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

Comparing libev/ev.pod (file contents):
Revision 1.253 by root, Tue Jul 14 18:33:48 2009 UTC vs.
Revision 1.272 by root, Tue Nov 24 06:39:28 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
…		…
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.
366		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_NOSIGFD>
		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.
		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,
371	but if that fails, expect a fairly low limit on the number of fds when	387	but if that fails, expect a fairly low limit on the number of fds when
…		…
394		410
395	This backend maps C<EV_READ> to C<POLLIN \| POLLERR \| POLLHUP>, and	411	This backend maps C<EV_READ> to C<POLLIN \| POLLERR \| POLLHUP>, and
396	C<EV_WRITE> to C<POLLOUT \| POLLERR \| POLLHUP>.	412	C<EV_WRITE> to C<POLLOUT \| POLLERR \| POLLHUP>.
397		413
398	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		415
		416	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		417	kernels).
399		418
400	For few fds, this backend is a bit little slower than poll and select,	419	For few fds, this backend is a bit little slower than poll and select,
401	but it scales phenomenally better. While poll and select usually scale	420	but it scales phenomenally better. While poll and select usually scale
402	like O(total_fds) where n is the total number of fds (or the highest fd),	421	like O(total_fds) where n is the total number of fds (or the highest fd),
403	epoll scales either O(1) or O(active_fds).	422	epoll scales either O(1) or O(active_fds).
…		…
518		537
519	It is definitely not recommended to use this flag.	538	It is definitely not recommended to use this flag.
520		539
521	=back	540	=back
522		541
523	If one or more of these are or'ed into the flags value, then only these	542	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	543	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.	544	here). If none are specified, all backends in C<ev_recommended_backends
		545	()> will be tried.
526		546
527	Example: This is the most typical usage.	547	Example: This is the most typical usage.
528		548
529	if (!ev_default_loop (0))	549	if (!ev_default_loop (0))
530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	550	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
573	as signal and child watchers) would need to be stopped manually.	593	as signal and child watchers) would need to be stopped manually.
574		594
575	In general it is not advisable to call this function except in the	595	In general it is not advisable to call this function except in the
576	rare occasion where you really need to free e.g. the signal handling	596	rare occasion where you really need to free e.g. the signal handling
577	pipe fds. If you need dynamically allocated loops it is better to use	597	pipe fds. If you need dynamically allocated loops it is better to use
578	C<ev_loop_new> and C<ev_loop_destroy>).	598	C<ev_loop_new> and C<ev_loop_destroy>.
579		599
580	=item ev_loop_destroy (loop)	600	=item ev_loop_destroy (loop)
581		601
582	Like C<ev_default_destroy>, but destroys an event loop created by an	602	Like C<ev_default_destroy>, but destroys an event loop created by an
583	earlier call to C<ev_loop_new>.	603	earlier call to C<ev_loop_new>.
…		…
687	event loop time (see C<ev_now_update>).	707	event loop time (see C<ev_now_update>).
688		708
689	=item ev_loop (loop, int flags)	709	=item ev_loop (loop, int flags)
690		710
691	Finally, this is it, the event handler. This function usually is called	711	Finally, this is it, the event handler. This function usually is called
692	after you initialised all your watchers and you want to start handling	712	after you have initialised all your watchers and you want to start
693	events.	713	handling events.
694		714
695	If the flags argument is specified as C<0>, it will not return until	715	If the flags argument is specified as C<0>, it will not return until
696	either no event watchers are active anymore or C<ev_unloop> was called.	716	either no event watchers are active anymore or C<ev_unloop> was called.
697		717
698	Please note that an explicit C<ev_unloop> is usually better than	718	Please note that an explicit C<ev_unloop> is usually better than
…		…
862		882
863	This call will simply invoke all pending watchers while resetting their	883	This call will simply invoke all pending watchers while resetting their
864	pending state. Normally, C<ev_loop> does this automatically when required,	884	pending state. Normally, C<ev_loop> does this automatically when required,
865	but when overriding the invoke callback this call comes handy.	885	but when overriding the invoke callback this call comes handy.
866		886
		887	=item int ev_pending_count (loop)
		888
		889	Returns the number of pending watchers - zero indicates that no watchers
		890	are pending.
		891
867	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))	892	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
868		893
869	This overrides the invoke pending functionality of the loop: Instead of	894	This overrides the invoke pending functionality of the loop: Instead of
870	invoking all pending watchers when there are any, C<ev_loop> will call	895	invoking all pending watchers when there are any, C<ev_loop> will call
871	this callback instead. This is useful, for example, when you want to	896	this callback instead. This is useful, for example, when you want to
…		…
889	suspended waiting for new events, and C<acquire> is called just	914	suspended waiting for new events, and C<acquire> is called just
890	afterwards.	915	afterwards.
891		916
892	Ideally, C<release> will just call your mutex_unlock function, and	917	Ideally, C<release> will just call your mutex_unlock function, and
893	C<acquire> will just call the mutex_lock function again.	918	C<acquire> will just call the mutex_lock function again.
		919
		920	While event loop modifications are allowed between invocations of
		921	C<release> and C<acquire> (that's their only purpose after all), no
		922	modifications done will affect the event loop, i.e. adding watchers will
		923	have no effect on the set of file descriptors being watched, or the time
		924	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		925	to take note of any changes you made.
		926
		927	In theory, threads executing C<ev_loop> will be async-cancel safe between
		928	invocations of C<release> and C<acquire>.
		929
		930	See also the locking example in the C<THREADS> section later in this
		931	document.
894		932
895	=item ev_set_userdata (loop, void *data)	933	=item ev_set_userdata (loop, void *data)
896		934
897	=item ev_userdata (loop)	935	=item ev_userdata (loop)
898		936
…		…
1737		1775
1738	If the event loop is suspended for a long time, you can also force an	1776	If the event loop is suspended for a long time, you can also force an
1739	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1777	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1740	()>.	1778	()>.
1741		1779
		1780	=head3 The special problems of suspended animation
		1781
		1782	When you leave the server world it is quite customary to hit machines that
		1783	can suspend/hibernate - what happens to the clocks during such a suspend?
		1784
		1785	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1786	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1787	to run until the system is suspended, but they will not advance while the
		1788	system is suspended. That means, on resume, it will be as if the program
		1789	was frozen for a few seconds, but the suspend time will not be counted
		1790	towards C<ev_timer> when a monotonic clock source is used. The real time
		1791	clock advanced as expected, but if it is used as sole clocksource, then a
		1792	long suspend would be detected as a time jump by libev, and timers would
		1793	be adjusted accordingly.
		1794
		1795	I would not be surprised to see different behaviour in different between
		1796	operating systems, OS versions or even different hardware.
		1797
		1798	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1799	time jump in the monotonic clocks and the realtime clock. If the program
		1800	is suspended for a very long time, and monotonic clock sources are in use,
		1801	then you can expect C<ev_timer>s to expire as the full suspension time
		1802	will be counted towards the timers. When no monotonic clock source is in
		1803	use, then libev will again assume a timejump and adjust accordingly.
		1804
		1805	It might be beneficial for this latter case to call C<ev_suspend>
		1806	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1807	deterministic behaviour in this case (you can do nothing against
		1808	C<SIGSTOP>).
		1809
1742	=head3 Watcher-Specific Functions and Data Members	1810	=head3 Watcher-Specific Functions and Data Members
1743		1811
1744	=over 4	1812	=over 4
1745		1813
1746	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1814	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1771	If the timer is repeating, either start it if necessary (with the	1839	If the timer is repeating, either start it if necessary (with the
1772	C<repeat> value), or reset the running timer to the C<repeat> value.	1840	C<repeat> value), or reset the running timer to the C<repeat> value.
1773		1841
1774	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	1842	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1775	usage example.	1843	usage example.
		1844
		1845	=item ev_timer_remaining (loop, ev_timer *)
		1846
		1847	Returns the remaining time until a timer fires. If the timer is active,
		1848	then this time is relative to the current event loop time, otherwise it's
		1849	the timeout value currently configured.
		1850
		1851	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1852	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1853	will return C<4>. When the timer expires and is restarted, it will return
		1854	roughly C<7> (likely slightly less as callback invocation takes some time,
		1855	too), and so on.
1776		1856
1777	=item ev_tstamp repeat [read-write]	1857	=item ev_tstamp repeat [read-write]
1778		1858
1779	The current C<repeat> value. Will be used each time the watcher times out	1859	The current C<repeat> value. Will be used each time the watcher times out
1780	or C<ev_timer_again> is called, and determines the next timeout (if any),	1860	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
2016	Signal watchers will trigger an event when the process receives a specific	2096	Signal watchers will trigger an event when the process receives a specific
2017	signal one or more times. Even though signals are very asynchronous, libev	2097	signal one or more times. Even though signals are very asynchronous, libev
2018	will try it's best to deliver signals synchronously, i.e. as part of the	2098	will try it's best to deliver signals synchronously, i.e. as part of the
2019	normal event processing, like any other event.	2099	normal event processing, like any other event.
2020		2100
2021	If you want signals asynchronously, just use C<sigaction> as you would	2101	If you want signals to be delivered truly asynchronously, just use
2022	do without libev and forget about sharing the signal. You can even use	2102	C<sigaction> as you would do without libev and forget about sharing
2023	C<ev_async> from a signal handler to synchronously wake up an event loop.	2103	the signal. You can even use C<ev_async> from a signal handler to
		2104	synchronously wake up an event loop.
2024		2105
2025	You can configure as many watchers as you like per signal. Only when the	2106	You can configure as many watchers as you like for the same signal, but
		2107	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2108	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2109	C<SIGINT> in both the default loop and another loop at the same time. At
		2110	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2111
2026	first watcher gets started will libev actually register a signal handler	2112	When the first watcher gets started will libev actually register something
2027	with the kernel (thus it coexists with your own signal handlers as long as	2113	with the kernel (thus it coexists with your own signal handlers as long as
2028	you don't register any with libev for the same signal). Similarly, when	2114	you don't register any with libev for the same signal).
2029	the last signal watcher for a signal is stopped, libev will reset the
2030	signal handler to SIG_DFL (regardless of what it was set to before).
2031		2115
2032	If possible and supported, libev will install its handlers with	2116	If possible and supported, libev will install its handlers with
2033	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2117	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2034	interrupted. If you have a problem with system calls getting interrupted by	2118	not be unduly interrupted. If you have a problem with system calls getting
2035	signals you can block all signals in an C<ev_check> watcher and unblock	2119	interrupted by signals you can block all signals in an C<ev_check> watcher
2036	them in an C<ev_prepare> watcher.	2120	and unblock them in an C<ev_prepare> watcher.
		2121
		2122	=head3 The special problem of inheritance over execve
		2123
		2124	Both the signal mask (C<sigprocmask>) and the signal disposition
		2125	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2126	stopping it again), that is, libev might or might not block the signal,
		2127	and might or might not set or restore the installed signal handler.
		2128
		2129	While this does not matter for the signal disposition (libev never
		2130	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2131	C<execve>), this matters for the signal mask: many programs do not expect
		2132	certain signals to be blocked.
		2133
		2134	This means that before calling C<exec> (from the child) you should reset
		2135	the signal mask to whatever "default" you expect (all clear is a good
		2136	choice usually).
		2137
		2138	The simplest way to ensure that the signal mask is reset in the child is
		2139	to install a fork handler with C<pthread_atfork> that resets it. That will
		2140	catch fork calls done by libraries (such as the libc) as well.
		2141
		2142	In current versions of libev, you can also ensure that the signal mask is
		2143	not blocking any signals (except temporarily, so thread users watch out)
		2144	by specifying the C<EVFLAG_NOSIGFD> when creating the event loop. This
		2145	is not guaranteed for future versions, however.
2037		2146
2038	=head3 Watcher-Specific Functions and Data Members	2147	=head3 Watcher-Specific Functions and Data Members
2039		2148
2040	=over 4	2149	=over 4
2041		2150
…		…
2086	libev)	2195	libev)
2087		2196
2088	=head3 Process Interaction	2197	=head3 Process Interaction
2089		2198
2090	Libev grabs C<SIGCHLD> as soon as the default event loop is	2199	Libev grabs C<SIGCHLD> as soon as the default event loop is
2091	initialised. This is necessary to guarantee proper behaviour even if	2200	initialised. This is necessary to guarantee proper behaviour even if the
2092	the first child watcher is started after the child exits. The occurrence	2201	first child watcher is started after the child exits. The occurrence
2093	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2202	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
2094	synchronously as part of the event loop processing. Libev always reaps all	2203	synchronously as part of the event loop processing. Libev always reaps all
2095	children, even ones not watched.	2204	children, even ones not watched.
2096		2205
2097	=head3 Overriding the Built-In Processing	2206	=head3 Overriding the Built-In Processing
…		…
2107	=head3 Stopping the Child Watcher	2216	=head3 Stopping the Child Watcher
2108		2217
2109	Currently, the child watcher never gets stopped, even when the	2218	Currently, the child watcher never gets stopped, even when the
2110	child terminates, so normally one needs to stop the watcher in the	2219	child terminates, so normally one needs to stop the watcher in the
2111	callback. Future versions of libev might stop the watcher automatically	2220	callback. Future versions of libev might stop the watcher automatically
2112	when a child exit is detected.	2221	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2222	problem).
2113		2223
2114	=head3 Watcher-Specific Functions and Data Members	2224	=head3 Watcher-Specific Functions and Data Members
2115		2225
2116	=over 4	2226	=over 4
2117		2227
…		…
3320	=item Ocaml	3430	=item Ocaml
3321		3431
3322	Erkki Seppala has written Ocaml bindings for libev, to be found at	3432	Erkki Seppala has written Ocaml bindings for libev, to be found at
3323	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	3433	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
3324		3434
		3435	=item Lua
		3436
		3437	Brian Maher has written a partial interface to libev
		3438	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3439	L<http://github.com/brimworks/lua-ev>.
		3440
3325	=back	3441	=back
3326		3442
3327		3443
3328	=head1 MACRO MAGIC	3444	=head1 MACRO MAGIC
3329		3445
…		…
3495	keeps libev from including F<config.h>, and it also defines dummy	3611	keeps libev from including F<config.h>, and it also defines dummy
3496	implementations for some libevent functions (such as logging, which is not	3612	implementations for some libevent functions (such as logging, which is not
3497	supported). It will also not define any of the structs usually found in	3613	supported). It will also not define any of the structs usually found in
3498	F<event.h> that are not directly supported by the libev core alone.	3614	F<event.h> that are not directly supported by the libev core alone.
3499		3615
3500	In stanbdalone mode, libev will still try to automatically deduce the	3616	In standalone mode, libev will still try to automatically deduce the
3501	configuration, but has to be more conservative.	3617	configuration, but has to be more conservative.
3502		3618
3503	=item EV_USE_MONOTONIC	3619	=item EV_USE_MONOTONIC
3504		3620
3505	If defined to be C<1>, libev will try to detect the availability of the	3621	If defined to be C<1>, libev will try to detect the availability of the
…		…
3570	be used is the winsock select). This means that it will call	3686	be used is the winsock select). This means that it will call
3571	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3687	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3572	it is assumed that all these functions actually work on fds, even	3688	it is assumed that all these functions actually work on fds, even
3573	on win32. Should not be defined on non-win32 platforms.	3689	on win32. Should not be defined on non-win32 platforms.
3574		3690
3575	=item EV_FD_TO_WIN32_HANDLE	3691	=item EV_FD_TO_WIN32_HANDLE(fd)
3576		3692
3577	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3693	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3578	file descriptors to socket handles. When not defining this symbol (the	3694	file descriptors to socket handles. When not defining this symbol (the
3579	default), then libev will call C<_get_osfhandle>, which is usually	3695	default), then libev will call C<_get_osfhandle>, which is usually
3580	correct. In some cases, programs use their own file descriptor management,	3696	correct. In some cases, programs use their own file descriptor management,
3581	in which case they can provide this function to map fds to socket handles.	3697	in which case they can provide this function to map fds to socket handles.
		3698
		3699	=item EV_WIN32_HANDLE_TO_FD(handle)
		3700
		3701	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3702	using the standard C<_open_osfhandle> function. For programs implementing
		3703	their own fd to handle mapping, overwriting this function makes it easier
		3704	to do so. This can be done by defining this macro to an appropriate value.
		3705
		3706	=item EV_WIN32_CLOSE_FD(fd)
		3707
		3708	If programs implement their own fd to handle mapping on win32, then this
		3709	macro can be used to override the C<close> function, useful to unregister
		3710	file descriptors again. Note that the replacement function has to close
		3711	the underlying OS handle.
3582		3712
3583	=item EV_USE_POLL	3713	=item EV_USE_POLL
3584		3714
3585	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3715	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3586	backend. Otherwise it will be enabled on non-win32 platforms. It	3716	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3732	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to	3862	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
3733	provide a bare-bones event library. See C<ev.h> for details on what parts	3863	provide a bare-bones event library. See C<ev.h> for details on what parts
3734	of the API are still available, and do not complain if this subset changes	3864	of the API are still available, and do not complain if this subset changes
3735	over time.	3865	over time.
3736		3866
		3867	=item EV_NSIG
		3868
		3869	The highest supported signal number, +1 (or, the number of
		3870	signals): Normally, libev tries to deduce the maximum number of signals
		3871	automatically, but sometimes this fails, in which case it can be
		3872	specified. Also, using a lower number than detected (C<32> should be
		3873	good for about any system in existance) can save some memory, as libev
		3874	statically allocates some 12-24 bytes per signal number.
		3875
3737	=item EV_PID_HASHSIZE	3876	=item EV_PID_HASHSIZE
3738		3877
3739	C<ev_child> watchers use a small hash table to distribute workload by	3878	C<ev_child> watchers use a small hash table to distribute workload by
3740	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3879	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
3741	than enough. If you need to manage thousands of children you might want to	3880	than enough. If you need to manage thousands of children you might want to
…		…
3928		4067
3929	=back	4068	=back
3930		4069
3931	=head4 THREAD LOCKING EXAMPLE	4070	=head4 THREAD LOCKING EXAMPLE
3932		4071
		4072	Here is a fictitious example of how to run an event loop in a different
		4073	thread than where callbacks are being invoked and watchers are
		4074	created/added/removed.
		4075
		4076	For a real-world example, see the C<EV::Loop::Async> perl module,
		4077	which uses exactly this technique (which is suited for many high-level
		4078	languages).
		4079
		4080	The example uses a pthread mutex to protect the loop data, a condition
		4081	variable to wait for callback invocations, an async watcher to notify the
		4082	event loop thread and an unspecified mechanism to wake up the main thread.
		4083
		4084	First, you need to associate some data with the event loop:
		4085
		4086	typedef struct {
		4087	mutex_t lock; /* global loop lock */
		4088	ev_async async_w;
		4089	thread_t tid;
		4090	cond_t invoke_cv;
		4091	} userdata;
		4092
		4093	void prepare_loop (EV_P)
		4094	{
		4095	// for simplicity, we use a static userdata struct.
		4096	static userdata u;
		4097
		4098	ev_async_init (&u->async_w, async_cb);
		4099	ev_async_start (EV_A_ &u->async_w);
		4100
		4101	pthread_mutex_init (&u->lock, 0);
		4102	pthread_cond_init (&u->invoke_cv, 0);
		4103
		4104	// now associate this with the loop
		4105	ev_set_userdata (EV_A_ u);
		4106	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4107	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4108
		4109	// then create the thread running ev_loop
		4110	pthread_create (&u->tid, 0, l_run, EV_A);
		4111	}
		4112
		4113	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4114	solely to wake up the event loop so it takes notice of any new watchers
		4115	that might have been added:
		4116
		4117	static void
		4118	async_cb (EV_P_ ev_async *w, int revents)
		4119	{
		4120	// just used for the side effects
		4121	}
		4122
		4123	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4124	protecting the loop data, respectively.
		4125
		4126	static void
		4127	l_release (EV_P)
		4128	{
		4129	userdata *u = ev_userdata (EV_A);
		4130	pthread_mutex_unlock (&u->lock);
		4131	}
		4132
		4133	static void
		4134	l_acquire (EV_P)
		4135	{
		4136	userdata *u = ev_userdata (EV_A);
		4137	pthread_mutex_lock (&u->lock);
		4138	}
		4139
		4140	The event loop thread first acquires the mutex, and then jumps straight
		4141	into C<ev_loop>:
		4142
		4143	void *
		4144	l_run (void *thr_arg)
		4145	{
		4146	struct ev_loop loop = (struct ev_loop )thr_arg;
		4147
		4148	l_acquire (EV_A);
		4149	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4150	ev_loop (EV_A_ 0);
		4151	l_release (EV_A);
		4152
		4153	return 0;
		4154	}
		4155
		4156	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4157	signal the main thread via some unspecified mechanism (signals? pipe
		4158	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4159	have been called (in a while loop because a) spurious wakeups are possible
		4160	and b) skipping inter-thread-communication when there are no pending
		4161	watchers is very beneficial):
		4162
		4163	static void
		4164	l_invoke (EV_P)
		4165	{
		4166	userdata *u = ev_userdata (EV_A);
		4167
		4168	while (ev_pending_count (EV_A))
		4169	{
		4170	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4171	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4172	}
		4173	}
		4174
		4175	Now, whenever the main thread gets told to invoke pending watchers, it
		4176	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4177	thread to continue:
		4178
		4179	static void
		4180	real_invoke_pending (EV_P)
		4181	{
		4182	userdata *u = ev_userdata (EV_A);
		4183
		4184	pthread_mutex_lock (&u->lock);
		4185	ev_invoke_pending (EV_A);
		4186	pthread_cond_signal (&u->invoke_cv);
		4187	pthread_mutex_unlock (&u->lock);
		4188	}
		4189
		4190	Whenever you want to start/stop a watcher or do other modifications to an
		4191	event loop, you will now have to lock:
		4192
		4193	ev_timer timeout_watcher;
		4194	userdata *u = ev_userdata (EV_A);
		4195
		4196	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4197
		4198	pthread_mutex_lock (&u->lock);
		4199	ev_timer_start (EV_A_ &timeout_watcher);
		4200	ev_async_send (EV_A_ &u->async_w);
		4201	pthread_mutex_unlock (&u->lock);
		4202
		4203	Note that sending the C<ev_async> watcher is required because otherwise
		4204	an event loop currently blocking in the kernel will have no knowledge
		4205	about the newly added timer. By waking up the loop it will pick up any new
		4206	watchers in the next event loop iteration.
		4207
3933	=head3 COROUTINES	4208	=head3 COROUTINES
3934		4209
3935	Libev is very accommodating to coroutines ("cooperative threads"):	4210	Libev is very accommodating to coroutines ("cooperative threads"):
3936	libev fully supports nesting calls to its functions from different	4211	libev fully supports nesting calls to its functions from different
3937	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4212	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3938	different coroutines, and switch freely between both coroutines running the	4213	different coroutines, and switch freely between both coroutines running
3939	loop, as long as you don't confuse yourself). The only exception is that	4214	the loop, as long as you don't confuse yourself). The only exception is
3940	you must not do this from C<ev_periodic> reschedule callbacks.	4215	that you must not do this from C<ev_periodic> reschedule callbacks.
3941		4216
3942	Care has been taken to ensure that libev does not keep local state inside	4217	Care has been taken to ensure that libev does not keep local state inside
3943	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4218	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3944	they do not call any callbacks.	4219	they do not call any callbacks.
3945		4220

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Comparing libev/ev.pod (file contents): Revision 1.253 by root, Tue Jul 14 18:33:48 2009 UTC vs. Revision 1.272 by root, Tue Nov 24 06:39:28 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.253 by root, Tue Jul 14 18:33:48 2009 UTC vs.
Revision 1.272 by root, Tue Nov 24 06:39:28 2009 UTC