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

Comparing libev/ev.pod (file contents):
Revision 1.144 by root, Mon Apr 7 12:33:29 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
…		…
196	See the description of C<ev_embed> watchers for more info.	196	See the description of C<ev_embed> watchers for more info.
197		197
198	=item ev_set_allocator (void (cb)(void *ptr, long size))	198	=item ev_set_allocator (void (cb)(void *ptr, long size))
199		199
200	Sets the allocation function to use (the prototype is similar - the	200	Sets the allocation function to use (the prototype is similar - the
201	semantics is identical - to the realloc C function). It is used to	201	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
202	allocate and free memory (no surprises here). If it returns zero when	202	used to allocate and free memory (no surprises here). If it returns zero
203	memory needs to be allocated, the library might abort or take some	203	when memory needs to be allocated (C<size != 0>), the library might abort
204	potentially destructive action. The default is your system realloc	204	or take some potentially destructive action.
205	function.	205
		206	Since some systems (at least OpenBSD and Darwin) fail to implement
		207	correct C<realloc> semantics, libev will use a wrapper around the system
		208	C<realloc> and C<free> functions by default.
206		209
207	You could override this function in high-availability programs to, say,	210	You could override this function in high-availability programs to, say,
208	free some memory if it cannot allocate memory, to use a special allocator,	211	free some memory if it cannot allocate memory, to use a special allocator,
209	or even to sleep a while and retry until some memory is available.	212	or even to sleep a while and retry until some memory is available.
210		213
211	Example: Replace the libev allocator with one that waits a bit and then	214	Example: Replace the libev allocator with one that waits a bit and then
212	retries).	215	retries (example requires a standards-compliant C<realloc>).
213		216
214	static void *	217	static void *
215	persistent_realloc (void *ptr, size_t size)	218	persistent_realloc (void *ptr, size_t size)
216	{	219	{
217	for (;;)	220	for (;;)
…		…
333	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
334	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
335	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
336	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
337	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
338	readyness notifications you get per iteration.	341	readiness notifications you get per iteration.
339		342
340	=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)
341		344
342	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
343	than select, but handles sparse fds better and has no artificial	346	than select, but handles sparse fds better and has no artificial
…		…
422	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
423	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
424	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
425	might perform better.	428	might perform better.
426		429
427	On the positive side, ignoring the spurious readyness notifications, this	430	On the positive side, ignoring the spurious readiness notifications, this
428	backend actually performed to specification in all tests and is fully	431	backend actually performed to specification in all tests and is fully
429	embeddable, which is a rare feat among the OS-specific backends.	432	embeddable, which is a rare feat among the OS-specific backends.
430		433
431	=item C<EVBACKEND_ALL>	434	=item C<EVBACKEND_ALL>
432		435
…		…
686	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
687	interactive servers (of course not for games), likewise for timeouts. It	690	interactive servers (of course not for games), likewise for timeouts. It
688	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>,
689	as this approsaches the timing granularity of most systems.	692	as this approsaches the timing granularity of most systems.
690		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
691	=back	705	=back
692		706
693		707
694	=head1 ANATOMY OF A WATCHER	708	=head1 ANATOMY OF A WATCHER
695		709
…		…
1029	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
1030	(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
1031	C<EVBACKEND_POLL>).	1045	C<EVBACKEND_POLL>).
1032		1046
1033	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
1034	receive "spurious" readyness notifications, that is your callback might	1048	receive "spurious" readiness notifications, that is your callback might
1035	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
1036	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
1037	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
1038	this situation even with a relatively standard program structure. Thus	1052	this situation even with a relatively standard program structure. Thus
1039	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
…		…
1148		1162
1149	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
1150	given time, and optionally repeating in regular intervals after that.	1164	given time, and optionally repeating in regular intervals after that.
1151		1165
1152	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
1153	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
1154	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
1155	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1169	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1156	monotonic clock option helps a lot here).	1170	monotonic clock option helps a lot here).
1157		1171
1158	The relative timeouts are calculated relative to the C<ev_now ()>	1172	The relative timeouts are calculated relative to the C<ev_now ()>
1159	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
…		…
1161	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
1162	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:
1163		1177
1164	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1178	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1165		1179
1166	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,
1167	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
1168	order of execution is undefined.	1182	order of execution is undefined.
1169		1183
1170	=head3 Watcher-Specific Functions and Data Members	1184	=head3 Watcher-Specific Functions and Data Members
1171		1185
…		…
1173		1187
1174	=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)
1175		1189
1176	=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)
1177		1191
1178	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>
1179	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
1180	timer will automatically be configured to trigger again C<repeat> seconds	1194	reached. If it is positive, then the timer will automatically be
1181	later, again, and again, until stopped manually.	1195	configured to trigger again C<repeat> seconds later, again, and again,
		1196	until stopped manually.
1182		1197
1183	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
1184	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
1185	exactly 10 second intervals. If, however, your program cannot keep up with	1200	trigger at exactly 10 second intervals. If, however, your program cannot
1186	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
1187	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.
1188		1203
1189	=item ev_timer_again (loop, ev_timer *)	1204	=item ev_timer_again (loop, ev_timer *)
1190		1205
1191	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
1192	repeating. The exact semantics are:	1207	repeating. The exact semantics are:
…		…
1269	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
1270	(and unfortunately a bit complex).	1285	(and unfortunately a bit complex).
1271		1286
1272	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)
1273	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
1274	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
1275	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 ()
1276	+ 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
1277	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
1278	roughly 10 seconds later).	1294	roughly 10 seconds later as it uses a relative timeout).
1279		1295
1280	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,
1281	triggering an event on each midnight, local time or other, complicated,	1297	such as triggering an event on each "midnight, local time", or other
1282	rules.	1298	complicated, rules.
1283		1299
1284	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
1285	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
1286	during the same loop iteration then order of execution is undefined.	1302	during the same loop iteration then order of execution is undefined.
1287		1303
1288	=head3 Watcher-Specific Functions and Data Members	1304	=head3 Watcher-Specific Functions and Data Members
1289		1305
1290	=over 4	1306	=over 4
…		…
1298		1314
1299	=over 4	1315	=over 4
1300		1316
1301	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1317	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1302		1318
1303	In this configuration the watcher triggers an event at the wallclock time	1319	In this configuration the watcher triggers an event after the wallclock
1304	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
1305	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
1306	system time reaches or surpasses this time.	1322	run when the system time reaches or surpasses this time.
1307		1323
1308	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1324	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1309		1325
1310	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
1311	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)
1312	and then repeat, regardless of any time jumps.	1328	and then repeat, regardless of any time jumps.
1313		1329
1314	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
1315	time:	1331	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1332	the hour:
1316		1333
1317	ev_periodic_set (&periodic, 0., 3600., 0);	1334	ev_periodic_set (&periodic, 0., 3600., 0);
1318		1335
1319	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,
1320	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
…		…
1325	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
1326	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.
1327		1344
1328	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
1329	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
1330	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).
1331		1353
1332	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1354	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1333		1355
1334	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
1335	ignored. Instead, each time the periodic watcher gets scheduled, the	1357	ignored. Instead, each time the periodic watcher gets scheduled, the
1336	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
1337	current time as second argument.	1359	current time as second argument.
1338		1360
1339	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,
1340	ever, or make any event loop modifications>. If you need to stop it,	1362	ever, or make ANY event loop modifications whatsoever>.
1341	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1342	starting an C<ev_prepare> watcher, which is legal).
1343		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
1344	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
1345	ev_tstamp now)>, e.g.:	1369	*w, ev_tstamp now)>, e.g.:
1346		1370
1347	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)
1348	{	1372	{
1349	return now + 60.;	1373	return now + 60.;
1350	}	1374	}
…		…
1352	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
1353	(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
1354	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
1355	might be called at other times, too.	1379	might be called at other times, too.
1356		1380
1357	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
1358	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1382	equal to the passed C<now> value >>.
1359		1383
1360	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
1361	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
1362	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
1363	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
1364	reason I omitted it as an example).	1388	reason I omitted it as an example).
1365		1389
1366	=back	1390	=back
…		…
1370	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
1371	when you changed some parameters or the reschedule callback would return	1395	when you changed some parameters or the reschedule callback would return
1372	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
1373	program when the crontabs have changed).	1397	program when the crontabs have changed).
1374		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
1375	=item ev_tstamp offset [read-write]	1404	=item ev_tstamp offset [read-write]
1376		1405
1377	When repeating, this contains the offset value, otherwise this is the	1406	When repeating, this contains the offset value, otherwise this is the
1378	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>).
1379		1408
…		…
1389	=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]
1390		1419
1391	The current reschedule callback, or C<0>, if this functionality is	1420	The current reschedule callback, or C<0>, if this functionality is
1392	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
1393	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.
1394
1395	=item ev_tstamp at [read-only]
1396
1397	When active, contains the absolute time that the watcher is supposed to
1398	trigger next.
1399		1423
1400	=back	1424	=back
1401		1425
1402	=head3 Examples	1426	=head3 Examples
1403		1427
…		…
1607	as even with OS-supported change notifications, this can be	1631	as even with OS-supported change notifications, this can be
1608	resource-intensive.	1632	resource-intensive.
1609		1633
1610	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
1611	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
1612	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
1613	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
1614	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,
1615	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
1616	polling.	1641	will be no polling.
1617		1642
1618	=head3 ABI Issues (Largefile Support)	1643	=head3 ABI Issues (Largefile Support)
1619		1644
1620	Libev by default (unless the user overrides this) uses the default	1645	Libev by default (unless the user overrides this) uses the default
1621	compilation environment, which means that on systems with optionally	1646	compilation environment, which means that on systems with optionally
…		…
1631	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
1632	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
1633	change detection where possible. The inotify descriptor will be created lazily	1658	change detection where possible. The inotify descriptor will be created lazily
1634	when the first C<ev_stat> watcher is being started.	1659	when the first C<ev_stat> watcher is being started.
1635		1660
1636	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
1637	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
1638	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
1639	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.
1640		1665
1641	(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
1642	implement this functionality, due to the requirement of having a file	1667	implement this functionality, due to the requirement of having a file
1643	descriptor open on the object at all times).	1668	descriptor open on the object at all times).
…		…
1646		1671
1647	The C<stat ()> syscall only supports full-second resolution portably, and	1672	The C<stat ()> syscall only supports full-second resolution portably, and
1648	even on systems where the resolution is higher, many filesystems still	1673	even on systems where the resolution is higher, many filesystems still
1649	only support whole seconds.	1674	only support whole seconds.
1650		1675
1651	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
1652	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
1653	your callback, which does something. When there is another update within	1678	calls your callback, which does something. When there is another update
1654	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.
1655		1681
1656	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
1657	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
1658	(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);
1659	is added to work around small timing inconsistencies of some operating	1685	ev_timer_again (loop, w)>).
1660	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).
1661		1695
1662	=head3 Watcher-Specific Functions and Data Members	1696	=head3 Watcher-Specific Functions and Data Members
1663		1697
1664	=over 4	1698	=over 4
1665		1699
…		…
1671	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
1672	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
1673	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
1674	path for as long as the watcher is active.	1708	path for as long as the watcher is active.
1675		1709
1676	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
1677	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
1678	last change was detected).	1712	was detected).
1679		1713
1680	=item ev_stat_stat (loop, ev_stat *)	1714	=item ev_stat_stat (loop, ev_stat *)
1681		1715
1682	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
1683	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
1684	detecting this change (while introducing a race condition). Can also be	1718	detecting this change (while introducing a race condition if you are not
1685	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.
1686		1721
1687	=item ev_statdata attr [read-only]	1722	=item ev_statdata attr [read-only]
1688		1723
1689	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
1690	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
1691	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
1692	was some error while C<stat>ing the file.	1728	some error while C<stat>ing the file.
1693		1729
1694	=item ev_statdata prev [read-only]	1730	=item ev_statdata prev [read-only]
1695		1731
1696	The previous attributes of the file. The callback gets invoked whenever	1732	The previous attributes of the file. The callback gets invoked whenever
1697	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>.
1698		1736
1699	=item ev_tstamp interval [read-only]	1737	=item ev_tstamp interval [read-only]
1700		1738
1701	The specified interval.	1739	The specified interval.
1702		1740
…		…
1756	}	1794	}
1757		1795
1758	...	1796	...
1759	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	1797	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1760	ev_stat_start (loop, &passwd);	1798	ev_stat_start (loop, &passwd);
1761	ev_timer_init (&timer, timer_cb, 0., 1.01);	1799	ev_timer_init (&timer, timer_cb, 0., 1.02);
1762		1800
1763		1801
1764	=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...
1765		1803
1766	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
…		…
1854		1892
1855	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>)
1856	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
1857	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,
1858	too) should not activate ("feed") events into libev. While libev fully	1896	too) should not activate ("feed") events into libev. While libev fully
1859	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
1860	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
1861	(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
1862	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
1863	coexist peacefully with others).	1901	coexist peacefully with others).
1864		1902
…		…
1879	=head3 Examples	1917	=head3 Examples
1880		1918
1881	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
1882	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
1883	(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
1884	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
1885	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
1886	into the Glib event loop).	1924	Glib event loop).
1887		1925
1888	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,
1889	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
1890	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
1891	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
…		…
2375		2413
2376	=item * Priorities are not currently supported. Initialising priorities	2414	=item * Priorities are not currently supported. Initialising priorities
2377	will fail and all watchers will have the same priority, even though there	2415	will fail and all watchers will have the same priority, even though there
2378	is an ev_pri field.	2416	is an ev_pri field.
2379		2417
		2418	=item * In libevent, the last base created gets the signals, in libev, the
		2419	first base created (== the default loop) gets the signals.
		2420
2380	=item * Other members are not supported.	2421	=item * Other members are not supported.
2381		2422
2382	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2423	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2383	to use the libev header file and library.	2424	to use the libev header file and library.
2384		2425
…		…
2960	defined to be C<0>, then they are not.	3001	defined to be C<0>, then they are not.
2961		3002
2962	=item EV_MINIMAL	3003	=item EV_MINIMAL
2963		3004
2964	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
2965	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
2966	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.
2967		3009
2968	=item EV_PID_HASHSIZE	3010	=item EV_PID_HASHSIZE
2969		3011
2970	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
2971	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
…		…
2977	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
2978	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>),
2979	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>
2980	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
2981	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.>
2982		3059
2983	=item EV_COMMON	3060	=item EV_COMMON
2984		3061
2985	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
2986	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
…		…
3156	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
3157	have many watchers waiting for the same fd or signal).	3234	have many watchers waiting for the same fd or signal).
3158		3235
3159	=item Finding the next timer in each loop iteration: O(1)	3236	=item Finding the next timer in each loop iteration: O(1)
3160		3237
3161	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
3162	beginning of the storage array.	3239	fixed position in the storage array.
3163		3240
3164	=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)
3165		3242
3166	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
3167	libev to recalculate its status (and possibly tell the kernel, depending	3244	libev to recalculate its status (and possibly tell the kernel, depending
…		…
3196	model. Libev still offers limited functionality on this platform in	3273	model. Libev still offers limited functionality on this platform in
3197	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
3198	descriptors. This only applies when using Win32 natively, not when using	3275	descriptors. This only applies when using Win32 natively, not when using
3199	e.g. cygwin.	3276	e.g. cygwin.
3200		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
3201	There is no supported compilation method available on windows except	3283	There is no supported compilation method available on windows except
3202	embedding it into other applications.	3284	embedding it into other applications.
3203		3285
3204	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
3205	abysmal performance of winsockets, using a large number of sockets is not	3287	the abysmal performance of winsockets, using a large number of sockets
3206	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
3207	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
3208	implementation for windows, as libev offers the POSIX model, which cannot	3290	different implementation for windows, as libev offers the POSIX readiness
3209	be implemented efficiently on windows (microsoft monopoly games).	3291	notification model, which cannot be implemented efficiently on windows
		3292	(microsoft monopoly games).
3210		3293
3211	=over 4	3294	=over 4
3212		3295
3213	=item The winsocket select function	3296	=item The winsocket select function
3214		3297
…		…
3228	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
3229	complexity in the O(n²) range when using win32.	3312	complexity in the O(n²) range when using win32.
3230		3313
3231	=item Limited number of file descriptors	3314	=item Limited number of file descriptors
3232		3315
3233	Windows has numerous arbitrary (and low) limits on things. Early versions	3316	Windows has numerous arbitrary (and low) limits on things.
3234	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
3235	(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
3236	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
3237	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).
3238		3323
3239	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>
3240	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
3241	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
3242	select emulation on windows).	3327	select emulation on windows).
…		…
3254	calling select (O(n²)) will likely make this unworkable.	3339	calling select (O(n²)) will likely make this unworkable.
3255		3340
3256	=back	3341	=back
3257		3342
3258		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
3259	=head1 AUTHOR	3417	=head1 AUTHOR
3260		3418
3261	Marc Lehmann <libev@schmorp.de>.	3419	Marc Lehmann <libev@schmorp.de>.
3262		3420

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing libev/ev.pod (file contents): Revision 1.144 by root, Mon Apr 7 12:33:29 2008 UTC vs. Revision 1.159 by root, Thu May 22 02:44:57 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.144 by root, Mon Apr 7 12:33:29 2008 UTC vs.
Revision 1.159 by root, Thu May 22 02:44:57 2008 UTC