[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 1.369 by root, Mon May 30 18:34:28 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
…		…
299	}	299	}
300		300
301	...	301	...
302	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
303		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	Its main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
304	=back	317	=back
305		318
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		320
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	321	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)	368	=item struct ev_loop *ev_loop_new (unsigned int flags)
356		369
357	This will create and initialise a new event loop object. If the loop	370	This will create and initialise a new event loop object. If the loop
358	could not be initialised, returns false.	371	could not be initialised, returns false.
359		372
360	Note that this function I<is> thread-safe, and one common way to use	373	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	374	threads is indeed to create one loop per thread, and using the default
362	default loop in the "main" or "initial" thread.	375	loop in the "main" or "initial" thread.
363		376
364	The flags argument can be used to specify special behaviour or specific	377	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>).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
366		379
367	The following flags are supported:	380	The following flags are supported:
…		…
419		432
420	Signalfd will not be used by default as this changes your signal mask, and	433	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	434	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	435	example) that can't properly initialise their signal masks.
423		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	When this flag is specified, then libev will avoid to modify the signal
		440	mask. Specifically, this means you ahve to make sure signals are unblocked
		441	when you want to receive them.
		442
		443	This behaviour is useful when you want to do your own signal handling, or
		444	want to handle signals only in specific threads and want to avoid libev
		445	unblocking the signals.
		446
		447	It's also required by POSIX in a threaded program, as libev calls
		448	C<sigprocmask>, whose behaviour is officially unspecified.
		449
		450	This flag's behaviour will become the default in future versions of libev.
		451
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	452	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		453
426	This is your standard select(2) backend. Not I<completely> standard, as	454	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,	455	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	456	but if that fails, expect a fairly low limit on the number of fds when
…		…
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	483	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		484
457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	485	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
458	kernels).	486	kernels).
459		487
460	For few fds, this backend is a bit little slower than poll and select,	488	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	489	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),	490	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).	491	fd), epoll scales either O(1) or O(active_fds).
464		492
465	The epoll mechanism deserves honorable mention as the most misdesigned	493	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	494	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	495	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	496	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
481	employing an additional generation counter and comparing that against the	509	employing an additional generation counter and comparing that against the
482	events to filter out spurious ones, recreating the set when required. Last	510	events to filter out spurious ones, recreating the set when required. Last
483	not least, it also refuses to work with some file descriptors which work	511	not least, it also refuses to work with some file descriptors which work
484	perfectly fine with C<select> (files, many character devices...).	512	perfectly fine with C<select> (files, many character devices...).
485		513
486	Epoll is truly the train wreck analog among event poll mechanisms.	514	Epoll is truly the train wreck analog among event poll mechanisms,
		515	a frankenpoll, cobbled together in a hurry, no thought to design or
		516	interaction with others.
487		517
488	While stopping, setting and starting an I/O watcher in the same iteration	518	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	519	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	520	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	521	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	587	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
558		588
559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	589	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)).	590	it's really slow, but it still scales very well (O(active_fds)).
561		591
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	592	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	593	file descriptor per loop iteration. For small and medium numbers of file
568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	594	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
569	might perform better.	595	might perform better.
570		596
571	On the positive side, with the exception of the spurious readiness	597	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	598	specification in all tests and is fully embeddable, which is a rare feat
574	OS-specific backends (I vastly prefer correctness over speed hacks).	599	among the OS-specific backends (I vastly prefer correctness over speed
		600	hacks).
		601
		602	On the negative side, the interface is I<bizarre> - so bizarre that
		603	even sun itself gets it wrong in their code examples: The event polling
		604	function sometimes returning events to the caller even though an error
		605	occurred, but with no indication whether it has done so or not (yes, it's
		606	even documented that way) - deadly for edge-triggered interfaces where
		607	you absolutely have to know whether an event occurred or not because you
		608	have to re-arm the watcher.
		609
		610	Fortunately libev seems to be able to work around these idiocies.
575		611
576	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	612	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
577	C<EVBACKEND_POLL>.	613	C<EVBACKEND_POLL>.
578		614
579	=item C<EVBACKEND_ALL>	615	=item C<EVBACKEND_ALL>
580		616
581	Try all backends (even potentially broken ones that wouldn't be tried	617	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	618	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	619	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
584		620
585	It is definitely not recommended to use this flag.	621	It is definitely not recommended to use this flag, use whatever
		622	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		623	at all.
		624
		625	=item C<EVBACKEND_MASK>
		626
		627	Not a backend at all, but a mask to select all backend bits from a
		628	C<flags> value, in case you want to mask out any backends from a flags
		629	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
586		630
587	=back	631	=back
588		632
589	If one or more of the backend flags are or'ed into the flags value,	633	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	634	then only these backends will be tried (in the reverse order as listed
…		…
677	prepare and check phases.	721	prepare and check phases.
678		722
679	=item unsigned int ev_depth (loop)	723	=item unsigned int ev_depth (loop)
680		724
681	Returns the number of times C<ev_run> was entered minus the number of	725	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.	726	times C<ev_run> was exited normally, in other words, the recursion depth.
683		727
684	Outside C<ev_run>, this number is zero. In a callback, this number is	728	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),	729	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
686	in which case it is higher.	730	in which case it is higher.
687		731
688	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	732	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	733	throwing an exception etc.), doesn't count as "exit" - consider this
690	ungentleman-like behaviour unless it's really convenient.	734	as a hint to avoid such ungentleman-like behaviour unless it's really
		735	convenient, in which case it is fully supported.
691		736
692	=item unsigned int ev_backend (loop)	737	=item unsigned int ev_backend (loop)
693		738
694	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	739	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
695	use.	740	use.
…		…
757	finished (especially in interactive programs), but having a program	802	finished (especially in interactive programs), but having a program
758	that automatically loops as long as it has to and no longer by virtue	803	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	804	of relying on its watchers stopping correctly, that is truly a thing of
760	beauty.	805	beauty.
761		806
		807	This function is also I<mostly> exception-safe - you can break out of
		808	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		809	exception and so on. This does not decrement the C<ev_depth> value, nor
		810	will it clear any outstanding C<EVBREAK_ONE> breaks.
		811
762	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	812	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	813	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	814	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	815	iteration of the loop. This is sometimes useful to poll and handle new
766	events while doing lengthy calculations, to keep the program responsive.	816	events while doing lengthy calculations, to keep the program responsive.
…		…
775	This is useful if you are waiting for some external event in conjunction	825	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	826	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	827	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.	828	usually a better approach for this kind of thing.
779		829
780	Here are the gory details of what C<ev_run> does:	830	Here are the gory details of what C<ev_run> does (this is for your
		831	understanding, not a guarantee that things will work exactly like this in
		832	future versions):
781		833
782	- Increment loop depth.	834	- Increment loop depth.
783	- Reset the ev_break status.	835	- Reset the ev_break status.
784	- Before the first iteration, call any pending watchers.	836	- Before the first iteration, call any pending watchers.
785	LOOP:	837	LOOP:
…		…
818	anymore.	870	anymore.
819		871
820	... queue jobs here, make sure they register event watchers as long	872	... 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..)	873	... as they still have work to do (even an idle watcher will do..)
822	ev_run (my_loop, 0);	874	ev_run (my_loop, 0);
823	... jobs done or somebody called unloop. yeah!	875	... jobs done or somebody called break. yeah!
824		876
825	=item ev_break (loop, how)	877	=item ev_break (loop, how)
826		878
827	Can be used to make a call to C<ev_run> return early (but only after it	879	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	880	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	881	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.	882	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
831		883
832	This "break state" will be cleared when entering C<ev_run> again.	884	This "break state" will be cleared on the next call to C<ev_run>.
833		885
834	It is safe to call C<ev_break> from outside any C<ev_run> calls, too.	886	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		887	which case it will have no effect.
835		888
836	=item ev_ref (loop)	889	=item ev_ref (loop)
837		890
838	=item ev_unref (loop)	891	=item ev_unref (loop)
839		892
…		…
860	running when nothing else is active.	913	running when nothing else is active.
861		914
862	ev_signal exitsig;	915	ev_signal exitsig;
863	ev_signal_init (&exitsig, sig_cb, SIGINT);	916	ev_signal_init (&exitsig, sig_cb, SIGINT);
864	ev_signal_start (loop, &exitsig);	917	ev_signal_start (loop, &exitsig);
865	evf_unref (loop);	918	ev_unref (loop);
866		919
867	Example: For some weird reason, unregister the above signal handler again.	920	Example: For some weird reason, unregister the above signal handler again.
868		921
869	ev_ref (loop);	922	ev_ref (loop);
870	ev_signal_stop (loop, &exitsig);	923	ev_signal_stop (loop, &exitsig);
…		…
982	See also the locking example in the C<THREADS> section later in this	1035	See also the locking example in the C<THREADS> section later in this
983	document.	1036	document.
984		1037
985	=item ev_set_userdata (loop, void *data)	1038	=item ev_set_userdata (loop, void *data)
986		1039
987	=item ev_userdata (loop)	1040	=item void *ev_userdata (loop)
988		1041
989	Set and retrieve a single C<void *> associated with a loop. When	1042	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	1043	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
991	C<0.>	1044	C<0>.
992		1045
993	These two functions can be used to associate arbitrary data with a loop,	1046	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	1047	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	1048	C<acquire> callbacks described above, but of course can be (ab-)used for
996	any other purpose as well.	1049	any other purpose as well.
…		…
1309	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1362	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1310	functions that do not need a watcher.	1363	functions that do not need a watcher.
1311		1364
1312	=back	1365	=back
1313		1366
1314	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1367	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1315		1368	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		1369
1379	=head2 WATCHER STATES	1370	=head2 WATCHER STATES
1380		1371
1381	There are various watcher states mentioned throughout this manual -	1372	There are various watcher states mentioned throughout this manual -
1382	active, pending and so on. In this section these states and the rules to	1373	active, pending and so on. In this section these states and the rules to
…		…
1389		1380
1390	Before a watcher can be registered with the event looop it has to be	1381	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	1382	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.	1383	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1393		1384
1394	In this state it is simply some block of memory that is suitable for use	1385	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.	1386	use in an event loop. It can be moved around, freed, reused etc. at
		1387	will - as long as you either keep the memory contents intact, or call
		1388	C<ev_TYPE_init> again.
1396		1389
1397	=item started/running/active	1390	=item started/running/active
1398		1391
1399	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1392	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	1393	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	1421	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	1422	of whether it was active or not, so stopping a watcher explicitly before
1430	freeing it is often a good idea.	1423	freeing it is often a good idea.
1431		1424
1432	While stopped (and not pending) the watcher is essentially in the	1425	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	1426	initialised state, that is, it can be reused, moved, modified in any way
1434	you wish.	1427	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1428	it again).
1435		1429
1436	=back	1430	=back
1437		1431
1438	=head2 WATCHER PRIORITY MODELS	1432	=head2 WATCHER PRIORITY MODELS
1439		1433
…		…
1568	In general you can register as many read and/or write event watchers per	1562	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	1563	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	1564	descriptors to non-blocking mode is also usually a good idea (but not
1571	required if you know what you are doing).	1565	required if you know what you are doing).
1572		1566
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	1567	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	1568	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	1569	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	1570	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	1571	with a relatively standard program structure. Thus it is best to always
1584	this situation even with a relatively standard program structure. Thus	1572	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.	1573	preferable to a program hanging until some data arrives.
1587		1574
1588	If you cannot run the fd in non-blocking mode (for example you should	1575	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	1576	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	1577	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	1578	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	1579	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	1580	use C<SIGALRM> and an interval timer, just to be sure you won't block
1594	indefinitely.	1581	indefinitely.
1595		1582
1596	But really, best use non-blocking mode.	1583	But really, best use non-blocking mode.
1597		1584
…		…
1625		1612
1626	There is no workaround possible except not registering events	1613	There is no workaround possible except not registering events
1627	for potentially C<dup ()>'ed file descriptors, or to resort to	1614	for potentially C<dup ()>'ed file descriptors, or to resort to
1628	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1615	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1629		1616
		1617	=head3 The special problem of files
		1618
		1619	Many people try to use C<select> (or libev) on file descriptors
		1620	representing files, and expect it to become ready when their program
		1621	doesn't block on disk accesses (which can take a long time on their own).
		1622
		1623	However, this cannot ever work in the "expected" way - you get a readiness
		1624	notification as soon as the kernel knows whether and how much data is
		1625	there, and in the case of open files, that's always the case, so you
		1626	always get a readiness notification instantly, and your read (or possibly
		1627	write) will still block on the disk I/O.
		1628
		1629	Another way to view it is that in the case of sockets, pipes, character
		1630	devices and so on, there is another party (the sender) that delivers data
		1631	on its own, but in the case of files, there is no such thing: the disk
		1632	will not send data on its own, simply because it doesn't know what you
		1633	wish to read - you would first have to request some data.
		1634
		1635	Since files are typically not-so-well supported by advanced notification
		1636	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1637	to files, even though you should not use it. The reason for this is
		1638	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1639	usually a tty, often a pipe, but also sometimes files or special devices
		1640	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1641	F</dev/urandom>), and even though the file might better be served with
		1642	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1643	it "just works" instead of freezing.
		1644
		1645	So avoid file descriptors pointing to files when you know it (e.g. use
		1646	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1647	when you rarely read from a file instead of from a socket, and want to
		1648	reuse the same code path.
		1649
1630	=head3 The special problem of fork	1650	=head3 The special problem of fork
1631		1651
1632	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1652	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	1653	useless behaviour. Libev fully supports fork, but needs to be told about
1634	it in the child.	1654	it in the child if you want to continue to use it in the child.
1635		1655
1636	To support fork in your programs, you either have to call	1656	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,	1657	()> 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	1658	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1639	C<EVBACKEND_POLL>.
1640		1659
1641	=head3 The special problem of SIGPIPE	1660	=head3 The special problem of SIGPIPE
1642		1661
1643	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1662	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	1663	when writing to a pipe whose other end has been closed, your program gets
…		…
2134		2153
2135	Another way to think about it (for the mathematically inclined) is that	2154	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	2155	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.	2156	time where C<time = offset (mod interval)>, regardless of any time jumps.
2138		2157
2139	For numerical stability it is preferable that the C<offset> value is near	2158	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	2159	interval value should be higher than C<1/8192> (which is around 100
2141	this value, and in fact is often specified as zero.	2160	microseconds) and C<offset> should be higher than C<0> and should have
		2161	at most a similar magnitude as the current time (say, within a factor of
		2162	ten). Typical values for offset are, in fact, C<0> or something between
		2163	C<0> and C<interval>, which is also the recommended range.
2142		2164
2143	Note also that there is an upper limit to how often a timer can fire (CPU	2165	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	2166	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	2167	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).	2168	millisecond (if the OS supports it and the machine is fast enough).
…		…
2289	=head3 The special problem of inheritance over fork/execve/pthread_create	2311	=head3 The special problem of inheritance over fork/execve/pthread_create
2290		2312
2291	Both the signal mask (C<sigprocmask>) and the signal disposition	2313	Both the signal mask (C<sigprocmask>) and the signal disposition
2292	(C<sigaction>) are unspecified after starting a signal watcher (and after	2314	(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,	2315	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.	2316	and might or might not set or restore the installed signal handler (but
		2317	see C<EVFLAG_NOSIGMASK>).
2295		2318
2296	While this does not matter for the signal disposition (libev never	2319	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	2320	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	2321	C<execve>), this matters for the signal mask: many programs do not expect
2299	certain signals to be blocked.	2322	certain signals to be blocked.
…		…
2312	I<has> to modify the signal mask, at least temporarily.	2335	I<has> to modify the signal mask, at least temporarily.
2313		2336
2314	So I can't stress this enough: I<If you do not reset your signal mask when	2337	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	2338	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.	2339	is not a libev-specific thing, this is true for most event libraries.
		2340
		2341	=head3 The special problem of threads signal handling
		2342
		2343	POSIX threads has problematic signal handling semantics, specifically,
		2344	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2345	threads in a process block signals, which is hard to achieve.
		2346
		2347	When you want to use sigwait (or mix libev signal handling with your own
		2348	for the same signals), you can tackle this problem by globally blocking
		2349	all signals before creating any threads (or creating them with a fully set
		2350	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2351	loops. Then designate one thread as "signal receiver thread" which handles
		2352	these signals. You can pass on any signals that libev might be interested
		2353	in by calling C<ev_feed_signal>.
2317		2354
2318	=head3 Watcher-Specific Functions and Data Members	2355	=head3 Watcher-Specific Functions and Data Members
2319		2356
2320	=over 4	2357	=over 4
2321		2358
…		…
3156	atexit (program_exits);	3193	atexit (program_exits);
3157		3194
3158		3195
3159	=head2 C<ev_async> - how to wake up an event loop	3196	=head2 C<ev_async> - how to wake up an event loop
3160		3197
3161	In general, you cannot use an C<ev_run> from multiple threads or other	3198	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	3199	asynchronous sources such as signal handlers (as opposed to multiple event
3163	loops - those are of course safe to use in different threads).	3200	loops - those are of course safe to use in different threads).
3164		3201
3165	Sometimes, however, you need to wake up an event loop you do not control,	3202	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>	3203	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.	3205	it by calling C<ev_async_send>, which is thread- and signal safe.
3169		3206
3170	This functionality is very similar to C<ev_signal> watchers, as signals,	3207	This functionality is very similar to C<ev_signal> watchers, as signals,
3171	too, are asynchronous in nature, and signals, too, will be compressed	3208	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	3209	(i.e. the number of callback invocations may be less than the number of
3173	C<ev_async_sent> calls).	3210	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3211	of "global async watchers" by using a watcher on an otherwise unused
		3212	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3213	even without knowing which loop owns the signal.
3174		3214
3175	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3215	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3176	just the default loop.	3216	just the default loop.
3177		3217
3178	=head3 Queueing	3218	=head3 Queueing
…		…
3273	trust me.	3313	trust me.
3274		3314
3275	=item ev_async_send (loop, ev_async *)	3315	=item ev_async_send (loop, ev_async *)
3276		3316
3277	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3317	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	3318	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3319	returns.
		3320
3279	C<ev_feed_event>, this call is safe to do from other threads, signal or	3321	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	3322	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3281	section below on what exactly this means).	3323	embedding section below on what exactly this means).
3282		3324
3283	Note that, as with other watchers in libev, multiple events might get	3325	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	3326	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>,	3327	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
3286	reset when the event loop detects that).	3328	reset when the event loop detects that).
…		…
3354	Feed an event on the given fd, as if a file descriptor backend detected	3396	Feed an event on the given fd, as if a file descriptor backend detected
3355	the given events it.	3397	the given events it.
3356		3398
3357	=item ev_feed_signal_event (loop, int signum)	3399	=item ev_feed_signal_event (loop, int signum)
3358		3400
3359	Feed an event as if the given signal occurred (C<loop> must be the default	3401	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3360	loop!).	3402	which is async-safe.
3361		3403
3362	=back	3404	=back
		3405
		3406
		3407	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3408
		3409	This section explains some common idioms that are not immediately
		3410	obvious. Note that examples are sprinkled over the whole manual, and this
		3411	section only contains stuff that wouldn't fit anywhere else.
		3412
		3413	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3414
		3415	Each watcher has, by default, a C<void *data> member that you can read
		3416	or modify at any time: libev will completely ignore it. This can be used
		3417	to associate arbitrary data with your watcher. If you need more data and
		3418	don't want to allocate memory separately and store a pointer to it in that
		3419	data member, you can also "subclass" the watcher type and provide your own
		3420	data:
		3421
		3422	struct my_io
		3423	{
		3424	ev_io io;
		3425	int otherfd;
		3426	void *somedata;
		3427	struct whatever *mostinteresting;
		3428	};
		3429
		3430	...
		3431	struct my_io w;
		3432	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3433
		3434	And since your callback will be called with a pointer to the watcher, you
		3435	can cast it back to your own type:
		3436
		3437	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3438	{
		3439	struct my_io w = (struct my_io )w_;
		3440	...
		3441	}
		3442
		3443	More interesting and less C-conformant ways of casting your callback
		3444	function type instead have been omitted.
		3445
		3446	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3447
		3448	Another common scenario is to use some data structure with multiple
		3449	embedded watchers, in effect creating your own watcher that combines
		3450	multiple libev event sources into one "super-watcher":
		3451
		3452	struct my_biggy
		3453	{
		3454	int some_data;
		3455	ev_timer t1;
		3456	ev_timer t2;
		3457	}
		3458
		3459	In this case getting the pointer to C<my_biggy> is a bit more
		3460	complicated: Either you store the address of your C<my_biggy> struct in
		3461	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3462	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3463	real programmers):
		3464
		3465	#include <stddef.h>
		3466
		3467	static void
		3468	t1_cb (EV_P_ ev_timer *w, int revents)
		3469	{
		3470	struct my_biggy big = (struct my_biggy *)
		3471	(((char *)w) - offsetof (struct my_biggy, t1));
		3472	}
		3473
		3474	static void
		3475	t2_cb (EV_P_ ev_timer *w, int revents)
		3476	{
		3477	struct my_biggy big = (struct my_biggy *)
		3478	(((char *)w) - offsetof (struct my_biggy, t2));
		3479	}
		3480
		3481	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3482
		3483	Often (especially in GUI toolkits) there are places where you have
		3484	I<modal> interaction, which is most easily implemented by recursively
		3485	invoking C<ev_run>.
		3486
		3487	This brings the problem of exiting - a callback might want to finish the
		3488	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3489	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3490	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3491	other combination: In these cases, C<ev_break> will not work alone.
		3492
		3493	The solution is to maintain "break this loop" variable for each C<ev_run>
		3494	invocation, and use a loop around C<ev_run> until the condition is
		3495	triggered, using C<EVRUN_ONCE>:
		3496
		3497	// main loop
		3498	int exit_main_loop = 0;
		3499
		3500	while (!exit_main_loop)
		3501	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3502
		3503	// in a model watcher
		3504	int exit_nested_loop = 0;
		3505
		3506	while (!exit_nested_loop)
		3507	ev_run (EV_A_ EVRUN_ONCE);
		3508
		3509	To exit from any of these loops, just set the corresponding exit variable:
		3510
		3511	// exit modal loop
		3512	exit_nested_loop = 1;
		3513
		3514	// exit main program, after modal loop is finished
		3515	exit_main_loop = 1;
		3516
		3517	// exit both
		3518	exit_main_loop = exit_nested_loop = 1;
		3519
		3520	=head2 THREAD LOCKING EXAMPLE
		3521
		3522	Here is a fictitious example of how to run an event loop in a different
		3523	thread from where callbacks are being invoked and watchers are
		3524	created/added/removed.
		3525
		3526	For a real-world example, see the C<EV::Loop::Async> perl module,
		3527	which uses exactly this technique (which is suited for many high-level
		3528	languages).
		3529
		3530	The example uses a pthread mutex to protect the loop data, a condition
		3531	variable to wait for callback invocations, an async watcher to notify the
		3532	event loop thread and an unspecified mechanism to wake up the main thread.
		3533
		3534	First, you need to associate some data with the event loop:
		3535
		3536	typedef struct {
		3537	mutex_t lock; /* global loop lock */
		3538	ev_async async_w;
		3539	thread_t tid;
		3540	cond_t invoke_cv;
		3541	} userdata;
		3542
		3543	void prepare_loop (EV_P)
		3544	{
		3545	// for simplicity, we use a static userdata struct.
		3546	static userdata u;
		3547
		3548	ev_async_init (&u->async_w, async_cb);
		3549	ev_async_start (EV_A_ &u->async_w);
		3550
		3551	pthread_mutex_init (&u->lock, 0);
		3552	pthread_cond_init (&u->invoke_cv, 0);
		3553
		3554	// now associate this with the loop
		3555	ev_set_userdata (EV_A_ u);
		3556	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3557	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3558
		3559	// then create the thread running ev_run
		3560	pthread_create (&u->tid, 0, l_run, EV_A);
		3561	}
		3562
		3563	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3564	solely to wake up the event loop so it takes notice of any new watchers
		3565	that might have been added:
		3566
		3567	static void
		3568	async_cb (EV_P_ ev_async *w, int revents)
		3569	{
		3570	// just used for the side effects
		3571	}
		3572
		3573	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3574	protecting the loop data, respectively.
		3575
		3576	static void
		3577	l_release (EV_P)
		3578	{
		3579	userdata *u = ev_userdata (EV_A);
		3580	pthread_mutex_unlock (&u->lock);
		3581	}
		3582
		3583	static void
		3584	l_acquire (EV_P)
		3585	{
		3586	userdata *u = ev_userdata (EV_A);
		3587	pthread_mutex_lock (&u->lock);
		3588	}
		3589
		3590	The event loop thread first acquires the mutex, and then jumps straight
		3591	into C<ev_run>:
		3592
		3593	void *
		3594	l_run (void *thr_arg)
		3595	{
		3596	struct ev_loop loop = (struct ev_loop )thr_arg;
		3597
		3598	l_acquire (EV_A);
		3599	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3600	ev_run (EV_A_ 0);
		3601	l_release (EV_A);
		3602
		3603	return 0;
		3604	}
		3605
		3606	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3607	signal the main thread via some unspecified mechanism (signals? pipe
		3608	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3609	have been called (in a while loop because a) spurious wakeups are possible
		3610	and b) skipping inter-thread-communication when there are no pending
		3611	watchers is very beneficial):
		3612
		3613	static void
		3614	l_invoke (EV_P)
		3615	{
		3616	userdata *u = ev_userdata (EV_A);
		3617
		3618	while (ev_pending_count (EV_A))
		3619	{
		3620	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3621	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3622	}
		3623	}
		3624
		3625	Now, whenever the main thread gets told to invoke pending watchers, it
		3626	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3627	thread to continue:
		3628
		3629	static void
		3630	real_invoke_pending (EV_P)
		3631	{
		3632	userdata *u = ev_userdata (EV_A);
		3633
		3634	pthread_mutex_lock (&u->lock);
		3635	ev_invoke_pending (EV_A);
		3636	pthread_cond_signal (&u->invoke_cv);
		3637	pthread_mutex_unlock (&u->lock);
		3638	}
		3639
		3640	Whenever you want to start/stop a watcher or do other modifications to an
		3641	event loop, you will now have to lock:
		3642
		3643	ev_timer timeout_watcher;
		3644	userdata *u = ev_userdata (EV_A);
		3645
		3646	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3647
		3648	pthread_mutex_lock (&u->lock);
		3649	ev_timer_start (EV_A_ &timeout_watcher);
		3650	ev_async_send (EV_A_ &u->async_w);
		3651	pthread_mutex_unlock (&u->lock);
		3652
		3653	Note that sending the C<ev_async> watcher is required because otherwise
		3654	an event loop currently blocking in the kernel will have no knowledge
		3655	about the newly added timer. By waking up the loop it will pick up any new
		3656	watchers in the next event loop iteration.
		3657
		3658	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3659
		3660	While the overhead of a callback that e.g. schedules a thread is small, it
		3661	is still an overhead. If you embed libev, and your main usage is with some
		3662	kind of threads or coroutines, you might want to customise libev so that
		3663	doesn't need callbacks anymore.
		3664
		3665	Imagine you have coroutines that you can switch to using a function
		3666	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3667	and that due to some magic, the currently active coroutine is stored in a
		3668	global called C<current_coro>. Then you can build your own "wait for libev
		3669	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3670	the differing C<;> conventions):
		3671
		3672	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3673	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3674
		3675	That means instead of having a C callback function, you store the
		3676	coroutine to switch to in each watcher, and instead of having libev call
		3677	your callback, you instead have it switch to that coroutine.
		3678
		3679	A coroutine might now wait for an event with a function called
		3680	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3681	matter when, or whether the watcher is active or not when this function is
		3682	called):
		3683
		3684	void
		3685	wait_for_event (ev_watcher *w)
		3686	{
		3687	ev_cb_set (w) = current_coro;
		3688	switch_to (libev_coro);
		3689	}
		3690
		3691	That basically suspends the coroutine inside C<wait_for_event> and
		3692	continues the libev coroutine, which, when appropriate, switches back to
		3693	this or any other coroutine. I am sure if you sue this your own :)
		3694
		3695	You can do similar tricks if you have, say, threads with an event queue -
		3696	instead of storing a coroutine, you store the queue object and instead of
		3697	switching to a coroutine, you push the watcher onto the queue and notify
		3698	any waiters.
		3699
		3700	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3701	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3702
		3703	// my_ev.h
		3704	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3705	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3706	#include "../libev/ev.h"
		3707
		3708	// my_ev.c
		3709	#define EV_H "my_ev.h"
		3710	#include "../libev/ev.c"
		3711
		3712	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3713	F<my_ev.c> into your project. When properly specifying include paths, you
		3714	can even use F<ev.h> as header file name directly.
3363		3715
3364		3716
3365	=head1 LIBEVENT EMULATION	3717	=head1 LIBEVENT EMULATION
3366		3718
3367	Libev offers a compatibility emulation layer for libevent. It cannot	3719	Libev offers a compatibility emulation layer for libevent. It cannot
3368	emulate the internals of libevent, so here are some usage hints:	3720	emulate the internals of libevent, so here are some usage hints:
3369		3721
3370	=over 4	3722	=over 4
		3723
		3724	=item * Only the libevent-1.4.1-beta API is being emulated.
		3725
		3726	This was the newest libevent version available when libev was implemented,
		3727	and is still mostly unchanged in 2010.
3371		3728
3372	=item * Use it by including <event.h>, as usual.	3729	=item * Use it by including <event.h>, as usual.
3373		3730
3374	=item * The following members are fully supported: ev_base, ev_callback,	3731	=item * The following members are fully supported: ev_base, ev_callback,
3375	ev_arg, ev_fd, ev_res, ev_events.	3732	ev_arg, ev_fd, ev_res, ev_events.
…		…
3381	=item * Priorities are not currently supported. Initialising priorities	3738	=item * Priorities are not currently supported. Initialising priorities
3382	will fail and all watchers will have the same priority, even though there	3739	will fail and all watchers will have the same priority, even though there
3383	is an ev_pri field.	3740	is an ev_pri field.
3384		3741
3385	=item * In libevent, the last base created gets the signals, in libev, the	3742	=item * In libevent, the last base created gets the signals, in libev, the
3386	first base created (== the default loop) gets the signals.	3743	base that registered the signal gets the signals.
3387		3744
3388	=item * Other members are not supported.	3745	=item * Other members are not supported.
3389		3746
3390	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3747	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3391	to use the libev header file and library.	3748	to use the libev header file and library.
…		…
3410	Care has been taken to keep the overhead low. The only data member the C++	3767	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	3768	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	3769	that the watcher is associated with (or no additional members at all if
3413	you disable C<EV_MULTIPLICITY> when embedding libev).	3770	you disable C<EV_MULTIPLICITY> when embedding libev).
3414		3771
3415	Currently, functions, and static and non-static member functions can be	3772	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	3773	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	3774	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	3775	you need support for other types of functors please contact the author
3419	it).	3776	(preferably after implementing it).
3420		3777
3421	Here is a list of things available in the C<ev> namespace:	3778	Here is a list of things available in the C<ev> namespace:
3422		3779
3423	=over 4	3780	=over 4
3424		3781
…		…
3852	F<event.h> that are not directly supported by the libev core alone.	4209	F<event.h> that are not directly supported by the libev core alone.
3853		4210
3854	In standalone mode, libev will still try to automatically deduce the	4211	In standalone mode, libev will still try to automatically deduce the
3855	configuration, but has to be more conservative.	4212	configuration, but has to be more conservative.
3856		4213
		4214	=item EV_USE_FLOOR
		4215
		4216	If defined to be C<1>, libev will use the C<floor ()> function for its
		4217	periodic reschedule calculations, otherwise libev will fall back on a
		4218	portable (slower) implementation. If you enable this, you usually have to
		4219	link against libm or something equivalent. Enabling this when the C<floor>
		4220	function is not available will fail, so the safe default is to not enable
		4221	this.
		4222
3857	=item EV_USE_MONOTONIC	4223	=item EV_USE_MONOTONIC
3858		4224
3859	If defined to be C<1>, libev will try to detect the availability of the	4225	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	4226	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,	4227	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:	4658	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4293		4659
4294	#include "ev_cpp.h"	4660	#include "ev_cpp.h"
4295	#include "ev.c"	4661	#include "ev.c"
4296		4662
4297	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4663	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4298		4664
4299	=head2 THREADS AND COROUTINES	4665	=head2 THREADS AND COROUTINES
4300		4666
4301	=head3 THREADS	4667	=head3 THREADS
4302		4668
…		…
4353	default loop and triggering an C<ev_async> watcher from the default loop	4719	default loop and triggering an C<ev_async> watcher from the default loop
4354	watcher callback into the event loop interested in the signal.	4720	watcher callback into the event loop interested in the signal.
4355		4721
4356	=back	4722	=back
4357		4723
4358	=head4 THREAD LOCKING EXAMPLE	4724	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		4725
4496	=head3 COROUTINES	4726	=head3 COROUTINES
4497		4727
4498	Libev is very accommodating to coroutines ("cooperative threads"):	4728	Libev is very accommodating to coroutines ("cooperative threads"):
4499	libev fully supports nesting calls to its functions from different	4729	libev fully supports nesting calls to its functions from different
…		…
5008	The physical time that is observed. It is apparently strictly monotonic :)	5238	The physical time that is observed. It is apparently strictly monotonic :)
5009		5239
5010	=item wall-clock time	5240	=item wall-clock time
5011		5241
5012	The time and date as shown on clocks. Unlike real time, it can actually	5242	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	5243	be wrong and jump forwards and backwards, e.g. when you adjust your
5014	clock.	5244	clock.
5015		5245
5016	=item watcher	5246	=item watcher
5017		5247
5018	A data structure that describes interest in certain events. Watchers need	5248	A data structure that describes interest in certain events. Watchers need
…		…
5021	=back	5251	=back
5022		5252
5023	=head1 AUTHOR	5253	=head1 AUTHOR
5024		5254
5025	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5255	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5026	Magnusson and Emanuele Giaquinta.	5256	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5027		5257

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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 1.369 by root, Mon May 30 18:34:28 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 1.369 by root, Mon May 30 18:34:28 2011 UTC