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

Comparing libev/ev.pod (file contents):
Revision 1.345 by root, Wed Nov 10 14:36:42 2010 UTC vs.
Revision 1.379 by root, Tue Jul 12 23:32:10 2011 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
…		…
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_update_now> 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
…		…
299	}	305	}
300		306
301	...	307	...
302	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
303		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
304	=back	323	=back
305		324
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		326
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
419		438
420	Signalfd will not be used by default as this changes your signal mask, and	439	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	440	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
423		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you have to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		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.
		455
		456	This flag's behaviour will become the default in future versions of libev.
		457
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		459
426	This is your standard select(2) backend. Not I<completely> standard, as	460	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,	461	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	462	but if that fails, expect a fairly low limit on the number of fds when
…		…
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		490
457	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
458	kernels).	492	kernels).
459		493
460	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
461	but it scales phenomenally better. While poll and select usually scale	495	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),	496	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).	497	fd), epoll scales either O(1) or O(active_fds).
464		498
465	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	502	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	505	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	506	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)	507	set, which can take considerable time (one syscall per file descriptor)
474	and is of course hard to detect.	508	and is of course hard to detect.
475		509
476	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	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	511	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	512	totally I<different> file descriptors (even already closed ones, so
479	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
480	on SMP systems). Libev tries to counter these spurious notifications by	514	(especially on SMP systems). Libev tries to counter these spurious
481	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
482	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
483	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
484	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
485		522
486	Epoll is truly the train wreck analog among event poll mechanisms.	523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
487		526
488	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
489	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
490	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
491	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
…		…
557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
558		597
559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	598	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)).	599	it's really slow, but it still scales very well (O(active_fds)).
561		600
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	601	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	602	file descriptor per loop iteration. For small and medium numbers of file
568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
569	might perform better.	604	might perform better.
570		605
571	On the positive side, with the exception of the spurious readiness	606	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	607	specification in all tests and is fully embeddable, which is a rare feat
574	OS-specific backends (I vastly prefer correctness over speed hacks).	608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returns events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
575		620
576	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
577	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
578		623
579	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
580		625
581	Try all backends (even potentially broken ones that wouldn't be tried	626	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	627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
584		629
585	It is definitely not recommended to use this flag.	630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
586		639
587	=back	640	=back
588		641
589	If one or more of the backend flags are or'ed into the flags value,	642	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	643	then only these backends will be tried (in the reverse order as listed
…		…
781	This is useful if you are waiting for some external event in conjunction	834	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	835	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	836	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.	837	usually a better approach for this kind of thing.
785		838
786	Here are the gory details of what C<ev_run> does:	839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
787		842
788	- Increment loop depth.	843	- Increment loop depth.
789	- Reset the ev_break status.	844	- Reset the ev_break status.
790	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
791	LOOP:	846	LOOP:
…		…
824	anymore.	879	anymore.
825		880
826	... queue jobs here, make sure they register event watchers as long	881	... 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..)	882	... as they still have work to do (even an idle watcher will do..)
828	ev_run (my_loop, 0);	883	ev_run (my_loop, 0);
829	... jobs done or somebody called unloop. yeah!	884	... jobs done or somebody called break. yeah!
830		885
831	=item ev_break (loop, how)	886	=item ev_break (loop, how)
832		887
833	Can be used to make a call to C<ev_run> return early (but only after it	888	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	889	has processed all outstanding events). The C<how> argument must be either
…		…
867	running when nothing else is active.	922	running when nothing else is active.
868		923
869	ev_signal exitsig;	924	ev_signal exitsig;
870	ev_signal_init (&exitsig, sig_cb, SIGINT);	925	ev_signal_init (&exitsig, sig_cb, SIGINT);
871	ev_signal_start (loop, &exitsig);	926	ev_signal_start (loop, &exitsig);
872	evf_unref (loop);	927	ev_unref (loop);
873		928
874	Example: For some weird reason, unregister the above signal handler again.	929	Example: For some weird reason, unregister the above signal handler again.
875		930
876	ev_ref (loop);	931	ev_ref (loop);
877	ev_signal_stop (loop, &exitsig);	932	ev_signal_stop (loop, &exitsig);
…		…
897	overhead for the actual polling but can deliver many events at once.	952	overhead for the actual polling but can deliver many events at once.
898		953
899	By setting a higher I<io collect interval> you allow libev to spend more	954	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,	955	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	956	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	957	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	958	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	959	sleep time ensures that libev will not poll for I/O events more often then
905	once per this interval, on average.	960	once per this interval, on average (as long as the host time resolution is
		961	good enough).
906		962
907	Likewise, by setting a higher I<timeout collect interval> you allow libev	963	Likewise, by setting a higher I<timeout collect interval> you allow libev
908	to spend more time collecting timeouts, at the expense of increased	964	to spend more time collecting timeouts, at the expense of increased
909	latency/jitter/inexactness (the watcher callback will be called	965	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	966	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
1316	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1372	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1317	functions that do not need a watcher.	1373	functions that do not need a watcher.
1318		1374
1319	=back	1375	=back
1320		1376
1321	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1377	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1322		1378	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		1379
1386	=head2 WATCHER STATES	1380	=head2 WATCHER STATES
1387		1381
1388	There are various watcher states mentioned throughout this manual -	1382	There are various watcher states mentioned throughout this manual -
1389	active, pending and so on. In this section these states and the rules to	1383	active, pending and so on. In this section these states and the rules to
…		…
1392		1386
1393	=over 4	1387	=over 4
1394		1388
1395	=item initialiased	1389	=item initialiased
1396		1390
1397	Before a watcher can be registered with the event looop it has to be	1391	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	1392	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.	1393	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1400		1394
1401	In this state it is simply some block of memory that is suitable for use	1395	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.	1396	use in an event loop. It can be moved around, freed, reused etc. at
		1397	will - as long as you either keep the memory contents intact, or call
		1398	C<ev_TYPE_init> again.
1403		1399
1404	=item started/running/active	1400	=item started/running/active
1405		1401
1406	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1402	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	1403	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	1431	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	1432	of whether it was active or not, so stopping a watcher explicitly before
1437	freeing it is often a good idea.	1433	freeing it is often a good idea.
1438		1434
1439	While stopped (and not pending) the watcher is essentially in the	1435	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	1436	initialised state, that is, it can be reused, moved, modified in any way
1441	you wish.	1437	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1438	it again).
1442		1439
1443	=back	1440	=back
1444		1441
1445	=head2 WATCHER PRIORITY MODELS	1442	=head2 WATCHER PRIORITY MODELS
1446		1443
…		…
1575	In general you can register as many read and/or write event watchers per	1572	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	1573	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	1574	descriptors to non-blocking mode is also usually a good idea (but not
1578	required if you know what you are doing).	1575	required if you know what you are doing).
1579		1576
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	1577	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	1578	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	1579	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	1580	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	1581	with a relatively standard program structure. Thus it is best to always
1591	this situation even with a relatively standard program structure. Thus	1582	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.	1583	preferable to a program hanging until some data arrives.
1594		1584
1595	If you cannot run the fd in non-blocking mode (for example you should	1585	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	1586	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	1587	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	1588	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	1589	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	1590	use C<SIGALRM> and an interval timer, just to be sure you won't block
1601	indefinitely.	1591	indefinitely.
1602		1592
1603	But really, best use non-blocking mode.	1593	But really, best use non-blocking mode.
1604		1594
…		…
1632		1622
1633	There is no workaround possible except not registering events	1623	There is no workaround possible except not registering events
1634	for potentially C<dup ()>'ed file descriptors, or to resort to	1624	for potentially C<dup ()>'ed file descriptors, or to resort to
1635	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636		1626
		1627	=head3 The special problem of files
		1628
		1629	Many people try to use C<select> (or libev) on file descriptors
		1630	representing files, and expect it to become ready when their program
		1631	doesn't block on disk accesses (which can take a long time on their own).
		1632
		1633	However, this cannot ever work in the "expected" way - you get a readiness
		1634	notification as soon as the kernel knows whether and how much data is
		1635	there, and in the case of open files, that's always the case, so you
		1636	always get a readiness notification instantly, and your read (or possibly
		1637	write) will still block on the disk I/O.
		1638
		1639	Another way to view it is that in the case of sockets, pipes, character
		1640	devices and so on, there is another party (the sender) that delivers data
		1641	on its own, but in the case of files, there is no such thing: the disk
		1642	will not send data on its own, simply because it doesn't know what you
		1643	wish to read - you would first have to request some data.
		1644
		1645	Since files are typically not-so-well supported by advanced notification
		1646	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1647	to files, even though you should not use it. The reason for this is
		1648	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1649	usually a tty, often a pipe, but also sometimes files or special devices
		1650	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1651	F</dev/urandom>), and even though the file might better be served with
		1652	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1653	it "just works" instead of freezing.
		1654
		1655	So avoid file descriptors pointing to files when you know it (e.g. use
		1656	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1657	when you rarely read from a file instead of from a socket, and want to
		1658	reuse the same code path.
		1659
1637	=head3 The special problem of fork	1660	=head3 The special problem of fork
1638		1661
1639	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1662	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	1663	useless behaviour. Libev fully supports fork, but needs to be told about
1641	it in the child.	1664	it in the child if you want to continue to use it in the child.
1642		1665
1643	To support fork in your programs, you either have to call	1666	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,	1667	()> 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	1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1646	C<EVBACKEND_POLL>.
1647		1669
1648	=head3 The special problem of SIGPIPE	1670	=head3 The special problem of SIGPIPE
1649		1671
1650	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1672	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	1673	when writing to a pipe whose other end has been closed, your program gets
…		…
2001	keep up with the timer (because it takes longer than those 10 seconds to	2023	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.	2024	do stuff) the timer will not fire more than once per event loop iteration.
2003		2025
2004	=item ev_timer_again (loop, ev_timer *)	2026	=item ev_timer_again (loop, ev_timer *)
2005		2027
2006	This will act as if the timer timed out and restart it again if it is	2028	This will act as if the timer timed out and restarts it again if it is
2007	repeating. The exact semantics are:	2029	repeating. The exact semantics are:
2008		2030
2009	If the timer is pending, its pending status is cleared.	2031	If the timer is pending, its pending status is cleared.
2010		2032
2011	If the timer is started but non-repeating, stop it (as if it timed out).	2033	If the timer is started but non-repeating, stop it (as if it timed out).
…		…
2141		2163
2142	Another way to think about it (for the mathematically inclined) is that	2164	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	2165	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.	2166	time where C<time = offset (mod interval)>, regardless of any time jumps.
2145		2167
2146	For numerical stability it is preferable that the C<offset> value is near	2168	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	2169	interval value should be higher than C<1/8192> (which is around 100
2148	this value, and in fact is often specified as zero.	2170	microseconds) and C<offset> should be higher than C<0> and should have
		2171	at most a similar magnitude as the current time (say, within a factor of
		2172	ten). Typical values for offset are, in fact, C<0> or something between
		2173	C<0> and C<interval>, which is also the recommended range.
2149		2174
2150	Note also that there is an upper limit to how often a timer can fire (CPU	2175	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	2176	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	2177	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).	2178	millisecond (if the OS supports it and the machine is fast enough).
…		…
2296	=head3 The special problem of inheritance over fork/execve/pthread_create	2321	=head3 The special problem of inheritance over fork/execve/pthread_create
2297		2322
2298	Both the signal mask (C<sigprocmask>) and the signal disposition	2323	Both the signal mask (C<sigprocmask>) and the signal disposition
2299	(C<sigaction>) are unspecified after starting a signal watcher (and after	2324	(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,	2325	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.	2326	and might or might not set or restore the installed signal handler (but
		2327	see C<EVFLAG_NOSIGMASK>).
2302		2328
2303	While this does not matter for the signal disposition (libev never	2329	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	2330	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	2331	C<execve>), this matters for the signal mask: many programs do not expect
2306	certain signals to be blocked.	2332	certain signals to be blocked.
…		…
2319	I<has> to modify the signal mask, at least temporarily.	2345	I<has> to modify the signal mask, at least temporarily.
2320		2346
2321	So I can't stress this enough: I<If you do not reset your signal mask when	2347	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	2348	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.	2349	is not a libev-specific thing, this is true for most event libraries.
		2350
		2351	=head3 The special problem of threads signal handling
		2352
		2353	POSIX threads has problematic signal handling semantics, specifically,
		2354	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2355	threads in a process block signals, which is hard to achieve.
		2356
		2357	When you want to use sigwait (or mix libev signal handling with your own
		2358	for the same signals), you can tackle this problem by globally blocking
		2359	all signals before creating any threads (or creating them with a fully set
		2360	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2361	loops. Then designate one thread as "signal receiver thread" which handles
		2362	these signals. You can pass on any signals that libev might be interested
		2363	in by calling C<ev_feed_signal>.
2324		2364
2325	=head3 Watcher-Specific Functions and Data Members	2365	=head3 Watcher-Specific Functions and Data Members
2326		2366
2327	=over 4	2367	=over 4
2328		2368
…		…
3163	atexit (program_exits);	3203	atexit (program_exits);
3164		3204
3165		3205
3166	=head2 C<ev_async> - how to wake up an event loop	3206	=head2 C<ev_async> - how to wake up an event loop
3167		3207
3168	In general, you cannot use an C<ev_run> from multiple threads or other	3208	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	3209	asynchronous sources such as signal handlers (as opposed to multiple event
3170	loops - those are of course safe to use in different threads).	3210	loops - those are of course safe to use in different threads).
3171		3211
3172	Sometimes, however, you need to wake up an event loop you do not control,	3212	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>	3213	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.	3215	it by calling C<ev_async_send>, which is thread- and signal safe.
3176		3216
3177	This functionality is very similar to C<ev_signal> watchers, as signals,	3217	This functionality is very similar to C<ev_signal> watchers, as signals,
3178	too, are asynchronous in nature, and signals, too, will be compressed	3218	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	3219	(i.e. the number of callback invocations may be less than the number of
3180	C<ev_async_sent> calls).	3220	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
3181		3221	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	3222	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3183	just the default loop.	3223	even without knowing which loop owns the signal.
3184		3224
3185	=head3 Queueing	3225	=head3 Queueing
3186		3226
3187	C<ev_async> does not support queueing of data in any way. The reason	3227	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	3228	is that the author does not know of a simple (or any) algorithm for a
…		…
3280	trust me.	3320	trust me.
3281		3321
3282	=item ev_async_send (loop, ev_async *)	3322	=item ev_async_send (loop, ev_async *)
3283		3323
3284	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3324	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	3325	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3326	returns.
		3327
3286	C<ev_feed_event>, this call is safe to do from other threads, signal or	3328	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	3329	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3288	section below on what exactly this means).	3330	embedding section below on what exactly this means).
3289		3331
3290	Note that, as with other watchers in libev, multiple events might get	3332	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	3333	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>,	3334	this is that C<ev_async> watchers are level-triggered: they are set on
3293	reset when the event loop detects that).	3335	C<ev_async_send>, reset when the event loop detects that).
3294		3336
3295	This call incurs the overhead of a system call only once per event loop	3337	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	3338	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.	3339	the event loop (or your program) is processing events. That means that
		3340	repeated calls are basically free (there is no need to avoid calls for
		3341	performance reasons) and that the overhead becomes smaller (typically
		3342	zero) under load.
3298		3343
3299	=item bool = ev_async_pending (ev_async *)	3344	=item bool = ev_async_pending (ev_async *)
3300		3345
3301	Returns a non-zero value when C<ev_async_send> has been called on the	3346	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	3347	watcher but the event has not yet been processed (or even noted) by the
…		…
3361	Feed an event on the given fd, as if a file descriptor backend detected	3406	Feed an event on the given fd, as if a file descriptor backend detected
3362	the given events it.	3407	the given events it.
3363		3408
3364	=item ev_feed_signal_event (loop, int signum)	3409	=item ev_feed_signal_event (loop, int signum)
3365		3410
3366	Feed an event as if the given signal occurred (C<loop> must be the default	3411	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3367	loop!).	3412	which is async-safe.
3368		3413
3369	=back	3414	=back
3370		3415
3371		3416
3372	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)	3417	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
3373		3418
3374	This section explains some common idioms that are not immediately	3419	This section explains some common idioms that are not immediately
3375	obvious. Note that examples are sprinkled over the whole manual, and this	3420	obvious. Note that examples are sprinkled over the whole manual, and this
3376	section only contains stuff that wouldn't fit anywhere else.	3421	section only contains stuff that wouldn't fit anywhere else.
3377		3422
3378	=over 4	3423	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3379		3424
3380	=item Model/nested event loop invocations and exit conditions.	3425	Each watcher has, by default, a C<void *data> member that you can read
		3426	or modify at any time: libev will completely ignore it. This can be used
		3427	to associate arbitrary data with your watcher. If you need more data and
		3428	don't want to allocate memory separately and store a pointer to it in that
		3429	data member, you can also "subclass" the watcher type and provide your own
		3430	data:
		3431
		3432	struct my_io
		3433	{
		3434	ev_io io;
		3435	int otherfd;
		3436	void *somedata;
		3437	struct whatever *mostinteresting;
		3438	};
		3439
		3440	...
		3441	struct my_io w;
		3442	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3443
		3444	And since your callback will be called with a pointer to the watcher, you
		3445	can cast it back to your own type:
		3446
		3447	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3448	{
		3449	struct my_io w = (struct my_io )w_;
		3450	...
		3451	}
		3452
		3453	More interesting and less C-conformant ways of casting your callback
		3454	function type instead have been omitted.
		3455
		3456	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3457
		3458	Another common scenario is to use some data structure with multiple
		3459	embedded watchers, in effect creating your own watcher that combines
		3460	multiple libev event sources into one "super-watcher":
		3461
		3462	struct my_biggy
		3463	{
		3464	int some_data;
		3465	ev_timer t1;
		3466	ev_timer t2;
		3467	}
		3468
		3469	In this case getting the pointer to C<my_biggy> is a bit more
		3470	complicated: Either you store the address of your C<my_biggy> struct in
		3471	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3472	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3473	real programmers):
		3474
		3475	#include <stddef.h>
		3476
		3477	static void
		3478	t1_cb (EV_P_ ev_timer *w, int revents)
		3479	{
		3480	struct my_biggy big = (struct my_biggy *)
		3481	(((char *)w) - offsetof (struct my_biggy, t1));
		3482	}
		3483
		3484	static void
		3485	t2_cb (EV_P_ ev_timer *w, int revents)
		3486	{
		3487	struct my_biggy big = (struct my_biggy *)
		3488	(((char *)w) - offsetof (struct my_biggy, t2));
		3489	}
		3490
		3491	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3381		3492
3382	Often (especially in GUI toolkits) there are places where you have	3493	Often (especially in GUI toolkits) there are places where you have
3383	I<modal> interaction, which is most easily implemented by recursively	3494	I<modal> interaction, which is most easily implemented by recursively
3384	invoking C<ev_run>.	3495	invoking C<ev_run>.
3385		3496
…		…
3414	exit_main_loop = 1;	3525	exit_main_loop = 1;
3415		3526
3416	// exit both	3527	// exit both
3417	exit_main_loop = exit_nested_loop = 1;	3528	exit_main_loop = exit_nested_loop = 1;
3418		3529
3419	=back	3530	=head2 THREAD LOCKING EXAMPLE
		3531
		3532	Here is a fictitious example of how to run an event loop in a different
		3533	thread from where callbacks are being invoked and watchers are
		3534	created/added/removed.
		3535
		3536	For a real-world example, see the C<EV::Loop::Async> perl module,
		3537	which uses exactly this technique (which is suited for many high-level
		3538	languages).
		3539
		3540	The example uses a pthread mutex to protect the loop data, a condition
		3541	variable to wait for callback invocations, an async watcher to notify the
		3542	event loop thread and an unspecified mechanism to wake up the main thread.
		3543
		3544	First, you need to associate some data with the event loop:
		3545
		3546	typedef struct {
		3547	mutex_t lock; /* global loop lock */
		3548	ev_async async_w;
		3549	thread_t tid;
		3550	cond_t invoke_cv;
		3551	} userdata;
		3552
		3553	void prepare_loop (EV_P)
		3554	{
		3555	// for simplicity, we use a static userdata struct.
		3556	static userdata u;
		3557
		3558	ev_async_init (&u->async_w, async_cb);
		3559	ev_async_start (EV_A_ &u->async_w);
		3560
		3561	pthread_mutex_init (&u->lock, 0);
		3562	pthread_cond_init (&u->invoke_cv, 0);
		3563
		3564	// now associate this with the loop
		3565	ev_set_userdata (EV_A_ u);
		3566	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3567	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3568
		3569	// then create the thread running ev_run
		3570	pthread_create (&u->tid, 0, l_run, EV_A);
		3571	}
		3572
		3573	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3574	solely to wake up the event loop so it takes notice of any new watchers
		3575	that might have been added:
		3576
		3577	static void
		3578	async_cb (EV_P_ ev_async *w, int revents)
		3579	{
		3580	// just used for the side effects
		3581	}
		3582
		3583	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3584	protecting the loop data, respectively.
		3585
		3586	static void
		3587	l_release (EV_P)
		3588	{
		3589	userdata *u = ev_userdata (EV_A);
		3590	pthread_mutex_unlock (&u->lock);
		3591	}
		3592
		3593	static void
		3594	l_acquire (EV_P)
		3595	{
		3596	userdata *u = ev_userdata (EV_A);
		3597	pthread_mutex_lock (&u->lock);
		3598	}
		3599
		3600	The event loop thread first acquires the mutex, and then jumps straight
		3601	into C<ev_run>:
		3602
		3603	void *
		3604	l_run (void *thr_arg)
		3605	{
		3606	struct ev_loop loop = (struct ev_loop )thr_arg;
		3607
		3608	l_acquire (EV_A);
		3609	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3610	ev_run (EV_A_ 0);
		3611	l_release (EV_A);
		3612
		3613	return 0;
		3614	}
		3615
		3616	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3617	signal the main thread via some unspecified mechanism (signals? pipe
		3618	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3619	have been called (in a while loop because a) spurious wakeups are possible
		3620	and b) skipping inter-thread-communication when there are no pending
		3621	watchers is very beneficial):
		3622
		3623	static void
		3624	l_invoke (EV_P)
		3625	{
		3626	userdata *u = ev_userdata (EV_A);
		3627
		3628	while (ev_pending_count (EV_A))
		3629	{
		3630	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3631	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3632	}
		3633	}
		3634
		3635	Now, whenever the main thread gets told to invoke pending watchers, it
		3636	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3637	thread to continue:
		3638
		3639	static void
		3640	real_invoke_pending (EV_P)
		3641	{
		3642	userdata *u = ev_userdata (EV_A);
		3643
		3644	pthread_mutex_lock (&u->lock);
		3645	ev_invoke_pending (EV_A);
		3646	pthread_cond_signal (&u->invoke_cv);
		3647	pthread_mutex_unlock (&u->lock);
		3648	}
		3649
		3650	Whenever you want to start/stop a watcher or do other modifications to an
		3651	event loop, you will now have to lock:
		3652
		3653	ev_timer timeout_watcher;
		3654	userdata *u = ev_userdata (EV_A);
		3655
		3656	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3657
		3658	pthread_mutex_lock (&u->lock);
		3659	ev_timer_start (EV_A_ &timeout_watcher);
		3660	ev_async_send (EV_A_ &u->async_w);
		3661	pthread_mutex_unlock (&u->lock);
		3662
		3663	Note that sending the C<ev_async> watcher is required because otherwise
		3664	an event loop currently blocking in the kernel will have no knowledge
		3665	about the newly added timer. By waking up the loop it will pick up any new
		3666	watchers in the next event loop iteration.
		3667
		3668	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3669
		3670	While the overhead of a callback that e.g. schedules a thread is small, it
		3671	is still an overhead. If you embed libev, and your main usage is with some
		3672	kind of threads or coroutines, you might want to customise libev so that
		3673	doesn't need callbacks anymore.
		3674
		3675	Imagine you have coroutines that you can switch to using a function
		3676	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3677	and that due to some magic, the currently active coroutine is stored in a
		3678	global called C<current_coro>. Then you can build your own "wait for libev
		3679	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3680	the differing C<;> conventions):
		3681
		3682	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3683	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3684
		3685	That means instead of having a C callback function, you store the
		3686	coroutine to switch to in each watcher, and instead of having libev call
		3687	your callback, you instead have it switch to that coroutine.
		3688
		3689	A coroutine might now wait for an event with a function called
		3690	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3691	matter when, or whether the watcher is active or not when this function is
		3692	called):
		3693
		3694	void
		3695	wait_for_event (ev_watcher *w)
		3696	{
		3697	ev_cb_set (w) = current_coro;
		3698	switch_to (libev_coro);
		3699	}
		3700
		3701	That basically suspends the coroutine inside C<wait_for_event> and
		3702	continues the libev coroutine, which, when appropriate, switches back to
		3703	this or any other coroutine. I am sure if you sue this your own :)
		3704
		3705	You can do similar tricks if you have, say, threads with an event queue -
		3706	instead of storing a coroutine, you store the queue object and instead of
		3707	switching to a coroutine, you push the watcher onto the queue and notify
		3708	any waiters.
		3709
		3710	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3711	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3712
		3713	// my_ev.h
		3714	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3715	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3716	#include "../libev/ev.h"
		3717
		3718	// my_ev.c
		3719	#define EV_H "my_ev.h"
		3720	#include "../libev/ev.c"
		3721
		3722	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3723	F<my_ev.c> into your project. When properly specifying include paths, you
		3724	can even use F<ev.h> as header file name directly.
3420		3725
3421		3726
3422	=head1 LIBEVENT EMULATION	3727	=head1 LIBEVENT EMULATION
3423		3728
3424	Libev offers a compatibility emulation layer for libevent. It cannot	3729	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3427	=over 4	3732	=over 4
3428		3733
3429	=item * Only the libevent-1.4.1-beta API is being emulated.	3734	=item * Only the libevent-1.4.1-beta API is being emulated.
3430		3735
3431	This was the newest libevent version available when libev was implemented,	3736	This was the newest libevent version available when libev was implemented,
3432	and is still mostly uncanged in 2010.	3737	and is still mostly unchanged in 2010.
3433		3738
3434	=item * Use it by including <event.h>, as usual.	3739	=item * Use it by including <event.h>, as usual.
3435		3740
3436	=item * The following members are fully supported: ev_base, ev_callback,	3741	=item * The following members are fully supported: ev_base, ev_callback,
3437	ev_arg, ev_fd, ev_res, ev_events.	3742	ev_arg, ev_fd, ev_res, ev_events.
…		…
3472	Care has been taken to keep the overhead low. The only data member the C++	3777	Care has been taken to keep the overhead low. The only data member the C++
3473	classes add (compared to plain C-style watchers) is the event loop pointer	3778	classes add (compared to plain C-style watchers) is the event loop pointer
3474	that the watcher is associated with (or no additional members at all if	3779	that the watcher is associated with (or no additional members at all if
3475	you disable C<EV_MULTIPLICITY> when embedding libev).	3780	you disable C<EV_MULTIPLICITY> when embedding libev).
3476		3781
3477	Currently, functions, and static and non-static member functions can be	3782	Currently, functions, static and non-static member functions and classes
3478	used as callbacks. Other types should be easy to add as long as they only	3783	with C<operator ()> can be used as callbacks. Other types should be easy
3479	need one additional pointer for context. If you need support for other	3784	to add as long as they only need one additional pointer for context. If
3480	types of functors please contact the author (preferably after implementing	3785	you need support for other types of functors please contact the author
3481	it).	3786	(preferably after implementing it).
3482		3787
3483	Here is a list of things available in the C<ev> namespace:	3788	Here is a list of things available in the C<ev> namespace:
3484		3789
3485	=over 4	3790	=over 4
3486		3791
…		…
3639	watchers in the constructor.	3944	watchers in the constructor.
3640		3945
3641	class myclass	3946	class myclass
3642	{	3947	{
3643	ev::io io ; void io_cb (ev::io &w, int revents);	3948	ev::io io ; void io_cb (ev::io &w, int revents);
3644	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	3949	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3645	ev::idle idle; void idle_cb (ev::idle &w, int revents);	3950	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3646		3951
3647	myclass (int fd)	3952	myclass (int fd)
3648	{	3953	{
3649	io .set <myclass, &myclass::io_cb > (this);	3954	io .set <myclass, &myclass::io_cb > (this);
…		…
3700	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4005	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3701		4006
3702	=item D	4007	=item D
3703		4008
3704	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4009	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3705	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4010	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3706		4011
3707	=item Ocaml	4012	=item Ocaml
3708		4013
3709	Erkki Seppala has written Ocaml bindings for libev, to be found at	4014	Erkki Seppala has written Ocaml bindings for libev, to be found at
3710	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4015	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3913	supported). It will also not define any of the structs usually found in	4218	supported). It will also not define any of the structs usually found in
3914	F<event.h> that are not directly supported by the libev core alone.	4219	F<event.h> that are not directly supported by the libev core alone.
3915		4220
3916	In standalone mode, libev will still try to automatically deduce the	4221	In standalone mode, libev will still try to automatically deduce the
3917	configuration, but has to be more conservative.	4222	configuration, but has to be more conservative.
		4223
		4224	=item EV_USE_FLOOR
		4225
		4226	If defined to be C<1>, libev will use the C<floor ()> function for its
		4227	periodic reschedule calculations, otherwise libev will fall back on a
		4228	portable (slower) implementation. If you enable this, you usually have to
		4229	link against libm or something equivalent. Enabling this when the C<floor>
		4230	function is not available will fail, so the safe default is to not enable
		4231	this.
3918		4232
3919	=item EV_USE_MONOTONIC	4233	=item EV_USE_MONOTONIC
3920		4234
3921	If defined to be C<1>, libev will try to detect the availability of the	4235	If defined to be C<1>, libev will try to detect the availability of the
3922	monotonic clock option at both compile time and runtime. Otherwise no	4236	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4055	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4369	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4056		4370
4057	=item EV_ATOMIC_T	4371	=item EV_ATOMIC_T
4058		4372
4059	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4373	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4060	access is atomic with respect to other threads or signal contexts. No such	4374	access is atomic and serialised with respect to other threads or signal
4061	type is easily found in the C language, so you can provide your own type	4375	contexts. No such type is easily found in the C language, so you can
4062	that you know is safe for your purposes. It is used both for signal handler "locking"	4376	provide your own type that you know is safe for your purposes. It is used
4063	as well as for signal and thread safety in C<ev_async> watchers.	4377	both for signal handler "locking" as well as for signal and thread safety
		4378	in C<ev_async> watchers.
4064		4379
4065	In the absence of this define, libev will use C<sig_atomic_t volatile>	4380	In the absence of this define, libev will use C<sig_atomic_t volatile>
4066	(from F<signal.h>), which is usually good enough on most platforms.	4381	(from F<signal.h>), which is usually good enough on most platforms,
		4382	although strictly speaking using a type that also implies a memory fence
		4383	is required.
4067		4384
4068	=item EV_H (h)	4385	=item EV_H (h)
4069		4386
4070	The name of the F<ev.h> header file used to include it. The default if	4387	The name of the F<ev.h> header file used to include it. The default if
4071	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4388	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
4354	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4671	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4355		4672
4356	#include "ev_cpp.h"	4673	#include "ev_cpp.h"
4357	#include "ev.c"	4674	#include "ev.c"
4358		4675
4359	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4676	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4360		4677
4361	=head2 THREADS AND COROUTINES	4678	=head2 THREADS AND COROUTINES
4362		4679
4363	=head3 THREADS	4680	=head3 THREADS
4364		4681
…		…
4415	default loop and triggering an C<ev_async> watcher from the default loop	4732	default loop and triggering an C<ev_async> watcher from the default loop
4416	watcher callback into the event loop interested in the signal.	4733	watcher callback into the event loop interested in the signal.
4417		4734
4418	=back	4735	=back
4419		4736
4420	=head4 THREAD LOCKING EXAMPLE	4737	See also L<THREAD LOCKING EXAMPLE>.
4421
4422	Here is a fictitious example of how to run an event loop in a different
4423	thread than where callbacks are being invoked and watchers are
4424	created/added/removed.
4425
4426	For a real-world example, see the C<EV::Loop::Async> perl module,
4427	which uses exactly this technique (which is suited for many high-level
4428	languages).
4429
4430	The example uses a pthread mutex to protect the loop data, a condition
4431	variable to wait for callback invocations, an async watcher to notify the
4432	event loop thread and an unspecified mechanism to wake up the main thread.
4433
4434	First, you need to associate some data with the event loop:
4435
4436	typedef struct {
4437	mutex_t lock; /* global loop lock */
4438	ev_async async_w;
4439	thread_t tid;
4440	cond_t invoke_cv;
4441	} userdata;
4442
4443	void prepare_loop (EV_P)
4444	{
4445	// for simplicity, we use a static userdata struct.
4446	static userdata u;
4447
4448	ev_async_init (&u->async_w, async_cb);
4449	ev_async_start (EV_A_ &u->async_w);
4450
4451	pthread_mutex_init (&u->lock, 0);
4452	pthread_cond_init (&u->invoke_cv, 0);
4453
4454	// now associate this with the loop
4455	ev_set_userdata (EV_A_ u);
4456	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4457	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4458
4459	// then create the thread running ev_loop
4460	pthread_create (&u->tid, 0, l_run, EV_A);
4461	}
4462
4463	The callback for the C<ev_async> watcher does nothing: the watcher is used
4464	solely to wake up the event loop so it takes notice of any new watchers
4465	that might have been added:
4466
4467	static void
4468	async_cb (EV_P_ ev_async *w, int revents)
4469	{
4470	// just used for the side effects
4471	}
4472
4473	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4474	protecting the loop data, respectively.
4475
4476	static void
4477	l_release (EV_P)
4478	{
4479	userdata *u = ev_userdata (EV_A);
4480	pthread_mutex_unlock (&u->lock);
4481	}
4482
4483	static void
4484	l_acquire (EV_P)
4485	{
4486	userdata *u = ev_userdata (EV_A);
4487	pthread_mutex_lock (&u->lock);
4488	}
4489
4490	The event loop thread first acquires the mutex, and then jumps straight
4491	into C<ev_run>:
4492
4493	void *
4494	l_run (void *thr_arg)
4495	{
4496	struct ev_loop loop = (struct ev_loop )thr_arg;
4497
4498	l_acquire (EV_A);
4499	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4500	ev_run (EV_A_ 0);
4501	l_release (EV_A);
4502
4503	return 0;
4504	}
4505
4506	Instead of invoking all pending watchers, the C<l_invoke> callback will
4507	signal the main thread via some unspecified mechanism (signals? pipe
4508	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4509	have been called (in a while loop because a) spurious wakeups are possible
4510	and b) skipping inter-thread-communication when there are no pending
4511	watchers is very beneficial):
4512
4513	static void
4514	l_invoke (EV_P)
4515	{
4516	userdata *u = ev_userdata (EV_A);
4517
4518	while (ev_pending_count (EV_A))
4519	{
4520	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4521	pthread_cond_wait (&u->invoke_cv, &u->lock);
4522	}
4523	}
4524
4525	Now, whenever the main thread gets told to invoke pending watchers, it
4526	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4527	thread to continue:
4528
4529	static void
4530	real_invoke_pending (EV_P)
4531	{
4532	userdata *u = ev_userdata (EV_A);
4533
4534	pthread_mutex_lock (&u->lock);
4535	ev_invoke_pending (EV_A);
4536	pthread_cond_signal (&u->invoke_cv);
4537	pthread_mutex_unlock (&u->lock);
4538	}
4539
4540	Whenever you want to start/stop a watcher or do other modifications to an
4541	event loop, you will now have to lock:
4542
4543	ev_timer timeout_watcher;
4544	userdata *u = ev_userdata (EV_A);
4545
4546	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4547
4548	pthread_mutex_lock (&u->lock);
4549	ev_timer_start (EV_A_ &timeout_watcher);
4550	ev_async_send (EV_A_ &u->async_w);
4551	pthread_mutex_unlock (&u->lock);
4552
4553	Note that sending the C<ev_async> watcher is required because otherwise
4554	an event loop currently blocking in the kernel will have no knowledge
4555	about the newly added timer. By waking up the loop it will pick up any new
4556	watchers in the next event loop iteration.
4557		4738
4558	=head3 COROUTINES	4739	=head3 COROUTINES
4559		4740
4560	Libev is very accommodating to coroutines ("cooperative threads"):	4741	Libev is very accommodating to coroutines ("cooperative threads"):
4561	libev fully supports nesting calls to its functions from different	4742	libev fully supports nesting calls to its functions from different
…		…
4726	requires, and its I/O model is fundamentally incompatible with the POSIX	4907	requires, and its I/O model is fundamentally incompatible with the POSIX
4727	model. Libev still offers limited functionality on this platform in	4908	model. Libev still offers limited functionality on this platform in
4728	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4909	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4729	descriptors. This only applies when using Win32 natively, not when using	4910	descriptors. This only applies when using Win32 natively, not when using
4730	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	4911	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4731	as every compielr comes with a slightly differently broken/incompatible	4912	as every compiler comes with a slightly differently broken/incompatible
4732	environment.	4913	environment.
4733		4914
4734	Lifting these limitations would basically require the full	4915	Lifting these limitations would basically require the full
4735	re-implementation of the I/O system. If you are into this kind of thing,	4916	re-implementation of the I/O system. If you are into this kind of thing,
4736	then note that glib does exactly that for you in a very portable way (note	4917	then note that glib does exactly that for you in a very portable way (note
…		…
4869		5050
4870	The type C<double> is used to represent timestamps. It is required to	5051	The type C<double> is used to represent timestamps. It is required to
4871	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5052	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4872	good enough for at least into the year 4000 with millisecond accuracy	5053	good enough for at least into the year 4000 with millisecond accuracy
4873	(the design goal for libev). This requirement is overfulfilled by	5054	(the design goal for libev). This requirement is overfulfilled by
4874	implementations using IEEE 754, which is basically all existing ones. With	5055	implementations using IEEE 754, which is basically all existing ones.
		5056
4875	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5057	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5058	year 2255 (and millisecond accuray till the year 287396 - by then, libev
		5059	is either obsolete or somebody patched it to use C<long double> or
		5060	something like that, just kidding).
4876		5061
4877	=back	5062	=back
4878		5063
4879	If you know of other additional requirements drop me a note.	5064	If you know of other additional requirements drop me a note.
4880		5065
…		…
4942	=item Processing ev_async_send: O(number_of_async_watchers)	5127	=item Processing ev_async_send: O(number_of_async_watchers)
4943		5128
4944	=item Processing signals: O(max_signal_number)	5129	=item Processing signals: O(max_signal_number)
4945		5130
4946	Sending involves a system call I<iff> there were no other C<ev_async_send>	5131	Sending involves a system call I<iff> there were no other C<ev_async_send>
4947	calls in the current loop iteration. Checking for async and signal events	5132	calls in the current loop iteration and the loop is currently
		5133	blocked. Checking for async and signal events involves iterating over all
4948	involves iterating over all running async watchers or all signal numbers.	5134	running async watchers or all signal numbers.
4949		5135
4950	=back	5136	=back
4951		5137
4952		5138
4953	=head1 PORTING FROM LIBEV 3.X TO 4.X	5139	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5070	The physical time that is observed. It is apparently strictly monotonic :)	5256	The physical time that is observed. It is apparently strictly monotonic :)
5071		5257
5072	=item wall-clock time	5258	=item wall-clock time
5073		5259
5074	The time and date as shown on clocks. Unlike real time, it can actually	5260	The time and date as shown on clocks. Unlike real time, it can actually
5075	be wrong and jump forwards and backwards, e.g. when the you adjust your	5261	be wrong and jump forwards and backwards, e.g. when you adjust your
5076	clock.	5262	clock.
5077		5263
5078	=item watcher	5264	=item watcher
5079		5265
5080	A data structure that describes interest in certain events. Watchers need	5266	A data structure that describes interest in certain events. Watchers need
…		…
5083	=back	5269	=back
5084		5270
5085	=head1 AUTHOR	5271	=head1 AUTHOR
5086		5272
5087	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5273	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5088	Magnusson and Emanuele Giaquinta.	5274	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5089		5275

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing libev/ev.pod (file contents): Revision 1.345 by root, Wed Nov 10 14:36:42 2010 UTC vs. Revision 1.379 by root, Tue Jul 12 23:32:10 2011 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.345 by root, Wed Nov 10 14:36:42 2010 UTC vs.
Revision 1.379 by root, Tue Jul 12 23:32:10 2011 UTC