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…		…
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
…		…
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	42	}
…		…
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
84	=head2 FEATURES	98	=head2 FEATURES
85		99
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
96		111
97	It also is quite fast (see this	112	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	114	for example).
100		115
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	124	this argument.
110		125
111	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
112		127
113	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (in practise
115	the beginning of 1970, details are complicated, don't ask). This type is	130	somewhere near the beginning of 1970, details are complicated, don't
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	ask). This type is called C<ev_tstamp>, which is what you should use
117	to the C<double> type in C, and when you need to do any calculations on	132	too. It usually aliases to the C<double> type in C. When you need to do
118	it, you should treat it as some floating point value. Unlike the name	133	any calculations on it, you should treat it as some floating point value.
		134
119	component C<stamp> might indicate, it is also used for time differences	135	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	136	time differences (e.g. delays) throughout libev.
121		137
122	=head1 ERROR HANDLING	138	=head1 ERROR HANDLING
123		139
124	Libev knows three classes of errors: operating system errors, usage errors	140	Libev knows three classes of errors: operating system errors, usage errors
125	and internal errors (bugs).	141	and internal errors (bugs).
…		…
176	as this indicates an incompatible change. Minor versions are usually	192	as this indicates an incompatible change. Minor versions are usually
177	compatible to older versions, so a larger minor version alone is usually	193	compatible to older versions, so a larger minor version alone is usually
178	not a problem.	194	not a problem.
179		195
180	Example: Make sure we haven't accidentally been linked against the wrong	196	Example: Make sure we haven't accidentally been linked against the wrong
181	version.	197	version (note, however, that this will not detect ABI mismatches :).
182		198
183	assert (("libev version mismatch",	199	assert (("libev version mismatch",
184	ev_version_major () == EV_VERSION_MAJOR	200	ev_version_major () == EV_VERSION_MAJOR
185	&& ev_version_minor () >= EV_VERSION_MINOR));	201	&& ev_version_minor () >= EV_VERSION_MINOR));
186		202
…		…
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
215	recommended ones.	231	recommended ones.
216		232
217	See the description of C<ev_embed> watchers for more info.	233	See the description of C<ev_embed> watchers for more info.
218		234
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
220		236
221	Sets the allocation function to use (the prototype is similar - the	237	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	238	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	239	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	240	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	266	}
251		267
252	...	268	...
253	ev_set_allocator (persistent_realloc);	269	ev_set_allocator (persistent_realloc);
254		270
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
256		272
257	Set the callback function to call on a retryable system call error (such	273	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	274	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	275	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	276	callback is set, then libev will expect it to remedy the situation, no
…		…
276		292
277	=back	293	=back
278		294
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		296
281	An event loop is described by a C<struct ev_loop *>. The library knows two	297	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	298	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	299	I<function>).
		300
		301	The library knows two types of such loops, the I<default> loop, which
		302	supports signals and child events, and dynamically created loops which do
		303	not.
284		304
285	=over 4	305	=over 4
286		306
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	307	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		308
…		…
294	If you don't know what event loop to use, use the one returned from this	314	If you don't know what event loop to use, use the one returned from this
295	function.	315	function.
296		316
297	Note that this function is I<not> thread-safe, so if you want to use it	317	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,	318	from multiple threads, you have to lock (note also that this is unlikely,
299	as loops cannot bes hared easily between threads anyway).	319	as loops cannot be shared easily between threads anyway).
300		320
301	The default loop is the only loop that can handle C<ev_signal> and	321	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	322	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	323	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	324	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
326	useful to try out specific backends to test their performance, or to work	346	useful to try out specific backends to test their performance, or to work
327	around bugs.	347	around bugs.
328		348
329	=item C<EVFLAG_FORKCHECK>	349	=item C<EVFLAG_FORKCHECK>
330		350
331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	351	Instead of calling C<ev_loop_fork> manually after a fork, you can also
332	a fork, you can also make libev check for a fork in each iteration by	352	make libev check for a fork in each iteration by enabling this flag.
333	enabling this flag.
334		353
335	This works by calling C<getpid ()> on every iteration of the loop,	354	This works by calling C<getpid ()> on every iteration of the loop,
336	and thus this might slow down your event loop if you do a lot of loop	355	and thus this might slow down your event loop if you do a lot of loop
337	iterations and little real work, but is usually not noticeable (on my	356	iterations and little real work, but is usually not noticeable (on my
338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
…		…
344	flag.	363	flag.
345		364
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	366	environment variable.
348		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_SIGNALFD>
		376
		377	When this flag is specified, then libev will attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		379	delivers signals synchronously, which makes it both faster and might make
		380	it possible to get the queued signal data. It can also simplify signal
		381	handling with threads, as long as you properly block signals in your
		382	threads that are not interested in handling them.
		383
		384	Signalfd will not be used by default as this changes your signal mask, and
		385	there are a lot of shoddy libraries and programs (glib's threadpool for
		386	example) that can't properly initialise their signal masks.
		387
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		389
351	This is your standard select(2) backend. Not I<completely> standard, as	390	This is your standard select(2) backend. Not I<completely> standard, as
352	libev tries to roll its own fd_set with no limits on the number of fds,	391	libev tries to roll its own fd_set with no limits on the number of fds,
353	but if that fails, expect a fairly low limit on the number of fds when	392	but if that fails, expect a fairly low limit on the number of fds when
…		…
359	writing a server, you should C<accept ()> in a loop to accept as many	398	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	399	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	400	a look at C<ev_set_io_collect_interval ()> to increase the amount of
362	readiness notifications you get per iteration.	401	readiness notifications you get per iteration.
363		402
		403	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		404	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		405	C<exceptfds> set on that platform).
		406
364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	407	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
365		408
366	And this is your standard poll(2) backend. It's more complicated	409	And this is your standard poll(2) backend. It's more complicated
367	than select, but handles sparse fds better and has no artificial	410	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	411	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,	412	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	413	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
371	performance tips.	414	performance tips.
372		415
		416	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		417	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		418
373	=item C<EVBACKEND_EPOLL> (value 4, Linux)	419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		420
		421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
374		423
375	For few fds, this backend is a bit little slower than poll and select,	424	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	425	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),	426	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	427	epoll scales either O(1) or O(active_fds).
379	of shortcomings, such as silently dropping events in some hard-to-detect	428
380	cases and requiring a system call per fd change, no fork support and bad	429	The epoll mechanism deserves honorable mention as the most misdesigned
381	support for dup.	430	of the more advanced event mechanisms: mere annoyances include silently
		431	dropping file descriptors, requiring a system call per change per file
		432	descriptor (and unnecessary guessing of parameters), problems with dup and
		433	so on. The biggest issue is fork races, however - if a program forks then
		434	I<both> parent and child process have to recreate the epoll set, which can
		435	take considerable time (one syscall per file descriptor) and is of course
		436	hard to detect.
		437
		438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		439	of course I<doesn't>, and epoll just loves to report events for totally
		440	I<different> file descriptors (even already closed ones, so one cannot
		441	even remove them from the set) than registered in the set (especially
		442	on SMP systems). Libev tries to counter these spurious notifications by
		443	employing an additional generation counter and comparing that against the
		444	events to filter out spurious ones, recreating the set when required.
382		445
383	While stopping, setting and starting an I/O watcher in the same iteration	446	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	447	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	448	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	449	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
387	very well if you register events for both fds.	450	file descriptors might not work very well if you register events for both
388		451	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		452
393	Best performance from this backend is achieved by not unregistering all	453	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.	454	watchers for a file descriptor until it has been closed, if possible,
395	keep at least one watcher active per fd at all times.	455	i.e. keep at least one watcher active per fd at all times. Stopping and
		456	starting a watcher (without re-setting it) also usually doesn't cause
		457	extra overhead. A fork can both result in spurious notifications as well
		458	as in libev having to destroy and recreate the epoll object, which can
		459	take considerable time and thus should be avoided.
		460
		461	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		462	faster than epoll for maybe up to a hundred file descriptors, depending on
		463	the usage. So sad.
396		464
397	While nominally embeddable in other event loops, this feature is broken in	465	While nominally embeddable in other event loops, this feature is broken in
398	all kernel versions tested so far.	466	all kernel versions tested so far.
		467
		468	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		469	C<EVBACKEND_POLL>.
399		470
400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	471	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
401		472
402	Kqueue deserves special mention, as at the time of this writing, it	473	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	474	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	475	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"	476	it's completely useless). Unlike epoll, however, whose brokenness
		477	is by design, these kqueue bugs can (and eventually will) be fixed
		478	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	479	"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)	480	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
408	system like NetBSD.	481	system like NetBSD.
409		482
410	You still can embed kqueue into a normal poll or select backend and use it	483	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	484	only for sockets (after having made sure that sockets work with kqueue on
…		…
413		486
414	It scales in the same way as the epoll backend, but the interface to the	487	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	488	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	489	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	490	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	491	two event changes per incident. Support for C<fork ()> is very bad (but
419	drops fds silently in similarly hard-to-detect cases.	492	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		493	cases
420		494
421	This backend usually performs well under most conditions.	495	This backend usually performs well under most conditions.
422		496
423	While nominally embeddable in other event loops, this doesn't work	497	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	498	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	499	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	500	(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	501	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
428	sockets.	502	also broken on OS X)) and, did I mention it, using it only for sockets.
		503
		504	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		505	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		506	C<NOTE_EOF>.
429		507
430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	508	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
431		509
432	This is not implemented yet (and might never be, unless you send me an	510	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	511	implementation). According to reports, C</dev/poll> only supports sockets
…		…
446	While this backend scales well, it requires one system call per active	524	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	525	file descriptor per loop iteration. For small and medium numbers of file
448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	526	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
449	might perform better.	527	might perform better.
450		528
451	On the positive side, ignoring the spurious readiness notifications, this	529	On the positive side, with the exception of the spurious readiness
452	backend actually performed to specification in all tests and is fully	530	notifications, this backend actually performed fully to specification
453	embeddable, which is a rare feat among the OS-specific backends.	531	in all tests and is fully embeddable, which is a rare feat among the
		532	OS-specific backends (I vastly prefer correctness over speed hacks).
		533
		534	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		535	C<EVBACKEND_POLL>.
454		536
455	=item C<EVBACKEND_ALL>	537	=item C<EVBACKEND_ALL>
456		538
457	Try all backends (even potentially broken ones that wouldn't be tried	539	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	540	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
460		542
461	It is definitely not recommended to use this flag.	543	It is definitely not recommended to use this flag.
462		544
463	=back	545	=back
464		546
465	If one or more of these are or'ed into the flags value, then only these	547	If one or more of the backend flags are or'ed into the flags value,
466	backends will be tried (in the reverse order as listed here). If none are	548	then only these backends will be tried (in the reverse order as listed
467	specified, all backends in C<ev_recommended_backends ()> will be tried.	549	here). If none are specified, all backends in C<ev_recommended_backends
		550	()> will be tried.
468		551
469	The most typical usage is like this:	552	Example: This is the most typical usage.
470		553
471	if (!ev_default_loop (0))	554	if (!ev_default_loop (0))
472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	555	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
473		556
474	Restrict libev to the select and poll backends, and do not allow	557	Example: Restrict libev to the select and poll backends, and do not allow
475	environment settings to be taken into account:	558	environment settings to be taken into account:
476		559
477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	560	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
478		561
479	Use whatever libev has to offer, but make sure that kqueue is used if	562	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	563	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):	564	private event loop and only if you know the OS supports your types of
		565	fds):
482		566
483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	567	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
484		568
485	=item struct ev_loop *ev_loop_new (unsigned int flags)	569	=item struct ev_loop *ev_loop_new (unsigned int flags)
486		570
487	Similar to C<ev_default_loop>, but always creates a new event loop that is	571	Similar to C<ev_default_loop>, but always creates a new event loop that is
488	always distinct from the default loop. Unlike the default loop, it cannot	572	always distinct from the default loop.
489	handle signal and child watchers, and attempts to do so will be greeted by
490	undefined behaviour (or a failed assertion if assertions are enabled).
491		573
492	Note that this function I<is> thread-safe, and the recommended way to use	574	Note that this function I<is> thread-safe, and one common way to use
493	libev with threads is indeed to create one loop per thread, and using the	575	libev with threads is indeed to create one loop per thread, and using the
494	default loop in the "main" or "initial" thread.	576	default loop in the "main" or "initial" thread.
495		577
496	Example: Try to create a event loop that uses epoll and nothing else.	578	Example: Try to create a event loop that uses epoll and nothing else.
497		579
…		…
499	if (!epoller)	581	if (!epoller)
500	fatal ("no epoll found here, maybe it hides under your chair");	582	fatal ("no epoll found here, maybe it hides under your chair");
501		583
502	=item ev_default_destroy ()	584	=item ev_default_destroy ()
503		585
504	Destroys the default loop again (frees all memory and kernel state	586	Destroys the default loop (frees all memory and kernel state etc.). None
505	etc.). None of the active event watchers will be stopped in the normal	587	of the active event watchers will be stopped in the normal sense, so
506	sense, so e.g. C<ev_is_active> might still return true. It is your	588	e.g. C<ev_is_active> might still return true. It is your responsibility to
507	responsibility to either stop all watchers cleanly yourself I<before>	589	either stop all watchers cleanly yourself I<before> calling this function,
508	calling this function, or cope with the fact afterwards (which is usually	590	or cope with the fact afterwards (which is usually the easiest thing, you
509	the easiest thing, you can just ignore the watchers and/or C<free ()> them	591	can just ignore the watchers and/or C<free ()> them for example).
510	for example).
511		592
512	Note that certain global state, such as signal state, will not be freed by	593	Note that certain global state, such as signal state (and installed signal
513	this function, and related watchers (such as signal and child watchers)	594	handlers), will not be freed by this function, and related watchers (such
514	would need to be stopped manually.	595	as signal and child watchers) would need to be stopped manually.
515		596
516	In general it is not advisable to call this function except in the	597	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	598	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	599	pipe fds. If you need dynamically allocated loops it is better to use
519	C<ev_loop_new> and C<ev_loop_destroy>).	600	C<ev_loop_new> and C<ev_loop_destroy>.
520		601
521	=item ev_loop_destroy (loop)	602	=item ev_loop_destroy (loop)
522		603
523	Like C<ev_default_destroy>, but destroys an event loop created by an	604	Like C<ev_default_destroy>, but destroys an event loop created by an
524	earlier call to C<ev_loop_new>.	605	earlier call to C<ev_loop_new>.
…		…
530	name, you can call it anytime, but it makes most sense after forking, in	611	name, you can call it anytime, but it makes most sense after forking, in
531	the child process (or both child and parent, but that again makes little	612	the child process (or both child and parent, but that again makes little
532	sense). You I<must> call it in the child before using any of the libev	613	sense). You I<must> call it in the child before using any of the libev
533	functions, and it will only take effect at the next C<ev_loop> iteration.	614	functions, and it will only take effect at the next C<ev_loop> iteration.
534		615
		616	Again, you I<have> to call it on I<any> loop that you want to re-use after
		617	a fork, I<even if you do not plan to use the loop in the parent>. This is
		618	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		619	during fork.
		620
535	On the other hand, you only need to call this function in the child	621	On the other hand, you only need to call this function in the child
536	process if and only if you want to use the event library in the child. If	622	process if and only if you want to use the event loop in the child. If you
537	you just fork+exec, you don't have to call it at all.	623	just fork+exec or create a new loop in the child, you don't have to call
		624	it at all.
538		625
539	The function itself is quite fast and it's usually not a problem to call	626	The function itself is quite fast and it's usually not a problem to call
540	it just in case after a fork. To make this easy, the function will fit in	627	it just in case after a fork. To make this easy, the function will fit in
541	quite nicely into a call to C<pthread_atfork>:	628	quite nicely into a call to C<pthread_atfork>:
542		629
…		…
544		631
545	=item ev_loop_fork (loop)	632	=item ev_loop_fork (loop)
546		633
547	Like C<ev_default_fork>, but acts on an event loop created by	634	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	635	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.	636	after fork that you want to re-use in the child, and how you keep track of
		637	them is entirely your own problem.
550		638
551	=item int ev_is_default_loop (loop)	639	=item int ev_is_default_loop (loop)
552		640
553	Returns true when the given loop actually is the default loop, false otherwise.	641	Returns true when the given loop is, in fact, the default loop, and false
		642	otherwise.
554		643
555	=item unsigned int ev_loop_count (loop)	644	=item unsigned int ev_iteration (loop)
556		645
557	Returns the count of loop iterations for the loop, which is identical to	646	Returns the current iteration count for the loop, which is identical to
558	the number of times libev did poll for new events. It starts at C<0> and	647	the number of times libev did poll for new events. It starts at C<0> and
559	happily wraps around with enough iterations.	648	happily wraps around with enough iterations.
560		649
561	This value can sometimes be useful as a generation counter of sorts (it	650	This value can sometimes be useful as a generation counter of sorts (it
562	"ticks" the number of loop iterations), as it roughly corresponds with	651	"ticks" the number of loop iterations), as it roughly corresponds with
563	C<ev_prepare> and C<ev_check> calls.	652	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		653	prepare and check phases.
		654
		655	=item unsigned int ev_depth (loop)
		656
		657	Returns the number of times C<ev_loop> was entered minus the number of
		658	times C<ev_loop> was exited, in other words, the recursion depth.
		659
		660	Outside C<ev_loop>, this number is zero. In a callback, this number is
		661	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		662	in which case it is higher.
		663
		664	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		665	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		666	ungentleman behaviour unless it's really convenient.
564		667
565	=item unsigned int ev_backend (loop)	668	=item unsigned int ev_backend (loop)
566		669
567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	670	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
568	use.	671	use.
…		…
583		686
584	This function is rarely useful, but when some event callback runs for a	687	This function is rarely useful, but when some event callback runs for a
585	very long time without entering the event loop, updating libev's idea of	688	very long time without entering the event loop, updating libev's idea of
586	the current time is a good idea.	689	the current time is a good idea.
587		690
588	See also "The special problem of time updates" in the C<ev_timer> section.	691	See also L<The special problem of time updates> in the C<ev_timer> section.
		692
		693	=item ev_suspend (loop)
		694
		695	=item ev_resume (loop)
		696
		697	These two functions suspend and resume a loop, for use when the loop is
		698	not used for a while and timeouts should not be processed.
		699
		700	A typical use case would be an interactive program such as a game: When
		701	the user presses C<^Z> to suspend the game and resumes it an hour later it
		702	would be best to handle timeouts as if no time had actually passed while
		703	the program was suspended. This can be achieved by calling C<ev_suspend>
		704	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		705	C<ev_resume> directly afterwards to resume timer processing.
		706
		707	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		708	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		709	will be rescheduled (that is, they will lose any events that would have
		710	occurred while suspended).
		711
		712	After calling C<ev_suspend> you B<must not> call I<any> function on the
		713	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		714	without a previous call to C<ev_suspend>.
		715
		716	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		717	event loop time (see C<ev_now_update>).
589		718
590	=item ev_loop (loop, int flags)	719	=item ev_loop (loop, int flags)
591		720
592	Finally, this is it, the event handler. This function usually is called	721	Finally, this is it, the event handler. This function usually is called
593	after you initialised all your watchers and you want to start handling	722	after you have initialised all your watchers and you want to start
594	events.	723	handling events.
595		724
596	If the flags argument is specified as C<0>, it will not return until	725	If the flags argument is specified as C<0>, it will not return until
597	either no event watchers are active anymore or C<ev_unloop> was called.	726	either no event watchers are active anymore or C<ev_unloop> was called.
598		727
599	Please note that an explicit C<ev_unloop> is usually better than	728	Please note that an explicit C<ev_unloop> is usually better than
600	relying on all watchers to be stopped when deciding when a program has	729	relying on all watchers to be stopped when deciding when a program has
601	finished (especially in interactive programs), but having a program that	730	finished (especially in interactive programs), but having a program
602	automatically loops as long as it has to and no longer by virtue of	731	that automatically loops as long as it has to and no longer by virtue
603	relying on its watchers stopping correctly is a thing of beauty.	732	of relying on its watchers stopping correctly, that is truly a thing of
		733	beauty.
604		734
605	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	735	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
606	those events and any outstanding ones, but will not block your process in	736	those events and any already outstanding ones, but will not block your
607	case there are no events and will return after one iteration of the loop.	737	process in case there are no events and will return after one iteration of
		738	the loop.
608		739
609	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	740	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
610	necessary) and will handle those and any outstanding ones. It will block	741	necessary) and will handle those and any already outstanding ones. It
611	your process until at least one new event arrives, and will return after	742	will block your process until at least one new event arrives (which could
612	one iteration of the loop. This is useful if you are waiting for some	743	be an event internal to libev itself, so there is no guarantee that a
613	external event in conjunction with something not expressible using other	744	user-registered callback will be called), and will return after one
		745	iteration of the loop.
		746
		747	This is useful if you are waiting for some external event in conjunction
		748	with something not expressible using other libev watchers (i.e. "roll your
614	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	749	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
615	usually a better approach for this kind of thing.	750	usually a better approach for this kind of thing.
616		751
617	Here are the gory details of what C<ev_loop> does:	752	Here are the gory details of what C<ev_loop> does:
618		753
619	- Before the first iteration, call any pending watchers.	754	- Before the first iteration, call any pending watchers.
…		…
629	any active watchers at all will result in not sleeping).	764	any active watchers at all will result in not sleeping).
630	- Sleep if the I/O and timer collect interval say so.	765	- Sleep if the I/O and timer collect interval say so.
631	- Block the process, waiting for any events.	766	- Block the process, waiting for any events.
632	- Queue all outstanding I/O (fd) events.	767	- Queue all outstanding I/O (fd) events.
633	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	768	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
634	- Queue all outstanding timers.	769	- Queue all expired timers.
635	- Queue all outstanding periodics.	770	- Queue all expired periodics.
636	- Unless any events are pending now, queue all idle watchers.	771	- Unless any events are pending now, queue all idle watchers.
637	- Queue all check watchers.	772	- Queue all check watchers.
638	- Call all queued watchers in reverse order (i.e. check watchers first).	773	- Call all queued watchers in reverse order (i.e. check watchers first).
639	Signals and child watchers are implemented as I/O watchers, and will	774	Signals and child watchers are implemented as I/O watchers, and will
640	be handled here by queueing them when their watcher gets executed.	775	be handled here by queueing them when their watcher gets executed.
…		…
657	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	792	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
658	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	793	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
659		794
660	This "unloop state" will be cleared when entering C<ev_loop> again.	795	This "unloop state" will be cleared when entering C<ev_loop> again.
661		796
		797	It is safe to call C<ev_unloop> from outside any C<ev_loop> calls.
		798
662	=item ev_ref (loop)	799	=item ev_ref (loop)
663		800
664	=item ev_unref (loop)	801	=item ev_unref (loop)
665		802
666	Ref/unref can be used to add or remove a reference count on the event	803	Ref/unref can be used to add or remove a reference count on the event
667	loop: Every watcher keeps one reference, and as long as the reference	804	loop: Every watcher keeps one reference, and as long as the reference
668	count is nonzero, C<ev_loop> will not return on its own. If you have	805	count is nonzero, C<ev_loop> will not return on its own.
669	a watcher you never unregister that should not keep C<ev_loop> from	806
670	returning, ev_unref() after starting, and ev_ref() before stopping it. For	807	This is useful when you have a watcher that you never intend to
		808	unregister, but that nevertheless should not keep C<ev_loop> from
		809	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		810	before stopping it.
		811
671	example, libev itself uses this for its internal signal pipe: It is not	812	As an example, libev itself uses this for its internal signal pipe: It
672	visible to the libev user and should not keep C<ev_loop> from exiting if	813	is not visible to the libev user and should not keep C<ev_loop> from
673	no event watchers registered by it are active. It is also an excellent	814	exiting if no event watchers registered by it are active. It is also an
674	way to do this for generic recurring timers or from within third-party	815	excellent way to do this for generic recurring timers or from within
675	libraries. Just remember to I<unref after start> and I<ref before stop>	816	third-party libraries. Just remember to I<unref after start> and I<ref
676	(but only if the watcher wasn't active before, or was active before,	817	before stop> (but only if the watcher wasn't active before, or was active
677	respectively).	818	before, respectively. Note also that libev might stop watchers itself
		819	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		820	in the callback).
678		821
679	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	822	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
680	running when nothing else is active.	823	running when nothing else is active.
681		824
682	struct ev_signal exitsig;	825	ev_signal exitsig;
683	ev_signal_init (&exitsig, sig_cb, SIGINT);	826	ev_signal_init (&exitsig, sig_cb, SIGINT);
684	ev_signal_start (loop, &exitsig);	827	ev_signal_start (loop, &exitsig);
685	evf_unref (loop);	828	evf_unref (loop);
686		829
687	Example: For some weird reason, unregister the above signal handler again.	830	Example: For some weird reason, unregister the above signal handler again.
…		…
701	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	844	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
702	allows libev to delay invocation of I/O and timer/periodic callbacks	845	allows libev to delay invocation of I/O and timer/periodic callbacks
703	to increase efficiency of loop iterations (or to increase power-saving	846	to increase efficiency of loop iterations (or to increase power-saving
704	opportunities).	847	opportunities).
705		848
706	The background is that sometimes your program runs just fast enough to	849	The idea is that sometimes your program runs just fast enough to handle
707	handle one (or very few) event(s) per loop iteration. While this makes	850	one (or very few) event(s) per loop iteration. While this makes the
708	the program responsive, it also wastes a lot of CPU time to poll for new	851	program responsive, it also wastes a lot of CPU time to poll for new
709	events, especially with backends like C<select ()> which have a high	852	events, especially with backends like C<select ()> which have a high
710	overhead for the actual polling but can deliver many events at once.	853	overhead for the actual polling but can deliver many events at once.
711		854
712	By setting a higher I<io collect interval> you allow libev to spend more	855	By setting a higher I<io collect interval> you allow libev to spend more
713	time collecting I/O events, so you can handle more events per iteration,	856	time collecting I/O events, so you can handle more events per iteration,
714	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	857	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
715	C<ev_timer>) will be not affected. Setting this to a non-null value will	858	C<ev_timer>) will be not affected. Setting this to a non-null value will
716	introduce an additional C<ev_sleep ()> call into most loop iterations.	859	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		860	sleep time ensures that libev will not poll for I/O events more often then
		861	once per this interval, on average.
717		862
718	Likewise, by setting a higher I<timeout collect interval> you allow libev	863	Likewise, by setting a higher I<timeout collect interval> you allow libev
719	to spend more time collecting timeouts, at the expense of increased	864	to spend more time collecting timeouts, at the expense of increased
720	latency (the watcher callback will be called later). C<ev_io> watchers	865	latency/jitter/inexactness (the watcher callback will be called
721	will not be affected. Setting this to a non-null value will not introduce	866	later). C<ev_io> watchers will not be affected. Setting this to a non-null
722	any overhead in libev.	867	value will not introduce any overhead in libev.
723		868
724	Many (busy) programs can usually benefit by setting the I/O collect	869	Many (busy) programs can usually benefit by setting the I/O collect
725	interval to a value near C<0.1> or so, which is often enough for	870	interval to a value near C<0.1> or so, which is often enough for
726	interactive servers (of course not for games), likewise for timeouts. It	871	interactive servers (of course not for games), likewise for timeouts. It
727	usually doesn't make much sense to set it to a lower value than C<0.01>,	872	usually doesn't make much sense to set it to a lower value than C<0.01>,
728	as this approaches the timing granularity of most systems.	873	as this approaches the timing granularity of most systems. Note that if
		874	you do transactions with the outside world and you can't increase the
		875	parallelity, then this setting will limit your transaction rate (if you
		876	need to poll once per transaction and the I/O collect interval is 0.01,
		877	then you can't do more than 100 transactions per second).
729		878
730	Setting the I<timeout collect interval> can improve the opportunity for	879	Setting the I<timeout collect interval> can improve the opportunity for
731	saving power, as the program will "bundle" timer callback invocations that	880	saving power, as the program will "bundle" timer callback invocations that
732	are "near" in time together, by delaying some, thus reducing the number of	881	are "near" in time together, by delaying some, thus reducing the number of
733	times the process sleeps and wakes up again. Another useful technique to	882	times the process sleeps and wakes up again. Another useful technique to
734	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	883	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
735	they fire on, say, one-second boundaries only.	884	they fire on, say, one-second boundaries only.
736		885
		886	Example: we only need 0.1s timeout granularity, and we wish not to poll
		887	more often than 100 times per second:
		888
		889	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		890	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		891
		892	=item ev_invoke_pending (loop)
		893
		894	This call will simply invoke all pending watchers while resetting their
		895	pending state. Normally, C<ev_loop> does this automatically when required,
		896	but when overriding the invoke callback this call comes handy.
		897
		898	=item int ev_pending_count (loop)
		899
		900	Returns the number of pending watchers - zero indicates that no watchers
		901	are pending.
		902
		903	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		904
		905	This overrides the invoke pending functionality of the loop: Instead of
		906	invoking all pending watchers when there are any, C<ev_loop> will call
		907	this callback instead. This is useful, for example, when you want to
		908	invoke the actual watchers inside another context (another thread etc.).
		909
		910	If you want to reset the callback, use C<ev_invoke_pending> as new
		911	callback.
		912
		913	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		914
		915	Sometimes you want to share the same loop between multiple threads. This
		916	can be done relatively simply by putting mutex_lock/unlock calls around
		917	each call to a libev function.
		918
		919	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		920	wait for it to return. One way around this is to wake up the loop via
		921	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		922	and I<acquire> callbacks on the loop.
		923
		924	When set, then C<release> will be called just before the thread is
		925	suspended waiting for new events, and C<acquire> is called just
		926	afterwards.
		927
		928	Ideally, C<release> will just call your mutex_unlock function, and
		929	C<acquire> will just call the mutex_lock function again.
		930
		931	While event loop modifications are allowed between invocations of
		932	C<release> and C<acquire> (that's their only purpose after all), no
		933	modifications done will affect the event loop, i.e. adding watchers will
		934	have no effect on the set of file descriptors being watched, or the time
		935	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		936	to take note of any changes you made.
		937
		938	In theory, threads executing C<ev_loop> will be async-cancel safe between
		939	invocations of C<release> and C<acquire>.
		940
		941	See also the locking example in the C<THREADS> section later in this
		942	document.
		943
		944	=item ev_set_userdata (loop, void *data)
		945
		946	=item ev_userdata (loop)
		947
		948	Set and retrieve a single C<void *> associated with a loop. When
		949	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		950	C<0.>
		951
		952	These two functions can be used to associate arbitrary data with a loop,
		953	and are intended solely for the C<invoke_pending_cb>, C<release> and
		954	C<acquire> callbacks described above, but of course can be (ab-)used for
		955	any other purpose as well.
		956
737	=item ev_loop_verify (loop)	957	=item ev_loop_verify (loop)
738		958
739	This function only does something when C<EV_VERIFY> support has been	959	This function only does something when C<EV_VERIFY> support has been
740	compiled in. It tries to go through all internal structures and checks	960	compiled in, which is the default for non-minimal builds. It tries to go
741	them for validity. If anything is found to be inconsistent, it will print	961	through all internal structures and checks them for validity. If anything
742	an error message to standard error and call C<abort ()>.	962	is found to be inconsistent, it will print an error message to standard
		963	error and call C<abort ()>.
743		964
744	This can be used to catch bugs inside libev itself: under normal	965	This can be used to catch bugs inside libev itself: under normal
745	circumstances, this function will never abort as of course libev keeps its	966	circumstances, this function will never abort as of course libev keeps its
746	data structures consistent.	967	data structures consistent.
747		968
748	=back	969	=back
749		970
750		971
751	=head1 ANATOMY OF A WATCHER	972	=head1 ANATOMY OF A WATCHER
752		973
		974	In the following description, uppercase C<TYPE> in names stands for the
		975	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		976	watchers and C<ev_io_start> for I/O watchers.
		977
753	A watcher is a structure that you create and register to record your	978	A watcher is a structure that you create and register to record your
754	interest in some event. For instance, if you want to wait for STDIN to	979	interest in some event. For instance, if you want to wait for STDIN to
755	become readable, you would create an C<ev_io> watcher for that:	980	become readable, you would create an C<ev_io> watcher for that:
756		981
757	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	982	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
758	{	983	{
759	ev_io_stop (w);	984	ev_io_stop (w);
760	ev_unloop (loop, EVUNLOOP_ALL);	985	ev_unloop (loop, EVUNLOOP_ALL);
761	}	986	}
762		987
763	struct ev_loop *loop = ev_default_loop (0);	988	struct ev_loop *loop = ev_default_loop (0);
		989
764	struct ev_io stdin_watcher;	990	ev_io stdin_watcher;
		991
765	ev_init (&stdin_watcher, my_cb);	992	ev_init (&stdin_watcher, my_cb);
766	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	993	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
767	ev_io_start (loop, &stdin_watcher);	994	ev_io_start (loop, &stdin_watcher);
		995
768	ev_loop (loop, 0);	996	ev_loop (loop, 0);
769		997
770	As you can see, you are responsible for allocating the memory for your	998	As you can see, you are responsible for allocating the memory for your
771	watcher structures (and it is usually a bad idea to do this on the stack,	999	watcher structures (and it is I<usually> a bad idea to do this on the
772	although this can sometimes be quite valid).	1000	stack).
		1001
		1002	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1003	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
773		1004
774	Each watcher structure must be initialised by a call to C<ev_init	1005	Each watcher structure must be initialised by a call to C<ev_init
775	(watcher *, callback)>, which expects a callback to be provided. This	1006	(watcher *, callback)>, which expects a callback to be provided. This
776	callback gets invoked each time the event occurs (or, in the case of I/O	1007	callback gets invoked each time the event occurs (or, in the case of I/O
777	watchers, each time the event loop detects that the file descriptor given	1008	watchers, each time the event loop detects that the file descriptor given
778	is readable and/or writable).	1009	is readable and/or writable).
779		1010
780	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1011	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
781	with arguments specific to this watcher type. There is also a macro	1012	macro to configure it, with arguments specific to the watcher type. There
782	to combine initialisation and setting in one call: C<< ev_<type>_init	1013	is also a macro to combine initialisation and setting in one call: C<<
783	(watcher *, callback, ...) >>.	1014	ev_TYPE_init (watcher *, callback, ...) >>.
784		1015
785	To make the watcher actually watch out for events, you have to start it	1016	To make the watcher actually watch out for events, you have to start it
786	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1017	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
787	*) >>), and you can stop watching for events at any time by calling the	1018	*) >>), and you can stop watching for events at any time by calling the
788	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1019	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
789		1020
790	As long as your watcher is active (has been started but not stopped) you	1021	As long as your watcher is active (has been started but not stopped) you
791	must not touch the values stored in it. Most specifically you must never	1022	must not touch the values stored in it. Most specifically you must never
792	reinitialise it or call its C<set> macro.	1023	reinitialise it or call its C<ev_TYPE_set> macro.
793		1024
794	Each and every callback receives the event loop pointer as first, the	1025	Each and every callback receives the event loop pointer as first, the
795	registered watcher structure as second, and a bitset of received events as	1026	registered watcher structure as second, and a bitset of received events as
796	third argument.	1027	third argument.
797		1028
…		…
806	=item C<EV_WRITE>	1037	=item C<EV_WRITE>
807		1038
808	The file descriptor in the C<ev_io> watcher has become readable and/or	1039	The file descriptor in the C<ev_io> watcher has become readable and/or
809	writable.	1040	writable.
810		1041
811	=item C<EV_TIMEOUT>	1042	=item C<EV_TIMER>
812		1043
813	The C<ev_timer> watcher has timed out.	1044	The C<ev_timer> watcher has timed out.
814		1045
815	=item C<EV_PERIODIC>	1046	=item C<EV_PERIODIC>
816		1047
…		…
855		1086
856	=item C<EV_ASYNC>	1087	=item C<EV_ASYNC>
857		1088
858	The given async watcher has been asynchronously notified (see C<ev_async>).	1089	The given async watcher has been asynchronously notified (see C<ev_async>).
859		1090
		1091	=item C<EV_CUSTOM>
		1092
		1093	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1094	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1095
860	=item C<EV_ERROR>	1096	=item C<EV_ERROR>
861		1097
862	An unspecified error has occurred, the watcher has been stopped. This might	1098	An unspecified error has occurred, the watcher has been stopped. This might
863	happen because the watcher could not be properly started because libev	1099	happen because the watcher could not be properly started because libev
864	ran out of memory, a file descriptor was found to be closed or any other	1100	ran out of memory, a file descriptor was found to be closed or any other
		1101	problem. Libev considers these application bugs.
		1102
865	problem. You best act on it by reporting the problem and somehow coping	1103	You best act on it by reporting the problem and somehow coping with the
866	with the watcher being stopped.	1104	watcher being stopped. Note that well-written programs should not receive
		1105	an error ever, so when your watcher receives it, this usually indicates a
		1106	bug in your program.
867		1107
868	Libev will usually signal a few "dummy" events together with an error,	1108	Libev will usually signal a few "dummy" events together with an error, for
869	for example it might indicate that a fd is readable or writable, and if	1109	example it might indicate that a fd is readable or writable, and if your
870	your callbacks is well-written it can just attempt the operation and cope	1110	callbacks is well-written it can just attempt the operation and cope with
871	with the error from read() or write(). This will not work in multi-threaded	1111	the error from read() or write(). This will not work in multi-threaded
872	programs, though, so beware.	1112	programs, though, as the fd could already be closed and reused for another
		1113	thing, so beware.
873		1114
874	=back	1115	=back
875		1116
876	=head2 GENERIC WATCHER FUNCTIONS	1117	=head2 GENERIC WATCHER FUNCTIONS
877
878	In the following description, C<TYPE> stands for the watcher type,
879	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
880		1118
881	=over 4	1119	=over 4
882		1120
883	=item C<ev_init> (ev_TYPE *watcher, callback)	1121	=item C<ev_init> (ev_TYPE *watcher, callback)
884		1122
…		…
890	which rolls both calls into one.	1128	which rolls both calls into one.
891		1129
892	You can reinitialise a watcher at any time as long as it has been stopped	1130	You can reinitialise a watcher at any time as long as it has been stopped
893	(or never started) and there are no pending events outstanding.	1131	(or never started) and there are no pending events outstanding.
894		1132
895	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1133	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
896	int revents)>.	1134	int revents)>.
897		1135
		1136	Example: Initialise an C<ev_io> watcher in two steps.
		1137
		1138	ev_io w;
		1139	ev_init (&w, my_cb);
		1140	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1141
898	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1142	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
899		1143
900	This macro initialises the type-specific parts of a watcher. You need to	1144	This macro initialises the type-specific parts of a watcher. You need to
901	call C<ev_init> at least once before you call this macro, but you can	1145	call C<ev_init> at least once before you call this macro, but you can
902	call C<ev_TYPE_set> any number of times. You must not, however, call this	1146	call C<ev_TYPE_set> any number of times. You must not, however, call this
903	macro on a watcher that is active (it can be pending, however, which is a	1147	macro on a watcher that is active (it can be pending, however, which is a
904	difference to the C<ev_init> macro).	1148	difference to the C<ev_init> macro).
905		1149
906	Although some watcher types do not have type-specific arguments	1150	Although some watcher types do not have type-specific arguments
907	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1151	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
908		1152
		1153	See C<ev_init>, above, for an example.
		1154
909	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1155	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
910		1156
911	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1157	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
912	calls into a single call. This is the most convenient method to initialise	1158	calls into a single call. This is the most convenient method to initialise
913	a watcher. The same limitations apply, of course.	1159	a watcher. The same limitations apply, of course.
914		1160
		1161	Example: Initialise and set an C<ev_io> watcher in one step.
		1162
		1163	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1164
915	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1165	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
916		1166
917	Starts (activates) the given watcher. Only active watchers will receive	1167	Starts (activates) the given watcher. Only active watchers will receive
918	events. If the watcher is already active nothing will happen.	1168	events. If the watcher is already active nothing will happen.
919		1169
		1170	Example: Start the C<ev_io> watcher that is being abused as example in this
		1171	whole section.
		1172
		1173	ev_io_start (EV_DEFAULT_UC, &w);
		1174
920	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1175	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
921		1176
922	Stops the given watcher again (if active) and clears the pending	1177	Stops the given watcher if active, and clears the pending status (whether
		1178	the watcher was active or not).
		1179
923	status. It is possible that stopped watchers are pending (for example,	1180	It is possible that stopped watchers are pending - for example,
924	non-repeating timers are being stopped when they become pending), but	1181	non-repeating timers are being stopped when they become pending - but
925	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1182	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
926	you want to free or reuse the memory used by the watcher it is therefore a	1183	pending. If you want to free or reuse the memory used by the watcher it is
927	good idea to always call its C<ev_TYPE_stop> function.	1184	therefore a good idea to always call its C<ev_TYPE_stop> function.
928		1185
929	=item bool ev_is_active (ev_TYPE *watcher)	1186	=item bool ev_is_active (ev_TYPE *watcher)
930		1187
931	Returns a true value iff the watcher is active (i.e. it has been started	1188	Returns a true value iff the watcher is active (i.e. it has been started
932	and not yet been stopped). As long as a watcher is active you must not modify	1189	and not yet been stopped). As long as a watcher is active you must not modify
…		…
948	=item ev_cb_set (ev_TYPE *watcher, callback)	1205	=item ev_cb_set (ev_TYPE *watcher, callback)
949		1206
950	Change the callback. You can change the callback at virtually any time	1207	Change the callback. You can change the callback at virtually any time
951	(modulo threads).	1208	(modulo threads).
952		1209
953	=item ev_set_priority (ev_TYPE *watcher, priority)	1210	=item ev_set_priority (ev_TYPE *watcher, int priority)
954		1211
955	=item int ev_priority (ev_TYPE *watcher)	1212	=item int ev_priority (ev_TYPE *watcher)
956		1213
957	Set and query the priority of the watcher. The priority is a small	1214	Set and query the priority of the watcher. The priority is a small
958	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1215	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
959	(default: C<-2>). Pending watchers with higher priority will be invoked	1216	(default: C<-2>). Pending watchers with higher priority will be invoked
960	before watchers with lower priority, but priority will not keep watchers	1217	before watchers with lower priority, but priority will not keep watchers
961	from being executed (except for C<ev_idle> watchers).	1218	from being executed (except for C<ev_idle> watchers).
962		1219
963	This means that priorities are I<only> used for ordering callback
964	invocation after new events have been received. This is useful, for
965	example, to reduce latency after idling, or more often, to bind two
966	watchers on the same event and make sure one is called first.
967
968	If you need to suppress invocation when higher priority events are pending	1220	If you need to suppress invocation when higher priority events are pending
969	you need to look at C<ev_idle> watchers, which provide this functionality.	1221	you need to look at C<ev_idle> watchers, which provide this functionality.
970		1222
971	You I<must not> change the priority of a watcher as long as it is active or	1223	You I<must not> change the priority of a watcher as long as it is active or
972	pending.	1224	pending.
973		1225
		1226	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1227	fine, as long as you do not mind that the priority value you query might
		1228	or might not have been clamped to the valid range.
		1229
974	The default priority used by watchers when no priority has been set is	1230	The default priority used by watchers when no priority has been set is
975	always C<0>, which is supposed to not be too high and not be too low :).	1231	always C<0>, which is supposed to not be too high and not be too low :).
976		1232
977	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1233	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
978	fine, as long as you do not mind that the priority value you query might	1234	priorities.
979	or might not have been adjusted to be within valid range.
980		1235
981	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1236	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
982		1237
983	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1238	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
984	C<loop> nor C<revents> need to be valid as long as the watcher callback	1239	C<loop> nor C<revents> need to be valid as long as the watcher callback
985	can deal with that fact.	1240	can deal with that fact, as both are simply passed through to the
		1241	callback.
986		1242
987	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1243	=item int ev_clear_pending (loop, ev_TYPE *watcher)
988		1244
989	If the watcher is pending, this function returns clears its pending status	1245	If the watcher is pending, this function clears its pending status and
990	and returns its C<revents> bitset (as if its callback was invoked). If the	1246	returns its C<revents> bitset (as if its callback was invoked). If the
991	watcher isn't pending it does nothing and returns C<0>.	1247	watcher isn't pending it does nothing and returns C<0>.
992		1248
		1249	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1250	callback to be invoked, which can be accomplished with this function.
		1251
		1252	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1253
		1254	Feeds the given event set into the event loop, as if the specified event
		1255	had happened for the specified watcher (which must be a pointer to an
		1256	initialised but not necessarily started event watcher). Obviously you must
		1257	not free the watcher as long as it has pending events.
		1258
		1259	Stopping the watcher, letting libev invoke it, or calling
		1260	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1261	not started in the first place.
		1262
		1263	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1264	functions that do not need a watcher.
		1265
993	=back	1266	=back
994		1267
995		1268
996	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1269	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
997		1270
998	Each watcher has, by default, a member C<void *data> that you can change	1271	Each watcher has, by default, a member C<void *data> that you can change
999	and read at any time, libev will completely ignore it. This can be used	1272	and read at any time: libev will completely ignore it. This can be used
1000	to associate arbitrary data with your watcher. If you need more data and	1273	to associate arbitrary data with your watcher. If you need more data and
1001	don't want to allocate memory and store a pointer to it in that data	1274	don't want to allocate memory and store a pointer to it in that data
1002	member, you can also "subclass" the watcher type and provide your own	1275	member, you can also "subclass" the watcher type and provide your own
1003	data:	1276	data:
1004		1277
1005	struct my_io	1278	struct my_io
1006	{	1279	{
1007	struct ev_io io;	1280	ev_io io;
1008	int otherfd;	1281	int otherfd;
1009	void *somedata;	1282	void *somedata;
1010	struct whatever *mostinteresting;	1283	struct whatever *mostinteresting;
1011	};	1284	};
1012		1285
…		…
1015	ev_io_init (&w.io, my_cb, fd, EV_READ);	1288	ev_io_init (&w.io, my_cb, fd, EV_READ);
1016		1289
1017	And since your callback will be called with a pointer to the watcher, you	1290	And since your callback will be called with a pointer to the watcher, you
1018	can cast it back to your own type:	1291	can cast it back to your own type:
1019		1292
1020	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1293	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1021	{	1294	{
1022	struct my_io *w = (struct my_io *)w_;	1295	struct my_io *w = (struct my_io *)w_;
1023	...	1296	...
1024	}	1297	}
1025		1298
…		…
1036	ev_timer t2;	1309	ev_timer t2;
1037	}	1310	}
1038		1311
1039	In this case getting the pointer to C<my_biggy> is a bit more	1312	In this case getting the pointer to C<my_biggy> is a bit more
1040	complicated: Either you store the address of your C<my_biggy> struct	1313	complicated: Either you store the address of your C<my_biggy> struct
1041	in the C<data> member of the watcher, or you need to use some pointer	1314	in the C<data> member of the watcher (for woozies), or you need to use
1042	arithmetic using C<offsetof> inside your watchers:	1315	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1316	programmers):
1043		1317
1044	#include <stddef.h>	1318	#include <stddef.h>
1045		1319
1046	static void	1320	static void
1047	t1_cb (EV_P_ struct ev_timer *w, int revents)	1321	t1_cb (EV_P_ ev_timer *w, int revents)
1048	{	1322	{
1049	struct my_biggy big = (struct my_biggy *	1323	struct my_biggy big = (struct my_biggy *)
1050	(((char *)w) - offsetof (struct my_biggy, t1));	1324	(((char *)w) - offsetof (struct my_biggy, t1));
1051	}	1325	}
1052		1326
1053	static void	1327	static void
1054	t2_cb (EV_P_ struct ev_timer *w, int revents)	1328	t2_cb (EV_P_ ev_timer *w, int revents)
1055	{	1329	{
1056	struct my_biggy big = (struct my_biggy *	1330	struct my_biggy big = (struct my_biggy *)
1057	(((char *)w) - offsetof (struct my_biggy, t2));	1331	(((char *)w) - offsetof (struct my_biggy, t2));
1058	}	1332	}
		1333
		1334	=head2 WATCHER PRIORITY MODELS
		1335
		1336	Many event loops support I<watcher priorities>, which are usually small
		1337	integers that influence the ordering of event callback invocation
		1338	between watchers in some way, all else being equal.
		1339
		1340	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1341	description for the more technical details such as the actual priority
		1342	range.
		1343
		1344	There are two common ways how these these priorities are being interpreted
		1345	by event loops:
		1346
		1347	In the more common lock-out model, higher priorities "lock out" invocation
		1348	of lower priority watchers, which means as long as higher priority
		1349	watchers receive events, lower priority watchers are not being invoked.
		1350
		1351	The less common only-for-ordering model uses priorities solely to order
		1352	callback invocation within a single event loop iteration: Higher priority
		1353	watchers are invoked before lower priority ones, but they all get invoked
		1354	before polling for new events.
		1355
		1356	Libev uses the second (only-for-ordering) model for all its watchers
		1357	except for idle watchers (which use the lock-out model).
		1358
		1359	The rationale behind this is that implementing the lock-out model for
		1360	watchers is not well supported by most kernel interfaces, and most event
		1361	libraries will just poll for the same events again and again as long as
		1362	their callbacks have not been executed, which is very inefficient in the
		1363	common case of one high-priority watcher locking out a mass of lower
		1364	priority ones.
		1365
		1366	Static (ordering) priorities are most useful when you have two or more
		1367	watchers handling the same resource: a typical usage example is having an
		1368	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1369	timeouts. Under load, data might be received while the program handles
		1370	other jobs, but since timers normally get invoked first, the timeout
		1371	handler will be executed before checking for data. In that case, giving
		1372	the timer a lower priority than the I/O watcher ensures that I/O will be
		1373	handled first even under adverse conditions (which is usually, but not
		1374	always, what you want).
		1375
		1376	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1377	will only be executed when no same or higher priority watchers have
		1378	received events, they can be used to implement the "lock-out" model when
		1379	required.
		1380
		1381	For example, to emulate how many other event libraries handle priorities,
		1382	you can associate an C<ev_idle> watcher to each such watcher, and in
		1383	the normal watcher callback, you just start the idle watcher. The real
		1384	processing is done in the idle watcher callback. This causes libev to
		1385	continuously poll and process kernel event data for the watcher, but when
		1386	the lock-out case is known to be rare (which in turn is rare :), this is
		1387	workable.
		1388
		1389	Usually, however, the lock-out model implemented that way will perform
		1390	miserably under the type of load it was designed to handle. In that case,
		1391	it might be preferable to stop the real watcher before starting the
		1392	idle watcher, so the kernel will not have to process the event in case
		1393	the actual processing will be delayed for considerable time.
		1394
		1395	Here is an example of an I/O watcher that should run at a strictly lower
		1396	priority than the default, and which should only process data when no
		1397	other events are pending:
		1398
		1399	ev_idle idle; // actual processing watcher
		1400	ev_io io; // actual event watcher
		1401
		1402	static void
		1403	io_cb (EV_P_ ev_io *w, int revents)
		1404	{
		1405	// stop the I/O watcher, we received the event, but
		1406	// are not yet ready to handle it.
		1407	ev_io_stop (EV_A_ w);
		1408
		1409	// start the idle watcher to handle the actual event.
		1410	// it will not be executed as long as other watchers
		1411	// with the default priority are receiving events.
		1412	ev_idle_start (EV_A_ &idle);
		1413	}
		1414
		1415	static void
		1416	idle_cb (EV_P_ ev_idle *w, int revents)
		1417	{
		1418	// actual processing
		1419	read (STDIN_FILENO, ...);
		1420
		1421	// have to start the I/O watcher again, as
		1422	// we have handled the event
		1423	ev_io_start (EV_P_ &io);
		1424	}
		1425
		1426	// initialisation
		1427	ev_idle_init (&idle, idle_cb);
		1428	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1429	ev_io_start (EV_DEFAULT_ &io);
		1430
		1431	In the "real" world, it might also be beneficial to start a timer, so that
		1432	low-priority connections can not be locked out forever under load. This
		1433	enables your program to keep a lower latency for important connections
		1434	during short periods of high load, while not completely locking out less
		1435	important ones.
1059		1436
1060		1437
1061	=head1 WATCHER TYPES	1438	=head1 WATCHER TYPES
1062		1439
1063	This section describes each watcher in detail, but will not repeat	1440	This section describes each watcher in detail, but will not repeat
…		…
1087	In general you can register as many read and/or write event watchers per	1464	In general you can register as many read and/or write event watchers per
1088	fd as you want (as long as you don't confuse yourself). Setting all file	1465	fd as you want (as long as you don't confuse yourself). Setting all file
1089	descriptors to non-blocking mode is also usually a good idea (but not	1466	descriptors to non-blocking mode is also usually a good idea (but not
1090	required if you know what you are doing).	1467	required if you know what you are doing).
1091		1468
1092	If you must do this, then force the use of a known-to-be-good backend	1469	If you cannot use non-blocking mode, then force the use of a
1093	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1470	known-to-be-good backend (at the time of this writing, this includes only
1094	C<EVBACKEND_POLL>).	1471	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1472	descriptors for which non-blocking operation makes no sense (such as
		1473	files) - libev doesn't guarantee any specific behaviour in that case.
1095		1474
1096	Another thing you have to watch out for is that it is quite easy to	1475	Another thing you have to watch out for is that it is quite easy to
1097	receive "spurious" readiness notifications, that is your callback might	1476	receive "spurious" readiness notifications, that is your callback might
1098	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1477	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1099	because there is no data. Not only are some backends known to create a	1478	because there is no data. Not only are some backends known to create a
1100	lot of those (for example Solaris ports), it is very easy to get into	1479	lot of those (for example Solaris ports), it is very easy to get into
1101	this situation even with a relatively standard program structure. Thus	1480	this situation even with a relatively standard program structure. Thus
1102	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1481	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1103	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1482	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1104		1483
1105	If you cannot run the fd in non-blocking mode (for example you should not	1484	If you cannot run the fd in non-blocking mode (for example you should
1106	play around with an Xlib connection), then you have to separately re-test	1485	not play around with an Xlib connection), then you have to separately
1107	whether a file descriptor is really ready with a known-to-be good interface	1486	re-test whether a file descriptor is really ready with a known-to-be good
1108	such as poll (fortunately in our Xlib example, Xlib already does this on	1487	interface such as poll (fortunately in our Xlib example, Xlib already
1109	its own, so its quite safe to use).	1488	does this on its own, so its quite safe to use). Some people additionally
		1489	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1490	indefinitely.
		1491
		1492	But really, best use non-blocking mode.
1110		1493
1111	=head3 The special problem of disappearing file descriptors	1494	=head3 The special problem of disappearing file descriptors
1112		1495
1113	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1496	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1114	descriptor (either by calling C<close> explicitly or by any other means,	1497	descriptor (either due to calling C<close> explicitly or any other means,
1115	such as C<dup>). The reason is that you register interest in some file	1498	such as C<dup2>). The reason is that you register interest in some file
1116	descriptor, but when it goes away, the operating system will silently drop	1499	descriptor, but when it goes away, the operating system will silently drop
1117	this interest. If another file descriptor with the same number then is	1500	this interest. If another file descriptor with the same number then is
1118	registered with libev, there is no efficient way to see that this is, in	1501	registered with libev, there is no efficient way to see that this is, in
1119	fact, a different file descriptor.	1502	fact, a different file descriptor.
1120		1503
…		…
1151	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1534	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1152	C<EVBACKEND_POLL>.	1535	C<EVBACKEND_POLL>.
1153		1536
1154	=head3 The special problem of SIGPIPE	1537	=head3 The special problem of SIGPIPE
1155		1538
1156	While not really specific to libev, it is easy to forget about SIGPIPE:	1539	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1157	when writing to a pipe whose other end has been closed, your program gets	1540	when writing to a pipe whose other end has been closed, your program gets
1158	send a SIGPIPE, which, by default, aborts your program. For most programs	1541	sent a SIGPIPE, which, by default, aborts your program. For most programs
1159	this is sensible behaviour, for daemons, this is usually undesirable.	1542	this is sensible behaviour, for daemons, this is usually undesirable.
1160		1543
1161	So when you encounter spurious, unexplained daemon exits, make sure you	1544	So when you encounter spurious, unexplained daemon exits, make sure you
1162	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1545	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1163	somewhere, as that would have given you a big clue).	1546	somewhere, as that would have given you a big clue).
1164		1547
		1548	=head3 The special problem of accept()ing when you can't
		1549
		1550	Many implementations of the POSIX C<accept> function (for example,
		1551	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1552	connection from the pending queue in all error cases.
		1553
		1554	For example, larger servers often run out of file descriptors (because
		1555	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1556	rejecting the connection, leading to libev signalling readiness on
		1557	the next iteration again (the connection still exists after all), and
		1558	typically causing the program to loop at 100% CPU usage.
		1559
		1560	Unfortunately, the set of errors that cause this issue differs between
		1561	operating systems, there is usually little the app can do to remedy the
		1562	situation, and no known thread-safe method of removing the connection to
		1563	cope with overload is known (to me).
		1564
		1565	One of the easiest ways to handle this situation is to just ignore it
		1566	- when the program encounters an overload, it will just loop until the
		1567	situation is over. While this is a form of busy waiting, no OS offers an
		1568	event-based way to handle this situation, so it's the best one can do.
		1569
		1570	A better way to handle the situation is to log any errors other than
		1571	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1572	messages, and continue as usual, which at least gives the user an idea of
		1573	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1574	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1575	usage.
		1576
		1577	If your program is single-threaded, then you could also keep a dummy file
		1578	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1579	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1580	close that fd, and create a new dummy fd. This will gracefully refuse
		1581	clients under typical overload conditions.
		1582
		1583	The last way to handle it is to simply log the error and C<exit>, as
		1584	is often done with C<malloc> failures, but this results in an easy
		1585	opportunity for a DoS attack.
1165		1586
1166	=head3 Watcher-Specific Functions	1587	=head3 Watcher-Specific Functions
1167		1588
1168	=over 4	1589	=over 4
1169		1590
1170	=item ev_io_init (ev_io *, callback, int fd, int events)	1591	=item ev_io_init (ev_io *, callback, int fd, int events)
1171		1592
1172	=item ev_io_set (ev_io *, int fd, int events)	1593	=item ev_io_set (ev_io *, int fd, int events)
1173		1594
1174	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1595	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1175	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1596	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1176	C<EV_READ | EV_WRITE> to receive the given events.	1597	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1177		1598
1178	=item int fd [read-only]	1599	=item int fd [read-only]
1179		1600
1180	The file descriptor being watched.	1601	The file descriptor being watched.
1181		1602
…		…
1190	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1611	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1191	readable, but only once. Since it is likely line-buffered, you could	1612	readable, but only once. Since it is likely line-buffered, you could
1192	attempt to read a whole line in the callback.	1613	attempt to read a whole line in the callback.
1193		1614
1194	static void	1615	static void
1195	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1616	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1196	{	1617	{
1197	ev_io_stop (loop, w);	1618	ev_io_stop (loop, w);
1198	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1619	.. read from stdin here (or from w->fd) and handle any I/O errors
1199	}	1620	}
1200		1621
1201	...	1622	...
1202	struct ev_loop *loop = ev_default_init (0);	1623	struct ev_loop *loop = ev_default_init (0);
1203	struct ev_io stdin_readable;	1624	ev_io stdin_readable;
1204	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1625	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1205	ev_io_start (loop, &stdin_readable);	1626	ev_io_start (loop, &stdin_readable);
1206	ev_loop (loop, 0);	1627	ev_loop (loop, 0);
1207		1628
1208		1629
…		…
1211	Timer watchers are simple relative timers that generate an event after a	1632	Timer watchers are simple relative timers that generate an event after a
1212	given time, and optionally repeating in regular intervals after that.	1633	given time, and optionally repeating in regular intervals after that.
1213		1634
1214	The timers are based on real time, that is, if you register an event that	1635	The timers are based on real time, that is, if you register an event that
1215	times out after an hour and you reset your system clock to January last	1636	times out after an hour and you reset your system clock to January last
1216	year, it will still time out after (roughly) and hour. "Roughly" because	1637	year, it will still time out after (roughly) one hour. "Roughly" because
1217	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1638	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1218	monotonic clock option helps a lot here).	1639	monotonic clock option helps a lot here).
1219		1640
1220	The callback is guaranteed to be invoked only after its timeout has passed,	1641	The callback is guaranteed to be invoked only I<after> its timeout has
1221	but if multiple timers become ready during the same loop iteration then	1642	passed (not I<at>, so on systems with very low-resolution clocks this
1222	order of execution is undefined.	1643	might introduce a small delay). If multiple timers become ready during the
		1644	same loop iteration then the ones with earlier time-out values are invoked
		1645	before ones of the same priority with later time-out values (but this is
		1646	no longer true when a callback calls C<ev_loop> recursively).
		1647
		1648	=head3 Be smart about timeouts
		1649
		1650	Many real-world problems involve some kind of timeout, usually for error
		1651	recovery. A typical example is an HTTP request - if the other side hangs,
		1652	you want to raise some error after a while.
		1653
		1654	What follows are some ways to handle this problem, from obvious and
		1655	inefficient to smart and efficient.
		1656
		1657	In the following, a 60 second activity timeout is assumed - a timeout that
		1658	gets reset to 60 seconds each time there is activity (e.g. each time some
		1659	data or other life sign was received).
		1660
		1661	=over 4
		1662
		1663	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1664
		1665	This is the most obvious, but not the most simple way: In the beginning,
		1666	start the watcher:
		1667
		1668	ev_timer_init (timer, callback, 60., 0.);
		1669	ev_timer_start (loop, timer);
		1670
		1671	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1672	and start it again:
		1673
		1674	ev_timer_stop (loop, timer);
		1675	ev_timer_set (timer, 60., 0.);
		1676	ev_timer_start (loop, timer);
		1677
		1678	This is relatively simple to implement, but means that each time there is
		1679	some activity, libev will first have to remove the timer from its internal
		1680	data structure and then add it again. Libev tries to be fast, but it's
		1681	still not a constant-time operation.
		1682
		1683	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1684
		1685	This is the easiest way, and involves using C<ev_timer_again> instead of
		1686	C<ev_timer_start>.
		1687
		1688	To implement this, configure an C<ev_timer> with a C<repeat> value
		1689	of C<60> and then call C<ev_timer_again> at start and each time you
		1690	successfully read or write some data. If you go into an idle state where
		1691	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1692	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1693
		1694	That means you can ignore both the C<ev_timer_start> function and the
		1695	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1696	member and C<ev_timer_again>.
		1697
		1698	At start:
		1699
		1700	ev_init (timer, callback);
		1701	timer->repeat = 60.;
		1702	ev_timer_again (loop, timer);
		1703
		1704	Each time there is some activity:
		1705
		1706	ev_timer_again (loop, timer);
		1707
		1708	It is even possible to change the time-out on the fly, regardless of
		1709	whether the watcher is active or not:
		1710
		1711	timer->repeat = 30.;
		1712	ev_timer_again (loop, timer);
		1713
		1714	This is slightly more efficient then stopping/starting the timer each time
		1715	you want to modify its timeout value, as libev does not have to completely
		1716	remove and re-insert the timer from/into its internal data structure.
		1717
		1718	It is, however, even simpler than the "obvious" way to do it.
		1719
		1720	=item 3. Let the timer time out, but then re-arm it as required.
		1721
		1722	This method is more tricky, but usually most efficient: Most timeouts are
		1723	relatively long compared to the intervals between other activity - in
		1724	our example, within 60 seconds, there are usually many I/O events with
		1725	associated activity resets.
		1726
		1727	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1728	but remember the time of last activity, and check for a real timeout only
		1729	within the callback:
		1730
		1731	ev_tstamp last_activity; // time of last activity
		1732
		1733	static void
		1734	callback (EV_P_ ev_timer *w, int revents)
		1735	{
		1736	ev_tstamp now = ev_now (EV_A);
		1737	ev_tstamp timeout = last_activity + 60.;
		1738
		1739	// if last_activity + 60. is older than now, we did time out
		1740	if (timeout < now)
		1741	{
		1742	// timeout occurred, take action
		1743	}
		1744	else
		1745	{
		1746	// callback was invoked, but there was some activity, re-arm
		1747	// the watcher to fire in last_activity + 60, which is
		1748	// guaranteed to be in the future, so "again" is positive:
		1749	w->repeat = timeout - now;
		1750	ev_timer_again (EV_A_ w);
		1751	}
		1752	}
		1753
		1754	To summarise the callback: first calculate the real timeout (defined
		1755	as "60 seconds after the last activity"), then check if that time has
		1756	been reached, which means something I<did>, in fact, time out. Otherwise
		1757	the callback was invoked too early (C<timeout> is in the future), so
		1758	re-schedule the timer to fire at that future time, to see if maybe we have
		1759	a timeout then.
		1760
		1761	Note how C<ev_timer_again> is used, taking advantage of the
		1762	C<ev_timer_again> optimisation when the timer is already running.
		1763
		1764	This scheme causes more callback invocations (about one every 60 seconds
		1765	minus half the average time between activity), but virtually no calls to
		1766	libev to change the timeout.
		1767
		1768	To start the timer, simply initialise the watcher and set C<last_activity>
		1769	to the current time (meaning we just have some activity :), then call the
		1770	callback, which will "do the right thing" and start the timer:
		1771
		1772	ev_init (timer, callback);
		1773	last_activity = ev_now (loop);
		1774	callback (loop, timer, EV_TIMER);
		1775
		1776	And when there is some activity, simply store the current time in
		1777	C<last_activity>, no libev calls at all:
		1778
		1779	last_activity = ev_now (loop);
		1780
		1781	This technique is slightly more complex, but in most cases where the
		1782	time-out is unlikely to be triggered, much more efficient.
		1783
		1784	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1785	callback :) - just change the timeout and invoke the callback, which will
		1786	fix things for you.
		1787
		1788	=item 4. Wee, just use a double-linked list for your timeouts.
		1789
		1790	If there is not one request, but many thousands (millions...), all
		1791	employing some kind of timeout with the same timeout value, then one can
		1792	do even better:
		1793
		1794	When starting the timeout, calculate the timeout value and put the timeout
		1795	at the I<end> of the list.
		1796
		1797	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1798	the list is expected to fire (for example, using the technique #3).
		1799
		1800	When there is some activity, remove the timer from the list, recalculate
		1801	the timeout, append it to the end of the list again, and make sure to
		1802	update the C<ev_timer> if it was taken from the beginning of the list.
		1803
		1804	This way, one can manage an unlimited number of timeouts in O(1) time for
		1805	starting, stopping and updating the timers, at the expense of a major
		1806	complication, and having to use a constant timeout. The constant timeout
		1807	ensures that the list stays sorted.
		1808
		1809	=back
		1810
		1811	So which method the best?
		1812
		1813	Method #2 is a simple no-brain-required solution that is adequate in most
		1814	situations. Method #3 requires a bit more thinking, but handles many cases
		1815	better, and isn't very complicated either. In most case, choosing either
		1816	one is fine, with #3 being better in typical situations.
		1817
		1818	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1819	rather complicated, but extremely efficient, something that really pays
		1820	off after the first million or so of active timers, i.e. it's usually
		1821	overkill :)
1223		1822
1224	=head3 The special problem of time updates	1823	=head3 The special problem of time updates
1225		1824
1226	Establishing the current time is a costly operation (it usually takes at	1825	Establishing the current time is a costly operation (it usually takes at
1227	least two system calls): EV therefore updates its idea of the current	1826	least two system calls): EV therefore updates its idea of the current
1228	time only before and after C<ev_loop> polls for new events, which causes	1827	time only before and after C<ev_loop> collects new events, which causes a
1229	a growing difference between C<ev_now ()> and C<ev_time ()> when handling	1828	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1230	lots of events.	1829	lots of events in one iteration.
1231		1830
1232	The relative timeouts are calculated relative to the C<ev_now ()>	1831	The relative timeouts are calculated relative to the C<ev_now ()>
1233	time. This is usually the right thing as this timestamp refers to the time	1832	time. This is usually the right thing as this timestamp refers to the time
1234	of the event triggering whatever timeout you are modifying/starting. If	1833	of the event triggering whatever timeout you are modifying/starting. If
1235	you suspect event processing to be delayed and you I<need> to base the	1834	you suspect event processing to be delayed and you I<need> to base the
…		…
1239		1838
1240	If the event loop is suspended for a long time, you can also force an	1839	If the event loop is suspended for a long time, you can also force an
1241	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1840	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1242	()>.	1841	()>.
1243		1842
		1843	=head3 The special problems of suspended animation
		1844
		1845	When you leave the server world it is quite customary to hit machines that
		1846	can suspend/hibernate - what happens to the clocks during such a suspend?
		1847
		1848	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1849	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1850	to run until the system is suspended, but they will not advance while the
		1851	system is suspended. That means, on resume, it will be as if the program
		1852	was frozen for a few seconds, but the suspend time will not be counted
		1853	towards C<ev_timer> when a monotonic clock source is used. The real time
		1854	clock advanced as expected, but if it is used as sole clocksource, then a
		1855	long suspend would be detected as a time jump by libev, and timers would
		1856	be adjusted accordingly.
		1857
		1858	I would not be surprised to see different behaviour in different between
		1859	operating systems, OS versions or even different hardware.
		1860
		1861	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1862	time jump in the monotonic clocks and the realtime clock. If the program
		1863	is suspended for a very long time, and monotonic clock sources are in use,
		1864	then you can expect C<ev_timer>s to expire as the full suspension time
		1865	will be counted towards the timers. When no monotonic clock source is in
		1866	use, then libev will again assume a timejump and adjust accordingly.
		1867
		1868	It might be beneficial for this latter case to call C<ev_suspend>
		1869	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1870	deterministic behaviour in this case (you can do nothing against
		1871	C<SIGSTOP>).
		1872
1244	=head3 Watcher-Specific Functions and Data Members	1873	=head3 Watcher-Specific Functions and Data Members
1245		1874
1246	=over 4	1875	=over 4
1247		1876
1248	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1877	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1271	If the timer is started but non-repeating, stop it (as if it timed out).	1900	If the timer is started but non-repeating, stop it (as if it timed out).
1272		1901
1273	If the timer is repeating, either start it if necessary (with the	1902	If the timer is repeating, either start it if necessary (with the
1274	C<repeat> value), or reset the running timer to the C<repeat> value.	1903	C<repeat> value), or reset the running timer to the C<repeat> value.
1275		1904
1276	This sounds a bit complicated, but here is a useful and typical	1905	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1277	example: Imagine you have a TCP connection and you want a so-called idle	1906	usage example.
1278	timeout, that is, you want to be called when there have been, say, 60
1279	seconds of inactivity on the socket. The easiest way to do this is to
1280	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1281	C<ev_timer_again> each time you successfully read or write some data. If
1282	you go into an idle state where you do not expect data to travel on the
1283	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1284	automatically restart it if need be.
1285		1907
1286	That means you can ignore the C<after> value and C<ev_timer_start>	1908	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1287	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1288		1909
1289	ev_timer_init (timer, callback, 0., 5.);	1910	Returns the remaining time until a timer fires. If the timer is active,
1290	ev_timer_again (loop, timer);	1911	then this time is relative to the current event loop time, otherwise it's
1291	...	1912	the timeout value currently configured.
1292	timer->again = 17.;
1293	ev_timer_again (loop, timer);
1294	...
1295	timer->again = 10.;
1296	ev_timer_again (loop, timer);
1297		1913
1298	This is more slightly efficient then stopping/starting the timer each time	1914	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1299	you want to modify its timeout value.	1915	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1916	will return C<4>. When the timer expires and is restarted, it will return
		1917	roughly C<7> (likely slightly less as callback invocation takes some time,
		1918	too), and so on.
1300		1919
1301	=item ev_tstamp repeat [read-write]	1920	=item ev_tstamp repeat [read-write]
1302		1921
1303	The current C<repeat> value. Will be used each time the watcher times out	1922	The current C<repeat> value. Will be used each time the watcher times out
1304	or C<ev_timer_again> is called and determines the next timeout (if any),	1923	or C<ev_timer_again> is called, and determines the next timeout (if any),
1305	which is also when any modifications are taken into account.	1924	which is also when any modifications are taken into account.
1306		1925
1307	=back	1926	=back
1308		1927
1309	=head3 Examples	1928	=head3 Examples
1310		1929
1311	Example: Create a timer that fires after 60 seconds.	1930	Example: Create a timer that fires after 60 seconds.
1312		1931
1313	static void	1932	static void
1314	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1933	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1315	{	1934	{
1316	.. one minute over, w is actually stopped right here	1935	.. one minute over, w is actually stopped right here
1317	}	1936	}
1318		1937
1319	struct ev_timer mytimer;	1938	ev_timer mytimer;
1320	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1939	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1321	ev_timer_start (loop, &mytimer);	1940	ev_timer_start (loop, &mytimer);
1322		1941
1323	Example: Create a timeout timer that times out after 10 seconds of	1942	Example: Create a timeout timer that times out after 10 seconds of
1324	inactivity.	1943	inactivity.
1325		1944
1326	static void	1945	static void
1327	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1946	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1328	{	1947	{
1329	.. ten seconds without any activity	1948	.. ten seconds without any activity
1330	}	1949	}
1331		1950
1332	struct ev_timer mytimer;	1951	ev_timer mytimer;
1333	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1952	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1334	ev_timer_again (&mytimer); /* start timer */	1953	ev_timer_again (&mytimer); /* start timer */
1335	ev_loop (loop, 0);	1954	ev_loop (loop, 0);
1336		1955
1337	// and in some piece of code that gets executed on any "activity":	1956	// and in some piece of code that gets executed on any "activity":
…		…
1342	=head2 C<ev_periodic> - to cron or not to cron?	1961	=head2 C<ev_periodic> - to cron or not to cron?
1343		1962
1344	Periodic watchers are also timers of a kind, but they are very versatile	1963	Periodic watchers are also timers of a kind, but they are very versatile
1345	(and unfortunately a bit complex).	1964	(and unfortunately a bit complex).
1346		1965
1347	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1966	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1348	but on wall clock time (absolute time). You can tell a periodic watcher	1967	relative time, the physical time that passes) but on wall clock time
1349	to trigger after some specific point in time. For example, if you tell a	1968	(absolute time, the thing you can read on your calender or clock). The
1350	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1969	difference is that wall clock time can run faster or slower than real
1351	+ 10.>, that is, an absolute time not a delay) and then reset your system	1970	time, and time jumps are not uncommon (e.g. when you adjust your
1352	clock to January of the previous year, then it will take more than year	1971	wrist-watch).
1353	to trigger the event (unlike an C<ev_timer>, which would still trigger
1354	roughly 10 seconds later as it uses a relative timeout).
1355		1972
		1973	You can tell a periodic watcher to trigger after some specific point
		1974	in time: for example, if you tell a periodic watcher to trigger "in 10
		1975	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1976	not a delay) and then reset your system clock to January of the previous
		1977	year, then it will take a year or more to trigger the event (unlike an
		1978	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1979	it, as it uses a relative timeout).
		1980
1356	C<ev_periodic>s can also be used to implement vastly more complex timers,	1981	C<ev_periodic> watchers can also be used to implement vastly more complex
1357	such as triggering an event on each "midnight, local time", or other	1982	timers, such as triggering an event on each "midnight, local time", or
1358	complicated, rules.	1983	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1984	those cannot react to time jumps.
1359		1985
1360	As with timers, the callback is guaranteed to be invoked only when the	1986	As with timers, the callback is guaranteed to be invoked only when the
1361	time (C<at>) has passed, but if multiple periodic timers become ready	1987	point in time where it is supposed to trigger has passed. If multiple
1362	during the same loop iteration then order of execution is undefined.	1988	timers become ready during the same loop iteration then the ones with
		1989	earlier time-out values are invoked before ones with later time-out values
		1990	(but this is no longer true when a callback calls C<ev_loop> recursively).
1363		1991
1364	=head3 Watcher-Specific Functions and Data Members	1992	=head3 Watcher-Specific Functions and Data Members
1365		1993
1366	=over 4	1994	=over 4
1367		1995
1368	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1996	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1369		1997
1370	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1998	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1371		1999
1372	Lots of arguments, lets sort it out... There are basically three modes of	2000	Lots of arguments, let's sort it out... There are basically three modes of
1373	operation, and we will explain them from simplest to complex:	2001	operation, and we will explain them from simplest to most complex:
1374		2002
1375	=over 4	2003	=over 4
1376		2004
1377	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2005	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1378		2006
1379	In this configuration the watcher triggers an event after the wall clock	2007	In this configuration the watcher triggers an event after the wall clock
1380	time C<at> has passed and doesn't repeat. It will not adjust when a time	2008	time C<offset> has passed. It will not repeat and will not adjust when a
1381	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2009	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1382	run when the system time reaches or surpasses this time.	2010	will be stopped and invoked when the system clock reaches or surpasses
		2011	this point in time.
1383		2012
1384	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2013	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1385		2014
1386	In this mode the watcher will always be scheduled to time out at the next	2015	In this mode the watcher will always be scheduled to time out at the next
1387	C<at + N * interval> time (for some integer N, which can also be negative)	2016	C<offset + N * interval> time (for some integer N, which can also be
1388	and then repeat, regardless of any time jumps.	2017	negative) and then repeat, regardless of any time jumps. The C<offset>
		2018	argument is merely an offset into the C<interval> periods.
1389		2019
1390	This can be used to create timers that do not drift with respect to system	2020	This can be used to create timers that do not drift with respect to the
1391	time, for example, here is a C<ev_periodic> that triggers each hour, on	2021	system clock, for example, here is an C<ev_periodic> that triggers each
1392	the hour:	2022	hour, on the hour (with respect to UTC):
1393		2023
1394	ev_periodic_set (&periodic, 0., 3600., 0);	2024	ev_periodic_set (&periodic, 0., 3600., 0);
1395		2025
1396	This doesn't mean there will always be 3600 seconds in between triggers,	2026	This doesn't mean there will always be 3600 seconds in between triggers,
1397	but only that the callback will be called when the system time shows a	2027	but only that the callback will be called when the system time shows a
1398	full hour (UTC), or more correctly, when the system time is evenly divisible	2028	full hour (UTC), or more correctly, when the system time is evenly divisible
1399	by 3600.	2029	by 3600.
1400		2030
1401	Another way to think about it (for the mathematically inclined) is that	2031	Another way to think about it (for the mathematically inclined) is that
1402	C<ev_periodic> will try to run the callback in this mode at the next possible	2032	C<ev_periodic> will try to run the callback in this mode at the next possible
1403	time where C<time = at (mod interval)>, regardless of any time jumps.	2033	time where C<time = offset (mod interval)>, regardless of any time jumps.
1404		2034
1405	For numerical stability it is preferable that the C<at> value is near	2035	For numerical stability it is preferable that the C<offset> value is near
1406	C<ev_now ()> (the current time), but there is no range requirement for	2036	C<ev_now ()> (the current time), but there is no range requirement for
1407	this value, and in fact is often specified as zero.	2037	this value, and in fact is often specified as zero.
1408		2038
1409	Note also that there is an upper limit to how often a timer can fire (CPU	2039	Note also that there is an upper limit to how often a timer can fire (CPU
1410	speed for example), so if C<interval> is very small then timing stability	2040	speed for example), so if C<interval> is very small then timing stability
1411	will of course deteriorate. Libev itself tries to be exact to be about one	2041	will of course deteriorate. Libev itself tries to be exact to be about one
1412	millisecond (if the OS supports it and the machine is fast enough).	2042	millisecond (if the OS supports it and the machine is fast enough).
1413		2043
1414	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2044	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1415		2045
1416	In this mode the values for C<interval> and C<at> are both being	2046	In this mode the values for C<interval> and C<offset> are both being
1417	ignored. Instead, each time the periodic watcher gets scheduled, the	2047	ignored. Instead, each time the periodic watcher gets scheduled, the
1418	reschedule callback will be called with the watcher as first, and the	2048	reschedule callback will be called with the watcher as first, and the
1419	current time as second argument.	2049	current time as second argument.
1420		2050
1421	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2051	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1422	ever, or make ANY event loop modifications whatsoever>.	2052	or make ANY other event loop modifications whatsoever, unless explicitly
		2053	allowed by documentation here>.
1423		2054
1424	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2055	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1425	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2056	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1426	only event loop modification you are allowed to do).	2057	only event loop modification you are allowed to do).
1427		2058
1428	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2059	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1429	*w, ev_tstamp now)>, e.g.:	2060	*w, ev_tstamp now)>, e.g.:
1430		2061
		2062	static ev_tstamp
1431	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2063	my_rescheduler (ev_periodic *w, ev_tstamp now)
1432	{	2064	{
1433	return now + 60.;	2065	return now + 60.;
1434	}	2066	}
1435		2067
1436	It must return the next time to trigger, based on the passed time value	2068	It must return the next time to trigger, based on the passed time value
…		…
1456	a different time than the last time it was called (e.g. in a crond like	2088	a different time than the last time it was called (e.g. in a crond like
1457	program when the crontabs have changed).	2089	program when the crontabs have changed).
1458		2090
1459	=item ev_tstamp ev_periodic_at (ev_periodic *)	2091	=item ev_tstamp ev_periodic_at (ev_periodic *)
1460		2092
1461	When active, returns the absolute time that the watcher is supposed to	2093	When active, returns the absolute time that the watcher is supposed
1462	trigger next.	2094	to trigger next. This is not the same as the C<offset> argument to
		2095	C<ev_periodic_set>, but indeed works even in interval and manual
		2096	rescheduling modes.
1463		2097
1464	=item ev_tstamp offset [read-write]	2098	=item ev_tstamp offset [read-write]
1465		2099
1466	When repeating, this contains the offset value, otherwise this is the	2100	When repeating, this contains the offset value, otherwise this is the
1467	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2101	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2102	although libev might modify this value for better numerical stability).
1468		2103
1469	Can be modified any time, but changes only take effect when the periodic	2104	Can be modified any time, but changes only take effect when the periodic
1470	timer fires or C<ev_periodic_again> is being called.	2105	timer fires or C<ev_periodic_again> is being called.
1471		2106
1472	=item ev_tstamp interval [read-write]	2107	=item ev_tstamp interval [read-write]
1473		2108
1474	The current interval value. Can be modified any time, but changes only	2109	The current interval value. Can be modified any time, but changes only
1475	take effect when the periodic timer fires or C<ev_periodic_again> is being	2110	take effect when the periodic timer fires or C<ev_periodic_again> is being
1476	called.	2111	called.
1477		2112
1478	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2113	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1479		2114
1480	The current reschedule callback, or C<0>, if this functionality is	2115	The current reschedule callback, or C<0>, if this functionality is
1481	switched off. Can be changed any time, but changes only take effect when	2116	switched off. Can be changed any time, but changes only take effect when
1482	the periodic timer fires or C<ev_periodic_again> is being called.	2117	the periodic timer fires or C<ev_periodic_again> is being called.
1483		2118
1484	=back	2119	=back
1485		2120
1486	=head3 Examples	2121	=head3 Examples
1487		2122
1488	Example: Call a callback every hour, or, more precisely, whenever the	2123	Example: Call a callback every hour, or, more precisely, whenever the
1489	system clock is divisible by 3600. The callback invocation times have	2124	system time is divisible by 3600. The callback invocation times have
1490	potentially a lot of jitter, but good long-term stability.	2125	potentially a lot of jitter, but good long-term stability.
1491		2126
1492	static void	2127	static void
1493	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2128	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1494	{	2129	{
1495	... its now a full hour (UTC, or TAI or whatever your clock follows)	2130	... its now a full hour (UTC, or TAI or whatever your clock follows)
1496	}	2131	}
1497		2132
1498	struct ev_periodic hourly_tick;	2133	ev_periodic hourly_tick;
1499	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2134	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1500	ev_periodic_start (loop, &hourly_tick);	2135	ev_periodic_start (loop, &hourly_tick);
1501		2136
1502	Example: The same as above, but use a reschedule callback to do it:	2137	Example: The same as above, but use a reschedule callback to do it:
1503		2138
1504	#include <math.h>	2139	#include <math.h>
1505		2140
1506	static ev_tstamp	2141	static ev_tstamp
1507	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2142	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1508	{	2143	{
1509	return fmod (now, 3600.) + 3600.;	2144	return now + (3600. - fmod (now, 3600.));
1510	}	2145	}
1511		2146
1512	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2147	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1513		2148
1514	Example: Call a callback every hour, starting now:	2149	Example: Call a callback every hour, starting now:
1515		2150
1516	struct ev_periodic hourly_tick;	2151	ev_periodic hourly_tick;
1517	ev_periodic_init (&hourly_tick, clock_cb,	2152	ev_periodic_init (&hourly_tick, clock_cb,
1518	fmod (ev_now (loop), 3600.), 3600., 0);	2153	fmod (ev_now (loop), 3600.), 3600., 0);
1519	ev_periodic_start (loop, &hourly_tick);	2154	ev_periodic_start (loop, &hourly_tick);
1520		2155
1521		2156
…		…
1524	Signal watchers will trigger an event when the process receives a specific	2159	Signal watchers will trigger an event when the process receives a specific
1525	signal one or more times. Even though signals are very asynchronous, libev	2160	signal one or more times. Even though signals are very asynchronous, libev
1526	will try it's best to deliver signals synchronously, i.e. as part of the	2161	will try it's best to deliver signals synchronously, i.e. as part of the
1527	normal event processing, like any other event.	2162	normal event processing, like any other event.
1528		2163
		2164	If you want signals to be delivered truly asynchronously, just use
		2165	C<sigaction> as you would do without libev and forget about sharing
		2166	the signal. You can even use C<ev_async> from a signal handler to
		2167	synchronously wake up an event loop.
		2168
1529	You can configure as many watchers as you like per signal. Only when the	2169	You can configure as many watchers as you like for the same signal, but
		2170	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2171	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2172	C<SIGINT> in both the default loop and another loop at the same time. At
		2173	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2174
1530	first watcher gets started will libev actually register a signal watcher	2175	When the first watcher gets started will libev actually register something
1531	with the kernel (thus it coexists with your own signal handlers as long	2176	with the kernel (thus it coexists with your own signal handlers as long as
1532	as you don't register any with libev). Similarly, when the last signal	2177	you don't register any with libev for the same signal).
1533	watcher for a signal is stopped libev will reset the signal handler to
1534	SIG_DFL (regardless of what it was set to before).
1535		2178
1536	If possible and supported, libev will install its handlers with	2179	If possible and supported, libev will install its handlers with
1537	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2180	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1538	interrupted. If you have a problem with system calls getting interrupted by	2181	not be unduly interrupted. If you have a problem with system calls getting
1539	signals you can block all signals in an C<ev_check> watcher and unblock	2182	interrupted by signals you can block all signals in an C<ev_check> watcher
1540	them in an C<ev_prepare> watcher.	2183	and unblock them in an C<ev_prepare> watcher.
		2184
		2185	=head3 The special problem of inheritance over fork/execve/pthread_create
		2186
		2187	Both the signal mask (C<sigprocmask>) and the signal disposition
		2188	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2189	stopping it again), that is, libev might or might not block the signal,
		2190	and might or might not set or restore the installed signal handler.
		2191
		2192	While this does not matter for the signal disposition (libev never
		2193	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2194	C<execve>), this matters for the signal mask: many programs do not expect
		2195	certain signals to be blocked.
		2196
		2197	This means that before calling C<exec> (from the child) you should reset
		2198	the signal mask to whatever "default" you expect (all clear is a good
		2199	choice usually).
		2200
		2201	The simplest way to ensure that the signal mask is reset in the child is
		2202	to install a fork handler with C<pthread_atfork> that resets it. That will
		2203	catch fork calls done by libraries (such as the libc) as well.
		2204
		2205	In current versions of libev, the signal will not be blocked indefinitely
		2206	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2207	the window of opportunity for problems, it will not go away, as libev
		2208	I<has> to modify the signal mask, at least temporarily.
		2209
		2210	So I can't stress this enough: I<If you do not reset your signal mask when
		2211	you expect it to be empty, you have a race condition in your code>. This
		2212	is not a libev-specific thing, this is true for most event libraries.
1541		2213
1542	=head3 Watcher-Specific Functions and Data Members	2214	=head3 Watcher-Specific Functions and Data Members
1543		2215
1544	=over 4	2216	=over 4
1545		2217
…		…
1556		2228
1557	=back	2229	=back
1558		2230
1559	=head3 Examples	2231	=head3 Examples
1560		2232
1561	Example: Try to exit cleanly on SIGINT and SIGTERM.	2233	Example: Try to exit cleanly on SIGINT.
1562		2234
1563	static void	2235	static void
1564	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2236	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1565	{	2237	{
1566	ev_unloop (loop, EVUNLOOP_ALL);	2238	ev_unloop (loop, EVUNLOOP_ALL);
1567	}	2239	}
1568		2240
1569	struct ev_signal signal_watcher;	2241	ev_signal signal_watcher;
1570	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2242	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1571	ev_signal_start (loop, &sigint_cb);	2243	ev_signal_start (loop, &signal_watcher);
1572		2244
1573		2245
1574	=head2 C<ev_child> - watch out for process status changes	2246	=head2 C<ev_child> - watch out for process status changes
1575		2247
1576	Child watchers trigger when your process receives a SIGCHLD in response to	2248	Child watchers trigger when your process receives a SIGCHLD in response to
1577	some child status changes (most typically when a child of yours dies). It	2249	some child status changes (most typically when a child of yours dies or
1578	is permissible to install a child watcher I<after> the child has been	2250	exits). It is permissible to install a child watcher I<after> the child
1579	forked (which implies it might have already exited), as long as the event	2251	has been forked (which implies it might have already exited), as long
1580	loop isn't entered (or is continued from a watcher).	2252	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2253	forking and then immediately registering a watcher for the child is fine,
		2254	but forking and registering a watcher a few event loop iterations later or
		2255	in the next callback invocation is not.
1581		2256
1582	Only the default event loop is capable of handling signals, and therefore	2257	Only the default event loop is capable of handling signals, and therefore
1583	you can only register child watchers in the default event loop.	2258	you can only register child watchers in the default event loop.
1584		2259
		2260	Due to some design glitches inside libev, child watchers will always be
		2261	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2262	libev)
		2263
1585	=head3 Process Interaction	2264	=head3 Process Interaction
1586		2265
1587	Libev grabs C<SIGCHLD> as soon as the default event loop is	2266	Libev grabs C<SIGCHLD> as soon as the default event loop is
1588	initialised. This is necessary to guarantee proper behaviour even if	2267	initialised. This is necessary to guarantee proper behaviour even if the
1589	the first child watcher is started after the child exits. The occurrence	2268	first child watcher is started after the child exits. The occurrence
1590	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2269	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1591	synchronously as part of the event loop processing. Libev always reaps all	2270	synchronously as part of the event loop processing. Libev always reaps all
1592	children, even ones not watched.	2271	children, even ones not watched.
1593		2272
1594	=head3 Overriding the Built-In Processing	2273	=head3 Overriding the Built-In Processing
…		…
1604	=head3 Stopping the Child Watcher	2283	=head3 Stopping the Child Watcher
1605		2284
1606	Currently, the child watcher never gets stopped, even when the	2285	Currently, the child watcher never gets stopped, even when the
1607	child terminates, so normally one needs to stop the watcher in the	2286	child terminates, so normally one needs to stop the watcher in the
1608	callback. Future versions of libev might stop the watcher automatically	2287	callback. Future versions of libev might stop the watcher automatically
1609	when a child exit is detected.	2288	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2289	problem).
1610		2290
1611	=head3 Watcher-Specific Functions and Data Members	2291	=head3 Watcher-Specific Functions and Data Members
1612		2292
1613	=over 4	2293	=over 4
1614		2294
…		…
1646	its completion.	2326	its completion.
1647		2327
1648	ev_child cw;	2328	ev_child cw;
1649		2329
1650	static void	2330	static void
1651	child_cb (EV_P_ struct ev_child *w, int revents)	2331	child_cb (EV_P_ ev_child *w, int revents)
1652	{	2332	{
1653	ev_child_stop (EV_A_ w);	2333	ev_child_stop (EV_A_ w);
1654	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2334	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1655	}	2335	}
1656		2336
…		…
1671		2351
1672		2352
1673	=head2 C<ev_stat> - did the file attributes just change?	2353	=head2 C<ev_stat> - did the file attributes just change?
1674		2354
1675	This watches a file system path for attribute changes. That is, it calls	2355	This watches a file system path for attribute changes. That is, it calls
1676	C<stat> regularly (or when the OS says it changed) and sees if it changed	2356	C<stat> on that path in regular intervals (or when the OS says it changed)
1677	compared to the last time, invoking the callback if it did.	2357	and sees if it changed compared to the last time, invoking the callback if
		2358	it did.
1678		2359
1679	The path does not need to exist: changing from "path exists" to "path does	2360	The path does not need to exist: changing from "path exists" to "path does
1680	not exist" is a status change like any other. The condition "path does	2361	not exist" is a status change like any other. The condition "path does not
1681	not exist" is signified by the C<st_nlink> field being zero (which is	2362	exist" (or more correctly "path cannot be stat'ed") is signified by the
1682	otherwise always forced to be at least one) and all the other fields of	2363	C<st_nlink> field being zero (which is otherwise always forced to be at
1683	the stat buffer having unspecified contents.	2364	least one) and all the other fields of the stat buffer having unspecified
		2365	contents.
1684		2366
1685	The path I<should> be absolute and I<must not> end in a slash. If it is	2367	The path I<must not> end in a slash or contain special components such as
		2368	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1686	relative and your working directory changes, the behaviour is undefined.	2369	your working directory changes, then the behaviour is undefined.
1687		2370
1688	Since there is no standard to do this, the portable implementation simply	2371	Since there is no portable change notification interface available, the
1689	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2372	portable implementation simply calls C<stat(2)> regularly on the path
1690	can specify a recommended polling interval for this case. If you specify	2373	to see if it changed somehow. You can specify a recommended polling
1691	a polling interval of C<0> (highly recommended!) then a I<suitable,	2374	interval for this case. If you specify a polling interval of C<0> (highly
1692	unspecified default> value will be used (which you can expect to be around	2375	recommended!) then a I<suitable, unspecified default> value will be used
1693	five seconds, although this might change dynamically). Libev will also	2376	(which you can expect to be around five seconds, although this might
1694	impose a minimum interval which is currently around C<0.1>, but thats	2377	change dynamically). Libev will also impose a minimum interval which is
1695	usually overkill.	2378	currently around C<0.1>, but that's usually overkill.
1696		2379
1697	This watcher type is not meant for massive numbers of stat watchers,	2380	This watcher type is not meant for massive numbers of stat watchers,
1698	as even with OS-supported change notifications, this can be	2381	as even with OS-supported change notifications, this can be
1699	resource-intensive.	2382	resource-intensive.
1700		2383
1701	At the time of this writing, only the Linux inotify interface is	2384	At the time of this writing, the only OS-specific interface implemented
1702	implemented (implementing kqueue support is left as an exercise for the	2385	is the Linux inotify interface (implementing kqueue support is left as an
1703	reader, note, however, that the author sees no way of implementing ev_stat	2386	exercise for the reader. Note, however, that the author sees no way of
1704	semantics with kqueue). Inotify will be used to give hints only and should	2387	implementing C<ev_stat> semantics with kqueue, except as a hint).
1705	not change the semantics of C<ev_stat> watchers, which means that libev
1706	sometimes needs to fall back to regular polling again even with inotify,
1707	but changes are usually detected immediately, and if the file exists there
1708	will be no polling.
1709		2388
1710	=head3 ABI Issues (Largefile Support)	2389	=head3 ABI Issues (Largefile Support)
1711		2390
1712	Libev by default (unless the user overrides this) uses the default	2391	Libev by default (unless the user overrides this) uses the default
1713	compilation environment, which means that on systems with large file	2392	compilation environment, which means that on systems with large file
1714	support disabled by default, you get the 32 bit version of the stat	2393	support disabled by default, you get the 32 bit version of the stat
1715	structure. When using the library from programs that change the ABI to	2394	structure. When using the library from programs that change the ABI to
1716	use 64 bit file offsets the programs will fail. In that case you have to	2395	use 64 bit file offsets the programs will fail. In that case you have to
1717	compile libev with the same flags to get binary compatibility. This is	2396	compile libev with the same flags to get binary compatibility. This is
1718	obviously the case with any flags that change the ABI, but the problem is	2397	obviously the case with any flags that change the ABI, but the problem is
1719	most noticeably disabled with ev_stat and large file support.	2398	most noticeably displayed with ev_stat and large file support.
1720		2399
1721	The solution for this is to lobby your distribution maker to make large	2400	The solution for this is to lobby your distribution maker to make large
1722	file interfaces available by default (as e.g. FreeBSD does) and not	2401	file interfaces available by default (as e.g. FreeBSD does) and not
1723	optional. Libev cannot simply switch on large file support because it has	2402	optional. Libev cannot simply switch on large file support because it has
1724	to exchange stat structures with application programs compiled using the	2403	to exchange stat structures with application programs compiled using the
1725	default compilation environment.	2404	default compilation environment.
1726		2405
1727	=head3 Inotify	2406	=head3 Inotify and Kqueue
1728		2407
1729	When C<inotify (7)> support has been compiled into libev (generally only	2408	When C<inotify (7)> support has been compiled into libev and present at
1730	available on Linux) and present at runtime, it will be used to speed up	2409	runtime, it will be used to speed up change detection where possible. The
1731	change detection where possible. The inotify descriptor will be created lazily	2410	inotify descriptor will be created lazily when the first C<ev_stat>
1732	when the first C<ev_stat> watcher is being started.	2411	watcher is being started.
1733		2412
1734	Inotify presence does not change the semantics of C<ev_stat> watchers	2413	Inotify presence does not change the semantics of C<ev_stat> watchers
1735	except that changes might be detected earlier, and in some cases, to avoid	2414	except that changes might be detected earlier, and in some cases, to avoid
1736	making regular C<stat> calls. Even in the presence of inotify support	2415	making regular C<stat> calls. Even in the presence of inotify support
1737	there are many cases where libev has to resort to regular C<stat> polling.	2416	there are many cases where libev has to resort to regular C<stat> polling,
		2417	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2418	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2419	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2420	xfs are fully working) libev usually gets away without polling.
1738		2421
1739	(There is no support for kqueue, as apparently it cannot be used to	2422	There is no support for kqueue, as apparently it cannot be used to
1740	implement this functionality, due to the requirement of having a file	2423	implement this functionality, due to the requirement of having a file
1741	descriptor open on the object at all times).	2424	descriptor open on the object at all times, and detecting renames, unlinks
		2425	etc. is difficult.
		2426
		2427	=head3 C<stat ()> is a synchronous operation
		2428
		2429	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2430	the process. The exception are C<ev_stat> watchers - those call C<stat
		2431	()>, which is a synchronous operation.
		2432
		2433	For local paths, this usually doesn't matter: unless the system is very
		2434	busy or the intervals between stat's are large, a stat call will be fast,
		2435	as the path data is usually in memory already (except when starting the
		2436	watcher).
		2437
		2438	For networked file systems, calling C<stat ()> can block an indefinite
		2439	time due to network issues, and even under good conditions, a stat call
		2440	often takes multiple milliseconds.
		2441
		2442	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2443	paths, although this is fully supported by libev.
1742		2444
1743	=head3 The special problem of stat time resolution	2445	=head3 The special problem of stat time resolution
1744		2446
1745	The C<stat ()> system call only supports full-second resolution portably, and	2447	The C<stat ()> system call only supports full-second resolution portably,
1746	even on systems where the resolution is higher, many file systems still	2448	and even on systems where the resolution is higher, most file systems
1747	only support whole seconds.	2449	still only support whole seconds.
1748		2450
1749	That means that, if the time is the only thing that changes, you can	2451	That means that, if the time is the only thing that changes, you can
1750	easily miss updates: on the first update, C<ev_stat> detects a change and	2452	easily miss updates: on the first update, C<ev_stat> detects a change and
1751	calls your callback, which does something. When there is another update	2453	calls your callback, which does something. When there is another update
1752	within the same second, C<ev_stat> will be unable to detect it as the stat	2454	within the same second, C<ev_stat> will be unable to detect unless the
1753	data does not change.	2455	stat data does change in other ways (e.g. file size).
1754		2456
1755	The solution to this is to delay acting on a change for slightly more	2457	The solution to this is to delay acting on a change for slightly more
1756	than a second (or till slightly after the next full second boundary), using	2458	than a second (or till slightly after the next full second boundary), using
1757	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2459	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1758	ev_timer_again (loop, w)>).	2460	ev_timer_again (loop, w)>).
…		…
1778	C<path>. The C<interval> is a hint on how quickly a change is expected to	2480	C<path>. The C<interval> is a hint on how quickly a change is expected to
1779	be detected and should normally be specified as C<0> to let libev choose	2481	be detected and should normally be specified as C<0> to let libev choose
1780	a suitable value. The memory pointed to by C<path> must point to the same	2482	a suitable value. The memory pointed to by C<path> must point to the same
1781	path for as long as the watcher is active.	2483	path for as long as the watcher is active.
1782		2484
1783	The callback will receive C<EV_STAT> when a change was detected, relative	2485	The callback will receive an C<EV_STAT> event when a change was detected,
1784	to the attributes at the time the watcher was started (or the last change	2486	relative to the attributes at the time the watcher was started (or the
1785	was detected).	2487	last change was detected).
1786		2488
1787	=item ev_stat_stat (loop, ev_stat *)	2489	=item ev_stat_stat (loop, ev_stat *)
1788		2490
1789	Updates the stat buffer immediately with new values. If you change the	2491	Updates the stat buffer immediately with new values. If you change the
1790	watched path in your callback, you could call this function to avoid	2492	watched path in your callback, you could call this function to avoid
…		…
1873		2575
1874		2576
1875	=head2 C<ev_idle> - when you've got nothing better to do...	2577	=head2 C<ev_idle> - when you've got nothing better to do...
1876		2578
1877	Idle watchers trigger events when no other events of the same or higher	2579	Idle watchers trigger events when no other events of the same or higher
1878	priority are pending (prepare, check and other idle watchers do not	2580	priority are pending (prepare, check and other idle watchers do not count
1879	count).	2581	as receiving "events").
1880		2582
1881	That is, as long as your process is busy handling sockets or timeouts	2583	That is, as long as your process is busy handling sockets or timeouts
1882	(or even signals, imagine) of the same or higher priority it will not be	2584	(or even signals, imagine) of the same or higher priority it will not be
1883	triggered. But when your process is idle (or only lower-priority watchers	2585	triggered. But when your process is idle (or only lower-priority watchers
1884	are pending), the idle watchers are being called once per event loop	2586	are pending), the idle watchers are being called once per event loop
…		…
1895		2597
1896	=head3 Watcher-Specific Functions and Data Members	2598	=head3 Watcher-Specific Functions and Data Members
1897		2599
1898	=over 4	2600	=over 4
1899		2601
1900	=item ev_idle_init (ev_signal *, callback)	2602	=item ev_idle_init (ev_idle *, callback)
1901		2603
1902	Initialises and configures the idle watcher - it has no parameters of any	2604	Initialises and configures the idle watcher - it has no parameters of any
1903	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2605	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1904	believe me.	2606	believe me.
1905		2607
…		…
1909		2611
1910	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2612	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1911	callback, free it. Also, use no error checking, as usual.	2613	callback, free it. Also, use no error checking, as usual.
1912		2614
1913	static void	2615	static void
1914	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2616	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1915	{	2617	{
1916	free (w);	2618	free (w);
1917	// now do something you wanted to do when the program has	2619	// now do something you wanted to do when the program has
1918	// no longer anything immediate to do.	2620	// no longer anything immediate to do.
1919	}	2621	}
1920		2622
1921	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2623	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1922	ev_idle_init (idle_watcher, idle_cb);	2624	ev_idle_init (idle_watcher, idle_cb);
1923	ev_idle_start (loop, idle_cb);	2625	ev_idle_start (loop, idle_watcher);
1924		2626
1925		2627
1926	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2628	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1927		2629
1928	Prepare and check watchers are usually (but not always) used in tandem:	2630	Prepare and check watchers are usually (but not always) used in pairs:
1929	prepare watchers get invoked before the process blocks and check watchers	2631	prepare watchers get invoked before the process blocks and check watchers
1930	afterwards.	2632	afterwards.
1931		2633
1932	You I<must not> call C<ev_loop> or similar functions that enter	2634	You I<must not> call C<ev_loop> or similar functions that enter
1933	the current event loop from either C<ev_prepare> or C<ev_check>	2635	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1936	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2638	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1937	C<ev_check> so if you have one watcher of each kind they will always be	2639	C<ev_check> so if you have one watcher of each kind they will always be
1938	called in pairs bracketing the blocking call.	2640	called in pairs bracketing the blocking call.
1939		2641
1940	Their main purpose is to integrate other event mechanisms into libev and	2642	Their main purpose is to integrate other event mechanisms into libev and
1941	their use is somewhat advanced. This could be used, for example, to track	2643	their use is somewhat advanced. They could be used, for example, to track
1942	variable changes, implement your own watchers, integrate net-snmp or a	2644	variable changes, implement your own watchers, integrate net-snmp or a
1943	coroutine library and lots more. They are also occasionally useful if	2645	coroutine library and lots more. They are also occasionally useful if
1944	you cache some data and want to flush it before blocking (for example,	2646	you cache some data and want to flush it before blocking (for example,
1945	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2647	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1946	watcher).	2648	watcher).
1947		2649
1948	This is done by examining in each prepare call which file descriptors need	2650	This is done by examining in each prepare call which file descriptors
1949	to be watched by the other library, registering C<ev_io> watchers for	2651	need to be watched by the other library, registering C<ev_io> watchers
1950	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2652	for them and starting an C<ev_timer> watcher for any timeouts (many
1951	provide just this functionality). Then, in the check watcher you check for	2653	libraries provide exactly this functionality). Then, in the check watcher,
1952	any events that occurred (by checking the pending status of all watchers	2654	you check for any events that occurred (by checking the pending status
1953	and stopping them) and call back into the library. The I/O and timer	2655	of all watchers and stopping them) and call back into the library. The
1954	callbacks will never actually be called (but must be valid nevertheless,	2656	I/O and timer callbacks will never actually be called (but must be valid
1955	because you never know, you know?).	2657	nevertheless, because you never know, you know?).
1956		2658
1957	As another example, the Perl Coro module uses these hooks to integrate	2659	As another example, the Perl Coro module uses these hooks to integrate
1958	coroutines into libev programs, by yielding to other active coroutines	2660	coroutines into libev programs, by yielding to other active coroutines
1959	during each prepare and only letting the process block if no coroutines	2661	during each prepare and only letting the process block if no coroutines
1960	are ready to run (it's actually more complicated: it only runs coroutines	2662	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1963	loop from blocking if lower-priority coroutines are active, thus mapping	2665	loop from blocking if lower-priority coroutines are active, thus mapping
1964	low-priority coroutines to idle/background tasks).	2666	low-priority coroutines to idle/background tasks).
1965		2667
1966	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2668	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1967	priority, to ensure that they are being run before any other watchers	2669	priority, to ensure that they are being run before any other watchers
		2670	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2671
1968	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2672	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1969	too) should not activate ("feed") events into libev. While libev fully	2673	activate ("feed") events into libev. While libev fully supports this, they
1970	supports this, they might get executed before other C<ev_check> watchers	2674	might get executed before other C<ev_check> watchers did their job. As
1971	did their job. As C<ev_check> watchers are often used to embed other	2675	C<ev_check> watchers are often used to embed other (non-libev) event
1972	(non-libev) event loops those other event loops might be in an unusable	2676	loops those other event loops might be in an unusable state until their
1973	state until their C<ev_check> watcher ran (always remind yourself to	2677	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1974	coexist peacefully with others).	2678	others).
1975		2679
1976	=head3 Watcher-Specific Functions and Data Members	2680	=head3 Watcher-Specific Functions and Data Members
1977		2681
1978	=over 4	2682	=over 4
1979		2683
…		…
1981		2685
1982	=item ev_check_init (ev_check *, callback)	2686	=item ev_check_init (ev_check *, callback)
1983		2687
1984	Initialises and configures the prepare or check watcher - they have no	2688	Initialises and configures the prepare or check watcher - they have no
1985	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2689	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1986	macros, but using them is utterly, utterly and completely pointless.	2690	macros, but using them is utterly, utterly, utterly and completely
		2691	pointless.
1987		2692
1988	=back	2693	=back
1989		2694
1990	=head3 Examples	2695	=head3 Examples
1991		2696
…		…
2004		2709
2005	static ev_io iow [nfd];	2710	static ev_io iow [nfd];
2006	static ev_timer tw;	2711	static ev_timer tw;
2007		2712
2008	static void	2713	static void
2009	io_cb (ev_loop *loop, ev_io *w, int revents)	2714	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2010	{	2715	{
2011	}	2716	}
2012		2717
2013	// create io watchers for each fd and a timer before blocking	2718	// create io watchers for each fd and a timer before blocking
2014	static void	2719	static void
2015	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2720	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2016	{	2721	{
2017	int timeout = 3600000;	2722	int timeout = 3600000;
2018	struct pollfd fds [nfd];	2723	struct pollfd fds [nfd];
2019	// actual code will need to loop here and realloc etc.	2724	// actual code will need to loop here and realloc etc.
2020	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2725	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2021		2726
2022	/* the callback is illegal, but won't be called as we stop during check */	2727	/* the callback is illegal, but won't be called as we stop during check */
2023	ev_timer_init (&tw, 0, timeout * 1e-3);	2728	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2024	ev_timer_start (loop, &tw);	2729	ev_timer_start (loop, &tw);
2025		2730
2026	// create one ev_io per pollfd	2731	// create one ev_io per pollfd
2027	for (int i = 0; i < nfd; ++i)	2732	for (int i = 0; i < nfd; ++i)
2028	{	2733	{
…		…
2035	}	2740	}
2036	}	2741	}
2037		2742
2038	// stop all watchers after blocking	2743	// stop all watchers after blocking
2039	static void	2744	static void
2040	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2745	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2041	{	2746	{
2042	ev_timer_stop (loop, &tw);	2747	ev_timer_stop (loop, &tw);
2043		2748
2044	for (int i = 0; i < nfd; ++i)	2749	for (int i = 0; i < nfd; ++i)
2045	{	2750	{
…		…
2084	}	2789	}
2085		2790
2086	// do not ever call adns_afterpoll	2791	// do not ever call adns_afterpoll
2087		2792
2088	Method 4: Do not use a prepare or check watcher because the module you	2793	Method 4: Do not use a prepare or check watcher because the module you
2089	want to embed is too inflexible to support it. Instead, you can override	2794	want to embed is not flexible enough to support it. Instead, you can
2090	their poll function. The drawback with this solution is that the main	2795	override their poll function. The drawback with this solution is that the
2091	loop is now no longer controllable by EV. The C<Glib::EV> module does	2796	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2092	this.	2797	this approach, effectively embedding EV as a client into the horrible
		2798	libglib event loop.
2093		2799
2094	static gint	2800	static gint
2095	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2801	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2096	{	2802	{
2097	int got_events = 0;	2803	int got_events = 0;
…		…
2128	prioritise I/O.	2834	prioritise I/O.
2129		2835
2130	As an example for a bug workaround, the kqueue backend might only support	2836	As an example for a bug workaround, the kqueue backend might only support
2131	sockets on some platform, so it is unusable as generic backend, but you	2837	sockets on some platform, so it is unusable as generic backend, but you
2132	still want to make use of it because you have many sockets and it scales	2838	still want to make use of it because you have many sockets and it scales
2133	so nicely. In this case, you would create a kqueue-based loop and embed it	2839	so nicely. In this case, you would create a kqueue-based loop and embed
2134	into your default loop (which might use e.g. poll). Overall operation will	2840	it into your default loop (which might use e.g. poll). Overall operation
2135	be a bit slower because first libev has to poll and then call kevent, but	2841	will be a bit slower because first libev has to call C<poll> and then
2136	at least you can use both at what they are best.	2842	C<kevent>, but at least you can use both mechanisms for what they are
		2843	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2137		2844
2138	As for prioritising I/O: rarely you have the case where some fds have	2845	As for prioritising I/O: under rare circumstances you have the case where
2139	to be watched and handled very quickly (with low latency), and even	2846	some fds have to be watched and handled very quickly (with low latency),
2140	priorities and idle watchers might have too much overhead. In this case	2847	and even priorities and idle watchers might have too much overhead. In
2141	you would put all the high priority stuff in one loop and all the rest in	2848	this case you would put all the high priority stuff in one loop and all
2142	a second one, and embed the second one in the first.	2849	the rest in a second one, and embed the second one in the first.
2143		2850
2144	As long as the watcher is active, the callback will be invoked every time	2851	As long as the watcher is active, the callback will be invoked every
2145	there might be events pending in the embedded loop. The callback must then	2852	time there might be events pending in the embedded loop. The callback
2146	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2853	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2147	their callbacks (you could also start an idle watcher to give the embedded	2854	sweep and invoke their callbacks (the callback doesn't need to invoke the
2148	loop strictly lower priority for example). You can also set the callback	2855	C<ev_embed_sweep> function directly, it could also start an idle watcher
2149	to C<0>, in which case the embed watcher will automatically execute the	2856	to give the embedded loop strictly lower priority for example).
2150	embedded loop sweep.
2151		2857
2152	As long as the watcher is started it will automatically handle events. The	2858	You can also set the callback to C<0>, in which case the embed watcher
2153	callback will be invoked whenever some events have been handled. You can	2859	will automatically execute the embedded loop sweep whenever necessary.
2154	set the callback to C<0> to avoid having to specify one if you are not
2155	interested in that.
2156		2860
2157	Also, there have not currently been made special provisions for forking:	2861	Fork detection will be handled transparently while the C<ev_embed> watcher
2158	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2862	is active, i.e., the embedded loop will automatically be forked when the
2159	but you will also have to stop and restart any C<ev_embed> watchers	2863	embedding loop forks. In other cases, the user is responsible for calling
2160	yourself.	2864	C<ev_loop_fork> on the embedded loop.
2161		2865
2162	Unfortunately, not all backends are embeddable, only the ones returned by	2866	Unfortunately, not all backends are embeddable: only the ones returned by
2163	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2867	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2164	portable one.	2868	portable one.
2165		2869
2166	So when you want to use this feature you will always have to be prepared	2870	So when you want to use this feature you will always have to be prepared
2167	that you cannot get an embeddable loop. The recommended way to get around	2871	that you cannot get an embeddable loop. The recommended way to get around
2168	this is to have a separate variables for your embeddable loop, try to	2872	this is to have a separate variables for your embeddable loop, try to
2169	create it, and if that fails, use the normal loop for everything.	2873	create it, and if that fails, use the normal loop for everything.
		2874
		2875	=head3 C<ev_embed> and fork
		2876
		2877	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2878	automatically be applied to the embedded loop as well, so no special
		2879	fork handling is required in that case. When the watcher is not running,
		2880	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2881	as applicable.
2170		2882
2171	=head3 Watcher-Specific Functions and Data Members	2883	=head3 Watcher-Specific Functions and Data Members
2172		2884
2173	=over 4	2885	=over 4
2174		2886
…		…
2202	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2914	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2203	used).	2915	used).
2204		2916
2205	struct ev_loop *loop_hi = ev_default_init (0);	2917	struct ev_loop *loop_hi = ev_default_init (0);
2206	struct ev_loop *loop_lo = 0;	2918	struct ev_loop *loop_lo = 0;
2207	struct ev_embed embed;	2919	ev_embed embed;
2208		2920
2209	// see if there is a chance of getting one that works	2921	// see if there is a chance of getting one that works
2210	// (remember that a flags value of 0 means autodetection)	2922	// (remember that a flags value of 0 means autodetection)
2211	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2923	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2212	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2924	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2226	kqueue implementation). Store the kqueue/socket-only event loop in	2938	kqueue implementation). Store the kqueue/socket-only event loop in
2227	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2939	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2228		2940
2229	struct ev_loop *loop = ev_default_init (0);	2941	struct ev_loop *loop = ev_default_init (0);
2230	struct ev_loop *loop_socket = 0;	2942	struct ev_loop *loop_socket = 0;
2231	struct ev_embed embed;	2943	ev_embed embed;
2232		2944
2233	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2945	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2234	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2946	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2235	{	2947	{
2236	ev_embed_init (&embed, 0, loop_socket);	2948	ev_embed_init (&embed, 0, loop_socket);
…		…
2251	event loop blocks next and before C<ev_check> watchers are being called,	2963	event loop blocks next and before C<ev_check> watchers are being called,
2252	and only in the child after the fork. If whoever good citizen calling	2964	and only in the child after the fork. If whoever good citizen calling
2253	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2965	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2254	handlers will be invoked, too, of course.	2966	handlers will be invoked, too, of course.
2255		2967
		2968	=head3 The special problem of life after fork - how is it possible?
		2969
		2970	Most uses of C<fork()> consist of forking, then some simple calls to set
		2971	up/change the process environment, followed by a call to C<exec()>. This
		2972	sequence should be handled by libev without any problems.
		2973
		2974	This changes when the application actually wants to do event handling
		2975	in the child, or both parent in child, in effect "continuing" after the
		2976	fork.
		2977
		2978	The default mode of operation (for libev, with application help to detect
		2979	forks) is to duplicate all the state in the child, as would be expected
		2980	when I<either> the parent I<or> the child process continues.
		2981
		2982	When both processes want to continue using libev, then this is usually the
		2983	wrong result. In that case, usually one process (typically the parent) is
		2984	supposed to continue with all watchers in place as before, while the other
		2985	process typically wants to start fresh, i.e. without any active watchers.
		2986
		2987	The cleanest and most efficient way to achieve that with libev is to
		2988	simply create a new event loop, which of course will be "empty", and
		2989	use that for new watchers. This has the advantage of not touching more
		2990	memory than necessary, and thus avoiding the copy-on-write, and the
		2991	disadvantage of having to use multiple event loops (which do not support
		2992	signal watchers).
		2993
		2994	When this is not possible, or you want to use the default loop for
		2995	other reasons, then in the process that wants to start "fresh", call
		2996	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2997	the default loop will "orphan" (not stop) all registered watchers, so you
		2998	have to be careful not to execute code that modifies those watchers. Note
		2999	also that in that case, you have to re-register any signal watchers.
		3000
2256	=head3 Watcher-Specific Functions and Data Members	3001	=head3 Watcher-Specific Functions and Data Members
2257		3002
2258	=over 4	3003	=over 4
2259		3004
2260	=item ev_fork_init (ev_signal *, callback)	3005	=item ev_fork_init (ev_signal *, callback)
…		…
2264	believe me.	3009	believe me.
2265		3010
2266	=back	3011	=back
2267		3012
2268		3013
2269	=head2 C<ev_async> - how to wake up another event loop	3014	=head2 C<ev_async> - how to wake up an event loop
2270		3015
2271	In general, you cannot use an C<ev_loop> from multiple threads or other	3016	In general, you cannot use an C<ev_loop> from multiple threads or other
2272	asynchronous sources such as signal handlers (as opposed to multiple event	3017	asynchronous sources such as signal handlers (as opposed to multiple event
2273	loops - those are of course safe to use in different threads).	3018	loops - those are of course safe to use in different threads).
2274		3019
2275	Sometimes, however, you need to wake up another event loop you do not	3020	Sometimes, however, you need to wake up an event loop you do not control,
2276	control, for example because it belongs to another thread. This is what	3021	for example because it belongs to another thread. This is what C<ev_async>
2277	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3022	watchers do: as long as the C<ev_async> watcher is active, you can signal
2278	can signal it by calling C<ev_async_send>, which is thread- and signal	3023	it by calling C<ev_async_send>, which is thread- and signal safe.
2279	safe.
2280		3024
2281	This functionality is very similar to C<ev_signal> watchers, as signals,	3025	This functionality is very similar to C<ev_signal> watchers, as signals,
2282	too, are asynchronous in nature, and signals, too, will be compressed	3026	too, are asynchronous in nature, and signals, too, will be compressed
2283	(i.e. the number of callback invocations may be less than the number of	3027	(i.e. the number of callback invocations may be less than the number of
2284	C<ev_async_sent> calls).	3028	C<ev_async_sent> calls).
…		…
2289	=head3 Queueing	3033	=head3 Queueing
2290		3034
2291	C<ev_async> does not support queueing of data in any way. The reason	3035	C<ev_async> does not support queueing of data in any way. The reason
2292	is that the author does not know of a simple (or any) algorithm for a	3036	is that the author does not know of a simple (or any) algorithm for a
2293	multiple-writer-single-reader queue that works in all cases and doesn't	3037	multiple-writer-single-reader queue that works in all cases and doesn't
2294	need elaborate support such as pthreads.	3038	need elaborate support such as pthreads or unportable memory access
		3039	semantics.
2295		3040
2296	That means that if you want to queue data, you have to provide your own	3041	That means that if you want to queue data, you have to provide your own
2297	queue. But at least I can tell you would implement locking around your	3042	queue. But at least I can tell you how to implement locking around your
2298	queue:	3043	queue:
2299		3044
2300	=over 4	3045	=over 4
2301		3046
2302	=item queueing from a signal handler context	3047	=item queueing from a signal handler context
2303		3048
2304	To implement race-free queueing, you simply add to the queue in the signal	3049	To implement race-free queueing, you simply add to the queue in the signal
2305	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3050	handler but you block the signal handler in the watcher callback. Here is
2306	some fictitious SIGUSR1 handler:	3051	an example that does that for some fictitious SIGUSR1 handler:
2307		3052
2308	static ev_async mysig;	3053	static ev_async mysig;
2309		3054
2310	static void	3055	static void
2311	sigusr1_handler (void)	3056	sigusr1_handler (void)
…		…
2377	=over 4	3122	=over 4
2378		3123
2379	=item ev_async_init (ev_async *, callback)	3124	=item ev_async_init (ev_async *, callback)
2380		3125
2381	Initialises and configures the async watcher - it has no parameters of any	3126	Initialises and configures the async watcher - it has no parameters of any
2382	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3127	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2383	believe me.	3128	trust me.
2384		3129
2385	=item ev_async_send (loop, ev_async *)	3130	=item ev_async_send (loop, ev_async *)
2386		3131
2387	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3132	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2388	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3133	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2389	C<ev_feed_event>, this call is safe to do in other threads, signal or	3134	C<ev_feed_event>, this call is safe to do from other threads, signal or
2390	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3135	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2391	section below on what exactly this means).	3136	section below on what exactly this means).
2392		3137
		3138	Note that, as with other watchers in libev, multiple events might get
		3139	compressed into a single callback invocation (another way to look at this
		3140	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3141	reset when the event loop detects that).
		3142
2393	This call incurs the overhead of a system call only once per loop iteration,	3143	This call incurs the overhead of a system call only once per event loop
2394	so while the overhead might be noticeable, it doesn't apply to repeated	3144	iteration, so while the overhead might be noticeable, it doesn't apply to
2395	calls to C<ev_async_send>.	3145	repeated calls to C<ev_async_send> for the same event loop.
2396		3146
2397	=item bool = ev_async_pending (ev_async *)	3147	=item bool = ev_async_pending (ev_async *)
2398		3148
2399	Returns a non-zero value when C<ev_async_send> has been called on the	3149	Returns a non-zero value when C<ev_async_send> has been called on the
2400	watcher but the event has not yet been processed (or even noted) by the	3150	watcher but the event has not yet been processed (or even noted) by the
…		…
2403	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3153	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2404	the loop iterates next and checks for the watcher to have become active,	3154	the loop iterates next and checks for the watcher to have become active,
2405	it will reset the flag again. C<ev_async_pending> can be used to very	3155	it will reset the flag again. C<ev_async_pending> can be used to very
2406	quickly check whether invoking the loop might be a good idea.	3156	quickly check whether invoking the loop might be a good idea.
2407		3157
2408	Not that this does I<not> check whether the watcher itself is pending, only	3158	Not that this does I<not> check whether the watcher itself is pending,
2409	whether it has been requested to make this watcher pending.	3159	only whether it has been requested to make this watcher pending: there
		3160	is a time window between the event loop checking and resetting the async
		3161	notification, and the callback being invoked.
2410		3162
2411	=back	3163	=back
2412		3164
2413		3165
2414	=head1 OTHER FUNCTIONS	3166	=head1 OTHER FUNCTIONS
…		…
2418	=over 4	3170	=over 4
2419		3171
2420	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3172	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2421		3173
2422	This function combines a simple timer and an I/O watcher, calls your	3174	This function combines a simple timer and an I/O watcher, calls your
2423	callback on whichever event happens first and automatically stop both	3175	callback on whichever event happens first and automatically stops both
2424	watchers. This is useful if you want to wait for a single event on an fd	3176	watchers. This is useful if you want to wait for a single event on an fd
2425	or timeout without having to allocate/configure/start/stop/free one or	3177	or timeout without having to allocate/configure/start/stop/free one or
2426	more watchers yourself.	3178	more watchers yourself.
2427		3179
2428	If C<fd> is less than 0, then no I/O watcher will be started and events	3180	If C<fd> is less than 0, then no I/O watcher will be started and the
2429	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3181	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2430	C<events> set will be created and started.	3182	the given C<fd> and C<events> set will be created and started.
2431		3183
2432	If C<timeout> is less than 0, then no timeout watcher will be	3184	If C<timeout> is less than 0, then no timeout watcher will be
2433	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3185	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2434	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3186	repeat = 0) will be started. C<0> is a valid timeout.
2435	dubious value.
2436		3187
2437	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3188	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2438	passed an C<revents> set like normal event callbacks (a combination of	3189	passed an C<revents> set like normal event callbacks (a combination of
2439	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3190	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2440	value passed to C<ev_once>:	3191	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3192	a timeout and an io event at the same time - you probably should give io
		3193	events precedence.
		3194
		3195	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2441		3196
2442	static void stdin_ready (int revents, void *arg)	3197	static void stdin_ready (int revents, void *arg)
2443	{	3198	{
		3199	if (revents & EV_READ)
		3200	/* stdin might have data for us, joy! */;
2444	if (revents & EV_TIMEOUT)	3201	else if (revents & EV_TIMER)
2445	/* doh, nothing entered */;	3202	/* doh, nothing entered */;
2446	else if (revents & EV_READ)
2447	/* stdin might have data for us, joy! */;
2448	}	3203	}
2449		3204
2450	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3205	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2451		3206
2452	=item ev_feed_event (ev_loop *, watcher *, int revents)
2453
2454	Feeds the given event set into the event loop, as if the specified event
2455	had happened for the specified watcher (which must be a pointer to an
2456	initialised but not necessarily started event watcher).
2457
2458	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3207	=item ev_feed_fd_event (loop, int fd, int revents)
2459		3208
2460	Feed an event on the given fd, as if a file descriptor backend detected	3209	Feed an event on the given fd, as if a file descriptor backend detected
2461	the given events it.	3210	the given events it.
2462		3211
2463	=item ev_feed_signal_event (ev_loop *loop, int signum)	3212	=item ev_feed_signal_event (loop, int signum)
2464		3213
2465	Feed an event as if the given signal occurred (C<loop> must be the default	3214	Feed an event as if the given signal occurred (C<loop> must be the default
2466	loop!).	3215	loop!).
2467		3216
2468	=back	3217	=back
…		…
2548		3297
2549	=over 4	3298	=over 4
2550		3299
2551	=item ev::TYPE::TYPE ()	3300	=item ev::TYPE::TYPE ()
2552		3301
2553	=item ev::TYPE::TYPE (struct ev_loop *)	3302	=item ev::TYPE::TYPE (loop)
2554		3303
2555	=item ev::TYPE::~TYPE	3304	=item ev::TYPE::~TYPE
2556		3305
2557	The constructor (optionally) takes an event loop to associate the watcher	3306	The constructor (optionally) takes an event loop to associate the watcher
2558	with. If it is omitted, it will use C<EV_DEFAULT>.	3307	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2590		3339
2591	myclass obj;	3340	myclass obj;
2592	ev::io iow;	3341	ev::io iow;
2593	iow.set <myclass, &myclass::io_cb> (&obj);	3342	iow.set <myclass, &myclass::io_cb> (&obj);
2594		3343
		3344	=item w->set (object *)
		3345
		3346	This is a variation of a method callback - leaving out the method to call
		3347	will default the method to C<operator ()>, which makes it possible to use
		3348	functor objects without having to manually specify the C<operator ()> all
		3349	the time. Incidentally, you can then also leave out the template argument
		3350	list.
		3351
		3352	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3353	int revents)>.
		3354
		3355	See the method-C<set> above for more details.
		3356
		3357	Example: use a functor object as callback.
		3358
		3359	struct myfunctor
		3360	{
		3361	void operator() (ev::io &w, int revents)
		3362	{
		3363	...
		3364	}
		3365	}
		3366
		3367	myfunctor f;
		3368
		3369	ev::io w;
		3370	w.set (&f);
		3371
2595	=item w->set<function> (void *data = 0)	3372	=item w->set<function> (void *data = 0)
2596		3373
2597	Also sets a callback, but uses a static method or plain function as	3374	Also sets a callback, but uses a static method or plain function as
2598	callback. The optional C<data> argument will be stored in the watcher's	3375	callback. The optional C<data> argument will be stored in the watcher's
2599	C<data> member and is free for you to use.	3376	C<data> member and is free for you to use.
2600		3377
2601	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3378	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2602		3379
2603	See the method-C<set> above for more details.	3380	See the method-C<set> above for more details.
2604		3381
2605	Example:	3382	Example: Use a plain function as callback.
2606		3383
2607	static void io_cb (ev::io &w, int revents) { }	3384	static void io_cb (ev::io &w, int revents) { }
2608	iow.set <io_cb> ();	3385	iow.set <io_cb> ();
2609		3386
2610	=item w->set (struct ev_loop *)	3387	=item w->set (loop)
2611		3388
2612	Associates a different C<struct ev_loop> with this watcher. You can only	3389	Associates a different C<struct ev_loop> with this watcher. You can only
2613	do this when the watcher is inactive (and not pending either).	3390	do this when the watcher is inactive (and not pending either).
2614		3391
2615	=item w->set ([arguments])	3392	=item w->set ([arguments])
…		…
2648	Example: Define a class with an IO and idle watcher, start one of them in	3425	Example: Define a class with an IO and idle watcher, start one of them in
2649	the constructor.	3426	the constructor.
2650		3427
2651	class myclass	3428	class myclass
2652	{	3429	{
2653	ev::io io; void io_cb (ev::io &w, int revents);	3430	ev::io io ; void io_cb (ev::io &w, int revents);
2654	ev:idle idle void idle_cb (ev::idle &w, int revents);	3431	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2655		3432
2656	myclass (int fd)	3433	myclass (int fd)
2657	{	3434	{
2658	io .set <myclass, &myclass::io_cb > (this);	3435	io .set <myclass, &myclass::io_cb > (this);
2659	idle.set <myclass, &myclass::idle_cb> (this);	3436	idle.set <myclass, &myclass::idle_cb> (this);
…		…
2675	=item Perl	3452	=item Perl
2676		3453
2677	The EV module implements the full libev API and is actually used to test	3454	The EV module implements the full libev API and is actually used to test
2678	libev. EV is developed together with libev. Apart from the EV core module,	3455	libev. EV is developed together with libev. Apart from the EV core module,
2679	there are additional modules that implement libev-compatible interfaces	3456	there are additional modules that implement libev-compatible interfaces
2680	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3457	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2681	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3458	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3459	and C<EV::Glib>).
2682		3460
2683	It can be found and installed via CPAN, its homepage is at	3461	It can be found and installed via CPAN, its homepage is at
2684	L<http://software.schmorp.de/pkg/EV>.	3462	L<http://software.schmorp.de/pkg/EV>.
2685		3463
2686	=item Python	3464	=item Python
2687		3465
2688	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3466	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2689	seems to be quite complete and well-documented. Note, however, that the	3467	seems to be quite complete and well-documented.
2690	patch they require for libev is outright dangerous as it breaks the ABI
2691	for everybody else, and therefore, should never be applied in an installed
2692	libev (if python requires an incompatible ABI then it needs to embed
2693	libev).
2694		3468
2695	=item Ruby	3469	=item Ruby
2696		3470
2697	Tony Arcieri has written a ruby extension that offers access to a subset	3471	Tony Arcieri has written a ruby extension that offers access to a subset
2698	of the libev API and adds file handle abstractions, asynchronous DNS and	3472	of the libev API and adds file handle abstractions, asynchronous DNS and
2699	more on top of it. It can be found via gem servers. Its homepage is at	3473	more on top of it. It can be found via gem servers. Its homepage is at
2700	L<http://rev.rubyforge.org/>.	3474	L<http://rev.rubyforge.org/>.
2701		3475
		3476	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3477	makes rev work even on mingw.
		3478
		3479	=item Haskell
		3480
		3481	A haskell binding to libev is available at
		3482	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3483
2702	=item D	3484	=item D
2703		3485
2704	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3486	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2705	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3487	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3488
		3489	=item Ocaml
		3490
		3491	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3492	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3493
		3494	=item Lua
		3495
		3496	Brian Maher has written a partial interface to libev for lua (at the
		3497	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3498	L<http://github.com/brimworks/lua-ev>.
2706		3499
2707	=back	3500	=back
2708		3501
2709		3502
2710	=head1 MACRO MAGIC	3503	=head1 MACRO MAGIC
…		…
2811		3604
2812	#define EV_STANDALONE 1	3605	#define EV_STANDALONE 1
2813	#include "ev.h"	3606	#include "ev.h"
2814		3607
2815	Both header files and implementation files can be compiled with a C++	3608	Both header files and implementation files can be compiled with a C++
2816	compiler (at least, thats a stated goal, and breakage will be treated	3609	compiler (at least, that's a stated goal, and breakage will be treated
2817	as a bug).	3610	as a bug).
2818		3611
2819	You need the following files in your source tree, or in a directory	3612	You need the following files in your source tree, or in a directory
2820	in your include path (e.g. in libev/ when using -Ilibev):	3613	in your include path (e.g. in libev/ when using -Ilibev):
2821		3614
…		…
2864	libev.m4	3657	libev.m4
2865		3658
2866	=head2 PREPROCESSOR SYMBOLS/MACROS	3659	=head2 PREPROCESSOR SYMBOLS/MACROS
2867		3660
2868	Libev can be configured via a variety of preprocessor symbols you have to	3661	Libev can be configured via a variety of preprocessor symbols you have to
2869	define before including any of its files. The default in the absence of	3662	define before including (or compiling) any of its files. The default in
2870	autoconf is noted for every option.	3663	the absence of autoconf is documented for every option.
		3664
		3665	Symbols marked with "(h)" do not change the ABI, and can have different
		3666	values when compiling libev vs. including F<ev.h>, so it is permissible
		3667	to redefine them before including F<ev.h> without breaking compatibility
		3668	to a compiled library. All other symbols change the ABI, which means all
		3669	users of libev and the libev code itself must be compiled with compatible
		3670	settings.
2871		3671
2872	=over 4	3672	=over 4
2873		3673
2874	=item EV_STANDALONE	3674	=item EV_STANDALONE (h)
2875		3675
2876	Must always be C<1> if you do not use autoconf configuration, which	3676	Must always be C<1> if you do not use autoconf configuration, which
2877	keeps libev from including F<config.h>, and it also defines dummy	3677	keeps libev from including F<config.h>, and it also defines dummy
2878	implementations for some libevent functions (such as logging, which is not	3678	implementations for some libevent functions (such as logging, which is not
2879	supported). It will also not define any of the structs usually found in	3679	supported). It will also not define any of the structs usually found in
2880	F<event.h> that are not directly supported by the libev core alone.	3680	F<event.h> that are not directly supported by the libev core alone.
2881		3681
		3682	In standalone mode, libev will still try to automatically deduce the
		3683	configuration, but has to be more conservative.
		3684
2882	=item EV_USE_MONOTONIC	3685	=item EV_USE_MONOTONIC
2883		3686
2884	If defined to be C<1>, libev will try to detect the availability of the	3687	If defined to be C<1>, libev will try to detect the availability of the
2885	monotonic clock option at both compile time and runtime. Otherwise no use	3688	monotonic clock option at both compile time and runtime. Otherwise no
2886	of the monotonic clock option will be attempted. If you enable this, you	3689	use of the monotonic clock option will be attempted. If you enable this,
2887	usually have to link against librt or something similar. Enabling it when	3690	you usually have to link against librt or something similar. Enabling it
2888	the functionality isn't available is safe, though, although you have	3691	when the functionality isn't available is safe, though, although you have
2889	to make sure you link against any libraries where the C<clock_gettime>	3692	to make sure you link against any libraries where the C<clock_gettime>
2890	function is hiding in (often F<-lrt>).	3693	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2891		3694
2892	=item EV_USE_REALTIME	3695	=item EV_USE_REALTIME
2893		3696
2894	If defined to be C<1>, libev will try to detect the availability of the	3697	If defined to be C<1>, libev will try to detect the availability of the
2895	real-time clock option at compile time (and assume its availability at	3698	real-time clock option at compile time (and assume its availability
2896	runtime if successful). Otherwise no use of the real-time clock option will	3699	at runtime if successful). Otherwise no use of the real-time clock
2897	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3700	option will be attempted. This effectively replaces C<gettimeofday>
2898	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3701	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2899	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3702	correctness. See the note about libraries in the description of
		3703	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3704	C<EV_USE_CLOCK_SYSCALL>.
		3705
		3706	=item EV_USE_CLOCK_SYSCALL
		3707
		3708	If defined to be C<1>, libev will try to use a direct syscall instead
		3709	of calling the system-provided C<clock_gettime> function. This option
		3710	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3711	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3712	programs needlessly. Using a direct syscall is slightly slower (in
		3713	theory), because no optimised vdso implementation can be used, but avoids
		3714	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3715	higher, as it simplifies linking (no need for C<-lrt>).
2900		3716
2901	=item EV_USE_NANOSLEEP	3717	=item EV_USE_NANOSLEEP
2902		3718
2903	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3719	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2904	and will use it for delays. Otherwise it will use C<select ()>.	3720	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2920		3736
2921	=item EV_SELECT_USE_FD_SET	3737	=item EV_SELECT_USE_FD_SET
2922		3738
2923	If defined to C<1>, then the select backend will use the system C<fd_set>	3739	If defined to C<1>, then the select backend will use the system C<fd_set>
2924	structure. This is useful if libev doesn't compile due to a missing	3740	structure. This is useful if libev doesn't compile due to a missing
2925	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3741	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2926	exotic systems. This usually limits the range of file descriptors to some	3742	on exotic systems. This usually limits the range of file descriptors to
2927	low limit such as 1024 or might have other limitations (winsocket only	3743	some low limit such as 1024 or might have other limitations (winsocket
2928	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3744	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2929	influence the size of the C<fd_set> used.	3745	configures the maximum size of the C<fd_set>.
2930		3746
2931	=item EV_SELECT_IS_WINSOCKET	3747	=item EV_SELECT_IS_WINSOCKET
2932		3748
2933	When defined to C<1>, the select backend will assume that	3749	When defined to C<1>, the select backend will assume that
2934	select/socket/connect etc. don't understand file descriptors but	3750	select/socket/connect etc. don't understand file descriptors but
…		…
2936	be used is the winsock select). This means that it will call	3752	be used is the winsock select). This means that it will call
2937	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3753	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2938	it is assumed that all these functions actually work on fds, even	3754	it is assumed that all these functions actually work on fds, even
2939	on win32. Should not be defined on non-win32 platforms.	3755	on win32. Should not be defined on non-win32 platforms.
2940		3756
2941	=item EV_FD_TO_WIN32_HANDLE	3757	=item EV_FD_TO_WIN32_HANDLE(fd)
2942		3758
2943	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3759	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2944	file descriptors to socket handles. When not defining this symbol (the	3760	file descriptors to socket handles. When not defining this symbol (the
2945	default), then libev will call C<_get_osfhandle>, which is usually	3761	default), then libev will call C<_get_osfhandle>, which is usually
2946	correct. In some cases, programs use their own file descriptor management,	3762	correct. In some cases, programs use their own file descriptor management,
2947	in which case they can provide this function to map fds to socket handles.	3763	in which case they can provide this function to map fds to socket handles.
		3764
		3765	=item EV_WIN32_HANDLE_TO_FD(handle)
		3766
		3767	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3768	using the standard C<_open_osfhandle> function. For programs implementing
		3769	their own fd to handle mapping, overwriting this function makes it easier
		3770	to do so. This can be done by defining this macro to an appropriate value.
		3771
		3772	=item EV_WIN32_CLOSE_FD(fd)
		3773
		3774	If programs implement their own fd to handle mapping on win32, then this
		3775	macro can be used to override the C<close> function, useful to unregister
		3776	file descriptors again. Note that the replacement function has to close
		3777	the underlying OS handle.
2948		3778
2949	=item EV_USE_POLL	3779	=item EV_USE_POLL
2950		3780
2951	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3781	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2952	backend. Otherwise it will be enabled on non-win32 platforms. It	3782	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2999	as well as for signal and thread safety in C<ev_async> watchers.	3829	as well as for signal and thread safety in C<ev_async> watchers.
3000		3830
3001	In the absence of this define, libev will use C<sig_atomic_t volatile>	3831	In the absence of this define, libev will use C<sig_atomic_t volatile>
3002	(from F<signal.h>), which is usually good enough on most platforms.	3832	(from F<signal.h>), which is usually good enough on most platforms.
3003		3833
3004	=item EV_H	3834	=item EV_H (h)
3005		3835
3006	The name of the F<ev.h> header file used to include it. The default if	3836	The name of the F<ev.h> header file used to include it. The default if
3007	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3837	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
3008	used to virtually rename the F<ev.h> header file in case of conflicts.	3838	used to virtually rename the F<ev.h> header file in case of conflicts.
3009		3839
3010	=item EV_CONFIG_H	3840	=item EV_CONFIG_H (h)
3011		3841
3012	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3842	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
3013	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3843	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3014	C<EV_H>, above.	3844	C<EV_H>, above.
3015		3845
3016	=item EV_EVENT_H	3846	=item EV_EVENT_H (h)
3017		3847
3018	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3848	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
3019	of how the F<event.h> header can be found, the default is C<"event.h">.	3849	of how the F<event.h> header can be found, the default is C<"event.h">.
3020		3850
3021	=item EV_PROTOTYPES	3851	=item EV_PROTOTYPES (h)
3022		3852
3023	If defined to be C<0>, then F<ev.h> will not define any function	3853	If defined to be C<0>, then F<ev.h> will not define any function
3024	prototypes, but still define all the structs and other symbols. This is	3854	prototypes, but still define all the structs and other symbols. This is
3025	occasionally useful if you want to provide your own wrapper functions	3855	occasionally useful if you want to provide your own wrapper functions
3026	around libev functions.	3856	around libev functions.
…		…
3045	When doing priority-based operations, libev usually has to linearly search	3875	When doing priority-based operations, libev usually has to linearly search
3046	all the priorities, so having many of them (hundreds) uses a lot of space	3876	all the priorities, so having many of them (hundreds) uses a lot of space
3047	and time, so using the defaults of five priorities (-2 .. +2) is usually	3877	and time, so using the defaults of five priorities (-2 .. +2) is usually
3048	fine.	3878	fine.
3049		3879
3050	If your embedding application does not need any priorities, defining these both to	3880	If your embedding application does not need any priorities, defining these
3051	C<0> will save some memory and CPU.	3881	both to C<0> will save some memory and CPU.
3052		3882
3053	=item EV_PERIODIC_ENABLE	3883	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3884	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3885	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3054		3886
3055	If undefined or defined to be C<1>, then periodic timers are supported. If	3887	If undefined or defined to be C<1> (and the platform supports it), then
3056	defined to be C<0>, then they are not. Disabling them saves a few kB of	3888	the respective watcher type is supported. If defined to be C<0>, then it
3057	code.	3889	is not. Disabling watcher types mainly saves code size.
3058		3890
3059	=item EV_IDLE_ENABLE	3891	=item EV_FEATURES
3060
3061	If undefined or defined to be C<1>, then idle watchers are supported. If
3062	defined to be C<0>, then they are not. Disabling them saves a few kB of
3063	code.
3064
3065	=item EV_EMBED_ENABLE
3066
3067	If undefined or defined to be C<1>, then embed watchers are supported. If
3068	defined to be C<0>, then they are not.
3069
3070	=item EV_STAT_ENABLE
3071
3072	If undefined or defined to be C<1>, then stat watchers are supported. If
3073	defined to be C<0>, then they are not.
3074
3075	=item EV_FORK_ENABLE
3076
3077	If undefined or defined to be C<1>, then fork watchers are supported. If
3078	defined to be C<0>, then they are not.
3079
3080	=item EV_ASYNC_ENABLE
3081
3082	If undefined or defined to be C<1>, then async watchers are supported. If
3083	defined to be C<0>, then they are not.
3084
3085	=item EV_MINIMAL
3086		3892
3087	If you need to shave off some kilobytes of code at the expense of some	3893	If you need to shave off some kilobytes of code at the expense of some
3088	speed, define this symbol to C<1>. Currently this is used to override some	3894	speed (but with the full API), you can define this symbol to request
3089	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3895	certain subsets of functionality. The default is to enable all features
3090	much smaller 2-heap for timer management over the default 4-heap.	3896	that can be enabled on the platform.
		3897
		3898	A typical way to use this symbol is to define it to C<0> (or to a bitset
		3899	with some broad features you want) and then selectively re-enable
		3900	additional parts you want, for example if you want everything minimal,
		3901	but multiple event loop support, async and child watchers and the poll
		3902	backend, use this:
		3903
		3904	#define EV_FEATURES 0
		3905	#define EV_MULTIPLICITY 1
		3906	#define EV_USE_POLL 1
		3907	#define EV_CHILD_ENABLE 1
		3908	#define EV_ASYNC_ENABLE 1
		3909
		3910	The actual value is a bitset, it can be a combination of the following
		3911	values:
		3912
		3913	=over 4
		3914
		3915	=item C<1> - faster/larger code
		3916
		3917	Use larger code to speed up some operations.
		3918
		3919	Currently this is used to override some inlining decisions (enlarging the
		3920	code size by roughly 30% on amd64).
		3921
		3922	When optimising for size, use of compiler flags such as C<-Os> with
		3923	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		3924	assertions.
		3925
		3926	=item C<2> - faster/larger data structures
		3927
		3928	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		3929	hash table sizes and so on. This will usually further increase code size
		3930	and can additionally have an effect on the size of data structures at
		3931	runtime.
		3932
		3933	=item C<4> - full API configuration
		3934
		3935	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		3936	enables multiplicity (C<EV_MULTIPLICITY>=1).
		3937
		3938	=item C<8> - full API
		3939
		3940	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		3941	details on which parts of the API are still available without this
		3942	feature, and do not complain if this subset changes over time.
		3943
		3944	=item C<16> - enable all optional watcher types
		3945
		3946	Enables all optional watcher types. If you want to selectively enable
		3947	only some watcher types other than I/O and timers (e.g. prepare,
		3948	embed, async, child...) you can enable them manually by defining
		3949	C<EV_watchertype_ENABLE> to C<1> instead.
		3950
		3951	=item C<32> - enable all backends
		3952
		3953	This enables all backends - without this feature, you need to enable at
		3954	least one backend manually (C<EV_USE_SELECT> is a good choice).
		3955
		3956	=item C<64> - enable OS-specific "helper" APIs
		3957
		3958	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		3959	default.
		3960
		3961	=back
		3962
		3963	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		3964	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		3965	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		3966	watchers, timers and monotonic clock support.
		3967
		3968	With an intelligent-enough linker (gcc+binutils are intelligent enough
		3969	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		3970	your program might be left out as well - a binary starting a timer and an
		3971	I/O watcher then might come out at only 5Kb.
		3972
		3973	=item EV_AVOID_STDIO
		3974
		3975	If this is set to C<1> at compiletime, then libev will avoid using stdio
		3976	functions (printf, scanf, perror etc.). This will increase the code size
		3977	somewhat, but if your program doesn't otherwise depend on stdio and your
		3978	libc allows it, this avoids linking in the stdio library which is quite
		3979	big.
		3980
		3981	Note that error messages might become less precise when this option is
		3982	enabled.
		3983
		3984	=item EV_NSIG
		3985
		3986	The highest supported signal number, +1 (or, the number of
		3987	signals): Normally, libev tries to deduce the maximum number of signals
		3988	automatically, but sometimes this fails, in which case it can be
		3989	specified. Also, using a lower number than detected (C<32> should be
		3990	good for about any system in existence) can save some memory, as libev
		3991	statically allocates some 12-24 bytes per signal number.
3091		3992
3092	=item EV_PID_HASHSIZE	3993	=item EV_PID_HASHSIZE
3093		3994
3094	C<ev_child> watchers use a small hash table to distribute workload by	3995	C<ev_child> watchers use a small hash table to distribute workload by
3095	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3996	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3096	than enough. If you need to manage thousands of children you might want to	3997	usually more than enough. If you need to manage thousands of children you
3097	increase this value (I<must> be a power of two).	3998	might want to increase this value (I<must> be a power of two).
3098		3999
3099	=item EV_INOTIFY_HASHSIZE	4000	=item EV_INOTIFY_HASHSIZE
3100		4001
3101	C<ev_stat> watchers use a small hash table to distribute workload by	4002	C<ev_stat> watchers use a small hash table to distribute workload by
3102	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4003	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3103	usually more than enough. If you need to manage thousands of C<ev_stat>	4004	disabled), usually more than enough. If you need to manage thousands of
3104	watchers you might want to increase this value (I<must> be a power of	4005	C<ev_stat> watchers you might want to increase this value (I<must> be a
3105	two).	4006	power of two).
3106		4007
3107	=item EV_USE_4HEAP	4008	=item EV_USE_4HEAP
3108		4009
3109	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4010	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3110	timer and periodics heap, libev uses a 4-heap when this symbol is defined	4011	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3111	to C<1>. The 4-heap uses more complicated (longer) code but has	4012	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3112	noticeably faster performance with many (thousands) of watchers.	4013	faster performance with many (thousands) of watchers.
3113		4014
3114	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4015	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3115	(disabled).	4016	will be C<0>.
3116		4017
3117	=item EV_HEAP_CACHE_AT	4018	=item EV_HEAP_CACHE_AT
3118		4019
3119	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4020	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3120	timer and periodics heap, libev can cache the timestamp (I<at>) within	4021	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3121	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4022	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3122	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4023	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3123	but avoids random read accesses on heap changes. This improves performance	4024	but avoids random read accesses on heap changes. This improves performance
3124	noticeably with with many (hundreds) of watchers.	4025	noticeably with many (hundreds) of watchers.
3125		4026
3126	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4027	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3127	(disabled).	4028	will be C<0>.
3128		4029
3129	=item EV_VERIFY	4030	=item EV_VERIFY
3130		4031
3131	Controls how much internal verification (see C<ev_loop_verify ()>) will	4032	Controls how much internal verification (see C<ev_loop_verify ()>) will
3132	be done: If set to C<0>, no internal verification code will be compiled	4033	be done: If set to C<0>, no internal verification code will be compiled
…		…
3134	called. If set to C<2>, then the internal verification code will be	4035	called. If set to C<2>, then the internal verification code will be
3135	called once per loop, which can slow down libev. If set to C<3>, then the	4036	called once per loop, which can slow down libev. If set to C<3>, then the
3136	verification code will be called very frequently, which will slow down	4037	verification code will be called very frequently, which will slow down
3137	libev considerably.	4038	libev considerably.
3138		4039
3139	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4040	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3140	C<0.>	4041	will be C<0>.
3141		4042
3142	=item EV_COMMON	4043	=item EV_COMMON
3143		4044
3144	By default, all watchers have a C<void *data> member. By redefining	4045	By default, all watchers have a C<void *data> member. By redefining
3145	this macro to a something else you can include more and other types of	4046	this macro to something else you can include more and other types of
3146	members. You have to define it each time you include one of the files,	4047	members. You have to define it each time you include one of the files,
3147	though, and it must be identical each time.	4048	though, and it must be identical each time.
3148		4049
3149	For example, the perl EV module uses something like this:	4050	For example, the perl EV module uses something like this:
3150		4051
…		…
3162	and the way callbacks are invoked and set. Must expand to a struct member	4063	and the way callbacks are invoked and set. Must expand to a struct member
3163	definition and a statement, respectively. See the F<ev.h> header file for	4064	definition and a statement, respectively. See the F<ev.h> header file for
3164	their default definitions. One possible use for overriding these is to	4065	their default definitions. One possible use for overriding these is to
3165	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4066	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3166	method calls instead of plain function calls in C++.	4067	method calls instead of plain function calls in C++.
		4068
		4069	=back
3167		4070
3168	=head2 EXPORTED API SYMBOLS	4071	=head2 EXPORTED API SYMBOLS
3169		4072
3170	If you need to re-export the API (e.g. via a DLL) and you need a list of	4073	If you need to re-export the API (e.g. via a DLL) and you need a list of
3171	exported symbols, you can use the provided F<Symbol.*> files which list	4074	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3201	file.	4104	file.
3202		4105
3203	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4106	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3204	that everybody includes and which overrides some configure choices:	4107	that everybody includes and which overrides some configure choices:
3205		4108
3206	#define EV_MINIMAL 1	4109	#define EV_FEATURES 8
3207	#define EV_USE_POLL 0	4110	#define EV_USE_SELECT 1
3208	#define EV_MULTIPLICITY 0
3209	#define EV_PERIODIC_ENABLE 0	4111	#define EV_PREPARE_ENABLE 1
		4112	#define EV_IDLE_ENABLE 1
3210	#define EV_STAT_ENABLE 0	4113	#define EV_SIGNAL_ENABLE 1
3211	#define EV_FORK_ENABLE 0	4114	#define EV_CHILD_ENABLE 1
		4115	#define EV_USE_STDEXCEPT 0
3212	#define EV_CONFIG_H <config.h>	4116	#define EV_CONFIG_H <config.h>
3213	#define EV_MINPRI 0
3214	#define EV_MAXPRI 0
3215		4117
3216	#include "ev++.h"	4118	#include "ev++.h"
3217		4119
3218	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4120	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3219		4121
3220	#include "ev_cpp.h"	4122	#include "ev_cpp.h"
3221	#include "ev.c"	4123	#include "ev.c"
3222		4124
		4125	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3223		4126
3224	=head1 THREADS AND COROUTINES	4127	=head2 THREADS AND COROUTINES
3225		4128
3226	=head2 THREADS	4129	=head3 THREADS
3227		4130
3228	Libev itself is completely thread-safe, but it uses no locking. This	4131	All libev functions are reentrant and thread-safe unless explicitly
		4132	documented otherwise, but libev implements no locking itself. This means
3229	means that you can use as many loops as you want in parallel, as long as	4133	that you can use as many loops as you want in parallel, as long as there
3230	only one thread ever calls into one libev function with the same loop	4134	are no concurrent calls into any libev function with the same loop
3231	parameter.	4135	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4136	of course): libev guarantees that different event loops share no data
		4137	structures that need any locking.
3232		4138
3233	Or put differently: calls with different loop parameters can be done in	4139	Or to put it differently: calls with different loop parameters can be done
3234	parallel from multiple threads, calls with the same loop parameter must be	4140	concurrently from multiple threads, calls with the same loop parameter
3235	done serially (but can be done from different threads, as long as only one	4141	must be done serially (but can be done from different threads, as long as
3236	thread ever is inside a call at any point in time, e.g. by using a mutex	4142	only one thread ever is inside a call at any point in time, e.g. by using
3237	per loop).	4143	a mutex per loop).
		4144
		4145	Specifically to support threads (and signal handlers), libev implements
		4146	so-called C<ev_async> watchers, which allow some limited form of
		4147	concurrency on the same event loop, namely waking it up "from the
		4148	outside".
3238		4149
3239	If you want to know which design (one loop, locking, or multiple loops	4150	If you want to know which design (one loop, locking, or multiple loops
3240	without or something else still) is best for your problem, then I cannot	4151	without or something else still) is best for your problem, then I cannot
3241	help you. I can give some generic advice however:	4152	help you, but here is some generic advice:
3242		4153
3243	=over 4	4154	=over 4
3244		4155
3245	=item * most applications have a main thread: use the default libev loop	4156	=item * most applications have a main thread: use the default libev loop
3246	in that thread, or create a separate thread running only the default loop.	4157	in that thread, or create a separate thread running only the default loop.
…		…
3258		4169
3259	Choosing a model is hard - look around, learn, know that usually you can do	4170	Choosing a model is hard - look around, learn, know that usually you can do
3260	better than you currently do :-)	4171	better than you currently do :-)
3261		4172
3262	=item * often you need to talk to some other thread which blocks in the	4173	=item * often you need to talk to some other thread which blocks in the
		4174	event loop.
		4175
3263	event loop - C<ev_async> watchers can be used to wake them up from other	4176	C<ev_async> watchers can be used to wake them up from other threads safely
3264	threads safely (or from signal contexts...).	4177	(or from signal contexts...).
		4178
		4179	An example use would be to communicate signals or other events that only
		4180	work in the default loop by registering the signal watcher with the
		4181	default loop and triggering an C<ev_async> watcher from the default loop
		4182	watcher callback into the event loop interested in the signal.
3265		4183
3266	=back	4184	=back
3267		4185
		4186	=head4 THREAD LOCKING EXAMPLE
		4187
		4188	Here is a fictitious example of how to run an event loop in a different
		4189	thread than where callbacks are being invoked and watchers are
		4190	created/added/removed.
		4191
		4192	For a real-world example, see the C<EV::Loop::Async> perl module,
		4193	which uses exactly this technique (which is suited for many high-level
		4194	languages).
		4195
		4196	The example uses a pthread mutex to protect the loop data, a condition
		4197	variable to wait for callback invocations, an async watcher to notify the
		4198	event loop thread and an unspecified mechanism to wake up the main thread.
		4199
		4200	First, you need to associate some data with the event loop:
		4201
		4202	typedef struct {
		4203	mutex_t lock; /* global loop lock */
		4204	ev_async async_w;
		4205	thread_t tid;
		4206	cond_t invoke_cv;
		4207	} userdata;
		4208
		4209	void prepare_loop (EV_P)
		4210	{
		4211	// for simplicity, we use a static userdata struct.
		4212	static userdata u;
		4213
		4214	ev_async_init (&u->async_w, async_cb);
		4215	ev_async_start (EV_A_ &u->async_w);
		4216
		4217	pthread_mutex_init (&u->lock, 0);
		4218	pthread_cond_init (&u->invoke_cv, 0);
		4219
		4220	// now associate this with the loop
		4221	ev_set_userdata (EV_A_ u);
		4222	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4223	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4224
		4225	// then create the thread running ev_loop
		4226	pthread_create (&u->tid, 0, l_run, EV_A);
		4227	}
		4228
		4229	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4230	solely to wake up the event loop so it takes notice of any new watchers
		4231	that might have been added:
		4232
		4233	static void
		4234	async_cb (EV_P_ ev_async *w, int revents)
		4235	{
		4236	// just used for the side effects
		4237	}
		4238
		4239	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4240	protecting the loop data, respectively.
		4241
		4242	static void
		4243	l_release (EV_P)
		4244	{
		4245	userdata *u = ev_userdata (EV_A);
		4246	pthread_mutex_unlock (&u->lock);
		4247	}
		4248
		4249	static void
		4250	l_acquire (EV_P)
		4251	{
		4252	userdata *u = ev_userdata (EV_A);
		4253	pthread_mutex_lock (&u->lock);
		4254	}
		4255
		4256	The event loop thread first acquires the mutex, and then jumps straight
		4257	into C<ev_loop>:
		4258
		4259	void *
		4260	l_run (void *thr_arg)
		4261	{
		4262	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4263
		4264	l_acquire (EV_A);
		4265	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4266	ev_loop (EV_A_ 0);
		4267	l_release (EV_A);
		4268
		4269	return 0;
		4270	}
		4271
		4272	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4273	signal the main thread via some unspecified mechanism (signals? pipe
		4274	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4275	have been called (in a while loop because a) spurious wakeups are possible
		4276	and b) skipping inter-thread-communication when there are no pending
		4277	watchers is very beneficial):
		4278
		4279	static void
		4280	l_invoke (EV_P)
		4281	{
		4282	userdata *u = ev_userdata (EV_A);
		4283
		4284	while (ev_pending_count (EV_A))
		4285	{
		4286	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4287	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4288	}
		4289	}
		4290
		4291	Now, whenever the main thread gets told to invoke pending watchers, it
		4292	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4293	thread to continue:
		4294
		4295	static void
		4296	real_invoke_pending (EV_P)
		4297	{
		4298	userdata *u = ev_userdata (EV_A);
		4299
		4300	pthread_mutex_lock (&u->lock);
		4301	ev_invoke_pending (EV_A);
		4302	pthread_cond_signal (&u->invoke_cv);
		4303	pthread_mutex_unlock (&u->lock);
		4304	}
		4305
		4306	Whenever you want to start/stop a watcher or do other modifications to an
		4307	event loop, you will now have to lock:
		4308
		4309	ev_timer timeout_watcher;
		4310	userdata *u = ev_userdata (EV_A);
		4311
		4312	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4313
		4314	pthread_mutex_lock (&u->lock);
		4315	ev_timer_start (EV_A_ &timeout_watcher);
		4316	ev_async_send (EV_A_ &u->async_w);
		4317	pthread_mutex_unlock (&u->lock);
		4318
		4319	Note that sending the C<ev_async> watcher is required because otherwise
		4320	an event loop currently blocking in the kernel will have no knowledge
		4321	about the newly added timer. By waking up the loop it will pick up any new
		4322	watchers in the next event loop iteration.
		4323
3268	=head2 COROUTINES	4324	=head3 COROUTINES
3269		4325
3270	Libev is much more accommodating to coroutines ("cooperative threads"):	4326	Libev is very accommodating to coroutines ("cooperative threads"):
3271	libev fully supports nesting calls to it's functions from different	4327	libev fully supports nesting calls to its functions from different
3272	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4328	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3273	different coroutines and switch freely between both coroutines running the	4329	different coroutines, and switch freely between both coroutines running
3274	loop, as long as you don't confuse yourself). The only exception is that	4330	the loop, as long as you don't confuse yourself). The only exception is
3275	you must not do this from C<ev_periodic> reschedule callbacks.	4331	that you must not do this from C<ev_periodic> reschedule callbacks.
3276		4332
3277	Care has been invested into making sure that libev does not keep local	4333	Care has been taken to ensure that libev does not keep local state inside
3278	state inside C<ev_loop>, and other calls do not usually allow coroutine	4334	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3279	switches.	4335	they do not call any callbacks.
3280		4336
		4337	=head2 COMPILER WARNINGS
3281		4338
3282	=head1 COMPLEXITIES	4339	Depending on your compiler and compiler settings, you might get no or a
		4340	lot of warnings when compiling libev code. Some people are apparently
		4341	scared by this.
3283		4342
3284	In this section the complexities of (many of) the algorithms used inside	4343	However, these are unavoidable for many reasons. For one, each compiler
3285	libev will be explained. For complexity discussions about backends see the	4344	has different warnings, and each user has different tastes regarding
3286	documentation for C<ev_default_init>.	4345	warning options. "Warn-free" code therefore cannot be a goal except when
		4346	targeting a specific compiler and compiler-version.
3287		4347
3288	All of the following are about amortised time: If an array needs to be	4348	Another reason is that some compiler warnings require elaborate
3289	extended, libev needs to realloc and move the whole array, but this	4349	workarounds, or other changes to the code that make it less clear and less
3290	happens asymptotically never with higher number of elements, so O(1) might	4350	maintainable.
3291	mean it might do a lengthy realloc operation in rare cases, but on average
3292	it is much faster and asymptotically approaches constant time.
3293		4351
3294	=over 4	4352	And of course, some compiler warnings are just plain stupid, or simply
		4353	wrong (because they don't actually warn about the condition their message
		4354	seems to warn about). For example, certain older gcc versions had some
		4355	warnings that resulted in an extreme number of false positives. These have
		4356	been fixed, but some people still insist on making code warn-free with
		4357	such buggy versions.
3295		4358
3296	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4359	While libev is written to generate as few warnings as possible,
		4360	"warn-free" code is not a goal, and it is recommended not to build libev
		4361	with any compiler warnings enabled unless you are prepared to cope with
		4362	them (e.g. by ignoring them). Remember that warnings are just that:
		4363	warnings, not errors, or proof of bugs.
3297		4364
3298	This means that, when you have a watcher that triggers in one hour and
3299	there are 100 watchers that would trigger before that then inserting will
3300	have to skip roughly seven (C<ld 100>) of these watchers.
3301		4365
3302	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4366	=head2 VALGRIND
3303		4367
3304	That means that changing a timer costs less than removing/adding them	4368	Valgrind has a special section here because it is a popular tool that is
3305	as only the relative motion in the event queue has to be paid for.	4369	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3306		4370
3307	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4371	If you think you found a bug (memory leak, uninitialised data access etc.)
		4372	in libev, then check twice: If valgrind reports something like:
3308		4373
3309	These just add the watcher into an array or at the head of a list.	4374	==2274== definitely lost: 0 bytes in 0 blocks.
		4375	==2274== possibly lost: 0 bytes in 0 blocks.
		4376	==2274== still reachable: 256 bytes in 1 blocks.
3310		4377
3311	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4378	Then there is no memory leak, just as memory accounted to global variables
		4379	is not a memleak - the memory is still being referenced, and didn't leak.
3312		4380
3313	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4381	Similarly, under some circumstances, valgrind might report kernel bugs
		4382	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4383	although an acceptable workaround has been found here), or it might be
		4384	confused.
3314		4385
3315	These watchers are stored in lists then need to be walked to find the	4386	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3316	correct watcher to remove. The lists are usually short (you don't usually	4387	make it into some kind of religion.
3317	have many watchers waiting for the same fd or signal).
3318		4388
3319	=item Finding the next timer in each loop iteration: O(1)	4389	If you are unsure about something, feel free to contact the mailing list
		4390	with the full valgrind report and an explanation on why you think this
		4391	is a bug in libev (best check the archives, too :). However, don't be
		4392	annoyed when you get a brisk "this is no bug" answer and take the chance
		4393	of learning how to interpret valgrind properly.
3320		4394
3321	By virtue of using a binary or 4-heap, the next timer is always found at a	4395	If you need, for some reason, empty reports from valgrind for your project
3322	fixed position in the storage array.	4396	I suggest using suppression lists.
3323		4397
3324	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3325		4398
3326	A change means an I/O watcher gets started or stopped, which requires	4399	=head1 PORTABILITY NOTES
3327	libev to recalculate its status (and possibly tell the kernel, depending
3328	on backend and whether C<ev_io_set> was used).
3329		4400
3330	=item Activating one watcher (putting it into the pending state): O(1)	4401	=head2 GNU/LINUX 32 BIT LIMITATIONS
3331		4402
3332	=item Priority handling: O(number_of_priorities)	4403	GNU/Linux is the only common platform that supports 64 bit file/large file
		4404	interfaces but I<disables> them by default.
3333		4405
3334	Priorities are implemented by allocating some space for each	4406	That means that libev compiled in the default environment doesn't support
3335	priority. When doing priority-based operations, libev usually has to	4407	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3336	linearly search all the priorities, but starting/stopping and activating
3337	watchers becomes O(1) w.r.t. priority handling.
3338		4408
3339	=item Sending an ev_async: O(1)	4409	Unfortunately, many programs try to work around this GNU/Linux issue
		4410	by enabling the large file API, which makes them incompatible with the
		4411	standard libev compiled for their system.
3340		4412
3341	=item Processing ev_async_send: O(number_of_async_watchers)	4413	Likewise, libev cannot enable the large file API itself as this would
		4414	suddenly make it incompatible to the default compile time environment,
		4415	i.e. all programs not using special compile switches.
3342		4416
3343	=item Processing signals: O(max_signal_number)	4417	=head2 OS/X AND DARWIN BUGS
3344		4418
3345	Sending involves a system call I<iff> there were no other C<ev_async_send>	4419	The whole thing is a bug if you ask me - basically any system interface
3346	calls in the current loop iteration. Checking for async and signal events	4420	you touch is broken, whether it is locales, poll, kqueue or even the
3347	involves iterating over all running async watchers or all signal numbers.	4421	OpenGL drivers.
3348		4422
3349	=back	4423	=head3 C<kqueue> is buggy
3350		4424
		4425	The kqueue syscall is broken in all known versions - most versions support
		4426	only sockets, many support pipes.
3351		4427
		4428	=head3 C<poll> is buggy
		4429
		4430	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4431	implementation by something calling C<kqueue> internally around the 10.5.6
		4432	release, so now C<kqueue> I<and> C<poll> are broken.
		4433
		4434	Libev tries to work around this by neither using C<kqueue> nor C<poll> by
		4435	default on this rotten platform, but of course you cna still ask for them
		4436	when creating a loop.
		4437
		4438	=head3 C<select> is buggy
		4439
		4440	All that's left is C<select>, and of course Apple found a way to fuck this
		4441	one up as well: On OS/X, C<select> actively limits the number of file
		4442	descriptors you can pass in to 1024 - your program suddenyl crashes when
		4443	you use more.
		4444
		4445	There is an undocumented "workaround" for this - defining
		4446	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4447	work on OS/X.
		4448
		4449	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4450
		4451	=head3 C<errno> reentrancy
		4452
		4453	The default compile environment on Solaris is unfortunately so
		4454	thread-unsafe that you can't even use components/libraries compiled
		4455	without C<-D_REENTRANT> (as long as they use C<errno>), which, of course,
		4456	isn't defined by default.
		4457
		4458	If you want to use libev in threaded environments you have to make sure
		4459	it's compiled with C<_REENTRANT> defined.
		4460
		4461	=head3 Event port backend
		4462
		4463	The scalable event interface for Solaris is called "event ports". Unfortunately,
		4464	this mechanism is very buggy. If you run into high CPU usage, your program
		4465	freezes or you get a large number of spurious wakeups, make sure you have
		4466	all the relevant and latest kernel patches applied. No, I don't know which
		4467	ones, but there are multiple ones.
		4468
		4469	If you can't get it to work, you can try running the program with
		4470	C<LIBEV_FLAGS=3> to only allow C<poll> and C<select> backends.
		4471
		4472	=head2 AIX POLL BUG
		4473
		4474	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4475	this by trying to avoid the poll backend altogether (i.e. it's not even
		4476	compiled in), which normally isn't a big problem as C<select> works fine
		4477	with large bitsets, and AIX is dead anyway.
		4478
3352	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4479	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4480
		4481	=head3 General issues
3353		4482
3354	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4483	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3355	requires, and its I/O model is fundamentally incompatible with the POSIX	4484	requires, and its I/O model is fundamentally incompatible with the POSIX
3356	model. Libev still offers limited functionality on this platform in	4485	model. Libev still offers limited functionality on this platform in
3357	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4486	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3358	descriptors. This only applies when using Win32 natively, not when using	4487	descriptors. This only applies when using Win32 natively, not when using
3359	e.g. cygwin.	4488	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4489	as every compielr comes with a slightly differently broken/incompatible
		4490	environment.
3360		4491
3361	Lifting these limitations would basically require the full	4492	Lifting these limitations would basically require the full
3362	re-implementation of the I/O system. If you are into these kinds of	4493	re-implementation of the I/O system. If you are into this kind of thing,
3363	things, then note that glib does exactly that for you in a very portable	4494	then note that glib does exactly that for you in a very portable way (note
3364	way (note also that glib is the slowest event library known to man).	4495	also that glib is the slowest event library known to man).
3365		4496
3366	There is no supported compilation method available on windows except	4497	There is no supported compilation method available on windows except
3367	embedding it into other applications.	4498	embedding it into other applications.
		4499
		4500	Sensible signal handling is officially unsupported by Microsoft - libev
		4501	tries its best, but under most conditions, signals will simply not work.
3368		4502
3369	Not a libev limitation but worth mentioning: windows apparently doesn't	4503	Not a libev limitation but worth mentioning: windows apparently doesn't
3370	accept large writes: instead of resulting in a partial write, windows will	4504	accept large writes: instead of resulting in a partial write, windows will
3371	either accept everything or return C<ENOBUFS> if the buffer is too large,	4505	either accept everything or return C<ENOBUFS> if the buffer is too large,
3372	so make sure you only write small amounts into your sockets (less than a	4506	so make sure you only write small amounts into your sockets (less than a
3373	megabyte seems safe, but thsi apparently depends on the amount of memory	4507	megabyte seems safe, but this apparently depends on the amount of memory
3374	available).	4508	available).
3375		4509
3376	Due to the many, low, and arbitrary limits on the win32 platform and	4510	Due to the many, low, and arbitrary limits on the win32 platform and
3377	the abysmal performance of winsockets, using a large number of sockets	4511	the abysmal performance of winsockets, using a large number of sockets
3378	is not recommended (and not reasonable). If your program needs to use	4512	is not recommended (and not reasonable). If your program needs to use
3379	more than a hundred or so sockets, then likely it needs to use a totally	4513	more than a hundred or so sockets, then likely it needs to use a totally
3380	different implementation for windows, as libev offers the POSIX readiness	4514	different implementation for windows, as libev offers the POSIX readiness
3381	notification model, which cannot be implemented efficiently on windows	4515	notification model, which cannot be implemented efficiently on windows
3382	(Microsoft monopoly games).	4516	(due to Microsoft monopoly games).
3383		4517
3384	A typical way to use libev under windows is to embed it (see the embedding	4518	A typical way to use libev under windows is to embed it (see the embedding
3385	section for details) and use the following F<evwrap.h> header file instead	4519	section for details) and use the following F<evwrap.h> header file instead
3386	of F<ev.h>:	4520	of F<ev.h>:
3387		4521
…		…
3389	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	4523	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3390		4524
3391	#include "ev.h"	4525	#include "ev.h"
3392		4526
3393	And compile the following F<evwrap.c> file into your project (make sure	4527	And compile the following F<evwrap.c> file into your project (make sure
3394	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	4528	you do I<not> compile the F<ev.c> or any other embedded source files!):
3395		4529
3396	#include "evwrap.h"	4530	#include "evwrap.h"
3397	#include "ev.c"	4531	#include "ev.c"
3398		4532
3399	=over 4
3400
3401	=item The winsocket select function	4533	=head3 The winsocket C<select> function
3402		4534
3403	The winsocket C<select> function doesn't follow POSIX in that it	4535	The winsocket C<select> function doesn't follow POSIX in that it
3404	requires socket I<handles> and not socket I<file descriptors> (it is	4536	requires socket I<handles> and not socket I<file descriptors> (it is
3405	also extremely buggy). This makes select very inefficient, and also	4537	also extremely buggy). This makes select very inefficient, and also
3406	requires a mapping from file descriptors to socket handles (the Microsoft	4538	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3415	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4547	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3416		4548
3417	Note that winsockets handling of fd sets is O(n), so you can easily get a	4549	Note that winsockets handling of fd sets is O(n), so you can easily get a
3418	complexity in the O(n²) range when using win32.	4550	complexity in the O(n²) range when using win32.
3419		4551
3420	=item Limited number of file descriptors	4552	=head3 Limited number of file descriptors
3421		4553
3422	Windows has numerous arbitrary (and low) limits on things.	4554	Windows has numerous arbitrary (and low) limits on things.
3423		4555
3424	Early versions of winsocket's select only supported waiting for a maximum	4556	Early versions of winsocket's select only supported waiting for a maximum
3425	of C<64> handles (probably owning to the fact that all windows kernels	4557	of C<64> handles (probably owning to the fact that all windows kernels
3426	can only wait for C<64> things at the same time internally; Microsoft	4558	can only wait for C<64> things at the same time internally; Microsoft
3427	recommends spawning a chain of threads and wait for 63 handles and the	4559	recommends spawning a chain of threads and wait for 63 handles and the
3428	previous thread in each. Great).	4560	previous thread in each. Sounds great!).
3429		4561
3430	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4562	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3431	to some high number (e.g. C<2048>) before compiling the winsocket select	4563	to some high number (e.g. C<2048>) before compiling the winsocket select
3432	call (which might be in libev or elsewhere, for example, perl does its own	4564	call (which might be in libev or elsewhere, for example, perl and many
3433	select emulation on windows).	4565	other interpreters do their own select emulation on windows).
3434		4566
3435	Another limit is the number of file descriptors in the Microsoft runtime	4567	Another limit is the number of file descriptors in the Microsoft runtime
3436	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4568	libraries, which by default is C<64> (there must be a hidden I<64>
3437	or something like this inside Microsoft). You can increase this by calling	4569	fetish or something like this inside Microsoft). You can increase this
3438	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4570	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3439	arbitrary limit), but is broken in many versions of the Microsoft runtime	4571	(another arbitrary limit), but is broken in many versions of the Microsoft
3440	libraries.
3441
3442	This might get you to about C<512> or C<2048> sockets (depending on	4572	runtime libraries. This might get you to about C<512> or C<2048> sockets
3443	windows version and/or the phase of the moon). To get more, you need to	4573	(depending on windows version and/or the phase of the moon). To get more,
3444	wrap all I/O functions and provide your own fd management, but the cost of	4574	you need to wrap all I/O functions and provide your own fd management, but
3445	calling select (O(n²)) will likely make this unworkable.	4575	the cost of calling select (O(n²)) will likely make this unworkable.
3446		4576
3447	=back
3448
3449
3450	=head1 PORTABILITY REQUIREMENTS	4577	=head2 PORTABILITY REQUIREMENTS
3451		4578
3452	In addition to a working ISO-C implementation, libev relies on a few	4579	In addition to a working ISO-C implementation and of course the
3453	additional extensions:	4580	backend-specific APIs, libev relies on a few additional extensions:
3454		4581
3455	=over 4	4582	=over 4
3456		4583
3457	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4584	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3458	calling conventions regardless of C<ev_watcher_type *>.	4585	calling conventions regardless of C<ev_watcher_type *>.
…		…
3464	calls them using an C<ev_watcher *> internally.	4591	calls them using an C<ev_watcher *> internally.
3465		4592
3466	=item C<sig_atomic_t volatile> must be thread-atomic as well	4593	=item C<sig_atomic_t volatile> must be thread-atomic as well
3467		4594
3468	The type C<sig_atomic_t volatile> (or whatever is defined as	4595	The type C<sig_atomic_t volatile> (or whatever is defined as
3469	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4596	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3470	threads. This is not part of the specification for C<sig_atomic_t>, but is	4597	threads. This is not part of the specification for C<sig_atomic_t>, but is
3471	believed to be sufficiently portable.	4598	believed to be sufficiently portable.
3472		4599
3473	=item C<sigprocmask> must work in a threaded environment	4600	=item C<sigprocmask> must work in a threaded environment
3474		4601
…		…
3483	except the initial one, and run the default loop in the initial thread as	4610	except the initial one, and run the default loop in the initial thread as
3484	well.	4611	well.
3485		4612
3486	=item C<long> must be large enough for common memory allocation sizes	4613	=item C<long> must be large enough for common memory allocation sizes
3487		4614
3488	To improve portability and simplify using libev, libev uses C<long>	4615	To improve portability and simplify its API, libev uses C<long> internally
3489	internally instead of C<size_t> when allocating its data structures. On	4616	instead of C<size_t> when allocating its data structures. On non-POSIX
3490	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4617	systems (Microsoft...) this might be unexpectedly low, but is still at
3491	is still at least 31 bits everywhere, which is enough for hundreds of	4618	least 31 bits everywhere, which is enough for hundreds of millions of
3492	millions of watchers.	4619	watchers.
3493		4620
3494	=item C<double> must hold a time value in seconds with enough accuracy	4621	=item C<double> must hold a time value in seconds with enough accuracy
3495		4622
3496	The type C<double> is used to represent timestamps. It is required to	4623	The type C<double> is used to represent timestamps. It is required to
3497	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4624	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3498	enough for at least into the year 4000. This requirement is fulfilled by	4625	enough for at least into the year 4000. This requirement is fulfilled by
3499	implementations implementing IEEE 754 (basically all existing ones).	4626	implementations implementing IEEE 754, which is basically all existing
		4627	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4628	2200.
3500		4629
3501	=back	4630	=back
3502		4631
3503	If you know of other additional requirements drop me a note.	4632	If you know of other additional requirements drop me a note.
3504		4633
3505		4634
3506	=head1 COMPILER WARNINGS	4635	=head1 ALGORITHMIC COMPLEXITIES
3507		4636
3508	Depending on your compiler and compiler settings, you might get no or a	4637	In this section the complexities of (many of) the algorithms used inside
3509	lot of warnings when compiling libev code. Some people are apparently	4638	libev will be documented. For complexity discussions about backends see
3510	scared by this.	4639	the documentation for C<ev_default_init>.
3511		4640
3512	However, these are unavoidable for many reasons. For one, each compiler	4641	All of the following are about amortised time: If an array needs to be
3513	has different warnings, and each user has different tastes regarding	4642	extended, libev needs to realloc and move the whole array, but this
3514	warning options. "Warn-free" code therefore cannot be a goal except when	4643	happens asymptotically rarer with higher number of elements, so O(1) might
3515	targeting a specific compiler and compiler-version.	4644	mean that libev does a lengthy realloc operation in rare cases, but on
		4645	average it is much faster and asymptotically approaches constant time.
3516		4646
3517	Another reason is that some compiler warnings require elaborate	4647	=over 4
3518	workarounds, or other changes to the code that make it less clear and less
3519	maintainable.
3520		4648
3521	And of course, some compiler warnings are just plain stupid, or simply	4649	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3522	wrong (because they don't actually warn about the condition their message
3523	seems to warn about).
3524		4650
3525	While libev is written to generate as few warnings as possible,	4651	This means that, when you have a watcher that triggers in one hour and
3526	"warn-free" code is not a goal, and it is recommended not to build libev	4652	there are 100 watchers that would trigger before that, then inserting will
3527	with any compiler warnings enabled unless you are prepared to cope with	4653	have to skip roughly seven (C<ld 100>) of these watchers.
3528	them (e.g. by ignoring them). Remember that warnings are just that:
3529	warnings, not errors, or proof of bugs.
3530		4654
		4655	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3531		4656
3532	=head1 VALGRIND	4657	That means that changing a timer costs less than removing/adding them,
		4658	as only the relative motion in the event queue has to be paid for.
3533		4659
3534	Valgrind has a special section here because it is a popular tool that is	4660	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3535	highly useful, but valgrind reports are very hard to interpret.
3536		4661
3537	If you think you found a bug (memory leak, uninitialised data access etc.)	4662	These just add the watcher into an array or at the head of a list.
3538	in libev, then check twice: If valgrind reports something like:
3539		4663
3540	==2274== definitely lost: 0 bytes in 0 blocks.	4664	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3541	==2274== possibly lost: 0 bytes in 0 blocks.
3542	==2274== still reachable: 256 bytes in 1 blocks.
3543		4665
3544	Then there is no memory leak. Similarly, under some circumstances,	4666	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3545	valgrind might report kernel bugs as if it were a bug in libev, or it
3546	might be confused (it is a very good tool, but only a tool).
3547		4667
3548	If you are unsure about something, feel free to contact the mailing list	4668	These watchers are stored in lists, so they need to be walked to find the
3549	with the full valgrind report and an explanation on why you think this is	4669	correct watcher to remove. The lists are usually short (you don't usually
3550	a bug in libev. However, don't be annoyed when you get a brisk "this is	4670	have many watchers waiting for the same fd or signal: one is typical, two
3551	no bug" answer and take the chance of learning how to interpret valgrind	4671	is rare).
3552	properly.
3553		4672
3554	If you need, for some reason, empty reports from valgrind for your project	4673	=item Finding the next timer in each loop iteration: O(1)
3555	I suggest using suppression lists.
3556		4674
		4675	By virtue of using a binary or 4-heap, the next timer is always found at a
		4676	fixed position in the storage array.
		4677
		4678	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4679
		4680	A change means an I/O watcher gets started or stopped, which requires
		4681	libev to recalculate its status (and possibly tell the kernel, depending
		4682	on backend and whether C<ev_io_set> was used).
		4683
		4684	=item Activating one watcher (putting it into the pending state): O(1)
		4685
		4686	=item Priority handling: O(number_of_priorities)
		4687
		4688	Priorities are implemented by allocating some space for each
		4689	priority. When doing priority-based operations, libev usually has to
		4690	linearly search all the priorities, but starting/stopping and activating
		4691	watchers becomes O(1) with respect to priority handling.
		4692
		4693	=item Sending an ev_async: O(1)
		4694
		4695	=item Processing ev_async_send: O(number_of_async_watchers)
		4696
		4697	=item Processing signals: O(max_signal_number)
		4698
		4699	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4700	calls in the current loop iteration. Checking for async and signal events
		4701	involves iterating over all running async watchers or all signal numbers.
		4702
		4703	=back
		4704
		4705
		4706	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4707
		4708	The major version 4 introduced some minor incompatible changes to the API.
		4709
		4710	At the moment, the C<ev.h> header file tries to implement superficial
		4711	compatibility, so most programs should still compile. Those might be
		4712	removed in later versions of libev, so better update early than late.
		4713
		4714	=over 4
		4715
		4716	=item C<ev_loop_count> renamed to C<ev_iteration>
		4717
		4718	=item C<ev_loop_depth> renamed to C<ev_depth>
		4719
		4720	=item C<ev_loop_verify> renamed to C<ev_verify>
		4721
		4722	Most functions working on C<struct ev_loop> objects don't have an
		4723	C<ev_loop_> prefix, so it was removed. Note that C<ev_loop_fork> is
		4724	still called C<ev_loop_fork> because it would otherwise clash with the
		4725	C<ev_fork> typedef.
		4726
		4727	=item C<EV_TIMEOUT> renamed to C<EV_TIMER> in C<revents>
		4728
		4729	This is a simple rename - all other watcher types use their name
		4730	as revents flag, and now C<ev_timer> does, too.
		4731
		4732	Both C<EV_TIMER> and C<EV_TIMEOUT> symbols were present in 3.x versions
		4733	and continue to be present for the foreseeable future, so this is mostly a
		4734	documentation change.
		4735
		4736	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4737
		4738	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4739	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4740	and work, but the library code will of course be larger.
		4741
		4742	=back
		4743
		4744
		4745	=head1 GLOSSARY
		4746
		4747	=over 4
		4748
		4749	=item active
		4750
		4751	A watcher is active as long as it has been started (has been attached to
		4752	an event loop) but not yet stopped (disassociated from the event loop).
		4753
		4754	=item application
		4755
		4756	In this document, an application is whatever is using libev.
		4757
		4758	=item callback
		4759
		4760	The address of a function that is called when some event has been
		4761	detected. Callbacks are being passed the event loop, the watcher that
		4762	received the event, and the actual event bitset.
		4763
		4764	=item callback invocation
		4765
		4766	The act of calling the callback associated with a watcher.
		4767
		4768	=item event
		4769
		4770	A change of state of some external event, such as data now being available
		4771	for reading on a file descriptor, time having passed or simply not having
		4772	any other events happening anymore.
		4773
		4774	In libev, events are represented as single bits (such as C<EV_READ> or
		4775	C<EV_TIMER>).
		4776
		4777	=item event library
		4778
		4779	A software package implementing an event model and loop.
		4780
		4781	=item event loop
		4782
		4783	An entity that handles and processes external events and converts them
		4784	into callback invocations.
		4785
		4786	=item event model
		4787
		4788	The model used to describe how an event loop handles and processes
		4789	watchers and events.
		4790
		4791	=item pending
		4792
		4793	A watcher is pending as soon as the corresponding event has been detected,
		4794	and stops being pending as soon as the watcher will be invoked or its
		4795	pending status is explicitly cleared by the application.
		4796
		4797	A watcher can be pending, but not active. Stopping a watcher also clears
		4798	its pending status.
		4799
		4800	=item real time
		4801
		4802	The physical time that is observed. It is apparently strictly monotonic :)
		4803
		4804	=item wall-clock time
		4805
		4806	The time and date as shown on clocks. Unlike real time, it can actually
		4807	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4808	clock.
		4809
		4810	=item watcher
		4811
		4812	A data structure that describes interest in certain events. Watchers need
		4813	to be started (attached to an event loop) before they can receive events.
		4814
		4815	=item watcher invocation
		4816
		4817	The act of calling the callback associated with a watcher.
		4818
		4819	=back
3557		4820
3558	=head1 AUTHOR	4821	=head1 AUTHOR
3559		4822
3560	Marc Lehmann <libev@schmorp.de>.	4823	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3561		4824

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