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

Comparing libev/ev.pod (file contents):
Revision 1.356 by root, Tue Jan 11 01:42:47 2011 UTC vs.
Revision 1.399 by root, Mon Apr 2 23:14:41 2012 UTC

…		…
58	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
59		59
60	// now wait for events to arrive	60	// now wait for events to arrive
61	ev_run (loop, 0);	61	ev_run (loop, 0);
62		62
63	// unloop was called, so exit	63	// break was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 ABOUT THIS DOCUMENT	67	=head1 ABOUT THIS DOCUMENT
68		68
…		…
174	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
175		175
176	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
178	you actually want to know. Also interesting is the combination of	178	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	179	C<ev_now_update> and C<ev_now>.
180		180
181	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
182		182
183	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
185	this is a sub-second-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
186		192
187	=item int ev_version_major ()	193	=item int ev_version_major ()
188		194
189	=item int ev_version_minor ()	195	=item int ev_version_minor ()
190		196
…		…
435	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
436		442
437	=item C<EVFLAG_NOSIGMASK>	443	=item C<EVFLAG_NOSIGMASK>
438		444
439	When this flag is specified, then libev will avoid to modify the signal	445	When this flag is specified, then libev will avoid to modify the signal
440	mask. Specifically, this means you ahve to make sure signals are unblocked	446	mask. Specifically, this means you have to make sure signals are unblocked
441	when you want to receive them.	447	when you want to receive them.
442		448
443	This behaviour is useful when you want to do your own signal handling, or	449	This behaviour is useful when you want to do your own signal handling, or
444	want to handle signals only in specific threads and want to avoid libev	450	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
446		455
447	This flag's behaviour will become the default in future versions of libev.	456	This flag's behaviour will become the default in future versions of libev.
448		457
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		459
…		…
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		490
482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
483	kernels).	492	kernels).
484		493
485	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
486	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
487	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
488	epoll scales either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
489		498
490	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	502	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
496	0.1ms) and so on. The biggest issue is fork races, however - if a program	505	0.1ms) and so on. The biggest issue is fork races, however - if a program
497	forks then I<both> parent and child process have to recreate the epoll	506	forks then I<both> parent and child process have to recreate the epoll
498	set, which can take considerable time (one syscall per file descriptor)	507	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	508	and is of course hard to detect.
500		509
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
502	of course I<doesn't>, and epoll just loves to report events for totally	511	but of course I<doesn't>, and epoll just loves to report events for
503	I<different> file descriptors (even already closed ones, so one cannot	512	totally I<different> file descriptors (even already closed ones, so
504	even remove them from the set) than registered in the set (especially	513	one cannot even remove them from the set) than registered in the set
505	on SMP systems). Libev tries to counter these spurious notifications by	514	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
507	events to filter out spurious ones, recreating the set when required. Last	516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
508	not least, it also refuses to work with some file descriptors which work	520	not least, it also refuses to work with some file descriptors which work
509	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
510		522
511	Epoll is truly the train wreck analog among event poll mechanisms,	523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
512	a frankenpoll, cobbled together in a hurry, no thought to design or	524	cobbled together in a hurry, no thought to design or interaction with
513	interaction with others.	525	others. Oh, the pain, will it ever stop...
514		526
515	While stopping, setting and starting an I/O watcher in the same iteration	527	While stopping, setting and starting an I/O watcher in the same iteration
516	will result in some caching, there is still a system call per such	528	will result in some caching, there is still a system call per such
517	incident (because the same I<file descriptor> could point to a different	529	incident (because the same I<file descriptor> could point to a different
518	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
555		567
556	It scales in the same way as the epoll backend, but the interface to the	568	It scales in the same way as the epoll backend, but the interface to the
557	kernel is more efficient (which says nothing about its actual speed, of	569	kernel is more efficient (which says nothing about its actual speed, of
558	course). While stopping, setting and starting an I/O watcher does never	570	course). While stopping, setting and starting an I/O watcher does never
559	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
560	two event changes per incident. Support for C<fork ()> is very bad (but	572	two event changes per incident. Support for C<fork ()> is very bad (you
561	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	573	might have to leak fd's on fork, but it's more sane than epoll) and it
562	cases	574	drops fds silently in similarly hard-to-detect cases
563		575
564	This backend usually performs well under most conditions.	576	This backend usually performs well under most conditions.
565		577
566	While nominally embeddable in other event loops, this doesn't work	578	While nominally embeddable in other event loops, this doesn't work
567	everywhere, so you might need to test for this. And since it is broken	579	everywhere, so you might need to test for this. And since it is broken
…		…
596	among the OS-specific backends (I vastly prefer correctness over speed	608	among the OS-specific backends (I vastly prefer correctness over speed
597	hacks).	609	hacks).
598		610
599	On the negative side, the interface is I<bizarre> - so bizarre that	611	On the negative side, the interface is I<bizarre> - so bizarre that
600	even sun itself gets it wrong in their code examples: The event polling	612	even sun itself gets it wrong in their code examples: The event polling
601	function sometimes returning events to the caller even though an error	613	function sometimes returns events to the caller even though an error
602	occurred, but with no indication whether it has done so or not (yes, it's	614	occurred, but with no indication whether it has done so or not (yes, it's
603	even documented that way) - deadly for edge-triggered interfaces where	615	even documented that way) - deadly for edge-triggered interfaces where you
604	you absolutely have to know whether an event occurred or not because you	616	absolutely have to know whether an event occurred or not because you have
605	have to re-arm the watcher.	617	to re-arm the watcher.
606		618
607	Fortunately libev seems to be able to work around these idiocies.	619	Fortunately libev seems to be able to work around these idiocies.
608		620
609	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
610	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
…		…
780	without a previous call to C<ev_suspend>.	792	without a previous call to C<ev_suspend>.
781		793
782	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	794	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
783	event loop time (see C<ev_now_update>).	795	event loop time (see C<ev_now_update>).
784		796
785	=item ev_run (loop, int flags)	797	=item bool ev_run (loop, int flags)
786		798
787	Finally, this is it, the event handler. This function usually is called	799	Finally, this is it, the event handler. This function usually is called
788	after you have initialised all your watchers and you want to start	800	after you have initialised all your watchers and you want to start
789	handling events. It will ask the operating system for any new events, call	801	handling events. It will ask the operating system for any new events, call
790	the watcher callbacks, an then repeat the whole process indefinitely: This	802	the watcher callbacks, and then repeat the whole process indefinitely: This
791	is why event loops are called I<loops>.	803	is why event loops are called I<loops>.
792		804
793	If the flags argument is specified as C<0>, it will keep handling events	805	If the flags argument is specified as C<0>, it will keep handling events
794	until either no event watchers are active anymore or C<ev_break> was	806	until either no event watchers are active anymore or C<ev_break> was
795	called.	807	called.
		808
		809	The return value is false if there are no more active watchers (which
		810	usually means "all jobs done" or "deadlock"), and true in all other cases
		811	(which usually means " you should call C<ev_run> again").
796		812
797	Please note that an explicit C<ev_break> is usually better than	813	Please note that an explicit C<ev_break> is usually better than
798	relying on all watchers to be stopped when deciding when a program has	814	relying on all watchers to be stopped when deciding when a program has
799	finished (especially in interactive programs), but having a program	815	finished (especially in interactive programs), but having a program
800	that automatically loops as long as it has to and no longer by virtue	816	that automatically loops as long as it has to and no longer by virtue
801	of relying on its watchers stopping correctly, that is truly a thing of	817	of relying on its watchers stopping correctly, that is truly a thing of
802	beauty.	818	beauty.
803		819
804	This function is also I<mostly> exception-safe - you can break out of	820	This function is I<mostly> exception-safe - you can break out of a
805	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++	821	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
806	exception and so on. This does not decrement the C<ev_depth> value, nor	822	exception and so on. This does not decrement the C<ev_depth> value, nor
807	will it clear any outstanding C<EVBREAK_ONE> breaks.	823	will it clear any outstanding C<EVBREAK_ONE> breaks.
808		824
809	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	825	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
810	those events and any already outstanding ones, but will not wait and	826	those events and any already outstanding ones, but will not wait and
…		…
822	This is useful if you are waiting for some external event in conjunction	838	This is useful if you are waiting for some external event in conjunction
823	with something not expressible using other libev watchers (i.e. "roll your	839	with something not expressible using other libev watchers (i.e. "roll your
824	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	840	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
825	usually a better approach for this kind of thing.	841	usually a better approach for this kind of thing.
826		842
827	Here are the gory details of what C<ev_run> does:	843	Here are the gory details of what C<ev_run> does (this is for your
		844	understanding, not a guarantee that things will work exactly like this in
		845	future versions):
828		846
829	- Increment loop depth.	847	- Increment loop depth.
830	- Reset the ev_break status.	848	- Reset the ev_break status.
831	- Before the first iteration, call any pending watchers.	849	- Before the first iteration, call any pending watchers.
832	LOOP:	850	LOOP:
…		…
865	anymore.	883	anymore.
866		884
867	... queue jobs here, make sure they register event watchers as long	885	... queue jobs here, make sure they register event watchers as long
868	... as they still have work to do (even an idle watcher will do..)	886	... as they still have work to do (even an idle watcher will do..)
869	ev_run (my_loop, 0);	887	ev_run (my_loop, 0);
870	... jobs done or somebody called unloop. yeah!	888	... jobs done or somebody called break. yeah!
871		889
872	=item ev_break (loop, how)	890	=item ev_break (loop, how)
873		891
874	Can be used to make a call to C<ev_run> return early (but only after it	892	Can be used to make a call to C<ev_run> return early (but only after it
875	has processed all outstanding events). The C<how> argument must be either	893	has processed all outstanding events). The C<how> argument must be either
…		…
938	overhead for the actual polling but can deliver many events at once.	956	overhead for the actual polling but can deliver many events at once.
939		957
940	By setting a higher I<io collect interval> you allow libev to spend more	958	By setting a higher I<io collect interval> you allow libev to spend more
941	time collecting I/O events, so you can handle more events per iteration,	959	time collecting I/O events, so you can handle more events per iteration,
942	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	960	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
943	C<ev_timer>) will be not affected. Setting this to a non-null value will	961	C<ev_timer>) will not be affected. Setting this to a non-null value will
944	introduce an additional C<ev_sleep ()> call into most loop iterations. The	962	introduce an additional C<ev_sleep ()> call into most loop iterations. The
945	sleep time ensures that libev will not poll for I/O events more often then	963	sleep time ensures that libev will not poll for I/O events more often then
946	once per this interval, on average.	964	once per this interval, on average (as long as the host time resolution is
		965	good enough).
947		966
948	Likewise, by setting a higher I<timeout collect interval> you allow libev	967	Likewise, by setting a higher I<timeout collect interval> you allow libev
949	to spend more time collecting timeouts, at the expense of increased	968	to spend more time collecting timeouts, at the expense of increased
950	latency/jitter/inexactness (the watcher callback will be called	969	latency/jitter/inexactness (the watcher callback will be called
951	later). C<ev_io> watchers will not be affected. Setting this to a non-null	970	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
1005	can be done relatively simply by putting mutex_lock/unlock calls around	1024	can be done relatively simply by putting mutex_lock/unlock calls around
1006	each call to a libev function.	1025	each call to a libev function.
1007		1026
1008	However, C<ev_run> can run an indefinite time, so it is not feasible	1027	However, C<ev_run> can run an indefinite time, so it is not feasible
1009	to wait for it to return. One way around this is to wake up the event	1028	to wait for it to return. One way around this is to wake up the event
1010	loop via C<ev_break> and C<av_async_send>, another way is to set these	1029	loop via C<ev_break> and C<ev_async_send>, another way is to set these
1011	I<release> and I<acquire> callbacks on the loop.	1030	I<release> and I<acquire> callbacks on the loop.
1012		1031
1013	When set, then C<release> will be called just before the thread is	1032	When set, then C<release> will be called just before the thread is
1014	suspended waiting for new events, and C<acquire> is called just	1033	suspended waiting for new events, and C<acquire> is called just
1015	afterwards.	1034	afterwards.
…		…
1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1376	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1358	functions that do not need a watcher.	1377	functions that do not need a watcher.
1359		1378
1360	=back	1379	=back
1361		1380
1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1381	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1363		1382	OWN COMPOSITE WATCHERS> idioms.
1364	Each watcher has, by default, a member C<void *data> that you can change
1365	and read at any time: libev will completely ignore it. This can be used
1366	to associate arbitrary data with your watcher. If you need more data and
1367	don't want to allocate memory and store a pointer to it in that data
1368	member, you can also "subclass" the watcher type and provide your own
1369	data:
1370
1371	struct my_io
1372	{
1373	ev_io io;
1374	int otherfd;
1375	void *somedata;
1376	struct whatever *mostinteresting;
1377	};
1378
1379	...
1380	struct my_io w;
1381	ev_io_init (&w.io, my_cb, fd, EV_READ);
1382
1383	And since your callback will be called with a pointer to the watcher, you
1384	can cast it back to your own type:
1385
1386	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1387	{
1388	struct my_io w = (struct my_io )w_;
1389	...
1390	}
1391
1392	More interesting and less C-conformant ways of casting your callback type
1393	instead have been omitted.
1394
1395	Another common scenario is to use some data structure with multiple
1396	embedded watchers:
1397
1398	struct my_biggy
1399	{
1400	int some_data;
1401	ev_timer t1;
1402	ev_timer t2;
1403	}
1404
1405	In this case getting the pointer to C<my_biggy> is a bit more
1406	complicated: Either you store the address of your C<my_biggy> struct
1407	in the C<data> member of the watcher (for woozies), or you need to use
1408	some pointer arithmetic using C<offsetof> inside your watchers (for real
1409	programmers):
1410
1411	#include <stddef.h>
1412
1413	static void
1414	t1_cb (EV_P_ ev_timer *w, int revents)
1415	{
1416	struct my_biggy big = (struct my_biggy *)
1417	(((char *)w) - offsetof (struct my_biggy, t1));
1418	}
1419
1420	static void
1421	t2_cb (EV_P_ ev_timer *w, int revents)
1422	{
1423	struct my_biggy big = (struct my_biggy *)
1424	(((char *)w) - offsetof (struct my_biggy, t2));
1425	}
1426		1383
1427	=head2 WATCHER STATES	1384	=head2 WATCHER STATES
1428		1385
1429	There are various watcher states mentioned throughout this manual -	1386	There are various watcher states mentioned throughout this manual -
1430	active, pending and so on. In this section these states and the rules to	1387	active, pending and so on. In this section these states and the rules to
…		…
1433		1390
1434	=over 4	1391	=over 4
1435		1392
1436	=item initialiased	1393	=item initialiased
1437		1394
1438	Before a watcher can be registered with the event looop it has to be	1395	Before a watcher can be registered with the event loop it has to be
1439	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1396	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1440	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1397	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1441		1398
1442	In this state it is simply some block of memory that is suitable for use	1399	In this state it is simply some block of memory that is suitable for
1443	in an event loop. It can be moved around, freed, reused etc. at will.	1400	use in an event loop. It can be moved around, freed, reused etc. at
		1401	will - as long as you either keep the memory contents intact, or call
		1402	C<ev_TYPE_init> again.
1444		1403
1445	=item started/running/active	1404	=item started/running/active
1446		1405
1447	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1406	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1448	property of the event loop, and is actively waiting for events. While in	1407	property of the event loop, and is actively waiting for events. While in
…		…
1476	latter will clear any pending state the watcher might be in, regardless	1435	latter will clear any pending state the watcher might be in, regardless
1477	of whether it was active or not, so stopping a watcher explicitly before	1436	of whether it was active or not, so stopping a watcher explicitly before
1478	freeing it is often a good idea.	1437	freeing it is often a good idea.
1479		1438
1480	While stopped (and not pending) the watcher is essentially in the	1439	While stopped (and not pending) the watcher is essentially in the
1481	initialised state, that is it can be reused, moved, modified in any way	1440	initialised state, that is, it can be reused, moved, modified in any way
1482	you wish.	1441	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1442	it again).
1483		1443
1484	=back	1444	=back
1485		1445
1486	=head2 WATCHER PRIORITY MODELS	1446	=head2 WATCHER PRIORITY MODELS
1487		1447
…		…
1680	always get a readiness notification instantly, and your read (or possibly	1640	always get a readiness notification instantly, and your read (or possibly
1681	write) will still block on the disk I/O.	1641	write) will still block on the disk I/O.
1682		1642
1683	Another way to view it is that in the case of sockets, pipes, character	1643	Another way to view it is that in the case of sockets, pipes, character
1684	devices and so on, there is another party (the sender) that delivers data	1644	devices and so on, there is another party (the sender) that delivers data
1685	on it's own, but in the case of files, there is no such thing: the disk	1645	on its own, but in the case of files, there is no such thing: the disk
1686	will not send data on it's own, simply because it doesn't know what you	1646	will not send data on its own, simply because it doesn't know what you
1687	wish to read - you would first have to request some data.	1647	wish to read - you would first have to request some data.
1688		1648
1689	Since files are typically not-so-well supported by advanced notification	1649	Since files are typically not-so-well supported by advanced notification
1690	mechanism, libev tries hard to emulate POSIX behaviour with respect	1650	mechanism, libev tries hard to emulate POSIX behaviour with respect
1691	to files, even though you should not use it. The reason for this is	1651	to files, even though you should not use it. The reason for this is
…		…
1815	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1775	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1816	monotonic clock option helps a lot here).	1776	monotonic clock option helps a lot here).
1817		1777
1818	The callback is guaranteed to be invoked only I<after> its timeout has	1778	The callback is guaranteed to be invoked only I<after> its timeout has
1819	passed (not I<at>, so on systems with very low-resolution clocks this	1779	passed (not I<at>, so on systems with very low-resolution clocks this
1820	might introduce a small delay). If multiple timers become ready during the	1780	might introduce a small delay, see "the special problem of being too
		1781	early", below). If multiple timers become ready during the same loop
1821	same loop iteration then the ones with earlier time-out values are invoked	1782	iteration then the ones with earlier time-out values are invoked before
1822	before ones of the same priority with later time-out values (but this is	1783	ones of the same priority with later time-out values (but this is no
1823	no longer true when a callback calls C<ev_run> recursively).	1784	longer true when a callback calls C<ev_run> recursively).
1824		1785
1825	=head3 Be smart about timeouts	1786	=head3 Be smart about timeouts
1826		1787
1827	Many real-world problems involve some kind of timeout, usually for error	1788	Many real-world problems involve some kind of timeout, usually for error
1828	recovery. A typical example is an HTTP request - if the other side hangs,	1789	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1903		1864
1904	In this case, it would be more efficient to leave the C<ev_timer> alone,	1865	In this case, it would be more efficient to leave the C<ev_timer> alone,
1905	but remember the time of last activity, and check for a real timeout only	1866	but remember the time of last activity, and check for a real timeout only
1906	within the callback:	1867	within the callback:
1907		1868
		1869	ev_tstamp timeout = 60.;
1908	ev_tstamp last_activity; // time of last activity	1870	ev_tstamp last_activity; // time of last activity
		1871	ev_timer timer;
1909		1872
1910	static void	1873	static void
1911	callback (EV_P_ ev_timer *w, int revents)	1874	callback (EV_P_ ev_timer *w, int revents)
1912	{	1875	{
1913	ev_tstamp now = ev_now (EV_A);	1876	// calculate when the timeout would happen
1914	ev_tstamp timeout = last_activity + 60.;	1877	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1915		1878
1916	// if last_activity + 60. is older than now, we did time out	1879	// if negative, it means we the timeout already occured
1917	if (timeout < now)	1880	if (after < 0.)
1918	{	1881	{
1919	// timeout occurred, take action	1882	// timeout occurred, take action
1920	}	1883	}
1921	else	1884	else
1922	{	1885	{
1923	// callback was invoked, but there was some activity, re-arm	1886	// callback was invoked, but there was some recent
1924	// the watcher to fire in last_activity + 60, which is	1887	// activity. simply restart the timer to time out
1925	// guaranteed to be in the future, so "again" is positive:	1888	// after "after" seconds, which is the earliest time
1926	w->repeat = timeout - now;	1889	// the timeout can occur.
		1890	ev_timer_set (w, after, 0.);
1927	ev_timer_again (EV_A_ w);	1891	ev_timer_start (EV_A_ w);
1928	}	1892	}
1929	}	1893	}
1930		1894
1931	To summarise the callback: first calculate the real timeout (defined	1895	To summarise the callback: first calculate in how many seconds the
1932	as "60 seconds after the last activity"), then check if that time has	1896	timeout will occur (by calculating the absolute time when it would occur,
1933	been reached, which means something I<did>, in fact, time out. Otherwise	1897	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1934	the callback was invoked too early (C<timeout> is in the future), so	1898	(EV_A)> from that).
1935	re-schedule the timer to fire at that future time, to see if maybe we have
1936	a timeout then.
1937		1899
1938	Note how C<ev_timer_again> is used, taking advantage of the	1900	If this value is negative, then we are already past the timeout, i.e. we
1939	C<ev_timer_again> optimisation when the timer is already running.	1901	timed out, and need to do whatever is needed in this case.
		1902
		1903	Otherwise, we now the earliest time at which the timeout would trigger,
		1904	and simply start the timer with this timeout value.
		1905
		1906	In other words, each time the callback is invoked it will check whether
		1907	the timeout cocured. If not, it will simply reschedule itself to check
		1908	again at the earliest time it could time out. Rinse. Repeat.
1940		1909
1941	This scheme causes more callback invocations (about one every 60 seconds	1910	This scheme causes more callback invocations (about one every 60 seconds
1942	minus half the average time between activity), but virtually no calls to	1911	minus half the average time between activity), but virtually no calls to
1943	libev to change the timeout.	1912	libev to change the timeout.
1944		1913
1945	To start the timer, simply initialise the watcher and set C<last_activity>	1914	To start the machinery, simply initialise the watcher and set
1946	to the current time (meaning we just have some activity :), then call the	1915	C<last_activity> to the current time (meaning there was some activity just
1947	callback, which will "do the right thing" and start the timer:	1916	now), then call the callback, which will "do the right thing" and start
		1917	the timer:
1948		1918
		1919	last_activity = ev_now (EV_A);
1949	ev_init (timer, callback);	1920	ev_init (&timer, callback);
1950	last_activity = ev_now (loop);	1921	callback (EV_A_ &timer, 0);
1951	callback (loop, timer, EV_TIMER);
1952		1922
1953	And when there is some activity, simply store the current time in	1923	When there is some activity, simply store the current time in
1954	C<last_activity>, no libev calls at all:	1924	C<last_activity>, no libev calls at all:
1955		1925
		1926	if (activity detected)
1956	last_activity = ev_now (loop);	1927	last_activity = ev_now (EV_A);
		1928
		1929	When your timeout value changes, then the timeout can be changed by simply
		1930	providing a new value, stopping the timer and calling the callback, which
		1931	will agaion do the right thing (for example, time out immediately :).
		1932
		1933	timeout = new_value;
		1934	ev_timer_stop (EV_A_ &timer);
		1935	callback (EV_A_ &timer, 0);
1957		1936
1958	This technique is slightly more complex, but in most cases where the	1937	This technique is slightly more complex, but in most cases where the
1959	time-out is unlikely to be triggered, much more efficient.	1938	time-out is unlikely to be triggered, much more efficient.
1960
1961	Changing the timeout is trivial as well (if it isn't hard-coded in the
1962	callback :) - just change the timeout and invoke the callback, which will
1963	fix things for you.
1964		1939
1965	=item 4. Wee, just use a double-linked list for your timeouts.	1940	=item 4. Wee, just use a double-linked list for your timeouts.
1966		1941
1967	If there is not one request, but many thousands (millions...), all	1942	If there is not one request, but many thousands (millions...), all
1968	employing some kind of timeout with the same timeout value, then one can	1943	employing some kind of timeout with the same timeout value, then one can
…		…
1995	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1970	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1996	rather complicated, but extremely efficient, something that really pays	1971	rather complicated, but extremely efficient, something that really pays
1997	off after the first million or so of active timers, i.e. it's usually	1972	off after the first million or so of active timers, i.e. it's usually
1998	overkill :)	1973	overkill :)
1999		1974
		1975	=head3 The special problem of being too early
		1976
		1977	If you ask a timer to call your callback after three seconds, then
		1978	you expect it to be invoked after three seconds - but of course, this
		1979	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1980	guaranteed to any precision by libev - imagine somebody suspending the
		1981	process with a STOP signal for a few hours for example.
		1982
		1983	So, libev tries to invoke your callback as soon as possible I<after> the
		1984	delay has occurred, but cannot guarantee this.
		1985
		1986	A less obvious failure mode is calling your callback too early: many event
		1987	loops compare timestamps with a "elapsed delay >= requested delay", but
		1988	this can cause your callback to be invoked much earlier than you would
		1989	expect.
		1990
		1991	To see why, imagine a system with a clock that only offers full second
		1992	resolution (think windows if you can't come up with a broken enough OS
		1993	yourself). If you schedule a one-second timer at the time 500.9, then the
		1994	event loop will schedule your timeout to elapse at a system time of 500
		1995	(500.9 truncated to the resolution) + 1, or 501.
		1996
		1997	If an event library looks at the timeout 0.1s later, it will see "501 >=
		1998	501" and invoke the callback 0.1s after it was started, even though a
		1999	one-second delay was requested - this is being "too early", despite best
		2000	intentions.
		2001
		2002	This is the reason why libev will never invoke the callback if the elapsed
		2003	delay equals the requested delay, but only when the elapsed delay is
		2004	larger than the requested delay. In the example above, libev would only invoke
		2005	the callback at system time 502, or 1.1s after the timer was started.
		2006
		2007	So, while libev cannot guarantee that your callback will be invoked
		2008	exactly when requested, it I<can> and I<does> guarantee that the requested
		2009	delay has actually elapsed, or in other words, it always errs on the "too
		2010	late" side of things.
		2011
2000	=head3 The special problem of time updates	2012	=head3 The special problem of time updates
2001		2013
2002	Establishing the current time is a costly operation (it usually takes at	2014	Establishing the current time is a costly operation (it usually takes
2003	least two system calls): EV therefore updates its idea of the current	2015	at least one system call): EV therefore updates its idea of the current
2004	time only before and after C<ev_run> collects new events, which causes a	2016	time only before and after C<ev_run> collects new events, which causes a
2005	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2017	growing difference between C<ev_now ()> and C<ev_time ()> when handling
2006	lots of events in one iteration.	2018	lots of events in one iteration.
2007		2019
2008	The relative timeouts are calculated relative to the C<ev_now ()>	2020	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
2014	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2026	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
2015		2027
2016	If the event loop is suspended for a long time, you can also force an	2028	If the event loop is suspended for a long time, you can also force an
2017	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2029	update of the time returned by C<ev_now ()> by calling C<ev_now_update
2018	()>.	2030	()>.
		2031
		2032	=head3 The special problem of unsynchronised clocks
		2033
		2034	Modern systems have a variety of clocks - libev itself uses the normal
		2035	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2036	jumps).
		2037
		2038	Neither of these clocks is synchronised with each other or any other clock
		2039	on the system, so C<ev_time ()> might return a considerably different time
		2040	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2041	a call to C<gettimeofday> might return a second count that is one higher
		2042	than a directly following call to C<time>.
		2043
		2044	The moral of this is to only compare libev-related timestamps with
		2045	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2046	a second or so.
		2047
		2048	One more problem arises due to this lack of synchronisation: if libev uses
		2049	the system monotonic clock and you compare timestamps from C<ev_time>
		2050	or C<ev_now> from when you started your timer and when your callback is
		2051	invoked, you will find that sometimes the callback is a bit "early".
		2052
		2053	This is because C<ev_timer>s work in real time, not wall clock time, so
		2054	libev makes sure your callback is not invoked before the delay happened,
		2055	I<measured according to the real time>, not the system clock.
		2056
		2057	If your timeouts are based on a physical timescale (e.g. "time out this
		2058	connection after 100 seconds") then this shouldn't bother you as it is
		2059	exactly the right behaviour.
		2060
		2061	If you want to compare wall clock/system timestamps to your timers, then
		2062	you need to use C<ev_periodic>s, as these are based on the wall clock
		2063	time, where your comparisons will always generate correct results.
2019		2064
2020	=head3 The special problems of suspended animation	2065	=head3 The special problems of suspended animation
2021		2066
2022	When you leave the server world it is quite customary to hit machines that	2067	When you leave the server world it is quite customary to hit machines that
2023	can suspend/hibernate - what happens to the clocks during such a suspend?	2068	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2067	keep up with the timer (because it takes longer than those 10 seconds to	2112	keep up with the timer (because it takes longer than those 10 seconds to
2068	do stuff) the timer will not fire more than once per event loop iteration.	2113	do stuff) the timer will not fire more than once per event loop iteration.
2069		2114
2070	=item ev_timer_again (loop, ev_timer *)	2115	=item ev_timer_again (loop, ev_timer *)
2071		2116
2072	This will act as if the timer timed out and restart it again if it is	2117	This will act as if the timer timed out, and restarts it again if it is
2073	repeating. The exact semantics are:	2118	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2119	timeout to the C<repeat> value and calling C<ev_timer_start>.
2074		2120
		2121	The exact semantics are as in the following rules, all of which will be
		2122	applied to the watcher:
		2123
		2124	=over 4
		2125
2075	If the timer is pending, its pending status is cleared.	2126	=item If the timer is pending, the pending status is always cleared.
2076		2127
2077	If the timer is started but non-repeating, stop it (as if it timed out).	2128	=item If the timer is started but non-repeating, stop it (as if it timed
		2129	out, without invoking it).
2078		2130
2079	If the timer is repeating, either start it if necessary (with the	2131	=item If the timer is repeating, make the C<repeat> value the new timeout
2080	C<repeat> value), or reset the running timer to the C<repeat> value.	2132	and start the timer, if necessary.
		2133
		2134	=back
2081		2135
2082	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2136	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
2083	usage example.	2137	usage example.
2084		2138
2085	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2139	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
…		…
2207		2261
2208	Another way to think about it (for the mathematically inclined) is that	2262	Another way to think about it (for the mathematically inclined) is that
2209	C<ev_periodic> will try to run the callback in this mode at the next possible	2263	C<ev_periodic> will try to run the callback in this mode at the next possible
2210	time where C<time = offset (mod interval)>, regardless of any time jumps.	2264	time where C<time = offset (mod interval)>, regardless of any time jumps.
2211		2265
2212	For numerical stability it is preferable that the C<offset> value is near	2266	The C<interval> I<MUST> be positive, and for numerical stability, the
2213	C<ev_now ()> (the current time), but there is no range requirement for	2267	interval value should be higher than C<1/8192> (which is around 100
2214	this value, and in fact is often specified as zero.	2268	microseconds) and C<offset> should be higher than C<0> and should have
		2269	at most a similar magnitude as the current time (say, within a factor of
		2270	ten). Typical values for offset are, in fact, C<0> or something between
		2271	C<0> and C<interval>, which is also the recommended range.
2215		2272
2216	Note also that there is an upper limit to how often a timer can fire (CPU	2273	Note also that there is an upper limit to how often a timer can fire (CPU
2217	speed for example), so if C<interval> is very small then timing stability	2274	speed for example), so if C<interval> is very small then timing stability
2218	will of course deteriorate. Libev itself tries to be exact to be about one	2275	will of course deteriorate. Libev itself tries to be exact to be about one
2219	millisecond (if the OS supports it and the machine is fast enough).	2276	millisecond (if the OS supports it and the machine is fast enough).
…		…
2362	=head3 The special problem of inheritance over fork/execve/pthread_create	2419	=head3 The special problem of inheritance over fork/execve/pthread_create
2363		2420
2364	Both the signal mask (C<sigprocmask>) and the signal disposition	2421	Both the signal mask (C<sigprocmask>) and the signal disposition
2365	(C<sigaction>) are unspecified after starting a signal watcher (and after	2422	(C<sigaction>) are unspecified after starting a signal watcher (and after
2366	stopping it again), that is, libev might or might not block the signal,	2423	stopping it again), that is, libev might or might not block the signal,
2367	and might or might not set or restore the installed signal handler.	2424	and might or might not set or restore the installed signal handler (but
		2425	see C<EVFLAG_NOSIGMASK>).
2368		2426
2369	While this does not matter for the signal disposition (libev never	2427	While this does not matter for the signal disposition (libev never
2370	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2428	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2371	C<execve>), this matters for the signal mask: many programs do not expect	2429	C<execve>), this matters for the signal mask: many programs do not expect
2372	certain signals to be blocked.	2430	certain signals to be blocked.
…		…
3243	atexit (program_exits);	3301	atexit (program_exits);
3244		3302
3245		3303
3246	=head2 C<ev_async> - how to wake up an event loop	3304	=head2 C<ev_async> - how to wake up an event loop
3247		3305
3248	In general, you cannot use an C<ev_run> from multiple threads or other	3306	In general, you cannot use an C<ev_loop> from multiple threads or other
3249	asynchronous sources such as signal handlers (as opposed to multiple event	3307	asynchronous sources such as signal handlers (as opposed to multiple event
3250	loops - those are of course safe to use in different threads).	3308	loops - those are of course safe to use in different threads).
3251		3309
3252	Sometimes, however, you need to wake up an event loop you do not control,	3310	Sometimes, however, you need to wake up an event loop you do not control,
3253	for example because it belongs to another thread. This is what C<ev_async>	3311	for example because it belongs to another thread. This is what C<ev_async>
…		…
3260	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3318	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
3261	of "global async watchers" by using a watcher on an otherwise unused	3319	of "global async watchers" by using a watcher on an otherwise unused
3262	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3320	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3263	even without knowing which loop owns the signal.	3321	even without knowing which loop owns the signal.
3264		3322
3265	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3266	just the default loop.
3267
3268	=head3 Queueing	3323	=head3 Queueing
3269		3324
3270	C<ev_async> does not support queueing of data in any way. The reason	3325	C<ev_async> does not support queueing of data in any way. The reason
3271	is that the author does not know of a simple (or any) algorithm for a	3326	is that the author does not know of a simple (or any) algorithm for a
3272	multiple-writer-single-reader queue that works in all cases and doesn't	3327	multiple-writer-single-reader queue that works in all cases and doesn't
…		…
3363	trust me.	3418	trust me.
3364		3419
3365	=item ev_async_send (loop, ev_async *)	3420	=item ev_async_send (loop, ev_async *)
3366		3421
3367	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3422	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3368	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3423	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3424	returns.
		3425
3369	C<ev_feed_event>, this call is safe to do from other threads, signal or	3426	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3370	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3427	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3371	section below on what exactly this means).	3428	embedding section below on what exactly this means).
3372		3429
3373	Note that, as with other watchers in libev, multiple events might get	3430	Note that, as with other watchers in libev, multiple events might get
3374	compressed into a single callback invocation (another way to look at this	3431	compressed into a single callback invocation (another way to look at
3375	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3432	this is that C<ev_async> watchers are level-triggered: they are set on
3376	reset when the event loop detects that).	3433	C<ev_async_send>, reset when the event loop detects that).
3377		3434
3378	This call incurs the overhead of a system call only once per event loop	3435	This call incurs the overhead of at most one extra system call per event
3379	iteration, so while the overhead might be noticeable, it doesn't apply to	3436	loop iteration, if the event loop is blocked, and no syscall at all if
3380	repeated calls to C<ev_async_send> for the same event loop.	3437	the event loop (or your program) is processing events. That means that
		3438	repeated calls are basically free (there is no need to avoid calls for
		3439	performance reasons) and that the overhead becomes smaller (typically
		3440	zero) under load.
3381		3441
3382	=item bool = ev_async_pending (ev_async *)	3442	=item bool = ev_async_pending (ev_async *)
3383		3443
3384	Returns a non-zero value when C<ev_async_send> has been called on the	3444	Returns a non-zero value when C<ev_async_send> has been called on the
3385	watcher but the event has not yet been processed (or even noted) by the	3445	watcher but the event has not yet been processed (or even noted) by the
…		…
3440	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3500	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3441		3501
3442	=item ev_feed_fd_event (loop, int fd, int revents)	3502	=item ev_feed_fd_event (loop, int fd, int revents)
3443		3503
3444	Feed an event on the given fd, as if a file descriptor backend detected	3504	Feed an event on the given fd, as if a file descriptor backend detected
3445	the given events it.	3505	the given events.
3446		3506
3447	=item ev_feed_signal_event (loop, int signum)	3507	=item ev_feed_signal_event (loop, int signum)
3448		3508
3449	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3509	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3450	which is async-safe.	3510	which is async-safe.
…		…
3455	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)	3515	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
3456		3516
3457	This section explains some common idioms that are not immediately	3517	This section explains some common idioms that are not immediately
3458	obvious. Note that examples are sprinkled over the whole manual, and this	3518	obvious. Note that examples are sprinkled over the whole manual, and this
3459	section only contains stuff that wouldn't fit anywhere else.	3519	section only contains stuff that wouldn't fit anywhere else.
		3520
		3521	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3522
		3523	Each watcher has, by default, a C<void *data> member that you can read
		3524	or modify at any time: libev will completely ignore it. This can be used
		3525	to associate arbitrary data with your watcher. If you need more data and
		3526	don't want to allocate memory separately and store a pointer to it in that
		3527	data member, you can also "subclass" the watcher type and provide your own
		3528	data:
		3529
		3530	struct my_io
		3531	{
		3532	ev_io io;
		3533	int otherfd;
		3534	void *somedata;
		3535	struct whatever *mostinteresting;
		3536	};
		3537
		3538	...
		3539	struct my_io w;
		3540	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3541
		3542	And since your callback will be called with a pointer to the watcher, you
		3543	can cast it back to your own type:
		3544
		3545	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3546	{
		3547	struct my_io w = (struct my_io )w_;
		3548	...
		3549	}
		3550
		3551	More interesting and less C-conformant ways of casting your callback
		3552	function type instead have been omitted.
		3553
		3554	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3555
		3556	Another common scenario is to use some data structure with multiple
		3557	embedded watchers, in effect creating your own watcher that combines
		3558	multiple libev event sources into one "super-watcher":
		3559
		3560	struct my_biggy
		3561	{
		3562	int some_data;
		3563	ev_timer t1;
		3564	ev_timer t2;
		3565	}
		3566
		3567	In this case getting the pointer to C<my_biggy> is a bit more
		3568	complicated: Either you store the address of your C<my_biggy> struct in
		3569	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3570	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3571	real programmers):
		3572
		3573	#include <stddef.h>
		3574
		3575	static void
		3576	t1_cb (EV_P_ ev_timer *w, int revents)
		3577	{
		3578	struct my_biggy big = (struct my_biggy *)
		3579	(((char *)w) - offsetof (struct my_biggy, t1));
		3580	}
		3581
		3582	static void
		3583	t2_cb (EV_P_ ev_timer *w, int revents)
		3584	{
		3585	struct my_biggy big = (struct my_biggy *)
		3586	(((char *)w) - offsetof (struct my_biggy, t2));
		3587	}
		3588
		3589	=head2 AVOIDING FINISHING BEFORE RETURNING
		3590
		3591	Often you have structures like this in event-based programs:
		3592
		3593	callback ()
		3594	{
		3595	free (request);
		3596	}
		3597
		3598	request = start_new_request (..., callback);
		3599
		3600	The intent is to start some "lengthy" operation. The C<request> could be
		3601	used to cancel the operation, or do other things with it.
		3602
		3603	It's not uncommon to have code paths in C<start_new_request> that
		3604	immediately invoke the callback, for example, to report errors. Or you add
		3605	some caching layer that finds that it can skip the lengthy aspects of the
		3606	operation and simply invoke the callback with the result.
		3607
		3608	The problem here is that this will happen I<before> C<start_new_request>
		3609	has returned, so C<request> is not set.
		3610
		3611	Even if you pass the request by some safer means to the callback, you
		3612	might want to do something to the request after starting it, such as
		3613	canceling it, which probably isn't working so well when the callback has
		3614	already been invoked.
		3615
		3616	A common way around all these issues is to make sure that
		3617	C<start_new_request> I<always> returns before the callback is invoked. If
		3618	C<start_new_request> immediately knows the result, it can artificially
		3619	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3620	for example, or more sneakily, by reusing an existing (stopped) watcher
		3621	and pushing it into the pending queue:
		3622
		3623	ev_set_cb (watcher, callback);
		3624	ev_feed_event (EV_A_ watcher, 0);
		3625
		3626	This way, C<start_new_request> can safely return before the callback is
		3627	invoked, while not delaying callback invocation too much.
3460		3628
3461	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS	3629	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3462		3630
3463	Often (especially in GUI toolkits) there are places where you have	3631	Often (especially in GUI toolkits) there are places where you have
3464	I<modal> interaction, which is most easily implemented by recursively	3632	I<modal> interaction, which is most easily implemented by recursively
…		…
3478	int exit_main_loop = 0;	3646	int exit_main_loop = 0;
3479		3647
3480	while (!exit_main_loop)	3648	while (!exit_main_loop)
3481	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3649	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3482		3650
3483	// in a model watcher	3651	// in a modal watcher
3484	int exit_nested_loop = 0;	3652	int exit_nested_loop = 0;
3485		3653
3486	while (!exit_nested_loop)	3654	while (!exit_nested_loop)
3487	ev_run (EV_A_ EVRUN_ONCE);	3655	ev_run (EV_A_ EVRUN_ONCE);
3488		3656
…		…
3498	exit_main_loop = exit_nested_loop = 1;	3666	exit_main_loop = exit_nested_loop = 1;
3499		3667
3500	=head2 THREAD LOCKING EXAMPLE	3668	=head2 THREAD LOCKING EXAMPLE
3501		3669
3502	Here is a fictitious example of how to run an event loop in a different	3670	Here is a fictitious example of how to run an event loop in a different
3503	thread than where callbacks are being invoked and watchers are	3671	thread from where callbacks are being invoked and watchers are
3504	created/added/removed.	3672	created/added/removed.
3505		3673
3506	For a real-world example, see the C<EV::Loop::Async> perl module,	3674	For a real-world example, see the C<EV::Loop::Async> perl module,
3507	which uses exactly this technique (which is suited for many high-level	3675	which uses exactly this technique (which is suited for many high-level
3508	languages).	3676	languages).
…		…
3534	// now associate this with the loop	3702	// now associate this with the loop
3535	ev_set_userdata (EV_A_ u);	3703	ev_set_userdata (EV_A_ u);
3536	ev_set_invoke_pending_cb (EV_A_ l_invoke);	3704	ev_set_invoke_pending_cb (EV_A_ l_invoke);
3537	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);	3705	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3538		3706
3539	// then create the thread running ev_loop	3707	// then create the thread running ev_run
3540	pthread_create (&u->tid, 0, l_run, EV_A);	3708	pthread_create (&u->tid, 0, l_run, EV_A);
3541	}	3709	}
3542		3710
3543	The callback for the C<ev_async> watcher does nothing: the watcher is used	3711	The callback for the C<ev_async> watcher does nothing: the watcher is used
3544	solely to wake up the event loop so it takes notice of any new watchers	3712	solely to wake up the event loop so it takes notice of any new watchers
…		…
3633	Note that sending the C<ev_async> watcher is required because otherwise	3801	Note that sending the C<ev_async> watcher is required because otherwise
3634	an event loop currently blocking in the kernel will have no knowledge	3802	an event loop currently blocking in the kernel will have no knowledge
3635	about the newly added timer. By waking up the loop it will pick up any new	3803	about the newly added timer. By waking up the loop it will pick up any new
3636	watchers in the next event loop iteration.	3804	watchers in the next event loop iteration.
3637		3805
		3806	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3807
		3808	While the overhead of a callback that e.g. schedules a thread is small, it
		3809	is still an overhead. If you embed libev, and your main usage is with some
		3810	kind of threads or coroutines, you might want to customise libev so that
		3811	doesn't need callbacks anymore.
		3812
		3813	Imagine you have coroutines that you can switch to using a function
		3814	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3815	and that due to some magic, the currently active coroutine is stored in a
		3816	global called C<current_coro>. Then you can build your own "wait for libev
		3817	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3818	the differing C<;> conventions):
		3819
		3820	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3821	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3822
		3823	That means instead of having a C callback function, you store the
		3824	coroutine to switch to in each watcher, and instead of having libev call
		3825	your callback, you instead have it switch to that coroutine.
		3826
		3827	A coroutine might now wait for an event with a function called
		3828	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3829	matter when, or whether the watcher is active or not when this function is
		3830	called):
		3831
		3832	void
		3833	wait_for_event (ev_watcher *w)
		3834	{
		3835	ev_cb_set (w) = current_coro;
		3836	switch_to (libev_coro);
		3837	}
		3838
		3839	That basically suspends the coroutine inside C<wait_for_event> and
		3840	continues the libev coroutine, which, when appropriate, switches back to
		3841	this or any other coroutine.
		3842
		3843	You can do similar tricks if you have, say, threads with an event queue -
		3844	instead of storing a coroutine, you store the queue object and instead of
		3845	switching to a coroutine, you push the watcher onto the queue and notify
		3846	any waiters.
		3847
		3848	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3849	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3850
		3851	// my_ev.h
		3852	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3853	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3854	#include "../libev/ev.h"
		3855
		3856	// my_ev.c
		3857	#define EV_H "my_ev.h"
		3858	#include "../libev/ev.c"
		3859
		3860	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3861	F<my_ev.c> into your project. When properly specifying include paths, you
		3862	can even use F<ev.h> as header file name directly.
		3863
3638		3864
3639	=head1 LIBEVENT EMULATION	3865	=head1 LIBEVENT EMULATION
3640		3866
3641	Libev offers a compatibility emulation layer for libevent. It cannot	3867	Libev offers a compatibility emulation layer for libevent. It cannot
3642	emulate the internals of libevent, so here are some usage hints:	3868	emulate the internals of libevent, so here are some usage hints:
…		…
3695	with C<operator ()> can be used as callbacks. Other types should be easy	3921	with C<operator ()> can be used as callbacks. Other types should be easy
3696	to add as long as they only need one additional pointer for context. If	3922	to add as long as they only need one additional pointer for context. If
3697	you need support for other types of functors please contact the author	3923	you need support for other types of functors please contact the author
3698	(preferably after implementing it).	3924	(preferably after implementing it).
3699		3925
		3926	For all this to work, your C++ compiler either has to use the same calling
		3927	conventions as your C compiler (for static member functions), or you have
		3928	to embed libev and compile libev itself as C++.
		3929
3700	Here is a list of things available in the C<ev> namespace:	3930	Here is a list of things available in the C<ev> namespace:
3701		3931
3702	=over 4	3932	=over 4
3703		3933
3704	=item C<ev::READ>, C<ev::WRITE> etc.	3934	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3713	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	3943	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3714		3944
3715	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	3945	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3716	the same name in the C<ev> namespace, with the exception of C<ev_signal>	3946	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3717	which is called C<ev::sig> to avoid clashes with the C<signal> macro	3947	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3718	defines by many implementations.	3948	defined by many implementations.
3719		3949
3720	All of those classes have these methods:	3950	All of those classes have these methods:
3721		3951
3722	=over 4	3952	=over 4
3723		3953
…		…
3856	watchers in the constructor.	4086	watchers in the constructor.
3857		4087
3858	class myclass	4088	class myclass
3859	{	4089	{
3860	ev::io io ; void io_cb (ev::io &w, int revents);	4090	ev::io io ; void io_cb (ev::io &w, int revents);
3861	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4091	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3862	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4092	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3863		4093
3864	myclass (int fd)	4094	myclass (int fd)
3865	{	4095	{
3866	io .set <myclass, &myclass::io_cb > (this);	4096	io .set <myclass, &myclass::io_cb > (this);
…		…
3917	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4147	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3918		4148
3919	=item D	4149	=item D
3920		4150
3921	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4151	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3922	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4152	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3923		4153
3924	=item Ocaml	4154	=item Ocaml
3925		4155
3926	Erkki Seppala has written Ocaml bindings for libev, to be found at	4156	Erkki Seppala has written Ocaml bindings for libev, to be found at
3927	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4157	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3975	suitable for use with C<EV_A>.	4205	suitable for use with C<EV_A>.
3976		4206
3977	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4207	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3978		4208
3979	Similar to the other two macros, this gives you the value of the default	4209	Similar to the other two macros, this gives you the value of the default
3980	loop, if multiple loops are supported ("ev loop default").	4210	loop, if multiple loops are supported ("ev loop default"). The default loop
		4211	will be initialised if it isn't already initialised.
		4212
		4213	For non-multiplicity builds, these macros do nothing, so you always have
		4214	to initialise the loop somewhere.
3981		4215
3982	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4216	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3983		4217
3984	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4218	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3985	default loop has been initialised (C<UC> == unchecked). Their behaviour	4219	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
4130	supported). It will also not define any of the structs usually found in	4364	supported). It will also not define any of the structs usually found in
4131	F<event.h> that are not directly supported by the libev core alone.	4365	F<event.h> that are not directly supported by the libev core alone.
4132		4366
4133	In standalone mode, libev will still try to automatically deduce the	4367	In standalone mode, libev will still try to automatically deduce the
4134	configuration, but has to be more conservative.	4368	configuration, but has to be more conservative.
		4369
		4370	=item EV_USE_FLOOR
		4371
		4372	If defined to be C<1>, libev will use the C<floor ()> function for its
		4373	periodic reschedule calculations, otherwise libev will fall back on a
		4374	portable (slower) implementation. If you enable this, you usually have to
		4375	link against libm or something equivalent. Enabling this when the C<floor>
		4376	function is not available will fail, so the safe default is to not enable
		4377	this.
4135		4378
4136	=item EV_USE_MONOTONIC	4379	=item EV_USE_MONOTONIC
4137		4380
4138	If defined to be C<1>, libev will try to detect the availability of the	4381	If defined to be C<1>, libev will try to detect the availability of the
4139	monotonic clock option at both compile time and runtime. Otherwise no	4382	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4269	If defined to be C<1>, libev will compile in support for the Linux inotify	4512	If defined to be C<1>, libev will compile in support for the Linux inotify
4270	interface to speed up C<ev_stat> watchers. Its actual availability will	4513	interface to speed up C<ev_stat> watchers. Its actual availability will
4271	be detected at runtime. If undefined, it will be enabled if the headers	4514	be detected at runtime. If undefined, it will be enabled if the headers
4272	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4515	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4273		4516
		4517	=item EV_NO_SMP
		4518
		4519	If defined to be C<1>, libev will assume that memory is always coherent
		4520	between threads, that is, threads can be used, but threads never run on
		4521	different cpus (or different cpu cores). This reduces dependencies
		4522	and makes libev faster.
		4523
		4524	=item EV_NO_THREADS
		4525
		4526	If defined to be C<1>, libev will assume that it will never be called
		4527	from different threads, which is a stronger assumption than C<EV_NO_SMP>,
		4528	above. This reduces dependencies and makes libev faster.
		4529
4274	=item EV_ATOMIC_T	4530	=item EV_ATOMIC_T
4275		4531
4276	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4532	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4277	access is atomic with respect to other threads or signal contexts. No such	4533	access is atomic and serialised with respect to other threads or signal
4278	type is easily found in the C language, so you can provide your own type	4534	contexts. No such type is easily found in the C language, so you can
4279	that you know is safe for your purposes. It is used both for signal handler "locking"	4535	provide your own type that you know is safe for your purposes. It is used
4280	as well as for signal and thread safety in C<ev_async> watchers.	4536	both for signal handler "locking" as well as for signal and thread safety
		4537	in C<ev_async> watchers.
4281		4538
4282	In the absence of this define, libev will use C<sig_atomic_t volatile>	4539	In the absence of this define, libev will use C<sig_atomic_t volatile>
4283	(from F<signal.h>), which is usually good enough on most platforms.	4540	(from F<signal.h>), which is usually good enough on most platforms,
		4541	although strictly speaking using a type that also implies a memory fence
		4542	is required.
4284		4543
4285	=item EV_H (h)	4544	=item EV_H (h)
4286		4545
4287	The name of the F<ev.h> header file used to include it. The default if	4546	The name of the F<ev.h> header file used to include it. The default if
4288	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4547	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
4312	will have the C<struct ev_loop *> as first argument, and you can create	4571	will have the C<struct ev_loop *> as first argument, and you can create
4313	additional independent event loops. Otherwise there will be no support	4572	additional independent event loops. Otherwise there will be no support
4314	for multiple event loops and there is no first event loop pointer	4573	for multiple event loops and there is no first event loop pointer
4315	argument. Instead, all functions act on the single default loop.	4574	argument. Instead, all functions act on the single default loop.
4316		4575
		4576	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4577	default loop when multiplicity is switched off - you always have to
		4578	initialise the loop manually in this case.
		4579
4317	=item EV_MINPRI	4580	=item EV_MINPRI
4318		4581
4319	=item EV_MAXPRI	4582	=item EV_MAXPRI
4320		4583
4321	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4584	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4418		4681
4419	With an intelligent-enough linker (gcc+binutils are intelligent enough	4682	With an intelligent-enough linker (gcc+binutils are intelligent enough
4420	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4683	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4421	your program might be left out as well - a binary starting a timer and an	4684	your program might be left out as well - a binary starting a timer and an
4422	I/O watcher then might come out at only 5Kb.	4685	I/O watcher then might come out at only 5Kb.
		4686
		4687	=item EV_API_STATIC
		4688
		4689	If this symbol is defined (by default it is not), then all identifiers
		4690	will have static linkage. This means that libev will not export any
		4691	identifiers, and you cannot link against libev anymore. This can be useful
		4692	when you embed libev, only want to use libev functions in a single file,
		4693	and do not want its identifiers to be visible.
		4694
		4695	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4696	wants to use libev.
		4697
		4698	This option only works when libev is compiled with a C compiler, as C++
		4699	doesn't support the required declaration syntax.
4423		4700
4424	=item EV_AVOID_STDIO	4701	=item EV_AVOID_STDIO
4425		4702
4426	If this is set to C<1> at compiletime, then libev will avoid using stdio	4703	If this is set to C<1> at compiletime, then libev will avoid using stdio
4427	functions (printf, scanf, perror etc.). This will increase the code size	4704	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4807	requires, and its I/O model is fundamentally incompatible with the POSIX	5084	requires, and its I/O model is fundamentally incompatible with the POSIX
4808	model. Libev still offers limited functionality on this platform in	5085	model. Libev still offers limited functionality on this platform in
4809	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5086	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4810	descriptors. This only applies when using Win32 natively, not when using	5087	descriptors. This only applies when using Win32 natively, not when using
4811	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5088	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4812	as every compielr comes with a slightly differently broken/incompatible	5089	as every compiler comes with a slightly differently broken/incompatible
4813	environment.	5090	environment.
4814		5091
4815	Lifting these limitations would basically require the full	5092	Lifting these limitations would basically require the full
4816	re-implementation of the I/O system. If you are into this kind of thing,	5093	re-implementation of the I/O system. If you are into this kind of thing,
4817	then note that glib does exactly that for you in a very portable way (note	5094	then note that glib does exactly that for you in a very portable way (note
…		…
4950		5227
4951	The type C<double> is used to represent timestamps. It is required to	5228	The type C<double> is used to represent timestamps. It is required to
4952	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5229	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4953	good enough for at least into the year 4000 with millisecond accuracy	5230	good enough for at least into the year 4000 with millisecond accuracy
4954	(the design goal for libev). This requirement is overfulfilled by	5231	(the design goal for libev). This requirement is overfulfilled by
4955	implementations using IEEE 754, which is basically all existing ones. With	5232	implementations using IEEE 754, which is basically all existing ones.
		5233
4956	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5234	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5235	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5236	is either obsolete or somebody patched it to use C<long double> or
		5237	something like that, just kidding).
4957		5238
4958	=back	5239	=back
4959		5240
4960	If you know of other additional requirements drop me a note.	5241	If you know of other additional requirements drop me a note.
4961		5242
…		…
5023	=item Processing ev_async_send: O(number_of_async_watchers)	5304	=item Processing ev_async_send: O(number_of_async_watchers)
5024		5305
5025	=item Processing signals: O(max_signal_number)	5306	=item Processing signals: O(max_signal_number)
5026		5307
5027	Sending involves a system call I<iff> there were no other C<ev_async_send>	5308	Sending involves a system call I<iff> there were no other C<ev_async_send>
5028	calls in the current loop iteration. Checking for async and signal events	5309	calls in the current loop iteration and the loop is currently
		5310	blocked. Checking for async and signal events involves iterating over all
5029	involves iterating over all running async watchers or all signal numbers.	5311	running async watchers or all signal numbers.
5030		5312
5031	=back	5313	=back
5032		5314
5033		5315
5034	=head1 PORTING FROM LIBEV 3.X TO 4.X	5316	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5151	The physical time that is observed. It is apparently strictly monotonic :)	5433	The physical time that is observed. It is apparently strictly monotonic :)
5152		5434
5153	=item wall-clock time	5435	=item wall-clock time
5154		5436
5155	The time and date as shown on clocks. Unlike real time, it can actually	5437	The time and date as shown on clocks. Unlike real time, it can actually
5156	be wrong and jump forwards and backwards, e.g. when the you adjust your	5438	be wrong and jump forwards and backwards, e.g. when you adjust your
5157	clock.	5439	clock.
5158		5440
5159	=item watcher	5441	=item watcher
5160		5442
5161	A data structure that describes interest in certain events. Watchers need	5443	A data structure that describes interest in certain events. Watchers need
…		…
5164	=back	5446	=back
5165		5447
5166	=head1 AUTHOR	5448	=head1 AUTHOR
5167		5449
5168	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5450	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5169	Magnusson and Emanuele Giaquinta.	5451	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5170		5452

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Comparing libev/ev.pod (file contents): Revision 1.356 by root, Tue Jan 11 01:42:47 2011 UTC vs. Revision 1.399 by root, Mon Apr 2 23:14:41 2012 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.356 by root, Tue Jan 11 01:42:47 2011 UTC vs.
Revision 1.399 by root, Mon Apr 2 23:14:41 2012 UTC