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Revision 1.351 by root, Mon Jan 10 14:24:26 2011 UTC vs.
Revision 1.429 by root, Fri Oct 11 07:50:43 2013 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
…		…
82		82
83	=head1 WHAT TO READ WHEN IN A HURRY	83	=head1 WHAT TO READ WHEN IN A HURRY
84		84
85	This manual tries to be very detailed, but unfortunately, this also makes	85	This manual tries to be very detailed, but unfortunately, this also makes
86	it very long. If you just want to know the basics of libev, I suggest	86	it very long. If you just want to know the basics of libev, I suggest
87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and	87	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and	88	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89	C<ev_timer> sections in L<WATCHER TYPES>.	89	C<ev_timer> sections in L</WATCHER TYPES>.
90		90
91	=head1 ABOUT LIBEV	91	=head1 ABOUT LIBEV
92		92
93	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
94	file descriptor being readable or a timeout occurring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
…		…
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
…		…
390		396
391	If this flag bit is or'ed into the flag value (or the program runs setuid	397	If this flag bit is or'ed into the flag value (or the program runs setuid
392	or setgid) then libev will I<not> look at the environment variable	398	or setgid) then libev will I<not> look at the environment variable
393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
394	override the flags completely if it is found in the environment. This is	400	override the flags completely if it is found in the environment. This is
395	useful to try out specific backends to test their performance, or to work	401	useful to try out specific backends to test their performance, to work
396	around bugs.	402	around bugs, or to make libev threadsafe (accessing environment variables
		403	cannot be done in a threadsafe way, but usually it works if no other
		404	thread modifies them).
397		405
398	=item C<EVFLAG_FORKCHECK>	406	=item C<EVFLAG_FORKCHECK>
399		407
400	Instead of calling C<ev_loop_fork> manually after a fork, you can also	408	Instead of calling C<ev_loop_fork> manually after a fork, you can also
401	make libev check for a fork in each iteration by enabling this flag.	409	make libev check for a fork in each iteration by enabling this flag.
…		…
435	example) that can't properly initialise their signal masks.	443	example) that can't properly initialise their signal masks.
436		444
437	=item C<EVFLAG_NOSIGMASK>	445	=item C<EVFLAG_NOSIGMASK>
438		446
439	When this flag is specified, then libev will avoid to modify the signal	447	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	448	mask. Specifically, this means you have to make sure signals are unblocked
441	when you want to receive them.	449	when you want to receive them.
442		450
443	This behaviour is useful when you want to do your own signal handling, or	451	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	452	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	453	unblocking the signals.
		454
		455	It's also required by POSIX in a threaded program, as libev calls
		456	C<sigprocmask>, whose behaviour is officially unspecified.
446		457
447	This flag's behaviour will become the default in future versions of libev.	458	This flag's behaviour will become the default in future versions of libev.
448		459
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	460	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		461
…		…
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	491	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		492
482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	493	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
483	kernels).	494	kernels).
484		495
485	For few fds, this backend is a bit little slower than poll and select,	496	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	497	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),	498	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).	499	fd), epoll scales either O(1) or O(active_fds).
489		500
490	The epoll mechanism deserves honorable mention as the most misdesigned	501	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	502	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	503	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	504	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	507	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	508	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)	509	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	510	and is of course hard to detect.
500		511
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	512	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	513	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	514	totally I<different> file descriptors (even already closed ones, so
504	even remove them from the set) than registered in the set (especially	515	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	516	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	517	notifications by employing an additional generation counter and comparing
507	events to filter out spurious ones, recreating the set when required. Last	518	that against the events to filter out spurious ones, recreating the set
		519	when required. Epoll also erroneously rounds down timeouts, but gives you
		520	no way to know when and by how much, so sometimes you have to busy-wait
		521	because epoll returns immediately despite a nonzero timeout. And last
508	not least, it also refuses to work with some file descriptors which work	522	not least, it also refuses to work with some file descriptors which work
509	perfectly fine with C<select> (files, many character devices...).	523	perfectly fine with C<select> (files, many character devices...).
510		524
511	Epoll is truly the train wreck analog among event poll mechanisms.	525	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		526	cobbled together in a hurry, no thought to design or interaction with
		527	others. Oh, the pain, will it ever stop...
512		528
513	While stopping, setting and starting an I/O watcher in the same iteration	529	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	530	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	531	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	532	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
553		569
554	It scales in the same way as the epoll backend, but the interface to the	570	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	571	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	572	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	573	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	574	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	575	might have to leak fd's on fork, but it's more sane than epoll) and it
560	cases	576	drops fds silently in similarly hard-to-detect cases.
561		577
562	This backend usually performs well under most conditions.	578	This backend usually performs well under most conditions.
563		579
564	While nominally embeddable in other event loops, this doesn't work	580	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	581	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	608	On the positive side, this backend actually performed fully to
593	specification in all tests and is fully embeddable, which is a rare feat	609	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	610	among the OS-specific backends (I vastly prefer correctness over speed
595	hacks).	611	hacks).
596		612
597	On the negative side, the interface is I<bizarre>, with the event polling	613	On the negative side, the interface is I<bizarre> - so bizarre that
		614	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	615	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	616	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	617	even documented that way) - deadly for edge-triggered interfaces where you
		618	absolutely have to know whether an event occurred or not because you have
		619	to re-arm the watcher.
		620
601	fortunately libev seems to be able to work around it.	621	Fortunately libev seems to be able to work around these idiocies.
602		622
603	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	623	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
604	C<EVBACKEND_POLL>.	624	C<EVBACKEND_POLL>.
605		625
606	=item C<EVBACKEND_ALL>	626	=item C<EVBACKEND_ALL>
…		…
666	reinitialise the kernel state for backends that have one. Despite the	686	reinitialise the kernel state for backends that have one. Despite the
667	name, you can call it anytime, but it makes most sense after forking, in	687	name, you can call it anytime, but it makes most sense after forking, in
668	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	688	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
669	child before resuming or calling C<ev_run>.	689	child before resuming or calling C<ev_run>.
670		690
671	Again, you I<have> to call it on I<any> loop that you want to re-use after	691	Again, you I<have> to call it on I<any> loop that you want to re-use after
672	a fork, I<even if you do not plan to use the loop in the parent>. This is	692	a fork, I<even if you do not plan to use the loop in the parent>. This is
673	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	693	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
674	during fork.	694	during fork.
675		695
676	On the other hand, you only need to call this function in the child	696	On the other hand, you only need to call this function in the child
…		…
746		766
747	This function is rarely useful, but when some event callback runs for a	767	This function is rarely useful, but when some event callback runs for a
748	very long time without entering the event loop, updating libev's idea of	768	very long time without entering the event loop, updating libev's idea of
749	the current time is a good idea.	769	the current time is a good idea.
750		770
751	See also L<The special problem of time updates> in the C<ev_timer> section.	771	See also L</The special problem of time updates> in the C<ev_timer> section.
752		772
753	=item ev_suspend (loop)	773	=item ev_suspend (loop)
754		774
755	=item ev_resume (loop)	775	=item ev_resume (loop)
756		776
…		…
774	without a previous call to C<ev_suspend>.	794	without a previous call to C<ev_suspend>.
775		795
776	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	796	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
777	event loop time (see C<ev_now_update>).	797	event loop time (see C<ev_now_update>).
778		798
779	=item ev_run (loop, int flags)	799	=item bool ev_run (loop, int flags)
780		800
781	Finally, this is it, the event handler. This function usually is called	801	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	802	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	803	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	804	the watcher callbacks, and then repeat the whole process indefinitely: This
785	is why event loops are called I<loops>.	805	is why event loops are called I<loops>.
786		806
787	If the flags argument is specified as C<0>, it will keep handling events	807	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	808	until either no event watchers are active anymore or C<ev_break> was
789	called.	809	called.
		810
		811	The return value is false if there are no more active watchers (which
		812	usually means "all jobs done" or "deadlock"), and true in all other cases
		813	(which usually means " you should call C<ev_run> again").
790		814
791	Please note that an explicit C<ev_break> is usually better than	815	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	816	relying on all watchers to be stopped when deciding when a program has
793	finished (especially in interactive programs), but having a program	817	finished (especially in interactive programs), but having a program
794	that automatically loops as long as it has to and no longer by virtue	818	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	819	of relying on its watchers stopping correctly, that is truly a thing of
796	beauty.	820	beauty.
797		821
798	This function is also I<mostly> exception-safe - you can break out of	822	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++	823	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	824	exception and so on. This does not decrement the C<ev_depth> value, nor
801	will it clear any outstanding C<EVBREAK_ONE> breaks.	825	will it clear any outstanding C<EVBREAK_ONE> breaks.
802		826
803	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	827	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	828	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	840	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	841	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	842	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.	843	usually a better approach for this kind of thing.
820		844
821	Here are the gory details of what C<ev_run> does:	845	Here are the gory details of what C<ev_run> does (this is for your
		846	understanding, not a guarantee that things will work exactly like this in
		847	future versions):
822		848
823	- Increment loop depth.	849	- Increment loop depth.
824	- Reset the ev_break status.	850	- Reset the ev_break status.
825	- Before the first iteration, call any pending watchers.	851	- Before the first iteration, call any pending watchers.
826	LOOP:	852	LOOP:
…		…
859	anymore.	885	anymore.
860		886
861	... queue jobs here, make sure they register event watchers as long	887	... 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..)	888	... as they still have work to do (even an idle watcher will do..)
863	ev_run (my_loop, 0);	889	ev_run (my_loop, 0);
864	... jobs done or somebody called unloop. yeah!	890	... jobs done or somebody called break. yeah!
865		891
866	=item ev_break (loop, how)	892	=item ev_break (loop, how)
867		893
868	Can be used to make a call to C<ev_run> return early (but only after it	894	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	895	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.	958	overhead for the actual polling but can deliver many events at once.
933		959
934	By setting a higher I<io collect interval> you allow libev to spend more	960	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,	961	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	962	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	963	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	964	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	965	sleep time ensures that libev will not poll for I/O events more often then
940	once per this interval, on average.	966	once per this interval, on average (as long as the host time resolution is
		967	good enough).
941		968
942	Likewise, by setting a higher I<timeout collect interval> you allow libev	969	Likewise, by setting a higher I<timeout collect interval> you allow libev
943	to spend more time collecting timeouts, at the expense of increased	970	to spend more time collecting timeouts, at the expense of increased
944	latency/jitter/inexactness (the watcher callback will be called	971	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	972	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.).	1018	invoke the actual watchers inside another context (another thread etc.).
992		1019
993	If you want to reset the callback, use C<ev_invoke_pending> as new	1020	If you want to reset the callback, use C<ev_invoke_pending> as new
994	callback.	1021	callback.
995		1022
996	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1023	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
997		1024
998	Sometimes you want to share the same loop between multiple threads. This	1025	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	1026	can be done relatively simply by putting mutex_lock/unlock calls around
1000	each call to a libev function.	1027	each call to a libev function.
1001		1028
1002	However, C<ev_run> can run an indefinite time, so it is not feasible	1029	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	1030	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	1031	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.	1032	I<release> and I<acquire> callbacks on the loop.
1006		1033
1007	When set, then C<release> will be called just before the thread is	1034	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	1035	suspended waiting for new events, and C<acquire> is called just
1009	afterwards.	1036	afterwards.
…		…
1149		1176
1150	=item C<EV_PREPARE>	1177	=item C<EV_PREPARE>
1151		1178
1152	=item C<EV_CHECK>	1179	=item C<EV_CHECK>
1153		1180
1154	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1181	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	1182	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	1183	just after C<ev_run> has gathered them, but before it queues any callbacks
		1184	for any received events. That means C<ev_prepare> watchers are the last
		1185	watchers invoked before the event loop sleeps or polls for new events, and
		1186	C<ev_check> watchers will be invoked before any other watchers of the same
		1187	or lower priority within an event loop iteration.
		1188
1157	received events. Callbacks of both watcher types can start and stop as	1189	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	1190	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	1191	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1160	C<ev_run> from blocking).	1192	blocking).
1161		1193
1162	=item C<EV_EMBED>	1194	=item C<EV_EMBED>
1163		1195
1164	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1196	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1165		1197
…		…
1288		1320
1289	=item callback ev_cb (ev_TYPE *watcher)	1321	=item callback ev_cb (ev_TYPE *watcher)
1290		1322
1291	Returns the callback currently set on the watcher.	1323	Returns the callback currently set on the watcher.
1292		1324
1293	=item ev_cb_set (ev_TYPE *watcher, callback)	1325	=item ev_set_cb (ev_TYPE *watcher, callback)
1294		1326
1295	Change the callback. You can change the callback at virtually any time	1327	Change the callback. You can change the callback at virtually any time
1296	(modulo threads).	1328	(modulo threads).
1297		1329
1298	=item ev_set_priority (ev_TYPE *watcher, int priority)	1330	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1316	or might not have been clamped to the valid range.	1348	or might not have been clamped to the valid range.
1317		1349
1318	The default priority used by watchers when no priority has been set is	1350	The default priority used by watchers when no priority has been set is
1319	always C<0>, which is supposed to not be too high and not be too low :).	1351	always C<0>, which is supposed to not be too high and not be too low :).
1320		1352
1321	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1353	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1322	priorities.	1354	priorities.
1323		1355
1324	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1356	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1325		1357
1326	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1358	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1351	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1383	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1352	functions that do not need a watcher.	1384	functions that do not need a watcher.
1353		1385
1354	=back	1386	=back
1355		1387
1356	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1388	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1357		1389	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		1390
1421	=head2 WATCHER STATES	1391	=head2 WATCHER STATES
1422		1392
1423	There are various watcher states mentioned throughout this manual -	1393	There are various watcher states mentioned throughout this manual -
1424	active, pending and so on. In this section these states and the rules to	1394	active, pending and so on. In this section these states and the rules to
1425	transition between them will be described in more detail - and while these	1395	transition between them will be described in more detail - and while these
1426	rules might look complicated, they usually do "the right thing".	1396	rules might look complicated, they usually do "the right thing".
1427		1397
1428	=over 4	1398	=over 4
1429		1399
1430	=item initialiased	1400	=item initialised
1431		1401
1432	Before a watcher can be registered with the event looop it has to be	1402	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	1403	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.	1404	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1435		1405
1436	In this state it is simply some block of memory that is suitable for use	1406	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.	1407	use in an event loop. It can be moved around, freed, reused etc. at
		1408	will - as long as you either keep the memory contents intact, or call
		1409	C<ev_TYPE_init> again.
1438		1410
1439	=item started/running/active	1411	=item started/running/active
1440		1412
1441	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1413	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	1414	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	1442	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	1443	of whether it was active or not, so stopping a watcher explicitly before
1472	freeing it is often a good idea.	1444	freeing it is often a good idea.
1473		1445
1474	While stopped (and not pending) the watcher is essentially in the	1446	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	1447	initialised state, that is, it can be reused, moved, modified in any way
1476	you wish.	1448	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1449	it again).
1477		1450
1478	=back	1451	=back
1479		1452
1480	=head2 WATCHER PRIORITY MODELS	1453	=head2 WATCHER PRIORITY MODELS
1481		1454
…		…
1610	In general you can register as many read and/or write event watchers per	1583	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	1584	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	1585	descriptors to non-blocking mode is also usually a good idea (but not
1613	required if you know what you are doing).	1586	required if you know what you are doing).
1614		1587
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	1588	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	1589	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	1590	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	1591	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	1592	with a relatively standard program structure. Thus it is best to always
1626	this situation even with a relatively standard program structure. Thus	1593	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.	1594	preferable to a program hanging until some data arrives.
1629		1595
1630	If you cannot run the fd in non-blocking mode (for example you should	1596	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	1597	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	1598	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	1599	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	1600	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	1601	use C<SIGALRM> and an interval timer, just to be sure you won't block
1636	indefinitely.	1602	indefinitely.
1637		1603
1638	But really, best use non-blocking mode.	1604	But really, best use non-blocking mode.
1639		1605
…		…
1667		1633
1668	There is no workaround possible except not registering events	1634	There is no workaround possible except not registering events
1669	for potentially C<dup ()>'ed file descriptors, or to resort to	1635	for potentially C<dup ()>'ed file descriptors, or to resort to
1670	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1636	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1671		1637
		1638	=head3 The special problem of files
		1639
		1640	Many people try to use C<select> (or libev) on file descriptors
		1641	representing files, and expect it to become ready when their program
		1642	doesn't block on disk accesses (which can take a long time on their own).
		1643
		1644	However, this cannot ever work in the "expected" way - you get a readiness
		1645	notification as soon as the kernel knows whether and how much data is
		1646	there, and in the case of open files, that's always the case, so you
		1647	always get a readiness notification instantly, and your read (or possibly
		1648	write) will still block on the disk I/O.
		1649
		1650	Another way to view it is that in the case of sockets, pipes, character
		1651	devices and so on, there is another party (the sender) that delivers data
		1652	on its own, but in the case of files, there is no such thing: the disk
		1653	will not send data on its own, simply because it doesn't know what you
		1654	wish to read - you would first have to request some data.
		1655
		1656	Since files are typically not-so-well supported by advanced notification
		1657	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1658	to files, even though you should not use it. The reason for this is
		1659	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1660	usually a tty, often a pipe, but also sometimes files or special devices
		1661	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1662	F</dev/urandom>), and even though the file might better be served with
		1663	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1664	it "just works" instead of freezing.
		1665
		1666	So avoid file descriptors pointing to files when you know it (e.g. use
		1667	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1668	when you rarely read from a file instead of from a socket, and want to
		1669	reuse the same code path.
		1670
1672	=head3 The special problem of fork	1671	=head3 The special problem of fork
1673		1672
1674	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1673	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	1674	useless behaviour. Libev fully supports fork, but needs to be told about
1676	it in the child.	1675	it in the child if you want to continue to use it in the child.
1677		1676
1678	To support fork in your programs, you either have to call	1677	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,	1678	()> 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	1679	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1681	C<EVBACKEND_POLL>.
1682		1680
1683	=head3 The special problem of SIGPIPE	1681	=head3 The special problem of SIGPIPE
1684		1682
1685	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1683	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	1684	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	1782	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1785	monotonic clock option helps a lot here).	1783	monotonic clock option helps a lot here).
1786		1784
1787	The callback is guaranteed to be invoked only I<after> its timeout has	1785	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	1786	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	1787	might introduce a small delay, see "the special problem of being too
		1788	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	1789	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	1790	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).	1791	longer true when a callback calls C<ev_run> recursively).
1793		1792
1794	=head3 Be smart about timeouts	1793	=head3 Be smart about timeouts
1795		1794
1796	Many real-world problems involve some kind of timeout, usually for error	1795	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,	1796	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1872		1871
1873	In this case, it would be more efficient to leave the C<ev_timer> alone,	1872	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	1873	but remember the time of last activity, and check for a real timeout only
1875	within the callback:	1874	within the callback:
1876		1875
		1876	ev_tstamp timeout = 60.;
1877	ev_tstamp last_activity; // time of last activity	1877	ev_tstamp last_activity; // time of last activity
		1878	ev_timer timer;
1878		1879
1879	static void	1880	static void
1880	callback (EV_P_ ev_timer *w, int revents)	1881	callback (EV_P_ ev_timer *w, int revents)
1881	{	1882	{
1882	ev_tstamp now = ev_now (EV_A);	1883	// calculate when the timeout would happen
1883	ev_tstamp timeout = last_activity + 60.;	1884	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1884		1885
1885	// if last_activity + 60. is older than now, we did time out	1886	// if negative, it means we the timeout already occurred
1886	if (timeout < now)	1887	if (after < 0.)
1887	{	1888	{
1888	// timeout occurred, take action	1889	// timeout occurred, take action
1889	}	1890	}
1890	else	1891	else
1891	{	1892	{
1892	// callback was invoked, but there was some activity, re-arm	1893	// callback was invoked, but there was some recent
1893	// the watcher to fire in last_activity + 60, which is	1894	// activity. simply restart the timer to time out
1894	// guaranteed to be in the future, so "again" is positive:	1895	// after "after" seconds, which is the earliest time
1895	w->repeat = timeout - now;	1896	// the timeout can occur.
		1897	ev_timer_set (w, after, 0.);
1896	ev_timer_again (EV_A_ w);	1898	ev_timer_start (EV_A_ w);
1897	}	1899	}
1898	}	1900	}
1899		1901
1900	To summarise the callback: first calculate the real timeout (defined	1902	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	1903	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	1904	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	1905	(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		1906
1907	Note how C<ev_timer_again> is used, taking advantage of the	1907	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.	1908	timed out, and need to do whatever is needed in this case.
		1909
		1910	Otherwise, we now the earliest time at which the timeout would trigger,
		1911	and simply start the timer with this timeout value.
		1912
		1913	In other words, each time the callback is invoked it will check whether
		1914	the timeout occurred. If not, it will simply reschedule itself to check
		1915	again at the earliest time it could time out. Rinse. Repeat.
1909		1916
1910	This scheme causes more callback invocations (about one every 60 seconds	1917	This scheme causes more callback invocations (about one every 60 seconds
1911	minus half the average time between activity), but virtually no calls to	1918	minus half the average time between activity), but virtually no calls to
1912	libev to change the timeout.	1919	libev to change the timeout.
1913		1920
1914	To start the timer, simply initialise the watcher and set C<last_activity>	1921	To start the machinery, simply initialise the watcher and set
1915	to the current time (meaning we just have some activity :), then call the	1922	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:	1923	now), then call the callback, which will "do the right thing" and start
		1924	the timer:
1917		1925
		1926	last_activity = ev_now (EV_A);
1918	ev_init (timer, callback);	1927	ev_init (&timer, callback);
1919	last_activity = ev_now (loop);	1928	callback (EV_A_ &timer, 0);
1920	callback (loop, timer, EV_TIMER);
1921		1929
1922	And when there is some activity, simply store the current time in	1930	When there is some activity, simply store the current time in
1923	C<last_activity>, no libev calls at all:	1931	C<last_activity>, no libev calls at all:
1924		1932
		1933	if (activity detected)
1925	last_activity = ev_now (loop);	1934	last_activity = ev_now (EV_A);
		1935
		1936	When your timeout value changes, then the timeout can be changed by simply
		1937	providing a new value, stopping the timer and calling the callback, which
		1938	will again do the right thing (for example, time out immediately :).
		1939
		1940	timeout = new_value;
		1941	ev_timer_stop (EV_A_ &timer);
		1942	callback (EV_A_ &timer, 0);
1926		1943
1927	This technique is slightly more complex, but in most cases where the	1944	This technique is slightly more complex, but in most cases where the
1928	time-out is unlikely to be triggered, much more efficient.	1945	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		1946
1934	=item 4. Wee, just use a double-linked list for your timeouts.	1947	=item 4. Wee, just use a double-linked list for your timeouts.
1935		1948
1936	If there is not one request, but many thousands (millions...), all	1949	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	1950	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	1977	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	1978	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	1979	off after the first million or so of active timers, i.e. it's usually
1967	overkill :)	1980	overkill :)
1968		1981
		1982	=head3 The special problem of being too early
		1983
		1984	If you ask a timer to call your callback after three seconds, then
		1985	you expect it to be invoked after three seconds - but of course, this
		1986	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1987	guaranteed to any precision by libev - imagine somebody suspending the
		1988	process with a STOP signal for a few hours for example.
		1989
		1990	So, libev tries to invoke your callback as soon as possible I<after> the
		1991	delay has occurred, but cannot guarantee this.
		1992
		1993	A less obvious failure mode is calling your callback too early: many event
		1994	loops compare timestamps with a "elapsed delay >= requested delay", but
		1995	this can cause your callback to be invoked much earlier than you would
		1996	expect.
		1997
		1998	To see why, imagine a system with a clock that only offers full second
		1999	resolution (think windows if you can't come up with a broken enough OS
		2000	yourself). If you schedule a one-second timer at the time 500.9, then the
		2001	event loop will schedule your timeout to elapse at a system time of 500
		2002	(500.9 truncated to the resolution) + 1, or 501.
		2003
		2004	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2005	501" and invoke the callback 0.1s after it was started, even though a
		2006	one-second delay was requested - this is being "too early", despite best
		2007	intentions.
		2008
		2009	This is the reason why libev will never invoke the callback if the elapsed
		2010	delay equals the requested delay, but only when the elapsed delay is
		2011	larger than the requested delay. In the example above, libev would only invoke
		2012	the callback at system time 502, or 1.1s after the timer was started.
		2013
		2014	So, while libev cannot guarantee that your callback will be invoked
		2015	exactly when requested, it I<can> and I<does> guarantee that the requested
		2016	delay has actually elapsed, or in other words, it always errs on the "too
		2017	late" side of things.
		2018
1969	=head3 The special problem of time updates	2019	=head3 The special problem of time updates
1970		2020
1971	Establishing the current time is a costly operation (it usually takes at	2021	Establishing the current time is a costly operation (it usually takes
1972	least two system calls): EV therefore updates its idea of the current	2022	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	2023	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	2024	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1975	lots of events in one iteration.	2025	lots of events in one iteration.
1976		2026
1977	The relative timeouts are calculated relative to the C<ev_now ()>	2027	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1983	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2033	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1984		2034
1985	If the event loop is suspended for a long time, you can also force an	2035	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	2036	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1987	()>.	2037	()>.
		2038
		2039	=head3 The special problem of unsynchronised clocks
		2040
		2041	Modern systems have a variety of clocks - libev itself uses the normal
		2042	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2043	jumps).
		2044
		2045	Neither of these clocks is synchronised with each other or any other clock
		2046	on the system, so C<ev_time ()> might return a considerably different time
		2047	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2048	a call to C<gettimeofday> might return a second count that is one higher
		2049	than a directly following call to C<time>.
		2050
		2051	The moral of this is to only compare libev-related timestamps with
		2052	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2053	a second or so.
		2054
		2055	One more problem arises due to this lack of synchronisation: if libev uses
		2056	the system monotonic clock and you compare timestamps from C<ev_time>
		2057	or C<ev_now> from when you started your timer and when your callback is
		2058	invoked, you will find that sometimes the callback is a bit "early".
		2059
		2060	This is because C<ev_timer>s work in real time, not wall clock time, so
		2061	libev makes sure your callback is not invoked before the delay happened,
		2062	I<measured according to the real time>, not the system clock.
		2063
		2064	If your timeouts are based on a physical timescale (e.g. "time out this
		2065	connection after 100 seconds") then this shouldn't bother you as it is
		2066	exactly the right behaviour.
		2067
		2068	If you want to compare wall clock/system timestamps to your timers, then
		2069	you need to use C<ev_periodic>s, as these are based on the wall clock
		2070	time, where your comparisons will always generate correct results.
1988		2071
1989	=head3 The special problems of suspended animation	2072	=head3 The special problems of suspended animation
1990		2073
1991	When you leave the server world it is quite customary to hit machines that	2074	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?	2075	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	2119	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.	2120	do stuff) the timer will not fire more than once per event loop iteration.
2038		2121
2039	=item ev_timer_again (loop, ev_timer *)	2122	=item ev_timer_again (loop, ev_timer *)
2040		2123
2041	This will act as if the timer timed out and restart it again if it is	2124	This will act as if the timer timed out, and restarts it again if it is
2042	repeating. The exact semantics are:	2125	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2126	timeout to the C<repeat> value and calling C<ev_timer_start>.
2043		2127
		2128	The exact semantics are as in the following rules, all of which will be
		2129	applied to the watcher:
		2130
		2131	=over 4
		2132
2044	If the timer is pending, its pending status is cleared.	2133	=item If the timer is pending, the pending status is always cleared.
2045		2134
2046	If the timer is started but non-repeating, stop it (as if it timed out).	2135	=item If the timer is started but non-repeating, stop it (as if it timed
		2136	out, without invoking it).
2047		2137
2048	If the timer is repeating, either start it if necessary (with the	2138	=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.	2139	and start the timer, if necessary.
2050		2140
		2141	=back
		2142
2051	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2143	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2052	usage example.	2144	usage example.
2053		2145
2054	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2146	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2055		2147
2056	Returns the remaining time until a timer fires. If the timer is active,	2148	Returns the remaining time until a timer fires. If the timer is active,
…		…
2176		2268
2177	Another way to think about it (for the mathematically inclined) is that	2269	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	2270	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.	2271	time where C<time = offset (mod interval)>, regardless of any time jumps.
2180		2272
2181	For numerical stability it is preferable that the C<offset> value is near	2273	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	2274	interval value should be higher than C<1/8192> (which is around 100
2183	this value, and in fact is often specified as zero.	2275	microseconds) and C<offset> should be higher than C<0> and should have
		2276	at most a similar magnitude as the current time (say, within a factor of
		2277	ten). Typical values for offset are, in fact, C<0> or something between
		2278	C<0> and C<interval>, which is also the recommended range.
2184		2279
2185	Note also that there is an upper limit to how often a timer can fire (CPU	2280	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	2281	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	2282	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).	2283	millisecond (if the OS supports it and the machine is fast enough).
…		…
2331	=head3 The special problem of inheritance over fork/execve/pthread_create	2426	=head3 The special problem of inheritance over fork/execve/pthread_create
2332		2427
2333	Both the signal mask (C<sigprocmask>) and the signal disposition	2428	Both the signal mask (C<sigprocmask>) and the signal disposition
2334	(C<sigaction>) are unspecified after starting a signal watcher (and after	2429	(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,	2430	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.	2431	and might or might not set or restore the installed signal handler (but
		2432	see C<EVFLAG_NOSIGMASK>).
2337		2433
2338	While this does not matter for the signal disposition (libev never	2434	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	2435	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	2436	C<execve>), this matters for the signal mask: many programs do not expect
2341	certain signals to be blocked.	2437	certain signals to be blocked.
…		…
2512		2608
2513	=head2 C<ev_stat> - did the file attributes just change?	2609	=head2 C<ev_stat> - did the file attributes just change?
2514		2610
2515	This watches a file system path for attribute changes. That is, it calls	2611	This watches a file system path for attribute changes. That is, it calls
2516	C<stat> on that path in regular intervals (or when the OS says it changed)	2612	C<stat> on that path in regular intervals (or when the OS says it changed)
2517	and sees if it changed compared to the last time, invoking the callback if	2613	and sees if it changed compared to the last time, invoking the callback
2518	it did.	2614	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2615	happen after the watcher has been started will be reported.
2519		2616
2520	The path does not need to exist: changing from "path exists" to "path does	2617	The path does not need to exist: changing from "path exists" to "path does
2521	not exist" is a status change like any other. The condition "path does not	2618	not exist" is a status change like any other. The condition "path does not
2522	exist" (or more correctly "path cannot be stat'ed") is signified by the	2619	exist" (or more correctly "path cannot be stat'ed") is signified by the
2523	C<st_nlink> field being zero (which is otherwise always forced to be at	2620	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2753	Apart from keeping your process non-blocking (which is a useful	2850	Apart from keeping your process non-blocking (which is a useful
2754	effect on its own sometimes), idle watchers are a good place to do	2851	effect on its own sometimes), idle watchers are a good place to do
2755	"pseudo-background processing", or delay processing stuff to after the	2852	"pseudo-background processing", or delay processing stuff to after the
2756	event loop has handled all outstanding events.	2853	event loop has handled all outstanding events.
2757		2854
		2855	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2856
		2857	As long as there is at least one active idle watcher, libev will never
		2858	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2859	For this to work, the idle watcher doesn't need to be invoked at all - the
		2860	lowest priority will do.
		2861
		2862	This mode of operation can be useful together with an C<ev_check> watcher,
		2863	to do something on each event loop iteration - for example to balance load
		2864	between different connections.
		2865
		2866	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2867	example.
		2868
2758	=head3 Watcher-Specific Functions and Data Members	2869	=head3 Watcher-Specific Functions and Data Members
2759		2870
2760	=over 4	2871	=over 4
2761		2872
2762	=item ev_idle_init (ev_idle *, callback)	2873	=item ev_idle_init (ev_idle *, callback)
…		…
2773	callback, free it. Also, use no error checking, as usual.	2884	callback, free it. Also, use no error checking, as usual.
2774		2885
2775	static void	2886	static void
2776	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2887	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2777	{	2888	{
		2889	// stop the watcher
		2890	ev_idle_stop (loop, w);
		2891
		2892	// now we can free it
2778	free (w);	2893	free (w);
		2894
2779	// now do something you wanted to do when the program has	2895	// now do something you wanted to do when the program has
2780	// no longer anything immediate to do.	2896	// no longer anything immediate to do.
2781	}	2897	}
2782		2898
2783	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2899	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2785	ev_idle_start (loop, idle_watcher);	2901	ev_idle_start (loop, idle_watcher);
2786		2902
2787		2903
2788	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2904	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2789		2905
2790	Prepare and check watchers are usually (but not always) used in pairs:	2906	Prepare and check watchers are often (but not always) used in pairs:
2791	prepare watchers get invoked before the process blocks and check watchers	2907	prepare watchers get invoked before the process blocks and check watchers
2792	afterwards.	2908	afterwards.
2793		2909
2794	You I<must not> call C<ev_run> or similar functions that enter	2910	You I<must not> call C<ev_run> or similar functions that enter
2795	the current event loop from either C<ev_prepare> or C<ev_check>	2911	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
2823	with priority higher than or equal to the event loop and one coroutine	2939	with priority higher than or equal to the event loop and one coroutine
2824	of lower priority, but only once, using idle watchers to keep the event	2940	of lower priority, but only once, using idle watchers to keep the event
2825	loop from blocking if lower-priority coroutines are active, thus mapping	2941	loop from blocking if lower-priority coroutines are active, thus mapping
2826	low-priority coroutines to idle/background tasks).	2942	low-priority coroutines to idle/background tasks).
2827		2943
2828	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2944	When used for this purpose, it is recommended to give C<ev_check> watchers
2829	priority, to ensure that they are being run before any other watchers	2945	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2830	after the poll (this doesn't matter for C<ev_prepare> watchers).	2946	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2947	watchers).
2831		2948
2832	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2949	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2833	activate ("feed") events into libev. While libev fully supports this, they	2950	activate ("feed") events into libev. While libev fully supports this, they
2834	might get executed before other C<ev_check> watchers did their job. As	2951	might get executed before other C<ev_check> watchers did their job. As
2835	C<ev_check> watchers are often used to embed other (non-libev) event	2952	C<ev_check> watchers are often used to embed other (non-libev) event
2836	loops those other event loops might be in an unusable state until their	2953	loops those other event loops might be in an unusable state until their
2837	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2954	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2838	others).	2955	others).
		2956
		2957	=head3 Abusing an C<ev_check> watcher for its side-effect
		2958
		2959	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2960	useful because they are called once per event loop iteration. For
		2961	example, if you want to handle a large number of connections fairly, you
		2962	normally only do a bit of work for each active connection, and if there
		2963	is more work to do, you wait for the next event loop iteration, so other
		2964	connections have a chance of making progress.
		2965
		2966	Using an C<ev_check> watcher is almost enough: it will be called on the
		2967	next event loop iteration. However, that isn't as soon as possible -
		2968	without external events, your C<ev_check> watcher will not be invoked.
		2969
		2970	This is where C<ev_idle> watchers come in handy - all you need is a
		2971	single global idle watcher that is active as long as you have one active
		2972	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2973	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2974	invoked. Neither watcher alone can do that.
2839		2975
2840	=head3 Watcher-Specific Functions and Data Members	2976	=head3 Watcher-Specific Functions and Data Members
2841		2977
2842	=over 4	2978	=over 4
2843		2979
…		…
3044		3180
3045	=over 4	3181	=over 4
3046		3182
3047	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3183	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
3048		3184
3049	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3185	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3050		3186
3051	Configures the watcher to embed the given loop, which must be	3187	Configures the watcher to embed the given loop, which must be
3052	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3188	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
3053	invoked automatically, otherwise it is the responsibility of the callback	3189	invoked automatically, otherwise it is the responsibility of the callback
3054	to invoke it (it will continue to be called until the sweep has been done,	3190	to invoke it (it will continue to be called until the sweep has been done,
…		…
3117		3253
3118	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3254	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3119		3255
3120	Fork watchers are called when a C<fork ()> was detected (usually because	3256	Fork watchers are called when a C<fork ()> was detected (usually because
3121	whoever is a good citizen cared to tell libev about it by calling	3257	whoever is a good citizen cared to tell libev about it by calling
3122	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3258	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3123	event loop blocks next and before C<ev_check> watchers are being called,	3259	and before C<ev_check> watchers are being called, and only in the child
3124	and only in the child after the fork. If whoever good citizen calling	3260	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3125	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3261	and calls it in the wrong process, the fork handlers will be invoked, too,
3126	handlers will be invoked, too, of course.	3262	of course.
3127		3263
3128	=head3 The special problem of life after fork - how is it possible?	3264	=head3 The special problem of life after fork - how is it possible?
3129		3265
3130	Most uses of C<fork()> consist of forking, then some simple calls to set	3266	Most uses of C<fork()> consist of forking, then some simple calls to set
3131	up/change the process environment, followed by a call to C<exec()>. This	3267	up/change the process environment, followed by a call to C<exec()>. This
…		…
3212	atexit (program_exits);	3348	atexit (program_exits);
3213		3349
3214		3350
3215	=head2 C<ev_async> - how to wake up an event loop	3351	=head2 C<ev_async> - how to wake up an event loop
3216		3352
3217	In general, you cannot use an C<ev_run> from multiple threads or other	3353	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	3354	asynchronous sources such as signal handlers (as opposed to multiple event
3219	loops - those are of course safe to use in different threads).	3355	loops - those are of course safe to use in different threads).
3220		3356
3221	Sometimes, however, you need to wake up an event loop you do not control,	3357	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>	3358	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.	3360	it by calling C<ev_async_send>, which is thread- and signal safe.
3225		3361
3226	This functionality is very similar to C<ev_signal> watchers, as signals,	3362	This functionality is very similar to C<ev_signal> watchers, as signals,
3227	too, are asynchronous in nature, and signals, too, will be compressed	3363	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	3364	(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	3365	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	3366	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,	3367	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3232	even without knowing which loop owns the signal.	3368	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		3369
3237	=head3 Queueing	3370	=head3 Queueing
3238		3371
3239	C<ev_async> does not support queueing of data in any way. The reason	3372	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	3373	is that the author does not know of a simple (or any) algorithm for a
…		…
3332	trust me.	3465	trust me.
3333		3466
3334	=item ev_async_send (loop, ev_async *)	3467	=item ev_async_send (loop, ev_async *)
3335		3468
3336	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3469	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	3470	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3471	returns.
		3472
3338	C<ev_feed_event>, this call is safe to do from other threads, signal or	3473	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	3474	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3340	section below on what exactly this means).	3475	embedding section below on what exactly this means).
3341		3476
3342	Note that, as with other watchers in libev, multiple events might get	3477	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	3478	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>,	3479	this is that C<ev_async> watchers are level-triggered: they are set on
3345	reset when the event loop detects that).	3480	C<ev_async_send>, reset when the event loop detects that).
3346		3481
3347	This call incurs the overhead of a system call only once per event loop	3482	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	3483	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.	3484	the event loop (or your program) is processing events. That means that
		3485	repeated calls are basically free (there is no need to avoid calls for
		3486	performance reasons) and that the overhead becomes smaller (typically
		3487	zero) under load.
3350		3488
3351	=item bool = ev_async_pending (ev_async *)	3489	=item bool = ev_async_pending (ev_async *)
3352		3490
3353	Returns a non-zero value when C<ev_async_send> has been called on the	3491	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	3492	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);	3547	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3410		3548
3411	=item ev_feed_fd_event (loop, int fd, int revents)	3549	=item ev_feed_fd_event (loop, int fd, int revents)
3412		3550
3413	Feed an event on the given fd, as if a file descriptor backend detected	3551	Feed an event on the given fd, as if a file descriptor backend detected
3414	the given events it.	3552	the given events.
3415		3553
3416	=item ev_feed_signal_event (loop, int signum)	3554	=item ev_feed_signal_event (loop, int signum)
3417		3555
3418	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3556	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3419	which is async-safe.	3557	which is async-safe.
…		…
3425		3563
3426	This section explains some common idioms that are not immediately	3564	This section explains some common idioms that are not immediately
3427	obvious. Note that examples are sprinkled over the whole manual, and this	3565	obvious. Note that examples are sprinkled over the whole manual, and this
3428	section only contains stuff that wouldn't fit anywhere else.	3566	section only contains stuff that wouldn't fit anywhere else.
3429		3567
3430	=over 4	3568	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3431		3569
3432	=item Model/nested event loop invocations and exit conditions.	3570	Each watcher has, by default, a C<void *data> member that you can read
		3571	or modify at any time: libev will completely ignore it. This can be used
		3572	to associate arbitrary data with your watcher. If you need more data and
		3573	don't want to allocate memory separately and store a pointer to it in that
		3574	data member, you can also "subclass" the watcher type and provide your own
		3575	data:
		3576
		3577	struct my_io
		3578	{
		3579	ev_io io;
		3580	int otherfd;
		3581	void *somedata;
		3582	struct whatever *mostinteresting;
		3583	};
		3584
		3585	...
		3586	struct my_io w;
		3587	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3588
		3589	And since your callback will be called with a pointer to the watcher, you
		3590	can cast it back to your own type:
		3591
		3592	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3593	{
		3594	struct my_io *w = (struct my_io *)w_;
		3595	...
		3596	}
		3597
		3598	More interesting and less C-conformant ways of casting your callback
		3599	function type instead have been omitted.
		3600
		3601	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3602
		3603	Another common scenario is to use some data structure with multiple
		3604	embedded watchers, in effect creating your own watcher that combines
		3605	multiple libev event sources into one "super-watcher":
		3606
		3607	struct my_biggy
		3608	{
		3609	int some_data;
		3610	ev_timer t1;
		3611	ev_timer t2;
		3612	}
		3613
		3614	In this case getting the pointer to C<my_biggy> is a bit more
		3615	complicated: Either you store the address of your C<my_biggy> struct in
		3616	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3617	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3618	real programmers):
		3619
		3620	#include <stddef.h>
		3621
		3622	static void
		3623	t1_cb (EV_P_ ev_timer *w, int revents)
		3624	{
		3625	struct my_biggy big = (struct my_biggy *)
		3626	(((char *)w) - offsetof (struct my_biggy, t1));
		3627	}
		3628
		3629	static void
		3630	t2_cb (EV_P_ ev_timer *w, int revents)
		3631	{
		3632	struct my_biggy big = (struct my_biggy *)
		3633	(((char *)w) - offsetof (struct my_biggy, t2));
		3634	}
		3635
		3636	=head2 AVOIDING FINISHING BEFORE RETURNING
		3637
		3638	Often you have structures like this in event-based programs:
		3639
		3640	callback ()
		3641	{
		3642	free (request);
		3643	}
		3644
		3645	request = start_new_request (..., callback);
		3646
		3647	The intent is to start some "lengthy" operation. The C<request> could be
		3648	used to cancel the operation, or do other things with it.
		3649
		3650	It's not uncommon to have code paths in C<start_new_request> that
		3651	immediately invoke the callback, for example, to report errors. Or you add
		3652	some caching layer that finds that it can skip the lengthy aspects of the
		3653	operation and simply invoke the callback with the result.
		3654
		3655	The problem here is that this will happen I<before> C<start_new_request>
		3656	has returned, so C<request> is not set.
		3657
		3658	Even if you pass the request by some safer means to the callback, you
		3659	might want to do something to the request after starting it, such as
		3660	canceling it, which probably isn't working so well when the callback has
		3661	already been invoked.
		3662
		3663	A common way around all these issues is to make sure that
		3664	C<start_new_request> I<always> returns before the callback is invoked. If
		3665	C<start_new_request> immediately knows the result, it can artificially
		3666	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3667	example, or more sneakily, by reusing an existing (stopped) watcher and
		3668	pushing it into the pending queue:
		3669
		3670	ev_set_cb (watcher, callback);
		3671	ev_feed_event (EV_A_ watcher, 0);
		3672
		3673	This way, C<start_new_request> can safely return before the callback is
		3674	invoked, while not delaying callback invocation too much.
		3675
		3676	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3433		3677
3434	Often (especially in GUI toolkits) there are places where you have	3678	Often (especially in GUI toolkits) there are places where you have
3435	I<modal> interaction, which is most easily implemented by recursively	3679	I<modal> interaction, which is most easily implemented by recursively
3436	invoking C<ev_run>.	3680	invoking C<ev_run>.
3437		3681
3438	This brings the problem of exiting - a callback might want to finish the	3682	This brings the problem of exiting - a callback might want to finish the
3439	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but	3683	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
3440	a modal "Are you sure?" dialog is still waiting), or just the nested one	3684	a modal "Are you sure?" dialog is still waiting), or just the nested one
3441	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some	3685	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
3442	other combination: In these cases, C<ev_break> will not work alone.	3686	other combination: In these cases, a simple C<ev_break> will not work.
3443		3687
3444	The solution is to maintain "break this loop" variable for each C<ev_run>	3688	The solution is to maintain "break this loop" variable for each C<ev_run>
3445	invocation, and use a loop around C<ev_run> until the condition is	3689	invocation, and use a loop around C<ev_run> until the condition is
3446	triggered, using C<EVRUN_ONCE>:	3690	triggered, using C<EVRUN_ONCE>:
3447		3691
…		…
3449	int exit_main_loop = 0;	3693	int exit_main_loop = 0;
3450		3694
3451	while (!exit_main_loop)	3695	while (!exit_main_loop)
3452	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3696	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3453		3697
3454	// in a model watcher	3698	// in a modal watcher
3455	int exit_nested_loop = 0;	3699	int exit_nested_loop = 0;
3456		3700
3457	while (!exit_nested_loop)	3701	while (!exit_nested_loop)
3458	ev_run (EV_A_ EVRUN_ONCE);	3702	ev_run (EV_A_ EVRUN_ONCE);
3459		3703
…		…
3466	exit_main_loop = 1;	3710	exit_main_loop = 1;
3467		3711
3468	// exit both	3712	// exit both
3469	exit_main_loop = exit_nested_loop = 1;	3713	exit_main_loop = exit_nested_loop = 1;
3470		3714
3471	=back	3715	=head2 THREAD LOCKING EXAMPLE
		3716
		3717	Here is a fictitious example of how to run an event loop in a different
		3718	thread from where callbacks are being invoked and watchers are
		3719	created/added/removed.
		3720
		3721	For a real-world example, see the C<EV::Loop::Async> perl module,
		3722	which uses exactly this technique (which is suited for many high-level
		3723	languages).
		3724
		3725	The example uses a pthread mutex to protect the loop data, a condition
		3726	variable to wait for callback invocations, an async watcher to notify the
		3727	event loop thread and an unspecified mechanism to wake up the main thread.
		3728
		3729	First, you need to associate some data with the event loop:
		3730
		3731	typedef struct {
		3732	mutex_t lock; /* global loop lock */
		3733	ev_async async_w;
		3734	thread_t tid;
		3735	cond_t invoke_cv;
		3736	} userdata;
		3737
		3738	void prepare_loop (EV_P)
		3739	{
		3740	// for simplicity, we use a static userdata struct.
		3741	static userdata u;
		3742
		3743	ev_async_init (&u->async_w, async_cb);
		3744	ev_async_start (EV_A_ &u->async_w);
		3745
		3746	pthread_mutex_init (&u->lock, 0);
		3747	pthread_cond_init (&u->invoke_cv, 0);
		3748
		3749	// now associate this with the loop
		3750	ev_set_userdata (EV_A_ u);
		3751	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3752	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3753
		3754	// then create the thread running ev_run
		3755	pthread_create (&u->tid, 0, l_run, EV_A);
		3756	}
		3757
		3758	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3759	solely to wake up the event loop so it takes notice of any new watchers
		3760	that might have been added:
		3761
		3762	static void
		3763	async_cb (EV_P_ ev_async *w, int revents)
		3764	{
		3765	// just used for the side effects
		3766	}
		3767
		3768	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3769	protecting the loop data, respectively.
		3770
		3771	static void
		3772	l_release (EV_P)
		3773	{
		3774	userdata *u = ev_userdata (EV_A);
		3775	pthread_mutex_unlock (&u->lock);
		3776	}
		3777
		3778	static void
		3779	l_acquire (EV_P)
		3780	{
		3781	userdata *u = ev_userdata (EV_A);
		3782	pthread_mutex_lock (&u->lock);
		3783	}
		3784
		3785	The event loop thread first acquires the mutex, and then jumps straight
		3786	into C<ev_run>:
		3787
		3788	void *
		3789	l_run (void *thr_arg)
		3790	{
		3791	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3792
		3793	l_acquire (EV_A);
		3794	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3795	ev_run (EV_A_ 0);
		3796	l_release (EV_A);
		3797
		3798	return 0;
		3799	}
		3800
		3801	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3802	signal the main thread via some unspecified mechanism (signals? pipe
		3803	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3804	have been called (in a while loop because a) spurious wakeups are possible
		3805	and b) skipping inter-thread-communication when there are no pending
		3806	watchers is very beneficial):
		3807
		3808	static void
		3809	l_invoke (EV_P)
		3810	{
		3811	userdata *u = ev_userdata (EV_A);
		3812
		3813	while (ev_pending_count (EV_A))
		3814	{
		3815	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3816	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3817	}
		3818	}
		3819
		3820	Now, whenever the main thread gets told to invoke pending watchers, it
		3821	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3822	thread to continue:
		3823
		3824	static void
		3825	real_invoke_pending (EV_P)
		3826	{
		3827	userdata *u = ev_userdata (EV_A);
		3828
		3829	pthread_mutex_lock (&u->lock);
		3830	ev_invoke_pending (EV_A);
		3831	pthread_cond_signal (&u->invoke_cv);
		3832	pthread_mutex_unlock (&u->lock);
		3833	}
		3834
		3835	Whenever you want to start/stop a watcher or do other modifications to an
		3836	event loop, you will now have to lock:
		3837
		3838	ev_timer timeout_watcher;
		3839	userdata *u = ev_userdata (EV_A);
		3840
		3841	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3842
		3843	pthread_mutex_lock (&u->lock);
		3844	ev_timer_start (EV_A_ &timeout_watcher);
		3845	ev_async_send (EV_A_ &u->async_w);
		3846	pthread_mutex_unlock (&u->lock);
		3847
		3848	Note that sending the C<ev_async> watcher is required because otherwise
		3849	an event loop currently blocking in the kernel will have no knowledge
		3850	about the newly added timer. By waking up the loop it will pick up any new
		3851	watchers in the next event loop iteration.
		3852
		3853	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3854
		3855	While the overhead of a callback that e.g. schedules a thread is small, it
		3856	is still an overhead. If you embed libev, and your main usage is with some
		3857	kind of threads or coroutines, you might want to customise libev so that
		3858	doesn't need callbacks anymore.
		3859
		3860	Imagine you have coroutines that you can switch to using a function
		3861	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3862	and that due to some magic, the currently active coroutine is stored in a
		3863	global called C<current_coro>. Then you can build your own "wait for libev
		3864	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3865	the differing C<;> conventions):
		3866
		3867	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3868	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3869
		3870	That means instead of having a C callback function, you store the
		3871	coroutine to switch to in each watcher, and instead of having libev call
		3872	your callback, you instead have it switch to that coroutine.
		3873
		3874	A coroutine might now wait for an event with a function called
		3875	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3876	matter when, or whether the watcher is active or not when this function is
		3877	called):
		3878
		3879	void
		3880	wait_for_event (ev_watcher *w)
		3881	{
		3882	ev_set_cb (w, current_coro);
		3883	switch_to (libev_coro);
		3884	}
		3885
		3886	That basically suspends the coroutine inside C<wait_for_event> and
		3887	continues the libev coroutine, which, when appropriate, switches back to
		3888	this or any other coroutine.
		3889
		3890	You can do similar tricks if you have, say, threads with an event queue -
		3891	instead of storing a coroutine, you store the queue object and instead of
		3892	switching to a coroutine, you push the watcher onto the queue and notify
		3893	any waiters.
		3894
		3895	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3896	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3897
		3898	// my_ev.h
		3899	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3900	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3901	#include "../libev/ev.h"
		3902
		3903	// my_ev.c
		3904	#define EV_H "my_ev.h"
		3905	#include "../libev/ev.c"
		3906
		3907	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3908	F<my_ev.c> into your project. When properly specifying include paths, you
		3909	can even use F<ev.h> as header file name directly.
3472		3910
3473		3911
3474	=head1 LIBEVENT EMULATION	3912	=head1 LIBEVENT EMULATION
3475		3913
3476	Libev offers a compatibility emulation layer for libevent. It cannot	3914	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3506		3944
3507	=back	3945	=back
3508		3946
3509	=head1 C++ SUPPORT	3947	=head1 C++ SUPPORT
3510		3948
		3949	=head2 C API
		3950
		3951	The normal C API should work fine when used from C++: both ev.h and the
		3952	libev sources can be compiled as C++. Therefore, code that uses the C API
		3953	will work fine.
		3954
		3955	Proper exception specifications might have to be added to callbacks passed
		3956	to libev: exceptions may be thrown only from watcher callbacks, all
		3957	other callbacks (allocator, syserr, loop acquire/release and periodic
		3958	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3959	()> specification. If you have code that needs to be compiled as both C
		3960	and C++ you can use the C<EV_THROW> macro for this:
		3961
		3962	static void
		3963	fatal_error (const char *msg) EV_THROW
		3964	{
		3965	perror (msg);
		3966	abort ();
		3967	}
		3968
		3969	...
		3970	ev_set_syserr_cb (fatal_error);
		3971
		3972	The only API functions that can currently throw exceptions are C<ev_run>,
		3973	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3974	because it runs cleanup watchers).
		3975
		3976	Throwing exceptions in watcher callbacks is only supported if libev itself
		3977	is compiled with a C++ compiler or your C and C++ environments allow
		3978	throwing exceptions through C libraries (most do).
		3979
		3980	=head2 C++ API
		3981
3511	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3982	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	3983	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.	3984	the callback model to a model using method callbacks on objects.
3514		3985
3515	To use it,	3986	To use it,
3516		3987
3517	#include <ev++.h>	3988	#include <ev++.h>
3518		3989
3519	This automatically includes F<ev.h> and puts all of its definitions (many	3990	This automatically includes F<ev.h> and puts all of its definitions (many
3520	of them macros) into the global namespace. All C++ specific things are	3991	of them macros) into the global namespace. All C++ specific things are
3521	put into the C<ev> namespace. It should support all the same embedding	3992	put into the C<ev> namespace. It should support all the same embedding
…		…
3530	with C<operator ()> can be used as callbacks. Other types should be easy	4001	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	4002	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	4003	you need support for other types of functors please contact the author
3533	(preferably after implementing it).	4004	(preferably after implementing it).
3534		4005
		4006	For all this to work, your C++ compiler either has to use the same calling
		4007	conventions as your C compiler (for static member functions), or you have
		4008	to embed libev and compile libev itself as C++.
		4009
3535	Here is a list of things available in the C<ev> namespace:	4010	Here is a list of things available in the C<ev> namespace:
3536		4011
3537	=over 4	4012	=over 4
3538		4013
3539	=item C<ev::READ>, C<ev::WRITE> etc.	4014	=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.	4023	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3549		4024
3550	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4025	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>	4026	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	4027	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3553	defines by many implementations.	4028	defined by many implementations.
3554		4029
3555	All of those classes have these methods:	4030	All of those classes have these methods:
3556		4031
3557	=over 4	4032	=over 4
3558		4033
…		…
3648	Associates a different C<struct ev_loop> with this watcher. You can only	4123	Associates a different C<struct ev_loop> with this watcher. You can only
3649	do this when the watcher is inactive (and not pending either).	4124	do this when the watcher is inactive (and not pending either).
3650		4125
3651	=item w->set ([arguments])	4126	=item w->set ([arguments])
3652		4127
3653	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4128	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3654	method or a suitable start method must be called at least once. Unlike the	4129	with the same arguments. Either this method or a suitable start method
3655	C counterpart, an active watcher gets automatically stopped and restarted	4130	must be called at least once. Unlike the C counterpart, an active watcher
3656	when reconfiguring it with this method.	4131	gets automatically stopped and restarted when reconfiguring it with this
		4132	method.
		4133
		4134	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4135	clashing with the C<set (loop)> method.
3657		4136
3658	=item w->start ()	4137	=item w->start ()
3659		4138
3660	Starts the watcher. Note that there is no C<loop> argument, as the	4139	Starts the watcher. Note that there is no C<loop> argument, as the
3661	constructor already stores the event loop.	4140	constructor already stores the event loop.
…		…
3691	watchers in the constructor.	4170	watchers in the constructor.
3692		4171
3693	class myclass	4172	class myclass
3694	{	4173	{
3695	ev::io io ; void io_cb (ev::io &w, int revents);	4174	ev::io io ; void io_cb (ev::io &w, int revents);
3696	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4175	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3697	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4176	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3698		4177
3699	myclass (int fd)	4178	myclass (int fd)
3700	{	4179	{
3701	io .set <myclass, &myclass::io_cb > (this);	4180	io .set <myclass, &myclass::io_cb > (this);
…		…
3752	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4231	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3753		4232
3754	=item D	4233	=item D
3755		4234
3756	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4235	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>.	4236	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3758		4237
3759	=item Ocaml	4238	=item Ocaml
3760		4239
3761	Erkki Seppala has written Ocaml bindings for libev, to be found at	4240	Erkki Seppala has written Ocaml bindings for libev, to be found at
3762	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4241	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3765		4244
3766	Brian Maher has written a partial interface to libev for lua (at the	4245	Brian Maher has written a partial interface to libev for lua (at the
3767	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4246	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3768	L<http://github.com/brimworks/lua-ev>.	4247	L<http://github.com/brimworks/lua-ev>.
3769		4248
		4249	=item Javascript
		4250
		4251	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4252
		4253	=item Others
		4254
		4255	There are others, and I stopped counting.
		4256
3770	=back	4257	=back
3771		4258
3772		4259
3773	=head1 MACRO MAGIC	4260	=head1 MACRO MAGIC
3774		4261
…		…
3810	suitable for use with C<EV_A>.	4297	suitable for use with C<EV_A>.
3811		4298
3812	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4299	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3813		4300
3814	Similar to the other two macros, this gives you the value of the default	4301	Similar to the other two macros, this gives you the value of the default
3815	loop, if multiple loops are supported ("ev loop default").	4302	loop, if multiple loops are supported ("ev loop default"). The default loop
		4303	will be initialised if it isn't already initialised.
		4304
		4305	For non-multiplicity builds, these macros do nothing, so you always have
		4306	to initialise the loop somewhere.
3816		4307
3817	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4308	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3818		4309
3819	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4310	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	4311	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3965	supported). It will also not define any of the structs usually found in	4456	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.	4457	F<event.h> that are not directly supported by the libev core alone.
3967		4458
3968	In standalone mode, libev will still try to automatically deduce the	4459	In standalone mode, libev will still try to automatically deduce the
3969	configuration, but has to be more conservative.	4460	configuration, but has to be more conservative.
		4461
		4462	=item EV_USE_FLOOR
		4463
		4464	If defined to be C<1>, libev will use the C<floor ()> function for its
		4465	periodic reschedule calculations, otherwise libev will fall back on a
		4466	portable (slower) implementation. If you enable this, you usually have to
		4467	link against libm or something equivalent. Enabling this when the C<floor>
		4468	function is not available will fail, so the safe default is to not enable
		4469	this.
3970		4470
3971	=item EV_USE_MONOTONIC	4471	=item EV_USE_MONOTONIC
3972		4472
3973	If defined to be C<1>, libev will try to detect the availability of the	4473	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	4474	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4059		4559
4060	If programs implement their own fd to handle mapping on win32, then this	4560	If programs implement their own fd to handle mapping on win32, then this
4061	macro can be used to override the C<close> function, useful to unregister	4561	macro can be used to override the C<close> function, useful to unregister
4062	file descriptors again. Note that the replacement function has to close	4562	file descriptors again. Note that the replacement function has to close
4063	the underlying OS handle.	4563	the underlying OS handle.
		4564
		4565	=item EV_USE_WSASOCKET
		4566
		4567	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4568	communication socket, which works better in some environments. Otherwise,
		4569	the normal C<socket> function will be used, which works better in other
		4570	environments.
4064		4571
4065	=item EV_USE_POLL	4572	=item EV_USE_POLL
4066		4573
4067	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4574	If defined to be C<1>, libev will compile in support for the C<poll>(2)
4068	backend. Otherwise it will be enabled on non-win32 platforms. It	4575	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
4104	If defined to be C<1>, libev will compile in support for the Linux inotify	4611	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	4612	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	4613	be detected at runtime. If undefined, it will be enabled if the headers
4107	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4614	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4108		4615
		4616	=item EV_NO_SMP
		4617
		4618	If defined to be C<1>, libev will assume that memory is always coherent
		4619	between threads, that is, threads can be used, but threads never run on
		4620	different cpus (or different cpu cores). This reduces dependencies
		4621	and makes libev faster.
		4622
		4623	=item EV_NO_THREADS
		4624
		4625	If defined to be C<1>, libev will assume that it will never be called from
		4626	different threads (that includes signal handlers), which is a stronger
		4627	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4628	libev faster.
		4629
4109	=item EV_ATOMIC_T	4630	=item EV_ATOMIC_T
4110		4631
4111	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4632	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	4633	access is atomic with respect to other threads or signal contexts. No
4113	type is easily found in the C language, so you can provide your own type	4634	such type is easily found in the C language, so you can provide your own
4114	that you know is safe for your purposes. It is used both for signal handler "locking"	4635	type that you know is safe for your purposes. It is used both for signal
4115	as well as for signal and thread safety in C<ev_async> watchers.	4636	handler "locking" as well as for signal and thread safety in C<ev_async>
		4637	watchers.
4116		4638
4117	In the absence of this define, libev will use C<sig_atomic_t volatile>	4639	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.	4640	(from F<signal.h>), which is usually good enough on most platforms.
4119		4641
4120	=item EV_H (h)	4642	=item EV_H (h)
…		…
4147	will have the C<struct ev_loop *> as first argument, and you can create	4669	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	4670	additional independent event loops. Otherwise there will be no support
4149	for multiple event loops and there is no first event loop pointer	4671	for multiple event loops and there is no first event loop pointer
4150	argument. Instead, all functions act on the single default loop.	4672	argument. Instead, all functions act on the single default loop.
4151		4673
		4674	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4675	default loop when multiplicity is switched off - you always have to
		4676	initialise the loop manually in this case.
		4677
4152	=item EV_MINPRI	4678	=item EV_MINPRI
4153		4679
4154	=item EV_MAXPRI	4680	=item EV_MAXPRI
4155		4681
4156	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4682	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4192	#define EV_USE_POLL 1	4718	#define EV_USE_POLL 1
4193	#define EV_CHILD_ENABLE 1	4719	#define EV_CHILD_ENABLE 1
4194	#define EV_ASYNC_ENABLE 1	4720	#define EV_ASYNC_ENABLE 1
4195		4721
4196	The actual value is a bitset, it can be a combination of the following	4722	The actual value is a bitset, it can be a combination of the following
4197	values:	4723	values (by default, all of these are enabled):
4198		4724
4199	=over 4	4725	=over 4
4200		4726
4201	=item C<1> - faster/larger code	4727	=item C<1> - faster/larger code
4202		4728
…		…
4206	code size by roughly 30% on amd64).	4732	code size by roughly 30% on amd64).
4207		4733
4208	When optimising for size, use of compiler flags such as C<-Os> with	4734	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	4735	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4210	assertions.	4736	assertions.
		4737
		4738	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4739	(e.g. gcc with C<-Os>).
4211		4740
4212	=item C<2> - faster/larger data structures	4741	=item C<2> - faster/larger data structures
4213		4742
4214	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4743	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	4744	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	4745	and can additionally have an effect on the size of data structures at
4217	runtime.	4746	runtime.
4218		4747
		4748	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4749	(e.g. gcc with C<-Os>).
		4750
4219	=item C<4> - full API configuration	4751	=item C<4> - full API configuration
4220		4752
4221	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4753	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4222	enables multiplicity (C<EV_MULTIPLICITY>=1).	4754	enables multiplicity (C<EV_MULTIPLICITY>=1).
4223		4755
…		…
4253		4785
4254	With an intelligent-enough linker (gcc+binutils are intelligent enough	4786	With an intelligent-enough linker (gcc+binutils are intelligent enough
4255	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4787	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	4788	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.	4789	I/O watcher then might come out at only 5Kb.
		4790
		4791	=item EV_API_STATIC
		4792
		4793	If this symbol is defined (by default it is not), then all identifiers
		4794	will have static linkage. This means that libev will not export any
		4795	identifiers, and you cannot link against libev anymore. This can be useful
		4796	when you embed libev, only want to use libev functions in a single file,
		4797	and do not want its identifiers to be visible.
		4798
		4799	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4800	wants to use libev.
		4801
		4802	This option only works when libev is compiled with a C compiler, as C++
		4803	doesn't support the required declaration syntax.
4258		4804
4259	=item EV_AVOID_STDIO	4805	=item EV_AVOID_STDIO
4260		4806
4261	If this is set to C<1> at compiletime, then libev will avoid using stdio	4807	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	4808	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:	4952	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4407		4953
4408	#include "ev_cpp.h"	4954	#include "ev_cpp.h"
4409	#include "ev.c"	4955	#include "ev.c"
4410		4956
4411	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4957	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4412		4958
4413	=head2 THREADS AND COROUTINES	4959	=head2 THREADS AND COROUTINES
4414		4960
4415	=head3 THREADS	4961	=head3 THREADS
4416		4962
…		…
4467	default loop and triggering an C<ev_async> watcher from the default loop	5013	default loop and triggering an C<ev_async> watcher from the default loop
4468	watcher callback into the event loop interested in the signal.	5014	watcher callback into the event loop interested in the signal.
4469		5015
4470	=back	5016	=back
4471		5017
4472	=head4 THREAD LOCKING EXAMPLE	5018	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		5019
4610	=head3 COROUTINES	5020	=head3 COROUTINES
4611		5021
4612	Libev is very accommodating to coroutines ("cooperative threads"):	5022	Libev is very accommodating to coroutines ("cooperative threads"):
4613	libev fully supports nesting calls to its functions from different	5023	libev fully supports nesting calls to its functions from different
…		…
4778	requires, and its I/O model is fundamentally incompatible with the POSIX	5188	requires, and its I/O model is fundamentally incompatible with the POSIX
4779	model. Libev still offers limited functionality on this platform in	5189	model. Libev still offers limited functionality on this platform in
4780	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5190	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4781	descriptors. This only applies when using Win32 natively, not when using	5191	descriptors. This only applies when using Win32 natively, not when using
4782	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5192	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4783	as every compielr comes with a slightly differently broken/incompatible	5193	as every compiler comes with a slightly differently broken/incompatible
4784	environment.	5194	environment.
4785		5195
4786	Lifting these limitations would basically require the full	5196	Lifting these limitations would basically require the full
4787	re-implementation of the I/O system. If you are into this kind of thing,	5197	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	5198	then note that glib does exactly that for you in a very portable way (note
…		…
4904	thread" or will block signals process-wide, both behaviours would	5314	thread" or will block signals process-wide, both behaviours would
4905	be compatible with libev. Interaction between C<sigprocmask> and	5315	be compatible with libev. Interaction between C<sigprocmask> and
4906	C<pthread_sigmask> could complicate things, however.	5316	C<pthread_sigmask> could complicate things, however.
4907		5317
4908	The most portable way to handle signals is to block signals in all threads	5318	The most portable way to handle signals is to block signals in all threads
4909	except the initial one, and run the default loop in the initial thread as	5319	except the initial one, and run the signal handling loop in the initial
4910	well.	5320	thread as well.
4911		5321
4912	=item C<long> must be large enough for common memory allocation sizes	5322	=item C<long> must be large enough for common memory allocation sizes
4913		5323
4914	To improve portability and simplify its API, libev uses C<long> internally	5324	To improve portability and simplify its API, libev uses C<long> internally
4915	instead of C<size_t> when allocating its data structures. On non-POSIX	5325	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4921		5331
4922	The type C<double> is used to represent timestamps. It is required to	5332	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	5333	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	5334	good enough for at least into the year 4000 with millisecond accuracy
4925	(the design goal for libev). This requirement is overfulfilled by	5335	(the design goal for libev). This requirement is overfulfilled by
4926	implementations using IEEE 754, which is basically all existing ones. With	5336	implementations using IEEE 754, which is basically all existing ones.
		5337
4927	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5338	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5339	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5340	is either obsolete or somebody patched it to use C<long double> or
		5341	something like that, just kidding).
4928		5342
4929	=back	5343	=back
4930		5344
4931	If you know of other additional requirements drop me a note.	5345	If you know of other additional requirements drop me a note.
4932		5346
…		…
4994	=item Processing ev_async_send: O(number_of_async_watchers)	5408	=item Processing ev_async_send: O(number_of_async_watchers)
4995		5409
4996	=item Processing signals: O(max_signal_number)	5410	=item Processing signals: O(max_signal_number)
4997		5411
4998	Sending involves a system call I<iff> there were no other C<ev_async_send>	5412	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	5413	calls in the current loop iteration and the loop is currently
		5414	blocked. Checking for async and signal events involves iterating over all
5000	involves iterating over all running async watchers or all signal numbers.	5415	running async watchers or all signal numbers.
5001		5416
5002	=back	5417	=back
5003		5418
5004		5419
5005	=head1 PORTING FROM LIBEV 3.X TO 4.X	5420	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5014	=over 4	5429	=over 4
5015		5430
5016	=item C<EV_COMPAT3> backwards compatibility mechanism	5431	=item C<EV_COMPAT3> backwards compatibility mechanism
5017		5432
5018	The backward compatibility mechanism can be controlled by	5433	The backward compatibility mechanism can be controlled by
5019	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5434	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
5020	section.	5435	section.
5021		5436
5022	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5437	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
5023		5438
5024	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5439	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5067	=over 4	5482	=over 4
5068		5483
5069	=item active	5484	=item active
5070		5485
5071	A watcher is active as long as it has been started and not yet stopped.	5486	A watcher is active as long as it has been started and not yet stopped.
5072	See L<WATCHER STATES> for details.	5487	See L</WATCHER STATES> for details.
5073		5488
5074	=item application	5489	=item application
5075		5490
5076	In this document, an application is whatever is using libev.	5491	In this document, an application is whatever is using libev.
5077		5492
…		…
5113	watchers and events.	5528	watchers and events.
5114		5529
5115	=item pending	5530	=item pending
5116		5531
5117	A watcher is pending as soon as the corresponding event has been	5532	A watcher is pending as soon as the corresponding event has been
5118	detected. See L<WATCHER STATES> for details.	5533	detected. See L</WATCHER STATES> for details.
5119		5534
5120	=item real time	5535	=item real time
5121		5536
5122	The physical time that is observed. It is apparently strictly monotonic :)	5537	The physical time that is observed. It is apparently strictly monotonic :)
5123		5538
5124	=item wall-clock time	5539	=item wall-clock time
5125		5540
5126	The time and date as shown on clocks. Unlike real time, it can actually	5541	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	5542	be wrong and jump forwards and backwards, e.g. when you adjust your
5128	clock.	5543	clock.
5129		5544
5130	=item watcher	5545	=item watcher
5131		5546
5132	A data structure that describes interest in certain events. Watchers need	5547	A data structure that describes interest in certain events. Watchers need
…		…
5135	=back	5550	=back
5136		5551
5137	=head1 AUTHOR	5552	=head1 AUTHOR
5138		5553
5139	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5554	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5140	Magnusson and Emanuele Giaquinta.	5555	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5141		5556

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