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

Comparing libev/ev.pod (file contents):
Revision 1.241 by root, Sat Apr 25 14:23:26 2009 UTC vs.
Revision 1.265 by root, Wed Aug 26 17:11:42 2009 UTC

…		…
98	=head2 FEATURES	98	=head2 FEATURES
99		99
100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
104	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
105	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
106	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
107	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
108	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
109	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
110		111
111	It also is quite fast (see this	112	It also is quite fast (see this
112	L<benchmark\|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark\|http://libev.schmorp.de/bench.html> comparing it to libevent
113	for example).	114	for example).
114		115
…		…
361	forget about forgetting to tell libev about forking) when you use this	362	forget about forgetting to tell libev about forking) when you use this
362	flag.	363	flag.
363		364
364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
365	environment variable.	366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_NOSIGNALFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
366		382
367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
368		384
369	This is your standard select(2) backend. Not I<completely> standard, as	385	This is your standard select(2) backend. Not I<completely> standard, as
370	libev tries to roll its own fd_set with no limits on the number of fds,	386	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
518		534
519	It is definitely not recommended to use this flag.	535	It is definitely not recommended to use this flag.
520		536
521	=back	537	=back
522		538
523	If one or more of these are or'ed into the flags value, then only these	539	If one or more of the backend flags are or'ed into the flags value,
524	backends will be tried (in the reverse order as listed here). If none are	540	then only these backends will be tried (in the reverse order as listed
525	specified, all backends in C<ev_recommended_backends ()> will be tried.	541	here). If none are specified, all backends in C<ev_recommended_backends
		542	()> will be tried.
526		543
527	Example: This is the most typical usage.	544	Example: This is the most typical usage.
528		545
529	if (!ev_default_loop (0))	546	if (!ev_default_loop (0))
530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	547	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
620	happily wraps around with enough iterations.	637	happily wraps around with enough iterations.
621		638
622	This value can sometimes be useful as a generation counter of sorts (it	639	This value can sometimes be useful as a generation counter of sorts (it
623	"ticks" the number of loop iterations), as it roughly corresponds with	640	"ticks" the number of loop iterations), as it roughly corresponds with
624	C<ev_prepare> and C<ev_check> calls.	641	C<ev_prepare> and C<ev_check> calls.
		642
		643	=item unsigned int ev_loop_depth (loop)
		644
		645	Returns the number of times C<ev_loop> was entered minus the number of
		646	times C<ev_loop> was exited, in other words, the recursion depth.
		647
		648	Outside C<ev_loop>, this number is zero. In a callback, this number is
		649	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		650	in which case it is higher.
		651
		652	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		653	etc.), doesn't count as exit.
625		654
626	=item unsigned int ev_backend (loop)	655	=item unsigned int ev_backend (loop)
627		656
628	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	657	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
629	use.	658	use.
…		…
811		840
812	By setting a higher I<io collect interval> you allow libev to spend more	841	By setting a higher I<io collect interval> you allow libev to spend more
813	time collecting I/O events, so you can handle more events per iteration,	842	time collecting I/O events, so you can handle more events per iteration,
814	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	843	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
815	C<ev_timer>) will be not affected. Setting this to a non-null value will	844	C<ev_timer>) will be not affected. Setting this to a non-null value will
816	introduce an additional C<ev_sleep ()> call into most loop iterations.	845	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		846	sleep time ensures that libev will not poll for I/O events more often then
		847	once per this interval, on average.
817		848
818	Likewise, by setting a higher I<timeout collect interval> you allow libev	849	Likewise, by setting a higher I<timeout collect interval> you allow libev
819	to spend more time collecting timeouts, at the expense of increased	850	to spend more time collecting timeouts, at the expense of increased
820	latency/jitter/inexactness (the watcher callback will be called	851	latency/jitter/inexactness (the watcher callback will be called
821	later). C<ev_io> watchers will not be affected. Setting this to a non-null	852	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
823		854
824	Many (busy) programs can usually benefit by setting the I/O collect	855	Many (busy) programs can usually benefit by setting the I/O collect
825	interval to a value near C<0.1> or so, which is often enough for	856	interval to a value near C<0.1> or so, which is often enough for
826	interactive servers (of course not for games), likewise for timeouts. It	857	interactive servers (of course not for games), likewise for timeouts. It
827	usually doesn't make much sense to set it to a lower value than C<0.01>,	858	usually doesn't make much sense to set it to a lower value than C<0.01>,
828	as this approaches the timing granularity of most systems.	859	as this approaches the timing granularity of most systems. Note that if
		860	you do transactions with the outside world and you can't increase the
		861	parallelity, then this setting will limit your transaction rate (if you
		862	need to poll once per transaction and the I/O collect interval is 0.01,
		863	then you can't do more than 100 transations per second).
829		864
830	Setting the I<timeout collect interval> can improve the opportunity for	865	Setting the I<timeout collect interval> can improve the opportunity for
831	saving power, as the program will "bundle" timer callback invocations that	866	saving power, as the program will "bundle" timer callback invocations that
832	are "near" in time together, by delaying some, thus reducing the number of	867	are "near" in time together, by delaying some, thus reducing the number of
833	times the process sleeps and wakes up again. Another useful technique to	868	times the process sleeps and wakes up again. Another useful technique to
834	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	869	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
835	they fire on, say, one-second boundaries only.	870	they fire on, say, one-second boundaries only.
		871
		872	Example: we only need 0.1s timeout granularity, and we wish not to poll
		873	more often than 100 times per second:
		874
		875	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		876	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		877
		878	=item ev_invoke_pending (loop)
		879
		880	This call will simply invoke all pending watchers while resetting their
		881	pending state. Normally, C<ev_loop> does this automatically when required,
		882	but when overriding the invoke callback this call comes handy.
		883
		884	=item int ev_pending_count (loop)
		885
		886	Returns the number of pending watchers - zero indicates that no watchers
		887	are pending.
		888
		889	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		890
		891	This overrides the invoke pending functionality of the loop: Instead of
		892	invoking all pending watchers when there are any, C<ev_loop> will call
		893	this callback instead. This is useful, for example, when you want to
		894	invoke the actual watchers inside another context (another thread etc.).
		895
		896	If you want to reset the callback, use C<ev_invoke_pending> as new
		897	callback.
		898
		899	=item ev_set_loop_release_cb (loop, void (release)(EV_P), void (acquire)(EV_P))
		900
		901	Sometimes you want to share the same loop between multiple threads. This
		902	can be done relatively simply by putting mutex_lock/unlock calls around
		903	each call to a libev function.
		904
		905	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		906	wait for it to return. One way around this is to wake up the loop via
		907	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		908	and I<acquire> callbacks on the loop.
		909
		910	When set, then C<release> will be called just before the thread is
		911	suspended waiting for new events, and C<acquire> is called just
		912	afterwards.
		913
		914	Ideally, C<release> will just call your mutex_unlock function, and
		915	C<acquire> will just call the mutex_lock function again.
		916
		917	While event loop modifications are allowed between invocations of
		918	C<release> and C<acquire> (that's their only purpose after all), no
		919	modifications done will affect the event loop, i.e. adding watchers will
		920	have no effect on the set of file descriptors being watched, or the time
		921	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		922	to take note of any changes you made.
		923
		924	In theory, threads executing C<ev_loop> will be async-cancel safe between
		925	invocations of C<release> and C<acquire>.
		926
		927	See also the locking example in the C<THREADS> section later in this
		928	document.
		929
		930	=item ev_set_userdata (loop, void *data)
		931
		932	=item ev_userdata (loop)
		933
		934	Set and retrieve a single C<void *> associated with a loop. When
		935	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		936	C<0.>
		937
		938	These two functions can be used to associate arbitrary data with a loop,
		939	and are intended solely for the C<invoke_pending_cb>, C<release> and
		940	C<acquire> callbacks described above, but of course can be (ab-)used for
		941	any other purpose as well.
836		942
837	=item ev_loop_verify (loop)	943	=item ev_loop_verify (loop)
838		944
839	This function only does something when C<EV_VERIFY> support has been	945	This function only does something when C<EV_VERIFY> support has been
840	compiled in, which is the default for non-minimal builds. It tries to go	946	compiled in, which is the default for non-minimal builds. It tries to go
…		…
1184	#include <stddef.h>	1290	#include <stddef.h>
1185		1291
1186	static void	1292	static void
1187	t1_cb (EV_P_ ev_timer *w, int revents)	1293	t1_cb (EV_P_ ev_timer *w, int revents)
1188	{	1294	{
1189	struct my_biggy big = (struct my_biggy *	1295	struct my_biggy big = (struct my_biggy *)
1190	(((char *)w) - offsetof (struct my_biggy, t1));	1296	(((char *)w) - offsetof (struct my_biggy, t1));
1191	}	1297	}
1192		1298
1193	static void	1299	static void
1194	t2_cb (EV_P_ ev_timer *w, int revents)	1300	t2_cb (EV_P_ ev_timer *w, int revents)
1195	{	1301	{
1196	struct my_biggy big = (struct my_biggy *	1302	struct my_biggy big = (struct my_biggy *)
1197	(((char *)w) - offsetof (struct my_biggy, t2));	1303	(((char *)w) - offsetof (struct my_biggy, t2));
1198	}	1304	}
1199		1305
1200	=head2 WATCHER PRIORITY MODELS	1306	=head2 WATCHER PRIORITY MODELS
1201		1307
…		…
1277	// with the default priority are receiving events.	1383	// with the default priority are receiving events.
1278	ev_idle_start (EV_A_ &idle);	1384	ev_idle_start (EV_A_ &idle);
1279	}	1385	}
1280		1386
1281	static void	1387	static void
1282	idle-cb (EV_P_ ev_idle *w, int revents)	1388	idle_cb (EV_P_ ev_idle *w, int revents)
1283	{	1389	{
1284	// actual processing	1390	// actual processing
1285	read (STDIN_FILENO, ...);	1391	read (STDIN_FILENO, ...);
1286		1392
1287	// have to start the I/O watcher again, as	1393	// have to start the I/O watcher again, as
…		…
1468		1574
1469	The callback is guaranteed to be invoked only I<after> its timeout has	1575	The callback is guaranteed to be invoked only I<after> its timeout has
1470	passed (not I<at>, so on systems with very low-resolution clocks this	1576	passed (not I<at>, so on systems with very low-resolution clocks this
1471	might introduce a small delay). If multiple timers become ready during the	1577	might introduce a small delay). If multiple timers become ready during the
1472	same loop iteration then the ones with earlier time-out values are invoked	1578	same loop iteration then the ones with earlier time-out values are invoked
1473	before ones with later time-out values (but this is no longer true when a	1579	before ones of the same priority with later time-out values (but this is
1474	callback calls C<ev_loop> recursively).	1580	no longer true when a callback calls C<ev_loop> recursively).
1475		1581
1476	=head3 Be smart about timeouts	1582	=head3 Be smart about timeouts
1477		1583
1478	Many real-world problems involve some kind of timeout, usually for error	1584	Many real-world problems involve some kind of timeout, usually for error
1479	recovery. A typical example is an HTTP request - if the other side hangs,	1585	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1523	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1629	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1524	member and C<ev_timer_again>.	1630	member and C<ev_timer_again>.
1525		1631
1526	At start:	1632	At start:
1527		1633
1528	ev_timer_init (timer, callback);	1634	ev_init (timer, callback);
1529	timer->repeat = 60.;	1635	timer->repeat = 60.;
1530	ev_timer_again (loop, timer);	1636	ev_timer_again (loop, timer);
1531		1637
1532	Each time there is some activity:	1638	Each time there is some activity:
1533		1639
…		…
1595		1701
1596	To start the timer, simply initialise the watcher and set C<last_activity>	1702	To start the timer, simply initialise the watcher and set C<last_activity>
1597	to the current time (meaning we just have some activity :), then call the	1703	to the current time (meaning we just have some activity :), then call the
1598	callback, which will "do the right thing" and start the timer:	1704	callback, which will "do the right thing" and start the timer:
1599		1705
1600	ev_timer_init (timer, callback);	1706	ev_init (timer, callback);
1601	last_activity = ev_now (loop);	1707	last_activity = ev_now (loop);
1602	callback (loop, timer, EV_TIMEOUT);	1708	callback (loop, timer, EV_TIMEOUT);
1603		1709
1604	And when there is some activity, simply store the current time in	1710	And when there is some activity, simply store the current time in
1605	C<last_activity>, no libev calls at all:	1711	C<last_activity>, no libev calls at all:
…		…
1666		1772
1667	If the event loop is suspended for a long time, you can also force an	1773	If the event loop is suspended for a long time, you can also force an
1668	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1774	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1669	()>.	1775	()>.
1670		1776
		1777	=head3 The special problems of suspended animation
		1778
		1779	When you leave the server world it is quite customary to hit machines that
		1780	can suspend/hibernate - what happens to the clocks during such a suspend?
		1781
		1782	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1783	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1784	to run until the system is suspended, but they will not advance while the
		1785	system is suspended. That means, on resume, it will be as if the program
		1786	was frozen for a few seconds, but the suspend time will not be counted
		1787	towards C<ev_timer> when a monotonic clock source is used. The real time
		1788	clock advanced as expected, but if it is used as sole clocksource, then a
		1789	long suspend would be detected as a time jump by libev, and timers would
		1790	be adjusted accordingly.
		1791
		1792	I would not be surprised to see different behaviour in different between
		1793	operating systems, OS versions or even different hardware.
		1794
		1795	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1796	time jump in the monotonic clocks and the realtime clock. If the program
		1797	is suspended for a very long time, and monotonic clock sources are in use,
		1798	then you can expect C<ev_timer>s to expire as the full suspension time
		1799	will be counted towards the timers. When no monotonic clock source is in
		1800	use, then libev will again assume a timejump and adjust accordingly.
		1801
		1802	It might be beneficial for this latter case to call C<ev_suspend>
		1803	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1804	deterministic behaviour in this case (you can do nothing against
		1805	C<SIGSTOP>).
		1806
1671	=head3 Watcher-Specific Functions and Data Members	1807	=head3 Watcher-Specific Functions and Data Members
1672		1808
1673	=over 4	1809	=over 4
1674		1810
1675	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1811	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1700	If the timer is repeating, either start it if necessary (with the	1836	If the timer is repeating, either start it if necessary (with the
1701	C<repeat> value), or reset the running timer to the C<repeat> value.	1837	C<repeat> value), or reset the running timer to the C<repeat> value.
1702		1838
1703	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	1839	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1704	usage example.	1840	usage example.
		1841
		1842	=item ev_timer_remaining (loop, ev_timer *)
		1843
		1844	Returns the remaining time until a timer fires. If the timer is active,
		1845	then this time is relative to the current event loop time, otherwise it's
		1846	the timeout value currently configured.
		1847
		1848	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1849	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1850	will return C<4>. When the timer expires and is restarted, it will return
		1851	roughly C<7> (likely slightly less as callback invocation takes some time,
		1852	too), and so on.
1705		1853
1706	=item ev_tstamp repeat [read-write]	1854	=item ev_tstamp repeat [read-write]
1707		1855
1708	The current C<repeat> value. Will be used each time the watcher times out	1856	The current C<repeat> value. Will be used each time the watcher times out
1709	or C<ev_timer_again> is called, and determines the next timeout (if any),	1857	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1945	Signal watchers will trigger an event when the process receives a specific	2093	Signal watchers will trigger an event when the process receives a specific
1946	signal one or more times. Even though signals are very asynchronous, libev	2094	signal one or more times. Even though signals are very asynchronous, libev
1947	will try it's best to deliver signals synchronously, i.e. as part of the	2095	will try it's best to deliver signals synchronously, i.e. as part of the
1948	normal event processing, like any other event.	2096	normal event processing, like any other event.
1949		2097
1950	If you want signals asynchronously, just use C<sigaction> as you would	2098	If you want signals to be delivered truly asynchronously, just use
1951	do without libev and forget about sharing the signal. You can even use	2099	C<sigaction> as you would do without libev and forget about sharing
1952	C<ev_async> from a signal handler to synchronously wake up an event loop.	2100	the signal. You can even use C<ev_async> from a signal handler to
		2101	synchronously wake up an event loop.
1953		2102
1954	You can configure as many watchers as you like per signal. Only when the	2103	You can configure as many watchers as you like for the same signal, but
		2104	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2105	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2106	C<SIGINT> in both the default loop and another loop at the same time. At
		2107	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2108
1955	first watcher gets started will libev actually register a signal handler	2109	When the first watcher gets started will libev actually register something
1956	with the kernel (thus it coexists with your own signal handlers as long as	2110	with the kernel (thus it coexists with your own signal handlers as long as
1957	you don't register any with libev for the same signal). Similarly, when	2111	you don't register any with libev for the same signal).
1958	the last signal watcher for a signal is stopped, libev will reset the
1959	signal handler to SIG_DFL (regardless of what it was set to before).
1960		2112
1961	If possible and supported, libev will install its handlers with	2113	If possible and supported, libev will install its handlers with
1962	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2114	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1963	interrupted. If you have a problem with system calls getting interrupted by	2115	not be unduly interrupted. If you have a problem with system calls getting
1964	signals you can block all signals in an C<ev_check> watcher and unblock	2116	interrupted by signals you can block all signals in an C<ev_check> watcher
1965	them in an C<ev_prepare> watcher.	2117	and unblock them in an C<ev_prepare> watcher.
		2118
		2119	=head3 The special problem of inheritance over execve
		2120
		2121	Both the signal mask (C<sigprocmask>) and the signal disposition
		2122	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2123	stopping it again), that is, libev might or might not block the signal,
		2124	and might or might not set or restore the installed signal handler.
		2125
		2126	While this does not matter for the signal disposition (libev never
		2127	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2128	C<execve>), this matters for the signal mask: many programs do not expect
		2129	many signals to be blocked.
		2130
		2131	This means that before calling C<exec> (from the child) you should reset
		2132	the signal mask to whatever "default" you expect (all clear is a good
		2133	choice usually).
1966		2134
1967	=head3 Watcher-Specific Functions and Data Members	2135	=head3 Watcher-Specific Functions and Data Members
1968		2136
1969	=over 4	2137	=over 4
1970		2138
…		…
2002	some child status changes (most typically when a child of yours dies or	2170	some child status changes (most typically when a child of yours dies or
2003	exits). It is permissible to install a child watcher I<after> the child	2171	exits). It is permissible to install a child watcher I<after> the child
2004	has been forked (which implies it might have already exited), as long	2172	has been forked (which implies it might have already exited), as long
2005	as the event loop isn't entered (or is continued from a watcher), i.e.,	2173	as the event loop isn't entered (or is continued from a watcher), i.e.,
2006	forking and then immediately registering a watcher for the child is fine,	2174	forking and then immediately registering a watcher for the child is fine,
2007	but forking and registering a watcher a few event loop iterations later is	2175	but forking and registering a watcher a few event loop iterations later or
2008	not.	2176	in the next callback invocation is not.
2009		2177
2010	Only the default event loop is capable of handling signals, and therefore	2178	Only the default event loop is capable of handling signals, and therefore
2011	you can only register child watchers in the default event loop.	2179	you can only register child watchers in the default event loop.
2012		2180
		2181	Due to some design glitches inside libev, child watchers will always be
		2182	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2183	libev)
		2184
2013	=head3 Process Interaction	2185	=head3 Process Interaction
2014		2186
2015	Libev grabs C<SIGCHLD> as soon as the default event loop is	2187	Libev grabs C<SIGCHLD> as soon as the default event loop is
2016	initialised. This is necessary to guarantee proper behaviour even if	2188	initialised. This is necessary to guarantee proper behaviour even if the
2017	the first child watcher is started after the child exits. The occurrence	2189	first child watcher is started after the child exits. The occurrence
2018	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2190	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
2019	synchronously as part of the event loop processing. Libev always reaps all	2191	synchronously as part of the event loop processing. Libev always reaps all
2020	children, even ones not watched.	2192	children, even ones not watched.
2021		2193
2022	=head3 Overriding the Built-In Processing	2194	=head3 Overriding the Built-In Processing
…		…
2032	=head3 Stopping the Child Watcher	2204	=head3 Stopping the Child Watcher
2033		2205
2034	Currently, the child watcher never gets stopped, even when the	2206	Currently, the child watcher never gets stopped, even when the
2035	child terminates, so normally one needs to stop the watcher in the	2207	child terminates, so normally one needs to stop the watcher in the
2036	callback. Future versions of libev might stop the watcher automatically	2208	callback. Future versions of libev might stop the watcher automatically
2037	when a child exit is detected.	2209	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2210	problem).
2038		2211
2039	=head3 Watcher-Specific Functions and Data Members	2212	=head3 Watcher-Specific Functions and Data Members
2040		2213
2041	=over 4	2214	=over 4
2042		2215
…		…
2368	// no longer anything immediate to do.	2541	// no longer anything immediate to do.
2369	}	2542	}
2370		2543
2371	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2544	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2372	ev_idle_init (idle_watcher, idle_cb);	2545	ev_idle_init (idle_watcher, idle_cb);
2373	ev_idle_start (loop, idle_cb);	2546	ev_idle_start (loop, idle_watcher);
2374		2547
2375		2548
2376	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2549	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2377		2550
2378	Prepare and check watchers are usually (but not always) used in pairs:	2551	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2471	struct pollfd fds [nfd];	2644	struct pollfd fds [nfd];
2472	// actual code will need to loop here and realloc etc.	2645	// actual code will need to loop here and realloc etc.
2473	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2646	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2474		2647
2475	/* the callback is illegal, but won't be called as we stop during check */	2648	/* the callback is illegal, but won't be called as we stop during check */
2476	ev_timer_init (&tw, 0, timeout * 1e-3);	2649	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2477	ev_timer_start (loop, &tw);	2650	ev_timer_start (loop, &tw);
2478		2651
2479	// create one ev_io per pollfd	2652	// create one ev_io per pollfd
2480	for (int i = 0; i < nfd; ++i)	2653	for (int i = 0; i < nfd; ++i)
2481	{	2654	{
…		…
3245	=item Ocaml	3418	=item Ocaml
3246		3419
3247	Erkki Seppala has written Ocaml bindings for libev, to be found at	3420	Erkki Seppala has written Ocaml bindings for libev, to be found at
3248	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	3421	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
3249		3422
		3423	=item Lua
		3424
		3425	Brian Maher has written a partial interface to libev
		3426	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3427	L<http://github.com/brimworks/lua-ev>.
		3428
3250	=back	3429	=back
3251		3430
3252		3431
3253	=head1 MACRO MAGIC	3432	=head1 MACRO MAGIC
3254		3433
…		…
3420	keeps libev from including F<config.h>, and it also defines dummy	3599	keeps libev from including F<config.h>, and it also defines dummy
3421	implementations for some libevent functions (such as logging, which is not	3600	implementations for some libevent functions (such as logging, which is not
3422	supported). It will also not define any of the structs usually found in	3601	supported). It will also not define any of the structs usually found in
3423	F<event.h> that are not directly supported by the libev core alone.	3602	F<event.h> that are not directly supported by the libev core alone.
3424		3603
3425	In stanbdalone mode, libev will still try to automatically deduce the	3604	In standalone mode, libev will still try to automatically deduce the
3426	configuration, but has to be more conservative.	3605	configuration, but has to be more conservative.
3427		3606
3428	=item EV_USE_MONOTONIC	3607	=item EV_USE_MONOTONIC
3429		3608
3430	If defined to be C<1>, libev will try to detect the availability of the	3609	If defined to be C<1>, libev will try to detect the availability of the
…		…
3495	be used is the winsock select). This means that it will call	3674	be used is the winsock select). This means that it will call
3496	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3675	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3497	it is assumed that all these functions actually work on fds, even	3676	it is assumed that all these functions actually work on fds, even
3498	on win32. Should not be defined on non-win32 platforms.	3677	on win32. Should not be defined on non-win32 platforms.
3499		3678
3500	=item EV_FD_TO_WIN32_HANDLE	3679	=item EV_FD_TO_WIN32_HANDLE(fd)
3501		3680
3502	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3681	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3503	file descriptors to socket handles. When not defining this symbol (the	3682	file descriptors to socket handles. When not defining this symbol (the
3504	default), then libev will call C<_get_osfhandle>, which is usually	3683	default), then libev will call C<_get_osfhandle>, which is usually
3505	correct. In some cases, programs use their own file descriptor management,	3684	correct. In some cases, programs use their own file descriptor management,
3506	in which case they can provide this function to map fds to socket handles.	3685	in which case they can provide this function to map fds to socket handles.
		3686
		3687	=item EV_WIN32_HANDLE_TO_FD(handle)
		3688
		3689	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3690	using the standard C<_open_osfhandle> function. For programs implementing
		3691	their own fd to handle mapping, overwriting this function makes it easier
		3692	to do so. This can be done by defining this macro to an appropriate value.
		3693
		3694	=item EV_WIN32_CLOSE_FD(fd)
		3695
		3696	If programs implement their own fd to handle mapping on win32, then this
		3697	macro can be used to override the C<close> function, useful to unregister
		3698	file descriptors again. Note that the replacement function has to close
		3699	the underlying OS handle.
3507		3700
3508	=item EV_USE_POLL	3701	=item EV_USE_POLL
3509		3702
3510	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3703	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3511	backend. Otherwise it will be enabled on non-win32 platforms. It	3704	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3643	defined to be C<0>, then they are not.	3836	defined to be C<0>, then they are not.
3644		3837
3645	=item EV_MINIMAL	3838	=item EV_MINIMAL
3646		3839
3647	If you need to shave off some kilobytes of code at the expense of some	3840	If you need to shave off some kilobytes of code at the expense of some
3648	speed, define this symbol to C<1>. Currently this is used to override some	3841	speed (but with the full API), define this symbol to C<1>. Currently this
3649	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3842	is used to override some inlining decisions, saves roughly 30% code size
3650	much smaller 2-heap for timer management over the default 4-heap.	3843	on amd64. It also selects a much smaller 2-heap for timer management over
		3844	the default 4-heap.
		3845
		3846	You can save even more by disabling watcher types you do not need
		3847	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3848	(C<-DNDEBUG>) will usually reduce code size a lot.
		3849
		3850	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3851	provide a bare-bones event library. See C<ev.h> for details on what parts
		3852	of the API are still available, and do not complain if this subset changes
		3853	over time.
		3854
		3855	=item EV_NSIG
		3856
		3857	The highest supported signal number, +1 (or, the number of
		3858	signals): Normally, libev tries to deduce the maximum number of signals
		3859	automatically, but sometimes this fails, in which case it can be
		3860	specified. Also, using a lower number than detected (C<32> should be
		3861	good for about any system in existance) can save some memory, as libev
		3862	statically allocates some 12-24 bytes per signal number.
3651		3863
3652	=item EV_PID_HASHSIZE	3864	=item EV_PID_HASHSIZE
3653		3865
3654	C<ev_child> watchers use a small hash table to distribute workload by	3866	C<ev_child> watchers use a small hash table to distribute workload by
3655	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3867	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3841	default loop and triggering an C<ev_async> watcher from the default loop	4053	default loop and triggering an C<ev_async> watcher from the default loop
3842	watcher callback into the event loop interested in the signal.	4054	watcher callback into the event loop interested in the signal.
3843		4055
3844	=back	4056	=back
3845		4057
		4058	=head4 THREAD LOCKING EXAMPLE
		4059
		4060	Here is a fictitious example of how to run an event loop in a different
		4061	thread than where callbacks are being invoked and watchers are
		4062	created/added/removed.
		4063
		4064	For a real-world example, see the C<EV::Loop::Async> perl module,
		4065	which uses exactly this technique (which is suited for many high-level
		4066	languages).
		4067
		4068	The example uses a pthread mutex to protect the loop data, a condition
		4069	variable to wait for callback invocations, an async watcher to notify the
		4070	event loop thread and an unspecified mechanism to wake up the main thread.
		4071
		4072	First, you need to associate some data with the event loop:
		4073
		4074	typedef struct {
		4075	mutex_t lock; /* global loop lock */
		4076	ev_async async_w;
		4077	thread_t tid;
		4078	cond_t invoke_cv;
		4079	} userdata;
		4080
		4081	void prepare_loop (EV_P)
		4082	{
		4083	// for simplicity, we use a static userdata struct.
		4084	static userdata u;
		4085
		4086	ev_async_init (&u->async_w, async_cb);
		4087	ev_async_start (EV_A_ &u->async_w);
		4088
		4089	pthread_mutex_init (&u->lock, 0);
		4090	pthread_cond_init (&u->invoke_cv, 0);
		4091
		4092	// now associate this with the loop
		4093	ev_set_userdata (EV_A_ u);
		4094	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4095	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4096
		4097	// then create the thread running ev_loop
		4098	pthread_create (&u->tid, 0, l_run, EV_A);
		4099	}
		4100
		4101	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4102	solely to wake up the event loop so it takes notice of any new watchers
		4103	that might have been added:
		4104
		4105	static void
		4106	async_cb (EV_P_ ev_async *w, int revents)
		4107	{
		4108	// just used for the side effects
		4109	}
		4110
		4111	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4112	protecting the loop data, respectively.
		4113
		4114	static void
		4115	l_release (EV_P)
		4116	{
		4117	userdata *u = ev_userdata (EV_A);
		4118	pthread_mutex_unlock (&u->lock);
		4119	}
		4120
		4121	static void
		4122	l_acquire (EV_P)
		4123	{
		4124	userdata *u = ev_userdata (EV_A);
		4125	pthread_mutex_lock (&u->lock);
		4126	}
		4127
		4128	The event loop thread first acquires the mutex, and then jumps straight
		4129	into C<ev_loop>:
		4130
		4131	void *
		4132	l_run (void *thr_arg)
		4133	{
		4134	struct ev_loop loop = (struct ev_loop )thr_arg;
		4135
		4136	l_acquire (EV_A);
		4137	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4138	ev_loop (EV_A_ 0);
		4139	l_release (EV_A);
		4140
		4141	return 0;
		4142	}
		4143
		4144	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4145	signal the main thread via some unspecified mechanism (signals? pipe
		4146	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4147	have been called (in a while loop because a) spurious wakeups are possible
		4148	and b) skipping inter-thread-communication when there are no pending
		4149	watchers is very beneficial):
		4150
		4151	static void
		4152	l_invoke (EV_P)
		4153	{
		4154	userdata *u = ev_userdata (EV_A);
		4155
		4156	while (ev_pending_count (EV_A))
		4157	{
		4158	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4159	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4160	}
		4161	}
		4162
		4163	Now, whenever the main thread gets told to invoke pending watchers, it
		4164	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4165	thread to continue:
		4166
		4167	static void
		4168	real_invoke_pending (EV_P)
		4169	{
		4170	userdata *u = ev_userdata (EV_A);
		4171
		4172	pthread_mutex_lock (&u->lock);
		4173	ev_invoke_pending (EV_A);
		4174	pthread_cond_signal (&u->invoke_cv);
		4175	pthread_mutex_unlock (&u->lock);
		4176	}
		4177
		4178	Whenever you want to start/stop a watcher or do other modifications to an
		4179	event loop, you will now have to lock:
		4180
		4181	ev_timer timeout_watcher;
		4182	userdata *u = ev_userdata (EV_A);
		4183
		4184	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4185
		4186	pthread_mutex_lock (&u->lock);
		4187	ev_timer_start (EV_A_ &timeout_watcher);
		4188	ev_async_send (EV_A_ &u->async_w);
		4189	pthread_mutex_unlock (&u->lock);
		4190
		4191	Note that sending the C<ev_async> watcher is required because otherwise
		4192	an event loop currently blocking in the kernel will have no knowledge
		4193	about the newly added timer. By waking up the loop it will pick up any new
		4194	watchers in the next event loop iteration.
		4195
3846	=head3 COROUTINES	4196	=head3 COROUTINES
3847		4197
3848	Libev is very accommodating to coroutines ("cooperative threads"):	4198	Libev is very accommodating to coroutines ("cooperative threads"):
3849	libev fully supports nesting calls to its functions from different	4199	libev fully supports nesting calls to its functions from different
3850	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4200	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3851	different coroutines, and switch freely between both coroutines running the	4201	different coroutines, and switch freely between both coroutines running
3852	loop, as long as you don't confuse yourself). The only exception is that	4202	the loop, as long as you don't confuse yourself). The only exception is
3853	you must not do this from C<ev_periodic> reschedule callbacks.	4203	that you must not do this from C<ev_periodic> reschedule callbacks.
3854		4204
3855	Care has been taken to ensure that libev does not keep local state inside	4205	Care has been taken to ensure that libev does not keep local state inside
3856	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4206	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3857	they do not call any callbacks.	4207	they do not call any callbacks.
3858		4208
…		…
4065	=item C<double> must hold a time value in seconds with enough accuracy	4415	=item C<double> must hold a time value in seconds with enough accuracy
4066		4416
4067	The type C<double> is used to represent timestamps. It is required to	4417	The type C<double> is used to represent timestamps. It is required to
4068	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4418	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
4069	enough for at least into the year 4000. This requirement is fulfilled by	4419	enough for at least into the year 4000. This requirement is fulfilled by
4070	implementations implementing IEEE 754 (basically all existing ones).	4420	implementations implementing IEEE 754, which is basically all existing
		4421	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4422	2200.
4071		4423
4072	=back	4424	=back
4073		4425
4074	If you know of other additional requirements drop me a note.	4426	If you know of other additional requirements drop me a note.
4075		4427

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Comparing libev/ev.pod (file contents): Revision 1.241 by root, Sat Apr 25 14:23:26 2009 UTC vs. Revision 1.265 by root, Wed Aug 26 17:11:42 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.241 by root, Sat Apr 25 14:23:26 2009 UTC vs.
Revision 1.265 by root, Wed Aug 26 17:11:42 2009 UTC