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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.64 by root, Fri Apr 25 06:54:08 2008 UTC vs.
Revision 1.84 by root, Fri Apr 25 13:48:42 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 for
147	events. C<poll> must be a string that is either C<r> or C<w>, which	147	events. C<poll> must be a string that is either C<r> or C<w>, which
148	creates a watcher waiting for "r"eadable or "w"ritable events,	148	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	The I/O watcher might use the underlying file descriptor or a copy of it.
153	copy of it alive/open.
154
155	It is not allowed to close a file handle as long as any watcher is active	153	You must not close a file handle as long as any watcher is active on the
156	on the underlying file descriptor.	154	underlying file descriptor.
157		155
158	Some event loops issue spurious readyness notifications, so you should	156	Some event loops issue spurious readyness notifications, so you should
159	always use non-blocking calls when reading/writing from/to your file	157	always use non-blocking calls when reading/writing from/to your file
160	handles.	158	handles.
		159
		160	Although the callback might get passed parameters, their value and
		161	presence is undefined and you cannot rely on them. Portable AnyEvent
		162	callbacks cannot use arguments passed to I/O watcher callbacks.
161		163
162	Example:	164	Example:
163		165
164	# wait for readability of STDIN, then read a line and disable the watcher	166	# wait for readability of STDIN, then read a line and disable the watcher
165	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	167	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
…		…
179		181
180	The timer callback will be invoked at most once: if you want a repeating	182	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	183	timer you have to create a new watcher (this is a limitation by both Tk
182	and Glib).	184	and Glib).
183		185
		186	Although the callback might get passed parameters, their value and
		187	presence is undefined and you cannot rely on them. Portable AnyEvent
		188	callbacks cannot use arguments passed to time watcher callbacks.
		189
184	Example:	190	Example:
185		191
186	# fire an event after 7.7 seconds	192	# fire an event after 7.7 seconds
187	my $w = AnyEvent->timer (after => 7.7, cb => sub {	193	my $w = AnyEvent->timer (after => 7.7, cb => sub {
188	warn "timeout\n";	194	warn "timeout\n";
…		…
253	watches for any child process exit). The watcher will trigger as often	259	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	260	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	261	signal handler for C<SIGCHLD>. The callback will be called with the pid
256	and exit status (as returned by waitpid).	262	and exit status (as returned by waitpid).
257		263
258	Example: wait for pid 1333	264	There is a slight catch to child watchers, however: you usually start them
		265	I<after> the child process was created, and this means the process could
		266	have exited already (and no SIGCHLD will be sent anymore).
		267
		268	Not all event models handle this correctly (POE doesn't), but even for
		269	event models that I<do> handle this correctly, they usually need to be
		270	loaded before the process exits (i.e. before you fork in the first place).
		271
		272	This means you cannot create a child watcher as the very first thing in an
		273	AnyEvent program, you I<have> to create at least one watcher before you
		274	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		275
		276	Example: fork a process and wait for it
		277
		278	my $done = AnyEvent->condvar;
		279
		280	AnyEvent::detect; # force event module to be initialised
		281
		282	my $pid = fork or exit 5;
259		283
260	my $w = AnyEvent->child (	284	my $w = AnyEvent->child (
261	pid => 1333,	285	pid => $pid,
262	cb => sub {	286	cb => sub {
263	my ($pid, $status) = @_;	287	my ($pid, $status) = @_;
264	warn "pid $pid exited with status $status";	288	warn "pid $pid exited with status $status";
		289	$done->broadcast;
265	},	290	},
266	);	291	);
		292
		293	# do something else, then wait for process exit
		294	$done->wait;
267		295
268	=head2 CONDITION VARIABLES	296	=head2 CONDITION VARIABLES
269		297
270	Condition variables can be created by calling the C<< AnyEvent->condvar >>	298	Condition variables can be created by calling the C<< AnyEvent->condvar >>
271	method without any arguments.	299	method without any arguments.
…		…
359	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.	387	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
360	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.	388	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
361	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	389	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
362	AnyEvent::Impl::Event based on Event, second best choice.	390	AnyEvent::Impl::Event based on Event, second best choice.
363	AnyEvent::Impl::Glib based on Glib, third-best choice.	391	AnyEvent::Impl::Glib based on Glib, third-best choice.
		392	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
364	AnyEvent::Impl::Tk based on Tk, very bad choice.	393	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).	394	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
367	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	395	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
368	AnyEvent::Impl::POE based on POE, not generic enough for full support.	396	AnyEvent::Impl::POE based on POE, not generic enough for full support.
369		397
370	There is no support for WxWidgets, as WxWidgets has no support for	398	There is no support for WxWidgets, as WxWidgets has no support for
…		…
706		734
707	=back	735	=back
708		736
709	=head1 EXAMPLE PROGRAM	737	=head1 EXAMPLE PROGRAM
710		738
711	The following program uses an IO watcher to read data from STDIN, a timer	739	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	740	to display a message once per second, and a condition variable to quit the
713	program when the user enters quit:	741	program when the user enters quit:
714		742
715	use AnyEvent;	743	use AnyEvent;
716		744
…		…
863	$quit->wait;	891	$quit->wait;
864		892
865		893
866	=head1 BENCHMARK	894	=head1 BENCHMARK
867		895
868	To give you an idea of the performance an doverheads that AnyEvent adds	896	To give you an idea of the performance and overheads that AnyEvent adds
869	over the backends, here is a benchmark of various supported backends. The	897	over the event loops themselves (and to give you an impression of the
870	benchmark creates a lot of timers (with zero timeout) and io events	898	speed of various event loops), here is a benchmark of various supported
871	(watching STDOUT, a pty, to become writable).	899	event models natively and with anyevent. The benchmark creates a lot of
		900	timers (with a zero timeout) and I/O watchers (watching STDOUT, a pty, to
		901	become writable, which it is), lets them fire exactly once and destroys
		902	them again.
872		903
873	Explanation of the fields:	904	Rewriting the benchmark to use many different sockets instead of using
		905	the same filehandle for all I/O watchers results in a much longer runtime
		906	(socket creation is expensive), but qualitatively the same figures, so it
		907	was not used.
874		908
		909	=head2 Explanation of the columns
		910
875	I<watcher> is the number of event watchers created/destroyed. Sicne	911	I<watcher> is the number of event watchers created/destroyed. Since
876	different event models have vastly different performance each backend was	912	different event models feature vastly different performances, each event
877	handed a number of watchers so that overall runtime is acceptable and	913	loop was given a number of watchers so that overall runtime is acceptable
878	similar to all backends (and keep them from crashing).	914	and similar between tested event loop (and keep them from crashing): Glib
		915	would probably take thousands of years if asked to process the same number
		916	of watchers as EV in this benchmark.
879		917
880	I<bytes> is the number of bytes (as measured by resident set size) used by	918	I<bytes> is the number of bytes (as measured by the resident set size,
881	each watcher.	919	RSS) consumed by each watcher. This method of measuring captures both C
		920	and Perl-based overheads.
882		921
883	I<create> is the time, in microseconds, to create a single watcher.	922	I<create> is the time, in microseconds (millionths of seconds), that it
		923	takes to create a single watcher. The callback is a closure shared between
		924	all watchers, to avoid adding memory overhead. That means closure creation
		925	and memory usage is not included in the figures.
884		926
885	I<invoke> is the time, in microseconds, used to invoke a simple callback	927	I<invoke> is the time, in microseconds, used to invoke a simple
886	that simply counts down.	928	callback. The callback simply counts down a Perl variable and after it was
		929	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		930	signal the end of this phase.
887		931
888	I<destroy> is the time, in microseconds, to destroy a single watcher.	932	I<destroy> is the time, in microseconds, that it takes to destroy a single
		933	watcher.
889		934
		935	=head2 Results
		936
890	name watcher bytes create invoke destroy comment	937	name watchers bytes create invoke destroy comment
891	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	938	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
892	EV/Any 100000 610 3.52 0.91 0.75	939	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
893	CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal	940	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
894	Perl/Any 10000 654 4.64 1.22 0.77 pure perl implementation	941	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
895	Event/Event 10000 523 28.05 21.38 5.22 Event native interface	942	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
896	Event/Any 10000 943 34.43 20.48 1.39	943	Event/Any 16000 936 39.17 33.63 1.43 Event + AnyEvent watchers
897	Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour	944	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
898	Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers	945	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
899	POE/Select 2000 6343 94.69 807.65 562.69 POE::Loop::Select
900	POE/Event 2000 6644 108.15 768.19 14.33 POE::Loop::Event	946	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		947	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
901		948
902	Discussion: The benchmark does I<not> bench scalability of the	949	=head2 Discussion
		950
		951	The benchmark does I<not> measure scalability of the event loop very
903	backend. For example a select-based backend (such as the pureperl one) can	952	well. For example, a select-based event loop (such as the pure perl one)
904	never compete with a backend using epoll. In this benchmark, only a single	953	can never compete with an event loop that uses epoll when the number of
905	filehandle is used.	954	file descriptors grows high. In this benchmark, all events become ready at
		955	the same time, so select/poll-based implementations get an unnatural speed
		956	boost.
906		957
907	EV is the sole leader regarding speed and memory use, which are both	958	C<EV> is the sole leader regarding speed and memory use, which are both
908	maximal/minimal. Even when going through AnyEvent, there is only one event	959	maximal/minimal, respectively. Even when going through AnyEvent, it uses
909	loop that uses less memory (the Event module natively), and no faster	960	far less memory than any other event loop and is still faster than Event
910	event model.	961	natively.
911		962
912	The pure perl implementation is hit in a few sweet spots (both the	963	The pure perl implementation is hit in a few sweet spots (both the
913	zero timeout and the use of a single fd hit optimisations in the perl	964	zero timeout and the use of a single fd hit optimisations in the perl
914	interpreter and the backend itself), but it shows that it adds very little	965	interpreter and the backend itself, and all watchers become ready at the
		966	same time). Nevertheless this shows that it adds very little overhead in
915	overhead in itself. Like any select-based backend it's performance becomes	967	itself. Like any select-based backend its performance becomes really bad
916	really bad with lots of file descriptors.	968	with lots of file descriptors (and few of them active), of course, but
		969	this was not subject of this benchmark.
917		970
918	The Event module has a relatively high setup and callback invocation cost,	971	The C<Event> module has a relatively high setup and callback invocation cost,
919	but overall scores on the third place.	972	but overall scores on the third place.
920		973
921	Glib has a little higher memory cost, a bit fster callback invocation and	974	C<Glib>'s memory usage is quite a bit bit higher, but it features a
922	has a similar speed as Event.	975	faster callback invocation and overall ends up in the same class as
		976	C<Event>. However, Glib scales extremely badly, doubling the number of
		977	watchers increases the processing time by more than a factor of four,
		978	making it completely unusable when using larger numbers of watchers
		979	(note that only a single file descriptor was used in the benchmark, so
		980	inefficiencies of C<poll> do not account for this).
923		981
924	The Tk backend works relatively well, the fact that it crashes with	982	The C<Tk> adaptor works relatively well. The fact that it crashes with
925	more than 2000 watchers is a big setback, however, as correctness takes	983	more than 2000 watchers is a big setback, however, as correctness takes
926	precedence over speed.	984	precedence over speed. Nevertheless, its performance is surprising, as the
		985	file descriptor is dup()ed for each watcher. This shows that the dup()
		986	employed by some adaptors is not a big performance issue (it does incur a
		987	hidden memory cost inside the kernel, though, that is not reflected in the
		988	figures above).
927		989
928	POE, regardless of backend (wether it's pure perl select backend or the	990	C<POE>, regardless of underlying event loop (wether using its pure perl
929	Event backend) shows abysmal performance and memory usage: Watchers use	991	select-based backend or the Event module) shows abysmal performance and
930	almost 30 times as much memory as EV watchers, and 10 times as much memory	992	memory usage: Watchers use almost 30 times as much memory as EV watchers,
931	as both Event or EV via AnyEvent.	993	and 10 times as much memory as both Event or EV via AnyEvent. Watcher
		994	invocation is almost 900 times slower than with AnyEvent's pure perl
		995	implementation. The design of the POE adaptor class in AnyEvent can not
		996	really account for this, as session creation overhead is small compared
		997	to execution of the state machine, which is coded pretty optimally within
		998	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.
932		999
		1000	=head2 Summary
		1001
933	Summary: using EV through AnyEvent is faster than any other event	1002	Using EV through AnyEvent is faster than any other event loop, but most
934	loop. The overhead AnyEvent adds can be very small, and you should avoid	1003	event loops have acceptable performance with or without AnyEvent.
935	POE like the plague if you want performance or reasonable memory usage.	1004
		1005	The overhead AnyEvent adds is usually much smaller than the overhead of
		1006	the actual event loop, only with extremely fast event loops such as the EV
		1007	adds AnyEvent significant overhead.
		1008
		1009	And you should simply avoid POE like the plague if you want performance or
		1010	reasonable memory usage.
936		1011
937		1012
938	=head1 FORK	1013	=head1 FORK
939		1014
940	Most event libraries are not fork-safe. The ones who are usually are	1015	Most event libraries are not fork-safe. The ones who are usually are

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Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.64 by root, Fri Apr 25 06:54:08 2008 UTC vs. Revision 1.84 by root, Fri Apr 25 13:48:42 2008 UTC

Diff Legend

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.64 by root, Fri Apr 25 06:54:08 2008 UTC vs.
Revision 1.84 by root, Fri Apr 25 13:48:42 2008 UTC