[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 1.132 by root, Sun May 25 01:05:27 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?
…		…
57	as those use one of the supported event loops. It is trivial to add new	57	as those use one of the supported event loops. It is trivial to add new
58	event loops to AnyEvent, too, so it is future-proof).	58	event loops to AnyEvent, too, so it is future-proof).
59		59
60	In addition to being free of having to use I<the one and only true event	60	In addition to being free of having to use I<the one and only true event
61	model>, AnyEvent also is free of bloat and policy: with POE or similar	61	model>, AnyEvent also is free of bloat and policy: with POE or similar
62	modules, you get an enourmous amount of code and strict rules you have to	62	modules, you get an enormous amount of code and strict rules you have to
63	follow. AnyEvent, on the other hand, is lean and up to the point, by only	63	follow. AnyEvent, on the other hand, is lean and up to the point, by only
64	offering the functionality that is necessary, in as thin as a wrapper as	64	offering the functionality that is necessary, in as thin as a wrapper as
65	technically possible.	65	technically possible.
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
71		70
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
…		…
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
…		…
107		108
108	=head1 WATCHERS	109	=head1 WATCHERS
109		110
110	AnyEvent has the central concept of a I<watcher>, which is an object that	111	AnyEvent has the central concept of a I<watcher>, which is an object that
111	stores relevant data for each kind of event you are waiting for, such as	112	stores relevant data for each kind of event you are waiting for, such as
112	the callback to call, the filehandle to watch, etc.	113	the callback to call, the file handle to watch, etc.
113		114
114	These watchers are normal Perl objects with normal Perl lifetime. After	115	These watchers are normal Perl objects with normal Perl lifetime. After
115	creating a watcher it will immediately "watch" for events and invoke the	116	creating a watcher it will immediately "watch" for events and invoke the
116	callback when the event occurs (of course, only when the event model	117	callback when the event occurs (of course, only when the event model
117	is in control).	118	is in control).
…		…
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 occurrences 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 guaranteed 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
236	between multiple watchers.	248	between multiple watchers.
237		249
238	This watcher might use C<%SIG>, so programs overwriting those signals	250	This watcher might use C<%SIG>, so programs overwriting those signals
…		…
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 condition variable is "false" until it becomes "true"
271	->broadcast >> method has been called.	316	by calling the C<send> method (or calling the condition variable as if it
		317	were a callback).
272		318
273	They are very useful to signal that a condition has been fulfilled, for	319	Condition variables are similar to callbacks, except that you can
		320	optionally wait for them. They can also be called merge points - points
		321	in time where multiple outstanding events have been processed. And yet
		322	another way to call them is transactions - each condition variable can be
		323	used to represent a transaction, which finishes at some point and delivers
		324	a result.
		325
		326	Condition variables are very useful to signal that something has finished,
274	example, if you write a module that does asynchronous http requests,	327	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	328	then a condition variable would be the ideal candidate to signal the
276	availability of results.	329	availability of results. The user can either act when the callback is
		330	called or can synchronously C<< ->recv >> for the results.
277		331
278	You can also use condition variables to block your main program until	332	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	333	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<<	334	could C<< ->recv >> in your main program until the user clicks the Quit
281	->broadcast >> the "quit" event.	335	button of your app, which would C<< ->send >> the "quit" event.
282		336
283	Note that condition variables recurse into the event loop - if you have	337	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	338	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
285	lose. Therefore, condition variables are good to export to your caller, but	339	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,	340	you should avoid making a blocking wait yourself, at least in callbacks,
287	as this asks for trouble.	341	as this asks for trouble.
288		342
289	This object has two methods:	343	Condition variables are represented by hash refs in perl, and the keys
		344	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		345	easy (it is often useful to build your own transaction class on top of
		346	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		347	it's C<new> method in your own C<new> method.
		348
		349	There are two "sides" to a condition variable - the "producer side" which
		350	eventually calls C<< -> send >>, and the "consumer side", which waits
		351	for the send to occur.
		352
		353	Example: wait for a timer.
		354
		355	# wait till the result is ready
		356	my $result_ready = AnyEvent->condvar;
		357
		358	# do something such as adding a timer
		359	# or socket watcher the calls $result_ready->send
		360	# when the "result" is ready.
		361	# in this case, we simply use a timer:
		362	my $w = AnyEvent->timer (
		363	after => 1,
		364	cb => sub { $result_ready->send },
		365	);
		366
		367	# this "blocks" (while handling events) till the callback
		368	# calls send
		369	$result_ready->recv;
		370
		371	Example: wait for a timer, but take advantage of the fact that
		372	condition variables are also code references.
		373
		374	my $done = AnyEvent->condvar;
		375	my $delay = AnyEvent->timer (after => 5, cb => $done);
		376	$done->recv;
		377
		378	=head3 METHODS FOR PRODUCERS
		379
		380	These methods should only be used by the producing side, i.e. the
		381	code/module that eventually sends the signal. Note that it is also
		382	the producer side which creates the condvar in most cases, but it isn't
		383	uncommon for the consumer to create it as well.
290		384
291	=over 4	385	=over 4
292		386
		387	=item $cv->send (...)
		388
		389	Flag the condition as ready - a running C<< ->recv >> and all further
		390	calls to C<recv> will (eventually) return after this method has been
		391	called. If nobody is waiting the send will be remembered.
		392
		393	If a callback has been set on the condition variable, it is called
		394	immediately from within send.
		395
		396	Any arguments passed to the C<send> call will be returned by all
		397	future C<< ->recv >> calls.
		398
		399	Condition variables are overloaded so one can call them directly (as a
		400	code reference). Calling them directly is the same as calling C<send>.
		401
		402	=item $cv->croak ($error)
		403
		404	Similar to send, but causes all call's to C<< ->recv >> to invoke
		405	C<Carp::croak> with the given error message/object/scalar.
		406
		407	This can be used to signal any errors to the condition variable
		408	user/consumer.
		409
		410	=item $cv->begin ([group callback])
		411
293	=item $cv->wait	412	=item $cv->end
294		413
295	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	414	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		415
		416	These two methods can be used to combine many transactions/events into
		417	one. For example, a function that pings many hosts in parallel might want
		418	to use a condition variable for the whole process.
		419
		420	Every call to C<< ->begin >> will increment a counter, and every call to
		421	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		422	>>, the (last) callback passed to C<begin> will be executed. That callback
		423	is I<supposed> to call C<< ->send >>, but that is not required. If no
		424	callback was set, C<send> will be called without any arguments.
		425
		426	Let's clarify this with the ping example:
		427
		428	my $cv = AnyEvent->condvar;
		429
		430	my %result;
		431	$cv->begin (sub { $cv->send (\%result) });
		432
		433	for my $host (@list_of_hosts) {
		434	$cv->begin;
		435	ping_host_then_call_callback $host, sub {
		436	$result{$host} = ...;
		437	$cv->end;
		438	};
		439	}
		440
		441	$cv->end;
		442
		443	This code fragment supposedly pings a number of hosts and calls
		444	C<send> after results for all then have have been gathered - in any
		445	order. To achieve this, the code issues a call to C<begin> when it starts
		446	each ping request and calls C<end> when it has received some result for
		447	it. Since C<begin> and C<end> only maintain a counter, the order in which
		448	results arrive is not relevant.
		449
		450	There is an additional bracketing call to C<begin> and C<end> outside the
		451	loop, which serves two important purposes: first, it sets the callback
		452	to be called once the counter reaches C<0>, and second, it ensures that
		453	C<send> is called even when C<no> hosts are being pinged (the loop
		454	doesn't execute once).
		455
		456	This is the general pattern when you "fan out" into multiple subrequests:
		457	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		458	is called at least once, and then, for each subrequest you start, call
		459	C<begin> and for each subrequest you finish, call C<end>.
		460
		461	=back
		462
		463	=head3 METHODS FOR CONSUMERS
		464
		465	These methods should only be used by the consuming side, i.e. the
		466	code awaits the condition.
		467
		468	=over 4
		469
		470	=item $cv->recv
		471
		472	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
296	called on c<$cv>, while servicing other watchers normally.	473	>> methods have been called on c<$cv>, while servicing other watchers
		474	normally.
297		475
298	You can only wait once on a condition - additional calls will return	476	You can only wait once on a condition - additional calls are valid but
299	immediately.	477	will return immediately.
		478
		479	If an error condition has been set by calling C<< ->croak >>, then this
		480	function will call C<croak>.
		481
		482	In list context, all parameters passed to C<send> will be returned,
		483	in scalar context only the first one will be returned.
300		484
301	Not all event models support a blocking wait - some die in that case	485	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	486	(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	487	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	488	caller decide whether the call will block or not (for example, by coupling
305	condition variables with some kind of request results and supporting	489	condition variables with some kind of request results and supporting
306	callbacks so the caller knows that getting the result will not block,	490	callbacks so the caller knows that getting the result will not block,
307	while still suppporting blocking waits if the caller so desires).	491	while still supporting blocking waits if the caller so desires).
308		492
309	Another reason I<never> to C<< ->wait >> in a module is that you cannot	493	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	494	sensibly have two C<< ->recv >>'s in parallel, as that would require
311	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	495	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
312	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	496	can supply.
313	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
314	from different coroutines, however).
315		497
316	=item $cv->broadcast	498	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		499	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		500	versions and also integrates coroutines into AnyEvent, making blocking
		501	C<< ->recv >> calls perfectly safe as long as they are done from another
		502	coroutine (one that doesn't run the event loop).
317		503
318	Flag the condition as ready - a running C<< ->wait >> and all further	504	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	505	only calling C<< ->recv >> from within that callback (or at a later
320	called. If nobody is waiting the broadcast will be remembered..	506	time). This will work even when the event loop does not support blocking
		507	waits otherwise.
		508
		509	=item $bool = $cv->ready
		510
		511	Returns true when the condition is "true", i.e. whether C<send> or
		512	C<croak> have been called.
		513
		514	=item $cb = $cv->cb ([new callback])
		515
		516	This is a mutator function that returns the callback set and optionally
		517	replaces it before doing so.
		518
		519	The callback will be called when the condition becomes "true", i.e. when
		520	C<send> or C<croak> are called. Calling C<recv> inside the callback
		521	or at any later time is guaranteed not to block.
321		522
322	=back	523	=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		524
342	=head1 GLOBAL VARIABLES AND FUNCTIONS	525	=head1 GLOBAL VARIABLES AND FUNCTIONS
343		526
344	=over 4	527	=over 4
345		528
…		…
351	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	534	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>).	535	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
353		536
354	The known classes so far are:	537	The known classes so far are:
355		538
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).	539	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
359	AnyEvent::Impl::Event based on Event, also second best choice :)	540	AnyEvent::Impl::Event based on Event, second best choice.
		541	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
360	AnyEvent::Impl::Glib based on Glib, third-best choice.	542	AnyEvent::Impl::Glib based on Glib, third-best choice.
361	AnyEvent::Impl::Tk based on Tk, very bad choice.	543	AnyEvent::Impl::Tk based on Tk, very bad choice.
362	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	544	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		545	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		546	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		547
		548	There is no support for WxWidgets, as WxWidgets has no support for
		549	watching file handles. However, you can use WxWidgets through the
		550	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		551	second, which was considered to be too horrible to even consider for
		552	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		553	it's adaptor.
		554
		555	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		556	autodetecting them.
363		557
364	=item AnyEvent::detect	558	=item AnyEvent::detect
365		559
366	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	560	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
367	if necessary. You should only call this function right before you would	561	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	562	have created an AnyEvent watcher anyway, that is, as late as possible at
369	runtime.	563	runtime.
370		564
		565	=item $guard = AnyEvent::post_detect { BLOCK }
		566
		567	Arranges for the code block to be executed as soon as the event model is
		568	autodetected (or immediately if this has already happened).
		569
		570	If called in scalar or list context, then it creates and returns an object
		571	that automatically removes the callback again when it is destroyed. See
		572	L<Coro::BDB> for a case where this is useful.
		573
		574	=item @AnyEvent::post_detect
		575
		576	If there are any code references in this array (you can C<push> to it
		577	before or after loading AnyEvent), then they will called directly after
		578	the event loop has been chosen.
		579
		580	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		581	if it contains a true value then the event loop has already been detected,
		582	and the array will be ignored.
		583
		584	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		585
371	=back	586	=back
372		587
373	=head1 WHAT TO DO IN A MODULE	588	=head1 WHAT TO DO IN A MODULE
374		589
375	As a module author, you should C<use AnyEvent> and call AnyEvent methods	590	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	593	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	594	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	595	by calling AnyEvent in your module body you force the user of your module
381	to load the event module first.	596	to load the event module first.
382		597
383	Never call C<< ->wait >> on a condition variable unless you I<know> that	598	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	599	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	600	because it will stall the whole program, and the whole point of using
386	events is to stay interactive.	601	events is to stay interactive.
387		602
388	It is fine, however, to call C<< ->wait >> when the user of your module	603	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	604	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 >>	605	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).	606	freely, as the user of your module knows what she is doing. always).
392		607
393	=head1 WHAT TO DO IN THE MAIN PROGRAM	608	=head1 WHAT TO DO IN THE MAIN PROGRAM
394		609
395	There will always be a single main program - the only place that should	610	There will always be a single main program - the only place that should
…		…
409		624
410	You can chose to use a rather inefficient pure-perl implementation by	625	You can chose to use a rather inefficient pure-perl implementation by
411	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	626	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
412	behaviour everywhere, but letting AnyEvent chose is generally better.	627	behaviour everywhere, but letting AnyEvent chose is generally better.
413		628
		629	=head1 OTHER MODULES
		630
		631	The following is a non-exhaustive list of additional modules that use
		632	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		633	in the same program. Some of the modules come with AnyEvent, some are
		634	available via CPAN.
		635
		636	=over 4
		637
		638	=item L<AnyEvent::Util>
		639
		640	Contains various utility functions that replace often-used but blocking
		641	functions such as C<inet_aton> by event-/callback-based versions.
		642
		643	=item L<AnyEvent::Handle>
		644
		645	Provide read and write buffers and manages watchers for reads and writes.
		646
		647	=item L<AnyEvent::Socket>
		648
		649	Provides various utility functions for (internet protocol) sockets,
		650	addresses and name resolution. Also functions to create non-blocking tcp
		651	connections or tcp servers, with IPv6 and SRV record support and more.
		652
		653	=item L<AnyEvent::HTTPD>
		654
		655	Provides a simple web application server framework.
		656
		657	=item L<AnyEvent::DNS>
		658
		659	Provides rich asynchronous DNS resolver capabilities.
		660
		661	=item L<AnyEvent::FastPing>
		662
		663	The fastest ping in the west.
		664
		665	=item L<Net::IRC3>
		666
		667	AnyEvent based IRC client module family.
		668
		669	=item L<Net::XMPP2>
		670
		671	AnyEvent based XMPP (Jabber protocol) module family.
		672
		673	=item L<Net::FCP>
		674
		675	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		676	of AnyEvent.
		677
		678	=item L<Event::ExecFlow>
		679
		680	High level API for event-based execution flow control.
		681
		682	=item L<Coro>
		683
		684	Has special support for AnyEvent via L<Coro::AnyEvent>.
		685
		686	=item L<AnyEvent::AIO>, L<IO::AIO>
		687
		688	Truly asynchronous I/O, should be in the toolbox of every event
		689	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		690	together.
		691
		692	=item L<AnyEvent::BDB>, L<BDB>
		693
		694	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		695	IO::AIO and AnyEvent together.
		696
		697	=item L<IO::Lambda>
		698
		699	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		700
		701	=back
		702
414	=cut	703	=cut
415		704
416	package AnyEvent;	705	package AnyEvent;
417		706
418	no warnings;	707	no warnings;
419	use strict;	708	use strict;
420		709
421	use Carp;	710	use Carp;
422		711
423	our $VERSION = '3.12';	712	our $VERSION = '4.03';
424	our $MODEL;	713	our $MODEL;
425		714
426	our $AUTOLOAD;	715	our $AUTOLOAD;
427	our @ISA;	716	our @ISA;
428		717
429	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	718	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
430		719
431	our @REGISTRY;	720	our @REGISTRY;
432		721
		722	our %PROTOCOL; # (ipv4\|ipv6) => (1\|2)
		723
		724	{
		725	my $idx;
		726	$PROTOCOL{$_} = ++$idx
		727	for split /\s,\s/, $ENV{PERL_ANYEVENT_PROTOCOLS} \|\| "ipv4,ipv6";
		728	}
		729
433	my @models = (	730	my @models = (
434	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
435	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
436	[EV:: => AnyEvent::Impl::EV::],	731	[EV:: => AnyEvent::Impl::EV::],
437	[Event:: => AnyEvent::Impl::Event::],	732	[Event:: => AnyEvent::Impl::Event::],
		733	[Tk:: => AnyEvent::Impl::Tk::],
		734	[Wx:: => AnyEvent::Impl::POE::],
		735	[Prima:: => AnyEvent::Impl::POE::],
		736	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		737	# everything below here will not be autoprobed as the pureperl backend should work everywhere
438	[Glib:: => AnyEvent::Impl::Glib::],	738	[Glib:: => AnyEvent::Impl::Glib::],
439	[Tk:: => AnyEvent::Impl::Tk::],	739	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
440	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	740	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		741	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
441	);	742	);
442		743
443	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	744	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
		745
		746	our @post_detect;
		747
		748	sub post_detect(&) {
		749	my ($cb) = @_;
		750
		751	if ($MODEL) {
		752	$cb->();
		753
		754	1
		755	} else {
		756	push @post_detect, $cb;
		757
		758	defined wantarray
		759	? bless \$cb, "AnyEvent::Util::PostDetect"
		760	: ()
		761	}
		762	}
		763
		764	sub AnyEvent::Util::PostDetect::DESTROY {
		765	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		766	}
444		767
445	sub detect() {	768	sub detect() {
446	unless ($MODEL) {	769	unless ($MODEL) {
447	no strict 'refs';	770	no strict 'refs';
448		771
		772	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		773	my $model = "AnyEvent::Impl::$1";
		774	if (eval "require $model") {
		775	$MODEL = $model;
		776	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		777	} else {
		778	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		779	}
		780	}
		781
449	# check for already loaded models	782	# check for already loaded models
		783	unless ($MODEL) {
450	for (@REGISTRY, @models) {	784	for (@REGISTRY, @models) {
451	my ($package, $model) = @$_;	785	my ($package, $model) = @$_;
452	if (${"$package\::VERSION"} > 0) {	786	if (${"$package\::VERSION"} > 0) {
453	if (eval "require $model") {	787	if (eval "require $model") {
454	$MODEL = $model;	788	$MODEL = $model;
455	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	789	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
456	last;	790	last;
		791	}
457	}	792	}
458	}	793	}
459	}
460		794
461	unless ($MODEL) {	795	unless ($MODEL) {
462	# try to load a model	796	# try to load a model
463		797
464	for (@REGISTRY, @models) {	798	for (@REGISTRY, @models) {
465	my ($package, $model) = @$_;	799	my ($package, $model) = @$_;
466	if (eval "require $package"	800	if (eval "require $package"
467	and ${"$package\::VERSION"} > 0	801	and ${"$package\::VERSION"} > 0
468	and eval "require $model") {	802	and eval "require $model") {
469	$MODEL = $model;	803	$MODEL = $model;
470	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	804	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
471	last;	805	last;
		806	}
472	}	807	}
		808
		809	$MODEL
		810	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
473	}	811	}
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	}	812	}
478		813
479	unshift @ISA, $MODEL;	814	unshift @ISA, $MODEL;
480	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	815	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		816
		817	(shift @post_detect)->() while @post_detect;
481	}	818	}
482		819
483	$MODEL	820	$MODEL
484	}	821	}
485		822
…		…
495	$class->$func (@_);	832	$class->$func (@_);
496	}	833	}
497		834
498	package AnyEvent::Base;	835	package AnyEvent::Base;
499		836
500	# default implementation for ->condvar, ->wait, ->broadcast	837	# default implementation for ->condvar
501		838
502	sub condvar {	839	sub condvar {
503	bless \my $flag, "AnyEvent::Base::CondVar"	840	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, 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	}	841	}
513		842
514	# default implementation for ->signal	843	# default implementation for ->signal
515		844
516	our %SIG_CB;	845	our %SIG_CB;
…		…
590	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	919	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
591		920
592	undef $CHLD_W unless keys %PID_CB;	921	undef $CHLD_W unless keys %PID_CB;
593	}	922	}
594		923
		924	package AnyEvent::CondVar;
		925
		926	our @ISA = AnyEvent::CondVar::Base::;
		927
		928	package AnyEvent::CondVar::Base;
		929
		930	use overload
		931	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		932	fallback => 1;
		933
		934	sub _send {
		935	# nop
		936	}
		937
		938	sub send {
		939	my $cv = shift;
		940	$cv->{_ae_sent} = [@_];
		941	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		942	$cv->_send;
		943	}
		944
		945	sub croak {
		946	$_[0]{_ae_croak} = $_[1];
		947	$_[0]->send;
		948	}
		949
		950	sub ready {
		951	$_[0]{_ae_sent}
		952	}
		953
		954	sub _wait {
		955	AnyEvent->one_event while !$_[0]{_ae_sent};
		956	}
		957
		958	sub recv {
		959	$_[0]->_wait;
		960
		961	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		962	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		963	}
		964
		965	sub cb {
		966	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		967	$_[0]{_ae_cb}
		968	}
		969
		970	sub begin {
		971	++$_[0]{_ae_counter};
		972	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		973	}
		974
		975	sub end {
		976	return if --$_[0]{_ae_counter};
		977	&{ $_[0]{_ae_end_cb} \|\| sub { $_[0]->send } };
		978	}
		979
		980	# undocumented/compatibility with pre-3.4
		981	*broadcast = \&send;
		982	*wait = \&_wait;
		983
595	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	984	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
596		985
597	This is an advanced topic that you do not normally need to use AnyEvent in	986	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	987	a module. This section is only of use to event loop authors who want to
599	provide AnyEvent compatibility.	988	provide AnyEvent compatibility.
…		…
637		1026
638	=head1 ENVIRONMENT VARIABLES	1027	=head1 ENVIRONMENT VARIABLES
639		1028
640	The following environment variables are used by this module:	1029	The following environment variables are used by this module:
641		1030
642	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, cause AnyEvent to	1031	=over 4
643	report to STDERR which event model it chooses.	1032
		1033	=item C<PERL_ANYEVENT_VERBOSE>
		1034
		1035	By default, AnyEvent will be completely silent except in fatal
		1036	conditions. You can set this environment variable to make AnyEvent more
		1037	talkative.
		1038
		1039	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1040	conditions, such as not being able to load the event model specified by
		1041	C<PERL_ANYEVENT_MODEL>.
		1042
		1043	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1044	model it chooses.
		1045
		1046	=item C<PERL_ANYEVENT_MODEL>
		1047
		1048	This can be used to specify the event model to be used by AnyEvent, before
		1049	auto detection and -probing kicks in. It must be a string consisting
		1050	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1051	and the resulting module name is loaded and if the load was successful,
		1052	used as event model. If it fails to load AnyEvent will proceed with
		1053	auto detection and -probing.
		1054
		1055	This functionality might change in future versions.
		1056
		1057	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1058	could start your program like this:
		1059
		1060	PERL_ANYEVENT_MODEL=Perl perl ...
		1061
		1062	=item C<PERL_ANYEVENT_PROTOCOLS>
		1063
		1064	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1065	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1066	of auto probing).
		1067
		1068	Must be set to a comma-separated list of protocols or address families,
		1069	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1070	used, and preference will be given to protocols mentioned earlier in the
		1071	list.
		1072
		1073	This variable can effectively be used for denial-of-service attacks
		1074	against local programs (e.g. when setuid), although the impact is likely
		1075	small, as the program has to handle connection errors already-
		1076
		1077	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1078	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1079	- only support IPv4, never try to resolve or contact IPv6
		1080	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1081	IPv6, but prefer IPv6 over IPv4.
		1082
		1083	=item C<PERL_ANYEVENT_EDNS0>
		1084
		1085	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1086	for DNS. This extension is generally useful to reduce DNS traffic, but
		1087	some (broken) firewalls drop such DNS packets, which is why it is off by
		1088	default.
		1089
		1090	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1091	EDNS0 in its DNS requests.
		1092
		1093	=back
644		1094
645	=head1 EXAMPLE PROGRAM	1095	=head1 EXAMPLE PROGRAM
646		1096
647	The following program uses an IO watcher to read data from STDIN, a timer	1097	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	1098	to display a message once per second, and a condition variable to quit the
649	program when the user enters quit:	1099	program when the user enters quit:
650		1100
651	use AnyEvent;	1101	use AnyEvent;
652		1102
…		…
657	poll => 'r',	1107	poll => 'r',
658	cb => sub {	1108	cb => sub {
659	warn "io event <$_[0]>\n"; # will always output <r>	1109	warn "io event <$_[0]>\n"; # will always output <r>
660	chomp (my $input = <STDIN>); # read a line	1110	chomp (my $input = <STDIN>); # read a line
661	warn "read: $input\n"; # output what has been read	1111	warn "read: $input\n"; # output what has been read
662	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1112	$cv->send if $input =~ /^q/i; # quit program if /^q/i
663	},	1113	},
664	);	1114	);
665		1115
666	my $time_watcher; # can only be used once	1116	my $time_watcher; # can only be used once
667		1117
…		…
672	});	1122	});
673	}	1123	}
674		1124
675	new_timer; # create first timer	1125	new_timer; # create first timer
676		1126
677	$cv->wait; # wait until user enters /^q/i	1127	$cv->recv; # wait until user enters /^q/i
678		1128
679	=head1 REAL-WORLD EXAMPLE	1129	=head1 REAL-WORLD EXAMPLE
680		1130
681	Consider the L<Net::FCP> module. It features (among others) the following	1131	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:	1132	API calls, which are to freenet what HTTP GET requests are to http:
…		…
732	syswrite $txn->{fh}, $txn->{request}	1182	syswrite $txn->{fh}, $txn->{request}
733	or die "connection or write error";	1183	or die "connection or write error";
734	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1184	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
735		1185
736	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1186	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
737	result and signals any possible waiters that the request ahs finished:	1187	result and signals any possible waiters that the request has finished:
738		1188
739	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1189	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
740		1190
741	if (end-of-file or data complete) {	1191	if (end-of-file or data complete) {
742	$txn->{result} = $txn->{buf};	1192	$txn->{result} = $txn->{buf};
743	$txn->{finished}->broadcast;	1193	$txn->{finished}->send;
744	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1194	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
745	}	1195	}
746		1196
747	The C<result> method, finally, just waits for the finished signal (if the	1197	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	1198	request was already finished, it doesn't wait, of course, and returns the
749	data:	1199	data:
750		1200
751	$txn->{finished}->wait;	1201	$txn->{finished}->recv;
752	return $txn->{result};	1202	return $txn->{result};
753		1203
754	The actual code goes further and collects all errors (C<die>s, exceptions)	1204	The actual code goes further and collects all errors (C<die>s, exceptions)
755	that occured during request processing. The C<result> method detects	1205	that occurred during request processing. The C<result> method detects
756	whether an exception as thrown (it is stored inside the $txn object)	1206	whether an exception as thrown (it is stored inside the $txn object)
757	and just throws the exception, which means connection errors and other	1207	and just throws the exception, which means connection errors and other
758	problems get reported tot he code that tries to use the result, not in a	1208	problems get reported tot he code that tries to use the result, not in a
759	random callback.	1209	random callback.
760		1210
…		…
791		1241
792	my $quit = AnyEvent->condvar;	1242	my $quit = AnyEvent->condvar;
793		1243
794	$fcp->txn_client_get ($url)->cb (sub {	1244	$fcp->txn_client_get ($url)->cb (sub {
795	...	1245	...
796	$quit->broadcast;	1246	$quit->send;
797	});	1247	});
798		1248
799	$quit->wait;	1249	$quit->recv;
		1250
		1251
		1252	=head1 BENCHMARKS
		1253
		1254	To give you an idea of the performance and overheads that AnyEvent adds
		1255	over the event loops themselves and to give you an impression of the speed
		1256	of various event loops I prepared some benchmarks.
		1257
		1258	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1259
		1260	Here is a benchmark of various supported event models used natively and
		1261	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1262	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1263	which it is), lets them fire exactly once and destroys them again.
		1264
		1265	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1266	distribution.
		1267
		1268	=head3 Explanation of the columns
		1269
		1270	I<watcher> is the number of event watchers created/destroyed. Since
		1271	different event models feature vastly different performances, each event
		1272	loop was given a number of watchers so that overall runtime is acceptable
		1273	and similar between tested event loop (and keep them from crashing): Glib
		1274	would probably take thousands of years if asked to process the same number
		1275	of watchers as EV in this benchmark.
		1276
		1277	I<bytes> is the number of bytes (as measured by the resident set size,
		1278	RSS) consumed by each watcher. This method of measuring captures both C
		1279	and Perl-based overheads.
		1280
		1281	I<create> is the time, in microseconds (millionths of seconds), that it
		1282	takes to create a single watcher. The callback is a closure shared between
		1283	all watchers, to avoid adding memory overhead. That means closure creation
		1284	and memory usage is not included in the figures.
		1285
		1286	I<invoke> is the time, in microseconds, used to invoke a simple
		1287	callback. The callback simply counts down a Perl variable and after it was
		1288	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1289	signal the end of this phase.
		1290
		1291	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1292	watcher.
		1293
		1294	=head3 Results
		1295
		1296	name watchers bytes create invoke destroy comment
		1297	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1298	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1299	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1300	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1301	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1302	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1303	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1304	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1305	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1306	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1307
		1308	=head3 Discussion
		1309
		1310	The benchmark does I<not> measure scalability of the event loop very
		1311	well. For example, a select-based event loop (such as the pure perl one)
		1312	can never compete with an event loop that uses epoll when the number of
		1313	file descriptors grows high. In this benchmark, all events become ready at
		1314	the same time, so select/poll-based implementations get an unnatural speed
		1315	boost.
		1316
		1317	Also, note that the number of watchers usually has a nonlinear effect on
		1318	overall speed, that is, creating twice as many watchers doesn't take twice
		1319	the time - usually it takes longer. This puts event loops tested with a
		1320	higher number of watchers at a disadvantage.
		1321
		1322	To put the range of results into perspective, consider that on the
		1323	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1324	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1325	cycles with POE.
		1326
		1327	C<EV> is the sole leader regarding speed and memory use, which are both
		1328	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1329	far less memory than any other event loop and is still faster than Event
		1330	natively.
		1331
		1332	The pure perl implementation is hit in a few sweet spots (both the
		1333	constant timeout and the use of a single fd hit optimisations in the perl
		1334	interpreter and the backend itself). Nevertheless this shows that it
		1335	adds very little overhead in itself. Like any select-based backend its
		1336	performance becomes really bad with lots of file descriptors (and few of
		1337	them active), of course, but this was not subject of this benchmark.
		1338
		1339	The C<Event> module has a relatively high setup and callback invocation
		1340	cost, but overall scores in on the third place.
		1341
		1342	C<Glib>'s memory usage is quite a bit higher, but it features a
		1343	faster callback invocation and overall ends up in the same class as
		1344	C<Event>. However, Glib scales extremely badly, doubling the number of
		1345	watchers increases the processing time by more than a factor of four,
		1346	making it completely unusable when using larger numbers of watchers
		1347	(note that only a single file descriptor was used in the benchmark, so
		1348	inefficiencies of C<poll> do not account for this).
		1349
		1350	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1351	more than 2000 watchers is a big setback, however, as correctness takes
		1352	precedence over speed. Nevertheless, its performance is surprising, as the
		1353	file descriptor is dup()ed for each watcher. This shows that the dup()
		1354	employed by some adaptors is not a big performance issue (it does incur a
		1355	hidden memory cost inside the kernel which is not reflected in the figures
		1356	above).
		1357
		1358	C<POE>, regardless of underlying event loop (whether using its pure perl
		1359	select-based backend or the Event module, the POE-EV backend couldn't
		1360	be tested because it wasn't working) shows abysmal performance and
		1361	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1362	as EV watchers, and 10 times as much memory as Event (the high memory
		1363	requirements are caused by requiring a session for each watcher). Watcher
		1364	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1365	implementation.
		1366
		1367	The design of the POE adaptor class in AnyEvent can not really account
		1368	for the performance issues, though, as session creation overhead is
		1369	small compared to execution of the state machine, which is coded pretty
		1370	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1371	using multiple sessions is not a good approach, especially regarding
		1372	memory usage, even the author of POE could not come up with a faster
		1373	design).
		1374
		1375	=head3 Summary
		1376
		1377	=over 4
		1378
		1379	=item * Using EV through AnyEvent is faster than any other event loop
		1380	(even when used without AnyEvent), but most event loops have acceptable
		1381	performance with or without AnyEvent.
		1382
		1383	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1384	the actual event loop, only with extremely fast event loops such as EV
		1385	adds AnyEvent significant overhead.
		1386
		1387	=item * You should avoid POE like the plague if you want performance or
		1388	reasonable memory usage.
		1389
		1390	=back
		1391
		1392	=head2 BENCHMARKING THE LARGE SERVER CASE
		1393
		1394	This benchmark actually benchmarks the event loop itself. It works by
		1395	creating a number of "servers": each server consists of a socket pair, a
		1396	timeout watcher that gets reset on activity (but never fires), and an I/O
		1397	watcher waiting for input on one side of the socket. Each time the socket
		1398	watcher reads a byte it will write that byte to a random other "server".
		1399
		1400	The effect is that there will be a lot of I/O watchers, only part of which
		1401	are active at any one point (so there is a constant number of active
		1402	fds for each loop iteration, but which fds these are is random). The
		1403	timeout is reset each time something is read because that reflects how
		1404	most timeouts work (and puts extra pressure on the event loops).
		1405
		1406	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1407	(1%) are active. This mirrors the activity of large servers with many
		1408	connections, most of which are idle at any one point in time.
		1409
		1410	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1411	distribution.
		1412
		1413	=head3 Explanation of the columns
		1414
		1415	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1416	each server has a read and write socket end).
		1417
		1418	I<create> is the time it takes to create a socket pair (which is
		1419	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1420
		1421	I<request>, the most important value, is the time it takes to handle a
		1422	single "request", that is, reading the token from the pipe and forwarding
		1423	it to another server. This includes deleting the old timeout and creating
		1424	a new one that moves the timeout into the future.
		1425
		1426	=head3 Results
		1427
		1428	name sockets create request
		1429	EV 20000 69.01 11.16
		1430	Perl 20000 73.32 35.87
		1431	Event 20000 212.62 257.32
		1432	Glib 20000 651.16 1896.30
		1433	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1434
		1435	=head3 Discussion
		1436
		1437	This benchmark I<does> measure scalability and overall performance of the
		1438	particular event loop.
		1439
		1440	EV is again fastest. Since it is using epoll on my system, the setup time
		1441	is relatively high, though.
		1442
		1443	Perl surprisingly comes second. It is much faster than the C-based event
		1444	loops Event and Glib.
		1445
		1446	Event suffers from high setup time as well (look at its code and you will
		1447	understand why). Callback invocation also has a high overhead compared to
		1448	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1449	uses select or poll in basically all documented configurations.
		1450
		1451	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1452	clearly fails to perform with many filehandles or in busy servers.
		1453
		1454	POE is still completely out of the picture, taking over 1000 times as long
		1455	as EV, and over 100 times as long as the Perl implementation, even though
		1456	it uses a C-based event loop in this case.
		1457
		1458	=head3 Summary
		1459
		1460	=over 4
		1461
		1462	=item * The pure perl implementation performs extremely well.
		1463
		1464	=item * Avoid Glib or POE in large projects where performance matters.
		1465
		1466	=back
		1467
		1468	=head2 BENCHMARKING SMALL SERVERS
		1469
		1470	While event loops should scale (and select-based ones do not...) even to
		1471	large servers, most programs we (or I :) actually write have only a few
		1472	I/O watchers.
		1473
		1474	In this benchmark, I use the same benchmark program as in the large server
		1475	case, but it uses only eight "servers", of which three are active at any
		1476	one time. This should reflect performance for a small server relatively
		1477	well.
		1478
		1479	The columns are identical to the previous table.
		1480
		1481	=head3 Results
		1482
		1483	name sockets create request
		1484	EV 16 20.00 6.54
		1485	Perl 16 25.75 12.62
		1486	Event 16 81.27 35.86
		1487	Glib 16 32.63 15.48
		1488	POE 16 261.87 276.28 uses POE::Loop::Event
		1489
		1490	=head3 Discussion
		1491
		1492	The benchmark tries to test the performance of a typical small
		1493	server. While knowing how various event loops perform is interesting, keep
		1494	in mind that their overhead in this case is usually not as important, due
		1495	to the small absolute number of watchers (that is, you need efficiency and
		1496	speed most when you have lots of watchers, not when you only have a few of
		1497	them).
		1498
		1499	EV is again fastest.
		1500
		1501	Perl again comes second. It is noticeably faster than the C-based event
		1502	loops Event and Glib, although the difference is too small to really
		1503	matter.
		1504
		1505	POE also performs much better in this case, but is is still far behind the
		1506	others.
		1507
		1508	=head3 Summary
		1509
		1510	=over 4
		1511
		1512	=item * C-based event loops perform very well with small number of
		1513	watchers, as the management overhead dominates.
		1514
		1515	=back
		1516
		1517
		1518	=head1 FORK
		1519
		1520	Most event libraries are not fork-safe. The ones who are usually are
		1521	because they rely on inefficient but fork-safe C<select> or C<poll>
		1522	calls. Only L<EV> is fully fork-aware.
		1523
		1524	If you have to fork, you must either do so I<before> creating your first
		1525	watcher OR you must not use AnyEvent at all in the child.
		1526
		1527
		1528	=head1 SECURITY CONSIDERATIONS
		1529
		1530	AnyEvent can be forced to load any event model via
		1531	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1532	execute arbitrary code or directly gain access, it can easily be used to
		1533	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1534	will not be active when the program uses a different event model than
		1535	specified in the variable.
		1536
		1537	You can make AnyEvent completely ignore this variable by deleting it
		1538	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1539
		1540	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1541
		1542	use AnyEvent;
		1543
		1544	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1545	be used to probe what backend is used and gain other information (which is
		1546	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1547
800		1548
801	=head1 SEE ALSO	1549	=head1 SEE ALSO
802		1550
803	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1551	Utility functions: L<AnyEvent::Util>.
804	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.
805		1552
806	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	1553	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1554	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1555
807	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,	1556	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
808	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.	1557	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1558	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1559	L<AnyEvent::Impl::POE>.
809		1560
		1561	Non-blocking file handles, sockets, TCP clients and
		1562	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1563
		1564	Asynchronous DNS: L<AnyEvent::DNS>.
		1565
		1566	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1567
810	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1568	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1569
811		1570
812	=head1 AUTHOR	1571	=head1 AUTHOR
813		1572
814	Marc Lehmann <schmorp@schmorp.de>	1573	Marc Lehmann <schmorp@schmorp.de>
815	http://home.schmorp.de/	1574	http://home.schmorp.de/

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Revision 1.54 by root, Tue Apr 22 05:12:19 2008 UTC vs.
Revision 1.132 by root, Sun May 25 01:05:27 2008 UTC