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

Comparing libev/ev.pod (file contents):
Revision 1.351 by root, Mon Jan 10 14:24:26 2011 UTC vs.
Revision 1.379 by root, Tue Jul 12 23:32:10 2011 UTC

…		…
58	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
59		59
60	// now wait for events to arrive	60	// now wait for events to arrive
61	ev_run (loop, 0);	61	ev_run (loop, 0);
62		62
63	// unloop was called, so exit	63	// break was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 ABOUT THIS DOCUMENT	67	=head1 ABOUT THIS DOCUMENT
68		68
…		…
178	you actually want to know. Also interesting is the combination of	178	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	179	C<ev_update_now> and C<ev_now>.
180		180
181	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
182		182
183	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
185	this is a sub-second-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
186		192
187	=item int ev_version_major ()	193	=item int ev_version_major ()
188		194
189	=item int ev_version_minor ()	195	=item int ev_version_minor ()
190		196
…		…
435	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
436		442
437	=item C<EVFLAG_NOSIGMASK>	443	=item C<EVFLAG_NOSIGMASK>
438		444
439	When this flag is specified, then libev will avoid to modify the signal	445	When this flag is specified, then libev will avoid to modify the signal
440	mask. Specifically, this means you ahve to make sure signals are unblocked	446	mask. Specifically, this means you have to make sure signals are unblocked
441	when you want to receive them.	447	when you want to receive them.
442		448
443	This behaviour is useful when you want to do your own signal handling, or	449	This behaviour is useful when you want to do your own signal handling, or
444	want to handle signals only in specific threads and want to avoid libev	450	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
446		455
447	This flag's behaviour will become the default in future versions of libev.	456	This flag's behaviour will become the default in future versions of libev.
448		457
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		459
…		…
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		490
482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
483	kernels).	492	kernels).
484		493
485	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
486	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
487	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
488	epoll scales either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
489		498
490	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	502	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
496	0.1ms) and so on. The biggest issue is fork races, however - if a program	505	0.1ms) and so on. The biggest issue is fork races, however - if a program
497	forks then I<both> parent and child process have to recreate the epoll	506	forks then I<both> parent and child process have to recreate the epoll
498	set, which can take considerable time (one syscall per file descriptor)	507	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	508	and is of course hard to detect.
500		509
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
502	of course I<doesn't>, and epoll just loves to report events for totally	511	but of course I<doesn't>, and epoll just loves to report events for
503	I<different> file descriptors (even already closed ones, so one cannot	512	totally I<different> file descriptors (even already closed ones, so
504	even remove them from the set) than registered in the set (especially	513	one cannot even remove them from the set) than registered in the set
505	on SMP systems). Libev tries to counter these spurious notifications by	514	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
507	events to filter out spurious ones, recreating the set when required. Last	516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
508	not least, it also refuses to work with some file descriptors which work	520	not least, it also refuses to work with some file descriptors which work
509	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
510		522
511	Epoll is truly the train wreck analog among event poll mechanisms.	523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
512		526
513	While stopping, setting and starting an I/O watcher in the same iteration	527	While stopping, setting and starting an I/O watcher in the same iteration
514	will result in some caching, there is still a system call per such	528	will result in some caching, there is still a system call per such
515	incident (because the same I<file descriptor> could point to a different	529	incident (because the same I<file descriptor> could point to a different
516	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
592	On the positive side, this backend actually performed fully to	606	On the positive side, this backend actually performed fully to
593	specification in all tests and is fully embeddable, which is a rare feat	607	specification in all tests and is fully embeddable, which is a rare feat
594	among the OS-specific backends (I vastly prefer correctness over speed	608	among the OS-specific backends (I vastly prefer correctness over speed
595	hacks).	609	hacks).
596		610
597	On the negative side, the interface is I<bizarre>, with the event polling	611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
598	function sometimes returning events to the caller even though an error	613	function sometimes returns events to the caller even though an error
599	occured, but with no indication whether it has done so or not (yes, it's	614	occurred, but with no indication whether it has done so or not (yes, it's
600	even documented that way) - deadly for edge-triggered interfaces, but	615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
601	fortunately libev seems to be able to work around it.	619	Fortunately libev seems to be able to work around these idiocies.
602		620
603	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
604	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
605		623
606	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
…		…
816	This is useful if you are waiting for some external event in conjunction	834	This is useful if you are waiting for some external event in conjunction
817	with something not expressible using other libev watchers (i.e. "roll your	835	with something not expressible using other libev watchers (i.e. "roll your
818	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	836	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
819	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
820		838
821	Here are the gory details of what C<ev_run> does:	839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
822		842
823	- Increment loop depth.	843	- Increment loop depth.
824	- Reset the ev_break status.	844	- Reset the ev_break status.
825	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
826	LOOP:	846	LOOP:
…		…
859	anymore.	879	anymore.
860		880
861	... queue jobs here, make sure they register event watchers as long	881	... queue jobs here, make sure they register event watchers as long
862	... as they still have work to do (even an idle watcher will do..)	882	... as they still have work to do (even an idle watcher will do..)
863	ev_run (my_loop, 0);	883	ev_run (my_loop, 0);
864	... jobs done or somebody called unloop. yeah!	884	... jobs done or somebody called break. yeah!
865		885
866	=item ev_break (loop, how)	886	=item ev_break (loop, how)
867		887
868	Can be used to make a call to C<ev_run> return early (but only after it	888	Can be used to make a call to C<ev_run> return early (but only after it
869	has processed all outstanding events). The C<how> argument must be either	889	has processed all outstanding events). The C<how> argument must be either
…		…
932	overhead for the actual polling but can deliver many events at once.	952	overhead for the actual polling but can deliver many events at once.
933		953
934	By setting a higher I<io collect interval> you allow libev to spend more	954	By setting a higher I<io collect interval> you allow libev to spend more
935	time collecting I/O events, so you can handle more events per iteration,	955	time collecting I/O events, so you can handle more events per iteration,
936	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	956	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
937	C<ev_timer>) will be not affected. Setting this to a non-null value will	957	C<ev_timer>) will not be affected. Setting this to a non-null value will
938	introduce an additional C<ev_sleep ()> call into most loop iterations. The	958	introduce an additional C<ev_sleep ()> call into most loop iterations. The
939	sleep time ensures that libev will not poll for I/O events more often then	959	sleep time ensures that libev will not poll for I/O events more often then
940	once per this interval, on average.	960	once per this interval, on average (as long as the host time resolution is
		961	good enough).
941		962
942	Likewise, by setting a higher I<timeout collect interval> you allow libev	963	Likewise, by setting a higher I<timeout collect interval> you allow libev
943	to spend more time collecting timeouts, at the expense of increased	964	to spend more time collecting timeouts, at the expense of increased
944	latency/jitter/inexactness (the watcher callback will be called	965	latency/jitter/inexactness (the watcher callback will be called
945	later). C<ev_io> watchers will not be affected. Setting this to a non-null	966	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
1351	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1372	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1352	functions that do not need a watcher.	1373	functions that do not need a watcher.
1353		1374
1354	=back	1375	=back
1355		1376
1356	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1377	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1357		1378	OWN COMPOSITE WATCHERS> idioms.
1358	Each watcher has, by default, a member C<void *data> that you can change
1359	and read at any time: libev will completely ignore it. This can be used
1360	to associate arbitrary data with your watcher. If you need more data and
1361	don't want to allocate memory and store a pointer to it in that data
1362	member, you can also "subclass" the watcher type and provide your own
1363	data:
1364
1365	struct my_io
1366	{
1367	ev_io io;
1368	int otherfd;
1369	void *somedata;
1370	struct whatever *mostinteresting;
1371	};
1372
1373	...
1374	struct my_io w;
1375	ev_io_init (&w.io, my_cb, fd, EV_READ);
1376
1377	And since your callback will be called with a pointer to the watcher, you
1378	can cast it back to your own type:
1379
1380	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1381	{
1382	struct my_io w = (struct my_io )w_;
1383	...
1384	}
1385
1386	More interesting and less C-conformant ways of casting your callback type
1387	instead have been omitted.
1388
1389	Another common scenario is to use some data structure with multiple
1390	embedded watchers:
1391
1392	struct my_biggy
1393	{
1394	int some_data;
1395	ev_timer t1;
1396	ev_timer t2;
1397	}
1398
1399	In this case getting the pointer to C<my_biggy> is a bit more
1400	complicated: Either you store the address of your C<my_biggy> struct
1401	in the C<data> member of the watcher (for woozies), or you need to use
1402	some pointer arithmetic using C<offsetof> inside your watchers (for real
1403	programmers):
1404
1405	#include <stddef.h>
1406
1407	static void
1408	t1_cb (EV_P_ ev_timer *w, int revents)
1409	{
1410	struct my_biggy big = (struct my_biggy *)
1411	(((char *)w) - offsetof (struct my_biggy, t1));
1412	}
1413
1414	static void
1415	t2_cb (EV_P_ ev_timer *w, int revents)
1416	{
1417	struct my_biggy big = (struct my_biggy *)
1418	(((char *)w) - offsetof (struct my_biggy, t2));
1419	}
1420		1379
1421	=head2 WATCHER STATES	1380	=head2 WATCHER STATES
1422		1381
1423	There are various watcher states mentioned throughout this manual -	1382	There are various watcher states mentioned throughout this manual -
1424	active, pending and so on. In this section these states and the rules to	1383	active, pending and so on. In this section these states and the rules to
…		…
1427		1386
1428	=over 4	1387	=over 4
1429		1388
1430	=item initialiased	1389	=item initialiased
1431		1390
1432	Before a watcher can be registered with the event looop it has to be	1391	Before a watcher can be registered with the event loop it has to be
1433	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1392	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1434	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1393	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1435		1394
1436	In this state it is simply some block of memory that is suitable for use	1395	In this state it is simply some block of memory that is suitable for
1437	in an event loop. It can be moved around, freed, reused etc. at will.	1396	use in an event loop. It can be moved around, freed, reused etc. at
		1397	will - as long as you either keep the memory contents intact, or call
		1398	C<ev_TYPE_init> again.
1438		1399
1439	=item started/running/active	1400	=item started/running/active
1440		1401
1441	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1402	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1442	property of the event loop, and is actively waiting for events. While in	1403	property of the event loop, and is actively waiting for events. While in
…		…
1470	latter will clear any pending state the watcher might be in, regardless	1431	latter will clear any pending state the watcher might be in, regardless
1471	of whether it was active or not, so stopping a watcher explicitly before	1432	of whether it was active or not, so stopping a watcher explicitly before
1472	freeing it is often a good idea.	1433	freeing it is often a good idea.
1473		1434
1474	While stopped (and not pending) the watcher is essentially in the	1435	While stopped (and not pending) the watcher is essentially in the
1475	initialised state, that is it can be reused, moved, modified in any way	1436	initialised state, that is, it can be reused, moved, modified in any way
1476	you wish.	1437	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1438	it again).
1477		1439
1478	=back	1440	=back
1479		1441
1480	=head2 WATCHER PRIORITY MODELS	1442	=head2 WATCHER PRIORITY MODELS
1481		1443
…		…
1610	In general you can register as many read and/or write event watchers per	1572	In general you can register as many read and/or write event watchers per
1611	fd as you want (as long as you don't confuse yourself). Setting all file	1573	fd as you want (as long as you don't confuse yourself). Setting all file
1612	descriptors to non-blocking mode is also usually a good idea (but not	1574	descriptors to non-blocking mode is also usually a good idea (but not
1613	required if you know what you are doing).	1575	required if you know what you are doing).
1614		1576
1615	If you cannot use non-blocking mode, then force the use of a
1616	known-to-be-good backend (at the time of this writing, this includes only
1617	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1618	descriptors for which non-blocking operation makes no sense (such as
1619	files) - libev doesn't guarantee any specific behaviour in that case.
1620
1621	Another thing you have to watch out for is that it is quite easy to	1577	Another thing you have to watch out for is that it is quite easy to
1622	receive "spurious" readiness notifications, that is your callback might	1578	receive "spurious" readiness notifications, that is, your callback might
1623	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1579	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1624	because there is no data. Not only are some backends known to create a	1580	because there is no data. It is very easy to get into this situation even
1625	lot of those (for example Solaris ports), it is very easy to get into	1581	with a relatively standard program structure. Thus it is best to always
1626	this situation even with a relatively standard program structure. Thus	1582	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1627	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1628	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1583	preferable to a program hanging until some data arrives.
1629		1584
1630	If you cannot run the fd in non-blocking mode (for example you should	1585	If you cannot run the fd in non-blocking mode (for example you should
1631	not play around with an Xlib connection), then you have to separately	1586	not play around with an Xlib connection), then you have to separately
1632	re-test whether a file descriptor is really ready with a known-to-be good	1587	re-test whether a file descriptor is really ready with a known-to-be good
1633	interface such as poll (fortunately in our Xlib example, Xlib already	1588	interface such as poll (fortunately in the case of Xlib, it already does
1634	does this on its own, so its quite safe to use). Some people additionally	1589	this on its own, so its quite safe to use). Some people additionally
1635	use C<SIGALRM> and an interval timer, just to be sure you won't block	1590	use C<SIGALRM> and an interval timer, just to be sure you won't block
1636	indefinitely.	1591	indefinitely.
1637		1592
1638	But really, best use non-blocking mode.	1593	But really, best use non-blocking mode.
1639		1594
…		…
1667		1622
1668	There is no workaround possible except not registering events	1623	There is no workaround possible except not registering events
1669	for potentially C<dup ()>'ed file descriptors, or to resort to	1624	for potentially C<dup ()>'ed file descriptors, or to resort to
1670	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1671		1626
		1627	=head3 The special problem of files
		1628
		1629	Many people try to use C<select> (or libev) on file descriptors
		1630	representing files, and expect it to become ready when their program
		1631	doesn't block on disk accesses (which can take a long time on their own).
		1632
		1633	However, this cannot ever work in the "expected" way - you get a readiness
		1634	notification as soon as the kernel knows whether and how much data is
		1635	there, and in the case of open files, that's always the case, so you
		1636	always get a readiness notification instantly, and your read (or possibly
		1637	write) will still block on the disk I/O.
		1638
		1639	Another way to view it is that in the case of sockets, pipes, character
		1640	devices and so on, there is another party (the sender) that delivers data
		1641	on its own, but in the case of files, there is no such thing: the disk
		1642	will not send data on its own, simply because it doesn't know what you
		1643	wish to read - you would first have to request some data.
		1644
		1645	Since files are typically not-so-well supported by advanced notification
		1646	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1647	to files, even though you should not use it. The reason for this is
		1648	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1649	usually a tty, often a pipe, but also sometimes files or special devices
		1650	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1651	F</dev/urandom>), and even though the file might better be served with
		1652	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1653	it "just works" instead of freezing.
		1654
		1655	So avoid file descriptors pointing to files when you know it (e.g. use
		1656	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1657	when you rarely read from a file instead of from a socket, and want to
		1658	reuse the same code path.
		1659
1672	=head3 The special problem of fork	1660	=head3 The special problem of fork
1673		1661
1674	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1662	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1675	useless behaviour. Libev fully supports fork, but needs to be told about	1663	useless behaviour. Libev fully supports fork, but needs to be told about
1676	it in the child.	1664	it in the child if you want to continue to use it in the child.
1677		1665
1678	To support fork in your programs, you either have to call	1666	To support fork in your child processes, you have to call C<ev_loop_fork
1679	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1667	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1680	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1681	C<EVBACKEND_POLL>.
1682		1669
1683	=head3 The special problem of SIGPIPE	1670	=head3 The special problem of SIGPIPE
1684		1671
1685	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1672	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1686	when writing to a pipe whose other end has been closed, your program gets	1673	when writing to a pipe whose other end has been closed, your program gets
…		…
2036	keep up with the timer (because it takes longer than those 10 seconds to	2023	keep up with the timer (because it takes longer than those 10 seconds to
2037	do stuff) the timer will not fire more than once per event loop iteration.	2024	do stuff) the timer will not fire more than once per event loop iteration.
2038		2025
2039	=item ev_timer_again (loop, ev_timer *)	2026	=item ev_timer_again (loop, ev_timer *)
2040		2027
2041	This will act as if the timer timed out and restart it again if it is	2028	This will act as if the timer timed out and restarts it again if it is
2042	repeating. The exact semantics are:	2029	repeating. The exact semantics are:
2043		2030
2044	If the timer is pending, its pending status is cleared.	2031	If the timer is pending, its pending status is cleared.
2045		2032
2046	If the timer is started but non-repeating, stop it (as if it timed out).	2033	If the timer is started but non-repeating, stop it (as if it timed out).
…		…
2176		2163
2177	Another way to think about it (for the mathematically inclined) is that	2164	Another way to think about it (for the mathematically inclined) is that
2178	C<ev_periodic> will try to run the callback in this mode at the next possible	2165	C<ev_periodic> will try to run the callback in this mode at the next possible
2179	time where C<time = offset (mod interval)>, regardless of any time jumps.	2166	time where C<time = offset (mod interval)>, regardless of any time jumps.
2180		2167
2181	For numerical stability it is preferable that the C<offset> value is near	2168	The C<interval> I<MUST> be positive, and for numerical stability, the
2182	C<ev_now ()> (the current time), but there is no range requirement for	2169	interval value should be higher than C<1/8192> (which is around 100
2183	this value, and in fact is often specified as zero.	2170	microseconds) and C<offset> should be higher than C<0> and should have
		2171	at most a similar magnitude as the current time (say, within a factor of
		2172	ten). Typical values for offset are, in fact, C<0> or something between
		2173	C<0> and C<interval>, which is also the recommended range.
2184		2174
2185	Note also that there is an upper limit to how often a timer can fire (CPU	2175	Note also that there is an upper limit to how often a timer can fire (CPU
2186	speed for example), so if C<interval> is very small then timing stability	2176	speed for example), so if C<interval> is very small then timing stability
2187	will of course deteriorate. Libev itself tries to be exact to be about one	2177	will of course deteriorate. Libev itself tries to be exact to be about one
2188	millisecond (if the OS supports it and the machine is fast enough).	2178	millisecond (if the OS supports it and the machine is fast enough).
…		…
2331	=head3 The special problem of inheritance over fork/execve/pthread_create	2321	=head3 The special problem of inheritance over fork/execve/pthread_create
2332		2322
2333	Both the signal mask (C<sigprocmask>) and the signal disposition	2323	Both the signal mask (C<sigprocmask>) and the signal disposition
2334	(C<sigaction>) are unspecified after starting a signal watcher (and after	2324	(C<sigaction>) are unspecified after starting a signal watcher (and after
2335	stopping it again), that is, libev might or might not block the signal,	2325	stopping it again), that is, libev might or might not block the signal,
2336	and might or might not set or restore the installed signal handler.	2326	and might or might not set or restore the installed signal handler (but
		2327	see C<EVFLAG_NOSIGMASK>).
2337		2328
2338	While this does not matter for the signal disposition (libev never	2329	While this does not matter for the signal disposition (libev never
2339	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2330	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2340	C<execve>), this matters for the signal mask: many programs do not expect	2331	C<execve>), this matters for the signal mask: many programs do not expect
2341	certain signals to be blocked.	2332	certain signals to be blocked.
…		…
3212	atexit (program_exits);	3203	atexit (program_exits);
3213		3204
3214		3205
3215	=head2 C<ev_async> - how to wake up an event loop	3206	=head2 C<ev_async> - how to wake up an event loop
3216		3207
3217	In general, you cannot use an C<ev_run> from multiple threads or other	3208	In general, you cannot use an C<ev_loop> from multiple threads or other
3218	asynchronous sources such as signal handlers (as opposed to multiple event	3209	asynchronous sources such as signal handlers (as opposed to multiple event
3219	loops - those are of course safe to use in different threads).	3210	loops - those are of course safe to use in different threads).
3220		3211
3221	Sometimes, however, you need to wake up an event loop you do not control,	3212	Sometimes, however, you need to wake up an event loop you do not control,
3222	for example because it belongs to another thread. This is what C<ev_async>	3213	for example because it belongs to another thread. This is what C<ev_async>
…		…
3229	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3220	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
3230	of "global async watchers" by using a watcher on an otherwise unused	3221	of "global async watchers" by using a watcher on an otherwise unused
3231	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3222	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3232	even without knowing which loop owns the signal.	3223	even without knowing which loop owns the signal.
3233		3224
3234	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3235	just the default loop.
3236
3237	=head3 Queueing	3225	=head3 Queueing
3238		3226
3239	C<ev_async> does not support queueing of data in any way. The reason	3227	C<ev_async> does not support queueing of data in any way. The reason
3240	is that the author does not know of a simple (or any) algorithm for a	3228	is that the author does not know of a simple (or any) algorithm for a
3241	multiple-writer-single-reader queue that works in all cases and doesn't	3229	multiple-writer-single-reader queue that works in all cases and doesn't
…		…
3332	trust me.	3320	trust me.
3333		3321
3334	=item ev_async_send (loop, ev_async *)	3322	=item ev_async_send (loop, ev_async *)
3335		3323
3336	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3324	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3337	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3325	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3326	returns.
		3327
3338	C<ev_feed_event>, this call is safe to do from other threads, signal or	3328	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3339	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3329	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3340	section below on what exactly this means).	3330	embedding section below on what exactly this means).
3341		3331
3342	Note that, as with other watchers in libev, multiple events might get	3332	Note that, as with other watchers in libev, multiple events might get
3343	compressed into a single callback invocation (another way to look at this	3333	compressed into a single callback invocation (another way to look at
3344	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3334	this is that C<ev_async> watchers are level-triggered: they are set on
3345	reset when the event loop detects that).	3335	C<ev_async_send>, reset when the event loop detects that).
3346		3336
3347	This call incurs the overhead of a system call only once per event loop	3337	This call incurs the overhead of at most one extra system call per event
3348	iteration, so while the overhead might be noticeable, it doesn't apply to	3338	loop iteration, if the event loop is blocked, and no syscall at all if
3349	repeated calls to C<ev_async_send> for the same event loop.	3339	the event loop (or your program) is processing events. That means that
		3340	repeated calls are basically free (there is no need to avoid calls for
		3341	performance reasons) and that the overhead becomes smaller (typically
		3342	zero) under load.
3350		3343
3351	=item bool = ev_async_pending (ev_async *)	3344	=item bool = ev_async_pending (ev_async *)
3352		3345
3353	Returns a non-zero value when C<ev_async_send> has been called on the	3346	Returns a non-zero value when C<ev_async_send> has been called on the
3354	watcher but the event has not yet been processed (or even noted) by the	3347	watcher but the event has not yet been processed (or even noted) by the
…		…
3425		3418
3426	This section explains some common idioms that are not immediately	3419	This section explains some common idioms that are not immediately
3427	obvious. Note that examples are sprinkled over the whole manual, and this	3420	obvious. Note that examples are sprinkled over the whole manual, and this
3428	section only contains stuff that wouldn't fit anywhere else.	3421	section only contains stuff that wouldn't fit anywhere else.
3429		3422
3430	=over 4	3423	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3431		3424
3432	=item Model/nested event loop invocations and exit conditions.	3425	Each watcher has, by default, a C<void *data> member that you can read
		3426	or modify at any time: libev will completely ignore it. This can be used
		3427	to associate arbitrary data with your watcher. If you need more data and
		3428	don't want to allocate memory separately and store a pointer to it in that
		3429	data member, you can also "subclass" the watcher type and provide your own
		3430	data:
		3431
		3432	struct my_io
		3433	{
		3434	ev_io io;
		3435	int otherfd;
		3436	void *somedata;
		3437	struct whatever *mostinteresting;
		3438	};
		3439
		3440	...
		3441	struct my_io w;
		3442	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3443
		3444	And since your callback will be called with a pointer to the watcher, you
		3445	can cast it back to your own type:
		3446
		3447	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3448	{
		3449	struct my_io w = (struct my_io )w_;
		3450	...
		3451	}
		3452
		3453	More interesting and less C-conformant ways of casting your callback
		3454	function type instead have been omitted.
		3455
		3456	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3457
		3458	Another common scenario is to use some data structure with multiple
		3459	embedded watchers, in effect creating your own watcher that combines
		3460	multiple libev event sources into one "super-watcher":
		3461
		3462	struct my_biggy
		3463	{
		3464	int some_data;
		3465	ev_timer t1;
		3466	ev_timer t2;
		3467	}
		3468
		3469	In this case getting the pointer to C<my_biggy> is a bit more
		3470	complicated: Either you store the address of your C<my_biggy> struct in
		3471	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3472	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3473	real programmers):
		3474
		3475	#include <stddef.h>
		3476
		3477	static void
		3478	t1_cb (EV_P_ ev_timer *w, int revents)
		3479	{
		3480	struct my_biggy big = (struct my_biggy *)
		3481	(((char *)w) - offsetof (struct my_biggy, t1));
		3482	}
		3483
		3484	static void
		3485	t2_cb (EV_P_ ev_timer *w, int revents)
		3486	{
		3487	struct my_biggy big = (struct my_biggy *)
		3488	(((char *)w) - offsetof (struct my_biggy, t2));
		3489	}
		3490
		3491	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3433		3492
3434	Often (especially in GUI toolkits) there are places where you have	3493	Often (especially in GUI toolkits) there are places where you have
3435	I<modal> interaction, which is most easily implemented by recursively	3494	I<modal> interaction, which is most easily implemented by recursively
3436	invoking C<ev_run>.	3495	invoking C<ev_run>.
3437		3496
…		…
3466	exit_main_loop = 1;	3525	exit_main_loop = 1;
3467		3526
3468	// exit both	3527	// exit both
3469	exit_main_loop = exit_nested_loop = 1;	3528	exit_main_loop = exit_nested_loop = 1;
3470		3529
3471	=back	3530	=head2 THREAD LOCKING EXAMPLE
		3531
		3532	Here is a fictitious example of how to run an event loop in a different
		3533	thread from where callbacks are being invoked and watchers are
		3534	created/added/removed.
		3535
		3536	For a real-world example, see the C<EV::Loop::Async> perl module,
		3537	which uses exactly this technique (which is suited for many high-level
		3538	languages).
		3539
		3540	The example uses a pthread mutex to protect the loop data, a condition
		3541	variable to wait for callback invocations, an async watcher to notify the
		3542	event loop thread and an unspecified mechanism to wake up the main thread.
		3543
		3544	First, you need to associate some data with the event loop:
		3545
		3546	typedef struct {
		3547	mutex_t lock; /* global loop lock */
		3548	ev_async async_w;
		3549	thread_t tid;
		3550	cond_t invoke_cv;
		3551	} userdata;
		3552
		3553	void prepare_loop (EV_P)
		3554	{
		3555	// for simplicity, we use a static userdata struct.
		3556	static userdata u;
		3557
		3558	ev_async_init (&u->async_w, async_cb);
		3559	ev_async_start (EV_A_ &u->async_w);
		3560
		3561	pthread_mutex_init (&u->lock, 0);
		3562	pthread_cond_init (&u->invoke_cv, 0);
		3563
		3564	// now associate this with the loop
		3565	ev_set_userdata (EV_A_ u);
		3566	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3567	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3568
		3569	// then create the thread running ev_run
		3570	pthread_create (&u->tid, 0, l_run, EV_A);
		3571	}
		3572
		3573	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3574	solely to wake up the event loop so it takes notice of any new watchers
		3575	that might have been added:
		3576
		3577	static void
		3578	async_cb (EV_P_ ev_async *w, int revents)
		3579	{
		3580	// just used for the side effects
		3581	}
		3582
		3583	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3584	protecting the loop data, respectively.
		3585
		3586	static void
		3587	l_release (EV_P)
		3588	{
		3589	userdata *u = ev_userdata (EV_A);
		3590	pthread_mutex_unlock (&u->lock);
		3591	}
		3592
		3593	static void
		3594	l_acquire (EV_P)
		3595	{
		3596	userdata *u = ev_userdata (EV_A);
		3597	pthread_mutex_lock (&u->lock);
		3598	}
		3599
		3600	The event loop thread first acquires the mutex, and then jumps straight
		3601	into C<ev_run>:
		3602
		3603	void *
		3604	l_run (void *thr_arg)
		3605	{
		3606	struct ev_loop loop = (struct ev_loop )thr_arg;
		3607
		3608	l_acquire (EV_A);
		3609	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3610	ev_run (EV_A_ 0);
		3611	l_release (EV_A);
		3612
		3613	return 0;
		3614	}
		3615
		3616	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3617	signal the main thread via some unspecified mechanism (signals? pipe
		3618	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3619	have been called (in a while loop because a) spurious wakeups are possible
		3620	and b) skipping inter-thread-communication when there are no pending
		3621	watchers is very beneficial):
		3622
		3623	static void
		3624	l_invoke (EV_P)
		3625	{
		3626	userdata *u = ev_userdata (EV_A);
		3627
		3628	while (ev_pending_count (EV_A))
		3629	{
		3630	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3631	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3632	}
		3633	}
		3634
		3635	Now, whenever the main thread gets told to invoke pending watchers, it
		3636	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3637	thread to continue:
		3638
		3639	static void
		3640	real_invoke_pending (EV_P)
		3641	{
		3642	userdata *u = ev_userdata (EV_A);
		3643
		3644	pthread_mutex_lock (&u->lock);
		3645	ev_invoke_pending (EV_A);
		3646	pthread_cond_signal (&u->invoke_cv);
		3647	pthread_mutex_unlock (&u->lock);
		3648	}
		3649
		3650	Whenever you want to start/stop a watcher or do other modifications to an
		3651	event loop, you will now have to lock:
		3652
		3653	ev_timer timeout_watcher;
		3654	userdata *u = ev_userdata (EV_A);
		3655
		3656	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3657
		3658	pthread_mutex_lock (&u->lock);
		3659	ev_timer_start (EV_A_ &timeout_watcher);
		3660	ev_async_send (EV_A_ &u->async_w);
		3661	pthread_mutex_unlock (&u->lock);
		3662
		3663	Note that sending the C<ev_async> watcher is required because otherwise
		3664	an event loop currently blocking in the kernel will have no knowledge
		3665	about the newly added timer. By waking up the loop it will pick up any new
		3666	watchers in the next event loop iteration.
		3667
		3668	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3669
		3670	While the overhead of a callback that e.g. schedules a thread is small, it
		3671	is still an overhead. If you embed libev, and your main usage is with some
		3672	kind of threads or coroutines, you might want to customise libev so that
		3673	doesn't need callbacks anymore.
		3674
		3675	Imagine you have coroutines that you can switch to using a function
		3676	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3677	and that due to some magic, the currently active coroutine is stored in a
		3678	global called C<current_coro>. Then you can build your own "wait for libev
		3679	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3680	the differing C<;> conventions):
		3681
		3682	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3683	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3684
		3685	That means instead of having a C callback function, you store the
		3686	coroutine to switch to in each watcher, and instead of having libev call
		3687	your callback, you instead have it switch to that coroutine.
		3688
		3689	A coroutine might now wait for an event with a function called
		3690	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3691	matter when, or whether the watcher is active or not when this function is
		3692	called):
		3693
		3694	void
		3695	wait_for_event (ev_watcher *w)
		3696	{
		3697	ev_cb_set (w) = current_coro;
		3698	switch_to (libev_coro);
		3699	}
		3700
		3701	That basically suspends the coroutine inside C<wait_for_event> and
		3702	continues the libev coroutine, which, when appropriate, switches back to
		3703	this or any other coroutine. I am sure if you sue this your own :)
		3704
		3705	You can do similar tricks if you have, say, threads with an event queue -
		3706	instead of storing a coroutine, you store the queue object and instead of
		3707	switching to a coroutine, you push the watcher onto the queue and notify
		3708	any waiters.
		3709
		3710	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3711	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3712
		3713	// my_ev.h
		3714	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3715	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3716	#include "../libev/ev.h"
		3717
		3718	// my_ev.c
		3719	#define EV_H "my_ev.h"
		3720	#include "../libev/ev.c"
		3721
		3722	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3723	F<my_ev.c> into your project. When properly specifying include paths, you
		3724	can even use F<ev.h> as header file name directly.
3472		3725
3473		3726
3474	=head1 LIBEVENT EMULATION	3727	=head1 LIBEVENT EMULATION
3475		3728
3476	Libev offers a compatibility emulation layer for libevent. It cannot	3729	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3691	watchers in the constructor.	3944	watchers in the constructor.
3692		3945
3693	class myclass	3946	class myclass
3694	{	3947	{
3695	ev::io io ; void io_cb (ev::io &w, int revents);	3948	ev::io io ; void io_cb (ev::io &w, int revents);
3696	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	3949	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3697	ev::idle idle; void idle_cb (ev::idle &w, int revents);	3950	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3698		3951
3699	myclass (int fd)	3952	myclass (int fd)
3700	{	3953	{
3701	io .set <myclass, &myclass::io_cb > (this);	3954	io .set <myclass, &myclass::io_cb > (this);
…		…
3752	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4005	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3753		4006
3754	=item D	4007	=item D
3755		4008
3756	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4009	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3757	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4010	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3758		4011
3759	=item Ocaml	4012	=item Ocaml
3760		4013
3761	Erkki Seppala has written Ocaml bindings for libev, to be found at	4014	Erkki Seppala has written Ocaml bindings for libev, to be found at
3762	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4015	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3965	supported). It will also not define any of the structs usually found in	4218	supported). It will also not define any of the structs usually found in
3966	F<event.h> that are not directly supported by the libev core alone.	4219	F<event.h> that are not directly supported by the libev core alone.
3967		4220
3968	In standalone mode, libev will still try to automatically deduce the	4221	In standalone mode, libev will still try to automatically deduce the
3969	configuration, but has to be more conservative.	4222	configuration, but has to be more conservative.
		4223
		4224	=item EV_USE_FLOOR
		4225
		4226	If defined to be C<1>, libev will use the C<floor ()> function for its
		4227	periodic reschedule calculations, otherwise libev will fall back on a
		4228	portable (slower) implementation. If you enable this, you usually have to
		4229	link against libm or something equivalent. Enabling this when the C<floor>
		4230	function is not available will fail, so the safe default is to not enable
		4231	this.
3970		4232
3971	=item EV_USE_MONOTONIC	4233	=item EV_USE_MONOTONIC
3972		4234
3973	If defined to be C<1>, libev will try to detect the availability of the	4235	If defined to be C<1>, libev will try to detect the availability of the
3974	monotonic clock option at both compile time and runtime. Otherwise no	4236	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4107	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4369	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4108		4370
4109	=item EV_ATOMIC_T	4371	=item EV_ATOMIC_T
4110		4372
4111	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4373	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4112	access is atomic with respect to other threads or signal contexts. No such	4374	access is atomic and serialised with respect to other threads or signal
4113	type is easily found in the C language, so you can provide your own type	4375	contexts. No such type is easily found in the C language, so you can
4114	that you know is safe for your purposes. It is used both for signal handler "locking"	4376	provide your own type that you know is safe for your purposes. It is used
4115	as well as for signal and thread safety in C<ev_async> watchers.	4377	both for signal handler "locking" as well as for signal and thread safety
		4378	in C<ev_async> watchers.
4116		4379
4117	In the absence of this define, libev will use C<sig_atomic_t volatile>	4380	In the absence of this define, libev will use C<sig_atomic_t volatile>
4118	(from F<signal.h>), which is usually good enough on most platforms.	4381	(from F<signal.h>), which is usually good enough on most platforms,
		4382	although strictly speaking using a type that also implies a memory fence
		4383	is required.
4119		4384
4120	=item EV_H (h)	4385	=item EV_H (h)
4121		4386
4122	The name of the F<ev.h> header file used to include it. The default if	4387	The name of the F<ev.h> header file used to include it. The default if
4123	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4388	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
4406	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4671	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4407		4672
4408	#include "ev_cpp.h"	4673	#include "ev_cpp.h"
4409	#include "ev.c"	4674	#include "ev.c"
4410		4675
4411	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4676	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4412		4677
4413	=head2 THREADS AND COROUTINES	4678	=head2 THREADS AND COROUTINES
4414		4679
4415	=head3 THREADS	4680	=head3 THREADS
4416		4681
…		…
4467	default loop and triggering an C<ev_async> watcher from the default loop	4732	default loop and triggering an C<ev_async> watcher from the default loop
4468	watcher callback into the event loop interested in the signal.	4733	watcher callback into the event loop interested in the signal.
4469		4734
4470	=back	4735	=back
4471		4736
4472	=head4 THREAD LOCKING EXAMPLE	4737	See also L<THREAD LOCKING EXAMPLE>.
4473
4474	Here is a fictitious example of how to run an event loop in a different
4475	thread than where callbacks are being invoked and watchers are
4476	created/added/removed.
4477
4478	For a real-world example, see the C<EV::Loop::Async> perl module,
4479	which uses exactly this technique (which is suited for many high-level
4480	languages).
4481
4482	The example uses a pthread mutex to protect the loop data, a condition
4483	variable to wait for callback invocations, an async watcher to notify the
4484	event loop thread and an unspecified mechanism to wake up the main thread.
4485
4486	First, you need to associate some data with the event loop:
4487
4488	typedef struct {
4489	mutex_t lock; /* global loop lock */
4490	ev_async async_w;
4491	thread_t tid;
4492	cond_t invoke_cv;
4493	} userdata;
4494
4495	void prepare_loop (EV_P)
4496	{
4497	// for simplicity, we use a static userdata struct.
4498	static userdata u;
4499
4500	ev_async_init (&u->async_w, async_cb);
4501	ev_async_start (EV_A_ &u->async_w);
4502
4503	pthread_mutex_init (&u->lock, 0);
4504	pthread_cond_init (&u->invoke_cv, 0);
4505
4506	// now associate this with the loop
4507	ev_set_userdata (EV_A_ u);
4508	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4509	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4510
4511	// then create the thread running ev_loop
4512	pthread_create (&u->tid, 0, l_run, EV_A);
4513	}
4514
4515	The callback for the C<ev_async> watcher does nothing: the watcher is used
4516	solely to wake up the event loop so it takes notice of any new watchers
4517	that might have been added:
4518
4519	static void
4520	async_cb (EV_P_ ev_async *w, int revents)
4521	{
4522	// just used for the side effects
4523	}
4524
4525	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4526	protecting the loop data, respectively.
4527
4528	static void
4529	l_release (EV_P)
4530	{
4531	userdata *u = ev_userdata (EV_A);
4532	pthread_mutex_unlock (&u->lock);
4533	}
4534
4535	static void
4536	l_acquire (EV_P)
4537	{
4538	userdata *u = ev_userdata (EV_A);
4539	pthread_mutex_lock (&u->lock);
4540	}
4541
4542	The event loop thread first acquires the mutex, and then jumps straight
4543	into C<ev_run>:
4544
4545	void *
4546	l_run (void *thr_arg)
4547	{
4548	struct ev_loop loop = (struct ev_loop )thr_arg;
4549
4550	l_acquire (EV_A);
4551	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4552	ev_run (EV_A_ 0);
4553	l_release (EV_A);
4554
4555	return 0;
4556	}
4557
4558	Instead of invoking all pending watchers, the C<l_invoke> callback will
4559	signal the main thread via some unspecified mechanism (signals? pipe
4560	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4561	have been called (in a while loop because a) spurious wakeups are possible
4562	and b) skipping inter-thread-communication when there are no pending
4563	watchers is very beneficial):
4564
4565	static void
4566	l_invoke (EV_P)
4567	{
4568	userdata *u = ev_userdata (EV_A);
4569
4570	while (ev_pending_count (EV_A))
4571	{
4572	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4573	pthread_cond_wait (&u->invoke_cv, &u->lock);
4574	}
4575	}
4576
4577	Now, whenever the main thread gets told to invoke pending watchers, it
4578	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4579	thread to continue:
4580
4581	static void
4582	real_invoke_pending (EV_P)
4583	{
4584	userdata *u = ev_userdata (EV_A);
4585
4586	pthread_mutex_lock (&u->lock);
4587	ev_invoke_pending (EV_A);
4588	pthread_cond_signal (&u->invoke_cv);
4589	pthread_mutex_unlock (&u->lock);
4590	}
4591
4592	Whenever you want to start/stop a watcher or do other modifications to an
4593	event loop, you will now have to lock:
4594
4595	ev_timer timeout_watcher;
4596	userdata *u = ev_userdata (EV_A);
4597
4598	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4599
4600	pthread_mutex_lock (&u->lock);
4601	ev_timer_start (EV_A_ &timeout_watcher);
4602	ev_async_send (EV_A_ &u->async_w);
4603	pthread_mutex_unlock (&u->lock);
4604
4605	Note that sending the C<ev_async> watcher is required because otherwise
4606	an event loop currently blocking in the kernel will have no knowledge
4607	about the newly added timer. By waking up the loop it will pick up any new
4608	watchers in the next event loop iteration.
4609		4738
4610	=head3 COROUTINES	4739	=head3 COROUTINES
4611		4740
4612	Libev is very accommodating to coroutines ("cooperative threads"):	4741	Libev is very accommodating to coroutines ("cooperative threads"):
4613	libev fully supports nesting calls to its functions from different	4742	libev fully supports nesting calls to its functions from different
…		…
4778	requires, and its I/O model is fundamentally incompatible with the POSIX	4907	requires, and its I/O model is fundamentally incompatible with the POSIX
4779	model. Libev still offers limited functionality on this platform in	4908	model. Libev still offers limited functionality on this platform in
4780	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4909	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4781	descriptors. This only applies when using Win32 natively, not when using	4910	descriptors. This only applies when using Win32 natively, not when using
4782	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	4911	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4783	as every compielr comes with a slightly differently broken/incompatible	4912	as every compiler comes with a slightly differently broken/incompatible
4784	environment.	4913	environment.
4785		4914
4786	Lifting these limitations would basically require the full	4915	Lifting these limitations would basically require the full
4787	re-implementation of the I/O system. If you are into this kind of thing,	4916	re-implementation of the I/O system. If you are into this kind of thing,
4788	then note that glib does exactly that for you in a very portable way (note	4917	then note that glib does exactly that for you in a very portable way (note
…		…
4921		5050
4922	The type C<double> is used to represent timestamps. It is required to	5051	The type C<double> is used to represent timestamps. It is required to
4923	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5052	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4924	good enough for at least into the year 4000 with millisecond accuracy	5053	good enough for at least into the year 4000 with millisecond accuracy
4925	(the design goal for libev). This requirement is overfulfilled by	5054	(the design goal for libev). This requirement is overfulfilled by
4926	implementations using IEEE 754, which is basically all existing ones. With	5055	implementations using IEEE 754, which is basically all existing ones.
		5056
4927	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5057	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5058	year 2255 (and millisecond accuray till the year 287396 - by then, libev
		5059	is either obsolete or somebody patched it to use C<long double> or
		5060	something like that, just kidding).
4928		5061
4929	=back	5062	=back
4930		5063
4931	If you know of other additional requirements drop me a note.	5064	If you know of other additional requirements drop me a note.
4932		5065
…		…
4994	=item Processing ev_async_send: O(number_of_async_watchers)	5127	=item Processing ev_async_send: O(number_of_async_watchers)
4995		5128
4996	=item Processing signals: O(max_signal_number)	5129	=item Processing signals: O(max_signal_number)
4997		5130
4998	Sending involves a system call I<iff> there were no other C<ev_async_send>	5131	Sending involves a system call I<iff> there were no other C<ev_async_send>
4999	calls in the current loop iteration. Checking for async and signal events	5132	calls in the current loop iteration and the loop is currently
		5133	blocked. Checking for async and signal events involves iterating over all
5000	involves iterating over all running async watchers or all signal numbers.	5134	running async watchers or all signal numbers.
5001		5135
5002	=back	5136	=back
5003		5137
5004		5138
5005	=head1 PORTING FROM LIBEV 3.X TO 4.X	5139	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5122	The physical time that is observed. It is apparently strictly monotonic :)	5256	The physical time that is observed. It is apparently strictly monotonic :)
5123		5257
5124	=item wall-clock time	5258	=item wall-clock time
5125		5259
5126	The time and date as shown on clocks. Unlike real time, it can actually	5260	The time and date as shown on clocks. Unlike real time, it can actually
5127	be wrong and jump forwards and backwards, e.g. when the you adjust your	5261	be wrong and jump forwards and backwards, e.g. when you adjust your
5128	clock.	5262	clock.
5129		5263
5130	=item watcher	5264	=item watcher
5131		5265
5132	A data structure that describes interest in certain events. Watchers need	5266	A data structure that describes interest in certain events. Watchers need
…		…
5135	=back	5269	=back
5136		5270
5137	=head1 AUTHOR	5271	=head1 AUTHOR
5138		5272
5139	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5273	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5140	Magnusson and Emanuele Giaquinta.	5274	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5141		5275

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Comparing libev/ev.pod (file contents): Revision 1.351 by root, Mon Jan 10 14:24:26 2011 UTC vs. Revision 1.379 by root, Tue Jul 12 23:32:10 2011 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.351 by root, Mon Jan 10 14:24:26 2011 UTC vs.
Revision 1.379 by root, Tue Jul 12 23:32:10 2011 UTC