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

Comparing libev/ev.pod (file contents):
Revision 1.243 by root, Sat Jun 20 20:22:35 2009 UTC vs.
Revision 1.255 by root, Tue Jul 14 19:11:31 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 ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		868
		869	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
		871	this callback instead. This is useful, for example, when you want to
		872	invoke the actual watchers inside another context (another thread etc.).
		873
		874	If you want to reset the callback, use C<ev_invoke_pending> as new
		875	callback.
		876
		877	=item ev_set_loop_release_cb (loop, void (release)(EV_P), void (acquire)(EV_P))
		878
		879	Sometimes you want to share the same loop between multiple threads. This
		880	can be done relatively simply by putting mutex_lock/unlock calls around
		881	each call to a libev function.
		882
		883	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		884	wait for it to return. One way around this is to wake up the loop via
		885	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		886	and I<acquire> callbacks on the loop.
		887
		888	When set, then C<release> will be called just before the thread is
		889	suspended waiting for new events, and C<acquire> is called just
		890	afterwards.
		891
		892	Ideally, C<release> will just call your mutex_unlock function, and
		893	C<acquire> will just call the mutex_lock function again.
		894
		895	While event loop modifications are allowed between invocations of
		896	C<release> and C<acquire> (that's their only purpose after all), no
		897	modifications done will affect the event loop, i.e. adding watchers will
		898	have no effect on the set of file descriptors being watched, or the time
		899	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		900	to take note of any changes you made.
		901
		902	In theory, threads executing C<ev_loop> will be async-cancel safe between
		903	invocations of C<release> and C<acquire>.
		904
		905	See also the locking example in the C<THREADS> section later in this
		906	document.
		907
		908	=item ev_set_userdata (loop, void *data)
		909
		910	=item ev_userdata (loop)
		911
		912	Set and retrieve a single C<void *> associated with a loop. When
		913	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		914	C<0.>
		915
		916	These two functions can be used to associate arbitrary data with a loop,
		917	and are intended solely for the C<invoke_pending_cb>, C<release> and
		918	C<acquire> callbacks described above, but of course can be (ab-)used for
		919	any other purpose as well.
836		920
837	=item ev_loop_verify (loop)	921	=item ev_loop_verify (loop)
838		922
839	This function only does something when C<EV_VERIFY> support has been	923	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	924	compiled in, which is the default for non-minimal builds. It tries to go
…		…
1468		1552
1469	The callback is guaranteed to be invoked only I<after> its timeout has	1553	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	1554	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	1555	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	1556	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	1557	before ones of the same priority with later time-out values (but this is
1474	callback calls C<ev_loop> recursively).	1558	no longer true when a callback calls C<ev_loop> recursively).
1475		1559
1476	=head3 Be smart about timeouts	1560	=head3 Be smart about timeouts
1477		1561
1478	Many real-world problems involve some kind of timeout, usually for error	1562	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,	1563	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
2002	some child status changes (most typically when a child of yours dies or	2086	some child status changes (most typically when a child of yours dies or
2003	exits). It is permissible to install a child watcher I<after> the child	2087	exits). It is permissible to install a child watcher I<after> the child
2004	has been forked (which implies it might have already exited), as long	2088	has been forked (which implies it might have already exited), as long
2005	as the event loop isn't entered (or is continued from a watcher), i.e.,	2089	as the event loop isn't entered (or is continued from a watcher), i.e.,
2006	forking and then immediately registering a watcher for the child is fine,	2090	forking and then immediately registering a watcher for the child is fine,
2007	but forking and registering a watcher a few event loop iterations later is	2091	but forking and registering a watcher a few event loop iterations later or
2008	not.	2092	in the next callback invocation is not.
2009		2093
2010	Only the default event loop is capable of handling signals, and therefore	2094	Only the default event loop is capable of handling signals, and therefore
2011	you can only register child watchers in the default event loop.	2095	you can only register child watchers in the default event loop.
		2096
		2097	Due to some design glitches inside libev, child watchers will always be
		2098	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2099	libev)
2012		2100
2013	=head3 Process Interaction	2101	=head3 Process Interaction
2014		2102
2015	Libev grabs C<SIGCHLD> as soon as the default event loop is	2103	Libev grabs C<SIGCHLD> as soon as the default event loop is
2016	initialised. This is necessary to guarantee proper behaviour even if	2104	initialised. This is necessary to guarantee proper behaviour even if
…		…
3643	defined to be C<0>, then they are not.	3731	defined to be C<0>, then they are not.
3644		3732
3645	=item EV_MINIMAL	3733	=item EV_MINIMAL
3646		3734
3647	If you need to shave off some kilobytes of code at the expense of some	3735	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	3736	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	3737	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.	3738	on amd64. It also selects a much smaller 2-heap for timer management over
		3739	the default 4-heap.
		3740
		3741	You can save even more by disabling watcher types you do not need
		3742	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3743	(C<-DNDEBUG>) will usually reduce code size a lot.
		3744
		3745	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3746	provide a bare-bones event library. See C<ev.h> for details on what parts
		3747	of the API are still available, and do not complain if this subset changes
		3748	over time.
3651		3749
3652	=item EV_PID_HASHSIZE	3750	=item EV_PID_HASHSIZE
3653		3751
3654	C<ev_child> watchers use a small hash table to distribute workload by	3752	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	3753	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	3939	default loop and triggering an C<ev_async> watcher from the default loop
3842	watcher callback into the event loop interested in the signal.	3940	watcher callback into the event loop interested in the signal.
3843		3941
3844	=back	3942	=back
3845		3943
		3944	=head4 THREAD LOCKING EXAMPLE
		3945
		3946	Here is a fictitious example of how to run an event loop in a different
		3947	thread than where callbacks are being invoked and watchers are
		3948	created/added/removed.
		3949
		3950	For a real-world example, see the C<EV::Loop::Async> perl module,
		3951	which uses exactly this technique (which is suited for many high-level
		3952	languages).
		3953
		3954	The example uses a pthread mutex to protect the loop data, a condition
		3955	variable to wait for callback invocations, an async watcher to notify the
		3956	event loop thread and an unspecified mechanism to wake up the main thread.
		3957
		3958	First, you need to associate some data with the event loop:
		3959
		3960	typedef struct {
		3961	mutex_t lock; /* global loop lock */
		3962	ev_async async_w;
		3963	thread_t tid;
		3964	cond_t invoke_cv;
		3965	} userdata;
		3966
		3967	void prepare_loop (EV_P)
		3968	{
		3969	// for simplicity, we use a static userdata struct.
		3970	static userdata u;
		3971
		3972	ev_async_init (&u->async_w, async_cb);
		3973	ev_async_start (EV_A_ &u->async_w);
		3974
		3975	pthread_mutex_init (&u->lock, 0);
		3976	pthread_cond_init (&u->invoke_cv, 0);
		3977
		3978	// now associate this with the loop
		3979	ev_set_userdata (EV_A_ u);
		3980	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3981	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3982
		3983	// then create the thread running ev_loop
		3984	pthread_create (&u->tid, 0, l_run, EV_A);
		3985	}
		3986
		3987	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3988	solely to wake up the event loop so it takes notice of any new watchers
		3989	that might have been added:
		3990
		3991	static void
		3992	async_cb (EV_P_ ev_async *w, int revents)
		3993	{
		3994	// just used for the side effects
		3995	}
		3996
		3997	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3998	protecting the loop data, respectively.
		3999
		4000	static void
		4001	l_release (EV_P)
		4002	{
		4003	userdata *u = ev_userdata (EV_A);
		4004	pthread_mutex_unlock (&u->lock);
		4005	}
		4006
		4007	static void
		4008	l_acquire (EV_P)
		4009	{
		4010	userdata *u = ev_userdata (EV_A);
		4011	pthread_mutex_lock (&u->lock);
		4012	}
		4013
		4014	The event loop thread first acquires the mutex, and then jumps straight
		4015	into C<ev_loop>:
		4016
		4017	void *
		4018	l_run (void *thr_arg)
		4019	{
		4020	struct ev_loop loop = (struct ev_loop )thr_arg;
		4021
		4022	l_acquire (EV_A);
		4023	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4024	ev_loop (EV_A_ 0);
		4025	l_release (EV_A);
		4026
		4027	return 0;
		4028	}
		4029
		4030	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4031	signal the main thread via some unspecified mechanism (signals? pipe
		4032	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4033	have been called:
		4034
		4035	static void
		4036	l_invoke (EV_P)
		4037	{
		4038	userdata *u = ev_userdata (EV_A);
		4039
		4040	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4041
		4042	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4043	}
		4044
		4045	Now, whenever the main thread gets told to invoke pending watchers, it
		4046	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4047	thread to continue:
		4048
		4049	static void
		4050	real_invoke_pending (EV_P)
		4051	{
		4052	userdata *u = ev_userdata (EV_A);
		4053
		4054	pthread_mutex_lock (&u->lock);
		4055	ev_invoke_pending (EV_A);
		4056	pthread_cond_signal (&u->invoke_cv);
		4057	pthread_mutex_unlock (&u->lock);
		4058	}
		4059
		4060	Whenever you want to start/stop a watcher or do other modifications to an
		4061	event loop, you will now have to lock:
		4062
		4063	ev_timer timeout_watcher;
		4064	userdata *u = ev_userdata (EV_A);
		4065
		4066	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4067
		4068	pthread_mutex_lock (&u->lock);
		4069	ev_timer_start (EV_A_ &timeout_watcher);
		4070	ev_async_send (EV_A_ &u->async_w);
		4071	pthread_mutex_unlock (&u->lock);
		4072
		4073	Note that sending the C<ev_async> watcher is required because otherwise
		4074	an event loop currently blocking in the kernel will have no knowledge
		4075	about the newly added timer. By waking up the loop it will pick up any new
		4076	watchers in the next event loop iteration.
		4077
3846	=head3 COROUTINES	4078	=head3 COROUTINES
3847		4079
3848	Libev is very accommodating to coroutines ("cooperative threads"):	4080	Libev is very accommodating to coroutines ("cooperative threads"):
3849	libev fully supports nesting calls to its functions from different	4081	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	4082	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	4083	different coroutines, and switch freely between both coroutines running
3852	loop, as long as you don't confuse yourself). The only exception is that	4084	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.	4085	that you must not do this from C<ev_periodic> reschedule callbacks.
3854		4086
3855	Care has been taken to ensure that libev does not keep local state inside	4087	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	4088	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3857	they do not call any callbacks.	4089	they do not call any callbacks.
3858		4090
…		…
4065	=item C<double> must hold a time value in seconds with enough accuracy	4297	=item C<double> must hold a time value in seconds with enough accuracy
4066		4298
4067	The type C<double> is used to represent timestamps. It is required to	4299	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	4300	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	4301	enough for at least into the year 4000. This requirement is fulfilled by
4070	implementations implementing IEEE 754 (basically all existing ones).	4302	implementations implementing IEEE 754, which is basically all existing
		4303	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4304	2200.
4071		4305
4072	=back	4306	=back
4073		4307
4074	If you know of other additional requirements drop me a note.	4308	If you know of other additional requirements drop me a note.
4075		4309

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Comparing libev/ev.pod (file contents): Revision 1.243 by root, Sat Jun 20 20:22:35 2009 UTC vs. Revision 1.255 by root, Tue Jul 14 19:11:31 2009 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.243 by root, Sat Jun 20 20:22:35 2009 UTC vs.
Revision 1.255 by root, Tue Jul 14 19:11:31 2009 UTC