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

Comparing libev/ev.pod (file contents):
Revision 1.238 by root, Sat Apr 18 12:10:41 2009 UTC vs.
Revision 1.264 by root, Wed Aug 19 23:44:51 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
…		…
1332	descriptors to non-blocking mode is also usually a good idea (but not	1438	descriptors to non-blocking mode is also usually a good idea (but not
1333	required if you know what you are doing).	1439	required if you know what you are doing).
1334		1440
1335	If you cannot use non-blocking mode, then force the use of a	1441	If you cannot use non-blocking mode, then force the use of a
1336	known-to-be-good backend (at the time of this writing, this includes only	1442	known-to-be-good backend (at the time of this writing, this includes only
1337	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1443	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1444	descriptors for which non-blocking operation makes no sense (such as
		1445	files) - libev doesn't guarentee any specific behaviour in that case.
1338		1446
1339	Another thing you have to watch out for is that it is quite easy to	1447	Another thing you have to watch out for is that it is quite easy to
1340	receive "spurious" readiness notifications, that is your callback might	1448	receive "spurious" readiness notifications, that is your callback might
1341	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1449	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1342	because there is no data. Not only are some backends known to create a	1450	because there is no data. Not only are some backends known to create a
…		…
1463	year, it will still time out after (roughly) one hour. "Roughly" because	1571	year, it will still time out after (roughly) one hour. "Roughly" because
1464	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1572	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1465	monotonic clock option helps a lot here).	1573	monotonic clock option helps a lot here).
1466		1574
1467	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
1468	passed. If multiple timers become ready during the same loop iteration	1576	passed (not I<at>, so on systems with very low-resolution clocks this
1469	then the ones with earlier time-out values are invoked before ones with	1577	might introduce a small delay). If multiple timers become ready during the
1470	later time-out values (but this is no longer true when a callback calls	1578	same loop iteration then the ones with earlier time-out values are invoked
1471	C<ev_loop> recursively).	1579	before ones of the same priority with later time-out values (but this is
		1580	no longer true when a callback calls C<ev_loop> recursively).
1472		1581
1473	=head3 Be smart about timeouts	1582	=head3 Be smart about timeouts
1474		1583
1475	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
1476	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,
…		…
1520	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>
1521	member and C<ev_timer_again>.	1630	member and C<ev_timer_again>.
1522		1631
1523	At start:	1632	At start:
1524		1633
1525	ev_timer_init (timer, callback);	1634	ev_init (timer, callback);
1526	timer->repeat = 60.;	1635	timer->repeat = 60.;
1527	ev_timer_again (loop, timer);	1636	ev_timer_again (loop, timer);
1528		1637
1529	Each time there is some activity:	1638	Each time there is some activity:
1530		1639
…		…
1592		1701
1593	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>
1594	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
1595	callback, which will "do the right thing" and start the timer:	1704	callback, which will "do the right thing" and start the timer:
1596		1705
1597	ev_timer_init (timer, callback);	1706	ev_init (timer, callback);
1598	last_activity = ev_now (loop);	1707	last_activity = ev_now (loop);
1599	callback (loop, timer, EV_TIMEOUT);	1708	callback (loop, timer, EV_TIMEOUT);
1600		1709
1601	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
1602	C<last_activity>, no libev calls at all:	1711	C<last_activity>, no libev calls at all:
…		…
1663		1772
1664	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
1665	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
1666	()>.	1775	()>.
1667		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
1668	=head3 Watcher-Specific Functions and Data Members	1807	=head3 Watcher-Specific Functions and Data Members
1669		1808
1670	=over 4	1809	=over 4
1671		1810
1672	=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)
…		…
1697	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
1698	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.
1699		1838
1700	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
1701	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.
1702		1853
1703	=item ev_tstamp repeat [read-write]	1854	=item ev_tstamp repeat [read-write]
1704		1855
1705	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
1706	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),
…		…
1942	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
1943	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
1944	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
1945	normal event processing, like any other event.	2096	normal event processing, like any other event.
1946		2097
1947	If you want signals asynchronously, just use C<sigaction> as you would	2098	If you want signals to be delivered truly asynchronously, just use
1948	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
1949	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.
1950		2102
1951	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
1952	first watcher gets started will libev actually register a signal handler	2109	When the first watcher gets started will libev actually register something
1953	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
1954	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).
1955	the last signal watcher for a signal is stopped, libev will reset the	2112
1956	signal handler to SIG_DFL (regardless of what it was set to before).	2113	Both the signal mask state (C<sigprocmask>) and the signal handler state
		2114	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2115	sotpping it again), that is, libev might or might not block the signal,
		2116	and might or might not set or restore the installed signal handler.
1957		2117
1958	If possible and supported, libev will install its handlers with	2118	If possible and supported, libev will install its handlers with
1959	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2119	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1960	interrupted. If you have a problem with system calls getting interrupted by	2120	not be unduly interrupted. If you have a problem with system calls getting
1961	signals you can block all signals in an C<ev_check> watcher and unblock	2121	interrupted by signals you can block all signals in an C<ev_check> watcher
1962	them in an C<ev_prepare> watcher.	2122	and unblock them in an C<ev_prepare> watcher.
1963		2123
1964	=head3 Watcher-Specific Functions and Data Members	2124	=head3 Watcher-Specific Functions and Data Members
1965		2125
1966	=over 4	2126	=over 4
1967		2127
…		…
1999	some child status changes (most typically when a child of yours dies or	2159	some child status changes (most typically when a child of yours dies or
2000	exits). It is permissible to install a child watcher I<after> the child	2160	exits). It is permissible to install a child watcher I<after> the child
2001	has been forked (which implies it might have already exited), as long	2161	has been forked (which implies it might have already exited), as long
2002	as the event loop isn't entered (or is continued from a watcher), i.e.,	2162	as the event loop isn't entered (or is continued from a watcher), i.e.,
2003	forking and then immediately registering a watcher for the child is fine,	2163	forking and then immediately registering a watcher for the child is fine,
2004	but forking and registering a watcher a few event loop iterations later is	2164	but forking and registering a watcher a few event loop iterations later or
2005	not.	2165	in the next callback invocation is not.
2006		2166
2007	Only the default event loop is capable of handling signals, and therefore	2167	Only the default event loop is capable of handling signals, and therefore
2008	you can only register child watchers in the default event loop.	2168	you can only register child watchers in the default event loop.
2009		2169
		2170	Due to some design glitches inside libev, child watchers will always be
		2171	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2172	libev)
		2173
2010	=head3 Process Interaction	2174	=head3 Process Interaction
2011		2175
2012	Libev grabs C<SIGCHLD> as soon as the default event loop is	2176	Libev grabs C<SIGCHLD> as soon as the default event loop is
2013	initialised. This is necessary to guarantee proper behaviour even if	2177	initialised. This is necessary to guarantee proper behaviour even if the
2014	the first child watcher is started after the child exits. The occurrence	2178	first child watcher is started after the child exits. The occurrence
2015	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2179	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
2016	synchronously as part of the event loop processing. Libev always reaps all	2180	synchronously as part of the event loop processing. Libev always reaps all
2017	children, even ones not watched.	2181	children, even ones not watched.
2018		2182
2019	=head3 Overriding the Built-In Processing	2183	=head3 Overriding the Built-In Processing
…		…
2029	=head3 Stopping the Child Watcher	2193	=head3 Stopping the Child Watcher
2030		2194
2031	Currently, the child watcher never gets stopped, even when the	2195	Currently, the child watcher never gets stopped, even when the
2032	child terminates, so normally one needs to stop the watcher in the	2196	child terminates, so normally one needs to stop the watcher in the
2033	callback. Future versions of libev might stop the watcher automatically	2197	callback. Future versions of libev might stop the watcher automatically
2034	when a child exit is detected.	2198	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2199	problem).
2035		2200
2036	=head3 Watcher-Specific Functions and Data Members	2201	=head3 Watcher-Specific Functions and Data Members
2037		2202
2038	=over 4	2203	=over 4
2039		2204
…		…
2365	// no longer anything immediate to do.	2530	// no longer anything immediate to do.
2366	}	2531	}
2367		2532
2368	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2533	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2369	ev_idle_init (idle_watcher, idle_cb);	2534	ev_idle_init (idle_watcher, idle_cb);
2370	ev_idle_start (loop, idle_cb);	2535	ev_idle_start (loop, idle_watcher);
2371		2536
2372		2537
2373	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2538	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2374		2539
2375	Prepare and check watchers are usually (but not always) used in pairs:	2540	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2468	struct pollfd fds [nfd];	2633	struct pollfd fds [nfd];
2469	// actual code will need to loop here and realloc etc.	2634	// actual code will need to loop here and realloc etc.
2470	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2635	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2471		2636
2472	/* the callback is illegal, but won't be called as we stop during check */	2637	/* the callback is illegal, but won't be called as we stop during check */
2473	ev_timer_init (&tw, 0, timeout * 1e-3);	2638	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2474	ev_timer_start (loop, &tw);	2639	ev_timer_start (loop, &tw);
2475		2640
2476	// create one ev_io per pollfd	2641	// create one ev_io per pollfd
2477	for (int i = 0; i < nfd; ++i)	2642	for (int i = 0; i < nfd; ++i)
2478	{	2643	{
…		…
3242	=item Ocaml	3407	=item Ocaml
3243		3408
3244	Erkki Seppala has written Ocaml bindings for libev, to be found at	3409	Erkki Seppala has written Ocaml bindings for libev, to be found at
3245	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	3410	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
3246		3411
		3412	=item Lua
		3413
		3414	Brian Maher has written a partial interface to libev
		3415	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3416	L<http://github.com/brimworks/lua-ev>.
		3417
3247	=back	3418	=back
3248		3419
3249		3420
3250	=head1 MACRO MAGIC	3421	=head1 MACRO MAGIC
3251		3422
…		…
3417	keeps libev from including F<config.h>, and it also defines dummy	3588	keeps libev from including F<config.h>, and it also defines dummy
3418	implementations for some libevent functions (such as logging, which is not	3589	implementations for some libevent functions (such as logging, which is not
3419	supported). It will also not define any of the structs usually found in	3590	supported). It will also not define any of the structs usually found in
3420	F<event.h> that are not directly supported by the libev core alone.	3591	F<event.h> that are not directly supported by the libev core alone.
3421		3592
3422	In stanbdalone mode, libev will still try to automatically deduce the	3593	In standalone mode, libev will still try to automatically deduce the
3423	configuration, but has to be more conservative.	3594	configuration, but has to be more conservative.
3424		3595
3425	=item EV_USE_MONOTONIC	3596	=item EV_USE_MONOTONIC
3426		3597
3427	If defined to be C<1>, libev will try to detect the availability of the	3598	If defined to be C<1>, libev will try to detect the availability of the
…		…
3492	be used is the winsock select). This means that it will call	3663	be used is the winsock select). This means that it will call
3493	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3664	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3494	it is assumed that all these functions actually work on fds, even	3665	it is assumed that all these functions actually work on fds, even
3495	on win32. Should not be defined on non-win32 platforms.	3666	on win32. Should not be defined on non-win32 platforms.
3496		3667
3497	=item EV_FD_TO_WIN32_HANDLE	3668	=item EV_FD_TO_WIN32_HANDLE(fd)
3498		3669
3499	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3670	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3500	file descriptors to socket handles. When not defining this symbol (the	3671	file descriptors to socket handles. When not defining this symbol (the
3501	default), then libev will call C<_get_osfhandle>, which is usually	3672	default), then libev will call C<_get_osfhandle>, which is usually
3502	correct. In some cases, programs use their own file descriptor management,	3673	correct. In some cases, programs use their own file descriptor management,
3503	in which case they can provide this function to map fds to socket handles.	3674	in which case they can provide this function to map fds to socket handles.
		3675
		3676	=item EV_WIN32_HANDLE_TO_FD(handle)
		3677
		3678	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3679	using the standard C<_open_osfhandle> function. For programs implementing
		3680	their own fd to handle mapping, overwriting this function makes it easier
		3681	to do so. This can be done by defining this macro to an appropriate value.
		3682
		3683	=item EV_WIN32_CLOSE_FD(fd)
		3684
		3685	If programs implement their own fd to handle mapping on win32, then this
		3686	macro can be used to override the C<close> function, useful to unregister
		3687	file descriptors again. Note that the replacement function has to close
		3688	the underlying OS handle.
3504		3689
3505	=item EV_USE_POLL	3690	=item EV_USE_POLL
3506		3691
3507	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3692	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3508	backend. Otherwise it will be enabled on non-win32 platforms. It	3693	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3640	defined to be C<0>, then they are not.	3825	defined to be C<0>, then they are not.
3641		3826
3642	=item EV_MINIMAL	3827	=item EV_MINIMAL
3643		3828
3644	If you need to shave off some kilobytes of code at the expense of some	3829	If you need to shave off some kilobytes of code at the expense of some
3645	speed, define this symbol to C<1>. Currently this is used to override some	3830	speed (but with the full API), define this symbol to C<1>. Currently this
3646	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3831	is used to override some inlining decisions, saves roughly 30% code size
3647	much smaller 2-heap for timer management over the default 4-heap.	3832	on amd64. It also selects a much smaller 2-heap for timer management over
		3833	the default 4-heap.
		3834
		3835	You can save even more by disabling watcher types you do not need
		3836	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3837	(C<-DNDEBUG>) will usually reduce code size a lot.
		3838
		3839	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3840	provide a bare-bones event library. See C<ev.h> for details on what parts
		3841	of the API are still available, and do not complain if this subset changes
		3842	over time.
		3843
		3844	=item EV_NSIG
		3845
		3846	The highest supported signal number, +1 (or, the number of
		3847	signals): Normally, libev tries to deduce the maximum number of signals
		3848	automatically, but sometimes this fails, in which case it can be
		3849	specified. Also, using a lower number than detected (C<32> should be
		3850	good for about any system in existance) can save some memory, as libev
		3851	statically allocates some 12-24 bytes per signal number.
3648		3852
3649	=item EV_PID_HASHSIZE	3853	=item EV_PID_HASHSIZE
3650		3854
3651	C<ev_child> watchers use a small hash table to distribute workload by	3855	C<ev_child> watchers use a small hash table to distribute workload by
3652	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3856	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3838	default loop and triggering an C<ev_async> watcher from the default loop	4042	default loop and triggering an C<ev_async> watcher from the default loop
3839	watcher callback into the event loop interested in the signal.	4043	watcher callback into the event loop interested in the signal.
3840		4044
3841	=back	4045	=back
3842		4046
		4047	=head4 THREAD LOCKING EXAMPLE
		4048
		4049	Here is a fictitious example of how to run an event loop in a different
		4050	thread than where callbacks are being invoked and watchers are
		4051	created/added/removed.
		4052
		4053	For a real-world example, see the C<EV::Loop::Async> perl module,
		4054	which uses exactly this technique (which is suited for many high-level
		4055	languages).
		4056
		4057	The example uses a pthread mutex to protect the loop data, a condition
		4058	variable to wait for callback invocations, an async watcher to notify the
		4059	event loop thread and an unspecified mechanism to wake up the main thread.
		4060
		4061	First, you need to associate some data with the event loop:
		4062
		4063	typedef struct {
		4064	mutex_t lock; /* global loop lock */
		4065	ev_async async_w;
		4066	thread_t tid;
		4067	cond_t invoke_cv;
		4068	} userdata;
		4069
		4070	void prepare_loop (EV_P)
		4071	{
		4072	// for simplicity, we use a static userdata struct.
		4073	static userdata u;
		4074
		4075	ev_async_init (&u->async_w, async_cb);
		4076	ev_async_start (EV_A_ &u->async_w);
		4077
		4078	pthread_mutex_init (&u->lock, 0);
		4079	pthread_cond_init (&u->invoke_cv, 0);
		4080
		4081	// now associate this with the loop
		4082	ev_set_userdata (EV_A_ u);
		4083	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4084	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4085
		4086	// then create the thread running ev_loop
		4087	pthread_create (&u->tid, 0, l_run, EV_A);
		4088	}
		4089
		4090	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4091	solely to wake up the event loop so it takes notice of any new watchers
		4092	that might have been added:
		4093
		4094	static void
		4095	async_cb (EV_P_ ev_async *w, int revents)
		4096	{
		4097	// just used for the side effects
		4098	}
		4099
		4100	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4101	protecting the loop data, respectively.
		4102
		4103	static void
		4104	l_release (EV_P)
		4105	{
		4106	userdata *u = ev_userdata (EV_A);
		4107	pthread_mutex_unlock (&u->lock);
		4108	}
		4109
		4110	static void
		4111	l_acquire (EV_P)
		4112	{
		4113	userdata *u = ev_userdata (EV_A);
		4114	pthread_mutex_lock (&u->lock);
		4115	}
		4116
		4117	The event loop thread first acquires the mutex, and then jumps straight
		4118	into C<ev_loop>:
		4119
		4120	void *
		4121	l_run (void *thr_arg)
		4122	{
		4123	struct ev_loop loop = (struct ev_loop )thr_arg;
		4124
		4125	l_acquire (EV_A);
		4126	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4127	ev_loop (EV_A_ 0);
		4128	l_release (EV_A);
		4129
		4130	return 0;
		4131	}
		4132
		4133	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4134	signal the main thread via some unspecified mechanism (signals? pipe
		4135	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4136	have been called (in a while loop because a) spurious wakeups are possible
		4137	and b) skipping inter-thread-communication when there are no pending
		4138	watchers is very beneficial):
		4139
		4140	static void
		4141	l_invoke (EV_P)
		4142	{
		4143	userdata *u = ev_userdata (EV_A);
		4144
		4145	while (ev_pending_count (EV_A))
		4146	{
		4147	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4148	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4149	}
		4150	}
		4151
		4152	Now, whenever the main thread gets told to invoke pending watchers, it
		4153	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4154	thread to continue:
		4155
		4156	static void
		4157	real_invoke_pending (EV_P)
		4158	{
		4159	userdata *u = ev_userdata (EV_A);
		4160
		4161	pthread_mutex_lock (&u->lock);
		4162	ev_invoke_pending (EV_A);
		4163	pthread_cond_signal (&u->invoke_cv);
		4164	pthread_mutex_unlock (&u->lock);
		4165	}
		4166
		4167	Whenever you want to start/stop a watcher or do other modifications to an
		4168	event loop, you will now have to lock:
		4169
		4170	ev_timer timeout_watcher;
		4171	userdata *u = ev_userdata (EV_A);
		4172
		4173	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4174
		4175	pthread_mutex_lock (&u->lock);
		4176	ev_timer_start (EV_A_ &timeout_watcher);
		4177	ev_async_send (EV_A_ &u->async_w);
		4178	pthread_mutex_unlock (&u->lock);
		4179
		4180	Note that sending the C<ev_async> watcher is required because otherwise
		4181	an event loop currently blocking in the kernel will have no knowledge
		4182	about the newly added timer. By waking up the loop it will pick up any new
		4183	watchers in the next event loop iteration.
		4184
3843	=head3 COROUTINES	4185	=head3 COROUTINES
3844		4186
3845	Libev is very accommodating to coroutines ("cooperative threads"):	4187	Libev is very accommodating to coroutines ("cooperative threads"):
3846	libev fully supports nesting calls to its functions from different	4188	libev fully supports nesting calls to its functions from different
3847	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4189	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3848	different coroutines, and switch freely between both coroutines running the	4190	different coroutines, and switch freely between both coroutines running
3849	loop, as long as you don't confuse yourself). The only exception is that	4191	the loop, as long as you don't confuse yourself). The only exception is
3850	you must not do this from C<ev_periodic> reschedule callbacks.	4192	that you must not do this from C<ev_periodic> reschedule callbacks.
3851		4193
3852	Care has been taken to ensure that libev does not keep local state inside	4194	Care has been taken to ensure that libev does not keep local state inside
3853	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4195	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3854	they do not call any callbacks.	4196	they do not call any callbacks.
3855		4197
…		…
3932	way (note also that glib is the slowest event library known to man).	4274	way (note also that glib is the slowest event library known to man).
3933		4275
3934	There is no supported compilation method available on windows except	4276	There is no supported compilation method available on windows except
3935	embedding it into other applications.	4277	embedding it into other applications.
3936		4278
		4279	Sensible signal handling is officially unsupported by Microsoft - libev
		4280	tries its best, but under most conditions, signals will simply not work.
		4281
3937	Not a libev limitation but worth mentioning: windows apparently doesn't	4282	Not a libev limitation but worth mentioning: windows apparently doesn't
3938	accept large writes: instead of resulting in a partial write, windows will	4283	accept large writes: instead of resulting in a partial write, windows will
3939	either accept everything or return C<ENOBUFS> if the buffer is too large,	4284	either accept everything or return C<ENOBUFS> if the buffer is too large,
3940	so make sure you only write small amounts into your sockets (less than a	4285	so make sure you only write small amounts into your sockets (less than a
3941	megabyte seems safe, but this apparently depends on the amount of memory	4286	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3945	the abysmal performance of winsockets, using a large number of sockets	4290	the abysmal performance of winsockets, using a large number of sockets
3946	is not recommended (and not reasonable). If your program needs to use	4291	is not recommended (and not reasonable). If your program needs to use
3947	more than a hundred or so sockets, then likely it needs to use a totally	4292	more than a hundred or so sockets, then likely it needs to use a totally
3948	different implementation for windows, as libev offers the POSIX readiness	4293	different implementation for windows, as libev offers the POSIX readiness
3949	notification model, which cannot be implemented efficiently on windows	4294	notification model, which cannot be implemented efficiently on windows
3950	(Microsoft monopoly games).	4295	(due to Microsoft monopoly games).
3951		4296
3952	A typical way to use libev under windows is to embed it (see the embedding	4297	A typical way to use libev under windows is to embed it (see the embedding
3953	section for details) and use the following F<evwrap.h> header file instead	4298	section for details) and use the following F<evwrap.h> header file instead
3954	of F<ev.h>:	4299	of F<ev.h>:
3955		4300
…		…
3991		4336
3992	Early versions of winsocket's select only supported waiting for a maximum	4337	Early versions of winsocket's select only supported waiting for a maximum
3993	of C<64> handles (probably owning to the fact that all windows kernels	4338	of C<64> handles (probably owning to the fact that all windows kernels
3994	can only wait for C<64> things at the same time internally; Microsoft	4339	can only wait for C<64> things at the same time internally; Microsoft
3995	recommends spawning a chain of threads and wait for 63 handles and the	4340	recommends spawning a chain of threads and wait for 63 handles and the
3996	previous thread in each. Great).	4341	previous thread in each. Sounds great!).
3997		4342
3998	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4343	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3999	to some high number (e.g. C<2048>) before compiling the winsocket select	4344	to some high number (e.g. C<2048>) before compiling the winsocket select
4000	call (which might be in libev or elsewhere, for example, perl does its own	4345	call (which might be in libev or elsewhere, for example, perl and many
4001	select emulation on windows).	4346	other interpreters do their own select emulation on windows).
4002		4347
4003	Another limit is the number of file descriptors in the Microsoft runtime	4348	Another limit is the number of file descriptors in the Microsoft runtime
4004	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4349	libraries, which by default is C<64> (there must be a hidden I<64>
4005	or something like this inside Microsoft). You can increase this by calling	4350	fetish or something like this inside Microsoft). You can increase this
4006	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4351	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
4007	arbitrary limit), but is broken in many versions of the Microsoft runtime	4352	(another arbitrary limit), but is broken in many versions of the Microsoft
4008	libraries.
4009
4010	This might get you to about C<512> or C<2048> sockets (depending on	4353	runtime libraries. This might get you to about C<512> or C<2048> sockets
4011	windows version and/or the phase of the moon). To get more, you need to	4354	(depending on windows version and/or the phase of the moon). To get more,
4012	wrap all I/O functions and provide your own fd management, but the cost of	4355	you need to wrap all I/O functions and provide your own fd management, but
4013	calling select (O(n²)) will likely make this unworkable.	4356	the cost of calling select (O(n²)) will likely make this unworkable.
4014		4357
4015	=back	4358	=back
4016		4359
4017	=head2 PORTABILITY REQUIREMENTS	4360	=head2 PORTABILITY REQUIREMENTS
4018		4361
…		…
4061	=item C<double> must hold a time value in seconds with enough accuracy	4404	=item C<double> must hold a time value in seconds with enough accuracy
4062		4405
4063	The type C<double> is used to represent timestamps. It is required to	4406	The type C<double> is used to represent timestamps. It is required to
4064	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4407	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
4065	enough for at least into the year 4000. This requirement is fulfilled by	4408	enough for at least into the year 4000. This requirement is fulfilled by
4066	implementations implementing IEEE 754 (basically all existing ones).	4409	implementations implementing IEEE 754, which is basically all existing
		4410	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4411	2200.
4067		4412
4068	=back	4413	=back
4069		4414
4070	If you know of other additional requirements drop me a note.	4415	If you know of other additional requirements drop me a note.
4071		4416

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Comparing libev/ev.pod (file contents): Revision 1.238 by root, Sat Apr 18 12:10:41 2009 UTC vs. Revision 1.264 by root, Wed Aug 19 23:44:51 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.238 by root, Sat Apr 18 12:10:41 2009 UTC vs.
Revision 1.264 by root, Wed Aug 19 23:44:51 2009 UTC