[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 1.370 by root, Thu Jun 2 23:42:40 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
…		…
305		305
306	This function can be used to "simulate" a signal receive. It is completely	306	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	307	safe to call this function at any time, from any context, including signal
308	handlers or random threads.	308	handlers or random threads.
309		309
310	It's main use is to customise signal handling in your process, especially	310	Its main use is to customise signal handling in your process, especially
311	in the presence of threads. For example, you could block signals	311	in the presence of threads. For example, you could block signals
312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when	312	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	313	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	314	mechanism to wait for signals, then "deliver" them to libev by calling
315	C<ev_feed_signal>.	315	C<ev_feed_signal>.
…		…
442		442
443	This behaviour is useful when you want to do your own signal handling, or	443	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	444	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	445	unblocking the signals.
446		446
		447	It's also required by POSIX in a threaded program, as libev calls
		448	C<sigprocmask>, whose behaviour is officially unspecified.
		449
447	This flag's behaviour will become the default in future versions of libev.	450	This flag's behaviour will become the default in future versions of libev.
448		451
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	452	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		453
451	This is your standard select(2) backend. Not I<completely> standard, as	454	This is your standard select(2) backend. Not I<completely> standard, as
…		…
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	483	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		484
482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	485	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
483	kernels).	486	kernels).
484		487
485	For few fds, this backend is a bit little slower than poll and select,	488	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	489	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),	490	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).	491	fd), epoll scales either O(1) or O(active_fds).
489		492
490	The epoll mechanism deserves honorable mention as the most misdesigned	493	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	494	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	495	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	496	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	499	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	500	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)	501	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	502	and is of course hard to detect.
500		503
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	504	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	505	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	506	totally I<different> file descriptors (even already closed ones, so
504	even remove them from the set) than registered in the set (especially	507	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	508	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	509	notifications by employing an additional generation counter and comparing
507	events to filter out spurious ones, recreating the set when required. Last	510	that against the events to filter out spurious ones, recreating the set
		511	when required. Epoll also errornously rounds down timeouts, but gives you
		512	no way to know when and by how much, so sometimes you have to busy-wait
		513	because epoll returns immediately despite a nonzero timeout. And last
508	not least, it also refuses to work with some file descriptors which work	514	not least, it also refuses to work with some file descriptors which work
509	perfectly fine with C<select> (files, many character devices...).	515	perfectly fine with C<select> (files, many character devices...).
510		516
511	Epoll is truly the train wreck analog among event poll mechanisms.	517	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		518	cobbled together in a hurry, no thought to design or interaction with
		519	others. Oh, the pain, will it ever stop...
512		520
513	While stopping, setting and starting an I/O watcher in the same iteration	521	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	522	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	523	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	524	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
582	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	590	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
583		591
584	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	592	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)).	593	it's really slow, but it still scales very well (O(active_fds)).
586		594
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	595	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	596	file descriptor per loop iteration. For small and medium numbers of file
593	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	597	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
594	might perform better.	598	might perform better.
595		599
596	On the positive side, with the exception of the spurious readiness	600	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	601	specification in all tests and is fully embeddable, which is a rare feat
599	OS-specific backends (I vastly prefer correctness over speed hacks).	602	among the OS-specific backends (I vastly prefer correctness over speed
		603	hacks).
		604
		605	On the negative side, the interface is I<bizarre> - so bizarre that
		606	even sun itself gets it wrong in their code examples: The event polling
		607	function sometimes returning events to the caller even though an error
		608	occurred, but with no indication whether it has done so or not (yes, it's
		609	even documented that way) - deadly for edge-triggered interfaces where
		610	you absolutely have to know whether an event occurred or not because you
		611	have to re-arm the watcher.
		612
		613	Fortunately libev seems to be able to work around these idiocies.
600		614
601	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	615	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
602	C<EVBACKEND_POLL>.	616	C<EVBACKEND_POLL>.
603		617
604	=item C<EVBACKEND_ALL>	618	=item C<EVBACKEND_ALL>
…		…
814	This is useful if you are waiting for some external event in conjunction	828	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	829	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	830	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.	831	usually a better approach for this kind of thing.
818		832
819	Here are the gory details of what C<ev_run> does:	833	Here are the gory details of what C<ev_run> does (this is for your
		834	understanding, not a guarantee that things will work exactly like this in
		835	future versions):
820		836
821	- Increment loop depth.	837	- Increment loop depth.
822	- Reset the ev_break status.	838	- Reset the ev_break status.
823	- Before the first iteration, call any pending watchers.	839	- Before the first iteration, call any pending watchers.
824	LOOP:	840	LOOP:
…		…
857	anymore.	873	anymore.
858		874
859	... queue jobs here, make sure they register event watchers as long	875	... 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..)	876	... as they still have work to do (even an idle watcher will do..)
861	ev_run (my_loop, 0);	877	ev_run (my_loop, 0);
862	... jobs done or somebody called unloop. yeah!	878	... jobs done or somebody called break. yeah!
863		879
864	=item ev_break (loop, how)	880	=item ev_break (loop, how)
865		881
866	Can be used to make a call to C<ev_run> return early (but only after it	882	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	883	has processed all outstanding events). The C<how> argument must be either
…		…
1349	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1365	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1350	functions that do not need a watcher.	1366	functions that do not need a watcher.
1351		1367
1352	=back	1368	=back
1353		1369
1354	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1370	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1355		1371	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		1372
1419	=head2 WATCHER STATES	1373	=head2 WATCHER STATES
1420		1374
1421	There are various watcher states mentioned throughout this manual -	1375	There are various watcher states mentioned throughout this manual -
1422	active, pending and so on. In this section these states and the rules to	1376	active, pending and so on. In this section these states and the rules to
…		…
1429		1383
1430	Before a watcher can be registered with the event looop it has to be	1384	Before a watcher can be registered with the event looop it has to be
1431	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1385	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.	1386	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1433		1387
1434	In this state it is simply some block of memory that is suitable for use	1388	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.	1389	use in an event loop. It can be moved around, freed, reused etc. at
		1390	will - as long as you either keep the memory contents intact, or call
		1391	C<ev_TYPE_init> again.
1436		1392
1437	=item started/running/active	1393	=item started/running/active
1438		1394
1439	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1395	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	1396	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	1424	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	1425	of whether it was active or not, so stopping a watcher explicitly before
1470	freeing it is often a good idea.	1426	freeing it is often a good idea.
1471		1427
1472	While stopped (and not pending) the watcher is essentially in the	1428	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	1429	initialised state, that is, it can be reused, moved, modified in any way
1474	you wish.	1430	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1431	it again).
1475		1432
1476	=back	1433	=back
1477		1434
1478	=head2 WATCHER PRIORITY MODELS	1435	=head2 WATCHER PRIORITY MODELS
1479		1436
…		…
1608	In general you can register as many read and/or write event watchers per	1565	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	1566	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	1567	descriptors to non-blocking mode is also usually a good idea (but not
1611	required if you know what you are doing).	1568	required if you know what you are doing).
1612		1569
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	1570	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	1571	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	1572	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	1573	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	1574	with a relatively standard program structure. Thus it is best to always
1624	this situation even with a relatively standard program structure. Thus	1575	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.	1576	preferable to a program hanging until some data arrives.
1627		1577
1628	If you cannot run the fd in non-blocking mode (for example you should	1578	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	1579	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	1580	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	1581	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	1582	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	1583	use C<SIGALRM> and an interval timer, just to be sure you won't block
1634	indefinitely.	1584	indefinitely.
1635		1585
1636	But really, best use non-blocking mode.	1586	But really, best use non-blocking mode.
1637		1587
…		…
1665		1615
1666	There is no workaround possible except not registering events	1616	There is no workaround possible except not registering events
1667	for potentially C<dup ()>'ed file descriptors, or to resort to	1617	for potentially C<dup ()>'ed file descriptors, or to resort to
1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1618	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1669		1619
		1620	=head3 The special problem of files
		1621
		1622	Many people try to use C<select> (or libev) on file descriptors
		1623	representing files, and expect it to become ready when their program
		1624	doesn't block on disk accesses (which can take a long time on their own).
		1625
		1626	However, this cannot ever work in the "expected" way - you get a readiness
		1627	notification as soon as the kernel knows whether and how much data is
		1628	there, and in the case of open files, that's always the case, so you
		1629	always get a readiness notification instantly, and your read (or possibly
		1630	write) will still block on the disk I/O.
		1631
		1632	Another way to view it is that in the case of sockets, pipes, character
		1633	devices and so on, there is another party (the sender) that delivers data
		1634	on its own, but in the case of files, there is no such thing: the disk
		1635	will not send data on its own, simply because it doesn't know what you
		1636	wish to read - you would first have to request some data.
		1637
		1638	Since files are typically not-so-well supported by advanced notification
		1639	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1640	to files, even though you should not use it. The reason for this is
		1641	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1642	usually a tty, often a pipe, but also sometimes files or special devices
		1643	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1644	F</dev/urandom>), and even though the file might better be served with
		1645	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1646	it "just works" instead of freezing.
		1647
		1648	So avoid file descriptors pointing to files when you know it (e.g. use
		1649	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1650	when you rarely read from a file instead of from a socket, and want to
		1651	reuse the same code path.
		1652
1670	=head3 The special problem of fork	1653	=head3 The special problem of fork
1671		1654
1672	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1655	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	1656	useless behaviour. Libev fully supports fork, but needs to be told about
1674	it in the child.	1657	it in the child if you want to continue to use it in the child.
1675		1658
1676	To support fork in your programs, you either have to call	1659	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,	1660	()> 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	1661	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1679	C<EVBACKEND_POLL>.
1680		1662
1681	=head3 The special problem of SIGPIPE	1663	=head3 The special problem of SIGPIPE
1682		1664
1683	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1665	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	1666	when writing to a pipe whose other end has been closed, your program gets
…		…
2174		2156
2175	Another way to think about it (for the mathematically inclined) is that	2157	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	2158	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.	2159	time where C<time = offset (mod interval)>, regardless of any time jumps.
2178		2160
2179	For numerical stability it is preferable that the C<offset> value is near	2161	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	2162	interval value should be higher than C<1/8192> (which is around 100
2181	this value, and in fact is often specified as zero.	2163	microseconds) and C<offset> should be higher than C<0> and should have
		2164	at most a similar magnitude as the current time (say, within a factor of
		2165	ten). Typical values for offset are, in fact, C<0> or something between
		2166	C<0> and C<interval>, which is also the recommended range.
2182		2167
2183	Note also that there is an upper limit to how often a timer can fire (CPU	2168	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	2169	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	2170	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).	2171	millisecond (if the OS supports it and the machine is fast enough).
…		…
2329	=head3 The special problem of inheritance over fork/execve/pthread_create	2314	=head3 The special problem of inheritance over fork/execve/pthread_create
2330		2315
2331	Both the signal mask (C<sigprocmask>) and the signal disposition	2316	Both the signal mask (C<sigprocmask>) and the signal disposition
2332	(C<sigaction>) are unspecified after starting a signal watcher (and after	2317	(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,	2318	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.	2319	and might or might not set or restore the installed signal handler (but
		2320	see C<EVFLAG_NOSIGMASK>).
2335		2321
2336	While this does not matter for the signal disposition (libev never	2322	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	2323	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	2324	C<execve>), this matters for the signal mask: many programs do not expect
2339	certain signals to be blocked.	2325	certain signals to be blocked.
…		…
3210	atexit (program_exits);	3196	atexit (program_exits);
3211		3197
3212		3198
3213	=head2 C<ev_async> - how to wake up an event loop	3199	=head2 C<ev_async> - how to wake up an event loop
3214		3200
3215	In general, you cannot use an C<ev_run> from multiple threads or other	3201	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	3202	asynchronous sources such as signal handlers (as opposed to multiple event
3217	loops - those are of course safe to use in different threads).	3203	loops - those are of course safe to use in different threads).
3218		3204
3219	Sometimes, however, you need to wake up an event loop you do not control,	3205	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>	3206	for example because it belongs to another thread. This is what C<ev_async>
…		…
3330	trust me.	3316	trust me.
3331		3317
3332	=item ev_async_send (loop, ev_async *)	3318	=item ev_async_send (loop, ev_async *)
3333		3319
3334	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3320	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	3321	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3322	returns.
		3323
3336	C<ev_feed_event>, this call is safe to do from other threads, signal or	3324	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	3325	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3338	section below on what exactly this means).	3326	embedding section below on what exactly this means).
3339		3327
3340	Note that, as with other watchers in libev, multiple events might get	3328	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	3329	compressed into a single callback invocation (another way to look at this
3342	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3330	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
3343	reset when the event loop detects that).	3331	reset when the event loop detects that).
…		…
3423		3411
3424	This section explains some common idioms that are not immediately	3412	This section explains some common idioms that are not immediately
3425	obvious. Note that examples are sprinkled over the whole manual, and this	3413	obvious. Note that examples are sprinkled over the whole manual, and this
3426	section only contains stuff that wouldn't fit anywhere else.	3414	section only contains stuff that wouldn't fit anywhere else.
3427		3415
3428	=over 4	3416	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3429		3417
3430	=item Model/nested event loop invocations and exit conditions.	3418	Each watcher has, by default, a C<void *data> member that you can read
		3419	or modify at any time: libev will completely ignore it. This can be used
		3420	to associate arbitrary data with your watcher. If you need more data and
		3421	don't want to allocate memory separately and store a pointer to it in that
		3422	data member, you can also "subclass" the watcher type and provide your own
		3423	data:
		3424
		3425	struct my_io
		3426	{
		3427	ev_io io;
		3428	int otherfd;
		3429	void *somedata;
		3430	struct whatever *mostinteresting;
		3431	};
		3432
		3433	...
		3434	struct my_io w;
		3435	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3436
		3437	And since your callback will be called with a pointer to the watcher, you
		3438	can cast it back to your own type:
		3439
		3440	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3441	{
		3442	struct my_io w = (struct my_io )w_;
		3443	...
		3444	}
		3445
		3446	More interesting and less C-conformant ways of casting your callback
		3447	function type instead have been omitted.
		3448
		3449	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3450
		3451	Another common scenario is to use some data structure with multiple
		3452	embedded watchers, in effect creating your own watcher that combines
		3453	multiple libev event sources into one "super-watcher":
		3454
		3455	struct my_biggy
		3456	{
		3457	int some_data;
		3458	ev_timer t1;
		3459	ev_timer t2;
		3460	}
		3461
		3462	In this case getting the pointer to C<my_biggy> is a bit more
		3463	complicated: Either you store the address of your C<my_biggy> struct in
		3464	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3465	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3466	real programmers):
		3467
		3468	#include <stddef.h>
		3469
		3470	static void
		3471	t1_cb (EV_P_ ev_timer *w, int revents)
		3472	{
		3473	struct my_biggy big = (struct my_biggy *)
		3474	(((char *)w) - offsetof (struct my_biggy, t1));
		3475	}
		3476
		3477	static void
		3478	t2_cb (EV_P_ ev_timer *w, int revents)
		3479	{
		3480	struct my_biggy big = (struct my_biggy *)
		3481	(((char *)w) - offsetof (struct my_biggy, t2));
		3482	}
		3483
		3484	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3431		3485
3432	Often (especially in GUI toolkits) there are places where you have	3486	Often (especially in GUI toolkits) there are places where you have
3433	I<modal> interaction, which is most easily implemented by recursively	3487	I<modal> interaction, which is most easily implemented by recursively
3434	invoking C<ev_run>.	3488	invoking C<ev_run>.
3435		3489
…		…
3464	exit_main_loop = 1;	3518	exit_main_loop = 1;
3465		3519
3466	// exit both	3520	// exit both
3467	exit_main_loop = exit_nested_loop = 1;	3521	exit_main_loop = exit_nested_loop = 1;
3468		3522
3469	=back	3523	=head2 THREAD LOCKING EXAMPLE
		3524
		3525	Here is a fictitious example of how to run an event loop in a different
		3526	thread from where callbacks are being invoked and watchers are
		3527	created/added/removed.
		3528
		3529	For a real-world example, see the C<EV::Loop::Async> perl module,
		3530	which uses exactly this technique (which is suited for many high-level
		3531	languages).
		3532
		3533	The example uses a pthread mutex to protect the loop data, a condition
		3534	variable to wait for callback invocations, an async watcher to notify the
		3535	event loop thread and an unspecified mechanism to wake up the main thread.
		3536
		3537	First, you need to associate some data with the event loop:
		3538
		3539	typedef struct {
		3540	mutex_t lock; /* global loop lock */
		3541	ev_async async_w;
		3542	thread_t tid;
		3543	cond_t invoke_cv;
		3544	} userdata;
		3545
		3546	void prepare_loop (EV_P)
		3547	{
		3548	// for simplicity, we use a static userdata struct.
		3549	static userdata u;
		3550
		3551	ev_async_init (&u->async_w, async_cb);
		3552	ev_async_start (EV_A_ &u->async_w);
		3553
		3554	pthread_mutex_init (&u->lock, 0);
		3555	pthread_cond_init (&u->invoke_cv, 0);
		3556
		3557	// now associate this with the loop
		3558	ev_set_userdata (EV_A_ u);
		3559	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3560	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3561
		3562	// then create the thread running ev_run
		3563	pthread_create (&u->tid, 0, l_run, EV_A);
		3564	}
		3565
		3566	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3567	solely to wake up the event loop so it takes notice of any new watchers
		3568	that might have been added:
		3569
		3570	static void
		3571	async_cb (EV_P_ ev_async *w, int revents)
		3572	{
		3573	// just used for the side effects
		3574	}
		3575
		3576	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3577	protecting the loop data, respectively.
		3578
		3579	static void
		3580	l_release (EV_P)
		3581	{
		3582	userdata *u = ev_userdata (EV_A);
		3583	pthread_mutex_unlock (&u->lock);
		3584	}
		3585
		3586	static void
		3587	l_acquire (EV_P)
		3588	{
		3589	userdata *u = ev_userdata (EV_A);
		3590	pthread_mutex_lock (&u->lock);
		3591	}
		3592
		3593	The event loop thread first acquires the mutex, and then jumps straight
		3594	into C<ev_run>:
		3595
		3596	void *
		3597	l_run (void *thr_arg)
		3598	{
		3599	struct ev_loop loop = (struct ev_loop )thr_arg;
		3600
		3601	l_acquire (EV_A);
		3602	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3603	ev_run (EV_A_ 0);
		3604	l_release (EV_A);
		3605
		3606	return 0;
		3607	}
		3608
		3609	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3610	signal the main thread via some unspecified mechanism (signals? pipe
		3611	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3612	have been called (in a while loop because a) spurious wakeups are possible
		3613	and b) skipping inter-thread-communication when there are no pending
		3614	watchers is very beneficial):
		3615
		3616	static void
		3617	l_invoke (EV_P)
		3618	{
		3619	userdata *u = ev_userdata (EV_A);
		3620
		3621	while (ev_pending_count (EV_A))
		3622	{
		3623	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3624	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3625	}
		3626	}
		3627
		3628	Now, whenever the main thread gets told to invoke pending watchers, it
		3629	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3630	thread to continue:
		3631
		3632	static void
		3633	real_invoke_pending (EV_P)
		3634	{
		3635	userdata *u = ev_userdata (EV_A);
		3636
		3637	pthread_mutex_lock (&u->lock);
		3638	ev_invoke_pending (EV_A);
		3639	pthread_cond_signal (&u->invoke_cv);
		3640	pthread_mutex_unlock (&u->lock);
		3641	}
		3642
		3643	Whenever you want to start/stop a watcher or do other modifications to an
		3644	event loop, you will now have to lock:
		3645
		3646	ev_timer timeout_watcher;
		3647	userdata *u = ev_userdata (EV_A);
		3648
		3649	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3650
		3651	pthread_mutex_lock (&u->lock);
		3652	ev_timer_start (EV_A_ &timeout_watcher);
		3653	ev_async_send (EV_A_ &u->async_w);
		3654	pthread_mutex_unlock (&u->lock);
		3655
		3656	Note that sending the C<ev_async> watcher is required because otherwise
		3657	an event loop currently blocking in the kernel will have no knowledge
		3658	about the newly added timer. By waking up the loop it will pick up any new
		3659	watchers in the next event loop iteration.
		3660
		3661	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3662
		3663	While the overhead of a callback that e.g. schedules a thread is small, it
		3664	is still an overhead. If you embed libev, and your main usage is with some
		3665	kind of threads or coroutines, you might want to customise libev so that
		3666	doesn't need callbacks anymore.
		3667
		3668	Imagine you have coroutines that you can switch to using a function
		3669	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3670	and that due to some magic, the currently active coroutine is stored in a
		3671	global called C<current_coro>. Then you can build your own "wait for libev
		3672	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3673	the differing C<;> conventions):
		3674
		3675	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3676	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3677
		3678	That means instead of having a C callback function, you store the
		3679	coroutine to switch to in each watcher, and instead of having libev call
		3680	your callback, you instead have it switch to that coroutine.
		3681
		3682	A coroutine might now wait for an event with a function called
		3683	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3684	matter when, or whether the watcher is active or not when this function is
		3685	called):
		3686
		3687	void
		3688	wait_for_event (ev_watcher *w)
		3689	{
		3690	ev_cb_set (w) = current_coro;
		3691	switch_to (libev_coro);
		3692	}
		3693
		3694	That basically suspends the coroutine inside C<wait_for_event> and
		3695	continues the libev coroutine, which, when appropriate, switches back to
		3696	this or any other coroutine. I am sure if you sue this your own :)
		3697
		3698	You can do similar tricks if you have, say, threads with an event queue -
		3699	instead of storing a coroutine, you store the queue object and instead of
		3700	switching to a coroutine, you push the watcher onto the queue and notify
		3701	any waiters.
		3702
		3703	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3704	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3705
		3706	// my_ev.h
		3707	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3708	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3709	#include "../libev/ev.h"
		3710
		3711	// my_ev.c
		3712	#define EV_H "my_ev.h"
		3713	#include "../libev/ev.c"
		3714
		3715	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3716	F<my_ev.c> into your project. When properly specifying include paths, you
		3717	can even use F<ev.h> as header file name directly.
3470		3718
3471		3719
3472	=head1 LIBEVENT EMULATION	3720	=head1 LIBEVENT EMULATION
3473		3721
3474	Libev offers a compatibility emulation layer for libevent. It cannot	3722	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3964	F<event.h> that are not directly supported by the libev core alone.	4212	F<event.h> that are not directly supported by the libev core alone.
3965		4213
3966	In standalone mode, libev will still try to automatically deduce the	4214	In standalone mode, libev will still try to automatically deduce the
3967	configuration, but has to be more conservative.	4215	configuration, but has to be more conservative.
3968		4216
		4217	=item EV_USE_FLOOR
		4218
		4219	If defined to be C<1>, libev will use the C<floor ()> function for its
		4220	periodic reschedule calculations, otherwise libev will fall back on a
		4221	portable (slower) implementation. If you enable this, you usually have to
		4222	link against libm or something equivalent. Enabling this when the C<floor>
		4223	function is not available will fail, so the safe default is to not enable
		4224	this.
		4225
3969	=item EV_USE_MONOTONIC	4226	=item EV_USE_MONOTONIC
3970		4227
3971	If defined to be C<1>, libev will try to detect the availability of the	4228	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	4229	monotonic clock option at both compile time and runtime. Otherwise no
3973	use of the monotonic clock option will be attempted. If you enable this,	4230	use of the monotonic clock option will be attempted. If you enable this,
…		…
4404	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4661	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4405		4662
4406	#include "ev_cpp.h"	4663	#include "ev_cpp.h"
4407	#include "ev.c"	4664	#include "ev.c"
4408		4665
4409	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4666	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4410		4667
4411	=head2 THREADS AND COROUTINES	4668	=head2 THREADS AND COROUTINES
4412		4669
4413	=head3 THREADS	4670	=head3 THREADS
4414		4671
…		…
4465	default loop and triggering an C<ev_async> watcher from the default loop	4722	default loop and triggering an C<ev_async> watcher from the default loop
4466	watcher callback into the event loop interested in the signal.	4723	watcher callback into the event loop interested in the signal.
4467		4724
4468	=back	4725	=back
4469		4726
4470	=head4 THREAD LOCKING EXAMPLE	4727	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		4728
4608	=head3 COROUTINES	4729	=head3 COROUTINES
4609		4730
4610	Libev is very accommodating to coroutines ("cooperative threads"):	4731	Libev is very accommodating to coroutines ("cooperative threads"):
4611	libev fully supports nesting calls to its functions from different	4732	libev fully supports nesting calls to its functions from different
…		…
5120	The physical time that is observed. It is apparently strictly monotonic :)	5241	The physical time that is observed. It is apparently strictly monotonic :)
5121		5242
5122	=item wall-clock time	5243	=item wall-clock time
5123		5244
5124	The time and date as shown on clocks. Unlike real time, it can actually	5245	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	5246	be wrong and jump forwards and backwards, e.g. when you adjust your
5126	clock.	5247	clock.
5127		5248
5128	=item watcher	5249	=item watcher
5129		5250
5130	A data structure that describes interest in certain events. Watchers need	5251	A data structure that describes interest in certain events. Watchers need
…		…
5133	=back	5254	=back
5134		5255
5135	=head1 AUTHOR	5256	=head1 AUTHOR
5136		5257
5137	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5258	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5138	Magnusson and Emanuele Giaquinta.	5259	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5139		5260

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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 1.370 by root, Thu Jun 2 23:42:40 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 1.370 by root, Thu Jun 2 23:42:40 2011 UTC