[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 1.371 by root, Sat Jun 4 05:25:03 2011 UTC

…		…
58	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
59		59
60	// now wait for events to arrive	60	// now wait for events to arrive
61	ev_run (loop, 0);	61	ev_run (loop, 0);
62		62
63	// unloop was called, so exit	63	// break was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 ABOUT THIS DOCUMENT	67	=head1 ABOUT THIS DOCUMENT
68		68
…		…
178	you actually want to know. Also interesting is the combination of	178	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	179	C<ev_update_now> and C<ev_now>.
180		180
181	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
182		182
183	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
185	this is a sub-second-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
186		192
187	=item int ev_version_major ()	193	=item int ev_version_major ()
188		194
189	=item int ev_version_minor ()	195	=item int ev_version_minor ()
190		196
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	247	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
243		249
244	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
245		251
246	=item ev_set_allocator (void (cb)(void *ptr, long size)) [NOT REENTRANT]	252	=item ev_set_allocator (void (cb)(void *ptr, long size))
247		253
248	Sets the allocation function to use (the prototype is similar - the	254	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	255	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	256	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	257	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
277	}	283	}
278		284
279	...	285	...
280	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
281		287
282	=item ev_set_syserr_cb (void (cb)(const char msg)); [NOT REENTRANT]	288	=item ev_set_syserr_cb (void (cb)(const char msg))
283		289
284	Set the callback function to call on a retryable system call error (such	290	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	291	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	292	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	293	callback is set, then libev will expect it to remedy the situation, no
…		…
299	}	305	}
300		306
301	...	307	...
302	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
303		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
304	=back	323	=back
305		324
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		326
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
355	=item struct ev_loop *ev_loop_new (unsigned int flags)	374	=item struct ev_loop *ev_loop_new (unsigned int flags)
356		375
357	This will create and initialise a new event loop object. If the loop	376	This will create and initialise a new event loop object. If the loop
358	could not be initialised, returns false.	377	could not be initialised, returns false.
359		378
360	Note that this function I<is> thread-safe, and one common way to use	379	This function is thread-safe, and one common way to use libev with
361	libev with threads is indeed to create one loop per thread, and using the	380	threads is indeed to create one loop per thread, and using the default
362	default loop in the "main" or "initial" thread.	381	loop in the "main" or "initial" thread.
363		382
364	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
365	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
366		385
367	The following flags are supported:	386	The following flags are supported:
…		…
402	environment variable.	421	environment variable.
403		422
404	=item C<EVFLAG_NOINOTIFY>	423	=item C<EVFLAG_NOINOTIFY>
405		424
406	When this flag is specified, then libev will not attempt to use the	425	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	426	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	427	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.	428	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
410		429
411	=item C<EVFLAG_SIGNALFD>	430	=item C<EVFLAG_SIGNALFD>
412		431
413	When this flag is specified, then libev will attempt to use the	432	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	433	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	434	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	435	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	436	handling with threads, as long as you properly block signals in your
418	threads that are not interested in handling them.	437	threads that are not interested in handling them.
419		438
420	Signalfd will not be used by default as this changes your signal mask, and	439	Signalfd will not be used by default as this changes your signal mask, and
421	there are a lot of shoddy libraries and programs (glib's threadpool for	440	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you ahve to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
		455
		456	This flag's behaviour will become the default in future versions of libev.
423		457
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		459
426	This is your standard select(2) backend. Not I<completely> standard, as	460	This is your standard select(2) backend. Not I<completely> standard, as
427	libev tries to roll its own fd_set with no limits on the number of fds,	461	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		490
457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
458	kernels).	492	kernels).
459		493
460	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
461	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
462	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
463	epoll scales either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
464		498
465	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	502	descriptor (and unnecessary guessing of parameters), problems with dup,
469	returning before the timeout value requiring additional iterations and so	503	returning before the timeout value, resulting in additional iterations
		504	(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	505	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	506	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	507	set, which can take considerable time (one syscall per file descriptor)
473	hard to detect.	508	and is of course hard to detect.
474		509
475	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
476	of course I<doesn't>, and epoll just loves to report events for totally	511	but of course I<doesn't>, and epoll just loves to report events for
477	I<different> file descriptors (even already closed ones, so one cannot	512	totally I<different> file descriptors (even already closed ones, so
478	even remove them from the set) than registered in the set (especially	513	one cannot even remove them from the set) than registered in the set
479	on SMP systems). Libev tries to counter these spurious notifications by	514	(especially on SMP systems). Libev tries to counter these spurious
480	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
481	events to filter out spurious ones, recreating the set when required. Last	516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also errornously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
482	not least, it also refuses to work with some file descriptors which work	520	not least, it also refuses to work with some file descriptors which work
483	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
484		526
485	While stopping, setting and starting an I/O watcher in the same iteration	527	While stopping, setting and starting an I/O watcher in the same iteration
486	will result in some caching, there is still a system call per such	528	will result in some caching, there is still a system call per such
487	incident (because the same I<file descriptor> could point to a different	529	incident (because the same I<file descriptor> could point to a different
488	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
554	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
555		597
556	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
557	it's really slow, but it still scales very well (O(active_fds)).	599	it's really slow, but it still scales very well (O(active_fds)).
558		600
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	601	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	602	file descriptor per loop iteration. For small and medium numbers of file
565	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
566	might perform better.	604	might perform better.
567		605
568	On the positive side, with the exception of the spurious readiness	606	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	607	specification in all tests and is fully embeddable, which is a rare feat
571	OS-specific backends (I vastly prefer correctness over speed hacks).	608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returning events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where
		616	you absolutely have to know whether an event occurred or not because you
		617	have to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
572		620
573	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
574	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
575		623
576	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
577		625
578	Try all backends (even potentially broken ones that wouldn't be tried	626	Try all backends (even potentially broken ones that wouldn't be tried
579	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
580	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
581		629
582	It is definitely not recommended to use this flag.	630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
583		639
584	=back	640	=back
585		641
586	If one or more of the backend flags are or'ed into the flags value,	642	If one or more of the backend flags are or'ed into the flags value,
587	then only these backends will be tried (in the reverse order as listed	643	then only these backends will be tried (in the reverse order as listed
…		…
616	This function is normally used on loop objects allocated by	672	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	673	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.	674	C<ev_default_loop>, in which case it is not thread-safe.
619		675
620	Note that it is not advisable to call this function on the default loop	676	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.	677	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>	678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
623	and C<ev_loop_destroy>.	679	and C<ev_loop_destroy>.
624		680
625	=item ev_loop_fork (loop)	681	=item ev_loop_fork (loop)
626		682
…		…
674	prepare and check phases.	730	prepare and check phases.
675		731
676	=item unsigned int ev_depth (loop)	732	=item unsigned int ev_depth (loop)
677		733
678	Returns the number of times C<ev_run> was entered minus the number of	734	Returns the number of times C<ev_run> was entered minus the number of
679	times C<ev_run> was exited, in other words, the recursion depth.	735	times C<ev_run> was exited normally, in other words, the recursion depth.
680		736
681	Outside C<ev_run>, this number is zero. In a callback, this number is	737	Outside C<ev_run>, this number is zero. In a callback, this number is
682	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	738	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
683	in which case it is higher.	739	in which case it is higher.
684		740
685	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	741	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	742	throwing an exception etc.), doesn't count as "exit" - consider this
687	ungentleman-like behaviour unless it's really convenient.	743	as a hint to avoid such ungentleman-like behaviour unless it's really
		744	convenient, in which case it is fully supported.
688		745
689	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
690		747
691	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	748	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
692	use.	749	use.
…		…
754	finished (especially in interactive programs), but having a program	811	finished (especially in interactive programs), but having a program
755	that automatically loops as long as it has to and no longer by virtue	812	that automatically loops as long as it has to and no longer by virtue
756	of relying on its watchers stopping correctly, that is truly a thing of	813	of relying on its watchers stopping correctly, that is truly a thing of
757	beauty.	814	beauty.
758		815
		816	This function is also I<mostly> exception-safe - you can break out of
		817	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		818	exception and so on. This does not decrement the C<ev_depth> value, nor
		819	will it clear any outstanding C<EVBREAK_ONE> breaks.
		820
759	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	821	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
760	those events and any already outstanding ones, but will not wait and	822	those events and any already outstanding ones, but will not wait and
761	block your process in case there are no events and will return after one	823	block your process in case there are no events and will return after one
762	iteration of the loop. This is sometimes useful to poll and handle new	824	iteration of the loop. This is sometimes useful to poll and handle new
763	events while doing lengthy calculations, to keep the program responsive.	825	events while doing lengthy calculations, to keep the program responsive.
…		…
772	This is useful if you are waiting for some external event in conjunction	834	This is useful if you are waiting for some external event in conjunction
773	with something not expressible using other libev watchers (i.e. "roll your	835	with something not expressible using other libev watchers (i.e. "roll your
774	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	836	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
775	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
776		838
777	Here are the gory details of what C<ev_run> does:	839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
778		842
779	- Increment loop depth.	843	- Increment loop depth.
780	- Reset the ev_break status.	844	- Reset the ev_break status.
781	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
782	LOOP:	846	LOOP:
…		…
815	anymore.	879	anymore.
816		880
817	... queue jobs here, make sure they register event watchers as long	881	... 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..)	882	... as they still have work to do (even an idle watcher will do..)
819	ev_run (my_loop, 0);	883	ev_run (my_loop, 0);
820	... jobs done or somebody called unloop. yeah!	884	... jobs done or somebody called break. yeah!
821		885
822	=item ev_break (loop, how)	886	=item ev_break (loop, how)
823		887
824	Can be used to make a call to C<ev_run> return early (but only after it	888	Can be used to make a call to C<ev_run> return early (but only after it
825	has processed all outstanding events). The C<how> argument must be either	889	has processed all outstanding events). The C<how> argument must be either
826	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	890	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
827	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	891	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
828		892
829	This "break state" will be cleared when entering C<ev_run> again.	893	This "break state" will be cleared on the next call to C<ev_run>.
830		894
831	It is safe to call C<ev_break> from outside any C<ev_run> calls, too.	895	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		896	which case it will have no effect.
832		897
833	=item ev_ref (loop)	898	=item ev_ref (loop)
834		899
835	=item ev_unref (loop)	900	=item ev_unref (loop)
836		901
…		…
857	running when nothing else is active.	922	running when nothing else is active.
858		923
859	ev_signal exitsig;	924	ev_signal exitsig;
860	ev_signal_init (&exitsig, sig_cb, SIGINT);	925	ev_signal_init (&exitsig, sig_cb, SIGINT);
861	ev_signal_start (loop, &exitsig);	926	ev_signal_start (loop, &exitsig);
862	evf_unref (loop);	927	ev_unref (loop);
863		928
864	Example: For some weird reason, unregister the above signal handler again.	929	Example: For some weird reason, unregister the above signal handler again.
865		930
866	ev_ref (loop);	931	ev_ref (loop);
867	ev_signal_stop (loop, &exitsig);	932	ev_signal_stop (loop, &exitsig);
…		…
979	See also the locking example in the C<THREADS> section later in this	1044	See also the locking example in the C<THREADS> section later in this
980	document.	1045	document.
981		1046
982	=item ev_set_userdata (loop, void *data)	1047	=item ev_set_userdata (loop, void *data)
983		1048
984	=item ev_userdata (loop)	1049	=item void *ev_userdata (loop)
985		1050
986	Set and retrieve a single C<void *> associated with a loop. When	1051	Set and retrieve a single C<void *> associated with a loop. When
987	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1052	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
988	C<0.>	1053	C<0>.
989		1054
990	These two functions can be used to associate arbitrary data with a loop,	1055	These two functions can be used to associate arbitrary data with a loop,
991	and are intended solely for the C<invoke_pending_cb>, C<release> and	1056	and are intended solely for the C<invoke_pending_cb>, C<release> and
992	C<acquire> callbacks described above, but of course can be (ab-)used for	1057	C<acquire> callbacks described above, but of course can be (ab-)used for
993	any other purpose as well.	1058	any other purpose as well.
…		…
1306	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1371	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1307	functions that do not need a watcher.	1372	functions that do not need a watcher.
1308		1373
1309	=back	1374	=back
1310		1375
1311	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1376	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1312		1377	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		1378
1376	=head2 WATCHER STATES	1379	=head2 WATCHER STATES
1377		1380
1378	There are various watcher states mentioned throughout this manual -	1381	There are various watcher states mentioned throughout this manual -
1379	active, pending and so on. In this section these states and the rules to	1382	active, pending and so on. In this section these states and the rules to
…		…
1386		1389
1387	Before a watcher can be registered with the event looop it has to be	1390	Before a watcher can be registered with the event looop it has to be
1388	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1391	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1389	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1392	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1390		1393
1391	In this state it is simply some block of memory that is suitable for use	1394	In this state it is simply some block of memory that is suitable for
1392	in an event loop. It can be moved around, freed, reused etc. at will.	1395	use in an event loop. It can be moved around, freed, reused etc. at
		1396	will - as long as you either keep the memory contents intact, or call
		1397	C<ev_TYPE_init> again.
1393		1398
1394	=item started/running/active	1399	=item started/running/active
1395		1400
1396	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1401	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1397	property of the event loop, and is actively waiting for events. While in	1402	property of the event loop, and is actively waiting for events. While in
…		…
1425	latter will clear any pending state the watcher might be in, regardless	1430	latter will clear any pending state the watcher might be in, regardless
1426	of whether it was active or not, so stopping a watcher explicitly before	1431	of whether it was active or not, so stopping a watcher explicitly before
1427	freeing it is often a good idea.	1432	freeing it is often a good idea.
1428		1433
1429	While stopped (and not pending) the watcher is essentially in the	1434	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	1435	initialised state, that is, it can be reused, moved, modified in any way
1431	you wish.	1436	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1437	it again).
1432		1438
1433	=back	1439	=back
1434		1440
1435	=head2 WATCHER PRIORITY MODELS	1441	=head2 WATCHER PRIORITY MODELS
1436		1442
…		…
1565	In general you can register as many read and/or write event watchers per	1571	In general you can register as many read and/or write event watchers per
1566	fd as you want (as long as you don't confuse yourself). Setting all file	1572	fd as you want (as long as you don't confuse yourself). Setting all file
1567	descriptors to non-blocking mode is also usually a good idea (but not	1573	descriptors to non-blocking mode is also usually a good idea (but not
1568	required if you know what you are doing).	1574	required if you know what you are doing).
1569		1575
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	1576	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	1577	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	1578	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	1579	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	1580	with a relatively standard program structure. Thus it is best to always
1581	this situation even with a relatively standard program structure. Thus	1581	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
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.	1582	preferable to a program hanging until some data arrives.
1584		1583
1585	If you cannot run the fd in non-blocking mode (for example you should	1584	If you cannot run the fd in non-blocking mode (for example you should
1586	not play around with an Xlib connection), then you have to separately	1585	not play around with an Xlib connection), then you have to separately
1587	re-test whether a file descriptor is really ready with a known-to-be good	1586	re-test whether a file descriptor is really ready with a known-to-be good
1588	interface such as poll (fortunately in our Xlib example, Xlib already	1587	interface such as poll (fortunately in the case of Xlib, it already does
1589	does this on its own, so its quite safe to use). Some people additionally	1588	this on its own, so its quite safe to use). Some people additionally
1590	use C<SIGALRM> and an interval timer, just to be sure you won't block	1589	use C<SIGALRM> and an interval timer, just to be sure you won't block
1591	indefinitely.	1590	indefinitely.
1592		1591
1593	But really, best use non-blocking mode.	1592	But really, best use non-blocking mode.
1594		1593
…		…
1622		1621
1623	There is no workaround possible except not registering events	1622	There is no workaround possible except not registering events
1624	for potentially C<dup ()>'ed file descriptors, or to resort to	1623	for potentially C<dup ()>'ed file descriptors, or to resort to
1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1624	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1626		1625
		1626	=head3 The special problem of files
		1627
		1628	Many people try to use C<select> (or libev) on file descriptors
		1629	representing files, and expect it to become ready when their program
		1630	doesn't block on disk accesses (which can take a long time on their own).
		1631
		1632	However, this cannot ever work in the "expected" way - you get a readiness
		1633	notification as soon as the kernel knows whether and how much data is
		1634	there, and in the case of open files, that's always the case, so you
		1635	always get a readiness notification instantly, and your read (or possibly
		1636	write) will still block on the disk I/O.
		1637
		1638	Another way to view it is that in the case of sockets, pipes, character
		1639	devices and so on, there is another party (the sender) that delivers data
		1640	on its own, but in the case of files, there is no such thing: the disk
		1641	will not send data on its own, simply because it doesn't know what you
		1642	wish to read - you would first have to request some data.
		1643
		1644	Since files are typically not-so-well supported by advanced notification
		1645	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1646	to files, even though you should not use it. The reason for this is
		1647	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1648	usually a tty, often a pipe, but also sometimes files or special devices
		1649	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1650	F</dev/urandom>), and even though the file might better be served with
		1651	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1652	it "just works" instead of freezing.
		1653
		1654	So avoid file descriptors pointing to files when you know it (e.g. use
		1655	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1656	when you rarely read from a file instead of from a socket, and want to
		1657	reuse the same code path.
		1658
1627	=head3 The special problem of fork	1659	=head3 The special problem of fork
1628		1660
1629	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1661	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1630	useless behaviour. Libev fully supports fork, but needs to be told about	1662	useless behaviour. Libev fully supports fork, but needs to be told about
1631	it in the child.	1663	it in the child if you want to continue to use it in the child.
1632		1664
1633	To support fork in your programs, you either have to call	1665	To support fork in your child processes, you have to call C<ev_loop_fork
1634	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1666	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1635	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1667	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636	C<EVBACKEND_POLL>.
1637		1668
1638	=head3 The special problem of SIGPIPE	1669	=head3 The special problem of SIGPIPE
1639		1670
1640	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1671	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1641	when writing to a pipe whose other end has been closed, your program gets	1672	when writing to a pipe whose other end has been closed, your program gets
…		…
2131		2162
2132	Another way to think about it (for the mathematically inclined) is that	2163	Another way to think about it (for the mathematically inclined) is that
2133	C<ev_periodic> will try to run the callback in this mode at the next possible	2164	C<ev_periodic> will try to run the callback in this mode at the next possible
2134	time where C<time = offset (mod interval)>, regardless of any time jumps.	2165	time where C<time = offset (mod interval)>, regardless of any time jumps.
2135		2166
2136	For numerical stability it is preferable that the C<offset> value is near	2167	The C<interval> I<MUST> be positive, and for numerical stability, the
2137	C<ev_now ()> (the current time), but there is no range requirement for	2168	interval value should be higher than C<1/8192> (which is around 100
2138	this value, and in fact is often specified as zero.	2169	microseconds) and C<offset> should be higher than C<0> and should have
		2170	at most a similar magnitude as the current time (say, within a factor of
		2171	ten). Typical values for offset are, in fact, C<0> or something between
		2172	C<0> and C<interval>, which is also the recommended range.
2139		2173
2140	Note also that there is an upper limit to how often a timer can fire (CPU	2174	Note also that there is an upper limit to how often a timer can fire (CPU
2141	speed for example), so if C<interval> is very small then timing stability	2175	speed for example), so if C<interval> is very small then timing stability
2142	will of course deteriorate. Libev itself tries to be exact to be about one	2176	will of course deteriorate. Libev itself tries to be exact to be about one
2143	millisecond (if the OS supports it and the machine is fast enough).	2177	millisecond (if the OS supports it and the machine is fast enough).
…		…
2257		2291
2258	=head2 C<ev_signal> - signal me when a signal gets signalled!	2292	=head2 C<ev_signal> - signal me when a signal gets signalled!
2259		2293
2260	Signal watchers will trigger an event when the process receives a specific	2294	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	2295	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	2296	will try its best to deliver signals synchronously, i.e. as part of the
2263	normal event processing, like any other event.	2297	normal event processing, like any other event.
2264		2298
2265	If you want signals to be delivered truly asynchronously, just use	2299	If you want signals to be delivered truly asynchronously, just use
2266	C<sigaction> as you would do without libev and forget about sharing	2300	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	2301	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	2320	=head3 The special problem of inheritance over fork/execve/pthread_create
2287		2321
2288	Both the signal mask (C<sigprocmask>) and the signal disposition	2322	Both the signal mask (C<sigprocmask>) and the signal disposition
2289	(C<sigaction>) are unspecified after starting a signal watcher (and after	2323	(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,	2324	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.	2325	and might or might not set or restore the installed signal handler (but
		2326	see C<EVFLAG_NOSIGMASK>).
2292		2327
2293	While this does not matter for the signal disposition (libev never	2328	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	2329	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	2330	C<execve>), this matters for the signal mask: many programs do not expect
2296	certain signals to be blocked.	2331	certain signals to be blocked.
…		…
2309	I<has> to modify the signal mask, at least temporarily.	2344	I<has> to modify the signal mask, at least temporarily.
2310		2345
2311	So I can't stress this enough: I<If you do not reset your signal mask when	2346	So I can't stress this enough: I<If you do not reset your signal mask when
2312	you expect it to be empty, you have a race condition in your code>. This	2347	you expect it to be empty, you have a race condition in your code>. This
2313	is not a libev-specific thing, this is true for most event libraries.	2348	is not a libev-specific thing, this is true for most event libraries.
		2349
		2350	=head3 The special problem of threads signal handling
		2351
		2352	POSIX threads has problematic signal handling semantics, specifically,
		2353	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2354	threads in a process block signals, which is hard to achieve.
		2355
		2356	When you want to use sigwait (or mix libev signal handling with your own
		2357	for the same signals), you can tackle this problem by globally blocking
		2358	all signals before creating any threads (or creating them with a fully set
		2359	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2360	loops. Then designate one thread as "signal receiver thread" which handles
		2361	these signals. You can pass on any signals that libev might be interested
		2362	in by calling C<ev_feed_signal>.
2314		2363
2315	=head3 Watcher-Specific Functions and Data Members	2364	=head3 Watcher-Specific Functions and Data Members
2316		2365
2317	=over 4	2366	=over 4
2318		2367
…		…
3153	atexit (program_exits);	3202	atexit (program_exits);
3154		3203
3155		3204
3156	=head2 C<ev_async> - how to wake up an event loop	3205	=head2 C<ev_async> - how to wake up an event loop
3157		3206
3158	In general, you cannot use an C<ev_run> from multiple threads or other	3207	In general, you cannot use an C<ev_loop> from multiple threads or other
3159	asynchronous sources such as signal handlers (as opposed to multiple event	3208	asynchronous sources such as signal handlers (as opposed to multiple event
3160	loops - those are of course safe to use in different threads).	3209	loops - those are of course safe to use in different threads).
3161		3210
3162	Sometimes, however, you need to wake up an event loop you do not control,	3211	Sometimes, however, you need to wake up an event loop you do not control,
3163	for example because it belongs to another thread. This is what C<ev_async>	3212	for example because it belongs to another thread. This is what C<ev_async>
…		…
3165	it by calling C<ev_async_send>, which is thread- and signal safe.	3214	it by calling C<ev_async_send>, which is thread- and signal safe.
3166		3215
3167	This functionality is very similar to C<ev_signal> watchers, as signals,	3216	This functionality is very similar to C<ev_signal> watchers, as signals,
3168	too, are asynchronous in nature, and signals, too, will be compressed	3217	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	3218	(i.e. the number of callback invocations may be less than the number of
3170	C<ev_async_sent> calls).	3219	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3220	of "global async watchers" by using a watcher on an otherwise unused
		3221	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3222	even without knowing which loop owns the signal.
3171		3223
3172	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3224	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3173	just the default loop.	3225	just the default loop.
3174		3226
3175	=head3 Queueing	3227	=head3 Queueing
…		…
3270	trust me.	3322	trust me.
3271		3323
3272	=item ev_async_send (loop, ev_async *)	3324	=item ev_async_send (loop, ev_async *)
3273		3325
3274	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3326	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3275	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3327	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3328	returns.
		3329
3276	C<ev_feed_event>, this call is safe to do from other threads, signal or	3330	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3277	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3331	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3278	section below on what exactly this means).	3332	embedding section below on what exactly this means).
3279		3333
3280	Note that, as with other watchers in libev, multiple events might get	3334	Note that, as with other watchers in libev, multiple events might get
3281	compressed into a single callback invocation (another way to look at this	3335	compressed into a single callback invocation (another way to look at this
3282	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3336	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
3283	reset when the event loop detects that).	3337	reset when the event loop detects that).
…		…
3351	Feed an event on the given fd, as if a file descriptor backend detected	3405	Feed an event on the given fd, as if a file descriptor backend detected
3352	the given events it.	3406	the given events it.
3353		3407
3354	=item ev_feed_signal_event (loop, int signum)	3408	=item ev_feed_signal_event (loop, int signum)
3355		3409
3356	Feed an event as if the given signal occurred (C<loop> must be the default	3410	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3357	loop!).	3411	which is async-safe.
3358		3412
3359	=back	3413	=back
		3414
		3415
		3416	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3417
		3418	This section explains some common idioms that are not immediately
		3419	obvious. Note that examples are sprinkled over the whole manual, and this
		3420	section only contains stuff that wouldn't fit anywhere else.
		3421
		3422	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3423
		3424	Each watcher has, by default, a C<void *data> member that you can read
		3425	or modify at any time: libev will completely ignore it. This can be used
		3426	to associate arbitrary data with your watcher. If you need more data and
		3427	don't want to allocate memory separately and store a pointer to it in that
		3428	data member, you can also "subclass" the watcher type and provide your own
		3429	data:
		3430
		3431	struct my_io
		3432	{
		3433	ev_io io;
		3434	int otherfd;
		3435	void *somedata;
		3436	struct whatever *mostinteresting;
		3437	};
		3438
		3439	...
		3440	struct my_io w;
		3441	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3442
		3443	And since your callback will be called with a pointer to the watcher, you
		3444	can cast it back to your own type:
		3445
		3446	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3447	{
		3448	struct my_io w = (struct my_io )w_;
		3449	...
		3450	}
		3451
		3452	More interesting and less C-conformant ways of casting your callback
		3453	function type instead have been omitted.
		3454
		3455	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3456
		3457	Another common scenario is to use some data structure with multiple
		3458	embedded watchers, in effect creating your own watcher that combines
		3459	multiple libev event sources into one "super-watcher":
		3460
		3461	struct my_biggy
		3462	{
		3463	int some_data;
		3464	ev_timer t1;
		3465	ev_timer t2;
		3466	}
		3467
		3468	In this case getting the pointer to C<my_biggy> is a bit more
		3469	complicated: Either you store the address of your C<my_biggy> struct in
		3470	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3471	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3472	real programmers):
		3473
		3474	#include <stddef.h>
		3475
		3476	static void
		3477	t1_cb (EV_P_ ev_timer *w, int revents)
		3478	{
		3479	struct my_biggy big = (struct my_biggy *)
		3480	(((char *)w) - offsetof (struct my_biggy, t1));
		3481	}
		3482
		3483	static void
		3484	t2_cb (EV_P_ ev_timer *w, int revents)
		3485	{
		3486	struct my_biggy big = (struct my_biggy *)
		3487	(((char *)w) - offsetof (struct my_biggy, t2));
		3488	}
		3489
		3490	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3491
		3492	Often (especially in GUI toolkits) there are places where you have
		3493	I<modal> interaction, which is most easily implemented by recursively
		3494	invoking C<ev_run>.
		3495
		3496	This brings the problem of exiting - a callback might want to finish the
		3497	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3498	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3499	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3500	other combination: In these cases, C<ev_break> will not work alone.
		3501
		3502	The solution is to maintain "break this loop" variable for each C<ev_run>
		3503	invocation, and use a loop around C<ev_run> until the condition is
		3504	triggered, using C<EVRUN_ONCE>:
		3505
		3506	// main loop
		3507	int exit_main_loop = 0;
		3508
		3509	while (!exit_main_loop)
		3510	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3511
		3512	// in a model watcher
		3513	int exit_nested_loop = 0;
		3514
		3515	while (!exit_nested_loop)
		3516	ev_run (EV_A_ EVRUN_ONCE);
		3517
		3518	To exit from any of these loops, just set the corresponding exit variable:
		3519
		3520	// exit modal loop
		3521	exit_nested_loop = 1;
		3522
		3523	// exit main program, after modal loop is finished
		3524	exit_main_loop = 1;
		3525
		3526	// exit both
		3527	exit_main_loop = exit_nested_loop = 1;
		3528
		3529	=head2 THREAD LOCKING EXAMPLE
		3530
		3531	Here is a fictitious example of how to run an event loop in a different
		3532	thread from where callbacks are being invoked and watchers are
		3533	created/added/removed.
		3534
		3535	For a real-world example, see the C<EV::Loop::Async> perl module,
		3536	which uses exactly this technique (which is suited for many high-level
		3537	languages).
		3538
		3539	The example uses a pthread mutex to protect the loop data, a condition
		3540	variable to wait for callback invocations, an async watcher to notify the
		3541	event loop thread and an unspecified mechanism to wake up the main thread.
		3542
		3543	First, you need to associate some data with the event loop:
		3544
		3545	typedef struct {
		3546	mutex_t lock; /* global loop lock */
		3547	ev_async async_w;
		3548	thread_t tid;
		3549	cond_t invoke_cv;
		3550	} userdata;
		3551
		3552	void prepare_loop (EV_P)
		3553	{
		3554	// for simplicity, we use a static userdata struct.
		3555	static userdata u;
		3556
		3557	ev_async_init (&u->async_w, async_cb);
		3558	ev_async_start (EV_A_ &u->async_w);
		3559
		3560	pthread_mutex_init (&u->lock, 0);
		3561	pthread_cond_init (&u->invoke_cv, 0);
		3562
		3563	// now associate this with the loop
		3564	ev_set_userdata (EV_A_ u);
		3565	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3566	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3567
		3568	// then create the thread running ev_run
		3569	pthread_create (&u->tid, 0, l_run, EV_A);
		3570	}
		3571
		3572	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3573	solely to wake up the event loop so it takes notice of any new watchers
		3574	that might have been added:
		3575
		3576	static void
		3577	async_cb (EV_P_ ev_async *w, int revents)
		3578	{
		3579	// just used for the side effects
		3580	}
		3581
		3582	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3583	protecting the loop data, respectively.
		3584
		3585	static void
		3586	l_release (EV_P)
		3587	{
		3588	userdata *u = ev_userdata (EV_A);
		3589	pthread_mutex_unlock (&u->lock);
		3590	}
		3591
		3592	static void
		3593	l_acquire (EV_P)
		3594	{
		3595	userdata *u = ev_userdata (EV_A);
		3596	pthread_mutex_lock (&u->lock);
		3597	}
		3598
		3599	The event loop thread first acquires the mutex, and then jumps straight
		3600	into C<ev_run>:
		3601
		3602	void *
		3603	l_run (void *thr_arg)
		3604	{
		3605	struct ev_loop loop = (struct ev_loop )thr_arg;
		3606
		3607	l_acquire (EV_A);
		3608	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3609	ev_run (EV_A_ 0);
		3610	l_release (EV_A);
		3611
		3612	return 0;
		3613	}
		3614
		3615	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3616	signal the main thread via some unspecified mechanism (signals? pipe
		3617	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3618	have been called (in a while loop because a) spurious wakeups are possible
		3619	and b) skipping inter-thread-communication when there are no pending
		3620	watchers is very beneficial):
		3621
		3622	static void
		3623	l_invoke (EV_P)
		3624	{
		3625	userdata *u = ev_userdata (EV_A);
		3626
		3627	while (ev_pending_count (EV_A))
		3628	{
		3629	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3630	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3631	}
		3632	}
		3633
		3634	Now, whenever the main thread gets told to invoke pending watchers, it
		3635	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3636	thread to continue:
		3637
		3638	static void
		3639	real_invoke_pending (EV_P)
		3640	{
		3641	userdata *u = ev_userdata (EV_A);
		3642
		3643	pthread_mutex_lock (&u->lock);
		3644	ev_invoke_pending (EV_A);
		3645	pthread_cond_signal (&u->invoke_cv);
		3646	pthread_mutex_unlock (&u->lock);
		3647	}
		3648
		3649	Whenever you want to start/stop a watcher or do other modifications to an
		3650	event loop, you will now have to lock:
		3651
		3652	ev_timer timeout_watcher;
		3653	userdata *u = ev_userdata (EV_A);
		3654
		3655	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3656
		3657	pthread_mutex_lock (&u->lock);
		3658	ev_timer_start (EV_A_ &timeout_watcher);
		3659	ev_async_send (EV_A_ &u->async_w);
		3660	pthread_mutex_unlock (&u->lock);
		3661
		3662	Note that sending the C<ev_async> watcher is required because otherwise
		3663	an event loop currently blocking in the kernel will have no knowledge
		3664	about the newly added timer. By waking up the loop it will pick up any new
		3665	watchers in the next event loop iteration.
		3666
		3667	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3668
		3669	While the overhead of a callback that e.g. schedules a thread is small, it
		3670	is still an overhead. If you embed libev, and your main usage is with some
		3671	kind of threads or coroutines, you might want to customise libev so that
		3672	doesn't need callbacks anymore.
		3673
		3674	Imagine you have coroutines that you can switch to using a function
		3675	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3676	and that due to some magic, the currently active coroutine is stored in a
		3677	global called C<current_coro>. Then you can build your own "wait for libev
		3678	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3679	the differing C<;> conventions):
		3680
		3681	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3682	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3683
		3684	That means instead of having a C callback function, you store the
		3685	coroutine to switch to in each watcher, and instead of having libev call
		3686	your callback, you instead have it switch to that coroutine.
		3687
		3688	A coroutine might now wait for an event with a function called
		3689	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3690	matter when, or whether the watcher is active or not when this function is
		3691	called):
		3692
		3693	void
		3694	wait_for_event (ev_watcher *w)
		3695	{
		3696	ev_cb_set (w) = current_coro;
		3697	switch_to (libev_coro);
		3698	}
		3699
		3700	That basically suspends the coroutine inside C<wait_for_event> and
		3701	continues the libev coroutine, which, when appropriate, switches back to
		3702	this or any other coroutine. I am sure if you sue this your own :)
		3703
		3704	You can do similar tricks if you have, say, threads with an event queue -
		3705	instead of storing a coroutine, you store the queue object and instead of
		3706	switching to a coroutine, you push the watcher onto the queue and notify
		3707	any waiters.
		3708
		3709	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3710	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3711
		3712	// my_ev.h
		3713	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3714	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3715	#include "../libev/ev.h"
		3716
		3717	// my_ev.c
		3718	#define EV_H "my_ev.h"
		3719	#include "../libev/ev.c"
		3720
		3721	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3722	F<my_ev.c> into your project. When properly specifying include paths, you
		3723	can even use F<ev.h> as header file name directly.
3360		3724
3361		3725
3362	=head1 LIBEVENT EMULATION	3726	=head1 LIBEVENT EMULATION
3363		3727
3364	Libev offers a compatibility emulation layer for libevent. It cannot	3728	Libev offers a compatibility emulation layer for libevent. It cannot
3365	emulate the internals of libevent, so here are some usage hints:	3729	emulate the internals of libevent, so here are some usage hints:
3366		3730
3367	=over 4	3731	=over 4
		3732
		3733	=item * Only the libevent-1.4.1-beta API is being emulated.
		3734
		3735	This was the newest libevent version available when libev was implemented,
		3736	and is still mostly unchanged in 2010.
3368		3737
3369	=item * Use it by including <event.h>, as usual.	3738	=item * Use it by including <event.h>, as usual.
3370		3739
3371	=item * The following members are fully supported: ev_base, ev_callback,	3740	=item * The following members are fully supported: ev_base, ev_callback,
3372	ev_arg, ev_fd, ev_res, ev_events.	3741	ev_arg, ev_fd, ev_res, ev_events.
…		…
3378	=item * Priorities are not currently supported. Initialising priorities	3747	=item * Priorities are not currently supported. Initialising priorities
3379	will fail and all watchers will have the same priority, even though there	3748	will fail and all watchers will have the same priority, even though there
3380	is an ev_pri field.	3749	is an ev_pri field.
3381		3750
3382	=item * In libevent, the last base created gets the signals, in libev, the	3751	=item * In libevent, the last base created gets the signals, in libev, the
3383	first base created (== the default loop) gets the signals.	3752	base that registered the signal gets the signals.
3384		3753
3385	=item * Other members are not supported.	3754	=item * Other members are not supported.
3386		3755
3387	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3756	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3388	to use the libev header file and library.	3757	to use the libev header file and library.
…		…
3407	Care has been taken to keep the overhead low. The only data member the C++	3776	Care has been taken to keep the overhead low. The only data member the C++
3408	classes add (compared to plain C-style watchers) is the event loop pointer	3777	classes add (compared to plain C-style watchers) is the event loop pointer
3409	that the watcher is associated with (or no additional members at all if	3778	that the watcher is associated with (or no additional members at all if
3410	you disable C<EV_MULTIPLICITY> when embedding libev).	3779	you disable C<EV_MULTIPLICITY> when embedding libev).
3411		3780
3412	Currently, functions, and static and non-static member functions can be	3781	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	3782	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	3783	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	3784	you need support for other types of functors please contact the author
3416	it).	3785	(preferably after implementing it).
3417		3786
3418	Here is a list of things available in the C<ev> namespace:	3787	Here is a list of things available in the C<ev> namespace:
3419		3788
3420	=over 4	3789	=over 4
3421		3790
…		…
3849	F<event.h> that are not directly supported by the libev core alone.	4218	F<event.h> that are not directly supported by the libev core alone.
3850		4219
3851	In standalone mode, libev will still try to automatically deduce the	4220	In standalone mode, libev will still try to automatically deduce the
3852	configuration, but has to be more conservative.	4221	configuration, but has to be more conservative.
3853		4222
		4223	=item EV_USE_FLOOR
		4224
		4225	If defined to be C<1>, libev will use the C<floor ()> function for its
		4226	periodic reschedule calculations, otherwise libev will fall back on a
		4227	portable (slower) implementation. If you enable this, you usually have to
		4228	link against libm or something equivalent. Enabling this when the C<floor>
		4229	function is not available will fail, so the safe default is to not enable
		4230	this.
		4231
3854	=item EV_USE_MONOTONIC	4232	=item EV_USE_MONOTONIC
3855		4233
3856	If defined to be C<1>, libev will try to detect the availability of the	4234	If defined to be C<1>, libev will try to detect the availability of the
3857	monotonic clock option at both compile time and runtime. Otherwise no	4235	monotonic clock option at both compile time and runtime. Otherwise no
3858	use of the monotonic clock option will be attempted. If you enable this,	4236	use of the monotonic clock option will be attempted. If you enable this,
…		…
4289	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4667	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4290		4668
4291	#include "ev_cpp.h"	4669	#include "ev_cpp.h"
4292	#include "ev.c"	4670	#include "ev.c"
4293		4671
4294	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4672	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4295		4673
4296	=head2 THREADS AND COROUTINES	4674	=head2 THREADS AND COROUTINES
4297		4675
4298	=head3 THREADS	4676	=head3 THREADS
4299		4677
…		…
4350	default loop and triggering an C<ev_async> watcher from the default loop	4728	default loop and triggering an C<ev_async> watcher from the default loop
4351	watcher callback into the event loop interested in the signal.	4729	watcher callback into the event loop interested in the signal.
4352		4730
4353	=back	4731	=back
4354		4732
4355	=head4 THREAD LOCKING EXAMPLE	4733	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		4734
4493	=head3 COROUTINES	4735	=head3 COROUTINES
4494		4736
4495	Libev is very accommodating to coroutines ("cooperative threads"):	4737	Libev is very accommodating to coroutines ("cooperative threads"):
4496	libev fully supports nesting calls to its functions from different	4738	libev fully supports nesting calls to its functions from different
…		…
5005	The physical time that is observed. It is apparently strictly monotonic :)	5247	The physical time that is observed. It is apparently strictly monotonic :)
5006		5248
5007	=item wall-clock time	5249	=item wall-clock time
5008		5250
5009	The time and date as shown on clocks. Unlike real time, it can actually	5251	The time and date as shown on clocks. Unlike real time, it can actually
5010	be wrong and jump forwards and backwards, e.g. when the you adjust your	5252	be wrong and jump forwards and backwards, e.g. when you adjust your
5011	clock.	5253	clock.
5012		5254
5013	=item watcher	5255	=item watcher
5014		5256
5015	A data structure that describes interest in certain events. Watchers need	5257	A data structure that describes interest in certain events. Watchers need
…		…
5018	=back	5260	=back
5019		5261
5020	=head1 AUTHOR	5262	=head1 AUTHOR
5021		5263
5022	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5264	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5023	Magnusson and Emanuele Giaquinta.	5265	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5024		5266

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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 1.371 by root, Sat Jun 4 05:25:03 2011 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.337 by root, Sun Oct 31 20:20:20 2010 UTC vs.
Revision 1.371 by root, Sat Jun 4 05:25:03 2011 UTC