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

Comparing libev/ev.pod (file contents):
Revision 1.352 by root, Mon Jan 10 14:30:15 2011 UTC vs.
Revision 1.394 by root, Tue Jan 24 16:37:12 2012 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
…		…
174	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
175		175
176	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
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_now_update> 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
…		…
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> - so bizarre that	611	On the negative side, the interface is I<bizarre> - so bizarre that
598	even sun itself gets it wrong in their code examples: The event polling	612	even sun itself gets it wrong in their code examples: The event polling
599	function sometimes returning events to the caller even though an error	613	function sometimes returns events to the caller even though an error
600	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
601	even documented that way) - deadly for edge-triggered interfaces where	615	even documented that way) - deadly for edge-triggered interfaces where you
602	you absolutely have to know whether an event occured or not because you	616	absolutely have to know whether an event occurred or not because you have
603	have to re-arm the watcher.	617	to re-arm the watcher.
604		618
605	Fortunately libev seems to be able to work around these idiocies.	619	Fortunately libev seems to be able to work around these idiocies.
606		620
607	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
608	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
…		…
820	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
821	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
822	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
823	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
824		838
825	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):
826		842
827	- Increment loop depth.	843	- Increment loop depth.
828	- Reset the ev_break status.	844	- Reset the ev_break status.
829	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
830	LOOP:	846	LOOP:
…		…
863	anymore.	879	anymore.
864		880
865	... queue jobs here, make sure they register event watchers as long	881	... queue jobs here, make sure they register event watchers as long
866	... 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..)
867	ev_run (my_loop, 0);	883	ev_run (my_loop, 0);
868	... jobs done or somebody called unloop. yeah!	884	... jobs done or somebody called break. yeah!
869		885
870	=item ev_break (loop, how)	886	=item ev_break (loop, how)
871		887
872	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
873	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
…		…
936	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.
937		953
938	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
939	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,
940	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
941	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
942	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
943	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
944	once per this interval, on average.	960	once per this interval, on average (as long as the host time resolution is
		961	good enough).
945		962
946	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
947	to spend more time collecting timeouts, at the expense of increased	964	to spend more time collecting timeouts, at the expense of increased
948	latency/jitter/inexactness (the watcher callback will be called	965	latency/jitter/inexactness (the watcher callback will be called
949	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
…		…
1003	can be done relatively simply by putting mutex_lock/unlock calls around	1020	can be done relatively simply by putting mutex_lock/unlock calls around
1004	each call to a libev function.	1021	each call to a libev function.
1005		1022
1006	However, C<ev_run> can run an indefinite time, so it is not feasible	1023	However, C<ev_run> can run an indefinite time, so it is not feasible
1007	to wait for it to return. One way around this is to wake up the event	1024	to wait for it to return. One way around this is to wake up the event
1008	loop via C<ev_break> and C<av_async_send>, another way is to set these	1025	loop via C<ev_break> and C<ev_async_send>, another way is to set these
1009	I<release> and I<acquire> callbacks on the loop.	1026	I<release> and I<acquire> callbacks on the loop.
1010		1027
1011	When set, then C<release> will be called just before the thread is	1028	When set, then C<release> will be called just before the thread is
1012	suspended waiting for new events, and C<acquire> is called just	1029	suspended waiting for new events, and C<acquire> is called just
1013	afterwards.	1030	afterwards.
…		…
1355	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
1356	functions that do not need a watcher.	1373	functions that do not need a watcher.
1357		1374
1358	=back	1375	=back
1359		1376
1360	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1377	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1361		1378	OWN COMPOSITE WATCHERS> idioms.
1362	Each watcher has, by default, a member C<void *data> that you can change
1363	and read at any time: libev will completely ignore it. This can be used
1364	to associate arbitrary data with your watcher. If you need more data and
1365	don't want to allocate memory and store a pointer to it in that data
1366	member, you can also "subclass" the watcher type and provide your own
1367	data:
1368
1369	struct my_io
1370	{
1371	ev_io io;
1372	int otherfd;
1373	void *somedata;
1374	struct whatever *mostinteresting;
1375	};
1376
1377	...
1378	struct my_io w;
1379	ev_io_init (&w.io, my_cb, fd, EV_READ);
1380
1381	And since your callback will be called with a pointer to the watcher, you
1382	can cast it back to your own type:
1383
1384	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1385	{
1386	struct my_io w = (struct my_io )w_;
1387	...
1388	}
1389
1390	More interesting and less C-conformant ways of casting your callback type
1391	instead have been omitted.
1392
1393	Another common scenario is to use some data structure with multiple
1394	embedded watchers:
1395
1396	struct my_biggy
1397	{
1398	int some_data;
1399	ev_timer t1;
1400	ev_timer t2;
1401	}
1402
1403	In this case getting the pointer to C<my_biggy> is a bit more
1404	complicated: Either you store the address of your C<my_biggy> struct
1405	in the C<data> member of the watcher (for woozies), or you need to use
1406	some pointer arithmetic using C<offsetof> inside your watchers (for real
1407	programmers):
1408
1409	#include <stddef.h>
1410
1411	static void
1412	t1_cb (EV_P_ ev_timer *w, int revents)
1413	{
1414	struct my_biggy big = (struct my_biggy *)
1415	(((char *)w) - offsetof (struct my_biggy, t1));
1416	}
1417
1418	static void
1419	t2_cb (EV_P_ ev_timer *w, int revents)
1420	{
1421	struct my_biggy big = (struct my_biggy *)
1422	(((char *)w) - offsetof (struct my_biggy, t2));
1423	}
1424		1379
1425	=head2 WATCHER STATES	1380	=head2 WATCHER STATES
1426		1381
1427	There are various watcher states mentioned throughout this manual -	1382	There are various watcher states mentioned throughout this manual -
1428	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
…		…
1431		1386
1432	=over 4	1387	=over 4
1433		1388
1434	=item initialiased	1389	=item initialiased
1435		1390
1436	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
1437	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
1438	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.
1439		1394
1440	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
1441	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.
1442		1399
1443	=item started/running/active	1400	=item started/running/active
1444		1401
1445	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
1446	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
…		…
1474	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
1475	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
1476	freeing it is often a good idea.	1433	freeing it is often a good idea.
1477		1434
1478	While stopped (and not pending) the watcher is essentially in the	1435	While stopped (and not pending) the watcher is essentially in the
1479	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
1480	you wish.	1437	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1438	it again).
1481		1439
1482	=back	1440	=back
1483		1441
1484	=head2 WATCHER PRIORITY MODELS	1442	=head2 WATCHER PRIORITY MODELS
1485		1443
…		…
1614	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
1615	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
1616	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
1617	required if you know what you are doing).	1575	required if you know what you are doing).
1618		1576
1619	If you cannot use non-blocking mode, then force the use of a
1620	known-to-be-good backend (at the time of this writing, this includes only
1621	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1622	descriptors for which non-blocking operation makes no sense (such as
1623	files) - libev doesn't guarantee any specific behaviour in that case.
1624
1625	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
1626	receive "spurious" readiness notifications, that is your callback might	1578	receive "spurious" readiness notifications, that is, your callback might
1627	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
1628	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
1629	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
1630	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
1631	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1632	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1583	preferable to a program hanging until some data arrives.
1633		1584
1634	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
1635	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
1636	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
1637	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
1638	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
1639	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
1640	indefinitely.	1591	indefinitely.
1641		1592
1642	But really, best use non-blocking mode.	1593	But really, best use non-blocking mode.
1643		1594
…		…
1671		1622
1672	There is no workaround possible except not registering events	1623	There is no workaround possible except not registering events
1673	for potentially C<dup ()>'ed file descriptors, or to resort to	1624	for potentially C<dup ()>'ed file descriptors, or to resort to
1674	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1675		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
1676	=head3 The special problem of fork	1660	=head3 The special problem of fork
1677		1661
1678	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
1679	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
1680	it in the child.	1664	it in the child if you want to continue to use it in the child.
1681		1665
1682	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
1683	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
1684	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1685	C<EVBACKEND_POLL>.
1686		1669
1687	=head3 The special problem of SIGPIPE	1670	=head3 The special problem of SIGPIPE
1688		1671
1689	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>:
1690	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
…		…
1788	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1771	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1789	monotonic clock option helps a lot here).	1772	monotonic clock option helps a lot here).
1790		1773
1791	The callback is guaranteed to be invoked only I<after> its timeout has	1774	The callback is guaranteed to be invoked only I<after> its timeout has
1792	passed (not I<at>, so on systems with very low-resolution clocks this	1775	passed (not I<at>, so on systems with very low-resolution clocks this
1793	might introduce a small delay). If multiple timers become ready during the	1776	might introduce a small delay, see "the special problem of being too
		1777	early", below). If multiple timers become ready during the same loop
1794	same loop iteration then the ones with earlier time-out values are invoked	1778	iteration then the ones with earlier time-out values are invoked before
1795	before ones of the same priority with later time-out values (but this is	1779	ones of the same priority with later time-out values (but this is no
1796	no longer true when a callback calls C<ev_run> recursively).	1780	longer true when a callback calls C<ev_run> recursively).
1797		1781
1798	=head3 Be smart about timeouts	1782	=head3 Be smart about timeouts
1799		1783
1800	Many real-world problems involve some kind of timeout, usually for error	1784	Many real-world problems involve some kind of timeout, usually for error
1801	recovery. A typical example is an HTTP request - if the other side hangs,	1785	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1876		1860
1877	In this case, it would be more efficient to leave the C<ev_timer> alone,	1861	In this case, it would be more efficient to leave the C<ev_timer> alone,
1878	but remember the time of last activity, and check for a real timeout only	1862	but remember the time of last activity, and check for a real timeout only
1879	within the callback:	1863	within the callback:
1880		1864
		1865	ev_tstamp timeout = 60.;
1881	ev_tstamp last_activity; // time of last activity	1866	ev_tstamp last_activity; // time of last activity
		1867	ev_timer timer;
1882		1868
1883	static void	1869	static void
1884	callback (EV_P_ ev_timer *w, int revents)	1870	callback (EV_P_ ev_timer *w, int revents)
1885	{	1871	{
1886	ev_tstamp now = ev_now (EV_A);	1872	// calculate when the timeout would happen
1887	ev_tstamp timeout = last_activity + 60.;	1873	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1888		1874
1889	// if last_activity + 60. is older than now, we did time out	1875	// if negative, it means we the timeout already occured
1890	if (timeout < now)	1876	if (after < 0.)
1891	{	1877	{
1892	// timeout occurred, take action	1878	// timeout occurred, take action
1893	}	1879	}
1894	else	1880	else
1895	{	1881	{
1896	// callback was invoked, but there was some activity, re-arm	1882	// callback was invoked, but there was some recent
1897	// the watcher to fire in last_activity + 60, which is	1883	// activity. simply restart the timer to time out
1898	// guaranteed to be in the future, so "again" is positive:	1884	// after "after" seconds, which is the earliest time
1899	w->repeat = timeout - now;	1885	// the timeout can occur.
		1886	ev_timer_set (w, after, 0.);
1900	ev_timer_again (EV_A_ w);	1887	ev_timer_start (EV_A_ w);
1901	}	1888	}
1902	}	1889	}
1903		1890
1904	To summarise the callback: first calculate the real timeout (defined	1891	To summarise the callback: first calculate in how many seconds the
1905	as "60 seconds after the last activity"), then check if that time has	1892	timeout will occur (by calculating the absolute time when it would occur,
1906	been reached, which means something I<did>, in fact, time out. Otherwise	1893	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1907	the callback was invoked too early (C<timeout> is in the future), so	1894	(EV_A)> from that).
1908	re-schedule the timer to fire at that future time, to see if maybe we have
1909	a timeout then.
1910		1895
1911	Note how C<ev_timer_again> is used, taking advantage of the	1896	If this value is negative, then we are already past the timeout, i.e. we
1912	C<ev_timer_again> optimisation when the timer is already running.	1897	timed out, and need to do whatever is needed in this case.
		1898
		1899	Otherwise, we now the earliest time at which the timeout would trigger,
		1900	and simply start the timer with this timeout value.
		1901
		1902	In other words, each time the callback is invoked it will check whether
		1903	the timeout cocured. If not, it will simply reschedule itself to check
		1904	again at the earliest time it could time out. Rinse. Repeat.
1913		1905
1914	This scheme causes more callback invocations (about one every 60 seconds	1906	This scheme causes more callback invocations (about one every 60 seconds
1915	minus half the average time between activity), but virtually no calls to	1907	minus half the average time between activity), but virtually no calls to
1916	libev to change the timeout.	1908	libev to change the timeout.
1917		1909
1918	To start the timer, simply initialise the watcher and set C<last_activity>	1910	To start the machinery, simply initialise the watcher and set
1919	to the current time (meaning we just have some activity :), then call the	1911	C<last_activity> to the current time (meaning there was some activity just
1920	callback, which will "do the right thing" and start the timer:	1912	now), then call the callback, which will "do the right thing" and start
		1913	the timer:
1921		1914
		1915	last_activity = ev_now (EV_A);
1922	ev_init (timer, callback);	1916	ev_init (&timer, callback);
1923	last_activity = ev_now (loop);	1917	callback (EV_A_ &timer, 0);
1924	callback (loop, timer, EV_TIMER);
1925		1918
1926	And when there is some activity, simply store the current time in	1919	When there is some activity, simply store the current time in
1927	C<last_activity>, no libev calls at all:	1920	C<last_activity>, no libev calls at all:
1928		1921
		1922	if (activity detected)
1929	last_activity = ev_now (loop);	1923	last_activity = ev_now (EV_A);
		1924
		1925	When your timeout value changes, then the timeout can be changed by simply
		1926	providing a new value, stopping the timer and calling the callback, which
		1927	will agaion do the right thing (for example, time out immediately :).
		1928
		1929	timeout = new_value;
		1930	ev_timer_stop (EV_A_ &timer);
		1931	callback (EV_A_ &timer, 0);
1930		1932
1931	This technique is slightly more complex, but in most cases where the	1933	This technique is slightly more complex, but in most cases where the
1932	time-out is unlikely to be triggered, much more efficient.	1934	time-out is unlikely to be triggered, much more efficient.
1933
1934	Changing the timeout is trivial as well (if it isn't hard-coded in the
1935	callback :) - just change the timeout and invoke the callback, which will
1936	fix things for you.
1937		1935
1938	=item 4. Wee, just use a double-linked list for your timeouts.	1936	=item 4. Wee, just use a double-linked list for your timeouts.
1939		1937
1940	If there is not one request, but many thousands (millions...), all	1938	If there is not one request, but many thousands (millions...), all
1941	employing some kind of timeout with the same timeout value, then one can	1939	employing some kind of timeout with the same timeout value, then one can
…		…
1968	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1966	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1969	rather complicated, but extremely efficient, something that really pays	1967	rather complicated, but extremely efficient, something that really pays
1970	off after the first million or so of active timers, i.e. it's usually	1968	off after the first million or so of active timers, i.e. it's usually
1971	overkill :)	1969	overkill :)
1972		1970
		1971	=head3 The special problem of being too early
		1972
		1973	If you ask a timer to call your callback after three seconds, then
		1974	you expect it to be invoked after three seconds - but of course, this
		1975	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1976	guaranteed to any precision by libev - imagine somebody suspending the
		1977	process with a STOP signal for a few hours for example.
		1978
		1979	So, libev tries to invoke your callback as soon as possible I<after> the
		1980	delay has occurred, but cannot guarantee this.
		1981
		1982	A less obvious failure mode is calling your callback too early: many event
		1983	loops compare timestamps with a "elapsed delay >= requested delay", but
		1984	this can cause your callback to be invoked much earlier than you would
		1985	expect.
		1986
		1987	To see why, imagine a system with a clock that only offers full second
		1988	resolution (think windows if you can't come up with a broken enough OS
		1989	yourself). If you schedule a one-second timer at the time 500.9, then the
		1990	event loop will schedule your timeout to elapse at a system time of 500
		1991	(500.9 truncated to the resolution) + 1, or 501.
		1992
		1993	If an event library looks at the timeout 0.1s later, it will see "501 >=
		1994	501" and invoke the callback 0.1s after it was started, even though a
		1995	one-second delay was requested - this is being "too early", despite best
		1996	intentions.
		1997
		1998	This is the reason why libev will never invoke the callback if the elapsed
		1999	delay equals the requested delay, but only when the elapsed delay is
		2000	larger than the requested delay. In the example above, libev would only invoke
		2001	the callback at system time 502, or 1.1s after the timer was started.
		2002
		2003	So, while libev cannot guarantee that your callback will be invoked
		2004	exactly when requested, it I<can> and I<does> guarantee that the requested
		2005	delay has actually elapsed, or in other words, it always errs on the "too
		2006	late" side of things.
		2007
1973	=head3 The special problem of time updates	2008	=head3 The special problem of time updates
1974		2009
1975	Establishing the current time is a costly operation (it usually takes at	2010	Establishing the current time is a costly operation (it usually takes
1976	least two system calls): EV therefore updates its idea of the current	2011	at least one system call): EV therefore updates its idea of the current
1977	time only before and after C<ev_run> collects new events, which causes a	2012	time only before and after C<ev_run> collects new events, which causes a
1978	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2013	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1979	lots of events in one iteration.	2014	lots of events in one iteration.
1980		2015
1981	The relative timeouts are calculated relative to the C<ev_now ()>	2016	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1987	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2022	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1988		2023
1989	If the event loop is suspended for a long time, you can also force an	2024	If the event loop is suspended for a long time, you can also force an
1990	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2025	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1991	()>.	2026	()>.
		2027
		2028	=head3 The special problem of unsynchronised clocks
		2029
		2030	Modern systems have a variety of clocks - libev itself uses the normal
		2031	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2032	jumps).
		2033
		2034	Neither of these clocks is synchronised with each other or any other clock
		2035	on the system, so C<ev_time ()> might return a considerably different time
		2036	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2037	a call to C<gettimeofday> might return a second count that is one higher
		2038	than a directly following call to C<time>.
		2039
		2040	The moral of this is to only compare libev-related timestamps with
		2041	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2042	a second or so.
		2043
		2044	One more problem arises due to this lack of synchronisation: if libev uses
		2045	the system monotonic clock and you compare timestamps from C<ev_time>
		2046	or C<ev_now> from when you started your timer and when your callback is
		2047	invoked, you will find that sometimes the callback is a bit "early".
		2048
		2049	This is because C<ev_timer>s work in real time, not wall clock time, so
		2050	libev makes sure your callback is not invoked before the delay happened,
		2051	I<measured according to the real time>, not the system clock.
		2052
		2053	If your timeouts are based on a physical timescale (e.g. "time out this
		2054	connection after 100 seconds") then this shouldn't bother you as it is
		2055	exactly the right behaviour.
		2056
		2057	If you want to compare wall clock/system timestamps to your timers, then
		2058	you need to use C<ev_periodic>s, as these are based on the wall clock
		2059	time, where your comparisons will always generate correct results.
1992		2060
1993	=head3 The special problems of suspended animation	2061	=head3 The special problems of suspended animation
1994		2062
1995	When you leave the server world it is quite customary to hit machines that	2063	When you leave the server world it is quite customary to hit machines that
1996	can suspend/hibernate - what happens to the clocks during such a suspend?	2064	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2040	keep up with the timer (because it takes longer than those 10 seconds to	2108	keep up with the timer (because it takes longer than those 10 seconds to
2041	do stuff) the timer will not fire more than once per event loop iteration.	2109	do stuff) the timer will not fire more than once per event loop iteration.
2042		2110
2043	=item ev_timer_again (loop, ev_timer *)	2111	=item ev_timer_again (loop, ev_timer *)
2044		2112
2045	This will act as if the timer timed out and restart it again if it is	2113	This will act as if the timer timed out, and restarts it again if it is
2046	repeating. The exact semantics are:	2114	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2115	timeout to the C<repeat> value and calling C<ev_timer_start>.
2047		2116
		2117	The exact semantics are as in the wollofing rules, all of which will be
		2118	applied to the watcher:
		2119
		2120	=over 4
		2121
2048	If the timer is pending, its pending status is cleared.	2122	=item If the timer is pending, the pending status is always cleared.
2049		2123
2050	If the timer is started but non-repeating, stop it (as if it timed out).	2124	=item If the timer is started but non-repeating, stop it (as if it timed
		2125	out, without invoking it).
2051		2126
2052	If the timer is repeating, either start it if necessary (with the	2127	=item If the timer is repeating, make the C<repeat> value the new timeout
2053	C<repeat> value), or reset the running timer to the C<repeat> value.	2128	and start the timer, if necessary.
		2129
		2130	=back
2054		2131
2055	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2132	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
2056	usage example.	2133	usage example.
2057		2134
2058	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2135	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
…		…
2180		2257
2181	Another way to think about it (for the mathematically inclined) is that	2258	Another way to think about it (for the mathematically inclined) is that
2182	C<ev_periodic> will try to run the callback in this mode at the next possible	2259	C<ev_periodic> will try to run the callback in this mode at the next possible
2183	time where C<time = offset (mod interval)>, regardless of any time jumps.	2260	time where C<time = offset (mod interval)>, regardless of any time jumps.
2184		2261
2185	For numerical stability it is preferable that the C<offset> value is near	2262	The C<interval> I<MUST> be positive, and for numerical stability, the
2186	C<ev_now ()> (the current time), but there is no range requirement for	2263	interval value should be higher than C<1/8192> (which is around 100
2187	this value, and in fact is often specified as zero.	2264	microseconds) and C<offset> should be higher than C<0> and should have
		2265	at most a similar magnitude as the current time (say, within a factor of
		2266	ten). Typical values for offset are, in fact, C<0> or something between
		2267	C<0> and C<interval>, which is also the recommended range.
2188		2268
2189	Note also that there is an upper limit to how often a timer can fire (CPU	2269	Note also that there is an upper limit to how often a timer can fire (CPU
2190	speed for example), so if C<interval> is very small then timing stability	2270	speed for example), so if C<interval> is very small then timing stability
2191	will of course deteriorate. Libev itself tries to be exact to be about one	2271	will of course deteriorate. Libev itself tries to be exact to be about one
2192	millisecond (if the OS supports it and the machine is fast enough).	2272	millisecond (if the OS supports it and the machine is fast enough).
…		…
2335	=head3 The special problem of inheritance over fork/execve/pthread_create	2415	=head3 The special problem of inheritance over fork/execve/pthread_create
2336		2416
2337	Both the signal mask (C<sigprocmask>) and the signal disposition	2417	Both the signal mask (C<sigprocmask>) and the signal disposition
2338	(C<sigaction>) are unspecified after starting a signal watcher (and after	2418	(C<sigaction>) are unspecified after starting a signal watcher (and after
2339	stopping it again), that is, libev might or might not block the signal,	2419	stopping it again), that is, libev might or might not block the signal,
2340	and might or might not set or restore the installed signal handler.	2420	and might or might not set or restore the installed signal handler (but
		2421	see C<EVFLAG_NOSIGMASK>).
2341		2422
2342	While this does not matter for the signal disposition (libev never	2423	While this does not matter for the signal disposition (libev never
2343	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2424	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2344	C<execve>), this matters for the signal mask: many programs do not expect	2425	C<execve>), this matters for the signal mask: many programs do not expect
2345	certain signals to be blocked.	2426	certain signals to be blocked.
…		…
3216	atexit (program_exits);	3297	atexit (program_exits);
3217		3298
3218		3299
3219	=head2 C<ev_async> - how to wake up an event loop	3300	=head2 C<ev_async> - how to wake up an event loop
3220		3301
3221	In general, you cannot use an C<ev_run> from multiple threads or other	3302	In general, you cannot use an C<ev_loop> from multiple threads or other
3222	asynchronous sources such as signal handlers (as opposed to multiple event	3303	asynchronous sources such as signal handlers (as opposed to multiple event
3223	loops - those are of course safe to use in different threads).	3304	loops - those are of course safe to use in different threads).
3224		3305
3225	Sometimes, however, you need to wake up an event loop you do not control,	3306	Sometimes, however, you need to wake up an event loop you do not control,
3226	for example because it belongs to another thread. This is what C<ev_async>	3307	for example because it belongs to another thread. This is what C<ev_async>
…		…
3233	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3314	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
3234	of "global async watchers" by using a watcher on an otherwise unused	3315	of "global async watchers" by using a watcher on an otherwise unused
3235	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3316	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3236	even without knowing which loop owns the signal.	3317	even without knowing which loop owns the signal.
3237		3318
3238	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3239	just the default loop.
3240
3241	=head3 Queueing	3319	=head3 Queueing
3242		3320
3243	C<ev_async> does not support queueing of data in any way. The reason	3321	C<ev_async> does not support queueing of data in any way. The reason
3244	is that the author does not know of a simple (or any) algorithm for a	3322	is that the author does not know of a simple (or any) algorithm for a
3245	multiple-writer-single-reader queue that works in all cases and doesn't	3323	multiple-writer-single-reader queue that works in all cases and doesn't
…		…
3336	trust me.	3414	trust me.
3337		3415
3338	=item ev_async_send (loop, ev_async *)	3416	=item ev_async_send (loop, ev_async *)
3339		3417
3340	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3418	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3341	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3419	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3420	returns.
		3421
3342	C<ev_feed_event>, this call is safe to do from other threads, signal or	3422	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3343	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3423	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3344	section below on what exactly this means).	3424	embedding section below on what exactly this means).
3345		3425
3346	Note that, as with other watchers in libev, multiple events might get	3426	Note that, as with other watchers in libev, multiple events might get
3347	compressed into a single callback invocation (another way to look at this	3427	compressed into a single callback invocation (another way to look at
3348	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3428	this is that C<ev_async> watchers are level-triggered: they are set on
3349	reset when the event loop detects that).	3429	C<ev_async_send>, reset when the event loop detects that).
3350		3430
3351	This call incurs the overhead of a system call only once per event loop	3431	This call incurs the overhead of at most one extra system call per event
3352	iteration, so while the overhead might be noticeable, it doesn't apply to	3432	loop iteration, if the event loop is blocked, and no syscall at all if
3353	repeated calls to C<ev_async_send> for the same event loop.	3433	the event loop (or your program) is processing events. That means that
		3434	repeated calls are basically free (there is no need to avoid calls for
		3435	performance reasons) and that the overhead becomes smaller (typically
		3436	zero) under load.
3354		3437
3355	=item bool = ev_async_pending (ev_async *)	3438	=item bool = ev_async_pending (ev_async *)
3356		3439
3357	Returns a non-zero value when C<ev_async_send> has been called on the	3440	Returns a non-zero value when C<ev_async_send> has been called on the
3358	watcher but the event has not yet been processed (or even noted) by the	3441	watcher but the event has not yet been processed (or even noted) by the
…		…
3413	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3496	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3414		3497
3415	=item ev_feed_fd_event (loop, int fd, int revents)	3498	=item ev_feed_fd_event (loop, int fd, int revents)
3416		3499
3417	Feed an event on the given fd, as if a file descriptor backend detected	3500	Feed an event on the given fd, as if a file descriptor backend detected
3418	the given events it.	3501	the given events.
3419		3502
3420	=item ev_feed_signal_event (loop, int signum)	3503	=item ev_feed_signal_event (loop, int signum)
3421		3504
3422	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3505	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3423	which is async-safe.	3506	which is async-safe.
…		…
3429		3512
3430	This section explains some common idioms that are not immediately	3513	This section explains some common idioms that are not immediately
3431	obvious. Note that examples are sprinkled over the whole manual, and this	3514	obvious. Note that examples are sprinkled over the whole manual, and this
3432	section only contains stuff that wouldn't fit anywhere else.	3515	section only contains stuff that wouldn't fit anywhere else.
3433		3516
3434	=over 4	3517	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3435		3518
3436	=item Model/nested event loop invocations and exit conditions.	3519	Each watcher has, by default, a C<void *data> member that you can read
		3520	or modify at any time: libev will completely ignore it. This can be used
		3521	to associate arbitrary data with your watcher. If you need more data and
		3522	don't want to allocate memory separately and store a pointer to it in that
		3523	data member, you can also "subclass" the watcher type and provide your own
		3524	data:
		3525
		3526	struct my_io
		3527	{
		3528	ev_io io;
		3529	int otherfd;
		3530	void *somedata;
		3531	struct whatever *mostinteresting;
		3532	};
		3533
		3534	...
		3535	struct my_io w;
		3536	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3537
		3538	And since your callback will be called with a pointer to the watcher, you
		3539	can cast it back to your own type:
		3540
		3541	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3542	{
		3543	struct my_io w = (struct my_io )w_;
		3544	...
		3545	}
		3546
		3547	More interesting and less C-conformant ways of casting your callback
		3548	function type instead have been omitted.
		3549
		3550	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3551
		3552	Another common scenario is to use some data structure with multiple
		3553	embedded watchers, in effect creating your own watcher that combines
		3554	multiple libev event sources into one "super-watcher":
		3555
		3556	struct my_biggy
		3557	{
		3558	int some_data;
		3559	ev_timer t1;
		3560	ev_timer t2;
		3561	}
		3562
		3563	In this case getting the pointer to C<my_biggy> is a bit more
		3564	complicated: Either you store the address of your C<my_biggy> struct in
		3565	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3566	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3567	real programmers):
		3568
		3569	#include <stddef.h>
		3570
		3571	static void
		3572	t1_cb (EV_P_ ev_timer *w, int revents)
		3573	{
		3574	struct my_biggy big = (struct my_biggy *)
		3575	(((char *)w) - offsetof (struct my_biggy, t1));
		3576	}
		3577
		3578	static void
		3579	t2_cb (EV_P_ ev_timer *w, int revents)
		3580	{
		3581	struct my_biggy big = (struct my_biggy *)
		3582	(((char *)w) - offsetof (struct my_biggy, t2));
		3583	}
		3584
		3585	=head2 AVOIDING FINISHING BEFORE RETURNING
		3586
		3587	Often you have structures like this in event-based programs:
		3588
		3589	callback ()
		3590	{
		3591	free (request);
		3592	}
		3593
		3594	request = start_new_request (..., callback);
		3595
		3596	The intent is to start some "lengthy" operation. The C<request> could be
		3597	used to cancel the operation, or do other things with it.
		3598
		3599	It's not uncommon to have code paths in C<start_new_request> that
		3600	immediately invoke the callback, for example, to report errors. Or you add
		3601	some caching layer that finds that it can skip the lengthy aspects of the
		3602	operation and simply invoke the callback with the result.
		3603
		3604	The problem here is that this will happen I<before> C<start_new_request>
		3605	has returned, so C<request> is not set.
		3606
		3607	Even if you pass the request by some safer means to the callback, you
		3608	might want to do something to the request after starting it, such as
		3609	canceling it, which probably isn't working so well when the callback has
		3610	already been invoked.
		3611
		3612	A common way around all these issues is to make sure that
		3613	C<start_new_request> I<always> returns before the callback is invoked. If
		3614	C<start_new_request> immediately knows the result, it can artificially
		3615	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3616	for example, or more sneakily, by reusing an existing (stopped) watcher
		3617	and pushing it into the pending queue:
		3618
		3619	ev_set_cb (watcher, callback);
		3620	ev_feed_event (EV_A_ watcher, 0);
		3621
		3622	This way, C<start_new_request> can safely return before the callback is
		3623	invoked, while not delaying callback invocation too much.
		3624
		3625	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3437		3626
3438	Often (especially in GUI toolkits) there are places where you have	3627	Often (especially in GUI toolkits) there are places where you have
3439	I<modal> interaction, which is most easily implemented by recursively	3628	I<modal> interaction, which is most easily implemented by recursively
3440	invoking C<ev_run>.	3629	invoking C<ev_run>.
3441		3630
…		…
3453	int exit_main_loop = 0;	3642	int exit_main_loop = 0;
3454		3643
3455	while (!exit_main_loop)	3644	while (!exit_main_loop)
3456	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3645	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3457		3646
3458	// in a model watcher	3647	// in a modal watcher
3459	int exit_nested_loop = 0;	3648	int exit_nested_loop = 0;
3460		3649
3461	while (!exit_nested_loop)	3650	while (!exit_nested_loop)
3462	ev_run (EV_A_ EVRUN_ONCE);	3651	ev_run (EV_A_ EVRUN_ONCE);
3463		3652
…		…
3470	exit_main_loop = 1;	3659	exit_main_loop = 1;
3471		3660
3472	// exit both	3661	// exit both
3473	exit_main_loop = exit_nested_loop = 1;	3662	exit_main_loop = exit_nested_loop = 1;
3474		3663
3475	=back	3664	=head2 THREAD LOCKING EXAMPLE
		3665
		3666	Here is a fictitious example of how to run an event loop in a different
		3667	thread from where callbacks are being invoked and watchers are
		3668	created/added/removed.
		3669
		3670	For a real-world example, see the C<EV::Loop::Async> perl module,
		3671	which uses exactly this technique (which is suited for many high-level
		3672	languages).
		3673
		3674	The example uses a pthread mutex to protect the loop data, a condition
		3675	variable to wait for callback invocations, an async watcher to notify the
		3676	event loop thread and an unspecified mechanism to wake up the main thread.
		3677
		3678	First, you need to associate some data with the event loop:
		3679
		3680	typedef struct {
		3681	mutex_t lock; /* global loop lock */
		3682	ev_async async_w;
		3683	thread_t tid;
		3684	cond_t invoke_cv;
		3685	} userdata;
		3686
		3687	void prepare_loop (EV_P)
		3688	{
		3689	// for simplicity, we use a static userdata struct.
		3690	static userdata u;
		3691
		3692	ev_async_init (&u->async_w, async_cb);
		3693	ev_async_start (EV_A_ &u->async_w);
		3694
		3695	pthread_mutex_init (&u->lock, 0);
		3696	pthread_cond_init (&u->invoke_cv, 0);
		3697
		3698	// now associate this with the loop
		3699	ev_set_userdata (EV_A_ u);
		3700	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3701	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3702
		3703	// then create the thread running ev_run
		3704	pthread_create (&u->tid, 0, l_run, EV_A);
		3705	}
		3706
		3707	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3708	solely to wake up the event loop so it takes notice of any new watchers
		3709	that might have been added:
		3710
		3711	static void
		3712	async_cb (EV_P_ ev_async *w, int revents)
		3713	{
		3714	// just used for the side effects
		3715	}
		3716
		3717	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3718	protecting the loop data, respectively.
		3719
		3720	static void
		3721	l_release (EV_P)
		3722	{
		3723	userdata *u = ev_userdata (EV_A);
		3724	pthread_mutex_unlock (&u->lock);
		3725	}
		3726
		3727	static void
		3728	l_acquire (EV_P)
		3729	{
		3730	userdata *u = ev_userdata (EV_A);
		3731	pthread_mutex_lock (&u->lock);
		3732	}
		3733
		3734	The event loop thread first acquires the mutex, and then jumps straight
		3735	into C<ev_run>:
		3736
		3737	void *
		3738	l_run (void *thr_arg)
		3739	{
		3740	struct ev_loop loop = (struct ev_loop )thr_arg;
		3741
		3742	l_acquire (EV_A);
		3743	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3744	ev_run (EV_A_ 0);
		3745	l_release (EV_A);
		3746
		3747	return 0;
		3748	}
		3749
		3750	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3751	signal the main thread via some unspecified mechanism (signals? pipe
		3752	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3753	have been called (in a while loop because a) spurious wakeups are possible
		3754	and b) skipping inter-thread-communication when there are no pending
		3755	watchers is very beneficial):
		3756
		3757	static void
		3758	l_invoke (EV_P)
		3759	{
		3760	userdata *u = ev_userdata (EV_A);
		3761
		3762	while (ev_pending_count (EV_A))
		3763	{
		3764	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3765	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3766	}
		3767	}
		3768
		3769	Now, whenever the main thread gets told to invoke pending watchers, it
		3770	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3771	thread to continue:
		3772
		3773	static void
		3774	real_invoke_pending (EV_P)
		3775	{
		3776	userdata *u = ev_userdata (EV_A);
		3777
		3778	pthread_mutex_lock (&u->lock);
		3779	ev_invoke_pending (EV_A);
		3780	pthread_cond_signal (&u->invoke_cv);
		3781	pthread_mutex_unlock (&u->lock);
		3782	}
		3783
		3784	Whenever you want to start/stop a watcher or do other modifications to an
		3785	event loop, you will now have to lock:
		3786
		3787	ev_timer timeout_watcher;
		3788	userdata *u = ev_userdata (EV_A);
		3789
		3790	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3791
		3792	pthread_mutex_lock (&u->lock);
		3793	ev_timer_start (EV_A_ &timeout_watcher);
		3794	ev_async_send (EV_A_ &u->async_w);
		3795	pthread_mutex_unlock (&u->lock);
		3796
		3797	Note that sending the C<ev_async> watcher is required because otherwise
		3798	an event loop currently blocking in the kernel will have no knowledge
		3799	about the newly added timer. By waking up the loop it will pick up any new
		3800	watchers in the next event loop iteration.
		3801
		3802	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3803
		3804	While the overhead of a callback that e.g. schedules a thread is small, it
		3805	is still an overhead. If you embed libev, and your main usage is with some
		3806	kind of threads or coroutines, you might want to customise libev so that
		3807	doesn't need callbacks anymore.
		3808
		3809	Imagine you have coroutines that you can switch to using a function
		3810	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3811	and that due to some magic, the currently active coroutine is stored in a
		3812	global called C<current_coro>. Then you can build your own "wait for libev
		3813	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3814	the differing C<;> conventions):
		3815
		3816	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3817	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3818
		3819	That means instead of having a C callback function, you store the
		3820	coroutine to switch to in each watcher, and instead of having libev call
		3821	your callback, you instead have it switch to that coroutine.
		3822
		3823	A coroutine might now wait for an event with a function called
		3824	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3825	matter when, or whether the watcher is active or not when this function is
		3826	called):
		3827
		3828	void
		3829	wait_for_event (ev_watcher *w)
		3830	{
		3831	ev_cb_set (w) = current_coro;
		3832	switch_to (libev_coro);
		3833	}
		3834
		3835	That basically suspends the coroutine inside C<wait_for_event> and
		3836	continues the libev coroutine, which, when appropriate, switches back to
		3837	this or any other coroutine.
		3838
		3839	You can do similar tricks if you have, say, threads with an event queue -
		3840	instead of storing a coroutine, you store the queue object and instead of
		3841	switching to a coroutine, you push the watcher onto the queue and notify
		3842	any waiters.
		3843
		3844	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3845	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3846
		3847	// my_ev.h
		3848	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3849	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3850	#include "../libev/ev.h"
		3851
		3852	// my_ev.c
		3853	#define EV_H "my_ev.h"
		3854	#include "../libev/ev.c"
		3855
		3856	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3857	F<my_ev.c> into your project. When properly specifying include paths, you
		3858	can even use F<ev.h> as header file name directly.
3476		3859
3477		3860
3478	=head1 LIBEVENT EMULATION	3861	=head1 LIBEVENT EMULATION
3479		3862
3480	Libev offers a compatibility emulation layer for libevent. It cannot	3863	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3552	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	3935	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3553		3936
3554	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	3937	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3555	the same name in the C<ev> namespace, with the exception of C<ev_signal>	3938	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3556	which is called C<ev::sig> to avoid clashes with the C<signal> macro	3939	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3557	defines by many implementations.	3940	defined by many implementations.
3558		3941
3559	All of those classes have these methods:	3942	All of those classes have these methods:
3560		3943
3561	=over 4	3944	=over 4
3562		3945
…		…
3695	watchers in the constructor.	4078	watchers in the constructor.
3696		4079
3697	class myclass	4080	class myclass
3698	{	4081	{
3699	ev::io io ; void io_cb (ev::io &w, int revents);	4082	ev::io io ; void io_cb (ev::io &w, int revents);
3700	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4083	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3701	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4084	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3702		4085
3703	myclass (int fd)	4086	myclass (int fd)
3704	{	4087	{
3705	io .set <myclass, &myclass::io_cb > (this);	4088	io .set <myclass, &myclass::io_cb > (this);
…		…
3756	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4139	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3757		4140
3758	=item D	4141	=item D
3759		4142
3760	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4143	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3761	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4144	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3762		4145
3763	=item Ocaml	4146	=item Ocaml
3764		4147
3765	Erkki Seppala has written Ocaml bindings for libev, to be found at	4148	Erkki Seppala has written Ocaml bindings for libev, to be found at
3766	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4149	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3814	suitable for use with C<EV_A>.	4197	suitable for use with C<EV_A>.
3815		4198
3816	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4199	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3817		4200
3818	Similar to the other two macros, this gives you the value of the default	4201	Similar to the other two macros, this gives you the value of the default
3819	loop, if multiple loops are supported ("ev loop default").	4202	loop, if multiple loops are supported ("ev loop default"). The default loop
		4203	will be initialised if it isn't already initialised.
		4204
		4205	For non-multiplicity builds, these macros do nothing, so you always have
		4206	to initialise the loop somewhere.
3820		4207
3821	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4208	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3822		4209
3823	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4210	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3824	default loop has been initialised (C<UC> == unchecked). Their behaviour	4211	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3969	supported). It will also not define any of the structs usually found in	4356	supported). It will also not define any of the structs usually found in
3970	F<event.h> that are not directly supported by the libev core alone.	4357	F<event.h> that are not directly supported by the libev core alone.
3971		4358
3972	In standalone mode, libev will still try to automatically deduce the	4359	In standalone mode, libev will still try to automatically deduce the
3973	configuration, but has to be more conservative.	4360	configuration, but has to be more conservative.
		4361
		4362	=item EV_USE_FLOOR
		4363
		4364	If defined to be C<1>, libev will use the C<floor ()> function for its
		4365	periodic reschedule calculations, otherwise libev will fall back on a
		4366	portable (slower) implementation. If you enable this, you usually have to
		4367	link against libm or something equivalent. Enabling this when the C<floor>
		4368	function is not available will fail, so the safe default is to not enable
		4369	this.
3974		4370
3975	=item EV_USE_MONOTONIC	4371	=item EV_USE_MONOTONIC
3976		4372
3977	If defined to be C<1>, libev will try to detect the availability of the	4373	If defined to be C<1>, libev will try to detect the availability of the
3978	monotonic clock option at both compile time and runtime. Otherwise no	4374	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4111	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4507	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4112		4508
4113	=item EV_ATOMIC_T	4509	=item EV_ATOMIC_T
4114		4510
4115	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4511	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4116	access is atomic with respect to other threads or signal contexts. No such	4512	access is atomic and serialised with respect to other threads or signal
4117	type is easily found in the C language, so you can provide your own type	4513	contexts. No such type is easily found in the C language, so you can
4118	that you know is safe for your purposes. It is used both for signal handler "locking"	4514	provide your own type that you know is safe for your purposes. It is used
4119	as well as for signal and thread safety in C<ev_async> watchers.	4515	both for signal handler "locking" as well as for signal and thread safety
		4516	in C<ev_async> watchers.
4120		4517
4121	In the absence of this define, libev will use C<sig_atomic_t volatile>	4518	In the absence of this define, libev will use C<sig_atomic_t volatile>
4122	(from F<signal.h>), which is usually good enough on most platforms.	4519	(from F<signal.h>), which is usually good enough on most platforms,
		4520	although strictly speaking using a type that also implies a memory fence
		4521	is required.
4123		4522
4124	=item EV_H (h)	4523	=item EV_H (h)
4125		4524
4126	The name of the F<ev.h> header file used to include it. The default if	4525	The name of the F<ev.h> header file used to include it. The default if
4127	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4526	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
4151	will have the C<struct ev_loop *> as first argument, and you can create	4550	will have the C<struct ev_loop *> as first argument, and you can create
4152	additional independent event loops. Otherwise there will be no support	4551	additional independent event loops. Otherwise there will be no support
4153	for multiple event loops and there is no first event loop pointer	4552	for multiple event loops and there is no first event loop pointer
4154	argument. Instead, all functions act on the single default loop.	4553	argument. Instead, all functions act on the single default loop.
4155		4554
		4555	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4556	default loop when multiplicity is switched off - you always have to
		4557	initialise the loop manually in this case.
		4558
4156	=item EV_MINPRI	4559	=item EV_MINPRI
4157		4560
4158	=item EV_MAXPRI	4561	=item EV_MAXPRI
4159		4562
4160	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4563	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4257		4660
4258	With an intelligent-enough linker (gcc+binutils are intelligent enough	4661	With an intelligent-enough linker (gcc+binutils are intelligent enough
4259	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4662	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4260	your program might be left out as well - a binary starting a timer and an	4663	your program might be left out as well - a binary starting a timer and an
4261	I/O watcher then might come out at only 5Kb.	4664	I/O watcher then might come out at only 5Kb.
		4665
		4666	=item EV_API_STATIC
		4667
		4668	If this symbol is defined (by default it is not), then all identifiers
		4669	will have static linkage. This means that libev will not export any
		4670	identifiers, and you cannot link against libev anymore. This can be useful
		4671	when you embed libev, only want to use libev functions in a single file,
		4672	and do not want its identifiers to be visible.
		4673
		4674	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4675	wants to use libev.
		4676
		4677	This option only works when libev is compiled with a C compiler, as C++
		4678	doesn't support the required declaration syntax.
4262		4679
4263	=item EV_AVOID_STDIO	4680	=item EV_AVOID_STDIO
4264		4681
4265	If this is set to C<1> at compiletime, then libev will avoid using stdio	4682	If this is set to C<1> at compiletime, then libev will avoid using stdio
4266	functions (printf, scanf, perror etc.). This will increase the code size	4683	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4410	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4827	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4411		4828
4412	#include "ev_cpp.h"	4829	#include "ev_cpp.h"
4413	#include "ev.c"	4830	#include "ev.c"
4414		4831
4415	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4832	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4416		4833
4417	=head2 THREADS AND COROUTINES	4834	=head2 THREADS AND COROUTINES
4418		4835
4419	=head3 THREADS	4836	=head3 THREADS
4420		4837
…		…
4471	default loop and triggering an C<ev_async> watcher from the default loop	4888	default loop and triggering an C<ev_async> watcher from the default loop
4472	watcher callback into the event loop interested in the signal.	4889	watcher callback into the event loop interested in the signal.
4473		4890
4474	=back	4891	=back
4475		4892
4476	=head4 THREAD LOCKING EXAMPLE	4893	See also L<THREAD LOCKING EXAMPLE>.
4477
4478	Here is a fictitious example of how to run an event loop in a different
4479	thread than where callbacks are being invoked and watchers are
4480	created/added/removed.
4481
4482	For a real-world example, see the C<EV::Loop::Async> perl module,
4483	which uses exactly this technique (which is suited for many high-level
4484	languages).
4485
4486	The example uses a pthread mutex to protect the loop data, a condition
4487	variable to wait for callback invocations, an async watcher to notify the
4488	event loop thread and an unspecified mechanism to wake up the main thread.
4489
4490	First, you need to associate some data with the event loop:
4491
4492	typedef struct {
4493	mutex_t lock; /* global loop lock */
4494	ev_async async_w;
4495	thread_t tid;
4496	cond_t invoke_cv;
4497	} userdata;
4498
4499	void prepare_loop (EV_P)
4500	{
4501	// for simplicity, we use a static userdata struct.
4502	static userdata u;
4503
4504	ev_async_init (&u->async_w, async_cb);
4505	ev_async_start (EV_A_ &u->async_w);
4506
4507	pthread_mutex_init (&u->lock, 0);
4508	pthread_cond_init (&u->invoke_cv, 0);
4509
4510	// now associate this with the loop
4511	ev_set_userdata (EV_A_ u);
4512	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4513	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4514
4515	// then create the thread running ev_loop
4516	pthread_create (&u->tid, 0, l_run, EV_A);
4517	}
4518
4519	The callback for the C<ev_async> watcher does nothing: the watcher is used
4520	solely to wake up the event loop so it takes notice of any new watchers
4521	that might have been added:
4522
4523	static void
4524	async_cb (EV_P_ ev_async *w, int revents)
4525	{
4526	// just used for the side effects
4527	}
4528
4529	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4530	protecting the loop data, respectively.
4531
4532	static void
4533	l_release (EV_P)
4534	{
4535	userdata *u = ev_userdata (EV_A);
4536	pthread_mutex_unlock (&u->lock);
4537	}
4538
4539	static void
4540	l_acquire (EV_P)
4541	{
4542	userdata *u = ev_userdata (EV_A);
4543	pthread_mutex_lock (&u->lock);
4544	}
4545
4546	The event loop thread first acquires the mutex, and then jumps straight
4547	into C<ev_run>:
4548
4549	void *
4550	l_run (void *thr_arg)
4551	{
4552	struct ev_loop loop = (struct ev_loop )thr_arg;
4553
4554	l_acquire (EV_A);
4555	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4556	ev_run (EV_A_ 0);
4557	l_release (EV_A);
4558
4559	return 0;
4560	}
4561
4562	Instead of invoking all pending watchers, the C<l_invoke> callback will
4563	signal the main thread via some unspecified mechanism (signals? pipe
4564	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4565	have been called (in a while loop because a) spurious wakeups are possible
4566	and b) skipping inter-thread-communication when there are no pending
4567	watchers is very beneficial):
4568
4569	static void
4570	l_invoke (EV_P)
4571	{
4572	userdata *u = ev_userdata (EV_A);
4573
4574	while (ev_pending_count (EV_A))
4575	{
4576	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4577	pthread_cond_wait (&u->invoke_cv, &u->lock);
4578	}
4579	}
4580
4581	Now, whenever the main thread gets told to invoke pending watchers, it
4582	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4583	thread to continue:
4584
4585	static void
4586	real_invoke_pending (EV_P)
4587	{
4588	userdata *u = ev_userdata (EV_A);
4589
4590	pthread_mutex_lock (&u->lock);
4591	ev_invoke_pending (EV_A);
4592	pthread_cond_signal (&u->invoke_cv);
4593	pthread_mutex_unlock (&u->lock);
4594	}
4595
4596	Whenever you want to start/stop a watcher or do other modifications to an
4597	event loop, you will now have to lock:
4598
4599	ev_timer timeout_watcher;
4600	userdata *u = ev_userdata (EV_A);
4601
4602	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4603
4604	pthread_mutex_lock (&u->lock);
4605	ev_timer_start (EV_A_ &timeout_watcher);
4606	ev_async_send (EV_A_ &u->async_w);
4607	pthread_mutex_unlock (&u->lock);
4608
4609	Note that sending the C<ev_async> watcher is required because otherwise
4610	an event loop currently blocking in the kernel will have no knowledge
4611	about the newly added timer. By waking up the loop it will pick up any new
4612	watchers in the next event loop iteration.
4613		4894
4614	=head3 COROUTINES	4895	=head3 COROUTINES
4615		4896
4616	Libev is very accommodating to coroutines ("cooperative threads"):	4897	Libev is very accommodating to coroutines ("cooperative threads"):
4617	libev fully supports nesting calls to its functions from different	4898	libev fully supports nesting calls to its functions from different
…		…
4782	requires, and its I/O model is fundamentally incompatible with the POSIX	5063	requires, and its I/O model is fundamentally incompatible with the POSIX
4783	model. Libev still offers limited functionality on this platform in	5064	model. Libev still offers limited functionality on this platform in
4784	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5065	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4785	descriptors. This only applies when using Win32 natively, not when using	5066	descriptors. This only applies when using Win32 natively, not when using
4786	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5067	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4787	as every compielr comes with a slightly differently broken/incompatible	5068	as every compiler comes with a slightly differently broken/incompatible
4788	environment.	5069	environment.
4789		5070
4790	Lifting these limitations would basically require the full	5071	Lifting these limitations would basically require the full
4791	re-implementation of the I/O system. If you are into this kind of thing,	5072	re-implementation of the I/O system. If you are into this kind of thing,
4792	then note that glib does exactly that for you in a very portable way (note	5073	then note that glib does exactly that for you in a very portable way (note
…		…
4925		5206
4926	The type C<double> is used to represent timestamps. It is required to	5207	The type C<double> is used to represent timestamps. It is required to
4927	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5208	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4928	good enough for at least into the year 4000 with millisecond accuracy	5209	good enough for at least into the year 4000 with millisecond accuracy
4929	(the design goal for libev). This requirement is overfulfilled by	5210	(the design goal for libev). This requirement is overfulfilled by
4930	implementations using IEEE 754, which is basically all existing ones. With	5211	implementations using IEEE 754, which is basically all existing ones.
		5212
4931	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5213	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5214	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5215	is either obsolete or somebody patched it to use C<long double> or
		5216	something like that, just kidding).
4932		5217
4933	=back	5218	=back
4934		5219
4935	If you know of other additional requirements drop me a note.	5220	If you know of other additional requirements drop me a note.
4936		5221
…		…
4998	=item Processing ev_async_send: O(number_of_async_watchers)	5283	=item Processing ev_async_send: O(number_of_async_watchers)
4999		5284
5000	=item Processing signals: O(max_signal_number)	5285	=item Processing signals: O(max_signal_number)
5001		5286
5002	Sending involves a system call I<iff> there were no other C<ev_async_send>	5287	Sending involves a system call I<iff> there were no other C<ev_async_send>
5003	calls in the current loop iteration. Checking for async and signal events	5288	calls in the current loop iteration and the loop is currently
		5289	blocked. Checking for async and signal events involves iterating over all
5004	involves iterating over all running async watchers or all signal numbers.	5290	running async watchers or all signal numbers.
5005		5291
5006	=back	5292	=back
5007		5293
5008		5294
5009	=head1 PORTING FROM LIBEV 3.X TO 4.X	5295	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5126	The physical time that is observed. It is apparently strictly monotonic :)	5412	The physical time that is observed. It is apparently strictly monotonic :)
5127		5413
5128	=item wall-clock time	5414	=item wall-clock time
5129		5415
5130	The time and date as shown on clocks. Unlike real time, it can actually	5416	The time and date as shown on clocks. Unlike real time, it can actually
5131	be wrong and jump forwards and backwards, e.g. when the you adjust your	5417	be wrong and jump forwards and backwards, e.g. when you adjust your
5132	clock.	5418	clock.
5133		5419
5134	=item watcher	5420	=item watcher
5135		5421
5136	A data structure that describes interest in certain events. Watchers need	5422	A data structure that describes interest in certain events. Watchers need
…		…
5139	=back	5425	=back
5140		5426
5141	=head1 AUTHOR	5427	=head1 AUTHOR
5142		5428
5143	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5429	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5144	Magnusson and Emanuele Giaquinta.	5430	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5145		5431

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Comparing libev/ev.pod (file contents): Revision 1.352 by root, Mon Jan 10 14:30:15 2011 UTC vs. Revision 1.394 by root, Tue Jan 24 16:37:12 2012 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.352 by root, Mon Jan 10 14:30:15 2011 UTC vs.
Revision 1.394 by root, Tue Jan 24 16:37:12 2012 UTC