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

Comparing libev/ev.pod (file contents):
Revision 1.120 by root, Fri Jan 25 15:45:09 2008 UTC vs.
Revision 1.159 by root, Thu May 22 02:44:57 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)
…		…
505	=item ev_loop_fork (loop)	524	=item ev_loop_fork (loop)
506		525
507	Like C<ev_default_fork>, but acts on an event loop created by	526	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	527	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.	528	after fork, and how you do this is entirely your own problem.
		529
		530	=item int ev_is_default_loop (loop)
		531
		532	Returns true when the given loop actually is the default loop, false otherwise.
510		533
511	=item unsigned int ev_loop_count (loop)	534	=item unsigned int ev_loop_count (loop)
512		535
513	Returns the count of loop iterations for the loop, which is identical to	536	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	537	the number of times libev did poll for new events. It starts at C<0> and
…		…
666	interval to a value near C<0.1> or so, which is often enough for	689	interval to a value near C<0.1> or so, which is often enough for
667	interactive servers (of course not for games), likewise for timeouts. It	690	interactive servers (of course not for games), likewise for timeouts. It
668	usually doesn't make much sense to set it to a lower value than C<0.01>,	691	usually doesn't make much sense to set it to a lower value than C<0.01>,
669	as this approsaches the timing granularity of most systems.	692	as this approsaches the timing granularity of most systems.
670		693
		694	=item ev_loop_verify (loop)
		695
		696	This function only does something when C<EV_VERIFY> support has been
		697	compiled in. It tries to go through all internal structures and checks
		698	them for validity. If anything is found to be inconsistent, it will print
		699	an error message to standard error and call C<abort ()>.
		700
		701	This can be used to catch bugs inside libev itself: under normal
		702	circumstances, this function will never abort as of course libev keeps its
		703	data structures consistent.
		704
671	=back	705	=back
672		706
673		707
674	=head1 ANATOMY OF A WATCHER	708	=head1 ANATOMY OF A WATCHER
675		709
…		…
773		807
774	=item C<EV_FORK>	808	=item C<EV_FORK>
775		809
776	The event loop has been resumed in the child process after fork (see	810	The event loop has been resumed in the child process after fork (see
777	C<ev_fork>).	811	C<ev_fork>).
		812
		813	=item C<EV_ASYNC>
		814
		815	The given async watcher has been asynchronously notified (see C<ev_async>).
778		816
779	=item C<EV_ERROR>	817	=item C<EV_ERROR>
780		818
781	An unspecified error has occured, the watcher has been stopped. This might	819	An unspecified error has occured, the watcher has been stopped. This might
782	happen because the watcher could not be properly started because libev	820	happen because the watcher could not be properly started because libev
…		…
1005	If you must do this, then force the use of a known-to-be-good backend	1043	If you must do this, then force the use of a known-to-be-good backend
1006	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1044	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1007	C<EVBACKEND_POLL>).	1045	C<EVBACKEND_POLL>).
1008		1046
1009	Another thing you have to watch out for is that it is quite easy to	1047	Another thing you have to watch out for is that it is quite easy to
1010	receive "spurious" readyness notifications, that is your callback might	1048	receive "spurious" readiness notifications, that is your callback might
1011	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1049	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1012	because there is no data. Not only are some backends known to create a	1050	because there is no data. Not only are some backends known to create a
1013	lot of those (for example solaris ports), it is very easy to get into	1051	lot of those (for example solaris ports), it is very easy to get into
1014	this situation even with a relatively standard program structure. Thus	1052	this situation even with a relatively standard program structure. Thus
1015	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1053	it is best to always use non-blocking I/O: An extra C<read>(2) returning
…		…
1062	To support fork in your programs, you either have to call	1100	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,	1101	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	1102	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1065	C<EVBACKEND_POLL>.	1103	C<EVBACKEND_POLL>.
1066		1104
		1105	=head3 The special problem of SIGPIPE
		1106
		1107	While not really specific to libev, it is easy to forget about SIGPIPE:
		1108	when reading from a pipe whose other end has been closed, your program
		1109	gets send a SIGPIPE, which, by default, aborts your program. For most
		1110	programs this is sensible behaviour, for daemons, this is usually
		1111	undesirable.
		1112
		1113	So when you encounter spurious, unexplained daemon exits, make sure you
		1114	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1115	somewhere, as that would have given you a big clue).
		1116
1067		1117
1068	=head3 Watcher-Specific Functions	1118	=head3 Watcher-Specific Functions
1069		1119
1070	=over 4	1120	=over 4
1071		1121
…		…
1112		1162
1113	Timer watchers are simple relative timers that generate an event after a	1163	Timer watchers are simple relative timers that generate an event after a
1114	given time, and optionally repeating in regular intervals after that.	1164	given time, and optionally repeating in regular intervals after that.
1115		1165
1116	The timers are based on real time, that is, if you register an event that	1166	The timers are based on real time, that is, if you register an event that
1117	times out after an hour and you reset your system clock to last years	1167	times out after an hour and you reset your system clock to january last
1118	time, it will still time out after (roughly) and hour. "Roughly" because	1168	year, it will still time out after (roughly) and hour. "Roughly" because
1119	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1169	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1120	monotonic clock option helps a lot here).	1170	monotonic clock option helps a lot here).
1121		1171
1122	The relative timeouts are calculated relative to the C<ev_now ()>	1172	The relative timeouts are calculated relative to the C<ev_now ()>
1123	time. This is usually the right thing as this timestamp refers to the time	1173	time. This is usually the right thing as this timestamp refers to the time
…		…
1125	you suspect event processing to be delayed and you I<need> to base the timeout	1175	you suspect event processing to be delayed and you I<need> to base the timeout
1126	on the current time, use something like this to adjust for this:	1176	on the current time, use something like this to adjust for this:
1127		1177
1128	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1178	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1129		1179
1130	The callback is guarenteed to be invoked only when its timeout has passed,	1180	The callback is guarenteed to be invoked only after its timeout has passed,
1131	but if multiple timers become ready during the same loop iteration then	1181	but if multiple timers become ready during the same loop iteration then
1132	order of execution is undefined.	1182	order of execution is undefined.
1133		1183
1134	=head3 Watcher-Specific Functions and Data Members	1184	=head3 Watcher-Specific Functions and Data Members
1135		1185
…		…
1137		1187
1138	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1188	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1139		1189
1140	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1190	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1141		1191
1142	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1192	Configure the timer to trigger after C<after> seconds. If C<repeat>
1143	C<0.>, then it will automatically be stopped. If it is positive, then the	1193	is C<0.>, then it will automatically be stopped once the timeout is
1144	timer will automatically be configured to trigger again C<repeat> seconds	1194	reached. If it is positive, then the timer will automatically be
1145	later, again, and again, until stopped manually.	1195	configured to trigger again C<repeat> seconds later, again, and again,
		1196	until stopped manually.
1146		1197
1147	The timer itself will do a best-effort at avoiding drift, that is, if you	1198	The timer itself will do a best-effort at avoiding drift, that is, if
1148	configure a timer to trigger every 10 seconds, then it will trigger at	1199	you configure a timer to trigger every 10 seconds, then it will normally
1149	exactly 10 second intervals. If, however, your program cannot keep up with	1200	trigger at exactly 10 second intervals. If, however, your program cannot
1150	the timer (because it takes longer than those 10 seconds to do stuff) the	1201	keep up with the timer (because it takes longer than those 10 seconds to
1151	timer will not fire more than once per event loop iteration.	1202	do stuff) the timer will not fire more than once per event loop iteration.
1152		1203
1153	=item ev_timer_again (loop)	1204	=item ev_timer_again (loop, ev_timer *)
1154		1205
1155	This will act as if the timer timed out and restart it again if it is	1206	This will act as if the timer timed out and restart it again if it is
1156	repeating. The exact semantics are:	1207	repeating. The exact semantics are:
1157		1208
1158	If the timer is pending, its pending status is cleared.	1209	If the timer is pending, its pending status is cleared.
…		…
1233	Periodic watchers are also timers of a kind, but they are very versatile	1284	Periodic watchers are also timers of a kind, but they are very versatile
1234	(and unfortunately a bit complex).	1285	(and unfortunately a bit complex).
1235		1286
1236	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1287	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
1237	but on wallclock time (absolute time). You can tell a periodic watcher	1288	but on wallclock time (absolute time). You can tell a periodic watcher
1238	to trigger "at" some specific point in time. For example, if you tell a	1289	to trigger after some specific point in time. For example, if you tell a
1239	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1290	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
1240	+ 10.>) and then reset your system clock to the last year, then it will	1291	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1292	clock to january of the previous year, then it will take more than year
1241	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1293	to trigger the event (unlike an C<ev_timer>, which would still trigger
1242	roughly 10 seconds later).	1294	roughly 10 seconds later as it uses a relative timeout).
1243		1295
1244	They can also be used to implement vastly more complex timers, such as	1296	C<ev_periodic>s can also be used to implement vastly more complex timers,
1245	triggering an event on each midnight, local time or other, complicated,	1297	such as triggering an event on each "midnight, local time", or other
1246	rules.	1298	complicated, rules.
1247		1299
1248	As with timers, the callback is guarenteed to be invoked only when the	1300	As with timers, the callback is guarenteed to be invoked only when the
1249	time (C<at>) has been passed, but if multiple periodic timers become ready	1301	time (C<at>) has passed, but if multiple periodic timers become ready
1250	during the same loop iteration then order of execution is undefined.	1302	during the same loop iteration then order of execution is undefined.
1251		1303
1252	=head3 Watcher-Specific Functions and Data Members	1304	=head3 Watcher-Specific Functions and Data Members
1253		1305
1254	=over 4	1306	=over 4
…		…
1262		1314
1263	=over 4	1315	=over 4
1264		1316
1265	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1317	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1266		1318
1267	In this configuration the watcher triggers an event at the wallclock time	1319	In this configuration the watcher triggers an event after the wallclock
1268	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1320	time C<at> has passed and doesn't repeat. It will not adjust when a time
1269	that is, if it is to be run at January 1st 2011 then it will run when the	1321	jump occurs, that is, if it is to be run at January 1st 2011 then it will
1270	system time reaches or surpasses this time.	1322	run when the system time reaches or surpasses this time.
1271		1323
1272	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1324	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1273		1325
1274	In this mode the watcher will always be scheduled to time out at the next	1326	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)	1327	C<at + N * interval> time (for some integer N, which can also be negative)
1276	and then repeat, regardless of any time jumps.	1328	and then repeat, regardless of any time jumps.
1277		1329
1278	This can be used to create timers that do not drift with respect to system	1330	This can be used to create timers that do not drift with respect to system
1279	time:	1331	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1332	the hour:
1280		1333
1281	ev_periodic_set (&periodic, 0., 3600., 0);	1334	ev_periodic_set (&periodic, 0., 3600., 0);
1282		1335
1283	This doesn't mean there will always be 3600 seconds in between triggers,	1336	This doesn't mean there will always be 3600 seconds in between triggers,
1284	but only that the the callback will be called when the system time shows a	1337	but only that the the callback will be called when the system time shows a
…		…
1289	C<ev_periodic> will try to run the callback in this mode at the next possible	1342	C<ev_periodic> will try to run the callback in this mode at the next possible
1290	time where C<time = at (mod interval)>, regardless of any time jumps.	1343	time where C<time = at (mod interval)>, regardless of any time jumps.
1291		1344
1292	For numerical stability it is preferable that the C<at> value is near	1345	For numerical stability it is preferable that the C<at> value is near
1293	C<ev_now ()> (the current time), but there is no range requirement for	1346	C<ev_now ()> (the current time), but there is no range requirement for
1294	this value.	1347	this value, and in fact is often specified as zero.
		1348
		1349	Note also that there is an upper limit to how often a timer can fire (cpu
		1350	speed for example), so if C<interval> is very small then timing stability
		1351	will of course detoriate. Libev itself tries to be exact to be about one
		1352	millisecond (if the OS supports it and the machine is fast enough).
1295		1353
1296	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1354	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1297		1355
1298	In this mode the values for C<interval> and C<at> are both being	1356	In this mode the values for C<interval> and C<at> are both being
1299	ignored. Instead, each time the periodic watcher gets scheduled, the	1357	ignored. Instead, each time the periodic watcher gets scheduled, the
1300	reschedule callback will be called with the watcher as first, and the	1358	reschedule callback will be called with the watcher as first, and the
1301	current time as second argument.	1359	current time as second argument.
1302		1360
1303	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1361	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1304	ever, or make any event loop modifications>. If you need to stop it,	1362	ever, or make ANY event loop modifications whatsoever>.
1305	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1306	starting an C<ev_prepare> watcher, which is legal).
1307		1363
		1364	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1365	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1366	only event loop modification you are allowed to do).
		1367
1308	Its prototype is C<ev_tstamp (reschedule_cb)(struct ev_periodic w,	1368	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
1309	ev_tstamp now)>, e.g.:	1369	*w, ev_tstamp now)>, e.g.:
1310		1370
1311	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1371	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1312	{	1372	{
1313	return now + 60.;	1373	return now + 60.;
1314	}	1374	}
…		…
1316	It must return the next time to trigger, based on the passed time value	1376	It must return the next time to trigger, based on the passed time value
1317	(that is, the lowest time value larger than to the second argument). It	1377	(that is, the lowest time value larger than to the second argument). It
1318	will usually be called just before the callback will be triggered, but	1378	will usually be called just before the callback will be triggered, but
1319	might be called at other times, too.	1379	might be called at other times, too.
1320		1380
1321	NOTE: I<< This callback must always return a time that is later than the	1381	NOTE: I<< This callback must always return a time that is higher than or
1322	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1382	equal to the passed C<now> value >>.
1323		1383
1324	This can be used to create very complex timers, such as a timer that	1384	This can be used to create very complex timers, such as a timer that
1325	triggers on each midnight, local time. To do this, you would calculate the	1385	triggers on "next midnight, local time". To do this, you would calculate the
1326	next midnight after C<now> and return the timestamp value for this. How	1386	next midnight after C<now> and return the timestamp value for this. How
1327	you do this is, again, up to you (but it is not trivial, which is the main	1387	you do this is, again, up to you (but it is not trivial, which is the main
1328	reason I omitted it as an example).	1388	reason I omitted it as an example).
1329		1389
1330	=back	1390	=back
…		…
1334	Simply stops and restarts the periodic watcher again. This is only useful	1394	Simply stops and restarts the periodic watcher again. This is only useful
1335	when you changed some parameters or the reschedule callback would return	1395	when you changed some parameters or the reschedule callback would return
1336	a different time than the last time it was called (e.g. in a crond like	1396	a different time than the last time it was called (e.g. in a crond like
1337	program when the crontabs have changed).	1397	program when the crontabs have changed).
1338		1398
		1399	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1400
		1401	When active, returns the absolute time that the watcher is supposed to
		1402	trigger next.
		1403
1339	=item ev_tstamp offset [read-write]	1404	=item ev_tstamp offset [read-write]
1340		1405
1341	When repeating, this contains the offset value, otherwise this is the	1406	When repeating, this contains the offset value, otherwise this is the
1342	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1407	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
1343		1408
…		…
1353	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]	1418	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]
1354		1419
1355	The current reschedule callback, or C<0>, if this functionality is	1420	The current reschedule callback, or C<0>, if this functionality is
1356	switched off. Can be changed any time, but changes only take effect when	1421	switched off. Can be changed any time, but changes only take effect when
1357	the periodic timer fires or C<ev_periodic_again> is being called.	1422	the periodic timer fires or C<ev_periodic_again> is being called.
1358
1359	=item ev_tstamp at [read-only]
1360
1361	When active, contains the absolute time that the watcher is supposed to
1362	trigger next.
1363		1423
1364	=back	1424	=back
1365		1425
1366	=head3 Examples	1426	=head3 Examples
1367		1427
…		…
1411	with the kernel (thus it coexists with your own signal handlers as long	1471	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	1472	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	1473	watcher for a signal is stopped libev will reset the signal handler to
1414	SIG_DFL (regardless of what it was set to before).	1474	SIG_DFL (regardless of what it was set to before).
1415		1475
		1476	If possible and supported, libev will install its handlers with
		1477	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1478	interrupted. If you have a problem with syscalls getting interrupted by
		1479	signals you can block all signals in an C<ev_check> watcher and unblock
		1480	them in an C<ev_prepare> watcher.
		1481
1416	=head3 Watcher-Specific Functions and Data Members	1482	=head3 Watcher-Specific Functions and Data Members
1417		1483
1418	=over 4	1484	=over 4
1419		1485
1420	=item ev_signal_init (ev_signal *, callback, int signum)	1486	=item ev_signal_init (ev_signal *, callback, int signum)
…		…
1428		1494
1429	The signal the watcher watches out for.	1495	The signal the watcher watches out for.
1430		1496
1431	=back	1497	=back
1432		1498
		1499	=head3 Examples
		1500
		1501	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1502
		1503	static void
		1504	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)
		1505	{
		1506	ev_unloop (loop, EVUNLOOP_ALL);
		1507	}
		1508
		1509	struct ev_signal signal_watcher;
		1510	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1511	ev_signal_start (loop, &sigint_cb);
		1512
1433		1513
1434	=head2 C<ev_child> - watch out for process status changes	1514	=head2 C<ev_child> - watch out for process status changes
1435		1515
1436	Child watchers trigger when your process receives a SIGCHLD in response to	1516	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).	1517	some child status changes (most typically when a child of yours dies). It
		1518	is permissible to install a child watcher I<after> the child has been
		1519	forked (which implies it might have already exited), as long as the event
		1520	loop isn't entered (or is continued from a watcher).
		1521
		1522	Only the default event loop is capable of handling signals, and therefore
		1523	you can only rgeister child watchers in the default event loop.
		1524
		1525	=head3 Process Interaction
		1526
		1527	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1528	initialised. This is necessary to guarantee proper behaviour even if
		1529	the first child watcher is started after the child exits. The occurance
		1530	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1531	synchronously as part of the event loop processing. Libev always reaps all
		1532	children, even ones not watched.
		1533
		1534	=head3 Overriding the Built-In Processing
		1535
		1536	Libev offers no special support for overriding the built-in child
		1537	processing, but if your application collides with libev's default child
		1538	handler, you can override it easily by installing your own handler for
		1539	C<SIGCHLD> after initialising the default loop, and making sure the
		1540	default loop never gets destroyed. You are encouraged, however, to use an
		1541	event-based approach to child reaping and thus use libev's support for
		1542	that, so other libev users can use C<ev_child> watchers freely.
1438		1543
1439	=head3 Watcher-Specific Functions and Data Members	1544	=head3 Watcher-Specific Functions and Data Members
1440		1545
1441	=over 4	1546	=over 4
1442		1547
…		…
1468		1573
1469	=back	1574	=back
1470		1575
1471	=head3 Examples	1576	=head3 Examples
1472		1577
1473	Example: Try to exit cleanly on SIGINT and SIGTERM.	1578	Example: C<fork()> a new process and install a child handler to wait for
		1579	its completion.
		1580
		1581	ev_child cw;
1474		1582
1475	static void	1583	static void
1476	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)	1584	child_cb (EV_P_ struct ev_child *w, int revents)
1477	{	1585	{
1478	ev_unloop (loop, EVUNLOOP_ALL);	1586	ev_child_stop (EV_A_ w);
		1587	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1479	}	1588	}
1480		1589
1481	struct ev_signal signal_watcher;	1590	pid_t pid = fork ();
1482	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1591
1483	ev_signal_start (loop, &sigint_cb);	1592	if (pid < 0)
		1593	// error
		1594	else if (pid == 0)
		1595	{
		1596	// the forked child executes here
		1597	exit (1);
		1598	}
		1599	else
		1600	{
		1601	ev_child_init (&cw, child_cb, pid, 0);
		1602	ev_child_start (EV_DEFAULT_ &cw);
		1603	}
1484		1604
1485		1605
1486	=head2 C<ev_stat> - did the file attributes just change?	1606	=head2 C<ev_stat> - did the file attributes just change?
1487		1607
1488	This watches a filesystem path for attribute changes. That is, it calls	1608	This watches a filesystem path for attribute changes. That is, it calls
…		…
1511	as even with OS-supported change notifications, this can be	1631	as even with OS-supported change notifications, this can be
1512	resource-intensive.	1632	resource-intensive.
1513		1633
1514	At the time of this writing, only the Linux inotify interface is	1634	At the time of this writing, only the Linux inotify interface is
1515	implemented (implementing kqueue support is left as an exercise for the	1635	implemented (implementing kqueue support is left as an exercise for the
		1636	reader, note, however, that the author sees no way of implementing ev_stat
1516	reader). Inotify will be used to give hints only and should not change the	1637	semantics with kqueue). Inotify will be used to give hints only and should
1517	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1638	not change the semantics of C<ev_stat> watchers, which means that libev
1518	to fall back to regular polling again even with inotify, but changes are	1639	sometimes needs to fall back to regular polling again even with inotify,
1519	usually detected immediately, and if the file exists there will be no	1640	but changes are usually detected immediately, and if the file exists there
1520	polling.	1641	will be no polling.
		1642
		1643	=head3 ABI Issues (Largefile Support)
		1644
		1645	Libev by default (unless the user overrides this) uses the default
		1646	compilation environment, which means that on systems with optionally
		1647	disabled large file support, you get the 32 bit version of the stat
		1648	structure. When using the library from programs that change the ABI to
		1649	use 64 bit file offsets the programs will fail. In that case you have to
		1650	compile libev with the same flags to get binary compatibility. This is
		1651	obviously the case with any flags that change the ABI, but the problem is
		1652	most noticably with ev_stat and largefile support.
1521		1653
1522	=head3 Inotify	1654	=head3 Inotify
1523		1655
1524	When C<inotify (7)> support has been compiled into libev (generally only	1656	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	1657	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	1658	change detection where possible. The inotify descriptor will be created lazily
1527	when the first C<ev_stat> watcher is being started.	1659	when the first C<ev_stat> watcher is being started.
1528		1660
1529	Inotify presense does not change the semantics of C<ev_stat> watchers	1661	Inotify presence does not change the semantics of C<ev_stat> watchers
1530	except that changes might be detected earlier, and in some cases, to avoid	1662	except that changes might be detected earlier, and in some cases, to avoid
1531	making regular C<stat> calls. Even in the presense of inotify support	1663	making regular C<stat> calls. Even in the presence of inotify support
1532	there are many cases where libev has to resort to regular C<stat> polling.	1664	there are many cases where libev has to resort to regular C<stat> polling.
1533		1665
1534	(There is no support for kqueue, as apparently it cannot be used to	1666	(There is no support for kqueue, as apparently it cannot be used to
1535	implement this functionality, due to the requirement of having a file	1667	implement this functionality, due to the requirement of having a file
1536	descriptor open on the object at all times).	1668	descriptor open on the object at all times).
…		…
1539		1671
1540	The C<stat ()> syscall only supports full-second resolution portably, and	1672	The C<stat ()> syscall only supports full-second resolution portably, and
1541	even on systems where the resolution is higher, many filesystems still	1673	even on systems where the resolution is higher, many filesystems still
1542	only support whole seconds.	1674	only support whole seconds.
1543		1675
1544	That means that, if the time is the only thing that changes, you might	1676	That means that, if the time is the only thing that changes, you can
1545	miss updates: on the first update, C<ev_stat> detects a change and calls	1677	easily miss updates: on the first update, C<ev_stat> detects a change and
1546	your callback, which does something. When there is another update within	1678	calls your callback, which does something. When there is another update
1547	the same second, C<ev_stat> will be unable to detect it.	1679	within the same second, C<ev_stat> will be unable to detect it as the stat
		1680	data does not change.
1548		1681
1549	The solution to this is to delay acting on a change for a second (or till	1682	The solution to this is to delay acting on a change for slightly more
1550	the next second boundary), using a roughly one-second delay C<ev_timer>	1683	than a second (or till slightly after the next full second boundary), using
1551	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	1684	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1552	is added to work around small timing inconsistencies of some operating	1685	ev_timer_again (loop, w)>).
1553	systems.	1686
		1687	The C<.02> offset is added to work around small timing inconsistencies
		1688	of some operating systems (where the second counter of the current time
		1689	might be be delayed. One such system is the Linux kernel, where a call to
		1690	C<gettimeofday> might return a timestamp with a full second later than
		1691	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1692	update file times then there will be a small window where the kernel uses
		1693	the previous second to update file times but libev might already execute
		1694	the timer callback).
1554		1695
1555	=head3 Watcher-Specific Functions and Data Members	1696	=head3 Watcher-Specific Functions and Data Members
1556		1697
1557	=over 4	1698	=over 4
1558		1699
…		…
1564	C<path>. The C<interval> is a hint on how quickly a change is expected to	1705	C<path>. The C<interval> is a hint on how quickly a change is expected to
1565	be detected and should normally be specified as C<0> to let libev choose	1706	be detected and should normally be specified as C<0> to let libev choose
1566	a suitable value. The memory pointed to by C<path> must point to the same	1707	a suitable value. The memory pointed to by C<path> must point to the same
1567	path for as long as the watcher is active.	1708	path for as long as the watcher is active.
1568		1709
1569	The callback will be receive C<EV_STAT> when a change was detected,	1710	The callback will receive C<EV_STAT> when a change was detected, relative
1570	relative to the attributes at the time the watcher was started (or the	1711	to the attributes at the time the watcher was started (or the last change
1571	last change was detected).	1712	was detected).
1572		1713
1573	=item ev_stat_stat (ev_stat *)	1714	=item ev_stat_stat (loop, ev_stat *)
1574		1715
1575	Updates the stat buffer immediately with new values. If you change the	1716	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	1717	watched path in your callback, you could call this function to avoid
1577	detecting this change (while introducing a race condition). Can also be	1718	detecting this change (while introducing a race condition if you are not
1578	useful simply to find out the new values.	1719	the only one changing the path). Can also be useful simply to find out the
		1720	new values.
1579		1721
1580	=item ev_statdata attr [read-only]	1722	=item ev_statdata attr [read-only]
1581		1723
1582	The most-recently detected attributes of the file. Although the type is of	1724	The most-recently detected attributes of the file. Although the type is
1583	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	1725	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1584	suitable for your system. If the C<st_nlink> member is C<0>, then there	1726	suitable for your system, but you can only rely on the POSIX-standardised
		1727	members to be present. If the C<st_nlink> member is C<0>, then there was
1585	was some error while C<stat>ing the file.	1728	some error while C<stat>ing the file.
1586		1729
1587	=item ev_statdata prev [read-only]	1730	=item ev_statdata prev [read-only]
1588		1731
1589	The previous attributes of the file. The callback gets invoked whenever	1732	The previous attributes of the file. The callback gets invoked whenever
1590	C<prev> != C<attr>.	1733	C<prev> != C<attr>, or, more precisely, one or more of these members
		1734	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1735	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1591		1736
1592	=item ev_tstamp interval [read-only]	1737	=item ev_tstamp interval [read-only]
1593		1738
1594	The specified interval.	1739	The specified interval.
1595		1740
…		…
1649	}	1794	}
1650		1795
1651	...	1796	...
1652	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	1797	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1653	ev_stat_start (loop, &passwd);	1798	ev_stat_start (loop, &passwd);
1654	ev_timer_init (&timer, timer_cb, 0., 1.01);	1799	ev_timer_init (&timer, timer_cb, 0., 1.02);
1655		1800
1656		1801
1657	=head2 C<ev_idle> - when you've got nothing better to do...	1802	=head2 C<ev_idle> - when you've got nothing better to do...
1658		1803
1659	Idle watchers trigger events when no other events of the same or higher	1804	Idle watchers trigger events when no other events of the same or higher
…		…
1695	static void	1840	static void
1696	idle_cb (struct ev_loop loop, struct ev_idle w, int revents)	1841	idle_cb (struct ev_loop loop, struct ev_idle w, int revents)
1697	{	1842	{
1698	free (w);	1843	free (w);
1699	// now do something you wanted to do when the program has	1844	// now do something you wanted to do when the program has
1700	// no longer asnything immediate to do.	1845	// no longer anything immediate to do.
1701	}	1846	}
1702		1847
1703	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	1848	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1704	ev_idle_init (idle_watcher, idle_cb);	1849	ev_idle_init (idle_watcher, idle_cb);
1705	ev_idle_start (loop, idle_cb);	1850	ev_idle_start (loop, idle_cb);
…		…
1747		1892
1748	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	1893	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1749	priority, to ensure that they are being run before any other watchers	1894	priority, to ensure that they are being run before any other watchers
1750	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	1895	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1751	too) should not activate ("feed") events into libev. While libev fully	1896	too) should not activate ("feed") events into libev. While libev fully
1752	supports this, they will be called before other C<ev_check> watchers	1897	supports this, they might get executed before other C<ev_check> watchers
1753	did their job. As C<ev_check> watchers are often used to embed other	1898	did their job. As C<ev_check> watchers are often used to embed other
1754	(non-libev) event loops those other event loops might be in an unusable	1899	(non-libev) event loops those other event loops might be in an unusable
1755	state until their C<ev_check> watcher ran (always remind yourself to	1900	state until their C<ev_check> watcher ran (always remind yourself to
1756	coexist peacefully with others).	1901	coexist peacefully with others).
1757		1902
…		…
1772	=head3 Examples	1917	=head3 Examples
1773		1918
1774	There are a number of principal ways to embed other event loops or modules	1919	There are a number of principal ways to embed other event loops or modules
1775	into libev. Here are some ideas on how to include libadns into libev	1920	into libev. Here are some ideas on how to include libadns into libev
1776	(there is a Perl module named C<EV::ADNS> that does this, which you could	1921	(there is a Perl module named C<EV::ADNS> that does this, which you could
1777	use for an actually working example. Another Perl module named C<EV::Glib>	1922	use as a working example. Another Perl module named C<EV::Glib> embeds a
1778	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	1923	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1779	into the Glib event loop).	1924	Glib event loop).
1780		1925
1781	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	1926	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1782	and in a check watcher, destroy them and call into libadns. What follows	1927	and in a check watcher, destroy them and call into libadns. What follows
1783	is pseudo-code only of course. This requires you to either use a low	1928	is pseudo-code only of course. This requires you to either use a low
1784	priority for the check watcher or use C<ev_clear_pending> explicitly, as	1929	priority for the check watcher or use C<ev_clear_pending> explicitly, as
…		…
2046	believe me.	2191	believe me.
2047		2192
2048	=back	2193	=back
2049		2194
2050		2195
		2196	=head2 C<ev_async> - how to wake up another event loop
		2197
		2198	In general, you cannot use an C<ev_loop> from multiple threads or other
		2199	asynchronous sources such as signal handlers (as opposed to multiple event
		2200	loops - those are of course safe to use in different threads).
		2201
		2202	Sometimes, however, you need to wake up another event loop you do not
		2203	control, for example because it belongs to another thread. This is what
		2204	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2205	can signal it by calling C<ev_async_send>, which is thread- and signal
		2206	safe.
		2207
		2208	This functionality is very similar to C<ev_signal> watchers, as signals,
		2209	too, are asynchronous in nature, and signals, too, will be compressed
		2210	(i.e. the number of callback invocations may be less than the number of
		2211	C<ev_async_sent> calls).
		2212
		2213	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2214	just the default loop.
		2215
		2216	=head3 Queueing
		2217
		2218	C<ev_async> does not support queueing of data in any way. The reason
		2219	is that the author does not know of a simple (or any) algorithm for a
		2220	multiple-writer-single-reader queue that works in all cases and doesn't
		2221	need elaborate support such as pthreads.
		2222
		2223	That means that if you want to queue data, you have to provide your own
		2224	queue. But at least I can tell you would implement locking around your
		2225	queue:
		2226
		2227	=over 4
		2228
		2229	=item queueing from a signal handler context
		2230
		2231	To implement race-free queueing, you simply add to the queue in the signal
		2232	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2233	some fictitiuous SIGUSR1 handler:
		2234
		2235	static ev_async mysig;
		2236
		2237	static void
		2238	sigusr1_handler (void)
		2239	{
		2240	sometype data;
		2241
		2242	// no locking etc.
		2243	queue_put (data);
		2244	ev_async_send (EV_DEFAULT_ &mysig);
		2245	}
		2246
		2247	static void
		2248	mysig_cb (EV_P_ ev_async *w, int revents)
		2249	{
		2250	sometype data;
		2251	sigset_t block, prev;
		2252
		2253	sigemptyset (&block);
		2254	sigaddset (&block, SIGUSR1);
		2255	sigprocmask (SIG_BLOCK, &block, &prev);
		2256
		2257	while (queue_get (&data))
		2258	process (data);
		2259
		2260	if (sigismember (&prev, SIGUSR1)
		2261	sigprocmask (SIG_UNBLOCK, &block, 0);
		2262	}
		2263
		2264	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2265	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2266	either...).
		2267
		2268	=item queueing from a thread context
		2269
		2270	The strategy for threads is different, as you cannot (easily) block
		2271	threads but you can easily preempt them, so to queue safely you need to
		2272	employ a traditional mutex lock, such as in this pthread example:
		2273
		2274	static ev_async mysig;
		2275	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2276
		2277	static void
		2278	otherthread (void)
		2279	{
		2280	// only need to lock the actual queueing operation
		2281	pthread_mutex_lock (&mymutex);
		2282	queue_put (data);
		2283	pthread_mutex_unlock (&mymutex);
		2284
		2285	ev_async_send (EV_DEFAULT_ &mysig);
		2286	}
		2287
		2288	static void
		2289	mysig_cb (EV_P_ ev_async *w, int revents)
		2290	{
		2291	pthread_mutex_lock (&mymutex);
		2292
		2293	while (queue_get (&data))
		2294	process (data);
		2295
		2296	pthread_mutex_unlock (&mymutex);
		2297	}
		2298
		2299	=back
		2300
		2301
		2302	=head3 Watcher-Specific Functions and Data Members
		2303
		2304	=over 4
		2305
		2306	=item ev_async_init (ev_async *, callback)
		2307
		2308	Initialises and configures the async watcher - it has no parameters of any
		2309	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2310	believe me.
		2311
		2312	=item ev_async_send (loop, ev_async *)
		2313
		2314	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2315	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2316	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2317	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2318	section below on what exactly this means).
		2319
		2320	This call incurs the overhead of a syscall only once per loop iteration,
		2321	so while the overhead might be noticable, it doesn't apply to repeated
		2322	calls to C<ev_async_send>.
		2323
		2324	=item bool = ev_async_pending (ev_async *)
		2325
		2326	Returns a non-zero value when C<ev_async_send> has been called on the
		2327	watcher but the event has not yet been processed (or even noted) by the
		2328	event loop.
		2329
		2330	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2331	the loop iterates next and checks for the watcher to have become active,
		2332	it will reset the flag again. C<ev_async_pending> can be used to very
		2333	quickly check wether invoking the loop might be a good idea.
		2334
		2335	Not that this does I<not> check wether the watcher itself is pending, only
		2336	wether it has been requested to make this watcher pending.
		2337
		2338	=back
		2339
		2340
2051	=head1 OTHER FUNCTIONS	2341	=head1 OTHER FUNCTIONS
2052		2342
2053	There are some other functions of possible interest. Described. Here. Now.	2343	There are some other functions of possible interest. Described. Here. Now.
2054		2344
2055	=over 4	2345	=over 4
…		…
2123		2413
2124	=item * Priorities are not currently supported. Initialising priorities	2414	=item * Priorities are not currently supported. Initialising priorities
2125	will fail and all watchers will have the same priority, even though there	2415	will fail and all watchers will have the same priority, even though there
2126	is an ev_pri field.	2416	is an ev_pri field.
2127		2417
		2418	=item * In libevent, the last base created gets the signals, in libev, the
		2419	first base created (== the default loop) gets the signals.
		2420
2128	=item * Other members are not supported.	2421	=item * Other members are not supported.
2129		2422
2130	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2423	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2131	to use the libev header file and library.	2424	to use the libev header file and library.
2132		2425
…		…
2282	Example: Define a class with an IO and idle watcher, start one of them in	2575	Example: Define a class with an IO and idle watcher, start one of them in
2283	the constructor.	2576	the constructor.
2284		2577
2285	class myclass	2578	class myclass
2286	{	2579	{
2287	ev_io io; void io_cb (ev::io &w, int revents);	2580	ev::io io; void io_cb (ev::io &w, int revents);
2288	ev_idle idle void idle_cb (ev::idle &w, int revents);	2581	ev:idle idle void idle_cb (ev::idle &w, int revents);
2289		2582
2290	myclass ();	2583	myclass (int fd)
2291	}
2292
2293	myclass::myclass (int fd)
2294	{	2584	{
2295	io .set <myclass, &myclass::io_cb > (this);	2585	io .set <myclass, &myclass::io_cb > (this);
2296	idle.set <myclass, &myclass::idle_cb> (this);	2586	idle.set <myclass, &myclass::idle_cb> (this);
2297		2587
2298	io.start (fd, ev::READ);	2588	io.start (fd, ev::READ);
		2589	}
2299	}	2590	};
		2591
		2592
		2593	=head1 OTHER LANGUAGE BINDINGS
		2594
		2595	Libev does not offer other language bindings itself, but bindings for a
		2596	numbe rof languages exist in the form of third-party packages. If you know
		2597	any interesting language binding in addition to the ones listed here, drop
		2598	me a note.
		2599
		2600	=over 4
		2601
		2602	=item Perl
		2603
		2604	The EV module implements the full libev API and is actually used to test
		2605	libev. EV is developed together with libev. Apart from the EV core module,
		2606	there are additional modules that implement libev-compatible interfaces
		2607	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2608	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2609
		2610	It can be found and installed via CPAN, its homepage is found at
		2611	L<http://software.schmorp.de/pkg/EV>.
		2612
		2613	=item Ruby
		2614
		2615	Tony Arcieri has written a ruby extension that offers access to a subset
		2616	of the libev API and adds filehandle abstractions, asynchronous DNS and
		2617	more on top of it. It can be found via gem servers. Its homepage is at
		2618	L<http://rev.rubyforge.org/>.
		2619
		2620	=item D
		2621
		2622	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2623	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2624
		2625	=back
2300		2626
2301		2627
2302	=head1 MACRO MAGIC	2628	=head1 MACRO MAGIC
2303		2629
2304	Libev can be compiled with a variety of options, the most fundamantal	2630	Libev can be compiled with a variety of options, the most fundamantal
…		…
2340		2666
2341	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	2667	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2342		2668
2343	Similar to the other two macros, this gives you the value of the default	2669	Similar to the other two macros, this gives you the value of the default
2344	loop, if multiple loops are supported ("ev loop default").	2670	loop, if multiple loops are supported ("ev loop default").
		2671
		2672	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2673
		2674	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2675	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2676	is undefined when the default loop has not been initialised by a previous
		2677	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2678
		2679	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2680	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2345		2681
2346	=back	2682	=back
2347		2683
2348	Example: Declare and initialise a check watcher, utilising the above	2684	Example: Declare and initialise a check watcher, utilising the above
2349	macros so it will work regardless of whether multiple loops are supported	2685	macros so it will work regardless of whether multiple loops are supported
…		…
2445		2781
2446	libev.m4	2782	libev.m4
2447		2783
2448	=head2 PREPROCESSOR SYMBOLS/MACROS	2784	=head2 PREPROCESSOR SYMBOLS/MACROS
2449		2785
2450	Libev can be configured via a variety of preprocessor symbols you have to define	2786	Libev can be configured via a variety of preprocessor symbols you have to
2451	before including any of its files. The default is not to build for multiplicity	2787	define before including any of its files. The default in the absense of
2452	and only include the select backend.	2788	autoconf is noted for every option.
2453		2789
2454	=over 4	2790	=over 4
2455		2791
2456	=item EV_STANDALONE	2792	=item EV_STANDALONE
2457		2793
…		…
2483	=item EV_USE_NANOSLEEP	2819	=item EV_USE_NANOSLEEP
2484		2820
2485	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	2821	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2486	and will use it for delays. Otherwise it will use C<select ()>.	2822	and will use it for delays. Otherwise it will use C<select ()>.
2487		2823
		2824	=item EV_USE_EVENTFD
		2825
		2826	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2827	available and will probe for kernel support at runtime. This will improve
		2828	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2829	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2830	2.7 or newer, otherwise disabled.
		2831
2488	=item EV_USE_SELECT	2832	=item EV_USE_SELECT
2489		2833
2490	If undefined or defined to be C<1>, libev will compile in support for the	2834	If undefined or defined to be C<1>, libev will compile in support for the
2491	C<select>(2) backend. No attempt at autodetection will be done: if no	2835	C<select>(2) backend. No attempt at autodetection will be done: if no
2492	other method takes over, select will be it. Otherwise the select backend	2836	other method takes over, select will be it. Otherwise the select backend
…		…
2528		2872
2529	=item EV_USE_EPOLL	2873	=item EV_USE_EPOLL
2530		2874
2531	If defined to be C<1>, libev will compile in support for the Linux	2875	If defined to be C<1>, libev will compile in support for the Linux
2532	C<epoll>(7) backend. Its availability will be detected at runtime,	2876	C<epoll>(7) backend. Its availability will be detected at runtime,
2533	otherwise another method will be used as fallback. This is the	2877	otherwise another method will be used as fallback. This is the preferred
2534	preferred backend for GNU/Linux systems.	2878	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2879	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2535		2880
2536	=item EV_USE_KQUEUE	2881	=item EV_USE_KQUEUE
2537		2882
2538	If defined to be C<1>, libev will compile in support for the BSD style	2883	If defined to be C<1>, libev will compile in support for the BSD style
2539	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	2884	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2558		2903
2559	=item EV_USE_INOTIFY	2904	=item EV_USE_INOTIFY
2560		2905
2561	If defined to be C<1>, libev will compile in support for the Linux inotify	2906	If defined to be C<1>, libev will compile in support for the Linux inotify
2562	interface to speed up C<ev_stat> watchers. Its actual availability will	2907	interface to speed up C<ev_stat> watchers. Its actual availability will
2563	be detected at runtime.	2908	be detected at runtime. If undefined, it will be enabled if the headers
		2909	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2910
		2911	=item EV_ATOMIC_T
		2912
		2913	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2914	access is atomic with respect to other threads or signal contexts. No such
		2915	type is easily found in the C language, so you can provide your own type
		2916	that you know is safe for your purposes. It is used both for signal handler "locking"
		2917	as well as for signal and thread safety in C<ev_async> watchers.
		2918
		2919	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2920	(from F<signal.h>), which is usually good enough on most platforms.
2564		2921
2565	=item EV_H	2922	=item EV_H
2566		2923
2567	The name of the F<ev.h> header file used to include it. The default if	2924	The name of the F<ev.h> header file used to include it. The default if
2568	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	2925	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
2636	=item EV_FORK_ENABLE	2993	=item EV_FORK_ENABLE
2637		2994
2638	If undefined or defined to be C<1>, then fork watchers are supported. If	2995	If undefined or defined to be C<1>, then fork watchers are supported. If
2639	defined to be C<0>, then they are not.	2996	defined to be C<0>, then they are not.
2640		2997
		2998	=item EV_ASYNC_ENABLE
		2999
		3000	If undefined or defined to be C<1>, then async watchers are supported. If
		3001	defined to be C<0>, then they are not.
		3002
2641	=item EV_MINIMAL	3003	=item EV_MINIMAL
2642		3004
2643	If you need to shave off some kilobytes of code at the expense of some	3005	If you need to shave off some kilobytes of code at the expense of some
2644	speed, define this symbol to C<1>. Currently only used for gcc to override	3006	speed, define this symbol to C<1>. Currently this is used to override some
2645	some inlining decisions, saves roughly 30% codesize of amd64.	3007	inlining decisions, saves roughly 30% codesize of amd64. It also selects a
		3008	much smaller 2-heap for timer management over the default 4-heap.
2646		3009
2647	=item EV_PID_HASHSIZE	3010	=item EV_PID_HASHSIZE
2648		3011
2649	C<ev_child> watchers use a small hash table to distribute workload by	3012	C<ev_child> watchers use a small hash table to distribute workload by
2650	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3013	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2656	C<ev_stat> watchers use a small hash table to distribute workload by	3019	C<ev_stat> watchers use a small hash table to distribute workload by
2657	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3020	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2658	usually more than enough. If you need to manage thousands of C<ev_stat>	3021	usually more than enough. If you need to manage thousands of C<ev_stat>
2659	watchers you might want to increase this value (I<must> be a power of	3022	watchers you might want to increase this value (I<must> be a power of
2660	two).	3023	two).
		3024
		3025	=item EV_USE_4HEAP
		3026
		3027	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3028	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3029	to C<1>. The 4-heap uses more complicated (longer) code but has
		3030	noticably faster performance with many (thousands) of watchers.
		3031
		3032	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3033	(disabled).
		3034
		3035	=item EV_HEAP_CACHE_AT
		3036
		3037	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3038	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3039	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3040	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3041	but avoids random read accesses on heap changes. This improves performance
		3042	noticably with with many (hundreds) of watchers.
		3043
		3044	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3045	(disabled).
		3046
		3047	=item EV_VERIFY
		3048
		3049	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3050	be done: If set to C<0>, no internal verification code will be compiled
		3051	in. If set to C<1>, then verification code will be compiled in, but not
		3052	called. If set to C<2>, then the internal verification code will be
		3053	called once per loop, which can slow down libev. If set to C<3>, then the
		3054	verification code will be called very frequently, which will slow down
		3055	libev considerably.
		3056
		3057	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3058	C<0.>
2661		3059
2662	=item EV_COMMON	3060	=item EV_COMMON
2663		3061
2664	By default, all watchers have a C<void *data> member. By redefining	3062	By default, all watchers have a C<void *data> member. By redefining
2665	this macro to a something else you can include more and other types of	3063	this macro to a something else you can include more and other types of
…		…
2739		3137
2740	#include "ev_cpp.h"	3138	#include "ev_cpp.h"
2741	#include "ev.c"	3139	#include "ev.c"
2742		3140
2743		3141
		3142	=head1 THREADS AND COROUTINES
		3143
		3144	=head2 THREADS
		3145
		3146	Libev itself is completely threadsafe, but it uses no locking. This
		3147	means that you can use as many loops as you want in parallel, as long as
		3148	only one thread ever calls into one libev function with the same loop
		3149	parameter.
		3150
		3151	Or put differently: calls with different loop parameters can be done in
		3152	parallel from multiple threads, calls with the same loop parameter must be
		3153	done serially (but can be done from different threads, as long as only one
		3154	thread ever is inside a call at any point in time, e.g. by using a mutex
		3155	per loop).
		3156
		3157	If you want to know which design is best for your problem, then I cannot
		3158	help you but by giving some generic advice:
		3159
		3160	=over 4
		3161
		3162	=item * most applications have a main thread: use the default libev loop
		3163	in that thread, or create a seperate thread running only the default loop.
		3164
		3165	This helps integrating other libraries or software modules that use libev
		3166	themselves and don't care/know about threading.
		3167
		3168	=item * one loop per thread is usually a good model.
		3169
		3170	Doing this is almost never wrong, sometimes a better-performance model
		3171	exists, but it is always a good start.
		3172
		3173	=item * other models exist, such as the leader/follower pattern, where one
		3174	loop is handed through multiple threads in a kind of round-robbin fashion.
		3175
		3176	Chosing a model is hard - look around, learn, know that usually you cna do
		3177	better than you currently do :-)
		3178
		3179	=item * often you need to talk to some other thread which blocks in the
		3180	event loop - C<ev_async> watchers can be used to wake them up from other
		3181	threads safely (or from signal contexts...).
		3182
		3183	=back
		3184
		3185	=head2 COROUTINES
		3186
		3187	Libev is much more accomodating to coroutines ("cooperative threads"):
		3188	libev fully supports nesting calls to it's functions from different
		3189	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3190	different coroutines and switch freely between both coroutines running the
		3191	loop, as long as you don't confuse yourself). The only exception is that
		3192	you must not do this from C<ev_periodic> reschedule callbacks.
		3193
		3194	Care has been invested into making sure that libev does not keep local
		3195	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3196	switches.
		3197
		3198
2744	=head1 COMPLEXITIES	3199	=head1 COMPLEXITIES
2745		3200
2746	In this section the complexities of (many of) the algorithms used inside	3201	In this section the complexities of (many of) the algorithms used inside
2747	libev will be explained. For complexity discussions about backends see the	3202	libev will be explained. For complexity discussions about backends see the
2748	documentation for C<ev_default_init>.	3203	documentation for C<ev_default_init>.
…		…
2764	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3219	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2765		3220
2766	That means that changing a timer costs less than removing/adding them	3221	That means that changing a timer costs less than removing/adding them
2767	as only the relative motion in the event queue has to be paid for.	3222	as only the relative motion in the event queue has to be paid for.
2768		3223
2769	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3224	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2770		3225
2771	These just add the watcher into an array or at the head of a list.	3226	These just add the watcher into an array or at the head of a list.
2772		3227
2773	=item Stopping check/prepare/idle watchers: O(1)	3228	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2774		3229
2775	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3230	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2776		3231
2777	These watchers are stored in lists then need to be walked to find the	3232	These watchers are stored in lists then need to be walked to find the
2778	correct watcher to remove. The lists are usually short (you don't usually	3233	correct watcher to remove. The lists are usually short (you don't usually
2779	have many watchers waiting for the same fd or signal).	3234	have many watchers waiting for the same fd or signal).
2780		3235
2781	=item Finding the next timer in each loop iteration: O(1)	3236	=item Finding the next timer in each loop iteration: O(1)
2782		3237
2783	By virtue of using a binary heap, the next timer is always found at the	3238	By virtue of using a binary or 4-heap, the next timer is always found at a
2784	beginning of the storage array.	3239	fixed position in the storage array.
2785		3240
2786	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3241	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2787		3242
2788	A change means an I/O watcher gets started or stopped, which requires	3243	A change means an I/O watcher gets started or stopped, which requires
2789	libev to recalculate its status (and possibly tell the kernel, depending	3244	libev to recalculate its status (and possibly tell the kernel, depending
…		…
2794	=item Priority handling: O(number_of_priorities)	3249	=item Priority handling: O(number_of_priorities)
2795		3250
2796	Priorities are implemented by allocating some space for each	3251	Priorities are implemented by allocating some space for each
2797	priority. When doing priority-based operations, libev usually has to	3252	priority. When doing priority-based operations, libev usually has to
2798	linearly search all the priorities, but starting/stopping and activating	3253	linearly search all the priorities, but starting/stopping and activating
2799	watchers becomes O(1) w.r.t. prioritiy handling.	3254	watchers becomes O(1) w.r.t. priority handling.
		3255
		3256	=item Sending an ev_async: O(1)
		3257
		3258	=item Processing ev_async_send: O(number_of_async_watchers)
		3259
		3260	=item Processing signals: O(max_signal_number)
		3261
		3262	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		3263	calls in the current loop iteration. Checking for async and signal events
		3264	involves iterating over all running async watchers or all signal numbers.
2800		3265
2801	=back	3266	=back
2802		3267
2803		3268
2804	=head1 Win32 platform limitations and workarounds	3269	=head1 Win32 platform limitations and workarounds
…		…
2808	model. Libev still offers limited functionality on this platform in	3273	model. Libev still offers limited functionality on this platform in
2809	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3274	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2810	descriptors. This only applies when using Win32 natively, not when using	3275	descriptors. This only applies when using Win32 natively, not when using
2811	e.g. cygwin.	3276	e.g. cygwin.
2812		3277
		3278	Lifting these limitations would basically require the full
		3279	re-implementation of the I/O system. If you are into these kinds of
		3280	things, then note that glib does exactly that for you in a very portable
		3281	way (note also that glib is the slowest event library known to man).
		3282
2813	There is no supported compilation method available on windows except	3283	There is no supported compilation method available on windows except
2814	embedding it into other applications.	3284	embedding it into other applications.
2815		3285
2816	Due to the many, low, and arbitrary limits on the win32 platform and the	3286	Due to the many, low, and arbitrary limits on the win32 platform and
2817	abysmal performance of winsockets, using a large number of sockets is not	3287	the abysmal performance of winsockets, using a large number of sockets
2818	recommended (and not reasonable). If your program needs to use more than	3288	is not recommended (and not reasonable). If your program needs to use
2819	a hundred or so sockets, then likely it needs to use a totally different	3289	more than a hundred or so sockets, then likely it needs to use a totally
2820	implementation for windows, as libev offers the POSIX model, which cannot	3290	different implementation for windows, as libev offers the POSIX readiness
2821	be implemented efficiently on windows (microsoft monopoly games).	3291	notification model, which cannot be implemented efficiently on windows
		3292	(microsoft monopoly games).
2822		3293
2823	=over 4	3294	=over 4
2824		3295
2825	=item The winsocket select function	3296	=item The winsocket select function
2826		3297
…		…
2840	Note that winsockets handling of fd sets is O(n), so you can easily get a	3311	Note that winsockets handling of fd sets is O(n), so you can easily get a
2841	complexity in the O(n²) range when using win32.	3312	complexity in the O(n²) range when using win32.
2842		3313
2843	=item Limited number of file descriptors	3314	=item Limited number of file descriptors
2844		3315
2845	Windows has numerous arbitrary (and low) limits on things. Early versions	3316	Windows has numerous arbitrary (and low) limits on things.
2846	of winsocket's select only supported waiting for a max. of C<64> handles	3317
		3318	Early versions of winsocket's select only supported waiting for a maximum
2847	(probably owning to the fact that all windows kernels can only wait for	3319	of C<64> handles (probably owning to the fact that all windows kernels
2848	C<64> things at the same time internally; microsoft recommends spawning a	3320	can only wait for C<64> things at the same time internally; microsoft
2849	chain of threads and wait for 63 handles and the previous thread in each).	3321	recommends spawning a chain of threads and wait for 63 handles and the
		3322	previous thread in each. Great).
2850		3323
2851	Newer versions support more handles, but you need to define C<FD_SETSIZE>	3324	Newer versions support more handles, but you need to define C<FD_SETSIZE>
2852	to some high number (e.g. C<2048>) before compiling the winsocket select	3325	to some high number (e.g. C<2048>) before compiling the winsocket select
2853	call (which might be in libev or elsewhere, for example, perl does its own	3326	call (which might be in libev or elsewhere, for example, perl does its own
2854	select emulation on windows).	3327	select emulation on windows).
…		…
2866	calling select (O(n²)) will likely make this unworkable.	3339	calling select (O(n²)) will likely make this unworkable.
2867		3340
2868	=back	3341	=back
2869		3342
2870		3343
		3344	=head1 PORTABILITY REQUIREMENTS
		3345
		3346	In addition to a working ISO-C implementation, libev relies on a few
		3347	additional extensions:
		3348
		3349	=over 4
		3350
		3351	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3352
		3353	The type C<sig_atomic_t volatile> (or whatever is defined as
		3354	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3355	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3356	believed to be sufficiently portable.
		3357
		3358	=item C<sigprocmask> must work in a threaded environment
		3359
		3360	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3361	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3362	pthread implementations will either allow C<sigprocmask> in the "main
		3363	thread" or will block signals process-wide, both behaviours would
		3364	be compatible with libev. Interaction between C<sigprocmask> and
		3365	C<pthread_sigmask> could complicate things, however.
		3366
		3367	The most portable way to handle signals is to block signals in all threads
		3368	except the initial one, and run the default loop in the initial thread as
		3369	well.
		3370
		3371	=item C<long> must be large enough for common memory allocation sizes
		3372
		3373	To improve portability and simplify using libev, libev uses C<long>
		3374	internally instead of C<size_t> when allocating its data structures. On
		3375	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3376	is still at least 31 bits everywhere, which is enough for hundreds of
		3377	millions of watchers.
		3378
		3379	=item C<double> must hold a time value in seconds with enough accuracy
		3380
		3381	The type C<double> is used to represent timestamps. It is required to
		3382	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3383	enough for at least into the year 4000. This requirement is fulfilled by
		3384	implementations implementing IEEE 754 (basically all existing ones).
		3385
		3386	=back
		3387
		3388	If you know of other additional requirements drop me a note.
		3389
		3390
		3391	=head1 VALGRIND
		3392
		3393	Valgrind has a special section here because it is a popular tool that is
		3394	highly useful, but valgrind reports are very hard to interpret.
		3395
		3396	If you think you found a bug (memory leak, uninitialised data access etc.)
		3397	in libev, then check twice: If valgrind reports something like:
		3398
		3399	==2274== definitely lost: 0 bytes in 0 blocks.
		3400	==2274== possibly lost: 0 bytes in 0 blocks.
		3401	==2274== still reachable: 256 bytes in 1 blocks.
		3402
		3403	then there is no memory leak. Similarly, under some circumstances,
		3404	valgrind might report kernel bugs as if it were a bug in libev, or it
		3405	might be confused (it is a very good tool, but only a tool).
		3406
		3407	If you are unsure about something, feel free to contact the mailing list
		3408	with the full valgrind report and an explanation on why you think this is
		3409	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3410	no bug" answer and take the chance of learning how to interpret valgrind
		3411	properly.
		3412
		3413	If you need, for some reason, empty reports from valgrind for your project
		3414	I suggest using suppression lists.
		3415
		3416
2871	=head1 AUTHOR	3417	=head1 AUTHOR
2872		3418
2873	Marc Lehmann <libev@schmorp.de>.	3419	Marc Lehmann <libev@schmorp.de>.
2874		3420

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Revision 1.120 by root, Fri Jan 25 15:45:09 2008 UTC vs.
Revision 1.159 by root, Thu May 22 02:44:57 2008 UTC