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

Comparing libev/ev.pod (file contents):
Revision 1.137 by root, Sun Mar 16 16:42:56 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
…		…
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 (;;)
…		…
256		259
257	An event loop is described by a C<struct ev_loop *>. The library knows two	260	An event loop is described by a C<struct ev_loop *>. The library knows two
258	types of such loops, the I<default> loop, which supports signals and child	261	types of such loops, the I<default> loop, which supports signals and child
259	events, and dynamically created loops which do not.	262	events, and dynamically created loops which do not.
260		263
261	If you use threads, a common model is to run the default event loop
262	in your main thread (or in a separate thread) and for each thread you
263	create, you also create another event loop. Libev itself does no locking
264	whatsoever, so if you mix calls to the same event loop in different
265	threads, make sure you lock (this is usually a bad idea, though, even if
266	done correctly, because it's hideous and inefficient).
267
268	=over 4	264	=over 4
269		265
270	=item struct ev_loop *ev_default_loop (unsigned int flags)	266	=item struct ev_loop *ev_default_loop (unsigned int flags)
271		267
272	This will initialise the default event loop if it hasn't been initialised	268	This will initialise the default event loop if it hasn't been initialised
…		…
274	false. If it already was initialised it simply returns it (and ignores the	270	false. If it already was initialised it simply returns it (and ignores the
275	flags. If that is troubling you, check C<ev_backend ()> afterwards).	271	flags. If that is troubling you, check C<ev_backend ()> afterwards).
276		272
277	If you don't know what event loop to use, use the one returned from this	273	If you don't know what event loop to use, use the one returned from this
278	function.	274	function.
		275
		276	Note that this function is I<not> thread-safe, so if you want to use it
		277	from multiple threads, you have to lock (note also that this is unlikely,
		278	as loops cannot bes hared easily between threads anyway).
279		279
280	The default loop is the only loop that can handle C<ev_signal> and	280	The default loop is the only loop that can handle C<ev_signal> and
281	C<ev_child> watchers, and to do this, it always registers a handler	281	C<ev_child> watchers, and to do this, it always registers a handler
282	for C<SIGCHLD>. If this is a problem for your app you can either	282	for C<SIGCHLD>. If this is a problem for your app you can either
283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
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
…		…
354	For few fds, this backend is a bit little slower than poll and select,	354	For few fds, this backend is a bit little slower than poll and select,
355	but it scales phenomenally better. While poll and select usually scale	355	but it scales phenomenally better. While poll and select usually scale
356	like O(total_fds) where n is the total number of fds (or the highest fd),	356	like O(total_fds) where n is the total number of fds (or the highest fd),
357	epoll scales either O(1) or O(active_fds). The epoll design has a number	357	epoll scales either O(1) or O(active_fds). The epoll design has a number
358	of shortcomings, such as silently dropping events in some hard-to-detect	358	of shortcomings, such as silently dropping events in some hard-to-detect
359	cases and rewiring a syscall per fd change, no fork support and bad	359	cases and requiring a syscall per fd change, no fork support and bad
360	support for dup.	360	support for dup.
361		361
362	While stopping, setting and starting an I/O watcher in the same iteration	362	While stopping, setting and starting an I/O watcher in the same iteration
363	will result in some caching, there is still a syscall per such incident	363	will result in some caching, there is still a syscall per such incident
364	(because the fd could point to a different file description now), so its	364	(because the fd could point to a different file description now), so its
…		…
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
…		…
465		465
466	Similar to C<ev_default_loop>, but always creates a new event loop that is	466	Similar to C<ev_default_loop>, but always creates a new event loop that is
467	always distinct from the default loop. Unlike the default loop, it cannot	467	always distinct from the default loop. Unlike the default loop, it cannot
468	handle signal and child watchers, and attempts to do so will be greeted by	468	handle signal and child watchers, and attempts to do so will be greeted by
469	undefined behaviour (or a failed assertion if assertions are enabled).	469	undefined behaviour (or a failed assertion if assertions are enabled).
		470
		471	Note that this function I<is> thread-safe, and the recommended way to use
		472	libev with threads is indeed to create one loop per thread, and using the
		473	default loop in the "main" or "initial" thread.
470		474
471	Example: Try to create a event loop that uses epoll and nothing else.	475	Example: Try to create a event loop that uses epoll and nothing else.
472		476
473	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);	477	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);
474	if (!epoller)	478	if (!epoller)
…		…
1028	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
1029	(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
1030	C<EVBACKEND_POLL>).	1034	C<EVBACKEND_POLL>).
1031		1035
1032	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
1033	receive "spurious" readyness notifications, that is your callback might	1037	receive "spurious" readiness notifications, that is your callback might
1034	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
1035	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
1036	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
1037	this situation even with a relatively standard program structure. Thus	1041	this situation even with a relatively standard program structure. Thus
1038	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
…		…
1085	To support fork in your programs, you either have to call	1089	To support fork in your programs, you either have to call
1086	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1090	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1087	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1091	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1088	C<EVBACKEND_POLL>.	1092	C<EVBACKEND_POLL>.
1089		1093
		1094	=head3 The special problem of SIGPIPE
		1095
		1096	While not really specific to libev, it is easy to forget about SIGPIPE:
		1097	when reading from a pipe whose other end has been closed, your program
		1098	gets send a SIGPIPE, which, by default, aborts your program. For most
		1099	programs this is sensible behaviour, for daemons, this is usually
		1100	undesirable.
		1101
		1102	So when you encounter spurious, unexplained daemon exits, make sure you
		1103	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1104	somewhere, as that would have given you a big clue).
		1105
1090		1106
1091	=head3 Watcher-Specific Functions	1107	=head3 Watcher-Specific Functions
1092		1108
1093	=over 4	1109	=over 4
1094		1110
…		…
1135		1151
1136	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
1137	given time, and optionally repeating in regular intervals after that.	1153	given time, and optionally repeating in regular intervals after that.
1138		1154
1139	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
1140	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
1141	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
1142	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1143	monotonic clock option helps a lot here).	1159	monotonic clock option helps a lot here).
1144		1160
1145	The relative timeouts are calculated relative to the C<ev_now ()>	1161	The relative timeouts are calculated relative to the C<ev_now ()>
1146	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
…		…
1148	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
1149	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:
1150		1166
1151	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1152		1168
1153	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,
1154	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
1155	order of execution is undefined.	1171	order of execution is undefined.
1156		1172
1157	=head3 Watcher-Specific Functions and Data Members	1173	=head3 Watcher-Specific Functions and Data Members
1158		1174
…		…
1160		1176
1161	=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)
1162		1178
1163	=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)
1164		1180
1165	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>
1166	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
1167	timer will automatically be configured to trigger again C<repeat> seconds	1183	reached. If it is positive, then the timer will automatically be
1168	later, again, and again, until stopped manually.	1184	configured to trigger again C<repeat> seconds later, again, and again,
		1185	until stopped manually.
1169		1186
1170	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
1171	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
1172	exactly 10 second intervals. If, however, your program cannot keep up with	1189	trigger at exactly 10 second intervals. If, however, your program cannot
1173	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
1174	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.
1175		1192
1176	=item ev_timer_again (loop, ev_timer *)	1193	=item ev_timer_again (loop, ev_timer *)
1177		1194
1178	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
1179	repeating. The exact semantics are:	1196	repeating. The exact semantics are:
…		…
1256	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
1257	(and unfortunately a bit complex).	1274	(and unfortunately a bit complex).
1258		1275
1259	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)
1260	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
1261	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
1262	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 ()
1263	+ 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
1264	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
1265	roughly 10 seconds later).	1283	roughly 10 seconds later as it uses a relative timeout).
1266		1284
1267	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,
1268	triggering an event on each midnight, local time or other, complicated,	1286	such as triggering an event on each "midnight, local time", or other
1269	rules.	1287	complicated, rules.
1270		1288
1271	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
1272	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
1273	during the same loop iteration then order of execution is undefined.	1291	during the same loop iteration then order of execution is undefined.
1274		1292
1275	=head3 Watcher-Specific Functions and Data Members	1293	=head3 Watcher-Specific Functions and Data Members
1276		1294
1277	=over 4	1295	=over 4
…		…
1285		1303
1286	=over 4	1304	=over 4
1287		1305
1288	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1306	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1289		1307
1290	In this configuration the watcher triggers an event at the wallclock time	1308	In this configuration the watcher triggers an event after the wallclock
1291	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
1292	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
1293	system time reaches or surpasses this time.	1311	run when the system time reaches or surpasses this time.
1294		1312
1295	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1313	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1296		1314
1297	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
1298	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)
1299	and then repeat, regardless of any time jumps.	1317	and then repeat, regardless of any time jumps.
1300		1318
1301	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
1302	time:	1320	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1321	the hour:
1303		1322
1304	ev_periodic_set (&periodic, 0., 3600., 0);	1323	ev_periodic_set (&periodic, 0., 3600., 0);
1305		1324
1306	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,
1307	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
…		…
1312	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
1313	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.
1314		1333
1315	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
1316	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
1317	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).
1318		1342
1319	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1343	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1320		1344
1321	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
1322	ignored. Instead, each time the periodic watcher gets scheduled, the	1346	ignored. Instead, each time the periodic watcher gets scheduled, the
1323	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
1324	current time as second argument.	1348	current time as second argument.
1325		1349
1326	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,
1327	ever, or make any event loop modifications>. If you need to stop it,	1351	ever, or make ANY event loop modifications whatsoever>.
1328	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1329	starting an C<ev_prepare> watcher, which is legal).
1330		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
1331	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
1332	ev_tstamp now)>, e.g.:	1358	*w, ev_tstamp now)>, e.g.:
1333		1359
1334	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)
1335	{	1361	{
1336	return now + 60.;	1362	return now + 60.;
1337	}	1363	}
…		…
1339	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
1340	(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
1341	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
1342	might be called at other times, too.	1368	might be called at other times, too.
1343		1369
1344	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
1345	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1371	equal to the passed C<now> value >>.
1346		1372
1347	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
1348	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
1349	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
1350	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
1351	reason I omitted it as an example).	1377	reason I omitted it as an example).
1352		1378
1353	=back	1379	=back
…		…
1357	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
1358	when you changed some parameters or the reschedule callback would return	1384	when you changed some parameters or the reschedule callback would return
1359	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
1360	program when the crontabs have changed).	1386	program when the crontabs have changed).
1361		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
1362	=item ev_tstamp offset [read-write]	1393	=item ev_tstamp offset [read-write]
1363		1394
1364	When repeating, this contains the offset value, otherwise this is the	1395	When repeating, this contains the offset value, otherwise this is the
1365	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>).
1366		1397
…		…
1376	=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]
1377		1408
1378	The current reschedule callback, or C<0>, if this functionality is	1409	The current reschedule callback, or C<0>, if this functionality is
1379	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
1380	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.
1381
1382	=item ev_tstamp at [read-only]
1383
1384	When active, contains the absolute time that the watcher is supposed to
1385	trigger next.
1386		1412
1387	=back	1413	=back
1388		1414
1389	=head3 Examples	1415	=head3 Examples
1390		1416
…		…
1594	as even with OS-supported change notifications, this can be	1620	as even with OS-supported change notifications, this can be
1595	resource-intensive.	1621	resource-intensive.
1596		1622
1597	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
1598	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
1599	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
1600	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
1601	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,
1602	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
1603	polling.	1630	will be no polling.
1604		1631
1605	=head3 ABI Issues (Largefile Support)	1632	=head3 ABI Issues (Largefile Support)
1606		1633
1607	Libev by default (unless the user overrides this) uses the default	1634	Libev by default (unless the user overrides this) uses the default
1608	compilation environment, which means that on systems with optionally	1635	compilation environment, which means that on systems with optionally
…		…
1618	When C<inotify (7)> support has been compiled into libev (generally only	1645	When C<inotify (7)> support has been compiled into libev (generally only
1619	available on Linux) and present at runtime, it will be used to speed up	1646	available on Linux) and present at runtime, it will be used to speed up
1620	change detection where possible. The inotify descriptor will be created lazily	1647	change detection where possible. The inotify descriptor will be created lazily
1621	when the first C<ev_stat> watcher is being started.	1648	when the first C<ev_stat> watcher is being started.
1622		1649
1623	Inotify presense does not change the semantics of C<ev_stat> watchers	1650	Inotify presence does not change the semantics of C<ev_stat> watchers
1624	except that changes might be detected earlier, and in some cases, to avoid	1651	except that changes might be detected earlier, and in some cases, to avoid
1625	making regular C<stat> calls. Even in the presense of inotify support	1652	making regular C<stat> calls. Even in the presence of inotify support
1626	there are many cases where libev has to resort to regular C<stat> polling.	1653	there are many cases where libev has to resort to regular C<stat> polling.
1627		1654
1628	(There is no support for kqueue, as apparently it cannot be used to	1655	(There is no support for kqueue, as apparently it cannot be used to
1629	implement this functionality, due to the requirement of having a file	1656	implement this functionality, due to the requirement of having a file
1630	descriptor open on the object at all times).	1657	descriptor open on the object at all times).
…		…
1633		1660
1634	The C<stat ()> syscall only supports full-second resolution portably, and	1661	The C<stat ()> syscall only supports full-second resolution portably, and
1635	even on systems where the resolution is higher, many filesystems still	1662	even on systems where the resolution is higher, many filesystems still
1636	only support whole seconds.	1663	only support whole seconds.
1637		1664
1638	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
1639	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
1640	your callback, which does something. When there is another update within	1667	calls your callback, which does something. When there is another update
1641	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.
1642		1670
1643	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
1644	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
1645	(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);
1646	is added to work around small timing inconsistencies of some operating	1674	ev_timer_again (loop, w)>).
1647	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).
1648		1684
1649	=head3 Watcher-Specific Functions and Data Members	1685	=head3 Watcher-Specific Functions and Data Members
1650		1686
1651	=over 4	1687	=over 4
1652		1688
…		…
1658	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
1659	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
1660	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
1661	path for as long as the watcher is active.	1697	path for as long as the watcher is active.
1662		1698
1663	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
1664	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
1665	last change was detected).	1701	was detected).
1666		1702
1667	=item ev_stat_stat (loop, ev_stat *)	1703	=item ev_stat_stat (loop, ev_stat *)
1668		1704
1669	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
1670	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
1671	detecting this change (while introducing a race condition). Can also be	1707	detecting this change (while introducing a race condition if you are not
1672	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.
1673		1710
1674	=item ev_statdata attr [read-only]	1711	=item ev_statdata attr [read-only]
1675		1712
1676	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
1677	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
1678	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
1679	was some error while C<stat>ing the file.	1717	some error while C<stat>ing the file.
1680		1718
1681	=item ev_statdata prev [read-only]	1719	=item ev_statdata prev [read-only]
1682		1720
1683	The previous attributes of the file. The callback gets invoked whenever	1721	The previous attributes of the file. The callback gets invoked whenever
1684	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>.
1685		1725
1686	=item ev_tstamp interval [read-only]	1726	=item ev_tstamp interval [read-only]
1687		1727
1688	The specified interval.	1728	The specified interval.
1689		1729
…		…
1743	}	1783	}
1744		1784
1745	...	1785	...
1746	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	1786	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1747	ev_stat_start (loop, &passwd);	1787	ev_stat_start (loop, &passwd);
1748	ev_timer_init (&timer, timer_cb, 0., 1.01);	1788	ev_timer_init (&timer, timer_cb, 0., 1.02);
1749		1789
1750		1790
1751	=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...
1752		1792
1753	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
…		…
1841		1881
1842	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>)
1843	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
1844	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,
1845	too) should not activate ("feed") events into libev. While libev fully	1885	too) should not activate ("feed") events into libev. While libev fully
1846	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
1847	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
1848	(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
1849	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
1850	coexist peacefully with others).	1890	coexist peacefully with others).
1851		1891
…		…
1866	=head3 Examples	1906	=head3 Examples
1867		1907
1868	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
1869	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
1870	(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
1871	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
1872	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
1873	into the Glib event loop).	1913	Glib event loop).
1874		1914
1875	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,
1876	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
1877	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
1878	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
…		…
2268		2308
2269	This call incurs the overhead of a syscall only once per loop iteration,	2309	This call incurs the overhead of a syscall only once per loop iteration,
2270	so while the overhead might be noticable, it doesn't apply to repeated	2310	so while the overhead might be noticable, it doesn't apply to repeated
2271	calls to C<ev_async_send>.	2311	calls to C<ev_async_send>.
2272		2312
		2313	=item bool = ev_async_pending (ev_async *)
		2314
		2315	Returns a non-zero value when C<ev_async_send> has been called on the
		2316	watcher but the event has not yet been processed (or even noted) by the
		2317	event loop.
		2318
		2319	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2320	the loop iterates next and checks for the watcher to have become active,
		2321	it will reset the flag again. C<ev_async_pending> can be used to very
		2322	quickly check wether invoking the loop might be a good idea.
		2323
		2324	Not that this does I<not> check wether the watcher itself is pending, only
		2325	wether it has been requested to make this watcher pending.
		2326
2273	=back	2327	=back
2274		2328
2275		2329
2276	=head1 OTHER FUNCTIONS	2330	=head1 OTHER FUNCTIONS
2277		2331
…		…
2348		2402
2349	=item * Priorities are not currently supported. Initialising priorities	2403	=item * Priorities are not currently supported. Initialising priorities
2350	will fail and all watchers will have the same priority, even though there	2404	will fail and all watchers will have the same priority, even though there
2351	is an ev_pri field.	2405	is an ev_pri field.
2352		2406
		2407	=item * In libevent, the last base created gets the signals, in libev, the
		2408	first base created (== the default loop) gets the signals.
		2409
2353	=item * Other members are not supported.	2410	=item * Other members are not supported.
2354		2411
2355	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2412	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2356	to use the libev header file and library.	2413	to use the libev header file and library.
2357		2414
…		…
2599	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	2656	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2600		2657
2601	Similar to the other two macros, this gives you the value of the default	2658	Similar to the other two macros, this gives you the value of the default
2602	loop, if multiple loops are supported ("ev loop default").	2659	loop, if multiple loops are supported ("ev loop default").
2603		2660
		2661	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2662
		2663	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2664	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2665	is undefined when the default loop has not been initialised by a previous
		2666	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2667
		2668	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2669	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2670
2604	=back	2671	=back
2605		2672
2606	Example: Declare and initialise a check watcher, utilising the above	2673	Example: Declare and initialise a check watcher, utilising the above
2607	macros so it will work regardless of whether multiple loops are supported	2674	macros so it will work regardless of whether multiple loops are supported
2608	or not.	2675	or not.
…		…
2703		2770
2704	libev.m4	2771	libev.m4
2705		2772
2706	=head2 PREPROCESSOR SYMBOLS/MACROS	2773	=head2 PREPROCESSOR SYMBOLS/MACROS
2707		2774
2708	Libev can be configured via a variety of preprocessor symbols you have to define	2775	Libev can be configured via a variety of preprocessor symbols you have to
2709	before including any of its files. The default is not to build for multiplicity	2776	define before including any of its files. The default in the absense of
2710	and only include the select backend.	2777	autoconf is noted for every option.
2711		2778
2712	=over 4	2779	=over 4
2713		2780
2714	=item EV_STANDALONE	2781	=item EV_STANDALONE
2715		2782
…		…
2741	=item EV_USE_NANOSLEEP	2808	=item EV_USE_NANOSLEEP
2742		2809
2743	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	2810	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2744	and will use it for delays. Otherwise it will use C<select ()>.	2811	and will use it for delays. Otherwise it will use C<select ()>.
2745		2812
		2813	=item EV_USE_EVENTFD
		2814
		2815	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2816	available and will probe for kernel support at runtime. This will improve
		2817	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2818	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2819	2.7 or newer, otherwise disabled.
		2820
2746	=item EV_USE_SELECT	2821	=item EV_USE_SELECT
2747		2822
2748	If undefined or defined to be C<1>, libev will compile in support for the	2823	If undefined or defined to be C<1>, libev will compile in support for the
2749	C<select>(2) backend. No attempt at autodetection will be done: if no	2824	C<select>(2) backend. No attempt at autodetection will be done: if no
2750	other method takes over, select will be it. Otherwise the select backend	2825	other method takes over, select will be it. Otherwise the select backend
…		…
2786		2861
2787	=item EV_USE_EPOLL	2862	=item EV_USE_EPOLL
2788		2863
2789	If defined to be C<1>, libev will compile in support for the Linux	2864	If defined to be C<1>, libev will compile in support for the Linux
2790	C<epoll>(7) backend. Its availability will be detected at runtime,	2865	C<epoll>(7) backend. Its availability will be detected at runtime,
2791	otherwise another method will be used as fallback. This is the	2866	otherwise another method will be used as fallback. This is the preferred
2792	preferred backend for GNU/Linux systems.	2867	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2868	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2793		2869
2794	=item EV_USE_KQUEUE	2870	=item EV_USE_KQUEUE
2795		2871
2796	If defined to be C<1>, libev will compile in support for the BSD style	2872	If defined to be C<1>, libev will compile in support for the BSD style
2797	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	2873	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2816		2892
2817	=item EV_USE_INOTIFY	2893	=item EV_USE_INOTIFY
2818		2894
2819	If defined to be C<1>, libev will compile in support for the Linux inotify	2895	If defined to be C<1>, libev will compile in support for the Linux inotify
2820	interface to speed up C<ev_stat> watchers. Its actual availability will	2896	interface to speed up C<ev_stat> watchers. Its actual availability will
2821	be detected at runtime.	2897	be detected at runtime. If undefined, it will be enabled if the headers
		2898	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2822		2899
2823	=item EV_ATOMIC_T	2900	=item EV_ATOMIC_T
2824		2901
2825	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	2902	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2826	access is atomic with respect to other threads or signal contexts. No such	2903	access is atomic with respect to other threads or signal contexts. No such
…		…
2913	defined to be C<0>, then they are not.	2990	defined to be C<0>, then they are not.
2914		2991
2915	=item EV_MINIMAL	2992	=item EV_MINIMAL
2916		2993
2917	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
2918	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
2919	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.
2920		2998
2921	=item EV_PID_HASHSIZE	2999	=item EV_PID_HASHSIZE
2922		3000
2923	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
2924	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
…		…
2930	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
2931	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>),
2932	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>
2933	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
2934	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).
2935		3035
2936	=item EV_COMMON	3036	=item EV_COMMON
2937		3037
2938	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
2939	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
…		…
3013		3113
3014	#include "ev_cpp.h"	3114	#include "ev_cpp.h"
3015	#include "ev.c"	3115	#include "ev.c"
3016		3116
3017		3117
		3118	=head1 THREADS AND COROUTINES
		3119
		3120	=head2 THREADS
		3121
		3122	Libev itself is completely threadsafe, but it uses no locking. This
		3123	means that you can use as many loops as you want in parallel, as long as
		3124	only one thread ever calls into one libev function with the same loop
		3125	parameter.
		3126
		3127	Or put differently: calls with different loop parameters can be done in
		3128	parallel from multiple threads, calls with the same loop parameter must be
		3129	done serially (but can be done from different threads, as long as only one
		3130	thread ever is inside a call at any point in time, e.g. by using a mutex
		3131	per loop).
		3132
		3133	If you want to know which design is best for your problem, then I cannot
		3134	help you but by giving some generic advice:
		3135
		3136	=over 4
		3137
		3138	=item * most applications have a main thread: use the default libev loop
		3139	in that thread, or create a seperate thread running only the default loop.
		3140
		3141	This helps integrating other libraries or software modules that use libev
		3142	themselves and don't care/know about threading.
		3143
		3144	=item * one loop per thread is usually a good model.
		3145
		3146	Doing this is almost never wrong, sometimes a better-performance model
		3147	exists, but it is always a good start.
		3148
		3149	=item * other models exist, such as the leader/follower pattern, where one
		3150	loop is handed through multiple threads in a kind of round-robbin fashion.
		3151
		3152	Chosing a model is hard - look around, learn, know that usually you cna do
		3153	better than you currently do :-)
		3154
		3155	=item * often you need to talk to some other thread which blocks in the
		3156	event loop - C<ev_async> watchers can be used to wake them up from other
		3157	threads safely (or from signal contexts...).
		3158
		3159	=back
		3160
		3161	=head2 COROUTINES
		3162
		3163	Libev is much more accomodating to coroutines ("cooperative threads"):
		3164	libev fully supports nesting calls to it's functions from different
		3165	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3166	different coroutines and switch freely between both coroutines running the
		3167	loop, as long as you don't confuse yourself). The only exception is that
		3168	you must not do this from C<ev_periodic> reschedule callbacks.
		3169
		3170	Care has been invested into making sure that libev does not keep local
		3171	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3172	switches.
		3173
		3174
3018	=head1 COMPLEXITIES	3175	=head1 COMPLEXITIES
3019		3176
3020	In this section the complexities of (many of) the algorithms used inside	3177	In this section the complexities of (many of) the algorithms used inside
3021	libev will be explained. For complexity discussions about backends see the	3178	libev will be explained. For complexity discussions about backends see the
3022	documentation for C<ev_default_init>.	3179	documentation for C<ev_default_init>.
…		…
3052	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
3053	have many watchers waiting for the same fd or signal).	3210	have many watchers waiting for the same fd or signal).
3054		3211
3055	=item Finding the next timer in each loop iteration: O(1)	3212	=item Finding the next timer in each loop iteration: O(1)
3056		3213
3057	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
3058	beginning of the storage array.	3215	fixed position in the storage array.
3059		3216
3060	=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)
3061		3218
3062	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
3063	libev to recalculate its status (and possibly tell the kernel, depending	3220	libev to recalculate its status (and possibly tell the kernel, depending
…		…
3092	model. Libev still offers limited functionality on this platform in	3249	model. Libev still offers limited functionality on this platform in
3093	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
3094	descriptors. This only applies when using Win32 natively, not when using	3251	descriptors. This only applies when using Win32 natively, not when using
3095	e.g. cygwin.	3252	e.g. cygwin.
3096		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
3097	There is no supported compilation method available on windows except	3259	There is no supported compilation method available on windows except
3098	embedding it into other applications.	3260	embedding it into other applications.
3099		3261
3100	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
3101	abysmal performance of winsockets, using a large number of sockets is not	3263	the abysmal performance of winsockets, using a large number of sockets
3102	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
3103	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
3104	implementation for windows, as libev offers the POSIX model, which cannot	3266	different implementation for windows, as libev offers the POSIX readiness
3105	be implemented efficiently on windows (microsoft monopoly games).	3267	notification model, which cannot be implemented efficiently on windows
		3268	(microsoft monopoly games).
3106		3269
3107	=over 4	3270	=over 4
3108		3271
3109	=item The winsocket select function	3272	=item The winsocket select function
3110		3273
…		…
3124	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
3125	complexity in the O(n²) range when using win32.	3288	complexity in the O(n²) range when using win32.
3126		3289
3127	=item Limited number of file descriptors	3290	=item Limited number of file descriptors
3128		3291
3129	Windows has numerous arbitrary (and low) limits on things. Early versions	3292	Windows has numerous arbitrary (and low) limits on things.
3130	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
3131	(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
3132	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
3133	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).
3134		3299
3135	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>
3136	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
3137	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
3138	select emulation on windows).	3303	select emulation on windows).
…		…
3150	calling select (O(n²)) will likely make this unworkable.	3315	calling select (O(n²)) will likely make this unworkable.
3151		3316
3152	=back	3317	=back
3153		3318
3154		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
3155	=head1 AUTHOR	3393	=head1 AUTHOR
3156		3394
3157	Marc Lehmann <libev@schmorp.de>.	3395	Marc Lehmann <libev@schmorp.de>.
3158		3396

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Revision 1.158 by root, Wed May 21 12:51:38 2008 UTC