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Revision 1.352 by root, Mon Jan 10 14:30:15 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
…		…
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> - so bizarre that	613	On the negative side, the interface is I<bizarre> - so bizarre that
598	even sun itself gets it wrong in their code examples: The event polling	614	even sun itself gets it wrong in their code examples: The event polling
599	function sometimes returning events to the caller even though an error	615	function sometimes returns events to the caller even though an error
600	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
601	even documented that way) - deadly for edge-triggered interfaces where	617	even documented that way) - deadly for edge-triggered interfaces where you
602	you absolutely have to know whether an event occured or not because you	618	absolutely have to know whether an event occurred or not because you have
603	have to re-arm the watcher.	619	to re-arm the watcher.
604		620
605	Fortunately libev seems to be able to work around these idiocies.	621	Fortunately libev seems to be able to work around these idiocies.
606		622
607	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
608	C<EVBACKEND_POLL>.	624	C<EVBACKEND_POLL>.
…		…
670	reinitialise the kernel state for backends that have one. Despite the	686	reinitialise the kernel state for backends that have one. Despite the
671	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
672	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
673	child before resuming or calling C<ev_run>.	689	child before resuming or calling C<ev_run>.
674		690
675	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
676	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
677	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	693	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
678	during fork.	694	during fork.
679		695
680	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
…		…
750		766
751	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
752	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
753	the current time is a good idea.	769	the current time is a good idea.
754		770
755	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.
756		772
757	=item ev_suspend (loop)	773	=item ev_suspend (loop)
758		774
759	=item ev_resume (loop)	775	=item ev_resume (loop)
760		776
…		…
778	without a previous call to C<ev_suspend>.	794	without a previous call to C<ev_suspend>.
779		795
780	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
781	event loop time (see C<ev_now_update>).	797	event loop time (see C<ev_now_update>).
782		798
783	=item ev_run (loop, int flags)	799	=item bool ev_run (loop, int flags)
784		800
785	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
786	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
787	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
788	the watcher callbacks, an then repeat the whole process indefinitely: This	804	the watcher callbacks, and then repeat the whole process indefinitely: This
789	is why event loops are called I<loops>.	805	is why event loops are called I<loops>.
790		806
791	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
792	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
793	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").
794		814
795	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
796	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
797	finished (especially in interactive programs), but having a program	817	finished (especially in interactive programs), but having a program
798	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
799	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
800	beauty.	820	beauty.
801		821
802	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
803	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++
804	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
805	will it clear any outstanding C<EVBREAK_ONE> breaks.	825	will it clear any outstanding C<EVBREAK_ONE> breaks.
806		826
807	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
808	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
…		…
820	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
821	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
822	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
823	usually a better approach for this kind of thing.	843	usually a better approach for this kind of thing.
824		844
825	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):
826		848
827	- Increment loop depth.	849	- Increment loop depth.
828	- Reset the ev_break status.	850	- Reset the ev_break status.
829	- Before the first iteration, call any pending watchers.	851	- Before the first iteration, call any pending watchers.
830	LOOP:	852	LOOP:
…		…
863	anymore.	885	anymore.
864		886
865	... queue jobs here, make sure they register event watchers as long	887	... queue jobs here, make sure they register event watchers as long
866	... 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..)
867	ev_run (my_loop, 0);	889	ev_run (my_loop, 0);
868	... jobs done or somebody called unloop. yeah!	890	... jobs done or somebody called break. yeah!
869		891
870	=item ev_break (loop, how)	892	=item ev_break (loop, how)
871		893
872	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
873	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
…		…
936	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.
937		959
938	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
939	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,
940	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
941	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
942	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
943	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
944	once per this interval, on average.	966	once per this interval, on average (as long as the host time resolution is
		967	good enough).
945		968
946	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
947	to spend more time collecting timeouts, at the expense of increased	970	to spend more time collecting timeouts, at the expense of increased
948	latency/jitter/inexactness (the watcher callback will be called	971	latency/jitter/inexactness (the watcher callback will be called
949	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
…		…
995	invoke the actual watchers inside another context (another thread etc.).	1018	invoke the actual watchers inside another context (another thread etc.).
996		1019
997	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
998	callback.	1021	callback.
999		1022
1000	=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 ())
1001		1024
1002	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
1003	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
1004	each call to a libev function.	1027	each call to a libev function.
1005		1028
1006	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
1007	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
1008	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
1009	I<release> and I<acquire> callbacks on the loop.	1032	I<release> and I<acquire> callbacks on the loop.
1010		1033
1011	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
1012	suspended waiting for new events, and C<acquire> is called just	1035	suspended waiting for new events, and C<acquire> is called just
1013	afterwards.	1036	afterwards.
…		…
1153		1176
1154	=item C<EV_PREPARE>	1177	=item C<EV_PREPARE>
1155		1178
1156	=item C<EV_CHECK>	1179	=item C<EV_CHECK>
1157		1180
1158	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
1159	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)
1160	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
1161	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
1162	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
1163	(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
1164	C<ev_run> from blocking).	1192	blocking).
1165		1193
1166	=item C<EV_EMBED>	1194	=item C<EV_EMBED>
1167		1195
1168	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.
1169		1197
…		…
1292		1320
1293	=item callback ev_cb (ev_TYPE *watcher)	1321	=item callback ev_cb (ev_TYPE *watcher)
1294		1322
1295	Returns the callback currently set on the watcher.	1323	Returns the callback currently set on the watcher.
1296		1324
1297	=item ev_cb_set (ev_TYPE *watcher, callback)	1325	=item ev_set_cb (ev_TYPE *watcher, callback)
1298		1326
1299	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
1300	(modulo threads).	1328	(modulo threads).
1301		1329
1302	=item ev_set_priority (ev_TYPE *watcher, int priority)	1330	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1320	or might not have been clamped to the valid range.	1348	or might not have been clamped to the valid range.
1321		1349
1322	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
1323	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 :).
1324		1352
1325	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
1326	priorities.	1354	priorities.
1327		1355
1328	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1356	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1329		1357
1330	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
…		…
1355	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
1356	functions that do not need a watcher.	1384	functions that do not need a watcher.
1357		1385
1358	=back	1386	=back
1359		1387
1360	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1388	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1361		1389	OWN COMPOSITE WATCHERS> idioms.
1362	Each watcher has, by default, a member C<void *data> that you can change
1363	and read at any time: libev will completely ignore it. This can be used
1364	to associate arbitrary data with your watcher. If you need more data and
1365	don't want to allocate memory and store a pointer to it in that data
1366	member, you can also "subclass" the watcher type and provide your own
1367	data:
1368
1369	struct my_io
1370	{
1371	ev_io io;
1372	int otherfd;
1373	void *somedata;
1374	struct whatever *mostinteresting;
1375	};
1376
1377	...
1378	struct my_io w;
1379	ev_io_init (&w.io, my_cb, fd, EV_READ);
1380
1381	And since your callback will be called with a pointer to the watcher, you
1382	can cast it back to your own type:
1383
1384	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1385	{
1386	struct my_io *w = (struct my_io *)w_;
1387	...
1388	}
1389
1390	More interesting and less C-conformant ways of casting your callback type
1391	instead have been omitted.
1392
1393	Another common scenario is to use some data structure with multiple
1394	embedded watchers:
1395
1396	struct my_biggy
1397	{
1398	int some_data;
1399	ev_timer t1;
1400	ev_timer t2;
1401	}
1402
1403	In this case getting the pointer to C<my_biggy> is a bit more
1404	complicated: Either you store the address of your C<my_biggy> struct
1405	in the C<data> member of the watcher (for woozies), or you need to use
1406	some pointer arithmetic using C<offsetof> inside your watchers (for real
1407	programmers):
1408
1409	#include <stddef.h>
1410
1411	static void
1412	t1_cb (EV_P_ ev_timer *w, int revents)
1413	{
1414	struct my_biggy big = (struct my_biggy *)
1415	(((char *)w) - offsetof (struct my_biggy, t1));
1416	}
1417
1418	static void
1419	t2_cb (EV_P_ ev_timer *w, int revents)
1420	{
1421	struct my_biggy big = (struct my_biggy *)
1422	(((char *)w) - offsetof (struct my_biggy, t2));
1423	}
1424		1390
1425	=head2 WATCHER STATES	1391	=head2 WATCHER STATES
1426		1392
1427	There are various watcher states mentioned throughout this manual -	1393	There are various watcher states mentioned throughout this manual -
1428	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
1429	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
1430	rules might look complicated, they usually do "the right thing".	1396	rules might look complicated, they usually do "the right thing".
1431		1397
1432	=over 4	1398	=over 4
1433		1399
1434	=item initialiased	1400	=item initialised
1435		1401
1436	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
1437	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
1438	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.
1439		1405
1440	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
1441	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.
1442		1410
1443	=item started/running/active	1411	=item started/running/active
1444		1412
1445	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
1446	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
…		…
1474	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
1475	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
1476	freeing it is often a good idea.	1444	freeing it is often a good idea.
1477		1445
1478	While stopped (and not pending) the watcher is essentially in the	1446	While stopped (and not pending) the watcher is essentially in the
1479	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
1480	you wish.	1448	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1449	it again).
1481		1450
1482	=back	1451	=back
1483		1452
1484	=head2 WATCHER PRIORITY MODELS	1453	=head2 WATCHER PRIORITY MODELS
1485		1454
…		…
1614	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
1615	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
1616	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
1617	required if you know what you are doing).	1586	required if you know what you are doing).
1618		1587
1619	If you cannot use non-blocking mode, then force the use of a
1620	known-to-be-good backend (at the time of this writing, this includes only
1621	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1622	descriptors for which non-blocking operation makes no sense (such as
1623	files) - libev doesn't guarantee any specific behaviour in that case.
1624
1625	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
1626	receive "spurious" readiness notifications, that is your callback might	1589	receive "spurious" readiness notifications, that is, your callback might
1627	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
1628	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
1629	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
1630	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
1631	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1632	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1594	preferable to a program hanging until some data arrives.
1633		1595
1634	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
1635	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
1636	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
1637	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
1638	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
1639	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
1640	indefinitely.	1602	indefinitely.
1641		1603
1642	But really, best use non-blocking mode.	1604	But really, best use non-blocking mode.
1643		1605
…		…
1671		1633
1672	There is no workaround possible except not registering events	1634	There is no workaround possible except not registering events
1673	for potentially C<dup ()>'ed file descriptors, or to resort to	1635	for potentially C<dup ()>'ed file descriptors, or to resort to
1674	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1636	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1675		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
1676	=head3 The special problem of fork	1671	=head3 The special problem of fork
1677		1672
1678	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
1679	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
1680	it in the child.	1675	it in the child if you want to continue to use it in the child.
1681		1676
1682	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
1683	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
1684	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1679	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1685	C<EVBACKEND_POLL>.
1686		1680
1687	=head3 The special problem of SIGPIPE	1681	=head3 The special problem of SIGPIPE
1688		1682
1689	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>:
1690	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
…		…
1788	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1782	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1789	monotonic clock option helps a lot here).	1783	monotonic clock option helps a lot here).
1790		1784
1791	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
1792	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
1793	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
1794	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
1795	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
1796	no longer true when a callback calls C<ev_run> recursively).	1791	longer true when a callback calls C<ev_run> recursively).
1797		1792
1798	=head3 Be smart about timeouts	1793	=head3 Be smart about timeouts
1799		1794
1800	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
1801	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,
…		…
1876		1871
1877	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,
1878	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
1879	within the callback:	1874	within the callback:
1880		1875
		1876	ev_tstamp timeout = 60.;
1881	ev_tstamp last_activity; // time of last activity	1877	ev_tstamp last_activity; // time of last activity
		1878	ev_timer timer;
1882		1879
1883	static void	1880	static void
1884	callback (EV_P_ ev_timer *w, int revents)	1881	callback (EV_P_ ev_timer *w, int revents)
1885	{	1882	{
1886	ev_tstamp now = ev_now (EV_A);	1883	// calculate when the timeout would happen
1887	ev_tstamp timeout = last_activity + 60.;	1884	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1888		1885
1889	// if last_activity + 60. is older than now, we did time out	1886	// if negative, it means we the timeout already occurred
1890	if (timeout < now)	1887	if (after < 0.)
1891	{	1888	{
1892	// timeout occurred, take action	1889	// timeout occurred, take action
1893	}	1890	}
1894	else	1891	else
1895	{	1892	{
1896	// callback was invoked, but there was some activity, re-arm	1893	// callback was invoked, but there was some recent
1897	// the watcher to fire in last_activity + 60, which is	1894	// activity. simply restart the timer to time out
1898	// guaranteed to be in the future, so "again" is positive:	1895	// after "after" seconds, which is the earliest time
1899	w->repeat = timeout - now;	1896	// the timeout can occur.
		1897	ev_timer_set (w, after, 0.);
1900	ev_timer_again (EV_A_ w);	1898	ev_timer_start (EV_A_ w);
1901	}	1899	}
1902	}	1900	}
1903		1901
1904	To summarise the callback: first calculate the real timeout (defined	1902	To summarise the callback: first calculate in how many seconds the
1905	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,
1906	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
1907	the callback was invoked too early (C<timeout> is in the future), so	1905	(EV_A)> from that).
1908	re-schedule the timer to fire at that future time, to see if maybe we have
1909	a timeout then.
1910		1906
1911	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
1912	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.
1913		1916
1914	This scheme causes more callback invocations (about one every 60 seconds	1917	This scheme causes more callback invocations (about one every 60 seconds
1915	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
1916	libev to change the timeout.	1919	libev to change the timeout.
1917		1920
1918	To start the timer, simply initialise the watcher and set C<last_activity>	1921	To start the machinery, simply initialise the watcher and set
1919	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
1920	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:
1921		1925
		1926	last_activity = ev_now (EV_A);
1922	ev_init (timer, callback);	1927	ev_init (&timer, callback);
1923	last_activity = ev_now (loop);	1928	callback (EV_A_ &timer, 0);
1924	callback (loop, timer, EV_TIMER);
1925		1929
1926	And when there is some activity, simply store the current time in	1930	When there is some activity, simply store the current time in
1927	C<last_activity>, no libev calls at all:	1931	C<last_activity>, no libev calls at all:
1928		1932
		1933	if (activity detected)
1929	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);
1930		1943
1931	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
1932	time-out is unlikely to be triggered, much more efficient.	1945	time-out is unlikely to be triggered, much more efficient.
1933
1934	Changing the timeout is trivial as well (if it isn't hard-coded in the
1935	callback :) - just change the timeout and invoke the callback, which will
1936	fix things for you.
1937		1946
1938	=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.
1939		1948
1940	If there is not one request, but many thousands (millions...), all	1949	If there is not one request, but many thousands (millions...), all
1941	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
…		…
1968	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
1969	rather complicated, but extremely efficient, something that really pays	1978	rather complicated, but extremely efficient, something that really pays
1970	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
1971	overkill :)	1980	overkill :)
1972		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
1973	=head3 The special problem of time updates	2019	=head3 The special problem of time updates
1974		2020
1975	Establishing the current time is a costly operation (it usually takes at	2021	Establishing the current time is a costly operation (it usually takes
1976	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
1977	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
1978	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
1979	lots of events in one iteration.	2025	lots of events in one iteration.
1980		2026
1981	The relative timeouts are calculated relative to the C<ev_now ()>	2027	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1987	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2033	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1988		2034
1989	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
1990	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
1991	()>.	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.
1992		2071
1993	=head3 The special problems of suspended animation	2072	=head3 The special problems of suspended animation
1994		2073
1995	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
1996	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?
…		…
2040	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
2041	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.
2042		2121
2043	=item ev_timer_again (loop, ev_timer *)	2122	=item ev_timer_again (loop, ev_timer *)
2044		2123
2045	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
2046	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>.
2047		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
2048	If the timer is pending, its pending status is cleared.	2133	=item If the timer is pending, the pending status is always cleared.
2049		2134
2050	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).
2051		2137
2052	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
2053	C<repeat> value), or reset the running timer to the C<repeat> value.	2139	and start the timer, if necessary.
2054		2140
		2141	=back
		2142
2055	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
2056	usage example.	2144	usage example.
2057		2145
2058	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2146	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2059		2147
2060	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,
…		…
2180		2268
2181	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
2182	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
2183	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.
2184		2272
2185	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
2186	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
2187	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.
2188		2279
2189	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
2190	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
2191	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
2192	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).
…		…
2335	=head3 The special problem of inheritance over fork/execve/pthread_create	2426	=head3 The special problem of inheritance over fork/execve/pthread_create
2336		2427
2337	Both the signal mask (C<sigprocmask>) and the signal disposition	2428	Both the signal mask (C<sigprocmask>) and the signal disposition
2338	(C<sigaction>) are unspecified after starting a signal watcher (and after	2429	(C<sigaction>) are unspecified after starting a signal watcher (and after
2339	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,
2340	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>).
2341		2433
2342	While this does not matter for the signal disposition (libev never	2434	While this does not matter for the signal disposition (libev never
2343	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
2344	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
2345	certain signals to be blocked.	2437	certain signals to be blocked.
…		…
2516		2608
2517	=head2 C<ev_stat> - did the file attributes just change?	2609	=head2 C<ev_stat> - did the file attributes just change?
2518		2610
2519	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
2520	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)
2521	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
2522	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.
2523		2616
2524	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
2525	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
2526	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
2527	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
…		…
2757	Apart from keeping your process non-blocking (which is a useful	2850	Apart from keeping your process non-blocking (which is a useful
2758	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
2759	"pseudo-background processing", or delay processing stuff to after the	2852	"pseudo-background processing", or delay processing stuff to after the
2760	event loop has handled all outstanding events.	2853	event loop has handled all outstanding events.
2761		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
2762	=head3 Watcher-Specific Functions and Data Members	2869	=head3 Watcher-Specific Functions and Data Members
2763		2870
2764	=over 4	2871	=over 4
2765		2872
2766	=item ev_idle_init (ev_idle *, callback)	2873	=item ev_idle_init (ev_idle *, callback)
…		…
2777	callback, free it. Also, use no error checking, as usual.	2884	callback, free it. Also, use no error checking, as usual.
2778		2885
2779	static void	2886	static void
2780	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2887	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2781	{	2888	{
		2889	// stop the watcher
		2890	ev_idle_stop (loop, w);
		2891
		2892	// now we can free it
2782	free (w);	2893	free (w);
		2894
2783	// now do something you wanted to do when the program has	2895	// now do something you wanted to do when the program has
2784	// no longer anything immediate to do.	2896	// no longer anything immediate to do.
2785	}	2897	}
2786		2898
2787	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2899	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2789	ev_idle_start (loop, idle_watcher);	2901	ev_idle_start (loop, idle_watcher);
2790		2902
2791		2903
2792	=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!
2793		2905
2794	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:
2795	prepare watchers get invoked before the process blocks and check watchers	2907	prepare watchers get invoked before the process blocks and check watchers
2796	afterwards.	2908	afterwards.
2797		2909
2798	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
2799	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>
…		…
2827	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
2828	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
2829	loop from blocking if lower-priority coroutines are active, thus mapping	2941	loop from blocking if lower-priority coroutines are active, thus mapping
2830	low-priority coroutines to idle/background tasks).	2942	low-priority coroutines to idle/background tasks).
2831		2943
2832	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
2833	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
2834	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).
2835		2948
2836	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
2837	activate ("feed") events into libev. While libev fully supports this, they	2950	activate ("feed") events into libev. While libev fully supports this, they
2838	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
2839	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
2840	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
2841	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
2842	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.
2843		2975
2844	=head3 Watcher-Specific Functions and Data Members	2976	=head3 Watcher-Specific Functions and Data Members
2845		2977
2846	=over 4	2978	=over 4
2847		2979
…		…
3048		3180
3049	=over 4	3181	=over 4
3050		3182
3051	=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)
3052		3184
3053	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3185	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3054		3186
3055	Configures the watcher to embed the given loop, which must be	3187	Configures the watcher to embed the given loop, which must be
3056	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
3057	invoked automatically, otherwise it is the responsibility of the callback	3189	invoked automatically, otherwise it is the responsibility of the callback
3058	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,
…		…
3121		3253
3122	=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
3123		3255
3124	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
3125	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
3126	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
3127	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
3128	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
3129	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,
3130	handlers will be invoked, too, of course.	3262	of course.
3131		3263
3132	=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?
3133		3265
3134	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
3135	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
…		…
3216	atexit (program_exits);	3348	atexit (program_exits);
3217		3349
3218		3350
3219	=head2 C<ev_async> - how to wake up an event loop	3351	=head2 C<ev_async> - how to wake up an event loop
3220		3352
3221	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
3222	asynchronous sources such as signal handlers (as opposed to multiple event	3354	asynchronous sources such as signal handlers (as opposed to multiple event
3223	loops - those are of course safe to use in different threads).	3355	loops - those are of course safe to use in different threads).
3224		3356
3225	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,
3226	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>
…		…
3228	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.
3229		3361
3230	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,
3231	too, are asynchronous in nature, and signals, too, will be compressed	3363	too, are asynchronous in nature, and signals, too, will be compressed
3232	(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
3233	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
3234	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
3235	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,
3236	even without knowing which loop owns the signal.	3368	even without knowing which loop owns the signal.
3237
3238	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3239	just the default loop.
3240		3369
3241	=head3 Queueing	3370	=head3 Queueing
3242		3371
3243	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
3244	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
…		…
3336	trust me.	3465	trust me.
3337		3466
3338	=item ev_async_send (loop, ev_async *)	3467	=item ev_async_send (loop, ev_async *)
3339		3468
3340	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
3341	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
3342	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,
3343	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
3344	section below on what exactly this means).	3475	embedding section below on what exactly this means).
3345		3476
3346	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
3347	compressed into a single callback invocation (another way to look at this	3478	compressed into a single callback invocation (another way to look at
3348	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
3349	reset when the event loop detects that).	3480	C<ev_async_send>, reset when the event loop detects that).
3350		3481
3351	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
3352	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
3353	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.
3354		3488
3355	=item bool = ev_async_pending (ev_async *)	3489	=item bool = ev_async_pending (ev_async *)
3356		3490
3357	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
3358	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
…		…
3413	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3547	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3414		3548
3415	=item ev_feed_fd_event (loop, int fd, int revents)	3549	=item ev_feed_fd_event (loop, int fd, int revents)
3416		3550
3417	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
3418	the given events it.	3552	the given events.
3419		3553
3420	=item ev_feed_signal_event (loop, int signum)	3554	=item ev_feed_signal_event (loop, int signum)
3421		3555
3422	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>,
3423	which is async-safe.	3557	which is async-safe.
…		…
3429		3563
3430	This section explains some common idioms that are not immediately	3564	This section explains some common idioms that are not immediately
3431	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
3432	section only contains stuff that wouldn't fit anywhere else.	3566	section only contains stuff that wouldn't fit anywhere else.
3433		3567
3434	=over 4	3568	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3435		3569
3436	=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
3437		3677
3438	Often (especially in GUI toolkits) there are places where you have	3678	Often (especially in GUI toolkits) there are places where you have
3439	I<modal> interaction, which is most easily implemented by recursively	3679	I<modal> interaction, which is most easily implemented by recursively
3440	invoking C<ev_run>.	3680	invoking C<ev_run>.
3441		3681
3442	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
3443	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
3444	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
3445	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
3446	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.
3447		3687
3448	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>
3449	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
3450	triggered, using C<EVRUN_ONCE>:	3690	triggered, using C<EVRUN_ONCE>:
3451		3691
…		…
3453	int exit_main_loop = 0;	3693	int exit_main_loop = 0;
3454		3694
3455	while (!exit_main_loop)	3695	while (!exit_main_loop)
3456	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3696	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3457		3697
3458	// in a model watcher	3698	// in a modal watcher
3459	int exit_nested_loop = 0;	3699	int exit_nested_loop = 0;
3460		3700
3461	while (!exit_nested_loop)	3701	while (!exit_nested_loop)
3462	ev_run (EV_A_ EVRUN_ONCE);	3702	ev_run (EV_A_ EVRUN_ONCE);
3463		3703
…		…
3470	exit_main_loop = 1;	3710	exit_main_loop = 1;
3471		3711
3472	// exit both	3712	// exit both
3473	exit_main_loop = exit_nested_loop = 1;	3713	exit_main_loop = exit_nested_loop = 1;
3474		3714
3475	=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.
3476		3910
3477		3911
3478	=head1 LIBEVENT EMULATION	3912	=head1 LIBEVENT EMULATION
3479		3913
3480	Libev offers a compatibility emulation layer for libevent. It cannot	3914	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3510		3944
3511	=back	3945	=back
3512		3946
3513	=head1 C++ SUPPORT	3947	=head1 C++ SUPPORT
3514		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
3515	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
3516	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
3517	the callback model to a model using method callbacks on objects.	3984	the callback model to a model using method callbacks on objects.
3518		3985
3519	To use it,	3986	To use it,
3520		3987
3521	#include <ev++.h>	3988	#include <ev++.h>
3522		3989
3523	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
3524	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
3525	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
…		…
3534	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
3535	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
3536	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
3537	(preferably after implementing it).	4004	(preferably after implementing it).
3538		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
3539	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:
3540		4011
3541	=over 4	4012	=over 4
3542		4013
3543	=item C<ev::READ>, C<ev::WRITE> etc.	4014	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3552	=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.
3553		4024
3554	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
3555	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>
3556	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
3557	defines by many implementations.	4028	defined by many implementations.
3558		4029
3559	All of those classes have these methods:	4030	All of those classes have these methods:
3560		4031
3561	=over 4	4032	=over 4
3562		4033
…		…
3652	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
3653	do this when the watcher is inactive (and not pending either).	4124	do this when the watcher is inactive (and not pending either).
3654		4125
3655	=item w->set ([arguments])	4126	=item w->set ([arguments])
3656		4127
3657	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>),
3658	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
3659	C counterpart, an active watcher gets automatically stopped and restarted	4130	must be called at least once. Unlike the C counterpart, an active watcher
3660	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.
3661		4136
3662	=item w->start ()	4137	=item w->start ()
3663		4138
3664	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
3665	constructor already stores the event loop.	4140	constructor already stores the event loop.
…		…
3695	watchers in the constructor.	4170	watchers in the constructor.
3696		4171
3697	class myclass	4172	class myclass
3698	{	4173	{
3699	ev::io io ; void io_cb (ev::io &w, int revents);	4174	ev::io io ; void io_cb (ev::io &w, int revents);
3700	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4175	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3701	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4176	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3702		4177
3703	myclass (int fd)	4178	myclass (int fd)
3704	{	4179	{
3705	io .set <myclass, &myclass::io_cb > (this);	4180	io .set <myclass, &myclass::io_cb > (this);
…		…
3756	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4231	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3757		4232
3758	=item D	4233	=item D
3759		4234
3760	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
3761	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>.
3762		4237
3763	=item Ocaml	4238	=item Ocaml
3764		4239
3765	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
3766	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4241	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3769		4244
3770	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
3771	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
3772	L<http://github.com/brimworks/lua-ev>.	4247	L<http://github.com/brimworks/lua-ev>.
3773		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
3774	=back	4257	=back
3775		4258
3776		4259
3777	=head1 MACRO MAGIC	4260	=head1 MACRO MAGIC
3778		4261
…		…
3814	suitable for use with C<EV_A>.	4297	suitable for use with C<EV_A>.
3815		4298
3816	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4299	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3817		4300
3818	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
3819	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.
3820		4307
3821	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4308	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3822		4309
3823	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
3824	default loop has been initialised (C<UC> == unchecked). Their behaviour	4311	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3969	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
3970	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.
3971		4458
3972	In standalone mode, libev will still try to automatically deduce the	4459	In standalone mode, libev will still try to automatically deduce the
3973	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.
3974		4470
3975	=item EV_USE_MONOTONIC	4471	=item EV_USE_MONOTONIC
3976		4472
3977	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
3978	monotonic clock option at both compile time and runtime. Otherwise no	4474	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4063		4559
4064	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
4065	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
4066	file descriptors again. Note that the replacement function has to close	4562	file descriptors again. Note that the replacement function has to close
4067	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.
4068		4571
4069	=item EV_USE_POLL	4572	=item EV_USE_POLL
4070		4573
4071	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)
4072	backend. Otherwise it will be enabled on non-win32 platforms. It	4575	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
4108	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
4109	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
4110	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
4111	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4614	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4112		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
4113	=item EV_ATOMIC_T	4630	=item EV_ATOMIC_T
4114		4631
4115	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
4116	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
4117	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
4118	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
4119	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.
4120		4638
4121	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>
4122	(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.
4123		4641
4124	=item EV_H (h)	4642	=item EV_H (h)
…		…
4151	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
4152	additional independent event loops. Otherwise there will be no support	4670	additional independent event loops. Otherwise there will be no support
4153	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
4154	argument. Instead, all functions act on the single default loop.	4672	argument. Instead, all functions act on the single default loop.
4155		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
4156	=item EV_MINPRI	4678	=item EV_MINPRI
4157		4679
4158	=item EV_MAXPRI	4680	=item EV_MAXPRI
4159		4681
4160	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
…		…
4196	#define EV_USE_POLL 1	4718	#define EV_USE_POLL 1
4197	#define EV_CHILD_ENABLE 1	4719	#define EV_CHILD_ENABLE 1
4198	#define EV_ASYNC_ENABLE 1	4720	#define EV_ASYNC_ENABLE 1
4199		4721
4200	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
4201	values:	4723	values (by default, all of these are enabled):
4202		4724
4203	=over 4	4725	=over 4
4204		4726
4205	=item C<1> - faster/larger code	4727	=item C<1> - faster/larger code
4206		4728
…		…
4210	code size by roughly 30% on amd64).	4732	code size by roughly 30% on amd64).
4211		4733
4212	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
4213	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
4214	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>).
4215		4740
4216	=item C<2> - faster/larger data structures	4741	=item C<2> - faster/larger data structures
4217		4742
4218	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
4219	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
4220	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
4221	runtime.	4746	runtime.
4222		4747
		4748	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4749	(e.g. gcc with C<-Os>).
		4750
4223	=item C<4> - full API configuration	4751	=item C<4> - full API configuration
4224		4752
4225	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
4226	enables multiplicity (C<EV_MULTIPLICITY>=1).	4754	enables multiplicity (C<EV_MULTIPLICITY>=1).
4227		4755
…		…
4257		4785
4258	With an intelligent-enough linker (gcc+binutils are intelligent enough	4786	With an intelligent-enough linker (gcc+binutils are intelligent enough
4259	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
4260	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
4261	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.
4262		4804
4263	=item EV_AVOID_STDIO	4805	=item EV_AVOID_STDIO
4264		4806
4265	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
4266	functions (printf, scanf, perror etc.). This will increase the code size	4808	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4410	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:
4411		4953
4412	#include "ev_cpp.h"	4954	#include "ev_cpp.h"
4413	#include "ev.c"	4955	#include "ev.c"
4414		4956
4415	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4957	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4416		4958
4417	=head2 THREADS AND COROUTINES	4959	=head2 THREADS AND COROUTINES
4418		4960
4419	=head3 THREADS	4961	=head3 THREADS
4420		4962
…		…
4471	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
4472	watcher callback into the event loop interested in the signal.	5014	watcher callback into the event loop interested in the signal.
4473		5015
4474	=back	5016	=back
4475		5017
4476	=head4 THREAD LOCKING EXAMPLE	5018	See also L</THREAD LOCKING EXAMPLE>.
4477
4478	Here is a fictitious example of how to run an event loop in a different
4479	thread than where callbacks are being invoked and watchers are
4480	created/added/removed.
4481
4482	For a real-world example, see the C<EV::Loop::Async> perl module,
4483	which uses exactly this technique (which is suited for many high-level
4484	languages).
4485
4486	The example uses a pthread mutex to protect the loop data, a condition
4487	variable to wait for callback invocations, an async watcher to notify the
4488	event loop thread and an unspecified mechanism to wake up the main thread.
4489
4490	First, you need to associate some data with the event loop:
4491
4492	typedef struct {
4493	mutex_t lock; /* global loop lock */
4494	ev_async async_w;
4495	thread_t tid;
4496	cond_t invoke_cv;
4497	} userdata;
4498
4499	void prepare_loop (EV_P)
4500	{
4501	// for simplicity, we use a static userdata struct.
4502	static userdata u;
4503
4504	ev_async_init (&u->async_w, async_cb);
4505	ev_async_start (EV_A_ &u->async_w);
4506
4507	pthread_mutex_init (&u->lock, 0);
4508	pthread_cond_init (&u->invoke_cv, 0);
4509
4510	// now associate this with the loop
4511	ev_set_userdata (EV_A_ u);
4512	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4513	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4514
4515	// then create the thread running ev_loop
4516	pthread_create (&u->tid, 0, l_run, EV_A);
4517	}
4518
4519	The callback for the C<ev_async> watcher does nothing: the watcher is used
4520	solely to wake up the event loop so it takes notice of any new watchers
4521	that might have been added:
4522
4523	static void
4524	async_cb (EV_P_ ev_async *w, int revents)
4525	{
4526	// just used for the side effects
4527	}
4528
4529	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4530	protecting the loop data, respectively.
4531
4532	static void
4533	l_release (EV_P)
4534	{
4535	userdata *u = ev_userdata (EV_A);
4536	pthread_mutex_unlock (&u->lock);
4537	}
4538
4539	static void
4540	l_acquire (EV_P)
4541	{
4542	userdata *u = ev_userdata (EV_A);
4543	pthread_mutex_lock (&u->lock);
4544	}
4545
4546	The event loop thread first acquires the mutex, and then jumps straight
4547	into C<ev_run>:
4548
4549	void *
4550	l_run (void *thr_arg)
4551	{
4552	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4553
4554	l_acquire (EV_A);
4555	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4556	ev_run (EV_A_ 0);
4557	l_release (EV_A);
4558
4559	return 0;
4560	}
4561
4562	Instead of invoking all pending watchers, the C<l_invoke> callback will
4563	signal the main thread via some unspecified mechanism (signals? pipe
4564	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4565	have been called (in a while loop because a) spurious wakeups are possible
4566	and b) skipping inter-thread-communication when there are no pending
4567	watchers is very beneficial):
4568
4569	static void
4570	l_invoke (EV_P)
4571	{
4572	userdata *u = ev_userdata (EV_A);
4573
4574	while (ev_pending_count (EV_A))
4575	{
4576	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4577	pthread_cond_wait (&u->invoke_cv, &u->lock);
4578	}
4579	}
4580
4581	Now, whenever the main thread gets told to invoke pending watchers, it
4582	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4583	thread to continue:
4584
4585	static void
4586	real_invoke_pending (EV_P)
4587	{
4588	userdata *u = ev_userdata (EV_A);
4589
4590	pthread_mutex_lock (&u->lock);
4591	ev_invoke_pending (EV_A);
4592	pthread_cond_signal (&u->invoke_cv);
4593	pthread_mutex_unlock (&u->lock);
4594	}
4595
4596	Whenever you want to start/stop a watcher or do other modifications to an
4597	event loop, you will now have to lock:
4598
4599	ev_timer timeout_watcher;
4600	userdata *u = ev_userdata (EV_A);
4601
4602	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4603
4604	pthread_mutex_lock (&u->lock);
4605	ev_timer_start (EV_A_ &timeout_watcher);
4606	ev_async_send (EV_A_ &u->async_w);
4607	pthread_mutex_unlock (&u->lock);
4608
4609	Note that sending the C<ev_async> watcher is required because otherwise
4610	an event loop currently blocking in the kernel will have no knowledge
4611	about the newly added timer. By waking up the loop it will pick up any new
4612	watchers in the next event loop iteration.
4613		5019
4614	=head3 COROUTINES	5020	=head3 COROUTINES
4615		5021
4616	Libev is very accommodating to coroutines ("cooperative threads"):	5022	Libev is very accommodating to coroutines ("cooperative threads"):
4617	libev fully supports nesting calls to its functions from different	5023	libev fully supports nesting calls to its functions from different
…		…
4782	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
4783	model. Libev still offers limited functionality on this platform in	5189	model. Libev still offers limited functionality on this platform in
4784	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
4785	descriptors. This only applies when using Win32 natively, not when using	5191	descriptors. This only applies when using Win32 natively, not when using
4786	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,
4787	as every compielr comes with a slightly differently broken/incompatible	5193	as every compiler comes with a slightly differently broken/incompatible
4788	environment.	5194	environment.
4789		5195
4790	Lifting these limitations would basically require the full	5196	Lifting these limitations would basically require the full
4791	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,
4792	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
…		…
4908	thread" or will block signals process-wide, both behaviours would	5314	thread" or will block signals process-wide, both behaviours would
4909	be compatible with libev. Interaction between C<sigprocmask> and	5315	be compatible with libev. Interaction between C<sigprocmask> and
4910	C<pthread_sigmask> could complicate things, however.	5316	C<pthread_sigmask> could complicate things, however.
4911		5317
4912	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
4913	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
4914	well.	5320	thread as well.
4915		5321
4916	=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
4917		5323
4918	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
4919	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
…		…
4925		5331
4926	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
4927	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
4928	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
4929	(the design goal for libev). This requirement is overfulfilled by	5335	(the design goal for libev). This requirement is overfulfilled by
4930	implementations using IEEE 754, which is basically all existing ones. With	5336	implementations using IEEE 754, which is basically all existing ones.
		5337
4931	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).
4932		5342
4933	=back	5343	=back
4934		5344
4935	If you know of other additional requirements drop me a note.	5345	If you know of other additional requirements drop me a note.
4936		5346
…		…
4998	=item Processing ev_async_send: O(number_of_async_watchers)	5408	=item Processing ev_async_send: O(number_of_async_watchers)
4999		5409
5000	=item Processing signals: O(max_signal_number)	5410	=item Processing signals: O(max_signal_number)
5001		5411
5002	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>
5003	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
5004	involves iterating over all running async watchers or all signal numbers.	5415	running async watchers or all signal numbers.
5005		5416
5006	=back	5417	=back
5007		5418
5008		5419
5009	=head1 PORTING FROM LIBEV 3.X TO 4.X	5420	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5018	=over 4	5429	=over 4
5019		5430
5020	=item C<EV_COMPAT3> backwards compatibility mechanism	5431	=item C<EV_COMPAT3> backwards compatibility mechanism
5021		5432
5022	The backward compatibility mechanism can be controlled by	5433	The backward compatibility mechanism can be controlled by
5023	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>
5024	section.	5435	section.
5025		5436
5026	=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
5027		5438
5028	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:
…		…
5071	=over 4	5482	=over 4
5072		5483
5073	=item active	5484	=item active
5074		5485
5075	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.
5076	See L<WATCHER STATES> for details.	5487	See L</WATCHER STATES> for details.
5077		5488
5078	=item application	5489	=item application
5079		5490
5080	In this document, an application is whatever is using libev.	5491	In this document, an application is whatever is using libev.
5081		5492
…		…
5117	watchers and events.	5528	watchers and events.
5118		5529
5119	=item pending	5530	=item pending
5120		5531
5121	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
5122	detected. See L<WATCHER STATES> for details.	5533	detected. See L</WATCHER STATES> for details.
5123		5534
5124	=item real time	5535	=item real time
5125		5536
5126	The physical time that is observed. It is apparently strictly monotonic :)	5537	The physical time that is observed. It is apparently strictly monotonic :)
5127		5538
5128	=item wall-clock time	5539	=item wall-clock time
5129		5540
5130	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
5131	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
5132	clock.	5543	clock.
5133		5544
5134	=item watcher	5545	=item watcher
5135		5546
5136	A data structure that describes interest in certain events. Watchers need	5547	A data structure that describes interest in certain events. Watchers need
…		…
5139	=back	5550	=back
5140		5551
5141	=head1 AUTHOR	5552	=head1 AUTHOR
5142		5553
5143	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5554	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5144	Magnusson and Emanuele Giaquinta.	5555	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5145		5556

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