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Revision 1.351 by root, Mon Jan 10 14:24:26 2011 UTC vs.
Revision 1.405 by root, Thu May 3 15:07:15 2012 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
…		…
174	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
175		175
176	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
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_now_update> 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))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
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))	288	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
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
…		…
435	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
436		442
437	=item C<EVFLAG_NOSIGMASK>	443	=item C<EVFLAG_NOSIGMASK>
438		444
439	When this flag is specified, then libev will avoid to modify the signal	445	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	446	mask. Specifically, this means you have to make sure signals are unblocked
441	when you want to receive them.	447	when you want to receive them.
442		448
443	This behaviour is useful when you want to do your own signal handling, or	449	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	450	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	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.
446		455
447	This flag's behaviour will become the default in future versions of libev.	456	This flag's behaviour will become the default in future versions of libev.
448		457
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		459
…		…
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		490
482	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
483	kernels).	492	kernels).
484		493
485	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
486	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
487	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
488	epoll scales either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
489		498
490	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	502	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
496	0.1ms) and so on. The biggest issue is fork races, however - if a program	505	0.1ms) and so on. The biggest issue is fork races, however - if a program
497	forks then I<both> parent and child process have to recreate the epoll	506	forks then I<both> parent and child process have to recreate the epoll
498	set, which can take considerable time (one syscall per file descriptor)	507	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	508	and is of course hard to detect.
500		509
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
502	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
503	I<different> file descriptors (even already closed ones, so one cannot	512	totally I<different> file descriptors (even already closed ones, so
504	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
505	on SMP systems). Libev tries to counter these spurious notifications by	514	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
507	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 erroneously 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
508	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
509	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
510		522
511	Epoll is truly the train wreck analog among event poll mechanisms.	523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
512		526
513	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
514	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
515	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
516	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
…		…
553		567
554	It scales in the same way as the epoll backend, but the interface to the	568	It scales in the same way as the epoll backend, but the interface to the
555	kernel is more efficient (which says nothing about its actual speed, of	569	kernel is more efficient (which says nothing about its actual speed, of
556	course). While stopping, setting and starting an I/O watcher does never	570	course). While stopping, setting and starting an I/O watcher does never
557	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
558	two event changes per incident. Support for C<fork ()> is very bad (but	572	two event changes per incident. Support for C<fork ()> is very bad (you
559	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	573	might have to leak fd's on fork, but it's more sane than epoll) and it
560	cases	574	drops fds silently in similarly hard-to-detect cases
561		575
562	This backend usually performs well under most conditions.	576	This backend usually performs well under most conditions.
563		577
564	While nominally embeddable in other event loops, this doesn't work	578	While nominally embeddable in other event loops, this doesn't work
565	everywhere, so you might need to test for this. And since it is broken	579	everywhere, so you might need to test for this. And since it is broken
…		…
592	On the positive side, this backend actually performed fully to	606	On the positive side, this backend actually performed fully to
593	specification in all tests and is fully embeddable, which is a rare feat	607	specification in all tests and is fully embeddable, which is a rare feat
594	among the OS-specific backends (I vastly prefer correctness over speed	608	among the OS-specific backends (I vastly prefer correctness over speed
595	hacks).	609	hacks).
596		610
597	On the negative side, the interface is I<bizarre>, with the event polling	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
598	function sometimes returning events to the caller even though an error	613	function sometimes returns events to the caller even though an error
599	occured, but with no indication whether it has done so or not (yes, it's	614	occurred, but with no indication whether it has done so or not (yes, it's
600	even documented that way) - deadly for edge-triggered interfaces, but	615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
601	fortunately libev seems to be able to work around it.	619	Fortunately libev seems to be able to work around these idiocies.
602		620
603	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
604	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
605		623
606	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
…		…
774	without a previous call to C<ev_suspend>.	792	without a previous call to C<ev_suspend>.
775		793
776	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	794	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
777	event loop time (see C<ev_now_update>).	795	event loop time (see C<ev_now_update>).
778		796
779	=item ev_run (loop, int flags)	797	=item bool ev_run (loop, int flags)
780		798
781	Finally, this is it, the event handler. This function usually is called	799	Finally, this is it, the event handler. This function usually is called
782	after you have initialised all your watchers and you want to start	800	after you have initialised all your watchers and you want to start
783	handling events. It will ask the operating system for any new events, call	801	handling events. It will ask the operating system for any new events, call
784	the watcher callbacks, an then repeat the whole process indefinitely: This	802	the watcher callbacks, and then repeat the whole process indefinitely: This
785	is why event loops are called I<loops>.	803	is why event loops are called I<loops>.
786		804
787	If the flags argument is specified as C<0>, it will keep handling events	805	If the flags argument is specified as C<0>, it will keep handling events
788	until either no event watchers are active anymore or C<ev_break> was	806	until either no event watchers are active anymore or C<ev_break> was
789	called.	807	called.
		808
		809	The return value is false if there are no more active watchers (which
		810	usually means "all jobs done" or "deadlock"), and true in all other cases
		811	(which usually means " you should call C<ev_run> again").
790		812
791	Please note that an explicit C<ev_break> is usually better than	813	Please note that an explicit C<ev_break> is usually better than
792	relying on all watchers to be stopped when deciding when a program has	814	relying on all watchers to be stopped when deciding when a program has
793	finished (especially in interactive programs), but having a program	815	finished (especially in interactive programs), but having a program
794	that automatically loops as long as it has to and no longer by virtue	816	that automatically loops as long as it has to and no longer by virtue
795	of relying on its watchers stopping correctly, that is truly a thing of	817	of relying on its watchers stopping correctly, that is truly a thing of
796	beauty.	818	beauty.
797		819
798	This function is also I<mostly> exception-safe - you can break out of	820	This function is I<mostly> exception-safe - you can break out of a
799	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++	821	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
800	exception and so on. This does not decrement the C<ev_depth> value, nor	822	exception and so on. This does not decrement the C<ev_depth> value, nor
801	will it clear any outstanding C<EVBREAK_ONE> breaks.	823	will it clear any outstanding C<EVBREAK_ONE> breaks.
802		824
803	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	825	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
804	those events and any already outstanding ones, but will not wait and	826	those events and any already outstanding ones, but will not wait and
…		…
816	This is useful if you are waiting for some external event in conjunction	838	This is useful if you are waiting for some external event in conjunction
817	with something not expressible using other libev watchers (i.e. "roll your	839	with something not expressible using other libev watchers (i.e. "roll your
818	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	840	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
819	usually a better approach for this kind of thing.	841	usually a better approach for this kind of thing.
820		842
821	Here are the gory details of what C<ev_run> does:	843	Here are the gory details of what C<ev_run> does (this is for your
		844	understanding, not a guarantee that things will work exactly like this in
		845	future versions):
822		846
823	- Increment loop depth.	847	- Increment loop depth.
824	- Reset the ev_break status.	848	- Reset the ev_break status.
825	- Before the first iteration, call any pending watchers.	849	- Before the first iteration, call any pending watchers.
826	LOOP:	850	LOOP:
…		…
859	anymore.	883	anymore.
860		884
861	... queue jobs here, make sure they register event watchers as long	885	... queue jobs here, make sure they register event watchers as long
862	... as they still have work to do (even an idle watcher will do..)	886	... as they still have work to do (even an idle watcher will do..)
863	ev_run (my_loop, 0);	887	ev_run (my_loop, 0);
864	... jobs done or somebody called unloop. yeah!	888	... jobs done or somebody called break. yeah!
865		889
866	=item ev_break (loop, how)	890	=item ev_break (loop, how)
867		891
868	Can be used to make a call to C<ev_run> return early (but only after it	892	Can be used to make a call to C<ev_run> return early (but only after it
869	has processed all outstanding events). The C<how> argument must be either	893	has processed all outstanding events). The C<how> argument must be either
…		…
932	overhead for the actual polling but can deliver many events at once.	956	overhead for the actual polling but can deliver many events at once.
933		957
934	By setting a higher I<io collect interval> you allow libev to spend more	958	By setting a higher I<io collect interval> you allow libev to spend more
935	time collecting I/O events, so you can handle more events per iteration,	959	time collecting I/O events, so you can handle more events per iteration,
936	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	960	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
937	C<ev_timer>) will be not affected. Setting this to a non-null value will	961	C<ev_timer>) will not be affected. Setting this to a non-null value will
938	introduce an additional C<ev_sleep ()> call into most loop iterations. The	962	introduce an additional C<ev_sleep ()> call into most loop iterations. The
939	sleep time ensures that libev will not poll for I/O events more often then	963	sleep time ensures that libev will not poll for I/O events more often then
940	once per this interval, on average.	964	once per this interval, on average (as long as the host time resolution is
		965	good enough).
941		966
942	Likewise, by setting a higher I<timeout collect interval> you allow libev	967	Likewise, by setting a higher I<timeout collect interval> you allow libev
943	to spend more time collecting timeouts, at the expense of increased	968	to spend more time collecting timeouts, at the expense of increased
944	latency/jitter/inexactness (the watcher callback will be called	969	latency/jitter/inexactness (the watcher callback will be called
945	later). C<ev_io> watchers will not be affected. Setting this to a non-null	970	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
991	invoke the actual watchers inside another context (another thread etc.).	1016	invoke the actual watchers inside another context (another thread etc.).
992		1017
993	If you want to reset the callback, use C<ev_invoke_pending> as new	1018	If you want to reset the callback, use C<ev_invoke_pending> as new
994	callback.	1019	callback.
995		1020
996	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1021	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
997		1022
998	Sometimes you want to share the same loop between multiple threads. This	1023	Sometimes you want to share the same loop between multiple threads. This
999	can be done relatively simply by putting mutex_lock/unlock calls around	1024	can be done relatively simply by putting mutex_lock/unlock calls around
1000	each call to a libev function.	1025	each call to a libev function.
1001		1026
1002	However, C<ev_run> can run an indefinite time, so it is not feasible	1027	However, C<ev_run> can run an indefinite time, so it is not feasible
1003	to wait for it to return. One way around this is to wake up the event	1028	to wait for it to return. One way around this is to wake up the event
1004	loop via C<ev_break> and C<av_async_send>, another way is to set these	1029	loop via C<ev_break> and C<ev_async_send>, another way is to set these
1005	I<release> and I<acquire> callbacks on the loop.	1030	I<release> and I<acquire> callbacks on the loop.
1006		1031
1007	When set, then C<release> will be called just before the thread is	1032	When set, then C<release> will be called just before the thread is
1008	suspended waiting for new events, and C<acquire> is called just	1033	suspended waiting for new events, and C<acquire> is called just
1009	afterwards.	1034	afterwards.
…		…
1149		1174
1150	=item C<EV_PREPARE>	1175	=item C<EV_PREPARE>
1151		1176
1152	=item C<EV_CHECK>	1177	=item C<EV_CHECK>
1153		1178
1154	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1179	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1155	to gather new events, and all C<ev_check> watchers are invoked just after	1180	gather new events, and all C<ev_check> watchers are queued (not invoked)
1156	C<ev_run> has gathered them, but before it invokes any callbacks for any	1181	just after C<ev_run> has gathered them, but before it queues any callbacks
		1182	for any received events. That means C<ev_prepare> watchers are the last
		1183	watchers invoked before the event loop sleeps or polls for new events, and
		1184	C<ev_check> watchers will be invoked before any other watchers of the same
		1185	or lower priority within an event loop iteration.
		1186
1157	received events. Callbacks of both watcher types can start and stop as	1187	Callbacks of both watcher types can start and stop as many watchers as
1158	many watchers as they want, and all of them will be taken into account	1188	they want, and all of them will be taken into account (for example, a
1159	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1189	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1160	C<ev_run> from blocking).	1190	blocking).
1161		1191
1162	=item C<EV_EMBED>	1192	=item C<EV_EMBED>
1163		1193
1164	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1194	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1165		1195
…		…
1351	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1381	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1352	functions that do not need a watcher.	1382	functions that do not need a watcher.
1353		1383
1354	=back	1384	=back
1355		1385
1356	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1386	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1357		1387	OWN COMPOSITE WATCHERS> idioms.
1358	Each watcher has, by default, a member C<void *data> that you can change
1359	and read at any time: libev will completely ignore it. This can be used
1360	to associate arbitrary data with your watcher. If you need more data and
1361	don't want to allocate memory and store a pointer to it in that data
1362	member, you can also "subclass" the watcher type and provide your own
1363	data:
1364
1365	struct my_io
1366	{
1367	ev_io io;
1368	int otherfd;
1369	void *somedata;
1370	struct whatever *mostinteresting;
1371	};
1372
1373	...
1374	struct my_io w;
1375	ev_io_init (&w.io, my_cb, fd, EV_READ);
1376
1377	And since your callback will be called with a pointer to the watcher, you
1378	can cast it back to your own type:
1379
1380	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1381	{
1382	struct my_io *w = (struct my_io *)w_;
1383	...
1384	}
1385
1386	More interesting and less C-conformant ways of casting your callback type
1387	instead have been omitted.
1388
1389	Another common scenario is to use some data structure with multiple
1390	embedded watchers:
1391
1392	struct my_biggy
1393	{
1394	int some_data;
1395	ev_timer t1;
1396	ev_timer t2;
1397	}
1398
1399	In this case getting the pointer to C<my_biggy> is a bit more
1400	complicated: Either you store the address of your C<my_biggy> struct
1401	in the C<data> member of the watcher (for woozies), or you need to use
1402	some pointer arithmetic using C<offsetof> inside your watchers (for real
1403	programmers):
1404
1405	#include <stddef.h>
1406
1407	static void
1408	t1_cb (EV_P_ ev_timer *w, int revents)
1409	{
1410	struct my_biggy big = (struct my_biggy *)
1411	(((char *)w) - offsetof (struct my_biggy, t1));
1412	}
1413
1414	static void
1415	t2_cb (EV_P_ ev_timer *w, int revents)
1416	{
1417	struct my_biggy big = (struct my_biggy *)
1418	(((char *)w) - offsetof (struct my_biggy, t2));
1419	}
1420		1388
1421	=head2 WATCHER STATES	1389	=head2 WATCHER STATES
1422		1390
1423	There are various watcher states mentioned throughout this manual -	1391	There are various watcher states mentioned throughout this manual -
1424	active, pending and so on. In this section these states and the rules to	1392	active, pending and so on. In this section these states and the rules to
…		…
1427		1395
1428	=over 4	1396	=over 4
1429		1397
1430	=item initialiased	1398	=item initialiased
1431		1399
1432	Before a watcher can be registered with the event looop it has to be	1400	Before a watcher can be registered with the event loop it has to be
1433	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1401	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1434	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1402	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1435		1403
1436	In this state it is simply some block of memory that is suitable for use	1404	In this state it is simply some block of memory that is suitable for
1437	in an event loop. It can be moved around, freed, reused etc. at will.	1405	use in an event loop. It can be moved around, freed, reused etc. at
		1406	will - as long as you either keep the memory contents intact, or call
		1407	C<ev_TYPE_init> again.
1438		1408
1439	=item started/running/active	1409	=item started/running/active
1440		1410
1441	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1411	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1442	property of the event loop, and is actively waiting for events. While in	1412	property of the event loop, and is actively waiting for events. While in
…		…
1470	latter will clear any pending state the watcher might be in, regardless	1440	latter will clear any pending state the watcher might be in, regardless
1471	of whether it was active or not, so stopping a watcher explicitly before	1441	of whether it was active or not, so stopping a watcher explicitly before
1472	freeing it is often a good idea.	1442	freeing it is often a good idea.
1473		1443
1474	While stopped (and not pending) the watcher is essentially in the	1444	While stopped (and not pending) the watcher is essentially in the
1475	initialised state, that is it can be reused, moved, modified in any way	1445	initialised state, that is, it can be reused, moved, modified in any way
1476	you wish.	1446	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1447	it again).
1477		1448
1478	=back	1449	=back
1479		1450
1480	=head2 WATCHER PRIORITY MODELS	1451	=head2 WATCHER PRIORITY MODELS
1481		1452
…		…
1610	In general you can register as many read and/or write event watchers per	1581	In general you can register as many read and/or write event watchers per
1611	fd as you want (as long as you don't confuse yourself). Setting all file	1582	fd as you want (as long as you don't confuse yourself). Setting all file
1612	descriptors to non-blocking mode is also usually a good idea (but not	1583	descriptors to non-blocking mode is also usually a good idea (but not
1613	required if you know what you are doing).	1584	required if you know what you are doing).
1614		1585
1615	If you cannot use non-blocking mode, then force the use of a
1616	known-to-be-good backend (at the time of this writing, this includes only
1617	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1618	descriptors for which non-blocking operation makes no sense (such as
1619	files) - libev doesn't guarantee any specific behaviour in that case.
1620
1621	Another thing you have to watch out for is that it is quite easy to	1586	Another thing you have to watch out for is that it is quite easy to
1622	receive "spurious" readiness notifications, that is your callback might	1587	receive "spurious" readiness notifications, that is, your callback might
1623	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1588	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1624	because there is no data. Not only are some backends known to create a	1589	because there is no data. It is very easy to get into this situation even
1625	lot of those (for example Solaris ports), it is very easy to get into	1590	with a relatively standard program structure. Thus it is best to always
1626	this situation even with a relatively standard program structure. Thus	1591	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1627	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1628	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1592	preferable to a program hanging until some data arrives.
1629		1593
1630	If you cannot run the fd in non-blocking mode (for example you should	1594	If you cannot run the fd in non-blocking mode (for example you should
1631	not play around with an Xlib connection), then you have to separately	1595	not play around with an Xlib connection), then you have to separately
1632	re-test whether a file descriptor is really ready with a known-to-be good	1596	re-test whether a file descriptor is really ready with a known-to-be good
1633	interface such as poll (fortunately in our Xlib example, Xlib already	1597	interface such as poll (fortunately in the case of Xlib, it already does
1634	does this on its own, so its quite safe to use). Some people additionally	1598	this on its own, so its quite safe to use). Some people additionally
1635	use C<SIGALRM> and an interval timer, just to be sure you won't block	1599	use C<SIGALRM> and an interval timer, just to be sure you won't block
1636	indefinitely.	1600	indefinitely.
1637		1601
1638	But really, best use non-blocking mode.	1602	But really, best use non-blocking mode.
1639		1603
…		…
1667		1631
1668	There is no workaround possible except not registering events	1632	There is no workaround possible except not registering events
1669	for potentially C<dup ()>'ed file descriptors, or to resort to	1633	for potentially C<dup ()>'ed file descriptors, or to resort to
1670	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1634	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1671		1635
		1636	=head3 The special problem of files
		1637
		1638	Many people try to use C<select> (or libev) on file descriptors
		1639	representing files, and expect it to become ready when their program
		1640	doesn't block on disk accesses (which can take a long time on their own).
		1641
		1642	However, this cannot ever work in the "expected" way - you get a readiness
		1643	notification as soon as the kernel knows whether and how much data is
		1644	there, and in the case of open files, that's always the case, so you
		1645	always get a readiness notification instantly, and your read (or possibly
		1646	write) will still block on the disk I/O.
		1647
		1648	Another way to view it is that in the case of sockets, pipes, character
		1649	devices and so on, there is another party (the sender) that delivers data
		1650	on its own, but in the case of files, there is no such thing: the disk
		1651	will not send data on its own, simply because it doesn't know what you
		1652	wish to read - you would first have to request some data.
		1653
		1654	Since files are typically not-so-well supported by advanced notification
		1655	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1656	to files, even though you should not use it. The reason for this is
		1657	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1658	usually a tty, often a pipe, but also sometimes files or special devices
		1659	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1660	F</dev/urandom>), and even though the file might better be served with
		1661	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1662	it "just works" instead of freezing.
		1663
		1664	So avoid file descriptors pointing to files when you know it (e.g. use
		1665	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1666	when you rarely read from a file instead of from a socket, and want to
		1667	reuse the same code path.
		1668
1672	=head3 The special problem of fork	1669	=head3 The special problem of fork
1673		1670
1674	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1671	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1675	useless behaviour. Libev fully supports fork, but needs to be told about	1672	useless behaviour. Libev fully supports fork, but needs to be told about
1676	it in the child.	1673	it in the child if you want to continue to use it in the child.
1677		1674
1678	To support fork in your programs, you either have to call	1675	To support fork in your child processes, you have to call C<ev_loop_fork
1679	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1676	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1680	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1677	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1681	C<EVBACKEND_POLL>.
1682		1678
1683	=head3 The special problem of SIGPIPE	1679	=head3 The special problem of SIGPIPE
1684		1680
1685	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1681	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1686	when writing to a pipe whose other end has been closed, your program gets	1682	when writing to a pipe whose other end has been closed, your program gets
…		…
1784	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1780	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1785	monotonic clock option helps a lot here).	1781	monotonic clock option helps a lot here).
1786		1782
1787	The callback is guaranteed to be invoked only I<after> its timeout has	1783	The callback is guaranteed to be invoked only I<after> its timeout has
1788	passed (not I<at>, so on systems with very low-resolution clocks this	1784	passed (not I<at>, so on systems with very low-resolution clocks this
1789	might introduce a small delay). If multiple timers become ready during the	1785	might introduce a small delay, see "the special problem of being too
		1786	early", below). If multiple timers become ready during the same loop
1790	same loop iteration then the ones with earlier time-out values are invoked	1787	iteration then the ones with earlier time-out values are invoked before
1791	before ones of the same priority with later time-out values (but this is	1788	ones of the same priority with later time-out values (but this is no
1792	no longer true when a callback calls C<ev_run> recursively).	1789	longer true when a callback calls C<ev_run> recursively).
1793		1790
1794	=head3 Be smart about timeouts	1791	=head3 Be smart about timeouts
1795		1792
1796	Many real-world problems involve some kind of timeout, usually for error	1793	Many real-world problems involve some kind of timeout, usually for error
1797	recovery. A typical example is an HTTP request - if the other side hangs,	1794	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1872		1869
1873	In this case, it would be more efficient to leave the C<ev_timer> alone,	1870	In this case, it would be more efficient to leave the C<ev_timer> alone,
1874	but remember the time of last activity, and check for a real timeout only	1871	but remember the time of last activity, and check for a real timeout only
1875	within the callback:	1872	within the callback:
1876		1873
		1874	ev_tstamp timeout = 60.;
1877	ev_tstamp last_activity; // time of last activity	1875	ev_tstamp last_activity; // time of last activity
		1876	ev_timer timer;
1878		1877
1879	static void	1878	static void
1880	callback (EV_P_ ev_timer *w, int revents)	1879	callback (EV_P_ ev_timer *w, int revents)
1881	{	1880	{
1882	ev_tstamp now = ev_now (EV_A);	1881	// calculate when the timeout would happen
1883	ev_tstamp timeout = last_activity + 60.;	1882	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1884		1883
1885	// if last_activity + 60. is older than now, we did time out	1884	// if negative, it means we the timeout already occurred
1886	if (timeout < now)	1885	if (after < 0.)
1887	{	1886	{
1888	// timeout occurred, take action	1887	// timeout occurred, take action
1889	}	1888	}
1890	else	1889	else
1891	{	1890	{
1892	// callback was invoked, but there was some activity, re-arm	1891	// callback was invoked, but there was some recent
1893	// the watcher to fire in last_activity + 60, which is	1892	// activity. simply restart the timer to time out
1894	// guaranteed to be in the future, so "again" is positive:	1893	// after "after" seconds, which is the earliest time
1895	w->repeat = timeout - now;	1894	// the timeout can occur.
		1895	ev_timer_set (w, after, 0.);
1896	ev_timer_again (EV_A_ w);	1896	ev_timer_start (EV_A_ w);
1897	}	1897	}
1898	}	1898	}
1899		1899
1900	To summarise the callback: first calculate the real timeout (defined	1900	To summarise the callback: first calculate in how many seconds the
1901	as "60 seconds after the last activity"), then check if that time has	1901	timeout will occur (by calculating the absolute time when it would occur,
1902	been reached, which means something I<did>, in fact, time out. Otherwise	1902	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1903	the callback was invoked too early (C<timeout> is in the future), so	1903	(EV_A)> from that).
1904	re-schedule the timer to fire at that future time, to see if maybe we have
1905	a timeout then.
1906		1904
1907	Note how C<ev_timer_again> is used, taking advantage of the	1905	If this value is negative, then we are already past the timeout, i.e. we
1908	C<ev_timer_again> optimisation when the timer is already running.	1906	timed out, and need to do whatever is needed in this case.
		1907
		1908	Otherwise, we now the earliest time at which the timeout would trigger,
		1909	and simply start the timer with this timeout value.
		1910
		1911	In other words, each time the callback is invoked it will check whether
		1912	the timeout occurred. If not, it will simply reschedule itself to check
		1913	again at the earliest time it could time out. Rinse. Repeat.
1909		1914
1910	This scheme causes more callback invocations (about one every 60 seconds	1915	This scheme causes more callback invocations (about one every 60 seconds
1911	minus half the average time between activity), but virtually no calls to	1916	minus half the average time between activity), but virtually no calls to
1912	libev to change the timeout.	1917	libev to change the timeout.
1913		1918
1914	To start the timer, simply initialise the watcher and set C<last_activity>	1919	To start the machinery, simply initialise the watcher and set
1915	to the current time (meaning we just have some activity :), then call the	1920	C<last_activity> to the current time (meaning there was some activity just
1916	callback, which will "do the right thing" and start the timer:	1921	now), then call the callback, which will "do the right thing" and start
		1922	the timer:
1917		1923
		1924	last_activity = ev_now (EV_A);
1918	ev_init (timer, callback);	1925	ev_init (&timer, callback);
1919	last_activity = ev_now (loop);	1926	callback (EV_A_ &timer, 0);
1920	callback (loop, timer, EV_TIMER);
1921		1927
1922	And when there is some activity, simply store the current time in	1928	When there is some activity, simply store the current time in
1923	C<last_activity>, no libev calls at all:	1929	C<last_activity>, no libev calls at all:
1924		1930
		1931	if (activity detected)
1925	last_activity = ev_now (loop);	1932	last_activity = ev_now (EV_A);
		1933
		1934	When your timeout value changes, then the timeout can be changed by simply
		1935	providing a new value, stopping the timer and calling the callback, which
		1936	will again do the right thing (for example, time out immediately :).
		1937
		1938	timeout = new_value;
		1939	ev_timer_stop (EV_A_ &timer);
		1940	callback (EV_A_ &timer, 0);
1926		1941
1927	This technique is slightly more complex, but in most cases where the	1942	This technique is slightly more complex, but in most cases where the
1928	time-out is unlikely to be triggered, much more efficient.	1943	time-out is unlikely to be triggered, much more efficient.
1929
1930	Changing the timeout is trivial as well (if it isn't hard-coded in the
1931	callback :) - just change the timeout and invoke the callback, which will
1932	fix things for you.
1933		1944
1934	=item 4. Wee, just use a double-linked list for your timeouts.	1945	=item 4. Wee, just use a double-linked list for your timeouts.
1935		1946
1936	If there is not one request, but many thousands (millions...), all	1947	If there is not one request, but many thousands (millions...), all
1937	employing some kind of timeout with the same timeout value, then one can	1948	employing some kind of timeout with the same timeout value, then one can
…		…
1964	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1975	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1965	rather complicated, but extremely efficient, something that really pays	1976	rather complicated, but extremely efficient, something that really pays
1966	off after the first million or so of active timers, i.e. it's usually	1977	off after the first million or so of active timers, i.e. it's usually
1967	overkill :)	1978	overkill :)
1968		1979
		1980	=head3 The special problem of being too early
		1981
		1982	If you ask a timer to call your callback after three seconds, then
		1983	you expect it to be invoked after three seconds - but of course, this
		1984	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1985	guaranteed to any precision by libev - imagine somebody suspending the
		1986	process with a STOP signal for a few hours for example.
		1987
		1988	So, libev tries to invoke your callback as soon as possible I<after> the
		1989	delay has occurred, but cannot guarantee this.
		1990
		1991	A less obvious failure mode is calling your callback too early: many event
		1992	loops compare timestamps with a "elapsed delay >= requested delay", but
		1993	this can cause your callback to be invoked much earlier than you would
		1994	expect.
		1995
		1996	To see why, imagine a system with a clock that only offers full second
		1997	resolution (think windows if you can't come up with a broken enough OS
		1998	yourself). If you schedule a one-second timer at the time 500.9, then the
		1999	event loop will schedule your timeout to elapse at a system time of 500
		2000	(500.9 truncated to the resolution) + 1, or 501.
		2001
		2002	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2003	501" and invoke the callback 0.1s after it was started, even though a
		2004	one-second delay was requested - this is being "too early", despite best
		2005	intentions.
		2006
		2007	This is the reason why libev will never invoke the callback if the elapsed
		2008	delay equals the requested delay, but only when the elapsed delay is
		2009	larger than the requested delay. In the example above, libev would only invoke
		2010	the callback at system time 502, or 1.1s after the timer was started.
		2011
		2012	So, while libev cannot guarantee that your callback will be invoked
		2013	exactly when requested, it I<can> and I<does> guarantee that the requested
		2014	delay has actually elapsed, or in other words, it always errs on the "too
		2015	late" side of things.
		2016
1969	=head3 The special problem of time updates	2017	=head3 The special problem of time updates
1970		2018
1971	Establishing the current time is a costly operation (it usually takes at	2019	Establishing the current time is a costly operation (it usually takes
1972	least two system calls): EV therefore updates its idea of the current	2020	at least one system call): EV therefore updates its idea of the current
1973	time only before and after C<ev_run> collects new events, which causes a	2021	time only before and after C<ev_run> collects new events, which causes a
1974	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2022	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1975	lots of events in one iteration.	2023	lots of events in one iteration.
1976		2024
1977	The relative timeouts are calculated relative to the C<ev_now ()>	2025	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1983	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2031	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1984		2032
1985	If the event loop is suspended for a long time, you can also force an	2033	If the event loop is suspended for a long time, you can also force an
1986	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2034	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1987	()>.	2035	()>.
		2036
		2037	=head3 The special problem of unsynchronised clocks
		2038
		2039	Modern systems have a variety of clocks - libev itself uses the normal
		2040	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2041	jumps).
		2042
		2043	Neither of these clocks is synchronised with each other or any other clock
		2044	on the system, so C<ev_time ()> might return a considerably different time
		2045	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2046	a call to C<gettimeofday> might return a second count that is one higher
		2047	than a directly following call to C<time>.
		2048
		2049	The moral of this is to only compare libev-related timestamps with
		2050	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2051	a second or so.
		2052
		2053	One more problem arises due to this lack of synchronisation: if libev uses
		2054	the system monotonic clock and you compare timestamps from C<ev_time>
		2055	or C<ev_now> from when you started your timer and when your callback is
		2056	invoked, you will find that sometimes the callback is a bit "early".
		2057
		2058	This is because C<ev_timer>s work in real time, not wall clock time, so
		2059	libev makes sure your callback is not invoked before the delay happened,
		2060	I<measured according to the real time>, not the system clock.
		2061
		2062	If your timeouts are based on a physical timescale (e.g. "time out this
		2063	connection after 100 seconds") then this shouldn't bother you as it is
		2064	exactly the right behaviour.
		2065
		2066	If you want to compare wall clock/system timestamps to your timers, then
		2067	you need to use C<ev_periodic>s, as these are based on the wall clock
		2068	time, where your comparisons will always generate correct results.
1988		2069
1989	=head3 The special problems of suspended animation	2070	=head3 The special problems of suspended animation
1990		2071
1991	When you leave the server world it is quite customary to hit machines that	2072	When you leave the server world it is quite customary to hit machines that
1992	can suspend/hibernate - what happens to the clocks during such a suspend?	2073	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2036	keep up with the timer (because it takes longer than those 10 seconds to	2117	keep up with the timer (because it takes longer than those 10 seconds to
2037	do stuff) the timer will not fire more than once per event loop iteration.	2118	do stuff) the timer will not fire more than once per event loop iteration.
2038		2119
2039	=item ev_timer_again (loop, ev_timer *)	2120	=item ev_timer_again (loop, ev_timer *)
2040		2121
2041	This will act as if the timer timed out and restart it again if it is	2122	This will act as if the timer timed out, and restarts it again if it is
2042	repeating. The exact semantics are:	2123	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2124	timeout to the C<repeat> value and calling C<ev_timer_start>.
2043		2125
		2126	The exact semantics are as in the following rules, all of which will be
		2127	applied to the watcher:
		2128
		2129	=over 4
		2130
2044	If the timer is pending, its pending status is cleared.	2131	=item If the timer is pending, the pending status is always cleared.
2045		2132
2046	If the timer is started but non-repeating, stop it (as if it timed out).	2133	=item If the timer is started but non-repeating, stop it (as if it timed
		2134	out, without invoking it).
2047		2135
2048	If the timer is repeating, either start it if necessary (with the	2136	=item If the timer is repeating, make the C<repeat> value the new timeout
2049	C<repeat> value), or reset the running timer to the C<repeat> value.	2137	and start the timer, if necessary.
		2138
		2139	=back
2050		2140
2051	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2141	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
2052	usage example.	2142	usage example.
2053		2143
2054	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2144	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
…		…
2176		2266
2177	Another way to think about it (for the mathematically inclined) is that	2267	Another way to think about it (for the mathematically inclined) is that
2178	C<ev_periodic> will try to run the callback in this mode at the next possible	2268	C<ev_periodic> will try to run the callback in this mode at the next possible
2179	time where C<time = offset (mod interval)>, regardless of any time jumps.	2269	time where C<time = offset (mod interval)>, regardless of any time jumps.
2180		2270
2181	For numerical stability it is preferable that the C<offset> value is near	2271	The C<interval> I<MUST> be positive, and for numerical stability, the
2182	C<ev_now ()> (the current time), but there is no range requirement for	2272	interval value should be higher than C<1/8192> (which is around 100
2183	this value, and in fact is often specified as zero.	2273	microseconds) and C<offset> should be higher than C<0> and should have
		2274	at most a similar magnitude as the current time (say, within a factor of
		2275	ten). Typical values for offset are, in fact, C<0> or something between
		2276	C<0> and C<interval>, which is also the recommended range.
2184		2277
2185	Note also that there is an upper limit to how often a timer can fire (CPU	2278	Note also that there is an upper limit to how often a timer can fire (CPU
2186	speed for example), so if C<interval> is very small then timing stability	2279	speed for example), so if C<interval> is very small then timing stability
2187	will of course deteriorate. Libev itself tries to be exact to be about one	2280	will of course deteriorate. Libev itself tries to be exact to be about one
2188	millisecond (if the OS supports it and the machine is fast enough).	2281	millisecond (if the OS supports it and the machine is fast enough).
…		…
2331	=head3 The special problem of inheritance over fork/execve/pthread_create	2424	=head3 The special problem of inheritance over fork/execve/pthread_create
2332		2425
2333	Both the signal mask (C<sigprocmask>) and the signal disposition	2426	Both the signal mask (C<sigprocmask>) and the signal disposition
2334	(C<sigaction>) are unspecified after starting a signal watcher (and after	2427	(C<sigaction>) are unspecified after starting a signal watcher (and after
2335	stopping it again), that is, libev might or might not block the signal,	2428	stopping it again), that is, libev might or might not block the signal,
2336	and might or might not set or restore the installed signal handler.	2429	and might or might not set or restore the installed signal handler (but
		2430	see C<EVFLAG_NOSIGMASK>).
2337		2431
2338	While this does not matter for the signal disposition (libev never	2432	While this does not matter for the signal disposition (libev never
2339	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2433	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2340	C<execve>), this matters for the signal mask: many programs do not expect	2434	C<execve>), this matters for the signal mask: many programs do not expect
2341	certain signals to be blocked.	2435	certain signals to be blocked.
…		…
3212	atexit (program_exits);	3306	atexit (program_exits);
3213		3307
3214		3308
3215	=head2 C<ev_async> - how to wake up an event loop	3309	=head2 C<ev_async> - how to wake up an event loop
3216		3310
3217	In general, you cannot use an C<ev_run> from multiple threads or other	3311	In general, you cannot use an C<ev_loop> from multiple threads or other
3218	asynchronous sources such as signal handlers (as opposed to multiple event	3312	asynchronous sources such as signal handlers (as opposed to multiple event
3219	loops - those are of course safe to use in different threads).	3313	loops - those are of course safe to use in different threads).
3220		3314
3221	Sometimes, however, you need to wake up an event loop you do not control,	3315	Sometimes, however, you need to wake up an event loop you do not control,
3222	for example because it belongs to another thread. This is what C<ev_async>	3316	for example because it belongs to another thread. This is what C<ev_async>
…		…
3224	it by calling C<ev_async_send>, which is thread- and signal safe.	3318	it by calling C<ev_async_send>, which is thread- and signal safe.
3225		3319
3226	This functionality is very similar to C<ev_signal> watchers, as signals,	3320	This functionality is very similar to C<ev_signal> watchers, as signals,
3227	too, are asynchronous in nature, and signals, too, will be compressed	3321	too, are asynchronous in nature, and signals, too, will be compressed
3228	(i.e. the number of callback invocations may be less than the number of	3322	(i.e. the number of callback invocations may be less than the number of
3229	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3323	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3230	of "global async watchers" by using a watcher on an otherwise unused	3324	of "global async watchers" by using a watcher on an otherwise unused
3231	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3325	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3232	even without knowing which loop owns the signal.	3326	even without knowing which loop owns the signal.
3233
3234	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3235	just the default loop.
3236		3327
3237	=head3 Queueing	3328	=head3 Queueing
3238		3329
3239	C<ev_async> does not support queueing of data in any way. The reason	3330	C<ev_async> does not support queueing of data in any way. The reason
3240	is that the author does not know of a simple (or any) algorithm for a	3331	is that the author does not know of a simple (or any) algorithm for a
…		…
3332	trust me.	3423	trust me.
3333		3424
3334	=item ev_async_send (loop, ev_async *)	3425	=item ev_async_send (loop, ev_async *)
3335		3426
3336	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3427	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3337	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3428	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3429	returns.
		3430
3338	C<ev_feed_event>, this call is safe to do from other threads, signal or	3431	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3339	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3432	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3340	section below on what exactly this means).	3433	embedding section below on what exactly this means).
3341		3434
3342	Note that, as with other watchers in libev, multiple events might get	3435	Note that, as with other watchers in libev, multiple events might get
3343	compressed into a single callback invocation (another way to look at this	3436	compressed into a single callback invocation (another way to look at
3344	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3437	this is that C<ev_async> watchers are level-triggered: they are set on
3345	reset when the event loop detects that).	3438	C<ev_async_send>, reset when the event loop detects that).
3346		3439
3347	This call incurs the overhead of a system call only once per event loop	3440	This call incurs the overhead of at most one extra system call per event
3348	iteration, so while the overhead might be noticeable, it doesn't apply to	3441	loop iteration, if the event loop is blocked, and no syscall at all if
3349	repeated calls to C<ev_async_send> for the same event loop.	3442	the event loop (or your program) is processing events. That means that
		3443	repeated calls are basically free (there is no need to avoid calls for
		3444	performance reasons) and that the overhead becomes smaller (typically
		3445	zero) under load.
3350		3446
3351	=item bool = ev_async_pending (ev_async *)	3447	=item bool = ev_async_pending (ev_async *)
3352		3448
3353	Returns a non-zero value when C<ev_async_send> has been called on the	3449	Returns a non-zero value when C<ev_async_send> has been called on the
3354	watcher but the event has not yet been processed (or even noted) by the	3450	watcher but the event has not yet been processed (or even noted) by the
…		…
3409	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3505	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3410		3506
3411	=item ev_feed_fd_event (loop, int fd, int revents)	3507	=item ev_feed_fd_event (loop, int fd, int revents)
3412		3508
3413	Feed an event on the given fd, as if a file descriptor backend detected	3509	Feed an event on the given fd, as if a file descriptor backend detected
3414	the given events it.	3510	the given events.
3415		3511
3416	=item ev_feed_signal_event (loop, int signum)	3512	=item ev_feed_signal_event (loop, int signum)
3417		3513
3418	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3514	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3419	which is async-safe.	3515	which is async-safe.
…		…
3425		3521
3426	This section explains some common idioms that are not immediately	3522	This section explains some common idioms that are not immediately
3427	obvious. Note that examples are sprinkled over the whole manual, and this	3523	obvious. Note that examples are sprinkled over the whole manual, and this
3428	section only contains stuff that wouldn't fit anywhere else.	3524	section only contains stuff that wouldn't fit anywhere else.
3429		3525
3430	=over 4	3526	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3431		3527
3432	=item Model/nested event loop invocations and exit conditions.	3528	Each watcher has, by default, a C<void *data> member that you can read
		3529	or modify at any time: libev will completely ignore it. This can be used
		3530	to associate arbitrary data with your watcher. If you need more data and
		3531	don't want to allocate memory separately and store a pointer to it in that
		3532	data member, you can also "subclass" the watcher type and provide your own
		3533	data:
		3534
		3535	struct my_io
		3536	{
		3537	ev_io io;
		3538	int otherfd;
		3539	void *somedata;
		3540	struct whatever *mostinteresting;
		3541	};
		3542
		3543	...
		3544	struct my_io w;
		3545	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3546
		3547	And since your callback will be called with a pointer to the watcher, you
		3548	can cast it back to your own type:
		3549
		3550	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3551	{
		3552	struct my_io *w = (struct my_io *)w_;
		3553	...
		3554	}
		3555
		3556	More interesting and less C-conformant ways of casting your callback
		3557	function type instead have been omitted.
		3558
		3559	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3560
		3561	Another common scenario is to use some data structure with multiple
		3562	embedded watchers, in effect creating your own watcher that combines
		3563	multiple libev event sources into one "super-watcher":
		3564
		3565	struct my_biggy
		3566	{
		3567	int some_data;
		3568	ev_timer t1;
		3569	ev_timer t2;
		3570	}
		3571
		3572	In this case getting the pointer to C<my_biggy> is a bit more
		3573	complicated: Either you store the address of your C<my_biggy> struct in
		3574	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3575	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3576	real programmers):
		3577
		3578	#include <stddef.h>
		3579
		3580	static void
		3581	t1_cb (EV_P_ ev_timer *w, int revents)
		3582	{
		3583	struct my_biggy big = (struct my_biggy *)
		3584	(((char *)w) - offsetof (struct my_biggy, t1));
		3585	}
		3586
		3587	static void
		3588	t2_cb (EV_P_ ev_timer *w, int revents)
		3589	{
		3590	struct my_biggy big = (struct my_biggy *)
		3591	(((char *)w) - offsetof (struct my_biggy, t2));
		3592	}
		3593
		3594	=head2 AVOIDING FINISHING BEFORE RETURNING
		3595
		3596	Often you have structures like this in event-based programs:
		3597
		3598	callback ()
		3599	{
		3600	free (request);
		3601	}
		3602
		3603	request = start_new_request (..., callback);
		3604
		3605	The intent is to start some "lengthy" operation. The C<request> could be
		3606	used to cancel the operation, or do other things with it.
		3607
		3608	It's not uncommon to have code paths in C<start_new_request> that
		3609	immediately invoke the callback, for example, to report errors. Or you add
		3610	some caching layer that finds that it can skip the lengthy aspects of the
		3611	operation and simply invoke the callback with the result.
		3612
		3613	The problem here is that this will happen I<before> C<start_new_request>
		3614	has returned, so C<request> is not set.
		3615
		3616	Even if you pass the request by some safer means to the callback, you
		3617	might want to do something to the request after starting it, such as
		3618	canceling it, which probably isn't working so well when the callback has
		3619	already been invoked.
		3620
		3621	A common way around all these issues is to make sure that
		3622	C<start_new_request> I<always> returns before the callback is invoked. If
		3623	C<start_new_request> immediately knows the result, it can artificially
		3624	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3625	for example, or more sneakily, by reusing an existing (stopped) watcher
		3626	and pushing it into the pending queue:
		3627
		3628	ev_set_cb (watcher, callback);
		3629	ev_feed_event (EV_A_ watcher, 0);
		3630
		3631	This way, C<start_new_request> can safely return before the callback is
		3632	invoked, while not delaying callback invocation too much.
		3633
		3634	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3433		3635
3434	Often (especially in GUI toolkits) there are places where you have	3636	Often (especially in GUI toolkits) there are places where you have
3435	I<modal> interaction, which is most easily implemented by recursively	3637	I<modal> interaction, which is most easily implemented by recursively
3436	invoking C<ev_run>.	3638	invoking C<ev_run>.
3437		3639
…		…
3449	int exit_main_loop = 0;	3651	int exit_main_loop = 0;
3450		3652
3451	while (!exit_main_loop)	3653	while (!exit_main_loop)
3452	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3654	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3453		3655
3454	// in a model watcher	3656	// in a modal watcher
3455	int exit_nested_loop = 0;	3657	int exit_nested_loop = 0;
3456		3658
3457	while (!exit_nested_loop)	3659	while (!exit_nested_loop)
3458	ev_run (EV_A_ EVRUN_ONCE);	3660	ev_run (EV_A_ EVRUN_ONCE);
3459		3661
…		…
3466	exit_main_loop = 1;	3668	exit_main_loop = 1;
3467		3669
3468	// exit both	3670	// exit both
3469	exit_main_loop = exit_nested_loop = 1;	3671	exit_main_loop = exit_nested_loop = 1;
3470		3672
3471	=back	3673	=head2 THREAD LOCKING EXAMPLE
		3674
		3675	Here is a fictitious example of how to run an event loop in a different
		3676	thread from where callbacks are being invoked and watchers are
		3677	created/added/removed.
		3678
		3679	For a real-world example, see the C<EV::Loop::Async> perl module,
		3680	which uses exactly this technique (which is suited for many high-level
		3681	languages).
		3682
		3683	The example uses a pthread mutex to protect the loop data, a condition
		3684	variable to wait for callback invocations, an async watcher to notify the
		3685	event loop thread and an unspecified mechanism to wake up the main thread.
		3686
		3687	First, you need to associate some data with the event loop:
		3688
		3689	typedef struct {
		3690	mutex_t lock; /* global loop lock */
		3691	ev_async async_w;
		3692	thread_t tid;
		3693	cond_t invoke_cv;
		3694	} userdata;
		3695
		3696	void prepare_loop (EV_P)
		3697	{
		3698	// for simplicity, we use a static userdata struct.
		3699	static userdata u;
		3700
		3701	ev_async_init (&u->async_w, async_cb);
		3702	ev_async_start (EV_A_ &u->async_w);
		3703
		3704	pthread_mutex_init (&u->lock, 0);
		3705	pthread_cond_init (&u->invoke_cv, 0);
		3706
		3707	// now associate this with the loop
		3708	ev_set_userdata (EV_A_ u);
		3709	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3710	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3711
		3712	// then create the thread running ev_run
		3713	pthread_create (&u->tid, 0, l_run, EV_A);
		3714	}
		3715
		3716	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3717	solely to wake up the event loop so it takes notice of any new watchers
		3718	that might have been added:
		3719
		3720	static void
		3721	async_cb (EV_P_ ev_async *w, int revents)
		3722	{
		3723	// just used for the side effects
		3724	}
		3725
		3726	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3727	protecting the loop data, respectively.
		3728
		3729	static void
		3730	l_release (EV_P)
		3731	{
		3732	userdata *u = ev_userdata (EV_A);
		3733	pthread_mutex_unlock (&u->lock);
		3734	}
		3735
		3736	static void
		3737	l_acquire (EV_P)
		3738	{
		3739	userdata *u = ev_userdata (EV_A);
		3740	pthread_mutex_lock (&u->lock);
		3741	}
		3742
		3743	The event loop thread first acquires the mutex, and then jumps straight
		3744	into C<ev_run>:
		3745
		3746	void *
		3747	l_run (void *thr_arg)
		3748	{
		3749	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3750
		3751	l_acquire (EV_A);
		3752	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3753	ev_run (EV_A_ 0);
		3754	l_release (EV_A);
		3755
		3756	return 0;
		3757	}
		3758
		3759	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3760	signal the main thread via some unspecified mechanism (signals? pipe
		3761	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3762	have been called (in a while loop because a) spurious wakeups are possible
		3763	and b) skipping inter-thread-communication when there are no pending
		3764	watchers is very beneficial):
		3765
		3766	static void
		3767	l_invoke (EV_P)
		3768	{
		3769	userdata *u = ev_userdata (EV_A);
		3770
		3771	while (ev_pending_count (EV_A))
		3772	{
		3773	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3774	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3775	}
		3776	}
		3777
		3778	Now, whenever the main thread gets told to invoke pending watchers, it
		3779	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3780	thread to continue:
		3781
		3782	static void
		3783	real_invoke_pending (EV_P)
		3784	{
		3785	userdata *u = ev_userdata (EV_A);
		3786
		3787	pthread_mutex_lock (&u->lock);
		3788	ev_invoke_pending (EV_A);
		3789	pthread_cond_signal (&u->invoke_cv);
		3790	pthread_mutex_unlock (&u->lock);
		3791	}
		3792
		3793	Whenever you want to start/stop a watcher or do other modifications to an
		3794	event loop, you will now have to lock:
		3795
		3796	ev_timer timeout_watcher;
		3797	userdata *u = ev_userdata (EV_A);
		3798
		3799	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3800
		3801	pthread_mutex_lock (&u->lock);
		3802	ev_timer_start (EV_A_ &timeout_watcher);
		3803	ev_async_send (EV_A_ &u->async_w);
		3804	pthread_mutex_unlock (&u->lock);
		3805
		3806	Note that sending the C<ev_async> watcher is required because otherwise
		3807	an event loop currently blocking in the kernel will have no knowledge
		3808	about the newly added timer. By waking up the loop it will pick up any new
		3809	watchers in the next event loop iteration.
		3810
		3811	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3812
		3813	While the overhead of a callback that e.g. schedules a thread is small, it
		3814	is still an overhead. If you embed libev, and your main usage is with some
		3815	kind of threads or coroutines, you might want to customise libev so that
		3816	doesn't need callbacks anymore.
		3817
		3818	Imagine you have coroutines that you can switch to using a function
		3819	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3820	and that due to some magic, the currently active coroutine is stored in a
		3821	global called C<current_coro>. Then you can build your own "wait for libev
		3822	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3823	the differing C<;> conventions):
		3824
		3825	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3826	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3827
		3828	That means instead of having a C callback function, you store the
		3829	coroutine to switch to in each watcher, and instead of having libev call
		3830	your callback, you instead have it switch to that coroutine.
		3831
		3832	A coroutine might now wait for an event with a function called
		3833	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3834	matter when, or whether the watcher is active or not when this function is
		3835	called):
		3836
		3837	void
		3838	wait_for_event (ev_watcher *w)
		3839	{
		3840	ev_cb_set (w) = current_coro;
		3841	switch_to (libev_coro);
		3842	}
		3843
		3844	That basically suspends the coroutine inside C<wait_for_event> and
		3845	continues the libev coroutine, which, when appropriate, switches back to
		3846	this or any other coroutine.
		3847
		3848	You can do similar tricks if you have, say, threads with an event queue -
		3849	instead of storing a coroutine, you store the queue object and instead of
		3850	switching to a coroutine, you push the watcher onto the queue and notify
		3851	any waiters.
		3852
		3853	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3854	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3855
		3856	// my_ev.h
		3857	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3858	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3859	#include "../libev/ev.h"
		3860
		3861	// my_ev.c
		3862	#define EV_H "my_ev.h"
		3863	#include "../libev/ev.c"
		3864
		3865	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3866	F<my_ev.c> into your project. When properly specifying include paths, you
		3867	can even use F<ev.h> as header file name directly.
3472		3868
3473		3869
3474	=head1 LIBEVENT EMULATION	3870	=head1 LIBEVENT EMULATION
3475		3871
3476	Libev offers a compatibility emulation layer for libevent. It cannot	3872	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3505	to use the libev header file and library.	3901	to use the libev header file and library.
3506		3902
3507	=back	3903	=back
3508		3904
3509	=head1 C++ SUPPORT	3905	=head1 C++ SUPPORT
		3906
		3907	=head2 C API
		3908
		3909	The normal C API should work fine when used from C++: both ev.h and the
		3910	libev sources can be compiled as C++. Therefore, code that uses the C API
		3911	will work fine.
		3912
		3913	Proper exception specifications might have to be added to callbacks passed
		3914	to libev: exceptions may be thrown only from watcher callbacks, all
		3915	other callbacks (allocator, syserr, loop acquire/release and periodioc
		3916	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3917	()> specification. If you have code that needs to be compiled as both C
		3918	and C++ you can use the C<EV_THROW> macro for this:
		3919
		3920	static void
		3921	fatal_error (const char *msg) EV_THROW
		3922	{
		3923	perror (msg);
		3924	abort ();
		3925	}
		3926
		3927	...
		3928	ev_set_syserr_cb (fatal_error);
		3929
		3930	The only API functions that can currently throw exceptions are C<ev_run>,
		3931	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3932	because it runs cleanup watchers).
		3933
		3934	Throwing exceptions in watcher callbacks is only supported if libev itself
		3935	is compiled with a C++ compiler or your C and C++ environments allow
		3936	throwing exceptions through C libraries (most do).
		3937
		3938	=head2 C++ API
3510		3939
3511	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3940	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3512	you to use some convenience methods to start/stop watchers and also change	3941	you to use some convenience methods to start/stop watchers and also change
3513	the callback model to a model using method callbacks on objects.	3942	the callback model to a model using method callbacks on objects.
3514		3943
…		…
3530	with C<operator ()> can be used as callbacks. Other types should be easy	3959	with C<operator ()> can be used as callbacks. Other types should be easy
3531	to add as long as they only need one additional pointer for context. If	3960	to add as long as they only need one additional pointer for context. If
3532	you need support for other types of functors please contact the author	3961	you need support for other types of functors please contact the author
3533	(preferably after implementing it).	3962	(preferably after implementing it).
3534		3963
		3964	For all this to work, your C++ compiler either has to use the same calling
		3965	conventions as your C compiler (for static member functions), or you have
		3966	to embed libev and compile libev itself as C++.
		3967
3535	Here is a list of things available in the C<ev> namespace:	3968	Here is a list of things available in the C<ev> namespace:
3536		3969
3537	=over 4	3970	=over 4
3538		3971
3539	=item C<ev::READ>, C<ev::WRITE> etc.	3972	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3548	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	3981	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3549		3982
3550	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	3983	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3551	the same name in the C<ev> namespace, with the exception of C<ev_signal>	3984	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3552	which is called C<ev::sig> to avoid clashes with the C<signal> macro	3985	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3553	defines by many implementations.	3986	defined by many implementations.
3554		3987
3555	All of those classes have these methods:	3988	All of those classes have these methods:
3556		3989
3557	=over 4	3990	=over 4
3558		3991
…		…
3691	watchers in the constructor.	4124	watchers in the constructor.
3692		4125
3693	class myclass	4126	class myclass
3694	{	4127	{
3695	ev::io io ; void io_cb (ev::io &w, int revents);	4128	ev::io io ; void io_cb (ev::io &w, int revents);
3696	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4129	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3697	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4130	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3698		4131
3699	myclass (int fd)	4132	myclass (int fd)
3700	{	4133	{
3701	io .set <myclass, &myclass::io_cb > (this);	4134	io .set <myclass, &myclass::io_cb > (this);
…		…
3752	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4185	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3753		4186
3754	=item D	4187	=item D
3755		4188
3756	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4189	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3757	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4190	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3758		4191
3759	=item Ocaml	4192	=item Ocaml
3760		4193
3761	Erkki Seppala has written Ocaml bindings for libev, to be found at	4194	Erkki Seppala has written Ocaml bindings for libev, to be found at
3762	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4195	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3810	suitable for use with C<EV_A>.	4243	suitable for use with C<EV_A>.
3811		4244
3812	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4245	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3813		4246
3814	Similar to the other two macros, this gives you the value of the default	4247	Similar to the other two macros, this gives you the value of the default
3815	loop, if multiple loops are supported ("ev loop default").	4248	loop, if multiple loops are supported ("ev loop default"). The default loop
		4249	will be initialised if it isn't already initialised.
		4250
		4251	For non-multiplicity builds, these macros do nothing, so you always have
		4252	to initialise the loop somewhere.
3816		4253
3817	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4254	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3818		4255
3819	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4256	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3820	default loop has been initialised (C<UC> == unchecked). Their behaviour	4257	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3965	supported). It will also not define any of the structs usually found in	4402	supported). It will also not define any of the structs usually found in
3966	F<event.h> that are not directly supported by the libev core alone.	4403	F<event.h> that are not directly supported by the libev core alone.
3967		4404
3968	In standalone mode, libev will still try to automatically deduce the	4405	In standalone mode, libev will still try to automatically deduce the
3969	configuration, but has to be more conservative.	4406	configuration, but has to be more conservative.
		4407
		4408	=item EV_USE_FLOOR
		4409
		4410	If defined to be C<1>, libev will use the C<floor ()> function for its
		4411	periodic reschedule calculations, otherwise libev will fall back on a
		4412	portable (slower) implementation. If you enable this, you usually have to
		4413	link against libm or something equivalent. Enabling this when the C<floor>
		4414	function is not available will fail, so the safe default is to not enable
		4415	this.
3970		4416
3971	=item EV_USE_MONOTONIC	4417	=item EV_USE_MONOTONIC
3972		4418
3973	If defined to be C<1>, libev will try to detect the availability of the	4419	If defined to be C<1>, libev will try to detect the availability of the
3974	monotonic clock option at both compile time and runtime. Otherwise no	4420	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4104	If defined to be C<1>, libev will compile in support for the Linux inotify	4550	If defined to be C<1>, libev will compile in support for the Linux inotify
4105	interface to speed up C<ev_stat> watchers. Its actual availability will	4551	interface to speed up C<ev_stat> watchers. Its actual availability will
4106	be detected at runtime. If undefined, it will be enabled if the headers	4552	be detected at runtime. If undefined, it will be enabled if the headers
4107	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4553	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4108		4554
		4555	=item EV_NO_SMP
		4556
		4557	If defined to be C<1>, libev will assume that memory is always coherent
		4558	between threads, that is, threads can be used, but threads never run on
		4559	different cpus (or different cpu cores). This reduces dependencies
		4560	and makes libev faster.
		4561
		4562	=item EV_NO_THREADS
		4563
		4564	If defined to be C<1>, libev will assume that it will never be called
		4565	from different threads, which is a stronger assumption than C<EV_NO_SMP>,
		4566	above. This reduces dependencies and makes libev faster.
		4567
4109	=item EV_ATOMIC_T	4568	=item EV_ATOMIC_T
4110		4569
4111	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4570	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4112	access is atomic with respect to other threads or signal contexts. No such	4571	access is atomic and serialised with respect to other threads or signal
4113	type is easily found in the C language, so you can provide your own type	4572	contexts. No such type is easily found in the C language, so you can
4114	that you know is safe for your purposes. It is used both for signal handler "locking"	4573	provide your own type that you know is safe for your purposes. It is used
4115	as well as for signal and thread safety in C<ev_async> watchers.	4574	both for signal handler "locking" as well as for signal and thread safety
		4575	in C<ev_async> watchers.
4116		4576
4117	In the absence of this define, libev will use C<sig_atomic_t volatile>	4577	In the absence of this define, libev will use C<sig_atomic_t volatile>
4118	(from F<signal.h>), which is usually good enough on most platforms.	4578	(from F<signal.h>), which is usually good enough on most platforms,
		4579	although strictly speaking using a type that also implies a memory fence
		4580	is required.
4119		4581
4120	=item EV_H (h)	4582	=item EV_H (h)
4121		4583
4122	The name of the F<ev.h> header file used to include it. The default if	4584	The name of the F<ev.h> header file used to include it. The default if
4123	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4585	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
4147	will have the C<struct ev_loop *> as first argument, and you can create	4609	will have the C<struct ev_loop *> as first argument, and you can create
4148	additional independent event loops. Otherwise there will be no support	4610	additional independent event loops. Otherwise there will be no support
4149	for multiple event loops and there is no first event loop pointer	4611	for multiple event loops and there is no first event loop pointer
4150	argument. Instead, all functions act on the single default loop.	4612	argument. Instead, all functions act on the single default loop.
4151		4613
		4614	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4615	default loop when multiplicity is switched off - you always have to
		4616	initialise the loop manually in this case.
		4617
4152	=item EV_MINPRI	4618	=item EV_MINPRI
4153		4619
4154	=item EV_MAXPRI	4620	=item EV_MAXPRI
4155		4621
4156	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4622	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4192	#define EV_USE_POLL 1	4658	#define EV_USE_POLL 1
4193	#define EV_CHILD_ENABLE 1	4659	#define EV_CHILD_ENABLE 1
4194	#define EV_ASYNC_ENABLE 1	4660	#define EV_ASYNC_ENABLE 1
4195		4661
4196	The actual value is a bitset, it can be a combination of the following	4662	The actual value is a bitset, it can be a combination of the following
4197	values:	4663	values (by default, all of these are enabled):
4198		4664
4199	=over 4	4665	=over 4
4200		4666
4201	=item C<1> - faster/larger code	4667	=item C<1> - faster/larger code
4202		4668
…		…
4206	code size by roughly 30% on amd64).	4672	code size by roughly 30% on amd64).
4207		4673
4208	When optimising for size, use of compiler flags such as C<-Os> with	4674	When optimising for size, use of compiler flags such as C<-Os> with
4209	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4675	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4210	assertions.	4676	assertions.
		4677
		4678	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4679	(e.g. gcc with C<-Os>).
4211		4680
4212	=item C<2> - faster/larger data structures	4681	=item C<2> - faster/larger data structures
4213		4682
4214	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4683	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4215	hash table sizes and so on. This will usually further increase code size	4684	hash table sizes and so on. This will usually further increase code size
4216	and can additionally have an effect on the size of data structures at	4685	and can additionally have an effect on the size of data structures at
4217	runtime.	4686	runtime.
4218		4687
		4688	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4689	(e.g. gcc with C<-Os>).
		4690
4219	=item C<4> - full API configuration	4691	=item C<4> - full API configuration
4220		4692
4221	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4693	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4222	enables multiplicity (C<EV_MULTIPLICITY>=1).	4694	enables multiplicity (C<EV_MULTIPLICITY>=1).
4223		4695
…		…
4253		4725
4254	With an intelligent-enough linker (gcc+binutils are intelligent enough	4726	With an intelligent-enough linker (gcc+binutils are intelligent enough
4255	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4727	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4256	your program might be left out as well - a binary starting a timer and an	4728	your program might be left out as well - a binary starting a timer and an
4257	I/O watcher then might come out at only 5Kb.	4729	I/O watcher then might come out at only 5Kb.
		4730
		4731	=item EV_API_STATIC
		4732
		4733	If this symbol is defined (by default it is not), then all identifiers
		4734	will have static linkage. This means that libev will not export any
		4735	identifiers, and you cannot link against libev anymore. This can be useful
		4736	when you embed libev, only want to use libev functions in a single file,
		4737	and do not want its identifiers to be visible.
		4738
		4739	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4740	wants to use libev.
		4741
		4742	This option only works when libev is compiled with a C compiler, as C++
		4743	doesn't support the required declaration syntax.
4258		4744
4259	=item EV_AVOID_STDIO	4745	=item EV_AVOID_STDIO
4260		4746
4261	If this is set to C<1> at compiletime, then libev will avoid using stdio	4747	If this is set to C<1> at compiletime, then libev will avoid using stdio
4262	functions (printf, scanf, perror etc.). This will increase the code size	4748	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4406	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4892	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4407		4893
4408	#include "ev_cpp.h"	4894	#include "ev_cpp.h"
4409	#include "ev.c"	4895	#include "ev.c"
4410		4896
4411	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4897	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4412		4898
4413	=head2 THREADS AND COROUTINES	4899	=head2 THREADS AND COROUTINES
4414		4900
4415	=head3 THREADS	4901	=head3 THREADS
4416		4902
…		…
4467	default loop and triggering an C<ev_async> watcher from the default loop	4953	default loop and triggering an C<ev_async> watcher from the default loop
4468	watcher callback into the event loop interested in the signal.	4954	watcher callback into the event loop interested in the signal.
4469		4955
4470	=back	4956	=back
4471		4957
4472	=head4 THREAD LOCKING EXAMPLE	4958	See also L<THREAD LOCKING EXAMPLE>.
4473
4474	Here is a fictitious example of how to run an event loop in a different
4475	thread than where callbacks are being invoked and watchers are
4476	created/added/removed.
4477
4478	For a real-world example, see the C<EV::Loop::Async> perl module,
4479	which uses exactly this technique (which is suited for many high-level
4480	languages).
4481
4482	The example uses a pthread mutex to protect the loop data, a condition
4483	variable to wait for callback invocations, an async watcher to notify the
4484	event loop thread and an unspecified mechanism to wake up the main thread.
4485
4486	First, you need to associate some data with the event loop:
4487
4488	typedef struct {
4489	mutex_t lock; /* global loop lock */
4490	ev_async async_w;
4491	thread_t tid;
4492	cond_t invoke_cv;
4493	} userdata;
4494
4495	void prepare_loop (EV_P)
4496	{
4497	// for simplicity, we use a static userdata struct.
4498	static userdata u;
4499
4500	ev_async_init (&u->async_w, async_cb);
4501	ev_async_start (EV_A_ &u->async_w);
4502
4503	pthread_mutex_init (&u->lock, 0);
4504	pthread_cond_init (&u->invoke_cv, 0);
4505
4506	// now associate this with the loop
4507	ev_set_userdata (EV_A_ u);
4508	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4509	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4510
4511	// then create the thread running ev_loop
4512	pthread_create (&u->tid, 0, l_run, EV_A);
4513	}
4514
4515	The callback for the C<ev_async> watcher does nothing: the watcher is used
4516	solely to wake up the event loop so it takes notice of any new watchers
4517	that might have been added:
4518
4519	static void
4520	async_cb (EV_P_ ev_async *w, int revents)
4521	{
4522	// just used for the side effects
4523	}
4524
4525	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4526	protecting the loop data, respectively.
4527
4528	static void
4529	l_release (EV_P)
4530	{
4531	userdata *u = ev_userdata (EV_A);
4532	pthread_mutex_unlock (&u->lock);
4533	}
4534
4535	static void
4536	l_acquire (EV_P)
4537	{
4538	userdata *u = ev_userdata (EV_A);
4539	pthread_mutex_lock (&u->lock);
4540	}
4541
4542	The event loop thread first acquires the mutex, and then jumps straight
4543	into C<ev_run>:
4544
4545	void *
4546	l_run (void *thr_arg)
4547	{
4548	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4549
4550	l_acquire (EV_A);
4551	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4552	ev_run (EV_A_ 0);
4553	l_release (EV_A);
4554
4555	return 0;
4556	}
4557
4558	Instead of invoking all pending watchers, the C<l_invoke> callback will
4559	signal the main thread via some unspecified mechanism (signals? pipe
4560	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4561	have been called (in a while loop because a) spurious wakeups are possible
4562	and b) skipping inter-thread-communication when there are no pending
4563	watchers is very beneficial):
4564
4565	static void
4566	l_invoke (EV_P)
4567	{
4568	userdata *u = ev_userdata (EV_A);
4569
4570	while (ev_pending_count (EV_A))
4571	{
4572	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4573	pthread_cond_wait (&u->invoke_cv, &u->lock);
4574	}
4575	}
4576
4577	Now, whenever the main thread gets told to invoke pending watchers, it
4578	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4579	thread to continue:
4580
4581	static void
4582	real_invoke_pending (EV_P)
4583	{
4584	userdata *u = ev_userdata (EV_A);
4585
4586	pthread_mutex_lock (&u->lock);
4587	ev_invoke_pending (EV_A);
4588	pthread_cond_signal (&u->invoke_cv);
4589	pthread_mutex_unlock (&u->lock);
4590	}
4591
4592	Whenever you want to start/stop a watcher or do other modifications to an
4593	event loop, you will now have to lock:
4594
4595	ev_timer timeout_watcher;
4596	userdata *u = ev_userdata (EV_A);
4597
4598	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4599
4600	pthread_mutex_lock (&u->lock);
4601	ev_timer_start (EV_A_ &timeout_watcher);
4602	ev_async_send (EV_A_ &u->async_w);
4603	pthread_mutex_unlock (&u->lock);
4604
4605	Note that sending the C<ev_async> watcher is required because otherwise
4606	an event loop currently blocking in the kernel will have no knowledge
4607	about the newly added timer. By waking up the loop it will pick up any new
4608	watchers in the next event loop iteration.
4609		4959
4610	=head3 COROUTINES	4960	=head3 COROUTINES
4611		4961
4612	Libev is very accommodating to coroutines ("cooperative threads"):	4962	Libev is very accommodating to coroutines ("cooperative threads"):
4613	libev fully supports nesting calls to its functions from different	4963	libev fully supports nesting calls to its functions from different
…		…
4778	requires, and its I/O model is fundamentally incompatible with the POSIX	5128	requires, and its I/O model is fundamentally incompatible with the POSIX
4779	model. Libev still offers limited functionality on this platform in	5129	model. Libev still offers limited functionality on this platform in
4780	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5130	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4781	descriptors. This only applies when using Win32 natively, not when using	5131	descriptors. This only applies when using Win32 natively, not when using
4782	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5132	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4783	as every compielr comes with a slightly differently broken/incompatible	5133	as every compiler comes with a slightly differently broken/incompatible
4784	environment.	5134	environment.
4785		5135
4786	Lifting these limitations would basically require the full	5136	Lifting these limitations would basically require the full
4787	re-implementation of the I/O system. If you are into this kind of thing,	5137	re-implementation of the I/O system. If you are into this kind of thing,
4788	then note that glib does exactly that for you in a very portable way (note	5138	then note that glib does exactly that for you in a very portable way (note
…		…
4921		5271
4922	The type C<double> is used to represent timestamps. It is required to	5272	The type C<double> is used to represent timestamps. It is required to
4923	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5273	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4924	good enough for at least into the year 4000 with millisecond accuracy	5274	good enough for at least into the year 4000 with millisecond accuracy
4925	(the design goal for libev). This requirement is overfulfilled by	5275	(the design goal for libev). This requirement is overfulfilled by
4926	implementations using IEEE 754, which is basically all existing ones. With	5276	implementations using IEEE 754, which is basically all existing ones.
		5277
4927	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5278	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5279	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5280	is either obsolete or somebody patched it to use C<long double> or
		5281	something like that, just kidding).
4928		5282
4929	=back	5283	=back
4930		5284
4931	If you know of other additional requirements drop me a note.	5285	If you know of other additional requirements drop me a note.
4932		5286
…		…
4994	=item Processing ev_async_send: O(number_of_async_watchers)	5348	=item Processing ev_async_send: O(number_of_async_watchers)
4995		5349
4996	=item Processing signals: O(max_signal_number)	5350	=item Processing signals: O(max_signal_number)
4997		5351
4998	Sending involves a system call I<iff> there were no other C<ev_async_send>	5352	Sending involves a system call I<iff> there were no other C<ev_async_send>
4999	calls in the current loop iteration. Checking for async and signal events	5353	calls in the current loop iteration and the loop is currently
		5354	blocked. Checking for async and signal events involves iterating over all
5000	involves iterating over all running async watchers or all signal numbers.	5355	running async watchers or all signal numbers.
5001		5356
5002	=back	5357	=back
5003		5358
5004		5359
5005	=head1 PORTING FROM LIBEV 3.X TO 4.X	5360	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5122	The physical time that is observed. It is apparently strictly monotonic :)	5477	The physical time that is observed. It is apparently strictly monotonic :)
5123		5478
5124	=item wall-clock time	5479	=item wall-clock time
5125		5480
5126	The time and date as shown on clocks. Unlike real time, it can actually	5481	The time and date as shown on clocks. Unlike real time, it can actually
5127	be wrong and jump forwards and backwards, e.g. when the you adjust your	5482	be wrong and jump forwards and backwards, e.g. when you adjust your
5128	clock.	5483	clock.
5129		5484
5130	=item watcher	5485	=item watcher
5131		5486
5132	A data structure that describes interest in certain events. Watchers need	5487	A data structure that describes interest in certain events. Watchers need
…		…
5135	=back	5490	=back
5136		5491
5137	=head1 AUTHOR	5492	=head1 AUTHOR
5138		5493
5139	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5494	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5140	Magnusson and Emanuele Giaquinta.	5495	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5141		5496

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