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

Comparing libev/ev.pod (file contents):
Revision 1.134 by root, Sat Mar 8 07:04:56 2008 UTC vs.
Revision 1.156 by root, Tue May 20 20:00:34 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://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
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
59	these event sources and provide your program with events.	73	these event sources and provide your program with events.
60		74
…		…
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
…		…
181	See the description of C<ev_embed> watchers for more info.	196	See the description of C<ev_embed> watchers for more info.
182		197
183	=item ev_set_allocator (void (cb)(void *ptr, long size))	198	=item ev_set_allocator (void (cb)(void *ptr, long size))
184		199
185	Sets the allocation function to use (the prototype is similar - the	200	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	201	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
187	allocate and free memory (no surprises here). If it returns zero when	202	used to allocate and free memory (no surprises here). If it returns zero
188	memory needs to be allocated, the library might abort or take some	203	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	204	or take some potentially destructive action.
190	function.	205
		206	Since some systems (at least OpenBSD and Darwin) fail to implement
		207	correct C<realloc> semantics, libev will use a wrapper around the system
		208	C<realloc> and C<free> functions by default.
191		209
192	You could override this function in high-availability programs to, say,	210	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	211	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	212	or even to sleep a while and retry until some memory is available.
195		213
196	Example: Replace the libev allocator with one that waits a bit and then	214	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	215	retries (example requires a standards-compliant C<realloc>).
198		216
199	static void *	217	static void *
200	persistent_realloc (void *ptr, size_t size)	218	persistent_realloc (void *ptr, size_t size)
201	{	219	{
202	for (;;)	220	for (;;)
…		…
241		259
242	An event loop is described by a C<struct ev_loop *>. The library knows two	260	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	261	types of such loops, the I<default> loop, which supports signals and child
244	events, and dynamically created loops which do not.	262	events, and dynamically created loops which do not.
245		263
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	264	=over 4
254		265
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	266	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		267
257	This will initialise the default event loop if it hasn't been initialised	268	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	270	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).	271	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		272
262	If you don't know what event loop to use, use the one returned from this	273	If you don't know what event loop to use, use the one returned from this
263	function.	274	function.
		275
		276	Note that this function is I<not> thread-safe, so if you want to use it
		277	from multiple threads, you have to lock (note also that this is unlikely,
		278	as loops cannot bes hared easily between threads anyway).
264		279
265	The default loop is the only loop that can handle C<ev_signal> and	280	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	281	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	282	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	283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
297	enabling this flag.	312	enabling this flag.
298		313
299	This works by calling C<getpid ()> on every iteration of the loop,	314	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	315	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	316	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	317	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	318	without a syscall and thus I<very> fast, but my GNU/Linux system also has
304	C<pthread_atfork> which is even faster).	319	C<pthread_atfork> which is even faster).
305		320
306	The big advantage of this flag is that you can forget about fork (and	321	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	322	forget about forgetting to tell libev about forking) when you use this
308	flag.	323	flag.
…		…
321	To get good performance out of this backend you need a high amount of	336	To get good performance out of this backend you need a high amount of
322	parallelity (most of the file descriptors should be busy). If you are	337	parallelity (most of the file descriptors should be busy). If you are
323	writing a server, you should C<accept ()> in a loop to accept as many	338	writing a server, you should C<accept ()> in a loop to accept as many
324	connections as possible during one iteration. You might also want to have	339	connections as possible during one iteration. You might also want to have
325	a look at C<ev_set_io_collect_interval ()> to increase the amount of	340	a look at C<ev_set_io_collect_interval ()> to increase the amount of
326	readyness notifications you get per iteration.	341	readiness notifications you get per iteration.
327		342
328	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
329		344
330	And this is your standard poll(2) backend. It's more complicated	345	And this is your standard poll(2) backend. It's more complicated
331	than select, but handles sparse fds better and has no artificial	346	than select, but handles sparse fds better and has no artificial
…		…
339	For few fds, this backend is a bit little slower than poll and select,	354	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	355	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),	356	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	357	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	358	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	359	cases and requiring a syscall per fd change, no fork support and bad
345	support for dup.	360	support for dup.
346		361
347	While stopping, setting and starting an I/O watcher in the same iteration	362	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	363	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	364	(because the fd could point to a different file description now), so its
…		…
410	While this backend scales well, it requires one system call per active	425	While this backend scales well, it requires one system call per active
411	file descriptor per loop iteration. For small and medium numbers of file	426	file descriptor per loop iteration. For small and medium numbers of file
412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
413	might perform better.	428	might perform better.
414		429
415	On the positive side, ignoring the spurious readyness notifications, this	430	On the positive side, ignoring the spurious readiness notifications, this
416	backend actually performed to specification in all tests and is fully	431	backend actually performed to specification in all tests and is fully
417	embeddable, which is a rare feat among the OS-specific backends.	432	embeddable, which is a rare feat among the OS-specific backends.
418		433
419	=item C<EVBACKEND_ALL>	434	=item C<EVBACKEND_ALL>
420		435
…		…
450		465
451	Similar to C<ev_default_loop>, but always creates a new event loop that is	466	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	467	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	468	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).	469	undefined behaviour (or a failed assertion if assertions are enabled).
		470
		471	Note that this function I<is> thread-safe, and the recommended way to use
		472	libev with threads is indeed to create one loop per thread, and using the
		473	default loop in the "main" or "initial" thread.
455		474
456	Example: Try to create a event loop that uses epoll and nothing else.	475	Example: Try to create a event loop that uses epoll and nothing else.
457		476
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);	477	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);
459	if (!epoller)	478	if (!epoller)
…		…
1013	If you must do this, then force the use of a known-to-be-good backend	1032	If you must do this, then force the use of a known-to-be-good backend
1014	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1033	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1015	C<EVBACKEND_POLL>).	1034	C<EVBACKEND_POLL>).
1016		1035
1017	Another thing you have to watch out for is that it is quite easy to	1036	Another thing you have to watch out for is that it is quite easy to
1018	receive "spurious" readyness notifications, that is your callback might	1037	receive "spurious" readiness notifications, that is your callback might
1019	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1038	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1020	because there is no data. Not only are some backends known to create a	1039	because there is no data. Not only are some backends known to create a
1021	lot of those (for example solaris ports), it is very easy to get into	1040	lot of those (for example solaris ports), it is very easy to get into
1022	this situation even with a relatively standard program structure. Thus	1041	this situation even with a relatively standard program structure. Thus
1023	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1042	it is best to always use non-blocking I/O: An extra C<read>(2) returning
…		…
1069		1088
1070	To support fork in your programs, you either have to call	1089	To support fork in your programs, you either have to call
1071	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1090	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1072	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1091	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1073	C<EVBACKEND_POLL>.	1092	C<EVBACKEND_POLL>.
		1093
		1094	=head3 The special problem of SIGPIPE
		1095
		1096	While not really specific to libev, it is easy to forget about SIGPIPE:
		1097	when reading from a pipe whose other end has been closed, your program
		1098	gets send a SIGPIPE, which, by default, aborts your program. For most
		1099	programs this is sensible behaviour, for daemons, this is usually
		1100	undesirable.
		1101
		1102	So when you encounter spurious, unexplained daemon exits, make sure you
		1103	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1104	somewhere, as that would have given you a big clue).
1074		1105
1075		1106
1076	=head3 Watcher-Specific Functions	1107	=head3 Watcher-Specific Functions
1077		1108
1078	=over 4	1109	=over 4
…		…
1342	Simply stops and restarts the periodic watcher again. This is only useful	1373	Simply stops and restarts the periodic watcher again. This is only useful
1343	when you changed some parameters or the reschedule callback would return	1374	when you changed some parameters or the reschedule callback would return
1344	a different time than the last time it was called (e.g. in a crond like	1375	a different time than the last time it was called (e.g. in a crond like
1345	program when the crontabs have changed).	1376	program when the crontabs have changed).
1346		1377
		1378	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1379
		1380	When active, returns the absolute time that the watcher is supposed to
		1381	trigger next.
		1382
1347	=item ev_tstamp offset [read-write]	1383	=item ev_tstamp offset [read-write]
1348		1384
1349	When repeating, this contains the offset value, otherwise this is the	1385	When repeating, this contains the offset value, otherwise this is the
1350	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1386	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
1351		1387
…		…
1361	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]	1397	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]
1362		1398
1363	The current reschedule callback, or C<0>, if this functionality is	1399	The current reschedule callback, or C<0>, if this functionality is
1364	switched off. Can be changed any time, but changes only take effect when	1400	switched off. Can be changed any time, but changes only take effect when
1365	the periodic timer fires or C<ev_periodic_again> is being called.	1401	the periodic timer fires or C<ev_periodic_again> is being called.
1366
1367	=item ev_tstamp at [read-only]
1368
1369	When active, contains the absolute time that the watcher is supposed to
1370	trigger next.
1371		1402
1372	=back	1403	=back
1373		1404
1374	=head3 Examples	1405	=head3 Examples
1375		1406
…		…
1418	first watcher gets started will libev actually register a signal watcher	1449	first watcher gets started will libev actually register a signal watcher
1419	with the kernel (thus it coexists with your own signal handlers as long	1450	with the kernel (thus it coexists with your own signal handlers as long
1420	as you don't register any with libev). Similarly, when the last signal	1451	as you don't register any with libev). Similarly, when the last signal
1421	watcher for a signal is stopped libev will reset the signal handler to	1452	watcher for a signal is stopped libev will reset the signal handler to
1422	SIG_DFL (regardless of what it was set to before).	1453	SIG_DFL (regardless of what it was set to before).
		1454
		1455	If possible and supported, libev will install its handlers with
		1456	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1457	interrupted. If you have a problem with syscalls getting interrupted by
		1458	signals you can block all signals in an C<ev_check> watcher and unblock
		1459	them in an C<ev_prepare> watcher.
1423		1460
1424	=head3 Watcher-Specific Functions and Data Members	1461	=head3 Watcher-Specific Functions and Data Members
1425		1462
1426	=over 4	1463	=over 4
1427		1464
…		…
1573	as even with OS-supported change notifications, this can be	1610	as even with OS-supported change notifications, this can be
1574	resource-intensive.	1611	resource-intensive.
1575		1612
1576	At the time of this writing, only the Linux inotify interface is	1613	At the time of this writing, only the Linux inotify interface is
1577	implemented (implementing kqueue support is left as an exercise for the	1614	implemented (implementing kqueue support is left as an exercise for the
		1615	reader, note, however, that the author sees no way of implementing ev_stat
1578	reader). Inotify will be used to give hints only and should not change the	1616	semantics with kqueue). Inotify will be used to give hints only and should
1579	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1617	not change the semantics of C<ev_stat> watchers, which means that libev
1580	to fall back to regular polling again even with inotify, but changes are	1618	sometimes needs to fall back to regular polling again even with inotify,
1581	usually detected immediately, and if the file exists there will be no	1619	but changes are usually detected immediately, and if the file exists there
1582	polling.	1620	will be no polling.
		1621
		1622	=head3 ABI Issues (Largefile Support)
		1623
		1624	Libev by default (unless the user overrides this) uses the default
		1625	compilation environment, which means that on systems with optionally
		1626	disabled large file support, you get the 32 bit version of the stat
		1627	structure. When using the library from programs that change the ABI to
		1628	use 64 bit file offsets the programs will fail. In that case you have to
		1629	compile libev with the same flags to get binary compatibility. This is
		1630	obviously the case with any flags that change the ABI, but the problem is
		1631	most noticably with ev_stat and largefile support.
1583		1632
1584	=head3 Inotify	1633	=head3 Inotify
1585		1634
1586	When C<inotify (7)> support has been compiled into libev (generally only	1635	When C<inotify (7)> support has been compiled into libev (generally only
1587	available on Linux) and present at runtime, it will be used to speed up	1636	available on Linux) and present at runtime, it will be used to speed up
1588	change detection where possible. The inotify descriptor will be created lazily	1637	change detection where possible. The inotify descriptor will be created lazily
1589	when the first C<ev_stat> watcher is being started.	1638	when the first C<ev_stat> watcher is being started.
1590		1639
1591	Inotify presense does not change the semantics of C<ev_stat> watchers	1640	Inotify presence does not change the semantics of C<ev_stat> watchers
1592	except that changes might be detected earlier, and in some cases, to avoid	1641	except that changes might be detected earlier, and in some cases, to avoid
1593	making regular C<stat> calls. Even in the presense of inotify support	1642	making regular C<stat> calls. Even in the presence of inotify support
1594	there are many cases where libev has to resort to regular C<stat> polling.	1643	there are many cases where libev has to resort to regular C<stat> polling.
1595		1644
1596	(There is no support for kqueue, as apparently it cannot be used to	1645	(There is no support for kqueue, as apparently it cannot be used to
1597	implement this functionality, due to the requirement of having a file	1646	implement this functionality, due to the requirement of having a file
1598	descriptor open on the object at all times).	1647	descriptor open on the object at all times).
…		…
1601		1650
1602	The C<stat ()> syscall only supports full-second resolution portably, and	1651	The C<stat ()> syscall only supports full-second resolution portably, and
1603	even on systems where the resolution is higher, many filesystems still	1652	even on systems where the resolution is higher, many filesystems still
1604	only support whole seconds.	1653	only support whole seconds.
1605		1654
1606	That means that, if the time is the only thing that changes, you might	1655	That means that, if the time is the only thing that changes, you can
1607	miss updates: on the first update, C<ev_stat> detects a change and calls	1656	easily miss updates: on the first update, C<ev_stat> detects a change and
1608	your callback, which does something. When there is another update within	1657	calls your callback, which does something. When there is another update
1609	the same second, C<ev_stat> will be unable to detect it.	1658	within the same second, C<ev_stat> will be unable to detect it as the stat
		1659	data does not change.
1610		1660
1611	The solution to this is to delay acting on a change for a second (or till	1661	The solution to this is to delay acting on a change for slightly more
1612	the next second boundary), using a roughly one-second delay C<ev_timer>	1662	than a second (or till slightly after the next full second boundary), using
1613	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	1663	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1614	is added to work around small timing inconsistencies of some operating	1664	ev_timer_again (loop, w)>).
1615	systems.	1665
		1666	The C<.02> offset is added to work around small timing inconsistencies
		1667	of some operating systems (where the second counter of the current time
		1668	might be be delayed. One such system is the Linux kernel, where a call to
		1669	C<gettimeofday> might return a timestamp with a full second later than
		1670	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1671	update file times then there will be a small window where the kernel uses
		1672	the previous second to update file times but libev might already execute
		1673	the timer callback).
1616		1674
1617	=head3 Watcher-Specific Functions and Data Members	1675	=head3 Watcher-Specific Functions and Data Members
1618		1676
1619	=over 4	1677	=over 4
1620		1678
…		…
1626	C<path>. The C<interval> is a hint on how quickly a change is expected to	1684	C<path>. The C<interval> is a hint on how quickly a change is expected to
1627	be detected and should normally be specified as C<0> to let libev choose	1685	be detected and should normally be specified as C<0> to let libev choose
1628	a suitable value. The memory pointed to by C<path> must point to the same	1686	a suitable value. The memory pointed to by C<path> must point to the same
1629	path for as long as the watcher is active.	1687	path for as long as the watcher is active.
1630		1688
1631	The callback will be receive C<EV_STAT> when a change was detected,	1689	The callback will receive C<EV_STAT> when a change was detected, relative
1632	relative to the attributes at the time the watcher was started (or the	1690	to the attributes at the time the watcher was started (or the last change
1633	last change was detected).	1691	was detected).
1634		1692
1635	=item ev_stat_stat (loop, ev_stat *)	1693	=item ev_stat_stat (loop, ev_stat *)
1636		1694
1637	Updates the stat buffer immediately with new values. If you change the	1695	Updates the stat buffer immediately with new values. If you change the
1638	watched path in your callback, you could call this fucntion to avoid	1696	watched path in your callback, you could call this function to avoid
1639	detecting this change (while introducing a race condition). Can also be	1697	detecting this change (while introducing a race condition if you are not
1640	useful simply to find out the new values.	1698	the only one changing the path). Can also be useful simply to find out the
		1699	new values.
1641		1700
1642	=item ev_statdata attr [read-only]	1701	=item ev_statdata attr [read-only]
1643		1702
1644	The most-recently detected attributes of the file. Although the type is of	1703	The most-recently detected attributes of the file. Although the type is
1645	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	1704	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1646	suitable for your system. If the C<st_nlink> member is C<0>, then there	1705	suitable for your system, but you can only rely on the POSIX-standardised
		1706	members to be present. If the C<st_nlink> member is C<0>, then there was
1647	was some error while C<stat>ing the file.	1707	some error while C<stat>ing the file.
1648		1708
1649	=item ev_statdata prev [read-only]	1709	=item ev_statdata prev [read-only]
1650		1710
1651	The previous attributes of the file. The callback gets invoked whenever	1711	The previous attributes of the file. The callback gets invoked whenever
1652	C<prev> != C<attr>.	1712	C<prev> != C<attr>, or, more precisely, one or more of these members
		1713	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1714	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1653		1715
1654	=item ev_tstamp interval [read-only]	1716	=item ev_tstamp interval [read-only]
1655		1717
1656	The specified interval.	1718	The specified interval.
1657		1719
…		…
1711	}	1773	}
1712		1774
1713	...	1775	...
1714	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	1776	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1715	ev_stat_start (loop, &passwd);	1777	ev_stat_start (loop, &passwd);
1716	ev_timer_init (&timer, timer_cb, 0., 1.01);	1778	ev_timer_init (&timer, timer_cb, 0., 1.02);
1717		1779
1718		1780
1719	=head2 C<ev_idle> - when you've got nothing better to do...	1781	=head2 C<ev_idle> - when you've got nothing better to do...
1720		1782
1721	Idle watchers trigger events when no other events of the same or higher	1783	Idle watchers trigger events when no other events of the same or higher
…		…
1809		1871
1810	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	1872	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1811	priority, to ensure that they are being run before any other watchers	1873	priority, to ensure that they are being run before any other watchers
1812	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	1874	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1813	too) should not activate ("feed") events into libev. While libev fully	1875	too) should not activate ("feed") events into libev. While libev fully
1814	supports this, they will be called before other C<ev_check> watchers	1876	supports this, they might get executed before other C<ev_check> watchers
1815	did their job. As C<ev_check> watchers are often used to embed other	1877	did their job. As C<ev_check> watchers are often used to embed other
1816	(non-libev) event loops those other event loops might be in an unusable	1878	(non-libev) event loops those other event loops might be in an unusable
1817	state until their C<ev_check> watcher ran (always remind yourself to	1879	state until their C<ev_check> watcher ran (always remind yourself to
1818	coexist peacefully with others).	1880	coexist peacefully with others).
1819		1881
…		…
1834	=head3 Examples	1896	=head3 Examples
1835		1897
1836	There are a number of principal ways to embed other event loops or modules	1898	There are a number of principal ways to embed other event loops or modules
1837	into libev. Here are some ideas on how to include libadns into libev	1899	into libev. Here are some ideas on how to include libadns into libev
1838	(there is a Perl module named C<EV::ADNS> that does this, which you could	1900	(there is a Perl module named C<EV::ADNS> that does this, which you could
1839	use for an actually working example. Another Perl module named C<EV::Glib>	1901	use as a working example. Another Perl module named C<EV::Glib> embeds a
1840	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	1902	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1841	into the Glib event loop).	1903	Glib event loop).
1842		1904
1843	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	1905	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1844	and in a check watcher, destroy them and call into libadns. What follows	1906	and in a check watcher, destroy them and call into libadns. What follows
1845	is pseudo-code only of course. This requires you to either use a low	1907	is pseudo-code only of course. This requires you to either use a low
1846	priority for the check watcher or use C<ev_clear_pending> explicitly, as	1908	priority for the check watcher or use C<ev_clear_pending> explicitly, as
…		…
2236		2298
2237	This call incurs the overhead of a syscall only once per loop iteration,	2299	This call incurs the overhead of a syscall only once per loop iteration,
2238	so while the overhead might be noticable, it doesn't apply to repeated	2300	so while the overhead might be noticable, it doesn't apply to repeated
2239	calls to C<ev_async_send>.	2301	calls to C<ev_async_send>.
2240		2302
		2303	=item bool = ev_async_pending (ev_async *)
		2304
		2305	Returns a non-zero value when C<ev_async_send> has been called on the
		2306	watcher but the event has not yet been processed (or even noted) by the
		2307	event loop.
		2308
		2309	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2310	the loop iterates next and checks for the watcher to have become active,
		2311	it will reset the flag again. C<ev_async_pending> can be used to very
		2312	quickly check wether invoking the loop might be a good idea.
		2313
		2314	Not that this does I<not> check wether the watcher itself is pending, only
		2315	wether it has been requested to make this watcher pending.
		2316
2241	=back	2317	=back
2242		2318
2243		2319
2244	=head1 OTHER FUNCTIONS	2320	=head1 OTHER FUNCTIONS
2245		2321
…		…
2316		2392
2317	=item * Priorities are not currently supported. Initialising priorities	2393	=item * Priorities are not currently supported. Initialising priorities
2318	will fail and all watchers will have the same priority, even though there	2394	will fail and all watchers will have the same priority, even though there
2319	is an ev_pri field.	2395	is an ev_pri field.
2320		2396
		2397	=item * In libevent, the last base created gets the signals, in libev, the
		2398	first base created (== the default loop) gets the signals.
		2399
2321	=item * Other members are not supported.	2400	=item * Other members are not supported.
2322		2401
2323	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2402	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2324	to use the libev header file and library.	2403	to use the libev header file and library.
2325		2404
…		…
2488	io.start (fd, ev::READ);	2567	io.start (fd, ev::READ);
2489	}	2568	}
2490	};	2569	};
2491		2570
2492		2571
		2572	=head1 OTHER LANGUAGE BINDINGS
		2573
		2574	Libev does not offer other language bindings itself, but bindings for a
		2575	numbe rof languages exist in the form of third-party packages. If you know
		2576	any interesting language binding in addition to the ones listed here, drop
		2577	me a note.
		2578
		2579	=over 4
		2580
		2581	=item Perl
		2582
		2583	The EV module implements the full libev API and is actually used to test
		2584	libev. EV is developed together with libev. Apart from the EV core module,
		2585	there are additional modules that implement libev-compatible interfaces
		2586	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2587	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2588
		2589	It can be found and installed via CPAN, its homepage is found at
		2590	L<http://software.schmorp.de/pkg/EV>.
		2591
		2592	=item Ruby
		2593
		2594	Tony Arcieri has written a ruby extension that offers access to a subset
		2595	of the libev API and adds filehandle abstractions, asynchronous DNS and
		2596	more on top of it. It can be found via gem servers. Its homepage is at
		2597	L<http://rev.rubyforge.org/>.
		2598
		2599	=item D
		2600
		2601	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2602	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2603
		2604	=back
		2605
		2606
2493	=head1 MACRO MAGIC	2607	=head1 MACRO MAGIC
2494		2608
2495	Libev can be compiled with a variety of options, the most fundamantal	2609	Libev can be compiled with a variety of options, the most fundamantal
2496	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	2610	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2497	functions and callbacks have an initial C<struct ev_loop *> argument.	2611	functions and callbacks have an initial C<struct ev_loop *> argument.
…		…
2531		2645
2532	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	2646	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2533		2647
2534	Similar to the other two macros, this gives you the value of the default	2648	Similar to the other two macros, this gives you the value of the default
2535	loop, if multiple loops are supported ("ev loop default").	2649	loop, if multiple loops are supported ("ev loop default").
		2650
		2651	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2652
		2653	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2654	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2655	is undefined when the default loop has not been initialised by a previous
		2656	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2657
		2658	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2659	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2536		2660
2537	=back	2661	=back
2538		2662
2539	Example: Declare and initialise a check watcher, utilising the above	2663	Example: Declare and initialise a check watcher, utilising the above
2540	macros so it will work regardless of whether multiple loops are supported	2664	macros so it will work regardless of whether multiple loops are supported
…		…
2636		2760
2637	libev.m4	2761	libev.m4
2638		2762
2639	=head2 PREPROCESSOR SYMBOLS/MACROS	2763	=head2 PREPROCESSOR SYMBOLS/MACROS
2640		2764
2641	Libev can be configured via a variety of preprocessor symbols you have to define	2765	Libev can be configured via a variety of preprocessor symbols you have to
2642	before including any of its files. The default is not to build for multiplicity	2766	define before including any of its files. The default in the absense of
2643	and only include the select backend.	2767	autoconf is noted for every option.
2644		2768
2645	=over 4	2769	=over 4
2646		2770
2647	=item EV_STANDALONE	2771	=item EV_STANDALONE
2648		2772
…		…
2674	=item EV_USE_NANOSLEEP	2798	=item EV_USE_NANOSLEEP
2675		2799
2676	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	2800	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2677	and will use it for delays. Otherwise it will use C<select ()>.	2801	and will use it for delays. Otherwise it will use C<select ()>.
2678		2802
		2803	=item EV_USE_EVENTFD
		2804
		2805	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2806	available and will probe for kernel support at runtime. This will improve
		2807	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2808	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2809	2.7 or newer, otherwise disabled.
		2810
2679	=item EV_USE_SELECT	2811	=item EV_USE_SELECT
2680		2812
2681	If undefined or defined to be C<1>, libev will compile in support for the	2813	If undefined or defined to be C<1>, libev will compile in support for the
2682	C<select>(2) backend. No attempt at autodetection will be done: if no	2814	C<select>(2) backend. No attempt at autodetection will be done: if no
2683	other method takes over, select will be it. Otherwise the select backend	2815	other method takes over, select will be it. Otherwise the select backend
…		…
2719		2851
2720	=item EV_USE_EPOLL	2852	=item EV_USE_EPOLL
2721		2853
2722	If defined to be C<1>, libev will compile in support for the Linux	2854	If defined to be C<1>, libev will compile in support for the Linux
2723	C<epoll>(7) backend. Its availability will be detected at runtime,	2855	C<epoll>(7) backend. Its availability will be detected at runtime,
2724	otherwise another method will be used as fallback. This is the	2856	otherwise another method will be used as fallback. This is the preferred
2725	preferred backend for GNU/Linux systems.	2857	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2858	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2726		2859
2727	=item EV_USE_KQUEUE	2860	=item EV_USE_KQUEUE
2728		2861
2729	If defined to be C<1>, libev will compile in support for the BSD style	2862	If defined to be C<1>, libev will compile in support for the BSD style
2730	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	2863	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2749		2882
2750	=item EV_USE_INOTIFY	2883	=item EV_USE_INOTIFY
2751		2884
2752	If defined to be C<1>, libev will compile in support for the Linux inotify	2885	If defined to be C<1>, libev will compile in support for the Linux inotify
2753	interface to speed up C<ev_stat> watchers. Its actual availability will	2886	interface to speed up C<ev_stat> watchers. Its actual availability will
2754	be detected at runtime.	2887	be detected at runtime. If undefined, it will be enabled if the headers
		2888	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2755		2889
2756	=item EV_ATOMIC_T	2890	=item EV_ATOMIC_T
2757		2891
2758	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	2892	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2759	access is atomic with respect to other threads or signal contexts. No such	2893	access is atomic with respect to other threads or signal contexts. No such
…		…
2846	defined to be C<0>, then they are not.	2980	defined to be C<0>, then they are not.
2847		2981
2848	=item EV_MINIMAL	2982	=item EV_MINIMAL
2849		2983
2850	If you need to shave off some kilobytes of code at the expense of some	2984	If you need to shave off some kilobytes of code at the expense of some
2851	speed, define this symbol to C<1>. Currently only used for gcc to override	2985	speed, define this symbol to C<1>. Currently this is used to override some
2852	some inlining decisions, saves roughly 30% codesize of amd64.	2986	inlining decisions, saves roughly 30% codesize of amd64. It also selects a
		2987	much smaller 2-heap for timer management over the default 4-heap.
2853		2988
2854	=item EV_PID_HASHSIZE	2989	=item EV_PID_HASHSIZE
2855		2990
2856	C<ev_child> watchers use a small hash table to distribute workload by	2991	C<ev_child> watchers use a small hash table to distribute workload by
2857	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	2992	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2863	C<ev_stat> watchers use a small hash table to distribute workload by	2998	C<ev_stat> watchers use a small hash table to distribute workload by
2864	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	2999	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2865	usually more than enough. If you need to manage thousands of C<ev_stat>	3000	usually more than enough. If you need to manage thousands of C<ev_stat>
2866	watchers you might want to increase this value (I<must> be a power of	3001	watchers you might want to increase this value (I<must> be a power of
2867	two).	3002	two).
		3003
		3004	=item EV_USE_4HEAP
		3005
		3006	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3007	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3008	to C<1>. The 4-heap uses more complicated (longer) code but has
		3009	noticably faster performance with many (thousands) of watchers.
		3010
		3011	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3012	(disabled).
		3013
		3014	=item EV_HEAP_CACHE_AT
		3015
		3016	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3017	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3018	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3019	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3020	but avoids random read accesses on heap changes. This improves performance
		3021	noticably with with many (hundreds) of watchers.
		3022
		3023	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3024	(disabled).
2868		3025
2869	=item EV_COMMON	3026	=item EV_COMMON
2870		3027
2871	By default, all watchers have a C<void *data> member. By redefining	3028	By default, all watchers have a C<void *data> member. By redefining
2872	this macro to a something else you can include more and other types of	3029	this macro to a something else you can include more and other types of
…		…
2946		3103
2947	#include "ev_cpp.h"	3104	#include "ev_cpp.h"
2948	#include "ev.c"	3105	#include "ev.c"
2949		3106
2950		3107
		3108	=head1 THREADS AND COROUTINES
		3109
		3110	=head2 THREADS
		3111
		3112	Libev itself is completely threadsafe, but it uses no locking. This
		3113	means that you can use as many loops as you want in parallel, as long as
		3114	only one thread ever calls into one libev function with the same loop
		3115	parameter.
		3116
		3117	Or put differently: calls with different loop parameters can be done in
		3118	parallel from multiple threads, calls with the same loop parameter must be
		3119	done serially (but can be done from different threads, as long as only one
		3120	thread ever is inside a call at any point in time, e.g. by using a mutex
		3121	per loop).
		3122
		3123	If you want to know which design is best for your problem, then I cannot
		3124	help you but by giving some generic advice:
		3125
		3126	=over 4
		3127
		3128	=item * most applications have a main thread: use the default libev loop
		3129	in that thread, or create a seperate thread running only the default loop.
		3130
		3131	This helps integrating other libraries or software modules that use libev
		3132	themselves and don't care/know about threading.
		3133
		3134	=item * one loop per thread is usually a good model.
		3135
		3136	Doing this is almost never wrong, sometimes a better-performance model
		3137	exists, but it is always a good start.
		3138
		3139	=item * other models exist, such as the leader/follower pattern, where one
		3140	loop is handed through multiple threads in a kind of round-robbin fashion.
		3141
		3142	Chosing a model is hard - look around, learn, know that usually you cna do
		3143	better than you currently do :-)
		3144
		3145	=item * often you need to talk to some other thread which blocks in the
		3146	event loop - C<ev_async> watchers can be used to wake them up from other
		3147	threads safely (or from signal contexts...).
		3148
		3149	=back
		3150
		3151	=head2 COROUTINES
		3152
		3153	Libev is much more accomodating to coroutines ("cooperative threads"):
		3154	libev fully supports nesting calls to it's functions from different
		3155	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3156	different coroutines and switch freely between both coroutines running the
		3157	loop, as long as you don't confuse yourself). The only exception is that
		3158	you must not do this from C<ev_periodic> reschedule callbacks.
		3159
		3160	Care has been invested into making sure that libev does not keep local
		3161	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3162	switches.
		3163
		3164
2951	=head1 COMPLEXITIES	3165	=head1 COMPLEXITIES
2952		3166
2953	In this section the complexities of (many of) the algorithms used inside	3167	In this section the complexities of (many of) the algorithms used inside
2954	libev will be explained. For complexity discussions about backends see the	3168	libev will be explained. For complexity discussions about backends see the
2955	documentation for C<ev_default_init>.	3169	documentation for C<ev_default_init>.
…		…
2985	correct watcher to remove. The lists are usually short (you don't usually	3199	correct watcher to remove. The lists are usually short (you don't usually
2986	have many watchers waiting for the same fd or signal).	3200	have many watchers waiting for the same fd or signal).
2987		3201
2988	=item Finding the next timer in each loop iteration: O(1)	3202	=item Finding the next timer in each loop iteration: O(1)
2989		3203
2990	By virtue of using a binary heap, the next timer is always found at the	3204	By virtue of using a binary or 4-heap, the next timer is always found at a
2991	beginning of the storage array.	3205	fixed position in the storage array.
2992		3206
2993	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3207	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2994		3208
2995	A change means an I/O watcher gets started or stopped, which requires	3209	A change means an I/O watcher gets started or stopped, which requires
2996	libev to recalculate its status (and possibly tell the kernel, depending	3210	libev to recalculate its status (and possibly tell the kernel, depending
…		…
3025	model. Libev still offers limited functionality on this platform in	3239	model. Libev still offers limited functionality on this platform in
3026	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3240	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3027	descriptors. This only applies when using Win32 natively, not when using	3241	descriptors. This only applies when using Win32 natively, not when using
3028	e.g. cygwin.	3242	e.g. cygwin.
3029		3243
		3244	Lifting these limitations would basically require the full
		3245	re-implementation of the I/O system. If you are into these kinds of
		3246	things, then note that glib does exactly that for you in a very portable
		3247	way (note also that glib is the slowest event library known to man).
		3248
3030	There is no supported compilation method available on windows except	3249	There is no supported compilation method available on windows except
3031	embedding it into other applications.	3250	embedding it into other applications.
3032		3251
3033	Due to the many, low, and arbitrary limits on the win32 platform and the	3252	Due to the many, low, and arbitrary limits on the win32 platform and
3034	abysmal performance of winsockets, using a large number of sockets is not	3253	the abysmal performance of winsockets, using a large number of sockets
3035	recommended (and not reasonable). If your program needs to use more than	3254	is not recommended (and not reasonable). If your program needs to use
3036	a hundred or so sockets, then likely it needs to use a totally different	3255	more than a hundred or so sockets, then likely it needs to use a totally
3037	implementation for windows, as libev offers the POSIX model, which cannot	3256	different implementation for windows, as libev offers the POSIX readiness
3038	be implemented efficiently on windows (microsoft monopoly games).	3257	notification model, which cannot be implemented efficiently on windows
		3258	(microsoft monopoly games).
3039		3259
3040	=over 4	3260	=over 4
3041		3261
3042	=item The winsocket select function	3262	=item The winsocket select function
3043		3263
…		…
3057	Note that winsockets handling of fd sets is O(n), so you can easily get a	3277	Note that winsockets handling of fd sets is O(n), so you can easily get a
3058	complexity in the O(n²) range when using win32.	3278	complexity in the O(n²) range when using win32.
3059		3279
3060	=item Limited number of file descriptors	3280	=item Limited number of file descriptors
3061		3281
3062	Windows has numerous arbitrary (and low) limits on things. Early versions	3282	Windows has numerous arbitrary (and low) limits on things.
3063	of winsocket's select only supported waiting for a max. of C<64> handles	3283
		3284	Early versions of winsocket's select only supported waiting for a maximum
3064	(probably owning to the fact that all windows kernels can only wait for	3285	of C<64> handles (probably owning to the fact that all windows kernels
3065	C<64> things at the same time internally; microsoft recommends spawning a	3286	can only wait for C<64> things at the same time internally; microsoft
3066	chain of threads and wait for 63 handles and the previous thread in each).	3287	recommends spawning a chain of threads and wait for 63 handles and the
		3288	previous thread in each. Great).
3067		3289
3068	Newer versions support more handles, but you need to define C<FD_SETSIZE>	3290	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3069	to some high number (e.g. C<2048>) before compiling the winsocket select	3291	to some high number (e.g. C<2048>) before compiling the winsocket select
3070	call (which might be in libev or elsewhere, for example, perl does its own	3292	call (which might be in libev or elsewhere, for example, perl does its own
3071	select emulation on windows).	3293	select emulation on windows).
…		…
3083	calling select (O(n²)) will likely make this unworkable.	3305	calling select (O(n²)) will likely make this unworkable.
3084		3306
3085	=back	3307	=back
3086		3308
3087		3309
		3310	=head1 PORTABILITY REQUIREMENTS
		3311
		3312	In addition to a working ISO-C implementation, libev relies on a few
		3313	additional extensions:
		3314
		3315	=over 4
		3316
		3317	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3318
		3319	The type C<sig_atomic_t volatile> (or whatever is defined as
		3320	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3321	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3322	believed to be sufficiently portable.
		3323
		3324	=item C<sigprocmask> must work in a threaded environment
		3325
		3326	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3327	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3328	pthread implementations will either allow C<sigprocmask> in the "main
		3329	thread" or will block signals process-wide, both behaviours would
		3330	be compatible with libev. Interaction between C<sigprocmask> and
		3331	C<pthread_sigmask> could complicate things, however.
		3332
		3333	The most portable way to handle signals is to block signals in all threads
		3334	except the initial one, and run the default loop in the initial thread as
		3335	well.
		3336
		3337	=item C<long> must be large enough for common memory allocation sizes
		3338
		3339	To improve portability and simplify using libev, libev uses C<long>
		3340	internally instead of C<size_t> when allocating its data structures. On
		3341	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3342	is still at least 31 bits everywhere, which is enough for hundreds of
		3343	millions of watchers.
		3344
		3345	=item C<double> must hold a time value in seconds with enough accuracy
		3346
		3347	The type C<double> is used to represent timestamps. It is required to
		3348	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3349	enough for at least into the year 4000. This requirement is fulfilled by
		3350	implementations implementing IEEE 754 (basically all existing ones).
		3351
		3352	=back
		3353
		3354	If you know of other additional requirements drop me a note.
		3355
		3356
		3357	=head1 VALGRIND
		3358
		3359	Valgrind has a special section here because it is a popular tool that is
		3360	highly useful, but valgrind reports are very hard to interpret.
		3361
		3362	If you think you found a bug (memory leak, uninitialised data access etc.)
		3363	in libev, then check twice: If valgrind reports something like:
		3364
		3365	==2274== definitely lost: 0 bytes in 0 blocks.
		3366	==2274== possibly lost: 0 bytes in 0 blocks.
		3367	==2274== still reachable: 256 bytes in 1 blocks.
		3368
		3369	then there is no memory leak. Similarly, under some circumstances,
		3370	valgrind might report kernel bugs as if it were a bug in libev, or it
		3371	might be confused (it is a very good tool, but only a tool).
		3372
		3373	If you are unsure about something, feel free to contact the mailing list
		3374	with the full valgrind report and an explanation on why you think this is
		3375	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3376	no bug" answer and take the chance of learning how to interpret valgrind
		3377	properly.
		3378
		3379	If you need, for some reason, empty reports from valgrind for your project
		3380	I suggest using suppression lists.
		3381
		3382
3088	=head1 AUTHOR	3383	=head1 AUTHOR
3089		3384
3090	Marc Lehmann <libev@schmorp.de>.	3385	Marc Lehmann <libev@schmorp.de>.
3091		3386

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Revision 1.156 by root, Tue May 20 20:00:34 2008 UTC