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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.70 by root, Fri Apr 25 07:25:44 2008 UTC vs.
Revision 1.82 by root, Fri Apr 25 13:32:39 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
…		…
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
…		…
864		884
865		885
866	=head1 BENCHMARK	886	=head1 BENCHMARK
867		887
868	To give you an idea of the performance and overheads that AnyEvent adds	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
869	over the event loops directly, here is a benchmark of various supported	890	speed of various event loops), here is a benchmark of various supported
870	event models natively and with anyevent. The benchmark creates a lot of	891	event models natively and with anyevent. The benchmark creates a lot of
871	timers (with a zero timeout) and io watchers (watching STDOUT, a pty, to	892	timers (with a zero timeout) and I/O watchers (watching STDOUT, a pty, to
872	become writable, which it is), lets them fire exactly once and destroys	893	become writable, which it is), lets them fire exactly once and destroys
873	them again.	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.
874		900
875	=head2 Explanation of the columns	901	=head2 Explanation of the columns
876		902
877	I<watcher> is the number of event watchers created/destroyed. Since	903	I<watcher> is the number of event watchers created/destroyed. Since
878	different event models feature vastly different performances, each event	904	different event models feature vastly different performances, each event
…		…
893	I<invoke> is the time, in microseconds, used to invoke a simple	919	I<invoke> is the time, in microseconds, used to invoke a simple
894	callback. The callback simply counts down a Perl variable and after it was	920	callback. The callback simply counts down a Perl variable and after it was
895	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to	921	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
896	signal the end of this phase.	922	signal the end of this phase.
897		923
898	I<destroy> is the time, in microseconds, that it takes destroy a single	924	I<destroy> is the time, in microseconds, that it takes to destroy a single
899	watcher.	925	watcher.
900		926
901	=head2 Results	927	=head2 Results
902		928
903	name watcher bytes create invoke destroy comment	929	name watchers bytes create invoke destroy comment
904	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	930	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
905	EV/Any 100000 610 3.52 0.91 0.75 EV + AnyEvent watchers	931	EV/Any 100000 610 3.52 0.91 0.75 EV + AnyEvent watchers
906	CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal	932	CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal
907	Perl/Any 16000 654 4.64 1.22 0.77 pure perl implementation	933	Perl/Any 100000 513 4.91 0.92 1.15 pure perl implementation
908	Event/Event 16000 523 28.05 21.38 0.86 Event native interface	934	Event/Event 16000 523 28.05 21.38 0.86 Event native interface
909	Event/Any 16000 943 34.43 20.48 1.39 Event + AnyEvent watchers	935	Event/Any 16000 943 34.43 20.48 1.39 Event + AnyEvent watchers
910	Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour	936	Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour
911	Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers	937	Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers
912	POE/Event 2000 6644 108.15 768.19 14.33 via POE::Loop::Event	938	POE/Event 2000 6644 108.15 768.19 14.33 via POE::Loop::Event
913	POE/Select 2000 6343 94.69 807.65 562.69 via POE::Loop::Select	939	POE/Select 2000 6343 94.69 807.65 562.69 via POE::Loop::Select
914		940
915	=head2 Discussion	941	=head2 Discussion
916		942
917	The benchmark does I<not> measure scalability of the event loop very	943	The benchmark does I<not> measure scalability of the event loop very
918	well. For example, a select-based event loop (such as the pure perl one)	944	well. For example, a select-based event loop (such as the pure perl one)
919	can never compete with an event loop that uses epoll when the number of	945	can never compete with an event loop that uses epoll when the number of
920	file descriptors grows high. In this benchmark, only a single filehandle	946	file descriptors grows high. In this benchmark, all events become ready at
921	is used (although some of the AnyEvent adaptors dup() its file descriptor	947	the same time, so select/poll-based implementations get an unnatural speed
922	to worka round bugs).	948	boost.
923		949
924	C<EV> is the sole leader regarding speed and memory use, which are both	950	C<EV> is the sole leader regarding speed and memory use, which are both
925	maximal/minimal, respectively. Even when going through AnyEvent, there is	951	maximal/minimal, respectively. Even when going through AnyEvent, there are
926	only one event loop that uses less memory (the C<Event> module natively), and	952	only two event loops that use slightly less memory (the C<Event> module
927	no faster event model, not event C<Event> natively.	953	natively and the pure perl backend), and no faster event models, not even
		954	C<Event> natively.
928		955
929	The pure perl implementation is hit in a few sweet spots (both the	956	The pure perl implementation is hit in a few sweet spots (both the
930	zero timeout and the use of a single fd hit optimisations in the perl	957	zero timeout and the use of a single fd hit optimisations in the perl
931	interpreter and the backend itself). Nevertheless tis shows that it	958	interpreter and the backend itself, and all watchers become ready at the
932	adds very little overhead in itself. Like any select-based backend its	959	same time). Nevertheless this shows that it adds very little overhead in
933	performance becomes really bad with lots of file descriptors, of course,	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
934	but this was not subjetc of this benchmark.	962	this was not subject of this benchmark.
935		963
936	The C<Event> module has a relatively high setup and callback invocation cost,	964	The C<Event> module has a relatively high setup and callback invocation cost,
937	but overall scores on the third place.	965	but overall scores on the third place.
938		966
939	C<Glib>'s memory usage is quite a bit bit higher, features a faster	967	C<Glib>'s memory usage is quite a bit bit higher, but it features a
940	callback invocation and overall lands in the same class as C<Event>.	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).
941		974
942	The C<Tk> adaptor works relatively well, the fact that it crashes with	975	The C<Tk> adaptor works relatively well. The fact that it crashes with
943	more than 2000 watchers is a big setback, however, as correctness takes	976	more than 2000 watchers is a big setback, however, as correctness takes
944	precedence over speed. Nevertheless, its performance is surprising, as the	977	precedence over speed. Nevertheless, its performance is surprising, as the
945	file descriptor is dup()ed for each watcher. This shows that the dup()	978	file descriptor is dup()ed for each watcher. This shows that the dup()
946	employed by some adaptors is not a big performance issue (it does incur a	979	employed by some adaptors is not a big performance issue (it does incur a
947	hidden memory cost inside the kernel, though).	980	hidden memory cost inside the kernel, though, that is not reflected in the
		981	figures above).
948		982
949	C<POE>, regardless of backend (wether using its pure perl select-based	983	C<POE>, regardless of underlying event loop (wether using its pure perl
950	backend or the Event backend) shows abysmal performance and memory	984	select-based backend or the Event module) shows abysmal performance and
951	usage: Watchers use almost 30 times as much memory as EV watchers, and 10	985	memory usage: Watchers use almost 30 times as much memory as EV watchers,
952	times as much memory as both Event or EV via AnyEvent. Watcher invocation	986	and 10 times as much memory as both Event or EV via AnyEvent. Watcher
953	is almost 700 times slower as with AnyEvent's pure perl implementation.	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.
954		992
		993	=head2 Summary
		994
955	Summary: using EV through AnyEvent is faster than any other event	995	Using EV through AnyEvent is faster than any other event loop, but most
956	loop. The overhead AnyEvent adds can be very small, and you should avoid	996	event loops have acceptable performance with or without AnyEvent.
957	POE like the plague if you want performance or reasonable memory usage.	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.
958		1004
959		1005
960	=head1 FORK	1006	=head1 FORK
961		1007
962	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

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Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.70 by root, Fri Apr 25 07:25:44 2008 UTC vs. Revision 1.82 by root, Fri Apr 25 13:32:39 2008 UTC

Diff Legend

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.70 by root, Fri Apr 25 07:25:44 2008 UTC vs.
Revision 1.82 by root, Fri Apr 25 13:32:39 2008 UTC