[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 1.257 by root, Wed Jul 15 16:08:24 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)
…		…
2007	but forking and registering a watcher a few event loop iterations later or	2126	but forking and registering a watcher a few event loop iterations later or
2008	in the next callback invocation is not.	2127	in the next callback invocation is not.
2009		2128
2010	Only the default event loop is capable of handling signals, and therefore	2129	Only the default event loop is capable of handling signals, and therefore
2011	you can only register child watchers in the default event loop.	2130	you can only register child watchers in the default event loop.
		2131
		2132	Due to some design glitches inside libev, child watchers will always be
		2133	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2134	libev)
2012		2135
2013	=head3 Process Interaction	2136	=head3 Process Interaction
2014		2137
2015	Libev grabs C<SIGCHLD> as soon as the default event loop is	2138	Libev grabs C<SIGCHLD> as soon as the default event loop is
2016	initialised. This is necessary to guarantee proper behaviour even if	2139	initialised. This is necessary to guarantee proper behaviour even if
…		…
3643	defined to be C<0>, then they are not.	3766	defined to be C<0>, then they are not.
3644		3767
3645	=item EV_MINIMAL	3768	=item EV_MINIMAL
3646		3769
3647	If you need to shave off some kilobytes of code at the expense of some	3770	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	3771	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	3772	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.	3773	on amd64. It also selects a much smaller 2-heap for timer management over
		3774	the default 4-heap.
		3775
		3776	You can save even more by disabling watcher types you do not need
		3777	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3778	(C<-DNDEBUG>) will usually reduce code size a lot.
		3779
		3780	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3781	provide a bare-bones event library. See C<ev.h> for details on what parts
		3782	of the API are still available, and do not complain if this subset changes
		3783	over time.
3651		3784
3652	=item EV_PID_HASHSIZE	3785	=item EV_PID_HASHSIZE
3653		3786
3654	C<ev_child> watchers use a small hash table to distribute workload by	3787	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	3788	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	3974	default loop and triggering an C<ev_async> watcher from the default loop
3842	watcher callback into the event loop interested in the signal.	3975	watcher callback into the event loop interested in the signal.
3843		3976
3844	=back	3977	=back
3845		3978
		3979	=head4 THREAD LOCKING EXAMPLE
		3980
		3981	Here is a fictitious example of how to run an event loop in a different
		3982	thread than where callbacks are being invoked and watchers are
		3983	created/added/removed.
		3984
		3985	For a real-world example, see the C<EV::Loop::Async> perl module,
		3986	which uses exactly this technique (which is suited for many high-level
		3987	languages).
		3988
		3989	The example uses a pthread mutex to protect the loop data, a condition
		3990	variable to wait for callback invocations, an async watcher to notify the
		3991	event loop thread and an unspecified mechanism to wake up the main thread.
		3992
		3993	First, you need to associate some data with the event loop:
		3994
		3995	typedef struct {
		3996	mutex_t lock; /* global loop lock */
		3997	ev_async async_w;
		3998	thread_t tid;
		3999	cond_t invoke_cv;
		4000	} userdata;
		4001
		4002	void prepare_loop (EV_P)
		4003	{
		4004	// for simplicity, we use a static userdata struct.
		4005	static userdata u;
		4006
		4007	ev_async_init (&u->async_w, async_cb);
		4008	ev_async_start (EV_A_ &u->async_w);
		4009
		4010	pthread_mutex_init (&u->lock, 0);
		4011	pthread_cond_init (&u->invoke_cv, 0);
		4012
		4013	// now associate this with the loop
		4014	ev_set_userdata (EV_A_ u);
		4015	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4016	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4017
		4018	// then create the thread running ev_loop
		4019	pthread_create (&u->tid, 0, l_run, EV_A);
		4020	}
		4021
		4022	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4023	solely to wake up the event loop so it takes notice of any new watchers
		4024	that might have been added:
		4025
		4026	static void
		4027	async_cb (EV_P_ ev_async *w, int revents)
		4028	{
		4029	// just used for the side effects
		4030	}
		4031
		4032	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4033	protecting the loop data, respectively.
		4034
		4035	static void
		4036	l_release (EV_P)
		4037	{
		4038	userdata *u = ev_userdata (EV_A);
		4039	pthread_mutex_unlock (&u->lock);
		4040	}
		4041
		4042	static void
		4043	l_acquire (EV_P)
		4044	{
		4045	userdata *u = ev_userdata (EV_A);
		4046	pthread_mutex_lock (&u->lock);
		4047	}
		4048
		4049	The event loop thread first acquires the mutex, and then jumps straight
		4050	into C<ev_loop>:
		4051
		4052	void *
		4053	l_run (void *thr_arg)
		4054	{
		4055	struct ev_loop loop = (struct ev_loop )thr_arg;
		4056
		4057	l_acquire (EV_A);
		4058	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4059	ev_loop (EV_A_ 0);
		4060	l_release (EV_A);
		4061
		4062	return 0;
		4063	}
		4064
		4065	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4066	signal the main thread via some unspecified mechanism (signals? pipe
		4067	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4068	have been called (in a while loop because a) spurious wakeups are possible
		4069	and b) skipping inter-thread-communication when there are no pending
		4070	watchers is very beneficial):
		4071
		4072	static void
		4073	l_invoke (EV_P)
		4074	{
		4075	userdata *u = ev_userdata (EV_A);
		4076
		4077	while (ev_pending_count (EV_A))
		4078	{
		4079	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4080	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4081	}
		4082	}
		4083
		4084	Now, whenever the main thread gets told to invoke pending watchers, it
		4085	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4086	thread to continue:
		4087
		4088	static void
		4089	real_invoke_pending (EV_P)
		4090	{
		4091	userdata *u = ev_userdata (EV_A);
		4092
		4093	pthread_mutex_lock (&u->lock);
		4094	ev_invoke_pending (EV_A);
		4095	pthread_cond_signal (&u->invoke_cv);
		4096	pthread_mutex_unlock (&u->lock);
		4097	}
		4098
		4099	Whenever you want to start/stop a watcher or do other modifications to an
		4100	event loop, you will now have to lock:
		4101
		4102	ev_timer timeout_watcher;
		4103	userdata *u = ev_userdata (EV_A);
		4104
		4105	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4106
		4107	pthread_mutex_lock (&u->lock);
		4108	ev_timer_start (EV_A_ &timeout_watcher);
		4109	ev_async_send (EV_A_ &u->async_w);
		4110	pthread_mutex_unlock (&u->lock);
		4111
		4112	Note that sending the C<ev_async> watcher is required because otherwise
		4113	an event loop currently blocking in the kernel will have no knowledge
		4114	about the newly added timer. By waking up the loop it will pick up any new
		4115	watchers in the next event loop iteration.
		4116
3846	=head3 COROUTINES	4117	=head3 COROUTINES
3847		4118
3848	Libev is very accommodating to coroutines ("cooperative threads"):	4119	Libev is very accommodating to coroutines ("cooperative threads"):
3849	libev fully supports nesting calls to its functions from different	4120	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	4121	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	4122	different coroutines, and switch freely between both coroutines running
3852	loop, as long as you don't confuse yourself). The only exception is that	4123	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.	4124	that you must not do this from C<ev_periodic> reschedule callbacks.
3854		4125
3855	Care has been taken to ensure that libev does not keep local state inside	4126	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	4127	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3857	they do not call any callbacks.	4128	they do not call any callbacks.
3858		4129
…		…
4065	=item C<double> must hold a time value in seconds with enough accuracy	4336	=item C<double> must hold a time value in seconds with enough accuracy
4066		4337
4067	The type C<double> is used to represent timestamps. It is required to	4338	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	4339	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	4340	enough for at least into the year 4000. This requirement is fulfilled by
4070	implementations implementing IEEE 754 (basically all existing ones).	4341	implementations implementing IEEE 754, which is basically all existing
		4342	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4343	2200.
4071		4344
4072	=back	4345	=back
4073		4346
4074	If you know of other additional requirements drop me a note.	4347	If you know of other additional requirements drop me a note.
4075		4348

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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 1.257 by root, Wed Jul 15 16:08:24 2009 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.244 by root, Mon Jun 29 04:41:34 2009 UTC vs.
Revision 1.257 by root, Wed Jul 15 16:08:24 2009 UTC