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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.54 by root, Tue Apr 22 05:12:19 2008 UTC vs.
Revision 1.96 by root, Sat Apr 26 11:16:16 2008 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported event loops	5	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
6		6
7	=head1 SYNOPSIS	7	=head1 SYNOPSIS
8		8
9	use AnyEvent;	9	use AnyEvent;
10		10
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>. The first one found is used. If none are found,	85	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
86	the module tries to load these modules in the stated order. The first one	86	L<POE>. The first one found is used. If none are found, the module tries
		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
87	that can be successfully loaded will be used. If, after this, still none	89	be successfully loaded will be used. If, after this, still none could be
88	could be found, AnyEvent will fall back to a pure-perl event loop, which	90	found, AnyEvent will fall back to a pure-perl event loop, which is not
89	is not very efficient, but should work everywhere.	91	very efficient, but should work everywhere.
90		92
91	Because AnyEvent first checks for modules that are already loaded, loading	93	Because AnyEvent first checks for modules that are already loaded, loading
92	an event model explicitly before first using AnyEvent will likely make	94	an event model explicitly before first using AnyEvent will likely make
93	that model the default. For example:	95	that model the default. For example:
94		96
…		…
134		136
135	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,
136	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
137	declared.	139	declared.
138		140
139	=head2 IO WATCHERS	141	=head2 I/O WATCHERS
140		142
141	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
142	with the following mandatory key-value pairs as arguments:	144	with the following mandatory key-value pairs as arguments:
143		145
144	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
145	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>,
146	creates a watcher waiting for "r"eadable or "w"ritable events,	148	which creates a watcher waiting for "r"eadable or "w"ritable events,
147	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
148	becomes ready.	150	becomes ready.
149		151
150	File handles will be kept alive, so as long as the watcher exists, the	152	Although the callback might get passed parameters, their value and
151	file handle exists, too.	153	presence is undefined and you cannot rely on them. Portable AnyEvent
		154	callbacks cannot use arguments passed to I/O watcher callbacks.
152		155
		156	The I/O watcher might use the underlying file descriptor or a copy of it.
153	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
154	on the underlying file descriptor.	158	underlying file descriptor.
155		159
156	Some event loops issue spurious readyness notifications, so you should	160	Some event loops issue spurious readyness notifications, so you should
157	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
158	handles.	162	handles.
159		163
…		…
170		174
171	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 >>
172	method with the following mandatory arguments:	176	method with the following mandatory arguments:
173		177
174	C<after> specifies after how many seconds (fractional values are	178	C<after> specifies after how many seconds (fractional values are
175	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
176	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.
177		185
178	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
179	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
180	and Glib).	188	and Glib).
181		189
…		…
206		214
207	There are two ways to handle timers: based on real time (relative, "fire	215	There are two ways to handle timers: based on real time (relative, "fire
208	in 10 seconds") and based on wallclock time (absolute, "fire at 12	216	in 10 seconds") and based on wallclock time (absolute, "fire at 12
209	o'clock").	217	o'clock").
210		218
211	While most event loops expect timers to specified in a relative way, they use	219	While most event loops expect timers to specified in a relative way, they
212	absolute time internally. This makes a difference when your clock "jumps",	220	use absolute time internally. This makes a difference when your clock
213	for example, when ntp decides to set your clock backwards from the wrong 2014-01-01 to	221	"jumps", for example, when ntp decides to set your clock backwards from
214	2008-01-01, a watcher that you created to fire "after" a second might actually take	222	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
215	six years to finally fire.	223	fire "after" a second might actually take six years to finally fire.
216		224
217	AnyEvent cannot compensate for this. The only event loop that is conscious	225	AnyEvent cannot compensate for this. The only event loop that is conscious
218	about these issues is L<EV>, which offers both relative (ev_timer) and	226	about these issues is L<EV>, which offers both relative (ev_timer, based
219	absolute (ev_periodic) timers.	227	on true relative time) and absolute (ev_periodic, based on wallclock time)
		228	timers.
220		229
221	AnyEvent always prefers relative timers, if available, matching the	230	AnyEvent always prefers relative timers, if available, matching the
222	AnyEvent API.	231	AnyEvent API.
223		232
224	=head2 SIGNAL WATCHERS	233	=head2 SIGNAL WATCHERS
225		234
226	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
227	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
228	be invoked whenever a signal occurs.	237	be invoked whenever a signal occurs.
229		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
230	Multiple signals occurances can be clumped together into one callback	243	Multiple signal occurances can be clumped together into one callback
231	invocation, and callback invocation will be synchronous. synchronous means	244	invocation, and callback invocation will be synchronous. synchronous means
232	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,
233	but it is guarenteed not to interrupt any other callbacks.	246	but it is guarenteed not to interrupt any other callbacks.
234		247
235	The main advantage of using these watchers is that you can share a signal	248	The main advantage of using these watchers is that you can share a signal
…		…
248		261
249	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
250	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
251	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
252	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
253	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.
254		268
255	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;
256		288
257	my $w = AnyEvent->child (	289	my $w = AnyEvent->child (
258	pid => 1333,	290	pid => $pid,
259	cb => sub {	291	cb => sub {
260	my ($pid, $status) = @_;	292	my ($pid, $status) = @_;
261	warn "pid $pid exited with status $status";	293	warn "pid $pid exited with status $status";
		294	$done->broadcast;
262	},	295	},
263	);	296	);
		297
		298	# do something else, then wait for process exit
		299	$done->wait;
264		300
265	=head2 CONDITION VARIABLES	301	=head2 CONDITION VARIABLES
266		302
267	Condition variables can be created by calling the C<< AnyEvent->condvar >>	303	Condition variables can be created by calling the C<< AnyEvent->condvar >>
268	method without any arguments.	304	method without any arguments.
…		…
353		389
354	The known classes so far are:	390	The known classes so far are:
355		391
356	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.	392	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
357	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.	393	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
358	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	394	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
359	AnyEvent::Impl::Event based on Event, also second best choice :)	395	AnyEvent::Impl::Event based on Event, second best choice.
360	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.
361	AnyEvent::Impl::Tk based on Tk, very bad choice.	398	AnyEvent::Impl::Tk based on Tk, very bad choice.
362	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	399	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		400	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		401	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		402
		403	There is no support for WxWidgets, as WxWidgets has no support for
		404	watching file handles. However, you can use WxWidgets through the
		405	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		406	second, which was considered to be too horrible to even consider for
		407	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		408	it's adaptor.
		409
		410	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		411	autodetecting them.
363		412
364	=item AnyEvent::detect	413	=item AnyEvent::detect
365		414
366	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	415	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
367	if necessary. You should only call this function right before you would	416	if necessary. You should only call this function right before you would
…		…
418	no warnings;	467	no warnings;
419	use strict;	468	use strict;
420		469
421	use Carp;	470	use Carp;
422		471
423	our $VERSION = '3.12';	472	our $VERSION = '3.3';
424	our $MODEL;	473	our $MODEL;
425		474
426	our $AUTOLOAD;	475	our $AUTOLOAD;
427	our @ISA;	476	our @ISA;
428		477
…		…
435	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],	484	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
436	[EV:: => AnyEvent::Impl::EV::],	485	[EV:: => AnyEvent::Impl::EV::],
437	[Event:: => AnyEvent::Impl::Event::],	486	[Event:: => AnyEvent::Impl::Event::],
438	[Glib:: => AnyEvent::Impl::Glib::],	487	[Glib:: => AnyEvent::Impl::Glib::],
439	[Tk:: => AnyEvent::Impl::Tk::],	488	[Tk:: => AnyEvent::Impl::Tk::],
		489	[Wx:: => AnyEvent::Impl::POE::],
		490	[Prima:: => AnyEvent::Impl::POE::],
440	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	491	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		492	# everything below here will not be autoprobed as the pureperl backend should work everywhere
		493	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		494	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		495	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
441	);	496	);
442		497
443	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	498	our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);
444		499
445	sub detect() {	500	sub detect() {
446	unless ($MODEL) {	501	unless ($MODEL) {
447	no strict 'refs';	502	no strict 'refs';
448		503
		504	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		505	my $model = "AnyEvent::Impl::$1";
		506	if (eval "require $model") {
		507	$MODEL = $model;
		508	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		509	} else {
		510	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		511	}
		512	}
		513
449	# check for already loaded models	514	# check for already loaded models
		515	unless ($MODEL) {
450	for (@REGISTRY, @models) {	516	for (@REGISTRY, @models) {
451	my ($package, $model) = @$_;	517	my ($package, $model) = @$_;
452	if (${"$package\::VERSION"} > 0) {	518	if (${"$package\::VERSION"} > 0) {
453	if (eval "require $model") {	519	if (eval "require $model") {
454	$MODEL = $model;	520	$MODEL = $model;
455	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	521	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
456	last;	522	last;
		523	}
457	}	524	}
458	}	525	}
459	}
460		526
461	unless ($MODEL) {	527	unless ($MODEL) {
462	# try to load a model	528	# try to load a model
463		529
464	for (@REGISTRY, @models) {	530	for (@REGISTRY, @models) {
465	my ($package, $model) = @$_;	531	my ($package, $model) = @$_;
466	if (eval "require $package"	532	if (eval "require $package"
467	and ${"$package\::VERSION"} > 0	533	and ${"$package\::VERSION"} > 0
468	and eval "require $model") {	534	and eval "require $model") {
469	$MODEL = $model;	535	$MODEL = $model;
470	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	536	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
471	last;	537	last;
		538	}
472	}	539	}
		540
		541	$MODEL
		542	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";
473	}	543	}
474
475	$MODEL
476	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event), Glib or Tk.";
477	}	544	}
478		545
479	unshift @ISA, $MODEL;	546	unshift @ISA, $MODEL;
480	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	547	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
481	}	548	}
…		…
637		704
638	=head1 ENVIRONMENT VARIABLES	705	=head1 ENVIRONMENT VARIABLES
639		706
640	The following environment variables are used by this module:	707	The following environment variables are used by this module:
641		708
642	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, cause AnyEvent to	709	=over 4
643	report to STDERR which event model it chooses.	710
		711	=item C<PERL_ANYEVENT_VERBOSE>
		712
		713	By default, AnyEvent will be completely silent except in fatal
		714	conditions. You can set this environment variable to make AnyEvent more
		715	talkative.
		716
		717	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		718	conditions, such as not being able to load the event model specified by
		719	C<PERL_ANYEVENT_MODEL>.
		720
		721	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		722	model it chooses.
		723
		724	=item C<PERL_ANYEVENT_MODEL>
		725
		726	This can be used to specify the event model to be used by AnyEvent, before
		727	autodetection and -probing kicks in. It must be a string consisting
		728	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		729	and the resulting module name is loaded and if the load was successful,
		730	used as event model. If it fails to load AnyEvent will proceed with
		731	autodetection and -probing.
		732
		733	This functionality might change in future versions.
		734
		735	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		736	could start your program like this:
		737
		738	PERL_ANYEVENT_MODEL=Perl perl ...
		739
		740	=back
644		741
645	=head1 EXAMPLE PROGRAM	742	=head1 EXAMPLE PROGRAM
646		743
647	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
648	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
649	program when the user enters quit:	746	program when the user enters quit:
650		747
651	use AnyEvent;	748	use AnyEvent;
652		749
…		…
796	$quit->broadcast;	893	$quit->broadcast;
797	});	894	});
798		895
799	$quit->wait;	896	$quit->wait;
800		897
		898
		899	=head1 BENCHMARKS
		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 speed
		903	of various event loops I prepared some benchmarks.
		904
		905	=head2 BENCHMARKING ANYEVENT OVERHEAD
		906
		907	Here is a benchmark of various supported event models used natively and
		908	through anyevent. The benchmark creates a lot of timers (with a zero
		909	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		910	which it is), lets them fire exactly once and destroys them again.
		911
		912	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		913	distribution.
		914
		915	=head3 Explanation of the columns
		916
		917	I<watcher> is the number of event watchers created/destroyed. Since
		918	different event models feature vastly different performances, each event
		919	loop was given a number of watchers so that overall runtime is acceptable
		920	and similar between tested event loop (and keep them from crashing): Glib
		921	would probably take thousands of years if asked to process the same number
		922	of watchers as EV in this benchmark.
		923
		924	I<bytes> is the number of bytes (as measured by the resident set size,
		925	RSS) consumed by each watcher. This method of measuring captures both C
		926	and Perl-based overheads.
		927
		928	I<create> is the time, in microseconds (millionths of seconds), that it
		929	takes to create a single watcher. The callback is a closure shared between
		930	all watchers, to avoid adding memory overhead. That means closure creation
		931	and memory usage is not included in the figures.
		932
		933	I<invoke> is the time, in microseconds, used to invoke a simple
		934	callback. The callback simply counts down a Perl variable and after it was
		935	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		936	signal the end of this phase.
		937
		938	I<destroy> is the time, in microseconds, that it takes to destroy a single
		939	watcher.
		940
		941	=head3 Results
		942
		943	name watchers bytes create invoke destroy comment
		944	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		945	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		946	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		947	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		948	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		949	Event/Any 16000 936 39.17 33.63 1.43 Event + AnyEvent watchers
		950	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		951	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		952	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		953	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		954
		955	=head3 Discussion
		956
		957	The benchmark does I<not> measure scalability of the event loop very
		958	well. For example, a select-based event loop (such as the pure perl one)
		959	can never compete with an event loop that uses epoll when the number of
		960	file descriptors grows high. In this benchmark, all events become ready at
		961	the same time, so select/poll-based implementations get an unnatural speed
		962	boost.
		963
		964	Also, note that the number of watchers usually has a nonlinear effect on
		965	overall speed, that is, creating twice as many watchers doesn't take twice
		966	the time - usually it takes longer. This puts event loops tested with a
		967	higher number of watchers at a disadvantage.
		968
		969	To put the range of results into perspective, consider that on the
		970	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		971	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		972	cycles with POE.
		973
		974	C<EV> is the sole leader regarding speed and memory use, which are both
		975	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		976	far less memory than any other event loop and is still faster than Event
		977	natively.
		978
		979	The pure perl implementation is hit in a few sweet spots (both the
		980	constant timeout and the use of a single fd hit optimisations in the perl
		981	interpreter and the backend itself). Nevertheless this shows that it
		982	adds very little overhead in itself. Like any select-based backend its
		983	performance becomes really bad with lots of file descriptors (and few of
		984	them active), of course, but this was not subject of this benchmark.
		985
		986	The C<Event> module has a relatively high setup and callback invocation
		987	cost, but overall scores in on the third place.
		988
		989	C<Glib>'s memory usage is quite a bit higher, but it features a
		990	faster callback invocation and overall ends up in the same class as
		991	C<Event>. However, Glib scales extremely badly, doubling the number of
		992	watchers increases the processing time by more than a factor of four,
		993	making it completely unusable when using larger numbers of watchers
		994	(note that only a single file descriptor was used in the benchmark, so
		995	inefficiencies of C<poll> do not account for this).
		996
		997	The C<Tk> adaptor works relatively well. The fact that it crashes with
		998	more than 2000 watchers is a big setback, however, as correctness takes
		999	precedence over speed. Nevertheless, its performance is surprising, as the
		1000	file descriptor is dup()ed for each watcher. This shows that the dup()
		1001	employed by some adaptors is not a big performance issue (it does incur a
		1002	hidden memory cost inside the kernel which is not reflected in the figures
		1003	above).
		1004
		1005	C<POE>, regardless of underlying event loop (whether using its pure
		1006	perl select-based backend or the Event module, the POE-EV backend
		1007	couldn't be tested because it wasn't working) shows abysmal performance
		1008	and memory usage: Watchers use almost 30 times as much memory as
		1009	EV watchers, and 10 times as much memory as Event (the high memory
		1010	requirements are caused by requiring a session for each watcher). Watcher
		1011	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1012	implementation. The design of the POE adaptor class in AnyEvent can not
		1013	really account for this, as session creation overhead is small compared
		1014	to execution of the state machine, which is coded pretty optimally within
		1015	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.
		1016
		1017	=head3 Summary
		1018
		1019	=over 4
		1020
		1021	=item * Using EV through AnyEvent is faster than any other event loop
		1022	(even when used without AnyEvent), but most event loops have acceptable
		1023	performance with or without AnyEvent.
		1024
		1025	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1026	the actual event loop, only with extremely fast event loops such as EV
		1027	adds AnyEvent significant overhead.
		1028
		1029	=item * You should avoid POE like the plague if you want performance or
		1030	reasonable memory usage.
		1031
		1032	=back
		1033
		1034	=head2 BENCHMARKING THE LARGE SERVER CASE
		1035
		1036	This benchmark atcually benchmarks the event loop itself. It works by
		1037	creating a number of "servers": each server consists of a socketpair, a
		1038	timeout watcher that gets reset on activity (but never fires), and an I/O
		1039	watcher waiting for input on one side of the socket. Each time the socket
		1040	watcher reads a byte it will write that byte to a random other "server".
		1041
		1042	The effect is that there will be a lot of I/O watchers, only part of which
		1043	are active at any one point (so there is a constant number of active
		1044	fds for each loop iterstaion, but which fds these are is random). The
		1045	timeout is reset each time something is read because that reflects how
		1046	most timeouts work (and puts extra pressure on the event loops).
		1047
		1048	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1049	(1%) are active. This mirrors the activity of large servers with many
		1050	connections, most of which are idle at any one point in time.
		1051
		1052	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1053	distribution.
		1054
		1055	=head3 Explanation of the columns
		1056
		1057	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1058	each server has a read and write socket end).
		1059
		1060	I<create> is the time it takes to create a socketpair (which is
		1061	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1062
		1063	I<request>, the most important value, is the time it takes to handle a
		1064	single "request", that is, reading the token from the pipe and forwarding
		1065	it to another server. This includes deleting the old timeout and creating
		1066	a new one that moves the timeout into the future.
		1067
		1068	=head3 Results
		1069
		1070	name sockets create request
		1071	EV 20000 69.01 11.16
		1072	Perl 20000 75.28 112.76
		1073	Event 20000 212.62 257.32
		1074	Glib 20000 651.16 1896.30
		1075	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1076
		1077	=head3 Discussion
		1078
		1079	This benchmark I<does> measure scalability and overall performance of the
		1080	particular event loop.
		1081
		1082	EV is again fastest. Since it is using epoll on my system, the setup time
		1083	is relatively high, though.
		1084
		1085	Perl surprisingly comes second. It is much faster than the C-based event
		1086	loops Event and Glib.
		1087
		1088	Event suffers from high setup time as well (look at its code and you will
		1089	understand why). Callback invocation also has a high overhead compared to
		1090	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1091	uses select or poll in basically all documented configurations.
		1092
		1093	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1094	clearly fails to perform with many filehandles or in busy servers.
		1095
		1096	POE is still completely out of the picture, taking over 1000 times as long
		1097	as EV, and over 100 times as long as the Perl implementation, even though
		1098	it uses a C-based event loop in this case.
		1099
		1100	=head3 Summary
		1101
		1102	=over 4
		1103
		1104	=item * The pure perl implementation performs extremely well, considering
		1105	that it uses select.
		1106
		1107	=item * Avoid Glib or POE in large projects where performance matters.
		1108
		1109	=back
		1110
		1111	=head2 BENCHMARKING SMALL SERVERS
		1112
		1113	While event loops should scale (and select-based ones do not...) even to
		1114	large servers, most programs we (or I :) actually write have only a few
		1115	I/O watchers.
		1116
		1117	In this benchmark, I use the same benchmark program as in the large server
		1118	case, but it uses only eight "servers", of which three are active at any
		1119	one time. This should reflect performance for a small server relatively
		1120	well.
		1121
		1122	The columns are identical to the previous table.
		1123
		1124	=head3 Results
		1125
		1126	name sockets create request
		1127	EV 16 20.00 6.54
		1128	Event 16 81.27 35.86
		1129	Glib 16 32.63 15.48
		1130	Perl 16 24.62 162.37
		1131	POE 16 261.87 276.28 uses POE::Loop::Event
		1132
		1133	=head3 Discussion
		1134
		1135	The benchmark tries to test the performance of a typical small
		1136	server. While knowing how various event loops perform is interesting, keep
		1137	in mind that their overhead in this case is usually not as important, due
		1138	to the small absolute number of watchers.
		1139
		1140	EV is again fastest.
		1141
		1142	The C-based event loops Event and Glib come in second this time, as the
		1143	overhead of running an iteration is much smaller in C than in Perl (little
		1144	code to execute in the inner loop, and perl's function calling overhead is
		1145	high, and updating all the data structures is costly).
		1146
		1147	The pure perl event loop is much slower, but still competitive.
		1148
		1149	POE also performs much better in this case, but is is stillf ar behind the
		1150	others.
		1151
		1152	=head3 Summary
		1153
		1154	=over 4
		1155
		1156	=item * C-based event loops perform very well with small number of
		1157	watchers, as the management overhead dominates.
		1158
		1159	=back
		1160
		1161
		1162	=head1 FORK
		1163
		1164	Most event libraries are not fork-safe. The ones who are usually are
		1165	because they are so inefficient. Only L<EV> is fully fork-aware.
		1166
		1167	If you have to fork, you must either do so I<before> creating your first
		1168	watcher OR you must not use AnyEvent at all in the child.
		1169
		1170
		1171	=head1 SECURITY CONSIDERATIONS
		1172
		1173	AnyEvent can be forced to load any event model via
		1174	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1175	execute arbitrary code or directly gain access, it can easily be used to
		1176	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1177	will not be active when the program uses a different event model than
		1178	specified in the variable.
		1179
		1180	You can make AnyEvent completely ignore this variable by deleting it
		1181	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1182
		1183	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1184
		1185	use AnyEvent;
		1186
		1187
801	=head1 SEE ALSO	1188	=head1 SEE ALSO
802		1189
803	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1190	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,
804	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.	1191	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
		1192	L<Event::Lib>, L<Qt>, L<POE>.
805		1193
806	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	1194	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
		1195	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,
		1196	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
807	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,	1197	L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.
808	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.
809		1198
810	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1199	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
		1200
811		1201
812	=head1 AUTHOR	1202	=head1 AUTHOR
813		1203
814	Marc Lehmann <schmorp@schmorp.de>	1204	Marc Lehmann <schmorp@schmorp.de>
815	http://home.schmorp.de/	1205	http://home.schmorp.de/

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Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.54 by root, Tue Apr 22 05:12:19 2008 UTC vs.
Revision 1.96 by root, Sat Apr 26 11:16:16 2008 UTC