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

Comparing libev/ev.pod (file contents):
Revision 1.146 by root, Fri Apr 11 00:31:19 2008 UTC vs.
Revision 1.159 by root, Thu May 22 02:44:57 2008 UTC

…		…
64		64
65	=head1 DESCRIPTION	65	=head1 DESCRIPTION
66		66
67	The newest version of this document is also available as an html-formatted	67	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	68	web page you might find easier to navigate when reading it for the first
69	time: L<http://cvs.schmorp.de/libev/ev.html>.	69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
70		70
71	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	73	these event sources and provide your program with events.
74		74
…		…
336	To get good performance out of this backend you need a high amount of	336	To get good performance out of this backend you need a high amount of
337	parallelity (most of the file descriptors should be busy). If you are	337	parallelity (most of the file descriptors should be busy). If you are
338	writing a server, you should C<accept ()> in a loop to accept as many	338	writing a server, you should C<accept ()> in a loop to accept as many
339	connections as possible during one iteration. You might also want to have	339	connections as possible during one iteration. You might also want to have
340	a look at C<ev_set_io_collect_interval ()> to increase the amount of	340	a look at C<ev_set_io_collect_interval ()> to increase the amount of
341	readyness notifications you get per iteration.	341	readiness notifications you get per iteration.
342		342
343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
344		344
345	And this is your standard poll(2) backend. It's more complicated	345	And this is your standard poll(2) backend. It's more complicated
346	than select, but handles sparse fds better and has no artificial	346	than select, but handles sparse fds better and has no artificial
…		…
425	While this backend scales well, it requires one system call per active	425	While this backend scales well, it requires one system call per active
426	file descriptor per loop iteration. For small and medium numbers of file	426	file descriptor per loop iteration. For small and medium numbers of file
427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
428	might perform better.	428	might perform better.
429		429
430	On the positive side, ignoring the spurious readyness notifications, this	430	On the positive side, ignoring the spurious readiness notifications, this
431	backend actually performed to specification in all tests and is fully	431	backend actually performed to specification in all tests and is fully
432	embeddable, which is a rare feat among the OS-specific backends.	432	embeddable, which is a rare feat among the OS-specific backends.
433		433
434	=item C<EVBACKEND_ALL>	434	=item C<EVBACKEND_ALL>
435		435
…		…
689	interval to a value near C<0.1> or so, which is often enough for	689	interval to a value near C<0.1> or so, which is often enough for
690	interactive servers (of course not for games), likewise for timeouts. It	690	interactive servers (of course not for games), likewise for timeouts. It
691	usually doesn't make much sense to set it to a lower value than C<0.01>,	691	usually doesn't make much sense to set it to a lower value than C<0.01>,
692	as this approsaches the timing granularity of most systems.	692	as this approsaches the timing granularity of most systems.
693		693
		694	=item ev_loop_verify (loop)
		695
		696	This function only does something when C<EV_VERIFY> support has been
		697	compiled in. It tries to go through all internal structures and checks
		698	them for validity. If anything is found to be inconsistent, it will print
		699	an error message to standard error and call C<abort ()>.
		700
		701	This can be used to catch bugs inside libev itself: under normal
		702	circumstances, this function will never abort as of course libev keeps its
		703	data structures consistent.
		704
694	=back	705	=back
695		706
696		707
697	=head1 ANATOMY OF A WATCHER	708	=head1 ANATOMY OF A WATCHER
698		709
…		…
1032	If you must do this, then force the use of a known-to-be-good backend	1043	If you must do this, then force the use of a known-to-be-good backend
1033	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1044	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1034	C<EVBACKEND_POLL>).	1045	C<EVBACKEND_POLL>).
1035		1046
1036	Another thing you have to watch out for is that it is quite easy to	1047	Another thing you have to watch out for is that it is quite easy to
1037	receive "spurious" readyness notifications, that is your callback might	1048	receive "spurious" readiness notifications, that is your callback might
1038	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1049	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1039	because there is no data. Not only are some backends known to create a	1050	because there is no data. Not only are some backends known to create a
1040	lot of those (for example solaris ports), it is very easy to get into	1051	lot of those (for example solaris ports), it is very easy to get into
1041	this situation even with a relatively standard program structure. Thus	1052	this situation even with a relatively standard program structure. Thus
1042	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1053	it is best to always use non-blocking I/O: An extra C<read>(2) returning
…		…
1151		1162
1152	Timer watchers are simple relative timers that generate an event after a	1163	Timer watchers are simple relative timers that generate an event after a
1153	given time, and optionally repeating in regular intervals after that.	1164	given time, and optionally repeating in regular intervals after that.
1154		1165
1155	The timers are based on real time, that is, if you register an event that	1166	The timers are based on real time, that is, if you register an event that
1156	times out after an hour and you reset your system clock to last years	1167	times out after an hour and you reset your system clock to january last
1157	time, it will still time out after (roughly) and hour. "Roughly" because	1168	year, it will still time out after (roughly) and hour. "Roughly" because
1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1169	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1159	monotonic clock option helps a lot here).	1170	monotonic clock option helps a lot here).
1160		1171
1161	The relative timeouts are calculated relative to the C<ev_now ()>	1172	The relative timeouts are calculated relative to the C<ev_now ()>
1162	time. This is usually the right thing as this timestamp refers to the time	1173	time. This is usually the right thing as this timestamp refers to the time
…		…
1164	you suspect event processing to be delayed and you I<need> to base the timeout	1175	you suspect event processing to be delayed and you I<need> to base the timeout
1165	on the current time, use something like this to adjust for this:	1176	on the current time, use something like this to adjust for this:
1166		1177
1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1178	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1168		1179
1169	The callback is guarenteed to be invoked only when its timeout has passed,	1180	The callback is guarenteed to be invoked only after its timeout has passed,
1170	but if multiple timers become ready during the same loop iteration then	1181	but if multiple timers become ready during the same loop iteration then
1171	order of execution is undefined.	1182	order of execution is undefined.
1172		1183
1173	=head3 Watcher-Specific Functions and Data Members	1184	=head3 Watcher-Specific Functions and Data Members
1174		1185
…		…
1176		1187
1177	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1188	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1178		1189
1179	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1190	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1180		1191
1181	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1192	Configure the timer to trigger after C<after> seconds. If C<repeat>
1182	C<0.>, then it will automatically be stopped. If it is positive, then the	1193	is C<0.>, then it will automatically be stopped once the timeout is
1183	timer will automatically be configured to trigger again C<repeat> seconds	1194	reached. If it is positive, then the timer will automatically be
1184	later, again, and again, until stopped manually.	1195	configured to trigger again C<repeat> seconds later, again, and again,
		1196	until stopped manually.
1185		1197
1186	The timer itself will do a best-effort at avoiding drift, that is, if you	1198	The timer itself will do a best-effort at avoiding drift, that is, if
1187	configure a timer to trigger every 10 seconds, then it will trigger at	1199	you configure a timer to trigger every 10 seconds, then it will normally
1188	exactly 10 second intervals. If, however, your program cannot keep up with	1200	trigger at exactly 10 second intervals. If, however, your program cannot
1189	the timer (because it takes longer than those 10 seconds to do stuff) the	1201	keep up with the timer (because it takes longer than those 10 seconds to
1190	timer will not fire more than once per event loop iteration.	1202	do stuff) the timer will not fire more than once per event loop iteration.
1191		1203
1192	=item ev_timer_again (loop, ev_timer *)	1204	=item ev_timer_again (loop, ev_timer *)
1193		1205
1194	This will act as if the timer timed out and restart it again if it is	1206	This will act as if the timer timed out and restart it again if it is
1195	repeating. The exact semantics are:	1207	repeating. The exact semantics are:
…		…
1272	Periodic watchers are also timers of a kind, but they are very versatile	1284	Periodic watchers are also timers of a kind, but they are very versatile
1273	(and unfortunately a bit complex).	1285	(and unfortunately a bit complex).
1274		1286
1275	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1287	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
1276	but on wallclock time (absolute time). You can tell a periodic watcher	1288	but on wallclock time (absolute time). You can tell a periodic watcher
1277	to trigger "at" some specific point in time. For example, if you tell a	1289	to trigger after some specific point in time. For example, if you tell a
1278	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1290	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
1279	+ 10.>) and then reset your system clock to the last year, then it will	1291	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1292	clock to january of the previous year, then it will take more than year
1280	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1293	to trigger the event (unlike an C<ev_timer>, which would still trigger
1281	roughly 10 seconds later).	1294	roughly 10 seconds later as it uses a relative timeout).
1282		1295
1283	They can also be used to implement vastly more complex timers, such as	1296	C<ev_periodic>s can also be used to implement vastly more complex timers,
1284	triggering an event on each midnight, local time or other, complicated,	1297	such as triggering an event on each "midnight, local time", or other
1285	rules.	1298	complicated, rules.
1286		1299
1287	As with timers, the callback is guarenteed to be invoked only when the	1300	As with timers, the callback is guarenteed to be invoked only when the
1288	time (C<at>) has been passed, but if multiple periodic timers become ready	1301	time (C<at>) has passed, but if multiple periodic timers become ready
1289	during the same loop iteration then order of execution is undefined.	1302	during the same loop iteration then order of execution is undefined.
1290		1303
1291	=head3 Watcher-Specific Functions and Data Members	1304	=head3 Watcher-Specific Functions and Data Members
1292		1305
1293	=over 4	1306	=over 4
…		…
1301		1314
1302	=over 4	1315	=over 4
1303		1316
1304	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1317	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1305		1318
1306	In this configuration the watcher triggers an event at the wallclock time	1319	In this configuration the watcher triggers an event after the wallclock
1307	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1320	time C<at> has passed and doesn't repeat. It will not adjust when a time
1308	that is, if it is to be run at January 1st 2011 then it will run when the	1321	jump occurs, that is, if it is to be run at January 1st 2011 then it will
1309	system time reaches or surpasses this time.	1322	run when the system time reaches or surpasses this time.
1310		1323
1311	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1324	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1312		1325
1313	In this mode the watcher will always be scheduled to time out at the next	1326	In this mode the watcher will always be scheduled to time out at the next
1314	C<at + N * interval> time (for some integer N, which can also be negative)	1327	C<at + N * interval> time (for some integer N, which can also be negative)
1315	and then repeat, regardless of any time jumps.	1328	and then repeat, regardless of any time jumps.
1316		1329
1317	This can be used to create timers that do not drift with respect to system	1330	This can be used to create timers that do not drift with respect to system
1318	time:	1331	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1332	the hour:
1319		1333
1320	ev_periodic_set (&periodic, 0., 3600., 0);	1334	ev_periodic_set (&periodic, 0., 3600., 0);
1321		1335
1322	This doesn't mean there will always be 3600 seconds in between triggers,	1336	This doesn't mean there will always be 3600 seconds in between triggers,
1323	but only that the the callback will be called when the system time shows a	1337	but only that the the callback will be called when the system time shows a
…		…
1328	C<ev_periodic> will try to run the callback in this mode at the next possible	1342	C<ev_periodic> will try to run the callback in this mode at the next possible
1329	time where C<time = at (mod interval)>, regardless of any time jumps.	1343	time where C<time = at (mod interval)>, regardless of any time jumps.
1330		1344
1331	For numerical stability it is preferable that the C<at> value is near	1345	For numerical stability it is preferable that the C<at> value is near
1332	C<ev_now ()> (the current time), but there is no range requirement for	1346	C<ev_now ()> (the current time), but there is no range requirement for
1333	this value.	1347	this value, and in fact is often specified as zero.
		1348
		1349	Note also that there is an upper limit to how often a timer can fire (cpu
		1350	speed for example), so if C<interval> is very small then timing stability
		1351	will of course detoriate. Libev itself tries to be exact to be about one
		1352	millisecond (if the OS supports it and the machine is fast enough).
1334		1353
1335	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1354	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1336		1355
1337	In this mode the values for C<interval> and C<at> are both being	1356	In this mode the values for C<interval> and C<at> are both being
1338	ignored. Instead, each time the periodic watcher gets scheduled, the	1357	ignored. Instead, each time the periodic watcher gets scheduled, the
1339	reschedule callback will be called with the watcher as first, and the	1358	reschedule callback will be called with the watcher as first, and the
1340	current time as second argument.	1359	current time as second argument.
1341		1360
1342	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1361	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1343	ever, or make any event loop modifications>. If you need to stop it,	1362	ever, or make ANY event loop modifications whatsoever>.
1344	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1345	starting an C<ev_prepare> watcher, which is legal).
1346		1363
		1364	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1365	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1366	only event loop modification you are allowed to do).
		1367
1347	Its prototype is C<ev_tstamp (reschedule_cb)(struct ev_periodic w,	1368	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
1348	ev_tstamp now)>, e.g.:	1369	*w, ev_tstamp now)>, e.g.:
1349		1370
1350	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1371	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1351	{	1372	{
1352	return now + 60.;	1373	return now + 60.;
1353	}	1374	}
…		…
1355	It must return the next time to trigger, based on the passed time value	1376	It must return the next time to trigger, based on the passed time value
1356	(that is, the lowest time value larger than to the second argument). It	1377	(that is, the lowest time value larger than to the second argument). It
1357	will usually be called just before the callback will be triggered, but	1378	will usually be called just before the callback will be triggered, but
1358	might be called at other times, too.	1379	might be called at other times, too.
1359		1380
1360	NOTE: I<< This callback must always return a time that is later than the	1381	NOTE: I<< This callback must always return a time that is higher than or
1361	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1382	equal to the passed C<now> value >>.
1362		1383
1363	This can be used to create very complex timers, such as a timer that	1384	This can be used to create very complex timers, such as a timer that
1364	triggers on each midnight, local time. To do this, you would calculate the	1385	triggers on "next midnight, local time". To do this, you would calculate the
1365	next midnight after C<now> and return the timestamp value for this. How	1386	next midnight after C<now> and return the timestamp value for this. How
1366	you do this is, again, up to you (but it is not trivial, which is the main	1387	you do this is, again, up to you (but it is not trivial, which is the main
1367	reason I omitted it as an example).	1388	reason I omitted it as an example).
1368		1389
1369	=back	1390	=back
…		…
1373	Simply stops and restarts the periodic watcher again. This is only useful	1394	Simply stops and restarts the periodic watcher again. This is only useful
1374	when you changed some parameters or the reschedule callback would return	1395	when you changed some parameters or the reschedule callback would return
1375	a different time than the last time it was called (e.g. in a crond like	1396	a different time than the last time it was called (e.g. in a crond like
1376	program when the crontabs have changed).	1397	program when the crontabs have changed).
1377		1398
		1399	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1400
		1401	When active, returns the absolute time that the watcher is supposed to
		1402	trigger next.
		1403
1378	=item ev_tstamp offset [read-write]	1404	=item ev_tstamp offset [read-write]
1379		1405
1380	When repeating, this contains the offset value, otherwise this is the	1406	When repeating, this contains the offset value, otherwise this is the
1381	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1407	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
1382		1408
…		…
1392	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]	1418	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]
1393		1419
1394	The current reschedule callback, or C<0>, if this functionality is	1420	The current reschedule callback, or C<0>, if this functionality is
1395	switched off. Can be changed any time, but changes only take effect when	1421	switched off. Can be changed any time, but changes only take effect when
1396	the periodic timer fires or C<ev_periodic_again> is being called.	1422	the periodic timer fires or C<ev_periodic_again> is being called.
1397
1398	=item ev_tstamp at [read-only]
1399
1400	When active, contains the absolute time that the watcher is supposed to
1401	trigger next.
1402		1423
1403	=back	1424	=back
1404		1425
1405	=head3 Examples	1426	=head3 Examples
1406		1427
…		…
1610	as even with OS-supported change notifications, this can be	1631	as even with OS-supported change notifications, this can be
1611	resource-intensive.	1632	resource-intensive.
1612		1633
1613	At the time of this writing, only the Linux inotify interface is	1634	At the time of this writing, only the Linux inotify interface is
1614	implemented (implementing kqueue support is left as an exercise for the	1635	implemented (implementing kqueue support is left as an exercise for the
		1636	reader, note, however, that the author sees no way of implementing ev_stat
1615	reader). Inotify will be used to give hints only and should not change the	1637	semantics with kqueue). Inotify will be used to give hints only and should
1616	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1638	not change the semantics of C<ev_stat> watchers, which means that libev
1617	to fall back to regular polling again even with inotify, but changes are	1639	sometimes needs to fall back to regular polling again even with inotify,
1618	usually detected immediately, and if the file exists there will be no	1640	but changes are usually detected immediately, and if the file exists there
1619	polling.	1641	will be no polling.
1620		1642
1621	=head3 ABI Issues (Largefile Support)	1643	=head3 ABI Issues (Largefile Support)
1622		1644
1623	Libev by default (unless the user overrides this) uses the default	1645	Libev by default (unless the user overrides this) uses the default
1624	compilation environment, which means that on systems with optionally	1646	compilation environment, which means that on systems with optionally
…		…
1634	When C<inotify (7)> support has been compiled into libev (generally only	1656	When C<inotify (7)> support has been compiled into libev (generally only
1635	available on Linux) and present at runtime, it will be used to speed up	1657	available on Linux) and present at runtime, it will be used to speed up
1636	change detection where possible. The inotify descriptor will be created lazily	1658	change detection where possible. The inotify descriptor will be created lazily
1637	when the first C<ev_stat> watcher is being started.	1659	when the first C<ev_stat> watcher is being started.
1638		1660
1639	Inotify presense does not change the semantics of C<ev_stat> watchers	1661	Inotify presence does not change the semantics of C<ev_stat> watchers
1640	except that changes might be detected earlier, and in some cases, to avoid	1662	except that changes might be detected earlier, and in some cases, to avoid
1641	making regular C<stat> calls. Even in the presense of inotify support	1663	making regular C<stat> calls. Even in the presence of inotify support
1642	there are many cases where libev has to resort to regular C<stat> polling.	1664	there are many cases where libev has to resort to regular C<stat> polling.
1643		1665
1644	(There is no support for kqueue, as apparently it cannot be used to	1666	(There is no support for kqueue, as apparently it cannot be used to
1645	implement this functionality, due to the requirement of having a file	1667	implement this functionality, due to the requirement of having a file
1646	descriptor open on the object at all times).	1668	descriptor open on the object at all times).
…		…
1649		1671
1650	The C<stat ()> syscall only supports full-second resolution portably, and	1672	The C<stat ()> syscall only supports full-second resolution portably, and
1651	even on systems where the resolution is higher, many filesystems still	1673	even on systems where the resolution is higher, many filesystems still
1652	only support whole seconds.	1674	only support whole seconds.
1653		1675
1654	That means that, if the time is the only thing that changes, you might	1676	That means that, if the time is the only thing that changes, you can
1655	miss updates: on the first update, C<ev_stat> detects a change and calls	1677	easily miss updates: on the first update, C<ev_stat> detects a change and
1656	your callback, which does something. When there is another update within	1678	calls your callback, which does something. When there is another update
1657	the same second, C<ev_stat> will be unable to detect it.	1679	within the same second, C<ev_stat> will be unable to detect it as the stat
		1680	data does not change.
1658		1681
1659	The solution to this is to delay acting on a change for a second (or till	1682	The solution to this is to delay acting on a change for slightly more
1660	the next second boundary), using a roughly one-second delay C<ev_timer>	1683	than a second (or till slightly after the next full second boundary), using
1661	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	1684	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1662	is added to work around small timing inconsistencies of some operating	1685	ev_timer_again (loop, w)>).
1663	systems.	1686
		1687	The C<.02> offset is added to work around small timing inconsistencies
		1688	of some operating systems (where the second counter of the current time
		1689	might be be delayed. One such system is the Linux kernel, where a call to
		1690	C<gettimeofday> might return a timestamp with a full second later than
		1691	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1692	update file times then there will be a small window where the kernel uses
		1693	the previous second to update file times but libev might already execute
		1694	the timer callback).
1664		1695
1665	=head3 Watcher-Specific Functions and Data Members	1696	=head3 Watcher-Specific Functions and Data Members
1666		1697
1667	=over 4	1698	=over 4
1668		1699
…		…
1674	C<path>. The C<interval> is a hint on how quickly a change is expected to	1705	C<path>. The C<interval> is a hint on how quickly a change is expected to
1675	be detected and should normally be specified as C<0> to let libev choose	1706	be detected and should normally be specified as C<0> to let libev choose
1676	a suitable value. The memory pointed to by C<path> must point to the same	1707	a suitable value. The memory pointed to by C<path> must point to the same
1677	path for as long as the watcher is active.	1708	path for as long as the watcher is active.
1678		1709
1679	The callback will be receive C<EV_STAT> when a change was detected,	1710	The callback will receive C<EV_STAT> when a change was detected, relative
1680	relative to the attributes at the time the watcher was started (or the	1711	to the attributes at the time the watcher was started (or the last change
1681	last change was detected).	1712	was detected).
1682		1713
1683	=item ev_stat_stat (loop, ev_stat *)	1714	=item ev_stat_stat (loop, ev_stat *)
1684		1715
1685	Updates the stat buffer immediately with new values. If you change the	1716	Updates the stat buffer immediately with new values. If you change the
1686	watched path in your callback, you could call this fucntion to avoid	1717	watched path in your callback, you could call this function to avoid
1687	detecting this change (while introducing a race condition). Can also be	1718	detecting this change (while introducing a race condition if you are not
1688	useful simply to find out the new values.	1719	the only one changing the path). Can also be useful simply to find out the
		1720	new values.
1689		1721
1690	=item ev_statdata attr [read-only]	1722	=item ev_statdata attr [read-only]
1691		1723
1692	The most-recently detected attributes of the file. Although the type is of	1724	The most-recently detected attributes of the file. Although the type is
1693	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	1725	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1694	suitable for your system. If the C<st_nlink> member is C<0>, then there	1726	suitable for your system, but you can only rely on the POSIX-standardised
		1727	members to be present. If the C<st_nlink> member is C<0>, then there was
1695	was some error while C<stat>ing the file.	1728	some error while C<stat>ing the file.
1696		1729
1697	=item ev_statdata prev [read-only]	1730	=item ev_statdata prev [read-only]
1698		1731
1699	The previous attributes of the file. The callback gets invoked whenever	1732	The previous attributes of the file. The callback gets invoked whenever
1700	C<prev> != C<attr>.	1733	C<prev> != C<attr>, or, more precisely, one or more of these members
		1734	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1735	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1701		1736
1702	=item ev_tstamp interval [read-only]	1737	=item ev_tstamp interval [read-only]
1703		1738
1704	The specified interval.	1739	The specified interval.
1705		1740
…		…
1759	}	1794	}
1760		1795
1761	...	1796	...
1762	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	1797	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1763	ev_stat_start (loop, &passwd);	1798	ev_stat_start (loop, &passwd);
1764	ev_timer_init (&timer, timer_cb, 0., 1.01);	1799	ev_timer_init (&timer, timer_cb, 0., 1.02);
1765		1800
1766		1801
1767	=head2 C<ev_idle> - when you've got nothing better to do...	1802	=head2 C<ev_idle> - when you've got nothing better to do...
1768		1803
1769	Idle watchers trigger events when no other events of the same or higher	1804	Idle watchers trigger events when no other events of the same or higher
…		…
1857		1892
1858	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	1893	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1859	priority, to ensure that they are being run before any other watchers	1894	priority, to ensure that they are being run before any other watchers
1860	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	1895	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1861	too) should not activate ("feed") events into libev. While libev fully	1896	too) should not activate ("feed") events into libev. While libev fully
1862	supports this, they will be called before other C<ev_check> watchers	1897	supports this, they might get executed before other C<ev_check> watchers
1863	did their job. As C<ev_check> watchers are often used to embed other	1898	did their job. As C<ev_check> watchers are often used to embed other
1864	(non-libev) event loops those other event loops might be in an unusable	1899	(non-libev) event loops those other event loops might be in an unusable
1865	state until their C<ev_check> watcher ran (always remind yourself to	1900	state until their C<ev_check> watcher ran (always remind yourself to
1866	coexist peacefully with others).	1901	coexist peacefully with others).
1867		1902
…		…
1882	=head3 Examples	1917	=head3 Examples
1883		1918
1884	There are a number of principal ways to embed other event loops or modules	1919	There are a number of principal ways to embed other event loops or modules
1885	into libev. Here are some ideas on how to include libadns into libev	1920	into libev. Here are some ideas on how to include libadns into libev
1886	(there is a Perl module named C<EV::ADNS> that does this, which you could	1921	(there is a Perl module named C<EV::ADNS> that does this, which you could
1887	use for an actually working example. Another Perl module named C<EV::Glib>	1922	use as a working example. Another Perl module named C<EV::Glib> embeds a
1888	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	1923	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1889	into the Glib event loop).	1924	Glib event loop).
1890		1925
1891	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	1926	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1892	and in a check watcher, destroy them and call into libadns. What follows	1927	and in a check watcher, destroy them and call into libadns. What follows
1893	is pseudo-code only of course. This requires you to either use a low	1928	is pseudo-code only of course. This requires you to either use a low
1894	priority for the check watcher or use C<ev_clear_pending> explicitly, as	1929	priority for the check watcher or use C<ev_clear_pending> explicitly, as
…		…
2966	defined to be C<0>, then they are not.	3001	defined to be C<0>, then they are not.
2967		3002
2968	=item EV_MINIMAL	3003	=item EV_MINIMAL
2969		3004
2970	If you need to shave off some kilobytes of code at the expense of some	3005	If you need to shave off some kilobytes of code at the expense of some
2971	speed, define this symbol to C<1>. Currently only used for gcc to override	3006	speed, define this symbol to C<1>. Currently this is used to override some
2972	some inlining decisions, saves roughly 30% codesize of amd64.	3007	inlining decisions, saves roughly 30% codesize of amd64. It also selects a
		3008	much smaller 2-heap for timer management over the default 4-heap.
2973		3009
2974	=item EV_PID_HASHSIZE	3010	=item EV_PID_HASHSIZE
2975		3011
2976	C<ev_child> watchers use a small hash table to distribute workload by	3012	C<ev_child> watchers use a small hash table to distribute workload by
2977	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3013	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2983	C<ev_stat> watchers use a small hash table to distribute workload by	3019	C<ev_stat> watchers use a small hash table to distribute workload by
2984	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3020	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2985	usually more than enough. If you need to manage thousands of C<ev_stat>	3021	usually more than enough. If you need to manage thousands of C<ev_stat>
2986	watchers you might want to increase this value (I<must> be a power of	3022	watchers you might want to increase this value (I<must> be a power of
2987	two).	3023	two).
		3024
		3025	=item EV_USE_4HEAP
		3026
		3027	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3028	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3029	to C<1>. The 4-heap uses more complicated (longer) code but has
		3030	noticably faster performance with many (thousands) of watchers.
		3031
		3032	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3033	(disabled).
		3034
		3035	=item EV_HEAP_CACHE_AT
		3036
		3037	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3038	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3039	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3040	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3041	but avoids random read accesses on heap changes. This improves performance
		3042	noticably with with many (hundreds) of watchers.
		3043
		3044	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3045	(disabled).
		3046
		3047	=item EV_VERIFY
		3048
		3049	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3050	be done: If set to C<0>, no internal verification code will be compiled
		3051	in. If set to C<1>, then verification code will be compiled in, but not
		3052	called. If set to C<2>, then the internal verification code will be
		3053	called once per loop, which can slow down libev. If set to C<3>, then the
		3054	verification code will be called very frequently, which will slow down
		3055	libev considerably.
		3056
		3057	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3058	C<0.>
2988		3059
2989	=item EV_COMMON	3060	=item EV_COMMON
2990		3061
2991	By default, all watchers have a C<void *data> member. By redefining	3062	By default, all watchers have a C<void *data> member. By redefining
2992	this macro to a something else you can include more and other types of	3063	this macro to a something else you can include more and other types of
…		…
3162	correct watcher to remove. The lists are usually short (you don't usually	3233	correct watcher to remove. The lists are usually short (you don't usually
3163	have many watchers waiting for the same fd or signal).	3234	have many watchers waiting for the same fd or signal).
3164		3235
3165	=item Finding the next timer in each loop iteration: O(1)	3236	=item Finding the next timer in each loop iteration: O(1)
3166		3237
3167	By virtue of using a binary heap, the next timer is always found at the	3238	By virtue of using a binary or 4-heap, the next timer is always found at a
3168	beginning of the storage array.	3239	fixed position in the storage array.
3169		3240
3170	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3241	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3171		3242
3172	A change means an I/O watcher gets started or stopped, which requires	3243	A change means an I/O watcher gets started or stopped, which requires
3173	libev to recalculate its status (and possibly tell the kernel, depending	3244	libev to recalculate its status (and possibly tell the kernel, depending
…		…
3202	model. Libev still offers limited functionality on this platform in	3273	model. Libev still offers limited functionality on this platform in
3203	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3274	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3204	descriptors. This only applies when using Win32 natively, not when using	3275	descriptors. This only applies when using Win32 natively, not when using
3205	e.g. cygwin.	3276	e.g. cygwin.
3206		3277
		3278	Lifting these limitations would basically require the full
		3279	re-implementation of the I/O system. If you are into these kinds of
		3280	things, then note that glib does exactly that for you in a very portable
		3281	way (note also that glib is the slowest event library known to man).
		3282
3207	There is no supported compilation method available on windows except	3283	There is no supported compilation method available on windows except
3208	embedding it into other applications.	3284	embedding it into other applications.
3209		3285
3210	Due to the many, low, and arbitrary limits on the win32 platform and the	3286	Due to the many, low, and arbitrary limits on the win32 platform and
3211	abysmal performance of winsockets, using a large number of sockets is not	3287	the abysmal performance of winsockets, using a large number of sockets
3212	recommended (and not reasonable). If your program needs to use more than	3288	is not recommended (and not reasonable). If your program needs to use
3213	a hundred or so sockets, then likely it needs to use a totally different	3289	more than a hundred or so sockets, then likely it needs to use a totally
3214	implementation for windows, as libev offers the POSIX model, which cannot	3290	different implementation for windows, as libev offers the POSIX readiness
3215	be implemented efficiently on windows (microsoft monopoly games).	3291	notification model, which cannot be implemented efficiently on windows
		3292	(microsoft monopoly games).
3216		3293
3217	=over 4	3294	=over 4
3218		3295
3219	=item The winsocket select function	3296	=item The winsocket select function
3220		3297
…		…
3234	Note that winsockets handling of fd sets is O(n), so you can easily get a	3311	Note that winsockets handling of fd sets is O(n), so you can easily get a
3235	complexity in the O(n²) range when using win32.	3312	complexity in the O(n²) range when using win32.
3236		3313
3237	=item Limited number of file descriptors	3314	=item Limited number of file descriptors
3238		3315
3239	Windows has numerous arbitrary (and low) limits on things. Early versions	3316	Windows has numerous arbitrary (and low) limits on things.
3240	of winsocket's select only supported waiting for a max. of C<64> handles	3317
		3318	Early versions of winsocket's select only supported waiting for a maximum
3241	(probably owning to the fact that all windows kernels can only wait for	3319	of C<64> handles (probably owning to the fact that all windows kernels
3242	C<64> things at the same time internally; microsoft recommends spawning a	3320	can only wait for C<64> things at the same time internally; microsoft
3243	chain of threads and wait for 63 handles and the previous thread in each).	3321	recommends spawning a chain of threads and wait for 63 handles and the
		3322	previous thread in each. Great).
3244		3323
3245	Newer versions support more handles, but you need to define C<FD_SETSIZE>	3324	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3246	to some high number (e.g. C<2048>) before compiling the winsocket select	3325	to some high number (e.g. C<2048>) before compiling the winsocket select
3247	call (which might be in libev or elsewhere, for example, perl does its own	3326	call (which might be in libev or elsewhere, for example, perl does its own
3248	select emulation on windows).	3327	select emulation on windows).
…		…
3260	calling select (O(n²)) will likely make this unworkable.	3339	calling select (O(n²)) will likely make this unworkable.
3261		3340
3262	=back	3341	=back
3263		3342
3264		3343
		3344	=head1 PORTABILITY REQUIREMENTS
		3345
		3346	In addition to a working ISO-C implementation, libev relies on a few
		3347	additional extensions:
		3348
		3349	=over 4
		3350
		3351	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3352
		3353	The type C<sig_atomic_t volatile> (or whatever is defined as
		3354	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3355	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3356	believed to be sufficiently portable.
		3357
		3358	=item C<sigprocmask> must work in a threaded environment
		3359
		3360	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3361	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3362	pthread implementations will either allow C<sigprocmask> in the "main
		3363	thread" or will block signals process-wide, both behaviours would
		3364	be compatible with libev. Interaction between C<sigprocmask> and
		3365	C<pthread_sigmask> could complicate things, however.
		3366
		3367	The most portable way to handle signals is to block signals in all threads
		3368	except the initial one, and run the default loop in the initial thread as
		3369	well.
		3370
		3371	=item C<long> must be large enough for common memory allocation sizes
		3372
		3373	To improve portability and simplify using libev, libev uses C<long>
		3374	internally instead of C<size_t> when allocating its data structures. On
		3375	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3376	is still at least 31 bits everywhere, which is enough for hundreds of
		3377	millions of watchers.
		3378
		3379	=item C<double> must hold a time value in seconds with enough accuracy
		3380
		3381	The type C<double> is used to represent timestamps. It is required to
		3382	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3383	enough for at least into the year 4000. This requirement is fulfilled by
		3384	implementations implementing IEEE 754 (basically all existing ones).
		3385
		3386	=back
		3387
		3388	If you know of other additional requirements drop me a note.
		3389
		3390
		3391	=head1 VALGRIND
		3392
		3393	Valgrind has a special section here because it is a popular tool that is
		3394	highly useful, but valgrind reports are very hard to interpret.
		3395
		3396	If you think you found a bug (memory leak, uninitialised data access etc.)
		3397	in libev, then check twice: If valgrind reports something like:
		3398
		3399	==2274== definitely lost: 0 bytes in 0 blocks.
		3400	==2274== possibly lost: 0 bytes in 0 blocks.
		3401	==2274== still reachable: 256 bytes in 1 blocks.
		3402
		3403	then there is no memory leak. Similarly, under some circumstances,
		3404	valgrind might report kernel bugs as if it were a bug in libev, or it
		3405	might be confused (it is a very good tool, but only a tool).
		3406
		3407	If you are unsure about something, feel free to contact the mailing list
		3408	with the full valgrind report and an explanation on why you think this is
		3409	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3410	no bug" answer and take the chance of learning how to interpret valgrind
		3411	properly.
		3412
		3413	If you need, for some reason, empty reports from valgrind for your project
		3414	I suggest using suppression lists.
		3415
		3416
3265	=head1 AUTHOR	3417	=head1 AUTHOR
3266		3418
3267	Marc Lehmann <libev@schmorp.de>.	3419	Marc Lehmann <libev@schmorp.de>.
3268		3420

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Comparing libev/ev.pod (file contents): Revision 1.146 by root, Fri Apr 11 00:31:19 2008 UTC vs. Revision 1.159 by root, Thu May 22 02:44:57 2008 UTC

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Revision 1.146 by root, Fri Apr 11 00:31:19 2008 UTC vs.
Revision 1.159 by root, Thu May 22 02:44:57 2008 UTC