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

Comparing libev/ev.pod (file contents):
Revision 1.247 by root, Wed Jul 8 02:46:05 2009 UTC vs.
Revision 1.259 by root, Sun Jul 19 01:36:34 2009 UTC

…		…
856	more often than 100 times per second:	856	more often than 100 times per second:
857		857
858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);	858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);	859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
860		860
		861	=item ev_invoke_pending (loop)
		862
		863	This call will simply invoke all pending watchers while resetting their
		864	pending state. Normally, C<ev_loop> does this automatically when required,
		865	but when overriding the invoke callback this call comes handy.
		866
		867	=item int ev_pending_count (loop)
		868
		869	Returns the number of pending watchers - zero indicates that no watchers
		870	are pending.
		871
		872	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		873
		874	This overrides the invoke pending functionality of the loop: Instead of
		875	invoking all pending watchers when there are any, C<ev_loop> will call
		876	this callback instead. This is useful, for example, when you want to
		877	invoke the actual watchers inside another context (another thread etc.).
		878
		879	If you want to reset the callback, use C<ev_invoke_pending> as new
		880	callback.
		881
		882	=item ev_set_loop_release_cb (loop, void (release)(EV_P), void (acquire)(EV_P))
		883
		884	Sometimes you want to share the same loop between multiple threads. This
		885	can be done relatively simply by putting mutex_lock/unlock calls around
		886	each call to a libev function.
		887
		888	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		889	wait for it to return. One way around this is to wake up the loop via
		890	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		891	and I<acquire> callbacks on the loop.
		892
		893	When set, then C<release> will be called just before the thread is
		894	suspended waiting for new events, and C<acquire> is called just
		895	afterwards.
		896
		897	Ideally, C<release> will just call your mutex_unlock function, and
		898	C<acquire> will just call the mutex_lock function again.
		899
		900	While event loop modifications are allowed between invocations of
		901	C<release> and C<acquire> (that's their only purpose after all), no
		902	modifications done will affect the event loop, i.e. adding watchers will
		903	have no effect on the set of file descriptors being watched, or the time
		904	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		905	to take note of any changes you made.
		906
		907	In theory, threads executing C<ev_loop> will be async-cancel safe between
		908	invocations of C<release> and C<acquire>.
		909
		910	See also the locking example in the C<THREADS> section later in this
		911	document.
		912
		913	=item ev_set_userdata (loop, void *data)
		914
		915	=item ev_userdata (loop)
		916
		917	Set and retrieve a single C<void *> associated with a loop. When
		918	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		919	C<0.>
		920
		921	These two functions can be used to associate arbitrary data with a loop,
		922	and are intended solely for the C<invoke_pending_cb>, C<release> and
		923	C<acquire> callbacks described above, but of course can be (ab-)used for
		924	any other purpose as well.
		925
861	=item ev_loop_verify (loop)	926	=item ev_loop_verify (loop)
862		927
863	This function only does something when C<EV_VERIFY> support has been	928	This function only does something when C<EV_VERIFY> support has been
864	compiled in, which is the default for non-minimal builds. It tries to go	929	compiled in, which is the default for non-minimal builds. It tries to go
865	through all internal structures and checks them for validity. If anything	930	through all internal structures and checks them for validity. If anything
…		…
1492		1557
1493	The callback is guaranteed to be invoked only I<after> its timeout has	1558	The callback is guaranteed to be invoked only I<after> its timeout has
1494	passed (not I<at>, so on systems with very low-resolution clocks this	1559	passed (not I<at>, so on systems with very low-resolution clocks this
1495	might introduce a small delay). If multiple timers become ready during the	1560	might introduce a small delay). If multiple timers become ready during the
1496	same loop iteration then the ones with earlier time-out values are invoked	1561	same loop iteration then the ones with earlier time-out values are invoked
1497	before ones with later time-out values (but this is no longer true when a	1562	before ones of the same priority with later time-out values (but this is
1498	callback calls C<ev_loop> recursively).	1563	no longer true when a callback calls C<ev_loop> recursively).
1499		1564
1500	=head3 Be smart about timeouts	1565	=head3 Be smart about timeouts
1501		1566
1502	Many real-world problems involve some kind of timeout, usually for error	1567	Many real-world problems involve some kind of timeout, usually for error
1503	recovery. A typical example is an HTTP request - if the other side hangs,	1568	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1690		1755
1691	If the event loop is suspended for a long time, you can also force an	1756	If the event loop is suspended for a long time, you can also force an
1692	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1757	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1693	()>.	1758	()>.
1694		1759
		1760	=head3 The special problems of suspended animation
		1761
		1762	When you leave the server world it is quite customary to hit machines that
		1763	can suspend/hibernate - what happens to the clocks during such a suspend?
		1764
		1765	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1766	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1767	to run until the system is suspended, but they will not advance while the
		1768	system is suspended. That means, on resume, it will be as if the program
		1769	was frozen for a few seconds, but the suspend time will not be counted
		1770	towards C<ev_timer> when a monotonic clock source is used. The real time
		1771	clock advanced as expected, but if it is used as sole clocksource, then a
		1772	long suspend would be detected as a time jump by libev, and timers would
		1773	be adjusted accordingly.
		1774
		1775	I would not be surprised to see different behaviour in different between
		1776	operating systems, OS versions or even different hardware.
		1777
		1778	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1779	time jump in the monotonic clocks and the realtime clock. If the program
		1780	is suspended for a very long time, and monotonic clock sources are in use,
		1781	then you can expect C<ev_timer>s to expire as the full suspension time
		1782	will be counted towards the timers. When no monotonic clock source is in
		1783	use, then libev will again assume a timejump and adjust accordingly.
		1784
		1785	It might be beneficial for this latter case to call C<ev_suspend>
		1786	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1787	deterministic behaviour in this case (you can do nothing against
		1788	C<SIGSTOP>).
		1789
1695	=head3 Watcher-Specific Functions and Data Members	1790	=head3 Watcher-Specific Functions and Data Members
1696		1791
1697	=over 4	1792	=over 4
1698		1793
1699	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1794	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1724	If the timer is repeating, either start it if necessary (with the	1819	If the timer is repeating, either start it if necessary (with the
1725	C<repeat> value), or reset the running timer to the C<repeat> value.	1820	C<repeat> value), or reset the running timer to the C<repeat> value.
1726		1821
1727	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	1822	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1728	usage example.	1823	usage example.
		1824
		1825	=item ev_timer_remaining (loop, ev_timer *)
		1826
		1827	Returns the remaining time until a timer fires. If the timer is active,
		1828	then this time is relative to the current event loop time, otherwise it's
		1829	the timeout value currently configured.
		1830
		1831	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1832	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1833	will return C<4>. When the timer expires and is restarted, it will return
		1834	roughly C<7> (likely slightly less as callback invocation takes some time,
		1835	too), and so on.
1729		1836
1730	=item ev_tstamp repeat [read-write]	1837	=item ev_tstamp repeat [read-write]
1731		1838
1732	The current C<repeat> value. Will be used each time the watcher times out	1839	The current C<repeat> value. Will be used each time the watcher times out
1733	or C<ev_timer_again> is called, and determines the next timeout (if any),	1840	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1969	Signal watchers will trigger an event when the process receives a specific	2076	Signal watchers will trigger an event when the process receives a specific
1970	signal one or more times. Even though signals are very asynchronous, libev	2077	signal one or more times. Even though signals are very asynchronous, libev
1971	will try it's best to deliver signals synchronously, i.e. as part of the	2078	will try it's best to deliver signals synchronously, i.e. as part of the
1972	normal event processing, like any other event.	2079	normal event processing, like any other event.
1973		2080
		2081	Note that only the default loop supports registering signal watchers
		2082	currently.
		2083
1974	If you want signals asynchronously, just use C<sigaction> as you would	2084	If you want signals asynchronously, just use C<sigaction> as you would
1975	do without libev and forget about sharing the signal. You can even use	2085	do without libev and forget about sharing the signal. You can even use
1976	C<ev_async> from a signal handler to synchronously wake up an event loop.	2086	C<ev_async> from a signal handler to synchronously wake up an event loop.
1977		2087
1978	You can configure as many watchers as you like per signal. Only when the	2088	You can configure as many watchers as you like per signal. Only when the
1979	first watcher gets started will libev actually register a signal handler	2089	first watcher gets started will libev actually register something with
1980	with the kernel (thus it coexists with your own signal handlers as long as	2090	the kernel (thus it coexists with your own signal handlers as long as you
1981	you don't register any with libev for the same signal). Similarly, when	2091	don't register any with libev for the same signal).
1982	the last signal watcher for a signal is stopped, libev will reset the	2092
1983	signal handler to SIG_DFL (regardless of what it was set to before).	2093	Both the signal mask state (C<sigprocmask>) and the signal handler state
		2094	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2095	sotpping it again), that is, libev might or might not block the signal,
		2096	and might or might not set or restore the installed signal handler.
1984		2097
1985	If possible and supported, libev will install its handlers with	2098	If possible and supported, libev will install its handlers with
1986	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2099	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1987	interrupted. If you have a problem with system calls getting interrupted by	2100	not be unduly interrupted. If you have a problem with system calls getting
1988	signals you can block all signals in an C<ev_check> watcher and unblock	2101	interrupted by signals you can block all signals in an C<ev_check> watcher
1989	them in an C<ev_prepare> watcher.	2102	and unblock them in an C<ev_prepare> watcher.
1990		2103
1991	=head3 Watcher-Specific Functions and Data Members	2104	=head3 Watcher-Specific Functions and Data Members
1992		2105
1993	=over 4	2106	=over 4
1994		2107
…		…
2032	in the next callback invocation is not.	2145	in the next callback invocation is not.
2033		2146
2034	Only the default event loop is capable of handling signals, and therefore	2147	Only the default event loop is capable of handling signals, and therefore
2035	you can only register child watchers in the default event loop.	2148	you can only register child watchers in the default event loop.
2036		2149
		2150	Due to some design glitches inside libev, child watchers will always be
		2151	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2152	libev)
		2153
2037	=head3 Process Interaction	2154	=head3 Process Interaction
2038		2155
2039	Libev grabs C<SIGCHLD> as soon as the default event loop is	2156	Libev grabs C<SIGCHLD> as soon as the default event loop is
2040	initialised. This is necessary to guarantee proper behaviour even if	2157	initialised. This is necessary to guarantee proper behaviour even if the
2041	the first child watcher is started after the child exits. The occurrence	2158	first child watcher is started after the child exits. The occurrence
2042	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2159	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
2043	synchronously as part of the event loop processing. Libev always reaps all	2160	synchronously as part of the event loop processing. Libev always reaps all
2044	children, even ones not watched.	2161	children, even ones not watched.
2045		2162
2046	=head3 Overriding the Built-In Processing	2163	=head3 Overriding the Built-In Processing
…		…
2056	=head3 Stopping the Child Watcher	2173	=head3 Stopping the Child Watcher
2057		2174
2058	Currently, the child watcher never gets stopped, even when the	2175	Currently, the child watcher never gets stopped, even when the
2059	child terminates, so normally one needs to stop the watcher in the	2176	child terminates, so normally one needs to stop the watcher in the
2060	callback. Future versions of libev might stop the watcher automatically	2177	callback. Future versions of libev might stop the watcher automatically
2061	when a child exit is detected.	2178	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2179	problem).
2062		2180
2063	=head3 Watcher-Specific Functions and Data Members	2181	=head3 Watcher-Specific Functions and Data Members
2064		2182
2065	=over 4	2183	=over 4
2066		2184
…		…
3667	defined to be C<0>, then they are not.	3785	defined to be C<0>, then they are not.
3668		3786
3669	=item EV_MINIMAL	3787	=item EV_MINIMAL
3670		3788
3671	If you need to shave off some kilobytes of code at the expense of some	3789	If you need to shave off some kilobytes of code at the expense of some
3672	speed, define this symbol to C<1>. Currently this is used to override some	3790	speed (but with the full API), define this symbol to C<1>. Currently this
3673	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3791	is used to override some inlining decisions, saves roughly 30% code size
3674	much smaller 2-heap for timer management over the default 4-heap.	3792	on amd64. It also selects a much smaller 2-heap for timer management over
		3793	the default 4-heap.
		3794
		3795	You can save even more by disabling watcher types you do not need
		3796	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3797	(C<-DNDEBUG>) will usually reduce code size a lot.
		3798
		3799	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3800	provide a bare-bones event library. See C<ev.h> for details on what parts
		3801	of the API are still available, and do not complain if this subset changes
		3802	over time.
3675		3803
3676	=item EV_PID_HASHSIZE	3804	=item EV_PID_HASHSIZE
3677		3805
3678	C<ev_child> watchers use a small hash table to distribute workload by	3806	C<ev_child> watchers use a small hash table to distribute workload by
3679	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3807	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3865	default loop and triggering an C<ev_async> watcher from the default loop	3993	default loop and triggering an C<ev_async> watcher from the default loop
3866	watcher callback into the event loop interested in the signal.	3994	watcher callback into the event loop interested in the signal.
3867		3995
3868	=back	3996	=back
3869		3997
		3998	=head4 THREAD LOCKING EXAMPLE
		3999
		4000	Here is a fictitious example of how to run an event loop in a different
		4001	thread than where callbacks are being invoked and watchers are
		4002	created/added/removed.
		4003
		4004	For a real-world example, see the C<EV::Loop::Async> perl module,
		4005	which uses exactly this technique (which is suited for many high-level
		4006	languages).
		4007
		4008	The example uses a pthread mutex to protect the loop data, a condition
		4009	variable to wait for callback invocations, an async watcher to notify the
		4010	event loop thread and an unspecified mechanism to wake up the main thread.
		4011
		4012	First, you need to associate some data with the event loop:
		4013
		4014	typedef struct {
		4015	mutex_t lock; /* global loop lock */
		4016	ev_async async_w;
		4017	thread_t tid;
		4018	cond_t invoke_cv;
		4019	} userdata;
		4020
		4021	void prepare_loop (EV_P)
		4022	{
		4023	// for simplicity, we use a static userdata struct.
		4024	static userdata u;
		4025
		4026	ev_async_init (&u->async_w, async_cb);
		4027	ev_async_start (EV_A_ &u->async_w);
		4028
		4029	pthread_mutex_init (&u->lock, 0);
		4030	pthread_cond_init (&u->invoke_cv, 0);
		4031
		4032	// now associate this with the loop
		4033	ev_set_userdata (EV_A_ u);
		4034	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4035	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4036
		4037	// then create the thread running ev_loop
		4038	pthread_create (&u->tid, 0, l_run, EV_A);
		4039	}
		4040
		4041	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4042	solely to wake up the event loop so it takes notice of any new watchers
		4043	that might have been added:
		4044
		4045	static void
		4046	async_cb (EV_P_ ev_async *w, int revents)
		4047	{
		4048	// just used for the side effects
		4049	}
		4050
		4051	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4052	protecting the loop data, respectively.
		4053
		4054	static void
		4055	l_release (EV_P)
		4056	{
		4057	userdata *u = ev_userdata (EV_A);
		4058	pthread_mutex_unlock (&u->lock);
		4059	}
		4060
		4061	static void
		4062	l_acquire (EV_P)
		4063	{
		4064	userdata *u = ev_userdata (EV_A);
		4065	pthread_mutex_lock (&u->lock);
		4066	}
		4067
		4068	The event loop thread first acquires the mutex, and then jumps straight
		4069	into C<ev_loop>:
		4070
		4071	void *
		4072	l_run (void *thr_arg)
		4073	{
		4074	struct ev_loop loop = (struct ev_loop )thr_arg;
		4075
		4076	l_acquire (EV_A);
		4077	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4078	ev_loop (EV_A_ 0);
		4079	l_release (EV_A);
		4080
		4081	return 0;
		4082	}
		4083
		4084	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4085	signal the main thread via some unspecified mechanism (signals? pipe
		4086	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4087	have been called (in a while loop because a) spurious wakeups are possible
		4088	and b) skipping inter-thread-communication when there are no pending
		4089	watchers is very beneficial):
		4090
		4091	static void
		4092	l_invoke (EV_P)
		4093	{
		4094	userdata *u = ev_userdata (EV_A);
		4095
		4096	while (ev_pending_count (EV_A))
		4097	{
		4098	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4099	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4100	}
		4101	}
		4102
		4103	Now, whenever the main thread gets told to invoke pending watchers, it
		4104	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4105	thread to continue:
		4106
		4107	static void
		4108	real_invoke_pending (EV_P)
		4109	{
		4110	userdata *u = ev_userdata (EV_A);
		4111
		4112	pthread_mutex_lock (&u->lock);
		4113	ev_invoke_pending (EV_A);
		4114	pthread_cond_signal (&u->invoke_cv);
		4115	pthread_mutex_unlock (&u->lock);
		4116	}
		4117
		4118	Whenever you want to start/stop a watcher or do other modifications to an
		4119	event loop, you will now have to lock:
		4120
		4121	ev_timer timeout_watcher;
		4122	userdata *u = ev_userdata (EV_A);
		4123
		4124	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4125
		4126	pthread_mutex_lock (&u->lock);
		4127	ev_timer_start (EV_A_ &timeout_watcher);
		4128	ev_async_send (EV_A_ &u->async_w);
		4129	pthread_mutex_unlock (&u->lock);
		4130
		4131	Note that sending the C<ev_async> watcher is required because otherwise
		4132	an event loop currently blocking in the kernel will have no knowledge
		4133	about the newly added timer. By waking up the loop it will pick up any new
		4134	watchers in the next event loop iteration.
		4135
3870	=head3 COROUTINES	4136	=head3 COROUTINES
3871		4137
3872	Libev is very accommodating to coroutines ("cooperative threads"):	4138	Libev is very accommodating to coroutines ("cooperative threads"):
3873	libev fully supports nesting calls to its functions from different	4139	libev fully supports nesting calls to its functions from different
3874	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4140	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3875	different coroutines, and switch freely between both coroutines running the	4141	different coroutines, and switch freely between both coroutines running
3876	loop, as long as you don't confuse yourself). The only exception is that	4142	the loop, as long as you don't confuse yourself). The only exception is
3877	you must not do this from C<ev_periodic> reschedule callbacks.	4143	that you must not do this from C<ev_periodic> reschedule callbacks.
3878		4144
3879	Care has been taken to ensure that libev does not keep local state inside	4145	Care has been taken to ensure that libev does not keep local state inside
3880	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4146	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3881	they do not call any callbacks.	4147	they do not call any callbacks.
3882		4148

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Comparing libev/ev.pod (file contents): Revision 1.247 by root, Wed Jul 8 02:46:05 2009 UTC vs. Revision 1.259 by root, Sun Jul 19 01:36:34 2009 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.247 by root, Wed Jul 8 02:46:05 2009 UTC vs.
Revision 1.259 by root, Sun Jul 19 01:36:34 2009 UTC