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

Comparing libev/ev.pod (file contents):
Revision 1.198 by root, Thu Oct 23 06:30:48 2008 UTC vs.
Revision 1.207 by root, Tue Oct 28 14:13:52 2008 UTC

…		…
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
14	// every watcher type has its own typedef'd struct	14	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	15	// with the name ev_TYPE
16	ev_io stdin_watcher;	16	ev_io stdin_watcher;
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
…		…
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<ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *> (the C<struct>
282	types of such loops, the I<default> loop, which supports signals and child	282	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	283	I<function>).
		284
		285	The library knows two types of such loops, the I<default> loop, which
		286	supports signals and child events, and dynamically created loops which do
		287	not.
284		288
285	=over 4	289	=over 4
286		290
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		292
…		…
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		385
382	For few fds, this backend is a bit little slower than poll and select,	386	For few fds, this backend is a bit little slower than poll and select,
383	but it scales phenomenally better. While poll and select usually scale	387	but it scales phenomenally better. While poll and select usually scale
384	like O(total_fds) where n is the total number of fds (or the highest fd),	388	like O(total_fds) where n is the total number of fds (or the highest fd),
385	epoll scales either O(1) or O(active_fds). The epoll design has a number	389	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	390
387	cases and requiring a system call per fd change, no fork support and bad	391	The epoll syscalls are the most misdesigned of the more advanced event
388	support for dup.	392	mechanisms: problems include silently dropping fds, requiring a system
		393	call per change per fd (and unnecessary guessing of parameters), problems
		394	with dup and so on. The biggest issue is fork races, however - if a
		395	program forks then I<both> parent and child process have to recreate the
		396	epoll set, which can take considerable time (one syscall per fd) and is of
		397	course hard to detect.
		398
		399	Epoll is also notoriously buggy - embedding epoll fds should work, but
		400	of course doesn't, and epoll just loves to report events for totally
		401	I<different> file descriptors (even already closed ones, so one cannot
		402	even remove them from the set) than registered in the set (especially
		403	on SMP systems). Libev tries to counter these spurious notifications by
		404	employing an additional generation counter and comparing that against the
		405	events to filter out spurious ones.
389		406
390	While stopping, setting and starting an I/O watcher in the same iteration	407	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	408	will result in some caching, there is still a system call per such incident
392	(because the fd could point to a different file description now), so its	409	(because the fd could point to a different file description now), so its
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	410	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
394	very well if you register events for both fds.	411	very well if you register events for both fds.
395		412
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399
400	Best performance from this backend is achieved by not unregistering all	413	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	414	watchers for a file descriptor until it has been closed, if possible,
402	i.e. keep at least one watcher active per fd at all times. Stopping and	415	i.e. keep at least one watcher active per fd at all times. Stopping and
403	starting a watcher (without re-setting it) also usually doesn't cause	416	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	417	extra overhead. A fork can both result in spurious notifications as well
		418	as in libev having to destroy and recreate the epoll object, which can
		419	take considerable time and thus should be avoided.
405		420
406	While nominally embeddable in other event loops, this feature is broken in	421	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	422	all kernel versions tested so far.
408		423
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	424	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
…		…
424		439
425	It scales in the same way as the epoll backend, but the interface to the	440	It scales in the same way as the epoll backend, but the interface to the
426	kernel is more efficient (which says nothing about its actual speed, of	441	kernel is more efficient (which says nothing about its actual speed, of
427	course). While stopping, setting and starting an I/O watcher does never	442	course). While stopping, setting and starting an I/O watcher does never
428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	443	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
429	two event changes per incident. Support for C<fork ()> is very bad and it	444	two event changes per incident. Support for C<fork ()> is very bad (but
430	drops fds silently in similarly hard-to-detect cases.	445	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		446	cases
431		447
432	This backend usually performs well under most conditions.	448	This backend usually performs well under most conditions.
433		449
434	While nominally embeddable in other event loops, this doesn't work	450	While nominally embeddable in other event loops, this doesn't work
435	everywhere, so you might need to test for this. And since it is broken	451	everywhere, so you might need to test for this. And since it is broken
…		…
464	might perform better.	480	might perform better.
465		481
466	On the positive side, with the exception of the spurious readiness	482	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	483	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	484	in all tests and is fully embeddable, which is a rare feat among the
469	OS-specific backends.	485	OS-specific backends (I vastly prefer correctness over speed hacks).
470		486
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	487	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	488	C<EVBACKEND_POLL>.
473		489
474	=item C<EVBACKEND_ALL>	490	=item C<EVBACKEND_ALL>
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	543	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	544	calling this function, or cope with the fact afterwards (which is usually
529	the easiest thing, you can just ignore the watchers and/or C<free ()> them	545	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	546	for example).
531		547
532	Note that certain global state, such as signal state, will not be freed by	548	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	549	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	550	as signal and child watchers) would need to be stopped manually.
535		551
536	In general it is not advisable to call this function except in the	552	In general it is not advisable to call this function except in the
537	rare occasion where you really need to free e.g. the signal handling	553	rare occasion where you really need to free e.g. the signal handling
538	pipe fds. If you need dynamically allocated loops it is better to use	554	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	555	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
768	they fire on, say, one-second boundaries only.	784	they fire on, say, one-second boundaries only.
769		785
770	=item ev_loop_verify (loop)	786	=item ev_loop_verify (loop)
771		787
772	This function only does something when C<EV_VERIFY> support has been	788	This function only does something when C<EV_VERIFY> support has been
773	compiled in. which is the default for non-minimal builds. It tries to go	789	compiled in, which is the default for non-minimal builds. It tries to go
774	through all internal structures and checks them for validity. If anything	790	through all internal structures and checks them for validity. If anything
775	is found to be inconsistent, it will print an error message to standard	791	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	792	error and call C<abort ()>.
777		793
778	This can be used to catch bugs inside libev itself: under normal	794	This can be used to catch bugs inside libev itself: under normal
…		…
781		797
782	=back	798	=back
783		799
784		800
785	=head1 ANATOMY OF A WATCHER	801	=head1 ANATOMY OF A WATCHER
		802
		803	In the following description, uppercase C<TYPE> in names stands for the
		804	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		805	watchers and C<ev_io_start> for I/O watchers.
786		806
787	A watcher is a structure that you create and register to record your	807	A watcher is a structure that you create and register to record your
788	interest in some event. For instance, if you want to wait for STDIN to	808	interest in some event. For instance, if you want to wait for STDIN to
789	become readable, you would create an C<ev_io> watcher for that:	809	become readable, you would create an C<ev_io> watcher for that:
790		810
…		…
793	ev_io_stop (w);	813	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	814	ev_unloop (loop, EVUNLOOP_ALL);
795	}	815	}
796		816
797	struct ev_loop *loop = ev_default_loop (0);	817	struct ev_loop *loop = ev_default_loop (0);
		818
798	ev_io stdin_watcher;	819	ev_io stdin_watcher;
		820
799	ev_init (&stdin_watcher, my_cb);	821	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	822	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	823	ev_io_start (loop, &stdin_watcher);
		824
802	ev_loop (loop, 0);	825	ev_loop (loop, 0);
803		826
804	As you can see, you are responsible for allocating the memory for your	827	As you can see, you are responsible for allocating the memory for your
805	watcher structures (and it is usually a bad idea to do this on the stack,	828	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	829	stack).
		830
		831	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		832	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
807		833
808	Each watcher structure must be initialised by a call to C<ev_init	834	Each watcher structure must be initialised by a call to C<ev_init
809	(watcher *, callback)>, which expects a callback to be provided. This	835	(watcher *, callback)>, which expects a callback to be provided. This
810	callback gets invoked each time the event occurs (or, in the case of I/O	836	callback gets invoked each time the event occurs (or, in the case of I/O
811	watchers, each time the event loop detects that the file descriptor given	837	watchers, each time the event loop detects that the file descriptor given
812	is readable and/or writable).	838	is readable and/or writable).
813		839
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	840	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
815	with arguments specific to this watcher type. There is also a macro	841	macro to configure it, with arguments specific to the watcher type. There
816	to combine initialisation and setting in one call: C<< ev_<type>_init	842	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	843	ev_TYPE_init (watcher *, callback, ...) >>.
818		844
819	To make the watcher actually watch out for events, you have to start it	845	To make the watcher actually watch out for events, you have to start it
820	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	846	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
821	*) >>), and you can stop watching for events at any time by calling the	847	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	848	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		849
824	As long as your watcher is active (has been started but not stopped) you	850	As long as your watcher is active (has been started but not stopped) you
825	must not touch the values stored in it. Most specifically you must never	851	must not touch the values stored in it. Most specifically you must never
826	reinitialise it or call its C<set> macro.	852	reinitialise it or call its C<ev_TYPE_set> macro.
827		853
828	Each and every callback receives the event loop pointer as first, the	854	Each and every callback receives the event loop pointer as first, the
829	registered watcher structure as second, and a bitset of received events as	855	registered watcher structure as second, and a bitset of received events as
830	third argument.	856	third argument.
831		857
…		…
912		938
913	=back	939	=back
914		940
915	=head2 GENERIC WATCHER FUNCTIONS	941	=head2 GENERIC WATCHER FUNCTIONS
916		942
917	In the following description, C<TYPE> stands for the watcher type,
918	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
919
920	=over 4	943	=over 4
921		944
922	=item C<ev_init> (ev_TYPE *watcher, callback)	945	=item C<ev_init> (ev_TYPE *watcher, callback)
923		946
924	This macro initialises the generic portion of a watcher. The contents	947	This macro initialises the generic portion of a watcher. The contents
…		…
1032	The default priority used by watchers when no priority has been set is	1055	The default priority used by watchers when no priority has been set is
1033	always C<0>, which is supposed to not be too high and not be too low :).	1056	always C<0>, which is supposed to not be too high and not be too low :).
1034		1057
1035	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1058	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1036	fine, as long as you do not mind that the priority value you query might	1059	fine, as long as you do not mind that the priority value you query might
1037	or might not have been adjusted to be within valid range.	1060	or might not have been clamped to the valid range.
1038		1061
1039	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1062	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1040		1063
1041	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1064	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1042	C<loop> nor C<revents> need to be valid as long as the watcher callback	1065	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1288	passed, but if multiple timers become ready during the same loop iteration	1311	passed, but if multiple timers become ready during the same loop iteration
1289	then order of execution is undefined.	1312	then order of execution is undefined.
1290		1313
1291	=head3 Be smart about timeouts	1314	=head3 Be smart about timeouts
1292		1315
1293	Many real-world problems invole some kind of time-out, usually for error	1316	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,	1317	recovery. A typical example is an HTTP request - if the other side hangs,
1295	you want to raise some error after a while.	1318	you want to raise some error after a while.
1296		1319
1297	Here are some ways on how to handle this problem, from simple and	1320	What follows are some ways to handle this problem, from obvious and
1298	inefficient to very efficient.	1321	inefficient to smart and efficient.
1299		1322
1300	In the following examples a 60 second activity timeout is assumed - a	1323	In the following, a 60 second activity timeout is assumed - a timeout that
1301	timeout that gets reset to 60 seconds each time some data ("a lifesign")	1324	gets reset to 60 seconds each time there is activity (e.g. each time some
1302	was received.	1325	data or other life sign was received).
1303		1326
1304	=over 4	1327	=over 4
1305		1328
1306	=item 1. Use a timer and stop, reinitialise, start it on activity.	1329	=item 1. Use a timer and stop, reinitialise and start it on activity.
1307		1330
1308	This is the most obvious, but not the most simple way: In the beginning,	1331	This is the most obvious, but not the most simple way: In the beginning,
1309	start the watcher:	1332	start the watcher:
1310		1333
1311	ev_timer_init (timer, callback, 60., 0.);	1334	ev_timer_init (timer, callback, 60., 0.);
1312	ev_timer_start (loop, timer);	1335	ev_timer_start (loop, timer);
1313		1336
1314	Then, each time there is some activity, C<ev_timer_stop> the timer,	1337	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
1315	initialise it again, and start it:	1338	and start it again:
1316		1339
1317	ev_timer_stop (loop, timer);	1340	ev_timer_stop (loop, timer);
1318	ev_timer_set (timer, 60., 0.);	1341	ev_timer_set (timer, 60., 0.);
1319	ev_timer_start (loop, timer);	1342	ev_timer_start (loop, timer);
1320		1343
1321	This is relatively simple to implement, but means that each time there	1344	This is relatively simple to implement, but means that each time there is
1322	is some activity, libev will first have to remove the timer from it's	1345	some activity, libev will first have to remove the timer from its internal
1323	internal data strcuture and then add it again.	1346	data structure and then add it again. Libev tries to be fast, but it's
		1347	still not a constant-time operation.
1324		1348
1325	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.	1349	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
1326		1350
1327	This is the easiest way, and involves using C<ev_timer_again> instead of	1351	This is the easiest way, and involves using C<ev_timer_again> instead of
1328	C<ev_timer_start>.	1352	C<ev_timer_start>.
1329		1353
1330	For this, configure an C<ev_timer> with a C<repeat> value of C<60> and	1354	To implement this, configure an C<ev_timer> with a C<repeat> value
1331	then call C<ev_timer_again> at start and each time you successfully read	1355	of C<60> and then call C<ev_timer_again> at start and each time you
1332	or write some data. If you go into an idle state where you do not expect	1356	successfully read or write some data. If you go into an idle state where
1333	data to travel on the socket, you can C<ev_timer_stop> the timer, and	1357	you do not expect data to travel on the socket, you can C<ev_timer_stop>
1334	C<ev_timer_again> will automatically restart it if need be.	1358	the timer, and C<ev_timer_again> will automatically restart it if need be.
1335		1359
1336	That means you can ignore the C<after> value and C<ev_timer_start>	1360	That means you can ignore both the C<ev_timer_start> function and the
1337	altogether and only ever use the C<repeat> value and C<ev_timer_again>.	1361	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1362	member and C<ev_timer_again>.
1338		1363
1339	At start:	1364	At start:
1340		1365
1341	ev_timer_init (timer, callback, 0., 60.);	1366	ev_timer_init (timer, callback);
		1367	timer->repeat = 60.;
1342	ev_timer_again (loop, timer);	1368	ev_timer_again (loop, timer);
1343		1369
1344	Each time you receive some data:	1370	Each time there is some activity:
1345		1371
1346	ev_timer_again (loop, timer);	1372	ev_timer_again (loop, timer);
1347		1373
1348	It is even possible to change the time-out on the fly:	1374	It is even possible to change the time-out on the fly, regardless of
		1375	whether the watcher is active or not:
1349		1376
1350	timer->repeat = 30.;	1377	timer->repeat = 30.;
1351	ev_timer_again (loop, timer);	1378	ev_timer_again (loop, timer);
1352		1379
1353	This is slightly more efficient then stopping/starting the timer each time	1380	This is slightly more efficient then stopping/starting the timer each time
1354	you want to modify its timeout value, as libev does not have to completely	1381	you want to modify its timeout value, as libev does not have to completely
1355	remove and re-insert the timer from/into it's internal data structure.	1382	remove and re-insert the timer from/into its internal data structure.
		1383
		1384	It is, however, even simpler than the "obvious" way to do it.
1356		1385
1357	=item 3. Let the timer time out, but then re-arm it as required.	1386	=item 3. Let the timer time out, but then re-arm it as required.
1358		1387
1359	This method is more tricky, but usually most efficient: Most timeouts are	1388	This method is more tricky, but usually most efficient: Most timeouts are
1360	relatively long compared to the loop iteration time - in our example,	1389	relatively long compared to the intervals between other activity - in
1361	within 60 seconds, there are usually many I/O events with associated	1390	our example, within 60 seconds, there are usually many I/O events with
1362	activity resets.	1391	associated activity resets.
1363		1392
1364	In this case, it would be more efficient to leave the C<ev_timer> alone,	1393	In this case, it would be more efficient to leave the C<ev_timer> alone,
1365	but remember the time of last activity, and check for a real timeout only	1394	but remember the time of last activity, and check for a real timeout only
1366	within the callback:	1395	within the callback:
1367		1396
1368	ev_tstamp last_activity; // time of last activity	1397	ev_tstamp last_activity; // time of last activity
1369		1398
1370	static void	1399	static void
1371	callback (EV_P_ ev_timer *w, int revents)	1400	callback (EV_P_ ev_timer *w, int revents)
1372	{	1401	{
1373	ev_tstamp now = ev_now (EV_A);	1402	ev_tstamp now = ev_now (EV_A);
1374	ev_tstamp timeout = last_activity + 60.;	1403	ev_tstamp timeout = last_activity + 60.;
1375		1404
1376	// if last_activity is older than now - timeout, we did time out	1405	// if last_activity + 60. is older than now, we did time out
1377	if (timeout < now)	1406	if (timeout < now)
1378	{	1407	{
1379	// timeout occured, take action	1408	// timeout occured, take action
1380	}	1409	}
1381	else	1410	else
1382	{	1411	{
1383	// callback was invoked, but there was some activity, re-arm	1412	// callback was invoked, but there was some activity, re-arm
1384	// to fire in last_activity + 60.	1413	// the watcher to fire in last_activity + 60, which is
		1414	// guaranteed to be in the future, so "again" is positive:
1385	w->again = timeout - now;	1415	w->again = timeout - now;
1386	ev_timer_again (EV_A_ w);	1416	ev_timer_again (EV_A_ w);
1387	}	1417	}
1388	}	1418	}
1389		1419
1390	To summarise the callback: first calculate the real time-out (defined as	1420	To summarise the callback: first calculate the real timeout (defined
1391	"60 seconds after the last activity"), then check if that time has been	1421	as "60 seconds after the last activity"), then check if that time has
1392	reached, which means there was a real timeout. Otherwise the callback was	1422	been reached, which means something I<did>, in fact, time out. Otherwise
1393	invoked too early (timeout is in the future), so re-schedule the timer to	1423	the callback was invoked too early (C<timeout> is in the future), so
1394	fire at that future time.	1424	re-schedule the timer to fire at that future time, to see if maybe we have
		1425	a timeout then.
1395		1426
1396	Note how C<ev_timer_again> is used, taking advantage of the	1427	Note how C<ev_timer_again> is used, taking advantage of the
1397	C<ev_timer_again> optimisation when the timer is already running.	1428	C<ev_timer_again> optimisation when the timer is already running.
1398		1429
1399	This scheme causes more callback invocations (about one every 60 seconds),	1430	This scheme causes more callback invocations (about one every 60 seconds
1400	but virtually no calls to libev to change the timeout.	1431	minus half the average time between activity), but virtually no calls to
		1432	libev to change the timeout.
1401		1433
1402	To start the timer, simply intiialise the watcher and C<last_activity>,	1434	To start the timer, simply initialise the watcher and set C<last_activity>
1403	then call the callback:	1435	to the current time (meaning we just have some activity :), then call the
		1436	callback, which will "do the right thing" and start the timer:
1404		1437
1405	ev_timer_init (timer, callback);	1438	ev_timer_init (timer, callback);
1406	last_activity = ev_now (loop);	1439	last_activity = ev_now (loop);
1407	callback (loop, timer, EV_TIMEOUT);	1440	callback (loop, timer, EV_TIMEOUT);
1408		1441
1409	And when there is some activity, simply remember the time in	1442	And when there is some activity, simply store the current time in
1410	C<last_activity>:	1443	C<last_activity>, no libev calls at all:
1411		1444
1412	last_actiivty = ev_now (loop);	1445	last_actiivty = ev_now (loop);
1413		1446
1414	This technique is slightly more complex, but in most cases where the	1447	This technique is slightly more complex, but in most cases where the
1415	time-out is unlikely to be triggered, much more efficient.	1448	time-out is unlikely to be triggered, much more efficient.
1416		1449
		1450	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1451	callback :) - just change the timeout and invoke the callback, which will
		1452	fix things for you.
		1453
		1454	=item 4. Wee, just use a double-linked list for your timeouts.
		1455
		1456	If there is not one request, but many thousands (millions...), all
		1457	employing some kind of timeout with the same timeout value, then one can
		1458	do even better:
		1459
		1460	When starting the timeout, calculate the timeout value and put the timeout
		1461	at the I<end> of the list.
		1462
		1463	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1464	the list is expected to fire (for example, using the technique #3).
		1465
		1466	When there is some activity, remove the timer from the list, recalculate
		1467	the timeout, append it to the end of the list again, and make sure to
		1468	update the C<ev_timer> if it was taken from the beginning of the list.
		1469
		1470	This way, one can manage an unlimited number of timeouts in O(1) time for
		1471	starting, stopping and updating the timers, at the expense of a major
		1472	complication, and having to use a constant timeout. The constant timeout
		1473	ensures that the list stays sorted.
		1474
1417	=back	1475	=back
		1476
		1477	So which method the best?
		1478
		1479	Method #2 is a simple no-brain-required solution that is adequate in most
		1480	situations. Method #3 requires a bit more thinking, but handles many cases
		1481	better, and isn't very complicated either. In most case, choosing either
		1482	one is fine, with #3 being better in typical situations.
		1483
		1484	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1485	rather complicated, but extremely efficient, something that really pays
		1486	off after the first million or so of active timers, i.e. it's usually
		1487	overkill :)
1418		1488
1419	=head3 The special problem of time updates	1489	=head3 The special problem of time updates
1420		1490
1421	Establishing the current time is a costly operation (it usually takes at	1491	Establishing the current time is a costly operation (it usually takes at
1422	least two system calls): EV therefore updates its idea of the current	1492	least two system calls): EV therefore updates its idea of the current
…		…
1852		1922
1853		1923
1854	=head2 C<ev_stat> - did the file attributes just change?	1924	=head2 C<ev_stat> - did the file attributes just change?
1855		1925
1856	This watches a file system path for attribute changes. That is, it calls	1926	This watches a file system path for attribute changes. That is, it calls
1857	C<stat> regularly (or when the OS says it changed) and sees if it changed	1927	C<stat> on that path in regular intervals (or when the OS says it changed)
1858	compared to the last time, invoking the callback if it did.	1928	and sees if it changed compared to the last time, invoking the callback if
		1929	it did.
1859		1930
1860	The path does not need to exist: changing from "path exists" to "path does	1931	The path does not need to exist: changing from "path exists" to "path does
1861	not exist" is a status change like any other. The condition "path does	1932	not exist" is a status change like any other. The condition "path does
1862	not exist" is signified by the C<st_nlink> field being zero (which is	1933	not exist" is signified by the C<st_nlink> field being zero (which is
1863	otherwise always forced to be at least one) and all the other fields of	1934	otherwise always forced to be at least one) and all the other fields of
1864	the stat buffer having unspecified contents.	1935	the stat buffer having unspecified contents.
1865		1936
1866	The path I<should> be absolute and I<must not> end in a slash. If it is	1937	The path I<must not> end in a slash or contain special components such as
		1938	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1867	relative and your working directory changes, the behaviour is undefined.	1939	your working directory changes, then the behaviour is undefined.
1868		1940
1869	Since there is no standard kernel interface to do this, the portable	1941	Since there is no portable change notification interface available, the
1870	implementation simply calls C<stat (2)> regularly on the path to see if	1942	portable implementation simply calls C<stat(2)> regularly on the path
1871	it changed somehow. You can specify a recommended polling interval for	1943	to see if it changed somehow. You can specify a recommended polling
1872	this case. If you specify a polling interval of C<0> (highly recommended!)	1944	interval for this case. If you specify a polling interval of C<0> (highly
1873	then a I<suitable, unspecified default> value will be used (which	1945	recommended!) then a I<suitable, unspecified default> value will be used
1874	you can expect to be around five seconds, although this might change	1946	(which you can expect to be around five seconds, although this might
1875	dynamically). Libev will also impose a minimum interval which is currently	1947	change dynamically). Libev will also impose a minimum interval which is
1876	around C<0.1>, but thats usually overkill.	1948	currently around C<0.1>, but thats usually overkill.
1877		1949
1878	This watcher type is not meant for massive numbers of stat watchers,	1950	This watcher type is not meant for massive numbers of stat watchers,
1879	as even with OS-supported change notifications, this can be	1951	as even with OS-supported change notifications, this can be
1880	resource-intensive.	1952	resource-intensive.
1881		1953
…		…
1891	support disabled by default, you get the 32 bit version of the stat	1963	support disabled by default, you get the 32 bit version of the stat
1892	structure. When using the library from programs that change the ABI to	1964	structure. When using the library from programs that change the ABI to
1893	use 64 bit file offsets the programs will fail. In that case you have to	1965	use 64 bit file offsets the programs will fail. In that case you have to
1894	compile libev with the same flags to get binary compatibility. This is	1966	compile libev with the same flags to get binary compatibility. This is
1895	obviously the case with any flags that change the ABI, but the problem is	1967	obviously the case with any flags that change the ABI, but the problem is
1896	most noticeably disabled with ev_stat and large file support.	1968	most noticeably displayed with ev_stat and large file support.
1897		1969
1898	The solution for this is to lobby your distribution maker to make large	1970	The solution for this is to lobby your distribution maker to make large
1899	file interfaces available by default (as e.g. FreeBSD does) and not	1971	file interfaces available by default (as e.g. FreeBSD does) and not
1900	optional. Libev cannot simply switch on large file support because it has	1972	optional. Libev cannot simply switch on large file support because it has
1901	to exchange stat structures with application programs compiled using the	1973	to exchange stat structures with application programs compiled using the
…		…
1920	descriptor open on the object at all times, and detecting renames, unlinks	1992	descriptor open on the object at all times, and detecting renames, unlinks
1921	etc. is difficult.	1993	etc. is difficult.
1922		1994
1923	=head3 The special problem of stat time resolution	1995	=head3 The special problem of stat time resolution
1924		1996
1925	The C<stat ()> system call only supports full-second resolution portably, and	1997	The C<stat ()> system call only supports full-second resolution portably,
1926	even on systems where the resolution is higher, most file systems still	1998	and even on systems where the resolution is higher, most file systems
1927	only support whole seconds.	1999	still only support whole seconds.
1928		2000
1929	That means that, if the time is the only thing that changes, you can	2001	That means that, if the time is the only thing that changes, you can
1930	easily miss updates: on the first update, C<ev_stat> detects a change and	2002	easily miss updates: on the first update, C<ev_stat> detects a change and
1931	calls your callback, which does something. When there is another update	2003	calls your callback, which does something. When there is another update
1932	within the same second, C<ev_stat> will be unable to detect unless the	2004	within the same second, C<ev_stat> will be unable to detect unless the
…		…
2900	=item D	2972	=item D
2901		2973
2902	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	2974	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2903	be found at L<http://proj.llucax.com.ar/wiki/evd>.	2975	be found at L<http://proj.llucax.com.ar/wiki/evd>.
2904		2976
		2977	=item Ocaml
		2978
		2979	Erkki Seppala has written Ocaml bindings for libev, to be found at
		2980	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		2981
2905	=back	2982	=back
2906		2983
2907		2984
2908	=head1 MACRO MAGIC	2985	=head1 MACRO MAGIC
2909		2986

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Comparing libev/ev.pod (file contents): Revision 1.198 by root, Thu Oct 23 06:30:48 2008 UTC vs. Revision 1.207 by root, Tue Oct 28 14:13:52 2008 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.198 by root, Thu Oct 23 06:30:48 2008 UTC vs.
Revision 1.207 by root, Tue Oct 28 14:13:52 2008 UTC