[ViewVC] Diff of: cvs/AnyEvent/lib/AnyEvent.pm

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.63 by root, Fri Apr 25 02:03:38 2008 UTC vs.
Revision 1.89 by root, Fri Apr 25 14:19:23 2008 UTC

…		…
80	module.	80	module.
81		81
82	During the first call of any watcher-creation method, the module tries	82	During the first call of any watcher-creation method, the module tries
83	to detect the currently loaded event loop by probing whether one of the	83	to detect the currently loaded event loop by probing whether one of the
84	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,	84	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,
85	L<Event>, L<Glib>, L<Tk>, L<AnyEvent::Impl::Perl>, L<Event::Lib>, L<Qt>,	85	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
86	L<POE>. The first one found is used. If none are found, the module tries	86	L<POE>. The first one found is used. If none are found, the module tries
87	to load these modules (excluding Event::Lib, Qt and POE as the pure perl	87	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
88	adaptor should always succeed) in the order given. The first one that can	88	adaptor should always succeed) in the order given. The first one that can
89	be successfully loaded will be used. If, after this, still none could be	89	be successfully loaded will be used. If, after this, still none could be
90	found, AnyEvent will fall back to a pure-perl event loop, which is not	90	found, AnyEvent will fall back to a pure-perl event loop, which is not
91	very efficient, but should work everywhere.	91	very efficient, but should work everywhere.
92		92
…		…
136		136
137	Note that C<my $w; $w => combination. This is necessary because in Perl,	137	Note that C<my $w; $w => combination. This is necessary because in Perl,
138	my variables are only visible after the statement in which they are	138	my variables are only visible after the statement in which they are
139	declared.	139	declared.
140		140
141	=head2 IO WATCHERS	141	=head2 I/O WATCHERS
142		142
143	You can create an I/O watcher by calling the C<< AnyEvent->io >> method	143	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
144	with the following mandatory key-value pairs as arguments:	144	with the following mandatory key-value pairs as arguments:
145		145
146	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for	146	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
147	events. C<poll> must be a string that is either C<r> or C<w>, which	147	for events. C<poll> must be a string that is either C<r> or C<w>,
148	creates a watcher waiting for "r"eadable or "w"ritable events,	148	which creates a watcher waiting for "r"eadable or "w"ritable events,
149	respectively. C<cb> is the callback to invoke each time the file handle	149	respectively. C<cb> is the callback to invoke each time the file handle
150	becomes ready.	150	becomes ready.
151		151
152	As long as the I/O watcher exists it will keep the file descriptor or a	152	Although the callback might get passed parameters, their value and
153	copy of it alive/open.	153	presence is undefined and you cannot rely on them. Portable AnyEvent
		154	callbacks cannot use arguments passed to I/O watcher callbacks.
154		155
		156	The I/O watcher might use the underlying file descriptor or a copy of it.
155	It is not allowed to close a file handle as long as any watcher is active	157	You must not close a file handle as long as any watcher is active on the
156	on the underlying file descriptor.	158	underlying file descriptor.
157		159
158	Some event loops issue spurious readyness notifications, so you should	160	Some event loops issue spurious readyness notifications, so you should
159	always use non-blocking calls when reading/writing from/to your file	161	always use non-blocking calls when reading/writing from/to your file
160	handles.	162	handles.
161		163
…		…
172		174
173	You can create a time watcher by calling the C<< AnyEvent->timer >>	175	You can create a time watcher by calling the C<< AnyEvent->timer >>
174	method with the following mandatory arguments:	176	method with the following mandatory arguments:
175		177
176	C<after> specifies after how many seconds (fractional values are	178	C<after> specifies after how many seconds (fractional values are
177	supported) should the timer activate. C<cb> the callback to invoke in that	179	supported) the callback should be invoked. C<cb> is the callback to invoke
178	case.	180	in that case.
		181
		182	Although the callback might get passed parameters, their value and
		183	presence is undefined and you cannot rely on them. Portable AnyEvent
		184	callbacks cannot use arguments passed to time watcher callbacks.
179		185
180	The timer callback will be invoked at most once: if you want a repeating	186	The timer callback will be invoked at most once: if you want a repeating
181	timer you have to create a new watcher (this is a limitation by both Tk	187	timer you have to create a new watcher (this is a limitation by both Tk
182	and Glib).	188	and Glib).
183		189
…		…
228		234
229	You can watch for signals using a signal watcher, C<signal> is the signal	235	You can watch for signals using a signal watcher, C<signal> is the signal
230	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to	236	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
231	be invoked whenever a signal occurs.	237	be invoked whenever a signal occurs.
232		238
		239	Although the callback might get passed parameters, their value and
		240	presence is undefined and you cannot rely on them. Portable AnyEvent
		241	callbacks cannot use arguments passed to signal watcher callbacks.
		242
233	Multiple signal occurances can be clumped together into one callback	243	Multiple signal occurances can be clumped together into one callback
234	invocation, and callback invocation will be synchronous. synchronous means	244	invocation, and callback invocation will be synchronous. synchronous means
235	that it might take a while until the signal gets handled by the process,	245	that it might take a while until the signal gets handled by the process,
236	but it is guarenteed not to interrupt any other callbacks.	246	but it is guarenteed not to interrupt any other callbacks.
237		247
…		…
251		261
252	The child process is specified by the C<pid> argument (if set to C<0>, it	262	The child process is specified by the C<pid> argument (if set to C<0>, it
253	watches for any child process exit). The watcher will trigger as often	263	watches for any child process exit). The watcher will trigger as often
254	as status change for the child are received. This works by installing a	264	as status change for the child are received. This works by installing a
255	signal handler for C<SIGCHLD>. The callback will be called with the pid	265	signal handler for C<SIGCHLD>. The callback will be called with the pid
256	and exit status (as returned by waitpid).	266	and exit status (as returned by waitpid), so unlike other watcher types,
		267	you I<can> rely on child watcher callback arguments.
257		268
258	Example: wait for pid 1333	269	There is a slight catch to child watchers, however: you usually start them
		270	I<after> the child process was created, and this means the process could
		271	have exited already (and no SIGCHLD will be sent anymore).
		272
		273	Not all event models handle this correctly (POE doesn't), but even for
		274	event models that I<do> handle this correctly, they usually need to be
		275	loaded before the process exits (i.e. before you fork in the first place).
		276
		277	This means you cannot create a child watcher as the very first thing in an
		278	AnyEvent program, you I<have> to create at least one watcher before you
		279	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		280
		281	Example: fork a process and wait for it
		282
		283	my $done = AnyEvent->condvar;
		284
		285	AnyEvent::detect; # force event module to be initialised
		286
		287	my $pid = fork or exit 5;
259		288
260	my $w = AnyEvent->child (	289	my $w = AnyEvent->child (
261	pid => 1333,	290	pid => $pid,
262	cb => sub {	291	cb => sub {
263	my ($pid, $status) = @_;	292	my ($pid, $status) = @_;
264	warn "pid $pid exited with status $status";	293	warn "pid $pid exited with status $status";
		294	$done->broadcast;
265	},	295	},
266	);	296	);
		297
		298	# do something else, then wait for process exit
		299	$done->wait;
267		300
268	=head2 CONDITION VARIABLES	301	=head2 CONDITION VARIABLES
269		302
270	Condition variables can be created by calling the C<< AnyEvent->condvar >>	303	Condition variables can be created by calling the C<< AnyEvent->condvar >>
271	method without any arguments.	304	method without any arguments.
…		…
359	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.	392	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
360	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.	393	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
361	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	394	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
362	AnyEvent::Impl::Event based on Event, second best choice.	395	AnyEvent::Impl::Event based on Event, second best choice.
363	AnyEvent::Impl::Glib based on Glib, third-best choice.	396	AnyEvent::Impl::Glib based on Glib, third-best choice.
		397	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
364	AnyEvent::Impl::Tk based on Tk, very bad choice.	398	AnyEvent::Impl::Tk based on Tk, very bad choice.
365	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
366	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).	399	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
367	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	400	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
368	AnyEvent::Impl::POE based on POE, not generic enough for full support.	401	AnyEvent::Impl::POE based on POE, not generic enough for full support.
369		402
370	There is no support for WxWidgets, as WxWidgets has no support for	403	There is no support for WxWidgets, as WxWidgets has no support for
…		…
706		739
707	=back	740	=back
708		741
709	=head1 EXAMPLE PROGRAM	742	=head1 EXAMPLE PROGRAM
710		743
711	The following program uses an IO watcher to read data from STDIN, a timer	744	The following program uses an I/O watcher to read data from STDIN, a timer
712	to display a message once per second, and a condition variable to quit the	745	to display a message once per second, and a condition variable to quit the
713	program when the user enters quit:	746	program when the user enters quit:
714		747
715	use AnyEvent;	748	use AnyEvent;
716		749
…		…
860	$quit->broadcast;	893	$quit->broadcast;
861	});	894	});
862		895
863	$quit->wait;	896	$quit->wait;
864		897
		898
		899	=head1 BENCHMARK
		900
		901	To give you an idea of the performance and overheads that AnyEvent adds
		902	over the event loops themselves (and to give you an impression of the
		903	speed of various event loops), here is a benchmark of various supported
		904	event models natively and with anyevent. The benchmark creates a lot of
		905	timers (with a zero timeout) and I/O watchers (watching STDOUT, a pty, to
		906	become writable, which it is), lets them fire exactly once and destroys
		907	them again.
		908
		909	Rewriting the benchmark to use many different sockets instead of using
		910	the same filehandle for all I/O watchers results in a much longer runtime
		911	(socket creation is expensive), but qualitatively the same figures, so it
		912	was not used.
		913
		914	=head2 Explanation of the columns
		915
		916	I<watcher> is the number of event watchers created/destroyed. Since
		917	different event models feature vastly different performances, each event
		918	loop was given a number of watchers so that overall runtime is acceptable
		919	and similar between tested event loop (and keep them from crashing): Glib
		920	would probably take thousands of years if asked to process the same number
		921	of watchers as EV in this benchmark.
		922
		923	I<bytes> is the number of bytes (as measured by the resident set size,
		924	RSS) consumed by each watcher. This method of measuring captures both C
		925	and Perl-based overheads.
		926
		927	I<create> is the time, in microseconds (millionths of seconds), that it
		928	takes to create a single watcher. The callback is a closure shared between
		929	all watchers, to avoid adding memory overhead. That means closure creation
		930	and memory usage is not included in the figures.
		931
		932	I<invoke> is the time, in microseconds, used to invoke a simple
		933	callback. The callback simply counts down a Perl variable and after it was
		934	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		935	signal the end of this phase.
		936
		937	I<destroy> is the time, in microseconds, that it takes to destroy a single
		938	watcher.
		939
		940	=head2 Results
		941
		942	name watchers bytes create invoke destroy comment
		943	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		944	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		945	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		946	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		947	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		948	Event/Any 16000 936 39.17 33.63 1.43 Event + AnyEvent watchers
		949	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		950	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		951	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		952	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		953
		954	=head2 Discussion
		955
		956	The benchmark does I<not> measure scalability of the event loop very
		957	well. For example, a select-based event loop (such as the pure perl one)
		958	can never compete with an event loop that uses epoll when the number of
		959	file descriptors grows high. In this benchmark, all events become ready at
		960	the same time, so select/poll-based implementations get an unnatural speed
		961	boost.
		962
		963	C<EV> is the sole leader regarding speed and memory use, which are both
		964	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		965	far less memory than any other event loop and is still faster than Event
		966	natively.
		967
		968	The pure perl implementation is hit in a few sweet spots (both the
		969	constant timeout and the use of a single fd hit optimisations in the perl
		970	interpreter and the backend itself). Nevertheless this shows that it
		971	adds very little overhead in itself. Like any select-based backend its
		972	performance becomes really bad with lots of file descriptors (and few of
		973	them active), of course, but this was not subject of this benchmark.
		974
		975	The C<Event> module has a relatively high setup and callback invocation cost,
		976	but overall scores on the third place.
		977
		978	C<Glib>'s memory usage is quite a bit bit higher, but it features a
		979	faster callback invocation and overall ends up in the same class as
		980	C<Event>. However, Glib scales extremely badly, doubling the number of
		981	watchers increases the processing time by more than a factor of four,
		982	making it completely unusable when using larger numbers of watchers
		983	(note that only a single file descriptor was used in the benchmark, so
		984	inefficiencies of C<poll> do not account for this).
		985
		986	The C<Tk> adaptor works relatively well. The fact that it crashes with
		987	more than 2000 watchers is a big setback, however, as correctness takes
		988	precedence over speed. Nevertheless, its performance is surprising, as the
		989	file descriptor is dup()ed for each watcher. This shows that the dup()
		990	employed by some adaptors is not a big performance issue (it does incur a
		991	hidden memory cost inside the kernel which is not reflected in the figures
		992	above).
		993
		994	C<POE>, regardless of underlying event loop (whether using its pure
		995	perl select-based backend or the Event module, the POE-EV backend
		996	couldn't be tested because it wasn't working) shows abysmal performance
		997	and memory usage: Watchers use almost 30 times as much memory as
		998	EV watchers, and 10 times as much memory as Event (the high memory
		999	requirements are caused by requiring a session for each watcher). Watcher
		1000	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1001	implementation. The design of the POE adaptor class in AnyEvent can not
		1002	really account for this, as session creation overhead is small compared
		1003	to execution of the state machine, which is coded pretty optimally within
		1004	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.
		1005
		1006	=head2 Summary
		1007
		1008	=over 4
		1009
		1010	=item * Using EV through AnyEvent is faster than any other event loop
		1011	(even when used without AnyEvent), but most event loops have acceptable
		1012	performance with or without AnyEvent.
		1013
		1014	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1015	the actual event loop, only with extremely fast event loops such as EV
		1016	adds AnyEvent significant overhead.
		1017
		1018	=item * You should simply avoid POE like the plague if you want performance or
		1019	reasonable memory usage.
		1020
		1021	=back
		1022
		1023
865	=head1 FORK	1024	=head1 FORK
866		1025
867	Most event libraries are not fork-safe. The ones who are usually are	1026	Most event libraries are not fork-safe. The ones who are usually are
868	because they are so inefficient. Only L<EV> is fully fork-aware.	1027	because they are so inefficient. Only L<EV> is fully fork-aware.
869		1028
870	If you have to fork, you must either do so I<before> creating your first	1029	If you have to fork, you must either do so I<before> creating your first
871	watcher OR you must not use AnyEvent at all in the child.	1030	watcher OR you must not use AnyEvent at all in the child.
		1031
872		1032
873	=head1 SECURITY CONSIDERATIONS	1033	=head1 SECURITY CONSIDERATIONS
874		1034
875	AnyEvent can be forced to load any event model via	1035	AnyEvent can be forced to load any event model via
876	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to	1036	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
…		…
884		1044
885	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1045	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
886		1046
887	use AnyEvent;	1047	use AnyEvent;
888		1048
		1049
889	=head1 SEE ALSO	1050	=head1 SEE ALSO
890		1051
891	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1052	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,
892	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,	1053	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
893	L<Event::Lib>, L<Qt>, L<POE>.	1054	L<Event::Lib>, L<Qt>, L<POE>.
…		…
897	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,	1058	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
898	L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.	1059	L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.
899		1060
900	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1061	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
901		1062
		1063
902	=head1 AUTHOR	1064	=head1 AUTHOR
903		1065
904	Marc Lehmann <schmorp@schmorp.de>	1066	Marc Lehmann <schmorp@schmorp.de>
905	http://home.schmorp.de/	1067	http://home.schmorp.de/
906		1068

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Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.63 by root, Fri Apr 25 02:03:38 2008 UTC vs. Revision 1.89 by root, Fri Apr 25 14:19:23 2008 UTC

Diff Legend

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.63 by root, Fri Apr 25 02:03:38 2008 UTC vs.
Revision 1.89 by root, Fri Apr 25 14:19:23 2008 UTC