[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 1.123 by root, Fri May 23 20:41:25 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, 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
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	...	16	...
17	});	17	});
18		18
19	my $w = AnyEvent->condvar; # stores whether a condition was flagged	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		20	$w->send; # wake up current and all future recv's
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	21	$w->recv; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all future wait's
22		22
23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)	23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		24
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	26	nowadays. So what is different about AnyEvent?
…		…
66		66
67	Of course, if you want lots of policy (this can arguably be somewhat	67	Of course, if you want lots of policy (this can arguably be somewhat
68	useful) and you want to force your users to use the one and only event	68	useful) and you want to force your users to use the one and only event
69	model, you should I<not> use this module.	69	model, you should I<not> use this module.
70		70
71
72	=head1 DESCRIPTION	71	=head1 DESCRIPTION
73		72
74	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
75	allows module authors to utilise an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
76	users to use the same event loop (as only a single event loop can coexist	75	users to use the same event loop (as only a single event loop can coexist
…		…
79	The interface itself is vaguely similar, but not identical to the L<Event>	78	The interface itself is vaguely similar, but not identical to the L<Event>
80	module.	79	module.
81		80
82	During the first call of any watcher-creation method, the module tries	81	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	82	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>,	83	following modules is already loaded: L<EV>,
85	L<Event>, L<Glib>, L<Tk>. The first one found is used. If none are found,	84	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	85	L<POE>. The first one found is used. If none are found, the module tries
		86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		87	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	88	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	89	found, AnyEvent will fall back to a pure-perl event loop, which is not
89	is not very efficient, but should work everywhere.	90	very efficient, but should work everywhere.
90		91
91	Because AnyEvent first checks for modules that are already loaded, loading	92	Because AnyEvent first checks for modules that are already loaded, loading
92	an event model explicitly before first using AnyEvent will likely make	93	an event model explicitly before first using AnyEvent will likely make
93	that model the default. For example:	94	that model the default. For example:
94		95
…		…
134		135
135	Note that C<my $w; $w => combination. This is necessary because in Perl,	136	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	137	my variables are only visible after the statement in which they are
137	declared.	138	declared.
138		139
139	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
140		141
141	You can create an I/O watcher by calling the C<< AnyEvent->io >> method	142	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
142	with the following mandatory key-value pairs as arguments:	143	with the following mandatory key-value pairs as arguments:
143		144
144	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for	145	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	146	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,	147	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	148	respectively. C<cb> is the callback to invoke each time the file handle
148	becomes ready.	149	becomes ready.
149		150
150	File handles will be kept alive, so as long as the watcher exists, the	151	Although the callback might get passed parameters, their value and
151	file handle exists, too.	152	presence is undefined and you cannot rely on them. Portable AnyEvent
		153	callbacks cannot use arguments passed to I/O watcher callbacks.
152		154
		155	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	156	You must not close a file handle as long as any watcher is active on the
154	on the underlying file descriptor.	157	underlying file descriptor.
155		158
156	Some event loops issue spurious readyness notifications, so you should	159	Some event loops issue spurious readyness notifications, so you should
157	always use non-blocking calls when reading/writing from/to your file	160	always use non-blocking calls when reading/writing from/to your file
158	handles.	161	handles.
159		162
…		…
170		173
171	You can create a time watcher by calling the C<< AnyEvent->timer >>	174	You can create a time watcher by calling the C<< AnyEvent->timer >>
172	method with the following mandatory arguments:	175	method with the following mandatory arguments:
173		176
174	C<after> specifies after how many seconds (fractional values are	177	C<after> specifies after how many seconds (fractional values are
175	supported) should the timer activate. C<cb> the callback to invoke in that	178	supported) the callback should be invoked. C<cb> is the callback to invoke
176	case.	179	in that case.
		180
		181	Although the callback might get passed parameters, their value and
		182	presence is undefined and you cannot rely on them. Portable AnyEvent
		183	callbacks cannot use arguments passed to time watcher callbacks.
177		184
178	The timer callback will be invoked at most once: if you want a repeating	185	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	186	timer you have to create a new watcher (this is a limitation by both Tk
180	and Glib).	187	and Glib).
181		188
…		…
206		213
207	There are two ways to handle timers: based on real time (relative, "fire	214	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	215	in 10 seconds") and based on wallclock time (absolute, "fire at 12
209	o'clock").	216	o'clock").
210		217
211	While most event loops expect timers to specified in a relative way, they use	218	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",	219	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	220	"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	221	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
215	six years to finally fire.	222	fire "after" a second might actually take six years to finally fire.
216		223
217	AnyEvent cannot compensate for this. The only event loop that is conscious	224	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	225	about these issues is L<EV>, which offers both relative (ev_timer, based
219	absolute (ev_periodic) timers.	226	on true relative time) and absolute (ev_periodic, based on wallclock time)
		227	timers.
220		228
221	AnyEvent always prefers relative timers, if available, matching the	229	AnyEvent always prefers relative timers, if available, matching the
222	AnyEvent API.	230	AnyEvent API.
223		231
224	=head2 SIGNAL WATCHERS	232	=head2 SIGNAL WATCHERS
225		233
226	You can watch for signals using a signal watcher, C<signal> is the signal	234	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	235	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
228	be invoked whenever a signal occurs.	236	be invoked whenever a signal occurs.
229		237
		238	Although the callback might get passed parameters, their value and
		239	presence is undefined and you cannot rely on them. Portable AnyEvent
		240	callbacks cannot use arguments passed to signal watcher callbacks.
		241
230	Multiple signals occurances can be clumped together into one callback	242	Multiple signal occurances can be clumped together into one callback
231	invocation, and callback invocation will be synchronous. synchronous means	243	invocation, and callback invocation will be synchronous. synchronous means
232	that it might take a while until the signal gets handled by the process,	244	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.	245	but it is guarenteed not to interrupt any other callbacks.
234		246
235	The main advantage of using these watchers is that you can share a signal	247	The main advantage of using these watchers is that you can share a signal
…		…
248		260
249	The child process is specified by the C<pid> argument (if set to C<0>, it	261	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	262	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	263	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	264	signal handler for C<SIGCHLD>. The callback will be called with the pid
253	and exit status (as returned by waitpid).	265	and exit status (as returned by waitpid), so unlike other watcher types,
		266	you I<can> rely on child watcher callback arguments.
254		267
255	Example: wait for pid 1333	268	There is a slight catch to child watchers, however: you usually start them
		269	I<after> the child process was created, and this means the process could
		270	have exited already (and no SIGCHLD will be sent anymore).
		271
		272	Not all event models handle this correctly (POE doesn't), but even for
		273	event models that I<do> handle this correctly, they usually need to be
		274	loaded before the process exits (i.e. before you fork in the first place).
		275
		276	This means you cannot create a child watcher as the very first thing in an
		277	AnyEvent program, you I<have> to create at least one watcher before you
		278	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		279
		280	Example: fork a process and wait for it
		281
		282	my $done = AnyEvent->condvar;
		283
		284	my $pid = fork or exit 5;
256		285
257	my $w = AnyEvent->child (	286	my $w = AnyEvent->child (
258	pid => 1333,	287	pid => $pid,
259	cb => sub {	288	cb => sub {
260	my ($pid, $status) = @_;	289	my ($pid, $status) = @_;
261	warn "pid $pid exited with status $status";	290	warn "pid $pid exited with status $status";
		291	$done->send;
262	},	292	},
263	);	293	);
264		294
		295	# do something else, then wait for process exit
		296	$done->recv;
		297
265	=head2 CONDITION VARIABLES	298	=head2 CONDITION VARIABLES
266		299
		300	If you are familiar with some event loops you will know that all of them
		301	require you to run some blocking "loop", "run" or similar function that
		302	will actively watch for new events and call your callbacks.
		303
		304	AnyEvent is different, it expects somebody else to run the event loop and
		305	will only block when necessary (usually when told by the user).
		306
		307	The instrument to do that is called a "condition variable", so called
		308	because they represent a condition that must become true.
		309
267	Condition variables can be created by calling the C<< AnyEvent->condvar >>	310	Condition variables can be created by calling the C<< AnyEvent->condvar
268	method without any arguments.	311	>> method, usually without arguments. The only argument pair allowed is
		312	C<cb>, which specifies a callback to be called when the condition variable
		313	becomes true.
269		314
270	A condition variable waits for a condition - precisely that the C<<	315	After creation, the conditon variable is "false" until it becomes "true"
271	->broadcast >> method has been called.	316	by calling the C<send> method.
272		317
273	They are very useful to signal that a condition has been fulfilled, for	318	Condition variables are similar to callbacks, except that you can
		319	optionally wait for them. They can also be called merge points - points
		320	in time where multiple outstandign events have been processed. And yet
		321	another way to call them is transations - each condition variable can be
		322	used to represent a transaction, which finishes at some point and delivers
		323	a result.
		324
		325	Condition variables are very useful to signal that something has finished,
274	example, if you write a module that does asynchronous http requests,	326	for example, if you write a module that does asynchronous http requests,
275	then a condition variable would be the ideal candidate to signal the	327	then a condition variable would be the ideal candidate to signal the
276	availability of results.	328	availability of results. The user can either act when the callback is
		329	called or can synchronously C<< ->recv >> for the results.
277		330
278	You can also use condition variables to block your main program until	331	You can also use them to simulate traditional event loops - for example,
279	an event occurs - for example, you could C<< ->wait >> in your main	332	you can block your main program until an event occurs - for example, you
280	program until the user clicks the Quit button in your app, which would C<<	333	could C<< ->recv >> in your main program until the user clicks the Quit
281	->broadcast >> the "quit" event.	334	button of your app, which would C<< ->send >> the "quit" event.
282		335
283	Note that condition variables recurse into the event loop - if you have	336	Note that condition variables recurse into the event loop - if you have
284	two pirces of code that call C<< ->wait >> in a round-robbin fashion, you	337	two pieces of code that call C<< ->recv >> in a round-robbin fashion, you
285	lose. Therefore, condition variables are good to export to your caller, but	338	lose. Therefore, condition variables are good to export to your caller, but
286	you should avoid making a blocking wait yourself, at least in callbacks,	339	you should avoid making a blocking wait yourself, at least in callbacks,
287	as this asks for trouble.	340	as this asks for trouble.
288		341
289	This object has two methods:	342	Condition variables are represented by hash refs in perl, and the keys
		343	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		344	easy (it is often useful to build your own transaction class on top of
		345	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		346	it's C<new> method in your own C<new> method.
		347
		348	There are two "sides" to a condition variable - the "producer side" which
		349	eventually calls C<< -> send >>, and the "consumer side", which waits
		350	for the send to occur.
		351
		352	Example:
		353
		354	# wait till the result is ready
		355	my $result_ready = AnyEvent->condvar;
		356
		357	# do something such as adding a timer
		358	# or socket watcher the calls $result_ready->send
		359	# when the "result" is ready.
		360	# in this case, we simply use a timer:
		361	my $w = AnyEvent->timer (
		362	after => 1,
		363	cb => sub { $result_ready->send },
		364	);
		365
		366	# this "blocks" (while handling events) till the callback
		367	# calls send
		368	$result_ready->recv;
		369
		370	=head3 METHODS FOR PRODUCERS
		371
		372	These methods should only be used by the producing side, i.e. the
		373	code/module that eventually sends the signal. Note that it is also
		374	the producer side which creates the condvar in most cases, but it isn't
		375	uncommon for the consumer to create it as well.
290		376
291	=over 4	377	=over 4
292		378
		379	=item $cv->send (...)
		380
		381	Flag the condition as ready - a running C<< ->recv >> and all further
		382	calls to C<recv> will (eventually) return after this method has been
		383	called. If nobody is waiting the send will be remembered.
		384
		385	If a callback has been set on the condition variable, it is called
		386	immediately from within send.
		387
		388	Any arguments passed to the C<send> call will be returned by all
		389	future C<< ->recv >> calls.
		390
		391	=item $cv->croak ($error)
		392
		393	Similar to send, but causes all call's to C<< ->recv >> to invoke
		394	C<Carp::croak> with the given error message/object/scalar.
		395
		396	This can be used to signal any errors to the condition variable
		397	user/consumer.
		398
		399	=item $cv->begin ([group callback])
		400
293	=item $cv->wait	401	=item $cv->end
294		402
295	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	403	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		404
		405	These two methods can be used to combine many transactions/events into
		406	one. For example, a function that pings many hosts in parallel might want
		407	to use a condition variable for the whole process.
		408
		409	Every call to C<< ->begin >> will increment a counter, and every call to
		410	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		411	>>, the (last) callback passed to C<begin> will be executed. That callback
		412	is I<supposed> to call C<< ->send >>, but that is not required. If no
		413	callback was set, C<send> will be called without any arguments.
		414
		415	Let's clarify this with the ping example:
		416
		417	my $cv = AnyEvent->condvar;
		418
		419	my %result;
		420	$cv->begin (sub { $cv->send (\%result) });
		421
		422	for my $host (@list_of_hosts) {
		423	$cv->begin;
		424	ping_host_then_call_callback $host, sub {
		425	$result{$host} = ...;
		426	$cv->end;
		427	};
		428	}
		429
		430	$cv->end;
		431
		432	This code fragment supposedly pings a number of hosts and calls
		433	C<send> after results for all then have have been gathered - in any
		434	order. To achieve this, the code issues a call to C<begin> when it starts
		435	each ping request and calls C<end> when it has received some result for
		436	it. Since C<begin> and C<end> only maintain a counter, the order in which
		437	results arrive is not relevant.
		438
		439	There is an additional bracketing call to C<begin> and C<end> outside the
		440	loop, which serves two important purposes: first, it sets the callback
		441	to be called once the counter reaches C<0>, and second, it ensures that
		442	C<send> is called even when C<no> hosts are being pinged (the loop
		443	doesn't execute once).
		444
		445	This is the general pattern when you "fan out" into multiple subrequests:
		446	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		447	is called at least once, and then, for each subrequest you start, call
		448	C<begin> and for eahc subrequest you finish, call C<end>.
		449
		450	=back
		451
		452	=head3 METHODS FOR CONSUMERS
		453
		454	These methods should only be used by the consuming side, i.e. the
		455	code awaits the condition.
		456
		457	=over 4
		458
		459	=item $cv->recv
		460
		461	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
296	called on c<$cv>, while servicing other watchers normally.	462	>> methods have been called on c<$cv>, while servicing other watchers
		463	normally.
297		464
298	You can only wait once on a condition - additional calls will return	465	You can only wait once on a condition - additional calls are valid but
299	immediately.	466	will return immediately.
		467
		468	If an error condition has been set by calling C<< ->croak >>, then this
		469	function will call C<croak>.
		470
		471	In list context, all parameters passed to C<send> will be returned,
		472	in scalar context only the first one will be returned.
300		473
301	Not all event models support a blocking wait - some die in that case	474	Not all event models support a blocking wait - some die in that case
302	(programs might want to do that to stay interactive), so I<if you are	475	(programs might want to do that to stay interactive), so I<if you are
303	using this from a module, never require a blocking wait>, but let the	476	using this from a module, never require a blocking wait>, but let the
304	caller decide whether the call will block or not (for example, by coupling	477	caller decide whether the call will block or not (for example, by coupling
305	condition variables with some kind of request results and supporting	478	condition variables with some kind of request results and supporting
306	callbacks so the caller knows that getting the result will not block,	479	callbacks so the caller knows that getting the result will not block,
307	while still suppporting blocking waits if the caller so desires).	480	while still suppporting blocking waits if the caller so desires).
308		481
309	Another reason I<never> to C<< ->wait >> in a module is that you cannot	482	Another reason I<never> to C<< ->recv >> in a module is that you cannot
310	sensibly have two C<< ->wait >>'s in parallel, as that would require	483	sensibly have two C<< ->recv >>'s in parallel, as that would require
311	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	484	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
312	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	485	can supply.
313	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
314	from different coroutines, however).
315		486
316	=item $cv->broadcast	487	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		488	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		489	versions and also integrates coroutines into AnyEvent, making blocking
		490	C<< ->recv >> calls perfectly safe as long as they are done from another
		491	coroutine (one that doesn't run the event loop).
317		492
318	Flag the condition as ready - a running C<< ->wait >> and all further	493	You can ensure that C<< -recv >> never blocks by setting a callback and
319	calls to C<wait> will (eventually) return after this method has been	494	only calling C<< ->recv >> from within that callback (or at a later
320	called. If nobody is waiting the broadcast will be remembered..	495	time). This will work even when the event loop does not support blocking
		496	waits otherwise.
		497
		498	=item $bool = $cv->ready
		499
		500	Returns true when the condition is "true", i.e. whether C<send> or
		501	C<croak> have been called.
		502
		503	=item $cb = $cv->cb ([new callback])
		504
		505	This is a mutator function that returns the callback set and optionally
		506	replaces it before doing so.
		507
		508	The callback will be called when the condition becomes "true", i.e. when
		509	C<send> or C<croak> are called. Calling C<recv> inside the callback
		510	or at any later time is guaranteed not to block.
321		511
322	=back	512	=back
323
324	Example:
325
326	# wait till the result is ready
327	my $result_ready = AnyEvent->condvar;
328
329	# do something such as adding a timer
330	# or socket watcher the calls $result_ready->broadcast
331	# when the "result" is ready.
332	# in this case, we simply use a timer:
333	my $w = AnyEvent->timer (
334	after => 1,
335	cb => sub { $result_ready->broadcast },
336	);
337
338	# this "blocks" (while handling events) till the watcher
339	# calls broadcast
340	$result_ready->wait;
341		513
342	=head1 GLOBAL VARIABLES AND FUNCTIONS	514	=head1 GLOBAL VARIABLES AND FUNCTIONS
343		515
344	=over 4	516	=over 4
345		517
…		…
351	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	523	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
352	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	524	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
353		525
354	The known classes so far are:	526	The known classes so far are:
355		527
356	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
357	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
358	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	528	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
359	AnyEvent::Impl::Event based on Event, also second best choice :)	529	AnyEvent::Impl::Event based on Event, second best choice.
		530	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
360	AnyEvent::Impl::Glib based on Glib, third-best choice.	531	AnyEvent::Impl::Glib based on Glib, third-best choice.
361	AnyEvent::Impl::Tk based on Tk, very bad choice.	532	AnyEvent::Impl::Tk based on Tk, very bad choice.
362	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	533	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		534	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		535	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		536
		537	There is no support for WxWidgets, as WxWidgets has no support for
		538	watching file handles. However, you can use WxWidgets through the
		539	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		540	second, which was considered to be too horrible to even consider for
		541	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		542	it's adaptor.
		543
		544	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		545	autodetecting them.
363		546
364	=item AnyEvent::detect	547	=item AnyEvent::detect
365		548
366	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	549	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
367	if necessary. You should only call this function right before you would	550	if necessary. You should only call this function right before you would
368	have created an AnyEvent watcher anyway, that is, as late as possible at	551	have created an AnyEvent watcher anyway, that is, as late as possible at
369	runtime.	552	runtime.
370		553
		554	=item $guard = AnyEvent::post_detect { BLOCK }
		555
		556	Arranges for the code block to be executed as soon as the event model is
		557	autodetected (or immediately if this has already happened).
		558
		559	If called in scalar or list context, then it creates and returns an object
		560	that automatically removes the callback again when it is destroyed. See
		561	L<Coro::BDB> for a case where this is useful.
		562
		563	=item @AnyEvent::post_detect
		564
		565	If there are any code references in this array (you can C<push> to it
		566	before or after loading AnyEvent), then they will called directly after
		567	the event loop has been chosen.
		568
		569	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		570	if it contains a true value then the event loop has already been detected,
		571	and the array will be ignored.
		572
		573	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		574
371	=back	575	=back
372		576
373	=head1 WHAT TO DO IN A MODULE	577	=head1 WHAT TO DO IN A MODULE
374		578
375	As a module author, you should C<use AnyEvent> and call AnyEvent methods	579	As a module author, you should C<use AnyEvent> and call AnyEvent methods
…		…
378	Be careful when you create watchers in the module body - AnyEvent will	582	Be careful when you create watchers in the module body - AnyEvent will
379	decide which event module to use as soon as the first method is called, so	583	decide which event module to use as soon as the first method is called, so
380	by calling AnyEvent in your module body you force the user of your module	584	by calling AnyEvent in your module body you force the user of your module
381	to load the event module first.	585	to load the event module first.
382		586
383	Never call C<< ->wait >> on a condition variable unless you I<know> that	587	Never call C<< ->recv >> on a condition variable unless you I<know> that
384	the C<< ->broadcast >> method has been called on it already. This is	588	the C<< ->send >> method has been called on it already. This is
385	because it will stall the whole program, and the whole point of using	589	because it will stall the whole program, and the whole point of using
386	events is to stay interactive.	590	events is to stay interactive.
387		591
388	It is fine, however, to call C<< ->wait >> when the user of your module	592	It is fine, however, to call C<< ->recv >> when the user of your module
389	requests it (i.e. if you create a http request object ad have a method	593	requests it (i.e. if you create a http request object ad have a method
390	called C<results> that returns the results, it should call C<< ->wait >>	594	called C<results> that returns the results, it should call C<< ->recv >>
391	freely, as the user of your module knows what she is doing. always).	595	freely, as the user of your module knows what she is doing. always).
392		596
393	=head1 WHAT TO DO IN THE MAIN PROGRAM	597	=head1 WHAT TO DO IN THE MAIN PROGRAM
394		598
395	There will always be a single main program - the only place that should	599	There will always be a single main program - the only place that should
…		…
409		613
410	You can chose to use a rather inefficient pure-perl implementation by	614	You can chose to use a rather inefficient pure-perl implementation by
411	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	615	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
412	behaviour everywhere, but letting AnyEvent chose is generally better.	616	behaviour everywhere, but letting AnyEvent chose is generally better.
413		617
		618	=head1 OTHER MODULES
		619
		620	The following is a non-exhaustive list of additional modules that use
		621	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		622	in the same program. Some of the modules come with AnyEvent, some are
		623	available via CPAN.
		624
		625	=over 4
		626
		627	=item L<AnyEvent::Util>
		628
		629	Contains various utility functions that replace often-used but blocking
		630	functions such as C<inet_aton> by event-/callback-based versions.
		631
		632	=item L<AnyEvent::Handle>
		633
		634	Provide read and write buffers and manages watchers for reads and writes.
		635
		636	=item L<AnyEvent::HTTPD>
		637
		638	Provides a simple web application server framework.
		639
		640	=item L<AnyEvent::DNS>
		641
		642	Provides asynchronous DNS resolver capabilities, beyond what
		643	L<AnyEvent::Util> offers.
		644
		645	=item L<AnyEvent::FastPing>
		646
		647	The fastest ping in the west.
		648
		649	=item L<Net::IRC3>
		650
		651	AnyEvent based IRC client module family.
		652
		653	=item L<Net::XMPP2>
		654
		655	AnyEvent based XMPP (Jabber protocol) module family.
		656
		657	=item L<Net::FCP>
		658
		659	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		660	of AnyEvent.
		661
		662	=item L<Event::ExecFlow>
		663
		664	High level API for event-based execution flow control.
		665
		666	=item L<Coro>
		667
		668	Has special support for AnyEvent via L<Coro::AnyEvent>.
		669
		670	=item L<AnyEvent::AIO>, L<IO::AIO>
		671
		672	Truly asynchronous I/O, should be in the toolbox of every event
		673	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		674	together.
		675
		676	=item L<AnyEvent::BDB>, L<BDB>
		677
		678	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		679	IO::AIO and AnyEvent together.
		680
		681	=item L<IO::Lambda>
		682
		683	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		684
		685	=back
		686
414	=cut	687	=cut
415		688
416	package AnyEvent;	689	package AnyEvent;
417		690
418	no warnings;	691	no warnings;
419	use strict;	692	use strict;
420		693
421	use Carp;	694	use Carp;
422		695
423	our $VERSION = '3.12';	696	our $VERSION = '3.6';
424	our $MODEL;	697	our $MODEL;
425		698
426	our $AUTOLOAD;	699	our $AUTOLOAD;
427	our @ISA;	700	our @ISA;
428		701
429	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	702	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
430		703
431	our @REGISTRY;	704	our @REGISTRY;
432		705
433	my @models = (	706	my @models = (
434	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
435	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
436	[EV:: => AnyEvent::Impl::EV::],	707	[EV:: => AnyEvent::Impl::EV::],
437	[Event:: => AnyEvent::Impl::Event::],	708	[Event:: => AnyEvent::Impl::Event::],
		709	[Tk:: => AnyEvent::Impl::Tk::],
		710	[Wx:: => AnyEvent::Impl::POE::],
		711	[Prima:: => AnyEvent::Impl::POE::],
		712	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		713	# everything below here will not be autoprobed as the pureperl backend should work everywhere
438	[Glib:: => AnyEvent::Impl::Glib::],	714	[Glib:: => AnyEvent::Impl::Glib::],
439	[Tk:: => AnyEvent::Impl::Tk::],	715	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
440	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	716	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		717	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
441	);	718	);
442		719
443	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	720	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
		721
		722	our @post_detect;
		723
		724	sub post_detect(&) {
		725	my ($cb) = @_;
		726
		727	if ($MODEL) {
		728	$cb->();
		729
		730	1
		731	} else {
		732	push @post_detect, $cb;
		733
		734	defined wantarray
		735	? bless \$cb, "AnyEvent::Util::PostDetect"
		736	: ()
		737	}
		738	}
		739
		740	sub AnyEvent::Util::PostDetect::DESTROY {
		741	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		742	}
444		743
445	sub detect() {	744	sub detect() {
446	unless ($MODEL) {	745	unless ($MODEL) {
447	no strict 'refs';	746	no strict 'refs';
448		747
		748	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		749	my $model = "AnyEvent::Impl::$1";
		750	if (eval "require $model") {
		751	$MODEL = $model;
		752	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		753	} else {
		754	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		755	}
		756	}
		757
449	# check for already loaded models	758	# check for already loaded models
		759	unless ($MODEL) {
450	for (@REGISTRY, @models) {	760	for (@REGISTRY, @models) {
451	my ($package, $model) = @$_;	761	my ($package, $model) = @$_;
452	if (${"$package\::VERSION"} > 0) {	762	if (${"$package\::VERSION"} > 0) {
453	if (eval "require $model") {	763	if (eval "require $model") {
454	$MODEL = $model;	764	$MODEL = $model;
455	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	765	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
456	last;	766	last;
		767	}
457	}	768	}
458	}	769	}
459	}
460		770
461	unless ($MODEL) {	771	unless ($MODEL) {
462	# try to load a model	772	# try to load a model
463		773
464	for (@REGISTRY, @models) {	774	for (@REGISTRY, @models) {
465	my ($package, $model) = @$_;	775	my ($package, $model) = @$_;
466	if (eval "require $package"	776	if (eval "require $package"
467	and ${"$package\::VERSION"} > 0	777	and ${"$package\::VERSION"} > 0
468	and eval "require $model") {	778	and eval "require $model") {
469	$MODEL = $model;	779	$MODEL = $model;
470	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	780	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
471	last;	781	last;
		782	}
472	}	783	}
		784
		785	$MODEL
		786	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
473	}	787	}
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	}	788	}
478		789
479	unshift @ISA, $MODEL;	790	unshift @ISA, $MODEL;
480	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	791	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		792
		793	(shift @post_detect)->() while @post_detect;
481	}	794	}
482		795
483	$MODEL	796	$MODEL
484	}	797	}
485		798
…		…
495	$class->$func (@_);	808	$class->$func (@_);
496	}	809	}
497		810
498	package AnyEvent::Base;	811	package AnyEvent::Base;
499		812
500	# default implementation for ->condvar, ->wait, ->broadcast	813	# default implementation for ->condvar
501		814
502	sub condvar {	815	sub condvar {
503	bless \my $flag, "AnyEvent::Base::CondVar"	816	bless {}, AnyEvent::CondVar::
504	}
505
506	sub AnyEvent::Base::CondVar::broadcast {
507	${$_[0]}++;
508	}
509
510	sub AnyEvent::Base::CondVar::wait {
511	AnyEvent->one_event while !${$_[0]};
512	}	817	}
513		818
514	# default implementation for ->signal	819	# default implementation for ->signal
515		820
516	our %SIG_CB;	821	our %SIG_CB;
…		…
590	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	895	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
591		896
592	undef $CHLD_W unless keys %PID_CB;	897	undef $CHLD_W unless keys %PID_CB;
593	}	898	}
594		899
		900	package AnyEvent::CondVar;
		901
		902	our @ISA = AnyEvent::CondVar::Base::;
		903
		904	package AnyEvent::CondVar::Base;
		905
		906	sub _send {
		907	# nop
		908	}
		909
		910	sub send {
		911	my $cv = shift;
		912	$cv->{_ae_sent} = [@_];
		913	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		914	$cv->_send;
		915	}
		916
		917	sub croak {
		918	$_[0]{_ae_croak} = $_[1];
		919	$_[0]->send;
		920	}
		921
		922	sub ready {
		923	$_[0]{_ae_sent}
		924	}
		925
		926	sub _wait {
		927	AnyEvent->one_event while !$_[0]{_ae_sent};
		928	}
		929
		930	sub recv {
		931	$_[0]->_wait;
		932
		933	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		934	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		935	}
		936
		937	sub cb {
		938	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		939	$_[0]{_ae_cb}
		940	}
		941
		942	sub begin {
		943	++$_[0]{_ae_counter};
		944	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		945	}
		946
		947	sub end {
		948	return if --$_[0]{_ae_counter};
		949	&{ $_[0]{_ae_end_cb} } if $_[0]{_ae_end_cb};
		950	}
		951
		952	# undocumented/compatibility with pre-3.4
		953	*broadcast = \&send;
		954	*wait = \&_wait;
		955
595	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	956	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
596		957
597	This is an advanced topic that you do not normally need to use AnyEvent in	958	This is an advanced topic that you do not normally need to use AnyEvent in
598	a module. This section is only of use to event loop authors who want to	959	a module. This section is only of use to event loop authors who want to
599	provide AnyEvent compatibility.	960	provide AnyEvent compatibility.
…		…
637		998
638	=head1 ENVIRONMENT VARIABLES	999	=head1 ENVIRONMENT VARIABLES
639		1000
640	The following environment variables are used by this module:	1001	The following environment variables are used by this module:
641		1002
642	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, cause AnyEvent to	1003	=over 4
643	report to STDERR which event model it chooses.	1004
		1005	=item C<PERL_ANYEVENT_VERBOSE>
		1006
		1007	By default, AnyEvent will be completely silent except in fatal
		1008	conditions. You can set this environment variable to make AnyEvent more
		1009	talkative.
		1010
		1011	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1012	conditions, such as not being able to load the event model specified by
		1013	C<PERL_ANYEVENT_MODEL>.
		1014
		1015	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1016	model it chooses.
		1017
		1018	=item C<PERL_ANYEVENT_MODEL>
		1019
		1020	This can be used to specify the event model to be used by AnyEvent, before
		1021	autodetection and -probing kicks in. It must be a string consisting
		1022	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1023	and the resulting module name is loaded and if the load was successful,
		1024	used as event model. If it fails to load AnyEvent will proceed with
		1025	autodetection and -probing.
		1026
		1027	This functionality might change in future versions.
		1028
		1029	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1030	could start your program like this:
		1031
		1032	PERL_ANYEVENT_MODEL=Perl perl ...
		1033
		1034	=back
644		1035
645	=head1 EXAMPLE PROGRAM	1036	=head1 EXAMPLE PROGRAM
646		1037
647	The following program uses an IO watcher to read data from STDIN, a timer	1038	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	1039	to display a message once per second, and a condition variable to quit the
649	program when the user enters quit:	1040	program when the user enters quit:
650		1041
651	use AnyEvent;	1042	use AnyEvent;
652		1043
…		…
657	poll => 'r',	1048	poll => 'r',
658	cb => sub {	1049	cb => sub {
659	warn "io event <$_[0]>\n"; # will always output <r>	1050	warn "io event <$_[0]>\n"; # will always output <r>
660	chomp (my $input = <STDIN>); # read a line	1051	chomp (my $input = <STDIN>); # read a line
661	warn "read: $input\n"; # output what has been read	1052	warn "read: $input\n"; # output what has been read
662	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1053	$cv->send if $input =~ /^q/i; # quit program if /^q/i
663	},	1054	},
664	);	1055	);
665		1056
666	my $time_watcher; # can only be used once	1057	my $time_watcher; # can only be used once
667		1058
…		…
672	});	1063	});
673	}	1064	}
674		1065
675	new_timer; # create first timer	1066	new_timer; # create first timer
676		1067
677	$cv->wait; # wait until user enters /^q/i	1068	$cv->recv; # wait until user enters /^q/i
678		1069
679	=head1 REAL-WORLD EXAMPLE	1070	=head1 REAL-WORLD EXAMPLE
680		1071
681	Consider the L<Net::FCP> module. It features (among others) the following	1072	Consider the L<Net::FCP> module. It features (among others) the following
682	API calls, which are to freenet what HTTP GET requests are to http:	1073	API calls, which are to freenet what HTTP GET requests are to http:
…		…
738		1129
739	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1130	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
740		1131
741	if (end-of-file or data complete) {	1132	if (end-of-file or data complete) {
742	$txn->{result} = $txn->{buf};	1133	$txn->{result} = $txn->{buf};
743	$txn->{finished}->broadcast;	1134	$txn->{finished}->send;
744	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1135	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
745	}	1136	}
746		1137
747	The C<result> method, finally, just waits for the finished signal (if the	1138	The C<result> method, finally, just waits for the finished signal (if the
748	request was already finished, it doesn't wait, of course, and returns the	1139	request was already finished, it doesn't wait, of course, and returns the
749	data:	1140	data:
750		1141
751	$txn->{finished}->wait;	1142	$txn->{finished}->recv;
752	return $txn->{result};	1143	return $txn->{result};
753		1144
754	The actual code goes further and collects all errors (C<die>s, exceptions)	1145	The actual code goes further and collects all errors (C<die>s, exceptions)
755	that occured during request processing. The C<result> method detects	1146	that occured during request processing. The C<result> method detects
756	whether an exception as thrown (it is stored inside the $txn object)	1147	whether an exception as thrown (it is stored inside the $txn object)
…		…
791		1182
792	my $quit = AnyEvent->condvar;	1183	my $quit = AnyEvent->condvar;
793		1184
794	$fcp->txn_client_get ($url)->cb (sub {	1185	$fcp->txn_client_get ($url)->cb (sub {
795	...	1186	...
796	$quit->broadcast;	1187	$quit->send;
797	});	1188	});
798		1189
799	$quit->wait;	1190	$quit->recv;
		1191
		1192
		1193	=head1 BENCHMARKS
		1194
		1195	To give you an idea of the performance and overheads that AnyEvent adds
		1196	over the event loops themselves and to give you an impression of the speed
		1197	of various event loops I prepared some benchmarks.
		1198
		1199	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1200
		1201	Here is a benchmark of various supported event models used natively and
		1202	through anyevent. The benchmark creates a lot of timers (with a zero
		1203	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1204	which it is), lets them fire exactly once and destroys them again.
		1205
		1206	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1207	distribution.
		1208
		1209	=head3 Explanation of the columns
		1210
		1211	I<watcher> is the number of event watchers created/destroyed. Since
		1212	different event models feature vastly different performances, each event
		1213	loop was given a number of watchers so that overall runtime is acceptable
		1214	and similar between tested event loop (and keep them from crashing): Glib
		1215	would probably take thousands of years if asked to process the same number
		1216	of watchers as EV in this benchmark.
		1217
		1218	I<bytes> is the number of bytes (as measured by the resident set size,
		1219	RSS) consumed by each watcher. This method of measuring captures both C
		1220	and Perl-based overheads.
		1221
		1222	I<create> is the time, in microseconds (millionths of seconds), that it
		1223	takes to create a single watcher. The callback is a closure shared between
		1224	all watchers, to avoid adding memory overhead. That means closure creation
		1225	and memory usage is not included in the figures.
		1226
		1227	I<invoke> is the time, in microseconds, used to invoke a simple
		1228	callback. The callback simply counts down a Perl variable and after it was
		1229	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1230	signal the end of this phase.
		1231
		1232	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1233	watcher.
		1234
		1235	=head3 Results
		1236
		1237	name watchers bytes create invoke destroy comment
		1238	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1239	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1240	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1241	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1242	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1243	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1244	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1245	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1246	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1247	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1248
		1249	=head3 Discussion
		1250
		1251	The benchmark does I<not> measure scalability of the event loop very
		1252	well. For example, a select-based event loop (such as the pure perl one)
		1253	can never compete with an event loop that uses epoll when the number of
		1254	file descriptors grows high. In this benchmark, all events become ready at
		1255	the same time, so select/poll-based implementations get an unnatural speed
		1256	boost.
		1257
		1258	Also, note that the number of watchers usually has a nonlinear effect on
		1259	overall speed, that is, creating twice as many watchers doesn't take twice
		1260	the time - usually it takes longer. This puts event loops tested with a
		1261	higher number of watchers at a disadvantage.
		1262
		1263	To put the range of results into perspective, consider that on the
		1264	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1265	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1266	cycles with POE.
		1267
		1268	C<EV> is the sole leader regarding speed and memory use, which are both
		1269	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1270	far less memory than any other event loop and is still faster than Event
		1271	natively.
		1272
		1273	The pure perl implementation is hit in a few sweet spots (both the
		1274	constant timeout and the use of a single fd hit optimisations in the perl
		1275	interpreter and the backend itself). Nevertheless this shows that it
		1276	adds very little overhead in itself. Like any select-based backend its
		1277	performance becomes really bad with lots of file descriptors (and few of
		1278	them active), of course, but this was not subject of this benchmark.
		1279
		1280	The C<Event> module has a relatively high setup and callback invocation
		1281	cost, but overall scores in on the third place.
		1282
		1283	C<Glib>'s memory usage is quite a bit higher, but it features a
		1284	faster callback invocation and overall ends up in the same class as
		1285	C<Event>. However, Glib scales extremely badly, doubling the number of
		1286	watchers increases the processing time by more than a factor of four,
		1287	making it completely unusable when using larger numbers of watchers
		1288	(note that only a single file descriptor was used in the benchmark, so
		1289	inefficiencies of C<poll> do not account for this).
		1290
		1291	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1292	more than 2000 watchers is a big setback, however, as correctness takes
		1293	precedence over speed. Nevertheless, its performance is surprising, as the
		1294	file descriptor is dup()ed for each watcher. This shows that the dup()
		1295	employed by some adaptors is not a big performance issue (it does incur a
		1296	hidden memory cost inside the kernel which is not reflected in the figures
		1297	above).
		1298
		1299	C<POE>, regardless of underlying event loop (whether using its pure perl
		1300	select-based backend or the Event module, the POE-EV backend couldn't
		1301	be tested because it wasn't working) shows abysmal performance and
		1302	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1303	as EV watchers, and 10 times as much memory as Event (the high memory
		1304	requirements are caused by requiring a session for each watcher). Watcher
		1305	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1306	implementation.
		1307
		1308	The design of the POE adaptor class in AnyEvent can not really account
		1309	for the performance issues, though, as session creation overhead is
		1310	small compared to execution of the state machine, which is coded pretty
		1311	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1312	using multiple sessions is not a good approach, especially regarding
		1313	memory usage, even the author of POE could not come up with a faster
		1314	design).
		1315
		1316	=head3 Summary
		1317
		1318	=over 4
		1319
		1320	=item * Using EV through AnyEvent is faster than any other event loop
		1321	(even when used without AnyEvent), but most event loops have acceptable
		1322	performance with or without AnyEvent.
		1323
		1324	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1325	the actual event loop, only with extremely fast event loops such as EV
		1326	adds AnyEvent significant overhead.
		1327
		1328	=item * You should avoid POE like the plague if you want performance or
		1329	reasonable memory usage.
		1330
		1331	=back
		1332
		1333	=head2 BENCHMARKING THE LARGE SERVER CASE
		1334
		1335	This benchmark atcually benchmarks the event loop itself. It works by
		1336	creating a number of "servers": each server consists of a socketpair, a
		1337	timeout watcher that gets reset on activity (but never fires), and an I/O
		1338	watcher waiting for input on one side of the socket. Each time the socket
		1339	watcher reads a byte it will write that byte to a random other "server".
		1340
		1341	The effect is that there will be a lot of I/O watchers, only part of which
		1342	are active at any one point (so there is a constant number of active
		1343	fds for each loop iterstaion, but which fds these are is random). The
		1344	timeout is reset each time something is read because that reflects how
		1345	most timeouts work (and puts extra pressure on the event loops).
		1346
		1347	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1348	(1%) are active. This mirrors the activity of large servers with many
		1349	connections, most of which are idle at any one point in time.
		1350
		1351	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1352	distribution.
		1353
		1354	=head3 Explanation of the columns
		1355
		1356	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1357	each server has a read and write socket end).
		1358
		1359	I<create> is the time it takes to create a socketpair (which is
		1360	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1361
		1362	I<request>, the most important value, is the time it takes to handle a
		1363	single "request", that is, reading the token from the pipe and forwarding
		1364	it to another server. This includes deleting the old timeout and creating
		1365	a new one that moves the timeout into the future.
		1366
		1367	=head3 Results
		1368
		1369	name sockets create request
		1370	EV 20000 69.01 11.16
		1371	Perl 20000 73.32 35.87
		1372	Event 20000 212.62 257.32
		1373	Glib 20000 651.16 1896.30
		1374	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1375
		1376	=head3 Discussion
		1377
		1378	This benchmark I<does> measure scalability and overall performance of the
		1379	particular event loop.
		1380
		1381	EV is again fastest. Since it is using epoll on my system, the setup time
		1382	is relatively high, though.
		1383
		1384	Perl surprisingly comes second. It is much faster than the C-based event
		1385	loops Event and Glib.
		1386
		1387	Event suffers from high setup time as well (look at its code and you will
		1388	understand why). Callback invocation also has a high overhead compared to
		1389	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1390	uses select or poll in basically all documented configurations.
		1391
		1392	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1393	clearly fails to perform with many filehandles or in busy servers.
		1394
		1395	POE is still completely out of the picture, taking over 1000 times as long
		1396	as EV, and over 100 times as long as the Perl implementation, even though
		1397	it uses a C-based event loop in this case.
		1398
		1399	=head3 Summary
		1400
		1401	=over 4
		1402
		1403	=item * The pure perl implementation performs extremely well.
		1404
		1405	=item * Avoid Glib or POE in large projects where performance matters.
		1406
		1407	=back
		1408
		1409	=head2 BENCHMARKING SMALL SERVERS
		1410
		1411	While event loops should scale (and select-based ones do not...) even to
		1412	large servers, most programs we (or I :) actually write have only a few
		1413	I/O watchers.
		1414
		1415	In this benchmark, I use the same benchmark program as in the large server
		1416	case, but it uses only eight "servers", of which three are active at any
		1417	one time. This should reflect performance for a small server relatively
		1418	well.
		1419
		1420	The columns are identical to the previous table.
		1421
		1422	=head3 Results
		1423
		1424	name sockets create request
		1425	EV 16 20.00 6.54
		1426	Perl 16 25.75 12.62
		1427	Event 16 81.27 35.86
		1428	Glib 16 32.63 15.48
		1429	POE 16 261.87 276.28 uses POE::Loop::Event
		1430
		1431	=head3 Discussion
		1432
		1433	The benchmark tries to test the performance of a typical small
		1434	server. While knowing how various event loops perform is interesting, keep
		1435	in mind that their overhead in this case is usually not as important, due
		1436	to the small absolute number of watchers (that is, you need efficiency and
		1437	speed most when you have lots of watchers, not when you only have a few of
		1438	them).
		1439
		1440	EV is again fastest.
		1441
		1442	Perl again comes second. It is noticably faster than the C-based event
		1443	loops Event and Glib, although the difference is too small to really
		1444	matter.
		1445
		1446	POE also performs much better in this case, but is is still far behind the
		1447	others.
		1448
		1449	=head3 Summary
		1450
		1451	=over 4
		1452
		1453	=item * C-based event loops perform very well with small number of
		1454	watchers, as the management overhead dominates.
		1455
		1456	=back
		1457
		1458
		1459	=head1 FORK
		1460
		1461	Most event libraries are not fork-safe. The ones who are usually are
		1462	because they rely on inefficient but fork-safe C<select> or C<poll>
		1463	calls. Only L<EV> is fully fork-aware.
		1464
		1465	If you have to fork, you must either do so I<before> creating your first
		1466	watcher OR you must not use AnyEvent at all in the child.
		1467
		1468
		1469	=head1 SECURITY CONSIDERATIONS
		1470
		1471	AnyEvent can be forced to load any event model via
		1472	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1473	execute arbitrary code or directly gain access, it can easily be used to
		1474	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1475	will not be active when the program uses a different event model than
		1476	specified in the variable.
		1477
		1478	You can make AnyEvent completely ignore this variable by deleting it
		1479	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1480
		1481	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1482
		1483	use AnyEvent;
		1484
		1485	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1486	be used to probe what backend is used and gain other information (which is
		1487	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1488
800		1489
801	=head1 SEE ALSO	1490	=head1 SEE ALSO
802		1491
803	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1492	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
804	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.	1493	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
805		1494
806	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
807	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,	1495	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
808	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.	1496	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1497	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1498	L<AnyEvent::Impl::POE>.
		1499
		1500	Asynchronous DNS: L<AnyEvent::DNS>.
		1501
		1502	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
809		1503
810	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1504	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
		1505
811		1506
812	=head1 AUTHOR	1507	=head1 AUTHOR
813		1508
814	Marc Lehmann <schmorp@schmorp.de>	1509	Marc Lehmann <schmorp@schmorp.de>
815	http://home.schmorp.de/	1510	http://home.schmorp.de/

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Revision 1.123 by root, Fri May 23 20:41:25 2008 UTC