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

Comparing libev/ev.pod (file contents):
Revision 1.242 by root, Thu Jun 18 18:16:54 2009 UTC vs.
Revision 1.256 by root, Tue Jul 14 20:31:21 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,
…		…
1523	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1612	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1524	member and C<ev_timer_again>.	1613	member and C<ev_timer_again>.
1525		1614
1526	At start:	1615	At start:
1527		1616
1528	ev_timer_init (timer, callback);	1617	ev_init (timer, callback);
1529	timer->repeat = 60.;	1618	timer->repeat = 60.;
1530	ev_timer_again (loop, timer);	1619	ev_timer_again (loop, timer);
1531		1620
1532	Each time there is some activity:	1621	Each time there is some activity:
1533		1622
…		…
1595		1684
1596	To start the timer, simply initialise the watcher and set C<last_activity>	1685	To start the timer, simply initialise the watcher and set C<last_activity>
1597	to the current time (meaning we just have some activity :), then call the	1686	to the current time (meaning we just have some activity :), then call the
1598	callback, which will "do the right thing" and start the timer:	1687	callback, which will "do the right thing" and start the timer:
1599		1688
1600	ev_timer_init (timer, callback);	1689	ev_init (timer, callback);
1601	last_activity = ev_now (loop);	1690	last_activity = ev_now (loop);
1602	callback (loop, timer, EV_TIMEOUT);	1691	callback (loop, timer, EV_TIMEOUT);
1603		1692
1604	And when there is some activity, simply store the current time in	1693	And when there is some activity, simply store the current time in
1605	C<last_activity>, no libev calls at all:	1694	C<last_activity>, no libev calls at all:
…		…
2002	some child status changes (most typically when a child of yours dies or	2091	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	2092	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	2093	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.,	2094	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,	2095	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	2096	but forking and registering a watcher a few event loop iterations later or
2008	not.	2097	in the next callback invocation is not.
2009		2098
2010	Only the default event loop is capable of handling signals, and therefore	2099	Only the default event loop is capable of handling signals, and therefore
2011	you can only register child watchers in the default event loop.	2100	you can only register child watchers in the default event loop.
		2101
		2102	Due to some design glitches inside libev, child watchers will always be
		2103	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2104	libev)
2012		2105
2013	=head3 Process Interaction	2106	=head3 Process Interaction
2014		2107
2015	Libev grabs C<SIGCHLD> as soon as the default event loop is	2108	Libev grabs C<SIGCHLD> as soon as the default event loop is
2016	initialised. This is necessary to guarantee proper behaviour even if	2109	initialised. This is necessary to guarantee proper behaviour even if
…		…
2471	struct pollfd fds [nfd];	2564	struct pollfd fds [nfd];
2472	// actual code will need to loop here and realloc etc.	2565	// actual code will need to loop here and realloc etc.
2473	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2566	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2474		2567
2475	/* the callback is illegal, but won't be called as we stop during check */	2568	/* the callback is illegal, but won't be called as we stop during check */
2476	ev_timer_init (&tw, 0, timeout * 1e-3);	2569	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2477	ev_timer_start (loop, &tw);	2570	ev_timer_start (loop, &tw);
2478		2571
2479	// create one ev_io per pollfd	2572	// create one ev_io per pollfd
2480	for (int i = 0; i < nfd; ++i)	2573	for (int i = 0; i < nfd; ++i)
2481	{	2574	{
…		…
3643	defined to be C<0>, then they are not.	3736	defined to be C<0>, then they are not.
3644		3737
3645	=item EV_MINIMAL	3738	=item EV_MINIMAL
3646		3739
3647	If you need to shave off some kilobytes of code at the expense of some	3740	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	3741	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	3742	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.	3743	on amd64. It also selects a much smaller 2-heap for timer management over
		3744	the default 4-heap.
		3745
		3746	You can save even more by disabling watcher types you do not need
		3747	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3748	(C<-DNDEBUG>) will usually reduce code size a lot.
		3749
		3750	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3751	provide a bare-bones event library. See C<ev.h> for details on what parts
		3752	of the API are still available, and do not complain if this subset changes
		3753	over time.
3651		3754
3652	=item EV_PID_HASHSIZE	3755	=item EV_PID_HASHSIZE
3653		3756
3654	C<ev_child> watchers use a small hash table to distribute workload by	3757	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	3758	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	3944	default loop and triggering an C<ev_async> watcher from the default loop
3842	watcher callback into the event loop interested in the signal.	3945	watcher callback into the event loop interested in the signal.
3843		3946
3844	=back	3947	=back
3845		3948
		3949	=head4 THREAD LOCKING EXAMPLE
		3950
		3951	Here is a fictitious example of how to run an event loop in a different
		3952	thread than where callbacks are being invoked and watchers are
		3953	created/added/removed.
		3954
		3955	For a real-world example, see the C<EV::Loop::Async> perl module,
		3956	which uses exactly this technique (which is suited for many high-level
		3957	languages).
		3958
		3959	The example uses a pthread mutex to protect the loop data, a condition
		3960	variable to wait for callback invocations, an async watcher to notify the
		3961	event loop thread and an unspecified mechanism to wake up the main thread.
		3962
		3963	First, you need to associate some data with the event loop:
		3964
		3965	typedef struct {
		3966	mutex_t lock; /* global loop lock */
		3967	ev_async async_w;
		3968	thread_t tid;
		3969	cond_t invoke_cv;
		3970	} userdata;
		3971
		3972	void prepare_loop (EV_P)
		3973	{
		3974	// for simplicity, we use a static userdata struct.
		3975	static userdata u;
		3976
		3977	ev_async_init (&u->async_w, async_cb);
		3978	ev_async_start (EV_A_ &u->async_w);
		3979
		3980	pthread_mutex_init (&u->lock, 0);
		3981	pthread_cond_init (&u->invoke_cv, 0);
		3982
		3983	// now associate this with the loop
		3984	ev_set_userdata (EV_A_ u);
		3985	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3986	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3987
		3988	// then create the thread running ev_loop
		3989	pthread_create (&u->tid, 0, l_run, EV_A);
		3990	}
		3991
		3992	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3993	solely to wake up the event loop so it takes notice of any new watchers
		3994	that might have been added:
		3995
		3996	static void
		3997	async_cb (EV_P_ ev_async *w, int revents)
		3998	{
		3999	// just used for the side effects
		4000	}
		4001
		4002	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4003	protecting the loop data, respectively.
		4004
		4005	static void
		4006	l_release (EV_P)
		4007	{
		4008	userdata *u = ev_userdata (EV_A);
		4009	pthread_mutex_unlock (&u->lock);
		4010	}
		4011
		4012	static void
		4013	l_acquire (EV_P)
		4014	{
		4015	userdata *u = ev_userdata (EV_A);
		4016	pthread_mutex_lock (&u->lock);
		4017	}
		4018
		4019	The event loop thread first acquires the mutex, and then jumps straight
		4020	into C<ev_loop>:
		4021
		4022	void *
		4023	l_run (void *thr_arg)
		4024	{
		4025	struct ev_loop loop = (struct ev_loop )thr_arg;
		4026
		4027	l_acquire (EV_A);
		4028	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4029	ev_loop (EV_A_ 0);
		4030	l_release (EV_A);
		4031
		4032	return 0;
		4033	}
		4034
		4035	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4036	signal the main thread via some unspecified mechanism (signals? pipe
		4037	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4038	have been called (in a while loop because a) spurious wakeups are possible
		4039	and b) skipping inter-thread-communication when there are no pending
		4040	watchers is very beneficial):
		4041
		4042	static void
		4043	l_invoke (EV_P)
		4044	{
		4045	userdata *u = ev_userdata (EV_A);
		4046
		4047	while (ev_pending_count (EV_A))
		4048	{
		4049	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4050	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4051	}
		4052	}
		4053
		4054	Now, whenever the main thread gets told to invoke pending watchers, it
		4055	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4056	thread to continue:
		4057
		4058	static void
		4059	real_invoke_pending (EV_P)
		4060	{
		4061	userdata *u = ev_userdata (EV_A);
		4062
		4063	pthread_mutex_lock (&u->lock);
		4064	ev_invoke_pending (EV_A);
		4065	pthread_cond_signal (&u->invoke_cv);
		4066	pthread_mutex_unlock (&u->lock);
		4067	}
		4068
		4069	Whenever you want to start/stop a watcher or do other modifications to an
		4070	event loop, you will now have to lock:
		4071
		4072	ev_timer timeout_watcher;
		4073	userdata *u = ev_userdata (EV_A);
		4074
		4075	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4076
		4077	pthread_mutex_lock (&u->lock);
		4078	ev_timer_start (EV_A_ &timeout_watcher);
		4079	ev_async_send (EV_A_ &u->async_w);
		4080	pthread_mutex_unlock (&u->lock);
		4081
		4082	Note that sending the C<ev_async> watcher is required because otherwise
		4083	an event loop currently blocking in the kernel will have no knowledge
		4084	about the newly added timer. By waking up the loop it will pick up any new
		4085	watchers in the next event loop iteration.
		4086
3846	=head3 COROUTINES	4087	=head3 COROUTINES
3847		4088
3848	Libev is very accommodating to coroutines ("cooperative threads"):	4089	Libev is very accommodating to coroutines ("cooperative threads"):
3849	libev fully supports nesting calls to its functions from different	4090	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	4091	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	4092	different coroutines, and switch freely between both coroutines running
3852	loop, as long as you don't confuse yourself). The only exception is that	4093	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.	4094	that you must not do this from C<ev_periodic> reschedule callbacks.
3854		4095
3855	Care has been taken to ensure that libev does not keep local state inside	4096	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	4097	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3857	they do not call any callbacks.	4098	they do not call any callbacks.
3858		4099
…		…
4065	=item C<double> must hold a time value in seconds with enough accuracy	4306	=item C<double> must hold a time value in seconds with enough accuracy
4066		4307
4067	The type C<double> is used to represent timestamps. It is required to	4308	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	4309	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	4310	enough for at least into the year 4000. This requirement is fulfilled by
4070	implementations implementing IEEE 754 (basically all existing ones).	4311	implementations implementing IEEE 754, which is basically all existing
		4312	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4313	2200.
4071		4314
4072	=back	4315	=back
4073		4316
4074	If you know of other additional requirements drop me a note.	4317	If you know of other additional requirements drop me a note.
4075		4318

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Comparing libev/ev.pod (file contents): Revision 1.242 by root, Thu Jun 18 18:16:54 2009 UTC vs. Revision 1.256 by root, Tue Jul 14 20:31:21 2009 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.242 by root, Thu Jun 18 18:16:54 2009 UTC vs.
Revision 1.256 by root, Tue Jul 14 20:31:21 2009 UTC