[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 1.258 by root, Wed Jul 15 16:58:53 2009 UTC

…		…
862		862
863	This call will simply invoke all pending watchers while resetting their	863	This call will simply invoke all pending watchers while resetting their
864	pending state. Normally, C<ev_loop> does this automatically when required,	864	pending state. Normally, C<ev_loop> does this automatically when required,
865	but when overriding the invoke callback this call comes handy.	865	but when overriding the invoke callback this call comes handy.
866		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
867	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))	872	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
868		873
869	This overrides the invoke pending functionality of the loop: Instead of	874	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	875	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	876	this callback instead. This is useful, for example, when you want to
…		…
889	suspended waiting for new events, and C<acquire> is called just	894	suspended waiting for new events, and C<acquire> is called just
890	afterwards.	895	afterwards.
891		896
892	Ideally, C<release> will just call your mutex_unlock function, and	897	Ideally, C<release> will just call your mutex_unlock function, and
893	C<acquire> will just call the mutex_lock function again.	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.
894		912
895	=item ev_set_userdata (loop, void *data)	913	=item ev_set_userdata (loop, void *data)
896		914
897	=item ev_userdata (loop)	915	=item ev_userdata (loop)
898		916
…		…
1737		1755
1738	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
1739	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
1740	()>.	1758	()>.
1741		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
1742	=head3 Watcher-Specific Functions and Data Members	1790	=head3 Watcher-Specific Functions and Data Members
1743		1791
1744	=over 4	1792	=over 4
1745		1793
1746	=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)
…		…
1771	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
1772	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.
1773		1821
1774	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
1775	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.
1776		1836
1777	=item ev_tstamp repeat [read-write]	1837	=item ev_tstamp repeat [read-write]
1778		1838
1779	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
1780	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),
…		…
3928		3988
3929	=back	3989	=back
3930		3990
3931	=head4 THREAD LOCKING EXAMPLE	3991	=head4 THREAD LOCKING EXAMPLE
3932		3992
		3993	Here is a fictitious example of how to run an event loop in a different
		3994	thread than where callbacks are being invoked and watchers are
		3995	created/added/removed.
		3996
		3997	For a real-world example, see the C<EV::Loop::Async> perl module,
		3998	which uses exactly this technique (which is suited for many high-level
		3999	languages).
		4000
		4001	The example uses a pthread mutex to protect the loop data, a condition
		4002	variable to wait for callback invocations, an async watcher to notify the
		4003	event loop thread and an unspecified mechanism to wake up the main thread.
		4004
		4005	First, you need to associate some data with the event loop:
		4006
		4007	typedef struct {
		4008	mutex_t lock; /* global loop lock */
		4009	ev_async async_w;
		4010	thread_t tid;
		4011	cond_t invoke_cv;
		4012	} userdata;
		4013
		4014	void prepare_loop (EV_P)
		4015	{
		4016	// for simplicity, we use a static userdata struct.
		4017	static userdata u;
		4018
		4019	ev_async_init (&u->async_w, async_cb);
		4020	ev_async_start (EV_A_ &u->async_w);
		4021
		4022	pthread_mutex_init (&u->lock, 0);
		4023	pthread_cond_init (&u->invoke_cv, 0);
		4024
		4025	// now associate this with the loop
		4026	ev_set_userdata (EV_A_ u);
		4027	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4028	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4029
		4030	// then create the thread running ev_loop
		4031	pthread_create (&u->tid, 0, l_run, EV_A);
		4032	}
		4033
		4034	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4035	solely to wake up the event loop so it takes notice of any new watchers
		4036	that might have been added:
		4037
		4038	static void
		4039	async_cb (EV_P_ ev_async *w, int revents)
		4040	{
		4041	// just used for the side effects
		4042	}
		4043
		4044	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4045	protecting the loop data, respectively.
		4046
		4047	static void
		4048	l_release (EV_P)
		4049	{
		4050	userdata *u = ev_userdata (EV_A);
		4051	pthread_mutex_unlock (&u->lock);
		4052	}
		4053
		4054	static void
		4055	l_acquire (EV_P)
		4056	{
		4057	userdata *u = ev_userdata (EV_A);
		4058	pthread_mutex_lock (&u->lock);
		4059	}
		4060
		4061	The event loop thread first acquires the mutex, and then jumps straight
		4062	into C<ev_loop>:
		4063
		4064	void *
		4065	l_run (void *thr_arg)
		4066	{
		4067	struct ev_loop loop = (struct ev_loop )thr_arg;
		4068
		4069	l_acquire (EV_A);
		4070	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4071	ev_loop (EV_A_ 0);
		4072	l_release (EV_A);
		4073
		4074	return 0;
		4075	}
		4076
		4077	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4078	signal the main thread via some unspecified mechanism (signals? pipe
		4079	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4080	have been called (in a while loop because a) spurious wakeups are possible
		4081	and b) skipping inter-thread-communication when there are no pending
		4082	watchers is very beneficial):
		4083
		4084	static void
		4085	l_invoke (EV_P)
		4086	{
		4087	userdata *u = ev_userdata (EV_A);
		4088
		4089	while (ev_pending_count (EV_A))
		4090	{
		4091	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4092	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4093	}
		4094	}
		4095
		4096	Now, whenever the main thread gets told to invoke pending watchers, it
		4097	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4098	thread to continue:
		4099
		4100	static void
		4101	real_invoke_pending (EV_P)
		4102	{
		4103	userdata *u = ev_userdata (EV_A);
		4104
		4105	pthread_mutex_lock (&u->lock);
		4106	ev_invoke_pending (EV_A);
		4107	pthread_cond_signal (&u->invoke_cv);
		4108	pthread_mutex_unlock (&u->lock);
		4109	}
		4110
		4111	Whenever you want to start/stop a watcher or do other modifications to an
		4112	event loop, you will now have to lock:
		4113
		4114	ev_timer timeout_watcher;
		4115	userdata *u = ev_userdata (EV_A);
		4116
		4117	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4118
		4119	pthread_mutex_lock (&u->lock);
		4120	ev_timer_start (EV_A_ &timeout_watcher);
		4121	ev_async_send (EV_A_ &u->async_w);
		4122	pthread_mutex_unlock (&u->lock);
		4123
		4124	Note that sending the C<ev_async> watcher is required because otherwise
		4125	an event loop currently blocking in the kernel will have no knowledge
		4126	about the newly added timer. By waking up the loop it will pick up any new
		4127	watchers in the next event loop iteration.
		4128
3933	=head3 COROUTINES	4129	=head3 COROUTINES
3934		4130
3935	Libev is very accommodating to coroutines ("cooperative threads"):	4131	Libev is very accommodating to coroutines ("cooperative threads"):
3936	libev fully supports nesting calls to its functions from different	4132	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	4133	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	4134	different coroutines, and switch freely between both coroutines running
3939	loop, as long as you don't confuse yourself). The only exception is that	4135	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.	4136	that you must not do this from C<ev_periodic> reschedule callbacks.
3941		4137
3942	Care has been taken to ensure that libev does not keep local state inside	4138	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	4139	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3944	they do not call any callbacks.	4140	they do not call any callbacks.
3945		4141

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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 1.258 by root, Wed Jul 15 16:58:53 2009 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.253 by root, Tue Jul 14 18:33:48 2009 UTC vs.
Revision 1.258 by root, Wed Jul 15 16:58:53 2009 UTC