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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
58	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
59		61
60	// now wait for events to arrive	62	// now wait for events to arrive
61	ev_run (loop, 0);	63	ev_run (loop, 0);
62		64
63	// unloop was called, so exit	65	// break was called, so exit
64	return 0;	66	return 0;
65	}	67	}
66		68
67	=head1 ABOUT THIS DOCUMENT	69	=head1 ABOUT THIS DOCUMENT
68		70
…		…
82		84
83	=head1 WHAT TO READ WHEN IN A HURRY	85	=head1 WHAT TO READ WHEN IN A HURRY
84		86
85	This manual tries to be very detailed, but unfortunately, this also makes	87	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	88	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	89	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	90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89	C<ev_timer> sections in L<WATCHER TYPES>.	91	C<ev_timer> sections in L</WATCHER TYPES>.
90		92
91	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
92		94
93	Libev is an event loop: you register interest in certain events (such as a	95	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	96	file descriptor being readable or a timeout occurring), and it will manage
…		…
174	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
175		177
176	Returns the current time as libev would use it. Please note that the	178	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	179	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	180	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	181	C<ev_now_update> and C<ev_now>.
180		182
181	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
182		184
183	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
185	this is a sub-second-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
186		194
187	=item int ev_version_major ()	195	=item int ev_version_major ()
188		196
189	=item int ev_version_minor ()	197	=item int ev_version_minor ()
190		198
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	249	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
243		251
244	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
245		253
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		255
248	Sets the allocation function to use (the prototype is similar - the	256	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	257	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	258	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	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
277	}	285	}
278		286
279	...	287	...
280	ev_set_allocator (persistent_realloc);	288	ev_set_allocator (persistent_realloc);
281		289
282	=item ev_set_syserr_cb (void (*cb)(const char *msg))	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		291
284	Set the callback function to call on a retryable system call error (such	292	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	293	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	294	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	295	callback is set, then libev will expect it to remedy the situation, no
…		…
299	}	307	}
300		308
301	...	309	...
302	ev_set_syserr_cb (fatal_error);	310	ev_set_syserr_cb (fatal_error);
303		311
		312	=item ev_feed_signal (int signum)
		313
		314	This function can be used to "simulate" a signal receive. It is completely
		315	safe to call this function at any time, from any context, including signal
		316	handlers or random threads.
		317
		318	Its main use is to customise signal handling in your process, especially
		319	in the presence of threads. For example, you could block signals
		320	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		321	creating any loops), and in one thread, use C<sigwait> or any other
		322	mechanism to wait for signals, then "deliver" them to libev by calling
		323	C<ev_feed_signal>.
		324
304	=back	325	=back
305		326
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		328
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	329	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
377		398
378	If this flag bit is or'ed into the flag value (or the program runs setuid	399	If this flag bit is or'ed into the flag value (or the program runs setuid
379	or setgid) then libev will I<not> look at the environment variable	400	or setgid) then libev will I<not> look at the environment variable
380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
381	override the flags completely if it is found in the environment. This is	402	override the flags completely if it is found in the environment. This is
382	useful to try out specific backends to test their performance, or to work	403	useful to try out specific backends to test their performance, to work
383	around bugs.	404	around bugs, or to make libev threadsafe (accessing environment variables
		405	cannot be done in a threadsafe way, but usually it works if no other
		406	thread modifies them).
384		407
385	=item C<EVFLAG_FORKCHECK>	408	=item C<EVFLAG_FORKCHECK>
386		409
387	Instead of calling C<ev_loop_fork> manually after a fork, you can also	410	Instead of calling C<ev_loop_fork> manually after a fork, you can also
388	make libev check for a fork in each iteration by enabling this flag.	411	make libev check for a fork in each iteration by enabling this flag.
…		…
393	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	416	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
394	without a system call and thus I<very> fast, but my GNU/Linux system also has	417	without a system call and thus I<very> fast, but my GNU/Linux system also has
395	C<pthread_atfork> which is even faster).	418	C<pthread_atfork> which is even faster).
396		419
397	The big advantage of this flag is that you can forget about fork (and	420	The big advantage of this flag is that you can forget about fork (and
398	forget about forgetting to tell libev about forking) when you use this	421	forget about forgetting to tell libev about forking, although you still
399	flag.	422	have to ignore C<SIGPIPE>) when you use this flag.
400		423
401	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	424	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
402	environment variable.	425	environment variable.
403		426
404	=item C<EVFLAG_NOINOTIFY>	427	=item C<EVFLAG_NOINOTIFY>
…		…
419		442
420	Signalfd will not be used by default as this changes your signal mask, and	443	Signalfd will not be used by default as this changes your signal mask, and
421	there are a lot of shoddy libraries and programs (glib's threadpool for	444	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	445	example) that can't properly initialise their signal masks.
423		446
		447	=item C<EVFLAG_NOSIGMASK>
		448
		449	When this flag is specified, then libev will avoid to modify the signal
		450	mask. Specifically, this means you have to make sure signals are unblocked
		451	when you want to receive them.
		452
		453	This behaviour is useful when you want to do your own signal handling, or
		454	want to handle signals only in specific threads and want to avoid libev
		455	unblocking the signals.
		456
		457	It's also required by POSIX in a threaded program, as libev calls
		458	C<sigprocmask>, whose behaviour is officially unspecified.
		459
		460	This flag's behaviour will become the default in future versions of libev.
		461
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	462	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		463
426	This is your standard select(2) backend. Not I<completely> standard, as	464	This is your standard select(2) backend. Not I<completely> standard, as
427	libev tries to roll its own fd_set with no limits on the number of fds,	465	libev tries to roll its own fd_set with no limits on the number of fds,
428	but if that fails, expect a fairly low limit on the number of fds when	466	but if that fails, expect a fairly low limit on the number of fds when
…		…
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	493	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		494
457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	495	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
458	kernels).	496	kernels).
459		497
460	For few fds, this backend is a bit little slower than poll and select,	498	For few fds, this backend is a bit little slower than poll and select, but
461	but it scales phenomenally better. While poll and select usually scale	499	it scales phenomenally better. While poll and select usually scale like
462	like O(total_fds) where n is the total number of fds (or the highest fd),	500	O(total_fds) where total_fds is the total number of fds (or the highest
463	epoll scales either O(1) or O(active_fds).	501	fd), epoll scales either O(1) or O(active_fds).
464		502
465	The epoll mechanism deserves honorable mention as the most misdesigned	503	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	504	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	505	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	506	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
471	0.1ms) and so on. The biggest issue is fork races, however - if a program	509	0.1ms) and so on. The biggest issue is fork races, however - if a program
472	forks then I<both> parent and child process have to recreate the epoll	510	forks then I<both> parent and child process have to recreate the epoll
473	set, which can take considerable time (one syscall per file descriptor)	511	set, which can take considerable time (one syscall per file descriptor)
474	and is of course hard to detect.	512	and is of course hard to detect.
475		513
476	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	514	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
477	of course I<doesn't>, and epoll just loves to report events for totally	515	but of course I<doesn't>, and epoll just loves to report events for
478	I<different> file descriptors (even already closed ones, so one cannot	516	totally I<different> file descriptors (even already closed ones, so
479	even remove them from the set) than registered in the set (especially	517	one cannot even remove them from the set) than registered in the set
480	on SMP systems). Libev tries to counter these spurious notifications by	518	(especially on SMP systems). Libev tries to counter these spurious
481	employing an additional generation counter and comparing that against the	519	notifications by employing an additional generation counter and comparing
482	events to filter out spurious ones, recreating the set when required. Last	520	that against the events to filter out spurious ones, recreating the set
		521	when required. Epoll also erroneously rounds down timeouts, but gives you
		522	no way to know when and by how much, so sometimes you have to busy-wait
		523	because epoll returns immediately despite a nonzero timeout. And last
483	not least, it also refuses to work with some file descriptors which work	524	not least, it also refuses to work with some file descriptors which work
484	perfectly fine with C<select> (files, many character devices...).	525	perfectly fine with C<select> (files, many character devices...).
485		526
486	Epoll is truly the train wreck analog among event poll mechanisms.	527	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		528	cobbled together in a hurry, no thought to design or interaction with
		529	others. Oh, the pain, will it ever stop...
487		530
488	While stopping, setting and starting an I/O watcher in the same iteration	531	While stopping, setting and starting an I/O watcher in the same iteration
489	will result in some caching, there is still a system call per such	532	will result in some caching, there is still a system call per such
490	incident (because the same I<file descriptor> could point to a different	533	incident (because the same I<file descriptor> could point to a different
491	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	534	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
528		571
529	It scales in the same way as the epoll backend, but the interface to the	572	It scales in the same way as the epoll backend, but the interface to the
530	kernel is more efficient (which says nothing about its actual speed, of	573	kernel is more efficient (which says nothing about its actual speed, of
531	course). While stopping, setting and starting an I/O watcher does never	574	course). While stopping, setting and starting an I/O watcher does never
532	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	575	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
533	two event changes per incident. Support for C<fork ()> is very bad (but	576	two event changes per incident. Support for C<fork ()> is very bad (you
534	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	577	might have to leak fd's on fork, but it's more sane than epoll) and it
535	cases	578	drops fds silently in similarly hard-to-detect cases.
536		579
537	This backend usually performs well under most conditions.	580	This backend usually performs well under most conditions.
538		581
539	While nominally embeddable in other event loops, this doesn't work	582	While nominally embeddable in other event loops, this doesn't work
540	everywhere, so you might need to test for this. And since it is broken	583	everywhere, so you might need to test for this. And since it is broken
…		…
557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	600	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
558		601
559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	602	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
560	it's really slow, but it still scales very well (O(active_fds)).	603	it's really slow, but it still scales very well (O(active_fds)).
561		604
562	Please note that Solaris event ports can deliver a lot of spurious
563	notifications, so you need to use non-blocking I/O or other means to avoid
564	blocking when no data (or space) is available.
565
566	While this backend scales well, it requires one system call per active	605	While this backend scales well, it requires one system call per active
567	file descriptor per loop iteration. For small and medium numbers of file	606	file descriptor per loop iteration. For small and medium numbers of file
568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	607	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
569	might perform better.	608	might perform better.
570		609
571	On the positive side, with the exception of the spurious readiness	610	On the positive side, this backend actually performed fully to
572	notifications, this backend actually performed fully to specification
573	in all tests and is fully embeddable, which is a rare feat among the	611	specification in all tests and is fully embeddable, which is a rare feat
574	OS-specific backends (I vastly prefer correctness over speed hacks).	612	among the OS-specific backends (I vastly prefer correctness over speed
		613	hacks).
		614
		615	On the negative side, the interface is I<bizarre> - so bizarre that
		616	even sun itself gets it wrong in their code examples: The event polling
		617	function sometimes returns events to the caller even though an error
		618	occurred, but with no indication whether it has done so or not (yes, it's
		619	even documented that way) - deadly for edge-triggered interfaces where you
		620	absolutely have to know whether an event occurred or not because you have
		621	to re-arm the watcher.
		622
		623	Fortunately libev seems to be able to work around these idiocies.
575		624
576	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	625	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
577	C<EVBACKEND_POLL>.	626	C<EVBACKEND_POLL>.
578		627
579	=item C<EVBACKEND_ALL>	628	=item C<EVBACKEND_ALL>
580		629
581	Try all backends (even potentially broken ones that wouldn't be tried	630	Try all backends (even potentially broken ones that wouldn't be tried
582	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	631	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	632	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
584		633
585	It is definitely not recommended to use this flag.	634	It is definitely not recommended to use this flag, use whatever
		635	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		636	at all.
		637
		638	=item C<EVBACKEND_MASK>
		639
		640	Not a backend at all, but a mask to select all backend bits from a
		641	C<flags> value, in case you want to mask out any backends from a flags
		642	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
586		643
587	=back	644	=back
588		645
589	If one or more of the backend flags are or'ed into the flags value,	646	If one or more of the backend flags are or'ed into the flags value,
590	then only these backends will be tried (in the reverse order as listed	647	then only these backends will be tried (in the reverse order as listed
…		…
625	If you need dynamically allocated loops it is better to use C<ev_loop_new>	682	If you need dynamically allocated loops it is better to use C<ev_loop_new>
626	and C<ev_loop_destroy>.	683	and C<ev_loop_destroy>.
627		684
628	=item ev_loop_fork (loop)	685	=item ev_loop_fork (loop)
629		686
630	This function sets a flag that causes subsequent C<ev_run> iterations to	687	This function sets a flag that causes subsequent C<ev_run> iterations
631	reinitialise the kernel state for backends that have one. Despite the	688	to reinitialise the kernel state for backends that have one. Despite
632	name, you can call it anytime, but it makes most sense after forking, in	689	the name, you can call it anytime you are allowed to start or stop
633	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	690	watchers (except inside an C<ev_prepare> callback), but it makes most
		691	sense after forking, in the child process. You I<must> call it (or use
634	child before resuming or calling C<ev_run>.	692	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
635		693
		694	In addition, if you want to reuse a loop (via this function or
		695	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		696
636	Again, you I<have> to call it on I<any> loop that you want to re-use after	697	Again, you I<have> to call it on I<any> loop that you want to re-use after
637	a fork, I<even if you do not plan to use the loop in the parent>. This is	698	a fork, I<even if you do not plan to use the loop in the parent>. This is
638	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	699	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
639	during fork.	700	during fork.
640		701
641	On the other hand, you only need to call this function in the child	702	On the other hand, you only need to call this function in the child
…		…
711		772
712	This function is rarely useful, but when some event callback runs for a	773	This function is rarely useful, but when some event callback runs for a
713	very long time without entering the event loop, updating libev's idea of	774	very long time without entering the event loop, updating libev's idea of
714	the current time is a good idea.	775	the current time is a good idea.
715		776
716	See also L<The special problem of time updates> in the C<ev_timer> section.	777	See also L</The special problem of time updates> in the C<ev_timer> section.
717		778
718	=item ev_suspend (loop)	779	=item ev_suspend (loop)
719		780
720	=item ev_resume (loop)	781	=item ev_resume (loop)
721		782
…		…
739	without a previous call to C<ev_suspend>.	800	without a previous call to C<ev_suspend>.
740		801
741	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	802	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
742	event loop time (see C<ev_now_update>).	803	event loop time (see C<ev_now_update>).
743		804
744	=item ev_run (loop, int flags)	805	=item bool ev_run (loop, int flags)
745		806
746	Finally, this is it, the event handler. This function usually is called	807	Finally, this is it, the event handler. This function usually is called
747	after you have initialised all your watchers and you want to start	808	after you have initialised all your watchers and you want to start
748	handling events. It will ask the operating system for any new events, call	809	handling events. It will ask the operating system for any new events, call
749	the watcher callbacks, an then repeat the whole process indefinitely: This	810	the watcher callbacks, and then repeat the whole process indefinitely: This
750	is why event loops are called I<loops>.	811	is why event loops are called I<loops>.
751		812
752	If the flags argument is specified as C<0>, it will keep handling events	813	If the flags argument is specified as C<0>, it will keep handling events
753	until either no event watchers are active anymore or C<ev_break> was	814	until either no event watchers are active anymore or C<ev_break> was
754	called.	815	called.
		816
		817	The return value is false if there are no more active watchers (which
		818	usually means "all jobs done" or "deadlock"), and true in all other cases
		819	(which usually means " you should call C<ev_run> again").
755		820
756	Please note that an explicit C<ev_break> is usually better than	821	Please note that an explicit C<ev_break> is usually better than
757	relying on all watchers to be stopped when deciding when a program has	822	relying on all watchers to be stopped when deciding when a program has
758	finished (especially in interactive programs), but having a program	823	finished (especially in interactive programs), but having a program
759	that automatically loops as long as it has to and no longer by virtue	824	that automatically loops as long as it has to and no longer by virtue
760	of relying on its watchers stopping correctly, that is truly a thing of	825	of relying on its watchers stopping correctly, that is truly a thing of
761	beauty.	826	beauty.
762		827
763	This function is also I<mostly> exception-safe - you can break out of	828	This function is I<mostly> exception-safe - you can break out of a
764	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++	829	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
765	exception and so on. This does not decrement the C<ev_depth> value, nor	830	exception and so on. This does not decrement the C<ev_depth> value, nor
766	will it clear any outstanding C<EVBREAK_ONE> breaks.	831	will it clear any outstanding C<EVBREAK_ONE> breaks.
767		832
768	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	833	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
769	those events and any already outstanding ones, but will not wait and	834	those events and any already outstanding ones, but will not wait and
…		…
781	This is useful if you are waiting for some external event in conjunction	846	This is useful if you are waiting for some external event in conjunction
782	with something not expressible using other libev watchers (i.e. "roll your	847	with something not expressible using other libev watchers (i.e. "roll your
783	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	848	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
784	usually a better approach for this kind of thing.	849	usually a better approach for this kind of thing.
785		850
786	Here are the gory details of what C<ev_run> does:	851	Here are the gory details of what C<ev_run> does (this is for your
		852	understanding, not a guarantee that things will work exactly like this in
		853	future versions):
787		854
788	- Increment loop depth.	855	- Increment loop depth.
789	- Reset the ev_break status.	856	- Reset the ev_break status.
790	- Before the first iteration, call any pending watchers.	857	- Before the first iteration, call any pending watchers.
791	LOOP:	858	LOOP:
…		…
824	anymore.	891	anymore.
825		892
826	... queue jobs here, make sure they register event watchers as long	893	... queue jobs here, make sure they register event watchers as long
827	... as they still have work to do (even an idle watcher will do..)	894	... as they still have work to do (even an idle watcher will do..)
828	ev_run (my_loop, 0);	895	ev_run (my_loop, 0);
829	... jobs done or somebody called unloop. yeah!	896	... jobs done or somebody called break. yeah!
830		897
831	=item ev_break (loop, how)	898	=item ev_break (loop, how)
832		899
833	Can be used to make a call to C<ev_run> return early (but only after it	900	Can be used to make a call to C<ev_run> return early (but only after it
834	has processed all outstanding events). The C<how> argument must be either	901	has processed all outstanding events). The C<how> argument must be either
…		…
867	running when nothing else is active.	934	running when nothing else is active.
868		935
869	ev_signal exitsig;	936	ev_signal exitsig;
870	ev_signal_init (&exitsig, sig_cb, SIGINT);	937	ev_signal_init (&exitsig, sig_cb, SIGINT);
871	ev_signal_start (loop, &exitsig);	938	ev_signal_start (loop, &exitsig);
872	evf_unref (loop);	939	ev_unref (loop);
873		940
874	Example: For some weird reason, unregister the above signal handler again.	941	Example: For some weird reason, unregister the above signal handler again.
875		942
876	ev_ref (loop);	943	ev_ref (loop);
877	ev_signal_stop (loop, &exitsig);	944	ev_signal_stop (loop, &exitsig);
…		…
897	overhead for the actual polling but can deliver many events at once.	964	overhead for the actual polling but can deliver many events at once.
898		965
899	By setting a higher I<io collect interval> you allow libev to spend more	966	By setting a higher I<io collect interval> you allow libev to spend more
900	time collecting I/O events, so you can handle more events per iteration,	967	time collecting I/O events, so you can handle more events per iteration,
901	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	968	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
902	C<ev_timer>) will be not affected. Setting this to a non-null value will	969	C<ev_timer>) will not be affected. Setting this to a non-null value will
903	introduce an additional C<ev_sleep ()> call into most loop iterations. The	970	introduce an additional C<ev_sleep ()> call into most loop iterations. The
904	sleep time ensures that libev will not poll for I/O events more often then	971	sleep time ensures that libev will not poll for I/O events more often then
905	once per this interval, on average.	972	once per this interval, on average (as long as the host time resolution is
		973	good enough).
906		974
907	Likewise, by setting a higher I<timeout collect interval> you allow libev	975	Likewise, by setting a higher I<timeout collect interval> you allow libev
908	to spend more time collecting timeouts, at the expense of increased	976	to spend more time collecting timeouts, at the expense of increased
909	latency/jitter/inexactness (the watcher callback will be called	977	latency/jitter/inexactness (the watcher callback will be called
910	later). C<ev_io> watchers will not be affected. Setting this to a non-null	978	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
956	invoke the actual watchers inside another context (another thread etc.).	1024	invoke the actual watchers inside another context (another thread etc.).
957		1025
958	If you want to reset the callback, use C<ev_invoke_pending> as new	1026	If you want to reset the callback, use C<ev_invoke_pending> as new
959	callback.	1027	callback.
960		1028
961	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1029	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
962		1030
963	Sometimes you want to share the same loop between multiple threads. This	1031	Sometimes you want to share the same loop between multiple threads. This
964	can be done relatively simply by putting mutex_lock/unlock calls around	1032	can be done relatively simply by putting mutex_lock/unlock calls around
965	each call to a libev function.	1033	each call to a libev function.
966		1034
967	However, C<ev_run> can run an indefinite time, so it is not feasible	1035	However, C<ev_run> can run an indefinite time, so it is not feasible
968	to wait for it to return. One way around this is to wake up the event	1036	to wait for it to return. One way around this is to wake up the event
969	loop via C<ev_break> and C<av_async_send>, another way is to set these	1037	loop via C<ev_break> and C<ev_async_send>, another way is to set these
970	I<release> and I<acquire> callbacks on the loop.	1038	I<release> and I<acquire> callbacks on the loop.
971		1039
972	When set, then C<release> will be called just before the thread is	1040	When set, then C<release> will be called just before the thread is
973	suspended waiting for new events, and C<acquire> is called just	1041	suspended waiting for new events, and C<acquire> is called just
974	afterwards.	1042	afterwards.
…		…
989	See also the locking example in the C<THREADS> section later in this	1057	See also the locking example in the C<THREADS> section later in this
990	document.	1058	document.
991		1059
992	=item ev_set_userdata (loop, void *data)	1060	=item ev_set_userdata (loop, void *data)
993		1061
994	=item ev_userdata (loop)	1062	=item void *ev_userdata (loop)
995		1063
996	Set and retrieve a single C<void *> associated with a loop. When	1064	Set and retrieve a single C<void *> associated with a loop. When
997	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1065	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
998	C<0>.	1066	C<0>.
999		1067
…		…
1114		1182
1115	=item C<EV_PREPARE>	1183	=item C<EV_PREPARE>
1116		1184
1117	=item C<EV_CHECK>	1185	=item C<EV_CHECK>
1118		1186
1119	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1187	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1120	to gather new events, and all C<ev_check> watchers are invoked just after	1188	gather new events, and all C<ev_check> watchers are queued (not invoked)
1121	C<ev_run> has gathered them, but before it invokes any callbacks for any	1189	just after C<ev_run> has gathered them, but before it queues any callbacks
		1190	for any received events. That means C<ev_prepare> watchers are the last
		1191	watchers invoked before the event loop sleeps or polls for new events, and
		1192	C<ev_check> watchers will be invoked before any other watchers of the same
		1193	or lower priority within an event loop iteration.
		1194
1122	received events. Callbacks of both watcher types can start and stop as	1195	Callbacks of both watcher types can start and stop as many watchers as
1123	many watchers as they want, and all of them will be taken into account	1196	they want, and all of them will be taken into account (for example, a
1124	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1197	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1125	C<ev_run> from blocking).	1198	blocking).
1126		1199
1127	=item C<EV_EMBED>	1200	=item C<EV_EMBED>
1128		1201
1129	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1202	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1130		1203
…		…
1253		1326
1254	=item callback ev_cb (ev_TYPE *watcher)	1327	=item callback ev_cb (ev_TYPE *watcher)
1255		1328
1256	Returns the callback currently set on the watcher.	1329	Returns the callback currently set on the watcher.
1257		1330
1258	=item ev_cb_set (ev_TYPE *watcher, callback)	1331	=item ev_set_cb (ev_TYPE *watcher, callback)
1259		1332
1260	Change the callback. You can change the callback at virtually any time	1333	Change the callback. You can change the callback at virtually any time
1261	(modulo threads).	1334	(modulo threads).
1262		1335
1263	=item ev_set_priority (ev_TYPE *watcher, int priority)	1336	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1281	or might not have been clamped to the valid range.	1354	or might not have been clamped to the valid range.
1282		1355
1283	The default priority used by watchers when no priority has been set is	1356	The default priority used by watchers when no priority has been set is
1284	always C<0>, which is supposed to not be too high and not be too low :).	1357	always C<0>, which is supposed to not be too high and not be too low :).
1285		1358
1286	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1359	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1287	priorities.	1360	priorities.
1288		1361
1289	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1362	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1290		1363
1291	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1364	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1316	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1389	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1317	functions that do not need a watcher.	1390	functions that do not need a watcher.
1318		1391
1319	=back	1392	=back
1320		1393
1321	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1394	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1322		1395	OWN COMPOSITE WATCHERS> idioms.
1323	Each watcher has, by default, a member C<void *data> that you can change
1324	and read at any time: libev will completely ignore it. This can be used
1325	to associate arbitrary data with your watcher. If you need more data and
1326	don't want to allocate memory and store a pointer to it in that data
1327	member, you can also "subclass" the watcher type and provide your own
1328	data:
1329
1330	struct my_io
1331	{
1332	ev_io io;
1333	int otherfd;
1334	void *somedata;
1335	struct whatever *mostinteresting;
1336	};
1337
1338	...
1339	struct my_io w;
1340	ev_io_init (&w.io, my_cb, fd, EV_READ);
1341
1342	And since your callback will be called with a pointer to the watcher, you
1343	can cast it back to your own type:
1344
1345	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1346	{
1347	struct my_io *w = (struct my_io *)w_;
1348	...
1349	}
1350
1351	More interesting and less C-conformant ways of casting your callback type
1352	instead have been omitted.
1353
1354	Another common scenario is to use some data structure with multiple
1355	embedded watchers:
1356
1357	struct my_biggy
1358	{
1359	int some_data;
1360	ev_timer t1;
1361	ev_timer t2;
1362	}
1363
1364	In this case getting the pointer to C<my_biggy> is a bit more
1365	complicated: Either you store the address of your C<my_biggy> struct
1366	in the C<data> member of the watcher (for woozies), or you need to use
1367	some pointer arithmetic using C<offsetof> inside your watchers (for real
1368	programmers):
1369
1370	#include <stddef.h>
1371
1372	static void
1373	t1_cb (EV_P_ ev_timer *w, int revents)
1374	{
1375	struct my_biggy big = (struct my_biggy *)
1376	(((char *)w) - offsetof (struct my_biggy, t1));
1377	}
1378
1379	static void
1380	t2_cb (EV_P_ ev_timer *w, int revents)
1381	{
1382	struct my_biggy big = (struct my_biggy *)
1383	(((char *)w) - offsetof (struct my_biggy, t2));
1384	}
1385		1396
1386	=head2 WATCHER STATES	1397	=head2 WATCHER STATES
1387		1398
1388	There are various watcher states mentioned throughout this manual -	1399	There are various watcher states mentioned throughout this manual -
1389	active, pending and so on. In this section these states and the rules to	1400	active, pending and so on. In this section these states and the rules to
1390	transition between them will be described in more detail - and while these	1401	transition between them will be described in more detail - and while these
1391	rules might look complicated, they usually do "the right thing".	1402	rules might look complicated, they usually do "the right thing".
1392		1403
1393	=over 4	1404	=over 4
1394		1405
1395	=item initialiased	1406	=item initialised
1396		1407
1397	Before a watcher can be registered with the event looop it has to be	1408	Before a watcher can be registered with the event loop it has to be
1398	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1409	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1399	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1410	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1400		1411
1401	In this state it is simply some block of memory that is suitable for use	1412	In this state it is simply some block of memory that is suitable for
1402	in an event loop. It can be moved around, freed, reused etc. at will.	1413	use in an event loop. It can be moved around, freed, reused etc. at
		1414	will - as long as you either keep the memory contents intact, or call
		1415	C<ev_TYPE_init> again.
1403		1416
1404	=item started/running/active	1417	=item started/running/active
1405		1418
1406	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1419	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1407	property of the event loop, and is actively waiting for events. While in	1420	property of the event loop, and is actively waiting for events. While in
…		…
1435	latter will clear any pending state the watcher might be in, regardless	1448	latter will clear any pending state the watcher might be in, regardless
1436	of whether it was active or not, so stopping a watcher explicitly before	1449	of whether it was active or not, so stopping a watcher explicitly before
1437	freeing it is often a good idea.	1450	freeing it is often a good idea.
1438		1451
1439	While stopped (and not pending) the watcher is essentially in the	1452	While stopped (and not pending) the watcher is essentially in the
1440	initialised state, that is it can be reused, moved, modified in any way	1453	initialised state, that is, it can be reused, moved, modified in any way
1441	you wish.	1454	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1455	it again).
1442		1456
1443	=back	1457	=back
1444		1458
1445	=head2 WATCHER PRIORITY MODELS	1459	=head2 WATCHER PRIORITY MODELS
1446		1460
…		…
1575	In general you can register as many read and/or write event watchers per	1589	In general you can register as many read and/or write event watchers per
1576	fd as you want (as long as you don't confuse yourself). Setting all file	1590	fd as you want (as long as you don't confuse yourself). Setting all file
1577	descriptors to non-blocking mode is also usually a good idea (but not	1591	descriptors to non-blocking mode is also usually a good idea (but not
1578	required if you know what you are doing).	1592	required if you know what you are doing).
1579		1593
1580	If you cannot use non-blocking mode, then force the use of a
1581	known-to-be-good backend (at the time of this writing, this includes only
1582	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1583	descriptors for which non-blocking operation makes no sense (such as
1584	files) - libev doesn't guarantee any specific behaviour in that case.
1585
1586	Another thing you have to watch out for is that it is quite easy to	1594	Another thing you have to watch out for is that it is quite easy to
1587	receive "spurious" readiness notifications, that is your callback might	1595	receive "spurious" readiness notifications, that is, your callback might
1588	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1596	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1589	because there is no data. Not only are some backends known to create a	1597	because there is no data. It is very easy to get into this situation even
1590	lot of those (for example Solaris ports), it is very easy to get into	1598	with a relatively standard program structure. Thus it is best to always
1591	this situation even with a relatively standard program structure. Thus	1599	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1592	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1593	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1600	preferable to a program hanging until some data arrives.
1594		1601
1595	If you cannot run the fd in non-blocking mode (for example you should	1602	If you cannot run the fd in non-blocking mode (for example you should
1596	not play around with an Xlib connection), then you have to separately	1603	not play around with an Xlib connection), then you have to separately
1597	re-test whether a file descriptor is really ready with a known-to-be good	1604	re-test whether a file descriptor is really ready with a known-to-be good
1598	interface such as poll (fortunately in our Xlib example, Xlib already	1605	interface such as poll (fortunately in the case of Xlib, it already does
1599	does this on its own, so its quite safe to use). Some people additionally	1606	this on its own, so its quite safe to use). Some people additionally
1600	use C<SIGALRM> and an interval timer, just to be sure you won't block	1607	use C<SIGALRM> and an interval timer, just to be sure you won't block
1601	indefinitely.	1608	indefinitely.
1602		1609
1603	But really, best use non-blocking mode.	1610	But really, best use non-blocking mode.
1604		1611
…		…
1632		1639
1633	There is no workaround possible except not registering events	1640	There is no workaround possible except not registering events
1634	for potentially C<dup ()>'ed file descriptors, or to resort to	1641	for potentially C<dup ()>'ed file descriptors, or to resort to
1635	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1642	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636		1643
		1644	=head3 The special problem of files
		1645
		1646	Many people try to use C<select> (or libev) on file descriptors
		1647	representing files, and expect it to become ready when their program
		1648	doesn't block on disk accesses (which can take a long time on their own).
		1649
		1650	However, this cannot ever work in the "expected" way - you get a readiness
		1651	notification as soon as the kernel knows whether and how much data is
		1652	there, and in the case of open files, that's always the case, so you
		1653	always get a readiness notification instantly, and your read (or possibly
		1654	write) will still block on the disk I/O.
		1655
		1656	Another way to view it is that in the case of sockets, pipes, character
		1657	devices and so on, there is another party (the sender) that delivers data
		1658	on its own, but in the case of files, there is no such thing: the disk
		1659	will not send data on its own, simply because it doesn't know what you
		1660	wish to read - you would first have to request some data.
		1661
		1662	Since files are typically not-so-well supported by advanced notification
		1663	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1664	to files, even though you should not use it. The reason for this is
		1665	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1666	usually a tty, often a pipe, but also sometimes files or special devices
		1667	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1668	F</dev/urandom>), and even though the file might better be served with
		1669	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1670	it "just works" instead of freezing.
		1671
		1672	So avoid file descriptors pointing to files when you know it (e.g. use
		1673	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1674	when you rarely read from a file instead of from a socket, and want to
		1675	reuse the same code path.
		1676
1637	=head3 The special problem of fork	1677	=head3 The special problem of fork
1638		1678
1639	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1679	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1640	useless behaviour. Libev fully supports fork, but needs to be told about	1680	useless behaviour. Libev fully supports fork, but needs to be told about
1641	it in the child.	1681	it in the child if you want to continue to use it in the child.
1642		1682
1643	To support fork in your programs, you either have to call	1683	To support fork in your child processes, you have to call C<ev_loop_fork
1644	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1684	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1645	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1685	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1646	C<EVBACKEND_POLL>.
1647		1686
1648	=head3 The special problem of SIGPIPE	1687	=head3 The special problem of SIGPIPE
1649		1688
1650	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1689	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1651	when writing to a pipe whose other end has been closed, your program gets	1690	when writing to a pipe whose other end has been closed, your program gets
…		…
1749	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1788	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1750	monotonic clock option helps a lot here).	1789	monotonic clock option helps a lot here).
1751		1790
1752	The callback is guaranteed to be invoked only I<after> its timeout has	1791	The callback is guaranteed to be invoked only I<after> its timeout has
1753	passed (not I<at>, so on systems with very low-resolution clocks this	1792	passed (not I<at>, so on systems with very low-resolution clocks this
1754	might introduce a small delay). If multiple timers become ready during the	1793	might introduce a small delay, see "the special problem of being too
		1794	early", below). If multiple timers become ready during the same loop
1755	same loop iteration then the ones with earlier time-out values are invoked	1795	iteration then the ones with earlier time-out values are invoked before
1756	before ones of the same priority with later time-out values (but this is	1796	ones of the same priority with later time-out values (but this is no
1757	no longer true when a callback calls C<ev_run> recursively).	1797	longer true when a callback calls C<ev_run> recursively).
1758		1798
1759	=head3 Be smart about timeouts	1799	=head3 Be smart about timeouts
1760		1800
1761	Many real-world problems involve some kind of timeout, usually for error	1801	Many real-world problems involve some kind of timeout, usually for error
1762	recovery. A typical example is an HTTP request - if the other side hangs,	1802	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1837		1877
1838	In this case, it would be more efficient to leave the C<ev_timer> alone,	1878	In this case, it would be more efficient to leave the C<ev_timer> alone,
1839	but remember the time of last activity, and check for a real timeout only	1879	but remember the time of last activity, and check for a real timeout only
1840	within the callback:	1880	within the callback:
1841		1881
		1882	ev_tstamp timeout = 60.;
1842	ev_tstamp last_activity; // time of last activity	1883	ev_tstamp last_activity; // time of last activity
		1884	ev_timer timer;
1843		1885
1844	static void	1886	static void
1845	callback (EV_P_ ev_timer *w, int revents)	1887	callback (EV_P_ ev_timer *w, int revents)
1846	{	1888	{
1847	ev_tstamp now = ev_now (EV_A);	1889	// calculate when the timeout would happen
1848	ev_tstamp timeout = last_activity + 60.;	1890	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1849		1891
1850	// if last_activity + 60. is older than now, we did time out	1892	// if negative, it means we the timeout already occurred
1851	if (timeout < now)	1893	if (after < 0.)
1852	{	1894	{
1853	// timeout occurred, take action	1895	// timeout occurred, take action
1854	}	1896	}
1855	else	1897	else
1856	{	1898	{
1857	// callback was invoked, but there was some activity, re-arm	1899	// callback was invoked, but there was some recent
1858	// the watcher to fire in last_activity + 60, which is	1900	// activity. simply restart the timer to time out
1859	// guaranteed to be in the future, so "again" is positive:	1901	// after "after" seconds, which is the earliest time
1860	w->repeat = timeout - now;	1902	// the timeout can occur.
		1903	ev_timer_set (w, after, 0.);
1861	ev_timer_again (EV_A_ w);	1904	ev_timer_start (EV_A_ w);
1862	}	1905	}
1863	}	1906	}
1864		1907
1865	To summarise the callback: first calculate the real timeout (defined	1908	To summarise the callback: first calculate in how many seconds the
1866	as "60 seconds after the last activity"), then check if that time has	1909	timeout will occur (by calculating the absolute time when it would occur,
1867	been reached, which means something I<did>, in fact, time out. Otherwise	1910	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1868	the callback was invoked too early (C<timeout> is in the future), so	1911	(EV_A)> from that).
1869	re-schedule the timer to fire at that future time, to see if maybe we have
1870	a timeout then.
1871		1912
1872	Note how C<ev_timer_again> is used, taking advantage of the	1913	If this value is negative, then we are already past the timeout, i.e. we
1873	C<ev_timer_again> optimisation when the timer is already running.	1914	timed out, and need to do whatever is needed in this case.
		1915
		1916	Otherwise, we now the earliest time at which the timeout would trigger,
		1917	and simply start the timer with this timeout value.
		1918
		1919	In other words, each time the callback is invoked it will check whether
		1920	the timeout occurred. If not, it will simply reschedule itself to check
		1921	again at the earliest time it could time out. Rinse. Repeat.
1874		1922
1875	This scheme causes more callback invocations (about one every 60 seconds	1923	This scheme causes more callback invocations (about one every 60 seconds
1876	minus half the average time between activity), but virtually no calls to	1924	minus half the average time between activity), but virtually no calls to
1877	libev to change the timeout.	1925	libev to change the timeout.
1878		1926
1879	To start the timer, simply initialise the watcher and set C<last_activity>	1927	To start the machinery, simply initialise the watcher and set
1880	to the current time (meaning we just have some activity :), then call the	1928	C<last_activity> to the current time (meaning there was some activity just
1881	callback, which will "do the right thing" and start the timer:	1929	now), then call the callback, which will "do the right thing" and start
		1930	the timer:
1882		1931
		1932	last_activity = ev_now (EV_A);
1883	ev_init (timer, callback);	1933	ev_init (&timer, callback);
1884	last_activity = ev_now (loop);	1934	callback (EV_A_ &timer, 0);
1885	callback (loop, timer, EV_TIMER);
1886		1935
1887	And when there is some activity, simply store the current time in	1936	When there is some activity, simply store the current time in
1888	C<last_activity>, no libev calls at all:	1937	C<last_activity>, no libev calls at all:
1889		1938
		1939	if (activity detected)
1890	last_activity = ev_now (loop);	1940	last_activity = ev_now (EV_A);
		1941
		1942	When your timeout value changes, then the timeout can be changed by simply
		1943	providing a new value, stopping the timer and calling the callback, which
		1944	will again do the right thing (for example, time out immediately :).
		1945
		1946	timeout = new_value;
		1947	ev_timer_stop (EV_A_ &timer);
		1948	callback (EV_A_ &timer, 0);
1891		1949
1892	This technique is slightly more complex, but in most cases where the	1950	This technique is slightly more complex, but in most cases where the
1893	time-out is unlikely to be triggered, much more efficient.	1951	time-out is unlikely to be triggered, much more efficient.
1894
1895	Changing the timeout is trivial as well (if it isn't hard-coded in the
1896	callback :) - just change the timeout and invoke the callback, which will
1897	fix things for you.
1898		1952
1899	=item 4. Wee, just use a double-linked list for your timeouts.	1953	=item 4. Wee, just use a double-linked list for your timeouts.
1900		1954
1901	If there is not one request, but many thousands (millions...), all	1955	If there is not one request, but many thousands (millions...), all
1902	employing some kind of timeout with the same timeout value, then one can	1956	employing some kind of timeout with the same timeout value, then one can
…		…
1929	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1983	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1930	rather complicated, but extremely efficient, something that really pays	1984	rather complicated, but extremely efficient, something that really pays
1931	off after the first million or so of active timers, i.e. it's usually	1985	off after the first million or so of active timers, i.e. it's usually
1932	overkill :)	1986	overkill :)
1933		1987
		1988	=head3 The special problem of being too early
		1989
		1990	If you ask a timer to call your callback after three seconds, then
		1991	you expect it to be invoked after three seconds - but of course, this
		1992	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1993	guaranteed to any precision by libev - imagine somebody suspending the
		1994	process with a STOP signal for a few hours for example.
		1995
		1996	So, libev tries to invoke your callback as soon as possible I<after> the
		1997	delay has occurred, but cannot guarantee this.
		1998
		1999	A less obvious failure mode is calling your callback too early: many event
		2000	loops compare timestamps with a "elapsed delay >= requested delay", but
		2001	this can cause your callback to be invoked much earlier than you would
		2002	expect.
		2003
		2004	To see why, imagine a system with a clock that only offers full second
		2005	resolution (think windows if you can't come up with a broken enough OS
		2006	yourself). If you schedule a one-second timer at the time 500.9, then the
		2007	event loop will schedule your timeout to elapse at a system time of 500
		2008	(500.9 truncated to the resolution) + 1, or 501.
		2009
		2010	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2011	501" and invoke the callback 0.1s after it was started, even though a
		2012	one-second delay was requested - this is being "too early", despite best
		2013	intentions.
		2014
		2015	This is the reason why libev will never invoke the callback if the elapsed
		2016	delay equals the requested delay, but only when the elapsed delay is
		2017	larger than the requested delay. In the example above, libev would only invoke
		2018	the callback at system time 502, or 1.1s after the timer was started.
		2019
		2020	So, while libev cannot guarantee that your callback will be invoked
		2021	exactly when requested, it I<can> and I<does> guarantee that the requested
		2022	delay has actually elapsed, or in other words, it always errs on the "too
		2023	late" side of things.
		2024
1934	=head3 The special problem of time updates	2025	=head3 The special problem of time updates
1935		2026
1936	Establishing the current time is a costly operation (it usually takes at	2027	Establishing the current time is a costly operation (it usually takes
1937	least two system calls): EV therefore updates its idea of the current	2028	at least one system call): EV therefore updates its idea of the current
1938	time only before and after C<ev_run> collects new events, which causes a	2029	time only before and after C<ev_run> collects new events, which causes a
1939	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2030	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1940	lots of events in one iteration.	2031	lots of events in one iteration.
1941		2032
1942	The relative timeouts are calculated relative to the C<ev_now ()>	2033	The relative timeouts are calculated relative to the C<ev_now ()>
1943	time. This is usually the right thing as this timestamp refers to the time	2034	time. This is usually the right thing as this timestamp refers to the time
1944	of the event triggering whatever timeout you are modifying/starting. If	2035	of the event triggering whatever timeout you are modifying/starting. If
1945	you suspect event processing to be delayed and you I<need> to base the	2036	you suspect event processing to be delayed and you I<need> to base the
1946	timeout on the current time, use something like this to adjust for this:	2037	timeout on the current time, use something like the following to adjust
		2038	for it:
1947		2039
1948	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2040	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1949		2041
1950	If the event loop is suspended for a long time, you can also force an	2042	If the event loop is suspended for a long time, you can also force an
1951	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2043	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1952	()>.	2044	()>, although that will push the event time of all outstanding events
		2045	further into the future.
		2046
		2047	=head3 The special problem of unsynchronised clocks
		2048
		2049	Modern systems have a variety of clocks - libev itself uses the normal
		2050	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2051	jumps).
		2052
		2053	Neither of these clocks is synchronised with each other or any other clock
		2054	on the system, so C<ev_time ()> might return a considerably different time
		2055	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2056	a call to C<gettimeofday> might return a second count that is one higher
		2057	than a directly following call to C<time>.
		2058
		2059	The moral of this is to only compare libev-related timestamps with
		2060	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2061	a second or so.
		2062
		2063	One more problem arises due to this lack of synchronisation: if libev uses
		2064	the system monotonic clock and you compare timestamps from C<ev_time>
		2065	or C<ev_now> from when you started your timer and when your callback is
		2066	invoked, you will find that sometimes the callback is a bit "early".
		2067
		2068	This is because C<ev_timer>s work in real time, not wall clock time, so
		2069	libev makes sure your callback is not invoked before the delay happened,
		2070	I<measured according to the real time>, not the system clock.
		2071
		2072	If your timeouts are based on a physical timescale (e.g. "time out this
		2073	connection after 100 seconds") then this shouldn't bother you as it is
		2074	exactly the right behaviour.
		2075
		2076	If you want to compare wall clock/system timestamps to your timers, then
		2077	you need to use C<ev_periodic>s, as these are based on the wall clock
		2078	time, where your comparisons will always generate correct results.
1953		2079
1954	=head3 The special problems of suspended animation	2080	=head3 The special problems of suspended animation
1955		2081
1956	When you leave the server world it is quite customary to hit machines that	2082	When you leave the server world it is quite customary to hit machines that
1957	can suspend/hibernate - what happens to the clocks during such a suspend?	2083	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2001	keep up with the timer (because it takes longer than those 10 seconds to	2127	keep up with the timer (because it takes longer than those 10 seconds to
2002	do stuff) the timer will not fire more than once per event loop iteration.	2128	do stuff) the timer will not fire more than once per event loop iteration.
2003		2129
2004	=item ev_timer_again (loop, ev_timer *)	2130	=item ev_timer_again (loop, ev_timer *)
2005		2131
2006	This will act as if the timer timed out and restart it again if it is	2132	This will act as if the timer timed out, and restarts it again if it is
2007	repeating. The exact semantics are:	2133	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2134	timeout to the C<repeat> value and calling C<ev_timer_start>.
2008		2135
		2136	The exact semantics are as in the following rules, all of which will be
		2137	applied to the watcher:
		2138
		2139	=over 4
		2140
2009	If the timer is pending, its pending status is cleared.	2141	=item If the timer is pending, the pending status is always cleared.
2010		2142
2011	If the timer is started but non-repeating, stop it (as if it timed out).	2143	=item If the timer is started but non-repeating, stop it (as if it timed
		2144	out, without invoking it).
2012		2145
2013	If the timer is repeating, either start it if necessary (with the	2146	=item If the timer is repeating, make the C<repeat> value the new timeout
2014	C<repeat> value), or reset the running timer to the C<repeat> value.	2147	and start the timer, if necessary.
2015		2148
		2149	=back
		2150
2016	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2151	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2017	usage example.	2152	usage example.
2018		2153
2019	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2154	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2020		2155
2021	Returns the remaining time until a timer fires. If the timer is active,	2156	Returns the remaining time until a timer fires. If the timer is active,
…		…
2074	Periodic watchers are also timers of a kind, but they are very versatile	2209	Periodic watchers are also timers of a kind, but they are very versatile
2075	(and unfortunately a bit complex).	2210	(and unfortunately a bit complex).
2076		2211
2077	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2212	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2078	relative time, the physical time that passes) but on wall clock time	2213	relative time, the physical time that passes) but on wall clock time
2079	(absolute time, the thing you can read on your calender or clock). The	2214	(absolute time, the thing you can read on your calendar or clock). The
2080	difference is that wall clock time can run faster or slower than real	2215	difference is that wall clock time can run faster or slower than real
2081	time, and time jumps are not uncommon (e.g. when you adjust your	2216	time, and time jumps are not uncommon (e.g. when you adjust your
2082	wrist-watch).	2217	wrist-watch).
2083		2218
2084	You can tell a periodic watcher to trigger after some specific point	2219	You can tell a periodic watcher to trigger after some specific point
…		…
2141		2276
2142	Another way to think about it (for the mathematically inclined) is that	2277	Another way to think about it (for the mathematically inclined) is that
2143	C<ev_periodic> will try to run the callback in this mode at the next possible	2278	C<ev_periodic> will try to run the callback in this mode at the next possible
2144	time where C<time = offset (mod interval)>, regardless of any time jumps.	2279	time where C<time = offset (mod interval)>, regardless of any time jumps.
2145		2280
2146	For numerical stability it is preferable that the C<offset> value is near	2281	The C<interval> I<MUST> be positive, and for numerical stability, the
2147	C<ev_now ()> (the current time), but there is no range requirement for	2282	interval value should be higher than C<1/8192> (which is around 100
2148	this value, and in fact is often specified as zero.	2283	microseconds) and C<offset> should be higher than C<0> and should have
		2284	at most a similar magnitude as the current time (say, within a factor of
		2285	ten). Typical values for offset are, in fact, C<0> or something between
		2286	C<0> and C<interval>, which is also the recommended range.
2149		2287
2150	Note also that there is an upper limit to how often a timer can fire (CPU	2288	Note also that there is an upper limit to how often a timer can fire (CPU
2151	speed for example), so if C<interval> is very small then timing stability	2289	speed for example), so if C<interval> is very small then timing stability
2152	will of course deteriorate. Libev itself tries to be exact to be about one	2290	will of course deteriorate. Libev itself tries to be exact to be about one
2153	millisecond (if the OS supports it and the machine is fast enough).	2291	millisecond (if the OS supports it and the machine is fast enough).
…		…
2261		2399
2262	ev_periodic hourly_tick;	2400	ev_periodic hourly_tick;
2263	ev_periodic_init (&hourly_tick, clock_cb,	2401	ev_periodic_init (&hourly_tick, clock_cb,
2264	fmod (ev_now (loop), 3600.), 3600., 0);	2402	fmod (ev_now (loop), 3600.), 3600., 0);
2265	ev_periodic_start (loop, &hourly_tick);	2403	ev_periodic_start (loop, &hourly_tick);
2266		2404
2267		2405
2268	=head2 C<ev_signal> - signal me when a signal gets signalled!	2406	=head2 C<ev_signal> - signal me when a signal gets signalled!
2269		2407
2270	Signal watchers will trigger an event when the process receives a specific	2408	Signal watchers will trigger an event when the process receives a specific
2271	signal one or more times. Even though signals are very asynchronous, libev	2409	signal one or more times. Even though signals are very asynchronous, libev
…		…
2281	only within the same loop, i.e. you can watch for C<SIGINT> in your	2419	only within the same loop, i.e. you can watch for C<SIGINT> in your
2282	default loop and for C<SIGIO> in another loop, but you cannot watch for	2420	default loop and for C<SIGIO> in another loop, but you cannot watch for
2283	C<SIGINT> in both the default loop and another loop at the same time. At	2421	C<SIGINT> in both the default loop and another loop at the same time. At
2284	the moment, C<SIGCHLD> is permanently tied to the default loop.	2422	the moment, C<SIGCHLD> is permanently tied to the default loop.
2285		2423
2286	When the first watcher gets started will libev actually register something	2424	Only after the first watcher for a signal is started will libev actually
2287	with the kernel (thus it coexists with your own signal handlers as long as	2425	register something with the kernel. It thus coexists with your own signal
2288	you don't register any with libev for the same signal).	2426	handlers as long as you don't register any with libev for the same signal.
2289		2427
2290	If possible and supported, libev will install its handlers with	2428	If possible and supported, libev will install its handlers with
2291	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2429	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2292	not be unduly interrupted. If you have a problem with system calls getting	2430	not be unduly interrupted. If you have a problem with system calls getting
2293	interrupted by signals you can block all signals in an C<ev_check> watcher	2431	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2296	=head3 The special problem of inheritance over fork/execve/pthread_create	2434	=head3 The special problem of inheritance over fork/execve/pthread_create
2297		2435
2298	Both the signal mask (C<sigprocmask>) and the signal disposition	2436	Both the signal mask (C<sigprocmask>) and the signal disposition
2299	(C<sigaction>) are unspecified after starting a signal watcher (and after	2437	(C<sigaction>) are unspecified after starting a signal watcher (and after
2300	stopping it again), that is, libev might or might not block the signal,	2438	stopping it again), that is, libev might or might not block the signal,
2301	and might or might not set or restore the installed signal handler.	2439	and might or might not set or restore the installed signal handler (but
		2440	see C<EVFLAG_NOSIGMASK>).
2302		2441
2303	While this does not matter for the signal disposition (libev never	2442	While this does not matter for the signal disposition (libev never
2304	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2443	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2305	C<execve>), this matters for the signal mask: many programs do not expect	2444	C<execve>), this matters for the signal mask: many programs do not expect
2306	certain signals to be blocked.	2445	certain signals to be blocked.
…		…
2319	I<has> to modify the signal mask, at least temporarily.	2458	I<has> to modify the signal mask, at least temporarily.
2320		2459
2321	So I can't stress this enough: I<If you do not reset your signal mask when	2460	So I can't stress this enough: I<If you do not reset your signal mask when
2322	you expect it to be empty, you have a race condition in your code>. This	2461	you expect it to be empty, you have a race condition in your code>. This
2323	is not a libev-specific thing, this is true for most event libraries.	2462	is not a libev-specific thing, this is true for most event libraries.
		2463
		2464	=head3 The special problem of threads signal handling
		2465
		2466	POSIX threads has problematic signal handling semantics, specifically,
		2467	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2468	threads in a process block signals, which is hard to achieve.
		2469
		2470	When you want to use sigwait (or mix libev signal handling with your own
		2471	for the same signals), you can tackle this problem by globally blocking
		2472	all signals before creating any threads (or creating them with a fully set
		2473	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2474	loops. Then designate one thread as "signal receiver thread" which handles
		2475	these signals. You can pass on any signals that libev might be interested
		2476	in by calling C<ev_feed_signal>.
2324		2477
2325	=head3 Watcher-Specific Functions and Data Members	2478	=head3 Watcher-Specific Functions and Data Members
2326		2479
2327	=over 4	2480	=over 4
2328		2481
…		…
2463		2616
2464	=head2 C<ev_stat> - did the file attributes just change?	2617	=head2 C<ev_stat> - did the file attributes just change?
2465		2618
2466	This watches a file system path for attribute changes. That is, it calls	2619	This watches a file system path for attribute changes. That is, it calls
2467	C<stat> on that path in regular intervals (or when the OS says it changed)	2620	C<stat> on that path in regular intervals (or when the OS says it changed)
2468	and sees if it changed compared to the last time, invoking the callback if	2621	and sees if it changed compared to the last time, invoking the callback
2469	it did.	2622	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2623	happen after the watcher has been started will be reported.
2470		2624
2471	The path does not need to exist: changing from "path exists" to "path does	2625	The path does not need to exist: changing from "path exists" to "path does
2472	not exist" is a status change like any other. The condition "path does not	2626	not exist" is a status change like any other. The condition "path does not
2473	exist" (or more correctly "path cannot be stat'ed") is signified by the	2627	exist" (or more correctly "path cannot be stat'ed") is signified by the
2474	C<st_nlink> field being zero (which is otherwise always forced to be at	2628	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2704	Apart from keeping your process non-blocking (which is a useful	2858	Apart from keeping your process non-blocking (which is a useful
2705	effect on its own sometimes), idle watchers are a good place to do	2859	effect on its own sometimes), idle watchers are a good place to do
2706	"pseudo-background processing", or delay processing stuff to after the	2860	"pseudo-background processing", or delay processing stuff to after the
2707	event loop has handled all outstanding events.	2861	event loop has handled all outstanding events.
2708		2862
		2863	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2864
		2865	As long as there is at least one active idle watcher, libev will never
		2866	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2867	For this to work, the idle watcher doesn't need to be invoked at all - the
		2868	lowest priority will do.
		2869
		2870	This mode of operation can be useful together with an C<ev_check> watcher,
		2871	to do something on each event loop iteration - for example to balance load
		2872	between different connections.
		2873
		2874	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2875	example.
		2876
2709	=head3 Watcher-Specific Functions and Data Members	2877	=head3 Watcher-Specific Functions and Data Members
2710		2878
2711	=over 4	2879	=over 4
2712		2880
2713	=item ev_idle_init (ev_idle *, callback)	2881	=item ev_idle_init (ev_idle *, callback)
…		…
2724	callback, free it. Also, use no error checking, as usual.	2892	callback, free it. Also, use no error checking, as usual.
2725		2893
2726	static void	2894	static void
2727	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2895	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2728	{	2896	{
		2897	// stop the watcher
		2898	ev_idle_stop (loop, w);
		2899
		2900	// now we can free it
2729	free (w);	2901	free (w);
		2902
2730	// now do something you wanted to do when the program has	2903	// now do something you wanted to do when the program has
2731	// no longer anything immediate to do.	2904	// no longer anything immediate to do.
2732	}	2905	}
2733		2906
2734	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2907	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2736	ev_idle_start (loop, idle_watcher);	2909	ev_idle_start (loop, idle_watcher);
2737		2910
2738		2911
2739	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2912	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2740		2913
2741	Prepare and check watchers are usually (but not always) used in pairs:	2914	Prepare and check watchers are often (but not always) used in pairs:
2742	prepare watchers get invoked before the process blocks and check watchers	2915	prepare watchers get invoked before the process blocks and check watchers
2743	afterwards.	2916	afterwards.
2744		2917
2745	You I<must not> call C<ev_run> or similar functions that enter	2918	You I<must not> call C<ev_run> (or similar functions that enter the
2746	the current event loop from either C<ev_prepare> or C<ev_check>	2919	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2747	watchers. Other loops than the current one are fine, however. The	2920	C<ev_check> watchers. Other loops than the current one are fine,
2748	rationale behind this is that you do not need to check for recursion in	2921	however. The rationale behind this is that you do not need to check
2749	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2922	for recursion in those watchers, i.e. the sequence will always be
2750	C<ev_check> so if you have one watcher of each kind they will always be	2923	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2751	called in pairs bracketing the blocking call.	2924	kind they will always be called in pairs bracketing the blocking call.
2752		2925
2753	Their main purpose is to integrate other event mechanisms into libev and	2926	Their main purpose is to integrate other event mechanisms into libev and
2754	their use is somewhat advanced. They could be used, for example, to track	2927	their use is somewhat advanced. They could be used, for example, to track
2755	variable changes, implement your own watchers, integrate net-snmp or a	2928	variable changes, implement your own watchers, integrate net-snmp or a
2756	coroutine library and lots more. They are also occasionally useful if	2929	coroutine library and lots more. They are also occasionally useful if
…		…
2774	with priority higher than or equal to the event loop and one coroutine	2947	with priority higher than or equal to the event loop and one coroutine
2775	of lower priority, but only once, using idle watchers to keep the event	2948	of lower priority, but only once, using idle watchers to keep the event
2776	loop from blocking if lower-priority coroutines are active, thus mapping	2949	loop from blocking if lower-priority coroutines are active, thus mapping
2777	low-priority coroutines to idle/background tasks).	2950	low-priority coroutines to idle/background tasks).
2778		2951
2779	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2952	When used for this purpose, it is recommended to give C<ev_check> watchers
2780	priority, to ensure that they are being run before any other watchers	2953	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2781	after the poll (this doesn't matter for C<ev_prepare> watchers).	2954	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2955	watchers).
2782		2956
2783	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2957	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2784	activate ("feed") events into libev. While libev fully supports this, they	2958	activate ("feed") events into libev. While libev fully supports this, they
2785	might get executed before other C<ev_check> watchers did their job. As	2959	might get executed before other C<ev_check> watchers did their job. As
2786	C<ev_check> watchers are often used to embed other (non-libev) event	2960	C<ev_check> watchers are often used to embed other (non-libev) event
2787	loops those other event loops might be in an unusable state until their	2961	loops those other event loops might be in an unusable state until their
2788	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2962	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2789	others).	2963	others).
		2964
		2965	=head3 Abusing an C<ev_check> watcher for its side-effect
		2966
		2967	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2968	useful because they are called once per event loop iteration. For
		2969	example, if you want to handle a large number of connections fairly, you
		2970	normally only do a bit of work for each active connection, and if there
		2971	is more work to do, you wait for the next event loop iteration, so other
		2972	connections have a chance of making progress.
		2973
		2974	Using an C<ev_check> watcher is almost enough: it will be called on the
		2975	next event loop iteration. However, that isn't as soon as possible -
		2976	without external events, your C<ev_check> watcher will not be invoked.
		2977
		2978	This is where C<ev_idle> watchers come in handy - all you need is a
		2979	single global idle watcher that is active as long as you have one active
		2980	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2981	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2982	invoked. Neither watcher alone can do that.
2790		2983
2791	=head3 Watcher-Specific Functions and Data Members	2984	=head3 Watcher-Specific Functions and Data Members
2792		2985
2793	=over 4	2986	=over 4
2794		2987
…		…
2995		3188
2996	=over 4	3189	=over 4
2997		3190
2998	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3191	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2999		3192
3000	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3193	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3001		3194
3002	Configures the watcher to embed the given loop, which must be	3195	Configures the watcher to embed the given loop, which must be
3003	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3196	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
3004	invoked automatically, otherwise it is the responsibility of the callback	3197	invoked automatically, otherwise it is the responsibility of the callback
3005	to invoke it (it will continue to be called until the sweep has been done,	3198	to invoke it (it will continue to be called until the sweep has been done,
…		…
3026	used).	3219	used).
3027		3220
3028	struct ev_loop *loop_hi = ev_default_init (0);	3221	struct ev_loop *loop_hi = ev_default_init (0);
3029	struct ev_loop *loop_lo = 0;	3222	struct ev_loop *loop_lo = 0;
3030	ev_embed embed;	3223	ev_embed embed;
3031		3224
3032	// see if there is a chance of getting one that works	3225	// see if there is a chance of getting one that works
3033	// (remember that a flags value of 0 means autodetection)	3226	// (remember that a flags value of 0 means autodetection)
3034	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3227	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3035	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3228	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3036	: 0;	3229	: 0;
…		…
3050	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3243	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3051		3244
3052	struct ev_loop *loop = ev_default_init (0);	3245	struct ev_loop *loop = ev_default_init (0);
3053	struct ev_loop *loop_socket = 0;	3246	struct ev_loop *loop_socket = 0;
3054	ev_embed embed;	3247	ev_embed embed;
3055		3248
3056	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3249	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3057	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3250	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3058	{	3251	{
3059	ev_embed_init (&embed, 0, loop_socket);	3252	ev_embed_init (&embed, 0, loop_socket);
3060	ev_embed_start (loop, &embed);	3253	ev_embed_start (loop, &embed);
…		…
3068		3261
3069	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3262	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3070		3263
3071	Fork watchers are called when a C<fork ()> was detected (usually because	3264	Fork watchers are called when a C<fork ()> was detected (usually because
3072	whoever is a good citizen cared to tell libev about it by calling	3265	whoever is a good citizen cared to tell libev about it by calling
3073	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3266	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3074	event loop blocks next and before C<ev_check> watchers are being called,	3267	and before C<ev_check> watchers are being called, and only in the child
3075	and only in the child after the fork. If whoever good citizen calling	3268	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3076	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3269	and calls it in the wrong process, the fork handlers will be invoked, too,
3077	handlers will be invoked, too, of course.	3270	of course.
3078		3271
3079	=head3 The special problem of life after fork - how is it possible?	3272	=head3 The special problem of life after fork - how is it possible?
3080		3273
3081	Most uses of C<fork()> consist of forking, then some simple calls to set	3274	Most uses of C<fork ()> consist of forking, then some simple calls to set
3082	up/change the process environment, followed by a call to C<exec()>. This	3275	up/change the process environment, followed by a call to C<exec()>. This
3083	sequence should be handled by libev without any problems.	3276	sequence should be handled by libev without any problems.
3084		3277
3085	This changes when the application actually wants to do event handling	3278	This changes when the application actually wants to do event handling
3086	in the child, or both parent in child, in effect "continuing" after the	3279	in the child, or both parent in child, in effect "continuing" after the
…		…
3163	atexit (program_exits);	3356	atexit (program_exits);
3164		3357
3165		3358
3166	=head2 C<ev_async> - how to wake up an event loop	3359	=head2 C<ev_async> - how to wake up an event loop
3167		3360
3168	In general, you cannot use an C<ev_run> from multiple threads or other	3361	In general, you cannot use an C<ev_loop> from multiple threads or other
3169	asynchronous sources such as signal handlers (as opposed to multiple event	3362	asynchronous sources such as signal handlers (as opposed to multiple event
3170	loops - those are of course safe to use in different threads).	3363	loops - those are of course safe to use in different threads).
3171		3364
3172	Sometimes, however, you need to wake up an event loop you do not control,	3365	Sometimes, however, you need to wake up an event loop you do not control,
3173	for example because it belongs to another thread. This is what C<ev_async>	3366	for example because it belongs to another thread. This is what C<ev_async>
…		…
3175	it by calling C<ev_async_send>, which is thread- and signal safe.	3368	it by calling C<ev_async_send>, which is thread- and signal safe.
3176		3369
3177	This functionality is very similar to C<ev_signal> watchers, as signals,	3370	This functionality is very similar to C<ev_signal> watchers, as signals,
3178	too, are asynchronous in nature, and signals, too, will be compressed	3371	too, are asynchronous in nature, and signals, too, will be compressed
3179	(i.e. the number of callback invocations may be less than the number of	3372	(i.e. the number of callback invocations may be less than the number of
3180	C<ev_async_sent> calls).	3373	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3181		3374	of "global async watchers" by using a watcher on an otherwise unused
3182	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3375	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3183	just the default loop.	3376	even without knowing which loop owns the signal.
3184		3377
3185	=head3 Queueing	3378	=head3 Queueing
3186		3379
3187	C<ev_async> does not support queueing of data in any way. The reason	3380	C<ev_async> does not support queueing of data in any way. The reason
3188	is that the author does not know of a simple (or any) algorithm for a	3381	is that the author does not know of a simple (or any) algorithm for a
…		…
3280	trust me.	3473	trust me.
3281		3474
3282	=item ev_async_send (loop, ev_async *)	3475	=item ev_async_send (loop, ev_async *)
3283		3476
3284	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3477	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3285	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3478	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3479	returns.
		3480
3286	C<ev_feed_event>, this call is safe to do from other threads, signal or	3481	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3287	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3482	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3288	section below on what exactly this means).	3483	embedding section below on what exactly this means).
3289		3484
3290	Note that, as with other watchers in libev, multiple events might get	3485	Note that, as with other watchers in libev, multiple events might get
3291	compressed into a single callback invocation (another way to look at this	3486	compressed into a single callback invocation (another way to look at
3292	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3487	this is that C<ev_async> watchers are level-triggered: they are set on
3293	reset when the event loop detects that).	3488	C<ev_async_send>, reset when the event loop detects that).
3294		3489
3295	This call incurs the overhead of a system call only once per event loop	3490	This call incurs the overhead of at most one extra system call per event
3296	iteration, so while the overhead might be noticeable, it doesn't apply to	3491	loop iteration, if the event loop is blocked, and no syscall at all if
3297	repeated calls to C<ev_async_send> for the same event loop.	3492	the event loop (or your program) is processing events. That means that
		3493	repeated calls are basically free (there is no need to avoid calls for
		3494	performance reasons) and that the overhead becomes smaller (typically
		3495	zero) under load.
3298		3496
3299	=item bool = ev_async_pending (ev_async *)	3497	=item bool = ev_async_pending (ev_async *)
3300		3498
3301	Returns a non-zero value when C<ev_async_send> has been called on the	3499	Returns a non-zero value when C<ev_async_send> has been called on the
3302	watcher but the event has not yet been processed (or even noted) by the	3500	watcher but the event has not yet been processed (or even noted) by the
…		…
3357	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3555	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3358		3556
3359	=item ev_feed_fd_event (loop, int fd, int revents)	3557	=item ev_feed_fd_event (loop, int fd, int revents)
3360		3558
3361	Feed an event on the given fd, as if a file descriptor backend detected	3559	Feed an event on the given fd, as if a file descriptor backend detected
3362	the given events it.	3560	the given events.
3363		3561
3364	=item ev_feed_signal_event (loop, int signum)	3562	=item ev_feed_signal_event (loop, int signum)
3365		3563
3366	Feed an event as if the given signal occurred (C<loop> must be the default	3564	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3367	loop!).	3565	which is async-safe.
3368		3566
3369	=back	3567	=back
		3568
		3569
		3570	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3571
		3572	This section explains some common idioms that are not immediately
		3573	obvious. Note that examples are sprinkled over the whole manual, and this
		3574	section only contains stuff that wouldn't fit anywhere else.
		3575
		3576	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3577
		3578	Each watcher has, by default, a C<void *data> member that you can read
		3579	or modify at any time: libev will completely ignore it. This can be used
		3580	to associate arbitrary data with your watcher. If you need more data and
		3581	don't want to allocate memory separately and store a pointer to it in that
		3582	data member, you can also "subclass" the watcher type and provide your own
		3583	data:
		3584
		3585	struct my_io
		3586	{
		3587	ev_io io;
		3588	int otherfd;
		3589	void *somedata;
		3590	struct whatever *mostinteresting;
		3591	};
		3592
		3593	...
		3594	struct my_io w;
		3595	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3596
		3597	And since your callback will be called with a pointer to the watcher, you
		3598	can cast it back to your own type:
		3599
		3600	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3601	{
		3602	struct my_io *w = (struct my_io *)w_;
		3603	...
		3604	}
		3605
		3606	More interesting and less C-conformant ways of casting your callback
		3607	function type instead have been omitted.
		3608
		3609	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3610
		3611	Another common scenario is to use some data structure with multiple
		3612	embedded watchers, in effect creating your own watcher that combines
		3613	multiple libev event sources into one "super-watcher":
		3614
		3615	struct my_biggy
		3616	{
		3617	int some_data;
		3618	ev_timer t1;
		3619	ev_timer t2;
		3620	}
		3621
		3622	In this case getting the pointer to C<my_biggy> is a bit more
		3623	complicated: Either you store the address of your C<my_biggy> struct in
		3624	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3625	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3626	real programmers):
		3627
		3628	#include <stddef.h>
		3629
		3630	static void
		3631	t1_cb (EV_P_ ev_timer *w, int revents)
		3632	{
		3633	struct my_biggy big = (struct my_biggy *)
		3634	(((char *)w) - offsetof (struct my_biggy, t1));
		3635	}
		3636
		3637	static void
		3638	t2_cb (EV_P_ ev_timer *w, int revents)
		3639	{
		3640	struct my_biggy big = (struct my_biggy *)
		3641	(((char *)w) - offsetof (struct my_biggy, t2));
		3642	}
		3643
		3644	=head2 AVOIDING FINISHING BEFORE RETURNING
		3645
		3646	Often you have structures like this in event-based programs:
		3647
		3648	callback ()
		3649	{
		3650	free (request);
		3651	}
		3652
		3653	request = start_new_request (..., callback);
		3654
		3655	The intent is to start some "lengthy" operation. The C<request> could be
		3656	used to cancel the operation, or do other things with it.
		3657
		3658	It's not uncommon to have code paths in C<start_new_request> that
		3659	immediately invoke the callback, for example, to report errors. Or you add
		3660	some caching layer that finds that it can skip the lengthy aspects of the
		3661	operation and simply invoke the callback with the result.
		3662
		3663	The problem here is that this will happen I<before> C<start_new_request>
		3664	has returned, so C<request> is not set.
		3665
		3666	Even if you pass the request by some safer means to the callback, you
		3667	might want to do something to the request after starting it, such as
		3668	canceling it, which probably isn't working so well when the callback has
		3669	already been invoked.
		3670
		3671	A common way around all these issues is to make sure that
		3672	C<start_new_request> I<always> returns before the callback is invoked. If
		3673	C<start_new_request> immediately knows the result, it can artificially
		3674	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3675	example, or more sneakily, by reusing an existing (stopped) watcher and
		3676	pushing it into the pending queue:
		3677
		3678	ev_set_cb (watcher, callback);
		3679	ev_feed_event (EV_A_ watcher, 0);
		3680
		3681	This way, C<start_new_request> can safely return before the callback is
		3682	invoked, while not delaying callback invocation too much.
		3683
		3684	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3685
		3686	Often (especially in GUI toolkits) there are places where you have
		3687	I<modal> interaction, which is most easily implemented by recursively
		3688	invoking C<ev_run>.
		3689
		3690	This brings the problem of exiting - a callback might want to finish the
		3691	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3692	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3693	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3694	other combination: In these cases, a simple C<ev_break> will not work.
		3695
		3696	The solution is to maintain "break this loop" variable for each C<ev_run>
		3697	invocation, and use a loop around C<ev_run> until the condition is
		3698	triggered, using C<EVRUN_ONCE>:
		3699
		3700	// main loop
		3701	int exit_main_loop = 0;
		3702
		3703	while (!exit_main_loop)
		3704	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3705
		3706	// in a modal watcher
		3707	int exit_nested_loop = 0;
		3708
		3709	while (!exit_nested_loop)
		3710	ev_run (EV_A_ EVRUN_ONCE);
		3711
		3712	To exit from any of these loops, just set the corresponding exit variable:
		3713
		3714	// exit modal loop
		3715	exit_nested_loop = 1;
		3716
		3717	// exit main program, after modal loop is finished
		3718	exit_main_loop = 1;
		3719
		3720	// exit both
		3721	exit_main_loop = exit_nested_loop = 1;
		3722
		3723	=head2 THREAD LOCKING EXAMPLE
		3724
		3725	Here is a fictitious example of how to run an event loop in a different
		3726	thread from where callbacks are being invoked and watchers are
		3727	created/added/removed.
		3728
		3729	For a real-world example, see the C<EV::Loop::Async> perl module,
		3730	which uses exactly this technique (which is suited for many high-level
		3731	languages).
		3732
		3733	The example uses a pthread mutex to protect the loop data, a condition
		3734	variable to wait for callback invocations, an async watcher to notify the
		3735	event loop thread and an unspecified mechanism to wake up the main thread.
		3736
		3737	First, you need to associate some data with the event loop:
		3738
		3739	typedef struct {
		3740	mutex_t lock; /* global loop lock */
		3741	ev_async async_w;
		3742	thread_t tid;
		3743	cond_t invoke_cv;
		3744	} userdata;
		3745
		3746	void prepare_loop (EV_P)
		3747	{
		3748	// for simplicity, we use a static userdata struct.
		3749	static userdata u;
		3750
		3751	ev_async_init (&u->async_w, async_cb);
		3752	ev_async_start (EV_A_ &u->async_w);
		3753
		3754	pthread_mutex_init (&u->lock, 0);
		3755	pthread_cond_init (&u->invoke_cv, 0);
		3756
		3757	// now associate this with the loop
		3758	ev_set_userdata (EV_A_ u);
		3759	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3760	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3761
		3762	// then create the thread running ev_run
		3763	pthread_create (&u->tid, 0, l_run, EV_A);
		3764	}
		3765
		3766	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3767	solely to wake up the event loop so it takes notice of any new watchers
		3768	that might have been added:
		3769
		3770	static void
		3771	async_cb (EV_P_ ev_async *w, int revents)
		3772	{
		3773	// just used for the side effects
		3774	}
		3775
		3776	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3777	protecting the loop data, respectively.
		3778
		3779	static void
		3780	l_release (EV_P)
		3781	{
		3782	userdata *u = ev_userdata (EV_A);
		3783	pthread_mutex_unlock (&u->lock);
		3784	}
		3785
		3786	static void
		3787	l_acquire (EV_P)
		3788	{
		3789	userdata *u = ev_userdata (EV_A);
		3790	pthread_mutex_lock (&u->lock);
		3791	}
		3792
		3793	The event loop thread first acquires the mutex, and then jumps straight
		3794	into C<ev_run>:
		3795
		3796	void *
		3797	l_run (void *thr_arg)
		3798	{
		3799	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3800
		3801	l_acquire (EV_A);
		3802	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3803	ev_run (EV_A_ 0);
		3804	l_release (EV_A);
		3805
		3806	return 0;
		3807	}
		3808
		3809	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3810	signal the main thread via some unspecified mechanism (signals? pipe
		3811	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3812	have been called (in a while loop because a) spurious wakeups are possible
		3813	and b) skipping inter-thread-communication when there are no pending
		3814	watchers is very beneficial):
		3815
		3816	static void
		3817	l_invoke (EV_P)
		3818	{
		3819	userdata *u = ev_userdata (EV_A);
		3820
		3821	while (ev_pending_count (EV_A))
		3822	{
		3823	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3824	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3825	}
		3826	}
		3827
		3828	Now, whenever the main thread gets told to invoke pending watchers, it
		3829	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3830	thread to continue:
		3831
		3832	static void
		3833	real_invoke_pending (EV_P)
		3834	{
		3835	userdata *u = ev_userdata (EV_A);
		3836
		3837	pthread_mutex_lock (&u->lock);
		3838	ev_invoke_pending (EV_A);
		3839	pthread_cond_signal (&u->invoke_cv);
		3840	pthread_mutex_unlock (&u->lock);
		3841	}
		3842
		3843	Whenever you want to start/stop a watcher or do other modifications to an
		3844	event loop, you will now have to lock:
		3845
		3846	ev_timer timeout_watcher;
		3847	userdata *u = ev_userdata (EV_A);
		3848
		3849	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3850
		3851	pthread_mutex_lock (&u->lock);
		3852	ev_timer_start (EV_A_ &timeout_watcher);
		3853	ev_async_send (EV_A_ &u->async_w);
		3854	pthread_mutex_unlock (&u->lock);
		3855
		3856	Note that sending the C<ev_async> watcher is required because otherwise
		3857	an event loop currently blocking in the kernel will have no knowledge
		3858	about the newly added timer. By waking up the loop it will pick up any new
		3859	watchers in the next event loop iteration.
		3860
		3861	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3862
		3863	While the overhead of a callback that e.g. schedules a thread is small, it
		3864	is still an overhead. If you embed libev, and your main usage is with some
		3865	kind of threads or coroutines, you might want to customise libev so that
		3866	doesn't need callbacks anymore.
		3867
		3868	Imagine you have coroutines that you can switch to using a function
		3869	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3870	and that due to some magic, the currently active coroutine is stored in a
		3871	global called C<current_coro>. Then you can build your own "wait for libev
		3872	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3873	the differing C<;> conventions):
		3874
		3875	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3876	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3877
		3878	That means instead of having a C callback function, you store the
		3879	coroutine to switch to in each watcher, and instead of having libev call
		3880	your callback, you instead have it switch to that coroutine.
		3881
		3882	A coroutine might now wait for an event with a function called
		3883	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3884	matter when, or whether the watcher is active or not when this function is
		3885	called):
		3886
		3887	void
		3888	wait_for_event (ev_watcher *w)
		3889	{
		3890	ev_set_cb (w, current_coro);
		3891	switch_to (libev_coro);
		3892	}
		3893
		3894	That basically suspends the coroutine inside C<wait_for_event> and
		3895	continues the libev coroutine, which, when appropriate, switches back to
		3896	this or any other coroutine.
		3897
		3898	You can do similar tricks if you have, say, threads with an event queue -
		3899	instead of storing a coroutine, you store the queue object and instead of
		3900	switching to a coroutine, you push the watcher onto the queue and notify
		3901	any waiters.
		3902
		3903	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3904	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3905
		3906	// my_ev.h
		3907	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3908	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3909	#include "../libev/ev.h"
		3910
		3911	// my_ev.c
		3912	#define EV_H "my_ev.h"
		3913	#include "../libev/ev.c"
		3914
		3915	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3916	F<my_ev.c> into your project. When properly specifying include paths, you
		3917	can even use F<ev.h> as header file name directly.
3370		3918
3371		3919
3372	=head1 LIBEVENT EMULATION	3920	=head1 LIBEVENT EMULATION
3373		3921
3374	Libev offers a compatibility emulation layer for libevent. It cannot	3922	Libev offers a compatibility emulation layer for libevent. It cannot
3375	emulate the internals of libevent, so here are some usage hints:	3923	emulate the internals of libevent, so here are some usage hints:
3376		3924
3377	=over 4	3925	=over 4
		3926
		3927	=item * Only the libevent-1.4.1-beta API is being emulated.
		3928
		3929	This was the newest libevent version available when libev was implemented,
		3930	and is still mostly unchanged in 2010.
3378		3931
3379	=item * Use it by including <event.h>, as usual.	3932	=item * Use it by including <event.h>, as usual.
3380		3933
3381	=item * The following members are fully supported: ev_base, ev_callback,	3934	=item * The following members are fully supported: ev_base, ev_callback,
3382	ev_arg, ev_fd, ev_res, ev_events.	3935	ev_arg, ev_fd, ev_res, ev_events.
…		…
3399		3952
3400	=back	3953	=back
3401		3954
3402	=head1 C++ SUPPORT	3955	=head1 C++ SUPPORT
3403		3956
		3957	=head2 C API
		3958
		3959	The normal C API should work fine when used from C++: both ev.h and the
		3960	libev sources can be compiled as C++. Therefore, code that uses the C API
		3961	will work fine.
		3962
		3963	Proper exception specifications might have to be added to callbacks passed
		3964	to libev: exceptions may be thrown only from watcher callbacks, all
		3965	other callbacks (allocator, syserr, loop acquire/release and periodic
		3966	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3967	()> specification. If you have code that needs to be compiled as both C
		3968	and C++ you can use the C<EV_THROW> macro for this:
		3969
		3970	static void
		3971	fatal_error (const char *msg) EV_THROW
		3972	{
		3973	perror (msg);
		3974	abort ();
		3975	}
		3976
		3977	...
		3978	ev_set_syserr_cb (fatal_error);
		3979
		3980	The only API functions that can currently throw exceptions are C<ev_run>,
		3981	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3982	because it runs cleanup watchers).
		3983
		3984	Throwing exceptions in watcher callbacks is only supported if libev itself
		3985	is compiled with a C++ compiler or your C and C++ environments allow
		3986	throwing exceptions through C libraries (most do).
		3987
		3988	=head2 C++ API
		3989
3404	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3990	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3405	you to use some convenience methods to start/stop watchers and also change	3991	you to use some convenience methods to start/stop watchers and also change
3406	the callback model to a model using method callbacks on objects.	3992	the callback model to a model using method callbacks on objects.
3407		3993
3408	To use it,	3994	To use it,
3409		3995
3410	#include <ev++.h>	3996	#include <ev++.h>
3411		3997
3412	This automatically includes F<ev.h> and puts all of its definitions (many	3998	This automatically includes F<ev.h> and puts all of its definitions (many
3413	of them macros) into the global namespace. All C++ specific things are	3999	of them macros) into the global namespace. All C++ specific things are
3414	put into the C<ev> namespace. It should support all the same embedding	4000	put into the C<ev> namespace. It should support all the same embedding
…		…
3417	Care has been taken to keep the overhead low. The only data member the C++	4003	Care has been taken to keep the overhead low. The only data member the C++
3418	classes add (compared to plain C-style watchers) is the event loop pointer	4004	classes add (compared to plain C-style watchers) is the event loop pointer
3419	that the watcher is associated with (or no additional members at all if	4005	that the watcher is associated with (or no additional members at all if
3420	you disable C<EV_MULTIPLICITY> when embedding libev).	4006	you disable C<EV_MULTIPLICITY> when embedding libev).
3421		4007
3422	Currently, functions, and static and non-static member functions can be	4008	Currently, functions, static and non-static member functions and classes
3423	used as callbacks. Other types should be easy to add as long as they only	4009	with C<operator ()> can be used as callbacks. Other types should be easy
3424	need one additional pointer for context. If you need support for other	4010	to add as long as they only need one additional pointer for context. If
3425	types of functors please contact the author (preferably after implementing	4011	you need support for other types of functors please contact the author
3426	it).	4012	(preferably after implementing it).
		4013
		4014	For all this to work, your C++ compiler either has to use the same calling
		4015	conventions as your C compiler (for static member functions), or you have
		4016	to embed libev and compile libev itself as C++.
3427		4017
3428	Here is a list of things available in the C<ev> namespace:	4018	Here is a list of things available in the C<ev> namespace:
3429		4019
3430	=over 4	4020	=over 4
3431		4021
…		…
3441	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4031	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3442		4032
3443	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4033	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3444	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4034	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3445	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4035	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3446	defines by many implementations.	4036	defined by many implementations.
3447		4037
3448	All of those classes have these methods:	4038	All of those classes have these methods:
3449		4039
3450	=over 4	4040	=over 4
3451		4041
…		…
3513	void operator() (ev::io &w, int revents)	4103	void operator() (ev::io &w, int revents)
3514	{	4104	{
3515	...	4105	...
3516	}	4106	}
3517	}	4107	}
3518		4108
3519	myfunctor f;	4109	myfunctor f;
3520		4110
3521	ev::io w;	4111	ev::io w;
3522	w.set (&f);	4112	w.set (&f);
3523		4113
…		…
3541	Associates a different C<struct ev_loop> with this watcher. You can only	4131	Associates a different C<struct ev_loop> with this watcher. You can only
3542	do this when the watcher is inactive (and not pending either).	4132	do this when the watcher is inactive (and not pending either).
3543		4133
3544	=item w->set ([arguments])	4134	=item w->set ([arguments])
3545		4135
3546	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4136	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3547	method or a suitable start method must be called at least once. Unlike the	4137	with the same arguments. Either this method or a suitable start method
3548	C counterpart, an active watcher gets automatically stopped and restarted	4138	must be called at least once. Unlike the C counterpart, an active watcher
3549	when reconfiguring it with this method.	4139	gets automatically stopped and restarted when reconfiguring it with this
		4140	method.
		4141
		4142	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4143	clashing with the C<set (loop)> method.
3550		4144
3551	=item w->start ()	4145	=item w->start ()
3552		4146
3553	Starts the watcher. Note that there is no C<loop> argument, as the	4147	Starts the watcher. Note that there is no C<loop> argument, as the
3554	constructor already stores the event loop.	4148	constructor already stores the event loop.
…		…
3584	watchers in the constructor.	4178	watchers in the constructor.
3585		4179
3586	class myclass	4180	class myclass
3587	{	4181	{
3588	ev::io io ; void io_cb (ev::io &w, int revents);	4182	ev::io io ; void io_cb (ev::io &w, int revents);
3589	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4183	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3590	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4184	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3591		4185
3592	myclass (int fd)	4186	myclass (int fd)
3593	{	4187	{
3594	io .set <myclass, &myclass::io_cb > (this);	4188	io .set <myclass, &myclass::io_cb > (this);
…		…
3645	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4239	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3646		4240
3647	=item D	4241	=item D
3648		4242
3649	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4243	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3650	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4244	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3651		4245
3652	=item Ocaml	4246	=item Ocaml
3653		4247
3654	Erkki Seppala has written Ocaml bindings for libev, to be found at	4248	Erkki Seppala has written Ocaml bindings for libev, to be found at
3655	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4249	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3658		4252
3659	Brian Maher has written a partial interface to libev for lua (at the	4253	Brian Maher has written a partial interface to libev for lua (at the
3660	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4254	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3661	L<http://github.com/brimworks/lua-ev>.	4255	L<http://github.com/brimworks/lua-ev>.
3662		4256
		4257	=item Javascript
		4258
		4259	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4260
		4261	=item Others
		4262
		4263	There are others, and I stopped counting.
		4264
3663	=back	4265	=back
3664		4266
3665		4267
3666	=head1 MACRO MAGIC	4268	=head1 MACRO MAGIC
3667		4269
…		…
3703	suitable for use with C<EV_A>.	4305	suitable for use with C<EV_A>.
3704		4306
3705	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4307	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3706		4308
3707	Similar to the other two macros, this gives you the value of the default	4309	Similar to the other two macros, this gives you the value of the default
3708	loop, if multiple loops are supported ("ev loop default").	4310	loop, if multiple loops are supported ("ev loop default"). The default loop
		4311	will be initialised if it isn't already initialised.
		4312
		4313	For non-multiplicity builds, these macros do nothing, so you always have
		4314	to initialise the loop somewhere.
3709		4315
3710	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4316	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3711		4317
3712	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4318	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3713	default loop has been initialised (C<UC> == unchecked). Their behaviour	4319	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3780	ev_vars.h	4386	ev_vars.h
3781	ev_wrap.h	4387	ev_wrap.h
3782		4388
3783	ev_win32.c required on win32 platforms only	4389	ev_win32.c required on win32 platforms only
3784		4390
3785	ev_select.c only when select backend is enabled (which is enabled by default)	4391	ev_select.c only when select backend is enabled
3786	ev_poll.c only when poll backend is enabled (disabled by default)	4392	ev_poll.c only when poll backend is enabled
3787	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4393	ev_epoll.c only when the epoll backend is enabled
3788	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4394	ev_kqueue.c only when the kqueue backend is enabled
3789	ev_port.c only when the solaris port backend is enabled (disabled by default)	4395	ev_port.c only when the solaris port backend is enabled
3790		4396
3791	F<ev.c> includes the backend files directly when enabled, so you only need	4397	F<ev.c> includes the backend files directly when enabled, so you only need
3792	to compile this single file.	4398	to compile this single file.
3793		4399
3794	=head3 LIBEVENT COMPATIBILITY API	4400	=head3 LIBEVENT COMPATIBILITY API
…		…
3858	supported). It will also not define any of the structs usually found in	4464	supported). It will also not define any of the structs usually found in
3859	F<event.h> that are not directly supported by the libev core alone.	4465	F<event.h> that are not directly supported by the libev core alone.
3860		4466
3861	In standalone mode, libev will still try to automatically deduce the	4467	In standalone mode, libev will still try to automatically deduce the
3862	configuration, but has to be more conservative.	4468	configuration, but has to be more conservative.
		4469
		4470	=item EV_USE_FLOOR
		4471
		4472	If defined to be C<1>, libev will use the C<floor ()> function for its
		4473	periodic reschedule calculations, otherwise libev will fall back on a
		4474	portable (slower) implementation. If you enable this, you usually have to
		4475	link against libm or something equivalent. Enabling this when the C<floor>
		4476	function is not available will fail, so the safe default is to not enable
		4477	this.
3863		4478
3864	=item EV_USE_MONOTONIC	4479	=item EV_USE_MONOTONIC
3865		4480
3866	If defined to be C<1>, libev will try to detect the availability of the	4481	If defined to be C<1>, libev will try to detect the availability of the
3867	monotonic clock option at both compile time and runtime. Otherwise no	4482	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3952		4567
3953	If programs implement their own fd to handle mapping on win32, then this	4568	If programs implement their own fd to handle mapping on win32, then this
3954	macro can be used to override the C<close> function, useful to unregister	4569	macro can be used to override the C<close> function, useful to unregister
3955	file descriptors again. Note that the replacement function has to close	4570	file descriptors again. Note that the replacement function has to close
3956	the underlying OS handle.	4571	the underlying OS handle.
		4572
		4573	=item EV_USE_WSASOCKET
		4574
		4575	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4576	communication socket, which works better in some environments. Otherwise,
		4577	the normal C<socket> function will be used, which works better in other
		4578	environments.
3957		4579
3958	=item EV_USE_POLL	4580	=item EV_USE_POLL
3959		4581
3960	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4582	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3961	backend. Otherwise it will be enabled on non-win32 platforms. It	4583	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3997	If defined to be C<1>, libev will compile in support for the Linux inotify	4619	If defined to be C<1>, libev will compile in support for the Linux inotify
3998	interface to speed up C<ev_stat> watchers. Its actual availability will	4620	interface to speed up C<ev_stat> watchers. Its actual availability will
3999	be detected at runtime. If undefined, it will be enabled if the headers	4621	be detected at runtime. If undefined, it will be enabled if the headers
4000	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4622	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4001		4623
		4624	=item EV_NO_SMP
		4625
		4626	If defined to be C<1>, libev will assume that memory is always coherent
		4627	between threads, that is, threads can be used, but threads never run on
		4628	different cpus (or different cpu cores). This reduces dependencies
		4629	and makes libev faster.
		4630
		4631	=item EV_NO_THREADS
		4632
		4633	If defined to be C<1>, libev will assume that it will never be called from
		4634	different threads (that includes signal handlers), which is a stronger
		4635	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4636	libev faster.
		4637
4002	=item EV_ATOMIC_T	4638	=item EV_ATOMIC_T
4003		4639
4004	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4640	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4005	access is atomic with respect to other threads or signal contexts. No such	4641	access is atomic with respect to other threads or signal contexts. No
4006	type is easily found in the C language, so you can provide your own type	4642	such type is easily found in the C language, so you can provide your own
4007	that you know is safe for your purposes. It is used both for signal handler "locking"	4643	type that you know is safe for your purposes. It is used both for signal
4008	as well as for signal and thread safety in C<ev_async> watchers.	4644	handler "locking" as well as for signal and thread safety in C<ev_async>
		4645	watchers.
4009		4646
4010	In the absence of this define, libev will use C<sig_atomic_t volatile>	4647	In the absence of this define, libev will use C<sig_atomic_t volatile>
4011	(from F<signal.h>), which is usually good enough on most platforms.	4648	(from F<signal.h>), which is usually good enough on most platforms.
4012		4649
4013	=item EV_H (h)	4650	=item EV_H (h)
…		…
4040	will have the C<struct ev_loop *> as first argument, and you can create	4677	will have the C<struct ev_loop *> as first argument, and you can create
4041	additional independent event loops. Otherwise there will be no support	4678	additional independent event loops. Otherwise there will be no support
4042	for multiple event loops and there is no first event loop pointer	4679	for multiple event loops and there is no first event loop pointer
4043	argument. Instead, all functions act on the single default loop.	4680	argument. Instead, all functions act on the single default loop.
4044		4681
		4682	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4683	default loop when multiplicity is switched off - you always have to
		4684	initialise the loop manually in this case.
		4685
4045	=item EV_MINPRI	4686	=item EV_MINPRI
4046		4687
4047	=item EV_MAXPRI	4688	=item EV_MAXPRI
4048		4689
4049	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4690	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4085	#define EV_USE_POLL 1	4726	#define EV_USE_POLL 1
4086	#define EV_CHILD_ENABLE 1	4727	#define EV_CHILD_ENABLE 1
4087	#define EV_ASYNC_ENABLE 1	4728	#define EV_ASYNC_ENABLE 1
4088		4729
4089	The actual value is a bitset, it can be a combination of the following	4730	The actual value is a bitset, it can be a combination of the following
4090	values:	4731	values (by default, all of these are enabled):
4091		4732
4092	=over 4	4733	=over 4
4093		4734
4094	=item C<1> - faster/larger code	4735	=item C<1> - faster/larger code
4095		4736
…		…
4099	code size by roughly 30% on amd64).	4740	code size by roughly 30% on amd64).
4100		4741
4101	When optimising for size, use of compiler flags such as C<-Os> with	4742	When optimising for size, use of compiler flags such as C<-Os> with
4102	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4743	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4103	assertions.	4744	assertions.
		4745
		4746	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4747	(e.g. gcc with C<-Os>).
4104		4748
4105	=item C<2> - faster/larger data structures	4749	=item C<2> - faster/larger data structures
4106		4750
4107	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4751	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4108	hash table sizes and so on. This will usually further increase code size	4752	hash table sizes and so on. This will usually further increase code size
4109	and can additionally have an effect on the size of data structures at	4753	and can additionally have an effect on the size of data structures at
4110	runtime.	4754	runtime.
4111		4755
		4756	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4757	(e.g. gcc with C<-Os>).
		4758
4112	=item C<4> - full API configuration	4759	=item C<4> - full API configuration
4113		4760
4114	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4761	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4115	enables multiplicity (C<EV_MULTIPLICITY>=1).	4762	enables multiplicity (C<EV_MULTIPLICITY>=1).
4116		4763
…		…
4146		4793
4147	With an intelligent-enough linker (gcc+binutils are intelligent enough	4794	With an intelligent-enough linker (gcc+binutils are intelligent enough
4148	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4795	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4149	your program might be left out as well - a binary starting a timer and an	4796	your program might be left out as well - a binary starting a timer and an
4150	I/O watcher then might come out at only 5Kb.	4797	I/O watcher then might come out at only 5Kb.
		4798
		4799	=item EV_API_STATIC
		4800
		4801	If this symbol is defined (by default it is not), then all identifiers
		4802	will have static linkage. This means that libev will not export any
		4803	identifiers, and you cannot link against libev anymore. This can be useful
		4804	when you embed libev, only want to use libev functions in a single file,
		4805	and do not want its identifiers to be visible.
		4806
		4807	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4808	wants to use libev.
		4809
		4810	This option only works when libev is compiled with a C compiler, as C++
		4811	doesn't support the required declaration syntax.
4151		4812
4152	=item EV_AVOID_STDIO	4813	=item EV_AVOID_STDIO
4153		4814
4154	If this is set to C<1> at compiletime, then libev will avoid using stdio	4815	If this is set to C<1> at compiletime, then libev will avoid using stdio
4155	functions (printf, scanf, perror etc.). This will increase the code size	4816	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4299	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4960	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4300		4961
4301	#include "ev_cpp.h"	4962	#include "ev_cpp.h"
4302	#include "ev.c"	4963	#include "ev.c"
4303		4964
4304	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4965	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4305		4966
4306	=head2 THREADS AND COROUTINES	4967	=head2 THREADS AND COROUTINES
4307		4968
4308	=head3 THREADS	4969	=head3 THREADS
4309		4970
…		…
4360	default loop and triggering an C<ev_async> watcher from the default loop	5021	default loop and triggering an C<ev_async> watcher from the default loop
4361	watcher callback into the event loop interested in the signal.	5022	watcher callback into the event loop interested in the signal.
4362		5023
4363	=back	5024	=back
4364		5025
4365	=head4 THREAD LOCKING EXAMPLE	5026	See also L</THREAD LOCKING EXAMPLE>.
4366
4367	Here is a fictitious example of how to run an event loop in a different
4368	thread than where callbacks are being invoked and watchers are
4369	created/added/removed.
4370
4371	For a real-world example, see the C<EV::Loop::Async> perl module,
4372	which uses exactly this technique (which is suited for many high-level
4373	languages).
4374
4375	The example uses a pthread mutex to protect the loop data, a condition
4376	variable to wait for callback invocations, an async watcher to notify the
4377	event loop thread and an unspecified mechanism to wake up the main thread.
4378
4379	First, you need to associate some data with the event loop:
4380
4381	typedef struct {
4382	mutex_t lock; /* global loop lock */
4383	ev_async async_w;
4384	thread_t tid;
4385	cond_t invoke_cv;
4386	} userdata;
4387
4388	void prepare_loop (EV_P)
4389	{
4390	// for simplicity, we use a static userdata struct.
4391	static userdata u;
4392
4393	ev_async_init (&u->async_w, async_cb);
4394	ev_async_start (EV_A_ &u->async_w);
4395
4396	pthread_mutex_init (&u->lock, 0);
4397	pthread_cond_init (&u->invoke_cv, 0);
4398
4399	// now associate this with the loop
4400	ev_set_userdata (EV_A_ u);
4401	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4402	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4403
4404	// then create the thread running ev_loop
4405	pthread_create (&u->tid, 0, l_run, EV_A);
4406	}
4407
4408	The callback for the C<ev_async> watcher does nothing: the watcher is used
4409	solely to wake up the event loop so it takes notice of any new watchers
4410	that might have been added:
4411
4412	static void
4413	async_cb (EV_P_ ev_async *w, int revents)
4414	{
4415	// just used for the side effects
4416	}
4417
4418	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4419	protecting the loop data, respectively.
4420
4421	static void
4422	l_release (EV_P)
4423	{
4424	userdata *u = ev_userdata (EV_A);
4425	pthread_mutex_unlock (&u->lock);
4426	}
4427
4428	static void
4429	l_acquire (EV_P)
4430	{
4431	userdata *u = ev_userdata (EV_A);
4432	pthread_mutex_lock (&u->lock);
4433	}
4434
4435	The event loop thread first acquires the mutex, and then jumps straight
4436	into C<ev_run>:
4437
4438	void *
4439	l_run (void *thr_arg)
4440	{
4441	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4442
4443	l_acquire (EV_A);
4444	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4445	ev_run (EV_A_ 0);
4446	l_release (EV_A);
4447
4448	return 0;
4449	}
4450
4451	Instead of invoking all pending watchers, the C<l_invoke> callback will
4452	signal the main thread via some unspecified mechanism (signals? pipe
4453	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4454	have been called (in a while loop because a) spurious wakeups are possible
4455	and b) skipping inter-thread-communication when there are no pending
4456	watchers is very beneficial):
4457
4458	static void
4459	l_invoke (EV_P)
4460	{
4461	userdata *u = ev_userdata (EV_A);
4462
4463	while (ev_pending_count (EV_A))
4464	{
4465	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4466	pthread_cond_wait (&u->invoke_cv, &u->lock);
4467	}
4468	}
4469
4470	Now, whenever the main thread gets told to invoke pending watchers, it
4471	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4472	thread to continue:
4473
4474	static void
4475	real_invoke_pending (EV_P)
4476	{
4477	userdata *u = ev_userdata (EV_A);
4478
4479	pthread_mutex_lock (&u->lock);
4480	ev_invoke_pending (EV_A);
4481	pthread_cond_signal (&u->invoke_cv);
4482	pthread_mutex_unlock (&u->lock);
4483	}
4484
4485	Whenever you want to start/stop a watcher or do other modifications to an
4486	event loop, you will now have to lock:
4487
4488	ev_timer timeout_watcher;
4489	userdata *u = ev_userdata (EV_A);
4490
4491	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4492
4493	pthread_mutex_lock (&u->lock);
4494	ev_timer_start (EV_A_ &timeout_watcher);
4495	ev_async_send (EV_A_ &u->async_w);
4496	pthread_mutex_unlock (&u->lock);
4497
4498	Note that sending the C<ev_async> watcher is required because otherwise
4499	an event loop currently blocking in the kernel will have no knowledge
4500	about the newly added timer. By waking up the loop it will pick up any new
4501	watchers in the next event loop iteration.
4502		5027
4503	=head3 COROUTINES	5028	=head3 COROUTINES
4504		5029
4505	Libev is very accommodating to coroutines ("cooperative threads"):	5030	Libev is very accommodating to coroutines ("cooperative threads"):
4506	libev fully supports nesting calls to its functions from different	5031	libev fully supports nesting calls to its functions from different
…		…
4671	requires, and its I/O model is fundamentally incompatible with the POSIX	5196	requires, and its I/O model is fundamentally incompatible with the POSIX
4672	model. Libev still offers limited functionality on this platform in	5197	model. Libev still offers limited functionality on this platform in
4673	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5198	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4674	descriptors. This only applies when using Win32 natively, not when using	5199	descriptors. This only applies when using Win32 natively, not when using
4675	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5200	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4676	as every compielr comes with a slightly differently broken/incompatible	5201	as every compiler comes with a slightly differently broken/incompatible
4677	environment.	5202	environment.
4678		5203
4679	Lifting these limitations would basically require the full	5204	Lifting these limitations would basically require the full
4680	re-implementation of the I/O system. If you are into this kind of thing,	5205	re-implementation of the I/O system. If you are into this kind of thing,
4681	then note that glib does exactly that for you in a very portable way (note	5206	then note that glib does exactly that for you in a very portable way (note
…		…
4775	structure (guaranteed by POSIX but not by ISO C for example), but it also	5300	structure (guaranteed by POSIX but not by ISO C for example), but it also
4776	assumes that the same (machine) code can be used to call any watcher	5301	assumes that the same (machine) code can be used to call any watcher
4777	callback: The watcher callbacks have different type signatures, but libev	5302	callback: The watcher callbacks have different type signatures, but libev
4778	calls them using an C<ev_watcher *> internally.	5303	calls them using an C<ev_watcher *> internally.
4779		5304
		5305	=item null pointers and integer zero are represented by 0 bytes
		5306
		5307	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5308	relies on this setting pointers and integers to null.
		5309
4780	=item pointer accesses must be thread-atomic	5310	=item pointer accesses must be thread-atomic
4781		5311
4782	Accessing a pointer value must be atomic, it must both be readable and	5312	Accessing a pointer value must be atomic, it must both be readable and
4783	writable in one piece - this is the case on all current architectures.	5313	writable in one piece - this is the case on all current architectures.
4784		5314
…		…
4797	thread" or will block signals process-wide, both behaviours would	5327	thread" or will block signals process-wide, both behaviours would
4798	be compatible with libev. Interaction between C<sigprocmask> and	5328	be compatible with libev. Interaction between C<sigprocmask> and
4799	C<pthread_sigmask> could complicate things, however.	5329	C<pthread_sigmask> could complicate things, however.
4800		5330
4801	The most portable way to handle signals is to block signals in all threads	5331	The most portable way to handle signals is to block signals in all threads
4802	except the initial one, and run the default loop in the initial thread as	5332	except the initial one, and run the signal handling loop in the initial
4803	well.	5333	thread as well.
4804		5334
4805	=item C<long> must be large enough for common memory allocation sizes	5335	=item C<long> must be large enough for common memory allocation sizes
4806		5336
4807	To improve portability and simplify its API, libev uses C<long> internally	5337	To improve portability and simplify its API, libev uses C<long> internally
4808	instead of C<size_t> when allocating its data structures. On non-POSIX	5338	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4814		5344
4815	The type C<double> is used to represent timestamps. It is required to	5345	The type C<double> is used to represent timestamps. It is required to
4816	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5346	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4817	good enough for at least into the year 4000 with millisecond accuracy	5347	good enough for at least into the year 4000 with millisecond accuracy
4818	(the design goal for libev). This requirement is overfulfilled by	5348	(the design goal for libev). This requirement is overfulfilled by
4819	implementations using IEEE 754, which is basically all existing ones. With	5349	implementations using IEEE 754, which is basically all existing ones.
		5350
4820	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5351	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5352	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5353	is either obsolete or somebody patched it to use C<long double> or
		5354	something like that, just kidding).
4821		5355
4822	=back	5356	=back
4823		5357
4824	If you know of other additional requirements drop me a note.	5358	If you know of other additional requirements drop me a note.
4825		5359
…		…
4887	=item Processing ev_async_send: O(number_of_async_watchers)	5421	=item Processing ev_async_send: O(number_of_async_watchers)
4888		5422
4889	=item Processing signals: O(max_signal_number)	5423	=item Processing signals: O(max_signal_number)
4890		5424
4891	Sending involves a system call I<iff> there were no other C<ev_async_send>	5425	Sending involves a system call I<iff> there were no other C<ev_async_send>
4892	calls in the current loop iteration. Checking for async and signal events	5426	calls in the current loop iteration and the loop is currently
		5427	blocked. Checking for async and signal events involves iterating over all
4893	involves iterating over all running async watchers or all signal numbers.	5428	running async watchers or all signal numbers.
4894		5429
4895	=back	5430	=back
4896		5431
4897		5432
4898	=head1 PORTING FROM LIBEV 3.X TO 4.X	5433	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4907	=over 4	5442	=over 4
4908		5443
4909	=item C<EV_COMPAT3> backwards compatibility mechanism	5444	=item C<EV_COMPAT3> backwards compatibility mechanism
4910		5445
4911	The backward compatibility mechanism can be controlled by	5446	The backward compatibility mechanism can be controlled by
4912	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5447	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
4913	section.	5448	section.
4914		5449
4915	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5450	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4916		5451
4917	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5452	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
4960	=over 4	5495	=over 4
4961		5496
4962	=item active	5497	=item active
4963		5498
4964	A watcher is active as long as it has been started and not yet stopped.	5499	A watcher is active as long as it has been started and not yet stopped.
4965	See L<WATCHER STATES> for details.	5500	See L</WATCHER STATES> for details.
4966		5501
4967	=item application	5502	=item application
4968		5503
4969	In this document, an application is whatever is using libev.	5504	In this document, an application is whatever is using libev.
4970		5505
…		…
5006	watchers and events.	5541	watchers and events.
5007		5542
5008	=item pending	5543	=item pending
5009		5544
5010	A watcher is pending as soon as the corresponding event has been	5545	A watcher is pending as soon as the corresponding event has been
5011	detected. See L<WATCHER STATES> for details.	5546	detected. See L</WATCHER STATES> for details.
5012		5547
5013	=item real time	5548	=item real time
5014		5549
5015	The physical time that is observed. It is apparently strictly monotonic :)	5550	The physical time that is observed. It is apparently strictly monotonic :)
5016		5551
5017	=item wall-clock time	5552	=item wall-clock time
5018		5553
5019	The time and date as shown on clocks. Unlike real time, it can actually	5554	The time and date as shown on clocks. Unlike real time, it can actually
5020	be wrong and jump forwards and backwards, e.g. when the you adjust your	5555	be wrong and jump forwards and backwards, e.g. when you adjust your
5021	clock.	5556	clock.
5022		5557
5023	=item watcher	5558	=item watcher
5024		5559
5025	A data structure that describes interest in certain events. Watchers need	5560	A data structure that describes interest in certain events. Watchers need
…		…
5028	=back	5563	=back
5029		5564
5030	=head1 AUTHOR	5565	=head1 AUTHOR
5031		5566
5032	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5567	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5033	Magnusson and Emanuele Giaquinta.	5568	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5034		5569

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