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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.62 by root, Fri Apr 25 02:03:18 2008 UTC vs.
Revision 1.83 by root, Fri Apr 25 13:39:08 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	It is not allowed to close a file handle as long as any watcher is active
156	on the underlying file descriptor.	154	on the 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
…		…
253	watches for any child process exit). The watcher will trigger as often	251	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	252	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	253	signal handler for C<SIGCHLD>. The callback will be called with the pid
256	and exit status (as returned by waitpid).	254	and exit status (as returned by waitpid).
257		255
258	Example: wait for pid 1333	256	There is a slight catch to child watchers, however: you usually start them
		257	I<after> the child process was created, and this means the process could
		258	have exited already (and no SIGCHLD will be sent anymore).
		259
		260	Not all event models handle this correctly (POE doesn't), but even for
		261	event models that I<do> handle this correctly, they usually need to be
		262	loaded before the process exits (i.e. before you fork in the first place).
		263
		264	This means you cannot create a child watcher as the very first thing in an
		265	AnyEvent program, you I<have> to create at least one watcher before you
		266	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		267
		268	Example: fork a process and wait for it
		269
		270	my $done = AnyEvent->condvar;
		271
		272	AnyEvent::detect; # force event module to be initialised
		273
		274	my $pid = fork or exit 5;
259		275
260	my $w = AnyEvent->child (	276	my $w = AnyEvent->child (
261	pid => 1333,	277	pid => $pid,
262	cb => sub {	278	cb => sub {
263	my ($pid, $status) = @_;	279	my ($pid, $status) = @_;
264	warn "pid $pid exited with status $status";	280	warn "pid $pid exited with status $status";
		281	$done->broadcast;
265	},	282	},
266	);	283	);
		284
		285	# do something else, then wait for process exit
		286	$done->wait;
267		287
268	=head2 CONDITION VARIABLES	288	=head2 CONDITION VARIABLES
269		289
270	Condition variables can be created by calling the C<< AnyEvent->condvar >>	290	Condition variables can be created by calling the C<< AnyEvent->condvar >>
271	method without any arguments.	291	method without any arguments.
…		…
359	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.	379	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
360	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.	380	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
361	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	381	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
362	AnyEvent::Impl::Event based on Event, second best choice.	382	AnyEvent::Impl::Event based on Event, second best choice.
363	AnyEvent::Impl::Glib based on Glib, third-best choice.	383	AnyEvent::Impl::Glib based on Glib, third-best choice.
		384	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
364	AnyEvent::Impl::Tk based on Tk, very bad choice.	385	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).	386	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
367	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	387	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
368	AnyEvent::Impl::POE based on POE, not generic enough for full support.	388	AnyEvent::Impl::POE based on POE, not generic enough for full support.
369		389
370	There is no support for WxWidgets, as WxWidgets has no support for	390	There is no support for WxWidgets, as WxWidgets has no support for
…		…
434	no warnings;	454	no warnings;
435	use strict;	455	use strict;
436		456
437	use Carp;	457	use Carp;
438		458
439	our $VERSION = '3.2';	459	our $VERSION = '3.3';
440	our $MODEL;	460	our $MODEL;
441		461
442	our $AUTOLOAD;	462	our $AUTOLOAD;
443	our @ISA;	463	our @ISA;
444		464
…		…
706		726
707	=back	727	=back
708		728
709	=head1 EXAMPLE PROGRAM	729	=head1 EXAMPLE PROGRAM
710		730
711	The following program uses an IO watcher to read data from STDIN, a timer	731	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	732	to display a message once per second, and a condition variable to quit the
713	program when the user enters quit:	733	program when the user enters quit:
714		734
715	use AnyEvent;	735	use AnyEvent;
716		736
…		…
860	$quit->broadcast;	880	$quit->broadcast;
861	});	881	});
862		882
863	$quit->wait;	883	$quit->wait;
864		884
		885
		886	=head1 BENCHMARK
		887
		888	To give you an idea of the performance and overheads that AnyEvent adds
		889	over the event loops themselves (and to give you an impression of the
		890	speed of various event loops), here is a benchmark of various supported
		891	event models natively and with anyevent. The benchmark creates a lot of
		892	timers (with a zero timeout) and I/O watchers (watching STDOUT, a pty, to
		893	become writable, which it is), lets them fire exactly once and destroys
		894	them again.
		895
		896	Rewriting the benchmark to use many different sockets instead of using
		897	the same filehandle for all I/O watchers results in a much longer runtime
		898	(socket creation is expensive), but qualitatively the same figures, so it
		899	was not used.
		900
		901	=head2 Explanation of the columns
		902
		903	I<watcher> is the number of event watchers created/destroyed. Since
		904	different event models feature vastly different performances, each event
		905	loop was given a number of watchers so that overall runtime is acceptable
		906	and similar between tested event loop (and keep them from crashing): Glib
		907	would probably take thousands of years if asked to process the same number
		908	of watchers as EV in this benchmark.
		909
		910	I<bytes> is the number of bytes (as measured by the resident set size,
		911	RSS) consumed by each watcher. This method of measuring captures both C
		912	and Perl-based overheads.
		913
		914	I<create> is the time, in microseconds (millionths of seconds), that it
		915	takes to create a single watcher. The callback is a closure shared between
		916	all watchers, to avoid adding memory overhead. That means closure creation
		917	and memory usage is not included in the figures.
		918
		919	I<invoke> is the time, in microseconds, used to invoke a simple
		920	callback. The callback simply counts down a Perl variable and after it was
		921	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		922	signal the end of this phase.
		923
		924	I<destroy> is the time, in microseconds, that it takes to destroy a single
		925	watcher.
		926
		927	=head2 Results
		928
		929	name watchers bytes create invoke destroy comment
		930	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		931	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		932	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		933	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		934	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		935	Event/Any 16000 936 39.17 33.63 1.43 Event + AnyEvent watchers
		936	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		937	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		938	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		939	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		940
		941	=head2 Discussion
		942
		943	The benchmark does I<not> measure scalability of the event loop very
		944	well. For example, a select-based event loop (such as the pure perl one)
		945	can never compete with an event loop that uses epoll when the number of
		946	file descriptors grows high. In this benchmark, all events become ready at
		947	the same time, so select/poll-based implementations get an unnatural speed
		948	boost.
		949
		950	C<EV> is the sole leader regarding speed and memory use, which are both
		951	maximal/minimal, respectively. Even when going through AnyEvent, there are
		952	only two event loops that use slightly less memory (the C<Event> module
		953	natively and the pure perl backend), and no faster event models, not even
		954	C<Event> natively.
		955
		956	The pure perl implementation is hit in a few sweet spots (both the
		957	zero timeout and the use of a single fd hit optimisations in the perl
		958	interpreter and the backend itself, and all watchers become ready at the
		959	same time). Nevertheless this shows that it adds very little overhead in
		960	itself. Like any select-based backend its performance becomes really bad
		961	with lots of file descriptors (and few of them active), of course, but
		962	this was not subject of this benchmark.
		963
		964	The C<Event> module has a relatively high setup and callback invocation cost,
		965	but overall scores on the third place.
		966
		967	C<Glib>'s memory usage is quite a bit bit higher, but it features a
		968	faster callback invocation and overall ends up in the same class as
		969	C<Event>. However, Glib scales extremely badly, doubling the number of
		970	watchers increases the processing time by more than a factor of four,
		971	making it completely unusable when using larger numbers of watchers
		972	(note that only a single file descriptor was used in the benchmark, so
		973	inefficiencies of C<poll> do not account for this).
		974
		975	The C<Tk> adaptor works relatively well. The fact that it crashes with
		976	more than 2000 watchers is a big setback, however, as correctness takes
		977	precedence over speed. Nevertheless, its performance is surprising, as the
		978	file descriptor is dup()ed for each watcher. This shows that the dup()
		979	employed by some adaptors is not a big performance issue (it does incur a
		980	hidden memory cost inside the kernel, though, that is not reflected in the
		981	figures above).
		982
		983	C<POE>, regardless of underlying event loop (wether using its pure perl
		984	select-based backend or the Event module) shows abysmal performance and
		985	memory usage: Watchers use almost 30 times as much memory as EV watchers,
		986	and 10 times as much memory as both Event or EV via AnyEvent. Watcher
		987	invocation is almost 900 times slower than with AnyEvent's pure perl
		988	implementation. The design of the POE adaptor class in AnyEvent can not
		989	really account for this, as session creation overhead is small compared
		990	to execution of the state machine, which is coded pretty optimally within
		991	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.
		992
		993	=head2 Summary
		994
		995	Using EV through AnyEvent is faster than any other event loop, but most
		996	event loops have acceptable performance with or without AnyEvent.
		997
		998	The overhead AnyEvent adds is usually much smaller than the overhead of
		999	the actual event loop, only with extremely fast event loops such as the EV
		1000	adds AnyEvent significant overhead.
		1001
		1002	And you should simply avoid POE like the plague if you want performance or
		1003	reasonable memory usage.
		1004
		1005
865	=head1 FORK	1006	=head1 FORK
866		1007
867	Most event libraries are not fork-safe. The ones who are usually are	1008	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.	1009	because they are so inefficient. Only L<EV> is fully fork-aware.
869		1010
870	If you have to fork, you must either do so I<before> creating your first	1011	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.	1012	watcher OR you must not use AnyEvent at all in the child.
		1013
872		1014
873	=head1 SECURITY CONSIDERATIONS	1015	=head1 SECURITY CONSIDERATIONS
874		1016
875	AnyEvent can be forced to load any event model via	1017	AnyEvent can be forced to load any event model via
876	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to	1018	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
…		…
884		1026
885	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1027	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
886		1028
887	use AnyEvent;	1029	use AnyEvent;
888		1030
		1031
889	=head1 SEE ALSO	1032	=head1 SEE ALSO
890		1033
891	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1034	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>,	1035	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
893	L<Event::Lib>, L<Qt>, L<POE>.	1036	L<Event::Lib>, L<Qt>, L<POE>.
…		…
897	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,	1040	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
898	L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.	1041	L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.
899		1042
900	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1043	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
901		1044
		1045
902	=head1 AUTHOR	1046	=head1 AUTHOR
903		1047
904	Marc Lehmann <schmorp@schmorp.de>	1048	Marc Lehmann <schmorp@schmorp.de>
905	http://home.schmorp.de/	1049	http://home.schmorp.de/
906		1050

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Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.62 by root, Fri Apr 25 02:03:18 2008 UTC vs. Revision 1.83 by root, Fri Apr 25 13:39:08 2008 UTC

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Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.62 by root, Fri Apr 25 02:03:18 2008 UTC vs.
Revision 1.83 by root, Fri Apr 25 13:39:08 2008 UTC