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

Comparing libev/ev.pod (file contents):
Revision 1.121 by root, Mon Jan 28 12:13:54 2008 UTC vs.
Revision 1.144 by root, Mon Apr 7 12:33:29 2008 UTC

…		…
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
13	ev_io stdin_watcher;	16	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	17	ev_timer timeout_watcher;
15		18
		19	// all watcher callbacks have a similar signature
16	/* called when data readable on stdin */	20	// this callback is called when data is readable on stdin
17	static void	21	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	22	stdin_cb (EV_P_ struct ev_io *w, int revents)
19	{	23	{
20	/* puts ("stdin ready"); */	24	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	25	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	31	}
24		32
		33	// another callback, this time for a time-out
25	static void	34	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
27	{	36	{
28	/* puts ("timeout"); */	37	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	40	}
31		41
32	int	42	int
33	main (void)	43	main (void)
34	{	44	{
		45	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	46	struct ev_loop *loop = ev_default_loop (0);
36		47
37	/* initialise an io watcher, then start it */	48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /STDIN_FILENO/ 0, EV_READ);	50	ev_io_init (&stdin_watcher, stdin_cb, /STDIN_FILENO/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	51	ev_io_start (loop, &stdin_watcher);
40		52
		53	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	54	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	56	ev_timer_start (loop, &timeout_watcher);
44		57
45	/* loop till timeout or data ready */	58	// now wait for events to arrive
46	ev_loop (loop, 0);	59	ev_loop (loop, 0);
47		60
		61	// unloop was called, so exit
48	return 0;	62	return 0;
49	}	63	}
50		64
51	=head1 DESCRIPTION	65	=head1 DESCRIPTION
52		66
53	The newest version of this document is also available as a html-formatted	67	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	68	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	69	time: L<http://cvs.schmorp.de/libev/ev.html>.
56		70
57	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occurring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
…		…
84	L<benchmark\|http://libev.schmorp.de/bench.html> comparing it to libevent	98	L<benchmark\|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	99	for example).
86		100
87	=head2 CONVENTIONS	101	=head2 CONVENTIONS
88		102
89	Libev is very configurable. In this manual the default configuration will	103	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	104	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	105	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	106	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	107	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	108	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		109	this argument.
95		110
96	=head2 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
97		112
98	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
…		…
241		256
242	An event loop is described by a C<struct ev_loop *>. The library knows two	257	An event loop is described by a C<struct ev_loop *>. The library knows two
243	types of such loops, the I<default> loop, which supports signals and child	258	types of such loops, the I<default> loop, which supports signals and child
244	events, and dynamically created loops which do not.	259	events, and dynamically created loops which do not.
245		260
246	If you use threads, a common model is to run the default event loop
247	in your main thread (or in a separate thread) and for each thread you
248	create, you also create another event loop. Libev itself does no locking
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252
253	=over 4	261	=over 4
254		262
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	263	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		264
257	This will initialise the default event loop if it hasn't been initialised	265	This will initialise the default event loop if it hasn't been initialised
…		…
259	false. If it already was initialised it simply returns it (and ignores the	267	false. If it already was initialised it simply returns it (and ignores the
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	268	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		269
262	If you don't know what event loop to use, use the one returned from this	270	If you don't know what event loop to use, use the one returned from this
263	function.	271	function.
		272
		273	Note that this function is I<not> thread-safe, so if you want to use it
		274	from multiple threads, you have to lock (note also that this is unlikely,
		275	as loops cannot bes hared easily between threads anyway).
264		276
265	The default loop is the only loop that can handle C<ev_signal> and	277	The default loop is the only loop that can handle C<ev_signal> and
266	C<ev_child> watchers, and to do this, it always registers a handler	278	C<ev_child> watchers, and to do this, it always registers a handler
267	for C<SIGCHLD>. If this is a problem for your app you can either	279	for C<SIGCHLD>. If this is a problem for your app you can either
268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	280	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
297	enabling this flag.	309	enabling this flag.
298		310
299	This works by calling C<getpid ()> on every iteration of the loop,	311	This works by calling C<getpid ()> on every iteration of the loop,
300	and thus this might slow down your event loop if you do a lot of loop	312	and thus this might slow down your event loop if you do a lot of loop
301	iterations and little real work, but is usually not noticeable (on my	313	iterations and little real work, but is usually not noticeable (on my
302	Linux system for example, C<getpid> is actually a simple 5-insn sequence	314	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
303	without a syscall and thus I<very> fast, but my Linux system also has	315	without a syscall and thus I<very> fast, but my GNU/Linux system also has
304	C<pthread_atfork> which is even faster).	316	C<pthread_atfork> which is even faster).
305		317
306	The big advantage of this flag is that you can forget about fork (and	318	The big advantage of this flag is that you can forget about fork (and
307	forget about forgetting to tell libev about forking) when you use this	319	forget about forgetting to tell libev about forking) when you use this
308	flag.	320	flag.
…		…
339	For few fds, this backend is a bit little slower than poll and select,	351	For few fds, this backend is a bit little slower than poll and select,
340	but it scales phenomenally better. While poll and select usually scale	352	but it scales phenomenally better. While poll and select usually scale
341	like O(total_fds) where n is the total number of fds (or the highest fd),	353	like O(total_fds) where n is the total number of fds (or the highest fd),
342	epoll scales either O(1) or O(active_fds). The epoll design has a number	354	epoll scales either O(1) or O(active_fds). The epoll design has a number
343	of shortcomings, such as silently dropping events in some hard-to-detect	355	of shortcomings, such as silently dropping events in some hard-to-detect
344	cases and rewiring a syscall per fd change, no fork support and bad	356	cases and requiring a syscall per fd change, no fork support and bad
345	support for dup.	357	support for dup.
346		358
347	While stopping, setting and starting an I/O watcher in the same iteration	359	While stopping, setting and starting an I/O watcher in the same iteration
348	will result in some caching, there is still a syscall per such incident	360	will result in some caching, there is still a syscall per such incident
349	(because the fd could point to a different file description now), so its	361	(because the fd could point to a different file description now), so its
…		…
451	Similar to C<ev_default_loop>, but always creates a new event loop that is	463	Similar to C<ev_default_loop>, but always creates a new event loop that is
452	always distinct from the default loop. Unlike the default loop, it cannot	464	always distinct from the default loop. Unlike the default loop, it cannot
453	handle signal and child watchers, and attempts to do so will be greeted by	465	handle signal and child watchers, and attempts to do so will be greeted by
454	undefined behaviour (or a failed assertion if assertions are enabled).	466	undefined behaviour (or a failed assertion if assertions are enabled).
455		467
		468	Note that this function I<is> thread-safe, and the recommended way to use
		469	libev with threads is indeed to create one loop per thread, and using the
		470	default loop in the "main" or "initial" thread.
		471
456	Example: Try to create a event loop that uses epoll and nothing else.	472	Example: Try to create a event loop that uses epoll and nothing else.
457		473
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);	474	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);
459	if (!epoller)	475	if (!epoller)
460	fatal ("no epoll found here, maybe it hides under your chair");	476	fatal ("no epoll found here, maybe it hides under your chair");
…		…
505	=item ev_loop_fork (loop)	521	=item ev_loop_fork (loop)
506		522
507	Like C<ev_default_fork>, but acts on an event loop created by	523	Like C<ev_default_fork>, but acts on an event loop created by
508	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	524	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
509	after fork, and how you do this is entirely your own problem.	525	after fork, and how you do this is entirely your own problem.
		526
		527	=item int ev_is_default_loop (loop)
		528
		529	Returns true when the given loop actually is the default loop, false otherwise.
510		530
511	=item unsigned int ev_loop_count (loop)	531	=item unsigned int ev_loop_count (loop)
512		532
513	Returns the count of loop iterations for the loop, which is identical to	533	Returns the count of loop iterations for the loop, which is identical to
514	the number of times libev did poll for new events. It starts at C<0> and	534	the number of times libev did poll for new events. It starts at C<0> and
…		…
774	=item C<EV_FORK>	794	=item C<EV_FORK>
775		795
776	The event loop has been resumed in the child process after fork (see	796	The event loop has been resumed in the child process after fork (see
777	C<ev_fork>).	797	C<ev_fork>).
778		798
		799	=item C<EV_ASYNC>
		800
		801	The given async watcher has been asynchronously notified (see C<ev_async>).
		802
779	=item C<EV_ERROR>	803	=item C<EV_ERROR>
780		804
781	An unspecified error has occured, the watcher has been stopped. This might	805	An unspecified error has occured, the watcher has been stopped. This might
782	happen because the watcher could not be properly started because libev	806	happen because the watcher could not be properly started because libev
783	ran out of memory, a file descriptor was found to be closed or any other	807	ran out of memory, a file descriptor was found to be closed or any other
…		…
1062	To support fork in your programs, you either have to call	1086	To support fork in your programs, you either have to call
1063	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1087	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1064	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1088	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1065	C<EVBACKEND_POLL>.	1089	C<EVBACKEND_POLL>.
1066		1090
		1091	=head3 The special problem of SIGPIPE
		1092
		1093	While not really specific to libev, it is easy to forget about SIGPIPE:
		1094	when reading from a pipe whose other end has been closed, your program
		1095	gets send a SIGPIPE, which, by default, aborts your program. For most
		1096	programs this is sensible behaviour, for daemons, this is usually
		1097	undesirable.
		1098
		1099	So when you encounter spurious, unexplained daemon exits, make sure you
		1100	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1101	somewhere, as that would have given you a big clue).
		1102
1067		1103
1068	=head3 Watcher-Specific Functions	1104	=head3 Watcher-Specific Functions
1069		1105
1070	=over 4	1106	=over 4
1071		1107
…		…
1148	configure a timer to trigger every 10 seconds, then it will trigger at	1184	configure a timer to trigger every 10 seconds, then it will trigger at
1149	exactly 10 second intervals. If, however, your program cannot keep up with	1185	exactly 10 second intervals. If, however, your program cannot keep up with
1150	the timer (because it takes longer than those 10 seconds to do stuff) the	1186	the timer (because it takes longer than those 10 seconds to do stuff) the
1151	timer will not fire more than once per event loop iteration.	1187	timer will not fire more than once per event loop iteration.
1152		1188
1153	=item ev_timer_again (loop)	1189	=item ev_timer_again (loop, ev_timer *)
1154		1190
1155	This will act as if the timer timed out and restart it again if it is	1191	This will act as if the timer timed out and restart it again if it is
1156	repeating. The exact semantics are:	1192	repeating. The exact semantics are:
1157		1193
1158	If the timer is pending, its pending status is cleared.	1194	If the timer is pending, its pending status is cleared.
…		…
1267	In this configuration the watcher triggers an event at the wallclock time	1303	In this configuration the watcher triggers an event at the wallclock time
1268	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1304	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
1269	that is, if it is to be run at January 1st 2011 then it will run when the	1305	that is, if it is to be run at January 1st 2011 then it will run when the
1270	system time reaches or surpasses this time.	1306	system time reaches or surpasses this time.
1271		1307
1272	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1308	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1273		1309
1274	In this mode the watcher will always be scheduled to time out at the next	1310	In this mode the watcher will always be scheduled to time out at the next
1275	C<at + N * interval> time (for some integer N, which can also be negative)	1311	C<at + N * interval> time (for some integer N, which can also be negative)
1276	and then repeat, regardless of any time jumps.	1312	and then repeat, regardless of any time jumps.
1277		1313
…		…
1411	with the kernel (thus it coexists with your own signal handlers as long	1447	with the kernel (thus it coexists with your own signal handlers as long
1412	as you don't register any with libev). Similarly, when the last signal	1448	as you don't register any with libev). Similarly, when the last signal
1413	watcher for a signal is stopped libev will reset the signal handler to	1449	watcher for a signal is stopped libev will reset the signal handler to
1414	SIG_DFL (regardless of what it was set to before).	1450	SIG_DFL (regardless of what it was set to before).
1415		1451
		1452	If possible and supported, libev will install its handlers with
		1453	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1454	interrupted. If you have a problem with syscalls getting interrupted by
		1455	signals you can block all signals in an C<ev_check> watcher and unblock
		1456	them in an C<ev_prepare> watcher.
		1457
1416	=head3 Watcher-Specific Functions and Data Members	1458	=head3 Watcher-Specific Functions and Data Members
1417		1459
1418	=over 4	1460	=over 4
1419		1461
1420	=item ev_signal_init (ev_signal *, callback, int signum)	1462	=item ev_signal_init (ev_signal *, callback, int signum)
…		…
1428		1470
1429	The signal the watcher watches out for.	1471	The signal the watcher watches out for.
1430		1472
1431	=back	1473	=back
1432		1474
		1475	=head3 Examples
		1476
		1477	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1478
		1479	static void
		1480	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)
		1481	{
		1482	ev_unloop (loop, EVUNLOOP_ALL);
		1483	}
		1484
		1485	struct ev_signal signal_watcher;
		1486	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1487	ev_signal_start (loop, &sigint_cb);
		1488
1433		1489
1434	=head2 C<ev_child> - watch out for process status changes	1490	=head2 C<ev_child> - watch out for process status changes
1435		1491
1436	Child watchers trigger when your process receives a SIGCHLD in response to	1492	Child watchers trigger when your process receives a SIGCHLD in response to
1437	some child status changes (most typically when a child of yours dies).	1493	some child status changes (most typically when a child of yours dies). It
		1494	is permissible to install a child watcher I<after> the child has been
		1495	forked (which implies it might have already exited), as long as the event
		1496	loop isn't entered (or is continued from a watcher).
		1497
		1498	Only the default event loop is capable of handling signals, and therefore
		1499	you can only rgeister child watchers in the default event loop.
		1500
		1501	=head3 Process Interaction
		1502
		1503	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1504	initialised. This is necessary to guarantee proper behaviour even if
		1505	the first child watcher is started after the child exits. The occurance
		1506	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1507	synchronously as part of the event loop processing. Libev always reaps all
		1508	children, even ones not watched.
		1509
		1510	=head3 Overriding the Built-In Processing
		1511
		1512	Libev offers no special support for overriding the built-in child
		1513	processing, but if your application collides with libev's default child
		1514	handler, you can override it easily by installing your own handler for
		1515	C<SIGCHLD> after initialising the default loop, and making sure the
		1516	default loop never gets destroyed. You are encouraged, however, to use an
		1517	event-based approach to child reaping and thus use libev's support for
		1518	that, so other libev users can use C<ev_child> watchers freely.
1438		1519
1439	=head3 Watcher-Specific Functions and Data Members	1520	=head3 Watcher-Specific Functions and Data Members
1440		1521
1441	=over 4	1522	=over 4
1442		1523
…		…
1468		1549
1469	=back	1550	=back
1470		1551
1471	=head3 Examples	1552	=head3 Examples
1472		1553
1473	Example: Try to exit cleanly on SIGINT and SIGTERM.	1554	Example: C<fork()> a new process and install a child handler to wait for
		1555	its completion.
		1556
		1557	ev_child cw;
1474		1558
1475	static void	1559	static void
1476	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)	1560	child_cb (EV_P_ struct ev_child *w, int revents)
1477	{	1561	{
1478	ev_unloop (loop, EVUNLOOP_ALL);	1562	ev_child_stop (EV_A_ w);
		1563	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1479	}	1564	}
1480		1565
1481	struct ev_signal signal_watcher;	1566	pid_t pid = fork ();
1482	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1567
1483	ev_signal_start (loop, &sigint_cb);	1568	if (pid < 0)
		1569	// error
		1570	else if (pid == 0)
		1571	{
		1572	// the forked child executes here
		1573	exit (1);
		1574	}
		1575	else
		1576	{
		1577	ev_child_init (&cw, child_cb, pid, 0);
		1578	ev_child_start (EV_DEFAULT_ &cw);
		1579	}
1484		1580
1485		1581
1486	=head2 C<ev_stat> - did the file attributes just change?	1582	=head2 C<ev_stat> - did the file attributes just change?
1487		1583
1488	This watches a filesystem path for attribute changes. That is, it calls	1584	This watches a filesystem path for attribute changes. That is, it calls
…		…
1517	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1613	semantics of C<ev_stat> watchers, which means that libev sometimes needs
1518	to fall back to regular polling again even with inotify, but changes are	1614	to fall back to regular polling again even with inotify, but changes are
1519	usually detected immediately, and if the file exists there will be no	1615	usually detected immediately, and if the file exists there will be no
1520	polling.	1616	polling.
1521		1617
		1618	=head3 ABI Issues (Largefile Support)
		1619
		1620	Libev by default (unless the user overrides this) uses the default
		1621	compilation environment, which means that on systems with optionally
		1622	disabled large file support, you get the 32 bit version of the stat
		1623	structure. When using the library from programs that change the ABI to
		1624	use 64 bit file offsets the programs will fail. In that case you have to
		1625	compile libev with the same flags to get binary compatibility. This is
		1626	obviously the case with any flags that change the ABI, but the problem is
		1627	most noticably with ev_stat and largefile support.
		1628
1522	=head3 Inotify	1629	=head3 Inotify
1523		1630
1524	When C<inotify (7)> support has been compiled into libev (generally only	1631	When C<inotify (7)> support has been compiled into libev (generally only
1525	available on Linux) and present at runtime, it will be used to speed up	1632	available on Linux) and present at runtime, it will be used to speed up
1526	change detection where possible. The inotify descriptor will be created lazily	1633	change detection where possible. The inotify descriptor will be created lazily
…		…
1568		1675
1569	The callback will be receive C<EV_STAT> when a change was detected,	1676	The callback will be receive C<EV_STAT> when a change was detected,
1570	relative to the attributes at the time the watcher was started (or the	1677	relative to the attributes at the time the watcher was started (or the
1571	last change was detected).	1678	last change was detected).
1572		1679
1573	=item ev_stat_stat (ev_stat *)	1680	=item ev_stat_stat (loop, ev_stat *)
1574		1681
1575	Updates the stat buffer immediately with new values. If you change the	1682	Updates the stat buffer immediately with new values. If you change the
1576	watched path in your callback, you could call this fucntion to avoid	1683	watched path in your callback, you could call this fucntion to avoid
1577	detecting this change (while introducing a race condition). Can also be	1684	detecting this change (while introducing a race condition). Can also be
1578	useful simply to find out the new values.	1685	useful simply to find out the new values.
…		…
2046	believe me.	2153	believe me.
2047		2154
2048	=back	2155	=back
2049		2156
2050		2157
		2158	=head2 C<ev_async> - how to wake up another event loop
		2159
		2160	In general, you cannot use an C<ev_loop> from multiple threads or other
		2161	asynchronous sources such as signal handlers (as opposed to multiple event
		2162	loops - those are of course safe to use in different threads).
		2163
		2164	Sometimes, however, you need to wake up another event loop you do not
		2165	control, for example because it belongs to another thread. This is what
		2166	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2167	can signal it by calling C<ev_async_send>, which is thread- and signal
		2168	safe.
		2169
		2170	This functionality is very similar to C<ev_signal> watchers, as signals,
		2171	too, are asynchronous in nature, and signals, too, will be compressed
		2172	(i.e. the number of callback invocations may be less than the number of
		2173	C<ev_async_sent> calls).
		2174
		2175	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2176	just the default loop.
		2177
		2178	=head3 Queueing
		2179
		2180	C<ev_async> does not support queueing of data in any way. The reason
		2181	is that the author does not know of a simple (or any) algorithm for a
		2182	multiple-writer-single-reader queue that works in all cases and doesn't
		2183	need elaborate support such as pthreads.
		2184
		2185	That means that if you want to queue data, you have to provide your own
		2186	queue. But at least I can tell you would implement locking around your
		2187	queue:
		2188
		2189	=over 4
		2190
		2191	=item queueing from a signal handler context
		2192
		2193	To implement race-free queueing, you simply add to the queue in the signal
		2194	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2195	some fictitiuous SIGUSR1 handler:
		2196
		2197	static ev_async mysig;
		2198
		2199	static void
		2200	sigusr1_handler (void)
		2201	{
		2202	sometype data;
		2203
		2204	// no locking etc.
		2205	queue_put (data);
		2206	ev_async_send (EV_DEFAULT_ &mysig);
		2207	}
		2208
		2209	static void
		2210	mysig_cb (EV_P_ ev_async *w, int revents)
		2211	{
		2212	sometype data;
		2213	sigset_t block, prev;
		2214
		2215	sigemptyset (&block);
		2216	sigaddset (&block, SIGUSR1);
		2217	sigprocmask (SIG_BLOCK, &block, &prev);
		2218
		2219	while (queue_get (&data))
		2220	process (data);
		2221
		2222	if (sigismember (&prev, SIGUSR1)
		2223	sigprocmask (SIG_UNBLOCK, &block, 0);
		2224	}
		2225
		2226	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2227	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2228	either...).
		2229
		2230	=item queueing from a thread context
		2231
		2232	The strategy for threads is different, as you cannot (easily) block
		2233	threads but you can easily preempt them, so to queue safely you need to
		2234	employ a traditional mutex lock, such as in this pthread example:
		2235
		2236	static ev_async mysig;
		2237	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2238
		2239	static void
		2240	otherthread (void)
		2241	{
		2242	// only need to lock the actual queueing operation
		2243	pthread_mutex_lock (&mymutex);
		2244	queue_put (data);
		2245	pthread_mutex_unlock (&mymutex);
		2246
		2247	ev_async_send (EV_DEFAULT_ &mysig);
		2248	}
		2249
		2250	static void
		2251	mysig_cb (EV_P_ ev_async *w, int revents)
		2252	{
		2253	pthread_mutex_lock (&mymutex);
		2254
		2255	while (queue_get (&data))
		2256	process (data);
		2257
		2258	pthread_mutex_unlock (&mymutex);
		2259	}
		2260
		2261	=back
		2262
		2263
		2264	=head3 Watcher-Specific Functions and Data Members
		2265
		2266	=over 4
		2267
		2268	=item ev_async_init (ev_async *, callback)
		2269
		2270	Initialises and configures the async watcher - it has no parameters of any
		2271	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2272	believe me.
		2273
		2274	=item ev_async_send (loop, ev_async *)
		2275
		2276	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2277	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2278	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2279	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2280	section below on what exactly this means).
		2281
		2282	This call incurs the overhead of a syscall only once per loop iteration,
		2283	so while the overhead might be noticable, it doesn't apply to repeated
		2284	calls to C<ev_async_send>.
		2285
		2286	=item bool = ev_async_pending (ev_async *)
		2287
		2288	Returns a non-zero value when C<ev_async_send> has been called on the
		2289	watcher but the event has not yet been processed (or even noted) by the
		2290	event loop.
		2291
		2292	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2293	the loop iterates next and checks for the watcher to have become active,
		2294	it will reset the flag again. C<ev_async_pending> can be used to very
		2295	quickly check wether invoking the loop might be a good idea.
		2296
		2297	Not that this does I<not> check wether the watcher itself is pending, only
		2298	wether it has been requested to make this watcher pending.
		2299
		2300	=back
		2301
		2302
2051	=head1 OTHER FUNCTIONS	2303	=head1 OTHER FUNCTIONS
2052		2304
2053	There are some other functions of possible interest. Described. Here. Now.	2305	There are some other functions of possible interest. Described. Here. Now.
2054		2306
2055	=over 4	2307	=over 4
…		…
2295	io.start (fd, ev::READ);	2547	io.start (fd, ev::READ);
2296	}	2548	}
2297	};	2549	};
2298		2550
2299		2551
		2552	=head1 OTHER LANGUAGE BINDINGS
		2553
		2554	Libev does not offer other language bindings itself, but bindings for a
		2555	numbe rof languages exist in the form of third-party packages. If you know
		2556	any interesting language binding in addition to the ones listed here, drop
		2557	me a note.
		2558
		2559	=over 4
		2560
		2561	=item Perl
		2562
		2563	The EV module implements the full libev API and is actually used to test
		2564	libev. EV is developed together with libev. Apart from the EV core module,
		2565	there are additional modules that implement libev-compatible interfaces
		2566	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2567	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2568
		2569	It can be found and installed via CPAN, its homepage is found at
		2570	L<http://software.schmorp.de/pkg/EV>.
		2571
		2572	=item Ruby
		2573
		2574	Tony Arcieri has written a ruby extension that offers access to a subset
		2575	of the libev API and adds filehandle abstractions, asynchronous DNS and
		2576	more on top of it. It can be found via gem servers. Its homepage is at
		2577	L<http://rev.rubyforge.org/>.
		2578
		2579	=item D
		2580
		2581	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2582	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2583
		2584	=back
		2585
		2586
2300	=head1 MACRO MAGIC	2587	=head1 MACRO MAGIC
2301		2588
2302	Libev can be compiled with a variety of options, the most fundamantal	2589	Libev can be compiled with a variety of options, the most fundamantal
2303	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	2590	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2304	functions and callbacks have an initial C<struct ev_loop *> argument.	2591	functions and callbacks have an initial C<struct ev_loop *> argument.
…		…
2338		2625
2339	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	2626	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2340		2627
2341	Similar to the other two macros, this gives you the value of the default	2628	Similar to the other two macros, this gives you the value of the default
2342	loop, if multiple loops are supported ("ev loop default").	2629	loop, if multiple loops are supported ("ev loop default").
		2630
		2631	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2632
		2633	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2634	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2635	is undefined when the default loop has not been initialised by a previous
		2636	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2637
		2638	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2639	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2343		2640
2344	=back	2641	=back
2345		2642
2346	Example: Declare and initialise a check watcher, utilising the above	2643	Example: Declare and initialise a check watcher, utilising the above
2347	macros so it will work regardless of whether multiple loops are supported	2644	macros so it will work regardless of whether multiple loops are supported
…		…
2443		2740
2444	libev.m4	2741	libev.m4
2445		2742
2446	=head2 PREPROCESSOR SYMBOLS/MACROS	2743	=head2 PREPROCESSOR SYMBOLS/MACROS
2447		2744
2448	Libev can be configured via a variety of preprocessor symbols you have to define	2745	Libev can be configured via a variety of preprocessor symbols you have to
2449	before including any of its files. The default is not to build for multiplicity	2746	define before including any of its files. The default in the absense of
2450	and only include the select backend.	2747	autoconf is noted for every option.
2451		2748
2452	=over 4	2749	=over 4
2453		2750
2454	=item EV_STANDALONE	2751	=item EV_STANDALONE
2455		2752
…		…
2481	=item EV_USE_NANOSLEEP	2778	=item EV_USE_NANOSLEEP
2482		2779
2483	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	2780	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2484	and will use it for delays. Otherwise it will use C<select ()>.	2781	and will use it for delays. Otherwise it will use C<select ()>.
2485		2782
		2783	=item EV_USE_EVENTFD
		2784
		2785	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2786	available and will probe for kernel support at runtime. This will improve
		2787	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2788	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2789	2.7 or newer, otherwise disabled.
		2790
2486	=item EV_USE_SELECT	2791	=item EV_USE_SELECT
2487		2792
2488	If undefined or defined to be C<1>, libev will compile in support for the	2793	If undefined or defined to be C<1>, libev will compile in support for the
2489	C<select>(2) backend. No attempt at autodetection will be done: if no	2794	C<select>(2) backend. No attempt at autodetection will be done: if no
2490	other method takes over, select will be it. Otherwise the select backend	2795	other method takes over, select will be it. Otherwise the select backend
…		…
2526		2831
2527	=item EV_USE_EPOLL	2832	=item EV_USE_EPOLL
2528		2833
2529	If defined to be C<1>, libev will compile in support for the Linux	2834	If defined to be C<1>, libev will compile in support for the Linux
2530	C<epoll>(7) backend. Its availability will be detected at runtime,	2835	C<epoll>(7) backend. Its availability will be detected at runtime,
2531	otherwise another method will be used as fallback. This is the	2836	otherwise another method will be used as fallback. This is the preferred
2532	preferred backend for GNU/Linux systems.	2837	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2838	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2533		2839
2534	=item EV_USE_KQUEUE	2840	=item EV_USE_KQUEUE
2535		2841
2536	If defined to be C<1>, libev will compile in support for the BSD style	2842	If defined to be C<1>, libev will compile in support for the BSD style
2537	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	2843	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2556		2862
2557	=item EV_USE_INOTIFY	2863	=item EV_USE_INOTIFY
2558		2864
2559	If defined to be C<1>, libev will compile in support for the Linux inotify	2865	If defined to be C<1>, libev will compile in support for the Linux inotify
2560	interface to speed up C<ev_stat> watchers. Its actual availability will	2866	interface to speed up C<ev_stat> watchers. Its actual availability will
2561	be detected at runtime.	2867	be detected at runtime. If undefined, it will be enabled if the headers
		2868	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2869
		2870	=item EV_ATOMIC_T
		2871
		2872	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2873	access is atomic with respect to other threads or signal contexts. No such
		2874	type is easily found in the C language, so you can provide your own type
		2875	that you know is safe for your purposes. It is used both for signal handler "locking"
		2876	as well as for signal and thread safety in C<ev_async> watchers.
		2877
		2878	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2879	(from F<signal.h>), which is usually good enough on most platforms.
2562		2880
2563	=item EV_H	2881	=item EV_H
2564		2882
2565	The name of the F<ev.h> header file used to include it. The default if	2883	The name of the F<ev.h> header file used to include it. The default if
2566	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	2884	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
2632	defined to be C<0>, then they are not.	2950	defined to be C<0>, then they are not.
2633		2951
2634	=item EV_FORK_ENABLE	2952	=item EV_FORK_ENABLE
2635		2953
2636	If undefined or defined to be C<1>, then fork watchers are supported. If	2954	If undefined or defined to be C<1>, then fork watchers are supported. If
		2955	defined to be C<0>, then they are not.
		2956
		2957	=item EV_ASYNC_ENABLE
		2958
		2959	If undefined or defined to be C<1>, then async watchers are supported. If
2637	defined to be C<0>, then they are not.	2960	defined to be C<0>, then they are not.
2638		2961
2639	=item EV_MINIMAL	2962	=item EV_MINIMAL
2640		2963
2641	If you need to shave off some kilobytes of code at the expense of some	2964	If you need to shave off some kilobytes of code at the expense of some
…		…
2737		3060
2738	#include "ev_cpp.h"	3061	#include "ev_cpp.h"
2739	#include "ev.c"	3062	#include "ev.c"
2740		3063
2741		3064
		3065	=head1 THREADS AND COROUTINES
		3066
		3067	=head2 THREADS
		3068
		3069	Libev itself is completely threadsafe, but it uses no locking. This
		3070	means that you can use as many loops as you want in parallel, as long as
		3071	only one thread ever calls into one libev function with the same loop
		3072	parameter.
		3073
		3074	Or put differently: calls with different loop parameters can be done in
		3075	parallel from multiple threads, calls with the same loop parameter must be
		3076	done serially (but can be done from different threads, as long as only one
		3077	thread ever is inside a call at any point in time, e.g. by using a mutex
		3078	per loop).
		3079
		3080	If you want to know which design is best for your problem, then I cannot
		3081	help you but by giving some generic advice:
		3082
		3083	=over 4
		3084
		3085	=item * most applications have a main thread: use the default libev loop
		3086	in that thread, or create a seperate thread running only the default loop.
		3087
		3088	This helps integrating other libraries or software modules that use libev
		3089	themselves and don't care/know about threading.
		3090
		3091	=item * one loop per thread is usually a good model.
		3092
		3093	Doing this is almost never wrong, sometimes a better-performance model
		3094	exists, but it is always a good start.
		3095
		3096	=item * other models exist, such as the leader/follower pattern, where one
		3097	loop is handed through multiple threads in a kind of round-robbin fashion.
		3098
		3099	Chosing a model is hard - look around, learn, know that usually you cna do
		3100	better than you currently do :-)
		3101
		3102	=item * often you need to talk to some other thread which blocks in the
		3103	event loop - C<ev_async> watchers can be used to wake them up from other
		3104	threads safely (or from signal contexts...).
		3105
		3106	=back
		3107
		3108	=head2 COROUTINES
		3109
		3110	Libev is much more accomodating to coroutines ("cooperative threads"):
		3111	libev fully supports nesting calls to it's functions from different
		3112	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3113	different coroutines and switch freely between both coroutines running the
		3114	loop, as long as you don't confuse yourself). The only exception is that
		3115	you must not do this from C<ev_periodic> reschedule callbacks.
		3116
		3117	Care has been invested into making sure that libev does not keep local
		3118	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3119	switches.
		3120
		3121
2742	=head1 COMPLEXITIES	3122	=head1 COMPLEXITIES
2743		3123
2744	In this section the complexities of (many of) the algorithms used inside	3124	In this section the complexities of (many of) the algorithms used inside
2745	libev will be explained. For complexity discussions about backends see the	3125	libev will be explained. For complexity discussions about backends see the
2746	documentation for C<ev_default_init>.	3126	documentation for C<ev_default_init>.
…		…
2762	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3142	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2763		3143
2764	That means that changing a timer costs less than removing/adding them	3144	That means that changing a timer costs less than removing/adding them
2765	as only the relative motion in the event queue has to be paid for.	3145	as only the relative motion in the event queue has to be paid for.
2766		3146
2767	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3147	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2768		3148
2769	These just add the watcher into an array or at the head of a list.	3149	These just add the watcher into an array or at the head of a list.
2770		3150
2771	=item Stopping check/prepare/idle watchers: O(1)	3151	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2772		3152
2773	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3153	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2774		3154
2775	These watchers are stored in lists then need to be walked to find the	3155	These watchers are stored in lists then need to be walked to find the
2776	correct watcher to remove. The lists are usually short (you don't usually	3156	correct watcher to remove. The lists are usually short (you don't usually
…		…
2792	=item Priority handling: O(number_of_priorities)	3172	=item Priority handling: O(number_of_priorities)
2793		3173
2794	Priorities are implemented by allocating some space for each	3174	Priorities are implemented by allocating some space for each
2795	priority. When doing priority-based operations, libev usually has to	3175	priority. When doing priority-based operations, libev usually has to
2796	linearly search all the priorities, but starting/stopping and activating	3176	linearly search all the priorities, but starting/stopping and activating
2797	watchers becomes O(1) w.r.t. prioritiy handling.	3177	watchers becomes O(1) w.r.t. priority handling.
		3178
		3179	=item Sending an ev_async: O(1)
		3180
		3181	=item Processing ev_async_send: O(number_of_async_watchers)
		3182
		3183	=item Processing signals: O(max_signal_number)
		3184
		3185	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		3186	calls in the current loop iteration. Checking for async and signal events
		3187	involves iterating over all running async watchers or all signal numbers.
2798		3188
2799	=back	3189	=back
2800		3190
2801		3191
2802	=head1 Win32 platform limitations and workarounds	3192	=head1 Win32 platform limitations and workarounds

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Comparing libev/ev.pod (file contents): Revision 1.121 by root, Mon Jan 28 12:13:54 2008 UTC vs. Revision 1.144 by root, Mon Apr 7 12:33:29 2008 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.121 by root, Mon Jan 28 12:13:54 2008 UTC vs.
Revision 1.144 by root, Mon Apr 7 12:33:29 2008 UTC