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

Comparing libev/ev.pod (file contents):
Revision 1.335 by root, Mon Oct 25 10:32:05 2010 UTC vs.
Revision 1.357 by root, Tue Jan 11 02:15:58 2011 UTC

…		…
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
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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:
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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	This flag's behaviour will become the default in future versions of libev.
423		448
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		450
426	This is your standard select(2) backend. Not I<completely> standard, as	451	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,	452	libev tries to roll its own fd_set with no limits on the number of fds,
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463	epoll scales either O(1) or O(active_fds).	488	epoll scales either O(1) or O(active_fds).
464		489
465	The epoll mechanism deserves honorable mention as the most misdesigned	490	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	491	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	492	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup and	493	descriptor (and unnecessary guessing of parameters), problems with dup,
		494	returning before the timeout value, resulting in additional iterations
		495	(and only giving 5ms accuracy while select on the same platform gives
469	so on. The biggest issue is fork races, however - if a program forks then	496	0.1ms) and so on. The biggest issue is fork races, however - if a program
470	I<both> parent and child process have to recreate the epoll set, which can	497	forks then I<both> parent and child process have to recreate the epoll
471	take considerable time (one syscall per file descriptor) and is of course	498	set, which can take considerable time (one syscall per file descriptor)
472	hard to detect.	499	and is of course hard to detect.
473		500
474	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
475	of course I<doesn't>, and epoll just loves to report events for totally	502	of course I<doesn't>, and epoll just loves to report events for totally
476	I<different> file descriptors (even already closed ones, so one cannot	503	I<different> file descriptors (even already closed ones, so one cannot
477	even remove them from the set) than registered in the set (especially	504	even remove them from the set) than registered in the set (especially
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479	employing an additional generation counter and comparing that against the	506	employing an additional generation counter and comparing that against the
480	events to filter out spurious ones, recreating the set when required. Last	507	events to filter out spurious ones, recreating the set when required. Last
481	not least, it also refuses to work with some file descriptors which work	508	not least, it also refuses to work with some file descriptors which work
482	perfectly fine with C<select> (files, many character devices...).	509	perfectly fine with C<select> (files, many character devices...).
483		510
		511	Epoll is truly the train wreck analog among event poll mechanisms,
		512	a frankenpoll, cobbled together in a hurry, no thought to design or
		513	interaction with others.
		514
484	While stopping, setting and starting an I/O watcher in the same iteration	515	While stopping, setting and starting an I/O watcher in the same iteration
485	will result in some caching, there is still a system call per such	516	will result in some caching, there is still a system call per such
486	incident (because the same I<file descriptor> could point to a different	517	incident (because the same I<file descriptor> could point to a different
487	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	518	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
488	file descriptors might not work very well if you register events for both	519	file descriptors might not work very well if you register events for both
…		…
553	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	584	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
554		585
555	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	586	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
556	it's really slow, but it still scales very well (O(active_fds)).	587	it's really slow, but it still scales very well (O(active_fds)).
557		588
558	Please note that Solaris event ports can deliver a lot of spurious
559	notifications, so you need to use non-blocking I/O or other means to avoid
560	blocking when no data (or space) is available.
561
562	While this backend scales well, it requires one system call per active	589	While this backend scales well, it requires one system call per active
563	file descriptor per loop iteration. For small and medium numbers of file	590	file descriptor per loop iteration. For small and medium numbers of file
564	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	591	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
565	might perform better.	592	might perform better.
566		593
567	On the positive side, with the exception of the spurious readiness	594	On the positive side, this backend actually performed fully to
568	notifications, this backend actually performed fully to specification
569	in all tests and is fully embeddable, which is a rare feat among the	595	specification in all tests and is fully embeddable, which is a rare feat
570	OS-specific backends (I vastly prefer correctness over speed hacks).	596	among the OS-specific backends (I vastly prefer correctness over speed
		597	hacks).
		598
		599	On the negative side, the interface is I<bizarre> - so bizarre that
		600	even sun itself gets it wrong in their code examples: The event polling
		601	function sometimes returning events to the caller even though an error
		602	occurred, but with no indication whether it has done so or not (yes, it's
		603	even documented that way) - deadly for edge-triggered interfaces where
		604	you absolutely have to know whether an event occurred or not because you
		605	have to re-arm the watcher.
		606
		607	Fortunately libev seems to be able to work around these idiocies.
571		608
572	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	609	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
573	C<EVBACKEND_POLL>.	610	C<EVBACKEND_POLL>.
574		611
575	=item C<EVBACKEND_ALL>	612	=item C<EVBACKEND_ALL>
576		613
577	Try all backends (even potentially broken ones that wouldn't be tried	614	Try all backends (even potentially broken ones that wouldn't be tried
578	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	615	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
579	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	616	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
580		617
581	It is definitely not recommended to use this flag.	618	It is definitely not recommended to use this flag, use whatever
		619	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		620	at all.
		621
		622	=item C<EVBACKEND_MASK>
		623
		624	Not a backend at all, but a mask to select all backend bits from a
		625	C<flags> value, in case you want to mask out any backends from a flags
		626	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
582		627
583	=back	628	=back
584		629
585	If one or more of the backend flags are or'ed into the flags value,	630	If one or more of the backend flags are or'ed into the flags value,
586	then only these backends will be tried (in the reverse order as listed	631	then only these backends will be tried (in the reverse order as listed
…		…
615	This function is normally used on loop objects allocated by	660	This function is normally used on loop objects allocated by
616	C<ev_loop_new>, but it can also be used on the default loop returned by	661	C<ev_loop_new>, but it can also be used on the default loop returned by
617	C<ev_default_loop>, in which case it is not thread-safe.	662	C<ev_default_loop>, in which case it is not thread-safe.
618		663
619	Note that it is not advisable to call this function on the default loop	664	Note that it is not advisable to call this function on the default loop
620	except in the rare occasion where you really need to free it's resources.	665	except in the rare occasion where you really need to free its resources.
621	If you need dynamically allocated loops it is better to use C<ev_loop_new>	666	If you need dynamically allocated loops it is better to use C<ev_loop_new>
622	and C<ev_loop_destroy>.	667	and C<ev_loop_destroy>.
623		668
624	=item ev_loop_fork (loop)	669	=item ev_loop_fork (loop)
625		670
…		…
673	prepare and check phases.	718	prepare and check phases.
674		719
675	=item unsigned int ev_depth (loop)	720	=item unsigned int ev_depth (loop)
676		721
677	Returns the number of times C<ev_run> was entered minus the number of	722	Returns the number of times C<ev_run> was entered minus the number of
678	times C<ev_run> was exited, in other words, the recursion depth.	723	times C<ev_run> was exited normally, in other words, the recursion depth.
679		724
680	Outside C<ev_run>, this number is zero. In a callback, this number is	725	Outside C<ev_run>, this number is zero. In a callback, this number is
681	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	726	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
682	in which case it is higher.	727	in which case it is higher.
683		728
684	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	729	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
685	etc.), doesn't count as "exit" - consider this as a hint to avoid such	730	throwing an exception etc.), doesn't count as "exit" - consider this
686	ungentleman-like behaviour unless it's really convenient.	731	as a hint to avoid such ungentleman-like behaviour unless it's really
		732	convenient, in which case it is fully supported.
687		733
688	=item unsigned int ev_backend (loop)	734	=item unsigned int ev_backend (loop)
689		735
690	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	736	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
691	use.	737	use.
…		…
752	relying on all watchers to be stopped when deciding when a program has	798	relying on all watchers to be stopped when deciding when a program has
753	finished (especially in interactive programs), but having a program	799	finished (especially in interactive programs), but having a program
754	that automatically loops as long as it has to and no longer by virtue	800	that automatically loops as long as it has to and no longer by virtue
755	of relying on its watchers stopping correctly, that is truly a thing of	801	of relying on its watchers stopping correctly, that is truly a thing of
756	beauty.	802	beauty.
		803
		804	This function is also I<mostly> exception-safe - you can break out of
		805	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		806	exception and so on. This does not decrement the C<ev_depth> value, nor
		807	will it clear any outstanding C<EVBREAK_ONE> breaks.
757		808
758	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	809	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
759	those events and any already outstanding ones, but will not wait and	810	those events and any already outstanding ones, but will not wait and
760	block your process in case there are no events and will return after one	811	block your process in case there are no events and will return after one
761	iteration of the loop. This is sometimes useful to poll and handle new	812	iteration of the loop. This is sometimes useful to poll and handle new
…		…
823	Can be used to make a call to C<ev_run> return early (but only after it	874	Can be used to make a call to C<ev_run> return early (but only after it
824	has processed all outstanding events). The C<how> argument must be either	875	has processed all outstanding events). The C<how> argument must be either
825	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	876	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
826	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	877	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
827		878
828	This "unloop state" will be cleared when entering C<ev_run> again.	879	This "break state" will be cleared on the next call to C<ev_run>.
829		880
830	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	881	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		882	which case it will have no effect.
831		883
832	=item ev_ref (loop)	884	=item ev_ref (loop)
833		885
834	=item ev_unref (loop)	886	=item ev_unref (loop)
835		887
…		…
856	running when nothing else is active.	908	running when nothing else is active.
857		909
858	ev_signal exitsig;	910	ev_signal exitsig;
859	ev_signal_init (&exitsig, sig_cb, SIGINT);	911	ev_signal_init (&exitsig, sig_cb, SIGINT);
860	ev_signal_start (loop, &exitsig);	912	ev_signal_start (loop, &exitsig);
861	evf_unref (loop);	913	ev_unref (loop);
862		914
863	Example: For some weird reason, unregister the above signal handler again.	915	Example: For some weird reason, unregister the above signal handler again.
864		916
865	ev_ref (loop);	917	ev_ref (loop);
866	ev_signal_stop (loop, &exitsig);	918	ev_signal_stop (loop, &exitsig);
…		…
978	See also the locking example in the C<THREADS> section later in this	1030	See also the locking example in the C<THREADS> section later in this
979	document.	1031	document.
980		1032
981	=item ev_set_userdata (loop, void *data)	1033	=item ev_set_userdata (loop, void *data)
982		1034
983	=item ev_userdata (loop)	1035	=item void *ev_userdata (loop)
984		1036
985	Set and retrieve a single C<void *> associated with a loop. When	1037	Set and retrieve a single C<void *> associated with a loop. When
986	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1038	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
987	C<0.>	1039	C<0>.
988		1040
989	These two functions can be used to associate arbitrary data with a loop,	1041	These two functions can be used to associate arbitrary data with a loop,
990	and are intended solely for the C<invoke_pending_cb>, C<release> and	1042	and are intended solely for the C<invoke_pending_cb>, C<release> and
991	C<acquire> callbacks described above, but of course can be (ab-)used for	1043	C<acquire> callbacks described above, but of course can be (ab-)used for
992	any other purpose as well.	1044	any other purpose as well.
…		…
1305	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1306	functions that do not need a watcher.	1358	functions that do not need a watcher.
1307		1359
1308	=back	1360	=back
1309		1361
1310	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1362	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1311		1363	OWN COMPOSITE WATCHERS> idioms.
1312	Each watcher has, by default, a member C<void *data> that you can change
1313	and read at any time: libev will completely ignore it. This can be used
1314	to associate arbitrary data with your watcher. If you need more data and
1315	don't want to allocate memory and store a pointer to it in that data
1316	member, you can also "subclass" the watcher type and provide your own
1317	data:
1318
1319	struct my_io
1320	{
1321	ev_io io;
1322	int otherfd;
1323	void *somedata;
1324	struct whatever *mostinteresting;
1325	};
1326
1327	...
1328	struct my_io w;
1329	ev_io_init (&w.io, my_cb, fd, EV_READ);
1330
1331	And since your callback will be called with a pointer to the watcher, you
1332	can cast it back to your own type:
1333
1334	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1335	{
1336	struct my_io w = (struct my_io )w_;
1337	...
1338	}
1339
1340	More interesting and less C-conformant ways of casting your callback type
1341	instead have been omitted.
1342
1343	Another common scenario is to use some data structure with multiple
1344	embedded watchers:
1345
1346	struct my_biggy
1347	{
1348	int some_data;
1349	ev_timer t1;
1350	ev_timer t2;
1351	}
1352
1353	In this case getting the pointer to C<my_biggy> is a bit more
1354	complicated: Either you store the address of your C<my_biggy> struct
1355	in the C<data> member of the watcher (for woozies), or you need to use
1356	some pointer arithmetic using C<offsetof> inside your watchers (for real
1357	programmers):
1358
1359	#include <stddef.h>
1360
1361	static void
1362	t1_cb (EV_P_ ev_timer *w, int revents)
1363	{
1364	struct my_biggy big = (struct my_biggy *)
1365	(((char *)w) - offsetof (struct my_biggy, t1));
1366	}
1367
1368	static void
1369	t2_cb (EV_P_ ev_timer *w, int revents)
1370	{
1371	struct my_biggy big = (struct my_biggy *)
1372	(((char *)w) - offsetof (struct my_biggy, t2));
1373	}
1374		1364
1375	=head2 WATCHER STATES	1365	=head2 WATCHER STATES
1376		1366
1377	There are various watcher states mentioned throughout this manual -	1367	There are various watcher states mentioned throughout this manual -
1378	active, pending and so on. In this section these states and the rules to	1368	active, pending and so on. In this section these states and the rules to
…		…
1564	In general you can register as many read and/or write event watchers per	1554	In general you can register as many read and/or write event watchers per
1565	fd as you want (as long as you don't confuse yourself). Setting all file	1555	fd as you want (as long as you don't confuse yourself). Setting all file
1566	descriptors to non-blocking mode is also usually a good idea (but not	1556	descriptors to non-blocking mode is also usually a good idea (but not
1567	required if you know what you are doing).	1557	required if you know what you are doing).
1568		1558
1569	If you cannot use non-blocking mode, then force the use of a
1570	known-to-be-good backend (at the time of this writing, this includes only
1571	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1572	descriptors for which non-blocking operation makes no sense (such as
1573	files) - libev doesn't guarantee any specific behaviour in that case.
1574
1575	Another thing you have to watch out for is that it is quite easy to	1559	Another thing you have to watch out for is that it is quite easy to
1576	receive "spurious" readiness notifications, that is your callback might	1560	receive "spurious" readiness notifications, that is, your callback might
1577	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1561	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1578	because there is no data. Not only are some backends known to create a	1562	because there is no data. It is very easy to get into this situation even
1579	lot of those (for example Solaris ports), it is very easy to get into	1563	with a relatively standard program structure. Thus it is best to always
1580	this situation even with a relatively standard program structure. Thus	1564	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1581	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1582	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1565	preferable to a program hanging until some data arrives.
1583		1566
1584	If you cannot run the fd in non-blocking mode (for example you should	1567	If you cannot run the fd in non-blocking mode (for example you should
1585	not play around with an Xlib connection), then you have to separately	1568	not play around with an Xlib connection), then you have to separately
1586	re-test whether a file descriptor is really ready with a known-to-be good	1569	re-test whether a file descriptor is really ready with a known-to-be good
1587	interface such as poll (fortunately in our Xlib example, Xlib already	1570	interface such as poll (fortunately in the case of Xlib, it already does
1588	does this on its own, so its quite safe to use). Some people additionally	1571	this on its own, so its quite safe to use). Some people additionally
1589	use C<SIGALRM> and an interval timer, just to be sure you won't block	1572	use C<SIGALRM> and an interval timer, just to be sure you won't block
1590	indefinitely.	1573	indefinitely.
1591		1574
1592	But really, best use non-blocking mode.	1575	But really, best use non-blocking mode.
1593		1576
…		…
1621		1604
1622	There is no workaround possible except not registering events	1605	There is no workaround possible except not registering events
1623	for potentially C<dup ()>'ed file descriptors, or to resort to	1606	for potentially C<dup ()>'ed file descriptors, or to resort to
1624	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1607	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1625		1608
		1609	=head3 The special problem of files
		1610
		1611	Many people try to use C<select> (or libev) on file descriptors
		1612	representing files, and expect it to become ready when their program
		1613	doesn't block on disk accesses (which can take a long time on their own).
		1614
		1615	However, this cannot ever work in the "expected" way - you get a readiness
		1616	notification as soon as the kernel knows whether and how much data is
		1617	there, and in the case of open files, that's always the case, so you
		1618	always get a readiness notification instantly, and your read (or possibly
		1619	write) will still block on the disk I/O.
		1620
		1621	Another way to view it is that in the case of sockets, pipes, character
		1622	devices and so on, there is another party (the sender) that delivers data
		1623	on it's own, but in the case of files, there is no such thing: the disk
		1624	will not send data on it's own, simply because it doesn't know what you
		1625	wish to read - you would first have to request some data.
		1626
		1627	Since files are typically not-so-well supported by advanced notification
		1628	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1629	to files, even though you should not use it. The reason for this is
		1630	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1631	usually a tty, often a pipe, but also sometimes files or special devices
		1632	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1633	F</dev/urandom>), and even though the file might better be served with
		1634	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1635	it "just works" instead of freezing.
		1636
		1637	So avoid file descriptors pointing to files when you know it (e.g. use
		1638	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1639	when you rarely read from a file instead of from a socket, and want to
		1640	reuse the same code path.
		1641
1626	=head3 The special problem of fork	1642	=head3 The special problem of fork
1627		1643
1628	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1644	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1629	useless behaviour. Libev fully supports fork, but needs to be told about	1645	useless behaviour. Libev fully supports fork, but needs to be told about
1630	it in the child.	1646	it in the child if you want to continue to use it in the child.
1631		1647
1632	To support fork in your programs, you either have to call	1648	To support fork in your child processes, you have to call C<ev_loop_fork
1633	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1649	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1634	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1650	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1635	C<EVBACKEND_POLL>.
1636		1651
1637	=head3 The special problem of SIGPIPE	1652	=head3 The special problem of SIGPIPE
1638		1653
1639	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1654	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1640	when writing to a pipe whose other end has been closed, your program gets	1655	when writing to a pipe whose other end has been closed, your program gets
…		…
2256		2271
2257	=head2 C<ev_signal> - signal me when a signal gets signalled!	2272	=head2 C<ev_signal> - signal me when a signal gets signalled!
2258		2273
2259	Signal watchers will trigger an event when the process receives a specific	2274	Signal watchers will trigger an event when the process receives a specific
2260	signal one or more times. Even though signals are very asynchronous, libev	2275	signal one or more times. Even though signals are very asynchronous, libev
2261	will try it's best to deliver signals synchronously, i.e. as part of the	2276	will try its best to deliver signals synchronously, i.e. as part of the
2262	normal event processing, like any other event.	2277	normal event processing, like any other event.
2263		2278
2264	If you want signals to be delivered truly asynchronously, just use	2279	If you want signals to be delivered truly asynchronously, just use
2265	C<sigaction> as you would do without libev and forget about sharing	2280	C<sigaction> as you would do without libev and forget about sharing
2266	the signal. You can even use C<ev_async> from a signal handler to	2281	the signal. You can even use C<ev_async> from a signal handler to
…		…
2308	I<has> to modify the signal mask, at least temporarily.	2323	I<has> to modify the signal mask, at least temporarily.
2309		2324
2310	So I can't stress this enough: I<If you do not reset your signal mask when	2325	So I can't stress this enough: I<If you do not reset your signal mask when
2311	you expect it to be empty, you have a race condition in your code>. This	2326	you expect it to be empty, you have a race condition in your code>. This
2312	is not a libev-specific thing, this is true for most event libraries.	2327	is not a libev-specific thing, this is true for most event libraries.
		2328
		2329	=head3 The special problem of threads signal handling
		2330
		2331	POSIX threads has problematic signal handling semantics, specifically,
		2332	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2333	threads in a process block signals, which is hard to achieve.
		2334
		2335	When you want to use sigwait (or mix libev signal handling with your own
		2336	for the same signals), you can tackle this problem by globally blocking
		2337	all signals before creating any threads (or creating them with a fully set
		2338	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2339	loops. Then designate one thread as "signal receiver thread" which handles
		2340	these signals. You can pass on any signals that libev might be interested
		2341	in by calling C<ev_feed_signal>.
2313		2342
2314	=head3 Watcher-Specific Functions and Data Members	2343	=head3 Watcher-Specific Functions and Data Members
2315		2344
2316	=over 4	2345	=over 4
2317		2346
…		…
3164	it by calling C<ev_async_send>, which is thread- and signal safe.	3193	it by calling C<ev_async_send>, which is thread- and signal safe.
3165		3194
3166	This functionality is very similar to C<ev_signal> watchers, as signals,	3195	This functionality is very similar to C<ev_signal> watchers, as signals,
3167	too, are asynchronous in nature, and signals, too, will be compressed	3196	too, are asynchronous in nature, and signals, too, will be compressed
3168	(i.e. the number of callback invocations may be less than the number of	3197	(i.e. the number of callback invocations may be less than the number of
3169	C<ev_async_sent> calls).	3198	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3199	of "global async watchers" by using a watcher on an otherwise unused
		3200	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3201	even without knowing which loop owns the signal.
3170		3202
3171	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3203	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3172	just the default loop.	3204	just the default loop.
3173		3205
3174	=head3 Queueing	3206	=head3 Queueing
…		…
3350	Feed an event on the given fd, as if a file descriptor backend detected	3382	Feed an event on the given fd, as if a file descriptor backend detected
3351	the given events it.	3383	the given events it.
3352		3384
3353	=item ev_feed_signal_event (loop, int signum)	3385	=item ev_feed_signal_event (loop, int signum)
3354		3386
3355	Feed an event as if the given signal occurred (C<loop> must be the default	3387	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3356	loop!).	3388	which is async-safe.
3357		3389
3358	=back	3390	=back
		3391
		3392
		3393	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3394
		3395	This section explains some common idioms that are not immediately
		3396	obvious. Note that examples are sprinkled over the whole manual, and this
		3397	section only contains stuff that wouldn't fit anywhere else.
		3398
		3399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3400
		3401	Each watcher has, by default, a C<void *data> member that you can read
		3402	or modify at any time: libev will completely ignore it. This can be used
		3403	to associate arbitrary data with your watcher. If you need more data and
		3404	don't want to allocate memory separately and store a pointer to it in that
		3405	data member, you can also "subclass" the watcher type and provide your own
		3406	data:
		3407
		3408	struct my_io
		3409	{
		3410	ev_io io;
		3411	int otherfd;
		3412	void *somedata;
		3413	struct whatever *mostinteresting;
		3414	};
		3415
		3416	...
		3417	struct my_io w;
		3418	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3419
		3420	And since your callback will be called with a pointer to the watcher, you
		3421	can cast it back to your own type:
		3422
		3423	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3424	{
		3425	struct my_io w = (struct my_io )w_;
		3426	...
		3427	}
		3428
		3429	More interesting and less C-conformant ways of casting your callback
		3430	function type instead have been omitted.
		3431
		3432	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3433
		3434	Another common scenario is to use some data structure with multiple
		3435	embedded watchers, in effect creating your own watcher that combines
		3436	multiple libev event sources into one "super-watcher":
		3437
		3438	struct my_biggy
		3439	{
		3440	int some_data;
		3441	ev_timer t1;
		3442	ev_timer t2;
		3443	}
		3444
		3445	In this case getting the pointer to C<my_biggy> is a bit more
		3446	complicated: Either you store the address of your C<my_biggy> struct in
		3447	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3448	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3449	real programmers):
		3450
		3451	#include <stddef.h>
		3452
		3453	static void
		3454	t1_cb (EV_P_ ev_timer *w, int revents)
		3455	{
		3456	struct my_biggy big = (struct my_biggy *)
		3457	(((char *)w) - offsetof (struct my_biggy, t1));
		3458	}
		3459
		3460	static void
		3461	t2_cb (EV_P_ ev_timer *w, int revents)
		3462	{
		3463	struct my_biggy big = (struct my_biggy *)
		3464	(((char *)w) - offsetof (struct my_biggy, t2));
		3465	}
		3466
		3467	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3468
		3469	Often (especially in GUI toolkits) there are places where you have
		3470	I<modal> interaction, which is most easily implemented by recursively
		3471	invoking C<ev_run>.
		3472
		3473	This brings the problem of exiting - a callback might want to finish the
		3474	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3475	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3476	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3477	other combination: In these cases, C<ev_break> will not work alone.
		3478
		3479	The solution is to maintain "break this loop" variable for each C<ev_run>
		3480	invocation, and use a loop around C<ev_run> until the condition is
		3481	triggered, using C<EVRUN_ONCE>:
		3482
		3483	// main loop
		3484	int exit_main_loop = 0;
		3485
		3486	while (!exit_main_loop)
		3487	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3488
		3489	// in a model watcher
		3490	int exit_nested_loop = 0;
		3491
		3492	while (!exit_nested_loop)
		3493	ev_run (EV_A_ EVRUN_ONCE);
		3494
		3495	To exit from any of these loops, just set the corresponding exit variable:
		3496
		3497	// exit modal loop
		3498	exit_nested_loop = 1;
		3499
		3500	// exit main program, after modal loop is finished
		3501	exit_main_loop = 1;
		3502
		3503	// exit both
		3504	exit_main_loop = exit_nested_loop = 1;
		3505
		3506	=head2 THREAD LOCKING EXAMPLE
		3507
		3508	Here is a fictitious example of how to run an event loop in a different
		3509	thread than where callbacks are being invoked and watchers are
		3510	created/added/removed.
		3511
		3512	For a real-world example, see the C<EV::Loop::Async> perl module,
		3513	which uses exactly this technique (which is suited for many high-level
		3514	languages).
		3515
		3516	The example uses a pthread mutex to protect the loop data, a condition
		3517	variable to wait for callback invocations, an async watcher to notify the
		3518	event loop thread and an unspecified mechanism to wake up the main thread.
		3519
		3520	First, you need to associate some data with the event loop:
		3521
		3522	typedef struct {
		3523	mutex_t lock; /* global loop lock */
		3524	ev_async async_w;
		3525	thread_t tid;
		3526	cond_t invoke_cv;
		3527	} userdata;
		3528
		3529	void prepare_loop (EV_P)
		3530	{
		3531	// for simplicity, we use a static userdata struct.
		3532	static userdata u;
		3533
		3534	ev_async_init (&u->async_w, async_cb);
		3535	ev_async_start (EV_A_ &u->async_w);
		3536
		3537	pthread_mutex_init (&u->lock, 0);
		3538	pthread_cond_init (&u->invoke_cv, 0);
		3539
		3540	// now associate this with the loop
		3541	ev_set_userdata (EV_A_ u);
		3542	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3543	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3544
		3545	// then create the thread running ev_loop
		3546	pthread_create (&u->tid, 0, l_run, EV_A);
		3547	}
		3548
		3549	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3550	solely to wake up the event loop so it takes notice of any new watchers
		3551	that might have been added:
		3552
		3553	static void
		3554	async_cb (EV_P_ ev_async *w, int revents)
		3555	{
		3556	// just used for the side effects
		3557	}
		3558
		3559	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3560	protecting the loop data, respectively.
		3561
		3562	static void
		3563	l_release (EV_P)
		3564	{
		3565	userdata *u = ev_userdata (EV_A);
		3566	pthread_mutex_unlock (&u->lock);
		3567	}
		3568
		3569	static void
		3570	l_acquire (EV_P)
		3571	{
		3572	userdata *u = ev_userdata (EV_A);
		3573	pthread_mutex_lock (&u->lock);
		3574	}
		3575
		3576	The event loop thread first acquires the mutex, and then jumps straight
		3577	into C<ev_run>:
		3578
		3579	void *
		3580	l_run (void *thr_arg)
		3581	{
		3582	struct ev_loop loop = (struct ev_loop )thr_arg;
		3583
		3584	l_acquire (EV_A);
		3585	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3586	ev_run (EV_A_ 0);
		3587	l_release (EV_A);
		3588
		3589	return 0;
		3590	}
		3591
		3592	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3593	signal the main thread via some unspecified mechanism (signals? pipe
		3594	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3595	have been called (in a while loop because a) spurious wakeups are possible
		3596	and b) skipping inter-thread-communication when there are no pending
		3597	watchers is very beneficial):
		3598
		3599	static void
		3600	l_invoke (EV_P)
		3601	{
		3602	userdata *u = ev_userdata (EV_A);
		3603
		3604	while (ev_pending_count (EV_A))
		3605	{
		3606	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3607	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3608	}
		3609	}
		3610
		3611	Now, whenever the main thread gets told to invoke pending watchers, it
		3612	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3613	thread to continue:
		3614
		3615	static void
		3616	real_invoke_pending (EV_P)
		3617	{
		3618	userdata *u = ev_userdata (EV_A);
		3619
		3620	pthread_mutex_lock (&u->lock);
		3621	ev_invoke_pending (EV_A);
		3622	pthread_cond_signal (&u->invoke_cv);
		3623	pthread_mutex_unlock (&u->lock);
		3624	}
		3625
		3626	Whenever you want to start/stop a watcher or do other modifications to an
		3627	event loop, you will now have to lock:
		3628
		3629	ev_timer timeout_watcher;
		3630	userdata *u = ev_userdata (EV_A);
		3631
		3632	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3633
		3634	pthread_mutex_lock (&u->lock);
		3635	ev_timer_start (EV_A_ &timeout_watcher);
		3636	ev_async_send (EV_A_ &u->async_w);
		3637	pthread_mutex_unlock (&u->lock);
		3638
		3639	Note that sending the C<ev_async> watcher is required because otherwise
		3640	an event loop currently blocking in the kernel will have no knowledge
		3641	about the newly added timer. By waking up the loop it will pick up any new
		3642	watchers in the next event loop iteration.
		3643
		3644	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3645
		3646	While the overhead of a callback that e.g. schedules a thread is small, it
		3647	is still an overhead. If you embed libev, and your main usage is with some
		3648	kind of threads or coroutines, you might want to customise libev so that
		3649	doesn't need callbacks anymore.
		3650
		3651	Imagine you have coroutines that you can switch to using a function
		3652	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3653	and that due to some magic, the currently active coroutine is stored in a
		3654	global called C<current_coro>. Then you can build your own "wait for libev
		3655	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3656	the differing C<;> conventions):
		3657
		3658	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3659	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3660
		3661	That means instead of having a C callback function, you store the
		3662	coroutine to switch to in each watcher, and instead of having libev call
		3663	your callback, you instead have it switch to that coroutine.
		3664
		3665	A coroutine might now wait for an event with a function called
		3666	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3667	matter when, or whether the watcher is active or not when this function is
		3668	called):
		3669
		3670	void
		3671	wait_for_event (ev_watcher *w)
		3672	{
		3673	ev_cb_set (w) = current_coro;
		3674	switch_to (libev_coro);
		3675	}
		3676
		3677	That basically suspends the coroutine inside C<wait_for_event> and
		3678	continues the libev coroutine, which, when appropriate, switches back to
		3679	this or any other coroutine. I am sure if you sue this your own :)
		3680
		3681	You can do similar tricks if you have, say, threads with an event queue -
		3682	instead of storing a coroutine, you store the queue object and instead of
		3683	switching to a coroutine, you push the watcher onto the queue and notify
		3684	any waiters.
		3685
		3686	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3687	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3688
		3689	// my_ev.h
		3690	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3691	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3692	#include "../libev/ev.h"
		3693
		3694	// my_ev.c
		3695	#define EV_H "my_ev.h"
		3696	#include "../libev/ev.c"
		3697
		3698	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3699	F<my_ev.c> into your project. When properly specifying include paths, you
		3700	can even use F<ev.h> as header file name directly.
3359		3701
3360		3702
3361	=head1 LIBEVENT EMULATION	3703	=head1 LIBEVENT EMULATION
3362		3704
3363	Libev offers a compatibility emulation layer for libevent. It cannot	3705	Libev offers a compatibility emulation layer for libevent. It cannot
3364	emulate the internals of libevent, so here are some usage hints:	3706	emulate the internals of libevent, so here are some usage hints:
3365		3707
3366	=over 4	3708	=over 4
		3709
		3710	=item * Only the libevent-1.4.1-beta API is being emulated.
		3711
		3712	This was the newest libevent version available when libev was implemented,
		3713	and is still mostly unchanged in 2010.
3367		3714
3368	=item * Use it by including <event.h>, as usual.	3715	=item * Use it by including <event.h>, as usual.
3369		3716
3370	=item * The following members are fully supported: ev_base, ev_callback,	3717	=item * The following members are fully supported: ev_base, ev_callback,
3371	ev_arg, ev_fd, ev_res, ev_events.	3718	ev_arg, ev_fd, ev_res, ev_events.
…		…
3377	=item * Priorities are not currently supported. Initialising priorities	3724	=item * Priorities are not currently supported. Initialising priorities
3378	will fail and all watchers will have the same priority, even though there	3725	will fail and all watchers will have the same priority, even though there
3379	is an ev_pri field.	3726	is an ev_pri field.
3380		3727
3381	=item * In libevent, the last base created gets the signals, in libev, the	3728	=item * In libevent, the last base created gets the signals, in libev, the
3382	first base created (== the default loop) gets the signals.	3729	base that registered the signal gets the signals.
3383		3730
3384	=item * Other members are not supported.	3731	=item * Other members are not supported.
3385		3732
3386	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3733	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3387	to use the libev header file and library.	3734	to use the libev header file and library.
…		…
3406	Care has been taken to keep the overhead low. The only data member the C++	3753	Care has been taken to keep the overhead low. The only data member the C++
3407	classes add (compared to plain C-style watchers) is the event loop pointer	3754	classes add (compared to plain C-style watchers) is the event loop pointer
3408	that the watcher is associated with (or no additional members at all if	3755	that the watcher is associated with (or no additional members at all if
3409	you disable C<EV_MULTIPLICITY> when embedding libev).	3756	you disable C<EV_MULTIPLICITY> when embedding libev).
3410		3757
3411	Currently, functions, and static and non-static member functions can be	3758	Currently, functions, static and non-static member functions and classes
3412	used as callbacks. Other types should be easy to add as long as they only	3759	with C<operator ()> can be used as callbacks. Other types should be easy
3413	need one additional pointer for context. If you need support for other	3760	to add as long as they only need one additional pointer for context. If
3414	types of functors please contact the author (preferably after implementing	3761	you need support for other types of functors please contact the author
3415	it).	3762	(preferably after implementing it).
3416		3763
3417	Here is a list of things available in the C<ev> namespace:	3764	Here is a list of things available in the C<ev> namespace:
3418		3765
3419	=over 4	3766	=over 4
3420		3767
…		…
4288	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4635	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4289		4636
4290	#include "ev_cpp.h"	4637	#include "ev_cpp.h"
4291	#include "ev.c"	4638	#include "ev.c"
4292		4639
4293	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4640	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4294		4641
4295	=head2 THREADS AND COROUTINES	4642	=head2 THREADS AND COROUTINES
4296		4643
4297	=head3 THREADS	4644	=head3 THREADS
4298		4645
…		…
4349	default loop and triggering an C<ev_async> watcher from the default loop	4696	default loop and triggering an C<ev_async> watcher from the default loop
4350	watcher callback into the event loop interested in the signal.	4697	watcher callback into the event loop interested in the signal.
4351		4698
4352	=back	4699	=back
4353		4700
4354	=head4 THREAD LOCKING EXAMPLE	4701	See also L<THREAD LOCKING EXAMPLE>.
4355
4356	Here is a fictitious example of how to run an event loop in a different
4357	thread than where callbacks are being invoked and watchers are
4358	created/added/removed.
4359
4360	For a real-world example, see the C<EV::Loop::Async> perl module,
4361	which uses exactly this technique (which is suited for many high-level
4362	languages).
4363
4364	The example uses a pthread mutex to protect the loop data, a condition
4365	variable to wait for callback invocations, an async watcher to notify the
4366	event loop thread and an unspecified mechanism to wake up the main thread.
4367
4368	First, you need to associate some data with the event loop:
4369
4370	typedef struct {
4371	mutex_t lock; /* global loop lock */
4372	ev_async async_w;
4373	thread_t tid;
4374	cond_t invoke_cv;
4375	} userdata;
4376
4377	void prepare_loop (EV_P)
4378	{
4379	// for simplicity, we use a static userdata struct.
4380	static userdata u;
4381
4382	ev_async_init (&u->async_w, async_cb);
4383	ev_async_start (EV_A_ &u->async_w);
4384
4385	pthread_mutex_init (&u->lock, 0);
4386	pthread_cond_init (&u->invoke_cv, 0);
4387
4388	// now associate this with the loop
4389	ev_set_userdata (EV_A_ u);
4390	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4391	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4392
4393	// then create the thread running ev_loop
4394	pthread_create (&u->tid, 0, l_run, EV_A);
4395	}
4396
4397	The callback for the C<ev_async> watcher does nothing: the watcher is used
4398	solely to wake up the event loop so it takes notice of any new watchers
4399	that might have been added:
4400
4401	static void
4402	async_cb (EV_P_ ev_async *w, int revents)
4403	{
4404	// just used for the side effects
4405	}
4406
4407	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4408	protecting the loop data, respectively.
4409
4410	static void
4411	l_release (EV_P)
4412	{
4413	userdata *u = ev_userdata (EV_A);
4414	pthread_mutex_unlock (&u->lock);
4415	}
4416
4417	static void
4418	l_acquire (EV_P)
4419	{
4420	userdata *u = ev_userdata (EV_A);
4421	pthread_mutex_lock (&u->lock);
4422	}
4423
4424	The event loop thread first acquires the mutex, and then jumps straight
4425	into C<ev_run>:
4426
4427	void *
4428	l_run (void *thr_arg)
4429	{
4430	struct ev_loop loop = (struct ev_loop )thr_arg;
4431
4432	l_acquire (EV_A);
4433	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4434	ev_run (EV_A_ 0);
4435	l_release (EV_A);
4436
4437	return 0;
4438	}
4439
4440	Instead of invoking all pending watchers, the C<l_invoke> callback will
4441	signal the main thread via some unspecified mechanism (signals? pipe
4442	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4443	have been called (in a while loop because a) spurious wakeups are possible
4444	and b) skipping inter-thread-communication when there are no pending
4445	watchers is very beneficial):
4446
4447	static void
4448	l_invoke (EV_P)
4449	{
4450	userdata *u = ev_userdata (EV_A);
4451
4452	while (ev_pending_count (EV_A))
4453	{
4454	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4455	pthread_cond_wait (&u->invoke_cv, &u->lock);
4456	}
4457	}
4458
4459	Now, whenever the main thread gets told to invoke pending watchers, it
4460	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4461	thread to continue:
4462
4463	static void
4464	real_invoke_pending (EV_P)
4465	{
4466	userdata *u = ev_userdata (EV_A);
4467
4468	pthread_mutex_lock (&u->lock);
4469	ev_invoke_pending (EV_A);
4470	pthread_cond_signal (&u->invoke_cv);
4471	pthread_mutex_unlock (&u->lock);
4472	}
4473
4474	Whenever you want to start/stop a watcher or do other modifications to an
4475	event loop, you will now have to lock:
4476
4477	ev_timer timeout_watcher;
4478	userdata *u = ev_userdata (EV_A);
4479
4480	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4481
4482	pthread_mutex_lock (&u->lock);
4483	ev_timer_start (EV_A_ &timeout_watcher);
4484	ev_async_send (EV_A_ &u->async_w);
4485	pthread_mutex_unlock (&u->lock);
4486
4487	Note that sending the C<ev_async> watcher is required because otherwise
4488	an event loop currently blocking in the kernel will have no knowledge
4489	about the newly added timer. By waking up the loop it will pick up any new
4490	watchers in the next event loop iteration.
4491		4702
4492	=head3 COROUTINES	4703	=head3 COROUTINES
4493		4704
4494	Libev is very accommodating to coroutines ("cooperative threads"):	4705	Libev is very accommodating to coroutines ("cooperative threads"):
4495	libev fully supports nesting calls to its functions from different	4706	libev fully supports nesting calls to its functions from different

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Comparing libev/ev.pod (file contents): Revision 1.335 by root, Mon Oct 25 10:32:05 2010 UTC vs. Revision 1.357 by root, Tue Jan 11 02:15:58 2011 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.335 by root, Mon Oct 25 10:32:05 2010 UTC vs.
Revision 1.357 by root, Tue Jan 11 02:15:58 2011 UTC