[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.196 by root, Tue Oct 21 20:04:14 2008 UTC vs.
Revision 1.213 by root, Wed Nov 5 02:48:45 2008 UTC

…		…
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	// every watcher type has its own typedef'd struct	14	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	15	// with the name ev_TYPE
16	ev_io stdin_watcher;	16	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	17	ev_timer timeout_watcher;
18		18
19	// all watcher callbacks have a similar signature	19	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	20	// this callback is called when data is readable on stdin
21	static void	21	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	22	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	23	{
24	puts ("stdin ready");	24	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	25	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	26	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	27	ev_io_stop (EV_A_ w);
…		…
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	30	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	31	}
32		32
33	// another callback, this time for a time-out	33	// another callback, this time for a time-out
34	static void	34	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	35	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	36	{
37	puts ("timeout");	37	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	38	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	39	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	40	}
41		41
42	int	42	int
43	main (void)	43	main (void)
44	{	44	{
45	// use the default event loop unless you have special needs	45	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	46	ev_loop *loop = ev_default_loop (0);
47		47
48	// initialise an io watcher, then start it	48	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	49	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /STDIN_FILENO/ 0, EV_READ);	50	ev_io_init (&stdin_watcher, stdin_cb, /STDIN_FILENO/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	51	ev_io_start (loop, &stdin_watcher);
…		…
103	Libev is very configurable. In this manual the default (and most common)	103	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	104	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	105	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	106	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	107	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	108	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	109	this argument.
110		110
111	=head2 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
112		112
113	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
…		…
276		276
277	=back	277	=back
278		278
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		280
281	An event loop is described by a C<struct ev_loop *>. The library knows two	281	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	282	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	283	I<function>).
		284
		285	The library knows two types of such loops, the I<default> loop, which
		286	supports signals and child events, and dynamically created loops which do
		287	not.
284		288
285	=over 4	289	=over 4
286		290
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		292
…		…
294	If you don't know what event loop to use, use the one returned from this	298	If you don't know what event loop to use, use the one returned from this
295	function.	299	function.
296		300
297	Note that this function is I<not> thread-safe, so if you want to use it	301	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,	302	from multiple threads, you have to lock (note also that this is unlikely,
299	as loops cannot bes hared easily between threads anyway).	303	as loops cannot be shared easily between threads anyway).
300		304
301	The default loop is the only loop that can handle C<ev_signal> and	305	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	306	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	307	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	308	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		385
382	For few fds, this backend is a bit little slower than poll and select,	386	For few fds, this backend is a bit little slower than poll and select,
383	but it scales phenomenally better. While poll and select usually scale	387	but it scales phenomenally better. While poll and select usually scale
384	like O(total_fds) where n is the total number of fds (or the highest fd),	388	like O(total_fds) where n is the total number of fds (or the highest fd),
385	epoll scales either O(1) or O(active_fds). The epoll design has a number	389	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	390
387	cases and requiring a system call per fd change, no fork support and bad	391	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	392	of the more advanced event mechanisms: mere annoyances include silently
		393	dropping file descriptors, requiring a system call per change per file
		394	descriptor (and unnecessary guessing of parameters), problems with dup and
		395	so on. The biggest issue is fork races, however - if a program forks then
		396	I<both> parent and child process have to recreate the epoll set, which can
		397	take considerable time (one syscall per file descriptor) and is of course
		398	hard to detect.
		399
		400	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		401	of course I<doesn't>, and epoll just loves to report events for totally
		402	I<different> file descriptors (even already closed ones, so one cannot
		403	even remove them from the set) than registered in the set (especially
		404	on SMP systems). Libev tries to counter these spurious notifications by
		405	employing an additional generation counter and comparing that against the
		406	events to filter out spurious ones, recreating the set when required.
389		407
390	While stopping, setting and starting an I/O watcher in the same iteration	408	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	409	will result in some caching, there is still a system call per such
392	(because the fd could point to a different file description now), so its	410	incident (because the same I<file descriptor> could point to a different
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	411	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	412	file descriptors might not work very well if you register events for both
395		413	file descriptors.
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399		414
400	Best performance from this backend is achieved by not unregistering all	415	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	416	watchers for a file descriptor until it has been closed, if possible,
402	i.e. keep at least one watcher active per fd at all times. Stopping and	417	i.e. keep at least one watcher active per fd at all times. Stopping and
403	starting a watcher (without re-setting it) also usually doesn't cause	418	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	419	extra overhead. A fork can both result in spurious notifications as well
		420	as in libev having to destroy and recreate the epoll object, which can
		421	take considerable time and thus should be avoided.
		422
		423	All this means that, in practise, C<EVBACKEND_SELECT> is as fast or faster
		424	then epoll for maybe up to a hundred file descriptors. So sad.
405		425
406	While nominally embeddable in other event loops, this feature is broken in	426	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	427	all kernel versions tested so far.
408		428
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	429	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	430	C<EVBACKEND_POLL>.
411		431
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	432	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		433
414	Kqueue deserves special mention, as at the time of this writing, it was	434	Kqueue deserves special mention, as at the time of this writing, it
415	broken on all BSDs except NetBSD (usually it doesn't work reliably with	435	was broken on all BSDs except NetBSD (usually it doesn't work reliably
416	anything but sockets and pipes, except on Darwin, where of course it's	436	with anything but sockets and pipes, except on Darwin, where of course
417	completely useless). For this reason it's not being "auto-detected" unless	437	it's completely useless). Unlike epoll, however, whose brokenness
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	438	is by design, these kqueue bugs can (and eventually will) be fixed
419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	439	without API changes to existing programs. For this reason it's not being
		440	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		441	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		442	system like NetBSD.
420		443
421	You still can embed kqueue into a normal poll or select backend and use it	444	You still can embed kqueue into a normal poll or select backend and use it
422	only for sockets (after having made sure that sockets work with kqueue on	445	only for sockets (after having made sure that sockets work with kqueue on
423	the target platform). See C<ev_embed> watchers for more info.	446	the target platform). See C<ev_embed> watchers for more info.
424		447
425	It scales in the same way as the epoll backend, but the interface to the	448	It scales in the same way as the epoll backend, but the interface to the
426	kernel is more efficient (which says nothing about its actual speed, of	449	kernel is more efficient (which says nothing about its actual speed, of
427	course). While stopping, setting and starting an I/O watcher does never	450	course). While stopping, setting and starting an I/O watcher does never
428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	451	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
429	two event changes per incident. Support for C<fork ()> is very bad and it	452	two event changes per incident. Support for C<fork ()> is very bad (but
430	drops fds silently in similarly hard-to-detect cases.	453	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		454	cases
431		455
432	This backend usually performs well under most conditions.	456	This backend usually performs well under most conditions.
433		457
434	While nominally embeddable in other event loops, this doesn't work	458	While nominally embeddable in other event loops, this doesn't work
435	everywhere, so you might need to test for this. And since it is broken	459	everywhere, so you might need to test for this. And since it is broken
…		…
464	might perform better.	488	might perform better.
465		489
466	On the positive side, with the exception of the spurious readiness	490	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	491	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	492	in all tests and is fully embeddable, which is a rare feat among the
469	OS-specific backends.	493	OS-specific backends (I vastly prefer correctness over speed hacks).
470		494
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	495	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	496	C<EVBACKEND_POLL>.
473		497
474	=item C<EVBACKEND_ALL>	498	=item C<EVBACKEND_ALL>
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	551	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	552	calling this function, or cope with the fact afterwards (which is usually
529	the easiest thing, you can just ignore the watchers and/or C<free ()> them	553	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	554	for example).
531		555
532	Note that certain global state, such as signal state, will not be freed by	556	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	557	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	558	as signal and child watchers) would need to be stopped manually.
535		559
536	In general it is not advisable to call this function except in the	560	In general it is not advisable to call this function except in the
537	rare occasion where you really need to free e.g. the signal handling	561	rare occasion where you really need to free e.g. the signal handling
538	pipe fds. If you need dynamically allocated loops it is better to use	562	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	563	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
631	the loop.	655	the loop.
632		656
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	657	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
634	necessary) and will handle those and any already outstanding ones. It	658	necessary) and will handle those and any already outstanding ones. It
635	will block your process until at least one new event arrives (which could	659	will block your process until at least one new event arrives (which could
636	be an event internal to libev itself, so there is no guarentee that a	660	be an event internal to libev itself, so there is no guarantee that a
637	user-registered callback will be called), and will return after one	661	user-registered callback will be called), and will return after one
638	iteration of the loop.	662	iteration of the loop.
639		663
640	This is useful if you are waiting for some external event in conjunction	664	This is useful if you are waiting for some external event in conjunction
641	with something not expressible using other libev watchers (i.e. "roll your	665	with something not expressible using other libev watchers (i.e. "roll your
…		…
710	respectively).	734	respectively).
711		735
712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	736	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
713	running when nothing else is active.	737	running when nothing else is active.
714		738
715	struct ev_signal exitsig;	739	ev_signal exitsig;
716	ev_signal_init (&exitsig, sig_cb, SIGINT);	740	ev_signal_init (&exitsig, sig_cb, SIGINT);
717	ev_signal_start (loop, &exitsig);	741	ev_signal_start (loop, &exitsig);
718	evf_unref (loop);	742	evf_unref (loop);
719		743
720	Example: For some weird reason, unregister the above signal handler again.	744	Example: For some weird reason, unregister the above signal handler again.
…		…
768	they fire on, say, one-second boundaries only.	792	they fire on, say, one-second boundaries only.
769		793
770	=item ev_loop_verify (loop)	794	=item ev_loop_verify (loop)
771		795
772	This function only does something when C<EV_VERIFY> support has been	796	This function only does something when C<EV_VERIFY> support has been
773	compiled in. which is the default for non-minimal builds. It tries to go	797	compiled in, which is the default for non-minimal builds. It tries to go
774	through all internal structures and checks them for validity. If anything	798	through all internal structures and checks them for validity. If anything
775	is found to be inconsistent, it will print an error message to standard	799	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	800	error and call C<abort ()>.
777		801
778	This can be used to catch bugs inside libev itself: under normal	802	This can be used to catch bugs inside libev itself: under normal
…		…
782	=back	806	=back
783		807
784		808
785	=head1 ANATOMY OF A WATCHER	809	=head1 ANATOMY OF A WATCHER
786		810
		811	In the following description, uppercase C<TYPE> in names stands for the
		812	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		813	watchers and C<ev_io_start> for I/O watchers.
		814
787	A watcher is a structure that you create and register to record your	815	A watcher is a structure that you create and register to record your
788	interest in some event. For instance, if you want to wait for STDIN to	816	interest in some event. For instance, if you want to wait for STDIN to
789	become readable, you would create an C<ev_io> watcher for that:	817	become readable, you would create an C<ev_io> watcher for that:
790		818
791	static void my_cb (struct ev_loop loop, struct ev_io w, int revents)	819	static void my_cb (struct ev_loop loop, ev_io w, int revents)
792	{	820	{
793	ev_io_stop (w);	821	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	822	ev_unloop (loop, EVUNLOOP_ALL);
795	}	823	}
796		824
797	struct ev_loop *loop = ev_default_loop (0);	825	struct ev_loop *loop = ev_default_loop (0);
		826
798	struct ev_io stdin_watcher;	827	ev_io stdin_watcher;
		828
799	ev_init (&stdin_watcher, my_cb);	829	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	830	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	831	ev_io_start (loop, &stdin_watcher);
		832
802	ev_loop (loop, 0);	833	ev_loop (loop, 0);
803		834
804	As you can see, you are responsible for allocating the memory for your	835	As you can see, you are responsible for allocating the memory for your
805	watcher structures (and it is usually a bad idea to do this on the stack,	836	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	837	stack).
		838
		839	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		840	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
807		841
808	Each watcher structure must be initialised by a call to C<ev_init	842	Each watcher structure must be initialised by a call to C<ev_init
809	(watcher *, callback)>, which expects a callback to be provided. This	843	(watcher *, callback)>, which expects a callback to be provided. This
810	callback gets invoked each time the event occurs (or, in the case of I/O	844	callback gets invoked each time the event occurs (or, in the case of I/O
811	watchers, each time the event loop detects that the file descriptor given	845	watchers, each time the event loop detects that the file descriptor given
812	is readable and/or writable).	846	is readable and/or writable).
813		847
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	848	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
815	with arguments specific to this watcher type. There is also a macro	849	macro to configure it, with arguments specific to the watcher type. There
816	to combine initialisation and setting in one call: C<< ev_<type>_init	850	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	851	ev_TYPE_init (watcher *, callback, ...) >>.
818		852
819	To make the watcher actually watch out for events, you have to start it	853	To make the watcher actually watch out for events, you have to start it
820	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	854	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
821	*) >>), and you can stop watching for events at any time by calling the	855	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	856	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		857
824	As long as your watcher is active (has been started but not stopped) you	858	As long as your watcher is active (has been started but not stopped) you
825	must not touch the values stored in it. Most specifically you must never	859	must not touch the values stored in it. Most specifically you must never
826	reinitialise it or call its C<set> macro.	860	reinitialise it or call its C<ev_TYPE_set> macro.
827		861
828	Each and every callback receives the event loop pointer as first, the	862	Each and every callback receives the event loop pointer as first, the
829	registered watcher structure as second, and a bitset of received events as	863	registered watcher structure as second, and a bitset of received events as
830	third argument.	864	third argument.
831		865
…		…
894	=item C<EV_ERROR>	928	=item C<EV_ERROR>
895		929
896	An unspecified error has occurred, the watcher has been stopped. This might	930	An unspecified error has occurred, the watcher has been stopped. This might
897	happen because the watcher could not be properly started because libev	931	happen because the watcher could not be properly started because libev
898	ran out of memory, a file descriptor was found to be closed or any other	932	ran out of memory, a file descriptor was found to be closed or any other
		933	problem. Libev considers these application bugs.
		934
899	problem. You best act on it by reporting the problem and somehow coping	935	You best act on it by reporting the problem and somehow coping with the
900	with the watcher being stopped.	936	watcher being stopped. Note that well-written programs should not receive
		937	an error ever, so when your watcher receives it, this usually indicates a
		938	bug in your program.
901		939
902	Libev will usually signal a few "dummy" events together with an error, for	940	Libev will usually signal a few "dummy" events together with an error, for
903	example it might indicate that a fd is readable or writable, and if your	941	example it might indicate that a fd is readable or writable, and if your
904	callbacks is well-written it can just attempt the operation and cope with	942	callbacks is well-written it can just attempt the operation and cope with
905	the error from read() or write(). This will not work in multi-threaded	943	the error from read() or write(). This will not work in multi-threaded
…		…
908		946
909	=back	947	=back
910		948
911	=head2 GENERIC WATCHER FUNCTIONS	949	=head2 GENERIC WATCHER FUNCTIONS
912		950
913	In the following description, C<TYPE> stands for the watcher type,
914	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
915
916	=over 4	951	=over 4
917		952
918	=item C<ev_init> (ev_TYPE *watcher, callback)	953	=item C<ev_init> (ev_TYPE *watcher, callback)
919		954
920	This macro initialises the generic portion of a watcher. The contents	955	This macro initialises the generic portion of a watcher. The contents
…		…
925	which rolls both calls into one.	960	which rolls both calls into one.
926		961
927	You can reinitialise a watcher at any time as long as it has been stopped	962	You can reinitialise a watcher at any time as long as it has been stopped
928	(or never started) and there are no pending events outstanding.	963	(or never started) and there are no pending events outstanding.
929		964
930	The callback is always of type C<void ()(ev_loop loop, ev_TYPE *watcher,	965	The callback is always of type C<void ()(struct ev_loop loop, ev_TYPE *watcher,
931	int revents)>.	966	int revents)>.
932		967
933	Example: Initialise an C<ev_io> watcher in two steps.	968	Example: Initialise an C<ev_io> watcher in two steps.
934		969
935	ev_io w;	970	ev_io w;
…		…
1028	The default priority used by watchers when no priority has been set is	1063	The default priority used by watchers when no priority has been set is
1029	always C<0>, which is supposed to not be too high and not be too low :).	1064	always C<0>, which is supposed to not be too high and not be too low :).
1030		1065
1031	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1066	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1032	fine, as long as you do not mind that the priority value you query might	1067	fine, as long as you do not mind that the priority value you query might
1033	or might not have been adjusted to be within valid range.	1068	or might not have been clamped to the valid range.
1034		1069
1035	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1070	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1036		1071
1037	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1072	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1038	C<loop> nor C<revents> need to be valid as long as the watcher callback	1073	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1060	member, you can also "subclass" the watcher type and provide your own	1095	member, you can also "subclass" the watcher type and provide your own
1061	data:	1096	data:
1062		1097
1063	struct my_io	1098	struct my_io
1064	{	1099	{
1065	struct ev_io io;	1100	ev_io io;
1066	int otherfd;	1101	int otherfd;
1067	void *somedata;	1102	void *somedata;
1068	struct whatever *mostinteresting;	1103	struct whatever *mostinteresting;
1069	};	1104	};
1070		1105
…		…
1073	ev_io_init (&w.io, my_cb, fd, EV_READ);	1108	ev_io_init (&w.io, my_cb, fd, EV_READ);
1074		1109
1075	And since your callback will be called with a pointer to the watcher, you	1110	And since your callback will be called with a pointer to the watcher, you
1076	can cast it back to your own type:	1111	can cast it back to your own type:
1077		1112
1078	static void my_cb (struct ev_loop loop, struct ev_io w_, int revents)	1113	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1079	{	1114	{
1080	struct my_io w = (struct my_io )w_;	1115	struct my_io w = (struct my_io )w_;
1081	...	1116	...
1082	}	1117	}
1083		1118
…		…
1101	programmers):	1136	programmers):
1102		1137
1103	#include <stddef.h>	1138	#include <stddef.h>
1104		1139
1105	static void	1140	static void
1106	t1_cb (EV_P_ struct ev_timer *w, int revents)	1141	t1_cb (EV_P_ ev_timer *w, int revents)
1107	{	1142	{
1108	struct my_biggy big = (struct my_biggy *	1143	struct my_biggy big = (struct my_biggy *
1109	(((char *)w) - offsetof (struct my_biggy, t1));	1144	(((char *)w) - offsetof (struct my_biggy, t1));
1110	}	1145	}
1111		1146
1112	static void	1147	static void
1113	t2_cb (EV_P_ struct ev_timer *w, int revents)	1148	t2_cb (EV_P_ ev_timer *w, int revents)
1114	{	1149	{
1115	struct my_biggy big = (struct my_biggy *	1150	struct my_biggy big = (struct my_biggy *
1116	(((char *)w) - offsetof (struct my_biggy, t2));	1151	(((char *)w) - offsetof (struct my_biggy, t2));
1117	}	1152	}
1118		1153
…		…
1253	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1288	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1254	readable, but only once. Since it is likely line-buffered, you could	1289	readable, but only once. Since it is likely line-buffered, you could
1255	attempt to read a whole line in the callback.	1290	attempt to read a whole line in the callback.
1256		1291
1257	static void	1292	static void
1258	stdin_readable_cb (struct ev_loop loop, struct ev_io w, int revents)	1293	stdin_readable_cb (struct ev_loop loop, ev_io w, int revents)
1259	{	1294	{
1260	ev_io_stop (loop, w);	1295	ev_io_stop (loop, w);
1261	.. read from stdin here (or from w->fd) and handle any I/O errors	1296	.. read from stdin here (or from w->fd) and handle any I/O errors
1262	}	1297	}
1263		1298
1264	...	1299	...
1265	struct ev_loop *loop = ev_default_init (0);	1300	struct ev_loop *loop = ev_default_init (0);
1266	struct ev_io stdin_readable;	1301	ev_io stdin_readable;
1267	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1302	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1268	ev_io_start (loop, &stdin_readable);	1303	ev_io_start (loop, &stdin_readable);
1269	ev_loop (loop, 0);	1304	ev_loop (loop, 0);
1270		1305
1271		1306
…		…
1282		1317
1283	The callback is guaranteed to be invoked only I<after> its timeout has	1318	The callback is guaranteed to be invoked only I<after> its timeout has
1284	passed, but if multiple timers become ready during the same loop iteration	1319	passed, but if multiple timers become ready during the same loop iteration
1285	then order of execution is undefined.	1320	then order of execution is undefined.
1286		1321
		1322	=head3 Be smart about timeouts
		1323
		1324	Many real-world problems involve some kind of timeout, usually for error
		1325	recovery. A typical example is an HTTP request - if the other side hangs,
		1326	you want to raise some error after a while.
		1327
		1328	What follows are some ways to handle this problem, from obvious and
		1329	inefficient to smart and efficient.
		1330
		1331	In the following, a 60 second activity timeout is assumed - a timeout that
		1332	gets reset to 60 seconds each time there is activity (e.g. each time some
		1333	data or other life sign was received).
		1334
		1335	=over 4
		1336
		1337	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1338
		1339	This is the most obvious, but not the most simple way: In the beginning,
		1340	start the watcher:
		1341
		1342	ev_timer_init (timer, callback, 60., 0.);
		1343	ev_timer_start (loop, timer);
		1344
		1345	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1346	and start it again:
		1347
		1348	ev_timer_stop (loop, timer);
		1349	ev_timer_set (timer, 60., 0.);
		1350	ev_timer_start (loop, timer);
		1351
		1352	This is relatively simple to implement, but means that each time there is
		1353	some activity, libev will first have to remove the timer from its internal
		1354	data structure and then add it again. Libev tries to be fast, but it's
		1355	still not a constant-time operation.
		1356
		1357	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1358
		1359	This is the easiest way, and involves using C<ev_timer_again> instead of
		1360	C<ev_timer_start>.
		1361
		1362	To implement this, configure an C<ev_timer> with a C<repeat> value
		1363	of C<60> and then call C<ev_timer_again> at start and each time you
		1364	successfully read or write some data. If you go into an idle state where
		1365	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1366	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1367
		1368	That means you can ignore both the C<ev_timer_start> function and the
		1369	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1370	member and C<ev_timer_again>.
		1371
		1372	At start:
		1373
		1374	ev_timer_init (timer, callback);
		1375	timer->repeat = 60.;
		1376	ev_timer_again (loop, timer);
		1377
		1378	Each time there is some activity:
		1379
		1380	ev_timer_again (loop, timer);
		1381
		1382	It is even possible to change the time-out on the fly, regardless of
		1383	whether the watcher is active or not:
		1384
		1385	timer->repeat = 30.;
		1386	ev_timer_again (loop, timer);
		1387
		1388	This is slightly more efficient then stopping/starting the timer each time
		1389	you want to modify its timeout value, as libev does not have to completely
		1390	remove and re-insert the timer from/into its internal data structure.
		1391
		1392	It is, however, even simpler than the "obvious" way to do it.
		1393
		1394	=item 3. Let the timer time out, but then re-arm it as required.
		1395
		1396	This method is more tricky, but usually most efficient: Most timeouts are
		1397	relatively long compared to the intervals between other activity - in
		1398	our example, within 60 seconds, there are usually many I/O events with
		1399	associated activity resets.
		1400
		1401	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1402	but remember the time of last activity, and check for a real timeout only
		1403	within the callback:
		1404
		1405	ev_tstamp last_activity; // time of last activity
		1406
		1407	static void
		1408	callback (EV_P_ ev_timer *w, int revents)
		1409	{
		1410	ev_tstamp now = ev_now (EV_A);
		1411	ev_tstamp timeout = last_activity + 60.;
		1412
		1413	// if last_activity + 60. is older than now, we did time out
		1414	if (timeout < now)
		1415	{
		1416	// timeout occured, take action
		1417	}
		1418	else
		1419	{
		1420	// callback was invoked, but there was some activity, re-arm
		1421	// the watcher to fire in last_activity + 60, which is
		1422	// guaranteed to be in the future, so "again" is positive:
		1423	w->again = timeout - now;
		1424	ev_timer_again (EV_A_ w);
		1425	}
		1426	}
		1427
		1428	To summarise the callback: first calculate the real timeout (defined
		1429	as "60 seconds after the last activity"), then check if that time has
		1430	been reached, which means something I<did>, in fact, time out. Otherwise
		1431	the callback was invoked too early (C<timeout> is in the future), so
		1432	re-schedule the timer to fire at that future time, to see if maybe we have
		1433	a timeout then.
		1434
		1435	Note how C<ev_timer_again> is used, taking advantage of the
		1436	C<ev_timer_again> optimisation when the timer is already running.
		1437
		1438	This scheme causes more callback invocations (about one every 60 seconds
		1439	minus half the average time between activity), but virtually no calls to
		1440	libev to change the timeout.
		1441
		1442	To start the timer, simply initialise the watcher and set C<last_activity>
		1443	to the current time (meaning we just have some activity :), then call the
		1444	callback, which will "do the right thing" and start the timer:
		1445
		1446	ev_timer_init (timer, callback);
		1447	last_activity = ev_now (loop);
		1448	callback (loop, timer, EV_TIMEOUT);
		1449
		1450	And when there is some activity, simply store the current time in
		1451	C<last_activity>, no libev calls at all:
		1452
		1453	last_actiivty = ev_now (loop);
		1454
		1455	This technique is slightly more complex, but in most cases where the
		1456	time-out is unlikely to be triggered, much more efficient.
		1457
		1458	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1459	callback :) - just change the timeout and invoke the callback, which will
		1460	fix things for you.
		1461
		1462	=item 4. Wee, just use a double-linked list for your timeouts.
		1463
		1464	If there is not one request, but many thousands (millions...), all
		1465	employing some kind of timeout with the same timeout value, then one can
		1466	do even better:
		1467
		1468	When starting the timeout, calculate the timeout value and put the timeout
		1469	at the I<end> of the list.
		1470
		1471	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1472	the list is expected to fire (for example, using the technique #3).
		1473
		1474	When there is some activity, remove the timer from the list, recalculate
		1475	the timeout, append it to the end of the list again, and make sure to
		1476	update the C<ev_timer> if it was taken from the beginning of the list.
		1477
		1478	This way, one can manage an unlimited number of timeouts in O(1) time for
		1479	starting, stopping and updating the timers, at the expense of a major
		1480	complication, and having to use a constant timeout. The constant timeout
		1481	ensures that the list stays sorted.
		1482
		1483	=back
		1484
		1485	So which method the best?
		1486
		1487	Method #2 is a simple no-brain-required solution that is adequate in most
		1488	situations. Method #3 requires a bit more thinking, but handles many cases
		1489	better, and isn't very complicated either. In most case, choosing either
		1490	one is fine, with #3 being better in typical situations.
		1491
		1492	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1493	rather complicated, but extremely efficient, something that really pays
		1494	off after the first million or so of active timers, i.e. it's usually
		1495	overkill :)
		1496
1287	=head3 The special problem of time updates	1497	=head3 The special problem of time updates
1288		1498
1289	Establishing the current time is a costly operation (it usually takes at	1499	Establishing the current time is a costly operation (it usually takes at
1290	least two system calls): EV therefore updates its idea of the current	1500	least two system calls): EV therefore updates its idea of the current
1291	time only before and after C<ev_loop> collects new events, which causes a	1501	time only before and after C<ev_loop> collects new events, which causes a
…		…
1334	If the timer is started but non-repeating, stop it (as if it timed out).	1544	If the timer is started but non-repeating, stop it (as if it timed out).
1335		1545
1336	If the timer is repeating, either start it if necessary (with the	1546	If the timer is repeating, either start it if necessary (with the
1337	C<repeat> value), or reset the running timer to the C<repeat> value.	1547	C<repeat> value), or reset the running timer to the C<repeat> value.
1338		1548
1339	This sounds a bit complicated, but here is a useful and typical	1549	This sounds a bit complicated, see "Be smart about timeouts", above, for a
1340	example: Imagine you have a TCP connection and you want a so-called idle	1550	usage example.
1341	timeout, that is, you want to be called when there have been, say, 60
1342	seconds of inactivity on the socket. The easiest way to do this is to
1343	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1344	C<ev_timer_again> each time you successfully read or write some data. If
1345	you go into an idle state where you do not expect data to travel on the
1346	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1347	automatically restart it if need be.
1348
1349	That means you can ignore the C<after> value and C<ev_timer_start>
1350	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1351
1352	ev_timer_init (timer, callback, 0., 5.);
1353	ev_timer_again (loop, timer);
1354	...
1355	timer->again = 17.;
1356	ev_timer_again (loop, timer);
1357	...
1358	timer->again = 10.;
1359	ev_timer_again (loop, timer);
1360
1361	This is more slightly efficient then stopping/starting the timer each time
1362	you want to modify its timeout value.
1363
1364	Note, however, that it is often even more efficient to remember the
1365	time of the last activity and let the timer time-out naturally. In the
1366	callback, you then check whether the time-out is real, or, if there was
1367	some activity, you reschedule the watcher to time-out in "last_activity +
1368	timeout - ev_now ()" seconds.
1369		1551
1370	=item ev_tstamp repeat [read-write]	1552	=item ev_tstamp repeat [read-write]
1371		1553
1372	The current C<repeat> value. Will be used each time the watcher times out	1554	The current C<repeat> value. Will be used each time the watcher times out
1373	or C<ev_timer_again> is called, and determines the next timeout (if any),	1555	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1378	=head3 Examples	1560	=head3 Examples
1379		1561
1380	Example: Create a timer that fires after 60 seconds.	1562	Example: Create a timer that fires after 60 seconds.
1381		1563
1382	static void	1564	static void
1383	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)	1565	one_minute_cb (struct ev_loop loop, ev_timer w, int revents)
1384	{	1566	{
1385	.. one minute over, w is actually stopped right here	1567	.. one minute over, w is actually stopped right here
1386	}	1568	}
1387		1569
1388	struct ev_timer mytimer;	1570	ev_timer mytimer;
1389	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1571	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1390	ev_timer_start (loop, &mytimer);	1572	ev_timer_start (loop, &mytimer);
1391		1573
1392	Example: Create a timeout timer that times out after 10 seconds of	1574	Example: Create a timeout timer that times out after 10 seconds of
1393	inactivity.	1575	inactivity.
1394		1576
1395	static void	1577	static void
1396	timeout_cb (struct ev_loop loop, struct ev_timer w, int revents)	1578	timeout_cb (struct ev_loop loop, ev_timer w, int revents)
1397	{	1579	{
1398	.. ten seconds without any activity	1580	.. ten seconds without any activity
1399	}	1581	}
1400		1582
1401	struct ev_timer mytimer;	1583	ev_timer mytimer;
1402	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1584	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1403	ev_timer_again (&mytimer); /* start timer */	1585	ev_timer_again (&mytimer); /* start timer */
1404	ev_loop (loop, 0);	1586	ev_loop (loop, 0);
1405		1587
1406	// and in some piece of code that gets executed on any "activity":	1588	// and in some piece of code that gets executed on any "activity":
…		…
1492		1674
1493	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1675	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1494	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1676	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1495	only event loop modification you are allowed to do).	1677	only event loop modification you are allowed to do).
1496		1678
1497	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1679	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1498	*w, ev_tstamp now)>, e.g.:	1680	*w, ev_tstamp now)>, e.g.:
1499		1681
		1682	static ev_tstamp
1500	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1683	my_rescheduler (ev_periodic *w, ev_tstamp now)
1501	{	1684	{
1502	return now + 60.;	1685	return now + 60.;
1503	}	1686	}
1504		1687
1505	It must return the next time to trigger, based on the passed time value	1688	It must return the next time to trigger, based on the passed time value
…		…
1542		1725
1543	The current interval value. Can be modified any time, but changes only	1726	The current interval value. Can be modified any time, but changes only
1544	take effect when the periodic timer fires or C<ev_periodic_again> is being	1727	take effect when the periodic timer fires or C<ev_periodic_again> is being
1545	called.	1728	called.
1546		1729
1547	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]	1730	=item ev_tstamp (reschedule_cb)(ev_periodic w, ev_tstamp now) [read-write]
1548		1731
1549	The current reschedule callback, or C<0>, if this functionality is	1732	The current reschedule callback, or C<0>, if this functionality is
1550	switched off. Can be changed any time, but changes only take effect when	1733	switched off. Can be changed any time, but changes only take effect when
1551	the periodic timer fires or C<ev_periodic_again> is being called.	1734	the periodic timer fires or C<ev_periodic_again> is being called.
1552		1735
…		…
1557	Example: Call a callback every hour, or, more precisely, whenever the	1740	Example: Call a callback every hour, or, more precisely, whenever the
1558	system time is divisible by 3600. The callback invocation times have	1741	system time is divisible by 3600. The callback invocation times have
1559	potentially a lot of jitter, but good long-term stability.	1742	potentially a lot of jitter, but good long-term stability.
1560		1743
1561	static void	1744	static void
1562	clock_cb (struct ev_loop loop, struct ev_io w, int revents)	1745	clock_cb (struct ev_loop loop, ev_io w, int revents)
1563	{	1746	{
1564	... its now a full hour (UTC, or TAI or whatever your clock follows)	1747	... its now a full hour (UTC, or TAI or whatever your clock follows)
1565	}	1748	}
1566		1749
1567	struct ev_periodic hourly_tick;	1750	ev_periodic hourly_tick;
1568	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1751	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1569	ev_periodic_start (loop, &hourly_tick);	1752	ev_periodic_start (loop, &hourly_tick);
1570		1753
1571	Example: The same as above, but use a reschedule callback to do it:	1754	Example: The same as above, but use a reschedule callback to do it:
1572		1755
1573	#include <math.h>	1756	#include <math.h>
1574		1757
1575	static ev_tstamp	1758	static ev_tstamp
1576	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1759	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1577	{	1760	{
1578	return now + (3600. - fmod (now, 3600.));	1761	return now + (3600. - fmod (now, 3600.));
1579	}	1762	}
1580		1763
1581	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1764	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1582		1765
1583	Example: Call a callback every hour, starting now:	1766	Example: Call a callback every hour, starting now:
1584		1767
1585	struct ev_periodic hourly_tick;	1768	ev_periodic hourly_tick;
1586	ev_periodic_init (&hourly_tick, clock_cb,	1769	ev_periodic_init (&hourly_tick, clock_cb,
1587	fmod (ev_now (loop), 3600.), 3600., 0);	1770	fmod (ev_now (loop), 3600.), 3600., 0);
1588	ev_periodic_start (loop, &hourly_tick);	1771	ev_periodic_start (loop, &hourly_tick);
1589		1772
1590		1773
…		…
1632	=head3 Examples	1815	=head3 Examples
1633		1816
1634	Example: Try to exit cleanly on SIGINT.	1817	Example: Try to exit cleanly on SIGINT.
1635		1818
1636	static void	1819	static void
1637	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)	1820	sigint_cb (struct ev_loop loop, ev_signal w, int revents)
1638	{	1821	{
1639	ev_unloop (loop, EVUNLOOP_ALL);	1822	ev_unloop (loop, EVUNLOOP_ALL);
1640	}	1823	}
1641		1824
1642	struct ev_signal signal_watcher;	1825	ev_signal signal_watcher;
1643	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1826	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1644	ev_signal_start (loop, &signal_watcher);	1827	ev_signal_start (loop, &signal_watcher);
1645		1828
1646		1829
1647	=head2 C<ev_child> - watch out for process status changes	1830	=head2 C<ev_child> - watch out for process status changes
…		…
1722	its completion.	1905	its completion.
1723		1906
1724	ev_child cw;	1907	ev_child cw;
1725		1908
1726	static void	1909	static void
1727	child_cb (EV_P_ struct ev_child *w, int revents)	1910	child_cb (EV_P_ ev_child *w, int revents)
1728	{	1911	{
1729	ev_child_stop (EV_A_ w);	1912	ev_child_stop (EV_A_ w);
1730	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	1913	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1731	}	1914	}
1732		1915
…		…
1747		1930
1748		1931
1749	=head2 C<ev_stat> - did the file attributes just change?	1932	=head2 C<ev_stat> - did the file attributes just change?
1750		1933
1751	This watches a file system path for attribute changes. That is, it calls	1934	This watches a file system path for attribute changes. That is, it calls
1752	C<stat> regularly (or when the OS says it changed) and sees if it changed	1935	C<stat> on that path in regular intervals (or when the OS says it changed)
1753	compared to the last time, invoking the callback if it did.	1936	and sees if it changed compared to the last time, invoking the callback if
		1937	it did.
1754		1938
1755	The path does not need to exist: changing from "path exists" to "path does	1939	The path does not need to exist: changing from "path exists" to "path does
1756	not exist" is a status change like any other. The condition "path does	1940	not exist" is a status change like any other. The condition "path does not
1757	not exist" is signified by the C<st_nlink> field being zero (which is	1941	exist" (or more correctly "path cannot be stat'ed") is signified by the
1758	otherwise always forced to be at least one) and all the other fields of	1942	C<st_nlink> field being zero (which is otherwise always forced to be at
1759	the stat buffer having unspecified contents.	1943	least one) and all the other fields of the stat buffer having unspecified
		1944	contents.
1760		1945
1761	The path I<should> be absolute and I<must not> end in a slash. If it is	1946	The path I<must not> end in a slash or contain special components such as
		1947	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1762	relative and your working directory changes, the behaviour is undefined.	1948	your working directory changes, then the behaviour is undefined.
1763		1949
1764	Since there is no standard kernel interface to do this, the portable	1950	Since there is no portable change notification interface available, the
1765	implementation simply calls C<stat (2)> regularly on the path to see if	1951	portable implementation simply calls C<stat(2)> regularly on the path
1766	it changed somehow. You can specify a recommended polling interval for	1952	to see if it changed somehow. You can specify a recommended polling
1767	this case. If you specify a polling interval of C<0> (highly recommended!)	1953	interval for this case. If you specify a polling interval of C<0> (highly
1768	then a I<suitable, unspecified default> value will be used (which	1954	recommended!) then a I<suitable, unspecified default> value will be used
1769	you can expect to be around five seconds, although this might change	1955	(which you can expect to be around five seconds, although this might
1770	dynamically). Libev will also impose a minimum interval which is currently	1956	change dynamically). Libev will also impose a minimum interval which is
1771	around C<0.1>, but thats usually overkill.	1957	currently around C<0.1>, but that's usually overkill.
1772		1958
1773	This watcher type is not meant for massive numbers of stat watchers,	1959	This watcher type is not meant for massive numbers of stat watchers,
1774	as even with OS-supported change notifications, this can be	1960	as even with OS-supported change notifications, this can be
1775	resource-intensive.	1961	resource-intensive.
1776		1962
1777	At the time of this writing, the only OS-specific interface implemented	1963	At the time of this writing, the only OS-specific interface implemented
1778	is the Linux inotify interface (implementing kqueue support is left as	1964	is the Linux inotify interface (implementing kqueue support is left as an
1779	an exercise for the reader. Note, however, that the author sees no way	1965	exercise for the reader. Note, however, that the author sees no way of
1780	of implementing C<ev_stat> semantics with kqueue).	1966	implementing C<ev_stat> semantics with kqueue, except as a hint).
1781		1967
1782	=head3 ABI Issues (Largefile Support)	1968	=head3 ABI Issues (Largefile Support)
1783		1969
1784	Libev by default (unless the user overrides this) uses the default	1970	Libev by default (unless the user overrides this) uses the default
1785	compilation environment, which means that on systems with large file	1971	compilation environment, which means that on systems with large file
1786	support disabled by default, you get the 32 bit version of the stat	1972	support disabled by default, you get the 32 bit version of the stat
1787	structure. When using the library from programs that change the ABI to	1973	structure. When using the library from programs that change the ABI to
1788	use 64 bit file offsets the programs will fail. In that case you have to	1974	use 64 bit file offsets the programs will fail. In that case you have to
1789	compile libev with the same flags to get binary compatibility. This is	1975	compile libev with the same flags to get binary compatibility. This is
1790	obviously the case with any flags that change the ABI, but the problem is	1976	obviously the case with any flags that change the ABI, but the problem is
1791	most noticeably disabled with ev_stat and large file support.	1977	most noticeably displayed with ev_stat and large file support.
1792		1978
1793	The solution for this is to lobby your distribution maker to make large	1979	The solution for this is to lobby your distribution maker to make large
1794	file interfaces available by default (as e.g. FreeBSD does) and not	1980	file interfaces available by default (as e.g. FreeBSD does) and not
1795	optional. Libev cannot simply switch on large file support because it has	1981	optional. Libev cannot simply switch on large file support because it has
1796	to exchange stat structures with application programs compiled using the	1982	to exchange stat structures with application programs compiled using the
1797	default compilation environment.	1983	default compilation environment.
1798		1984
1799	=head3 Inotify and Kqueue	1985	=head3 Inotify and Kqueue
1800		1986
1801	When C<inotify (7)> support has been compiled into libev (generally	1987	When C<inotify (7)> support has been compiled into libev and present at
1802	only available with Linux 2.6.25 or above due to bugs in earlier	1988	runtime, it will be used to speed up change detection where possible. The
1803	implementations) and present at runtime, it will be used to speed up	1989	inotify descriptor will be created lazily when the first C<ev_stat>
1804	change detection where possible. The inotify descriptor will be created	1990	watcher is being started.
1805	lazily when the first C<ev_stat> watcher is being started.
1806		1991
1807	Inotify presence does not change the semantics of C<ev_stat> watchers	1992	Inotify presence does not change the semantics of C<ev_stat> watchers
1808	except that changes might be detected earlier, and in some cases, to avoid	1993	except that changes might be detected earlier, and in some cases, to avoid
1809	making regular C<stat> calls. Even in the presence of inotify support	1994	making regular C<stat> calls. Even in the presence of inotify support
1810	there are many cases where libev has to resort to regular C<stat> polling,	1995	there are many cases where libev has to resort to regular C<stat> polling,
1811	but as long as the path exists, libev usually gets away without polling.	1996	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		1997	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		1998	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		1999	xfs are fully working) libev usually gets away without polling.
1812		2000
1813	There is no support for kqueue, as apparently it cannot be used to	2001	There is no support for kqueue, as apparently it cannot be used to
1814	implement this functionality, due to the requirement of having a file	2002	implement this functionality, due to the requirement of having a file
1815	descriptor open on the object at all times, and detecting renames, unlinks	2003	descriptor open on the object at all times, and detecting renames, unlinks
1816	etc. is difficult.	2004	etc. is difficult.
1817		2005
		2006	=head3 C<stat ()> is a synchronous operation
		2007
		2008	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2009	the process. The exception are C<ev_stat> watchers - those call C<stat
		2010	()>, which is a synchronous operation.
		2011
		2012	For local paths, this usually doesn't matter: unless the system is very
		2013	busy or the intervals between stat's are large, a stat call will be fast,
		2014	as the path data is suually in memory already (except when starting the
		2015	watcher).
		2016
		2017	For networked file systems, calling C<stat ()> can block an indefinite
		2018	time due to network issues, and even under good conditions, a stat call
		2019	often takes multiple milliseconds.
		2020
		2021	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2022	paths, although this is fully supported by libev.
		2023
1818	=head3 The special problem of stat time resolution	2024	=head3 The special problem of stat time resolution
1819		2025
1820	The C<stat ()> system call only supports full-second resolution portably, and	2026	The C<stat ()> system call only supports full-second resolution portably,
1821	even on systems where the resolution is higher, most file systems still	2027	and even on systems where the resolution is higher, most file systems
1822	only support whole seconds.	2028	still only support whole seconds.
1823		2029
1824	That means that, if the time is the only thing that changes, you can	2030	That means that, if the time is the only thing that changes, you can
1825	easily miss updates: on the first update, C<ev_stat> detects a change and	2031	easily miss updates: on the first update, C<ev_stat> detects a change and
1826	calls your callback, which does something. When there is another update	2032	calls your callback, which does something. When there is another update
1827	within the same second, C<ev_stat> will be unable to detect unless the	2033	within the same second, C<ev_stat> will be unable to detect unless the
…		…
1984		2190
1985	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2191	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1986	callback, free it. Also, use no error checking, as usual.	2192	callback, free it. Also, use no error checking, as usual.
1987		2193
1988	static void	2194	static void
1989	idle_cb (struct ev_loop loop, struct ev_idle w, int revents)	2195	idle_cb (struct ev_loop loop, ev_idle w, int revents)
1990	{	2196	{
1991	free (w);	2197	free (w);
1992	// now do something you wanted to do when the program has	2198	// now do something you wanted to do when the program has
1993	// no longer anything immediate to do.	2199	// no longer anything immediate to do.
1994	}	2200	}
1995		2201
1996	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2202	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1997	ev_idle_init (idle_watcher, idle_cb);	2203	ev_idle_init (idle_watcher, idle_cb);
1998	ev_idle_start (loop, idle_cb);	2204	ev_idle_start (loop, idle_cb);
1999		2205
2000		2206
2001	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2207	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
…		…
2082		2288
2083	static ev_io iow [nfd];	2289	static ev_io iow [nfd];
2084	static ev_timer tw;	2290	static ev_timer tw;
2085		2291
2086	static void	2292	static void
2087	io_cb (ev_loop loop, ev_io w, int revents)	2293	io_cb (struct ev_loop loop, ev_io w, int revents)
2088	{	2294	{
2089	}	2295	}
2090		2296
2091	// create io watchers for each fd and a timer before blocking	2297	// create io watchers for each fd and a timer before blocking
2092	static void	2298	static void
2093	adns_prepare_cb (ev_loop loop, ev_prepare w, int revents)	2299	adns_prepare_cb (struct ev_loop loop, ev_prepare w, int revents)
2094	{	2300	{
2095	int timeout = 3600000;	2301	int timeout = 3600000;
2096	struct pollfd fds [nfd];	2302	struct pollfd fds [nfd];
2097	// actual code will need to loop here and realloc etc.	2303	// actual code will need to loop here and realloc etc.
2098	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2304	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
…		…
2113	}	2319	}
2114	}	2320	}
2115		2321
2116	// stop all watchers after blocking	2322	// stop all watchers after blocking
2117	static void	2323	static void
2118	adns_check_cb (ev_loop loop, ev_check w, int revents)	2324	adns_check_cb (struct ev_loop loop, ev_check w, int revents)
2119	{	2325	{
2120	ev_timer_stop (loop, &tw);	2326	ev_timer_stop (loop, &tw);
2121		2327
2122	for (int i = 0; i < nfd; ++i)	2328	for (int i = 0; i < nfd; ++i)
2123	{	2329	{
…		…
2291	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2497	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2292	used).	2498	used).
2293		2499
2294	struct ev_loop *loop_hi = ev_default_init (0);	2500	struct ev_loop *loop_hi = ev_default_init (0);
2295	struct ev_loop *loop_lo = 0;	2501	struct ev_loop *loop_lo = 0;
2296	struct ev_embed embed;	2502	ev_embed embed;
2297		2503
2298	// see if there is a chance of getting one that works	2504	// see if there is a chance of getting one that works
2299	// (remember that a flags value of 0 means autodetection)	2505	// (remember that a flags value of 0 means autodetection)
2300	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2506	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2301	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2507	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2315	kqueue implementation). Store the kqueue/socket-only event loop in	2521	kqueue implementation). Store the kqueue/socket-only event loop in
2316	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2522	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2317		2523
2318	struct ev_loop *loop = ev_default_init (0);	2524	struct ev_loop *loop = ev_default_init (0);
2319	struct ev_loop *loop_socket = 0;	2525	struct ev_loop *loop_socket = 0;
2320	struct ev_embed embed;	2526	ev_embed embed;
2321		2527
2322	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2528	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2323	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2529	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2324	{	2530	{
2325	ev_embed_init (&embed, 0, loop_socket);	2531	ev_embed_init (&embed, 0, loop_socket);
…		…
2466	=over 4	2672	=over 4
2467		2673
2468	=item ev_async_init (ev_async *, callback)	2674	=item ev_async_init (ev_async *, callback)
2469		2675
2470	Initialises and configures the async watcher - it has no parameters of any	2676	Initialises and configures the async watcher - it has no parameters of any
2471	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	2677	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2472	trust me.	2678	trust me.
2473		2679
2474	=item ev_async_send (loop, ev_async *)	2680	=item ev_async_send (loop, ev_async *)
2475		2681
2476	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	2682	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
…		…
2539	/* doh, nothing entered */;	2745	/* doh, nothing entered */;
2540	}	2746	}
2541		2747
2542	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2748	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2543		2749
2544	=item ev_feed_event (ev_loop , watcher , int revents)	2750	=item ev_feed_event (struct ev_loop , watcher , int revents)
2545		2751
2546	Feeds the given event set into the event loop, as if the specified event	2752	Feeds the given event set into the event loop, as if the specified event
2547	had happened for the specified watcher (which must be a pointer to an	2753	had happened for the specified watcher (which must be a pointer to an
2548	initialised but not necessarily started event watcher).	2754	initialised but not necessarily started event watcher).
2549		2755
2550	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2756	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2551		2757
2552	Feed an event on the given fd, as if a file descriptor backend detected	2758	Feed an event on the given fd, as if a file descriptor backend detected
2553	the given events it.	2759	the given events it.
2554		2760
2555	=item ev_feed_signal_event (ev_loop *loop, int signum)	2761	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2556		2762
2557	Feed an event as if the given signal occurred (C<loop> must be the default	2763	Feed an event as if the given signal occurred (C<loop> must be the default
2558	loop!).	2764	loop!).
2559		2765
2560	=back	2766	=back
…		…
2795	=item D	3001	=item D
2796		3002
2797	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3003	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2798	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3004	be found at L<http://proj.llucax.com.ar/wiki/evd>.
2799		3005
		3006	=item Ocaml
		3007
		3008	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3009	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3010
2800	=back	3011	=back
2801		3012
2802		3013
2803	=head1 MACRO MAGIC	3014	=head1 MACRO MAGIC
2804		3015
…		…
2904		3115
2905	#define EV_STANDALONE 1	3116	#define EV_STANDALONE 1
2906	#include "ev.h"	3117	#include "ev.h"
2907		3118
2908	Both header files and implementation files can be compiled with a C++	3119	Both header files and implementation files can be compiled with a C++
2909	compiler (at least, thats a stated goal, and breakage will be treated	3120	compiler (at least, that's a stated goal, and breakage will be treated
2910	as a bug).	3121	as a bug).
2911		3122
2912	You need the following files in your source tree, or in a directory	3123	You need the following files in your source tree, or in a directory
2913	in your include path (e.g. in libev/ when using -Ilibev):	3124	in your include path (e.g. in libev/ when using -Ilibev):
2914		3125
…		…
3386	loop, as long as you don't confuse yourself). The only exception is that	3597	loop, as long as you don't confuse yourself). The only exception is that
3387	you must not do this from C<ev_periodic> reschedule callbacks.	3598	you must not do this from C<ev_periodic> reschedule callbacks.
3388		3599
3389	Care has been taken to ensure that libev does not keep local state inside	3600	Care has been taken to ensure that libev does not keep local state inside
3390	C<ev_loop>, and other calls do not usually allow for coroutine switches as	3601	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3391	they do not clal any callbacks.	3602	they do not call any callbacks.
3392		3603
3393	=head2 COMPILER WARNINGS	3604	=head2 COMPILER WARNINGS
3394		3605
3395	Depending on your compiler and compiler settings, you might get no or a	3606	Depending on your compiler and compiler settings, you might get no or a
3396	lot of warnings when compiling libev code. Some people are apparently	3607	lot of warnings when compiling libev code. Some people are apparently
…		…
3430	==2274== definitely lost: 0 bytes in 0 blocks.	3641	==2274== definitely lost: 0 bytes in 0 blocks.
3431	==2274== possibly lost: 0 bytes in 0 blocks.	3642	==2274== possibly lost: 0 bytes in 0 blocks.
3432	==2274== still reachable: 256 bytes in 1 blocks.	3643	==2274== still reachable: 256 bytes in 1 blocks.
3433		3644
3434	Then there is no memory leak, just as memory accounted to global variables	3645	Then there is no memory leak, just as memory accounted to global variables
3435	is not a memleak - the memory is still being refernced, and didn't leak.	3646	is not a memleak - the memory is still being referenced, and didn't leak.
3436		3647
3437	Similarly, under some circumstances, valgrind might report kernel bugs	3648	Similarly, under some circumstances, valgrind might report kernel bugs
3438	as if it were a bug in libev (e.g. in realloc or in the poll backend,	3649	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3439	although an acceptable workaround has been found here), or it might be	3650	although an acceptable workaround has been found here), or it might be
3440	confused.	3651	confused.
…		…
3678	=back	3889	=back
3679		3890
3680		3891
3681	=head1 AUTHOR	3892	=head1 AUTHOR
3682		3893
3683	Marc Lehmann <libev@schmorp.de>.	3894	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3684		3895

Diff Legend

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

Comparing libev/ev.pod (file contents): Revision 1.196 by root, Tue Oct 21 20:04:14 2008 UTC vs. Revision 1.213 by root, Wed Nov 5 02:48:45 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.196 by root, Tue Oct 21 20:04:14 2008 UTC vs.
Revision 1.213 by root, Wed Nov 5 02:48:45 2008 UTC