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

Comparing libev/ev.pod (file contents):
Revision 1.349 by root, Mon Jan 10 01:58:55 2011 UTC vs.
Revision 1.380 by root, Mon Jul 25 03:47:28 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
…		…
305		311
306	This function can be used to "simulate" a signal receive. It is completely	312	This function can be used to "simulate" a signal receive. It is completely
307	safe to call this function at any time, from any context, including signal	313	safe to call this function at any time, from any context, including signal
308	handlers or random threads.	314	handlers or random threads.
309		315
310	It's main use is to customise signal handling in your process, especially	316	Its main use is to customise signal handling in your process, especially
311	in the presence of threads. For example, you could block signals	317	in the presence of threads. For example, you could block signals
312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when	318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
313	creating any loops), and in one thread, use C<sigwait> or any other	319	creating any loops), and in one thread, use C<sigwait> or any other
314	mechanism to wait for signals, then "deliver" them to libev by calling	320	mechanism to wait for signals, then "deliver" them to libev by calling
315	C<ev_feed_signal>.	321	C<ev_feed_signal>.
…		…
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,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
512		526
513	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
514	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
515	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
516	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
…		…
582	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
583		597
584	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,
585	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)).
586		600
587	Please note that Solaris event ports can deliver a lot of spurious
588	notifications, so you need to use non-blocking I/O or other means to avoid
589	blocking when no data (or space) is available.
590
591	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
592	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
593	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
594	might perform better.	604	might perform better.
595		605
596	On the positive side, with the exception of the spurious readiness	606	On the positive side, this backend actually performed fully to
597	notifications, this backend actually performed fully to specification
598	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
599	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.
600		620
601	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
602	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
603		623
604	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
…		…
814	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
815	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
816	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
817	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
818		838
819	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):
820		842
821	- Increment loop depth.	843	- Increment loop depth.
822	- Reset the ev_break status.	844	- Reset the ev_break status.
823	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
824	LOOP:	846	LOOP:
…		…
857	anymore.	879	anymore.
858		880
859	... queue jobs here, make sure they register event watchers as long	881	... queue jobs here, make sure they register event watchers as long
860	... 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..)
861	ev_run (my_loop, 0);	883	ev_run (my_loop, 0);
862	... jobs done or somebody called unloop. yeah!	884	... jobs done or somebody called break. yeah!
863		885
864	=item ev_break (loop, how)	886	=item ev_break (loop, how)
865		887
866	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
867	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
…		…
930	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.
931		953
932	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
933	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,
934	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
935	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
936	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
937	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
938	once per this interval, on average.	960	once per this interval, on average (as long as the host time resolution is
		961	good enough).
939		962
940	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
941	to spend more time collecting timeouts, at the expense of increased	964	to spend more time collecting timeouts, at the expense of increased
942	latency/jitter/inexactness (the watcher callback will be called	965	latency/jitter/inexactness (the watcher callback will be called
943	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
…		…
1349	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
1350	functions that do not need a watcher.	1373	functions that do not need a watcher.
1351		1374
1352	=back	1375	=back
1353		1376
1354	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1377	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1355		1378	OWN COMPOSITE WATCHERS> idioms.
1356	Each watcher has, by default, a member C<void *data> that you can change
1357	and read at any time: libev will completely ignore it. This can be used
1358	to associate arbitrary data with your watcher. If you need more data and
1359	don't want to allocate memory and store a pointer to it in that data
1360	member, you can also "subclass" the watcher type and provide your own
1361	data:
1362
1363	struct my_io
1364	{
1365	ev_io io;
1366	int otherfd;
1367	void *somedata;
1368	struct whatever *mostinteresting;
1369	};
1370
1371	...
1372	struct my_io w;
1373	ev_io_init (&w.io, my_cb, fd, EV_READ);
1374
1375	And since your callback will be called with a pointer to the watcher, you
1376	can cast it back to your own type:
1377
1378	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1379	{
1380	struct my_io w = (struct my_io )w_;
1381	...
1382	}
1383
1384	More interesting and less C-conformant ways of casting your callback type
1385	instead have been omitted.
1386
1387	Another common scenario is to use some data structure with multiple
1388	embedded watchers:
1389
1390	struct my_biggy
1391	{
1392	int some_data;
1393	ev_timer t1;
1394	ev_timer t2;
1395	}
1396
1397	In this case getting the pointer to C<my_biggy> is a bit more
1398	complicated: Either you store the address of your C<my_biggy> struct
1399	in the C<data> member of the watcher (for woozies), or you need to use
1400	some pointer arithmetic using C<offsetof> inside your watchers (for real
1401	programmers):
1402
1403	#include <stddef.h>
1404
1405	static void
1406	t1_cb (EV_P_ ev_timer *w, int revents)
1407	{
1408	struct my_biggy big = (struct my_biggy *)
1409	(((char *)w) - offsetof (struct my_biggy, t1));
1410	}
1411
1412	static void
1413	t2_cb (EV_P_ ev_timer *w, int revents)
1414	{
1415	struct my_biggy big = (struct my_biggy *)
1416	(((char *)w) - offsetof (struct my_biggy, t2));
1417	}
1418		1379
1419	=head2 WATCHER STATES	1380	=head2 WATCHER STATES
1420		1381
1421	There are various watcher states mentioned throughout this manual -	1382	There are various watcher states mentioned throughout this manual -
1422	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
…		…
1425		1386
1426	=over 4	1387	=over 4
1427		1388
1428	=item initialiased	1389	=item initialiased
1429		1390
1430	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
1431	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
1432	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.
1433		1394
1434	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
1435	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.
1436		1399
1437	=item started/running/active	1400	=item started/running/active
1438		1401
1439	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
1440	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
…		…
1468	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
1469	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
1470	freeing it is often a good idea.	1433	freeing it is often a good idea.
1471		1434
1472	While stopped (and not pending) the watcher is essentially in the	1435	While stopped (and not pending) the watcher is essentially in the
1473	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
1474	you wish.	1437	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1438	it again).
1475		1439
1476	=back	1440	=back
1477		1441
1478	=head2 WATCHER PRIORITY MODELS	1442	=head2 WATCHER PRIORITY MODELS
1479		1443
…		…
1608	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
1609	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
1610	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
1611	required if you know what you are doing).	1575	required if you know what you are doing).
1612		1576
1613	If you cannot use non-blocking mode, then force the use of a
1614	known-to-be-good backend (at the time of this writing, this includes only
1615	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1616	descriptors for which non-blocking operation makes no sense (such as
1617	files) - libev doesn't guarantee any specific behaviour in that case.
1618
1619	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
1620	receive "spurious" readiness notifications, that is your callback might	1578	receive "spurious" readiness notifications, that is, your callback might
1621	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
1622	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
1623	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
1624	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
1625	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1626	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1583	preferable to a program hanging until some data arrives.
1627		1584
1628	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
1629	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
1630	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
1631	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
1632	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
1633	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
1634	indefinitely.	1591	indefinitely.
1635		1592
1636	But really, best use non-blocking mode.	1593	But really, best use non-blocking mode.
1637		1594
…		…
1665		1622
1666	There is no workaround possible except not registering events	1623	There is no workaround possible except not registering events
1667	for potentially C<dup ()>'ed file descriptors, or to resort to	1624	for potentially C<dup ()>'ed file descriptors, or to resort to
1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1669		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
1670	=head3 The special problem of fork	1660	=head3 The special problem of fork
1671		1661
1672	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
1673	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
1674	it in the child.	1664	it in the child if you want to continue to use it in the child.
1675		1665
1676	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
1677	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
1678	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1679	C<EVBACKEND_POLL>.
1680		1669
1681	=head3 The special problem of SIGPIPE	1670	=head3 The special problem of SIGPIPE
1682		1671
1683	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>:
1684	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
…		…
2034	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
2035	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.
2036		2025
2037	=item ev_timer_again (loop, ev_timer *)	2026	=item ev_timer_again (loop, ev_timer *)
2038		2027
2039	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
2040	repeating. The exact semantics are:	2029	repeating. The exact semantics are:
2041		2030
2042	If the timer is pending, its pending status is cleared.	2031	If the timer is pending, its pending status is cleared.
2043		2032
2044	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).
…		…
2174		2163
2175	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
2176	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
2177	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.
2178		2167
2179	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
2180	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
2181	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.
2182		2174
2183	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
2184	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
2185	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
2186	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).
…		…
2329	=head3 The special problem of inheritance over fork/execve/pthread_create	2321	=head3 The special problem of inheritance over fork/execve/pthread_create
2330		2322
2331	Both the signal mask (C<sigprocmask>) and the signal disposition	2323	Both the signal mask (C<sigprocmask>) and the signal disposition
2332	(C<sigaction>) are unspecified after starting a signal watcher (and after	2324	(C<sigaction>) are unspecified after starting a signal watcher (and after
2333	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,
2334	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>).
2335		2328
2336	While this does not matter for the signal disposition (libev never	2329	While this does not matter for the signal disposition (libev never
2337	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
2338	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
2339	certain signals to be blocked.	2332	certain signals to be blocked.
…		…
3210	atexit (program_exits);	3203	atexit (program_exits);
3211		3204
3212		3205
3213	=head2 C<ev_async> - how to wake up an event loop	3206	=head2 C<ev_async> - how to wake up an event loop
3214		3207
3215	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
3216	asynchronous sources such as signal handlers (as opposed to multiple event	3209	asynchronous sources such as signal handlers (as opposed to multiple event
3217	loops - those are of course safe to use in different threads).	3210	loops - those are of course safe to use in different threads).
3218		3211
3219	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,
3220	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>
…		…
3227	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3220	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
3228	of "global async watchers" by using a watcher on an otherwise unused	3221	of "global async watchers" by using a watcher on an otherwise unused
3229	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3222	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3230	even without knowing which loop owns the signal.	3223	even without knowing which loop owns the signal.
3231		3224
3232	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3233	just the default loop.
3234
3235	=head3 Queueing	3225	=head3 Queueing
3236		3226
3237	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
3238	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
3239	multiple-writer-single-reader queue that works in all cases and doesn't	3229	multiple-writer-single-reader queue that works in all cases and doesn't
…		…
3330	trust me.	3320	trust me.
3331		3321
3332	=item ev_async_send (loop, ev_async *)	3322	=item ev_async_send (loop, ev_async *)
3333		3323
3334	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
3335	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
3336	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,
3337	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
3338	section below on what exactly this means).	3330	embedding section below on what exactly this means).
3339		3331
3340	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
3341	compressed into a single callback invocation (another way to look at this	3333	compressed into a single callback invocation (another way to look at
3342	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
3343	reset when the event loop detects that).	3335	C<ev_async_send>, reset when the event loop detects that).
3344		3336
3345	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
3346	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
3347	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.
3348		3343
3349	=item bool = ev_async_pending (ev_async *)	3344	=item bool = ev_async_pending (ev_async *)
3350		3345
3351	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
3352	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
…		…
3423		3418
3424	This section explains some common idioms that are not immediately	3419	This section explains some common idioms that are not immediately
3425	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
3426	section only contains stuff that wouldn't fit anywhere else.	3421	section only contains stuff that wouldn't fit anywhere else.
3427		3422
3428	=over 4	3423	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3429		3424
3430	=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
3431		3492
3432	Often (especially in GUI toolkits) there are places where you have	3493	Often (especially in GUI toolkits) there are places where you have
3433	I<modal> interaction, which is most easily implemented by recursively	3494	I<modal> interaction, which is most easily implemented by recursively
3434	invoking C<ev_run>.	3495	invoking C<ev_run>.
3435		3496
…		…
3464	exit_main_loop = 1;	3525	exit_main_loop = 1;
3465		3526
3466	// exit both	3527	// exit both
3467	exit_main_loop = exit_nested_loop = 1;	3528	exit_main_loop = exit_nested_loop = 1;
3468		3529
3469	=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.
3470		3725
3471		3726
3472	=head1 LIBEVENT EMULATION	3727	=head1 LIBEVENT EMULATION
3473		3728
3474	Libev offers a compatibility emulation layer for libevent. It cannot	3729	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3689	watchers in the constructor.	3944	watchers in the constructor.
3690		3945
3691	class myclass	3946	class myclass
3692	{	3947	{
3693	ev::io io ; void io_cb (ev::io &w, int revents);	3948	ev::io io ; void io_cb (ev::io &w, int revents);
3694	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	3949	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3695	ev::idle idle; void idle_cb (ev::idle &w, int revents);	3950	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3696		3951
3697	myclass (int fd)	3952	myclass (int fd)
3698	{	3953	{
3699	io .set <myclass, &myclass::io_cb > (this);	3954	io .set <myclass, &myclass::io_cb > (this);
…		…
3750	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4005	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3751		4006
3752	=item D	4007	=item D
3753		4008
3754	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
3755	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>.
3756		4011
3757	=item Ocaml	4012	=item Ocaml
3758		4013
3759	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
3760	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4015	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3808	suitable for use with C<EV_A>.	4063	suitable for use with C<EV_A>.
3809		4064
3810	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4065	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3811		4066
3812	Similar to the other two macros, this gives you the value of the default	4067	Similar to the other two macros, this gives you the value of the default
3813	loop, if multiple loops are supported ("ev loop default").	4068	loop, if multiple loops are supported ("ev loop default"). The default loop
		4069	will be initialised if it isn't already initialised.
		4070
		4071	For non-multiplicity builds, these macros do nothing, so you always have
		4072	to initialise the loop somewhere.
3814		4073
3815	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4074	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3816		4075
3817	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4076	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3818	default loop has been initialised (C<UC> == unchecked). Their behaviour	4077	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3963	supported). It will also not define any of the structs usually found in	4222	supported). It will also not define any of the structs usually found in
3964	F<event.h> that are not directly supported by the libev core alone.	4223	F<event.h> that are not directly supported by the libev core alone.
3965		4224
3966	In standalone mode, libev will still try to automatically deduce the	4225	In standalone mode, libev will still try to automatically deduce the
3967	configuration, but has to be more conservative.	4226	configuration, but has to be more conservative.
		4227
		4228	=item EV_USE_FLOOR
		4229
		4230	If defined to be C<1>, libev will use the C<floor ()> function for its
		4231	periodic reschedule calculations, otherwise libev will fall back on a
		4232	portable (slower) implementation. If you enable this, you usually have to
		4233	link against libm or something equivalent. Enabling this when the C<floor>
		4234	function is not available will fail, so the safe default is to not enable
		4235	this.
3968		4236
3969	=item EV_USE_MONOTONIC	4237	=item EV_USE_MONOTONIC
3970		4238
3971	If defined to be C<1>, libev will try to detect the availability of the	4239	If defined to be C<1>, libev will try to detect the availability of the
3972	monotonic clock option at both compile time and runtime. Otherwise no	4240	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4105	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4373	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4106		4374
4107	=item EV_ATOMIC_T	4375	=item EV_ATOMIC_T
4108		4376
4109	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4377	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4110	access is atomic with respect to other threads or signal contexts. No such	4378	access is atomic and serialised with respect to other threads or signal
4111	type is easily found in the C language, so you can provide your own type	4379	contexts. No such type is easily found in the C language, so you can
4112	that you know is safe for your purposes. It is used both for signal handler "locking"	4380	provide your own type that you know is safe for your purposes. It is used
4113	as well as for signal and thread safety in C<ev_async> watchers.	4381	both for signal handler "locking" as well as for signal and thread safety
		4382	in C<ev_async> watchers.
4114		4383
4115	In the absence of this define, libev will use C<sig_atomic_t volatile>	4384	In the absence of this define, libev will use C<sig_atomic_t volatile>
4116	(from F<signal.h>), which is usually good enough on most platforms.	4385	(from F<signal.h>), which is usually good enough on most platforms,
		4386	although strictly speaking using a type that also implies a memory fence
		4387	is required.
4117		4388
4118	=item EV_H (h)	4389	=item EV_H (h)
4119		4390
4120	The name of the F<ev.h> header file used to include it. The default if	4391	The name of the F<ev.h> header file used to include it. The default if
4121	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4392	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
4144	If undefined or defined to C<1>, then all event-loop-specific functions	4415	If undefined or defined to C<1>, then all event-loop-specific functions
4145	will have the C<struct ev_loop *> as first argument, and you can create	4416	will have the C<struct ev_loop *> as first argument, and you can create
4146	additional independent event loops. Otherwise there will be no support	4417	additional independent event loops. Otherwise there will be no support
4147	for multiple event loops and there is no first event loop pointer	4418	for multiple event loops and there is no first event loop pointer
4148	argument. Instead, all functions act on the single default loop.	4419	argument. Instead, all functions act on the single default loop.
		4420
		4421	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4422	default loop when multiplicity is switched off - you always have to
		4423	initialise the loop manually in this case.
4149		4424
4150	=item EV_MINPRI	4425	=item EV_MINPRI
4151		4426
4152	=item EV_MAXPRI	4427	=item EV_MAXPRI
4153		4428
…		…
4404	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4679	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4405		4680
4406	#include "ev_cpp.h"	4681	#include "ev_cpp.h"
4407	#include "ev.c"	4682	#include "ev.c"
4408		4683
4409	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4684	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4410		4685
4411	=head2 THREADS AND COROUTINES	4686	=head2 THREADS AND COROUTINES
4412		4687
4413	=head3 THREADS	4688	=head3 THREADS
4414		4689
…		…
4465	default loop and triggering an C<ev_async> watcher from the default loop	4740	default loop and triggering an C<ev_async> watcher from the default loop
4466	watcher callback into the event loop interested in the signal.	4741	watcher callback into the event loop interested in the signal.
4467		4742
4468	=back	4743	=back
4469		4744
4470	=head4 THREAD LOCKING EXAMPLE	4745	See also L<THREAD LOCKING EXAMPLE>.
4471
4472	Here is a fictitious example of how to run an event loop in a different
4473	thread than where callbacks are being invoked and watchers are
4474	created/added/removed.
4475
4476	For a real-world example, see the C<EV::Loop::Async> perl module,
4477	which uses exactly this technique (which is suited for many high-level
4478	languages).
4479
4480	The example uses a pthread mutex to protect the loop data, a condition
4481	variable to wait for callback invocations, an async watcher to notify the
4482	event loop thread and an unspecified mechanism to wake up the main thread.
4483
4484	First, you need to associate some data with the event loop:
4485
4486	typedef struct {
4487	mutex_t lock; /* global loop lock */
4488	ev_async async_w;
4489	thread_t tid;
4490	cond_t invoke_cv;
4491	} userdata;
4492
4493	void prepare_loop (EV_P)
4494	{
4495	// for simplicity, we use a static userdata struct.
4496	static userdata u;
4497
4498	ev_async_init (&u->async_w, async_cb);
4499	ev_async_start (EV_A_ &u->async_w);
4500
4501	pthread_mutex_init (&u->lock, 0);
4502	pthread_cond_init (&u->invoke_cv, 0);
4503
4504	// now associate this with the loop
4505	ev_set_userdata (EV_A_ u);
4506	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4507	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4508
4509	// then create the thread running ev_loop
4510	pthread_create (&u->tid, 0, l_run, EV_A);
4511	}
4512
4513	The callback for the C<ev_async> watcher does nothing: the watcher is used
4514	solely to wake up the event loop so it takes notice of any new watchers
4515	that might have been added:
4516
4517	static void
4518	async_cb (EV_P_ ev_async *w, int revents)
4519	{
4520	// just used for the side effects
4521	}
4522
4523	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4524	protecting the loop data, respectively.
4525
4526	static void
4527	l_release (EV_P)
4528	{
4529	userdata *u = ev_userdata (EV_A);
4530	pthread_mutex_unlock (&u->lock);
4531	}
4532
4533	static void
4534	l_acquire (EV_P)
4535	{
4536	userdata *u = ev_userdata (EV_A);
4537	pthread_mutex_lock (&u->lock);
4538	}
4539
4540	The event loop thread first acquires the mutex, and then jumps straight
4541	into C<ev_run>:
4542
4543	void *
4544	l_run (void *thr_arg)
4545	{
4546	struct ev_loop loop = (struct ev_loop )thr_arg;
4547
4548	l_acquire (EV_A);
4549	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4550	ev_run (EV_A_ 0);
4551	l_release (EV_A);
4552
4553	return 0;
4554	}
4555
4556	Instead of invoking all pending watchers, the C<l_invoke> callback will
4557	signal the main thread via some unspecified mechanism (signals? pipe
4558	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4559	have been called (in a while loop because a) spurious wakeups are possible
4560	and b) skipping inter-thread-communication when there are no pending
4561	watchers is very beneficial):
4562
4563	static void
4564	l_invoke (EV_P)
4565	{
4566	userdata *u = ev_userdata (EV_A);
4567
4568	while (ev_pending_count (EV_A))
4569	{
4570	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4571	pthread_cond_wait (&u->invoke_cv, &u->lock);
4572	}
4573	}
4574
4575	Now, whenever the main thread gets told to invoke pending watchers, it
4576	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4577	thread to continue:
4578
4579	static void
4580	real_invoke_pending (EV_P)
4581	{
4582	userdata *u = ev_userdata (EV_A);
4583
4584	pthread_mutex_lock (&u->lock);
4585	ev_invoke_pending (EV_A);
4586	pthread_cond_signal (&u->invoke_cv);
4587	pthread_mutex_unlock (&u->lock);
4588	}
4589
4590	Whenever you want to start/stop a watcher or do other modifications to an
4591	event loop, you will now have to lock:
4592
4593	ev_timer timeout_watcher;
4594	userdata *u = ev_userdata (EV_A);
4595
4596	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4597
4598	pthread_mutex_lock (&u->lock);
4599	ev_timer_start (EV_A_ &timeout_watcher);
4600	ev_async_send (EV_A_ &u->async_w);
4601	pthread_mutex_unlock (&u->lock);
4602
4603	Note that sending the C<ev_async> watcher is required because otherwise
4604	an event loop currently blocking in the kernel will have no knowledge
4605	about the newly added timer. By waking up the loop it will pick up any new
4606	watchers in the next event loop iteration.
4607		4746
4608	=head3 COROUTINES	4747	=head3 COROUTINES
4609		4748
4610	Libev is very accommodating to coroutines ("cooperative threads"):	4749	Libev is very accommodating to coroutines ("cooperative threads"):
4611	libev fully supports nesting calls to its functions from different	4750	libev fully supports nesting calls to its functions from different
…		…
4776	requires, and its I/O model is fundamentally incompatible with the POSIX	4915	requires, and its I/O model is fundamentally incompatible with the POSIX
4777	model. Libev still offers limited functionality on this platform in	4916	model. Libev still offers limited functionality on this platform in
4778	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4917	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4779	descriptors. This only applies when using Win32 natively, not when using	4918	descriptors. This only applies when using Win32 natively, not when using
4780	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	4919	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4781	as every compielr comes with a slightly differently broken/incompatible	4920	as every compiler comes with a slightly differently broken/incompatible
4782	environment.	4921	environment.
4783		4922
4784	Lifting these limitations would basically require the full	4923	Lifting these limitations would basically require the full
4785	re-implementation of the I/O system. If you are into this kind of thing,	4924	re-implementation of the I/O system. If you are into this kind of thing,
4786	then note that glib does exactly that for you in a very portable way (note	4925	then note that glib does exactly that for you in a very portable way (note
…		…
4919		5058
4920	The type C<double> is used to represent timestamps. It is required to	5059	The type C<double> is used to represent timestamps. It is required to
4921	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5060	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4922	good enough for at least into the year 4000 with millisecond accuracy	5061	good enough for at least into the year 4000 with millisecond accuracy
4923	(the design goal for libev). This requirement is overfulfilled by	5062	(the design goal for libev). This requirement is overfulfilled by
4924	implementations using IEEE 754, which is basically all existing ones. With	5063	implementations using IEEE 754, which is basically all existing ones.
		5064
4925	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5065	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5066	year 2255 (and millisecond accuray till the year 287396 - by then, libev
		5067	is either obsolete or somebody patched it to use C<long double> or
		5068	something like that, just kidding).
4926		5069
4927	=back	5070	=back
4928		5071
4929	If you know of other additional requirements drop me a note.	5072	If you know of other additional requirements drop me a note.
4930		5073
…		…
4992	=item Processing ev_async_send: O(number_of_async_watchers)	5135	=item Processing ev_async_send: O(number_of_async_watchers)
4993		5136
4994	=item Processing signals: O(max_signal_number)	5137	=item Processing signals: O(max_signal_number)
4995		5138
4996	Sending involves a system call I<iff> there were no other C<ev_async_send>	5139	Sending involves a system call I<iff> there were no other C<ev_async_send>
4997	calls in the current loop iteration. Checking for async and signal events	5140	calls in the current loop iteration and the loop is currently
		5141	blocked. Checking for async and signal events involves iterating over all
4998	involves iterating over all running async watchers or all signal numbers.	5142	running async watchers or all signal numbers.
4999		5143
5000	=back	5144	=back
5001		5145
5002		5146
5003	=head1 PORTING FROM LIBEV 3.X TO 4.X	5147	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5120	The physical time that is observed. It is apparently strictly monotonic :)	5264	The physical time that is observed. It is apparently strictly monotonic :)
5121		5265
5122	=item wall-clock time	5266	=item wall-clock time
5123		5267
5124	The time and date as shown on clocks. Unlike real time, it can actually	5268	The time and date as shown on clocks. Unlike real time, it can actually
5125	be wrong and jump forwards and backwards, e.g. when the you adjust your	5269	be wrong and jump forwards and backwards, e.g. when you adjust your
5126	clock.	5270	clock.
5127		5271
5128	=item watcher	5272	=item watcher
5129		5273
5130	A data structure that describes interest in certain events. Watchers need	5274	A data structure that describes interest in certain events. Watchers need
…		…
5133	=back	5277	=back
5134		5278
5135	=head1 AUTHOR	5279	=head1 AUTHOR
5136		5280
5137	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5281	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5138	Magnusson and Emanuele Giaquinta.	5282	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5139		5283

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Comparing libev/ev.pod (file contents): Revision 1.349 by root, Mon Jan 10 01:58:55 2011 UTC vs. Revision 1.380 by root, Mon Jul 25 03:47:28 2011 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.349 by root, Mon Jan 10 01:58:55 2011 UTC vs.
Revision 1.380 by root, Mon Jul 25 03:47:28 2011 UTC