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Revision 1.171 by root, Wed Jul 16 21:17:59 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
		23	=head1 INTRODUCTION/TUTORIAL
		24
		25	This manpage is mainly a reference manual. If you are interested
		26	in a tutorial or some gentle introduction, have a look at the
		27	L<AnyEvent::Intro> manpage.
22		28
23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)	29	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		30
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	31	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	32	nowadays. So what is different about AnyEvent?
27		33
28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of	34	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
29	policy> and AnyEvent is I<small and efficient>.	35	policy> and AnyEvent is I<small and efficient>.
30		36
31	First and foremost, I<AnyEvent is not an event model> itself, it only	37	First and foremost, I<AnyEvent is not an event model> itself, it only
32	interfaces to whatever event model the main program happens to use in a	38	interfaces to whatever event model the main program happens to use, in a
33	pragmatic way. For event models and certain classes of immortals alike,	39	pragmatic way. For event models and certain classes of immortals alike,
34	the statement "there can only be one" is a bitter reality: In general,	40	the statement "there can only be one" is a bitter reality: In general,
35	only one event loop can be active at the same time in a process. AnyEvent	41	only one event loop can be active at the same time in a process. AnyEvent
36	helps hiding the differences between those event loops.	42	cannot change this, but it can hide the differences between those event
		43	loops.
37		44
38	The goal of AnyEvent is to offer module authors the ability to do event	45	The goal of AnyEvent is to offer module authors the ability to do event
39	programming (waiting for I/O or timer events) without subscribing to a	46	programming (waiting for I/O or timer events) without subscribing to a
40	religion, a way of living, and most importantly: without forcing your	47	religion, a way of living, and most importantly: without forcing your
41	module users into the same thing by forcing them to use the same event	48	module users into the same thing by forcing them to use the same event
42	model you use.	49	model you use.
43		50
44	For modules like POE or IO::Async (which is a total misnomer as it is	51	For modules like POE or IO::Async (which is a total misnomer as it is
45	actually doing all I/O I<synchronously>...), using them in your module is	52	actually doing all I/O I<synchronously>...), using them in your module is
46	like joining a cult: After you joined, you are dependent on them and you	53	like joining a cult: After you joined, you are dependent on them and you
47	cannot use anything else, as it is simply incompatible to everything that	54	cannot use anything else, as they are simply incompatible to everything
48	isn't itself. What's worse, all the potential users of your module are	55	that isn't them. What's worse, all the potential users of your
49	I<also> forced to use the same event loop you use.	56	module are I<also> forced to use the same event loop you use.
50		57
51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	58	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	59	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
53	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if	60	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
54	your module uses one of those, every user of your module has to use it,	61	your module uses one of those, every user of your module has to use it,
55	too. But if your module uses AnyEvent, it works transparently with all	62	too. But if your module uses AnyEvent, it works transparently with all
56	event models it supports (including stuff like POE and IO::Async, as long	63	event models it supports (including stuff like IO::Async, as long as those
57	as those use one of the supported event loops. It is trivial to add new	64	use one of the supported event loops. It is trivial to add new event loops
58	event loops to AnyEvent, too, so it is future-proof).	65	to AnyEvent, too, so it is future-proof).
59		66
60	In addition to being free of having to use I<the one and only true event	67	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	68	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	69	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	70	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	71	offering the functionality that is necessary, in as thin as a wrapper as
65	technically possible.	72	technically possible.
66		73
		74	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		75	of useful functionality, such as an asynchronous DNS resolver, 100%
		76	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		77	such as Windows) and lots of real-world knowledge and workarounds for
		78	platform bugs and differences.
		79
67	Of course, if you want lots of policy (this can arguably be somewhat	80	Now, if you I<do 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	81	useful) and you want to force your users to use the one and only event
69	model, you should I<not> use this module.	82	model, you should I<not> use this module.
70
71		83
72	=head1 DESCRIPTION	84	=head1 DESCRIPTION
73		85
74	L<AnyEvent> provides an identical interface to multiple event loops. This	86	L<AnyEvent> provides an identical interface to multiple event loops. This
75	allows module authors to utilise an event loop without forcing module	87	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>	91	The interface itself is vaguely similar, but not identical to the L<Event>
80	module.	92	module.
81		93
82	During the first call of any watcher-creation method, the module tries	94	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	95	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>,	96	following modules is already loaded: L<EV>,
85	L<Event>, L<Glib>, L<Tk>. The first one found is used. If none are found,	97	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	98	L<POE>. The first one found is used. If none are found, the module tries
		99	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		100	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	101	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	102	found, AnyEvent will fall back to a pure-perl event loop, which is not
89	is not very efficient, but should work everywhere.	103	very efficient, but should work everywhere.
90		104
91	Because AnyEvent first checks for modules that are already loaded, loading	105	Because AnyEvent first checks for modules that are already loaded, loading
92	an event model explicitly before first using AnyEvent will likely make	106	an event model explicitly before first using AnyEvent will likely make
93	that model the default. For example:	107	that model the default. For example:
94		108
…		…
101	starts using it, all bets are off. Maybe you should tell their authors to	115	starts using it, all bets are off. Maybe you should tell their authors to
102	use AnyEvent so their modules work together with others seamlessly...	116	use AnyEvent so their modules work together with others seamlessly...
103		117
104	The pure-perl implementation of AnyEvent is called	118	The pure-perl implementation of AnyEvent is called
105	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	119	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
106	explicitly.	120	explicitly and enjoy the high availability of that event loop :)
107		121
108	=head1 WATCHERS	122	=head1 WATCHERS
109		123
110	AnyEvent has the central concept of a I<watcher>, which is an object that	124	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	125	stores relevant data for each kind of event you are waiting for, such as
112	the callback to call, the filehandle to watch, etc.	126	the callback to call, the file handle to watch, etc.
113		127
114	These watchers are normal Perl objects with normal Perl lifetime. After	128	These watchers are normal Perl objects with normal Perl lifetime. After
115	creating a watcher it will immediately "watch" for events and invoke the	129	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	130	callback when the event occurs (of course, only when the event model
117	is in control).	131	is in control).
…		…
125	Many watchers either are used with "recursion" (repeating timers for	139	Many watchers either are used with "recursion" (repeating timers for
126	example), or need to refer to their watcher object in other ways.	140	example), or need to refer to their watcher object in other ways.
127		141
128	An any way to achieve that is this pattern:	142	An any way to achieve that is this pattern:
129		143
130	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	144	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
131	# you can use $w here, for example to undef it	145	# you can use $w here, for example to undef it
132	undef $w;	146	undef $w;
133	});	147	});
134		148
135	Note that C<my $w; $w => combination. This is necessary because in Perl,	149	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	150	my variables are only visible after the statement in which they are
137	declared.	151	declared.
138		152
139	=head2 IO WATCHERS	153	=head2 I/O WATCHERS
140		154
141	You can create an I/O watcher by calling the C<< AnyEvent->io >> method	155	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
142	with the following mandatory key-value pairs as arguments:	156	with the following mandatory key-value pairs as arguments:
143		157
144	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for	158	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for events
		159	(AnyEvent might or might not keep a reference to this file handle). C<poll>
145	events. C<poll> must be a string that is either C<r> or C<w>, which	160	must be a string that is either C<r> or C<w>, which creates a watcher
146	creates a watcher waiting for "r"eadable or "w"ritable events,	161	waiting for "r"eadable or "w"ritable events, respectively. C<cb> is the
147	respectively. C<cb> is the callback to invoke each time the file handle	162	callback to invoke each time the file handle becomes ready.
148	becomes ready.
149		163
150	File handles will be kept alive, so as long as the watcher exists, the	164	Although the callback might get passed parameters, their value and
151	file handle exists, too.	165	presence is undefined and you cannot rely on them. Portable AnyEvent
		166	callbacks cannot use arguments passed to I/O watcher callbacks.
152		167
		168	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	169	You must not close a file handle as long as any watcher is active on the
154	on the underlying file descriptor.	170	underlying file descriptor.
155		171
156	Some event loops issue spurious readyness notifications, so you should	172	Some event loops issue spurious readyness notifications, so you should
157	always use non-blocking calls when reading/writing from/to your file	173	always use non-blocking calls when reading/writing from/to your file
158	handles.	174	handles.
159		175
160	Example:
161
162	# wait for readability of STDIN, then read a line and disable the watcher	176	Example: wait for readability of STDIN, then read a line and disable the
		177	watcher.
		178
163	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	179	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
164	chomp (my $input = <STDIN>);	180	chomp (my $input = <STDIN>);
165	warn "read: $input\n";	181	warn "read: $input\n";
166	undef $w;	182	undef $w;
167	});	183	});
…		…
170		186
171	You can create a time watcher by calling the C<< AnyEvent->timer >>	187	You can create a time watcher by calling the C<< AnyEvent->timer >>
172	method with the following mandatory arguments:	188	method with the following mandatory arguments:
173		189
174	C<after> specifies after how many seconds (fractional values are	190	C<after> specifies after how many seconds (fractional values are
175	supported) should the timer activate. C<cb> the callback to invoke in that	191	supported) the callback should be invoked. C<cb> is the callback to invoke
176	case.	192	in that case.
177		193
178	The timer callback will be invoked at most once: if you want a repeating	194	Although the callback might get passed parameters, their value and
179	timer you have to create a new watcher (this is a limitation by both Tk	195	presence is undefined and you cannot rely on them. Portable AnyEvent
180	and Glib).	196	callbacks cannot use arguments passed to time watcher callbacks.
181		197
182	Example:	198	The callback will normally be invoked once only. If you specify another
		199	parameter, C<interval>, as a strictly positive number (> 0), then the
		200	callback will be invoked regularly at that interval (in fractional
		201	seconds) after the first invocation. If C<interval> is specified with a
		202	false value, then it is treated as if it were missing.
183		203
		204	The callback will be rescheduled before invoking the callback, but no
		205	attempt is done to avoid timer drift in most backends, so the interval is
		206	only approximate.
		207
184	# fire an event after 7.7 seconds	208	Example: fire an event after 7.7 seconds.
		209
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	210	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	211	warn "timeout\n";
187	});	212	});
188		213
189	# to cancel the timer:	214	# to cancel the timer:
190	undef $w;	215	undef $w;
191		216
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	217	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		218
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	219	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		220	warn "timeout\n";
200	};	221	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		222
205	=head3 TIMING ISSUES	223	=head3 TIMING ISSUES
206		224
207	There are two ways to handle timers: based on real time (relative, "fire	225	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	226	in 10 seconds") and based on wallclock time (absolute, "fire at 12
209	o'clock").	227	o'clock").
210		228
211	While most event loops expect timers to specified in a relative way, they use	229	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",	230	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	231	"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	232	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
215	six years to finally fire.	233	fire "after" a second might actually take six years to finally fire.
216		234
217	AnyEvent cannot compensate for this. The only event loop that is conscious	235	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	236	about these issues is L<EV>, which offers both relative (ev_timer, based
219	absolute (ev_periodic) timers.	237	on true relative time) and absolute (ev_periodic, based on wallclock time)
		238	timers.
220		239
221	AnyEvent always prefers relative timers, if available, matching the	240	AnyEvent always prefers relative timers, if available, matching the
222	AnyEvent API.	241	AnyEvent API.
223		242
		243	AnyEvent has two additional methods that return the "current time":
		244
		245	=over 4
		246
		247	=item AnyEvent->time
		248
		249	This returns the "current wallclock time" as a fractional number of
		250	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		251	return, and the result is guaranteed to be compatible with those).
		252
		253	It progresses independently of any event loop processing, i.e. each call
		254	will check the system clock, which usually gets updated frequently.
		255
		256	=item AnyEvent->now
		257
		258	This also returns the "current wallclock time", but unlike C<time>, above,
		259	this value might change only once per event loop iteration, depending on
		260	the event loop (most return the same time as C<time>, above). This is the
		261	time that AnyEvent's timers get scheduled against.
		262
		263	I<In almost all cases (in all cases if you don't care), this is the
		264	function to call when you want to know the current time.>
		265
		266	This function is also often faster then C<< AnyEvent->time >>, and
		267	thus the preferred method if you want some timestamp (for example,
		268	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		269
		270	The rest of this section is only of relevance if you try to be very exact
		271	with your timing, you can skip it without bad conscience.
		272
		273	For a practical example of when these times differ, consider L<Event::Lib>
		274	and L<EV> and the following set-up:
		275
		276	The event loop is running and has just invoked one of your callback at
		277	time=500 (assume no other callbacks delay processing). In your callback,
		278	you wait a second by executing C<sleep 1> (blocking the process for a
		279	second) and then (at time=501) you create a relative timer that fires
		280	after three seconds.
		281
		282	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		283	both return C<501>, because that is the current time, and the timer will
		284	be scheduled to fire at time=504 (C<501> + C<3>).
		285
		286	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		287	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		288	last event processing phase started. With L<EV>, your timer gets scheduled
		289	to run at time=503 (C<500> + C<3>).
		290
		291	In one sense, L<Event::Lib> is more exact, as it uses the current time
		292	regardless of any delays introduced by event processing. However, most
		293	callbacks do not expect large delays in processing, so this causes a
		294	higher drift (and a lot more system calls to get the current time).
		295
		296	In another sense, L<EV> is more exact, as your timer will be scheduled at
		297	the same time, regardless of how long event processing actually took.
		298
		299	In either case, if you care (and in most cases, you don't), then you
		300	can get whatever behaviour you want with any event loop, by taking the
		301	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		302	account.
		303
		304	=back
		305
224	=head2 SIGNAL WATCHERS	306	=head2 SIGNAL WATCHERS
225		307
226	You can watch for signals using a signal watcher, C<signal> is the signal	308	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	309	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
228	be invoked whenever a signal occurs.	310	callback to be invoked whenever a signal occurs.
229		311
		312	Although the callback might get passed parameters, their value and
		313	presence is undefined and you cannot rely on them. Portable AnyEvent
		314	callbacks cannot use arguments passed to signal watcher callbacks.
		315
230	Multiple signals occurances can be clumped together into one callback	316	Multiple signal occurrences can be clumped together into one callback
231	invocation, and callback invocation will be synchronous. synchronous means	317	invocation, and callback invocation will be synchronous. Synchronous means
232	that it might take a while until the signal gets handled by the process,	318	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.	319	but it is guaranteed not to interrupt any other callbacks.
234		320
235	The main advantage of using these watchers is that you can share a signal	321	The main advantage of using these watchers is that you can share a signal
236	between multiple watchers.	322	between multiple watchers.
237		323
238	This watcher might use C<%SIG>, so programs overwriting those signals	324	This watcher might use C<%SIG>, so programs overwriting those signals
…		…
248		334
249	The child process is specified by the C<pid> argument (if set to C<0>, it	335	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	336	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	337	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	338	signal handler for C<SIGCHLD>. The callback will be called with the pid
253	and exit status (as returned by waitpid).	339	and exit status (as returned by waitpid), so unlike other watcher types,
		340	you I<can> rely on child watcher callback arguments.
254		341
255	Example: wait for pid 1333	342	There is a slight catch to child watchers, however: you usually start them
		343	I<after> the child process was created, and this means the process could
		344	have exited already (and no SIGCHLD will be sent anymore).
256		345
		346	Not all event models handle this correctly (POE doesn't), but even for
		347	event models that I<do> handle this correctly, they usually need to be
		348	loaded before the process exits (i.e. before you fork in the first place).
		349
		350	This means you cannot create a child watcher as the very first thing in an
		351	AnyEvent program, you I<have> to create at least one watcher before you
		352	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		353
		354	Example: fork a process and wait for it
		355
		356	my $done = AnyEvent->condvar;
		357
		358	my $pid = fork or exit 5;
		359
257	my $w = AnyEvent->child (	360	my $w = AnyEvent->child (
258	pid => 1333,	361	pid => $pid,
259	cb => sub {	362	cb => sub {
260	my ($pid, $status) = @_;	363	my ($pid, $status) = @_;
261	warn "pid $pid exited with status $status";	364	warn "pid $pid exited with status $status";
		365	$done->send;
262	},	366	},
263	);	367	);
		368
		369	# do something else, then wait for process exit
		370	$done->recv;
264		371
265	=head2 CONDITION VARIABLES	372	=head2 CONDITION VARIABLES
266		373
		374	If you are familiar with some event loops you will know that all of them
		375	require you to run some blocking "loop", "run" or similar function that
		376	will actively watch for new events and call your callbacks.
		377
		378	AnyEvent is different, it expects somebody else to run the event loop and
		379	will only block when necessary (usually when told by the user).
		380
		381	The instrument to do that is called a "condition variable", so called
		382	because they represent a condition that must become true.
		383
267	Condition variables can be created by calling the C<< AnyEvent->condvar >>	384	Condition variables can be created by calling the C<< AnyEvent->condvar
268	method without any arguments.	385	>> method, usually without arguments. The only argument pair allowed is
		386	C<cb>, which specifies a callback to be called when the condition variable
		387	becomes true.
269		388
270	A condition variable waits for a condition - precisely that the C<<	389	After creation, the condition variable is "false" until it becomes "true"
271	->broadcast >> method has been called.	390	by calling the C<send> method (or calling the condition variable as if it
		391	were a callback, read about the caveats in the description for the C<<
		392	->send >> method).
272		393
273	They are very useful to signal that a condition has been fulfilled, for	394	Condition variables are similar to callbacks, except that you can
		395	optionally wait for them. They can also be called merge points - points
		396	in time where multiple outstanding events have been processed. And yet
		397	another way to call them is transactions - each condition variable can be
		398	used to represent a transaction, which finishes at some point and delivers
		399	a result.
		400
		401	Condition variables are very useful to signal that something has finished,
274	example, if you write a module that does asynchronous http requests,	402	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	403	then a condition variable would be the ideal candidate to signal the
276	availability of results.	404	availability of results. The user can either act when the callback is
		405	called or can synchronously C<< ->recv >> for the results.
277		406
278	You can also use condition variables to block your main program until	407	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	408	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<<	409	could C<< ->recv >> in your main program until the user clicks the Quit
281	->broadcast >> the "quit" event.	410	button of your app, which would C<< ->send >> the "quit" event.
282		411
283	Note that condition variables recurse into the event loop - if you have	412	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	413	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	414	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,	415	you should avoid making a blocking wait yourself, at least in callbacks,
287	as this asks for trouble.	416	as this asks for trouble.
288		417
289	This object has two methods:	418	Condition variables are represented by hash refs in perl, and the keys
		419	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		420	easy (it is often useful to build your own transaction class on top of
		421	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		422	it's C<new> method in your own C<new> method.
		423
		424	There are two "sides" to a condition variable - the "producer side" which
		425	eventually calls C<< -> send >>, and the "consumer side", which waits
		426	for the send to occur.
		427
		428	Example: wait for a timer.
		429
		430	# wait till the result is ready
		431	my $result_ready = AnyEvent->condvar;
		432
		433	# do something such as adding a timer
		434	# or socket watcher the calls $result_ready->send
		435	# when the "result" is ready.
		436	# in this case, we simply use a timer:
		437	my $w = AnyEvent->timer (
		438	after => 1,
		439	cb => sub { $result_ready->send },
		440	);
		441
		442	# this "blocks" (while handling events) till the callback
		443	# calls send
		444	$result_ready->recv;
		445
		446	Example: wait for a timer, but take advantage of the fact that
		447	condition variables are also code references.
		448
		449	my $done = AnyEvent->condvar;
		450	my $delay = AnyEvent->timer (after => 5, cb => $done);
		451	$done->recv;
		452
		453	=head3 METHODS FOR PRODUCERS
		454
		455	These methods should only be used by the producing side, i.e. the
		456	code/module that eventually sends the signal. Note that it is also
		457	the producer side which creates the condvar in most cases, but it isn't
		458	uncommon for the consumer to create it as well.
290		459
291	=over 4	460	=over 4
292		461
		462	=item $cv->send (...)
		463
		464	Flag the condition as ready - a running C<< ->recv >> and all further
		465	calls to C<recv> will (eventually) return after this method has been
		466	called. If nobody is waiting the send will be remembered.
		467
		468	If a callback has been set on the condition variable, it is called
		469	immediately from within send.
		470
		471	Any arguments passed to the C<send> call will be returned by all
		472	future C<< ->recv >> calls.
		473
		474	Condition variables are overloaded so one can call them directly
		475	(as a code reference). Calling them directly is the same as calling
		476	C<send>. Note, however, that many C-based event loops do not handle
		477	overloading, so as tempting as it may be, passing a condition variable
		478	instead of a callback does not work. Both the pure perl and EV loops
		479	support overloading, however, as well as all functions that use perl to
		480	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		481	example).
		482
		483	=item $cv->croak ($error)
		484
		485	Similar to send, but causes all call's to C<< ->recv >> to invoke
		486	C<Carp::croak> with the given error message/object/scalar.
		487
		488	This can be used to signal any errors to the condition variable
		489	user/consumer.
		490
		491	=item $cv->begin ([group callback])
		492
293	=item $cv->wait	493	=item $cv->end
294		494
295	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	495	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		496
		497	These two methods can be used to combine many transactions/events into
		498	one. For example, a function that pings many hosts in parallel might want
		499	to use a condition variable for the whole process.
		500
		501	Every call to C<< ->begin >> will increment a counter, and every call to
		502	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		503	>>, the (last) callback passed to C<begin> will be executed. That callback
		504	is I<supposed> to call C<< ->send >>, but that is not required. If no
		505	callback was set, C<send> will be called without any arguments.
		506
		507	Let's clarify this with the ping example:
		508
		509	my $cv = AnyEvent->condvar;
		510
		511	my %result;
		512	$cv->begin (sub { $cv->send (\%result) });
		513
		514	for my $host (@list_of_hosts) {
		515	$cv->begin;
		516	ping_host_then_call_callback $host, sub {
		517	$result{$host} = ...;
		518	$cv->end;
		519	};
		520	}
		521
		522	$cv->end;
		523
		524	This code fragment supposedly pings a number of hosts and calls
		525	C<send> after results for all then have have been gathered - in any
		526	order. To achieve this, the code issues a call to C<begin> when it starts
		527	each ping request and calls C<end> when it has received some result for
		528	it. Since C<begin> and C<end> only maintain a counter, the order in which
		529	results arrive is not relevant.
		530
		531	There is an additional bracketing call to C<begin> and C<end> outside the
		532	loop, which serves two important purposes: first, it sets the callback
		533	to be called once the counter reaches C<0>, and second, it ensures that
		534	C<send> is called even when C<no> hosts are being pinged (the loop
		535	doesn't execute once).
		536
		537	This is the general pattern when you "fan out" into multiple subrequests:
		538	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		539	is called at least once, and then, for each subrequest you start, call
		540	C<begin> and for each subrequest you finish, call C<end>.
		541
		542	=back
		543
		544	=head3 METHODS FOR CONSUMERS
		545
		546	These methods should only be used by the consuming side, i.e. the
		547	code awaits the condition.
		548
		549	=over 4
		550
		551	=item $cv->recv
		552
		553	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
296	called on c<$cv>, while servicing other watchers normally.	554	>> methods have been called on c<$cv>, while servicing other watchers
		555	normally.
297		556
298	You can only wait once on a condition - additional calls will return	557	You can only wait once on a condition - additional calls are valid but
299	immediately.	558	will return immediately.
		559
		560	If an error condition has been set by calling C<< ->croak >>, then this
		561	function will call C<croak>.
		562
		563	In list context, all parameters passed to C<send> will be returned,
		564	in scalar context only the first one will be returned.
300		565
301	Not all event models support a blocking wait - some die in that case	566	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	567	(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	568	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	569	caller decide whether the call will block or not (for example, by coupling
305	condition variables with some kind of request results and supporting	570	condition variables with some kind of request results and supporting
306	callbacks so the caller knows that getting the result will not block,	571	callbacks so the caller knows that getting the result will not block,
307	while still suppporting blocking waits if the caller so desires).	572	while still supporting blocking waits if the caller so desires).
308		573
309	Another reason I<never> to C<< ->wait >> in a module is that you cannot	574	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	575	sensibly have two C<< ->recv >>'s in parallel, as that would require
311	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	576	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
312	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	577	can supply.
313	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
314	from different coroutines, however).
315		578
316	=item $cv->broadcast	579	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		580	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		581	versions and also integrates coroutines into AnyEvent, making blocking
		582	C<< ->recv >> calls perfectly safe as long as they are done from another
		583	coroutine (one that doesn't run the event loop).
317		584
318	Flag the condition as ready - a running C<< ->wait >> and all further	585	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	586	only calling C<< ->recv >> from within that callback (or at a later
320	called. If nobody is waiting the broadcast will be remembered..	587	time). This will work even when the event loop does not support blocking
		588	waits otherwise.
		589
		590	=item $bool = $cv->ready
		591
		592	Returns true when the condition is "true", i.e. whether C<send> or
		593	C<croak> have been called.
		594
		595	=item $cb = $cv->cb ([new callback])
		596
		597	This is a mutator function that returns the callback set and optionally
		598	replaces it before doing so.
		599
		600	The callback will be called when the condition becomes "true", i.e. when
		601	C<send> or C<croak> are called, with the only argument being the condition
		602	variable itself. Calling C<recv> inside the callback or at any later time
		603	is guaranteed not to block.
321		604
322	=back	605	=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		606
342	=head1 GLOBAL VARIABLES AND FUNCTIONS	607	=head1 GLOBAL VARIABLES AND FUNCTIONS
343		608
344	=over 4	609	=over 4
345		610
…		…
351	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	616	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>).	617	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
353		618
354	The known classes so far are:	619	The known classes so far are:
355		620
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).	621	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
359	AnyEvent::Impl::Event based on Event, also second best choice :)	622	AnyEvent::Impl::Event based on Event, second best choice.
		623	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
360	AnyEvent::Impl::Glib based on Glib, third-best choice.	624	AnyEvent::Impl::Glib based on Glib, third-best choice.
361	AnyEvent::Impl::Tk based on Tk, very bad choice.	625	AnyEvent::Impl::Tk based on Tk, very bad choice.
362	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	626	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		627	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		628	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		629
		630	There is no support for WxWidgets, as WxWidgets has no support for
		631	watching file handles. However, you can use WxWidgets through the
		632	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		633	second, which was considered to be too horrible to even consider for
		634	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		635	it's adaptor.
		636
		637	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		638	autodetecting them.
363		639
364	=item AnyEvent::detect	640	=item AnyEvent::detect
365		641
366	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	642	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
367	if necessary. You should only call this function right before you would	643	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	644	have created an AnyEvent watcher anyway, that is, as late as possible at
369	runtime.	645	runtime.
370		646
		647	=item $guard = AnyEvent::post_detect { BLOCK }
		648
		649	Arranges for the code block to be executed as soon as the event model is
		650	autodetected (or immediately if this has already happened).
		651
		652	If called in scalar or list context, then it creates and returns an object
		653	that automatically removes the callback again when it is destroyed. See
		654	L<Coro::BDB> for a case where this is useful.
		655
		656	=item @AnyEvent::post_detect
		657
		658	If there are any code references in this array (you can C<push> to it
		659	before or after loading AnyEvent), then they will called directly after
		660	the event loop has been chosen.
		661
		662	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		663	if it contains a true value then the event loop has already been detected,
		664	and the array will be ignored.
		665
		666	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		667
371	=back	668	=back
372		669
373	=head1 WHAT TO DO IN A MODULE	670	=head1 WHAT TO DO IN A MODULE
374		671
375	As a module author, you should C<use AnyEvent> and call AnyEvent methods	672	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	675	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	676	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	677	by calling AnyEvent in your module body you force the user of your module
381	to load the event module first.	678	to load the event module first.
382		679
383	Never call C<< ->wait >> on a condition variable unless you I<know> that	680	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	681	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	682	because it will stall the whole program, and the whole point of using
386	events is to stay interactive.	683	events is to stay interactive.
387		684
388	It is fine, however, to call C<< ->wait >> when the user of your module	685	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	686	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 >>	687	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).	688	freely, as the user of your module knows what she is doing. always).
392		689
393	=head1 WHAT TO DO IN THE MAIN PROGRAM	690	=head1 WHAT TO DO IN THE MAIN PROGRAM
394		691
395	There will always be a single main program - the only place that should	692	There will always be a single main program - the only place that should
…		…
397		694
398	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	695	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
399	do anything special (it does not need to be event-based) and let AnyEvent	696	do anything special (it does not need to be event-based) and let AnyEvent
400	decide which implementation to chose if some module relies on it.	697	decide which implementation to chose if some module relies on it.
401		698
402	If the main program relies on a specific event model. For example, in	699	If the main program relies on a specific event model - for example, in
403	Gtk2 programs you have to rely on the Glib module. You should load the	700	Gtk2 programs you have to rely on the Glib module - you should load the
404	event module before loading AnyEvent or any module that uses it: generally	701	event module before loading AnyEvent or any module that uses it: generally
405	speaking, you should load it as early as possible. The reason is that	702	speaking, you should load it as early as possible. The reason is that
406	modules might create watchers when they are loaded, and AnyEvent will	703	modules might create watchers when they are loaded, and AnyEvent will
407	decide on the event model to use as soon as it creates watchers, and it	704	decide on the event model to use as soon as it creates watchers, and it
408	might chose the wrong one unless you load the correct one yourself.	705	might chose the wrong one unless you load the correct one yourself.
409		706
410	You can chose to use a rather inefficient pure-perl implementation by	707	You can chose to use a pure-perl implementation by loading the
411	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	708	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
412	behaviour everywhere, but letting AnyEvent chose is generally better.	709	everywhere, but letting AnyEvent chose the model is generally better.
		710
		711	=head2 MAINLOOP EMULATION
		712
		713	Sometimes (often for short test scripts, or even standalone programs who
		714	only want to use AnyEvent), you do not want to run a specific event loop.
		715
		716	In that case, you can use a condition variable like this:
		717
		718	AnyEvent->condvar->recv;
		719
		720	This has the effect of entering the event loop and looping forever.
		721
		722	Note that usually your program has some exit condition, in which case
		723	it is better to use the "traditional" approach of storing a condition
		724	variable somewhere, waiting for it, and sending it when the program should
		725	exit cleanly.
		726
		727
		728	=head1 OTHER MODULES
		729
		730	The following is a non-exhaustive list of additional modules that use
		731	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		732	in the same program. Some of the modules come with AnyEvent, some are
		733	available via CPAN.
		734
		735	=over 4
		736
		737	=item L<AnyEvent::Util>
		738
		739	Contains various utility functions that replace often-used but blocking
		740	functions such as C<inet_aton> by event-/callback-based versions.
		741
		742	=item L<AnyEvent::Socket>
		743
		744	Provides various utility functions for (internet protocol) sockets,
		745	addresses and name resolution. Also functions to create non-blocking tcp
		746	connections or tcp servers, with IPv6 and SRV record support and more.
		747
		748	=item L<AnyEvent::Handle>
		749
		750	Provide read and write buffers, manages watchers for reads and writes,
		751	supports raw and formatted I/O, I/O queued and fully transparent and
		752	non-blocking SSL/TLS.
		753
		754	=item L<AnyEvent::DNS>
		755
		756	Provides rich asynchronous DNS resolver capabilities.
		757
		758	=item L<AnyEvent::HTTP>
		759
		760	A simple-to-use HTTP library that is capable of making a lot of concurrent
		761	HTTP requests.
		762
		763	=item L<AnyEvent::HTTPD>
		764
		765	Provides a simple web application server framework.
		766
		767	=item L<AnyEvent::FastPing>
		768
		769	The fastest ping in the west.
		770
		771	=item L<AnyEvent::DBI>
		772
		773	Executes L<DBI> requests asynchronously in a proxy process.
		774
		775	=item L<AnyEvent::AIO>
		776
		777	Truly asynchronous I/O, should be in the toolbox of every event
		778	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		779	together.
		780
		781	=item L<AnyEvent::BDB>
		782
		783	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		784	L<BDB> and AnyEvent together.
		785
		786	=item L<AnyEvent::GPSD>
		787
		788	A non-blocking interface to gpsd, a daemon delivering GPS information.
		789
		790	=item L<AnyEvent::IGS>
		791
		792	A non-blocking interface to the Internet Go Server protocol (used by
		793	L<App::IGS>).
		794
		795	=item L<Net::IRC3>
		796
		797	AnyEvent based IRC client module family.
		798
		799	=item L<Net::XMPP2>
		800
		801	AnyEvent based XMPP (Jabber protocol) module family.
		802
		803	=item L<Net::FCP>
		804
		805	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		806	of AnyEvent.
		807
		808	=item L<Event::ExecFlow>
		809
		810	High level API for event-based execution flow control.
		811
		812	=item L<Coro>
		813
		814	Has special support for AnyEvent via L<Coro::AnyEvent>.
		815
		816	=item L<IO::Lambda>
		817
		818	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		819
		820	=back
413		821
414	=cut	822	=cut
415		823
416	package AnyEvent;	824	package AnyEvent;
417		825
418	no warnings;	826	no warnings;
419	use strict;	827	use strict;
420		828
421	use Carp;	829	use Carp;
422		830
423	our $VERSION = '3.12';	831	our $VERSION = 4.21;
424	our $MODEL;	832	our $MODEL;
425		833
426	our $AUTOLOAD;	834	our $AUTOLOAD;
427	our @ISA;	835	our @ISA;
428		836
		837	our @REGISTRY;
		838
		839	our $WIN32;
		840
		841	BEGIN {
		842	my $win32 = ! ! ($^O =~ /mswin32/i);
		843	eval "sub WIN32(){ $win32 }";
		844	}
		845
429	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	846	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
430		847
431	our @REGISTRY;	848	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		849
		850	{
		851	my $idx;
		852	$PROTOCOL{$_} = ++$idx
		853	for reverse split /\s*,\s*/,
		854	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		855	}
432		856
433	my @models = (	857	my @models = (
434	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
435	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
436	[EV:: => AnyEvent::Impl::EV::],	858	[EV:: => AnyEvent::Impl::EV::],
437	[Event:: => AnyEvent::Impl::Event::],	859	[Event:: => AnyEvent::Impl::Event::],
438	[Glib:: => AnyEvent::Impl::Glib::],
439	[Tk:: => AnyEvent::Impl::Tk::],
440	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	860	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		861	# everything below here will not be autoprobed
		862	# as the pureperl backend should work everywhere
		863	# and is usually faster
		864	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		865	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		866	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		867	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		868	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		869	[Wx:: => AnyEvent::Impl::POE::],
		870	[Prima:: => AnyEvent::Impl::POE::],
441	);	871	);
442		872
443	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	873	our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
		874
		875	our @post_detect;
		876
		877	sub post_detect(&) {
		878	my ($cb) = @_;
		879
		880	if ($MODEL) {
		881	$cb->();
		882
		883	1
		884	} else {
		885	push @post_detect, $cb;
		886
		887	defined wantarray
		888	? bless \$cb, "AnyEvent::Util::PostDetect"
		889	: ()
		890	}
		891	}
		892
		893	sub AnyEvent::Util::PostDetect::DESTROY {
		894	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		895	}
444		896
445	sub detect() {	897	sub detect() {
446	unless ($MODEL) {	898	unless ($MODEL) {
447	no strict 'refs';	899	no strict 'refs';
		900	local $SIG{__DIE__};
		901
		902	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		903	my $model = "AnyEvent::Impl::$1";
		904	if (eval "require $model") {
		905	$MODEL = $model;
		906	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		907	} else {
		908	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		909	}
		910	}
448		911
449	# check for already loaded models	912	# check for already loaded models
		913	unless ($MODEL) {
450	for (@REGISTRY, @models) {	914	for (@REGISTRY, @models) {
451	my ($package, $model) = @$_;	915	my ($package, $model) = @$_;
452	if (${"$package\::VERSION"} > 0) {	916	if (${"$package\::VERSION"} > 0) {
453	if (eval "require $model") {	917	if (eval "require $model") {
454	$MODEL = $model;	918	$MODEL = $model;
455	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	919	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
456	last;	920	last;
		921	}
457	}	922	}
458	}	923	}
		924
		925	unless ($MODEL) {
		926	# try to load a model
		927
		928	for (@REGISTRY, @models) {
		929	my ($package, $model) = @$_;
		930	if (eval "require $package"
		931	and ${"$package\::VERSION"} > 0
		932	and eval "require $model") {
		933	$MODEL = $model;
		934	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		935	last;
		936	}
		937	}
		938
		939	$MODEL
		940	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		941	}
459	}	942	}
460		943
461	unless ($MODEL) {	944	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
462	# try to load a model
463
464	for (@REGISTRY, @models) {
465	my ($package, $model) = @$_;
466	if (eval "require $package"
467	and ${"$package\::VERSION"} > 0
468	and eval "require $model") {
469	$MODEL = $model;
470	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
471	last;
472	}
473	}
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	}
478		945
479	unshift @ISA, $MODEL;	946	unshift @ISA, $MODEL;
480	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	947
		948	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		949
		950	(shift @post_detect)->() while @post_detect;
481	}	951	}
482		952
483	$MODEL	953	$MODEL
484	}	954	}
485		955
…		…
493		963
494	my $class = shift;	964	my $class = shift;
495	$class->$func (@_);	965	$class->$func (@_);
496	}	966	}
497		967
		968	# utility function to dup a filehandle. this is used by many backends
		969	# to support binding more than one watcher per filehandle (they usually
		970	# allow only one watcher per fd, so we dup it to get a different one).
		971	sub _dupfh($$$$) {
		972	my ($poll, $fh, $r, $w) = @_;
		973
		974	require Fcntl;
		975
		976	# cygwin requires the fh mode to be matching, unix doesn't
		977	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		978	: $poll eq "w" ? ($w, ">")
		979	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		980
		981	open my $fh2, "$mode&" . fileno $fh
		982	or die "cannot dup() filehandle: $!";
		983
		984	# we assume CLOEXEC is already set by perl in all important cases
		985
		986	($fh2, $rw)
		987	}
		988
498	package AnyEvent::Base;	989	package AnyEvent::Base;
499		990
		991	# default implementation for now and time
		992
		993	use Time::HiRes ();
		994
		995	sub time { Time::HiRes::time }
		996	sub now { Time::HiRes::time }
		997
500	# default implementation for ->condvar, ->wait, ->broadcast	998	# default implementation for ->condvar
501		999
502	sub condvar {	1000	sub condvar {
503	bless \my $flag, "AnyEvent::Base::CondVar"	1001	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	}	1002	}
513		1003
514	# default implementation for ->signal	1004	# default implementation for ->signal
515		1005
516	our %SIG_CB;	1006	our %SIG_CB;
…		…
532	sub AnyEvent::Base::Signal::DESTROY {	1022	sub AnyEvent::Base::Signal::DESTROY {
533	my ($signal, $cb) = @{$_[0]};	1023	my ($signal, $cb) = @{$_[0]};
534		1024
535	delete $SIG_CB{$signal}{$cb};	1025	delete $SIG_CB{$signal}{$cb};
536		1026
537	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };	1027	delete $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
538	}	1028	}
539		1029
540	# default implementation for ->child	1030	# default implementation for ->child
541		1031
542	our %PID_CB;	1032	our %PID_CB;
…		…
569	or Carp::croak "required option 'pid' is missing";	1059	or Carp::croak "required option 'pid' is missing";
570		1060
571	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1061	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
572		1062
573	unless ($WNOHANG) {	1063	unless ($WNOHANG) {
574	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1064	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
575	}	1065	}
576		1066
577	unless ($CHLD_W) {	1067	unless ($CHLD_W) {
578	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	1068	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
579	# child could be a zombie already, so make at least one round	1069	# child could be a zombie already, so make at least one round
…		…
589	delete $PID_CB{$pid}{$cb};	1079	delete $PID_CB{$pid}{$cb};
590	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1080	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
591		1081
592	undef $CHLD_W unless keys %PID_CB;	1082	undef $CHLD_W unless keys %PID_CB;
593	}	1083	}
		1084
		1085	package AnyEvent::CondVar;
		1086
		1087	our @ISA = AnyEvent::CondVar::Base::;
		1088
		1089	package AnyEvent::CondVar::Base;
		1090
		1091	use overload
		1092	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1093	fallback => 1;
		1094
		1095	sub _send {
		1096	# nop
		1097	}
		1098
		1099	sub send {
		1100	my $cv = shift;
		1101	$cv->{_ae_sent} = [@_];
		1102	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1103	$cv->_send;
		1104	}
		1105
		1106	sub croak {
		1107	$_[0]{_ae_croak} = $_[1];
		1108	$_[0]->send;
		1109	}
		1110
		1111	sub ready {
		1112	$_[0]{_ae_sent}
		1113	}
		1114
		1115	sub _wait {
		1116	AnyEvent->one_event while !$_[0]{_ae_sent};
		1117	}
		1118
		1119	sub recv {
		1120	$_[0]->_wait;
		1121
		1122	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1123	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1124	}
		1125
		1126	sub cb {
		1127	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1128	$_[0]{_ae_cb}
		1129	}
		1130
		1131	sub begin {
		1132	++$_[0]{_ae_counter};
		1133	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1134	}
		1135
		1136	sub end {
		1137	return if --$_[0]{_ae_counter};
		1138	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1139	}
		1140
		1141	# undocumented/compatibility with pre-3.4
		1142	*broadcast = \&send;
		1143	*wait = \&_wait;
594		1144
595	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1145	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
596		1146
597	This is an advanced topic that you do not normally need to use AnyEvent in	1147	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	1148	a module. This section is only of use to event loop authors who want to
…		…
637		1187
638	=head1 ENVIRONMENT VARIABLES	1188	=head1 ENVIRONMENT VARIABLES
639		1189
640	The following environment variables are used by this module:	1190	The following environment variables are used by this module:
641		1191
642	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, cause AnyEvent to	1192	=over 4
643	report to STDERR which event model it chooses.	1193
		1194	=item C<PERL_ANYEVENT_VERBOSE>
		1195
		1196	By default, AnyEvent will be completely silent except in fatal
		1197	conditions. You can set this environment variable to make AnyEvent more
		1198	talkative.
		1199
		1200	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1201	conditions, such as not being able to load the event model specified by
		1202	C<PERL_ANYEVENT_MODEL>.
		1203
		1204	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1205	model it chooses.
		1206
		1207	=item C<PERL_ANYEVENT_STRICT>
		1208
		1209	AnyEvent does not do much argument checking by default, as thorough
		1210	argument checking is very costly. Setting this variable to a true value
		1211	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1212	check the arguments passed to most method calls. If it finds any problems
		1213	it will croak.
		1214
		1215	In other words, enables "strict" mode.
		1216
		1217	Unlike C<use strict> it is definitely recommended ot keep it off in
		1218	production.
		1219
		1220	=item C<PERL_ANYEVENT_MODEL>
		1221
		1222	This can be used to specify the event model to be used by AnyEvent, before
		1223	auto detection and -probing kicks in. It must be a string consisting
		1224	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1225	and the resulting module name is loaded and if the load was successful,
		1226	used as event model. If it fails to load AnyEvent will proceed with
		1227	auto detection and -probing.
		1228
		1229	This functionality might change in future versions.
		1230
		1231	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1232	could start your program like this:
		1233
		1234	PERL_ANYEVENT_MODEL=Perl perl ...
		1235
		1236	=item C<PERL_ANYEVENT_PROTOCOLS>
		1237
		1238	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1239	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1240	of auto probing).
		1241
		1242	Must be set to a comma-separated list of protocols or address families,
		1243	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1244	used, and preference will be given to protocols mentioned earlier in the
		1245	list.
		1246
		1247	This variable can effectively be used for denial-of-service attacks
		1248	against local programs (e.g. when setuid), although the impact is likely
		1249	small, as the program has to handle connection errors already-
		1250
		1251	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1252	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1253	- only support IPv4, never try to resolve or contact IPv6
		1254	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1255	IPv6, but prefer IPv6 over IPv4.
		1256
		1257	=item C<PERL_ANYEVENT_EDNS0>
		1258
		1259	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1260	for DNS. This extension is generally useful to reduce DNS traffic, but
		1261	some (broken) firewalls drop such DNS packets, which is why it is off by
		1262	default.
		1263
		1264	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1265	EDNS0 in its DNS requests.
		1266
		1267	=item C<PERL_ANYEVENT_MAX_FORKS>
		1268
		1269	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1270	will create in parallel.
		1271
		1272	=back
644		1273
645	=head1 EXAMPLE PROGRAM	1274	=head1 EXAMPLE PROGRAM
646		1275
647	The following program uses an IO watcher to read data from STDIN, a timer	1276	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	1277	to display a message once per second, and a condition variable to quit the
649	program when the user enters quit:	1278	program when the user enters quit:
650		1279
651	use AnyEvent;	1280	use AnyEvent;
652		1281
…		…
657	poll => 'r',	1286	poll => 'r',
658	cb => sub {	1287	cb => sub {
659	warn "io event <$_[0]>\n"; # will always output <r>	1288	warn "io event <$_[0]>\n"; # will always output <r>
660	chomp (my $input = <STDIN>); # read a line	1289	chomp (my $input = <STDIN>); # read a line
661	warn "read: $input\n"; # output what has been read	1290	warn "read: $input\n"; # output what has been read
662	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1291	$cv->send if $input =~ /^q/i; # quit program if /^q/i
663	},	1292	},
664	);	1293	);
665		1294
666	my $time_watcher; # can only be used once	1295	my $time_watcher; # can only be used once
667		1296
…		…
672	});	1301	});
673	}	1302	}
674		1303
675	new_timer; # create first timer	1304	new_timer; # create first timer
676		1305
677	$cv->wait; # wait until user enters /^q/i	1306	$cv->recv; # wait until user enters /^q/i
678		1307
679	=head1 REAL-WORLD EXAMPLE	1308	=head1 REAL-WORLD EXAMPLE
680		1309
681	Consider the L<Net::FCP> module. It features (among others) the following	1310	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:	1311	API calls, which are to freenet what HTTP GET requests are to http:
…		…
732	syswrite $txn->{fh}, $txn->{request}	1361	syswrite $txn->{fh}, $txn->{request}
733	or die "connection or write error";	1362	or die "connection or write error";
734	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1363	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
735		1364
736	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1365	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:	1366	result and signals any possible waiters that the request has finished:
738		1367
739	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1368	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
740		1369
741	if (end-of-file or data complete) {	1370	if (end-of-file or data complete) {
742	$txn->{result} = $txn->{buf};	1371	$txn->{result} = $txn->{buf};
743	$txn->{finished}->broadcast;	1372	$txn->{finished}->send;
744	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1373	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
745	}	1374	}
746		1375
747	The C<result> method, finally, just waits for the finished signal (if the	1376	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	1377	request was already finished, it doesn't wait, of course, and returns the
749	data:	1378	data:
750		1379
751	$txn->{finished}->wait;	1380	$txn->{finished}->recv;
752	return $txn->{result};	1381	return $txn->{result};
753		1382
754	The actual code goes further and collects all errors (C<die>s, exceptions)	1383	The actual code goes further and collects all errors (C<die>s, exceptions)
755	that occured during request processing. The C<result> method detects	1384	that occurred during request processing. The C<result> method detects
756	whether an exception as thrown (it is stored inside the $txn object)	1385	whether an exception as thrown (it is stored inside the $txn object)
757	and just throws the exception, which means connection errors and other	1386	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	1387	problems get reported tot he code that tries to use the result, not in a
759	random callback.	1388	random callback.
760		1389
…		…
791		1420
792	my $quit = AnyEvent->condvar;	1421	my $quit = AnyEvent->condvar;
793		1422
794	$fcp->txn_client_get ($url)->cb (sub {	1423	$fcp->txn_client_get ($url)->cb (sub {
795	...	1424	...
796	$quit->broadcast;	1425	$quit->send;
797	});	1426	});
798		1427
799	$quit->wait;	1428	$quit->recv;
		1429
		1430
		1431	=head1 BENCHMARKS
		1432
		1433	To give you an idea of the performance and overheads that AnyEvent adds
		1434	over the event loops themselves and to give you an impression of the speed
		1435	of various event loops I prepared some benchmarks.
		1436
		1437	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1438
		1439	Here is a benchmark of various supported event models used natively and
		1440	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1441	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1442	which it is), lets them fire exactly once and destroys them again.
		1443
		1444	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1445	distribution.
		1446
		1447	=head3 Explanation of the columns
		1448
		1449	I<watcher> is the number of event watchers created/destroyed. Since
		1450	different event models feature vastly different performances, each event
		1451	loop was given a number of watchers so that overall runtime is acceptable
		1452	and similar between tested event loop (and keep them from crashing): Glib
		1453	would probably take thousands of years if asked to process the same number
		1454	of watchers as EV in this benchmark.
		1455
		1456	I<bytes> is the number of bytes (as measured by the resident set size,
		1457	RSS) consumed by each watcher. This method of measuring captures both C
		1458	and Perl-based overheads.
		1459
		1460	I<create> is the time, in microseconds (millionths of seconds), that it
		1461	takes to create a single watcher. The callback is a closure shared between
		1462	all watchers, to avoid adding memory overhead. That means closure creation
		1463	and memory usage is not included in the figures.
		1464
		1465	I<invoke> is the time, in microseconds, used to invoke a simple
		1466	callback. The callback simply counts down a Perl variable and after it was
		1467	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1468	signal the end of this phase.
		1469
		1470	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1471	watcher.
		1472
		1473	=head3 Results
		1474
		1475	name watchers bytes create invoke destroy comment
		1476	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1477	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1478	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1479	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1480	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1481	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1482	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1483	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1484	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1485	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1486
		1487	=head3 Discussion
		1488
		1489	The benchmark does I<not> measure scalability of the event loop very
		1490	well. For example, a select-based event loop (such as the pure perl one)
		1491	can never compete with an event loop that uses epoll when the number of
		1492	file descriptors grows high. In this benchmark, all events become ready at
		1493	the same time, so select/poll-based implementations get an unnatural speed
		1494	boost.
		1495
		1496	Also, note that the number of watchers usually has a nonlinear effect on
		1497	overall speed, that is, creating twice as many watchers doesn't take twice
		1498	the time - usually it takes longer. This puts event loops tested with a
		1499	higher number of watchers at a disadvantage.
		1500
		1501	To put the range of results into perspective, consider that on the
		1502	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1503	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1504	cycles with POE.
		1505
		1506	C<EV> is the sole leader regarding speed and memory use, which are both
		1507	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1508	far less memory than any other event loop and is still faster than Event
		1509	natively.
		1510
		1511	The pure perl implementation is hit in a few sweet spots (both the
		1512	constant timeout and the use of a single fd hit optimisations in the perl
		1513	interpreter and the backend itself). Nevertheless this shows that it
		1514	adds very little overhead in itself. Like any select-based backend its
		1515	performance becomes really bad with lots of file descriptors (and few of
		1516	them active), of course, but this was not subject of this benchmark.
		1517
		1518	The C<Event> module has a relatively high setup and callback invocation
		1519	cost, but overall scores in on the third place.
		1520
		1521	C<Glib>'s memory usage is quite a bit higher, but it features a
		1522	faster callback invocation and overall ends up in the same class as
		1523	C<Event>. However, Glib scales extremely badly, doubling the number of
		1524	watchers increases the processing time by more than a factor of four,
		1525	making it completely unusable when using larger numbers of watchers
		1526	(note that only a single file descriptor was used in the benchmark, so
		1527	inefficiencies of C<poll> do not account for this).
		1528
		1529	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1530	more than 2000 watchers is a big setback, however, as correctness takes
		1531	precedence over speed. Nevertheless, its performance is surprising, as the
		1532	file descriptor is dup()ed for each watcher. This shows that the dup()
		1533	employed by some adaptors is not a big performance issue (it does incur a
		1534	hidden memory cost inside the kernel which is not reflected in the figures
		1535	above).
		1536
		1537	C<POE>, regardless of underlying event loop (whether using its pure perl
		1538	select-based backend or the Event module, the POE-EV backend couldn't
		1539	be tested because it wasn't working) shows abysmal performance and
		1540	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1541	as EV watchers, and 10 times as much memory as Event (the high memory
		1542	requirements are caused by requiring a session for each watcher). Watcher
		1543	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1544	implementation.
		1545
		1546	The design of the POE adaptor class in AnyEvent can not really account
		1547	for the performance issues, though, as session creation overhead is
		1548	small compared to execution of the state machine, which is coded pretty
		1549	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1550	using multiple sessions is not a good approach, especially regarding
		1551	memory usage, even the author of POE could not come up with a faster
		1552	design).
		1553
		1554	=head3 Summary
		1555
		1556	=over 4
		1557
		1558	=item * Using EV through AnyEvent is faster than any other event loop
		1559	(even when used without AnyEvent), but most event loops have acceptable
		1560	performance with or without AnyEvent.
		1561
		1562	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1563	the actual event loop, only with extremely fast event loops such as EV
		1564	adds AnyEvent significant overhead.
		1565
		1566	=item * You should avoid POE like the plague if you want performance or
		1567	reasonable memory usage.
		1568
		1569	=back
		1570
		1571	=head2 BENCHMARKING THE LARGE SERVER CASE
		1572
		1573	This benchmark actually benchmarks the event loop itself. It works by
		1574	creating a number of "servers": each server consists of a socket pair, a
		1575	timeout watcher that gets reset on activity (but never fires), and an I/O
		1576	watcher waiting for input on one side of the socket. Each time the socket
		1577	watcher reads a byte it will write that byte to a random other "server".
		1578
		1579	The effect is that there will be a lot of I/O watchers, only part of which
		1580	are active at any one point (so there is a constant number of active
		1581	fds for each loop iteration, but which fds these are is random). The
		1582	timeout is reset each time something is read because that reflects how
		1583	most timeouts work (and puts extra pressure on the event loops).
		1584
		1585	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1586	(1%) are active. This mirrors the activity of large servers with many
		1587	connections, most of which are idle at any one point in time.
		1588
		1589	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1590	distribution.
		1591
		1592	=head3 Explanation of the columns
		1593
		1594	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1595	each server has a read and write socket end).
		1596
		1597	I<create> is the time it takes to create a socket pair (which is
		1598	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1599
		1600	I<request>, the most important value, is the time it takes to handle a
		1601	single "request", that is, reading the token from the pipe and forwarding
		1602	it to another server. This includes deleting the old timeout and creating
		1603	a new one that moves the timeout into the future.
		1604
		1605	=head3 Results
		1606
		1607	name sockets create request
		1608	EV 20000 69.01 11.16
		1609	Perl 20000 73.32 35.87
		1610	Event 20000 212.62 257.32
		1611	Glib 20000 651.16 1896.30
		1612	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1613
		1614	=head3 Discussion
		1615
		1616	This benchmark I<does> measure scalability and overall performance of the
		1617	particular event loop.
		1618
		1619	EV is again fastest. Since it is using epoll on my system, the setup time
		1620	is relatively high, though.
		1621
		1622	Perl surprisingly comes second. It is much faster than the C-based event
		1623	loops Event and Glib.
		1624
		1625	Event suffers from high setup time as well (look at its code and you will
		1626	understand why). Callback invocation also has a high overhead compared to
		1627	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1628	uses select or poll in basically all documented configurations.
		1629
		1630	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1631	clearly fails to perform with many filehandles or in busy servers.
		1632
		1633	POE is still completely out of the picture, taking over 1000 times as long
		1634	as EV, and over 100 times as long as the Perl implementation, even though
		1635	it uses a C-based event loop in this case.
		1636
		1637	=head3 Summary
		1638
		1639	=over 4
		1640
		1641	=item * The pure perl implementation performs extremely well.
		1642
		1643	=item * Avoid Glib or POE in large projects where performance matters.
		1644
		1645	=back
		1646
		1647	=head2 BENCHMARKING SMALL SERVERS
		1648
		1649	While event loops should scale (and select-based ones do not...) even to
		1650	large servers, most programs we (or I :) actually write have only a few
		1651	I/O watchers.
		1652
		1653	In this benchmark, I use the same benchmark program as in the large server
		1654	case, but it uses only eight "servers", of which three are active at any
		1655	one time. This should reflect performance for a small server relatively
		1656	well.
		1657
		1658	The columns are identical to the previous table.
		1659
		1660	=head3 Results
		1661
		1662	name sockets create request
		1663	EV 16 20.00 6.54
		1664	Perl 16 25.75 12.62
		1665	Event 16 81.27 35.86
		1666	Glib 16 32.63 15.48
		1667	POE 16 261.87 276.28 uses POE::Loop::Event
		1668
		1669	=head3 Discussion
		1670
		1671	The benchmark tries to test the performance of a typical small
		1672	server. While knowing how various event loops perform is interesting, keep
		1673	in mind that their overhead in this case is usually not as important, due
		1674	to the small absolute number of watchers (that is, you need efficiency and
		1675	speed most when you have lots of watchers, not when you only have a few of
		1676	them).
		1677
		1678	EV is again fastest.
		1679
		1680	Perl again comes second. It is noticeably faster than the C-based event
		1681	loops Event and Glib, although the difference is too small to really
		1682	matter.
		1683
		1684	POE also performs much better in this case, but is is still far behind the
		1685	others.
		1686
		1687	=head3 Summary
		1688
		1689	=over 4
		1690
		1691	=item * C-based event loops perform very well with small number of
		1692	watchers, as the management overhead dominates.
		1693
		1694	=back
		1695
		1696
		1697	=head1 FORK
		1698
		1699	Most event libraries are not fork-safe. The ones who are usually are
		1700	because they rely on inefficient but fork-safe C<select> or C<poll>
		1701	calls. Only L<EV> is fully fork-aware.
		1702
		1703	If you have to fork, you must either do so I<before> creating your first
		1704	watcher OR you must not use AnyEvent at all in the child.
		1705
		1706
		1707	=head1 SECURITY CONSIDERATIONS
		1708
		1709	AnyEvent can be forced to load any event model via
		1710	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1711	execute arbitrary code or directly gain access, it can easily be used to
		1712	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1713	will not be active when the program uses a different event model than
		1714	specified in the variable.
		1715
		1716	You can make AnyEvent completely ignore this variable by deleting it
		1717	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1718
		1719	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1720
		1721	use AnyEvent;
		1722
		1723	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1724	be used to probe what backend is used and gain other information (which is
		1725	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		1726	$ENV{PERL_ANYEGENT_STRICT}.
		1727
		1728
		1729	=head1 BUGS
		1730
		1731	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		1732	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		1733	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		1734	mamleaks, such as leaking on C<map> and C<grep> but it is usually not as
		1735	pronounced).
		1736
800		1737
801	=head1 SEE ALSO	1738	=head1 SEE ALSO
802		1739
803	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1740	Utility functions: L<AnyEvent::Util>.
804	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.
805		1741
806	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	1742	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1743	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1744
807	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,	1745	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
808	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.	1746	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1747	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1748	L<AnyEvent::Impl::POE>.
809		1749
		1750	Non-blocking file handles, sockets, TCP clients and
		1751	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1752
		1753	Asynchronous DNS: L<AnyEvent::DNS>.
		1754
		1755	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1756
810	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1757	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1758
811		1759
812	=head1 AUTHOR	1760	=head1 AUTHOR
813		1761
814	Marc Lehmann <schmorp@schmorp.de>	1762	Marc Lehmann <schmorp@schmorp.de>
815	http://home.schmorp.de/	1763	http://home.schmorp.de/
816		1764
817	=cut	1765	=cut
818		1766
819	1	1767	1
820		1768

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