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

Comparing libev/ev.pod (file contents):
Revision 1.337 by root, Sun Oct 31 20:20:20 2010 UTC vs.
Revision 1.366 by sf-exg, Thu Feb 3 16:21:08 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
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	241	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	242	& ev_supported_backends ()>, likewise for recommended ones.
243		243
244	See the description of C<ev_embed> watchers for more info.	244	See the description of C<ev_embed> watchers for more info.
245		245
246	=item ev_set_allocator (void (cb)(void *ptr, long size)) [NOT REENTRANT]	246	=item ev_set_allocator (void (cb)(void *ptr, long size))
247		247
248	Sets the allocation function to use (the prototype is similar - the	248	Sets the allocation function to use (the prototype is similar - the
249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
250	used to allocate and free memory (no surprises here). If it returns zero	250	used to allocate and free memory (no surprises here). If it returns zero
251	when memory needs to be allocated (C<size != 0>), the library might abort	251	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
277	}	277	}
278		278
279	...	279	...
280	ev_set_allocator (persistent_realloc);	280	ev_set_allocator (persistent_realloc);
281		281
282	=item ev_set_syserr_cb (void (cb)(const char msg)); [NOT REENTRANT]	282	=item ev_set_syserr_cb (void (cb)(const char msg))
283		283
284	Set the callback function to call on a retryable system call error (such	284	Set the callback function to call on a retryable system call error (such
285	as failed select, poll, epoll_wait). The message is a printable string	285	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	286	indicating the system call or subsystem causing the problem. If this
287	callback is set, then libev will expect it to remedy the situation, no	287	callback is set, then libev will expect it to remedy the situation, no
…		…
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:
…		…
402	environment variable.	415	environment variable.
403		416
404	=item C<EVFLAG_NOINOTIFY>	417	=item C<EVFLAG_NOINOTIFY>
405		418
406	When this flag is specified, then libev will not attempt to use the	419	When this flag is specified, then libev will not attempt to use the
407	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	420	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
408	testing, this flag can be useful to conserve inotify file descriptors, as	421	testing, this flag can be useful to conserve inotify file descriptors, as
409	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	422	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
410		423
411	=item C<EVFLAG_SIGNALFD>	424	=item C<EVFLAG_SIGNALFD>
412		425
413	When this flag is specified, then libev will attempt to use the	426	When this flag is specified, then libev will attempt to use the
414	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	427	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
415	delivers signals synchronously, which makes it both faster and might make	428	delivers signals synchronously, which makes it both faster and might make
416	it possible to get the queued signal data. It can also simplify signal	429	it possible to get the queued signal data. It can also simplify signal
417	handling with threads, as long as you properly block signals in your	430	handling with threads, as long as you properly block signals in your
418	threads that are not interested in handling them.	431	threads that are not interested in handling them.
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.
		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.
423		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,
…		…
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,
469	returning before the timeout value requiring additional iterations and so	497	returning before the timeout value, resulting in additional iterations
		498	(and only giving 5ms accuracy while select on the same platform gives
470	on. The biggest issue is fork races, however - if a program forks then	499	0.1ms) and so on. The biggest issue is fork races, however - if a program
471	I<both> parent and child process have to recreate the epoll set, which can	500	forks then I<both> parent and child process have to recreate the epoll
472	take considerable time (one syscall per file descriptor) and is of course	501	set, which can take considerable time (one syscall per file descriptor)
473	hard to detect.	502	and is of course hard to detect.
474		503
475	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	504	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
476	of course I<doesn't>, and epoll just loves to report events for totally	505	of course I<doesn't>, and epoll just loves to report events for totally
477	I<different> file descriptors (even already closed ones, so one cannot	506	I<different> file descriptors (even already closed ones, so one cannot
478	even remove them from the set) than registered in the set (especially	507	even remove them from the set) than registered in the set (especially
…		…
480	employing an additional generation counter and comparing that against the	509	employing an additional generation counter and comparing that against the
481	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
482	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
483	perfectly fine with C<select> (files, many character devices...).	512	perfectly fine with C<select> (files, many character devices...).
484		513
		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.
		517
485	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
486	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
487	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
488	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
489	file descriptors might not work very well if you register events for both	522	file descriptors might not work very well if you register events for both
…		…
554	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	587	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
555		588
556	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,
557	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)).
558		591
559	Please note that Solaris event ports can deliver a lot of spurious
560	notifications, so you need to use non-blocking I/O or other means to avoid
561	blocking when no data (or space) is available.
562
563	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
564	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
565	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	594	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
566	might perform better.	595	might perform better.
567		596
568	On the positive side, with the exception of the spurious readiness	597	On the positive side, this backend actually performed fully to
569	notifications, this backend actually performed fully to specification
570	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
571	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.
572		611
573	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
574	C<EVBACKEND_POLL>.	613	C<EVBACKEND_POLL>.
575		614
576	=item C<EVBACKEND_ALL>	615	=item C<EVBACKEND_ALL>
577		616
578	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
579	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
580	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	619	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
581		620
582	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).
583		630
584	=back	631	=back
585		632
586	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,
587	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
…		…
616	This function is normally used on loop objects allocated by	663	This function is normally used on loop objects allocated by
617	C<ev_loop_new>, but it can also be used on the default loop returned by	664	C<ev_loop_new>, but it can also be used on the default loop returned by
618	C<ev_default_loop>, in which case it is not thread-safe.	665	C<ev_default_loop>, in which case it is not thread-safe.
619		666
620	Note that it is not advisable to call this function on the default loop	667	Note that it is not advisable to call this function on the default loop
621	except in the rare occasion where you really need to free it's resources.	668	except in the rare occasion where you really need to free its resources.
622	If you need dynamically allocated loops it is better to use C<ev_loop_new>	669	If you need dynamically allocated loops it is better to use C<ev_loop_new>
623	and C<ev_loop_destroy>.	670	and C<ev_loop_destroy>.
624		671
625	=item ev_loop_fork (loop)	672	=item ev_loop_fork (loop)
626		673
…		…
674	prepare and check phases.	721	prepare and check phases.
675		722
676	=item unsigned int ev_depth (loop)	723	=item unsigned int ev_depth (loop)
677		724
678	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
679	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.
680		727
681	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
682	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),
683	in which case it is higher.	730	in which case it is higher.
684		731
685	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	732	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
686	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
687	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.
688		736
689	=item unsigned int ev_backend (loop)	737	=item unsigned int ev_backend (loop)
690		738
691	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
692	use.	740	use.
…		…
753	relying on all watchers to be stopped when deciding when a program has	801	relying on all watchers to be stopped when deciding when a program has
754	finished (especially in interactive programs), but having a program	802	finished (especially in interactive programs), but having a program
755	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
756	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
757	beauty.	805	beauty.
		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.
758		811
759	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
760	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
761	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
762	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
…		…
815	anymore.	868	anymore.
816		869
817	... queue jobs here, make sure they register event watchers as long	870	... queue jobs here, make sure they register event watchers as long
818	... as they still have work to do (even an idle watcher will do..)	871	... as they still have work to do (even an idle watcher will do..)
819	ev_run (my_loop, 0);	872	ev_run (my_loop, 0);
820	... jobs done or somebody called unloop. yeah!	873	... jobs done or somebody called break. yeah!
821		874
822	=item ev_break (loop, how)	875	=item ev_break (loop, how)
823		876
824	Can be used to make a call to C<ev_run> return early (but only after it	877	Can be used to make a call to C<ev_run> return early (but only after it
825	has processed all outstanding events). The C<how> argument must be either	878	has processed all outstanding events). The C<how> argument must be either
826	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	879	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
827	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	880	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
828		881
829	This "break state" will be cleared when entering C<ev_run> again.	882	This "break state" will be cleared on the next call to C<ev_run>.
830		883
831	It is safe to call C<ev_break> from outside any C<ev_run> calls, too.	884	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		885	which case it will have no effect.
832		886
833	=item ev_ref (loop)	887	=item ev_ref (loop)
834		888
835	=item ev_unref (loop)	889	=item ev_unref (loop)
836		890
…		…
857	running when nothing else is active.	911	running when nothing else is active.
858		912
859	ev_signal exitsig;	913	ev_signal exitsig;
860	ev_signal_init (&exitsig, sig_cb, SIGINT);	914	ev_signal_init (&exitsig, sig_cb, SIGINT);
861	ev_signal_start (loop, &exitsig);	915	ev_signal_start (loop, &exitsig);
862	evf_unref (loop);	916	ev_unref (loop);
863		917
864	Example: For some weird reason, unregister the above signal handler again.	918	Example: For some weird reason, unregister the above signal handler again.
865		919
866	ev_ref (loop);	920	ev_ref (loop);
867	ev_signal_stop (loop, &exitsig);	921	ev_signal_stop (loop, &exitsig);
…		…
979	See also the locking example in the C<THREADS> section later in this	1033	See also the locking example in the C<THREADS> section later in this
980	document.	1034	document.
981		1035
982	=item ev_set_userdata (loop, void *data)	1036	=item ev_set_userdata (loop, void *data)
983		1037
984	=item ev_userdata (loop)	1038	=item void *ev_userdata (loop)
985		1039
986	Set and retrieve a single C<void *> associated with a loop. When	1040	Set and retrieve a single C<void *> associated with a loop. When
987	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1041	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
988	C<0.>	1042	C<0>.
989		1043
990	These two functions can be used to associate arbitrary data with a loop,	1044	These two functions can be used to associate arbitrary data with a loop,
991	and are intended solely for the C<invoke_pending_cb>, C<release> and	1045	and are intended solely for the C<invoke_pending_cb>, C<release> and
992	C<acquire> callbacks described above, but of course can be (ab-)used for	1046	C<acquire> callbacks described above, but of course can be (ab-)used for
993	any other purpose as well.	1047	any other purpose as well.
…		…
1306	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1360	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1307	functions that do not need a watcher.	1361	functions that do not need a watcher.
1308		1362
1309	=back	1363	=back
1310		1364
1311	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1365	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1312		1366	OWN COMPOSITE WATCHERS> idioms.
1313	Each watcher has, by default, a member C<void *data> that you can change
1314	and read at any time: libev will completely ignore it. This can be used
1315	to associate arbitrary data with your watcher. If you need more data and
1316	don't want to allocate memory and store a pointer to it in that data
1317	member, you can also "subclass" the watcher type and provide your own
1318	data:
1319
1320	struct my_io
1321	{
1322	ev_io io;
1323	int otherfd;
1324	void *somedata;
1325	struct whatever *mostinteresting;
1326	};
1327
1328	...
1329	struct my_io w;
1330	ev_io_init (&w.io, my_cb, fd, EV_READ);
1331
1332	And since your callback will be called with a pointer to the watcher, you
1333	can cast it back to your own type:
1334
1335	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1336	{
1337	struct my_io w = (struct my_io )w_;
1338	...
1339	}
1340
1341	More interesting and less C-conformant ways of casting your callback type
1342	instead have been omitted.
1343
1344	Another common scenario is to use some data structure with multiple
1345	embedded watchers:
1346
1347	struct my_biggy
1348	{
1349	int some_data;
1350	ev_timer t1;
1351	ev_timer t2;
1352	}
1353
1354	In this case getting the pointer to C<my_biggy> is a bit more
1355	complicated: Either you store the address of your C<my_biggy> struct
1356	in the C<data> member of the watcher (for woozies), or you need to use
1357	some pointer arithmetic using C<offsetof> inside your watchers (for real
1358	programmers):
1359
1360	#include <stddef.h>
1361
1362	static void
1363	t1_cb (EV_P_ ev_timer *w, int revents)
1364	{
1365	struct my_biggy big = (struct my_biggy *)
1366	(((char *)w) - offsetof (struct my_biggy, t1));
1367	}
1368
1369	static void
1370	t2_cb (EV_P_ ev_timer *w, int revents)
1371	{
1372	struct my_biggy big = (struct my_biggy *)
1373	(((char *)w) - offsetof (struct my_biggy, t2));
1374	}
1375		1367
1376	=head2 WATCHER STATES	1368	=head2 WATCHER STATES
1377		1369
1378	There are various watcher states mentioned throughout this manual -	1370	There are various watcher states mentioned throughout this manual -
1379	active, pending and so on. In this section these states and the rules to	1371	active, pending and so on. In this section these states and the rules to
…		…
1386		1378
1387	Before a watcher can be registered with the event looop it has to be	1379	Before a watcher can be registered with the event looop it has to be
1388	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1380	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1389	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1381	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1390		1382
1391	In this state it is simply some block of memory that is suitable for use	1383	In this state it is simply some block of memory that is suitable for
1392	in an event loop. It can be moved around, freed, reused etc. at will.	1384	use in an event loop. It can be moved around, freed, reused etc. at
		1385	will - as long as you either keep the memory contents intact, or call
		1386	C<ev_TYPE_init> again.
1393		1387
1394	=item started/running/active	1388	=item started/running/active
1395		1389
1396	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1390	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1397	property of the event loop, and is actively waiting for events. While in	1391	property of the event loop, and is actively waiting for events. While in
…		…
1425	latter will clear any pending state the watcher might be in, regardless	1419	latter will clear any pending state the watcher might be in, regardless
1426	of whether it was active or not, so stopping a watcher explicitly before	1420	of whether it was active or not, so stopping a watcher explicitly before
1427	freeing it is often a good idea.	1421	freeing it is often a good idea.
1428		1422
1429	While stopped (and not pending) the watcher is essentially in the	1423	While stopped (and not pending) the watcher is essentially in the
1430	initialised state, that is it can be reused, moved, modified in any way	1424	initialised state, that is, it can be reused, moved, modified in any way
1431	you wish.	1425	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1426	it again).
1432		1427
1433	=back	1428	=back
1434		1429
1435	=head2 WATCHER PRIORITY MODELS	1430	=head2 WATCHER PRIORITY MODELS
1436		1431
…		…
1565	In general you can register as many read and/or write event watchers per	1560	In general you can register as many read and/or write event watchers per
1566	fd as you want (as long as you don't confuse yourself). Setting all file	1561	fd as you want (as long as you don't confuse yourself). Setting all file
1567	descriptors to non-blocking mode is also usually a good idea (but not	1562	descriptors to non-blocking mode is also usually a good idea (but not
1568	required if you know what you are doing).	1563	required if you know what you are doing).
1569		1564
1570	If you cannot use non-blocking mode, then force the use of a
1571	known-to-be-good backend (at the time of this writing, this includes only
1572	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1573	descriptors for which non-blocking operation makes no sense (such as
1574	files) - libev doesn't guarantee any specific behaviour in that case.
1575
1576	Another thing you have to watch out for is that it is quite easy to	1565	Another thing you have to watch out for is that it is quite easy to
1577	receive "spurious" readiness notifications, that is your callback might	1566	receive "spurious" readiness notifications, that is, your callback might
1578	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1567	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1579	because there is no data. Not only are some backends known to create a	1568	because there is no data. It is very easy to get into this situation even
1580	lot of those (for example Solaris ports), it is very easy to get into	1569	with a relatively standard program structure. Thus it is best to always
1581	this situation even with a relatively standard program structure. Thus	1570	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1582	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1583	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1571	preferable to a program hanging until some data arrives.
1584		1572
1585	If you cannot run the fd in non-blocking mode (for example you should	1573	If you cannot run the fd in non-blocking mode (for example you should
1586	not play around with an Xlib connection), then you have to separately	1574	not play around with an Xlib connection), then you have to separately
1587	re-test whether a file descriptor is really ready with a known-to-be good	1575	re-test whether a file descriptor is really ready with a known-to-be good
1588	interface such as poll (fortunately in our Xlib example, Xlib already	1576	interface such as poll (fortunately in the case of Xlib, it already does
1589	does this on its own, so its quite safe to use). Some people additionally	1577	this on its own, so its quite safe to use). Some people additionally
1590	use C<SIGALRM> and an interval timer, just to be sure you won't block	1578	use C<SIGALRM> and an interval timer, just to be sure you won't block
1591	indefinitely.	1579	indefinitely.
1592		1580
1593	But really, best use non-blocking mode.	1581	But really, best use non-blocking mode.
1594		1582
…		…
1622		1610
1623	There is no workaround possible except not registering events	1611	There is no workaround possible except not registering events
1624	for potentially C<dup ()>'ed file descriptors, or to resort to	1612	for potentially C<dup ()>'ed file descriptors, or to resort to
1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1613	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1626		1614
		1615	=head3 The special problem of files
		1616
		1617	Many people try to use C<select> (or libev) on file descriptors
		1618	representing files, and expect it to become ready when their program
		1619	doesn't block on disk accesses (which can take a long time on their own).
		1620
		1621	However, this cannot ever work in the "expected" way - you get a readiness
		1622	notification as soon as the kernel knows whether and how much data is
		1623	there, and in the case of open files, that's always the case, so you
		1624	always get a readiness notification instantly, and your read (or possibly
		1625	write) will still block on the disk I/O.
		1626
		1627	Another way to view it is that in the case of sockets, pipes, character
		1628	devices and so on, there is another party (the sender) that delivers data
		1629	on its own, but in the case of files, there is no such thing: the disk
		1630	will not send data on its own, simply because it doesn't know what you
		1631	wish to read - you would first have to request some data.
		1632
		1633	Since files are typically not-so-well supported by advanced notification
		1634	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1635	to files, even though you should not use it. The reason for this is
		1636	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1637	usually a tty, often a pipe, but also sometimes files or special devices
		1638	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1639	F</dev/urandom>), and even though the file might better be served with
		1640	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1641	it "just works" instead of freezing.
		1642
		1643	So avoid file descriptors pointing to files when you know it (e.g. use
		1644	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1645	when you rarely read from a file instead of from a socket, and want to
		1646	reuse the same code path.
		1647
1627	=head3 The special problem of fork	1648	=head3 The special problem of fork
1628		1649
1629	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1650	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1630	useless behaviour. Libev fully supports fork, but needs to be told about	1651	useless behaviour. Libev fully supports fork, but needs to be told about
1631	it in the child.	1652	it in the child if you want to continue to use it in the child.
1632		1653
1633	To support fork in your programs, you either have to call	1654	To support fork in your child processes, you have to call C<ev_loop_fork
1634	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1655	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1635	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636	C<EVBACKEND_POLL>.
1637		1657
1638	=head3 The special problem of SIGPIPE	1658	=head3 The special problem of SIGPIPE
1639		1659
1640	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1660	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1641	when writing to a pipe whose other end has been closed, your program gets	1661	when writing to a pipe whose other end has been closed, your program gets
…		…
2257		2277
2258	=head2 C<ev_signal> - signal me when a signal gets signalled!	2278	=head2 C<ev_signal> - signal me when a signal gets signalled!
2259		2279
2260	Signal watchers will trigger an event when the process receives a specific	2280	Signal watchers will trigger an event when the process receives a specific
2261	signal one or more times. Even though signals are very asynchronous, libev	2281	signal one or more times. Even though signals are very asynchronous, libev
2262	will try it's best to deliver signals synchronously, i.e. as part of the	2282	will try its best to deliver signals synchronously, i.e. as part of the
2263	normal event processing, like any other event.	2283	normal event processing, like any other event.
2264		2284
2265	If you want signals to be delivered truly asynchronously, just use	2285	If you want signals to be delivered truly asynchronously, just use
2266	C<sigaction> as you would do without libev and forget about sharing	2286	C<sigaction> as you would do without libev and forget about sharing
2267	the signal. You can even use C<ev_async> from a signal handler to	2287	the signal. You can even use C<ev_async> from a signal handler to
…		…
2286	=head3 The special problem of inheritance over fork/execve/pthread_create	2306	=head3 The special problem of inheritance over fork/execve/pthread_create
2287		2307
2288	Both the signal mask (C<sigprocmask>) and the signal disposition	2308	Both the signal mask (C<sigprocmask>) and the signal disposition
2289	(C<sigaction>) are unspecified after starting a signal watcher (and after	2309	(C<sigaction>) are unspecified after starting a signal watcher (and after
2290	stopping it again), that is, libev might or might not block the signal,	2310	stopping it again), that is, libev might or might not block the signal,
2291	and might or might not set or restore the installed signal handler.	2311	and might or might not set or restore the installed signal handler (but
		2312	see C<EVFLAG_NOSIGMASK>).
2292		2313
2293	While this does not matter for the signal disposition (libev never	2314	While this does not matter for the signal disposition (libev never
2294	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2315	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2295	C<execve>), this matters for the signal mask: many programs do not expect	2316	C<execve>), this matters for the signal mask: many programs do not expect
2296	certain signals to be blocked.	2317	certain signals to be blocked.
…		…
2309	I<has> to modify the signal mask, at least temporarily.	2330	I<has> to modify the signal mask, at least temporarily.
2310		2331
2311	So I can't stress this enough: I<If you do not reset your signal mask when	2332	So I can't stress this enough: I<If you do not reset your signal mask when
2312	you expect it to be empty, you have a race condition in your code>. This	2333	you expect it to be empty, you have a race condition in your code>. This
2313	is not a libev-specific thing, this is true for most event libraries.	2334	is not a libev-specific thing, this is true for most event libraries.
		2335
		2336	=head3 The special problem of threads signal handling
		2337
		2338	POSIX threads has problematic signal handling semantics, specifically,
		2339	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2340	threads in a process block signals, which is hard to achieve.
		2341
		2342	When you want to use sigwait (or mix libev signal handling with your own
		2343	for the same signals), you can tackle this problem by globally blocking
		2344	all signals before creating any threads (or creating them with a fully set
		2345	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2346	loops. Then designate one thread as "signal receiver thread" which handles
		2347	these signals. You can pass on any signals that libev might be interested
		2348	in by calling C<ev_feed_signal>.
2314		2349
2315	=head3 Watcher-Specific Functions and Data Members	2350	=head3 Watcher-Specific Functions and Data Members
2316		2351
2317	=over 4	2352	=over 4
2318		2353
…		…
3153	atexit (program_exits);	3188	atexit (program_exits);
3154		3189
3155		3190
3156	=head2 C<ev_async> - how to wake up an event loop	3191	=head2 C<ev_async> - how to wake up an event loop
3157		3192
3158	In general, you cannot use an C<ev_run> from multiple threads or other	3193	In general, you cannot use an C<ev_loop> from multiple threads or other
3159	asynchronous sources such as signal handlers (as opposed to multiple event	3194	asynchronous sources such as signal handlers (as opposed to multiple event
3160	loops - those are of course safe to use in different threads).	3195	loops - those are of course safe to use in different threads).
3161		3196
3162	Sometimes, however, you need to wake up an event loop you do not control,	3197	Sometimes, however, you need to wake up an event loop you do not control,
3163	for example because it belongs to another thread. This is what C<ev_async>	3198	for example because it belongs to another thread. This is what C<ev_async>
…		…
3165	it by calling C<ev_async_send>, which is thread- and signal safe.	3200	it by calling C<ev_async_send>, which is thread- and signal safe.
3166		3201
3167	This functionality is very similar to C<ev_signal> watchers, as signals,	3202	This functionality is very similar to C<ev_signal> watchers, as signals,
3168	too, are asynchronous in nature, and signals, too, will be compressed	3203	too, are asynchronous in nature, and signals, too, will be compressed
3169	(i.e. the number of callback invocations may be less than the number of	3204	(i.e. the number of callback invocations may be less than the number of
3170	C<ev_async_sent> calls).	3205	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3206	of "global async watchers" by using a watcher on an otherwise unused
		3207	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3208	even without knowing which loop owns the signal.
3171		3209
3172	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3210	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3173	just the default loop.	3211	just the default loop.
3174		3212
3175	=head3 Queueing	3213	=head3 Queueing
…		…
3270	trust me.	3308	trust me.
3271		3309
3272	=item ev_async_send (loop, ev_async *)	3310	=item ev_async_send (loop, ev_async *)
3273		3311
3274	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3312	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3275	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3313	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3314	returns.
		3315
3276	C<ev_feed_event>, this call is safe to do from other threads, signal or	3316	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3277	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3317	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3278	section below on what exactly this means).	3318	embedding section below on what exactly this means).
3279		3319
3280	Note that, as with other watchers in libev, multiple events might get	3320	Note that, as with other watchers in libev, multiple events might get
3281	compressed into a single callback invocation (another way to look at this	3321	compressed into a single callback invocation (another way to look at this
3282	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3322	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
3283	reset when the event loop detects that).	3323	reset when the event loop detects that).
…		…
3351	Feed an event on the given fd, as if a file descriptor backend detected	3391	Feed an event on the given fd, as if a file descriptor backend detected
3352	the given events it.	3392	the given events it.
3353		3393
3354	=item ev_feed_signal_event (loop, int signum)	3394	=item ev_feed_signal_event (loop, int signum)
3355		3395
3356	Feed an event as if the given signal occurred (C<loop> must be the default	3396	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3357	loop!).	3397	which is async-safe.
3358		3398
3359	=back	3399	=back
		3400
		3401
		3402	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3403
		3404	This section explains some common idioms that are not immediately
		3405	obvious. Note that examples are sprinkled over the whole manual, and this
		3406	section only contains stuff that wouldn't fit anywhere else.
		3407
		3408	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3409
		3410	Each watcher has, by default, a C<void *data> member that you can read
		3411	or modify at any time: libev will completely ignore it. This can be used
		3412	to associate arbitrary data with your watcher. If you need more data and
		3413	don't want to allocate memory separately and store a pointer to it in that
		3414	data member, you can also "subclass" the watcher type and provide your own
		3415	data:
		3416
		3417	struct my_io
		3418	{
		3419	ev_io io;
		3420	int otherfd;
		3421	void *somedata;
		3422	struct whatever *mostinteresting;
		3423	};
		3424
		3425	...
		3426	struct my_io w;
		3427	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3428
		3429	And since your callback will be called with a pointer to the watcher, you
		3430	can cast it back to your own type:
		3431
		3432	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3433	{
		3434	struct my_io w = (struct my_io )w_;
		3435	...
		3436	}
		3437
		3438	More interesting and less C-conformant ways of casting your callback
		3439	function type instead have been omitted.
		3440
		3441	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3442
		3443	Another common scenario is to use some data structure with multiple
		3444	embedded watchers, in effect creating your own watcher that combines
		3445	multiple libev event sources into one "super-watcher":
		3446
		3447	struct my_biggy
		3448	{
		3449	int some_data;
		3450	ev_timer t1;
		3451	ev_timer t2;
		3452	}
		3453
		3454	In this case getting the pointer to C<my_biggy> is a bit more
		3455	complicated: Either you store the address of your C<my_biggy> struct in
		3456	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3457	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3458	real programmers):
		3459
		3460	#include <stddef.h>
		3461
		3462	static void
		3463	t1_cb (EV_P_ ev_timer *w, int revents)
		3464	{
		3465	struct my_biggy big = (struct my_biggy *)
		3466	(((char *)w) - offsetof (struct my_biggy, t1));
		3467	}
		3468
		3469	static void
		3470	t2_cb (EV_P_ ev_timer *w, int revents)
		3471	{
		3472	struct my_biggy big = (struct my_biggy *)
		3473	(((char *)w) - offsetof (struct my_biggy, t2));
		3474	}
		3475
		3476	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3477
		3478	Often (especially in GUI toolkits) there are places where you have
		3479	I<modal> interaction, which is most easily implemented by recursively
		3480	invoking C<ev_run>.
		3481
		3482	This brings the problem of exiting - a callback might want to finish the
		3483	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3484	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3485	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3486	other combination: In these cases, C<ev_break> will not work alone.
		3487
		3488	The solution is to maintain "break this loop" variable for each C<ev_run>
		3489	invocation, and use a loop around C<ev_run> until the condition is
		3490	triggered, using C<EVRUN_ONCE>:
		3491
		3492	// main loop
		3493	int exit_main_loop = 0;
		3494
		3495	while (!exit_main_loop)
		3496	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3497
		3498	// in a model watcher
		3499	int exit_nested_loop = 0;
		3500
		3501	while (!exit_nested_loop)
		3502	ev_run (EV_A_ EVRUN_ONCE);
		3503
		3504	To exit from any of these loops, just set the corresponding exit variable:
		3505
		3506	// exit modal loop
		3507	exit_nested_loop = 1;
		3508
		3509	// exit main program, after modal loop is finished
		3510	exit_main_loop = 1;
		3511
		3512	// exit both
		3513	exit_main_loop = exit_nested_loop = 1;
		3514
		3515	=head2 THREAD LOCKING EXAMPLE
		3516
		3517	Here is a fictitious example of how to run an event loop in a different
		3518	thread from where callbacks are being invoked and watchers are
		3519	created/added/removed.
		3520
		3521	For a real-world example, see the C<EV::Loop::Async> perl module,
		3522	which uses exactly this technique (which is suited for many high-level
		3523	languages).
		3524
		3525	The example uses a pthread mutex to protect the loop data, a condition
		3526	variable to wait for callback invocations, an async watcher to notify the
		3527	event loop thread and an unspecified mechanism to wake up the main thread.
		3528
		3529	First, you need to associate some data with the event loop:
		3530
		3531	typedef struct {
		3532	mutex_t lock; /* global loop lock */
		3533	ev_async async_w;
		3534	thread_t tid;
		3535	cond_t invoke_cv;
		3536	} userdata;
		3537
		3538	void prepare_loop (EV_P)
		3539	{
		3540	// for simplicity, we use a static userdata struct.
		3541	static userdata u;
		3542
		3543	ev_async_init (&u->async_w, async_cb);
		3544	ev_async_start (EV_A_ &u->async_w);
		3545
		3546	pthread_mutex_init (&u->lock, 0);
		3547	pthread_cond_init (&u->invoke_cv, 0);
		3548
		3549	// now associate this with the loop
		3550	ev_set_userdata (EV_A_ u);
		3551	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3552	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3553
		3554	// then create the thread running ev_run
		3555	pthread_create (&u->tid, 0, l_run, EV_A);
		3556	}
		3557
		3558	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3559	solely to wake up the event loop so it takes notice of any new watchers
		3560	that might have been added:
		3561
		3562	static void
		3563	async_cb (EV_P_ ev_async *w, int revents)
		3564	{
		3565	// just used for the side effects
		3566	}
		3567
		3568	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3569	protecting the loop data, respectively.
		3570
		3571	static void
		3572	l_release (EV_P)
		3573	{
		3574	userdata *u = ev_userdata (EV_A);
		3575	pthread_mutex_unlock (&u->lock);
		3576	}
		3577
		3578	static void
		3579	l_acquire (EV_P)
		3580	{
		3581	userdata *u = ev_userdata (EV_A);
		3582	pthread_mutex_lock (&u->lock);
		3583	}
		3584
		3585	The event loop thread first acquires the mutex, and then jumps straight
		3586	into C<ev_run>:
		3587
		3588	void *
		3589	l_run (void *thr_arg)
		3590	{
		3591	struct ev_loop loop = (struct ev_loop )thr_arg;
		3592
		3593	l_acquire (EV_A);
		3594	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3595	ev_run (EV_A_ 0);
		3596	l_release (EV_A);
		3597
		3598	return 0;
		3599	}
		3600
		3601	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3602	signal the main thread via some unspecified mechanism (signals? pipe
		3603	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3604	have been called (in a while loop because a) spurious wakeups are possible
		3605	and b) skipping inter-thread-communication when there are no pending
		3606	watchers is very beneficial):
		3607
		3608	static void
		3609	l_invoke (EV_P)
		3610	{
		3611	userdata *u = ev_userdata (EV_A);
		3612
		3613	while (ev_pending_count (EV_A))
		3614	{
		3615	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3616	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3617	}
		3618	}
		3619
		3620	Now, whenever the main thread gets told to invoke pending watchers, it
		3621	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3622	thread to continue:
		3623
		3624	static void
		3625	real_invoke_pending (EV_P)
		3626	{
		3627	userdata *u = ev_userdata (EV_A);
		3628
		3629	pthread_mutex_lock (&u->lock);
		3630	ev_invoke_pending (EV_A);
		3631	pthread_cond_signal (&u->invoke_cv);
		3632	pthread_mutex_unlock (&u->lock);
		3633	}
		3634
		3635	Whenever you want to start/stop a watcher or do other modifications to an
		3636	event loop, you will now have to lock:
		3637
		3638	ev_timer timeout_watcher;
		3639	userdata *u = ev_userdata (EV_A);
		3640
		3641	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3642
		3643	pthread_mutex_lock (&u->lock);
		3644	ev_timer_start (EV_A_ &timeout_watcher);
		3645	ev_async_send (EV_A_ &u->async_w);
		3646	pthread_mutex_unlock (&u->lock);
		3647
		3648	Note that sending the C<ev_async> watcher is required because otherwise
		3649	an event loop currently blocking in the kernel will have no knowledge
		3650	about the newly added timer. By waking up the loop it will pick up any new
		3651	watchers in the next event loop iteration.
		3652
		3653	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3654
		3655	While the overhead of a callback that e.g. schedules a thread is small, it
		3656	is still an overhead. If you embed libev, and your main usage is with some
		3657	kind of threads or coroutines, you might want to customise libev so that
		3658	doesn't need callbacks anymore.
		3659
		3660	Imagine you have coroutines that you can switch to using a function
		3661	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3662	and that due to some magic, the currently active coroutine is stored in a
		3663	global called C<current_coro>. Then you can build your own "wait for libev
		3664	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3665	the differing C<;> conventions):
		3666
		3667	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3668	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3669
		3670	That means instead of having a C callback function, you store the
		3671	coroutine to switch to in each watcher, and instead of having libev call
		3672	your callback, you instead have it switch to that coroutine.
		3673
		3674	A coroutine might now wait for an event with a function called
		3675	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3676	matter when, or whether the watcher is active or not when this function is
		3677	called):
		3678
		3679	void
		3680	wait_for_event (ev_watcher *w)
		3681	{
		3682	ev_cb_set (w) = current_coro;
		3683	switch_to (libev_coro);
		3684	}
		3685
		3686	That basically suspends the coroutine inside C<wait_for_event> and
		3687	continues the libev coroutine, which, when appropriate, switches back to
		3688	this or any other coroutine. I am sure if you sue this your own :)
		3689
		3690	You can do similar tricks if you have, say, threads with an event queue -
		3691	instead of storing a coroutine, you store the queue object and instead of
		3692	switching to a coroutine, you push the watcher onto the queue and notify
		3693	any waiters.
		3694
		3695	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3696	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3697
		3698	// my_ev.h
		3699	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3700	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3701	#include "../libev/ev.h"
		3702
		3703	// my_ev.c
		3704	#define EV_H "my_ev.h"
		3705	#include "../libev/ev.c"
		3706
		3707	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3708	F<my_ev.c> into your project. When properly specifying include paths, you
		3709	can even use F<ev.h> as header file name directly.
3360		3710
3361		3711
3362	=head1 LIBEVENT EMULATION	3712	=head1 LIBEVENT EMULATION
3363		3713
3364	Libev offers a compatibility emulation layer for libevent. It cannot	3714	Libev offers a compatibility emulation layer for libevent. It cannot
3365	emulate the internals of libevent, so here are some usage hints:	3715	emulate the internals of libevent, so here are some usage hints:
3366		3716
3367	=over 4	3717	=over 4
		3718
		3719	=item * Only the libevent-1.4.1-beta API is being emulated.
		3720
		3721	This was the newest libevent version available when libev was implemented,
		3722	and is still mostly unchanged in 2010.
3368		3723
3369	=item * Use it by including <event.h>, as usual.	3724	=item * Use it by including <event.h>, as usual.
3370		3725
3371	=item * The following members are fully supported: ev_base, ev_callback,	3726	=item * The following members are fully supported: ev_base, ev_callback,
3372	ev_arg, ev_fd, ev_res, ev_events.	3727	ev_arg, ev_fd, ev_res, ev_events.
…		…
3378	=item * Priorities are not currently supported. Initialising priorities	3733	=item * Priorities are not currently supported. Initialising priorities
3379	will fail and all watchers will have the same priority, even though there	3734	will fail and all watchers will have the same priority, even though there
3380	is an ev_pri field.	3735	is an ev_pri field.
3381		3736
3382	=item * In libevent, the last base created gets the signals, in libev, the	3737	=item * In libevent, the last base created gets the signals, in libev, the
3383	first base created (== the default loop) gets the signals.	3738	base that registered the signal gets the signals.
3384		3739
3385	=item * Other members are not supported.	3740	=item * Other members are not supported.
3386		3741
3387	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3742	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3388	to use the libev header file and library.	3743	to use the libev header file and library.
…		…
3407	Care has been taken to keep the overhead low. The only data member the C++	3762	Care has been taken to keep the overhead low. The only data member the C++
3408	classes add (compared to plain C-style watchers) is the event loop pointer	3763	classes add (compared to plain C-style watchers) is the event loop pointer
3409	that the watcher is associated with (or no additional members at all if	3764	that the watcher is associated with (or no additional members at all if
3410	you disable C<EV_MULTIPLICITY> when embedding libev).	3765	you disable C<EV_MULTIPLICITY> when embedding libev).
3411		3766
3412	Currently, functions, and static and non-static member functions can be	3767	Currently, functions, static and non-static member functions and classes
3413	used as callbacks. Other types should be easy to add as long as they only	3768	with C<operator ()> can be used as callbacks. Other types should be easy
3414	need one additional pointer for context. If you need support for other	3769	to add as long as they only need one additional pointer for context. If
3415	types of functors please contact the author (preferably after implementing	3770	you need support for other types of functors please contact the author
3416	it).	3771	(preferably after implementing it).
3417		3772
3418	Here is a list of things available in the C<ev> namespace:	3773	Here is a list of things available in the C<ev> namespace:
3419		3774
3420	=over 4	3775	=over 4
3421		3776
…		…
4289	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4644	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4290		4645
4291	#include "ev_cpp.h"	4646	#include "ev_cpp.h"
4292	#include "ev.c"	4647	#include "ev.c"
4293		4648
4294	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4649	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4295		4650
4296	=head2 THREADS AND COROUTINES	4651	=head2 THREADS AND COROUTINES
4297		4652
4298	=head3 THREADS	4653	=head3 THREADS
4299		4654
…		…
4350	default loop and triggering an C<ev_async> watcher from the default loop	4705	default loop and triggering an C<ev_async> watcher from the default loop
4351	watcher callback into the event loop interested in the signal.	4706	watcher callback into the event loop interested in the signal.
4352		4707
4353	=back	4708	=back
4354		4709
4355	=head4 THREAD LOCKING EXAMPLE	4710	See also L<THREAD LOCKING EXAMPLE>.
4356
4357	Here is a fictitious example of how to run an event loop in a different
4358	thread than where callbacks are being invoked and watchers are
4359	created/added/removed.
4360
4361	For a real-world example, see the C<EV::Loop::Async> perl module,
4362	which uses exactly this technique (which is suited for many high-level
4363	languages).
4364
4365	The example uses a pthread mutex to protect the loop data, a condition
4366	variable to wait for callback invocations, an async watcher to notify the
4367	event loop thread and an unspecified mechanism to wake up the main thread.
4368
4369	First, you need to associate some data with the event loop:
4370
4371	typedef struct {
4372	mutex_t lock; /* global loop lock */
4373	ev_async async_w;
4374	thread_t tid;
4375	cond_t invoke_cv;
4376	} userdata;
4377
4378	void prepare_loop (EV_P)
4379	{
4380	// for simplicity, we use a static userdata struct.
4381	static userdata u;
4382
4383	ev_async_init (&u->async_w, async_cb);
4384	ev_async_start (EV_A_ &u->async_w);
4385
4386	pthread_mutex_init (&u->lock, 0);
4387	pthread_cond_init (&u->invoke_cv, 0);
4388
4389	// now associate this with the loop
4390	ev_set_userdata (EV_A_ u);
4391	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4392	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4393
4394	// then create the thread running ev_loop
4395	pthread_create (&u->tid, 0, l_run, EV_A);
4396	}
4397
4398	The callback for the C<ev_async> watcher does nothing: the watcher is used
4399	solely to wake up the event loop so it takes notice of any new watchers
4400	that might have been added:
4401
4402	static void
4403	async_cb (EV_P_ ev_async *w, int revents)
4404	{
4405	// just used for the side effects
4406	}
4407
4408	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4409	protecting the loop data, respectively.
4410
4411	static void
4412	l_release (EV_P)
4413	{
4414	userdata *u = ev_userdata (EV_A);
4415	pthread_mutex_unlock (&u->lock);
4416	}
4417
4418	static void
4419	l_acquire (EV_P)
4420	{
4421	userdata *u = ev_userdata (EV_A);
4422	pthread_mutex_lock (&u->lock);
4423	}
4424
4425	The event loop thread first acquires the mutex, and then jumps straight
4426	into C<ev_run>:
4427
4428	void *
4429	l_run (void *thr_arg)
4430	{
4431	struct ev_loop loop = (struct ev_loop )thr_arg;
4432
4433	l_acquire (EV_A);
4434	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4435	ev_run (EV_A_ 0);
4436	l_release (EV_A);
4437
4438	return 0;
4439	}
4440
4441	Instead of invoking all pending watchers, the C<l_invoke> callback will
4442	signal the main thread via some unspecified mechanism (signals? pipe
4443	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4444	have been called (in a while loop because a) spurious wakeups are possible
4445	and b) skipping inter-thread-communication when there are no pending
4446	watchers is very beneficial):
4447
4448	static void
4449	l_invoke (EV_P)
4450	{
4451	userdata *u = ev_userdata (EV_A);
4452
4453	while (ev_pending_count (EV_A))
4454	{
4455	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4456	pthread_cond_wait (&u->invoke_cv, &u->lock);
4457	}
4458	}
4459
4460	Now, whenever the main thread gets told to invoke pending watchers, it
4461	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4462	thread to continue:
4463
4464	static void
4465	real_invoke_pending (EV_P)
4466	{
4467	userdata *u = ev_userdata (EV_A);
4468
4469	pthread_mutex_lock (&u->lock);
4470	ev_invoke_pending (EV_A);
4471	pthread_cond_signal (&u->invoke_cv);
4472	pthread_mutex_unlock (&u->lock);
4473	}
4474
4475	Whenever you want to start/stop a watcher or do other modifications to an
4476	event loop, you will now have to lock:
4477
4478	ev_timer timeout_watcher;
4479	userdata *u = ev_userdata (EV_A);
4480
4481	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4482
4483	pthread_mutex_lock (&u->lock);
4484	ev_timer_start (EV_A_ &timeout_watcher);
4485	ev_async_send (EV_A_ &u->async_w);
4486	pthread_mutex_unlock (&u->lock);
4487
4488	Note that sending the C<ev_async> watcher is required because otherwise
4489	an event loop currently blocking in the kernel will have no knowledge
4490	about the newly added timer. By waking up the loop it will pick up any new
4491	watchers in the next event loop iteration.
4492		4711
4493	=head3 COROUTINES	4712	=head3 COROUTINES
4494		4713
4495	Libev is very accommodating to coroutines ("cooperative threads"):	4714	Libev is very accommodating to coroutines ("cooperative threads"):
4496	libev fully supports nesting calls to its functions from different	4715	libev fully supports nesting calls to its functions from different
…		…
5005	The physical time that is observed. It is apparently strictly monotonic :)	5224	The physical time that is observed. It is apparently strictly monotonic :)
5006		5225
5007	=item wall-clock time	5226	=item wall-clock time
5008		5227
5009	The time and date as shown on clocks. Unlike real time, it can actually	5228	The time and date as shown on clocks. Unlike real time, it can actually
5010	be wrong and jump forwards and backwards, e.g. when the you adjust your	5229	be wrong and jump forwards and backwards, e.g. when you adjust your
5011	clock.	5230	clock.
5012		5231
5013	=item watcher	5232	=item watcher
5014		5233
5015	A data structure that describes interest in certain events. Watchers need	5234	A data structure that describes interest in certain events. Watchers need
…		…
5018	=back	5237	=back
5019		5238
5020	=head1 AUTHOR	5239	=head1 AUTHOR
5021		5240
5022	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5241	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5023	Magnusson and Emanuele Giaquinta.	5242	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5024		5243

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Comparing libev/ev.pod (file contents): Revision 1.337 by root, Sun Oct 31 20:20:20 2010 UTC vs. Revision 1.366 by sf-exg, Thu Feb 3 16:21:08 2011 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.337 by root, Sun Oct 31 20:20:20 2010 UTC vs.
Revision 1.366 by sf-exg, Thu Feb 3 16:21:08 2011 UTC