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Revision 1.175 by root, Sun Jul 27 08:43:32 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
11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { ... });
		12
		13	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		14	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		15
		16	print AnyEvent->now; # prints current event loop time
		17	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		18
		19	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		20
		21	my $w = AnyEvent->child (pid => $pid, cb => sub {
		22	my ($pid, $status) = @_;
12	...	23	...
13	});	24	});
14		25
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	...
17	});
18
19	my $w = AnyEvent->condvar; # stores wether a condition was flagged	26	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		27	$w->send; # wake up current and all future recv's
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	28	$w->recv; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all future wait's	29	# use a condvar in callback mode:
		30	$w->cb (sub { $_[0]->recv });
		31
		32	=head1 INTRODUCTION/TUTORIAL
		33
		34	This manpage is mainly a reference manual. If you are interested
		35	in a tutorial or some gentle introduction, have a look at the
		36	L<AnyEvent::Intro> manpage.
22		37
23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)	38	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		39
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	40	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	41	nowadays. So what is different about AnyEvent?
27		42
28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of	43	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
29	policy> and AnyEvent is I<small and efficient>.	44	policy> and AnyEvent is I<small and efficient>.
30		45
31	First and foremost, I<AnyEvent is not an event model> itself, it only	46	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	47	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,	48	pragmatic way. For event models and certain classes of immortals alike,
34	the statement "there can only be one" is a bitter reality, and AnyEvent	49	the statement "there can only be one" is a bitter reality: In general,
35	helps hiding the differences.	50	only one event loop can be active at the same time in a process. AnyEvent
		51	cannot change this, but it can hide the differences between those event
		52	loops.
36		53
37	The goal of AnyEvent is to offer module authors the ability to do event	54	The goal of AnyEvent is to offer module authors the ability to do event
38	programming (waiting for I/O or timer events) without subscribing to a	55	programming (waiting for I/O or timer events) without subscribing to a
39	religion, a way of living, and most importantly: without forcing your	56	religion, a way of living, and most importantly: without forcing your
40	module users into the same thing by forcing them to use the same event	57	module users into the same thing by forcing them to use the same event
41	model you use.	58	model you use.
42		59
43	For modules like POE or IO::Async (which is actually doing all I/O	60	For modules like POE or IO::Async (which is a total misnomer as it is
44	I<synchronously>...), using them in your module is like joining a	61	actually doing all I/O I<synchronously>...), using them in your module is
45	cult: After you joined, you are dependent on them and you cannot use	62	like joining a cult: After you joined, you are dependent on them and you
46	anything else, as it is simply incompatible to everything that isn't	63	cannot use anything else, as they are simply incompatible to everything
47	itself.	64	that isn't them. What's worse, all the potential users of your
		65	module are I<also> forced to use the same event loop you use.
48		66
49	AnyEvent + POE works fine. AnyEvent + Glib works fine. AnyEvent + Tk	67	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	works fine etc. etc. but none of these work together with the rest: POE	68	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51	+ IO::Async? no go. Tk + Event? no go. If your module uses one of	69	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
52	those, every user of your module has to use it, too. If your module	70	your module uses one of those, every user of your module has to use it,
53	uses AnyEvent, it works transparently with all event models it supports	71	too. But if your module uses AnyEvent, it works transparently with all
54	(including stuff like POE and IO::Async).	72	event models it supports (including stuff like IO::Async, as long as those
		73	use one of the supported event loops. It is trivial to add new event loops
		74	to AnyEvent, too, so it is future-proof).
55		75
56	In addition of being free of having to use I<the one and only true event	76	In addition to being free of having to use I<the one and only true event
57	model>, AnyEvent also is free of bloat and policy: with POE or similar	77	model>, AnyEvent also is free of bloat and policy: with POE or similar
58	modules, you get an enourmous amount of code and strict rules you have	78	modules, you get an enormous amount of code and strict rules you have to
59	to follow. AnyEvent, on the other hand, is lean and to the point by only	79	follow. AnyEvent, on the other hand, is lean and up to the point, by only
60	offering the functionality that is useful, in as thin as a wrapper as	80	offering the functionality that is necessary, in as thin as a wrapper as
61	technically possible.	81	technically possible.
62		82
		83	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		84	of useful functionality, such as an asynchronous DNS resolver, 100%
		85	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		86	such as Windows) and lots of real-world knowledge and workarounds for
		87	platform bugs and differences.
		88
63	Of course, if you want lots of policy (this can arguably be somewhat	89	Now, if you I<do want> lots of policy (this can arguably be somewhat
64	useful) and you want to force your users to use the one and only event	90	useful) and you want to force your users to use the one and only event
65	model, you should I<not> use this module.	91	model, you should I<not> use this module.
66
67		92
68	=head1 DESCRIPTION	93	=head1 DESCRIPTION
69		94
70	L<AnyEvent> provides an identical interface to multiple event loops. This	95	L<AnyEvent> provides an identical interface to multiple event loops. This
71	allows module authors to utilise an event loop without forcing module	96	allows module authors to utilise an event loop without forcing module
72	users to use the same event loop (as only a single event loop can coexist	97	users to use the same event loop (as only a single event loop can coexist
73	peacefully at any one time).	98	peacefully at any one time).
74		99
75	The interface itself is vaguely similar but not identical to the Event	100	The interface itself is vaguely similar, but not identical to the L<Event>
76	module.	101	module.
77		102
78	On the first call of any method, the module tries to detect the currently	103	During the first call of any watcher-creation method, the module tries
79	loaded event loop by probing wether any of the following modules is	104	to detect the currently loaded event loop by probing whether one of the
80	loaded: L<Coro::EV>, L<Coro::Event>, L<EV>, L<Event>, L<Glib>, L<Tk>. The	105	following modules is already loaded: L<EV>,
		106	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
81	first one found is used. If none are found, the module tries to load these	107	L<POE>. The first one found is used. If none are found, the module tries
82	modules in the order given. The first one that could be successfully	108	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
83	loaded will be used. If still none could be found, AnyEvent will fall back	109	adaptor should always succeed) in the order given. The first one that can
84	to a pure-perl event loop, which is also not very efficient.	110	be successfully loaded will be used. If, after this, still none could be
		111	found, AnyEvent will fall back to a pure-perl event loop, which is not
		112	very efficient, but should work everywhere.
85		113
86	Because AnyEvent first checks for modules that are already loaded, loading	114	Because AnyEvent first checks for modules that are already loaded, loading
87	an Event model explicitly before first using AnyEvent will likely make	115	an event model explicitly before first using AnyEvent will likely make
88	that model the default. For example:	116	that model the default. For example:
89		117
90	use Tk;	118	use Tk;
91	use AnyEvent;	119	use AnyEvent;
92		120
93	# .. AnyEvent will likely default to Tk	121	# .. AnyEvent will likely default to Tk
94		122
		123	The I<likely> means that, if any module loads another event model and
		124	starts using it, all bets are off. Maybe you should tell their authors to
		125	use AnyEvent so their modules work together with others seamlessly...
		126
95	The pure-perl implementation of AnyEvent is called	127	The pure-perl implementation of AnyEvent is called
96	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	128	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
97	explicitly.	129	explicitly and enjoy the high availability of that event loop :)
98		130
99	=head1 WATCHERS	131	=head1 WATCHERS
100		132
101	AnyEvent has the central concept of a I<watcher>, which is an object that	133	AnyEvent has the central concept of a I<watcher>, which is an object that
102	stores relevant data for each kind of event you are waiting for, such as	134	stores relevant data for each kind of event you are waiting for, such as
103	the callback to call, the filehandle to watch, etc.	135	the callback to call, the file handle to watch, etc.
104		136
105	These watchers are normal Perl objects with normal Perl lifetime. After	137	These watchers are normal Perl objects with normal Perl lifetime. After
106	creating a watcher it will immediately "watch" for events and invoke	138	creating a watcher it will immediately "watch" for events and invoke the
		139	callback when the event occurs (of course, only when the event model
		140	is in control).
		141
107	the callback. To disable the watcher you have to destroy it (e.g. by	142	To disable the watcher you have to destroy it (e.g. by setting the
108	setting the variable that stores it to C<undef> or otherwise deleting all	143	variable you store it in to C<undef> or otherwise deleting all references
109	references to it).	144	to it).
110		145
111	All watchers are created by calling a method on the C<AnyEvent> class.	146	All watchers are created by calling a method on the C<AnyEvent> class.
112		147
		148	Many watchers either are used with "recursion" (repeating timers for
		149	example), or need to refer to their watcher object in other ways.
		150
		151	An any way to achieve that is this pattern:
		152
		153	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		154	# you can use $w here, for example to undef it
		155	undef $w;
		156	});
		157
		158	Note that C<my $w; $w => combination. This is necessary because in Perl,
		159	my variables are only visible after the statement in which they are
		160	declared.
		161
113	=head2 IO WATCHERS	162	=head2 I/O WATCHERS
114		163
115	You can create I/O watcher by calling the C<< AnyEvent->io >> method with	164	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
116	the following mandatory arguments:	165	with the following mandatory key-value pairs as arguments:
117		166
118	C<fh> the Perl I<filehandle> (not filedescriptor) to watch for	167	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for events
		168	(AnyEvent might or might not keep a reference to this file handle). C<poll>
119	events. C<poll> must be a string that is either C<r> or C<w>, that creates	169	must be a string that is either C<r> or C<w>, which creates a watcher
120	a watcher waiting for "r"eadable or "w"ritable events. C<cb> the callback	170	waiting for "r"eadable or "w"ritable events, respectively. C<cb> is the
121	to invoke everytime the filehandle becomes ready.	171	callback to invoke each time the file handle becomes ready.
122		172
123	Filehandles will be kept alive, so as long as the watcher exists, the	173	Although the callback might get passed parameters, their value and
124	filehandle exists, too.	174	presence is undefined and you cannot rely on them. Portable AnyEvent
		175	callbacks cannot use arguments passed to I/O watcher callbacks.
125		176
126	Example:	177	The I/O watcher might use the underlying file descriptor or a copy of it.
		178	You must not close a file handle as long as any watcher is active on the
		179	underlying file descriptor.
127		180
		181	Some event loops issue spurious readyness notifications, so you should
		182	always use non-blocking calls when reading/writing from/to your file
		183	handles.
		184
128	# wait for readability of STDIN, then read a line and disable the watcher	185	Example: wait for readability of STDIN, then read a line and disable the
		186	watcher.
		187
129	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	188	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
130	chomp (my $input = <STDIN>);	189	chomp (my $input = <STDIN>);
131	warn "read: $input\n";	190	warn "read: $input\n";
132	undef $w;	191	undef $w;
133	});	192	});
…		…
135	=head2 TIME WATCHERS	194	=head2 TIME WATCHERS
136		195
137	You can create a time watcher by calling the C<< AnyEvent->timer >>	196	You can create a time watcher by calling the C<< AnyEvent->timer >>
138	method with the following mandatory arguments:	197	method with the following mandatory arguments:
139		198
140	C<after> after how many seconds (fractions are supported) should the timer	199	C<after> specifies after how many seconds (fractional values are
141	activate. C<cb> the callback to invoke.	200	supported) the callback should be invoked. C<cb> is the callback to invoke
		201	in that case.
142		202
143	The timer callback will be invoked at most once: if you want a repeating	203	Although the callback might get passed parameters, their value and
144	timer you have to create a new watcher (this is a limitation by both Tk	204	presence is undefined and you cannot rely on them. Portable AnyEvent
145	and Glib).	205	callbacks cannot use arguments passed to time watcher callbacks.
146		206
147	Example:	207	The callback will normally be invoked once only. If you specify another
		208	parameter, C<interval>, as a strictly positive number (> 0), then the
		209	callback will be invoked regularly at that interval (in fractional
		210	seconds) after the first invocation. If C<interval> is specified with a
		211	false value, then it is treated as if it were missing.
148		212
		213	The callback will be rescheduled before invoking the callback, but no
		214	attempt is done to avoid timer drift in most backends, so the interval is
		215	only approximate.
		216
149	# fire an event after 7.7 seconds	217	Example: fire an event after 7.7 seconds.
		218
150	my $w = AnyEvent->timer (after => 7.7, cb => sub {	219	my $w = AnyEvent->timer (after => 7.7, cb => sub {
151	warn "timeout\n";	220	warn "timeout\n";
152	});	221	});
153		222
154	# to cancel the timer:	223	# to cancel the timer:
155	undef $w;	224	undef $w;
156		225
157	=head2 CONDITION WATCHERS	226	Example 2: fire an event after 0.5 seconds, then roughly every second.
158		227
159	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	228	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
160	method without any arguments.	229	warn "timeout\n";
		230	};
161		231
162	A condition watcher watches for a condition - precisely that the C<<	232	=head3 TIMING ISSUES
163	->broadcast >> method has been called.
164		233
165	Note that condition watchers recurse into the event loop - if you have	234	There are two ways to handle timers: based on real time (relative, "fire
166	two watchers that call C<< ->wait >> in a round-robbin fashion, you	235	in 10 seconds") and based on wallclock time (absolute, "fire at 12
167	lose. Therefore, condition watchers are good to export to your caller, but	236	o'clock").
168	you should avoid making a blocking wait, at least in callbacks, as this
169	usually asks for trouble.
170		237
171	The watcher has only two methods:	238	While most event loops expect timers to specified in a relative way, they
		239	use absolute time internally. This makes a difference when your clock
		240	"jumps", for example, when ntp decides to set your clock backwards from
		241	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		242	fire "after" a second might actually take six years to finally fire.
		243
		244	AnyEvent cannot compensate for this. The only event loop that is conscious
		245	about these issues is L<EV>, which offers both relative (ev_timer, based
		246	on true relative time) and absolute (ev_periodic, based on wallclock time)
		247	timers.
		248
		249	AnyEvent always prefers relative timers, if available, matching the
		250	AnyEvent API.
		251
		252	AnyEvent has two additional methods that return the "current time":
172		253
173	=over 4	254	=over 4
174		255
		256	=item AnyEvent->time
		257
		258	This returns the "current wallclock time" as a fractional number of
		259	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		260	return, and the result is guaranteed to be compatible with those).
		261
		262	It progresses independently of any event loop processing, i.e. each call
		263	will check the system clock, which usually gets updated frequently.
		264
		265	=item AnyEvent->now
		266
		267	This also returns the "current wallclock time", but unlike C<time>, above,
		268	this value might change only once per event loop iteration, depending on
		269	the event loop (most return the same time as C<time>, above). This is the
		270	time that AnyEvent's timers get scheduled against.
		271
		272	I<In almost all cases (in all cases if you don't care), this is the
		273	function to call when you want to know the current time.>
		274
		275	This function is also often faster then C<< AnyEvent->time >>, and
		276	thus the preferred method if you want some timestamp (for example,
		277	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		278
		279	The rest of this section is only of relevance if you try to be very exact
		280	with your timing, you can skip it without bad conscience.
		281
		282	For a practical example of when these times differ, consider L<Event::Lib>
		283	and L<EV> and the following set-up:
		284
		285	The event loop is running and has just invoked one of your callback at
		286	time=500 (assume no other callbacks delay processing). In your callback,
		287	you wait a second by executing C<sleep 1> (blocking the process for a
		288	second) and then (at time=501) you create a relative timer that fires
		289	after three seconds.
		290
		291	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		292	both return C<501>, because that is the current time, and the timer will
		293	be scheduled to fire at time=504 (C<501> + C<3>).
		294
		295	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		296	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		297	last event processing phase started. With L<EV>, your timer gets scheduled
		298	to run at time=503 (C<500> + C<3>).
		299
		300	In one sense, L<Event::Lib> is more exact, as it uses the current time
		301	regardless of any delays introduced by event processing. However, most
		302	callbacks do not expect large delays in processing, so this causes a
		303	higher drift (and a lot more system calls to get the current time).
		304
		305	In another sense, L<EV> is more exact, as your timer will be scheduled at
		306	the same time, regardless of how long event processing actually took.
		307
		308	In either case, if you care (and in most cases, you don't), then you
		309	can get whatever behaviour you want with any event loop, by taking the
		310	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		311	account.
		312
		313	=back
		314
		315	=head2 SIGNAL WATCHERS
		316
		317	You can watch for signals using a signal watcher, C<signal> is the signal
		318	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		319	callback to be invoked whenever a signal occurs.
		320
		321	Although the callback might get passed parameters, their value and
		322	presence is undefined and you cannot rely on them. Portable AnyEvent
		323	callbacks cannot use arguments passed to signal watcher callbacks.
		324
		325	Multiple signal occurrences can be clumped together into one callback
		326	invocation, and callback invocation will be synchronous. Synchronous means
		327	that it might take a while until the signal gets handled by the process,
		328	but it is guaranteed not to interrupt any other callbacks.
		329
		330	The main advantage of using these watchers is that you can share a signal
		331	between multiple watchers.
		332
		333	This watcher might use C<%SIG>, so programs overwriting those signals
		334	directly will likely not work correctly.
		335
		336	Example: exit on SIGINT
		337
		338	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		339
		340	=head2 CHILD PROCESS WATCHERS
		341
		342	You can also watch on a child process exit and catch its exit status.
		343
		344	The child process is specified by the C<pid> argument (if set to C<0>, it
		345	watches for any child process exit). The watcher will trigger as often
		346	as status change for the child are received. This works by installing a
		347	signal handler for C<SIGCHLD>. The callback will be called with the pid
		348	and exit status (as returned by waitpid), so unlike other watcher types,
		349	you I<can> rely on child watcher callback arguments.
		350
		351	There is a slight catch to child watchers, however: you usually start them
		352	I<after> the child process was created, and this means the process could
		353	have exited already (and no SIGCHLD will be sent anymore).
		354
		355	Not all event models handle this correctly (POE doesn't), but even for
		356	event models that I<do> handle this correctly, they usually need to be
		357	loaded before the process exits (i.e. before you fork in the first place).
		358
		359	This means you cannot create a child watcher as the very first thing in an
		360	AnyEvent program, you I<have> to create at least one watcher before you
		361	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		362
		363	Example: fork a process and wait for it
		364
		365	my $done = AnyEvent->condvar;
		366
		367	my $pid = fork or exit 5;
		368
		369	my $w = AnyEvent->child (
		370	pid => $pid,
		371	cb => sub {
		372	my ($pid, $status) = @_;
		373	warn "pid $pid exited with status $status";
		374	$done->send;
		375	},
		376	);
		377
		378	# do something else, then wait for process exit
		379	$done->recv;
		380
		381	=head2 CONDITION VARIABLES
		382
		383	If you are familiar with some event loops you will know that all of them
		384	require you to run some blocking "loop", "run" or similar function that
		385	will actively watch for new events and call your callbacks.
		386
		387	AnyEvent is different, it expects somebody else to run the event loop and
		388	will only block when necessary (usually when told by the user).
		389
		390	The instrument to do that is called a "condition variable", so called
		391	because they represent a condition that must become true.
		392
		393	Condition variables can be created by calling the C<< AnyEvent->condvar
		394	>> method, usually without arguments. The only argument pair allowed is
		395
		396	C<cb>, which specifies a callback to be called when the condition variable
		397	becomes true, with the condition variable as the first argument (but not
		398	the results).
		399
		400	After creation, the condition variable is "false" until it becomes "true"
		401	by calling the C<send> method (or calling the condition variable as if it
		402	were a callback, read about the caveats in the description for the C<<
		403	->send >> method).
		404
		405	Condition variables are similar to callbacks, except that you can
		406	optionally wait for them. They can also be called merge points - points
		407	in time where multiple outstanding events have been processed. And yet
		408	another way to call them is transactions - each condition variable can be
		409	used to represent a transaction, which finishes at some point and delivers
		410	a result.
		411
		412	Condition variables are very useful to signal that something has finished,
		413	for example, if you write a module that does asynchronous http requests,
		414	then a condition variable would be the ideal candidate to signal the
		415	availability of results. The user can either act when the callback is
		416	called or can synchronously C<< ->recv >> for the results.
		417
		418	You can also use them to simulate traditional event loops - for example,
		419	you can block your main program until an event occurs - for example, you
		420	could C<< ->recv >> in your main program until the user clicks the Quit
		421	button of your app, which would C<< ->send >> the "quit" event.
		422
		423	Note that condition variables recurse into the event loop - if you have
		424	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		425	lose. Therefore, condition variables are good to export to your caller, but
		426	you should avoid making a blocking wait yourself, at least in callbacks,
		427	as this asks for trouble.
		428
		429	Condition variables are represented by hash refs in perl, and the keys
		430	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		431	easy (it is often useful to build your own transaction class on top of
		432	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		433	it's C<new> method in your own C<new> method.
		434
		435	There are two "sides" to a condition variable - the "producer side" which
		436	eventually calls C<< -> send >>, and the "consumer side", which waits
		437	for the send to occur.
		438
		439	Example: wait for a timer.
		440
		441	# wait till the result is ready
		442	my $result_ready = AnyEvent->condvar;
		443
		444	# do something such as adding a timer
		445	# or socket watcher the calls $result_ready->send
		446	# when the "result" is ready.
		447	# in this case, we simply use a timer:
		448	my $w = AnyEvent->timer (
		449	after => 1,
		450	cb => sub { $result_ready->send },
		451	);
		452
		453	# this "blocks" (while handling events) till the callback
		454	# calls send
		455	$result_ready->recv;
		456
		457	Example: wait for a timer, but take advantage of the fact that
		458	condition variables are also code references.
		459
		460	my $done = AnyEvent->condvar;
		461	my $delay = AnyEvent->timer (after => 5, cb => $done);
		462	$done->recv;
		463
		464	Example: Imagine an API that returns a condvar and doesn't support
		465	callbacks. This is how you make a synchronous call, for example from
		466	the main program:
		467
		468	use AnyEvent::CouchDB;
		469
		470	...
		471
		472	my @info = $couchdb->info->recv;
		473
		474	And this is how you would just ste a callback to be called whenever the
		475	results are available:
		476
		477	$couchdb->info->cb (sub {
		478	my @info = $_[0]->recv;
		479	});
		480
		481	=head3 METHODS FOR PRODUCERS
		482
		483	These methods should only be used by the producing side, i.e. the
		484	code/module that eventually sends the signal. Note that it is also
		485	the producer side which creates the condvar in most cases, but it isn't
		486	uncommon for the consumer to create it as well.
		487
		488	=over 4
		489
		490	=item $cv->send (...)
		491
		492	Flag the condition as ready - a running C<< ->recv >> and all further
		493	calls to C<recv> will (eventually) return after this method has been
		494	called. If nobody is waiting the send will be remembered.
		495
		496	If a callback has been set on the condition variable, it is called
		497	immediately from within send.
		498
		499	Any arguments passed to the C<send> call will be returned by all
		500	future C<< ->recv >> calls.
		501
		502	Condition variables are overloaded so one can call them directly
		503	(as a code reference). Calling them directly is the same as calling
		504	C<send>. Note, however, that many C-based event loops do not handle
		505	overloading, so as tempting as it may be, passing a condition variable
		506	instead of a callback does not work. Both the pure perl and EV loops
		507	support overloading, however, as well as all functions that use perl to
		508	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		509	example).
		510
		511	=item $cv->croak ($error)
		512
		513	Similar to send, but causes all call's to C<< ->recv >> to invoke
		514	C<Carp::croak> with the given error message/object/scalar.
		515
		516	This can be used to signal any errors to the condition variable
		517	user/consumer.
		518
		519	=item $cv->begin ([group callback])
		520
175	=item $cv->wait	521	=item $cv->end
176		522
177	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	523	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		524
		525	These two methods can be used to combine many transactions/events into
		526	one. For example, a function that pings many hosts in parallel might want
		527	to use a condition variable for the whole process.
		528
		529	Every call to C<< ->begin >> will increment a counter, and every call to
		530	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		531	>>, the (last) callback passed to C<begin> will be executed. That callback
		532	is I<supposed> to call C<< ->send >>, but that is not required. If no
		533	callback was set, C<send> will be called without any arguments.
		534
		535	Let's clarify this with the ping example:
		536
		537	my $cv = AnyEvent->condvar;
		538
		539	my %result;
		540	$cv->begin (sub { $cv->send (\%result) });
		541
		542	for my $host (@list_of_hosts) {
		543	$cv->begin;
		544	ping_host_then_call_callback $host, sub {
		545	$result{$host} = ...;
		546	$cv->end;
		547	};
		548	}
		549
		550	$cv->end;
		551
		552	This code fragment supposedly pings a number of hosts and calls
		553	C<send> after results for all then have have been gathered - in any
		554	order. To achieve this, the code issues a call to C<begin> when it starts
		555	each ping request and calls C<end> when it has received some result for
		556	it. Since C<begin> and C<end> only maintain a counter, the order in which
		557	results arrive is not relevant.
		558
		559	There is an additional bracketing call to C<begin> and C<end> outside the
		560	loop, which serves two important purposes: first, it sets the callback
		561	to be called once the counter reaches C<0>, and second, it ensures that
		562	C<send> is called even when C<no> hosts are being pinged (the loop
		563	doesn't execute once).
		564
		565	This is the general pattern when you "fan out" into multiple subrequests:
		566	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		567	is called at least once, and then, for each subrequest you start, call
		568	C<begin> and for each subrequest you finish, call C<end>.
		569
		570	=back
		571
		572	=head3 METHODS FOR CONSUMERS
		573
		574	These methods should only be used by the consuming side, i.e. the
		575	code awaits the condition.
		576
		577	=over 4
		578
		579	=item $cv->recv
		580
		581	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
178	called on c<$cv>, while servicing other watchers normally.	582	>> methods have been called on c<$cv>, while servicing other watchers
		583	normally.
179		584
180	You can only wait once on a condition - additional calls will return	585	You can only wait once on a condition - additional calls are valid but
181	immediately.	586	will return immediately.
		587
		588	If an error condition has been set by calling C<< ->croak >>, then this
		589	function will call C<croak>.
		590
		591	In list context, all parameters passed to C<send> will be returned,
		592	in scalar context only the first one will be returned.
182		593
183	Not all event models support a blocking wait - some die in that case	594	Not all event models support a blocking wait - some die in that case
184	(programs might want to do that so they stay interactive), so I<if you	595	(programs might want to do that to stay interactive), so I<if you are
185	are using this from a module, never require a blocking wait>, but let the	596	using this from a module, never require a blocking wait>, but let the
186	caller decide wether the call will block or not (for example, by coupling	597	caller decide whether the call will block or not (for example, by coupling
187	condition variables with some kind of request results and supporting	598	condition variables with some kind of request results and supporting
188	callbacks so the caller knows that getting the result will not block,	599	callbacks so the caller knows that getting the result will not block,
189	while still suppporting blocking waits if the caller so desires).	600	while still supporting blocking waits if the caller so desires).
190		601
191	Another reason I<never> to C<< ->wait >> in a module is that you cannot	602	Another reason I<never> to C<< ->recv >> in a module is that you cannot
192	sensibly have two C<< ->wait >>'s in parallel, as that would require	603	sensibly have two C<< ->recv >>'s in parallel, as that would require
193	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	604	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
194	can supply (the coroutine-aware backends C<Coro::EV> and C<Coro::Event>	605	can supply.
195	explicitly support concurrent C<< ->wait >>'s from different coroutines,
196	however).
197		606
198	=item $cv->broadcast	607	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		608	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		609	versions and also integrates coroutines into AnyEvent, making blocking
		610	C<< ->recv >> calls perfectly safe as long as they are done from another
		611	coroutine (one that doesn't run the event loop).
199		612
200	Flag the condition as ready - a running C<< ->wait >> and all further	613	You can ensure that C<< -recv >> never blocks by setting a callback and
201	calls to C<wait> will return after this method has been called. If nobody	614	only calling C<< ->recv >> from within that callback (or at a later
202	is waiting the broadcast will be remembered..	615	time). This will work even when the event loop does not support blocking
		616	waits otherwise.
203		617
204	Example:	618	=item $bool = $cv->ready
205		619
206	# wait till the result is ready	620	Returns true when the condition is "true", i.e. whether C<send> or
207	my $result_ready = AnyEvent->condvar;	621	C<croak> have been called.
208		622
209	# do something such as adding a timer	623	=item $cb = $cv->cb ($cb->($cv))
210	# or socket watcher the calls $result_ready->broadcast
211	# when the "result" is ready.
212		624
213	$result_ready->wait;	625	This is a mutator function that returns the callback set and optionally
		626	replaces it before doing so.
		627
		628	The callback will be called when the condition becomes "true", i.e. when
		629	C<send> or C<croak> are called, with the only argument being the condition
		630	variable itself. Calling C<recv> inside the callback or at any later time
		631	is guaranteed not to block.
214		632
215	=back	633	=back
216		634
217	=head2 SIGNAL WATCHERS	635	=head1 GLOBAL VARIABLES AND FUNCTIONS
218
219	You can listen for signals using a signal watcher, C<signal> is the signal
220	I<name> without any C<SIG> prefix. Multiple signals events can be clumped
221	together into one callback invocation, and callback invocation might or
222	might not be asynchronous.
223
224	These watchers might use C<%SIG>, so programs overwriting those signals
225	directly will likely not work correctly.
226
227	Example: exit on SIGINT
228
229	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
230
231	=head2 CHILD PROCESS WATCHERS
232
233	You can also listen for the status of a child process specified by the
234	C<pid> argument (or any child if the pid argument is 0). The watcher will
235	trigger as often as status change for the child are received. This works
236	by installing a signal handler for C<SIGCHLD>. The callback will be called with
237	the pid and exit status (as returned by waitpid).
238
239	Example: wait for pid 1333
240
241	my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });
242
243	=head1 GLOBALS
244		636
245	=over 4	637	=over 4
246		638
247	=item $AnyEvent::MODEL	639	=item $AnyEvent::MODEL
248		640
…		…
252	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	644	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
253	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	645	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
254		646
255	The known classes so far are:	647	The known classes so far are:
256		648
257	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
258	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
259	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	649	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
260	AnyEvent::Impl::Event based on Event, also second best choice :)	650	AnyEvent::Impl::Event based on Event, second best choice.
		651	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
261	AnyEvent::Impl::Glib based on Glib, third-best choice.	652	AnyEvent::Impl::Glib based on Glib, third-best choice.
262	AnyEvent::Impl::Tk based on Tk, very bad choice.	653	AnyEvent::Impl::Tk based on Tk, very bad choice.
263	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	654	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		655	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		656	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		657
		658	There is no support for WxWidgets, as WxWidgets has no support for
		659	watching file handles. However, you can use WxWidgets through the
		660	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		661	second, which was considered to be too horrible to even consider for
		662	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		663	it's adaptor.
		664
		665	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		666	autodetecting them.
264		667
265	=item AnyEvent::detect	668	=item AnyEvent::detect
266		669
267	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if	670	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
268	necessary. You should only call this function right before you would have	671	if necessary. You should only call this function right before you would
269	created an AnyEvent watcher anyway, that is, very late at runtime.	672	have created an AnyEvent watcher anyway, that is, as late as possible at
		673	runtime.
		674
		675	=item $guard = AnyEvent::post_detect { BLOCK }
		676
		677	Arranges for the code block to be executed as soon as the event model is
		678	autodetected (or immediately if this has already happened).
		679
		680	If called in scalar or list context, then it creates and returns an object
		681	that automatically removes the callback again when it is destroyed. See
		682	L<Coro::BDB> for a case where this is useful.
		683
		684	=item @AnyEvent::post_detect
		685
		686	If there are any code references in this array (you can C<push> to it
		687	before or after loading AnyEvent), then they will called directly after
		688	the event loop has been chosen.
		689
		690	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		691	if it contains a true value then the event loop has already been detected,
		692	and the array will be ignored.
		693
		694	Best use C<AnyEvent::post_detect { BLOCK }> instead.
270		695
271	=back	696	=back
272		697
273	=head1 WHAT TO DO IN A MODULE	698	=head1 WHAT TO DO IN A MODULE
274		699
275	As a module author, you should "use AnyEvent" and call AnyEvent methods	700	As a module author, you should C<use AnyEvent> and call AnyEvent methods
276	freely, but you should not load a specific event module or rely on it.	701	freely, but you should not load a specific event module or rely on it.
277		702
278	Be careful when you create watchers in the module body - Anyevent will	703	Be careful when you create watchers in the module body - AnyEvent will
279	decide which event module to use as soon as the first method is called, so	704	decide which event module to use as soon as the first method is called, so
280	by calling AnyEvent in your module body you force the user of your module	705	by calling AnyEvent in your module body you force the user of your module
281	to load the event module first.	706	to load the event module first.
282		707
		708	Never call C<< ->recv >> on a condition variable unless you I<know> that
		709	the C<< ->send >> method has been called on it already. This is
		710	because it will stall the whole program, and the whole point of using
		711	events is to stay interactive.
		712
		713	It is fine, however, to call C<< ->recv >> when the user of your module
		714	requests it (i.e. if you create a http request object ad have a method
		715	called C<results> that returns the results, it should call C<< ->recv >>
		716	freely, as the user of your module knows what she is doing. always).
		717
283	=head1 WHAT TO DO IN THE MAIN PROGRAM	718	=head1 WHAT TO DO IN THE MAIN PROGRAM
284		719
285	There will always be a single main program - the only place that should	720	There will always be a single main program - the only place that should
286	dictate which event model to use.	721	dictate which event model to use.
287		722
288	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	723	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
289	do anything special and let AnyEvent decide which implementation to chose.	724	do anything special (it does not need to be event-based) and let AnyEvent
		725	decide which implementation to chose if some module relies on it.
290		726
291	If the main program relies on a specific event model (for example, in Gtk2	727	If the main program relies on a specific event model - for example, in
292	programs you have to rely on either Glib or Glib::Event), you should load	728	Gtk2 programs you have to rely on the Glib module - you should load the
293	it before loading AnyEvent or any module that uses it, generally, as early	729	event module before loading AnyEvent or any module that uses it: generally
294	as possible. The reason is that modules might create watchers when they	730	speaking, you should load it as early as possible. The reason is that
295	are loaded, and AnyEvent will decide on the event model to use as soon as	731	modules might create watchers when they are loaded, and AnyEvent will
296	it creates watchers, and it might chose the wrong one unless you load the	732	decide on the event model to use as soon as it creates watchers, and it
297	correct one yourself.	733	might chose the wrong one unless you load the correct one yourself.
298		734
299	You can chose to use a rather inefficient pure-perl implementation by	735	You can chose to use a pure-perl implementation by loading the
300	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	736	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
301	generally better.	737	everywhere, but letting AnyEvent chose the model is generally better.
		738
		739	=head2 MAINLOOP EMULATION
		740
		741	Sometimes (often for short test scripts, or even standalone programs who
		742	only want to use AnyEvent), you do not want to run a specific event loop.
		743
		744	In that case, you can use a condition variable like this:
		745
		746	AnyEvent->condvar->recv;
		747
		748	This has the effect of entering the event loop and looping forever.
		749
		750	Note that usually your program has some exit condition, in which case
		751	it is better to use the "traditional" approach of storing a condition
		752	variable somewhere, waiting for it, and sending it when the program should
		753	exit cleanly.
		754
		755
		756	=head1 OTHER MODULES
		757
		758	The following is a non-exhaustive list of additional modules that use
		759	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		760	in the same program. Some of the modules come with AnyEvent, some are
		761	available via CPAN.
		762
		763	=over 4
		764
		765	=item L<AnyEvent::Util>
		766
		767	Contains various utility functions that replace often-used but blocking
		768	functions such as C<inet_aton> by event-/callback-based versions.
		769
		770	=item L<AnyEvent::Socket>
		771
		772	Provides various utility functions for (internet protocol) sockets,
		773	addresses and name resolution. Also functions to create non-blocking tcp
		774	connections or tcp servers, with IPv6 and SRV record support and more.
		775
		776	=item L<AnyEvent::Handle>
		777
		778	Provide read and write buffers, manages watchers for reads and writes,
		779	supports raw and formatted I/O, I/O queued and fully transparent and
		780	non-blocking SSL/TLS.
		781
		782	=item L<AnyEvent::DNS>
		783
		784	Provides rich asynchronous DNS resolver capabilities.
		785
		786	=item L<AnyEvent::HTTP>
		787
		788	A simple-to-use HTTP library that is capable of making a lot of concurrent
		789	HTTP requests.
		790
		791	=item L<AnyEvent::HTTPD>
		792
		793	Provides a simple web application server framework.
		794
		795	=item L<AnyEvent::FastPing>
		796
		797	The fastest ping in the west.
		798
		799	=item L<AnyEvent::DBI>
		800
		801	Executes L<DBI> requests asynchronously in a proxy process.
		802
		803	=item L<AnyEvent::AIO>
		804
		805	Truly asynchronous I/O, should be in the toolbox of every event
		806	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		807	together.
		808
		809	=item L<AnyEvent::BDB>
		810
		811	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		812	L<BDB> and AnyEvent together.
		813
		814	=item L<AnyEvent::GPSD>
		815
		816	A non-blocking interface to gpsd, a daemon delivering GPS information.
		817
		818	=item L<AnyEvent::IGS>
		819
		820	A non-blocking interface to the Internet Go Server protocol (used by
		821	L<App::IGS>).
		822
		823	=item L<Net::IRC3>
		824
		825	AnyEvent based IRC client module family.
		826
		827	=item L<Net::XMPP2>
		828
		829	AnyEvent based XMPP (Jabber protocol) module family.
		830
		831	=item L<Net::FCP>
		832
		833	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		834	of AnyEvent.
		835
		836	=item L<Event::ExecFlow>
		837
		838	High level API for event-based execution flow control.
		839
		840	=item L<Coro>
		841
		842	Has special support for AnyEvent via L<Coro::AnyEvent>.
		843
		844	=item L<IO::Lambda>
		845
		846	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		847
		848	=back
302		849
303	=cut	850	=cut
304		851
305	package AnyEvent;	852	package AnyEvent;
306		853
307	no warnings;	854	no warnings;
308	use strict;	855	use strict;
309		856
310	use Carp;	857	use Carp;
311		858
312	our $VERSION = '3.0';	859	our $VERSION = 4.23;
313	our $MODEL;	860	our $MODEL;
314		861
315	our $AUTOLOAD;	862	our $AUTOLOAD;
316	our @ISA;	863	our @ISA;
317		864
		865	our @REGISTRY;
		866
		867	our $WIN32;
		868
		869	BEGIN {
		870	my $win32 = ! ! ($^O =~ /mswin32/i);
		871	eval "sub WIN32(){ $win32 }";
		872	}
		873
318	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	874	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
319		875
320	our @REGISTRY;	876	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		877
		878	{
		879	my $idx;
		880	$PROTOCOL{$_} = ++$idx
		881	for reverse split /\s*,\s*/,
		882	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		883	}
321		884
322	my @models = (	885	my @models = (
323	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
324	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
325	[EV:: => AnyEvent::Impl::EV::],	886	[EV:: => AnyEvent::Impl::EV::],
326	[Event:: => AnyEvent::Impl::Event::],	887	[Event:: => AnyEvent::Impl::Event::],
327	[Glib:: => AnyEvent::Impl::Glib::],
328	[Tk:: => AnyEvent::Impl::Tk::],
329	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	888	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		889	# everything below here will not be autoprobed
		890	# as the pureperl backend should work everywhere
		891	# and is usually faster
		892	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		893	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		894	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		895	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		896	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		897	[Wx:: => AnyEvent::Impl::POE::],
		898	[Prima:: => AnyEvent::Impl::POE::],
330	);	899	);
331		900
332	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	901	our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
		902
		903	our @post_detect;
		904
		905	sub post_detect(&) {
		906	my ($cb) = @_;
		907
		908	if ($MODEL) {
		909	$cb->();
		910
		911	1
		912	} else {
		913	push @post_detect, $cb;
		914
		915	defined wantarray
		916	? bless \$cb, "AnyEvent::Util::PostDetect"
		917	: ()
		918	}
		919	}
		920
		921	sub AnyEvent::Util::PostDetect::DESTROY {
		922	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		923	}
333		924
334	sub detect() {	925	sub detect() {
335	unless ($MODEL) {	926	unless ($MODEL) {
336	no strict 'refs';	927	no strict 'refs';
		928	local $SIG{__DIE__};
		929
		930	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		931	my $model = "AnyEvent::Impl::$1";
		932	if (eval "require $model") {
		933	$MODEL = $model;
		934	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		935	} else {
		936	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		937	}
		938	}
337		939
338	# check for already loaded models	940	# check for already loaded models
		941	unless ($MODEL) {
339	for (@REGISTRY, @models) {	942	for (@REGISTRY, @models) {
340	my ($package, $model) = @$_;	943	my ($package, $model) = @$_;
341	if (${"$package\::VERSION"} > 0) {	944	if (${"$package\::VERSION"} > 0) {
342	if (eval "require $model") {	945	if (eval "require $model") {
343	$MODEL = $model;	946	$MODEL = $model;
344	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	947	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
345	last;	948	last;
		949	}
346	}	950	}
347	}	951	}
		952
		953	unless ($MODEL) {
		954	# try to load a model
		955
		956	for (@REGISTRY, @models) {
		957	my ($package, $model) = @$_;
		958	if (eval "require $package"
		959	and ${"$package\::VERSION"} > 0
		960	and eval "require $model") {
		961	$MODEL = $model;
		962	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		963	last;
		964	}
		965	}
		966
		967	$MODEL
		968	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		969	}
348	}	970	}
349		971
350	unless ($MODEL) {	972	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
351	# try to load a model
352
353	for (@REGISTRY, @models) {
354	my ($package, $model) = @$_;
355	if (eval "require $package"
356	and ${"$package\::VERSION"} > 0
357	and eval "require $model") {
358	$MODEL = $model;
359	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
360	last;
361	}
362	}
363
364	$MODEL
365	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.";
366	}
367		973
368	unshift @ISA, $MODEL;	974	unshift @ISA, $MODEL;
369	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	975
		976	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		977
		978	(shift @post_detect)->() while @post_detect;
370	}	979	}
371		980
372	$MODEL	981	$MODEL
373	}	982	}
374		983
…		…
382		991
383	my $class = shift;	992	my $class = shift;
384	$class->$func (@_);	993	$class->$func (@_);
385	}	994	}
386		995
		996	# utility function to dup a filehandle. this is used by many backends
		997	# to support binding more than one watcher per filehandle (they usually
		998	# allow only one watcher per fd, so we dup it to get a different one).
		999	sub _dupfh($$$$) {
		1000	my ($poll, $fh, $r, $w) = @_;
		1001
		1002	require Fcntl;
		1003
		1004	# cygwin requires the fh mode to be matching, unix doesn't
		1005	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1006	: $poll eq "w" ? ($w, ">")
		1007	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1008
		1009	open my $fh2, "$mode&" . fileno $fh
		1010	or die "cannot dup() filehandle: $!";
		1011
		1012	# we assume CLOEXEC is already set by perl in all important cases
		1013
		1014	($fh2, $rw)
		1015	}
		1016
387	package AnyEvent::Base;	1017	package AnyEvent::Base;
388		1018
		1019	# default implementation for now and time
		1020
		1021	use Time::HiRes ();
		1022
		1023	sub time { Time::HiRes::time }
		1024	sub now { Time::HiRes::time }
		1025
389	# default implementation for ->condvar, ->wait, ->broadcast	1026	# default implementation for ->condvar
390		1027
391	sub condvar {	1028	sub condvar {
392	bless \my $flag, "AnyEvent::Base::CondVar"	1029	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
393	}
394
395	sub AnyEvent::Base::CondVar::broadcast {
396	${$_[0]}++;
397	}
398
399	sub AnyEvent::Base::CondVar::wait {
400	AnyEvent->one_event while !${$_[0]};
401	}	1030	}
402		1031
403	# default implementation for ->signal	1032	# default implementation for ->signal
404		1033
405	our %SIG_CB;	1034	our %SIG_CB;
…		…
421	sub AnyEvent::Base::Signal::DESTROY {	1050	sub AnyEvent::Base::Signal::DESTROY {
422	my ($signal, $cb) = @{$_[0]};	1051	my ($signal, $cb) = @{$_[0]};
423		1052
424	delete $SIG_CB{$signal}{$cb};	1053	delete $SIG_CB{$signal}{$cb};
425		1054
426	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };	1055	delete $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
427	}	1056	}
428		1057
429	# default implementation for ->child	1058	# default implementation for ->child
430		1059
431	our %PID_CB;	1060	our %PID_CB;
…		…
458	or Carp::croak "required option 'pid' is missing";	1087	or Carp::croak "required option 'pid' is missing";
459		1088
460	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1089	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
461		1090
462	unless ($WNOHANG) {	1091	unless ($WNOHANG) {
463	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1092	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
464	}	1093	}
465		1094
466	unless ($CHLD_W) {	1095	unless ($CHLD_W) {
467	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	1096	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
468	# child could be a zombie already, so make at least one round	1097	# child could be a zombie already, so make at least one round
…		…
479	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1108	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
480		1109
481	undef $CHLD_W unless keys %PID_CB;	1110	undef $CHLD_W unless keys %PID_CB;
482	}	1111	}
483		1112
		1113	package AnyEvent::CondVar;
		1114
		1115	our @ISA = AnyEvent::CondVar::Base::;
		1116
		1117	package AnyEvent::CondVar::Base;
		1118
		1119	use overload
		1120	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1121	fallback => 1;
		1122
		1123	sub _send {
		1124	# nop
		1125	}
		1126
		1127	sub send {
		1128	my $cv = shift;
		1129	$cv->{_ae_sent} = [@_];
		1130	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1131	$cv->_send;
		1132	}
		1133
		1134	sub croak {
		1135	$_[0]{_ae_croak} = $_[1];
		1136	$_[0]->send;
		1137	}
		1138
		1139	sub ready {
		1140	$_[0]{_ae_sent}
		1141	}
		1142
		1143	sub _wait {
		1144	AnyEvent->one_event while !$_[0]{_ae_sent};
		1145	}
		1146
		1147	sub recv {
		1148	$_[0]->_wait;
		1149
		1150	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1151	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1152	}
		1153
		1154	sub cb {
		1155	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1156	$_[0]{_ae_cb}
		1157	}
		1158
		1159	sub begin {
		1160	++$_[0]{_ae_counter};
		1161	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1162	}
		1163
		1164	sub end {
		1165	return if --$_[0]{_ae_counter};
		1166	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1167	}
		1168
		1169	# undocumented/compatibility with pre-3.4
		1170	*broadcast = \&send;
		1171	*wait = \&_wait;
		1172
484	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1173	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1174
		1175	This is an advanced topic that you do not normally need to use AnyEvent in
		1176	a module. This section is only of use to event loop authors who want to
		1177	provide AnyEvent compatibility.
485		1178
486	If you need to support another event library which isn't directly	1179	If you need to support another event library which isn't directly
487	supported by AnyEvent, you can supply your own interface to it by	1180	supported by AnyEvent, you can supply your own interface to it by
488	pushing, before the first watcher gets created, the package name of	1181	pushing, before the first watcher gets created, the package name of
489	the event module and the package name of the interface to use onto	1182	the event module and the package name of the interface to use onto
490	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	1183	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
491	AnyEvent.	1184	AnyEvent, so it is reasonably cheap.
492		1185
493	Example:	1186	Example:
494		1187
495	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	1188	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
496		1189
497	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	1190	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
498	package/class when it finds the C<urxvt> package/module is loaded. When	1191	package/class when it finds the C<urxvt> package/module is already loaded.
		1192
499	AnyEvent is loaded and asked to find a suitable event model, it will	1193	When AnyEvent is loaded and asked to find a suitable event model, it
500	first check for the presence of urxvt.	1194	will first check for the presence of urxvt by trying to C<use> the
		1195	C<urxvt::anyevent> module.
501		1196
502	The class should provide implementations for all watcher types (see	1197	The class should provide implementations for all watcher types. See
503	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	1198	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
504	(Source code) and so on for actual examples, use C<perldoc -m	1199	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
505	AnyEvent::Impl::Glib> to see the sources).	1200	see the sources.
506		1201
		1202	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1203	provide suitable (hopefully) replacements.
		1204
507	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	1205	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
508	uses the above line as-is. An interface isn't included in AnyEvent	1206	terminal emulator uses the above line as-is. An interface isn't included
509	because it doesn't make sense outside the embedded interpreter inside	1207	in AnyEvent because it doesn't make sense outside the embedded interpreter
510	I<rxvt-unicode>, and it is updated and maintained as part of the	1208	inside I<rxvt-unicode>, and it is updated and maintained as part of the
511	I<rxvt-unicode> distribution.	1209	I<rxvt-unicode> distribution.
512		1210
513	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1211	I<rxvt-unicode> also cheats a bit by not providing blocking access to
514	condition variables: code blocking while waiting for a condition will	1212	condition variables: code blocking while waiting for a condition will
515	C<die>. This still works with most modules/usages, and blocking calls must	1213	C<die>. This still works with most modules/usages, and blocking calls must
516	not be in an interactive application, so it makes sense.	1214	not be done in an interactive application, so it makes sense.
517		1215
518	=head1 ENVIRONMENT VARIABLES	1216	=head1 ENVIRONMENT VARIABLES
519		1217
520	The following environment variables are used by this module:	1218	The following environment variables are used by this module:
521		1219
522	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	1220	=over 4
523	model gets used.
524		1221
		1222	=item C<PERL_ANYEVENT_VERBOSE>
		1223
		1224	By default, AnyEvent will be completely silent except in fatal
		1225	conditions. You can set this environment variable to make AnyEvent more
		1226	talkative.
		1227
		1228	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1229	conditions, such as not being able to load the event model specified by
		1230	C<PERL_ANYEVENT_MODEL>.
		1231
		1232	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1233	model it chooses.
		1234
		1235	=item C<PERL_ANYEVENT_STRICT>
		1236
		1237	AnyEvent does not do much argument checking by default, as thorough
		1238	argument checking is very costly. Setting this variable to a true value
		1239	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1240	check the arguments passed to most method calls. If it finds any problems
		1241	it will croak.
		1242
		1243	In other words, enables "strict" mode.
		1244
		1245	Unlike C<use strict> it is definitely recommended ot keep it off in
		1246	production.
		1247
		1248	=item C<PERL_ANYEVENT_MODEL>
		1249
		1250	This can be used to specify the event model to be used by AnyEvent, before
		1251	auto detection and -probing kicks in. It must be a string consisting
		1252	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1253	and the resulting module name is loaded and if the load was successful,
		1254	used as event model. If it fails to load AnyEvent will proceed with
		1255	auto detection and -probing.
		1256
		1257	This functionality might change in future versions.
		1258
		1259	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1260	could start your program like this:
		1261
		1262	PERL_ANYEVENT_MODEL=Perl perl ...
		1263
		1264	=item C<PERL_ANYEVENT_PROTOCOLS>
		1265
		1266	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1267	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1268	of auto probing).
		1269
		1270	Must be set to a comma-separated list of protocols or address families,
		1271	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1272	used, and preference will be given to protocols mentioned earlier in the
		1273	list.
		1274
		1275	This variable can effectively be used for denial-of-service attacks
		1276	against local programs (e.g. when setuid), although the impact is likely
		1277	small, as the program has to handle connection errors already-
		1278
		1279	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1280	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1281	- only support IPv4, never try to resolve or contact IPv6
		1282	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1283	IPv6, but prefer IPv6 over IPv4.
		1284
		1285	=item C<PERL_ANYEVENT_EDNS0>
		1286
		1287	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1288	for DNS. This extension is generally useful to reduce DNS traffic, but
		1289	some (broken) firewalls drop such DNS packets, which is why it is off by
		1290	default.
		1291
		1292	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1293	EDNS0 in its DNS requests.
		1294
		1295	=item C<PERL_ANYEVENT_MAX_FORKS>
		1296
		1297	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1298	will create in parallel.
		1299
		1300	=back
		1301
525	=head1 EXAMPLE	1302	=head1 EXAMPLE PROGRAM
526		1303
527	The following program uses an io watcher to read data from stdin, a timer	1304	The following program uses an I/O watcher to read data from STDIN, a timer
528	to display a message once per second, and a condvar to exit the program	1305	to display a message once per second, and a condition variable to quit the
529	when the user enters quit:	1306	program when the user enters quit:
530		1307
531	use AnyEvent;	1308	use AnyEvent;
532		1309
533	my $cv = AnyEvent->condvar;	1310	my $cv = AnyEvent->condvar;
534		1311
535	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1312	my $io_watcher = AnyEvent->io (
		1313	fh => \*STDIN,
		1314	poll => 'r',
		1315	cb => sub {
536	warn "io event <$_[0]>\n"; # will always output <r>	1316	warn "io event <$_[0]>\n"; # will always output <r>
537	chomp (my $input = <STDIN>); # read a line	1317	chomp (my $input = <STDIN>); # read a line
538	warn "read: $input\n"; # output what has been read	1318	warn "read: $input\n"; # output what has been read
539	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1319	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1320	},
540	});	1321	);
541		1322
542	my $time_watcher; # can only be used once	1323	my $time_watcher; # can only be used once
543		1324
544	sub new_timer {	1325	sub new_timer {
545	$timer = AnyEvent->timer (after => 1, cb => sub {	1326	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
548	});	1329	});
549	}	1330	}
550		1331
551	new_timer; # create first timer	1332	new_timer; # create first timer
552		1333
553	$cv->wait; # wait until user enters /^q/i	1334	$cv->recv; # wait until user enters /^q/i
554		1335
555	=head1 REAL-WORLD EXAMPLE	1336	=head1 REAL-WORLD EXAMPLE
556		1337
557	Consider the L<Net::FCP> module. It features (among others) the following	1338	Consider the L<Net::FCP> module. It features (among others) the following
558	API calls, which are to freenet what HTTP GET requests are to http:	1339	API calls, which are to freenet what HTTP GET requests are to http:
…		…
608	syswrite $txn->{fh}, $txn->{request}	1389	syswrite $txn->{fh}, $txn->{request}
609	or die "connection or write error";	1390	or die "connection or write error";
610	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1391	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
611		1392
612	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1393	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
613	result and signals any possible waiters that the request ahs finished:	1394	result and signals any possible waiters that the request has finished:
614		1395
615	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1396	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
616		1397
617	if (end-of-file or data complete) {	1398	if (end-of-file or data complete) {
618	$txn->{result} = $txn->{buf};	1399	$txn->{result} = $txn->{buf};
619	$txn->{finished}->broadcast;	1400	$txn->{finished}->send;
620	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1401	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
621	}	1402	}
622		1403
623	The C<result> method, finally, just waits for the finished signal (if the	1404	The C<result> method, finally, just waits for the finished signal (if the
624	request was already finished, it doesn't wait, of course, and returns the	1405	request was already finished, it doesn't wait, of course, and returns the
625	data:	1406	data:
626		1407
627	$txn->{finished}->wait;	1408	$txn->{finished}->recv;
628	return $txn->{result};	1409	return $txn->{result};
629		1410
630	The actual code goes further and collects all errors (C<die>s, exceptions)	1411	The actual code goes further and collects all errors (C<die>s, exceptions)
631	that occured during request processing. The C<result> method detects	1412	that occurred during request processing. The C<result> method detects
632	wether an exception as thrown (it is stored inside the $txn object)	1413	whether an exception as thrown (it is stored inside the $txn object)
633	and just throws the exception, which means connection errors and other	1414	and just throws the exception, which means connection errors and other
634	problems get reported tot he code that tries to use the result, not in a	1415	problems get reported tot he code that tries to use the result, not in a
635	random callback.	1416	random callback.
636		1417
637	All of this enables the following usage styles:	1418	All of this enables the following usage styles:
…		…
667		1448
668	my $quit = AnyEvent->condvar;	1449	my $quit = AnyEvent->condvar;
669		1450
670	$fcp->txn_client_get ($url)->cb (sub {	1451	$fcp->txn_client_get ($url)->cb (sub {
671	...	1452	...
672	$quit->broadcast;	1453	$quit->send;
673	});	1454	});
674		1455
675	$quit->wait;	1456	$quit->recv;
		1457
		1458
		1459	=head1 BENCHMARKS
		1460
		1461	To give you an idea of the performance and overheads that AnyEvent adds
		1462	over the event loops themselves and to give you an impression of the speed
		1463	of various event loops I prepared some benchmarks.
		1464
		1465	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1466
		1467	Here is a benchmark of various supported event models used natively and
		1468	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1469	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1470	which it is), lets them fire exactly once and destroys them again.
		1471
		1472	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1473	distribution.
		1474
		1475	=head3 Explanation of the columns
		1476
		1477	I<watcher> is the number of event watchers created/destroyed. Since
		1478	different event models feature vastly different performances, each event
		1479	loop was given a number of watchers so that overall runtime is acceptable
		1480	and similar between tested event loop (and keep them from crashing): Glib
		1481	would probably take thousands of years if asked to process the same number
		1482	of watchers as EV in this benchmark.
		1483
		1484	I<bytes> is the number of bytes (as measured by the resident set size,
		1485	RSS) consumed by each watcher. This method of measuring captures both C
		1486	and Perl-based overheads.
		1487
		1488	I<create> is the time, in microseconds (millionths of seconds), that it
		1489	takes to create a single watcher. The callback is a closure shared between
		1490	all watchers, to avoid adding memory overhead. That means closure creation
		1491	and memory usage is not included in the figures.
		1492
		1493	I<invoke> is the time, in microseconds, used to invoke a simple
		1494	callback. The callback simply counts down a Perl variable and after it was
		1495	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1496	signal the end of this phase.
		1497
		1498	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1499	watcher.
		1500
		1501	=head3 Results
		1502
		1503	name watchers bytes create invoke destroy comment
		1504	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1505	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1506	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1507	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1508	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1509	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1510	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1511	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1512	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1513	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1514
		1515	=head3 Discussion
		1516
		1517	The benchmark does I<not> measure scalability of the event loop very
		1518	well. For example, a select-based event loop (such as the pure perl one)
		1519	can never compete with an event loop that uses epoll when the number of
		1520	file descriptors grows high. In this benchmark, all events become ready at
		1521	the same time, so select/poll-based implementations get an unnatural speed
		1522	boost.
		1523
		1524	Also, note that the number of watchers usually has a nonlinear effect on
		1525	overall speed, that is, creating twice as many watchers doesn't take twice
		1526	the time - usually it takes longer. This puts event loops tested with a
		1527	higher number of watchers at a disadvantage.
		1528
		1529	To put the range of results into perspective, consider that on the
		1530	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1531	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1532	cycles with POE.
		1533
		1534	C<EV> is the sole leader regarding speed and memory use, which are both
		1535	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1536	far less memory than any other event loop and is still faster than Event
		1537	natively.
		1538
		1539	The pure perl implementation is hit in a few sweet spots (both the
		1540	constant timeout and the use of a single fd hit optimisations in the perl
		1541	interpreter and the backend itself). Nevertheless this shows that it
		1542	adds very little overhead in itself. Like any select-based backend its
		1543	performance becomes really bad with lots of file descriptors (and few of
		1544	them active), of course, but this was not subject of this benchmark.
		1545
		1546	The C<Event> module has a relatively high setup and callback invocation
		1547	cost, but overall scores in on the third place.
		1548
		1549	C<Glib>'s memory usage is quite a bit higher, but it features a
		1550	faster callback invocation and overall ends up in the same class as
		1551	C<Event>. However, Glib scales extremely badly, doubling the number of
		1552	watchers increases the processing time by more than a factor of four,
		1553	making it completely unusable when using larger numbers of watchers
		1554	(note that only a single file descriptor was used in the benchmark, so
		1555	inefficiencies of C<poll> do not account for this).
		1556
		1557	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1558	more than 2000 watchers is a big setback, however, as correctness takes
		1559	precedence over speed. Nevertheless, its performance is surprising, as the
		1560	file descriptor is dup()ed for each watcher. This shows that the dup()
		1561	employed by some adaptors is not a big performance issue (it does incur a
		1562	hidden memory cost inside the kernel which is not reflected in the figures
		1563	above).
		1564
		1565	C<POE>, regardless of underlying event loop (whether using its pure perl
		1566	select-based backend or the Event module, the POE-EV backend couldn't
		1567	be tested because it wasn't working) shows abysmal performance and
		1568	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1569	as EV watchers, and 10 times as much memory as Event (the high memory
		1570	requirements are caused by requiring a session for each watcher). Watcher
		1571	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1572	implementation.
		1573
		1574	The design of the POE adaptor class in AnyEvent can not really account
		1575	for the performance issues, though, as session creation overhead is
		1576	small compared to execution of the state machine, which is coded pretty
		1577	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1578	using multiple sessions is not a good approach, especially regarding
		1579	memory usage, even the author of POE could not come up with a faster
		1580	design).
		1581
		1582	=head3 Summary
		1583
		1584	=over 4
		1585
		1586	=item * Using EV through AnyEvent is faster than any other event loop
		1587	(even when used without AnyEvent), but most event loops have acceptable
		1588	performance with or without AnyEvent.
		1589
		1590	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1591	the actual event loop, only with extremely fast event loops such as EV
		1592	adds AnyEvent significant overhead.
		1593
		1594	=item * You should avoid POE like the plague if you want performance or
		1595	reasonable memory usage.
		1596
		1597	=back
		1598
		1599	=head2 BENCHMARKING THE LARGE SERVER CASE
		1600
		1601	This benchmark actually benchmarks the event loop itself. It works by
		1602	creating a number of "servers": each server consists of a socket pair, a
		1603	timeout watcher that gets reset on activity (but never fires), and an I/O
		1604	watcher waiting for input on one side of the socket. Each time the socket
		1605	watcher reads a byte it will write that byte to a random other "server".
		1606
		1607	The effect is that there will be a lot of I/O watchers, only part of which
		1608	are active at any one point (so there is a constant number of active
		1609	fds for each loop iteration, but which fds these are is random). The
		1610	timeout is reset each time something is read because that reflects how
		1611	most timeouts work (and puts extra pressure on the event loops).
		1612
		1613	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1614	(1%) are active. This mirrors the activity of large servers with many
		1615	connections, most of which are idle at any one point in time.
		1616
		1617	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1618	distribution.
		1619
		1620	=head3 Explanation of the columns
		1621
		1622	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1623	each server has a read and write socket end).
		1624
		1625	I<create> is the time it takes to create a socket pair (which is
		1626	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1627
		1628	I<request>, the most important value, is the time it takes to handle a
		1629	single "request", that is, reading the token from the pipe and forwarding
		1630	it to another server. This includes deleting the old timeout and creating
		1631	a new one that moves the timeout into the future.
		1632
		1633	=head3 Results
		1634
		1635	name sockets create request
		1636	EV 20000 69.01 11.16
		1637	Perl 20000 73.32 35.87
		1638	Event 20000 212.62 257.32
		1639	Glib 20000 651.16 1896.30
		1640	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1641
		1642	=head3 Discussion
		1643
		1644	This benchmark I<does> measure scalability and overall performance of the
		1645	particular event loop.
		1646
		1647	EV is again fastest. Since it is using epoll on my system, the setup time
		1648	is relatively high, though.
		1649
		1650	Perl surprisingly comes second. It is much faster than the C-based event
		1651	loops Event and Glib.
		1652
		1653	Event suffers from high setup time as well (look at its code and you will
		1654	understand why). Callback invocation also has a high overhead compared to
		1655	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1656	uses select or poll in basically all documented configurations.
		1657
		1658	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1659	clearly fails to perform with many filehandles or in busy servers.
		1660
		1661	POE is still completely out of the picture, taking over 1000 times as long
		1662	as EV, and over 100 times as long as the Perl implementation, even though
		1663	it uses a C-based event loop in this case.
		1664
		1665	=head3 Summary
		1666
		1667	=over 4
		1668
		1669	=item * The pure perl implementation performs extremely well.
		1670
		1671	=item * Avoid Glib or POE in large projects where performance matters.
		1672
		1673	=back
		1674
		1675	=head2 BENCHMARKING SMALL SERVERS
		1676
		1677	While event loops should scale (and select-based ones do not...) even to
		1678	large servers, most programs we (or I :) actually write have only a few
		1679	I/O watchers.
		1680
		1681	In this benchmark, I use the same benchmark program as in the large server
		1682	case, but it uses only eight "servers", of which three are active at any
		1683	one time. This should reflect performance for a small server relatively
		1684	well.
		1685
		1686	The columns are identical to the previous table.
		1687
		1688	=head3 Results
		1689
		1690	name sockets create request
		1691	EV 16 20.00 6.54
		1692	Perl 16 25.75 12.62
		1693	Event 16 81.27 35.86
		1694	Glib 16 32.63 15.48
		1695	POE 16 261.87 276.28 uses POE::Loop::Event
		1696
		1697	=head3 Discussion
		1698
		1699	The benchmark tries to test the performance of a typical small
		1700	server. While knowing how various event loops perform is interesting, keep
		1701	in mind that their overhead in this case is usually not as important, due
		1702	to the small absolute number of watchers (that is, you need efficiency and
		1703	speed most when you have lots of watchers, not when you only have a few of
		1704	them).
		1705
		1706	EV is again fastest.
		1707
		1708	Perl again comes second. It is noticeably faster than the C-based event
		1709	loops Event and Glib, although the difference is too small to really
		1710	matter.
		1711
		1712	POE also performs much better in this case, but is is still far behind the
		1713	others.
		1714
		1715	=head3 Summary
		1716
		1717	=over 4
		1718
		1719	=item * C-based event loops perform very well with small number of
		1720	watchers, as the management overhead dominates.
		1721
		1722	=back
		1723
		1724
		1725	=head1 FORK
		1726
		1727	Most event libraries are not fork-safe. The ones who are usually are
		1728	because they rely on inefficient but fork-safe C<select> or C<poll>
		1729	calls. Only L<EV> is fully fork-aware.
		1730
		1731	If you have to fork, you must either do so I<before> creating your first
		1732	watcher OR you must not use AnyEvent at all in the child.
		1733
		1734
		1735	=head1 SECURITY CONSIDERATIONS
		1736
		1737	AnyEvent can be forced to load any event model via
		1738	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1739	execute arbitrary code or directly gain access, it can easily be used to
		1740	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1741	will not be active when the program uses a different event model than
		1742	specified in the variable.
		1743
		1744	You can make AnyEvent completely ignore this variable by deleting it
		1745	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1746
		1747	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1748
		1749	use AnyEvent;
		1750
		1751	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1752	be used to probe what backend is used and gain other information (which is
		1753	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		1754	$ENV{PERL_ANYEGENT_STRICT}.
		1755
		1756
		1757	=head1 BUGS
		1758
		1759	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		1760	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		1761	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		1762	mamleaks, such as leaking on C<map> and C<grep> but it is usually not as
		1763	pronounced).
		1764
676		1765
677	=head1 SEE ALSO	1766	=head1 SEE ALSO
678		1767
679	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1768	Utility functions: L<AnyEvent::Util>.
680	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.
681		1769
682	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	1770	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1771	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1772
683	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,	1773	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
684	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.	1774	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1775	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1776	L<AnyEvent::Impl::POE>.
685		1777
		1778	Non-blocking file handles, sockets, TCP clients and
		1779	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1780
		1781	Asynchronous DNS: L<AnyEvent::DNS>.
		1782
		1783	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1784
686	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1785	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
687		1786
688	=head1	1787
		1788	=head1 AUTHOR
		1789
		1790	Marc Lehmann <schmorp@schmorp.de>
		1791	http://home.schmorp.de/
689		1792
690	=cut	1793	=cut
691		1794
692	1	1795	1
693		1796

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