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

Comparing libev/ev.pod (file contents):
Revision 1.187 by root, Mon Sep 29 03:31:14 2008 UTC vs.
Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC

…		…
17	ev_timer timeout_watcher;	17	ev_timer timeout_watcher;
18		18
19	// all watcher callbacks have a similar signature	19	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	20	// this callback is called when data is readable on stdin
21	static void	21	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	22	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	23	{
24	puts ("stdin ready");	24	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	25	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	26	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	27	ev_io_stop (EV_A_ w);
…		…
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	30	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	31	}
32		32
33	// another callback, this time for a time-out	33	// another callback, this time for a time-out
34	static void	34	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	35	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	36	{
37	puts ("timeout");	37	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	38	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	39	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	40	}
41		41
42	int	42	int
43	main (void)	43	main (void)
44	{	44	{
45	// use the default event loop unless you have special needs	45	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	46	ev_loop *loop = ev_default_loop (0);
47		47
48	// 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	49	// this one will watch for stdin to become readable
50	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);
51	ev_io_start (loop, &stdin_watcher);	51	ev_io_start (loop, &stdin_watcher);
…		…
103	Libev is very configurable. In this manual the default (and most common)	103	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	104	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	105	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	106	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	107	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	108	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	109	this argument.
110		110
111	=head2 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
112		112
113	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
…		…
276		276
277	=back	277	=back
278		278
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		280
281	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<ev_loop *>. The library knows two
282	types of such loops, the I<default> loop, which supports signals and child	282	types of such loops, the I<default> loop, which supports signals and child
283	events, and dynamically created loops which do not.	283	events, and dynamically created loops which do not.
284		284
285	=over 4	285	=over 4
286		286
…		…
685	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	685	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
687		687
688	This "unloop state" will be cleared when entering C<ev_loop> again.	688	This "unloop state" will be cleared when entering C<ev_loop> again.
689		689
		690	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		691
690	=item ev_ref (loop)	692	=item ev_ref (loop)
691		693
692	=item ev_unref (loop)	694	=item ev_unref (loop)
693		695
694	Ref/unref can be used to add or remove a reference count on the event	696	Ref/unref can be used to add or remove a reference count on the event
…		…
708	respectively).	710	respectively).
709		711
710	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
711	running when nothing else is active.	713	running when nothing else is active.
712		714
713	struct ev_signal exitsig;	715	ev_signal exitsig;
714	ev_signal_init (&exitsig, sig_cb, SIGINT);	716	ev_signal_init (&exitsig, sig_cb, SIGINT);
715	ev_signal_start (loop, &exitsig);	717	ev_signal_start (loop, &exitsig);
716	evf_unref (loop);	718	evf_unref (loop);
717		719
718	Example: For some weird reason, unregister the above signal handler again.	720	Example: For some weird reason, unregister the above signal handler again.
…		…
784		786
785	A watcher is a structure that you create and register to record your	787	A watcher is a structure that you create and register to record your
786	interest in some event. For instance, if you want to wait for STDIN to	788	interest in some event. For instance, if you want to wait for STDIN to
787	become readable, you would create an C<ev_io> watcher for that:	789	become readable, you would create an C<ev_io> watcher for that:
788		790
789	static void my_cb (struct ev_loop loop, struct ev_io w, int revents)	791	static void my_cb (struct ev_loop loop, ev_io w, int revents)
790	{	792	{
791	ev_io_stop (w);	793	ev_io_stop (w);
792	ev_unloop (loop, EVUNLOOP_ALL);	794	ev_unloop (loop, EVUNLOOP_ALL);
793	}	795	}
794		796
795	struct ev_loop *loop = ev_default_loop (0);	797	struct ev_loop *loop = ev_default_loop (0);
796	struct ev_io stdin_watcher;	798	ev_io stdin_watcher;
797	ev_init (&stdin_watcher, my_cb);	799	ev_init (&stdin_watcher, my_cb);
798	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
799	ev_io_start (loop, &stdin_watcher);	801	ev_io_start (loop, &stdin_watcher);
800	ev_loop (loop, 0);	802	ev_loop (loop, 0);
801		803
…		…
892	=item C<EV_ERROR>	894	=item C<EV_ERROR>
893		895
894	An unspecified error has occurred, the watcher has been stopped. This might	896	An unspecified error has occurred, the watcher has been stopped. This might
895	happen because the watcher could not be properly started because libev	897	happen because the watcher could not be properly started because libev
896	ran out of memory, a file descriptor was found to be closed or any other	898	ran out of memory, a file descriptor was found to be closed or any other
		899	problem. Libev considers these application bugs.
		900
897	problem. You best act on it by reporting the problem and somehow coping	901	You best act on it by reporting the problem and somehow coping with the
898	with the watcher being stopped.	902	watcher being stopped. Note that well-written programs should not receive
		903	an error ever, so when your watcher receives it, this usually indicates a
		904	bug in your program.
899		905
900	Libev will usually signal a few "dummy" events together with an error, for	906	Libev will usually signal a few "dummy" events together with an error, for
901	example it might indicate that a fd is readable or writable, and if your	907	example it might indicate that a fd is readable or writable, and if your
902	callbacks is well-written it can just attempt the operation and cope with	908	callbacks is well-written it can just attempt the operation and cope with
903	the error from read() or write(). This will not work in multi-threaded	909	the error from read() or write(). This will not work in multi-threaded
…		…
923	which rolls both calls into one.	929	which rolls both calls into one.
924		930
925	You can reinitialise a watcher at any time as long as it has been stopped	931	You can reinitialise a watcher at any time as long as it has been stopped
926	(or never started) and there are no pending events outstanding.	932	(or never started) and there are no pending events outstanding.
927		933
928	The callback is always of type C<void ()(ev_loop loop, ev_TYPE *watcher,	934	The callback is always of type C<void ()(struct ev_loop loop, ev_TYPE *watcher,
929	int revents)>.	935	int revents)>.
930		936
931	Example: Initialise an C<ev_io> watcher in two steps.	937	Example: Initialise an C<ev_io> watcher in two steps.
932		938
933	ev_io w;	939	ev_io w;
…		…
967		973
968	ev_io_start (EV_DEFAULT_UC, &w);	974	ev_io_start (EV_DEFAULT_UC, &w);
969		975
970	=item C<ev_TYPE_stop> (loop , ev_TYPE watcher)	976	=item C<ev_TYPE_stop> (loop , ev_TYPE watcher)
971		977
972	Stops the given watcher again (if active) and clears the pending	978	Stops the given watcher if active, and clears the pending status (whether
		979	the watcher was active or not).
		980
973	status. It is possible that stopped watchers are pending (for example,	981	It is possible that stopped watchers are pending - for example,
974	non-repeating timers are being stopped when they become pending), but	982	non-repeating timers are being stopped when they become pending - but
975	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	983	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
976	you want to free or reuse the memory used by the watcher it is therefore a	984	pending. If you want to free or reuse the memory used by the watcher it is
977	good idea to always call its C<ev_TYPE_stop> function.	985	therefore a good idea to always call its C<ev_TYPE_stop> function.
978		986
979	=item bool ev_is_active (ev_TYPE *watcher)	987	=item bool ev_is_active (ev_TYPE *watcher)
980		988
981	Returns a true value iff the watcher is active (i.e. it has been started	989	Returns a true value iff the watcher is active (i.e. it has been started
982	and not yet been stopped). As long as a watcher is active you must not modify	990	and not yet been stopped). As long as a watcher is active you must not modify
…		…
1056	member, you can also "subclass" the watcher type and provide your own	1064	member, you can also "subclass" the watcher type and provide your own
1057	data:	1065	data:
1058		1066
1059	struct my_io	1067	struct my_io
1060	{	1068	{
1061	struct ev_io io;	1069	ev_io io;
1062	int otherfd;	1070	int otherfd;
1063	void *somedata;	1071	void *somedata;
1064	struct whatever *mostinteresting;	1072	struct whatever *mostinteresting;
1065	};	1073	};
1066		1074
…		…
1069	ev_io_init (&w.io, my_cb, fd, EV_READ);	1077	ev_io_init (&w.io, my_cb, fd, EV_READ);
1070		1078
1071	And since your callback will be called with a pointer to the watcher, you	1079	And since your callback will be called with a pointer to the watcher, you
1072	can cast it back to your own type:	1080	can cast it back to your own type:
1073		1081
1074	static void my_cb (struct ev_loop loop, struct ev_io w_, int revents)	1082	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1075	{	1083	{
1076	struct my_io w = (struct my_io )w_;	1084	struct my_io w = (struct my_io )w_;
1077	...	1085	...
1078	}	1086	}
1079		1087
…		…
1097	programmers):	1105	programmers):
1098		1106
1099	#include <stddef.h>	1107	#include <stddef.h>
1100		1108
1101	static void	1109	static void
1102	t1_cb (EV_P_ struct ev_timer *w, int revents)	1110	t1_cb (EV_P_ ev_timer *w, int revents)
1103	{	1111	{
1104	struct my_biggy big = (struct my_biggy *	1112	struct my_biggy big = (struct my_biggy *
1105	(((char *)w) - offsetof (struct my_biggy, t1));	1113	(((char *)w) - offsetof (struct my_biggy, t1));
1106	}	1114	}
1107		1115
1108	static void	1116	static void
1109	t2_cb (EV_P_ struct ev_timer *w, int revents)	1117	t2_cb (EV_P_ ev_timer *w, int revents)
1110	{	1118	{
1111	struct my_biggy big = (struct my_biggy *	1119	struct my_biggy big = (struct my_biggy *
1112	(((char *)w) - offsetof (struct my_biggy, t2));	1120	(((char *)w) - offsetof (struct my_biggy, t2));
1113	}	1121	}
1114		1122
…		…
1249	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1257	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1250	readable, but only once. Since it is likely line-buffered, you could	1258	readable, but only once. Since it is likely line-buffered, you could
1251	attempt to read a whole line in the callback.	1259	attempt to read a whole line in the callback.
1252		1260
1253	static void	1261	static void
1254	stdin_readable_cb (struct ev_loop loop, struct ev_io w, int revents)	1262	stdin_readable_cb (struct ev_loop loop, ev_io w, int revents)
1255	{	1263	{
1256	ev_io_stop (loop, w);	1264	ev_io_stop (loop, w);
1257	.. read from stdin here (or from w->fd) and handle any I/O errors	1265	.. read from stdin here (or from w->fd) and handle any I/O errors
1258	}	1266	}
1259		1267
1260	...	1268	...
1261	struct ev_loop *loop = ev_default_init (0);	1269	struct ev_loop *loop = ev_default_init (0);
1262	struct ev_io stdin_readable;	1270	ev_io stdin_readable;
1263	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1271	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1264	ev_io_start (loop, &stdin_readable);	1272	ev_io_start (loop, &stdin_readable);
1265	ev_loop (loop, 0);	1273	ev_loop (loop, 0);
1266		1274
1267		1275
…		…
1278		1286
1279	The callback is guaranteed to be invoked only I<after> its timeout has	1287	The callback is guaranteed to be invoked only I<after> its timeout has
1280	passed, but if multiple timers become ready during the same loop iteration	1288	passed, but if multiple timers become ready during the same loop iteration
1281	then order of execution is undefined.	1289	then order of execution is undefined.
1282		1290
		1291	=head3 Be smart about timeouts
		1292
		1293	Many real-world problems involve some kind of timeout, usually for error
		1294	recovery. A typical example is an HTTP request - if the other side hangs,
		1295	you want to raise some error after a while.
		1296
		1297	What follows are some ways to handle this problem, from obvious and
		1298	inefficient to smart and efficient.
		1299
		1300	In the following, a 60 second activity timeout is assumed - a timeout that
		1301	gets reset to 60 seconds each time there is activity (e.g. each time some
		1302	data or other life sign was received).
		1303
		1304	=over 4
		1305
		1306	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1307
		1308	This is the most obvious, but not the most simple way: In the beginning,
		1309	start the watcher:
		1310
		1311	ev_timer_init (timer, callback, 60., 0.);
		1312	ev_timer_start (loop, timer);
		1313
		1314	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1315	and start it again:
		1316
		1317	ev_timer_stop (loop, timer);
		1318	ev_timer_set (timer, 60., 0.);
		1319	ev_timer_start (loop, timer);
		1320
		1321	This is relatively simple to implement, but means that each time there is
		1322	some activity, libev will first have to remove the timer from its internal
		1323	data structure and then add it again. Libev tries to be fast, but it's
		1324	still not a constant-time operation.
		1325
		1326	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1327
		1328	This is the easiest way, and involves using C<ev_timer_again> instead of
		1329	C<ev_timer_start>.
		1330
		1331	To implement this, configure an C<ev_timer> with a C<repeat> value
		1332	of C<60> and then call C<ev_timer_again> at start and each time you
		1333	successfully read or write some data. If you go into an idle state where
		1334	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1335	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1336
		1337	That means you can ignore both the C<ev_timer_start> function and the
		1338	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1339	member and C<ev_timer_again>.
		1340
		1341	At start:
		1342
		1343	ev_timer_init (timer, callback);
		1344	timer->repeat = 60.;
		1345	ev_timer_again (loop, timer);
		1346
		1347	Each time there is some activity:
		1348
		1349	ev_timer_again (loop, timer);
		1350
		1351	It is even possible to change the time-out on the fly, regardless of
		1352	whether the watcher is active or not:
		1353
		1354	timer->repeat = 30.;
		1355	ev_timer_again (loop, timer);
		1356
		1357	This is slightly more efficient then stopping/starting the timer each time
		1358	you want to modify its timeout value, as libev does not have to completely
		1359	remove and re-insert the timer from/into its internal data structure.
		1360
		1361	It is, however, even simpler than the "obvious" way to do it.
		1362
		1363	=item 3. Let the timer time out, but then re-arm it as required.
		1364
		1365	This method is more tricky, but usually most efficient: Most timeouts are
		1366	relatively long compared to the intervals between other activity - in
		1367	our example, within 60 seconds, there are usually many I/O events with
		1368	associated activity resets.
		1369
		1370	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1371	but remember the time of last activity, and check for a real timeout only
		1372	within the callback:
		1373
		1374	ev_tstamp last_activity; // time of last activity
		1375
		1376	static void
		1377	callback (EV_P_ ev_timer *w, int revents)
		1378	{
		1379	ev_tstamp now = ev_now (EV_A);
		1380	ev_tstamp timeout = last_activity + 60.;
		1381
		1382	// if last_activity + 60. is older than now, we did time out
		1383	if (timeout < now)
		1384	{
		1385	// timeout occured, take action
		1386	}
		1387	else
		1388	{
		1389	// callback was invoked, but there was some activity, re-arm
		1390	// the watcher to fire in last_activity + 60, which is
		1391	// guaranteed to be in the future, so "again" is positive:
		1392	w->again = timeout - now;
		1393	ev_timer_again (EV_A_ w);
		1394	}
		1395	}
		1396
		1397	To summarise the callback: first calculate the real timeout (defined
		1398	as "60 seconds after the last activity"), then check if that time has
		1399	been reached, which means something I<did>, in fact, time out. Otherwise
		1400	the callback was invoked too early (C<timeout> is in the future), so
		1401	re-schedule the timer to fire at that future time, to see if maybe we have
		1402	a timeout then.
		1403
		1404	Note how C<ev_timer_again> is used, taking advantage of the
		1405	C<ev_timer_again> optimisation when the timer is already running.
		1406
		1407	This scheme causes more callback invocations (about one every 60 seconds
		1408	minus half the average time between activity), but virtually no calls to
		1409	libev to change the timeout.
		1410
		1411	To start the timer, simply initialise the watcher and set C<last_activity>
		1412	to the current time (meaning we just have some activity :), then call the
		1413	callback, which will "do the right thing" and start the timer:
		1414
		1415	ev_timer_init (timer, callback);
		1416	last_activity = ev_now (loop);
		1417	callback (loop, timer, EV_TIMEOUT);
		1418
		1419	And when there is some activity, simply store the current time in
		1420	C<last_activity>, no libev calls at all:
		1421
		1422	last_actiivty = ev_now (loop);
		1423
		1424	This technique is slightly more complex, but in most cases where the
		1425	time-out is unlikely to be triggered, much more efficient.
		1426
		1427	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1428	callback :) - just change the timeout and invoke the callback, which will
		1429	fix things for you.
		1430
		1431	=item 4. Whee, use a double-linked list for your timeouts.
		1432
		1433	If there is not one request, but many thousands, all employing some kind
		1434	of timeout with the same timeout value, then one can do even better:
		1435
		1436	When starting the timeout, calculate the timeout value and put the timeout
		1437	at the I<end> of the list.
		1438
		1439	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1440	the list is expected to fire (for example, using the technique #3).
		1441
		1442	When there is some activity, remove the timer from the list, recalculate
		1443	the timeout, append it to the end of the list again, and make sure to
		1444	update the C<ev_timer> if it was taken from the beginning of the list.
		1445
		1446	This way, one can manage an unlimited number of timeouts in O(1) time for
		1447	starting, stopping and updating the timers, at the expense of a major
		1448	complication, and having to use a constant timeout. The constant timeout
		1449	ensures that the list stays sorted.
		1450
		1451	=back
		1452
		1453	So what method is the best?
		1454
		1455	The method #2 is a simple no-brain-required solution that is adequate in
		1456	most situations. Method #3 requires a bit more thinking, but handles many
		1457	cases better, and isn't very complicated either. In most case, choosing
		1458	either one is fine.
		1459
		1460	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1461	rather complicated, but extremely efficient, something that really pays
		1462	off after the first or so million of active timers, i.e. it's usually
		1463	overkill :)
		1464
1283	=head3 The special problem of time updates	1465	=head3 The special problem of time updates
1284		1466
1285	Establishing the current time is a costly operation (it usually takes at	1467	Establishing the current time is a costly operation (it usually takes at
1286	least two system calls): EV therefore updates its idea of the current	1468	least two system calls): EV therefore updates its idea of the current
1287	time only before and after C<ev_loop> collects new events, which causes a	1469	time only before and after C<ev_loop> collects new events, which causes a
…		…
1330	If the timer is started but non-repeating, stop it (as if it timed out).	1512	If the timer is started but non-repeating, stop it (as if it timed out).
1331		1513
1332	If the timer is repeating, either start it if necessary (with the	1514	If the timer is repeating, either start it if necessary (with the
1333	C<repeat> value), or reset the running timer to the C<repeat> value.	1515	C<repeat> value), or reset the running timer to the C<repeat> value.
1334		1516
1335	This sounds a bit complicated, but here is a useful and typical	1517	This sounds a bit complicated, see "Be smart about timeouts", above, for a
1336	example: Imagine you have a TCP connection and you want a so-called idle	1518	usage example.
1337	timeout, that is, you want to be called when there have been, say, 60
1338	seconds of inactivity on the socket. The easiest way to do this is to
1339	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1340	C<ev_timer_again> each time you successfully read or write some data. If
1341	you go into an idle state where you do not expect data to travel on the
1342	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1343	automatically restart it if need be.
1344
1345	That means you can ignore the C<after> value and C<ev_timer_start>
1346	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1347
1348	ev_timer_init (timer, callback, 0., 5.);
1349	ev_timer_again (loop, timer);
1350	...
1351	timer->again = 17.;
1352	ev_timer_again (loop, timer);
1353	...
1354	timer->again = 10.;
1355	ev_timer_again (loop, timer);
1356
1357	This is more slightly efficient then stopping/starting the timer each time
1358	you want to modify its timeout value.
1359
1360	Note, however, that it is often even more efficient to remember the
1361	time of the last activity and let the timer time-out naturally. In the
1362	callback, you then check whether the time-out is real, or, if there was
1363	some activity, you reschedule the watcher to time-out in "last_activity +
1364	timeout - ev_now ()" seconds.
1365		1519
1366	=item ev_tstamp repeat [read-write]	1520	=item ev_tstamp repeat [read-write]
1367		1521
1368	The current C<repeat> value. Will be used each time the watcher times out	1522	The current C<repeat> value. Will be used each time the watcher times out
1369	or C<ev_timer_again> is called, and determines the next timeout (if any),	1523	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1374	=head3 Examples	1528	=head3 Examples
1375		1529
1376	Example: Create a timer that fires after 60 seconds.	1530	Example: Create a timer that fires after 60 seconds.
1377		1531
1378	static void	1532	static void
1379	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)	1533	one_minute_cb (struct ev_loop loop, ev_timer w, int revents)
1380	{	1534	{
1381	.. one minute over, w is actually stopped right here	1535	.. one minute over, w is actually stopped right here
1382	}	1536	}
1383		1537
1384	struct ev_timer mytimer;	1538	ev_timer mytimer;
1385	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1539	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1386	ev_timer_start (loop, &mytimer);	1540	ev_timer_start (loop, &mytimer);
1387		1541
1388	Example: Create a timeout timer that times out after 10 seconds of	1542	Example: Create a timeout timer that times out after 10 seconds of
1389	inactivity.	1543	inactivity.
1390		1544
1391	static void	1545	static void
1392	timeout_cb (struct ev_loop loop, struct ev_timer w, int revents)	1546	timeout_cb (struct ev_loop loop, ev_timer w, int revents)
1393	{	1547	{
1394	.. ten seconds without any activity	1548	.. ten seconds without any activity
1395	}	1549	}
1396		1550
1397	struct ev_timer mytimer;	1551	ev_timer mytimer;
1398	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1552	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1399	ev_timer_again (&mytimer); /* start timer */	1553	ev_timer_again (&mytimer); /* start timer */
1400	ev_loop (loop, 0);	1554	ev_loop (loop, 0);
1401		1555
1402	// and in some piece of code that gets executed on any "activity":	1556	// and in some piece of code that gets executed on any "activity":
…		…
1488		1642
1489	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1643	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1490	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1644	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1491	only event loop modification you are allowed to do).	1645	only event loop modification you are allowed to do).
1492		1646
1493	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1647	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1494	*w, ev_tstamp now)>, e.g.:	1648	*w, ev_tstamp now)>, e.g.:
1495		1649
		1650	static ev_tstamp
1496	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1651	my_rescheduler (ev_periodic *w, ev_tstamp now)
1497	{	1652	{
1498	return now + 60.;	1653	return now + 60.;
1499	}	1654	}
1500		1655
1501	It must return the next time to trigger, based on the passed time value	1656	It must return the next time to trigger, based on the passed time value
…		…
1538		1693
1539	The current interval value. Can be modified any time, but changes only	1694	The current interval value. Can be modified any time, but changes only
1540	take effect when the periodic timer fires or C<ev_periodic_again> is being	1695	take effect when the periodic timer fires or C<ev_periodic_again> is being
1541	called.	1696	called.
1542		1697
1543	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]	1698	=item ev_tstamp (reschedule_cb)(ev_periodic w, ev_tstamp now) [read-write]
1544		1699
1545	The current reschedule callback, or C<0>, if this functionality is	1700	The current reschedule callback, or C<0>, if this functionality is
1546	switched off. Can be changed any time, but changes only take effect when	1701	switched off. Can be changed any time, but changes only take effect when
1547	the periodic timer fires or C<ev_periodic_again> is being called.	1702	the periodic timer fires or C<ev_periodic_again> is being called.
1548		1703
…		…
1553	Example: Call a callback every hour, or, more precisely, whenever the	1708	Example: Call a callback every hour, or, more precisely, whenever the
1554	system time is divisible by 3600. The callback invocation times have	1709	system time is divisible by 3600. The callback invocation times have
1555	potentially a lot of jitter, but good long-term stability.	1710	potentially a lot of jitter, but good long-term stability.
1556		1711
1557	static void	1712	static void
1558	clock_cb (struct ev_loop loop, struct ev_io w, int revents)	1713	clock_cb (struct ev_loop loop, ev_io w, int revents)
1559	{	1714	{
1560	... its now a full hour (UTC, or TAI or whatever your clock follows)	1715	... its now a full hour (UTC, or TAI or whatever your clock follows)
1561	}	1716	}
1562		1717
1563	struct ev_periodic hourly_tick;	1718	ev_periodic hourly_tick;
1564	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1719	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1565	ev_periodic_start (loop, &hourly_tick);	1720	ev_periodic_start (loop, &hourly_tick);
1566		1721
1567	Example: The same as above, but use a reschedule callback to do it:	1722	Example: The same as above, but use a reschedule callback to do it:
1568		1723
1569	#include <math.h>	1724	#include <math.h>
1570		1725
1571	static ev_tstamp	1726	static ev_tstamp
1572	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1727	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1573	{	1728	{
1574	return now + (3600. - fmod (now, 3600.));	1729	return now + (3600. - fmod (now, 3600.));
1575	}	1730	}
1576		1731
1577	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1732	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1578		1733
1579	Example: Call a callback every hour, starting now:	1734	Example: Call a callback every hour, starting now:
1580		1735
1581	struct ev_periodic hourly_tick;	1736	ev_periodic hourly_tick;
1582	ev_periodic_init (&hourly_tick, clock_cb,	1737	ev_periodic_init (&hourly_tick, clock_cb,
1583	fmod (ev_now (loop), 3600.), 3600., 0);	1738	fmod (ev_now (loop), 3600.), 3600., 0);
1584	ev_periodic_start (loop, &hourly_tick);	1739	ev_periodic_start (loop, &hourly_tick);
1585		1740
1586		1741
…		…
1625		1780
1626	=back	1781	=back
1627		1782
1628	=head3 Examples	1783	=head3 Examples
1629		1784
1630	Example: Try to exit cleanly on SIGINT and SIGTERM.	1785	Example: Try to exit cleanly on SIGINT.
1631		1786
1632	static void	1787	static void
1633	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)	1788	sigint_cb (struct ev_loop loop, ev_signal w, int revents)
1634	{	1789	{
1635	ev_unloop (loop, EVUNLOOP_ALL);	1790	ev_unloop (loop, EVUNLOOP_ALL);
1636	}	1791	}
1637		1792
1638	struct ev_signal signal_watcher;	1793	ev_signal signal_watcher;
1639	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1794	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1640	ev_signal_start (loop, &sigint_cb);	1795	ev_signal_start (loop, &signal_watcher);
1641		1796
1642		1797
1643	=head2 C<ev_child> - watch out for process status changes	1798	=head2 C<ev_child> - watch out for process status changes
1644		1799
1645	Child watchers trigger when your process receives a SIGCHLD in response to	1800	Child watchers trigger when your process receives a SIGCHLD in response to
…		…
1718	its completion.	1873	its completion.
1719		1874
1720	ev_child cw;	1875	ev_child cw;
1721		1876
1722	static void	1877	static void
1723	child_cb (EV_P_ struct ev_child *w, int revents)	1878	child_cb (EV_P_ ev_child *w, int revents)
1724	{	1879	{
1725	ev_child_stop (EV_A_ w);	1880	ev_child_stop (EV_A_ w);
1726	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	1881	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1727	}	1882	}
1728		1883
…		…
1792	to exchange stat structures with application programs compiled using the	1947	to exchange stat structures with application programs compiled using the
1793	default compilation environment.	1948	default compilation environment.
1794		1949
1795	=head3 Inotify and Kqueue	1950	=head3 Inotify and Kqueue
1796		1951
1797	When C<inotify (7)> support has been compiled into libev (generally only	1952	When C<inotify (7)> support has been compiled into libev (generally
		1953	only available with Linux 2.6.25 or above due to bugs in earlier
1798	available with Linux) and present at runtime, it will be used to speed up	1954	implementations) and present at runtime, it will be used to speed up
1799	change detection where possible. The inotify descriptor will be created lazily	1955	change detection where possible. The inotify descriptor will be created
1800	when the first C<ev_stat> watcher is being started.	1956	lazily when the first C<ev_stat> watcher is being started.
1801		1957
1802	Inotify presence does not change the semantics of C<ev_stat> watchers	1958	Inotify presence does not change the semantics of C<ev_stat> watchers
1803	except that changes might be detected earlier, and in some cases, to avoid	1959	except that changes might be detected earlier, and in some cases, to avoid
1804	making regular C<stat> calls. Even in the presence of inotify support	1960	making regular C<stat> calls. Even in the presence of inotify support
1805	there are many cases where libev has to resort to regular C<stat> polling,	1961	there are many cases where libev has to resort to regular C<stat> polling,
…		…
1979		2135
1980	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2136	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1981	callback, free it. Also, use no error checking, as usual.	2137	callback, free it. Also, use no error checking, as usual.
1982		2138
1983	static void	2139	static void
1984	idle_cb (struct ev_loop loop, struct ev_idle w, int revents)	2140	idle_cb (struct ev_loop loop, ev_idle w, int revents)
1985	{	2141	{
1986	free (w);	2142	free (w);
1987	// now do something you wanted to do when the program has	2143	// now do something you wanted to do when the program has
1988	// no longer anything immediate to do.	2144	// no longer anything immediate to do.
1989	}	2145	}
1990		2146
1991	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2147	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1992	ev_idle_init (idle_watcher, idle_cb);	2148	ev_idle_init (idle_watcher, idle_cb);
1993	ev_idle_start (loop, idle_cb);	2149	ev_idle_start (loop, idle_cb);
1994		2150
1995		2151
1996	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2152	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
…		…
2077		2233
2078	static ev_io iow [nfd];	2234	static ev_io iow [nfd];
2079	static ev_timer tw;	2235	static ev_timer tw;
2080		2236
2081	static void	2237	static void
2082	io_cb (ev_loop loop, ev_io w, int revents)	2238	io_cb (struct ev_loop loop, ev_io w, int revents)
2083	{	2239	{
2084	}	2240	}
2085		2241
2086	// create io watchers for each fd and a timer before blocking	2242	// create io watchers for each fd and a timer before blocking
2087	static void	2243	static void
2088	adns_prepare_cb (ev_loop loop, ev_prepare w, int revents)	2244	adns_prepare_cb (struct ev_loop loop, ev_prepare w, int revents)
2089	{	2245	{
2090	int timeout = 3600000;	2246	int timeout = 3600000;
2091	struct pollfd fds [nfd];	2247	struct pollfd fds [nfd];
2092	// actual code will need to loop here and realloc etc.	2248	// actual code will need to loop here and realloc etc.
2093	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2249	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
…		…
2108	}	2264	}
2109	}	2265	}
2110		2266
2111	// stop all watchers after blocking	2267	// stop all watchers after blocking
2112	static void	2268	static void
2113	adns_check_cb (ev_loop loop, ev_check w, int revents)	2269	adns_check_cb (struct ev_loop loop, ev_check w, int revents)
2114	{	2270	{
2115	ev_timer_stop (loop, &tw);	2271	ev_timer_stop (loop, &tw);
2116		2272
2117	for (int i = 0; i < nfd; ++i)	2273	for (int i = 0; i < nfd; ++i)
2118	{	2274	{
…		…
2286	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2442	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2287	used).	2443	used).
2288		2444
2289	struct ev_loop *loop_hi = ev_default_init (0);	2445	struct ev_loop *loop_hi = ev_default_init (0);
2290	struct ev_loop *loop_lo = 0;	2446	struct ev_loop *loop_lo = 0;
2291	struct ev_embed embed;	2447	ev_embed embed;
2292		2448
2293	// see if there is a chance of getting one that works	2449	// see if there is a chance of getting one that works
2294	// (remember that a flags value of 0 means autodetection)	2450	// (remember that a flags value of 0 means autodetection)
2295	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2451	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2296	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2452	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2310	kqueue implementation). Store the kqueue/socket-only event loop in	2466	kqueue implementation). Store the kqueue/socket-only event loop in
2311	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2467	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2312		2468
2313	struct ev_loop *loop = ev_default_init (0);	2469	struct ev_loop *loop = ev_default_init (0);
2314	struct ev_loop *loop_socket = 0;	2470	struct ev_loop *loop_socket = 0;
2315	struct ev_embed embed;	2471	ev_embed embed;
2316		2472
2317	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2473	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2318	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2474	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2319	{	2475	{
2320	ev_embed_init (&embed, 0, loop_socket);	2476	ev_embed_init (&embed, 0, loop_socket);
…		…
2384	=over 4	2540	=over 4
2385		2541
2386	=item queueing from a signal handler context	2542	=item queueing from a signal handler context
2387		2543
2388	To implement race-free queueing, you simply add to the queue in the signal	2544	To implement race-free queueing, you simply add to the queue in the signal
2389	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2545	handler but you block the signal handler in the watcher callback. Here is
2390	some fictitious SIGUSR1 handler:	2546	an example that does that for some fictitious SIGUSR1 handler:
2391		2547
2392	static ev_async mysig;	2548	static ev_async mysig;
2393		2549
2394	static void	2550	static void
2395	sigusr1_handler (void)	2551	sigusr1_handler (void)
…		…
2502	=over 4	2658	=over 4
2503		2659
2504	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2660	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2505		2661
2506	This function combines a simple timer and an I/O watcher, calls your	2662	This function combines a simple timer and an I/O watcher, calls your
2507	callback on whichever event happens first and automatically stop both	2663	callback on whichever event happens first and automatically stops both
2508	watchers. This is useful if you want to wait for a single event on an fd	2664	watchers. This is useful if you want to wait for a single event on an fd
2509	or timeout without having to allocate/configure/start/stop/free one or	2665	or timeout without having to allocate/configure/start/stop/free one or
2510	more watchers yourself.	2666	more watchers yourself.
2511		2667
2512	If C<fd> is less than 0, then no I/O watcher will be started and events	2668	If C<fd> is less than 0, then no I/O watcher will be started and the
2513	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2669	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2514	C<events> set will be created and started.	2670	the given C<fd> and C<events> set will be created and started.
2515		2671
2516	If C<timeout> is less than 0, then no timeout watcher will be	2672	If C<timeout> is less than 0, then no timeout watcher will be
2517	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2673	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2518	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2674	repeat = 0) will be started. C<0> is a valid timeout.
2519	dubious value.
2520		2675
2521	The callback has the type C<void (cb)(int revents, void arg)> and gets	2676	The callback has the type C<void (cb)(int revents, void arg)> and gets
2522	passed an C<revents> set like normal event callbacks (a combination of	2677	passed an C<revents> set like normal event callbacks (a combination of
2523	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2678	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2524	value passed to C<ev_once>:	2679	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2680	a timeout and an io event at the same time - you probably should give io
		2681	events precedence.
		2682
		2683	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2525		2684
2526	static void stdin_ready (int revents, void *arg)	2685	static void stdin_ready (int revents, void *arg)
2527	{	2686	{
		2687	if (revents & EV_READ)
		2688	/* stdin might have data for us, joy! */;
2528	if (revents & EV_TIMEOUT)	2689	else if (revents & EV_TIMEOUT)
2529	/* doh, nothing entered */;	2690	/* doh, nothing entered */;
2530	else if (revents & EV_READ)
2531	/* stdin might have data for us, joy! */;
2532	}	2691	}
2533		2692
2534	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2693	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2535		2694
2536	=item ev_feed_event (ev_loop , watcher , int revents)	2695	=item ev_feed_event (struct ev_loop , watcher , int revents)
2537		2696
2538	Feeds the given event set into the event loop, as if the specified event	2697	Feeds the given event set into the event loop, as if the specified event
2539	had happened for the specified watcher (which must be a pointer to an	2698	had happened for the specified watcher (which must be a pointer to an
2540	initialised but not necessarily started event watcher).	2699	initialised but not necessarily started event watcher).
2541		2700
2542	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2701	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2543		2702
2544	Feed an event on the given fd, as if a file descriptor backend detected	2703	Feed an event on the given fd, as if a file descriptor backend detected
2545	the given events it.	2704	the given events it.
2546		2705
2547	=item ev_feed_signal_event (ev_loop *loop, int signum)	2706	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2548		2707
2549	Feed an event as if the given signal occurred (C<loop> must be the default	2708	Feed an event as if the given signal occurred (C<loop> must be the default
2550	loop!).	2709	loop!).
2551		2710
2552	=back	2711	=back
…		…
3306	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3465	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3307		3466
3308	#include "ev_cpp.h"	3467	#include "ev_cpp.h"
3309	#include "ev.c"	3468	#include "ev.c"
3310		3469
		3470	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3311		3471
3312	=head1 THREADS AND COROUTINES	3472	=head2 THREADS AND COROUTINES
3313		3473
3314	=head2 THREADS	3474	=head3 THREADS
3315		3475
3316	All libev functions are reentrant and thread-safe unless explicitly	3476	All libev functions are reentrant and thread-safe unless explicitly
3317	documented otherwise, but it uses no locking itself. This means that you	3477	documented otherwise, but libev implements no locking itself. This means
3318	can use as many loops as you want in parallel, as long as there are no	3478	that you can use as many loops as you want in parallel, as long as there
3319	concurrent calls into any libev function with the same loop parameter	3479	are no concurrent calls into any libev function with the same loop
3320	(C<ev_default_*> calls have an implicit default loop parameter, of	3480	parameter (C<ev_default_*> calls have an implicit default loop parameter,
3321	course): libev guarantees that different event loops share no data	3481	of course): libev guarantees that different event loops share no data
3322	structures that need any locking.	3482	structures that need any locking.
3323		3483
3324	Or to put it differently: calls with different loop parameters can be done	3484	Or to put it differently: calls with different loop parameters can be done
3325	concurrently from multiple threads, calls with the same loop parameter	3485	concurrently from multiple threads, calls with the same loop parameter
3326	must be done serially (but can be done from different threads, as long as	3486	must be done serially (but can be done from different threads, as long as
…		…
3366	default loop and triggering an C<ev_async> watcher from the default loop	3526	default loop and triggering an C<ev_async> watcher from the default loop
3367	watcher callback into the event loop interested in the signal.	3527	watcher callback into the event loop interested in the signal.
3368		3528
3369	=back	3529	=back
3370		3530
3371	=head2 COROUTINES	3531	=head3 COROUTINES
3372		3532
3373	Libev is much more accommodating to coroutines ("cooperative threads"):	3533	Libev is very accommodating to coroutines ("cooperative threads"):
3374	libev fully supports nesting calls to it's functions from different	3534	libev fully supports nesting calls to its functions from different
3375	coroutines (e.g. you can call C<ev_loop> on the same loop from two	3535	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3376	different coroutines and switch freely between both coroutines running the	3536	different coroutines, and switch freely between both coroutines running the
3377	loop, as long as you don't confuse yourself). The only exception is that	3537	loop, as long as you don't confuse yourself). The only exception is that
3378	you must not do this from C<ev_periodic> reschedule callbacks.	3538	you must not do this from C<ev_periodic> reschedule callbacks.
3379		3539
3380	Care has been taken to ensure that libev does not keep local state inside	3540	Care has been taken to ensure that libev does not keep local state inside
3381	C<ev_loop>, and other calls do not usually allow coroutine switches.	3541	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3542	they do not clal any callbacks.
3382		3543
		3544	=head2 COMPILER WARNINGS
3383		3545
3384	=head1 COMPLEXITIES	3546	Depending on your compiler and compiler settings, you might get no or a
		3547	lot of warnings when compiling libev code. Some people are apparently
		3548	scared by this.
3385		3549
3386	In this section the complexities of (many of) the algorithms used inside	3550	However, these are unavoidable for many reasons. For one, each compiler
3387	libev will be explained. For complexity discussions about backends see the	3551	has different warnings, and each user has different tastes regarding
3388	documentation for C<ev_default_init>.	3552	warning options. "Warn-free" code therefore cannot be a goal except when
		3553	targeting a specific compiler and compiler-version.
3389		3554
3390	All of the following are about amortised time: If an array needs to be	3555	Another reason is that some compiler warnings require elaborate
3391	extended, libev needs to realloc and move the whole array, but this	3556	workarounds, or other changes to the code that make it less clear and less
3392	happens asymptotically never with higher number of elements, so O(1) might	3557	maintainable.
3393	mean it might do a lengthy realloc operation in rare cases, but on average
3394	it is much faster and asymptotically approaches constant time.
3395		3558
3396	=over 4	3559	And of course, some compiler warnings are just plain stupid, or simply
		3560	wrong (because they don't actually warn about the condition their message
		3561	seems to warn about). For example, certain older gcc versions had some
		3562	warnings that resulted an extreme number of false positives. These have
		3563	been fixed, but some people still insist on making code warn-free with
		3564	such buggy versions.
3397		3565
3398	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3566	While libev is written to generate as few warnings as possible,
		3567	"warn-free" code is not a goal, and it is recommended not to build libev
		3568	with any compiler warnings enabled unless you are prepared to cope with
		3569	them (e.g. by ignoring them). Remember that warnings are just that:
		3570	warnings, not errors, or proof of bugs.
3399		3571
3400	This means that, when you have a watcher that triggers in one hour and
3401	there are 100 watchers that would trigger before that then inserting will
3402	have to skip roughly seven (C<ld 100>) of these watchers.
3403		3572
3404	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3573	=head2 VALGRIND
3405		3574
3406	That means that changing a timer costs less than removing/adding them	3575	Valgrind has a special section here because it is a popular tool that is
3407	as only the relative motion in the event queue has to be paid for.	3576	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3408		3577
3409	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	3578	If you think you found a bug (memory leak, uninitialised data access etc.)
		3579	in libev, then check twice: If valgrind reports something like:
3410		3580
3411	These just add the watcher into an array or at the head of a list.	3581	==2274== definitely lost: 0 bytes in 0 blocks.
		3582	==2274== possibly lost: 0 bytes in 0 blocks.
		3583	==2274== still reachable: 256 bytes in 1 blocks.
3412		3584
3413	=item Stopping check/prepare/idle/fork/async watchers: O(1)	3585	Then there is no memory leak, just as memory accounted to global variables
		3586	is not a memleak - the memory is still being refernced, and didn't leak.
3414		3587
3415	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3588	Similarly, under some circumstances, valgrind might report kernel bugs
		3589	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3590	although an acceptable workaround has been found here), or it might be
		3591	confused.
3416		3592
3417	These watchers are stored in lists then need to be walked to find the	3593	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3418	correct watcher to remove. The lists are usually short (you don't usually	3594	make it into some kind of religion.
3419	have many watchers waiting for the same fd or signal).
3420		3595
3421	=item Finding the next timer in each loop iteration: O(1)	3596	If you are unsure about something, feel free to contact the mailing list
		3597	with the full valgrind report and an explanation on why you think this
		3598	is a bug in libev (best check the archives, too :). However, don't be
		3599	annoyed when you get a brisk "this is no bug" answer and take the chance
		3600	of learning how to interpret valgrind properly.
3422		3601
3423	By virtue of using a binary or 4-heap, the next timer is always found at a	3602	If you need, for some reason, empty reports from valgrind for your project
3424	fixed position in the storage array.	3603	I suggest using suppression lists.
3425		3604
3426	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3427		3605
3428	A change means an I/O watcher gets started or stopped, which requires	3606	=head1 PORTABILITY NOTES
3429	libev to recalculate its status (and possibly tell the kernel, depending
3430	on backend and whether C<ev_io_set> was used).
3431		3607
3432	=item Activating one watcher (putting it into the pending state): O(1)
3433
3434	=item Priority handling: O(number_of_priorities)
3435
3436	Priorities are implemented by allocating some space for each
3437	priority. When doing priority-based operations, libev usually has to
3438	linearly search all the priorities, but starting/stopping and activating
3439	watchers becomes O(1) with respect to priority handling.
3440
3441	=item Sending an ev_async: O(1)
3442
3443	=item Processing ev_async_send: O(number_of_async_watchers)
3444
3445	=item Processing signals: O(max_signal_number)
3446
3447	Sending involves a system call I<iff> there were no other C<ev_async_send>
3448	calls in the current loop iteration. Checking for async and signal events
3449	involves iterating over all running async watchers or all signal numbers.
3450
3451	=back
3452
3453
3454	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	3608	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3455		3609
3456	Win32 doesn't support any of the standards (e.g. POSIX) that libev	3610	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3457	requires, and its I/O model is fundamentally incompatible with the POSIX	3611	requires, and its I/O model is fundamentally incompatible with the POSIX
3458	model. Libev still offers limited functionality on this platform in	3612	model. Libev still offers limited functionality on this platform in
3459	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3613	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3546	wrap all I/O functions and provide your own fd management, but the cost of	3700	wrap all I/O functions and provide your own fd management, but the cost of
3547	calling select (O(n²)) will likely make this unworkable.	3701	calling select (O(n²)) will likely make this unworkable.
3548		3702
3549	=back	3703	=back
3550		3704
3551
3552	=head1 PORTABILITY REQUIREMENTS	3705	=head2 PORTABILITY REQUIREMENTS
3553		3706
3554	In addition to a working ISO-C implementation, libev relies on a few	3707	In addition to a working ISO-C implementation and of course the
3555	additional extensions:	3708	backend-specific APIs, libev relies on a few additional extensions:
3556		3709
3557	=over 4	3710	=over 4
3558		3711
3559	=item C<void ()(ev_watcher_type , int revents)> must have compatible	3712	=item C<void ()(ev_watcher_type , int revents)> must have compatible
3560	calling conventions regardless of C<ev_watcher_type *>.	3713	calling conventions regardless of C<ev_watcher_type *>.
…		…
3585	except the initial one, and run the default loop in the initial thread as	3738	except the initial one, and run the default loop in the initial thread as
3586	well.	3739	well.
3587		3740
3588	=item C<long> must be large enough for common memory allocation sizes	3741	=item C<long> must be large enough for common memory allocation sizes
3589		3742
3590	To improve portability and simplify using libev, libev uses C<long>	3743	To improve portability and simplify its API, libev uses C<long> internally
3591	internally instead of C<size_t> when allocating its data structures. On	3744	instead of C<size_t> when allocating its data structures. On non-POSIX
3592	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	3745	systems (Microsoft...) this might be unexpectedly low, but is still at
3593	is still at least 31 bits everywhere, which is enough for hundreds of	3746	least 31 bits everywhere, which is enough for hundreds of millions of
3594	millions of watchers.	3747	watchers.
3595		3748
3596	=item C<double> must hold a time value in seconds with enough accuracy	3749	=item C<double> must hold a time value in seconds with enough accuracy
3597		3750
3598	The type C<double> is used to represent timestamps. It is required to	3751	The type C<double> is used to represent timestamps. It is required to
3599	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	3752	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
…		…
3603	=back	3756	=back
3604		3757
3605	If you know of other additional requirements drop me a note.	3758	If you know of other additional requirements drop me a note.
3606		3759
3607		3760
3608	=head1 COMPILER WARNINGS	3761	=head1 ALGORITHMIC COMPLEXITIES
3609		3762
3610	Depending on your compiler and compiler settings, you might get no or a	3763	In this section the complexities of (many of) the algorithms used inside
3611	lot of warnings when compiling libev code. Some people are apparently	3764	libev will be documented. For complexity discussions about backends see
3612	scared by this.	3765	the documentation for C<ev_default_init>.
3613		3766
3614	However, these are unavoidable for many reasons. For one, each compiler	3767	All of the following are about amortised time: If an array needs to be
3615	has different warnings, and each user has different tastes regarding	3768	extended, libev needs to realloc and move the whole array, but this
3616	warning options. "Warn-free" code therefore cannot be a goal except when	3769	happens asymptotically rarer with higher number of elements, so O(1) might
3617	targeting a specific compiler and compiler-version.	3770	mean that libev does a lengthy realloc operation in rare cases, but on
		3771	average it is much faster and asymptotically approaches constant time.
3618		3772
3619	Another reason is that some compiler warnings require elaborate	3773	=over 4
3620	workarounds, or other changes to the code that make it less clear and less
3621	maintainable.
3622		3774
3623	And of course, some compiler warnings are just plain stupid, or simply	3775	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3624	wrong (because they don't actually warn about the condition their message
3625	seems to warn about).
3626		3776
3627	While libev is written to generate as few warnings as possible,	3777	This means that, when you have a watcher that triggers in one hour and
3628	"warn-free" code is not a goal, and it is recommended not to build libev	3778	there are 100 watchers that would trigger before that, then inserting will
3629	with any compiler warnings enabled unless you are prepared to cope with	3779	have to skip roughly seven (C<ld 100>) of these watchers.
3630	them (e.g. by ignoring them). Remember that warnings are just that:
3631	warnings, not errors, or proof of bugs.
3632		3780
		3781	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3633		3782
3634	=head1 VALGRIND	3783	That means that changing a timer costs less than removing/adding them,
		3784	as only the relative motion in the event queue has to be paid for.
3635		3785
3636	Valgrind has a special section here because it is a popular tool that is	3786	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3637	highly useful, but valgrind reports are very hard to interpret.
3638		3787
3639	If you think you found a bug (memory leak, uninitialised data access etc.)	3788	These just add the watcher into an array or at the head of a list.
3640	in libev, then check twice: If valgrind reports something like:
3641		3789
3642	==2274== definitely lost: 0 bytes in 0 blocks.	3790	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3643	==2274== possibly lost: 0 bytes in 0 blocks.
3644	==2274== still reachable: 256 bytes in 1 blocks.
3645		3791
3646	Then there is no memory leak. Similarly, under some circumstances,	3792	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3647	valgrind might report kernel bugs as if it were a bug in libev, or it
3648	might be confused (it is a very good tool, but only a tool).
3649		3793
3650	If you are unsure about something, feel free to contact the mailing list	3794	These watchers are stored in lists, so they need to be walked to find the
3651	with the full valgrind report and an explanation on why you think this is	3795	correct watcher to remove. The lists are usually short (you don't usually
3652	a bug in libev. However, don't be annoyed when you get a brisk "this is	3796	have many watchers waiting for the same fd or signal: one is typical, two
3653	no bug" answer and take the chance of learning how to interpret valgrind	3797	is rare).
3654	properly.
3655		3798
3656	If you need, for some reason, empty reports from valgrind for your project	3799	=item Finding the next timer in each loop iteration: O(1)
3657	I suggest using suppression lists.	3800
		3801	By virtue of using a binary or 4-heap, the next timer is always found at a
		3802	fixed position in the storage array.
		3803
		3804	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3805
		3806	A change means an I/O watcher gets started or stopped, which requires
		3807	libev to recalculate its status (and possibly tell the kernel, depending
		3808	on backend and whether C<ev_io_set> was used).
		3809
		3810	=item Activating one watcher (putting it into the pending state): O(1)
		3811
		3812	=item Priority handling: O(number_of_priorities)
		3813
		3814	Priorities are implemented by allocating some space for each
		3815	priority. When doing priority-based operations, libev usually has to
		3816	linearly search all the priorities, but starting/stopping and activating
		3817	watchers becomes O(1) with respect to priority handling.
		3818
		3819	=item Sending an ev_async: O(1)
		3820
		3821	=item Processing ev_async_send: O(number_of_async_watchers)
		3822
		3823	=item Processing signals: O(max_signal_number)
		3824
		3825	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3826	calls in the current loop iteration. Checking for async and signal events
		3827	involves iterating over all running async watchers or all signal numbers.
		3828
		3829	=back
3658		3830
3659		3831
3660	=head1 AUTHOR	3832	=head1 AUTHOR
3661		3833
3662	Marc Lehmann <libev@schmorp.de>.	3834	Marc Lehmann <libev@schmorp.de>.

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Comparing libev/ev.pod (file contents): Revision 1.187 by root, Mon Sep 29 03:31:14 2008 UTC vs. Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC

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Revision 1.187 by root, Mon Sep 29 03:31:14 2008 UTC vs.
Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC