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

Comparing libev/ev.pod (file contents):
Revision 1.340 by root, Wed Nov 3 20:03:21 2010 UTC vs.
Revision 1.371 by root, Sat Jun 4 05:25:03 2011 UTC

…		…
58	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
59		59
60	// now wait for events to arrive	60	// now wait for events to arrive
61	ev_run (loop, 0);	61	ev_run (loop, 0);
62		62
63	// unloop was called, so exit	63	// break was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 ABOUT THIS DOCUMENT	67	=head1 ABOUT THIS DOCUMENT
68		68
…		…
178	you actually want to know. Also interesting is the combination of	178	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	179	C<ev_update_now> and C<ev_now>.
180		180
181	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
182		182
183	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
185	this is a sub-second-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
186		192
187	=item int ev_version_major ()	193	=item int ev_version_major ()
188		194
189	=item int ev_version_minor ()	195	=item int ev_version_minor ()
190		196
…		…
299	}	305	}
300		306
301	...	307	...
302	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
303		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
304	=back	323	=back
305		324
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		326
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
355	=item struct ev_loop *ev_loop_new (unsigned int flags)	374	=item struct ev_loop *ev_loop_new (unsigned int flags)
356		375
357	This will create and initialise a new event loop object. If the loop	376	This will create and initialise a new event loop object. If the loop
358	could not be initialised, returns false.	377	could not be initialised, returns false.
359		378
360	Note that this function I<is> thread-safe, and one common way to use	379	This function is thread-safe, and one common way to use libev with
361	libev with threads is indeed to create one loop per thread, and using the	380	threads is indeed to create one loop per thread, and using the default
362	default loop in the "main" or "initial" thread.	381	loop in the "main" or "initial" thread.
363		382
364	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
365	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
366		385
367	The following flags are supported:	386	The following flags are supported:
…		…
419		438
420	Signalfd will not be used by default as this changes your signal mask, and	439	Signalfd will not be used by default as this changes your signal mask, and
421	there are a lot of shoddy libraries and programs (glib's threadpool for	440	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
423		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you ahve to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
		455
		456	This flag's behaviour will become the default in future versions of libev.
		457
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		459
426	This is your standard select(2) backend. Not I<completely> standard, as	460	This is your standard select(2) backend. Not I<completely> standard, as
427	libev tries to roll its own fd_set with no limits on the number of fds,	461	libev tries to roll its own fd_set with no limits on the number of fds,
428	but if that fails, expect a fairly low limit on the number of fds when	462	but if that fails, expect a fairly low limit on the number of fds when
…		…
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		490
457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
458	kernels).	492	kernels).
459		493
460	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
461	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
462	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
463	epoll scales either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
464		498
465	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	502	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
471	0.1ms) and so on. The biggest issue is fork races, however - if a program	505	0.1ms) and so on. The biggest issue is fork races, however - if a program
472	forks then I<both> parent and child process have to recreate the epoll	506	forks then I<both> parent and child process have to recreate the epoll
473	set, which can take considerable time (one syscall per file descriptor)	507	set, which can take considerable time (one syscall per file descriptor)
474	and is of course hard to detect.	508	and is of course hard to detect.
475		509
476	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
477	of course I<doesn't>, and epoll just loves to report events for totally	511	but of course I<doesn't>, and epoll just loves to report events for
478	I<different> file descriptors (even already closed ones, so one cannot	512	totally I<different> file descriptors (even already closed ones, so
479	even remove them from the set) than registered in the set (especially	513	one cannot even remove them from the set) than registered in the set
480	on SMP systems). Libev tries to counter these spurious notifications by	514	(especially on SMP systems). Libev tries to counter these spurious
481	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
482	events to filter out spurious ones, recreating the set when required. Last	516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also errornously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
483	not least, it also refuses to work with some file descriptors which work	520	not least, it also refuses to work with some file descriptors which work
484	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
485		522
486	Epoll is truly the train wreck analog among event poll mechanisms.	523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
487		526
488	While stopping, setting and starting an I/O watcher in the same iteration	527	While stopping, setting and starting an I/O watcher in the same iteration
489	will result in some caching, there is still a system call per such	528	will result in some caching, there is still a system call per such
490	incident (because the same I<file descriptor> could point to a different	529	incident (because the same I<file descriptor> could point to a different
491	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
558		597
559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
560	it's really slow, but it still scales very well (O(active_fds)).	599	it's really slow, but it still scales very well (O(active_fds)).
561		600
562	Please note that Solaris event ports can deliver a lot of spurious
563	notifications, so you need to use non-blocking I/O or other means to avoid
564	blocking when no data (or space) is available.
565
566	While this backend scales well, it requires one system call per active	601	While this backend scales well, it requires one system call per active
567	file descriptor per loop iteration. For small and medium numbers of file	602	file descriptor per loop iteration. For small and medium numbers of file
568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
569	might perform better.	604	might perform better.
570		605
571	On the positive side, with the exception of the spurious readiness	606	On the positive side, this backend actually performed fully to
572	notifications, this backend actually performed fully to specification
573	in all tests and is fully embeddable, which is a rare feat among the	607	specification in all tests and is fully embeddable, which is a rare feat
574	OS-specific backends (I vastly prefer correctness over speed hacks).	608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returning events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where
		616	you absolutely have to know whether an event occurred or not because you
		617	have to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
575		620
576	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
577	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
578		623
579	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
580		625
581	Try all backends (even potentially broken ones that wouldn't be tried	626	Try all backends (even potentially broken ones that wouldn't be tried
582	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
584		629
585	It is definitely not recommended to use this flag.	630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
586		639
587	=back	640	=back
588		641
589	If one or more of the backend flags are or'ed into the flags value,	642	If one or more of the backend flags are or'ed into the flags value,
590	then only these backends will be tried (in the reverse order as listed	643	then only these backends will be tried (in the reverse order as listed
…		…
677	prepare and check phases.	730	prepare and check phases.
678		731
679	=item unsigned int ev_depth (loop)	732	=item unsigned int ev_depth (loop)
680		733
681	Returns the number of times C<ev_run> was entered minus the number of	734	Returns the number of times C<ev_run> was entered minus the number of
682	times C<ev_run> was exited, in other words, the recursion depth.	735	times C<ev_run> was exited normally, in other words, the recursion depth.
683		736
684	Outside C<ev_run>, this number is zero. In a callback, this number is	737	Outside C<ev_run>, this number is zero. In a callback, this number is
685	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	738	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
686	in which case it is higher.	739	in which case it is higher.
687		740
688	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	741	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
689	etc.), doesn't count as "exit" - consider this as a hint to avoid such	742	throwing an exception etc.), doesn't count as "exit" - consider this
690	ungentleman-like behaviour unless it's really convenient.	743	as a hint to avoid such ungentleman-like behaviour unless it's really
		744	convenient, in which case it is fully supported.
691		745
692	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
693		747
694	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	748	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
695	use.	749	use.
…		…
757	finished (especially in interactive programs), but having a program	811	finished (especially in interactive programs), but having a program
758	that automatically loops as long as it has to and no longer by virtue	812	that automatically loops as long as it has to and no longer by virtue
759	of relying on its watchers stopping correctly, that is truly a thing of	813	of relying on its watchers stopping correctly, that is truly a thing of
760	beauty.	814	beauty.
761		815
		816	This function is also I<mostly> exception-safe - you can break out of
		817	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		818	exception and so on. This does not decrement the C<ev_depth> value, nor
		819	will it clear any outstanding C<EVBREAK_ONE> breaks.
		820
762	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	821	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
763	those events and any already outstanding ones, but will not wait and	822	those events and any already outstanding ones, but will not wait and
764	block your process in case there are no events and will return after one	823	block your process in case there are no events and will return after one
765	iteration of the loop. This is sometimes useful to poll and handle new	824	iteration of the loop. This is sometimes useful to poll and handle new
766	events while doing lengthy calculations, to keep the program responsive.	825	events while doing lengthy calculations, to keep the program responsive.
…		…
775	This is useful if you are waiting for some external event in conjunction	834	This is useful if you are waiting for some external event in conjunction
776	with something not expressible using other libev watchers (i.e. "roll your	835	with something not expressible using other libev watchers (i.e. "roll your
777	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	836	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
778	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
779		838
780	Here are the gory details of what C<ev_run> does:	839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
781		842
782	- Increment loop depth.	843	- Increment loop depth.
783	- Reset the ev_break status.	844	- Reset the ev_break status.
784	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
785	LOOP:	846	LOOP:
…		…
818	anymore.	879	anymore.
819		880
820	... queue jobs here, make sure they register event watchers as long	881	... queue jobs here, make sure they register event watchers as long
821	... as they still have work to do (even an idle watcher will do..)	882	... as they still have work to do (even an idle watcher will do..)
822	ev_run (my_loop, 0);	883	ev_run (my_loop, 0);
823	... jobs done or somebody called unloop. yeah!	884	... jobs done or somebody called break. yeah!
824		885
825	=item ev_break (loop, how)	886	=item ev_break (loop, how)
826		887
827	Can be used to make a call to C<ev_run> return early (but only after it	888	Can be used to make a call to C<ev_run> return early (but only after it
828	has processed all outstanding events). The C<how> argument must be either	889	has processed all outstanding events). The C<how> argument must be either
829	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	890	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
830	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	891	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
831		892
832	This "break state" will be cleared when entering C<ev_run> again.	893	This "break state" will be cleared on the next call to C<ev_run>.
833		894
834	It is safe to call C<ev_break> from outside any C<ev_run> calls, too.	895	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		896	which case it will have no effect.
835		897
836	=item ev_ref (loop)	898	=item ev_ref (loop)
837		899
838	=item ev_unref (loop)	900	=item ev_unref (loop)
839		901
…		…
860	running when nothing else is active.	922	running when nothing else is active.
861		923
862	ev_signal exitsig;	924	ev_signal exitsig;
863	ev_signal_init (&exitsig, sig_cb, SIGINT);	925	ev_signal_init (&exitsig, sig_cb, SIGINT);
864	ev_signal_start (loop, &exitsig);	926	ev_signal_start (loop, &exitsig);
865	evf_unref (loop);	927	ev_unref (loop);
866		928
867	Example: For some weird reason, unregister the above signal handler again.	929	Example: For some weird reason, unregister the above signal handler again.
868		930
869	ev_ref (loop);	931	ev_ref (loop);
870	ev_signal_stop (loop, &exitsig);	932	ev_signal_stop (loop, &exitsig);
…		…
982	See also the locking example in the C<THREADS> section later in this	1044	See also the locking example in the C<THREADS> section later in this
983	document.	1045	document.
984		1046
985	=item ev_set_userdata (loop, void *data)	1047	=item ev_set_userdata (loop, void *data)
986		1048
987	=item ev_userdata (loop)	1049	=item void *ev_userdata (loop)
988		1050
989	Set and retrieve a single C<void *> associated with a loop. When	1051	Set and retrieve a single C<void *> associated with a loop. When
990	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1052	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
991	C<0.>	1053	C<0>.
992		1054
993	These two functions can be used to associate arbitrary data with a loop,	1055	These two functions can be used to associate arbitrary data with a loop,
994	and are intended solely for the C<invoke_pending_cb>, C<release> and	1056	and are intended solely for the C<invoke_pending_cb>, C<release> and
995	C<acquire> callbacks described above, but of course can be (ab-)used for	1057	C<acquire> callbacks described above, but of course can be (ab-)used for
996	any other purpose as well.	1058	any other purpose as well.
…		…
1309	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1371	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1310	functions that do not need a watcher.	1372	functions that do not need a watcher.
1311		1373
1312	=back	1374	=back
1313		1375
1314	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1376	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1315		1377	OWN COMPOSITE WATCHERS> idioms.
1316	Each watcher has, by default, a member C<void *data> that you can change
1317	and read at any time: libev will completely ignore it. This can be used
1318	to associate arbitrary data with your watcher. If you need more data and
1319	don't want to allocate memory and store a pointer to it in that data
1320	member, you can also "subclass" the watcher type and provide your own
1321	data:
1322
1323	struct my_io
1324	{
1325	ev_io io;
1326	int otherfd;
1327	void *somedata;
1328	struct whatever *mostinteresting;
1329	};
1330
1331	...
1332	struct my_io w;
1333	ev_io_init (&w.io, my_cb, fd, EV_READ);
1334
1335	And since your callback will be called with a pointer to the watcher, you
1336	can cast it back to your own type:
1337
1338	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1339	{
1340	struct my_io w = (struct my_io )w_;
1341	...
1342	}
1343
1344	More interesting and less C-conformant ways of casting your callback type
1345	instead have been omitted.
1346
1347	Another common scenario is to use some data structure with multiple
1348	embedded watchers:
1349
1350	struct my_biggy
1351	{
1352	int some_data;
1353	ev_timer t1;
1354	ev_timer t2;
1355	}
1356
1357	In this case getting the pointer to C<my_biggy> is a bit more
1358	complicated: Either you store the address of your C<my_biggy> struct
1359	in the C<data> member of the watcher (for woozies), or you need to use
1360	some pointer arithmetic using C<offsetof> inside your watchers (for real
1361	programmers):
1362
1363	#include <stddef.h>
1364
1365	static void
1366	t1_cb (EV_P_ ev_timer *w, int revents)
1367	{
1368	struct my_biggy big = (struct my_biggy *)
1369	(((char *)w) - offsetof (struct my_biggy, t1));
1370	}
1371
1372	static void
1373	t2_cb (EV_P_ ev_timer *w, int revents)
1374	{
1375	struct my_biggy big = (struct my_biggy *)
1376	(((char *)w) - offsetof (struct my_biggy, t2));
1377	}
1378		1378
1379	=head2 WATCHER STATES	1379	=head2 WATCHER STATES
1380		1380
1381	There are various watcher states mentioned throughout this manual -	1381	There are various watcher states mentioned throughout this manual -
1382	active, pending and so on. In this section these states and the rules to	1382	active, pending and so on. In this section these states and the rules to
…		…
1389		1389
1390	Before a watcher can be registered with the event looop it has to be	1390	Before a watcher can be registered with the event looop it has to be
1391	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1391	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1392	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1392	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1393		1393
1394	In this state it is simply some block of memory that is suitable for use	1394	In this state it is simply some block of memory that is suitable for
1395	in an event loop. It can be moved around, freed, reused etc. at will.	1395	use in an event loop. It can be moved around, freed, reused etc. at
		1396	will - as long as you either keep the memory contents intact, or call
		1397	C<ev_TYPE_init> again.
1396		1398
1397	=item started/running/active	1399	=item started/running/active
1398		1400
1399	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1401	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1400	property of the event loop, and is actively waiting for events. While in	1402	property of the event loop, and is actively waiting for events. While in
…		…
1428	latter will clear any pending state the watcher might be in, regardless	1430	latter will clear any pending state the watcher might be in, regardless
1429	of whether it was active or not, so stopping a watcher explicitly before	1431	of whether it was active or not, so stopping a watcher explicitly before
1430	freeing it is often a good idea.	1432	freeing it is often a good idea.
1431		1433
1432	While stopped (and not pending) the watcher is essentially in the	1434	While stopped (and not pending) the watcher is essentially in the
1433	initialised state, that is it can be reused, moved, modified in any way	1435	initialised state, that is, it can be reused, moved, modified in any way
1434	you wish.	1436	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1437	it again).
1435		1438
1436	=back	1439	=back
1437		1440
1438	=head2 WATCHER PRIORITY MODELS	1441	=head2 WATCHER PRIORITY MODELS
1439		1442
…		…
1568	In general you can register as many read and/or write event watchers per	1571	In general you can register as many read and/or write event watchers per
1569	fd as you want (as long as you don't confuse yourself). Setting all file	1572	fd as you want (as long as you don't confuse yourself). Setting all file
1570	descriptors to non-blocking mode is also usually a good idea (but not	1573	descriptors to non-blocking mode is also usually a good idea (but not
1571	required if you know what you are doing).	1574	required if you know what you are doing).
1572		1575
1573	If you cannot use non-blocking mode, then force the use of a
1574	known-to-be-good backend (at the time of this writing, this includes only
1575	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1576	descriptors for which non-blocking operation makes no sense (such as
1577	files) - libev doesn't guarantee any specific behaviour in that case.
1578
1579	Another thing you have to watch out for is that it is quite easy to	1576	Another thing you have to watch out for is that it is quite easy to
1580	receive "spurious" readiness notifications, that is your callback might	1577	receive "spurious" readiness notifications, that is, your callback might
1581	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1578	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1582	because there is no data. Not only are some backends known to create a	1579	because there is no data. It is very easy to get into this situation even
1583	lot of those (for example Solaris ports), it is very easy to get into	1580	with a relatively standard program structure. Thus it is best to always
1584	this situation even with a relatively standard program structure. Thus	1581	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1585	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1586	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1582	preferable to a program hanging until some data arrives.
1587		1583
1588	If you cannot run the fd in non-blocking mode (for example you should	1584	If you cannot run the fd in non-blocking mode (for example you should
1589	not play around with an Xlib connection), then you have to separately	1585	not play around with an Xlib connection), then you have to separately
1590	re-test whether a file descriptor is really ready with a known-to-be good	1586	re-test whether a file descriptor is really ready with a known-to-be good
1591	interface such as poll (fortunately in our Xlib example, Xlib already	1587	interface such as poll (fortunately in the case of Xlib, it already does
1592	does this on its own, so its quite safe to use). Some people additionally	1588	this on its own, so its quite safe to use). Some people additionally
1593	use C<SIGALRM> and an interval timer, just to be sure you won't block	1589	use C<SIGALRM> and an interval timer, just to be sure you won't block
1594	indefinitely.	1590	indefinitely.
1595		1591
1596	But really, best use non-blocking mode.	1592	But really, best use non-blocking mode.
1597		1593
…		…
1625		1621
1626	There is no workaround possible except not registering events	1622	There is no workaround possible except not registering events
1627	for potentially C<dup ()>'ed file descriptors, or to resort to	1623	for potentially C<dup ()>'ed file descriptors, or to resort to
1628	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1624	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1629		1625
		1626	=head3 The special problem of files
		1627
		1628	Many people try to use C<select> (or libev) on file descriptors
		1629	representing files, and expect it to become ready when their program
		1630	doesn't block on disk accesses (which can take a long time on their own).
		1631
		1632	However, this cannot ever work in the "expected" way - you get a readiness
		1633	notification as soon as the kernel knows whether and how much data is
		1634	there, and in the case of open files, that's always the case, so you
		1635	always get a readiness notification instantly, and your read (or possibly
		1636	write) will still block on the disk I/O.
		1637
		1638	Another way to view it is that in the case of sockets, pipes, character
		1639	devices and so on, there is another party (the sender) that delivers data
		1640	on its own, but in the case of files, there is no such thing: the disk
		1641	will not send data on its own, simply because it doesn't know what you
		1642	wish to read - you would first have to request some data.
		1643
		1644	Since files are typically not-so-well supported by advanced notification
		1645	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1646	to files, even though you should not use it. The reason for this is
		1647	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1648	usually a tty, often a pipe, but also sometimes files or special devices
		1649	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1650	F</dev/urandom>), and even though the file might better be served with
		1651	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1652	it "just works" instead of freezing.
		1653
		1654	So avoid file descriptors pointing to files when you know it (e.g. use
		1655	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1656	when you rarely read from a file instead of from a socket, and want to
		1657	reuse the same code path.
		1658
1630	=head3 The special problem of fork	1659	=head3 The special problem of fork
1631		1660
1632	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1661	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1633	useless behaviour. Libev fully supports fork, but needs to be told about	1662	useless behaviour. Libev fully supports fork, but needs to be told about
1634	it in the child.	1663	it in the child if you want to continue to use it in the child.
1635		1664
1636	To support fork in your programs, you either have to call	1665	To support fork in your child processes, you have to call C<ev_loop_fork
1637	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1666	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1638	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1667	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1639	C<EVBACKEND_POLL>.
1640		1668
1641	=head3 The special problem of SIGPIPE	1669	=head3 The special problem of SIGPIPE
1642		1670
1643	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1671	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1644	when writing to a pipe whose other end has been closed, your program gets	1672	when writing to a pipe whose other end has been closed, your program gets
…		…
2134		2162
2135	Another way to think about it (for the mathematically inclined) is that	2163	Another way to think about it (for the mathematically inclined) is that
2136	C<ev_periodic> will try to run the callback in this mode at the next possible	2164	C<ev_periodic> will try to run the callback in this mode at the next possible
2137	time where C<time = offset (mod interval)>, regardless of any time jumps.	2165	time where C<time = offset (mod interval)>, regardless of any time jumps.
2138		2166
2139	For numerical stability it is preferable that the C<offset> value is near	2167	The C<interval> I<MUST> be positive, and for numerical stability, the
2140	C<ev_now ()> (the current time), but there is no range requirement for	2168	interval value should be higher than C<1/8192> (which is around 100
2141	this value, and in fact is often specified as zero.	2169	microseconds) and C<offset> should be higher than C<0> and should have
		2170	at most a similar magnitude as the current time (say, within a factor of
		2171	ten). Typical values for offset are, in fact, C<0> or something between
		2172	C<0> and C<interval>, which is also the recommended range.
2142		2173
2143	Note also that there is an upper limit to how often a timer can fire (CPU	2174	Note also that there is an upper limit to how often a timer can fire (CPU
2144	speed for example), so if C<interval> is very small then timing stability	2175	speed for example), so if C<interval> is very small then timing stability
2145	will of course deteriorate. Libev itself tries to be exact to be about one	2176	will of course deteriorate. Libev itself tries to be exact to be about one
2146	millisecond (if the OS supports it and the machine is fast enough).	2177	millisecond (if the OS supports it and the machine is fast enough).
…		…
2289	=head3 The special problem of inheritance over fork/execve/pthread_create	2320	=head3 The special problem of inheritance over fork/execve/pthread_create
2290		2321
2291	Both the signal mask (C<sigprocmask>) and the signal disposition	2322	Both the signal mask (C<sigprocmask>) and the signal disposition
2292	(C<sigaction>) are unspecified after starting a signal watcher (and after	2323	(C<sigaction>) are unspecified after starting a signal watcher (and after
2293	stopping it again), that is, libev might or might not block the signal,	2324	stopping it again), that is, libev might or might not block the signal,
2294	and might or might not set or restore the installed signal handler.	2325	and might or might not set or restore the installed signal handler (but
		2326	see C<EVFLAG_NOSIGMASK>).
2295		2327
2296	While this does not matter for the signal disposition (libev never	2328	While this does not matter for the signal disposition (libev never
2297	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2329	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2298	C<execve>), this matters for the signal mask: many programs do not expect	2330	C<execve>), this matters for the signal mask: many programs do not expect
2299	certain signals to be blocked.	2331	certain signals to be blocked.
…		…
2312	I<has> to modify the signal mask, at least temporarily.	2344	I<has> to modify the signal mask, at least temporarily.
2313		2345
2314	So I can't stress this enough: I<If you do not reset your signal mask when	2346	So I can't stress this enough: I<If you do not reset your signal mask when
2315	you expect it to be empty, you have a race condition in your code>. This	2347	you expect it to be empty, you have a race condition in your code>. This
2316	is not a libev-specific thing, this is true for most event libraries.	2348	is not a libev-specific thing, this is true for most event libraries.
		2349
		2350	=head3 The special problem of threads signal handling
		2351
		2352	POSIX threads has problematic signal handling semantics, specifically,
		2353	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2354	threads in a process block signals, which is hard to achieve.
		2355
		2356	When you want to use sigwait (or mix libev signal handling with your own
		2357	for the same signals), you can tackle this problem by globally blocking
		2358	all signals before creating any threads (or creating them with a fully set
		2359	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2360	loops. Then designate one thread as "signal receiver thread" which handles
		2361	these signals. You can pass on any signals that libev might be interested
		2362	in by calling C<ev_feed_signal>.
2317		2363
2318	=head3 Watcher-Specific Functions and Data Members	2364	=head3 Watcher-Specific Functions and Data Members
2319		2365
2320	=over 4	2366	=over 4
2321		2367
…		…
3156	atexit (program_exits);	3202	atexit (program_exits);
3157		3203
3158		3204
3159	=head2 C<ev_async> - how to wake up an event loop	3205	=head2 C<ev_async> - how to wake up an event loop
3160		3206
3161	In general, you cannot use an C<ev_run> from multiple threads or other	3207	In general, you cannot use an C<ev_loop> from multiple threads or other
3162	asynchronous sources such as signal handlers (as opposed to multiple event	3208	asynchronous sources such as signal handlers (as opposed to multiple event
3163	loops - those are of course safe to use in different threads).	3209	loops - those are of course safe to use in different threads).
3164		3210
3165	Sometimes, however, you need to wake up an event loop you do not control,	3211	Sometimes, however, you need to wake up an event loop you do not control,
3166	for example because it belongs to another thread. This is what C<ev_async>	3212	for example because it belongs to another thread. This is what C<ev_async>
…		…
3168	it by calling C<ev_async_send>, which is thread- and signal safe.	3214	it by calling C<ev_async_send>, which is thread- and signal safe.
3169		3215
3170	This functionality is very similar to C<ev_signal> watchers, as signals,	3216	This functionality is very similar to C<ev_signal> watchers, as signals,
3171	too, are asynchronous in nature, and signals, too, will be compressed	3217	too, are asynchronous in nature, and signals, too, will be compressed
3172	(i.e. the number of callback invocations may be less than the number of	3218	(i.e. the number of callback invocations may be less than the number of
3173	C<ev_async_sent> calls).	3219	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3220	of "global async watchers" by using a watcher on an otherwise unused
		3221	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3222	even without knowing which loop owns the signal.
3174		3223
3175	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3224	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3176	just the default loop.	3225	just the default loop.
3177		3226
3178	=head3 Queueing	3227	=head3 Queueing
…		…
3273	trust me.	3322	trust me.
3274		3323
3275	=item ev_async_send (loop, ev_async *)	3324	=item ev_async_send (loop, ev_async *)
3276		3325
3277	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3326	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3278	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3327	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3328	returns.
		3329
3279	C<ev_feed_event>, this call is safe to do from other threads, signal or	3330	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3280	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3331	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3281	section below on what exactly this means).	3332	embedding section below on what exactly this means).
3282		3333
3283	Note that, as with other watchers in libev, multiple events might get	3334	Note that, as with other watchers in libev, multiple events might get
3284	compressed into a single callback invocation (another way to look at this	3335	compressed into a single callback invocation (another way to look at this
3285	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3336	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
3286	reset when the event loop detects that).	3337	reset when the event loop detects that).
…		…
3354	Feed an event on the given fd, as if a file descriptor backend detected	3405	Feed an event on the given fd, as if a file descriptor backend detected
3355	the given events it.	3406	the given events it.
3356		3407
3357	=item ev_feed_signal_event (loop, int signum)	3408	=item ev_feed_signal_event (loop, int signum)
3358		3409
3359	Feed an event as if the given signal occurred (C<loop> must be the default	3410	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3360	loop!).	3411	which is async-safe.
3361		3412
3362	=back	3413	=back
		3414
		3415
		3416	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3417
		3418	This section explains some common idioms that are not immediately
		3419	obvious. Note that examples are sprinkled over the whole manual, and this
		3420	section only contains stuff that wouldn't fit anywhere else.
		3421
		3422	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3423
		3424	Each watcher has, by default, a C<void *data> member that you can read
		3425	or modify at any time: libev will completely ignore it. This can be used
		3426	to associate arbitrary data with your watcher. If you need more data and
		3427	don't want to allocate memory separately and store a pointer to it in that
		3428	data member, you can also "subclass" the watcher type and provide your own
		3429	data:
		3430
		3431	struct my_io
		3432	{
		3433	ev_io io;
		3434	int otherfd;
		3435	void *somedata;
		3436	struct whatever *mostinteresting;
		3437	};
		3438
		3439	...
		3440	struct my_io w;
		3441	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3442
		3443	And since your callback will be called with a pointer to the watcher, you
		3444	can cast it back to your own type:
		3445
		3446	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3447	{
		3448	struct my_io w = (struct my_io )w_;
		3449	...
		3450	}
		3451
		3452	More interesting and less C-conformant ways of casting your callback
		3453	function type instead have been omitted.
		3454
		3455	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3456
		3457	Another common scenario is to use some data structure with multiple
		3458	embedded watchers, in effect creating your own watcher that combines
		3459	multiple libev event sources into one "super-watcher":
		3460
		3461	struct my_biggy
		3462	{
		3463	int some_data;
		3464	ev_timer t1;
		3465	ev_timer t2;
		3466	}
		3467
		3468	In this case getting the pointer to C<my_biggy> is a bit more
		3469	complicated: Either you store the address of your C<my_biggy> struct in
		3470	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3471	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3472	real programmers):
		3473
		3474	#include <stddef.h>
		3475
		3476	static void
		3477	t1_cb (EV_P_ ev_timer *w, int revents)
		3478	{
		3479	struct my_biggy big = (struct my_biggy *)
		3480	(((char *)w) - offsetof (struct my_biggy, t1));
		3481	}
		3482
		3483	static void
		3484	t2_cb (EV_P_ ev_timer *w, int revents)
		3485	{
		3486	struct my_biggy big = (struct my_biggy *)
		3487	(((char *)w) - offsetof (struct my_biggy, t2));
		3488	}
		3489
		3490	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3491
		3492	Often (especially in GUI toolkits) there are places where you have
		3493	I<modal> interaction, which is most easily implemented by recursively
		3494	invoking C<ev_run>.
		3495
		3496	This brings the problem of exiting - a callback might want to finish the
		3497	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3498	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3499	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3500	other combination: In these cases, C<ev_break> will not work alone.
		3501
		3502	The solution is to maintain "break this loop" variable for each C<ev_run>
		3503	invocation, and use a loop around C<ev_run> until the condition is
		3504	triggered, using C<EVRUN_ONCE>:
		3505
		3506	// main loop
		3507	int exit_main_loop = 0;
		3508
		3509	while (!exit_main_loop)
		3510	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3511
		3512	// in a model watcher
		3513	int exit_nested_loop = 0;
		3514
		3515	while (!exit_nested_loop)
		3516	ev_run (EV_A_ EVRUN_ONCE);
		3517
		3518	To exit from any of these loops, just set the corresponding exit variable:
		3519
		3520	// exit modal loop
		3521	exit_nested_loop = 1;
		3522
		3523	// exit main program, after modal loop is finished
		3524	exit_main_loop = 1;
		3525
		3526	// exit both
		3527	exit_main_loop = exit_nested_loop = 1;
		3528
		3529	=head2 THREAD LOCKING EXAMPLE
		3530
		3531	Here is a fictitious example of how to run an event loop in a different
		3532	thread from where callbacks are being invoked and watchers are
		3533	created/added/removed.
		3534
		3535	For a real-world example, see the C<EV::Loop::Async> perl module,
		3536	which uses exactly this technique (which is suited for many high-level
		3537	languages).
		3538
		3539	The example uses a pthread mutex to protect the loop data, a condition
		3540	variable to wait for callback invocations, an async watcher to notify the
		3541	event loop thread and an unspecified mechanism to wake up the main thread.
		3542
		3543	First, you need to associate some data with the event loop:
		3544
		3545	typedef struct {
		3546	mutex_t lock; /* global loop lock */
		3547	ev_async async_w;
		3548	thread_t tid;
		3549	cond_t invoke_cv;
		3550	} userdata;
		3551
		3552	void prepare_loop (EV_P)
		3553	{
		3554	// for simplicity, we use a static userdata struct.
		3555	static userdata u;
		3556
		3557	ev_async_init (&u->async_w, async_cb);
		3558	ev_async_start (EV_A_ &u->async_w);
		3559
		3560	pthread_mutex_init (&u->lock, 0);
		3561	pthread_cond_init (&u->invoke_cv, 0);
		3562
		3563	// now associate this with the loop
		3564	ev_set_userdata (EV_A_ u);
		3565	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3566	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3567
		3568	// then create the thread running ev_run
		3569	pthread_create (&u->tid, 0, l_run, EV_A);
		3570	}
		3571
		3572	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3573	solely to wake up the event loop so it takes notice of any new watchers
		3574	that might have been added:
		3575
		3576	static void
		3577	async_cb (EV_P_ ev_async *w, int revents)
		3578	{
		3579	// just used for the side effects
		3580	}
		3581
		3582	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3583	protecting the loop data, respectively.
		3584
		3585	static void
		3586	l_release (EV_P)
		3587	{
		3588	userdata *u = ev_userdata (EV_A);
		3589	pthread_mutex_unlock (&u->lock);
		3590	}
		3591
		3592	static void
		3593	l_acquire (EV_P)
		3594	{
		3595	userdata *u = ev_userdata (EV_A);
		3596	pthread_mutex_lock (&u->lock);
		3597	}
		3598
		3599	The event loop thread first acquires the mutex, and then jumps straight
		3600	into C<ev_run>:
		3601
		3602	void *
		3603	l_run (void *thr_arg)
		3604	{
		3605	struct ev_loop loop = (struct ev_loop )thr_arg;
		3606
		3607	l_acquire (EV_A);
		3608	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3609	ev_run (EV_A_ 0);
		3610	l_release (EV_A);
		3611
		3612	return 0;
		3613	}
		3614
		3615	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3616	signal the main thread via some unspecified mechanism (signals? pipe
		3617	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3618	have been called (in a while loop because a) spurious wakeups are possible
		3619	and b) skipping inter-thread-communication when there are no pending
		3620	watchers is very beneficial):
		3621
		3622	static void
		3623	l_invoke (EV_P)
		3624	{
		3625	userdata *u = ev_userdata (EV_A);
		3626
		3627	while (ev_pending_count (EV_A))
		3628	{
		3629	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3630	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3631	}
		3632	}
		3633
		3634	Now, whenever the main thread gets told to invoke pending watchers, it
		3635	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3636	thread to continue:
		3637
		3638	static void
		3639	real_invoke_pending (EV_P)
		3640	{
		3641	userdata *u = ev_userdata (EV_A);
		3642
		3643	pthread_mutex_lock (&u->lock);
		3644	ev_invoke_pending (EV_A);
		3645	pthread_cond_signal (&u->invoke_cv);
		3646	pthread_mutex_unlock (&u->lock);
		3647	}
		3648
		3649	Whenever you want to start/stop a watcher or do other modifications to an
		3650	event loop, you will now have to lock:
		3651
		3652	ev_timer timeout_watcher;
		3653	userdata *u = ev_userdata (EV_A);
		3654
		3655	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3656
		3657	pthread_mutex_lock (&u->lock);
		3658	ev_timer_start (EV_A_ &timeout_watcher);
		3659	ev_async_send (EV_A_ &u->async_w);
		3660	pthread_mutex_unlock (&u->lock);
		3661
		3662	Note that sending the C<ev_async> watcher is required because otherwise
		3663	an event loop currently blocking in the kernel will have no knowledge
		3664	about the newly added timer. By waking up the loop it will pick up any new
		3665	watchers in the next event loop iteration.
		3666
		3667	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3668
		3669	While the overhead of a callback that e.g. schedules a thread is small, it
		3670	is still an overhead. If you embed libev, and your main usage is with some
		3671	kind of threads or coroutines, you might want to customise libev so that
		3672	doesn't need callbacks anymore.
		3673
		3674	Imagine you have coroutines that you can switch to using a function
		3675	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3676	and that due to some magic, the currently active coroutine is stored in a
		3677	global called C<current_coro>. Then you can build your own "wait for libev
		3678	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3679	the differing C<;> conventions):
		3680
		3681	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3682	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3683
		3684	That means instead of having a C callback function, you store the
		3685	coroutine to switch to in each watcher, and instead of having libev call
		3686	your callback, you instead have it switch to that coroutine.
		3687
		3688	A coroutine might now wait for an event with a function called
		3689	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3690	matter when, or whether the watcher is active or not when this function is
		3691	called):
		3692
		3693	void
		3694	wait_for_event (ev_watcher *w)
		3695	{
		3696	ev_cb_set (w) = current_coro;
		3697	switch_to (libev_coro);
		3698	}
		3699
		3700	That basically suspends the coroutine inside C<wait_for_event> and
		3701	continues the libev coroutine, which, when appropriate, switches back to
		3702	this or any other coroutine. I am sure if you sue this your own :)
		3703
		3704	You can do similar tricks if you have, say, threads with an event queue -
		3705	instead of storing a coroutine, you store the queue object and instead of
		3706	switching to a coroutine, you push the watcher onto the queue and notify
		3707	any waiters.
		3708
		3709	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3710	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3711
		3712	// my_ev.h
		3713	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3714	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3715	#include "../libev/ev.h"
		3716
		3717	// my_ev.c
		3718	#define EV_H "my_ev.h"
		3719	#include "../libev/ev.c"
		3720
		3721	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3722	F<my_ev.c> into your project. When properly specifying include paths, you
		3723	can even use F<ev.h> as header file name directly.
3363		3724
3364		3725
3365	=head1 LIBEVENT EMULATION	3726	=head1 LIBEVENT EMULATION
3366		3727
3367	Libev offers a compatibility emulation layer for libevent. It cannot	3728	Libev offers a compatibility emulation layer for libevent. It cannot
3368	emulate the internals of libevent, so here are some usage hints:	3729	emulate the internals of libevent, so here are some usage hints:
3369		3730
3370	=over 4	3731	=over 4
		3732
		3733	=item * Only the libevent-1.4.1-beta API is being emulated.
		3734
		3735	This was the newest libevent version available when libev was implemented,
		3736	and is still mostly unchanged in 2010.
3371		3737
3372	=item * Use it by including <event.h>, as usual.	3738	=item * Use it by including <event.h>, as usual.
3373		3739
3374	=item * The following members are fully supported: ev_base, ev_callback,	3740	=item * The following members are fully supported: ev_base, ev_callback,
3375	ev_arg, ev_fd, ev_res, ev_events.	3741	ev_arg, ev_fd, ev_res, ev_events.
…		…
3381	=item * Priorities are not currently supported. Initialising priorities	3747	=item * Priorities are not currently supported. Initialising priorities
3382	will fail and all watchers will have the same priority, even though there	3748	will fail and all watchers will have the same priority, even though there
3383	is an ev_pri field.	3749	is an ev_pri field.
3384		3750
3385	=item * In libevent, the last base created gets the signals, in libev, the	3751	=item * In libevent, the last base created gets the signals, in libev, the
3386	first base created (== the default loop) gets the signals.	3752	base that registered the signal gets the signals.
3387		3753
3388	=item * Other members are not supported.	3754	=item * Other members are not supported.
3389		3755
3390	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3756	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3391	to use the libev header file and library.	3757	to use the libev header file and library.
…		…
3410	Care has been taken to keep the overhead low. The only data member the C++	3776	Care has been taken to keep the overhead low. The only data member the C++
3411	classes add (compared to plain C-style watchers) is the event loop pointer	3777	classes add (compared to plain C-style watchers) is the event loop pointer
3412	that the watcher is associated with (or no additional members at all if	3778	that the watcher is associated with (or no additional members at all if
3413	you disable C<EV_MULTIPLICITY> when embedding libev).	3779	you disable C<EV_MULTIPLICITY> when embedding libev).
3414		3780
3415	Currently, functions, and static and non-static member functions can be	3781	Currently, functions, static and non-static member functions and classes
3416	used as callbacks. Other types should be easy to add as long as they only	3782	with C<operator ()> can be used as callbacks. Other types should be easy
3417	need one additional pointer for context. If you need support for other	3783	to add as long as they only need one additional pointer for context. If
3418	types of functors please contact the author (preferably after implementing	3784	you need support for other types of functors please contact the author
3419	it).	3785	(preferably after implementing it).
3420		3786
3421	Here is a list of things available in the C<ev> namespace:	3787	Here is a list of things available in the C<ev> namespace:
3422		3788
3423	=over 4	3789	=over 4
3424		3790
…		…
3852	F<event.h> that are not directly supported by the libev core alone.	4218	F<event.h> that are not directly supported by the libev core alone.
3853		4219
3854	In standalone mode, libev will still try to automatically deduce the	4220	In standalone mode, libev will still try to automatically deduce the
3855	configuration, but has to be more conservative.	4221	configuration, but has to be more conservative.
3856		4222
		4223	=item EV_USE_FLOOR
		4224
		4225	If defined to be C<1>, libev will use the C<floor ()> function for its
		4226	periodic reschedule calculations, otherwise libev will fall back on a
		4227	portable (slower) implementation. If you enable this, you usually have to
		4228	link against libm or something equivalent. Enabling this when the C<floor>
		4229	function is not available will fail, so the safe default is to not enable
		4230	this.
		4231
3857	=item EV_USE_MONOTONIC	4232	=item EV_USE_MONOTONIC
3858		4233
3859	If defined to be C<1>, libev will try to detect the availability of the	4234	If defined to be C<1>, libev will try to detect the availability of the
3860	monotonic clock option at both compile time and runtime. Otherwise no	4235	monotonic clock option at both compile time and runtime. Otherwise no
3861	use of the monotonic clock option will be attempted. If you enable this,	4236	use of the monotonic clock option will be attempted. If you enable this,
…		…
4292	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4667	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4293		4668
4294	#include "ev_cpp.h"	4669	#include "ev_cpp.h"
4295	#include "ev.c"	4670	#include "ev.c"
4296		4671
4297	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4672	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4298		4673
4299	=head2 THREADS AND COROUTINES	4674	=head2 THREADS AND COROUTINES
4300		4675
4301	=head3 THREADS	4676	=head3 THREADS
4302		4677
…		…
4353	default loop and triggering an C<ev_async> watcher from the default loop	4728	default loop and triggering an C<ev_async> watcher from the default loop
4354	watcher callback into the event loop interested in the signal.	4729	watcher callback into the event loop interested in the signal.
4355		4730
4356	=back	4731	=back
4357		4732
4358	=head4 THREAD LOCKING EXAMPLE	4733	See also L<THREAD LOCKING EXAMPLE>.
4359
4360	Here is a fictitious example of how to run an event loop in a different
4361	thread than where callbacks are being invoked and watchers are
4362	created/added/removed.
4363
4364	For a real-world example, see the C<EV::Loop::Async> perl module,
4365	which uses exactly this technique (which is suited for many high-level
4366	languages).
4367
4368	The example uses a pthread mutex to protect the loop data, a condition
4369	variable to wait for callback invocations, an async watcher to notify the
4370	event loop thread and an unspecified mechanism to wake up the main thread.
4371
4372	First, you need to associate some data with the event loop:
4373
4374	typedef struct {
4375	mutex_t lock; /* global loop lock */
4376	ev_async async_w;
4377	thread_t tid;
4378	cond_t invoke_cv;
4379	} userdata;
4380
4381	void prepare_loop (EV_P)
4382	{
4383	// for simplicity, we use a static userdata struct.
4384	static userdata u;
4385
4386	ev_async_init (&u->async_w, async_cb);
4387	ev_async_start (EV_A_ &u->async_w);
4388
4389	pthread_mutex_init (&u->lock, 0);
4390	pthread_cond_init (&u->invoke_cv, 0);
4391
4392	// now associate this with the loop
4393	ev_set_userdata (EV_A_ u);
4394	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4395	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4396
4397	// then create the thread running ev_loop
4398	pthread_create (&u->tid, 0, l_run, EV_A);
4399	}
4400
4401	The callback for the C<ev_async> watcher does nothing: the watcher is used
4402	solely to wake up the event loop so it takes notice of any new watchers
4403	that might have been added:
4404
4405	static void
4406	async_cb (EV_P_ ev_async *w, int revents)
4407	{
4408	// just used for the side effects
4409	}
4410
4411	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4412	protecting the loop data, respectively.
4413
4414	static void
4415	l_release (EV_P)
4416	{
4417	userdata *u = ev_userdata (EV_A);
4418	pthread_mutex_unlock (&u->lock);
4419	}
4420
4421	static void
4422	l_acquire (EV_P)
4423	{
4424	userdata *u = ev_userdata (EV_A);
4425	pthread_mutex_lock (&u->lock);
4426	}
4427
4428	The event loop thread first acquires the mutex, and then jumps straight
4429	into C<ev_run>:
4430
4431	void *
4432	l_run (void *thr_arg)
4433	{
4434	struct ev_loop loop = (struct ev_loop )thr_arg;
4435
4436	l_acquire (EV_A);
4437	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4438	ev_run (EV_A_ 0);
4439	l_release (EV_A);
4440
4441	return 0;
4442	}
4443
4444	Instead of invoking all pending watchers, the C<l_invoke> callback will
4445	signal the main thread via some unspecified mechanism (signals? pipe
4446	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4447	have been called (in a while loop because a) spurious wakeups are possible
4448	and b) skipping inter-thread-communication when there are no pending
4449	watchers is very beneficial):
4450
4451	static void
4452	l_invoke (EV_P)
4453	{
4454	userdata *u = ev_userdata (EV_A);
4455
4456	while (ev_pending_count (EV_A))
4457	{
4458	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4459	pthread_cond_wait (&u->invoke_cv, &u->lock);
4460	}
4461	}
4462
4463	Now, whenever the main thread gets told to invoke pending watchers, it
4464	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4465	thread to continue:
4466
4467	static void
4468	real_invoke_pending (EV_P)
4469	{
4470	userdata *u = ev_userdata (EV_A);
4471
4472	pthread_mutex_lock (&u->lock);
4473	ev_invoke_pending (EV_A);
4474	pthread_cond_signal (&u->invoke_cv);
4475	pthread_mutex_unlock (&u->lock);
4476	}
4477
4478	Whenever you want to start/stop a watcher or do other modifications to an
4479	event loop, you will now have to lock:
4480
4481	ev_timer timeout_watcher;
4482	userdata *u = ev_userdata (EV_A);
4483
4484	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4485
4486	pthread_mutex_lock (&u->lock);
4487	ev_timer_start (EV_A_ &timeout_watcher);
4488	ev_async_send (EV_A_ &u->async_w);
4489	pthread_mutex_unlock (&u->lock);
4490
4491	Note that sending the C<ev_async> watcher is required because otherwise
4492	an event loop currently blocking in the kernel will have no knowledge
4493	about the newly added timer. By waking up the loop it will pick up any new
4494	watchers in the next event loop iteration.
4495		4734
4496	=head3 COROUTINES	4735	=head3 COROUTINES
4497		4736
4498	Libev is very accommodating to coroutines ("cooperative threads"):	4737	Libev is very accommodating to coroutines ("cooperative threads"):
4499	libev fully supports nesting calls to its functions from different	4738	libev fully supports nesting calls to its functions from different
…		…
5008	The physical time that is observed. It is apparently strictly monotonic :)	5247	The physical time that is observed. It is apparently strictly monotonic :)
5009		5248
5010	=item wall-clock time	5249	=item wall-clock time
5011		5250
5012	The time and date as shown on clocks. Unlike real time, it can actually	5251	The time and date as shown on clocks. Unlike real time, it can actually
5013	be wrong and jump forwards and backwards, e.g. when the you adjust your	5252	be wrong and jump forwards and backwards, e.g. when you adjust your
5014	clock.	5253	clock.
5015		5254
5016	=item watcher	5255	=item watcher
5017		5256
5018	A data structure that describes interest in certain events. Watchers need	5257	A data structure that describes interest in certain events. Watchers need
…		…
5021	=back	5260	=back
5022		5261
5023	=head1 AUTHOR	5262	=head1 AUTHOR
5024		5263
5025	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5264	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5026	Magnusson and Emanuele Giaquinta.	5265	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5027		5266

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Comparing libev/ev.pod (file contents): Revision 1.340 by root, Wed Nov 3 20:03:21 2010 UTC vs. Revision 1.371 by root, Sat Jun 4 05:25:03 2011 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.340 by root, Wed Nov 3 20:03:21 2010 UTC vs.
Revision 1.371 by root, Sat Jun 4 05:25:03 2011 UTC