	On the positive side, with the exception of the spurious readiness
452	backend actually performed to specification in all tests and is fully	506	notifications, this backend actually performed fully to specification
453	embeddable, which is a rare feat among the OS-specific backends.	507	in all tests and is fully embeddable, which is a rare feat among the
		508	OS-specific backends (I vastly prefer correctness over speed hacks).
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
454		512
455	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
456		514
457	Try all backends (even potentially broken ones that wouldn't be tried	515	Try all backends (even potentially broken ones that wouldn't be tried
458	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	516	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
464		522
465	If one or more of these are or'ed into the flags value, then only these	523	If one or more of these are or'ed into the flags value, then only these
466	backends will be tried (in the reverse order as listed here). If none are	524	backends will be tried (in the reverse order as listed here). If none are
467	specified, all backends in C<ev_recommended_backends ()> will be tried.	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
468		526
469	The most typical usage is like this:	527	Example: This is the most typical usage.
470		528
471	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
473		531
474	Restrict libev to the select and poll backends, and do not allow	532	Example: Restrict libev to the select and poll backends, and do not allow
475	environment settings to be taken into account:	533	environment settings to be taken into account:
476		534
477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
478		536
479	Use whatever libev has to offer, but make sure that kqueue is used if	537	Example: Use whatever libev has to offer, but make sure that kqueue is
480	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
481	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
482		541
483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
484		543
485	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
486		545
…		…
507	responsibility to either stop all watchers cleanly yourself I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
508	calling this function, or cope with the fact afterwards (which is usually	567	calling this function, or cope with the fact afterwards (which is usually
509	the easiest thing, you can just ignore the watchers and/or C<free ()> them	568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
510	for example).	569	for example).
511		570
512	Note that certain global state, such as signal state, will not be freed by	571	Note that certain global state, such as signal state (and installed signal
513	this function, and related watchers (such as signal and child watchers)	572	handlers), will not be freed by this function, and related watchers (such
514	would need to be stopped manually.	573	as signal and child watchers) would need to be stopped manually.
515		574
516	In general it is not advisable to call this function except in the	575	In general it is not advisable to call this function except in the
517	rare occasion where you really need to free e.g. the signal handling	576	rare occasion where you really need to free e.g. the signal handling
518	pipe fds. If you need dynamically allocated loops it is better to use	577	pipe fds. If you need dynamically allocated loops it is better to use
519	C<ev_loop_new> and C<ev_loop_destroy>).	578	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
544		603
545	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
546		605
547	Like C<ev_default_fork>, but acts on an event loop created by	606	Like C<ev_default_fork>, but acts on an event loop created by
548	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	607	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
549	after fork, and how you do this is entirely your own problem.	608	after fork that you want to re-use in the child, and how you do this is
		609	entirely your own problem.
550		610
551	=item int ev_is_default_loop (loop)	611	=item int ev_is_default_loop (loop)
552		612
553	Returns true when the given loop actually is the default loop, false otherwise.	613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
554		615
555	=item unsigned int ev_loop_count (loop)	616	=item unsigned int ev_loop_count (loop)
556		617
557	Returns the count of loop iterations for the loop, which is identical to	618	Returns the count of loop iterations for the loop, which is identical to
558	the number of times libev did poll for new events. It starts at C<0> and	619	the number of times libev did poll for new events. It starts at C<0> and
…		…
573	received events and started processing them. This timestamp does not	634	received events and started processing them. This timestamp does not
574	change as long as callbacks are being processed, and this is also the base	635	change as long as callbacks are being processed, and this is also the base
575	time used for relative timers. You can treat it as the timestamp of the	636	time used for relative timers. You can treat it as the timestamp of the
576	event occurring (or more correctly, libev finding out about it).	637	event occurring (or more correctly, libev finding out about it).
577		638
		639	=item ev_now_update (loop)
		640
		641	Establishes the current time by querying the kernel, updating the time
		642	returned by C<ev_now ()> in the progress. This is a costly operation and
		643	is usually done automatically within C<ev_loop ()>.
		644
		645	This function is rarely useful, but when some event callback runs for a
		646	very long time without entering the event loop, updating libev's idea of
		647	the current time is a good idea.
		648
		649	See also L<The special problem of time updates> in the C<ev_timer> section.
		650
		651	=item ev_suspend (loop)
		652
		653	=item ev_resume (loop)
		654
		655	These two functions suspend and resume a loop, for use when the loop is
		656	not used for a while and timeouts should not be processed.
		657
		658	A typical use case would be an interactive program such as a game: When
		659	the user presses C<^Z> to suspend the game and resumes it an hour later it
		660	would be best to handle timeouts as if no time had actually passed while
		661	the program was suspended. This can be achieved by calling C<ev_suspend>
		662	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		663	C<ev_resume> directly afterwards to resume timer processing.
		664
		665	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		666	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		667	will be rescheduled (that is, they will lose any events that would have
		668	occured while suspended).
		669
		670	After calling C<ev_suspend> you B<must not> call I<any> function on the
		671	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		672	without a previous call to C<ev_suspend>.
		673
		674	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		675	event loop time (see C<ev_now_update>).
		676
578	=item ev_loop (loop, int flags)	677	=item ev_loop (loop, int flags)
579		678
580	Finally, this is it, the event handler. This function usually is called	679	Finally, this is it, the event handler. This function usually is called
581	after you initialised all your watchers and you want to start handling	680	after you initialised all your watchers and you want to start handling
582	events.	681	events.
…		…
584	If the flags argument is specified as C<0>, it will not return until	683	If the flags argument is specified as C<0>, it will not return until
585	either no event watchers are active anymore or C<ev_unloop> was called.	684	either no event watchers are active anymore or C<ev_unloop> was called.
586		685
587	Please note that an explicit C<ev_unloop> is usually better than	686	Please note that an explicit C<ev_unloop> is usually better than
588	relying on all watchers to be stopped when deciding when a program has	687	relying on all watchers to be stopped when deciding when a program has
589	finished (especially in interactive programs), but having a program that	688	finished (especially in interactive programs), but having a program
590	automatically loops as long as it has to and no longer by virtue of	689	that automatically loops as long as it has to and no longer by virtue
591	relying on its watchers stopping correctly is a thing of beauty.	690	of relying on its watchers stopping correctly, that is truly a thing of
		691	beauty.
592		692
593	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	693	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
594	those events and any outstanding ones, but will not block your process in	694	those events and any already outstanding ones, but will not block your
595	case there are no events and will return after one iteration of the loop.	695	process in case there are no events and will return after one iteration of
		696	the loop.
596		697
597	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	698	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
598	necessary) and will handle those and any outstanding ones. It will block	699	necessary) and will handle those and any already outstanding ones. It
599	your process until at least one new event arrives, and will return after	700	will block your process until at least one new event arrives (which could
600	one iteration of the loop. This is useful if you are waiting for some	701	be an event internal to libev itself, so there is no guarantee that a
601	external event in conjunction with something not expressible using other	702	user-registered callback will be called), and will return after one
		703	iteration of the loop.
		704
		705	This is useful if you are waiting for some external event in conjunction
		706	with something not expressible using other libev watchers (i.e. "roll your
602	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	707	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
603	usually a better approach for this kind of thing.	708	usually a better approach for this kind of thing.
604		709
605	Here are the gory details of what C<ev_loop> does:	710	Here are the gory details of what C<ev_loop> does:
606		711
607	- Before the first iteration, call any pending watchers.	712	- Before the first iteration, call any pending watchers.
…		…
617	any active watchers at all will result in not sleeping).	722	any active watchers at all will result in not sleeping).
618	- Sleep if the I/O and timer collect interval say so.	723	- Sleep if the I/O and timer collect interval say so.
619	- Block the process, waiting for any events.	724	- Block the process, waiting for any events.
620	- Queue all outstanding I/O (fd) events.	725	- Queue all outstanding I/O (fd) events.
621	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	726	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
622	- Queue all outstanding timers.	727	- Queue all expired timers.
623	- Queue all outstanding periodics.	728	- Queue all expired periodics.
624	- Unless any events are pending now, queue all idle watchers.	729	- Unless any events are pending now, queue all idle watchers.
625	- Queue all check watchers.	730	- Queue all check watchers.
626	- Call all queued watchers in reverse order (i.e. check watchers first).	731	- Call all queued watchers in reverse order (i.e. check watchers first).
627	Signals and child watchers are implemented as I/O watchers, and will	732	Signals and child watchers are implemented as I/O watchers, and will
628	be handled here by queueing them when their watcher gets executed.	733	be handled here by queueing them when their watcher gets executed.
…		…
645	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	750	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
646	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	751	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
647		752
648	This "unloop state" will be cleared when entering C<ev_loop> again.	753	This "unloop state" will be cleared when entering C<ev_loop> again.
649		754
		755	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		756
650	=item ev_ref (loop)	757	=item ev_ref (loop)
651		758
652	=item ev_unref (loop)	759	=item ev_unref (loop)
653		760
654	Ref/unref can be used to add or remove a reference count on the event	761	Ref/unref can be used to add or remove a reference count on the event
655	loop: Every watcher keeps one reference, and as long as the reference	762	loop: Every watcher keeps one reference, and as long as the reference
656	count is nonzero, C<ev_loop> will not return on its own. If you have	763	count is nonzero, C<ev_loop> will not return on its own.
		764
657	a watcher you never unregister that should not keep C<ev_loop> from	765	If you have a watcher you never unregister that should not keep C<ev_loop>
658	returning, ev_unref() after starting, and ev_ref() before stopping it. For	766	from returning, call ev_unref() after starting, and ev_ref() before
		767	stopping it.
		768
659	example, libev itself uses this for its internal signal pipe: It is not	769	As an example, libev itself uses this for its internal signal pipe: It
660	visible to the libev user and should not keep C<ev_loop> from exiting if	770	is not visible to the libev user and should not keep C<ev_loop> from
661	no event watchers registered by it are active. It is also an excellent	771	exiting if no event watchers registered by it are active. It is also an
662	way to do this for generic recurring timers or from within third-party	772	excellent way to do this for generic recurring timers or from within
663	libraries. Just remember to I<unref after start> and I<ref before stop>	773	third-party libraries. Just remember to I<unref after start> and I<ref
664	(but only if the watcher wasn't active before, or was active before,	774	before stop> (but only if the watcher wasn't active before, or was active
665	respectively).	775	before, respectively. Note also that libev might stop watchers itself
		776	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		777	in the callback).
666		778
667	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	779	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
668	running when nothing else is active.	780	running when nothing else is active.
669		781
670	struct ev_signal exitsig;	782	ev_signal exitsig;
671	ev_signal_init (&exitsig, sig_cb, SIGINT);	783	ev_signal_init (&exitsig, sig_cb, SIGINT);
672	ev_signal_start (loop, &exitsig);	784	ev_signal_start (loop, &exitsig);
673	evf_unref (loop);	785	evf_unref (loop);
674		786
675	Example: For some weird reason, unregister the above signal handler again.	787	Example: For some weird reason, unregister the above signal handler again.
…		…
689	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	801	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
690	allows libev to delay invocation of I/O and timer/periodic callbacks	802	allows libev to delay invocation of I/O and timer/periodic callbacks
691	to increase efficiency of loop iterations (or to increase power-saving	803	to increase efficiency of loop iterations (or to increase power-saving
692	opportunities).	804	opportunities).
693		805
694	The background is that sometimes your program runs just fast enough to	806	The idea is that sometimes your program runs just fast enough to handle
695	handle one (or very few) event(s) per loop iteration. While this makes	807	one (or very few) event(s) per loop iteration. While this makes the
696	the program responsive, it also wastes a lot of CPU time to poll for new	808	program responsive, it also wastes a lot of CPU time to poll for new
697	events, especially with backends like C<select ()> which have a high	809	events, especially with backends like C<select ()> which have a high
698	overhead for the actual polling but can deliver many events at once.	810	overhead for the actual polling but can deliver many events at once.
699		811
700	By setting a higher I<io collect interval> you allow libev to spend more	812	By setting a higher I<io collect interval> you allow libev to spend more
701	time collecting I/O events, so you can handle more events per iteration,	813	time collecting I/O events, so you can handle more events per iteration,
…		…
703	C<ev_timer>) will be not affected. Setting this to a non-null value will	815	C<ev_timer>) will be not affected. Setting this to a non-null value will
704	introduce an additional C<ev_sleep ()> call into most loop iterations.	816	introduce an additional C<ev_sleep ()> call into most loop iterations.
705		817
706	Likewise, by setting a higher I<timeout collect interval> you allow libev	818	Likewise, by setting a higher I<timeout collect interval> you allow libev
707	to spend more time collecting timeouts, at the expense of increased	819	to spend more time collecting timeouts, at the expense of increased
708	latency (the watcher callback will be called later). C<ev_io> watchers	820	latency/jitter/inexactness (the watcher callback will be called
709	will not be affected. Setting this to a non-null value will not introduce	821	later). C<ev_io> watchers will not be affected. Setting this to a non-null
710	any overhead in libev.	822	value will not introduce any overhead in libev.
711		823
712	Many (busy) programs can usually benefit by setting the I/O collect	824	Many (busy) programs can usually benefit by setting the I/O collect
713	interval to a value near C<0.1> or so, which is often enough for	825	interval to a value near C<0.1> or so, which is often enough for
714	interactive servers (of course not for games), likewise for timeouts. It	826	interactive servers (of course not for games), likewise for timeouts. It
715	usually doesn't make much sense to set it to a lower value than C<0.01>,	827	usually doesn't make much sense to set it to a lower value than C<0.01>,
…		…
723	they fire on, say, one-second boundaries only.	835	they fire on, say, one-second boundaries only.
724		836
725	=item ev_loop_verify (loop)	837	=item ev_loop_verify (loop)
726		838
727	This function only does something when C<EV_VERIFY> support has been	839	This function only does something when C<EV_VERIFY> support has been
728	compiled in. It tries to go through all internal structures and checks	840	compiled in, which is the default for non-minimal builds. It tries to go
729	them for validity. If anything is found to be inconsistent, it will print	841	through all internal structures and checks them for validity. If anything
730	an error message to standard error and call C<abort ()>.	842	is found to be inconsistent, it will print an error message to standard
		843	error and call C<abort ()>.
731		844
732	This can be used to catch bugs inside libev itself: under normal	845	This can be used to catch bugs inside libev itself: under normal
733	circumstances, this function will never abort as of course libev keeps its	846	circumstances, this function will never abort as of course libev keeps its
734	data structures consistent.	847	data structures consistent.
735		848
736	=back	849	=back
737		850
738		851
739	=head1 ANATOMY OF A WATCHER	852	=head1 ANATOMY OF A WATCHER
740		853
		854	In the following description, uppercase C<TYPE> in names stands for the
		855	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		856	watchers and C<ev_io_start> for I/O watchers.
		857
741	A watcher is a structure that you create and register to record your	858	A watcher is a structure that you create and register to record your
742	interest in some event. For instance, if you want to wait for STDIN to	859	interest in some event. For instance, if you want to wait for STDIN to
743	become readable, you would create an C<ev_io> watcher for that:	860	become readable, you would create an C<ev_io> watcher for that:
744		861
745	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	862	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
746	{	863	{
747	ev_io_stop (w);	864	ev_io_stop (w);
748	ev_unloop (loop, EVUNLOOP_ALL);	865	ev_unloop (loop, EVUNLOOP_ALL);
749	}	866	}
750		867
751	struct ev_loop *loop = ev_default_loop (0);	868	struct ev_loop *loop = ev_default_loop (0);
		869
752	struct ev_io stdin_watcher;	870	ev_io stdin_watcher;
		871
753	ev_init (&stdin_watcher, my_cb);	872	ev_init (&stdin_watcher, my_cb);
754	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	873	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
755	ev_io_start (loop, &stdin_watcher);	874	ev_io_start (loop, &stdin_watcher);
		875
756	ev_loop (loop, 0);	876	ev_loop (loop, 0);
757		877
758	As you can see, you are responsible for allocating the memory for your	878	As you can see, you are responsible for allocating the memory for your
759	watcher structures (and it is usually a bad idea to do this on the stack,	879	watcher structures (and it is I<usually> a bad idea to do this on the
760	although this can sometimes be quite valid).	880	stack).
		881
		882	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		883	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
761		884
762	Each watcher structure must be initialised by a call to C<ev_init	885	Each watcher structure must be initialised by a call to C<ev_init
763	(watcher *, callback)>, which expects a callback to be provided. This	886	(watcher *, callback)>, which expects a callback to be provided. This
764	callback gets invoked each time the event occurs (or, in the case of I/O	887	callback gets invoked each time the event occurs (or, in the case of I/O
765	watchers, each time the event loop detects that the file descriptor given	888	watchers, each time the event loop detects that the file descriptor given
766	is readable and/or writable).	889	is readable and/or writable).
767		890
768	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	891	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
769	with arguments specific to this watcher type. There is also a macro	892	macro to configure it, with arguments specific to the watcher type. There
770	to combine initialisation and setting in one call: C<< ev_<type>_init	893	is also a macro to combine initialisation and setting in one call: C<<
771	(watcher *, callback, ...) >>.	894	ev_TYPE_init (watcher *, callback, ...) >>.
772		895
773	To make the watcher actually watch out for events, you have to start it	896	To make the watcher actually watch out for events, you have to start it
774	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	897	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
775	*) >>), and you can stop watching for events at any time by calling the	898	*) >>), and you can stop watching for events at any time by calling the
776	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	899	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
777		900
778	As long as your watcher is active (has been started but not stopped) you	901	As long as your watcher is active (has been started but not stopped) you
779	must not touch the values stored in it. Most specifically you must never	902	must not touch the values stored in it. Most specifically you must never
780	reinitialise it or call its C<set> macro.	903	reinitialise it or call its C<ev_TYPE_set> macro.
781		904
782	Each and every callback receives the event loop pointer as first, the	905	Each and every callback receives the event loop pointer as first, the
783	registered watcher structure as second, and a bitset of received events as	906	registered watcher structure as second, and a bitset of received events as
784	third argument.	907	third argument.
785		908
…		…
843		966
844	=item C<EV_ASYNC>	967	=item C<EV_ASYNC>
845		968
846	The given async watcher has been asynchronously notified (see C<ev_async>).	969	The given async watcher has been asynchronously notified (see C<ev_async>).
847		970
		971	=item C<EV_CUSTOM>
		972
		973	Not ever sent (or otherwise used) by libev itself, but can be freely used
		974	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		975
848	=item C<EV_ERROR>	976	=item C<EV_ERROR>
849		977
850	An unspecified error has occurred, the watcher has been stopped. This might	978	An unspecified error has occurred, the watcher has been stopped. This might
851	happen because the watcher could not be properly started because libev	979	happen because the watcher could not be properly started because libev
852	ran out of memory, a file descriptor was found to be closed or any other	980	ran out of memory, a file descriptor was found to be closed or any other
		981	problem. Libev considers these application bugs.
		982
853	problem. You best act on it by reporting the problem and somehow coping	983	You best act on it by reporting the problem and somehow coping with the
854	with the watcher being stopped.	984	watcher being stopped. Note that well-written programs should not receive
		985	an error ever, so when your watcher receives it, this usually indicates a
		986	bug in your program.
855		987
856	Libev will usually signal a few "dummy" events together with an error,	988	Libev will usually signal a few "dummy" events together with an error, for
857	for example it might indicate that a fd is readable or writable, and if	989	example it might indicate that a fd is readable or writable, and if your
858	your callbacks is well-written it can just attempt the operation and cope	990	callbacks is well-written it can just attempt the operation and cope with
859	with the error from read() or write(). This will not work in multi-threaded	991	the error from read() or write(). This will not work in multi-threaded
860	programs, though, so beware.	992	programs, though, as the fd could already be closed and reused for another
		993	thing, so beware.
861		994
862	=back	995	=back
863		996
864	=head2 GENERIC WATCHER FUNCTIONS	997	=head2 GENERIC WATCHER FUNCTIONS
865
866	In the following description, C<TYPE> stands for the watcher type,
867	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
868		998
869	=over 4	999	=over 4
870		1000
871	=item C<ev_init> (ev_TYPE *watcher, callback)	1001	=item C<ev_init> (ev_TYPE *watcher, callback)
872		1002
…		…
878	which rolls both calls into one.	1008	which rolls both calls into one.
879		1009
880	You can reinitialise a watcher at any time as long as it has been stopped	1010	You can reinitialise a watcher at any time as long as it has been stopped
881	(or never started) and there are no pending events outstanding.	1011	(or never started) and there are no pending events outstanding.
882		1012
883	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1013	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
884	int revents)>.	1014	int revents)>.
		1015
		1016	Example: Initialise an C<ev_io> watcher in two steps.
		1017
		1018	ev_io w;
		1019	ev_init (&w, my_cb);
		1020	ev_io_set (&w, STDIN_FILENO, EV_READ);
885		1021
886	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1022	=item C<ev_TYPE_set> (ev_TYPE *, [args])
887		1023
888	This macro initialises the type-specific parts of a watcher. You need to	1024	This macro initialises the type-specific parts of a watcher. You need to
889	call C<ev_init> at least once before you call this macro, but you can	1025	call C<ev_init> at least once before you call this macro, but you can
…		…
892	difference to the C<ev_init> macro).	1028	difference to the C<ev_init> macro).
893		1029
894	Although some watcher types do not have type-specific arguments	1030	Although some watcher types do not have type-specific arguments
895	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1031	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
896		1032
		1033	See C<ev_init>, above, for an example.
		1034
897	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1035	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
898		1036
899	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1037	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
900	calls into a single call. This is the most convenient method to initialise	1038	calls into a single call. This is the most convenient method to initialise
901	a watcher. The same limitations apply, of course.	1039	a watcher. The same limitations apply, of course.
902		1040
		1041	Example: Initialise and set an C<ev_io> watcher in one step.
		1042
		1043	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1044
903	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1045	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
904		1046
905	Starts (activates) the given watcher. Only active watchers will receive	1047	Starts (activates) the given watcher. Only active watchers will receive
906	events. If the watcher is already active nothing will happen.	1048	events. If the watcher is already active nothing will happen.
907		1049
		1050	Example: Start the C<ev_io> watcher that is being abused as example in this
		1051	whole section.
		1052
		1053	ev_io_start (EV_DEFAULT_UC, &w);
		1054
908	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1055	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
909		1056
910	Stops the given watcher again (if active) and clears the pending	1057	Stops the given watcher if active, and clears the pending status (whether
		1058	the watcher was active or not).
		1059
911	status. It is possible that stopped watchers are pending (for example,	1060	It is possible that stopped watchers are pending - for example,
912	non-repeating timers are being stopped when they become pending), but	1061	non-repeating timers are being stopped when they become pending - but
913	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1062	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
914	you want to free or reuse the memory used by the watcher it is therefore a	1063	pending. If you want to free or reuse the memory used by the watcher it is
915	good idea to always call its C<ev_TYPE_stop> function.	1064	therefore a good idea to always call its C<ev_TYPE_stop> function.
916		1065
917	=item bool ev_is_active (ev_TYPE *watcher)	1066	=item bool ev_is_active (ev_TYPE *watcher)
918		1067
919	Returns a true value iff the watcher is active (i.e. it has been started	1068	Returns a true value iff the watcher is active (i.e. it has been started
920	and not yet been stopped). As long as a watcher is active you must not modify	1069	and not yet been stopped). As long as a watcher is active you must not modify
…		…
946	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1095	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
947	(default: C<-2>). Pending watchers with higher priority will be invoked	1096	(default: C<-2>). Pending watchers with higher priority will be invoked
948	before watchers with lower priority, but priority will not keep watchers	1097	before watchers with lower priority, but priority will not keep watchers
949	from being executed (except for C<ev_idle> watchers).	1098	from being executed (except for C<ev_idle> watchers).
950		1099
951	This means that priorities are I<only> used for ordering callback
952	invocation after new events have been received. This is useful, for
953	example, to reduce latency after idling, or more often, to bind two
954	watchers on the same event and make sure one is called first.
955
956	If you need to suppress invocation when higher priority events are pending	1100	If you need to suppress invocation when higher priority events are pending
957	you need to look at C<ev_idle> watchers, which provide this functionality.	1101	you need to look at C<ev_idle> watchers, which provide this functionality.
958		1102
959	You I<must not> change the priority of a watcher as long as it is active or	1103	You I<must not> change the priority of a watcher as long as it is active or
960	pending.	1104	pending.
961		1105
		1106	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1107	fine, as long as you do not mind that the priority value you query might
		1108	or might not have been clamped to the valid range.
		1109
962	The default priority used by watchers when no priority has been set is	1110	The default priority used by watchers when no priority has been set is
963	always C<0>, which is supposed to not be too high and not be too low :).	1111	always C<0>, which is supposed to not be too high and not be too low :).
964		1112
965	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1113	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
966	fine, as long as you do not mind that the priority value you query might	1114	priorities.
967	or might not have been adjusted to be within valid range.
968		1115
969	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1116	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
970		1117
971	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1118	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
972	C<loop> nor C<revents> need to be valid as long as the watcher callback	1119	C<loop> nor C<revents> need to be valid as long as the watcher callback
973	can deal with that fact.	1120	can deal with that fact, as both are simply passed through to the
		1121	callback.
974		1122
975	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1123	=item int ev_clear_pending (loop, ev_TYPE *watcher)
976		1124
977	If the watcher is pending, this function returns clears its pending status	1125	If the watcher is pending, this function clears its pending status and
978	and returns its C<revents> bitset (as if its callback was invoked). If the	1126	returns its C<revents> bitset (as if its callback was invoked). If the
979	watcher isn't pending it does nothing and returns C<0>.	1127	watcher isn't pending it does nothing and returns C<0>.
980		1128
		1129	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1130	callback to be invoked, which can be accomplished with this function.
		1131
981	=back	1132	=back
982		1133
983		1134
984	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1135	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
985		1136
986	Each watcher has, by default, a member C<void *data> that you can change	1137	Each watcher has, by default, a member C<void *data> that you can change
987	and read at any time, libev will completely ignore it. This can be used	1138	and read at any time: libev will completely ignore it. This can be used
988	to associate arbitrary data with your watcher. If you need more data and	1139	to associate arbitrary data with your watcher. If you need more data and
989	don't want to allocate memory and store a pointer to it in that data	1140	don't want to allocate memory and store a pointer to it in that data
990	member, you can also "subclass" the watcher type and provide your own	1141	member, you can also "subclass" the watcher type and provide your own
991	data:	1142	data:
992		1143
993	struct my_io	1144	struct my_io
994	{	1145	{
995	struct ev_io io;	1146	ev_io io;
996	int otherfd;	1147	int otherfd;
997	void *somedata;	1148	void *somedata;
998	struct whatever *mostinteresting;	1149	struct whatever *mostinteresting;
999	}	1150	};
		1151
		1152	...
		1153	struct my_io w;
		1154	ev_io_init (&w.io, my_cb, fd, EV_READ);
1000		1155
1001	And since your callback will be called with a pointer to the watcher, you	1156	And since your callback will be called with a pointer to the watcher, you
1002	can cast it back to your own type:	1157	can cast it back to your own type:
1003		1158
1004	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1159	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1005	{	1160	{
1006	struct my_io *w = (struct my_io *)w_;	1161	struct my_io *w = (struct my_io *)w_;
1007	...	1162	...
1008	}	1163	}
1009		1164
1010	More interesting and less C-conformant ways of casting your callback type	1165	More interesting and less C-conformant ways of casting your callback type
1011	instead have been omitted.	1166	instead have been omitted.
1012		1167
1013	Another common scenario is having some data structure with multiple	1168	Another common scenario is to use some data structure with multiple
1014	watchers:	1169	embedded watchers:
1015		1170
1016	struct my_biggy	1171	struct my_biggy
1017	{	1172	{
1018	int some_data;	1173	int some_data;
1019	ev_timer t1;	1174	ev_timer t1;
1020	ev_timer t2;	1175	ev_timer t2;
1021	}	1176	}
1022		1177
1023	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1178	In this case getting the pointer to C<my_biggy> is a bit more
1024	you need to use C<offsetof>:	1179	complicated: Either you store the address of your C<my_biggy> struct
		1180	in the C<data> member of the watcher (for woozies), or you need to use
		1181	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1182	programmers):
1025		1183
1026	#include <stddef.h>	1184	#include <stddef.h>
1027		1185
1028	static void	1186	static void
1029	t1_cb (EV_P_ struct ev_timer *w, int revents)	1187	t1_cb (EV_P_ ev_timer *w, int revents)
1030	{	1188	{
1031	struct my_biggy big = (struct my_biggy *	1189	struct my_biggy big = (struct my_biggy *
1032	(((char *)w) - offsetof (struct my_biggy, t1));	1190	(((char *)w) - offsetof (struct my_biggy, t1));
1033	}	1191	}
1034		1192
1035	static void	1193	static void
1036	t2_cb (EV_P_ struct ev_timer *w, int revents)	1194	t2_cb (EV_P_ ev_timer *w, int revents)
1037	{	1195	{
1038	struct my_biggy big = (struct my_biggy *	1196	struct my_biggy big = (struct my_biggy *
1039	(((char *)w) - offsetof (struct my_biggy, t2));	1197	(((char *)w) - offsetof (struct my_biggy, t2));
1040	}	1198	}
		1199
		1200	=head2 WATCHER PRIORITY MODELS
		1201
		1202	Many event loops support I<watcher priorities>, which are usually small
		1203	integers that influence the ordering of event callback invocation
		1204	between watchers in some way, all else being equal.
		1205
		1206	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1207	description for the more technical details such as the actual priority
		1208	range.
		1209
		1210	There are two common ways how these these priorities are being interpreted
		1211	by event loops:
		1212
		1213	In the more common lock-out model, higher priorities "lock out" invocation
		1214	of lower priority watchers, which means as long as higher priority
		1215	watchers receive events, lower priority watchers are not being invoked.
		1216
		1217	The less common only-for-ordering model uses priorities solely to order
		1218	callback invocation within a single event loop iteration: Higher priority
		1219	watchers are invoked before lower priority ones, but they all get invoked
		1220	before polling for new events.
		1221
		1222	Libev uses the second (only-for-ordering) model for all its watchers
		1223	except for idle watchers (which use the lock-out model).
		1224
		1225	The rationale behind this is that implementing the lock-out model for
		1226	watchers is not well supported by most kernel interfaces, and most event
		1227	libraries will just poll for the same events again and again as long as
		1228	their callbacks have not been executed, which is very inefficient in the
		1229	common case of one high-priority watcher locking out a mass of lower
		1230	priority ones.
		1231
		1232	Static (ordering) priorities are most useful when you have two or more
		1233	watchers handling the same resource: a typical usage example is having an
		1234	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1235	timeouts. Under load, data might be received while the program handles
		1236	other jobs, but since timers normally get invoked first, the timeout
		1237	handler will be executed before checking for data. In that case, giving
		1238	the timer a lower priority than the I/O watcher ensures that I/O will be
		1239	handled first even under adverse conditions (which is usually, but not
		1240	always, what you want).
		1241
		1242	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1243	will only be executed when no same or higher priority watchers have
		1244	received events, they can be used to implement the "lock-out" model when
		1245	required.
		1246
		1247	For example, to emulate how many other event libraries handle priorities,
		1248	you can associate an C<ev_idle> watcher to each such watcher, and in
		1249	the normal watcher callback, you just start the idle watcher. The real
		1250	processing is done in the idle watcher callback. This causes libev to
		1251	continously poll and process kernel event data for the watcher, but when
		1252	the lock-out case is known to be rare (which in turn is rare :), this is
		1253	workable.
		1254
		1255	Usually, however, the lock-out model implemented that way will perform
		1256	miserably under the type of load it was designed to handle. In that case,
		1257	it might be preferable to stop the real watcher before starting the
		1258	idle watcher, so the kernel will not have to process the event in case
		1259	the actual processing will be delayed for considerable time.
		1260
		1261	Here is an example of an I/O watcher that should run at a strictly lower
		1262	priority than the default, and which should only process data when no
		1263	other events are pending:
		1264
		1265	ev_idle idle; // actual processing watcher
		1266	ev_io io; // actual event watcher
		1267
		1268	static void
		1269	io_cb (EV_P_ ev_io *w, int revents)
		1270	{
		1271	// stop the I/O watcher, we received the event, but
		1272	// are not yet ready to handle it.
		1273	ev_io_stop (EV_A_ w);
		1274
		1275	// start the idle watcher to ahndle the actual event.
		1276	// it will not be executed as long as other watchers
		1277	// with the default priority are receiving events.
		1278	ev_idle_start (EV_A_ &idle);
		1279	}
		1280
		1281	static void
		1282	idle-cb (EV_P_ ev_idle *w, int revents)
		1283	{
		1284	// actual processing
		1285	read (STDIN_FILENO, ...);
		1286
		1287	// have to start the I/O watcher again, as
		1288	// we have handled the event
		1289	ev_io_start (EV_P_ &io);
		1290	}
		1291
		1292	// initialisation
		1293	ev_idle_init (&idle, idle_cb);
		1294	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1295	ev_io_start (EV_DEFAULT_ &io);
		1296
		1297	In the "real" world, it might also be beneficial to start a timer, so that
		1298	low-priority connections can not be locked out forever under load. This
		1299	enables your program to keep a lower latency for important connections
		1300	during short periods of high load, while not completely locking out less
		1301	important ones.
1041		1302
1042		1303
1043	=head1 WATCHER TYPES	1304	=head1 WATCHER TYPES
1044		1305
1045	This section describes each watcher in detail, but will not repeat	1306	This section describes each watcher in detail, but will not repeat
…		…
1069	In general you can register as many read and/or write event watchers per	1330	In general you can register as many read and/or write event watchers per
1070	fd as you want (as long as you don't confuse yourself). Setting all file	1331	fd as you want (as long as you don't confuse yourself). Setting all file
1071	descriptors to non-blocking mode is also usually a good idea (but not	1332	descriptors to non-blocking mode is also usually a good idea (but not
1072	required if you know what you are doing).	1333	required if you know what you are doing).
1073		1334
1074	If you must do this, then force the use of a known-to-be-good backend	1335	If you cannot use non-blocking mode, then force the use of a
1075	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1336	known-to-be-good backend (at the time of this writing, this includes only
1076	C<EVBACKEND_POLL>).	1337	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
1077		1338
1078	Another thing you have to watch out for is that it is quite easy to	1339	Another thing you have to watch out for is that it is quite easy to
1079	receive "spurious" readiness notifications, that is your callback might	1340	receive "spurious" readiness notifications, that is your callback might
1080	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1341	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1081	because there is no data. Not only are some backends known to create a	1342	because there is no data. Not only are some backends known to create a
1082	lot of those (for example Solaris ports), it is very easy to get into	1343	lot of those (for example Solaris ports), it is very easy to get into
1083	this situation even with a relatively standard program structure. Thus	1344	this situation even with a relatively standard program structure. Thus
1084	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1345	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1085	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1346	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1086		1347
1087	If you cannot run the fd in non-blocking mode (for example you should not	1348	If you cannot run the fd in non-blocking mode (for example you should
1088	play around with an Xlib connection), then you have to separately re-test	1349	not play around with an Xlib connection), then you have to separately
1089	whether a file descriptor is really ready with a known-to-be good interface	1350	re-test whether a file descriptor is really ready with a known-to-be good
1090	such as poll (fortunately in our Xlib example, Xlib already does this on	1351	interface such as poll (fortunately in our Xlib example, Xlib already
1091	its own, so its quite safe to use).	1352	does this on its own, so its quite safe to use). Some people additionally
		1353	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1354	indefinitely.
		1355
		1356	But really, best use non-blocking mode.
1092		1357
1093	=head3 The special problem of disappearing file descriptors	1358	=head3 The special problem of disappearing file descriptors
1094		1359
1095	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1360	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1096	descriptor (either by calling C<close> explicitly or by any other means,	1361	descriptor (either due to calling C<close> explicitly or any other means,
1097	such as C<dup>). The reason is that you register interest in some file	1362	such as C<dup2>). The reason is that you register interest in some file
1098	descriptor, but when it goes away, the operating system will silently drop	1363	descriptor, but when it goes away, the operating system will silently drop
1099	this interest. If another file descriptor with the same number then is	1364	this interest. If another file descriptor with the same number then is
1100	registered with libev, there is no efficient way to see that this is, in	1365	registered with libev, there is no efficient way to see that this is, in
1101	fact, a different file descriptor.	1366	fact, a different file descriptor.
1102		1367
…		…
1133	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1398	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1134	C<EVBACKEND_POLL>.	1399	C<EVBACKEND_POLL>.
1135		1400
1136	=head3 The special problem of SIGPIPE	1401	=head3 The special problem of SIGPIPE
1137		1402
1138	While not really specific to libev, it is easy to forget about SIGPIPE:	1403	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1139	when writing to a pipe whose other end has been closed, your program gets	1404	when writing to a pipe whose other end has been closed, your program gets
1140	send a SIGPIPE, which, by default, aborts your program. For most programs	1405	sent a SIGPIPE, which, by default, aborts your program. For most programs
1141	this is sensible behaviour, for daemons, this is usually undesirable.	1406	this is sensible behaviour, for daemons, this is usually undesirable.
1142		1407
1143	So when you encounter spurious, unexplained daemon exits, make sure you	1408	So when you encounter spurious, unexplained daemon exits, make sure you
1144	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1409	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1145	somewhere, as that would have given you a big clue).	1410	somewhere, as that would have given you a big clue).
…		…
1152	=item ev_io_init (ev_io *, callback, int fd, int events)	1417	=item ev_io_init (ev_io *, callback, int fd, int events)
1153		1418
1154	=item ev_io_set (ev_io *, int fd, int events)	1419	=item ev_io_set (ev_io *, int fd, int events)
1155		1420
1156	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1421	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1157	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1422	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1158	C<EV_READ | EV_WRITE> to receive the given events.	1423	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1159		1424
1160	=item int fd [read-only]	1425	=item int fd [read-only]
1161		1426
1162	The file descriptor being watched.	1427	The file descriptor being watched.
1163		1428
…		…
1172	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1437	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1173	readable, but only once. Since it is likely line-buffered, you could	1438	readable, but only once. Since it is likely line-buffered, you could
1174	attempt to read a whole line in the callback.	1439	attempt to read a whole line in the callback.
1175		1440
1176	static void	1441	static void
1177	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1442	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1178	{	1443	{
1179	ev_io_stop (loop, w);	1444	ev_io_stop (loop, w);
1180	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1445	.. read from stdin here (or from w->fd) and handle any I/O errors
1181	}	1446	}
1182		1447
1183	...	1448	...
1184	struct ev_loop *loop = ev_default_init (0);	1449	struct ev_loop *loop = ev_default_init (0);
1185	struct ev_io stdin_readable;	1450	ev_io stdin_readable;
1186	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1451	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1187	ev_io_start (loop, &stdin_readable);	1452	ev_io_start (loop, &stdin_readable);
1188	ev_loop (loop, 0);	1453	ev_loop (loop, 0);
1189		1454
1190		1455
…		…
1193	Timer watchers are simple relative timers that generate an event after a	1458	Timer watchers are simple relative timers that generate an event after a
1194	given time, and optionally repeating in regular intervals after that.	1459	given time, and optionally repeating in regular intervals after that.
1195		1460
1196	The timers are based on real time, that is, if you register an event that	1461	The timers are based on real time, that is, if you register an event that
1197	times out after an hour and you reset your system clock to January last	1462	times out after an hour and you reset your system clock to January last
1198	year, it will still time out after (roughly) and hour. "Roughly" because	1463	year, it will still time out after (roughly) one hour. "Roughly" because
1199	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1464	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1200	monotonic clock option helps a lot here).	1465	monotonic clock option helps a lot here).
		1466
		1467	The callback is guaranteed to be invoked only I<after> its timeout has
		1468	passed. If multiple timers become ready during the same loop iteration
		1469	then the ones with earlier time-out values are invoked before ones with
		1470	later time-out values (but this is no longer true when a callback calls
		1471	C<ev_loop> recursively).
		1472
		1473	=head3 Be smart about timeouts
		1474
		1475	Many real-world problems involve some kind of timeout, usually for error
		1476	recovery. A typical example is an HTTP request - if the other side hangs,
		1477	you want to raise some error after a while.
		1478
		1479	What follows are some ways to handle this problem, from obvious and
		1480	inefficient to smart and efficient.
		1481
		1482	In the following, a 60 second activity timeout is assumed - a timeout that
		1483	gets reset to 60 seconds each time there is activity (e.g. each time some
		1484	data or other life sign was received).
		1485
		1486	=over 4
		1487
		1488	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1489
		1490	This is the most obvious, but not the most simple way: In the beginning,
		1491	start the watcher:
		1492
		1493	ev_timer_init (timer, callback, 60., 0.);
		1494	ev_timer_start (loop, timer);
		1495
		1496	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1497	and start it again:
		1498
		1499	ev_timer_stop (loop, timer);
		1500	ev_timer_set (timer, 60., 0.);
		1501	ev_timer_start (loop, timer);
		1502
		1503	This is relatively simple to implement, but means that each time there is
		1504	some activity, libev will first have to remove the timer from its internal
		1505	data structure and then add it again. Libev tries to be fast, but it's
		1506	still not a constant-time operation.
		1507
		1508	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1509
		1510	This is the easiest way, and involves using C<ev_timer_again> instead of
		1511	C<ev_timer_start>.
		1512
		1513	To implement this, configure an C<ev_timer> with a C<repeat> value
		1514	of C<60> and then call C<ev_timer_again> at start and each time you
		1515	successfully read or write some data. If you go into an idle state where
		1516	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1517	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1518
		1519	That means you can ignore both the C<ev_timer_start> function and the
		1520	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1521	member and C<ev_timer_again>.
		1522
		1523	At start:
		1524
		1525	ev_timer_init (timer, callback);
		1526	timer->repeat = 60.;
		1527	ev_timer_again (loop, timer);
		1528
		1529	Each time there is some activity:
		1530
		1531	ev_timer_again (loop, timer);
		1532
		1533	It is even possible to change the time-out on the fly, regardless of
		1534	whether the watcher is active or not:
		1535
		1536	timer->repeat = 30.;
		1537	ev_timer_again (loop, timer);
		1538
		1539	This is slightly more efficient then stopping/starting the timer each time
		1540	you want to modify its timeout value, as libev does not have to completely
		1541	remove and re-insert the timer from/into its internal data structure.
		1542
		1543	It is, however, even simpler than the "obvious" way to do it.
		1544
		1545	=item 3. Let the timer time out, but then re-arm it as required.
		1546
		1547	This method is more tricky, but usually most efficient: Most timeouts are
		1548	relatively long compared to the intervals between other activity - in
		1549	our example, within 60 seconds, there are usually many I/O events with
		1550	associated activity resets.
		1551
		1552	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1553	but remember the time of last activity, and check for a real timeout only
		1554	within the callback:
		1555
		1556	ev_tstamp last_activity; // time of last activity
		1557
		1558	static void
		1559	callback (EV_P_ ev_timer *w, int revents)
		1560	{
		1561	ev_tstamp now = ev_now (EV_A);
		1562	ev_tstamp timeout = last_activity + 60.;
		1563
		1564	// if last_activity + 60. is older than now, we did time out
		1565	if (timeout < now)
		1566	{
		1567	// timeout occured, take action
		1568	}
		1569	else
		1570	{
		1571	// callback was invoked, but there was some activity, re-arm
		1572	// the watcher to fire in last_activity + 60, which is
		1573	// guaranteed to be in the future, so "again" is positive:
		1574	w->repeat = timeout - now;
		1575	ev_timer_again (EV_A_ w);
		1576	}
		1577	}
		1578
		1579	To summarise the callback: first calculate the real timeout (defined
		1580	as "60 seconds after the last activity"), then check if that time has
		1581	been reached, which means something I<did>, in fact, time out. Otherwise
		1582	the callback was invoked too early (C<timeout> is in the future), so
		1583	re-schedule the timer to fire at that future time, to see if maybe we have
		1584	a timeout then.
		1585
		1586	Note how C<ev_timer_again> is used, taking advantage of the
		1587	C<ev_timer_again> optimisation when the timer is already running.
		1588
		1589	This scheme causes more callback invocations (about one every 60 seconds
		1590	minus half the average time between activity), but virtually no calls to
		1591	libev to change the timeout.
		1592
		1593	To start the timer, simply initialise the watcher and set C<last_activity>
		1594	to the current time (meaning we just have some activity :), then call the
		1595	callback, which will "do the right thing" and start the timer:
		1596
		1597	ev_timer_init (timer, callback);
		1598	last_activity = ev_now (loop);
		1599	callback (loop, timer, EV_TIMEOUT);
		1600
		1601	And when there is some activity, simply store the current time in
		1602	C<last_activity>, no libev calls at all:
		1603
		1604	last_actiivty = ev_now (loop);
		1605
		1606	This technique is slightly more complex, but in most cases where the
		1607	time-out is unlikely to be triggered, much more efficient.
		1608
		1609	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1610	callback :) - just change the timeout and invoke the callback, which will
		1611	fix things for you.
		1612
		1613	=item 4. Wee, just use a double-linked list for your timeouts.
		1614
		1615	If there is not one request, but many thousands (millions...), all
		1616	employing some kind of timeout with the same timeout value, then one can
		1617	do even better:
		1618
		1619	When starting the timeout, calculate the timeout value and put the timeout
		1620	at the I<end> of the list.
		1621
		1622	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1623	the list is expected to fire (for example, using the technique #3).
		1624
		1625	When there is some activity, remove the timer from the list, recalculate
		1626	the timeout, append it to the end of the list again, and make sure to
		1627	update the C<ev_timer> if it was taken from the beginning of the list.
		1628
		1629	This way, one can manage an unlimited number of timeouts in O(1) time for
		1630	starting, stopping and updating the timers, at the expense of a major
		1631	complication, and having to use a constant timeout. The constant timeout
		1632	ensures that the list stays sorted.
		1633
		1634	=back
		1635
		1636	So which method the best?
		1637
		1638	Method #2 is a simple no-brain-required solution that is adequate in most
		1639	situations. Method #3 requires a bit more thinking, but handles many cases
		1640	better, and isn't very complicated either. In most case, choosing either
		1641	one is fine, with #3 being better in typical situations.
		1642
		1643	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1644	rather complicated, but extremely efficient, something that really pays
		1645	off after the first million or so of active timers, i.e. it's usually
		1646	overkill :)
		1647
		1648	=head3 The special problem of time updates
		1649
		1650	Establishing the current time is a costly operation (it usually takes at
		1651	least two system calls): EV therefore updates its idea of the current
		1652	time only before and after C<ev_loop> collects new events, which causes a
		1653	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1654	lots of events in one iteration.
1201		1655
1202	The relative timeouts are calculated relative to the C<ev_now ()>	1656	The relative timeouts are calculated relative to the C<ev_now ()>
1203	time. This is usually the right thing as this timestamp refers to the time	1657	time. This is usually the right thing as this timestamp refers to the time
1204	of the event triggering whatever timeout you are modifying/starting. If	1658	of the event triggering whatever timeout you are modifying/starting. If
1205	you suspect event processing to be delayed and you I<need> to base the timeout	1659	you suspect event processing to be delayed and you I<need> to base the
1206	on the current time, use something like this to adjust for this:	1660	timeout on the current time, use something like this to adjust for this:
1207		1661
1208	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1662	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1209		1663
1210	The callback is guaranteed to be invoked only after its timeout has passed,	1664	If the event loop is suspended for a long time, you can also force an
1211	but if multiple timers become ready during the same loop iteration then	1665	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1212	order of execution is undefined.	1666	()>.
1213		1667
1214	=head3 Watcher-Specific Functions and Data Members	1668	=head3 Watcher-Specific Functions and Data Members
1215		1669
1216	=over 4	1670	=over 4
1217		1671
…		…
1241	If the timer is started but non-repeating, stop it (as if it timed out).	1695	If the timer is started but non-repeating, stop it (as if it timed out).
1242		1696
1243	If the timer is repeating, either start it if necessary (with the	1697	If the timer is repeating, either start it if necessary (with the
1244	C<repeat> value), or reset the running timer to the C<repeat> value.	1698	C<repeat> value), or reset the running timer to the C<repeat> value.
1245		1699
1246	This sounds a bit complicated, but here is a useful and typical	1700	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1247	example: Imagine you have a TCP connection and you want a so-called idle	1701	usage example.
1248	timeout, that is, you want to be called when there have been, say, 60
1249	seconds of inactivity on the socket. The easiest way to do this is to
1250	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1251	C<ev_timer_again> each time you successfully read or write some data. If
1252	you go into an idle state where you do not expect data to travel on the
1253	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1254	automatically restart it if need be.
1255
1256	That means you can ignore the C<after> value and C<ev_timer_start>
1257	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1258
1259	ev_timer_init (timer, callback, 0., 5.);
1260	ev_timer_again (loop, timer);
1261	...
1262	timer->again = 17.;
1263	ev_timer_again (loop, timer);
1264	...
1265	timer->again = 10.;
1266	ev_timer_again (loop, timer);
1267
1268	This is more slightly efficient then stopping/starting the timer each time
1269	you want to modify its timeout value.
1270		1702
1271	=item ev_tstamp repeat [read-write]	1703	=item ev_tstamp repeat [read-write]
1272		1704
1273	The current C<repeat> value. Will be used each time the watcher times out	1705	The current C<repeat> value. Will be used each time the watcher times out
1274	or C<ev_timer_again> is called and determines the next timeout (if any),	1706	or C<ev_timer_again> is called, and determines the next timeout (if any),
1275	which is also when any modifications are taken into account.	1707	which is also when any modifications are taken into account.
1276		1708
1277	=back	1709	=back
1278		1710
1279	=head3 Examples	1711	=head3 Examples
1280		1712
1281	Example: Create a timer that fires after 60 seconds.	1713	Example: Create a timer that fires after 60 seconds.
1282		1714
1283	static void	1715	static void
1284	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1716	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1285	{	1717	{
1286	.. one minute over, w is actually stopped right here	1718	.. one minute over, w is actually stopped right here
1287	}	1719	}
1288		1720
1289	struct ev_timer mytimer;	1721	ev_timer mytimer;
1290	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1722	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1291	ev_timer_start (loop, &mytimer);	1723	ev_timer_start (loop, &mytimer);
1292		1724
1293	Example: Create a timeout timer that times out after 10 seconds of	1725	Example: Create a timeout timer that times out after 10 seconds of
1294	inactivity.	1726	inactivity.
1295		1727
1296	static void	1728	static void
1297	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1729	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1298	{	1730	{
1299	.. ten seconds without any activity	1731	.. ten seconds without any activity
1300	}	1732	}
1301		1733
1302	struct ev_timer mytimer;	1734	ev_timer mytimer;
1303	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1735	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1304	ev_timer_again (&mytimer); /* start timer */	1736	ev_timer_again (&mytimer); /* start timer */
1305	ev_loop (loop, 0);	1737	ev_loop (loop, 0);
1306		1738
1307	// and in some piece of code that gets executed on any "activity":	1739	// and in some piece of code that gets executed on any "activity":
…		…
1312	=head2 C<ev_periodic> - to cron or not to cron?	1744	=head2 C<ev_periodic> - to cron or not to cron?
1313		1745
1314	Periodic watchers are also timers of a kind, but they are very versatile	1746	Periodic watchers are also timers of a kind, but they are very versatile
1315	(and unfortunately a bit complex).	1747	(and unfortunately a bit complex).
1316		1748
1317	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1749	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1318	but on wall clock time (absolute time). You can tell a periodic watcher	1750	relative time, the physical time that passes) but on wall clock time
1319	to trigger after some specific point in time. For example, if you tell a	1751	(absolute time, the thing you can read on your calender or clock). The
1320	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1752	difference is that wall clock time can run faster or slower than real
1321	+ 10.>, that is, an absolute time not a delay) and then reset your system	1753	time, and time jumps are not uncommon (e.g. when you adjust your
1322	clock to January of the previous year, then it will take more than year	1754	wrist-watch).
1323	to trigger the event (unlike an C<ev_timer>, which would still trigger
1324	roughly 10 seconds later as it uses a relative timeout).
1325		1755
		1756	You can tell a periodic watcher to trigger after some specific point
		1757	in time: for example, if you tell a periodic watcher to trigger "in 10
		1758	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1759	not a delay) and then reset your system clock to January of the previous
		1760	year, then it will take a year or more to trigger the event (unlike an
		1761	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1762	it, as it uses a relative timeout).
		1763
1326	C<ev_periodic>s can also be used to implement vastly more complex timers,	1764	C<ev_periodic> watchers can also be used to implement vastly more complex
1327	such as triggering an event on each "midnight, local time", or other	1765	timers, such as triggering an event on each "midnight, local time", or
1328	complicated, rules.	1766	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1767	those cannot react to time jumps.
1329		1768
1330	As with timers, the callback is guaranteed to be invoked only when the	1769	As with timers, the callback is guaranteed to be invoked only when the
1331	time (C<at>) has passed, but if multiple periodic timers become ready	1770	point in time where it is supposed to trigger has passed. If multiple
1332	during the same loop iteration then order of execution is undefined.	1771	timers become ready during the same loop iteration then the ones with
		1772	earlier time-out values are invoked before ones with later time-out values
		1773	(but this is no longer true when a callback calls C<ev_loop> recursively).
1333		1774
1334	=head3 Watcher-Specific Functions and Data Members	1775	=head3 Watcher-Specific Functions and Data Members
1335		1776
1336	=over 4	1777	=over 4
1337		1778
1338	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1779	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1339		1780
1340	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1781	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1341		1782
1342	Lots of arguments, lets sort it out... There are basically three modes of	1783	Lots of arguments, let's sort it out... There are basically three modes of
1343	operation, and we will explain them from simplest to complex:	1784	operation, and we will explain them from simplest to most complex:
1344		1785
1345	=over 4	1786	=over 4
1346		1787
1347	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1788	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1348		1789
1349	In this configuration the watcher triggers an event after the wall clock	1790	In this configuration the watcher triggers an event after the wall clock
1350	time C<at> has passed and doesn't repeat. It will not adjust when a time	1791	time C<offset> has passed. It will not repeat and will not adjust when a
1351	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1792	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1352	run when the system time reaches or surpasses this time.	1793	will be stopped and invoked when the system clock reaches or surpasses
		1794	this point in time.
1353		1795
1354	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1796	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1355		1797
1356	In this mode the watcher will always be scheduled to time out at the next	1798	In this mode the watcher will always be scheduled to time out at the next
1357	C<at + N * interval> time (for some integer N, which can also be negative)	1799	C<offset + N * interval> time (for some integer N, which can also be
1358	and then repeat, regardless of any time jumps.	1800	negative) and then repeat, regardless of any time jumps. The C<offset>
		1801	argument is merely an offset into the C<interval> periods.
1359		1802
1360	This can be used to create timers that do not drift with respect to system	1803	This can be used to create timers that do not drift with respect to the
1361	time, for example, here is a C<ev_periodic> that triggers each hour, on	1804	system clock, for example, here is an C<ev_periodic> that triggers each
1362	the hour:	1805	hour, on the hour (with respect to UTC):
1363		1806
1364	ev_periodic_set (&periodic, 0., 3600., 0);	1807	ev_periodic_set (&periodic, 0., 3600., 0);
1365		1808
1366	This doesn't mean there will always be 3600 seconds in between triggers,	1809	This doesn't mean there will always be 3600 seconds in between triggers,
1367	but only that the callback will be called when the system time shows a	1810	but only that the callback will be called when the system time shows a
1368	full hour (UTC), or more correctly, when the system time is evenly divisible	1811	full hour (UTC), or more correctly, when the system time is evenly divisible
1369	by 3600.	1812	by 3600.
1370		1813
1371	Another way to think about it (for the mathematically inclined) is that	1814	Another way to think about it (for the mathematically inclined) is that
1372	C<ev_periodic> will try to run the callback in this mode at the next possible	1815	C<ev_periodic> will try to run the callback in this mode at the next possible
1373	time where C<time = at (mod interval)>, regardless of any time jumps.	1816	time where C<time = offset (mod interval)>, regardless of any time jumps.
1374		1817
1375	For numerical stability it is preferable that the C<at> value is near	1818	For numerical stability it is preferable that the C<offset> value is near
1376	C<ev_now ()> (the current time), but there is no range requirement for	1819	C<ev_now ()> (the current time), but there is no range requirement for
1377	this value, and in fact is often specified as zero.	1820	this value, and in fact is often specified as zero.
1378		1821
1379	Note also that there is an upper limit to how often a timer can fire (CPU	1822	Note also that there is an upper limit to how often a timer can fire (CPU
1380	speed for example), so if C<interval> is very small then timing stability	1823	speed for example), so if C<interval> is very small then timing stability
1381	will of course deteriorate. Libev itself tries to be exact to be about one	1824	will of course deteriorate. Libev itself tries to be exact to be about one
1382	millisecond (if the OS supports it and the machine is fast enough).	1825	millisecond (if the OS supports it and the machine is fast enough).
1383		1826
1384	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1827	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1385		1828
1386	In this mode the values for C<interval> and C<at> are both being	1829	In this mode the values for C<interval> and C<offset> are both being
1387	ignored. Instead, each time the periodic watcher gets scheduled, the	1830	ignored. Instead, each time the periodic watcher gets scheduled, the
1388	reschedule callback will be called with the watcher as first, and the	1831	reschedule callback will be called with the watcher as first, and the
1389	current time as second argument.	1832	current time as second argument.
1390		1833
1391	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1834	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1392	ever, or make ANY event loop modifications whatsoever>.	1835	or make ANY other event loop modifications whatsoever, unless explicitly
		1836	allowed by documentation here>.
1393		1837
1394	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1838	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1395	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1839	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1396	only event loop modification you are allowed to do).	1840	only event loop modification you are allowed to do).
1397		1841
1398	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1842	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1399	*w, ev_tstamp now)>, e.g.:	1843	*w, ev_tstamp now)>, e.g.:
1400		1844
		1845	static ev_tstamp
1401	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1846	my_rescheduler (ev_periodic *w, ev_tstamp now)
1402	{	1847	{
1403	return now + 60.;	1848	return now + 60.;
1404	}	1849	}
1405		1850
1406	It must return the next time to trigger, based on the passed time value	1851	It must return the next time to trigger, based on the passed time value
…		…
1426	a different time than the last time it was called (e.g. in a crond like	1871	a different time than the last time it was called (e.g. in a crond like
1427	program when the crontabs have changed).	1872	program when the crontabs have changed).
1428		1873
1429	=item ev_tstamp ev_periodic_at (ev_periodic *)	1874	=item ev_tstamp ev_periodic_at (ev_periodic *)
1430		1875
1431	When active, returns the absolute time that the watcher is supposed to	1876	When active, returns the absolute time that the watcher is supposed
1432	trigger next.	1877	to trigger next. This is not the same as the C<offset> argument to
		1878	C<ev_periodic_set>, but indeed works even in interval and manual
		1879	rescheduling modes.
1433		1880
1434	=item ev_tstamp offset [read-write]	1881	=item ev_tstamp offset [read-write]
1435		1882
1436	When repeating, this contains the offset value, otherwise this is the	1883	When repeating, this contains the offset value, otherwise this is the
1437	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1884	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1885	although libev might modify this value for better numerical stability).
1438		1886
1439	Can be modified any time, but changes only take effect when the periodic	1887	Can be modified any time, but changes only take effect when the periodic
1440	timer fires or C<ev_periodic_again> is being called.	1888	timer fires or C<ev_periodic_again> is being called.
1441		1889
1442	=item ev_tstamp interval [read-write]	1890	=item ev_tstamp interval [read-write]
1443		1891
1444	The current interval value. Can be modified any time, but changes only	1892	The current interval value. Can be modified any time, but changes only
1445	take effect when the periodic timer fires or C<ev_periodic_again> is being	1893	take effect when the periodic timer fires or C<ev_periodic_again> is being
1446	called.	1894	called.
1447		1895
1448	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1896	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1449		1897
1450	The current reschedule callback, or C<0>, if this functionality is	1898	The current reschedule callback, or C<0>, if this functionality is
1451	switched off. Can be changed any time, but changes only take effect when	1899	switched off. Can be changed any time, but changes only take effect when
1452	the periodic timer fires or C<ev_periodic_again> is being called.	1900	the periodic timer fires or C<ev_periodic_again> is being called.
1453		1901
1454	=back	1902	=back
1455		1903
1456	=head3 Examples	1904	=head3 Examples
1457		1905
1458	Example: Call a callback every hour, or, more precisely, whenever the	1906	Example: Call a callback every hour, or, more precisely, whenever the
1459	system clock is divisible by 3600. The callback invocation times have	1907	system time is divisible by 3600. The callback invocation times have
1460	potentially a lot of jitter, but good long-term stability.	1908	potentially a lot of jitter, but good long-term stability.
1461		1909
1462	static void	1910	static void
1463	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1911	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1464	{	1912	{
1465	... its now a full hour (UTC, or TAI or whatever your clock follows)	1913	... its now a full hour (UTC, or TAI or whatever your clock follows)
1466	}	1914	}
1467		1915
1468	struct ev_periodic hourly_tick;	1916	ev_periodic hourly_tick;
1469	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1917	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1470	ev_periodic_start (loop, &hourly_tick);	1918	ev_periodic_start (loop, &hourly_tick);
1471		1919
1472	Example: The same as above, but use a reschedule callback to do it:	1920	Example: The same as above, but use a reschedule callback to do it:
1473		1921
1474	#include <math.h>	1922	#include <math.h>
1475		1923
1476	static ev_tstamp	1924	static ev_tstamp
1477	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1925	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1478	{	1926	{
1479	return fmod (now, 3600.) + 3600.;	1927	return now + (3600. - fmod (now, 3600.));
1480	}	1928	}
1481		1929
1482	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1930	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1483		1931
1484	Example: Call a callback every hour, starting now:	1932	Example: Call a callback every hour, starting now:
1485		1933
1486	struct ev_periodic hourly_tick;	1934	ev_periodic hourly_tick;
1487	ev_periodic_init (&hourly_tick, clock_cb,	1935	ev_periodic_init (&hourly_tick, clock_cb,
1488	fmod (ev_now (loop), 3600.), 3600., 0);	1936	fmod (ev_now (loop), 3600.), 3600., 0);
1489	ev_periodic_start (loop, &hourly_tick);	1937	ev_periodic_start (loop, &hourly_tick);
1490		1938
1491		1939
…		…
1494	Signal watchers will trigger an event when the process receives a specific	1942	Signal watchers will trigger an event when the process receives a specific
1495	signal one or more times. Even though signals are very asynchronous, libev	1943	signal one or more times. Even though signals are very asynchronous, libev
1496	will try it's best to deliver signals synchronously, i.e. as part of the	1944	will try it's best to deliver signals synchronously, i.e. as part of the
1497	normal event processing, like any other event.	1945	normal event processing, like any other event.
1498		1946
		1947	If you want signals asynchronously, just use C<sigaction> as you would
		1948	do without libev and forget about sharing the signal. You can even use
		1949	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1950
1499	You can configure as many watchers as you like per signal. Only when the	1951	You can configure as many watchers as you like per signal. Only when the
1500	first watcher gets started will libev actually register a signal watcher	1952	first watcher gets started will libev actually register a signal handler
1501	with the kernel (thus it coexists with your own signal handlers as long	1953	with the kernel (thus it coexists with your own signal handlers as long as
1502	as you don't register any with libev). Similarly, when the last signal	1954	you don't register any with libev for the same signal). Similarly, when
1503	watcher for a signal is stopped libev will reset the signal handler to	1955	the last signal watcher for a signal is stopped, libev will reset the
1504	SIG_DFL (regardless of what it was set to before).	1956	signal handler to SIG_DFL (regardless of what it was set to before).
1505		1957
1506	If possible and supported, libev will install its handlers with	1958	If possible and supported, libev will install its handlers with
1507	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	1959	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
1508	interrupted. If you have a problem with system calls getting interrupted by	1960	interrupted. If you have a problem with system calls getting interrupted by
1509	signals you can block all signals in an C<ev_check> watcher and unblock	1961	signals you can block all signals in an C<ev_check> watcher and unblock
…		…
1526		1978
1527	=back	1979	=back
1528		1980
1529	=head3 Examples	1981	=head3 Examples
1530		1982
1531	Example: Try to exit cleanly on SIGINT and SIGTERM.	1983	Example: Try to exit cleanly on SIGINT.
1532		1984
1533	static void	1985	static void
1534	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1986	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1535	{	1987	{
1536	ev_unloop (loop, EVUNLOOP_ALL);	1988	ev_unloop (loop, EVUNLOOP_ALL);
1537	}	1989	}
1538		1990
1539	struct ev_signal signal_watcher;	1991	ev_signal signal_watcher;
1540	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1992	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1541	ev_signal_start (loop, &sigint_cb);	1993	ev_signal_start (loop, &signal_watcher);
1542		1994
1543		1995
1544	=head2 C<ev_child> - watch out for process status changes	1996	=head2 C<ev_child> - watch out for process status changes
1545		1997
1546	Child watchers trigger when your process receives a SIGCHLD in response to	1998	Child watchers trigger when your process receives a SIGCHLD in response to
1547	some child status changes (most typically when a child of yours dies). It	1999	some child status changes (most typically when a child of yours dies or
1548	is permissible to install a child watcher I<after> the child has been	2000	exits). It is permissible to install a child watcher I<after> the child
1549	forked (which implies it might have already exited), as long as the event	2001	has been forked (which implies it might have already exited), as long
1550	loop isn't entered (or is continued from a watcher).	2002	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2003	forking and then immediately registering a watcher for the child is fine,
		2004	but forking and registering a watcher a few event loop iterations later is
		2005	not.
1551		2006
1552	Only the default event loop is capable of handling signals, and therefore	2007	Only the default event loop is capable of handling signals, and therefore
1553	you can only register child watchers in the default event loop.	2008	you can only register child watchers in the default event loop.
1554		2009
1555	=head3 Process Interaction	2010	=head3 Process Interaction
…		…
1616	its completion.	2071	its completion.
1617		2072
1618	ev_child cw;	2073	ev_child cw;
1619		2074
1620	static void	2075	static void
1621	child_cb (EV_P_ struct ev_child *w, int revents)	2076	child_cb (EV_P_ ev_child *w, int revents)
1622	{	2077	{
1623	ev_child_stop (EV_A_ w);	2078	ev_child_stop (EV_A_ w);
1624	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2079	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1625	}	2080	}
1626		2081
…		…
1641		2096
1642		2097
1643	=head2 C<ev_stat> - did the file attributes just change?	2098	=head2 C<ev_stat> - did the file attributes just change?
1644		2099
1645	This watches a file system path for attribute changes. That is, it calls	2100	This watches a file system path for attribute changes. That is, it calls
1646	C<stat> regularly (or when the OS says it changed) and sees if it changed	2101	C<stat> on that path in regular intervals (or when the OS says it changed)
1647	compared to the last time, invoking the callback if it did.	2102	and sees if it changed compared to the last time, invoking the callback if
		2103	it did.
1648		2104
1649	The path does not need to exist: changing from "path exists" to "path does	2105	The path does not need to exist: changing from "path exists" to "path does
1650	not exist" is a status change like any other. The condition "path does	2106	not exist" is a status change like any other. The condition "path does not
1651	not exist" is signified by the C<st_nlink> field being zero (which is	2107	exist" (or more correctly "path cannot be stat'ed") is signified by the
1652	otherwise always forced to be at least one) and all the other fields of	2108	C<st_nlink> field being zero (which is otherwise always forced to be at
1653	the stat buffer having unspecified contents.	2109	least one) and all the other fields of the stat buffer having unspecified
		2110	contents.
1654		2111
1655	The path I<should> be absolute and I<must not> end in a slash. If it is	2112	The path I<must not> end in a slash or contain special components such as
		2113	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1656	relative and your working directory changes, the behaviour is undefined.	2114	your working directory changes, then the behaviour is undefined.
1657		2115
1658	Since there is no standard to do this, the portable implementation simply	2116	Since there is no portable change notification interface available, the
1659	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2117	portable implementation simply calls C<stat(2)> regularly on the path
1660	can specify a recommended polling interval for this case. If you specify	2118	to see if it changed somehow. You can specify a recommended polling
1661	a polling interval of C<0> (highly recommended!) then a I<suitable,	2119	interval for this case. If you specify a polling interval of C<0> (highly
1662	unspecified default> value will be used (which you can expect to be around	2120	recommended!) then a I<suitable, unspecified default> value will be used
1663	five seconds, although this might change dynamically). Libev will also	2121	(which you can expect to be around five seconds, although this might
1664	impose a minimum interval which is currently around C<0.1>, but thats	2122	change dynamically). Libev will also impose a minimum interval which is
1665	usually overkill.	2123	currently around C<0.1>, but that's usually overkill.
1666		2124
1667	This watcher type is not meant for massive numbers of stat watchers,	2125	This watcher type is not meant for massive numbers of stat watchers,
1668	as even with OS-supported change notifications, this can be	2126	as even with OS-supported change notifications, this can be
1669	resource-intensive.	2127	resource-intensive.
1670		2128
1671	At the time of this writing, only the Linux inotify interface is	2129	At the time of this writing, the only OS-specific interface implemented
1672	implemented (implementing kqueue support is left as an exercise for the	2130	is the Linux inotify interface (implementing kqueue support is left as an
1673	reader, note, however, that the author sees no way of implementing ev_stat	2131	exercise for the reader. Note, however, that the author sees no way of
1674	semantics with kqueue). Inotify will be used to give hints only and should	2132	implementing C<ev_stat> semantics with kqueue, except as a hint).
1675	not change the semantics of C<ev_stat> watchers, which means that libev
1676	sometimes needs to fall back to regular polling again even with inotify,
1677	but changes are usually detected immediately, and if the file exists there
1678	will be no polling.
1679		2133
1680	=head3 ABI Issues (Largefile Support)	2134	=head3 ABI Issues (Largefile Support)
1681		2135
1682	Libev by default (unless the user overrides this) uses the default	2136	Libev by default (unless the user overrides this) uses the default
1683	compilation environment, which means that on systems with large file	2137	compilation environment, which means that on systems with large file
1684	support disabled by default, you get the 32 bit version of the stat	2138	support disabled by default, you get the 32 bit version of the stat
1685	structure. When using the library from programs that change the ABI to	2139	structure. When using the library from programs that change the ABI to
1686	use 64 bit file offsets the programs will fail. In that case you have to	2140	use 64 bit file offsets the programs will fail. In that case you have to
1687	compile libev with the same flags to get binary compatibility. This is	2141	compile libev with the same flags to get binary compatibility. This is
1688	obviously the case with any flags that change the ABI, but the problem is	2142	obviously the case with any flags that change the ABI, but the problem is
1689	most noticeably disabled with ev_stat and large file support.	2143	most noticeably displayed with ev_stat and large file support.
1690		2144
1691	The solution for this is to lobby your distribution maker to make large	2145	The solution for this is to lobby your distribution maker to make large
1692	file interfaces available by default (as e.g. FreeBSD does) and not	2146	file interfaces available by default (as e.g. FreeBSD does) and not
1693	optional. Libev cannot simply switch on large file support because it has	2147	optional. Libev cannot simply switch on large file support because it has
1694	to exchange stat structures with application programs compiled using the	2148	to exchange stat structures with application programs compiled using the
1695	default compilation environment.	2149	default compilation environment.
1696		2150
1697	=head3 Inotify	2151	=head3 Inotify and Kqueue
1698		2152
1699	When C<inotify (7)> support has been compiled into libev (generally only	2153	When C<inotify (7)> support has been compiled into libev and present at
1700	available on Linux) and present at runtime, it will be used to speed up	2154	runtime, it will be used to speed up change detection where possible. The
1701	change detection where possible. The inotify descriptor will be created lazily	2155	inotify descriptor will be created lazily when the first C<ev_stat>
1702	when the first C<ev_stat> watcher is being started.	2156	watcher is being started.
1703		2157
1704	Inotify presence does not change the semantics of C<ev_stat> watchers	2158	Inotify presence does not change the semantics of C<ev_stat> watchers
1705	except that changes might be detected earlier, and in some cases, to avoid	2159	except that changes might be detected earlier, and in some cases, to avoid
1706	making regular C<stat> calls. Even in the presence of inotify support	2160	making regular C<stat> calls. Even in the presence of inotify support
1707	there are many cases where libev has to resort to regular C<stat> polling.	2161	there are many cases where libev has to resort to regular C<stat> polling,
		2162	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2163	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2164	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2165	xfs are fully working) libev usually gets away without polling.
1708		2166
1709	(There is no support for kqueue, as apparently it cannot be used to	2167	There is no support for kqueue, as apparently it cannot be used to
1710	implement this functionality, due to the requirement of having a file	2168	implement this functionality, due to the requirement of having a file
1711	descriptor open on the object at all times).	2169	descriptor open on the object at all times, and detecting renames, unlinks
		2170	etc. is difficult.
		2171
		2172	=head3 C<stat ()> is a synchronous operation
		2173
		2174	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2175	the process. The exception are C<ev_stat> watchers - those call C<stat
		2176	()>, which is a synchronous operation.
		2177
		2178	For local paths, this usually doesn't matter: unless the system is very
		2179	busy or the intervals between stat's are large, a stat call will be fast,
		2180	as the path data is usually in memory already (except when starting the
		2181	watcher).
		2182
		2183	For networked file systems, calling C<stat ()> can block an indefinite
		2184	time due to network issues, and even under good conditions, a stat call
		2185	often takes multiple milliseconds.
		2186
		2187	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2188	paths, although this is fully supported by libev.
1712		2189
1713	=head3 The special problem of stat time resolution	2190	=head3 The special problem of stat time resolution
1714		2191
1715	The C<stat ()> system call only supports full-second resolution portably, and	2192	The C<stat ()> system call only supports full-second resolution portably,
1716	even on systems where the resolution is higher, many file systems still	2193	and even on systems where the resolution is higher, most file systems
1717	only support whole seconds.	2194	still only support whole seconds.
1718		2195
1719	That means that, if the time is the only thing that changes, you can	2196	That means that, if the time is the only thing that changes, you can
1720	easily miss updates: on the first update, C<ev_stat> detects a change and	2197	easily miss updates: on the first update, C<ev_stat> detects a change and
1721	calls your callback, which does something. When there is another update	2198	calls your callback, which does something. When there is another update
1722	within the same second, C<ev_stat> will be unable to detect it as the stat	2199	within the same second, C<ev_stat> will be unable to detect unless the
1723	data does not change.	2200	stat data does change in other ways (e.g. file size).
1724		2201
1725	The solution to this is to delay acting on a change for slightly more	2202	The solution to this is to delay acting on a change for slightly more
1726	than a second (or till slightly after the next full second boundary), using	2203	than a second (or till slightly after the next full second boundary), using
1727	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2204	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1728	ev_timer_again (loop, w)>).	2205	ev_timer_again (loop, w)>).
…		…
1748	C<path>. The C<interval> is a hint on how quickly a change is expected to	2225	C<path>. The C<interval> is a hint on how quickly a change is expected to
1749	be detected and should normally be specified as C<0> to let libev choose	2226	be detected and should normally be specified as C<0> to let libev choose
1750	a suitable value. The memory pointed to by C<path> must point to the same	2227	a suitable value. The memory pointed to by C<path> must point to the same
1751	path for as long as the watcher is active.	2228	path for as long as the watcher is active.
1752		2229
1753	The callback will receive C<EV_STAT> when a change was detected, relative	2230	The callback will receive an C<EV_STAT> event when a change was detected,
1754	to the attributes at the time the watcher was started (or the last change	2231	relative to the attributes at the time the watcher was started (or the
1755	was detected).	2232	last change was detected).
1756		2233
1757	=item ev_stat_stat (loop, ev_stat *)	2234	=item ev_stat_stat (loop, ev_stat *)
1758		2235
1759	Updates the stat buffer immediately with new values. If you change the	2236	Updates the stat buffer immediately with new values. If you change the
1760	watched path in your callback, you could call this function to avoid	2237	watched path in your callback, you could call this function to avoid
…		…
1843		2320
1844		2321
1845	=head2 C<ev_idle> - when you've got nothing better to do...	2322	=head2 C<ev_idle> - when you've got nothing better to do...
1846		2323
1847	Idle watchers trigger events when no other events of the same or higher	2324	Idle watchers trigger events when no other events of the same or higher
1848	priority are pending (prepare, check and other idle watchers do not	2325	priority are pending (prepare, check and other idle watchers do not count
1849	count).	2326	as receiving "events").
1850		2327
1851	That is, as long as your process is busy handling sockets or timeouts	2328	That is, as long as your process is busy handling sockets or timeouts
1852	(or even signals, imagine) of the same or higher priority it will not be	2329	(or even signals, imagine) of the same or higher priority it will not be
1853	triggered. But when your process is idle (or only lower-priority watchers	2330	triggered. But when your process is idle (or only lower-priority watchers
1854	are pending), the idle watchers are being called once per event loop	2331	are pending), the idle watchers are being called once per event loop
…		…
1865		2342
1866	=head3 Watcher-Specific Functions and Data Members	2343	=head3 Watcher-Specific Functions and Data Members
1867		2344
1868	=over 4	2345	=over 4
1869		2346
1870	=item ev_idle_init (ev_signal *, callback)	2347	=item ev_idle_init (ev_idle *, callback)
1871		2348
1872	Initialises and configures the idle watcher - it has no parameters of any	2349	Initialises and configures the idle watcher - it has no parameters of any
1873	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2350	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1874	believe me.	2351	believe me.
1875		2352
…		…
1879		2356
1880	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2357	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1881	callback, free it. Also, use no error checking, as usual.	2358	callback, free it. Also, use no error checking, as usual.
1882		2359
1883	static void	2360	static void
1884	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2361	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1885	{	2362	{
1886	free (w);	2363	free (w);
1887	// now do something you wanted to do when the program has	2364	// now do something you wanted to do when the program has
1888	// no longer anything immediate to do.	2365	// no longer anything immediate to do.
1889	}	2366	}
1890		2367
1891	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2368	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1892	ev_idle_init (idle_watcher, idle_cb);	2369	ev_idle_init (idle_watcher, idle_cb);
1893	ev_idle_start (loop, idle_cb);	2370	ev_idle_start (loop, idle_cb);
1894		2371
1895		2372
1896	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2373	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1897		2374
1898	Prepare and check watchers are usually (but not always) used in tandem:	2375	Prepare and check watchers are usually (but not always) used in pairs:
1899	prepare watchers get invoked before the process blocks and check watchers	2376	prepare watchers get invoked before the process blocks and check watchers
1900	afterwards.	2377	afterwards.
1901		2378
1902	You I<must not> call C<ev_loop> or similar functions that enter	2379	You I<must not> call C<ev_loop> or similar functions that enter
1903	the current event loop from either C<ev_prepare> or C<ev_check>	2380	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1906	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2383	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1907	C<ev_check> so if you have one watcher of each kind they will always be	2384	C<ev_check> so if you have one watcher of each kind they will always be
1908	called in pairs bracketing the blocking call.	2385	called in pairs bracketing the blocking call.
1909		2386
1910	Their main purpose is to integrate other event mechanisms into libev and	2387	Their main purpose is to integrate other event mechanisms into libev and
1911	their use is somewhat advanced. This could be used, for example, to track	2388	their use is somewhat advanced. They could be used, for example, to track
1912	variable changes, implement your own watchers, integrate net-snmp or a	2389	variable changes, implement your own watchers, integrate net-snmp or a
1913	coroutine library and lots more. They are also occasionally useful if	2390	coroutine library and lots more. They are also occasionally useful if
1914	you cache some data and want to flush it before blocking (for example,	2391	you cache some data and want to flush it before blocking (for example,
1915	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2392	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1916	watcher).	2393	watcher).
1917		2394
1918	This is done by examining in each prepare call which file descriptors need	2395	This is done by examining in each prepare call which file descriptors
1919	to be watched by the other library, registering C<ev_io> watchers for	2396	need to be watched by the other library, registering C<ev_io> watchers
1920	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2397	for them and starting an C<ev_timer> watcher for any timeouts (many
1921	provide just this functionality). Then, in the check watcher you check for	2398	libraries provide exactly this functionality). Then, in the check watcher,
1922	any events that occurred (by checking the pending status of all watchers	2399	you check for any events that occurred (by checking the pending status
1923	and stopping them) and call back into the library. The I/O and timer	2400	of all watchers and stopping them) and call back into the library. The
1924	callbacks will never actually be called (but must be valid nevertheless,	2401	I/O and timer callbacks will never actually be called (but must be valid
1925	because you never know, you know?).	2402	nevertheless, because you never know, you know?).
1926		2403
1927	As another example, the Perl Coro module uses these hooks to integrate	2404	As another example, the Perl Coro module uses these hooks to integrate
1928	coroutines into libev programs, by yielding to other active coroutines	2405	coroutines into libev programs, by yielding to other active coroutines
1929	during each prepare and only letting the process block if no coroutines	2406	during each prepare and only letting the process block if no coroutines
1930	are ready to run (it's actually more complicated: it only runs coroutines	2407	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1933	loop from blocking if lower-priority coroutines are active, thus mapping	2410	loop from blocking if lower-priority coroutines are active, thus mapping
1934	low-priority coroutines to idle/background tasks).	2411	low-priority coroutines to idle/background tasks).
1935		2412
1936	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2413	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1937	priority, to ensure that they are being run before any other watchers	2414	priority, to ensure that they are being run before any other watchers
		2415	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2416
1938	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2417	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1939	too) should not activate ("feed") events into libev. While libev fully	2418	activate ("feed") events into libev. While libev fully supports this, they
1940	supports this, they might get executed before other C<ev_check> watchers	2419	might get executed before other C<ev_check> watchers did their job. As
1941	did their job. As C<ev_check> watchers are often used to embed other	2420	C<ev_check> watchers are often used to embed other (non-libev) event
1942	(non-libev) event loops those other event loops might be in an unusable	2421	loops those other event loops might be in an unusable state until their
1943	state until their C<ev_check> watcher ran (always remind yourself to	2422	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1944	coexist peacefully with others).	2423	others).
1945		2424
1946	=head3 Watcher-Specific Functions and Data Members	2425	=head3 Watcher-Specific Functions and Data Members
1947		2426
1948	=over 4	2427	=over 4
1949		2428
…		…
1951		2430
1952	=item ev_check_init (ev_check *, callback)	2431	=item ev_check_init (ev_check *, callback)
1953		2432
1954	Initialises and configures the prepare or check watcher - they have no	2433	Initialises and configures the prepare or check watcher - they have no
1955	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2434	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1956	macros, but using them is utterly, utterly and completely pointless.	2435	macros, but using them is utterly, utterly, utterly and completely
		2436	pointless.
1957		2437
1958	=back	2438	=back
1959		2439
1960	=head3 Examples	2440	=head3 Examples
1961		2441
…		…
1974		2454
1975	static ev_io iow [nfd];	2455	static ev_io iow [nfd];
1976	static ev_timer tw;	2456	static ev_timer tw;
1977		2457
1978	static void	2458	static void
1979	io_cb (ev_loop *loop, ev_io *w, int revents)	2459	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1980	{	2460	{
1981	}	2461	}
1982		2462
1983	// create io watchers for each fd and a timer before blocking	2463	// create io watchers for each fd and a timer before blocking
1984	static void	2464	static void
1985	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2465	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1986	{	2466	{
1987	int timeout = 3600000;	2467	int timeout = 3600000;
1988	struct pollfd fds [nfd];	2468	struct pollfd fds [nfd];
1989	// actual code will need to loop here and realloc etc.	2469	// actual code will need to loop here and realloc etc.
1990	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2470	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
…		…
2005	}	2485	}
2006	}	2486	}
2007		2487
2008	// stop all watchers after blocking	2488	// stop all watchers after blocking
2009	static void	2489	static void
2010	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2490	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2011	{	2491	{
2012	ev_timer_stop (loop, &tw);	2492	ev_timer_stop (loop, &tw);
2013		2493
2014	for (int i = 0; i < nfd; ++i)	2494	for (int i = 0; i < nfd; ++i)
2015	{	2495	{
…		…
2054	}	2534	}
2055		2535
2056	// do not ever call adns_afterpoll	2536	// do not ever call adns_afterpoll
2057		2537
2058	Method 4: Do not use a prepare or check watcher because the module you	2538	Method 4: Do not use a prepare or check watcher because the module you
2059	want to embed is too inflexible to support it. Instead, you can override	2539	want to embed is not flexible enough to support it. Instead, you can
2060	their poll function. The drawback with this solution is that the main	2540	override their poll function. The drawback with this solution is that the
2061	loop is now no longer controllable by EV. The C<Glib::EV> module does	2541	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2062	this.	2542	this approach, effectively embedding EV as a client into the horrible
		2543	libglib event loop.
2063		2544
2064	static gint	2545	static gint
2065	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2546	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2066	{	2547	{
2067	int got_events = 0;	2548	int got_events = 0;
…		…
2098	prioritise I/O.	2579	prioritise I/O.
2099		2580
2100	As an example for a bug workaround, the kqueue backend might only support	2581	As an example for a bug workaround, the kqueue backend might only support
2101	sockets on some platform, so it is unusable as generic backend, but you	2582	sockets on some platform, so it is unusable as generic backend, but you
2102	still want to make use of it because you have many sockets and it scales	2583	still want to make use of it because you have many sockets and it scales
2103	so nicely. In this case, you would create a kqueue-based loop and embed it	2584	so nicely. In this case, you would create a kqueue-based loop and embed
2104	into your default loop (which might use e.g. poll). Overall operation will	2585	it into your default loop (which might use e.g. poll). Overall operation
2105	be a bit slower because first libev has to poll and then call kevent, but	2586	will be a bit slower because first libev has to call C<poll> and then
2106	at least you can use both at what they are best.	2587	C<kevent>, but at least you can use both mechanisms for what they are
		2588	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2107		2589
2108	As for prioritising I/O: rarely you have the case where some fds have	2590	As for prioritising I/O: under rare circumstances you have the case where
2109	to be watched and handled very quickly (with low latency), and even	2591	some fds have to be watched and handled very quickly (with low latency),
2110	priorities and idle watchers might have too much overhead. In this case	2592	and even priorities and idle watchers might have too much overhead. In
2111	you would put all the high priority stuff in one loop and all the rest in	2593	this case you would put all the high priority stuff in one loop and all
2112	a second one, and embed the second one in the first.	2594	the rest in a second one, and embed the second one in the first.
2113		2595
2114	As long as the watcher is active, the callback will be invoked every time	2596	As long as the watcher is active, the callback will be invoked every
2115	there might be events pending in the embedded loop. The callback must then	2597	time there might be events pending in the embedded loop. The callback
2116	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2598	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2117	their callbacks (you could also start an idle watcher to give the embedded	2599	sweep and invoke their callbacks (the callback doesn't need to invoke the
2118	loop strictly lower priority for example). You can also set the callback	2600	C<ev_embed_sweep> function directly, it could also start an idle watcher
2119	to C<0>, in which case the embed watcher will automatically execute the	2601	to give the embedded loop strictly lower priority for example).
2120	embedded loop sweep.
2121		2602
2122	As long as the watcher is started it will automatically handle events. The	2603	You can also set the callback to C<0>, in which case the embed watcher
2123	callback will be invoked whenever some events have been handled. You can	2604	will automatically execute the embedded loop sweep whenever necessary.
2124	set the callback to C<0> to avoid having to specify one if you are not
2125	interested in that.
2126		2605
2127	Also, there have not currently been made special provisions for forking:	2606	Fork detection will be handled transparently while the C<ev_embed> watcher
2128	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2607	is active, i.e., the embedded loop will automatically be forked when the
2129	but you will also have to stop and restart any C<ev_embed> watchers	2608	embedding loop forks. In other cases, the user is responsible for calling
2130	yourself.	2609	C<ev_loop_fork> on the embedded loop.
2131		2610
2132	Unfortunately, not all backends are embeddable, only the ones returned by	2611	Unfortunately, not all backends are embeddable: only the ones returned by
2133	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2612	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2134	portable one.	2613	portable one.
2135		2614
2136	So when you want to use this feature you will always have to be prepared	2615	So when you want to use this feature you will always have to be prepared
2137	that you cannot get an embeddable loop. The recommended way to get around	2616	that you cannot get an embeddable loop. The recommended way to get around
2138	this is to have a separate variables for your embeddable loop, try to	2617	this is to have a separate variables for your embeddable loop, try to
2139	create it, and if that fails, use the normal loop for everything.	2618	create it, and if that fails, use the normal loop for everything.
		2619
		2620	=head3 C<ev_embed> and fork
		2621
		2622	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2623	automatically be applied to the embedded loop as well, so no special
		2624	fork handling is required in that case. When the watcher is not running,
		2625	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2626	as applicable.
2140		2627
2141	=head3 Watcher-Specific Functions and Data Members	2628	=head3 Watcher-Specific Functions and Data Members
2142		2629
2143	=over 4	2630	=over 4
2144		2631
…		…
2172	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2659	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2173	used).	2660	used).
2174		2661
2175	struct ev_loop *loop_hi = ev_default_init (0);	2662	struct ev_loop *loop_hi = ev_default_init (0);
2176	struct ev_loop *loop_lo = 0;	2663	struct ev_loop *loop_lo = 0;
2177	struct ev_embed embed;	2664	ev_embed embed;
2178		2665
2179	// see if there is a chance of getting one that works	2666	// see if there is a chance of getting one that works
2180	// (remember that a flags value of 0 means autodetection)	2667	// (remember that a flags value of 0 means autodetection)
2181	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2668	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2182	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2669	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2196	kqueue implementation). Store the kqueue/socket-only event loop in	2683	kqueue implementation). Store the kqueue/socket-only event loop in
2197	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2684	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2198		2685
2199	struct ev_loop *loop = ev_default_init (0);	2686	struct ev_loop *loop = ev_default_init (0);
2200	struct ev_loop *loop_socket = 0;	2687	struct ev_loop *loop_socket = 0;
2201	struct ev_embed embed;	2688	ev_embed embed;
2202		2689
2203	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2690	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2204	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2691	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2205	{	2692	{
2206	ev_embed_init (&embed, 0, loop_socket);	2693	ev_embed_init (&embed, 0, loop_socket);
…		…
2221	event loop blocks next and before C<ev_check> watchers are being called,	2708	event loop blocks next and before C<ev_check> watchers are being called,
2222	and only in the child after the fork. If whoever good citizen calling	2709	and only in the child after the fork. If whoever good citizen calling
2223	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2710	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2224	handlers will be invoked, too, of course.	2711	handlers will be invoked, too, of course.
2225		2712
		2713	=head3 The special problem of life after fork - how is it possible?
		2714
		2715	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2716	up/change the process environment, followed by a call to C<exec()>. This
		2717	sequence should be handled by libev without any problems.
		2718
		2719	This changes when the application actually wants to do event handling
		2720	in the child, or both parent in child, in effect "continuing" after the
		2721	fork.
		2722
		2723	The default mode of operation (for libev, with application help to detect
		2724	forks) is to duplicate all the state in the child, as would be expected
		2725	when I<either> the parent I<or> the child process continues.
		2726
		2727	When both processes want to continue using libev, then this is usually the
		2728	wrong result. In that case, usually one process (typically the parent) is
		2729	supposed to continue with all watchers in place as before, while the other
		2730	process typically wants to start fresh, i.e. without any active watchers.
		2731
		2732	The cleanest and most efficient way to achieve that with libev is to
		2733	simply create a new event loop, which of course will be "empty", and
		2734	use that for new watchers. This has the advantage of not touching more
		2735	memory than necessary, and thus avoiding the copy-on-write, and the
		2736	disadvantage of having to use multiple event loops (which do not support
		2737	signal watchers).
		2738
		2739	When this is not possible, or you want to use the default loop for
		2740	other reasons, then in the process that wants to start "fresh", call
		2741	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2742	the default loop will "orphan" (not stop) all registered watchers, so you
		2743	have to be careful not to execute code that modifies those watchers. Note
		2744	also that in that case, you have to re-register any signal watchers.
		2745
2226	=head3 Watcher-Specific Functions and Data Members	2746	=head3 Watcher-Specific Functions and Data Members
2227		2747
2228	=over 4	2748	=over 4
2229		2749
2230	=item ev_fork_init (ev_signal *, callback)	2750	=item ev_fork_init (ev_signal *, callback)
…		…
2262	is that the author does not know of a simple (or any) algorithm for a	2782	is that the author does not know of a simple (or any) algorithm for a
2263	multiple-writer-single-reader queue that works in all cases and doesn't	2783	multiple-writer-single-reader queue that works in all cases and doesn't
2264	need elaborate support such as pthreads.	2784	need elaborate support such as pthreads.
2265		2785
2266	That means that if you want to queue data, you have to provide your own	2786	That means that if you want to queue data, you have to provide your own
2267	queue. But at least I can tell you would implement locking around your	2787	queue. But at least I can tell you how to implement locking around your
2268	queue:	2788	queue:
2269		2789
2270	=over 4	2790	=over 4
2271		2791
2272	=item queueing from a signal handler context	2792	=item queueing from a signal handler context
2273		2793
2274	To implement race-free queueing, you simply add to the queue in the signal	2794	To implement race-free queueing, you simply add to the queue in the signal
2275	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2795	handler but you block the signal handler in the watcher callback. Here is
2276	some fictitious SIGUSR1 handler:	2796	an example that does that for some fictitious SIGUSR1 handler:
2277		2797
2278	static ev_async mysig;	2798	static ev_async mysig;
2279		2799
2280	static void	2800	static void
2281	sigusr1_handler (void)	2801	sigusr1_handler (void)
…		…
2347	=over 4	2867	=over 4
2348		2868
2349	=item ev_async_init (ev_async *, callback)	2869	=item ev_async_init (ev_async *, callback)
2350		2870
2351	Initialises and configures the async watcher - it has no parameters of any	2871	Initialises and configures the async watcher - it has no parameters of any
2352	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	2872	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2353	believe me.	2873	trust me.
2354		2874
2355	=item ev_async_send (loop, ev_async *)	2875	=item ev_async_send (loop, ev_async *)
2356		2876
2357	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	2877	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2358	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	2878	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2359	C<ev_feed_event>, this call is safe to do in other threads, signal or	2879	C<ev_feed_event>, this call is safe to do from other threads, signal or
2360	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	2880	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2361	section below on what exactly this means).	2881	section below on what exactly this means).
2362		2882
		2883	Note that, as with other watchers in libev, multiple events might get
		2884	compressed into a single callback invocation (another way to look at this
		2885	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2886	reset when the event loop detects that).
		2887
2363	This call incurs the overhead of a system call only once per loop iteration,	2888	This call incurs the overhead of a system call only once per event loop
2364	so while the overhead might be noticeable, it doesn't apply to repeated	2889	iteration, so while the overhead might be noticeable, it doesn't apply to
2365	calls to C<ev_async_send>.	2890	repeated calls to C<ev_async_send> for the same event loop.
2366		2891
2367	=item bool = ev_async_pending (ev_async *)	2892	=item bool = ev_async_pending (ev_async *)
2368		2893
2369	Returns a non-zero value when C<ev_async_send> has been called on the	2894	Returns a non-zero value when C<ev_async_send> has been called on the
2370	watcher but the event has not yet been processed (or even noted) by the	2895	watcher but the event has not yet been processed (or even noted) by the
…		…
2373	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	2898	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2374	the loop iterates next and checks for the watcher to have become active,	2899	the loop iterates next and checks for the watcher to have become active,
2375	it will reset the flag again. C<ev_async_pending> can be used to very	2900	it will reset the flag again. C<ev_async_pending> can be used to very
2376	quickly check whether invoking the loop might be a good idea.	2901	quickly check whether invoking the loop might be a good idea.
2377		2902
2378	Not that this does I<not> check whether the watcher itself is pending, only	2903	Not that this does I<not> check whether the watcher itself is pending,
2379	whether it has been requested to make this watcher pending.	2904	only whether it has been requested to make this watcher pending: there
		2905	is a time window between the event loop checking and resetting the async
		2906	notification, and the callback being invoked.
2380		2907
2381	=back	2908	=back
2382		2909
2383		2910
2384	=head1 OTHER FUNCTIONS	2911	=head1 OTHER FUNCTIONS
…		…
2388	=over 4	2915	=over 4
2389		2916
2390	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2917	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2391		2918
2392	This function combines a simple timer and an I/O watcher, calls your	2919	This function combines a simple timer and an I/O watcher, calls your
2393	callback on whichever event happens first and automatically stop both	2920	callback on whichever event happens first and automatically stops both
2394	watchers. This is useful if you want to wait for a single event on an fd	2921	watchers. This is useful if you want to wait for a single event on an fd
2395	or timeout without having to allocate/configure/start/stop/free one or	2922	or timeout without having to allocate/configure/start/stop/free one or
2396	more watchers yourself.	2923	more watchers yourself.
2397		2924
2398	If C<fd> is less than 0, then no I/O watcher will be started and events	2925	If C<fd> is less than 0, then no I/O watcher will be started and the
2399	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2926	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2400	C<events> set will be created and started.	2927	the given C<fd> and C<events> set will be created and started.
2401		2928
2402	If C<timeout> is less than 0, then no timeout watcher will be	2929	If C<timeout> is less than 0, then no timeout watcher will be
2403	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2930	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2404	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2931	repeat = 0) will be started. C<0> is a valid timeout.
2405	dubious value.
2406		2932
2407	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2933	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2408	passed an C<revents> set like normal event callbacks (a combination of	2934	passed an C<revents> set like normal event callbacks (a combination of
2409	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2935	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2410	value passed to C<ev_once>:	2936	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2937	a timeout and an io event at the same time - you probably should give io
		2938	events precedence.
		2939
		2940	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2411		2941
2412	static void stdin_ready (int revents, void *arg)	2942	static void stdin_ready (int revents, void *arg)
2413	{	2943	{
		2944	if (revents & EV_READ)
		2945	/* stdin might have data for us, joy! */;
2414	if (revents & EV_TIMEOUT)	2946	else if (revents & EV_TIMEOUT)
2415	/* doh, nothing entered */;	2947	/* doh, nothing entered */;
2416	else if (revents & EV_READ)
2417	/* stdin might have data for us, joy! */;
2418	}	2948	}
2419		2949
2420	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2950	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2421		2951
2422	=item ev_feed_event (ev_loop *, watcher *, int revents)	2952	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2423		2953
2424	Feeds the given event set into the event loop, as if the specified event	2954	Feeds the given event set into the event loop, as if the specified event
2425	had happened for the specified watcher (which must be a pointer to an	2955	had happened for the specified watcher (which must be a pointer to an
2426	initialised but not necessarily started event watcher).	2956	initialised but not necessarily started event watcher).
2427		2957
2428	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2958	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2429		2959
2430	Feed an event on the given fd, as if a file descriptor backend detected	2960	Feed an event on the given fd, as if a file descriptor backend detected
2431	the given events it.	2961	the given events it.
2432		2962
2433	=item ev_feed_signal_event (ev_loop *loop, int signum)	2963	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2434		2964
2435	Feed an event as if the given signal occurred (C<loop> must be the default	2965	Feed an event as if the given signal occurred (C<loop> must be the default
2436	loop!).	2966	loop!).
2437		2967
2438	=back	2968	=back
…		…
2560		3090
2561	myclass obj;	3091	myclass obj;
2562	ev::io iow;	3092	ev::io iow;
2563	iow.set <myclass, &myclass::io_cb> (&obj);	3093	iow.set <myclass, &myclass::io_cb> (&obj);
2564		3094
		3095	=item w->set (object *)
		3096
		3097	This is an B<experimental> feature that might go away in a future version.
		3098
		3099	This is a variation of a method callback - leaving out the method to call
		3100	will default the method to C<operator ()>, which makes it possible to use
		3101	functor objects without having to manually specify the C<operator ()> all
		3102	the time. Incidentally, you can then also leave out the template argument
		3103	list.
		3104
		3105	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3106	int revents)>.
		3107
		3108	See the method-C<set> above for more details.
		3109
		3110	Example: use a functor object as callback.
		3111
		3112	struct myfunctor
		3113	{
		3114	void operator() (ev::io &w, int revents)
		3115	{
		3116	...
		3117	}
		3118	}
		3119
		3120	myfunctor f;
		3121
		3122	ev::io w;
		3123	w.set (&f);
		3124
2565	=item w->set<function> (void *data = 0)	3125	=item w->set<function> (void *data = 0)
2566		3126
2567	Also sets a callback, but uses a static method or plain function as	3127	Also sets a callback, but uses a static method or plain function as
2568	callback. The optional C<data> argument will be stored in the watcher's	3128	callback. The optional C<data> argument will be stored in the watcher's
2569	C<data> member and is free for you to use.	3129	C<data> member and is free for you to use.
2570		3130
2571	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3131	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2572		3132
2573	See the method-C<set> above for more details.	3133	See the method-C<set> above for more details.
2574		3134
2575	Example:	3135	Example: Use a plain function as callback.
2576		3136
2577	static void io_cb (ev::io &w, int revents) { }	3137	static void io_cb (ev::io &w, int revents) { }
2578	iow.set <io_cb> ();	3138	iow.set <io_cb> ();
2579		3139
2580	=item w->set (struct ev_loop *)	3140	=item w->set (struct ev_loop *)
…		…
2618	Example: Define a class with an IO and idle watcher, start one of them in	3178	Example: Define a class with an IO and idle watcher, start one of them in
2619	the constructor.	3179	the constructor.
2620		3180
2621	class myclass	3181	class myclass
2622	{	3182	{
2623	ev::io io; void io_cb (ev::io &w, int revents);	3183	ev::io io ; void io_cb (ev::io &w, int revents);
2624	ev:idle idle void idle_cb (ev::idle &w, int revents);	3184	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2625		3185
2626	myclass (int fd)	3186	myclass (int fd)
2627	{	3187	{
2628	io .set <myclass, &myclass::io_cb > (this);	3188	io .set <myclass, &myclass::io_cb > (this);
2629	idle.set <myclass, &myclass::idle_cb> (this);	3189	idle.set <myclass, &myclass::idle_cb> (this);
…		…
2645	=item Perl	3205	=item Perl
2646		3206
2647	The EV module implements the full libev API and is actually used to test	3207	The EV module implements the full libev API and is actually used to test
2648	libev. EV is developed together with libev. Apart from the EV core module,	3208	libev. EV is developed together with libev. Apart from the EV core module,
2649	there are additional modules that implement libev-compatible interfaces	3209	there are additional modules that implement libev-compatible interfaces
2650	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3210	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2651	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3211	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3212	and C<EV::Glib>).
2652		3213
2653	It can be found and installed via CPAN, its homepage is at	3214	It can be found and installed via CPAN, its homepage is at
2654	L<http://software.schmorp.de/pkg/EV>.	3215	L<http://software.schmorp.de/pkg/EV>.
2655		3216
2656	=item Python	3217	=item Python
2657		3218
2658	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3219	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2659	seems to be quite complete and well-documented. Note, however, that the	3220	seems to be quite complete and well-documented.
2660	patch they require for libev is outright dangerous as it breaks the ABI
2661	for everybody else, and therefore, should never be applied in an installed
2662	libev (if python requires an incompatible ABI then it needs to embed
2663	libev).
2664		3221
2665	=item Ruby	3222	=item Ruby
2666		3223
2667	Tony Arcieri has written a ruby extension that offers access to a subset	3224	Tony Arcieri has written a ruby extension that offers access to a subset
2668	of the libev API and adds file handle abstractions, asynchronous DNS and	3225	of the libev API and adds file handle abstractions, asynchronous DNS and
2669	more on top of it. It can be found via gem servers. Its homepage is at	3226	more on top of it. It can be found via gem servers. Its homepage is at
2670	L<http://rev.rubyforge.org/>.	3227	L<http://rev.rubyforge.org/>.
2671		3228
		3229	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3230	makes rev work even on mingw.
		3231
		3232	=item Haskell
		3233
		3234	A haskell binding to libev is available at
		3235	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3236
2672	=item D	3237	=item D
2673		3238
2674	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3239	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2675	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3240	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3241
		3242	=item Ocaml
		3243
		3244	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3245	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
2676		3246
2677	=back	3247	=back
2678		3248
2679		3249
2680	=head1 MACRO MAGIC	3250	=head1 MACRO MAGIC
…		…
2781		3351
2782	#define EV_STANDALONE 1	3352	#define EV_STANDALONE 1
2783	#include "ev.h"	3353	#include "ev.h"
2784		3354
2785	Both header files and implementation files can be compiled with a C++	3355	Both header files and implementation files can be compiled with a C++
2786	compiler (at least, thats a stated goal, and breakage will be treated	3356	compiler (at least, that's a stated goal, and breakage will be treated
2787	as a bug).	3357	as a bug).
2788		3358
2789	You need the following files in your source tree, or in a directory	3359	You need the following files in your source tree, or in a directory
2790	in your include path (e.g. in libev/ when using -Ilibev):	3360	in your include path (e.g. in libev/ when using -Ilibev):
2791		3361
…		…
2835		3405
2836	=head2 PREPROCESSOR SYMBOLS/MACROS	3406	=head2 PREPROCESSOR SYMBOLS/MACROS
2837		3407
2838	Libev can be configured via a variety of preprocessor symbols you have to	3408	Libev can be configured via a variety of preprocessor symbols you have to
2839	define before including any of its files. The default in the absence of	3409	define before including any of its files. The default in the absence of
2840	autoconf is noted for every option.	3410	autoconf is documented for every option.
2841		3411
2842	=over 4	3412	=over 4
2843		3413
2844	=item EV_STANDALONE	3414	=item EV_STANDALONE
2845		3415
…		…
2847	keeps libev from including F<config.h>, and it also defines dummy	3417	keeps libev from including F<config.h>, and it also defines dummy
2848	implementations for some libevent functions (such as logging, which is not	3418	implementations for some libevent functions (such as logging, which is not
2849	supported). It will also not define any of the structs usually found in	3419	supported). It will also not define any of the structs usually found in
2850	F<event.h> that are not directly supported by the libev core alone.	3420	F<event.h> that are not directly supported by the libev core alone.
2851		3421
		3422	In stanbdalone mode, libev will still try to automatically deduce the
		3423	configuration, but has to be more conservative.
		3424
2852	=item EV_USE_MONOTONIC	3425	=item EV_USE_MONOTONIC
2853		3426
2854	If defined to be C<1>, libev will try to detect the availability of the	3427	If defined to be C<1>, libev will try to detect the availability of the
2855	monotonic clock option at both compile time and runtime. Otherwise no use	3428	monotonic clock option at both compile time and runtime. Otherwise no
2856	of the monotonic clock option will be attempted. If you enable this, you	3429	use of the monotonic clock option will be attempted. If you enable this,
2857	usually have to link against librt or something similar. Enabling it when	3430	you usually have to link against librt or something similar. Enabling it
2858	the functionality isn't available is safe, though, although you have	3431	when the functionality isn't available is safe, though, although you have
2859	to make sure you link against any libraries where the C<clock_gettime>	3432	to make sure you link against any libraries where the C<clock_gettime>
2860	function is hiding in (often F<-lrt>).	3433	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2861		3434
2862	=item EV_USE_REALTIME	3435	=item EV_USE_REALTIME
2863		3436
2864	If defined to be C<1>, libev will try to detect the availability of the	3437	If defined to be C<1>, libev will try to detect the availability of the
2865	real-time clock option at compile time (and assume its availability at	3438	real-time clock option at compile time (and assume its availability
2866	runtime if successful). Otherwise no use of the real-time clock option will	3439	at runtime if successful). Otherwise no use of the real-time clock
2867	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3440	option will be attempted. This effectively replaces C<gettimeofday>
2868	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3441	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2869	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3442	correctness. See the note about libraries in the description of
		3443	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3444	C<EV_USE_CLOCK_SYSCALL>.
		3445
		3446	=item EV_USE_CLOCK_SYSCALL
		3447
		3448	If defined to be C<1>, libev will try to use a direct syscall instead
		3449	of calling the system-provided C<clock_gettime> function. This option
		3450	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3451	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3452	programs needlessly. Using a direct syscall is slightly slower (in
		3453	theory), because no optimised vdso implementation can be used, but avoids
		3454	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3455	higher, as it simplifies linking (no need for C<-lrt>).
2870		3456
2871	=item EV_USE_NANOSLEEP	3457	=item EV_USE_NANOSLEEP
2872		3458
2873	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3459	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2874	and will use it for delays. Otherwise it will use C<select ()>.	3460	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2890		3476
2891	=item EV_SELECT_USE_FD_SET	3477	=item EV_SELECT_USE_FD_SET
2892		3478
2893	If defined to C<1>, then the select backend will use the system C<fd_set>	3479	If defined to C<1>, then the select backend will use the system C<fd_set>
2894	structure. This is useful if libev doesn't compile due to a missing	3480	structure. This is useful if libev doesn't compile due to a missing
2895	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3481	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2896	exotic systems. This usually limits the range of file descriptors to some	3482	on exotic systems. This usually limits the range of file descriptors to
2897	low limit such as 1024 or might have other limitations (winsocket only	3483	some low limit such as 1024 or might have other limitations (winsocket
2898	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3484	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2899	influence the size of the C<fd_set> used.	3485	configures the maximum size of the C<fd_set>.
2900		3486
2901	=item EV_SELECT_IS_WINSOCKET	3487	=item EV_SELECT_IS_WINSOCKET
2902		3488
2903	When defined to C<1>, the select backend will assume that	3489	When defined to C<1>, the select backend will assume that
2904	select/socket/connect etc. don't understand file descriptors but	3490	select/socket/connect etc. don't understand file descriptors but
…		…
3015	When doing priority-based operations, libev usually has to linearly search	3601	When doing priority-based operations, libev usually has to linearly search
3016	all the priorities, so having many of them (hundreds) uses a lot of space	3602	all the priorities, so having many of them (hundreds) uses a lot of space
3017	and time, so using the defaults of five priorities (-2 .. +2) is usually	3603	and time, so using the defaults of five priorities (-2 .. +2) is usually
3018	fine.	3604	fine.
3019		3605
3020	If your embedding application does not need any priorities, defining these both to	3606	If your embedding application does not need any priorities, defining these
3021	C<0> will save some memory and CPU.	3607	both to C<0> will save some memory and CPU.
3022		3608
3023	=item EV_PERIODIC_ENABLE	3609	=item EV_PERIODIC_ENABLE
3024		3610
3025	If undefined or defined to be C<1>, then periodic timers are supported. If	3611	If undefined or defined to be C<1>, then periodic timers are supported. If
3026	defined to be C<0>, then they are not. Disabling them saves a few kB of	3612	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
3033	code.	3619	code.
3034		3620
3035	=item EV_EMBED_ENABLE	3621	=item EV_EMBED_ENABLE
3036		3622
3037	If undefined or defined to be C<1>, then embed watchers are supported. If	3623	If undefined or defined to be C<1>, then embed watchers are supported. If
3038	defined to be C<0>, then they are not.	3624	defined to be C<0>, then they are not. Embed watchers rely on most other
		3625	watcher types, which therefore must not be disabled.
3039		3626
3040	=item EV_STAT_ENABLE	3627	=item EV_STAT_ENABLE
3041		3628
3042	If undefined or defined to be C<1>, then stat watchers are supported. If	3629	If undefined or defined to be C<1>, then stat watchers are supported. If
3043	defined to be C<0>, then they are not.	3630	defined to be C<0>, then they are not.
…		…
3075	two).	3662	two).
3076		3663
3077	=item EV_USE_4HEAP	3664	=item EV_USE_4HEAP
3078		3665
3079	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3666	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3080	timer and periodics heap, libev uses a 4-heap when this symbol is defined	3667	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3081	to C<1>. The 4-heap uses more complicated (longer) code but has	3668	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3082	noticeably faster performance with many (thousands) of watchers.	3669	faster performance with many (thousands) of watchers.
3083		3670
3084	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3671	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3085	(disabled).	3672	(disabled).
3086		3673
3087	=item EV_HEAP_CACHE_AT	3674	=item EV_HEAP_CACHE_AT
3088		3675
3089	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3676	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3090	timer and periodics heap, libev can cache the timestamp (I<at>) within	3677	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3091	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	3678	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3092	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	3679	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3093	but avoids random read accesses on heap changes. This improves performance	3680	but avoids random read accesses on heap changes. This improves performance
3094	noticeably with with many (hundreds) of watchers.	3681	noticeably with many (hundreds) of watchers.
3095		3682
3096	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3683	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3097	(disabled).	3684	(disabled).
3098		3685
3099	=item EV_VERIFY	3686	=item EV_VERIFY
…		…
3105	called once per loop, which can slow down libev. If set to C<3>, then the	3692	called once per loop, which can slow down libev. If set to C<3>, then the
3106	verification code will be called very frequently, which will slow down	3693	verification code will be called very frequently, which will slow down
3107	libev considerably.	3694	libev considerably.
3108		3695
3109	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	3696	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
3110	C<0.>	3697	C<0>.
3111		3698
3112	=item EV_COMMON	3699	=item EV_COMMON
3113		3700
3114	By default, all watchers have a C<void *data> member. By redefining	3701	By default, all watchers have a C<void *data> member. By redefining
3115	this macro to a something else you can include more and other types of	3702	this macro to a something else you can include more and other types of
…		…
3132	and the way callbacks are invoked and set. Must expand to a struct member	3719	and the way callbacks are invoked and set. Must expand to a struct member
3133	definition and a statement, respectively. See the F<ev.h> header file for	3720	definition and a statement, respectively. See the F<ev.h> header file for
3134	their default definitions. One possible use for overriding these is to	3721	their default definitions. One possible use for overriding these is to
3135	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3722	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3136	method calls instead of plain function calls in C++.	3723	method calls instead of plain function calls in C++.
		3724
		3725	=back
3137		3726
3138	=head2 EXPORTED API SYMBOLS	3727	=head2 EXPORTED API SYMBOLS
3139		3728
3140	If you need to re-export the API (e.g. via a DLL) and you need a list of	3729	If you need to re-export the API (e.g. via a DLL) and you need a list of
3141	exported symbols, you can use the provided F<Symbol.*> files which list	3730	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3188	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3777	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3189		3778
3190	#include "ev_cpp.h"	3779	#include "ev_cpp.h"
3191	#include "ev.c"	3780	#include "ev.c"
3192		3781
		3782	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3193		3783
3194	=head1 THREADS AND COROUTINES	3784	=head2 THREADS AND COROUTINES
3195		3785
3196	=head2 THREADS	3786	=head3 THREADS
3197		3787
3198	Libev itself is completely thread-safe, but it uses no locking. This	3788	All libev functions are reentrant and thread-safe unless explicitly
		3789	documented otherwise, but libev implements no locking itself. This means
3199	means that you can use as many loops as you want in parallel, as long as	3790	that you can use as many loops as you want in parallel, as long as there
3200	only one thread ever calls into one libev function with the same loop	3791	are no concurrent calls into any libev function with the same loop
3201	parameter.	3792	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3793	of course): libev guarantees that different event loops share no data
		3794	structures that need any locking.
3202		3795
3203	Or put differently: calls with different loop parameters can be done in	3796	Or to put it differently: calls with different loop parameters can be done
3204	parallel from multiple threads, calls with the same loop parameter must be	3797	concurrently from multiple threads, calls with the same loop parameter
3205	done serially (but can be done from different threads, as long as only one	3798	must be done serially (but can be done from different threads, as long as
3206	thread ever is inside a call at any point in time, e.g. by using a mutex	3799	only one thread ever is inside a call at any point in time, e.g. by using
3207	per loop).	3800	a mutex per loop).
		3801
		3802	Specifically to support threads (and signal handlers), libev implements
		3803	so-called C<ev_async> watchers, which allow some limited form of
		3804	concurrency on the same event loop, namely waking it up "from the
		3805	outside".
3208		3806
3209	If you want to know which design (one loop, locking, or multiple loops	3807	If you want to know which design (one loop, locking, or multiple loops
3210	without or something else still) is best for your problem, then I cannot	3808	without or something else still) is best for your problem, then I cannot
3211	help you. I can give some generic advice however:	3809	help you, but here is some generic advice:
3212		3810
3213	=over 4	3811	=over 4
3214		3812
3215	=item * most applications have a main thread: use the default libev loop	3813	=item * most applications have a main thread: use the default libev loop
3216	in that thread, or create a separate thread running only the default loop.	3814	in that thread, or create a separate thread running only the default loop.
…		…
3228		3826
3229	Choosing a model is hard - look around, learn, know that usually you can do	3827	Choosing a model is hard - look around, learn, know that usually you can do
3230	better than you currently do :-)	3828	better than you currently do :-)
3231		3829
3232	=item * often you need to talk to some other thread which blocks in the	3830	=item * often you need to talk to some other thread which blocks in the
		3831	event loop.
		3832
3233	event loop - C<ev_async> watchers can be used to wake them up from other	3833	C<ev_async> watchers can be used to wake them up from other threads safely
3234	threads safely (or from signal contexts...).	3834	(or from signal contexts...).
		3835
		3836	An example use would be to communicate signals or other events that only
		3837	work in the default loop by registering the signal watcher with the
		3838	default loop and triggering an C<ev_async> watcher from the default loop
		3839	watcher callback into the event loop interested in the signal.
3235		3840
3236	=back	3841	=back
3237		3842
3238	=head2 COROUTINES	3843	=head3 COROUTINES
3239		3844
3240	Libev is much more accommodating to coroutines ("cooperative threads"):	3845	Libev is very accommodating to coroutines ("cooperative threads"):
3241	libev fully supports nesting calls to it's functions from different	3846	libev fully supports nesting calls to its functions from different
3242	coroutines (e.g. you can call C<ev_loop> on the same loop from two	3847	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3243	different coroutines and switch freely between both coroutines running the	3848	different coroutines, and switch freely between both coroutines running the
3244	loop, as long as you don't confuse yourself). The only exception is that	3849	loop, as long as you don't confuse yourself). The only exception is that
3245	you must not do this from C<ev_periodic> reschedule callbacks.	3850	you must not do this from C<ev_periodic> reschedule callbacks.
3246		3851
3247	Care has been invested into making sure that libev does not keep local	3852	Care has been taken to ensure that libev does not keep local state inside
3248	state inside C<ev_loop>, and other calls do not usually allow coroutine	3853	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3249	switches.	3854	they do not call any callbacks.
3250		3855
		3856	=head2 COMPILER WARNINGS
3251		3857
3252	=head1 COMPLEXITIES	3858	Depending on your compiler and compiler settings, you might get no or a
		3859	lot of warnings when compiling libev code. Some people are apparently
		3860	scared by this.
3253		3861
3254	In this section the complexities of (many of) the algorithms used inside	3862	However, these are unavoidable for many reasons. For one, each compiler
3255	libev will be explained. For complexity discussions about backends see the	3863	has different warnings, and each user has different tastes regarding
3256	documentation for C<ev_default_init>.	3864	warning options. "Warn-free" code therefore cannot be a goal except when
		3865	targeting a specific compiler and compiler-version.
3257		3866
3258	All of the following are about amortised time: If an array needs to be	3867	Another reason is that some compiler warnings require elaborate
3259	extended, libev needs to realloc and move the whole array, but this	3868	workarounds, or other changes to the code that make it less clear and less
3260	happens asymptotically never with higher number of elements, so O(1) might	3869	maintainable.
3261	mean it might do a lengthy realloc operation in rare cases, but on average
3262	it is much faster and asymptotically approaches constant time.
3263		3870
3264	=over 4	3871	And of course, some compiler warnings are just plain stupid, or simply
		3872	wrong (because they don't actually warn about the condition their message
		3873	seems to warn about). For example, certain older gcc versions had some
		3874	warnings that resulted an extreme number of false positives. These have
		3875	been fixed, but some people still insist on making code warn-free with
		3876	such buggy versions.
3265		3877
3266	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3878	While libev is written to generate as few warnings as possible,
		3879	"warn-free" code is not a goal, and it is recommended not to build libev
		3880	with any compiler warnings enabled unless you are prepared to cope with
		3881	them (e.g. by ignoring them). Remember that warnings are just that:
		3882	warnings, not errors, or proof of bugs.
3267		3883
3268	This means that, when you have a watcher that triggers in one hour and
3269	there are 100 watchers that would trigger before that then inserting will
3270	have to skip roughly seven (C<ld 100>) of these watchers.
3271		3884
3272	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3885	=head2 VALGRIND
3273		3886
3274	That means that changing a timer costs less than removing/adding them	3887	Valgrind has a special section here because it is a popular tool that is
3275	as only the relative motion in the event queue has to be paid for.	3888	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3276		3889
3277	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	3890	If you think you found a bug (memory leak, uninitialised data access etc.)
		3891	in libev, then check twice: If valgrind reports something like:
3278		3892
3279	These just add the watcher into an array or at the head of a list.	3893	==2274== definitely lost: 0 bytes in 0 blocks.
		3894	==2274== possibly lost: 0 bytes in 0 blocks.
		3895	==2274== still reachable: 256 bytes in 1 blocks.
3280		3896
3281	=item Stopping check/prepare/idle/fork/async watchers: O(1)	3897	Then there is no memory leak, just as memory accounted to global variables
		3898	is not a memleak - the memory is still being referenced, and didn't leak.
3282		3899
3283	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3900	Similarly, under some circumstances, valgrind might report kernel bugs
		3901	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3902	although an acceptable workaround has been found here), or it might be
		3903	confused.
3284		3904
3285	These watchers are stored in lists then need to be walked to find the	3905	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3286	correct watcher to remove. The lists are usually short (you don't usually	3906	make it into some kind of religion.
3287	have many watchers waiting for the same fd or signal).
3288		3907
3289	=item Finding the next timer in each loop iteration: O(1)	3908	If you are unsure about something, feel free to contact the mailing list
		3909	with the full valgrind report and an explanation on why you think this
		3910	is a bug in libev (best check the archives, too :). However, don't be
		3911	annoyed when you get a brisk "this is no bug" answer and take the chance
		3912	of learning how to interpret valgrind properly.
3290		3913
3291	By virtue of using a binary or 4-heap, the next timer is always found at a	3914	If you need, for some reason, empty reports from valgrind for your project
3292	fixed position in the storage array.	3915	I suggest using suppression lists.
3293		3916
3294	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3295		3917
3296	A change means an I/O watcher gets started or stopped, which requires	3918	=head1 PORTABILITY NOTES
3297	libev to recalculate its status (and possibly tell the kernel, depending
3298	on backend and whether C<ev_io_set> was used).
3299		3919
3300	=item Activating one watcher (putting it into the pending state): O(1)
3301
3302	=item Priority handling: O(number_of_priorities)
3303
3304	Priorities are implemented by allocating some space for each
3305	priority. When doing priority-based operations, libev usually has to
3306	linearly search all the priorities, but starting/stopping and activating
3307	watchers becomes O(1) w.r.t. priority handling.
3308
3309	=item Sending an ev_async: O(1)
3310
3311	=item Processing ev_async_send: O(number_of_async_watchers)
3312
3313	=item Processing signals: O(max_signal_number)
3314
3315	Sending involves a system call I<iff> there were no other C<ev_async_send>
3316	calls in the current loop iteration. Checking for async and signal events
3317	involves iterating over all running async watchers or all signal numbers.
3318
3319	=back
3320
3321
3322	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	3920	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3323		3921
3324	Win32 doesn't support any of the standards (e.g. POSIX) that libev	3922	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3325	requires, and its I/O model is fundamentally incompatible with the POSIX	3923	requires, and its I/O model is fundamentally incompatible with the POSIX
3326	model. Libev still offers limited functionality on this platform in	3924	model. Libev still offers limited functionality on this platform in
3327	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3925	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3338		3936
3339	Not a libev limitation but worth mentioning: windows apparently doesn't	3937	Not a libev limitation but worth mentioning: windows apparently doesn't
3340	accept large writes: instead of resulting in a partial write, windows will	3938	accept large writes: instead of resulting in a partial write, windows will
3341	either accept everything or return C<ENOBUFS> if the buffer is too large,	3939	either accept everything or return C<ENOBUFS> if the buffer is too large,
3342	so make sure you only write small amounts into your sockets (less than a	3940	so make sure you only write small amounts into your sockets (less than a
3343	megabyte seems safe, but thsi apparently depends on the amount of memory	3941	megabyte seems safe, but this apparently depends on the amount of memory
3344	available).	3942	available).
3345		3943
3346	Due to the many, low, and arbitrary limits on the win32 platform and	3944	Due to the many, low, and arbitrary limits on the win32 platform and
3347	the abysmal performance of winsockets, using a large number of sockets	3945	the abysmal performance of winsockets, using a large number of sockets
3348	is not recommended (and not reasonable). If your program needs to use	3946	is not recommended (and not reasonable). If your program needs to use
…		…
3359	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	3957	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3360		3958
3361	#include "ev.h"	3959	#include "ev.h"
3362		3960
3363	And compile the following F<evwrap.c> file into your project (make sure	3961	And compile the following F<evwrap.c> file into your project (make sure
3364	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	3962	you do I<not> compile the F<ev.c> or any other embedded source files!):
3365		3963
3366	#include "evwrap.h"	3964	#include "evwrap.h"
3367	#include "ev.c"	3965	#include "ev.c"
3368		3966
3369	=over 4	3967	=over 4
…		…
3414	wrap all I/O functions and provide your own fd management, but the cost of	4012	wrap all I/O functions and provide your own fd management, but the cost of
3415	calling select (O(n²)) will likely make this unworkable.	4013	calling select (O(n²)) will likely make this unworkable.
3416		4014
3417	=back	4015	=back
3418		4016
3419
3420	=head1 PORTABILITY REQUIREMENTS	4017	=head2 PORTABILITY REQUIREMENTS
3421		4018
3422	In addition to a working ISO-C implementation, libev relies on a few	4019	In addition to a working ISO-C implementation and of course the
3423	additional extensions:	4020	backend-specific APIs, libev relies on a few additional extensions:
3424		4021
3425	=over 4	4022	=over 4
3426		4023
3427	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4024	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3428	calling conventions regardless of C<ev_watcher_type *>.	4025	calling conventions regardless of C<ev_watcher_type *>.
…		…
3434	calls them using an C<ev_watcher *> internally.	4031	calls them using an C<ev_watcher *> internally.
3435		4032
3436	=item C<sig_atomic_t volatile> must be thread-atomic as well	4033	=item C<sig_atomic_t volatile> must be thread-atomic as well
3437		4034
3438	The type C<sig_atomic_t volatile> (or whatever is defined as	4035	The type C<sig_atomic_t volatile> (or whatever is defined as
3439	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4036	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3440	threads. This is not part of the specification for C<sig_atomic_t>, but is	4037	threads. This is not part of the specification for C<sig_atomic_t>, but is
3441	believed to be sufficiently portable.	4038	believed to be sufficiently portable.
3442		4039
3443	=item C<sigprocmask> must work in a threaded environment	4040	=item C<sigprocmask> must work in a threaded environment
3444		4041
…		…
3453	except the initial one, and run the default loop in the initial thread as	4050	except the initial one, and run the default loop in the initial thread as
3454	well.	4051	well.
3455		4052
3456	=item C<long> must be large enough for common memory allocation sizes	4053	=item C<long> must be large enough for common memory allocation sizes
3457		4054
3458	To improve portability and simplify using libev, libev uses C<long>	4055	To improve portability and simplify its API, libev uses C<long> internally
3459	internally instead of C<size_t> when allocating its data structures. On	4056	instead of C<size_t> when allocating its data structures. On non-POSIX
3460	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4057	systems (Microsoft...) this might be unexpectedly low, but is still at
3461	is still at least 31 bits everywhere, which is enough for hundreds of	4058	least 31 bits everywhere, which is enough for hundreds of millions of
3462	millions of watchers.	4059	watchers.
3463		4060
3464	=item C<double> must hold a time value in seconds with enough accuracy	4061	=item C<double> must hold a time value in seconds with enough accuracy
3465		4062
3466	The type C<double> is used to represent timestamps. It is required to	4063	The type C<double> is used to represent timestamps. It is required to
3467	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4064	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
…		…
3471	=back	4068	=back
3472		4069
3473	If you know of other additional requirements drop me a note.	4070	If you know of other additional requirements drop me a note.
3474		4071
3475		4072
3476	=head1 COMPILER WARNINGS	4073	=head1 ALGORITHMIC COMPLEXITIES
3477		4074
3478	Depending on your compiler and compiler settings, you might get no or a	4075	In this section the complexities of (many of) the algorithms used inside
3479	lot of warnings when compiling libev code. Some people are apparently	4076	libev will be documented. For complexity discussions about backends see
3480	scared by this.	4077	the documentation for C<ev_default_init>.
3481		4078
3482	However, these are unavoidable for many reasons. For one, each compiler	4079	All of the following are about amortised time: If an array needs to be
3483	has different warnings, and each user has different tastes regarding	4080	extended, libev needs to realloc and move the whole array, but this
3484	warning options. "Warn-free" code therefore cannot be a goal except when	4081	happens asymptotically rarer with higher number of elements, so O(1) might
3485	targeting a specific compiler and compiler-version.	4082	mean that libev does a lengthy realloc operation in rare cases, but on
		4083	average it is much faster and asymptotically approaches constant time.
3486		4084
3487	Another reason is that some compiler warnings require elaborate	4085	=over 4
3488	workarounds, or other changes to the code that make it less clear and less
3489	maintainable.
3490		4086
3491	And of course, some compiler warnings are just plain stupid, or simply	4087	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3492	wrong (because they don't actually warn about the condition their message
3493	seems to warn about).
3494		4088
3495	While libev is written to generate as few warnings as possible,	4089	This means that, when you have a watcher that triggers in one hour and
3496	"warn-free" code is not a goal, and it is recommended not to build libev	4090	there are 100 watchers that would trigger before that, then inserting will
3497	with any compiler warnings enabled unless you are prepared to cope with	4091	have to skip roughly seven (C<ld 100>) of these watchers.
3498	them (e.g. by ignoring them). Remember that warnings are just that:
3499	warnings, not errors, or proof of bugs.
3500		4092
		4093	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3501		4094
3502	=head1 VALGRIND	4095	That means that changing a timer costs less than removing/adding them,
		4096	as only the relative motion in the event queue has to be paid for.
3503		4097
3504	Valgrind has a special section here because it is a popular tool that is	4098	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3505	highly useful, but valgrind reports are very hard to interpret.
3506		4099
3507	If you think you found a bug (memory leak, uninitialised data access etc.)	4100	These just add the watcher into an array or at the head of a list.
3508	in libev, then check twice: If valgrind reports something like:
3509		4101
3510	==2274== definitely lost: 0 bytes in 0 blocks.	4102	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3511	==2274== possibly lost: 0 bytes in 0 blocks.
3512	==2274== still reachable: 256 bytes in 1 blocks.
3513		4103
3514	Then there is no memory leak. Similarly, under some circumstances,	4104	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3515	valgrind might report kernel bugs as if it were a bug in libev, or it
3516	might be confused (it is a very good tool, but only a tool).
3517		4105
3518	If you are unsure about something, feel free to contact the mailing list	4106	These watchers are stored in lists, so they need to be walked to find the
3519	with the full valgrind report and an explanation on why you think this is	4107	correct watcher to remove. The lists are usually short (you don't usually
3520	a bug in libev. However, don't be annoyed when you get a brisk "this is	4108	have many watchers waiting for the same fd or signal: one is typical, two
3521	no bug" answer and take the chance of learning how to interpret valgrind	4109	is rare).
3522	properly.
3523		4110
3524	If you need, for some reason, empty reports from valgrind for your project	4111	=item Finding the next timer in each loop iteration: O(1)
3525	I suggest using suppression lists.
3526		4112
		4113	By virtue of using a binary or 4-heap, the next timer is always found at a
		4114	fixed position in the storage array.
		4115
		4116	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4117
		4118	A change means an I/O watcher gets started or stopped, which requires
		4119	libev to recalculate its status (and possibly tell the kernel, depending
		4120	on backend and whether C<ev_io_set> was used).
		4121
		4122	=item Activating one watcher (putting it into the pending state): O(1)
		4123
		4124	=item Priority handling: O(number_of_priorities)
		4125
		4126	Priorities are implemented by allocating some space for each
		4127	priority. When doing priority-based operations, libev usually has to
		4128	linearly search all the priorities, but starting/stopping and activating
		4129	watchers becomes O(1) with respect to priority handling.
		4130
		4131	=item Sending an ev_async: O(1)
		4132
		4133	=item Processing ev_async_send: O(number_of_async_watchers)
		4134
		4135	=item Processing signals: O(max_signal_number)
		4136
		4137	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4138	calls in the current loop iteration. Checking for async and signal events
		4139	involves iterating over all running async watchers or all signal numbers.
		4140
		4141	=back
		4142
		4143
		4144	=head1 GLOSSARY
		4145
		4146	=over 4
		4147
		4148	=item active
		4149
		4150	A watcher is active as long as it has been started (has been attached to
		4151	an event loop) but not yet stopped (disassociated from the event loop).
		4152
		4153	=item application
		4154
		4155	In this document, an application is whatever is using libev.
		4156
		4157	=item callback
		4158
		4159	The address of a function that is called when some event has been
		4160	detected. Callbacks are being passed the event loop, the watcher that
		4161	received the event, and the actual event bitset.
		4162
		4163	=item callback invocation
		4164
		4165	The act of calling the callback associated with a watcher.
		4166
		4167	=item event
		4168
		4169	A change of state of some external event, such as data now being available
		4170	for reading on a file descriptor, time having passed or simply not having
		4171	any other events happening anymore.
		4172
		4173	In libev, events are represented as single bits (such as C<EV_READ> or
		4174	C<EV_TIMEOUT>).
		4175
		4176	=item event library
		4177
		4178	A software package implementing an event model and loop.
		4179
		4180	=item event loop
		4181
		4182	An entity that handles and processes external events and converts them
		4183	into callback invocations.
		4184
		4185	=item event model
		4186
		4187	The model used to describe how an event loop handles and processes
		4188	watchers and events.
		4189
		4190	=item pending
		4191
		4192	A watcher is pending as soon as the corresponding event has been detected,
		4193	and stops being pending as soon as the watcher will be invoked or its
		4194	pending status is explicitly cleared by the application.
		4195
		4196	A watcher can be pending, but not active. Stopping a watcher also clears
		4197	its pending status.
		4198
		4199	=item real time
		4200
		4201	The physical time that is observed. It is apparently strictly monotonic :)
		4202
		4203	=item wall-clock time
		4204
		4205	The time and date as shown on clocks. Unlike real time, it can actually
		4206	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4207	clock.
		4208
		4209	=item watcher
		4210
		4211	A data structure that describes interest in certain events. Watchers need
		4212	to be started (attached to an event loop) before they can receive events.
		4213
		4214	=item watcher invocation
		4215
		4216	The act of calling the callback associated with a watcher.
		4217
		4218	=back
3527		4219
3528	=head1 AUTHOR	4220	=head1 AUTHOR
3529		4221
3530	Marc Lehmann <libev@schmorp.de>.	4222	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3531		4223

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines