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

Comparing libev/ev.pod (file contents):
Revision 1.194 by root, Mon Oct 20 16:08:36 2008 UTC vs.
Revision 1.214 by root, Wed Nov 5 03:52:15 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> can be as fast or
		424	faster then epoll for maybe up to a hundred file descriptors, depending on
		425	the usage. So sad.
405		426
406	While nominally embeddable in other event loops, this feature is broken in	427	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	428	all kernel versions tested so far.
408		429
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	430	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	431	C<EVBACKEND_POLL>.
411		432
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	433	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		434
414	Kqueue deserves special mention, as at the time of this writing, it was	435	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	436	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	437	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	438	it's completely useless). Unlike epoll, however, whose brokenness
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	439	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.	440	without API changes to existing programs. For this reason it's not being
		441	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		442	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		443	system like NetBSD.
420		444
421	You still can embed kqueue into a normal poll or select backend and use it	445	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	446	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.	447	the target platform). See C<ev_embed> watchers for more info.
424		448
425	It scales in the same way as the epoll backend, but the interface to the	449	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	450	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	451	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	452	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	453	two event changes per incident. Support for C<fork ()> is very bad (but
430	drops fds silently in similarly hard-to-detect cases.	454	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		455	cases
431		456
432	This backend usually performs well under most conditions.	457	This backend usually performs well under most conditions.
433		458
434	While nominally embeddable in other event loops, this doesn't work	459	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	460	everywhere, so you might need to test for this. And since it is broken
…		…
464	might perform better.	489	might perform better.
465		490
466	On the positive side, with the exception of the spurious readiness	491	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	492	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	493	in all tests and is fully embeddable, which is a rare feat among the
469	OS-specific backends.	494	OS-specific backends (I vastly prefer correctness over speed hacks).
470		495
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	496	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	497	C<EVBACKEND_POLL>.
473		498
474	=item C<EVBACKEND_ALL>	499	=item C<EVBACKEND_ALL>
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	552	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	553	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	554	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	555	for example).
531		556
532	Note that certain global state, such as signal state, will not be freed by	557	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	558	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	559	as signal and child watchers) would need to be stopped manually.
535		560
536	In general it is not advisable to call this function except in the	561	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	562	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	563	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	564	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
631	the loop.	656	the loop.
632		657
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	658	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	659	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	660	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	661	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	662	user-registered callback will be called), and will return after one
638	iteration of the loop.	663	iteration of the loop.
639		664
640	This is useful if you are waiting for some external event in conjunction	665	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	666	with something not expressible using other libev watchers (i.e. "roll your
…		…
710	respectively).	735	respectively).
711		736
712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	737	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
713	running when nothing else is active.	738	running when nothing else is active.
714		739
715	struct ev_signal exitsig;	740	ev_signal exitsig;
716	ev_signal_init (&exitsig, sig_cb, SIGINT);	741	ev_signal_init (&exitsig, sig_cb, SIGINT);
717	ev_signal_start (loop, &exitsig);	742	ev_signal_start (loop, &exitsig);
718	evf_unref (loop);	743	evf_unref (loop);
719		744
720	Example: For some weird reason, unregister the above signal handler again.	745	Example: For some weird reason, unregister the above signal handler again.
…		…
768	they fire on, say, one-second boundaries only.	793	they fire on, say, one-second boundaries only.
769		794
770	=item ev_loop_verify (loop)	795	=item ev_loop_verify (loop)
771		796
772	This function only does something when C<EV_VERIFY> support has been	797	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	798	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	799	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	800	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	801	error and call C<abort ()>.
777		802
778	This can be used to catch bugs inside libev itself: under normal	803	This can be used to catch bugs inside libev itself: under normal
…		…
782	=back	807	=back
783		808
784		809
785	=head1 ANATOMY OF A WATCHER	810	=head1 ANATOMY OF A WATCHER
786		811
		812	In the following description, uppercase C<TYPE> in names stands for the
		813	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		814	watchers and C<ev_io_start> for I/O watchers.
		815
787	A watcher is a structure that you create and register to record your	816	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	817	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:	818	become readable, you would create an C<ev_io> watcher for that:
790		819
791	static void my_cb (struct ev_loop loop, struct ev_io w, int revents)	820	static void my_cb (struct ev_loop loop, ev_io w, int revents)
792	{	821	{
793	ev_io_stop (w);	822	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	823	ev_unloop (loop, EVUNLOOP_ALL);
795	}	824	}
796		825
797	struct ev_loop *loop = ev_default_loop (0);	826	struct ev_loop *loop = ev_default_loop (0);
		827
798	struct ev_io stdin_watcher;	828	ev_io stdin_watcher;
		829
799	ev_init (&stdin_watcher, my_cb);	830	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	831	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	832	ev_io_start (loop, &stdin_watcher);
		833
802	ev_loop (loop, 0);	834	ev_loop (loop, 0);
803		835
804	As you can see, you are responsible for allocating the memory for your	836	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,	837	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	838	stack).
		839
		840	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		841	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
807		842
808	Each watcher structure must be initialised by a call to C<ev_init	843	Each watcher structure must be initialised by a call to C<ev_init
809	(watcher *, callback)>, which expects a callback to be provided. This	844	(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	845	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	846	watchers, each time the event loop detects that the file descriptor given
812	is readable and/or writable).	847	is readable and/or writable).
813		848
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	849	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	850	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	851	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	852	ev_TYPE_init (watcher *, callback, ...) >>.
818		853
819	To make the watcher actually watch out for events, you have to start it	854	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	855	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	856	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	857	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		858
824	As long as your watcher is active (has been started but not stopped) you	859	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	860	must not touch the values stored in it. Most specifically you must never
826	reinitialise it or call its C<set> macro.	861	reinitialise it or call its C<ev_TYPE_set> macro.
827		862
828	Each and every callback receives the event loop pointer as first, the	863	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	864	registered watcher structure as second, and a bitset of received events as
830	third argument.	865	third argument.
831		866
…		…
894	=item C<EV_ERROR>	929	=item C<EV_ERROR>
895		930
896	An unspecified error has occurred, the watcher has been stopped. This might	931	An unspecified error has occurred, the watcher has been stopped. This might
897	happen because the watcher could not be properly started because libev	932	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	933	ran out of memory, a file descriptor was found to be closed or any other
		934	problem. Libev considers these application bugs.
		935
899	problem. You best act on it by reporting the problem and somehow coping	936	You best act on it by reporting the problem and somehow coping with the
900	with the watcher being stopped.	937	watcher being stopped. Note that well-written programs should not receive
		938	an error ever, so when your watcher receives it, this usually indicates a
		939	bug in your program.
901		940
902	Libev will usually signal a few "dummy" events together with an error, for	941	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	942	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	943	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	944	the error from read() or write(). This will not work in multi-threaded
…		…
908		947
909	=back	948	=back
910		949
911	=head2 GENERIC WATCHER FUNCTIONS	950	=head2 GENERIC WATCHER FUNCTIONS
912		951
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	952	=over 4
917		953
918	=item C<ev_init> (ev_TYPE *watcher, callback)	954	=item C<ev_init> (ev_TYPE *watcher, callback)
919		955
920	This macro initialises the generic portion of a watcher. The contents	956	This macro initialises the generic portion of a watcher. The contents
…		…
925	which rolls both calls into one.	961	which rolls both calls into one.
926		962
927	You can reinitialise a watcher at any time as long as it has been stopped	963	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.	964	(or never started) and there are no pending events outstanding.
929		965
930	The callback is always of type C<void ()(ev_loop loop, ev_TYPE *watcher,	966	The callback is always of type C<void ()(struct ev_loop loop, ev_TYPE *watcher,
931	int revents)>.	967	int revents)>.
932		968
933	Example: Initialise an C<ev_io> watcher in two steps.	969	Example: Initialise an C<ev_io> watcher in two steps.
934		970
935	ev_io w;	971	ev_io w;
…		…
969		1005
970	ev_io_start (EV_DEFAULT_UC, &w);	1006	ev_io_start (EV_DEFAULT_UC, &w);
971		1007
972	=item C<ev_TYPE_stop> (loop , ev_TYPE watcher)	1008	=item C<ev_TYPE_stop> (loop , ev_TYPE watcher)
973		1009
974	Stops the given watcher again (if active) and clears the pending	1010	Stops the given watcher if active, and clears the pending status (whether
		1011	the watcher was active or not).
		1012
975	status. It is possible that stopped watchers are pending (for example,	1013	It is possible that stopped watchers are pending - for example,
976	non-repeating timers are being stopped when they become pending), but	1014	non-repeating timers are being stopped when they become pending - but
977	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1015	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
978	you want to free or reuse the memory used by the watcher it is therefore a	1016	pending. If you want to free or reuse the memory used by the watcher it is
979	good idea to always call its C<ev_TYPE_stop> function.	1017	therefore a good idea to always call its C<ev_TYPE_stop> function.
980		1018
981	=item bool ev_is_active (ev_TYPE *watcher)	1019	=item bool ev_is_active (ev_TYPE *watcher)
982		1020
983	Returns a true value iff the watcher is active (i.e. it has been started	1021	Returns a true value iff the watcher is active (i.e. it has been started
984	and not yet been stopped). As long as a watcher is active you must not modify	1022	and not yet been stopped). As long as a watcher is active you must not modify
…		…
1026	The default priority used by watchers when no priority has been set is	1064	The default priority used by watchers when no priority has been set is
1027	always C<0>, which is supposed to not be too high and not be too low :).	1065	always C<0>, which is supposed to not be too high and not be too low :).
1028		1066
1029	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1067	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1030	fine, as long as you do not mind that the priority value you query might	1068	fine, as long as you do not mind that the priority value you query might
1031	or might not have been adjusted to be within valid range.	1069	or might not have been clamped to the valid range.
1032		1070
1033	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1071	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1034		1072
1035	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1073	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1036	C<loop> nor C<revents> need to be valid as long as the watcher callback	1074	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1058	member, you can also "subclass" the watcher type and provide your own	1096	member, you can also "subclass" the watcher type and provide your own
1059	data:	1097	data:
1060		1098
1061	struct my_io	1099	struct my_io
1062	{	1100	{
1063	struct ev_io io;	1101	ev_io io;
1064	int otherfd;	1102	int otherfd;
1065	void *somedata;	1103	void *somedata;
1066	struct whatever *mostinteresting;	1104	struct whatever *mostinteresting;
1067	};	1105	};
1068		1106
…		…
1071	ev_io_init (&w.io, my_cb, fd, EV_READ);	1109	ev_io_init (&w.io, my_cb, fd, EV_READ);
1072		1110
1073	And since your callback will be called with a pointer to the watcher, you	1111	And since your callback will be called with a pointer to the watcher, you
1074	can cast it back to your own type:	1112	can cast it back to your own type:
1075		1113
1076	static void my_cb (struct ev_loop loop, struct ev_io w_, int revents)	1114	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1077	{	1115	{
1078	struct my_io w = (struct my_io )w_;	1116	struct my_io w = (struct my_io )w_;
1079	...	1117	...
1080	}	1118	}
1081		1119
…		…
1099	programmers):	1137	programmers):
1100		1138
1101	#include <stddef.h>	1139	#include <stddef.h>
1102		1140
1103	static void	1141	static void
1104	t1_cb (EV_P_ struct ev_timer *w, int revents)	1142	t1_cb (EV_P_ ev_timer *w, int revents)
1105	{	1143	{
1106	struct my_biggy big = (struct my_biggy *	1144	struct my_biggy big = (struct my_biggy *
1107	(((char *)w) - offsetof (struct my_biggy, t1));	1145	(((char *)w) - offsetof (struct my_biggy, t1));
1108	}	1146	}
1109		1147
1110	static void	1148	static void
1111	t2_cb (EV_P_ struct ev_timer *w, int revents)	1149	t2_cb (EV_P_ ev_timer *w, int revents)
1112	{	1150	{
1113	struct my_biggy big = (struct my_biggy *	1151	struct my_biggy big = (struct my_biggy *
1114	(((char *)w) - offsetof (struct my_biggy, t2));	1152	(((char *)w) - offsetof (struct my_biggy, t2));
1115	}	1153	}
1116		1154
…		…
1251	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1289	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1252	readable, but only once. Since it is likely line-buffered, you could	1290	readable, but only once. Since it is likely line-buffered, you could
1253	attempt to read a whole line in the callback.	1291	attempt to read a whole line in the callback.
1254		1292
1255	static void	1293	static void
1256	stdin_readable_cb (struct ev_loop loop, struct ev_io w, int revents)	1294	stdin_readable_cb (struct ev_loop loop, ev_io w, int revents)
1257	{	1295	{
1258	ev_io_stop (loop, w);	1296	ev_io_stop (loop, w);
1259	.. read from stdin here (or from w->fd) and handle any I/O errors	1297	.. read from stdin here (or from w->fd) and handle any I/O errors
1260	}	1298	}
1261		1299
1262	...	1300	...
1263	struct ev_loop *loop = ev_default_init (0);	1301	struct ev_loop *loop = ev_default_init (0);
1264	struct ev_io stdin_readable;	1302	ev_io stdin_readable;
1265	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1303	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1266	ev_io_start (loop, &stdin_readable);	1304	ev_io_start (loop, &stdin_readable);
1267	ev_loop (loop, 0);	1305	ev_loop (loop, 0);
1268		1306
1269		1307
…		…
1280		1318
1281	The callback is guaranteed to be invoked only I<after> its timeout has	1319	The callback is guaranteed to be invoked only I<after> its timeout has
1282	passed, but if multiple timers become ready during the same loop iteration	1320	passed, but if multiple timers become ready during the same loop iteration
1283	then order of execution is undefined.	1321	then order of execution is undefined.
1284		1322
		1323	=head3 Be smart about timeouts
		1324
		1325	Many real-world problems involve some kind of timeout, usually for error
		1326	recovery. A typical example is an HTTP request - if the other side hangs,
		1327	you want to raise some error after a while.
		1328
		1329	What follows are some ways to handle this problem, from obvious and
		1330	inefficient to smart and efficient.
		1331
		1332	In the following, a 60 second activity timeout is assumed - a timeout that
		1333	gets reset to 60 seconds each time there is activity (e.g. each time some
		1334	data or other life sign was received).
		1335
		1336	=over 4
		1337
		1338	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1339
		1340	This is the most obvious, but not the most simple way: In the beginning,
		1341	start the watcher:
		1342
		1343	ev_timer_init (timer, callback, 60., 0.);
		1344	ev_timer_start (loop, timer);
		1345
		1346	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1347	and start it again:
		1348
		1349	ev_timer_stop (loop, timer);
		1350	ev_timer_set (timer, 60., 0.);
		1351	ev_timer_start (loop, timer);
		1352
		1353	This is relatively simple to implement, but means that each time there is
		1354	some activity, libev will first have to remove the timer from its internal
		1355	data structure and then add it again. Libev tries to be fast, but it's
		1356	still not a constant-time operation.
		1357
		1358	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1359
		1360	This is the easiest way, and involves using C<ev_timer_again> instead of
		1361	C<ev_timer_start>.
		1362
		1363	To implement this, configure an C<ev_timer> with a C<repeat> value
		1364	of C<60> and then call C<ev_timer_again> at start and each time you
		1365	successfully read or write some data. If you go into an idle state where
		1366	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1367	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1368
		1369	That means you can ignore both the C<ev_timer_start> function and the
		1370	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1371	member and C<ev_timer_again>.
		1372
		1373	At start:
		1374
		1375	ev_timer_init (timer, callback);
		1376	timer->repeat = 60.;
		1377	ev_timer_again (loop, timer);
		1378
		1379	Each time there is some activity:
		1380
		1381	ev_timer_again (loop, timer);
		1382
		1383	It is even possible to change the time-out on the fly, regardless of
		1384	whether the watcher is active or not:
		1385
		1386	timer->repeat = 30.;
		1387	ev_timer_again (loop, timer);
		1388
		1389	This is slightly more efficient then stopping/starting the timer each time
		1390	you want to modify its timeout value, as libev does not have to completely
		1391	remove and re-insert the timer from/into its internal data structure.
		1392
		1393	It is, however, even simpler than the "obvious" way to do it.
		1394
		1395	=item 3. Let the timer time out, but then re-arm it as required.
		1396
		1397	This method is more tricky, but usually most efficient: Most timeouts are
		1398	relatively long compared to the intervals between other activity - in
		1399	our example, within 60 seconds, there are usually many I/O events with
		1400	associated activity resets.
		1401
		1402	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1403	but remember the time of last activity, and check for a real timeout only
		1404	within the callback:
		1405
		1406	ev_tstamp last_activity; // time of last activity
		1407
		1408	static void
		1409	callback (EV_P_ ev_timer *w, int revents)
		1410	{
		1411	ev_tstamp now = ev_now (EV_A);
		1412	ev_tstamp timeout = last_activity + 60.;
		1413
		1414	// if last_activity + 60. is older than now, we did time out
		1415	if (timeout < now)
		1416	{
		1417	// timeout occured, take action
		1418	}
		1419	else
		1420	{
		1421	// callback was invoked, but there was some activity, re-arm
		1422	// the watcher to fire in last_activity + 60, which is
		1423	// guaranteed to be in the future, so "again" is positive:
		1424	w->again = timeout - now;
		1425	ev_timer_again (EV_A_ w);
		1426	}
		1427	}
		1428
		1429	To summarise the callback: first calculate the real timeout (defined
		1430	as "60 seconds after the last activity"), then check if that time has
		1431	been reached, which means something I<did>, in fact, time out. Otherwise
		1432	the callback was invoked too early (C<timeout> is in the future), so
		1433	re-schedule the timer to fire at that future time, to see if maybe we have
		1434	a timeout then.
		1435
		1436	Note how C<ev_timer_again> is used, taking advantage of the
		1437	C<ev_timer_again> optimisation when the timer is already running.
		1438
		1439	This scheme causes more callback invocations (about one every 60 seconds
		1440	minus half the average time between activity), but virtually no calls to
		1441	libev to change the timeout.
		1442
		1443	To start the timer, simply initialise the watcher and set C<last_activity>
		1444	to the current time (meaning we just have some activity :), then call the
		1445	callback, which will "do the right thing" and start the timer:
		1446
		1447	ev_timer_init (timer, callback);
		1448	last_activity = ev_now (loop);
		1449	callback (loop, timer, EV_TIMEOUT);
		1450
		1451	And when there is some activity, simply store the current time in
		1452	C<last_activity>, no libev calls at all:
		1453
		1454	last_actiivty = ev_now (loop);
		1455
		1456	This technique is slightly more complex, but in most cases where the
		1457	time-out is unlikely to be triggered, much more efficient.
		1458
		1459	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1460	callback :) - just change the timeout and invoke the callback, which will
		1461	fix things for you.
		1462
		1463	=item 4. Wee, just use a double-linked list for your timeouts.
		1464
		1465	If there is not one request, but many thousands (millions...), all
		1466	employing some kind of timeout with the same timeout value, then one can
		1467	do even better:
		1468
		1469	When starting the timeout, calculate the timeout value and put the timeout
		1470	at the I<end> of the list.
		1471
		1472	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1473	the list is expected to fire (for example, using the technique #3).
		1474
		1475	When there is some activity, remove the timer from the list, recalculate
		1476	the timeout, append it to the end of the list again, and make sure to
		1477	update the C<ev_timer> if it was taken from the beginning of the list.
		1478
		1479	This way, one can manage an unlimited number of timeouts in O(1) time for
		1480	starting, stopping and updating the timers, at the expense of a major
		1481	complication, and having to use a constant timeout. The constant timeout
		1482	ensures that the list stays sorted.
		1483
		1484	=back
		1485
		1486	So which method the best?
		1487
		1488	Method #2 is a simple no-brain-required solution that is adequate in most
		1489	situations. Method #3 requires a bit more thinking, but handles many cases
		1490	better, and isn't very complicated either. In most case, choosing either
		1491	one is fine, with #3 being better in typical situations.
		1492
		1493	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1494	rather complicated, but extremely efficient, something that really pays
		1495	off after the first million or so of active timers, i.e. it's usually
		1496	overkill :)
		1497
1285	=head3 The special problem of time updates	1498	=head3 The special problem of time updates
1286		1499
1287	Establishing the current time is a costly operation (it usually takes at	1500	Establishing the current time is a costly operation (it usually takes at
1288	least two system calls): EV therefore updates its idea of the current	1501	least two system calls): EV therefore updates its idea of the current
1289	time only before and after C<ev_loop> collects new events, which causes a	1502	time only before and after C<ev_loop> collects new events, which causes a
…		…
1332	If the timer is started but non-repeating, stop it (as if it timed out).	1545	If the timer is started but non-repeating, stop it (as if it timed out).
1333		1546
1334	If the timer is repeating, either start it if necessary (with the	1547	If the timer is repeating, either start it if necessary (with the
1335	C<repeat> value), or reset the running timer to the C<repeat> value.	1548	C<repeat> value), or reset the running timer to the C<repeat> value.
1336		1549
1337	This sounds a bit complicated, but here is a useful and typical	1550	This sounds a bit complicated, see "Be smart about timeouts", above, for a
1338	example: Imagine you have a TCP connection and you want a so-called idle	1551	usage example.
1339	timeout, that is, you want to be called when there have been, say, 60
1340	seconds of inactivity on the socket. The easiest way to do this is to
1341	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1342	C<ev_timer_again> each time you successfully read or write some data. If
1343	you go into an idle state where you do not expect data to travel on the
1344	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1345	automatically restart it if need be.
1346
1347	That means you can ignore the C<after> value and C<ev_timer_start>
1348	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1349
1350	ev_timer_init (timer, callback, 0., 5.);
1351	ev_timer_again (loop, timer);
1352	...
1353	timer->again = 17.;
1354	ev_timer_again (loop, timer);
1355	...
1356	timer->again = 10.;
1357	ev_timer_again (loop, timer);
1358
1359	This is more slightly efficient then stopping/starting the timer each time
1360	you want to modify its timeout value.
1361
1362	Note, however, that it is often even more efficient to remember the
1363	time of the last activity and let the timer time-out naturally. In the
1364	callback, you then check whether the time-out is real, or, if there was
1365	some activity, you reschedule the watcher to time-out in "last_activity +
1366	timeout - ev_now ()" seconds.
1367		1552
1368	=item ev_tstamp repeat [read-write]	1553	=item ev_tstamp repeat [read-write]
1369		1554
1370	The current C<repeat> value. Will be used each time the watcher times out	1555	The current C<repeat> value. Will be used each time the watcher times out
1371	or C<ev_timer_again> is called, and determines the next timeout (if any),	1556	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1376	=head3 Examples	1561	=head3 Examples
1377		1562
1378	Example: Create a timer that fires after 60 seconds.	1563	Example: Create a timer that fires after 60 seconds.
1379		1564
1380	static void	1565	static void
1381	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)	1566	one_minute_cb (struct ev_loop loop, ev_timer w, int revents)
1382	{	1567	{
1383	.. one minute over, w is actually stopped right here	1568	.. one minute over, w is actually stopped right here
1384	}	1569	}
1385		1570
1386	struct ev_timer mytimer;	1571	ev_timer mytimer;
1387	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1572	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1388	ev_timer_start (loop, &mytimer);	1573	ev_timer_start (loop, &mytimer);
1389		1574
1390	Example: Create a timeout timer that times out after 10 seconds of	1575	Example: Create a timeout timer that times out after 10 seconds of
1391	inactivity.	1576	inactivity.
1392		1577
1393	static void	1578	static void
1394	timeout_cb (struct ev_loop loop, struct ev_timer w, int revents)	1579	timeout_cb (struct ev_loop loop, ev_timer w, int revents)
1395	{	1580	{
1396	.. ten seconds without any activity	1581	.. ten seconds without any activity
1397	}	1582	}
1398		1583
1399	struct ev_timer mytimer;	1584	ev_timer mytimer;
1400	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1585	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1401	ev_timer_again (&mytimer); /* start timer */	1586	ev_timer_again (&mytimer); /* start timer */
1402	ev_loop (loop, 0);	1587	ev_loop (loop, 0);
1403		1588
1404	// and in some piece of code that gets executed on any "activity":	1589	// and in some piece of code that gets executed on any "activity":
…		…
1490		1675
1491	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1676	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1492	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1677	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1493	only event loop modification you are allowed to do).	1678	only event loop modification you are allowed to do).
1494		1679
1495	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1680	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1496	*w, ev_tstamp now)>, e.g.:	1681	*w, ev_tstamp now)>, e.g.:
1497		1682
		1683	static ev_tstamp
1498	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1684	my_rescheduler (ev_periodic *w, ev_tstamp now)
1499	{	1685	{
1500	return now + 60.;	1686	return now + 60.;
1501	}	1687	}
1502		1688
1503	It must return the next time to trigger, based on the passed time value	1689	It must return the next time to trigger, based on the passed time value
…		…
1540		1726
1541	The current interval value. Can be modified any time, but changes only	1727	The current interval value. Can be modified any time, but changes only
1542	take effect when the periodic timer fires or C<ev_periodic_again> is being	1728	take effect when the periodic timer fires or C<ev_periodic_again> is being
1543	called.	1729	called.
1544		1730
1545	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]	1731	=item ev_tstamp (reschedule_cb)(ev_periodic w, ev_tstamp now) [read-write]
1546		1732
1547	The current reschedule callback, or C<0>, if this functionality is	1733	The current reschedule callback, or C<0>, if this functionality is
1548	switched off. Can be changed any time, but changes only take effect when	1734	switched off. Can be changed any time, but changes only take effect when
1549	the periodic timer fires or C<ev_periodic_again> is being called.	1735	the periodic timer fires or C<ev_periodic_again> is being called.
1550		1736
…		…
1555	Example: Call a callback every hour, or, more precisely, whenever the	1741	Example: Call a callback every hour, or, more precisely, whenever the
1556	system time is divisible by 3600. The callback invocation times have	1742	system time is divisible by 3600. The callback invocation times have
1557	potentially a lot of jitter, but good long-term stability.	1743	potentially a lot of jitter, but good long-term stability.
1558		1744
1559	static void	1745	static void
1560	clock_cb (struct ev_loop loop, struct ev_io w, int revents)	1746	clock_cb (struct ev_loop loop, ev_io w, int revents)
1561	{	1747	{
1562	... its now a full hour (UTC, or TAI or whatever your clock follows)	1748	... its now a full hour (UTC, or TAI or whatever your clock follows)
1563	}	1749	}
1564		1750
1565	struct ev_periodic hourly_tick;	1751	ev_periodic hourly_tick;
1566	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1752	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1567	ev_periodic_start (loop, &hourly_tick);	1753	ev_periodic_start (loop, &hourly_tick);
1568		1754
1569	Example: The same as above, but use a reschedule callback to do it:	1755	Example: The same as above, but use a reschedule callback to do it:
1570		1756
1571	#include <math.h>	1757	#include <math.h>
1572		1758
1573	static ev_tstamp	1759	static ev_tstamp
1574	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1760	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1575	{	1761	{
1576	return now + (3600. - fmod (now, 3600.));	1762	return now + (3600. - fmod (now, 3600.));
1577	}	1763	}
1578		1764
1579	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1765	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1580		1766
1581	Example: Call a callback every hour, starting now:	1767	Example: Call a callback every hour, starting now:
1582		1768
1583	struct ev_periodic hourly_tick;	1769	ev_periodic hourly_tick;
1584	ev_periodic_init (&hourly_tick, clock_cb,	1770	ev_periodic_init (&hourly_tick, clock_cb,
1585	fmod (ev_now (loop), 3600.), 3600., 0);	1771	fmod (ev_now (loop), 3600.), 3600., 0);
1586	ev_periodic_start (loop, &hourly_tick);	1772	ev_periodic_start (loop, &hourly_tick);
1587		1773
1588		1774
…		…
1630	=head3 Examples	1816	=head3 Examples
1631		1817
1632	Example: Try to exit cleanly on SIGINT.	1818	Example: Try to exit cleanly on SIGINT.
1633		1819
1634	static void	1820	static void
1635	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)	1821	sigint_cb (struct ev_loop loop, ev_signal w, int revents)
1636	{	1822	{
1637	ev_unloop (loop, EVUNLOOP_ALL);	1823	ev_unloop (loop, EVUNLOOP_ALL);
1638	}	1824	}
1639		1825
1640	struct ev_signal signal_watcher;	1826	ev_signal signal_watcher;
1641	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1827	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1642	ev_signal_start (loop, &signal_watcher);	1828	ev_signal_start (loop, &signal_watcher);
1643		1829
1644		1830
1645	=head2 C<ev_child> - watch out for process status changes	1831	=head2 C<ev_child> - watch out for process status changes
…		…
1720	its completion.	1906	its completion.
1721		1907
1722	ev_child cw;	1908	ev_child cw;
1723		1909
1724	static void	1910	static void
1725	child_cb (EV_P_ struct ev_child *w, int revents)	1911	child_cb (EV_P_ ev_child *w, int revents)
1726	{	1912	{
1727	ev_child_stop (EV_A_ w);	1913	ev_child_stop (EV_A_ w);
1728	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	1914	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1729	}	1915	}
1730		1916
…		…
1745		1931
1746		1932
1747	=head2 C<ev_stat> - did the file attributes just change?	1933	=head2 C<ev_stat> - did the file attributes just change?
1748		1934
1749	This watches a file system path for attribute changes. That is, it calls	1935	This watches a file system path for attribute changes. That is, it calls
1750	C<stat> regularly (or when the OS says it changed) and sees if it changed	1936	C<stat> on that path in regular intervals (or when the OS says it changed)
1751	compared to the last time, invoking the callback if it did.	1937	and sees if it changed compared to the last time, invoking the callback if
		1938	it did.
1752		1939
1753	The path does not need to exist: changing from "path exists" to "path does	1940	The path does not need to exist: changing from "path exists" to "path does
1754	not exist" is a status change like any other. The condition "path does	1941	not exist" is a status change like any other. The condition "path does not
1755	not exist" is signified by the C<st_nlink> field being zero (which is	1942	exist" (or more correctly "path cannot be stat'ed") is signified by the
1756	otherwise always forced to be at least one) and all the other fields of	1943	C<st_nlink> field being zero (which is otherwise always forced to be at
1757	the stat buffer having unspecified contents.	1944	least one) and all the other fields of the stat buffer having unspecified
		1945	contents.
1758		1946
1759	The path I<should> be absolute and I<must not> end in a slash. If it is	1947	The path I<must not> end in a slash or contain special components such as
		1948	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1760	relative and your working directory changes, the behaviour is undefined.	1949	your working directory changes, then the behaviour is undefined.
1761		1950
1762	Since there is no standard kernel interface to do this, the portable	1951	Since there is no portable change notification interface available, the
1763	implementation simply calls C<stat (2)> regularly on the path to see if	1952	portable implementation simply calls C<stat(2)> regularly on the path
1764	it changed somehow. You can specify a recommended polling interval for	1953	to see if it changed somehow. You can specify a recommended polling
1765	this case. If you specify a polling interval of C<0> (highly recommended!)	1954	interval for this case. If you specify a polling interval of C<0> (highly
1766	then a I<suitable, unspecified default> value will be used (which	1955	recommended!) then a I<suitable, unspecified default> value will be used
1767	you can expect to be around five seconds, although this might change	1956	(which you can expect to be around five seconds, although this might
1768	dynamically). Libev will also impose a minimum interval which is currently	1957	change dynamically). Libev will also impose a minimum interval which is
1769	around C<0.1>, but thats usually overkill.	1958	currently around C<0.1>, but that's usually overkill.
1770		1959
1771	This watcher type is not meant for massive numbers of stat watchers,	1960	This watcher type is not meant for massive numbers of stat watchers,
1772	as even with OS-supported change notifications, this can be	1961	as even with OS-supported change notifications, this can be
1773	resource-intensive.	1962	resource-intensive.
1774		1963
1775	At the time of this writing, the only OS-specific interface implemented	1964	At the time of this writing, the only OS-specific interface implemented
1776	is the Linux inotify interface (implementing kqueue support is left as	1965	is the Linux inotify interface (implementing kqueue support is left as an
1777	an exercise for the reader. Note, however, that the author sees no way	1966	exercise for the reader. Note, however, that the author sees no way of
1778	of implementing C<ev_stat> semantics with kqueue).	1967	implementing C<ev_stat> semantics with kqueue, except as a hint).
1779		1968
1780	=head3 ABI Issues (Largefile Support)	1969	=head3 ABI Issues (Largefile Support)
1781		1970
1782	Libev by default (unless the user overrides this) uses the default	1971	Libev by default (unless the user overrides this) uses the default
1783	compilation environment, which means that on systems with large file	1972	compilation environment, which means that on systems with large file
1784	support disabled by default, you get the 32 bit version of the stat	1973	support disabled by default, you get the 32 bit version of the stat
1785	structure. When using the library from programs that change the ABI to	1974	structure. When using the library from programs that change the ABI to
1786	use 64 bit file offsets the programs will fail. In that case you have to	1975	use 64 bit file offsets the programs will fail. In that case you have to
1787	compile libev with the same flags to get binary compatibility. This is	1976	compile libev with the same flags to get binary compatibility. This is
1788	obviously the case with any flags that change the ABI, but the problem is	1977	obviously the case with any flags that change the ABI, but the problem is
1789	most noticeably disabled with ev_stat and large file support.	1978	most noticeably displayed with ev_stat and large file support.
1790		1979
1791	The solution for this is to lobby your distribution maker to make large	1980	The solution for this is to lobby your distribution maker to make large
1792	file interfaces available by default (as e.g. FreeBSD does) and not	1981	file interfaces available by default (as e.g. FreeBSD does) and not
1793	optional. Libev cannot simply switch on large file support because it has	1982	optional. Libev cannot simply switch on large file support because it has
1794	to exchange stat structures with application programs compiled using the	1983	to exchange stat structures with application programs compiled using the
1795	default compilation environment.	1984	default compilation environment.
1796		1985
1797	=head3 Inotify and Kqueue	1986	=head3 Inotify and Kqueue
1798		1987
1799	When C<inotify (7)> support has been compiled into libev (generally only	1988	When C<inotify (7)> support has been compiled into libev and present at
1800	available with Linux) and present at runtime, it will be used to speed up	1989	runtime, it will be used to speed up change detection where possible. The
1801	change detection where possible. The inotify descriptor will be created lazily	1990	inotify descriptor will be created lazily when the first C<ev_stat>
1802	when the first C<ev_stat> watcher is being started.	1991	watcher is being started.
1803		1992
1804	Inotify presence does not change the semantics of C<ev_stat> watchers	1993	Inotify presence does not change the semantics of C<ev_stat> watchers
1805	except that changes might be detected earlier, and in some cases, to avoid	1994	except that changes might be detected earlier, and in some cases, to avoid
1806	making regular C<stat> calls. Even in the presence of inotify support	1995	making regular C<stat> calls. Even in the presence of inotify support
1807	there are many cases where libev has to resort to regular C<stat> polling,	1996	there are many cases where libev has to resort to regular C<stat> polling,
1808	but as long as the path exists, libev usually gets away without polling.	1997	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		1998	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		1999	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2000	xfs are fully working) libev usually gets away without polling.
1809		2001
1810	There is no support for kqueue, as apparently it cannot be used to	2002	There is no support for kqueue, as apparently it cannot be used to
1811	implement this functionality, due to the requirement of having a file	2003	implement this functionality, due to the requirement of having a file
1812	descriptor open on the object at all times, and detecting renames, unlinks	2004	descriptor open on the object at all times, and detecting renames, unlinks
1813	etc. is difficult.	2005	etc. is difficult.
1814		2006
		2007	=head3 C<stat ()> is a synchronous operation
		2008
		2009	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2010	the process. The exception are C<ev_stat> watchers - those call C<stat
		2011	()>, which is a synchronous operation.
		2012
		2013	For local paths, this usually doesn't matter: unless the system is very
		2014	busy or the intervals between stat's are large, a stat call will be fast,
		2015	as the path data is suually in memory already (except when starting the
		2016	watcher).
		2017
		2018	For networked file systems, calling C<stat ()> can block an indefinite
		2019	time due to network issues, and even under good conditions, a stat call
		2020	often takes multiple milliseconds.
		2021
		2022	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2023	paths, although this is fully supported by libev.
		2024
1815	=head3 The special problem of stat time resolution	2025	=head3 The special problem of stat time resolution
1816		2026
1817	The C<stat ()> system call only supports full-second resolution portably, and	2027	The C<stat ()> system call only supports full-second resolution portably,
1818	even on systems where the resolution is higher, most file systems still	2028	and even on systems where the resolution is higher, most file systems
1819	only support whole seconds.	2029	still only support whole seconds.
1820		2030
1821	That means that, if the time is the only thing that changes, you can	2031	That means that, if the time is the only thing that changes, you can
1822	easily miss updates: on the first update, C<ev_stat> detects a change and	2032	easily miss updates: on the first update, C<ev_stat> detects a change and
1823	calls your callback, which does something. When there is another update	2033	calls your callback, which does something. When there is another update
1824	within the same second, C<ev_stat> will be unable to detect unless the	2034	within the same second, C<ev_stat> will be unable to detect unless the
…		…
1981		2191
1982	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2192	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1983	callback, free it. Also, use no error checking, as usual.	2193	callback, free it. Also, use no error checking, as usual.
1984		2194
1985	static void	2195	static void
1986	idle_cb (struct ev_loop loop, struct ev_idle w, int revents)	2196	idle_cb (struct ev_loop loop, ev_idle w, int revents)
1987	{	2197	{
1988	free (w);	2198	free (w);
1989	// now do something you wanted to do when the program has	2199	// now do something you wanted to do when the program has
1990	// no longer anything immediate to do.	2200	// no longer anything immediate to do.
1991	}	2201	}
1992		2202
1993	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2203	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1994	ev_idle_init (idle_watcher, idle_cb);	2204	ev_idle_init (idle_watcher, idle_cb);
1995	ev_idle_start (loop, idle_cb);	2205	ev_idle_start (loop, idle_cb);
1996		2206
1997		2207
1998	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2208	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
…		…
2079		2289
2080	static ev_io iow [nfd];	2290	static ev_io iow [nfd];
2081	static ev_timer tw;	2291	static ev_timer tw;
2082		2292
2083	static void	2293	static void
2084	io_cb (ev_loop loop, ev_io w, int revents)	2294	io_cb (struct ev_loop loop, ev_io w, int revents)
2085	{	2295	{
2086	}	2296	}
2087		2297
2088	// create io watchers for each fd and a timer before blocking	2298	// create io watchers for each fd and a timer before blocking
2089	static void	2299	static void
2090	adns_prepare_cb (ev_loop loop, ev_prepare w, int revents)	2300	adns_prepare_cb (struct ev_loop loop, ev_prepare w, int revents)
2091	{	2301	{
2092	int timeout = 3600000;	2302	int timeout = 3600000;
2093	struct pollfd fds [nfd];	2303	struct pollfd fds [nfd];
2094	// actual code will need to loop here and realloc etc.	2304	// actual code will need to loop here and realloc etc.
2095	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2305	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
…		…
2110	}	2320	}
2111	}	2321	}
2112		2322
2113	// stop all watchers after blocking	2323	// stop all watchers after blocking
2114	static void	2324	static void
2115	adns_check_cb (ev_loop loop, ev_check w, int revents)	2325	adns_check_cb (struct ev_loop loop, ev_check w, int revents)
2116	{	2326	{
2117	ev_timer_stop (loop, &tw);	2327	ev_timer_stop (loop, &tw);
2118		2328
2119	for (int i = 0; i < nfd; ++i)	2329	for (int i = 0; i < nfd; ++i)
2120	{	2330	{
…		…
2288	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2498	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2289	used).	2499	used).
2290		2500
2291	struct ev_loop *loop_hi = ev_default_init (0);	2501	struct ev_loop *loop_hi = ev_default_init (0);
2292	struct ev_loop *loop_lo = 0;	2502	struct ev_loop *loop_lo = 0;
2293	struct ev_embed embed;	2503	ev_embed embed;
2294		2504
2295	// see if there is a chance of getting one that works	2505	// see if there is a chance of getting one that works
2296	// (remember that a flags value of 0 means autodetection)	2506	// (remember that a flags value of 0 means autodetection)
2297	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2507	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2298	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2508	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2312	kqueue implementation). Store the kqueue/socket-only event loop in	2522	kqueue implementation). Store the kqueue/socket-only event loop in
2313	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2523	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2314		2524
2315	struct ev_loop *loop = ev_default_init (0);	2525	struct ev_loop *loop = ev_default_init (0);
2316	struct ev_loop *loop_socket = 0;	2526	struct ev_loop *loop_socket = 0;
2317	struct ev_embed embed;	2527	ev_embed embed;
2318		2528
2319	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2529	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2320	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2530	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2321	{	2531	{
2322	ev_embed_init (&embed, 0, loop_socket);	2532	ev_embed_init (&embed, 0, loop_socket);
…		…
2463	=over 4	2673	=over 4
2464		2674
2465	=item ev_async_init (ev_async *, callback)	2675	=item ev_async_init (ev_async *, callback)
2466		2676
2467	Initialises and configures the async watcher - it has no parameters of any	2677	Initialises and configures the async watcher - it has no parameters of any
2468	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	2678	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2469	trust me.	2679	trust me.
2470		2680
2471	=item ev_async_send (loop, ev_async *)	2681	=item ev_async_send (loop, ev_async *)
2472		2682
2473	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	2683	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
…		…
2536	/* doh, nothing entered */;	2746	/* doh, nothing entered */;
2537	}	2747	}
2538		2748
2539	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2749	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2540		2750
2541	=item ev_feed_event (ev_loop , watcher , int revents)	2751	=item ev_feed_event (struct ev_loop , watcher , int revents)
2542		2752
2543	Feeds the given event set into the event loop, as if the specified event	2753	Feeds the given event set into the event loop, as if the specified event
2544	had happened for the specified watcher (which must be a pointer to an	2754	had happened for the specified watcher (which must be a pointer to an
2545	initialised but not necessarily started event watcher).	2755	initialised but not necessarily started event watcher).
2546		2756
2547	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2757	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2548		2758
2549	Feed an event on the given fd, as if a file descriptor backend detected	2759	Feed an event on the given fd, as if a file descriptor backend detected
2550	the given events it.	2760	the given events it.
2551		2761
2552	=item ev_feed_signal_event (ev_loop *loop, int signum)	2762	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2553		2763
2554	Feed an event as if the given signal occurred (C<loop> must be the default	2764	Feed an event as if the given signal occurred (C<loop> must be the default
2555	loop!).	2765	loop!).
2556		2766
2557	=back	2767	=back
…		…
2792	=item D	3002	=item D
2793		3003
2794	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3004	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2795	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3005	be found at L<http://proj.llucax.com.ar/wiki/evd>.
2796		3006
		3007	=item Ocaml
		3008
		3009	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3010	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3011
2797	=back	3012	=back
2798		3013
2799		3014
2800	=head1 MACRO MAGIC	3015	=head1 MACRO MAGIC
2801		3016
…		…
2901		3116
2902	#define EV_STANDALONE 1	3117	#define EV_STANDALONE 1
2903	#include "ev.h"	3118	#include "ev.h"
2904		3119
2905	Both header files and implementation files can be compiled with a C++	3120	Both header files and implementation files can be compiled with a C++
2906	compiler (at least, thats a stated goal, and breakage will be treated	3121	compiler (at least, that's a stated goal, and breakage will be treated
2907	as a bug).	3122	as a bug).
2908		3123
2909	You need the following files in your source tree, or in a directory	3124	You need the following files in your source tree, or in a directory
2910	in your include path (e.g. in libev/ when using -Ilibev):	3125	in your include path (e.g. in libev/ when using -Ilibev):
2911		3126
…		…
3383	loop, as long as you don't confuse yourself). The only exception is that	3598	loop, as long as you don't confuse yourself). The only exception is that
3384	you must not do this from C<ev_periodic> reschedule callbacks.	3599	you must not do this from C<ev_periodic> reschedule callbacks.
3385		3600
3386	Care has been taken to ensure that libev does not keep local state inside	3601	Care has been taken to ensure that libev does not keep local state inside
3387	C<ev_loop>, and other calls do not usually allow for coroutine switches as	3602	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3388	they do not clal any callbacks.	3603	they do not call any callbacks.
3389		3604
3390	=head2 COMPILER WARNINGS	3605	=head2 COMPILER WARNINGS
3391		3606
3392	Depending on your compiler and compiler settings, you might get no or a	3607	Depending on your compiler and compiler settings, you might get no or a
3393	lot of warnings when compiling libev code. Some people are apparently	3608	lot of warnings when compiling libev code. Some people are apparently
…		…
3427	==2274== definitely lost: 0 bytes in 0 blocks.	3642	==2274== definitely lost: 0 bytes in 0 blocks.
3428	==2274== possibly lost: 0 bytes in 0 blocks.	3643	==2274== possibly lost: 0 bytes in 0 blocks.
3429	==2274== still reachable: 256 bytes in 1 blocks.	3644	==2274== still reachable: 256 bytes in 1 blocks.
3430		3645
3431	Then there is no memory leak, just as memory accounted to global variables	3646	Then there is no memory leak, just as memory accounted to global variables
3432	is not a memleak - the memory is still being refernced, and didn't leak.	3647	is not a memleak - the memory is still being referenced, and didn't leak.
3433		3648
3434	Similarly, under some circumstances, valgrind might report kernel bugs	3649	Similarly, under some circumstances, valgrind might report kernel bugs
3435	as if it were a bug in libev (e.g. in realloc or in the poll backend,	3650	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3436	although an acceptable workaround has been found here), or it might be	3651	although an acceptable workaround has been found here), or it might be
3437	confused.	3652	confused.
…		…
3675	=back	3890	=back
3676		3891
3677		3892
3678	=head1 AUTHOR	3893	=head1 AUTHOR
3679		3894
3680	Marc Lehmann <libev@schmorp.de>.	3895	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3681		3896

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Comparing libev/ev.pod (file contents): Revision 1.194 by root, Mon Oct 20 16:08:36 2008 UTC vs. Revision 1.214 by root, Wed Nov 5 03:52:15 2008 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.194 by root, Mon Oct 20 16:08:36 2008 UTC vs.
Revision 1.214 by root, Wed Nov 5 03:52:15 2008 UTC