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

Comparing libev/ev.pod (file contents):
Revision 1.244 by root, Mon Jun 29 04:41:34 2009 UTC vs.
Revision 1.258 by root, Wed Jul 15 16:58:53 2009 UTC

…		…
620	happily wraps around with enough iterations.	620	happily wraps around with enough iterations.
621		621
622	This value can sometimes be useful as a generation counter of sorts (it	622	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	623	"ticks" the number of loop iterations), as it roughly corresponds with
624	C<ev_prepare> and C<ev_check> calls.	624	C<ev_prepare> and C<ev_check> calls.
		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
625		637
626	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
627		639
628	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
629	use.	641	use.
…		…
811		823
812	By setting a higher I<io collect interval> you allow libev to spend more	824	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,	825	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	826	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	827	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.	828	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		829	sleep time ensures that libev will not poll for I/O events more often then
		830	once per this interval, on average.
817		831
818	Likewise, by setting a higher I<timeout collect interval> you allow libev	832	Likewise, by setting a higher I<timeout collect interval> you allow libev
819	to spend more time collecting timeouts, at the expense of increased	833	to spend more time collecting timeouts, at the expense of increased
820	latency/jitter/inexactness (the watcher callback will be called	834	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	835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
823		837
824	Many (busy) programs can usually benefit by setting the I/O collect	838	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	839	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	840	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>,	841	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.	842	as this approaches the timing granularity of most systems. Note that if
		843	you do transactions with the outside world and you can't increase the
		844	parallelity, then this setting will limit your transaction rate (if you
		845	need to poll once per transaction and the I/O collect interval is 0.01,
		846	then you can't do more than 100 transations per second).
829		847
830	Setting the I<timeout collect interval> can improve the opportunity for	848	Setting the I<timeout collect interval> can improve the opportunity for
831	saving power, as the program will "bundle" timer callback invocations that	849	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	850	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	851	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	852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
835	they fire on, say, one-second boundaries only.	853	they fire on, say, one-second boundaries only.
		854
		855	Example: we only need 0.1s timeout granularity, and we wish not to poll
		856	more often than 100 times per second:
		857
		858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		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.
836		925
837	=item ev_loop_verify (loop)	926	=item ev_loop_verify (loop)
838		927
839	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
840	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
…		…
1468		1557
1469	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
1470	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
1471	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
1472	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
1473	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
1474	callback calls C<ev_loop> recursively).	1563	no longer true when a callback calls C<ev_loop> recursively).
1475		1564
1476	=head3 Be smart about timeouts	1565	=head3 Be smart about timeouts
1477		1566
1478	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
1479	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,
…		…
1666		1755
1667	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
1668	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
1669	()>.	1758	()>.
1670		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
1671	=head3 Watcher-Specific Functions and Data Members	1790	=head3 Watcher-Specific Functions and Data Members
1672		1791
1673	=over 4	1792	=over 4
1674		1793
1675	=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)
…		…
1700	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
1701	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.
1702		1821
1703	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
1704	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.
1705		1836
1706	=item ev_tstamp repeat [read-write]	1837	=item ev_tstamp repeat [read-write]
1707		1838
1708	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
1709	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),
…		…
2007	but forking and registering a watcher a few event loop iterations later or	2138	but forking and registering a watcher a few event loop iterations later or
2008	in the next callback invocation is not.	2139	in the next callback invocation is not.
2009		2140
2010	Only the default event loop is capable of handling signals, and therefore	2141	Only the default event loop is capable of handling signals, and therefore
2011	you can only register child watchers in the default event loop.	2142	you can only register child watchers in the default event loop.
		2143
		2144	Due to some design glitches inside libev, child watchers will always be
		2145	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2146	libev)
2012		2147
2013	=head3 Process Interaction	2148	=head3 Process Interaction
2014		2149
2015	Libev grabs C<SIGCHLD> as soon as the default event loop is	2150	Libev grabs C<SIGCHLD> as soon as the default event loop is
2016	initialised. This is necessary to guarantee proper behaviour even if	2151	initialised. This is necessary to guarantee proper behaviour even if
…		…
3643	defined to be C<0>, then they are not.	3778	defined to be C<0>, then they are not.
3644		3779
3645	=item EV_MINIMAL	3780	=item EV_MINIMAL
3646		3781
3647	If you need to shave off some kilobytes of code at the expense of some	3782	If you need to shave off some kilobytes of code at the expense of some
3648	speed, define this symbol to C<1>. Currently this is used to override some	3783	speed (but with the full API), define this symbol to C<1>. Currently this
3649	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3784	is used to override some inlining decisions, saves roughly 30% code size
3650	much smaller 2-heap for timer management over the default 4-heap.	3785	on amd64. It also selects a much smaller 2-heap for timer management over
		3786	the default 4-heap.
		3787
		3788	You can save even more by disabling watcher types you do not need
		3789	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3790	(C<-DNDEBUG>) will usually reduce code size a lot.
		3791
		3792	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3793	provide a bare-bones event library. See C<ev.h> for details on what parts
		3794	of the API are still available, and do not complain if this subset changes
		3795	over time.
3651		3796
3652	=item EV_PID_HASHSIZE	3797	=item EV_PID_HASHSIZE
3653		3798
3654	C<ev_child> watchers use a small hash table to distribute workload by	3799	C<ev_child> watchers use a small hash table to distribute workload by
3655	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3800	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3841	default loop and triggering an C<ev_async> watcher from the default loop	3986	default loop and triggering an C<ev_async> watcher from the default loop
3842	watcher callback into the event loop interested in the signal.	3987	watcher callback into the event loop interested in the signal.
3843		3988
3844	=back	3989	=back
3845		3990
		3991	=head4 THREAD LOCKING EXAMPLE
		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
3846	=head3 COROUTINES	4129	=head3 COROUTINES
3847		4130
3848	Libev is very accommodating to coroutines ("cooperative threads"):	4131	Libev is very accommodating to coroutines ("cooperative threads"):
3849	libev fully supports nesting calls to its functions from different	4132	libev fully supports nesting calls to its functions from different
3850	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4133	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3851	different coroutines, and switch freely between both coroutines running the	4134	different coroutines, and switch freely between both coroutines running
3852	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
3853	you must not do this from C<ev_periodic> reschedule callbacks.	4136	that you must not do this from C<ev_periodic> reschedule callbacks.
3854		4137
3855	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
3856	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
3857	they do not call any callbacks.	4140	they do not call any callbacks.
3858		4141
…		…
4065	=item C<double> must hold a time value in seconds with enough accuracy	4348	=item C<double> must hold a time value in seconds with enough accuracy
4066		4349
4067	The type C<double> is used to represent timestamps. It is required to	4350	The type C<double> is used to represent timestamps. It is required to
4068	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4351	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
4069	enough for at least into the year 4000. This requirement is fulfilled by	4352	enough for at least into the year 4000. This requirement is fulfilled by
4070	implementations implementing IEEE 754 (basically all existing ones).	4353	implementations implementing IEEE 754, which is basically all existing
		4354	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4355	2200.
4071		4356
4072	=back	4357	=back
4073		4358
4074	If you know of other additional requirements drop me a note.	4359	If you know of other additional requirements drop me a note.
4075		4360

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Comparing libev/ev.pod (file contents): Revision 1.244 by root, Mon Jun 29 04:41:34 2009 UTC vs. Revision 1.258 by root, Wed Jul 15 16:58:53 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.244 by root, Mon Jun 29 04:41:34 2009 UTC vs.
Revision 1.258 by root, Wed Jul 15 16:58:53 2009 UTC