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

Comparing libev/ev.pod (file contents):
Revision 1.147 by root, Wed Apr 23 08:21:02 2008 UTC vs.
Revision 1.158 by root, Wed May 21 12:51:38 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
…		…
1032	If you must do this, then force the use of a known-to-be-good backend	1032	If you must do this, then force the use of a known-to-be-good backend
1033	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1033	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1034	C<EVBACKEND_POLL>).	1034	C<EVBACKEND_POLL>).
1035		1035
1036	Another thing you have to watch out for is that it is quite easy to	1036	Another thing you have to watch out for is that it is quite easy to
1037	receive "spurious" readyness notifications, that is your callback might	1037	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	1038	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	1039	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	1040	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	1041	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	1042	it is best to always use non-blocking I/O: An extra C<read>(2) returning
…		…
1151		1151
1152	Timer watchers are simple relative timers that generate an event after a	1152	Timer watchers are simple relative timers that generate an event after a
1153	given time, and optionally repeating in regular intervals after that.	1153	given time, and optionally repeating in regular intervals after that.
1154		1154
1155	The timers are based on real time, that is, if you register an event that	1155	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	1156	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	1157	year, it will still time out after (roughly) and hour. "Roughly" because
1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1159	monotonic clock option helps a lot here).	1159	monotonic clock option helps a lot here).
1160		1160
1161	The relative timeouts are calculated relative to the C<ev_now ()>	1161	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	1162	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	1164	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:	1165	on the current time, use something like this to adjust for this:
1166		1166
1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1168		1168
1169	The callback is guarenteed to be invoked only when its timeout has passed,	1169	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	1170	but if multiple timers become ready during the same loop iteration then
1171	order of execution is undefined.	1171	order of execution is undefined.
1172		1172
1173	=head3 Watcher-Specific Functions and Data Members	1173	=head3 Watcher-Specific Functions and Data Members
1174		1174
…		…
1176		1176
1177	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1177	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1178		1178
1179	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1179	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1180		1180
1181	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1181	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	1182	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	1183	reached. If it is positive, then the timer will automatically be
1184	later, again, and again, until stopped manually.	1184	configured to trigger again C<repeat> seconds later, again, and again,
		1185	until stopped manually.
1185		1186
1186	The timer itself will do a best-effort at avoiding drift, that is, if you	1187	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	1188	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	1189	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	1190	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.	1191	do stuff) the timer will not fire more than once per event loop iteration.
1191		1192
1192	=item ev_timer_again (loop, ev_timer *)	1193	=item ev_timer_again (loop, ev_timer *)
1193		1194
1194	This will act as if the timer timed out and restart it again if it is	1195	This will act as if the timer timed out and restart it again if it is
1195	repeating. The exact semantics are:	1196	repeating. The exact semantics are:
…		…
1272	Periodic watchers are also timers of a kind, but they are very versatile	1273	Periodic watchers are also timers of a kind, but they are very versatile
1273	(and unfortunately a bit complex).	1274	(and unfortunately a bit complex).
1274		1275
1275	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1276	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	1277	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	1278	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 ()	1279	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	1280	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1281	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	1282	to trigger the event (unlike an C<ev_timer>, which would still trigger
1281	roughly 10 seconds later).	1283	roughly 10 seconds later as it uses a relative timeout).
1282		1284
1283	They can also be used to implement vastly more complex timers, such as	1285	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,	1286	such as triggering an event on each "midnight, local time", or other
1285	rules.	1287	complicated, rules.
1286		1288
1287	As with timers, the callback is guarenteed to be invoked only when the	1289	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	1290	time (C<at>) has passed, but if multiple periodic timers become ready
1289	during the same loop iteration then order of execution is undefined.	1291	during the same loop iteration then order of execution is undefined.
1290		1292
1291	=head3 Watcher-Specific Functions and Data Members	1293	=head3 Watcher-Specific Functions and Data Members
1292		1294
1293	=over 4	1295	=over 4
…		…
1301		1303
1302	=over 4	1304	=over 4
1303		1305
1304	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1306	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1305		1307
1306	In this configuration the watcher triggers an event at the wallclock time	1308	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,	1309	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	1310	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.	1311	run when the system time reaches or surpasses this time.
1310		1312
1311	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1313	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1312		1314
1313	In this mode the watcher will always be scheduled to time out at the next	1315	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)	1316	C<at + N * interval> time (for some integer N, which can also be negative)
1315	and then repeat, regardless of any time jumps.	1317	and then repeat, regardless of any time jumps.
1316		1318
1317	This can be used to create timers that do not drift with respect to system	1319	This can be used to create timers that do not drift with respect to system
1318	time:	1320	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1321	the hour:
1319		1322
1320	ev_periodic_set (&periodic, 0., 3600., 0);	1323	ev_periodic_set (&periodic, 0., 3600., 0);
1321		1324
1322	This doesn't mean there will always be 3600 seconds in between triggers,	1325	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	1326	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	1331	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.	1332	time where C<time = at (mod interval)>, regardless of any time jumps.
1330		1333
1331	For numerical stability it is preferable that the C<at> value is near	1334	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	1335	C<ev_now ()> (the current time), but there is no range requirement for
1333	this value.	1336	this value, and in fact is often specified as zero.
		1337
		1338	Note also that there is an upper limit to how often a timer can fire (cpu
		1339	speed for example), so if C<interval> is very small then timing stability
		1340	will of course detoriate. Libev itself tries to be exact to be about one
		1341	millisecond (if the OS supports it and the machine is fast enough).
1334		1342
1335	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1343	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1336		1344
1337	In this mode the values for C<interval> and C<at> are both being	1345	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	1346	ignored. Instead, each time the periodic watcher gets scheduled, the
1339	reschedule callback will be called with the watcher as first, and the	1347	reschedule callback will be called with the watcher as first, and the
1340	current time as second argument.	1348	current time as second argument.
1341		1349
1342	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1350	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,	1351	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		1352
		1353	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1354	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1355	only event loop modification you are allowed to do).
		1356
1347	Its prototype is C<ev_tstamp (reschedule_cb)(struct ev_periodic w,	1357	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
1348	ev_tstamp now)>, e.g.:	1358	*w, ev_tstamp now)>, e.g.:
1349		1359
1350	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1360	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1351	{	1361	{
1352	return now + 60.;	1362	return now + 60.;
1353	}	1363	}
…		…
1355	It must return the next time to trigger, based on the passed time value	1365	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	1366	(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	1367	will usually be called just before the callback will be triggered, but
1358	might be called at other times, too.	1368	might be called at other times, too.
1359		1369
1360	NOTE: I<< This callback must always return a time that is later than the	1370	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.	1371	equal to the passed C<now> value >>.
1362		1372
1363	This can be used to create very complex timers, such as a timer that	1373	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	1374	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	1375	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	1376	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).	1377	reason I omitted it as an example).
1368		1378
1369	=back	1379	=back
…		…
1373	Simply stops and restarts the periodic watcher again. This is only useful	1383	Simply stops and restarts the periodic watcher again. This is only useful
1374	when you changed some parameters or the reschedule callback would return	1384	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	1385	a different time than the last time it was called (e.g. in a crond like
1376	program when the crontabs have changed).	1386	program when the crontabs have changed).
1377		1387
		1388	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1389
		1390	When active, returns the absolute time that the watcher is supposed to
		1391	trigger next.
		1392
1378	=item ev_tstamp offset [read-write]	1393	=item ev_tstamp offset [read-write]
1379		1394
1380	When repeating, this contains the offset value, otherwise this is the	1395	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>).	1396	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
1382		1397
…		…
1392	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]	1407	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]
1393		1408
1394	The current reschedule callback, or C<0>, if this functionality is	1409	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	1410	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.	1411	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		1412
1403	=back	1413	=back
1404		1414
1405	=head3 Examples	1415	=head3 Examples
1406		1416
…		…
1610	as even with OS-supported change notifications, this can be	1620	as even with OS-supported change notifications, this can be
1611	resource-intensive.	1621	resource-intensive.
1612		1622
1613	At the time of this writing, only the Linux inotify interface is	1623	At the time of this writing, only the Linux inotify interface is
1614	implemented (implementing kqueue support is left as an exercise for the	1624	implemented (implementing kqueue support is left as an exercise for the
		1625	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	1626	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	1627	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	1628	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	1629	but changes are usually detected immediately, and if the file exists there
1619	polling.	1630	will be no polling.
1620		1631
1621	=head3 ABI Issues (Largefile Support)	1632	=head3 ABI Issues (Largefile Support)
1622		1633
1623	Libev by default (unless the user overrides this) uses the default	1634	Libev by default (unless the user overrides this) uses the default
1624	compilation environment, which means that on systems with optionally	1635	compilation environment, which means that on systems with optionally
…		…
1649		1660
1650	The C<stat ()> syscall only supports full-second resolution portably, and	1661	The C<stat ()> syscall only supports full-second resolution portably, and
1651	even on systems where the resolution is higher, many filesystems still	1662	even on systems where the resolution is higher, many filesystems still
1652	only support whole seconds.	1663	only support whole seconds.
1653		1664
1654	That means that, if the time is the only thing that changes, you might	1665	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	1666	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	1667	calls your callback, which does something. When there is another update
1657	the same second, C<ev_stat> will be unable to detect it.	1668	within the same second, C<ev_stat> will be unable to detect it as the stat
		1669	data does not change.
1658		1670
1659	The solution to this is to delay acting on a change for a second (or till	1671	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>	1672	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>	1673	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	1674	ev_timer_again (loop, w)>).
1663	systems.	1675
		1676	The C<.02> offset is added to work around small timing inconsistencies
		1677	of some operating systems (where the second counter of the current time
		1678	might be be delayed. One such system is the Linux kernel, where a call to
		1679	C<gettimeofday> might return a timestamp with a full second later than
		1680	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1681	update file times then there will be a small window where the kernel uses
		1682	the previous second to update file times but libev might already execute
		1683	the timer callback).
1664		1684
1665	=head3 Watcher-Specific Functions and Data Members	1685	=head3 Watcher-Specific Functions and Data Members
1666		1686
1667	=over 4	1687	=over 4
1668		1688
…		…
1674	C<path>. The C<interval> is a hint on how quickly a change is expected to	1694	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	1695	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	1696	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.	1697	path for as long as the watcher is active.
1678		1698
1679	The callback will be receive C<EV_STAT> when a change was detected,	1699	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	1700	to the attributes at the time the watcher was started (or the last change
1681	last change was detected).	1701	was detected).
1682		1702
1683	=item ev_stat_stat (loop, ev_stat *)	1703	=item ev_stat_stat (loop, ev_stat *)
1684		1704
1685	Updates the stat buffer immediately with new values. If you change the	1705	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	1706	watched path in your callback, you could call this function to avoid
1687	detecting this change (while introducing a race condition). Can also be	1707	detecting this change (while introducing a race condition if you are not
1688	useful simply to find out the new values.	1708	the only one changing the path). Can also be useful simply to find out the
		1709	new values.
1689		1710
1690	=item ev_statdata attr [read-only]	1711	=item ev_statdata attr [read-only]
1691		1712
1692	The most-recently detected attributes of the file. Although the type is of	1713	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	1714	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	1715	suitable for your system, but you can only rely on the POSIX-standardised
		1716	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.	1717	some error while C<stat>ing the file.
1696		1718
1697	=item ev_statdata prev [read-only]	1719	=item ev_statdata prev [read-only]
1698		1720
1699	The previous attributes of the file. The callback gets invoked whenever	1721	The previous attributes of the file. The callback gets invoked whenever
1700	C<prev> != C<attr>.	1722	C<prev> != C<attr>, or, more precisely, one or more of these members
		1723	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1724	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1701		1725
1702	=item ev_tstamp interval [read-only]	1726	=item ev_tstamp interval [read-only]
1703		1727
1704	The specified interval.	1728	The specified interval.
1705		1729
…		…
1759	}	1783	}
1760		1784
1761	...	1785	...
1762	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	1786	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1763	ev_stat_start (loop, &passwd);	1787	ev_stat_start (loop, &passwd);
1764	ev_timer_init (&timer, timer_cb, 0., 1.01);	1788	ev_timer_init (&timer, timer_cb, 0., 1.02);
1765		1789
1766		1790
1767	=head2 C<ev_idle> - when you've got nothing better to do...	1791	=head2 C<ev_idle> - when you've got nothing better to do...
1768		1792
1769	Idle watchers trigger events when no other events of the same or higher	1793	Idle watchers trigger events when no other events of the same or higher
…		…
1857		1881
1858	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	1882	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	1883	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,	1884	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	1885	too) should not activate ("feed") events into libev. While libev fully
1862	supports this, they will be called before other C<ev_check> watchers	1886	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	1887	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	1888	(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	1889	state until their C<ev_check> watcher ran (always remind yourself to
1866	coexist peacefully with others).	1890	coexist peacefully with others).
1867		1891
…		…
1882	=head3 Examples	1906	=head3 Examples
1883		1907
1884	There are a number of principal ways to embed other event loops or modules	1908	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	1909	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	1910	(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>	1911	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	1912	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1889	into the Glib event loop).	1913	Glib event loop).
1890		1914
1891	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	1915	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	1916	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	1917	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	1918	priority for the check watcher or use C<ev_clear_pending> explicitly, as
…		…
2966	defined to be C<0>, then they are not.	2990	defined to be C<0>, then they are not.
2967		2991
2968	=item EV_MINIMAL	2992	=item EV_MINIMAL
2969		2993
2970	If you need to shave off some kilobytes of code at the expense of some	2994	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	2995	speed, define this symbol to C<1>. Currently this is used to override some
2972	some inlining decisions, saves roughly 30% codesize of amd64.	2996	inlining decisions, saves roughly 30% codesize of amd64. It also selects a
		2997	much smaller 2-heap for timer management over the default 4-heap.
2973		2998
2974	=item EV_PID_HASHSIZE	2999	=item EV_PID_HASHSIZE
2975		3000
2976	C<ev_child> watchers use a small hash table to distribute workload by	3001	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	3002	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	3008	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>),	3009	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>	3010	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	3011	watchers you might want to increase this value (I<must> be a power of
2987	two).	3012	two).
		3013
		3014	=item EV_USE_4HEAP
		3015
		3016	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3017	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3018	to C<1>. The 4-heap uses more complicated (longer) code but has
		3019	noticably faster performance with many (thousands) of watchers.
		3020
		3021	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3022	(disabled).
		3023
		3024	=item EV_HEAP_CACHE_AT
		3025
		3026	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3027	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3028	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3029	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3030	but avoids random read accesses on heap changes. This improves performance
		3031	noticably with with many (hundreds) of watchers.
		3032
		3033	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3034	(disabled).
2988		3035
2989	=item EV_COMMON	3036	=item EV_COMMON
2990		3037
2991	By default, all watchers have a C<void *data> member. By redefining	3038	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	3039	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	3209	correct watcher to remove. The lists are usually short (you don't usually
3163	have many watchers waiting for the same fd or signal).	3210	have many watchers waiting for the same fd or signal).
3164		3211
3165	=item Finding the next timer in each loop iteration: O(1)	3212	=item Finding the next timer in each loop iteration: O(1)
3166		3213
3167	By virtue of using a binary heap, the next timer is always found at the	3214	By virtue of using a binary or 4-heap, the next timer is always found at a
3168	beginning of the storage array.	3215	fixed position in the storage array.
3169		3216
3170	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3217	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3171		3218
3172	A change means an I/O watcher gets started or stopped, which requires	3219	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	3220	libev to recalculate its status (and possibly tell the kernel, depending
…		…
3202	model. Libev still offers limited functionality on this platform in	3249	model. Libev still offers limited functionality on this platform in
3203	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3250	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3204	descriptors. This only applies when using Win32 natively, not when using	3251	descriptors. This only applies when using Win32 natively, not when using
3205	e.g. cygwin.	3252	e.g. cygwin.
3206		3253
		3254	Lifting these limitations would basically require the full
		3255	re-implementation of the I/O system. If you are into these kinds of
		3256	things, then note that glib does exactly that for you in a very portable
		3257	way (note also that glib is the slowest event library known to man).
		3258
3207	There is no supported compilation method available on windows except	3259	There is no supported compilation method available on windows except
3208	embedding it into other applications.	3260	embedding it into other applications.
3209		3261
3210	Due to the many, low, and arbitrary limits on the win32 platform and the	3262	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	3263	the abysmal performance of winsockets, using a large number of sockets
3212	recommended (and not reasonable). If your program needs to use more than	3264	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	3265	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	3266	different implementation for windows, as libev offers the POSIX readiness
3215	be implemented efficiently on windows (microsoft monopoly games).	3267	notification model, which cannot be implemented efficiently on windows
		3268	(microsoft monopoly games).
3216		3269
3217	=over 4	3270	=over 4
3218		3271
3219	=item The winsocket select function	3272	=item The winsocket select function
3220		3273
…		…
3234	Note that winsockets handling of fd sets is O(n), so you can easily get a	3287	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.	3288	complexity in the O(n²) range when using win32.
3236		3289
3237	=item Limited number of file descriptors	3290	=item Limited number of file descriptors
3238		3291
3239	Windows has numerous arbitrary (and low) limits on things. Early versions	3292	Windows has numerous arbitrary (and low) limits on things.
3240	of winsocket's select only supported waiting for a max. of C<64> handles	3293
		3294	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	3295	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	3296	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).	3297	recommends spawning a chain of threads and wait for 63 handles and the
		3298	previous thread in each. Great).
3244		3299
3245	Newer versions support more handles, but you need to define C<FD_SETSIZE>	3300	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	3301	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	3302	call (which might be in libev or elsewhere, for example, perl does its own
3248	select emulation on windows).	3303	select emulation on windows).
…		…
3260	calling select (O(n²)) will likely make this unworkable.	3315	calling select (O(n²)) will likely make this unworkable.
3261		3316
3262	=back	3317	=back
3263		3318
3264		3319
		3320	=head1 PORTABILITY REQUIREMENTS
		3321
		3322	In addition to a working ISO-C implementation, libev relies on a few
		3323	additional extensions:
		3324
		3325	=over 4
		3326
		3327	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3328
		3329	The type C<sig_atomic_t volatile> (or whatever is defined as
		3330	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3331	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3332	believed to be sufficiently portable.
		3333
		3334	=item C<sigprocmask> must work in a threaded environment
		3335
		3336	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3337	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3338	pthread implementations will either allow C<sigprocmask> in the "main
		3339	thread" or will block signals process-wide, both behaviours would
		3340	be compatible with libev. Interaction between C<sigprocmask> and
		3341	C<pthread_sigmask> could complicate things, however.
		3342
		3343	The most portable way to handle signals is to block signals in all threads
		3344	except the initial one, and run the default loop in the initial thread as
		3345	well.
		3346
		3347	=item C<long> must be large enough for common memory allocation sizes
		3348
		3349	To improve portability and simplify using libev, libev uses C<long>
		3350	internally instead of C<size_t> when allocating its data structures. On
		3351	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3352	is still at least 31 bits everywhere, which is enough for hundreds of
		3353	millions of watchers.
		3354
		3355	=item C<double> must hold a time value in seconds with enough accuracy
		3356
		3357	The type C<double> is used to represent timestamps. It is required to
		3358	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3359	enough for at least into the year 4000. This requirement is fulfilled by
		3360	implementations implementing IEEE 754 (basically all existing ones).
		3361
		3362	=back
		3363
		3364	If you know of other additional requirements drop me a note.
		3365
		3366
		3367	=head1 VALGRIND
		3368
		3369	Valgrind has a special section here because it is a popular tool that is
		3370	highly useful, but valgrind reports are very hard to interpret.
		3371
		3372	If you think you found a bug (memory leak, uninitialised data access etc.)
		3373	in libev, then check twice: If valgrind reports something like:
		3374
		3375	==2274== definitely lost: 0 bytes in 0 blocks.
		3376	==2274== possibly lost: 0 bytes in 0 blocks.
		3377	==2274== still reachable: 256 bytes in 1 blocks.
		3378
		3379	then there is no memory leak. Similarly, under some circumstances,
		3380	valgrind might report kernel bugs as if it were a bug in libev, or it
		3381	might be confused (it is a very good tool, but only a tool).
		3382
		3383	If you are unsure about something, feel free to contact the mailing list
		3384	with the full valgrind report and an explanation on why you think this is
		3385	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3386	no bug" answer and take the chance of learning how to interpret valgrind
		3387	properly.
		3388
		3389	If you need, for some reason, empty reports from valgrind for your project
		3390	I suggest using suppression lists.
		3391
		3392
3265	=head1 AUTHOR	3393	=head1 AUTHOR
3266		3394
3267	Marc Lehmann <libev@schmorp.de>.	3395	Marc Lehmann <libev@schmorp.de>.
3268		3396

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Comparing libev/ev.pod (file contents): Revision 1.147 by root, Wed Apr 23 08:21:02 2008 UTC vs. Revision 1.158 by root, Wed May 21 12:51:38 2008 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.147 by root, Wed Apr 23 08:21:02 2008 UTC vs.
Revision 1.158 by root, Wed May 21 12:51:38 2008 UTC