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…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - provide framework for multiple event loops
3		3
4	Event, Coro, Glib, Tk, Perl - various supported event loops	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
		5	loops
5		6
6	SYNOPSIS	7	SYNOPSIS
7	use AnyEvent;	8	use AnyEvent;
8		9
9	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {
12		13
13	my $w = AnyEvent->timer (after => $seconds, cb => sub {	14	my $w = AnyEvent->timer (after => $seconds, cb => sub {
14	...	15	...
15	});	16	});
16		17
17	my $w = AnyEvent->condvar; # stores wether a condition was flagged	18	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		19	$w->send; # wake up current and all future recv's
18	$w->wait; # enters "main loop" till $condvar gets ->broadcast	20	$w->recv; # enters "main loop" till $condvar gets ->send
19	$w->broadcast; # wake up current and all future wait's	21
		22	INTRODUCTION/TUTORIAL
		23	This manpage is mainly a reference manual. If you are interested in a
		24	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		25	manpage.
		26
		27	WHY YOU SHOULD USE THIS MODULE (OR NOT)
		28	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		29	nowadays. So what is different about AnyEvent?
		30
		31	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
		32	policy* and AnyEvent is small and efficient.
		33
		34	First and foremost, AnyEvent is not an event model itself, it only
		35	interfaces to whatever event model the main program happens to use in a
		36	pragmatic way. For event models and certain classes of immortals alike,
		37	the statement "there can only be one" is a bitter reality: In general,
		38	only one event loop can be active at the same time in a process.
		39	AnyEvent helps hiding the differences between those event loops.
		40
		41	The goal of AnyEvent is to offer module authors the ability to do event
		42	programming (waiting for I/O or timer events) without subscribing to a
		43	religion, a way of living, and most importantly: without forcing your
		44	module users into the same thing by forcing them to use the same event
		45	model you use.
		46
		47	For modules like POE or IO::Async (which is a total misnomer as it is
		48	actually doing all I/O synchronously...), using them in your module is
		49	like joining a cult: After you joined, you are dependent on them and you
		50	cannot use anything else, as it is simply incompatible to everything
		51	that isn't itself. What's worse, all the potential users of your module
		52	are also forced to use the same event loop you use.
		53
		54	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		55	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		56	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
		57	module uses one of those, every user of your module has to use it, too.
		58	But if your module uses AnyEvent, it works transparently with all event
		59	models it supports (including stuff like POE and IO::Async, as long as
		60	those use one of the supported event loops. It is trivial to add new
		61	event loops to AnyEvent, too, so it is future-proof).
		62
		63	In addition to being free of having to use *the one and only true event
		64	model*, AnyEvent also is free of bloat and policy: with POE or similar
		65	modules, you get an enormous amount of code and strict rules you have to
		66	follow. AnyEvent, on the other hand, is lean and up to the point, by
		67	only offering the functionality that is necessary, in as thin as a
		68	wrapper as technically possible.
		69
		70	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
		71	useful functionality, such as an asynchronous DNS resolver, 100%
		72	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		73	such as Windows) and lots of real-world knowledge and workarounds for
		74	platform bugs and differences.
		75
		76	Now, if you do want lots of policy (this can arguably be somewhat
		77	useful) and you want to force your users to use the one and only event
		78	model, you should not use this module.
20		79
21	DESCRIPTION	80	DESCRIPTION
22	AnyEvent provides an identical interface to multiple event loops. This	81	AnyEvent provides an identical interface to multiple event loops. This
23	allows module authors to utilise an event loop without forcing module	82	allows module authors to utilise an event loop without forcing module
24	users to use the same event loop (as only a single event loop can	83	users to use the same event loop (as only a single event loop can
25	coexist peacefully at any one time).	84	coexist peacefully at any one time).
26		85
27	The interface itself is vaguely similar but not identical to the Event	86	The interface itself is vaguely similar, but not identical to the Event
28	module.	87	module.
29		88
30	On the first call of any method, the module tries to detect the	89	During the first call of any watcher-creation method, the module tries
31	currently loaded event loop by probing wether any of the following	90	to detect the currently loaded event loop by probing whether one of the
32	modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is	91	following modules is already loaded: EV, Event, Glib,
		92	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
33	used. If none is found, the module tries to load these modules in the	93	used. If none are found, the module tries to load these modules
34	order given. The first one that could be successfully loaded will be	94	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
35	used. If still none could be found, AnyEvent will fall back to a	95	always succeed) in the order given. The first one that can be
36	pure-perl event loop, which is also not very efficient.	96	successfully loaded will be used. If, after this, still none could be
		97	found, AnyEvent will fall back to a pure-perl event loop, which is not
		98	very efficient, but should work everywhere.
37		99
38	Because AnyEvent first checks for modules that are already loaded,	100	Because AnyEvent first checks for modules that are already loaded,
39	loading an Event model explicitly before first using AnyEvent will	101	loading an event model explicitly before first using AnyEvent will
40	likely make that model the default. For example:	102	likely make that model the default. For example:
41		103
42	use Tk;	104	use Tk;
43	use AnyEvent;	105	use AnyEvent;
44		106
45	# .. AnyEvent will likely default to Tk	107	# .. AnyEvent will likely default to Tk
46		108
		109	The likely means that, if any module loads another event model and
		110	starts using it, all bets are off. Maybe you should tell their authors
		111	to use AnyEvent so their modules work together with others seamlessly...
		112
47	The pure-perl implementation of AnyEvent is called	113	The pure-perl implementation of AnyEvent is called
48	"AnyEvent::Impl::Perl". Like other event modules you can load it	114	"AnyEvent::Impl::Perl". Like other event modules you can load it
49	explicitly.	115	explicitly and enjoy the high availability of that event loop :)
50		116
51	WATCHERS	117	WATCHERS
52	AnyEvent has the central concept of a watcher, which is an object that	118	AnyEvent has the central concept of a watcher, which is an object that
53	stores relevant data for each kind of event you are waiting for, such as	119	stores relevant data for each kind of event you are waiting for, such as
54	the callback to call, the filehandle to watch, etc.	120	the callback to call, the file handle to watch, etc.
55		121
56	These watchers are normal Perl objects with normal Perl lifetime. After	122	These watchers are normal Perl objects with normal Perl lifetime. After
57	creating a watcher it will immediately "watch" for events and invoke the	123	creating a watcher it will immediately "watch" for events and invoke the
		124	callback when the event occurs (of course, only when the event model is
		125	in control).
		126
58	callback. To disable the watcher you have to destroy it (e.g. by setting	127	To disable the watcher you have to destroy it (e.g. by setting the
59	the variable that stores it to "undef" or otherwise deleting all	128	variable you store it in to "undef" or otherwise deleting all references
60	references to it).	129	to it).
61		130
62	All watchers are created by calling a method on the "AnyEvent" class.	131	All watchers are created by calling a method on the "AnyEvent" class.
63		132
		133	Many watchers either are used with "recursion" (repeating timers for
		134	example), or need to refer to their watcher object in other ways.
		135
		136	An any way to achieve that is this pattern:
		137
		138	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		139	# you can use $w here, for example to undef it
		140	undef $w;
		141	});
		142
		143	Note that "my $w; $w =" combination. This is necessary because in Perl,
		144	my variables are only visible after the statement in which they are
		145	declared.
		146
64	IO WATCHERS	147	I/O WATCHERS
65	You can create I/O watcher by calling the "AnyEvent->io" method with the	148	You can create an I/O watcher by calling the "AnyEvent->io" method with
66	following mandatory arguments:	149	the following mandatory key-value pairs as arguments:
67		150
68	"fh" the Perl filehandle (not filedescriptor) to watch for events.	151	"fh" the Perl file handle (not file descriptor) to watch for events.
69	"poll" must be a string that is either "r" or "w", that creates a	152	"poll" must be a string that is either "r" or "w", which creates a
70	watcher waiting for "r"eadable or "w"ritable events. "cb" teh callback	153	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
71	to invoke everytime the filehandle becomes ready.	154	is the callback to invoke each time the file handle becomes ready.
72		155
73	Only one io watcher per "fh" and "poll" combination is allowed (i.e. on	156	Although the callback might get passed parameters, their value and
74	a socket you can have one r + one w, not any more (limitation comes from	157	presence is undefined and you cannot rely on them. Portable AnyEvent
75	Tk - if you are sure you are not using Tk this limitation is gone).	158	callbacks cannot use arguments passed to I/O watcher callbacks.
76		159
77	Filehandles will be kept alive, so as long as the watcher exists, the	160	The I/O watcher might use the underlying file descriptor or a copy of
78	filehandle exists, too.	161	it. You must not close a file handle as long as any watcher is active on
		162	the underlying file descriptor.
		163
		164	Some event loops issue spurious readyness notifications, so you should
		165	always use non-blocking calls when reading/writing from/to your file
		166	handles.
79		167
80	Example:	168	Example:
81		169
82	# wait for readability of STDIN, then read a line and disable the watcher	170	# wait for readability of STDIN, then read a line and disable the watcher
83	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	171	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
…		…
88		176
89	TIME WATCHERS	177	TIME WATCHERS
90	You can create a time watcher by calling the "AnyEvent->timer" method	178	You can create a time watcher by calling the "AnyEvent->timer" method
91	with the following mandatory arguments:	179	with the following mandatory arguments:
92		180
93	"after" after how many seconds (fractions are supported) should the	181	"after" specifies after how many seconds (fractional values are
94	timer activate. "cb" the callback to invoke.	182	supported) the callback should be invoked. "cb" is the callback to
		183	invoke in that case.
		184
		185	Although the callback might get passed parameters, their value and
		186	presence is undefined and you cannot rely on them. Portable AnyEvent
		187	callbacks cannot use arguments passed to time watcher callbacks.
95		188
96	The timer callback will be invoked at most once: if you want a repeating	189	The timer callback will be invoked at most once: if you want a repeating
97	timer you have to create a new watcher (this is a limitation by both Tk	190	timer you have to create a new watcher (this is a limitation by both Tk
98	and Glib).	191	and Glib).
99		192
…		…
103	my $w = AnyEvent->timer (after => 7.7, cb => sub {	196	my $w = AnyEvent->timer (after => 7.7, cb => sub {
104	warn "timeout\n";	197	warn "timeout\n";
105	});	198	});
106		199
107	# to cancel the timer:	200	# to cancel the timer:
108	undef $w	201	undef $w;
109		202
110	CONDITION WATCHERS
111	Condition watchers can be created by calling the "AnyEvent->condvar"
112	method without any arguments.
113
114	A condition watcher watches for a condition - precisely that the
115	"->broadcast" method has been called.
116
117	The watcher has only two methods:
118
119	$cv->wait
120	Wait (blocking if necessary) until the "->broadcast" method has been
121	called on c<$cv>, while servicing other watchers normally.
122
123	Not all event models support a blocking wait - some die in that
124	case, so if you are using this from a module, never require a
125	blocking wait, but let the caller decide wether the call will block
126	or not (for example, by coupling condition variables with some kind
127	of request results and supporting callbacks so the caller knows that
128	getting the result will not block, while still suppporting blockign
129	waits if the caller so desires).
130
131	You can only wait once on a condition - additional calls will return
132	immediately.
133
134	$cv->broadcast
135	Flag the condition as ready - a running "->wait" and all further
136	calls to "wait" will return after this method has been called. If
137	nobody is waiting the broadcast will be remembered..
138
139	Example:	203	Example 2:
140		204
141	# wait till the result is ready	205	# fire an event after 0.5 seconds, then roughly every second
142	my $result_ready = AnyEvent->condvar;	206	my $w;
143		207
144	# do something such as adding a timer	208	my $cb = sub {
145	# or socket watcher the calls $result_ready->broadcast	209	# cancel the old timer while creating a new one
146	# when the "result" is ready.	210	$w = AnyEvent->timer (after => 1, cb => $cb);
		211	};
147		212
148	$result_ready->wait;	213	# start the "loop" by creating the first watcher
		214	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		215
		216	TIMING ISSUES
		217	There are two ways to handle timers: based on real time (relative, "fire
		218	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		219	o'clock").
		220
		221	While most event loops expect timers to specified in a relative way,
		222	they use absolute time internally. This makes a difference when your
		223	clock "jumps", for example, when ntp decides to set your clock backwards
		224	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
		225	supposed to fire "after" a second might actually take six years to
		226	finally fire.
		227
		228	AnyEvent cannot compensate for this. The only event loop that is
		229	conscious about these issues is EV, which offers both relative
		230	(ev_timer, based on true relative time) and absolute (ev_periodic, based
		231	on wallclock time) timers.
		232
		233	AnyEvent always prefers relative timers, if available, matching the
		234	AnyEvent API.
		235
		236	AnyEvent has two additional methods that return the "current time":
		237
		238	AnyEvent->time
		239	This returns the "current wallclock time" as a fractional number of
		240	seconds since the Epoch (the same thing as "time" or
		241	"Time::HiRes::time" return, and the result is guaranteed to be
		242	compatible with those).
		243
		244	It progresses independently of any event loop processing, i.e. each
		245	call will check the system clock, which usually gets updated
		246	frequently.
		247
		248	AnyEvent->now
		249	This also returns the "current wallclock time", but unlike "time",
		250	above, this value might change only once per event loop iteration,
		251	depending on the event loop (most return the same time as "time",
		252	above). This is the time that AnyEvent's timers get scheduled
		253	against.
		254
		255	*In almost all cases (in all cases if you don't care), this is the
		256	function to call when you want to know the current time.*
		257
		258	This function is also often faster then "AnyEvent->time", and thus
		259	the preferred method if you want some timestamp (for example,
		260	AnyEvent::Handle uses this to update it's activity timeouts).
		261
		262	The rest of this section is only of relevance if you try to be very
		263	exact with your timing, you can skip it without bad conscience.
		264
		265	For a practical example of when these times differ, consider
		266	Event::Lib and EV and the following set-up:
		267
		268	The event loop is running and has just invoked one of your callback
		269	at time=500 (assume no other callbacks delay processing). In your
		270	callback, you wait a second by executing "sleep 1" (blocking the
		271	process for a second) and then (at time=501) you create a relative
		272	timer that fires after three seconds.
		273
		274	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		275	return 501, because that is the current time, and the timer will be
		276	scheduled to fire at time=504 (501 + 3).
		277
		278	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		279	but "AnyEvent->now" returns 500, as that is the time the last event
		280	processing phase started. With EV, your timer gets scheduled to run
		281	at time=503 (500 + 3).
		282
		283	In one sense, Event::Lib is more exact, as it uses the current time
		284	regardless of any delays introduced by event processing. However,
		285	most callbacks do not expect large delays in processing, so this
		286	causes a higher drift (and a lot more system calls to get the
		287	current time).
		288
		289	In another sense, EV is more exact, as your timer will be scheduled
		290	at the same time, regardless of how long event processing actually
		291	took.
		292
		293	In either case, if you care (and in most cases, you don't), then you
		294	can get whatever behaviour you want with any event loop, by taking
		295	the difference between "AnyEvent->time" and "AnyEvent->now" into
		296	account.
149		297
150	SIGNAL WATCHERS	298	SIGNAL WATCHERS
151	You can listen for signals using a signal watcher, "signal" is the	299	You can watch for signals using a signal watcher, "signal" is the signal
152	signal name without any "SIG" prefix. Multiple signals events can be	300	name without any "SIG" prefix, "cb" is the Perl callback to be invoked
153	clumped together into one callback invocation, and callback invocation	301	whenever a signal occurs.
154	might or might not be asynchronous.
155		302
		303	Although the callback might get passed parameters, their value and
		304	presence is undefined and you cannot rely on them. Portable AnyEvent
		305	callbacks cannot use arguments passed to signal watcher callbacks.
		306
		307	Multiple signal occurrences can be clumped together into one callback
		308	invocation, and callback invocation will be synchronous. Synchronous
		309	means that it might take a while until the signal gets handled by the
		310	process, but it is guaranteed not to interrupt any other callbacks.
		311
		312	The main advantage of using these watchers is that you can share a
		313	signal between multiple watchers.
		314
156	These watchers might use %SIG, so programs overwriting those signals	315	This watcher might use %SIG, so programs overwriting those signals
157	directly will likely not work correctly.	316	directly will likely not work correctly.
158		317
159	Example: exit on SIGINT	318	Example: exit on SIGINT
160		319
161	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	320	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
162		321
163	CHILD PROCESS WATCHERS	322	CHILD PROCESS WATCHERS
164	You can also listen for the status of a child process specified by the	323	You can also watch on a child process exit and catch its exit status.
165	"pid" argument. The watcher will only trigger once. This works by
166	installing a signal handler for "SIGCHLD".
167		324
		325	The child process is specified by the "pid" argument (if set to 0, it
		326	watches for any child process exit). The watcher will trigger as often
		327	as status change for the child are received. This works by installing a
		328	signal handler for "SIGCHLD". The callback will be called with the pid
		329	and exit status (as returned by waitpid), so unlike other watcher types,
		330	you can rely on child watcher callback arguments.
		331
		332	There is a slight catch to child watchers, however: you usually start
		333	them after the child process was created, and this means the process
		334	could have exited already (and no SIGCHLD will be sent anymore).
		335
		336	Not all event models handle this correctly (POE doesn't), but even for
		337	event models that do handle this correctly, they usually need to be
		338	loaded before the process exits (i.e. before you fork in the first
		339	place).
		340
		341	This means you cannot create a child watcher as the very first thing in
		342	an AnyEvent program, you have to create at least one watcher before
		343	you "fork" the child (alternatively, you can call "AnyEvent::detect").
		344
		345	Example: fork a process and wait for it
		346
		347	my $done = AnyEvent->condvar;
		348
		349	my $pid = fork or exit 5;
		350
		351	my $w = AnyEvent->child (
		352	pid => $pid,
		353	cb => sub {
		354	my ($pid, $status) = @_;
		355	warn "pid $pid exited with status $status";
		356	$done->send;
		357	},
		358	);
		359
		360	# do something else, then wait for process exit
		361	$done->recv;
		362
		363	CONDITION VARIABLES
		364	If you are familiar with some event loops you will know that all of them
		365	require you to run some blocking "loop", "run" or similar function that
		366	will actively watch for new events and call your callbacks.
		367
		368	AnyEvent is different, it expects somebody else to run the event loop
		369	and will only block when necessary (usually when told by the user).
		370
		371	The instrument to do that is called a "condition variable", so called
		372	because they represent a condition that must become true.
		373
		374	Condition variables can be created by calling the "AnyEvent->condvar"
		375	method, usually without arguments. The only argument pair allowed is
		376	"cb", which specifies a callback to be called when the condition
		377	variable becomes true.
		378
		379	After creation, the condition variable is "false" until it becomes
		380	"true" by calling the "send" method (or calling the condition variable
		381	as if it were a callback, read about the caveats in the description for
		382	the "->send" method).
		383
		384	Condition variables are similar to callbacks, except that you can
		385	optionally wait for them. They can also be called merge points - points
		386	in time where multiple outstanding events have been processed. And yet
		387	another way to call them is transactions - each condition variable can
		388	be used to represent a transaction, which finishes at some point and
		389	delivers a result.
		390
		391	Condition variables are very useful to signal that something has
		392	finished, for example, if you write a module that does asynchronous http
		393	requests, then a condition variable would be the ideal candidate to
		394	signal the availability of results. The user can either act when the
		395	callback is called or can synchronously "->recv" for the results.
		396
		397	You can also use them to simulate traditional event loops - for example,
		398	you can block your main program until an event occurs - for example, you
		399	could "->recv" in your main program until the user clicks the Quit
		400	button of your app, which would "->send" the "quit" event.
		401
		402	Note that condition variables recurse into the event loop - if you have
		403	two pieces of code that call "->recv" in a round-robin fashion, you
		404	lose. Therefore, condition variables are good to export to your caller,
		405	but you should avoid making a blocking wait yourself, at least in
		406	callbacks, as this asks for trouble.
		407
		408	Condition variables are represented by hash refs in perl, and the keys
		409	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		410	(it is often useful to build your own transaction class on top of
		411	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		412	it's "new" method in your own "new" method.
		413
		414	There are two "sides" to a condition variable - the "producer side"
		415	which eventually calls "-> send", and the "consumer side", which waits
		416	for the send to occur.
		417
168	Example: wait for pid 1333	418	Example: wait for a timer.
169		419
170	my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });	420	# wait till the result is ready
		421	my $result_ready = AnyEvent->condvar;
171		422
172	GLOBALS	423	# do something such as adding a timer
		424	# or socket watcher the calls $result_ready->send
		425	# when the "result" is ready.
		426	# in this case, we simply use a timer:
		427	my $w = AnyEvent->timer (
		428	after => 1,
		429	cb => sub { $result_ready->send },
		430	);
		431
		432	# this "blocks" (while handling events) till the callback
		433	# calls send
		434	$result_ready->recv;
		435
		436	Example: wait for a timer, but take advantage of the fact that condition
		437	variables are also code references.
		438
		439	my $done = AnyEvent->condvar;
		440	my $delay = AnyEvent->timer (after => 5, cb => $done);
		441	$done->recv;
		442
		443	METHODS FOR PRODUCERS
		444	These methods should only be used by the producing side, i.e. the
		445	code/module that eventually sends the signal. Note that it is also the
		446	producer side which creates the condvar in most cases, but it isn't
		447	uncommon for the consumer to create it as well.
		448
		449	$cv->send (...)
		450	Flag the condition as ready - a running "->recv" and all further
		451	calls to "recv" will (eventually) return after this method has been
		452	called. If nobody is waiting the send will be remembered.
		453
		454	If a callback has been set on the condition variable, it is called
		455	immediately from within send.
		456
		457	Any arguments passed to the "send" call will be returned by all
		458	future "->recv" calls.
		459
		460	Condition variables are overloaded so one can call them directly (as
		461	a code reference). Calling them directly is the same as calling
		462	"send". Note, however, that many C-based event loops do not handle
		463	overloading, so as tempting as it may be, passing a condition
		464	variable instead of a callback does not work. Both the pure perl and
		465	EV loops support overloading, however, as well as all functions that
		466	use perl to invoke a callback (as in AnyEvent::Socket and
		467	AnyEvent::DNS for example).
		468
		469	$cv->croak ($error)
		470	Similar to send, but causes all call's to "->recv" to invoke
		471	"Carp::croak" with the given error message/object/scalar.
		472
		473	This can be used to signal any errors to the condition variable
		474	user/consumer.
		475
		476	$cv->begin ([group callback])
		477	$cv->end
		478	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		479
		480	These two methods can be used to combine many transactions/events
		481	into one. For example, a function that pings many hosts in parallel
		482	might want to use a condition variable for the whole process.
		483
		484	Every call to "->begin" will increment a counter, and every call to
		485	"->end" will decrement it. If the counter reaches 0 in "->end", the
		486	(last) callback passed to "begin" will be executed. That callback is
		487	supposed to call "->send", but that is not required. If no
		488	callback was set, "send" will be called without any arguments.
		489
		490	Let's clarify this with the ping example:
		491
		492	my $cv = AnyEvent->condvar;
		493
		494	my %result;
		495	$cv->begin (sub { $cv->send (\%result) });
		496
		497	for my $host (@list_of_hosts) {
		498	$cv->begin;
		499	ping_host_then_call_callback $host, sub {
		500	$result{$host} = ...;
		501	$cv->end;
		502	};
		503	}
		504
		505	$cv->end;
		506
		507	This code fragment supposedly pings a number of hosts and calls
		508	"send" after results for all then have have been gathered - in any
		509	order. To achieve this, the code issues a call to "begin" when it
		510	starts each ping request and calls "end" when it has received some
		511	result for it. Since "begin" and "end" only maintain a counter, the
		512	order in which results arrive is not relevant.
		513
		514	There is an additional bracketing call to "begin" and "end" outside
		515	the loop, which serves two important purposes: first, it sets the
		516	callback to be called once the counter reaches 0, and second, it
		517	ensures that "send" is called even when "no" hosts are being pinged
		518	(the loop doesn't execute once).
		519
		520	This is the general pattern when you "fan out" into multiple
		521	subrequests: use an outer "begin"/"end" pair to set the callback and
		522	ensure "end" is called at least once, and then, for each subrequest
		523	you start, call "begin" and for each subrequest you finish, call
		524	"end".
		525
		526	METHODS FOR CONSUMERS
		527	These methods should only be used by the consuming side, i.e. the code
		528	awaits the condition.
		529
		530	$cv->recv
		531	Wait (blocking if necessary) until the "->send" or "->croak" methods
		532	have been called on c<$cv>, while servicing other watchers normally.
		533
		534	You can only wait once on a condition - additional calls are valid
		535	but will return immediately.
		536
		537	If an error condition has been set by calling "->croak", then this
		538	function will call "croak".
		539
		540	In list context, all parameters passed to "send" will be returned,
		541	in scalar context only the first one will be returned.
		542
		543	Not all event models support a blocking wait - some die in that case
		544	(programs might want to do that to stay interactive), so *if you are
		545	using this from a module, never require a blocking wait*, but let
		546	the caller decide whether the call will block or not (for example,
		547	by coupling condition variables with some kind of request results
		548	and supporting callbacks so the caller knows that getting the result
		549	will not block, while still supporting blocking waits if the caller
		550	so desires).
		551
		552	Another reason never to "->recv" in a module is that you cannot
		553	sensibly have two "->recv"'s in parallel, as that would require
		554	multiple interpreters or coroutines/threads, none of which
		555	"AnyEvent" can supply.
		556
		557	The Coro module, however, can and does supply coroutines and, in
		558	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
		559	versions and also integrates coroutines into AnyEvent, making
		560	blocking "->recv" calls perfectly safe as long as they are done from
		561	another coroutine (one that doesn't run the event loop).
		562
		563	You can ensure that "-recv" never blocks by setting a callback and
		564	only calling "->recv" from within that callback (or at a later
		565	time). This will work even when the event loop does not support
		566	blocking waits otherwise.
		567
		568	$bool = $cv->ready
		569	Returns true when the condition is "true", i.e. whether "send" or
		570	"croak" have been called.
		571
		572	$cb = $cv->cb ([new callback])
		573	This is a mutator function that returns the callback set and
		574	optionally replaces it before doing so.
		575
		576	The callback will be called when the condition becomes "true", i.e.
		577	when "send" or "croak" are called, with the only argument being the
		578	condition variable itself. Calling "recv" inside the callback or at
		579	any later time is guaranteed not to block.
		580
		581	GLOBAL VARIABLES AND FUNCTIONS
173	$AnyEvent::MODEL	582	$AnyEvent::MODEL
174	Contains "undef" until the first watcher is being created. Then it	583	Contains "undef" until the first watcher is being created. Then it
175	contains the event model that is being used, which is the name of	584	contains the event model that is being used, which is the name of
176	the Perl class implementing the model. This class is usually one of	585	the Perl class implementing the model. This class is usually one of
177	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	586	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
178	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	587	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
179		588
180	The known classes so far are:	589	The known classes so far are:
181		590
182	AnyEvent::Impl::Coro based on Coro::Event, best choise.	591	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
183	AnyEvent::Impl::Event based on Event, also best choice :)	592	AnyEvent::Impl::Event based on Event, second best choice.
		593	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
184	AnyEvent::Impl::Glib based on Glib, second-best choice.	594	AnyEvent::Impl::Glib based on Glib, third-best choice.
185	AnyEvent::Impl::Tk based on Tk, very bad choice.	595	AnyEvent::Impl::Tk based on Tk, very bad choice.
186	AnyEvent::Impl::Perl pure-perl implementation, inefficient.	596	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		597	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		598	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		599
		600	There is no support for WxWidgets, as WxWidgets has no support for
		601	watching file handles. However, you can use WxWidgets through the
		602	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		603	second, which was considered to be too horrible to even consider for
		604	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
		605	using it's adaptor.
		606
		607	AnyEvent knows about Prima and Wx and will try to use POE when
		608	autodetecting them.
187		609
188	AnyEvent::detect	610	AnyEvent::detect
189	Returns $AnyEvent::MODEL, forcing autodetection of the event model	611	Returns $AnyEvent::MODEL, forcing autodetection of the event model
190	if necessary. You should only call this function right before you	612	if necessary. You should only call this function right before you
191	would have created an AnyEvent watcher anyway, that is, very late at	613	would have created an AnyEvent watcher anyway, that is, as late as
192	runtime.	614	possible at runtime.
		615
		616	$guard = AnyEvent::post_detect { BLOCK }
		617	Arranges for the code block to be executed as soon as the event
		618	model is autodetected (or immediately if this has already happened).
		619
		620	If called in scalar or list context, then it creates and returns an
		621	object that automatically removes the callback again when it is
		622	destroyed. See Coro::BDB for a case where this is useful.
		623
		624	@AnyEvent::post_detect
		625	If there are any code references in this array (you can "push" to it
		626	before or after loading AnyEvent), then they will called directly
		627	after the event loop has been chosen.
		628
		629	You should check $AnyEvent::MODEL before adding to this array,
		630	though: if it contains a true value then the event loop has already
		631	been detected, and the array will be ignored.
		632
		633	Best use "AnyEvent::post_detect { BLOCK }" instead.
193		634
194	WHAT TO DO IN A MODULE	635	WHAT TO DO IN A MODULE
195	As a module author, you should "use AnyEvent" and call AnyEvent methods	636	As a module author, you should "use AnyEvent" and call AnyEvent methods
196	freely, but you should not load a specific event module or rely on it.	637	freely, but you should not load a specific event module or rely on it.
197		638
198	Be careful when you create watchers in the module body - Anyevent will	639	Be careful when you create watchers in the module body - AnyEvent will
199	decide which event module to use as soon as the first method is called,	640	decide which event module to use as soon as the first method is called,
200	so by calling AnyEvent in your module body you force the user of your	641	so by calling AnyEvent in your module body you force the user of your
201	module to load the event module first.	642	module to load the event module first.
202		643
		644	Never call "->recv" on a condition variable unless you know that the
		645	"->send" method has been called on it already. This is because it will
		646	stall the whole program, and the whole point of using events is to stay
		647	interactive.
		648
		649	It is fine, however, to call "->recv" when the user of your module
		650	requests it (i.e. if you create a http request object ad have a method
		651	called "results" that returns the results, it should call "->recv"
		652	freely, as the user of your module knows what she is doing. always).
		653
203	WHAT TO DO IN THE MAIN PROGRAM	654	WHAT TO DO IN THE MAIN PROGRAM
204	There will always be a single main program - the only place that should	655	There will always be a single main program - the only place that should
205	dictate which event model to use.	656	dictate which event model to use.
206		657
207	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	658	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
208	do anything special and let AnyEvent decide which implementation to	659	do anything special (it does not need to be event-based) and let
209	chose.	660	AnyEvent decide which implementation to chose if some module relies on
		661	it.
210		662
211	If the main program relies on a specific event model (for example, in	663	If the main program relies on a specific event model - for example, in
212	Gtk2 programs you have to rely on either Glib or Glib::Event), you	664	Gtk2 programs you have to rely on the Glib module - you should load the
213	should load it before loading AnyEvent or any module that uses it,	665	event module before loading AnyEvent or any module that uses it:
214	generally, as early as possible. The reason is that modules might create	666	generally speaking, you should load it as early as possible. The reason
215	watchers when they are loaded, and AnyEvent will decide on the event	667	is that modules might create watchers when they are loaded, and AnyEvent
216	model to use as soon as it creates watchers, and it might chose the	668	will decide on the event model to use as soon as it creates watchers,
217	wrong one unless you load the correct one yourself.	669	and it might chose the wrong one unless you load the correct one
		670	yourself.
218		671
219	You can chose to use a rather inefficient pure-perl implementation by	672	You can chose to use a pure-perl implementation by loading the
220	loading the "AnyEvent::Impl::Perl" module, but letting AnyEvent chose is	673	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
221	generally better.	674	everywhere, but letting AnyEvent chose the model is generally better.
		675
		676	MAINLOOP EMULATION
		677	Sometimes (often for short test scripts, or even standalone programs who
		678	only want to use AnyEvent), you do not want to run a specific event
		679	loop.
		680
		681	In that case, you can use a condition variable like this:
		682
		683	AnyEvent->condvar->recv;
		684
		685	This has the effect of entering the event loop and looping forever.
		686
		687	Note that usually your program has some exit condition, in which case it
		688	is better to use the "traditional" approach of storing a condition
		689	variable somewhere, waiting for it, and sending it when the program
		690	should exit cleanly.
		691
		692	OTHER MODULES
		693	The following is a non-exhaustive list of additional modules that use
		694	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		695	in the same program. Some of the modules come with AnyEvent, some are
		696	available via CPAN.
		697
		698	AnyEvent::Util
		699	Contains various utility functions that replace often-used but
		700	blocking functions such as "inet_aton" by event-/callback-based
		701	versions.
		702
		703	AnyEvent::Handle
		704	Provide read and write buffers and manages watchers for reads and
		705	writes.
		706
		707	AnyEvent::Socket
		708	Provides various utility functions for (internet protocol) sockets,
		709	addresses and name resolution. Also functions to create non-blocking
		710	tcp connections or tcp servers, with IPv6 and SRV record support and
		711	more.
		712
		713	AnyEvent::DNS
		714	Provides rich asynchronous DNS resolver capabilities.
		715
		716	AnyEvent::HTTPD
		717	Provides a simple web application server framework.
		718
		719	AnyEvent::FastPing
		720	The fastest ping in the west.
		721
		722	Net::IRC3
		723	AnyEvent based IRC client module family.
		724
		725	Net::XMPP2
		726	AnyEvent based XMPP (Jabber protocol) module family.
		727
		728	Net::FCP
		729	AnyEvent-based implementation of the Freenet Client Protocol,
		730	birthplace of AnyEvent.
		731
		732	Event::ExecFlow
		733	High level API for event-based execution flow control.
		734
		735	Coro
		736	Has special support for AnyEvent via Coro::AnyEvent.
		737
		738	AnyEvent::AIO, IO::AIO
		739	Truly asynchronous I/O, should be in the toolbox of every event
		740	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		741	together.
		742
		743	AnyEvent::BDB, BDB
		744	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
		745	fuses IO::AIO and AnyEvent together.
		746
		747	IO::Lambda
		748	The lambda approach to I/O - don't ask, look there. Can use
		749	AnyEvent.
222		750
223	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	751	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		752	This is an advanced topic that you do not normally need to use AnyEvent
		753	in a module. This section is only of use to event loop authors who want
		754	to provide AnyEvent compatibility.
		755
224	If you need to support another event library which isn't directly	756	If you need to support another event library which isn't directly
225	supported by AnyEvent, you can supply your own interface to it by	757	supported by AnyEvent, you can supply your own interface to it by
226	pushing, before the first watcher gets created, the package name of the	758	pushing, before the first watcher gets created, the package name of the
227	event module and the package name of the interface to use onto	759	event module and the package name of the interface to use onto
228	@AnyEvent::REGISTRY. You can do that before and even without loading	760	@AnyEvent::REGISTRY. You can do that before and even without loading
229	AnyEvent.	761	AnyEvent, so it is reasonably cheap.
230		762
231	Example:	763	Example:
232		764
233	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	765	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
234		766
235	This tells AnyEvent to (literally) use the "urxvt::anyevent::"	767	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
236	package/class when it finds the "urxvt" package/module is loaded. When	768	package/class when it finds the "urxvt" package/module is already
		769	loaded.
		770
237	AnyEvent is loaded and asked to find a suitable event model, it will	771	When AnyEvent is loaded and asked to find a suitable event model, it
238	first check for the presence of urxvt.	772	will first check for the presence of urxvt by trying to "use" the
		773	"urxvt::anyevent" module.
239		774
240	The class should provide implementations for all watcher types (see	775	The class should provide implementations for all watcher types. See
241	AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code)	776	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
242	and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to	777	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
243	see the sources).	778	the sources.
244		779
		780	If you don't provide "signal" and "child" watchers than AnyEvent will
		781	provide suitable (hopefully) replacements.
		782
245	The above isn't fictitious, the rxvt-unicode (a.k.a. urxvt) uses the	783	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
246	above line as-is. An interface isn't included in AnyEvent because it	784	terminal emulator uses the above line as-is. An interface isn't included
247	doesn't make sense outside the embedded interpreter inside	785	in AnyEvent because it doesn't make sense outside the embedded
248	rxvt-unicode, and it is updated and maintained as part of the	786	interpreter inside rxvt-unicode, and it is updated and maintained as
249	rxvt-unicode distribution.	787	part of the rxvt-unicode distribution.
250		788
251	rxvt-unicode also cheats a bit by not providing blocking access to	789	rxvt-unicode also cheats a bit by not providing blocking access to
252	condition variables: code blocking while waiting for a condition will	790	condition variables: code blocking while waiting for a condition will
253	"die". This still works with most modules/usages, and blocking calls	791	"die". This still works with most modules/usages, and blocking calls
254	must not be in an interactive application, so it makes sense.	792	must not be done in an interactive application, so it makes sense.
255		793
256	ENVIRONMENT VARIABLES	794	ENVIRONMENT VARIABLES
257	The following environment variables are used by this module:	795	The following environment variables are used by this module:
258		796
259	"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event	797	"PERL_ANYEVENT_VERBOSE"
260	model gets used.	798	By default, AnyEvent will be completely silent except in fatal
		799	conditions. You can set this environment variable to make AnyEvent
		800	more talkative.
261		801
262	EXAMPLE	802	When set to 1 or higher, causes AnyEvent to warn about unexpected
		803	conditions, such as not being able to load the event model specified
		804	by "PERL_ANYEVENT_MODEL".
		805
		806	When set to 2 or higher, cause AnyEvent to report to STDERR which
		807	event model it chooses.
		808
		809	"PERL_ANYEVENT_MODEL"
		810	This can be used to specify the event model to be used by AnyEvent,
		811	before auto detection and -probing kicks in. It must be a string
		812	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		813	gets prepended and the resulting module name is loaded and if the
		814	load was successful, used as event model. If it fails to load
		815	AnyEvent will proceed with auto detection and -probing.
		816
		817	This functionality might change in future versions.
		818
		819	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		820	could start your program like this:
		821
		822	PERL_ANYEVENT_MODEL=Perl perl ...
		823
		824	"PERL_ANYEVENT_PROTOCOLS"
		825	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		826	preferences for IPv4 or IPv6. The default is unspecified (and might
		827	change, or be the result of auto probing).
		828
		829	Must be set to a comma-separated list of protocols or address
		830	families, current supported: "ipv4" and "ipv6". Only protocols
		831	mentioned will be used, and preference will be given to protocols
		832	mentioned earlier in the list.
		833
		834	This variable can effectively be used for denial-of-service attacks
		835	against local programs (e.g. when setuid), although the impact is
		836	likely small, as the program has to handle connection errors
		837	already-
		838
		839	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		840	IPv6, but support both and try to use both.
		841	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		842	resolve or contact IPv6 addresses.
		843	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		844	prefer IPv6 over IPv4.
		845
		846	"PERL_ANYEVENT_EDNS0"
		847	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		848	for DNS. This extension is generally useful to reduce DNS traffic,
		849	but some (broken) firewalls drop such DNS packets, which is why it
		850	is off by default.
		851
		852	Setting this variable to 1 will cause AnyEvent::DNS to announce
		853	EDNS0 in its DNS requests.
		854
		855	"PERL_ANYEVENT_MAX_FORKS"
		856	The maximum number of child processes that
		857	"AnyEvent::Util::fork_call" will create in parallel.
		858
		859	EXAMPLE PROGRAM
263	The following program uses an io watcher to read data from stdin, a	860	The following program uses an I/O watcher to read data from STDIN, a
264	timer to display a message once per second, and a condvar to exit the	861	timer to display a message once per second, and a condition variable to
265	program when the user enters quit:	862	quit the program when the user enters quit:
266		863
267	use AnyEvent;	864	use AnyEvent;
268		865
269	my $cv = AnyEvent->condvar;	866	my $cv = AnyEvent->condvar;
270		867
271	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	868	my $io_watcher = AnyEvent->io (
		869	fh => \*STDIN,
		870	poll => 'r',
		871	cb => sub {
272	warn "io event <$_[0]>\n"; # will always output <r>	872	warn "io event <$_[0]>\n"; # will always output <r>
273	chomp (my $input = <STDIN>); # read a line	873	chomp (my $input = <STDIN>); # read a line
274	warn "read: $input\n"; # output what has been read	874	warn "read: $input\n"; # output what has been read
275	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	875	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		876	},
276	});	877	);
277		878
278	my $time_watcher; # can only be used once	879	my $time_watcher; # can only be used once
279		880
280	sub new_timer {	881	sub new_timer {
281	$timer = AnyEvent->timer (after => 1, cb => sub {	882	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
284	});	885	});
285	}	886	}
286		887
287	new_timer; # create first timer	888	new_timer; # create first timer
288		889
289	$cv->wait; # wait until user enters /^q/i	890	$cv->recv; # wait until user enters /^q/i
290		891
291	REAL-WORLD EXAMPLE	892	REAL-WORLD EXAMPLE
292	Consider the Net::FCP module. It features (among others) the following	893	Consider the Net::FCP module. It features (among others) the following
293	API calls, which are to freenet what HTTP GET requests are to http:	894	API calls, which are to freenet what HTTP GET requests are to http:
294		895
…		…
343	syswrite $txn->{fh}, $txn->{request}	944	syswrite $txn->{fh}, $txn->{request}
344	or die "connection or write error";	945	or die "connection or write error";
345	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	946	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
346		947
347	Again, "fh_ready_r" waits till all data has arrived, and then stores the	948	Again, "fh_ready_r" waits till all data has arrived, and then stores the
348	result and signals any possible waiters that the request ahs finished:	949	result and signals any possible waiters that the request has finished:
349		950
350	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	951	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
351		952
352	if (end-of-file or data complete) {	953	if (end-of-file or data complete) {
353	$txn->{result} = $txn->{buf};	954	$txn->{result} = $txn->{buf};
354	$txn->{finished}->broadcast;	955	$txn->{finished}->send;
355	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	956	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
356	}	957	}
357		958
358	The "result" method, finally, just waits for the finished signal (if the	959	The "result" method, finally, just waits for the finished signal (if the
359	request was already finished, it doesn't wait, of course, and returns	960	request was already finished, it doesn't wait, of course, and returns
360	the data:	961	the data:
361		962
362	$txn->{finished}->wait;	963	$txn->{finished}->recv;
363	return $txn->{result};	964	return $txn->{result};
364		965
365	The actual code goes further and collects all errors ("die"s,	966	The actual code goes further and collects all errors ("die"s,
366	exceptions) that occured during request processing. The "result" method	967	exceptions) that occurred during request processing. The "result" method
367	detects wether an exception as thrown (it is stored inside the $txn	968	detects whether an exception as thrown (it is stored inside the $txn
368	object) and just throws the exception, which means connection errors and	969	object) and just throws the exception, which means connection errors and
369	other problems get reported tot he code that tries to use the result,	970	other problems get reported tot he code that tries to use the result,
370	not in a random callback.	971	not in a random callback.
371		972
372	All of this enables the following usage styles:	973	All of this enables the following usage styles:
373		974
374	1. Blocking:	975	1. Blocking:
375		976
376	my $data = $fcp->client_get ($url);	977	my $data = $fcp->client_get ($url);
377		978
378	2. Blocking, but parallelizing:	979	2. Blocking, but running in parallel:
379		980
380	my @datas = map $_->result,	981	my @datas = map $_->result,
381	map $fcp->txn_client_get ($_),	982	map $fcp->txn_client_get ($_),
382	@urls;	983	@urls;
383		984
384	Both blocking examples work without the module user having to know	985	Both blocking examples work without the module user having to know
385	anything about events.	986	anything about events.
386		987
387	3a. Event-based in a main program, using any support Event module:	988	3a. Event-based in a main program, using any supported event module:
388		989
389	use Event;	990	use EV;
390		991
391	$fcp->txn_client_get ($url)->cb (sub {	992	$fcp->txn_client_get ($url)->cb (sub {
392	my $txn = shift;	993	my $txn = shift;
393	my $data = $txn->result;	994	my $data = $txn->result;
394	...	995	...
395	});	996	});
396		997
397	Event::loop;	998	EV::loop;
398		999
399	3b. The module user could use AnyEvent, too:	1000	3b. The module user could use AnyEvent, too:
400		1001
401	use AnyEvent;	1002	use AnyEvent;
402		1003
403	my $quit = AnyEvent->condvar;	1004	my $quit = AnyEvent->condvar;
404		1005
405	$fcp->txn_client_get ($url)->cb (sub {	1006	$fcp->txn_client_get ($url)->cb (sub {
406	...	1007	...
407	$quit->broadcast;	1008	$quit->send;
408	});	1009	});
409		1010
410	$quit->wait;	1011	$quit->recv;
		1012
		1013	BENCHMARKS
		1014	To give you an idea of the performance and overheads that AnyEvent adds
		1015	over the event loops themselves and to give you an impression of the
		1016	speed of various event loops I prepared some benchmarks.
		1017
		1018	BENCHMARKING ANYEVENT OVERHEAD
		1019	Here is a benchmark of various supported event models used natively and
		1020	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1021	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1022	which it is), lets them fire exactly once and destroys them again.
		1023
		1024	Source code for this benchmark is found as eg/bench in the AnyEvent
		1025	distribution.
		1026
		1027	Explanation of the columns
		1028	watcher is the number of event watchers created/destroyed. Since
		1029	different event models feature vastly different performances, each event
		1030	loop was given a number of watchers so that overall runtime is
		1031	acceptable and similar between tested event loop (and keep them from
		1032	crashing): Glib would probably take thousands of years if asked to
		1033	process the same number of watchers as EV in this benchmark.
		1034
		1035	bytes is the number of bytes (as measured by the resident set size,
		1036	RSS) consumed by each watcher. This method of measuring captures both C
		1037	and Perl-based overheads.
		1038
		1039	create is the time, in microseconds (millionths of seconds), that it
		1040	takes to create a single watcher. The callback is a closure shared
		1041	between all watchers, to avoid adding memory overhead. That means
		1042	closure creation and memory usage is not included in the figures.
		1043
		1044	invoke is the time, in microseconds, used to invoke a simple callback.
		1045	The callback simply counts down a Perl variable and after it was invoked
		1046	"watcher" times, it would "->send" a condvar once to signal the end of
		1047	this phase.
		1048
		1049	destroy is the time, in microseconds, that it takes to destroy a
		1050	single watcher.
		1051
		1052	Results
		1053	name watchers bytes create invoke destroy comment
		1054	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1055	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1056	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1057	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1058	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1059	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1060	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1061	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1062	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1063	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1064
		1065	Discussion
		1066	The benchmark does not measure scalability of the event loop very
		1067	well. For example, a select-based event loop (such as the pure perl one)
		1068	can never compete with an event loop that uses epoll when the number of
		1069	file descriptors grows high. In this benchmark, all events become ready
		1070	at the same time, so select/poll-based implementations get an unnatural
		1071	speed boost.
		1072
		1073	Also, note that the number of watchers usually has a nonlinear effect on
		1074	overall speed, that is, creating twice as many watchers doesn't take
		1075	twice the time - usually it takes longer. This puts event loops tested
		1076	with a higher number of watchers at a disadvantage.
		1077
		1078	To put the range of results into perspective, consider that on the
		1079	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1080	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
		1081	CPU cycles with POE.
		1082
		1083	"EV" is the sole leader regarding speed and memory use, which are both
		1084	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1085	far less memory than any other event loop and is still faster than Event
		1086	natively.
		1087
		1088	The pure perl implementation is hit in a few sweet spots (both the
		1089	constant timeout and the use of a single fd hit optimisations in the
		1090	perl interpreter and the backend itself). Nevertheless this shows that
		1091	it adds very little overhead in itself. Like any select-based backend
		1092	its performance becomes really bad with lots of file descriptors (and
		1093	few of them active), of course, but this was not subject of this
		1094	benchmark.
		1095
		1096	The "Event" module has a relatively high setup and callback invocation
		1097	cost, but overall scores in on the third place.
		1098
		1099	"Glib"'s memory usage is quite a bit higher, but it features a faster
		1100	callback invocation and overall ends up in the same class as "Event".
		1101	However, Glib scales extremely badly, doubling the number of watchers
		1102	increases the processing time by more than a factor of four, making it
		1103	completely unusable when using larger numbers of watchers (note that
		1104	only a single file descriptor was used in the benchmark, so
		1105	inefficiencies of "poll" do not account for this).
		1106
		1107	The "Tk" adaptor works relatively well. The fact that it crashes with
		1108	more than 2000 watchers is a big setback, however, as correctness takes
		1109	precedence over speed. Nevertheless, its performance is surprising, as
		1110	the file descriptor is dup()ed for each watcher. This shows that the
		1111	dup() employed by some adaptors is not a big performance issue (it does
		1112	incur a hidden memory cost inside the kernel which is not reflected in
		1113	the figures above).
		1114
		1115	"POE", regardless of underlying event loop (whether using its pure perl
		1116	select-based backend or the Event module, the POE-EV backend couldn't be
		1117	tested because it wasn't working) shows abysmal performance and memory
		1118	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
		1119	watchers, and 10 times as much memory as Event (the high memory
		1120	requirements are caused by requiring a session for each watcher).
		1121	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1122	pure perl implementation.
		1123
		1124	The design of the POE adaptor class in AnyEvent can not really account
		1125	for the performance issues, though, as session creation overhead is
		1126	small compared to execution of the state machine, which is coded pretty
		1127	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1128	using multiple sessions is not a good approach, especially regarding
		1129	memory usage, even the author of POE could not come up with a faster
		1130	design).
		1131
		1132	Summary
		1133	* Using EV through AnyEvent is faster than any other event loop (even
		1134	when used without AnyEvent), but most event loops have acceptable
		1135	performance with or without AnyEvent.
		1136
		1137	* The overhead AnyEvent adds is usually much smaller than the overhead
		1138	of the actual event loop, only with extremely fast event loops such
		1139	as EV adds AnyEvent significant overhead.
		1140
		1141	* You should avoid POE like the plague if you want performance or
		1142	reasonable memory usage.
		1143
		1144	BENCHMARKING THE LARGE SERVER CASE
		1145	This benchmark actually benchmarks the event loop itself. It works by
		1146	creating a number of "servers": each server consists of a socket pair, a
		1147	timeout watcher that gets reset on activity (but never fires), and an
		1148	I/O watcher waiting for input on one side of the socket. Each time the
		1149	socket watcher reads a byte it will write that byte to a random other
		1150	"server".
		1151
		1152	The effect is that there will be a lot of I/O watchers, only part of
		1153	which are active at any one point (so there is a constant number of
		1154	active fds for each loop iteration, but which fds these are is random).
		1155	The timeout is reset each time something is read because that reflects
		1156	how most timeouts work (and puts extra pressure on the event loops).
		1157
		1158	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
		1159	100 (1%) are active. This mirrors the activity of large servers with
		1160	many connections, most of which are idle at any one point in time.
		1161
		1162	Source code for this benchmark is found as eg/bench2 in the AnyEvent
		1163	distribution.
		1164
		1165	Explanation of the columns
		1166	sockets is the number of sockets, and twice the number of "servers"
		1167	(as each server has a read and write socket end).
		1168
		1169	create is the time it takes to create a socket pair (which is
		1170	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1171
		1172	request, the most important value, is the time it takes to handle a
		1173	single "request", that is, reading the token from the pipe and
		1174	forwarding it to another server. This includes deleting the old timeout
		1175	and creating a new one that moves the timeout into the future.
		1176
		1177	Results
		1178	name sockets create request
		1179	EV 20000 69.01 11.16
		1180	Perl 20000 73.32 35.87
		1181	Event 20000 212.62 257.32
		1182	Glib 20000 651.16 1896.30
		1183	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1184
		1185	Discussion
		1186	This benchmark does measure scalability and overall performance of the
		1187	particular event loop.
		1188
		1189	EV is again fastest. Since it is using epoll on my system, the setup
		1190	time is relatively high, though.
		1191
		1192	Perl surprisingly comes second. It is much faster than the C-based event
		1193	loops Event and Glib.
		1194
		1195	Event suffers from high setup time as well (look at its code and you
		1196	will understand why). Callback invocation also has a high overhead
		1197	compared to the "$_->() for .."-style loop that the Perl event loop
		1198	uses. Event uses select or poll in basically all documented
		1199	configurations.
		1200
		1201	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1202	clearly fails to perform with many filehandles or in busy servers.
		1203
		1204	POE is still completely out of the picture, taking over 1000 times as
		1205	long as EV, and over 100 times as long as the Perl implementation, even
		1206	though it uses a C-based event loop in this case.
		1207
		1208	Summary
		1209	* The pure perl implementation performs extremely well.
		1210
		1211	* Avoid Glib or POE in large projects where performance matters.
		1212
		1213	BENCHMARKING SMALL SERVERS
		1214	While event loops should scale (and select-based ones do not...) even to
		1215	large servers, most programs we (or I :) actually write have only a few
		1216	I/O watchers.
		1217
		1218	In this benchmark, I use the same benchmark program as in the large
		1219	server case, but it uses only eight "servers", of which three are active
		1220	at any one time. This should reflect performance for a small server
		1221	relatively well.
		1222
		1223	The columns are identical to the previous table.
		1224
		1225	Results
		1226	name sockets create request
		1227	EV 16 20.00 6.54
		1228	Perl 16 25.75 12.62
		1229	Event 16 81.27 35.86
		1230	Glib 16 32.63 15.48
		1231	POE 16 261.87 276.28 uses POE::Loop::Event
		1232
		1233	Discussion
		1234	The benchmark tries to test the performance of a typical small server.
		1235	While knowing how various event loops perform is interesting, keep in
		1236	mind that their overhead in this case is usually not as important, due
		1237	to the small absolute number of watchers (that is, you need efficiency
		1238	and speed most when you have lots of watchers, not when you only have a
		1239	few of them).
		1240
		1241	EV is again fastest.
		1242
		1243	Perl again comes second. It is noticeably faster than the C-based event
		1244	loops Event and Glib, although the difference is too small to really
		1245	matter.
		1246
		1247	POE also performs much better in this case, but is is still far behind
		1248	the others.
		1249
		1250	Summary
		1251	* C-based event loops perform very well with small number of watchers,
		1252	as the management overhead dominates.
		1253
		1254	FORK
		1255	Most event libraries are not fork-safe. The ones who are usually are
		1256	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1257	Only EV is fully fork-aware.
		1258
		1259	If you have to fork, you must either do so before creating your first
		1260	watcher OR you must not use AnyEvent at all in the child.
		1261
		1262	SECURITY CONSIDERATIONS
		1263	AnyEvent can be forced to load any event model via
		1264	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
		1265	to execute arbitrary code or directly gain access, it can easily be used
		1266	to make the program hang or malfunction in subtle ways, as AnyEvent
		1267	watchers will not be active when the program uses a different event
		1268	model than specified in the variable.
		1269
		1270	You can make AnyEvent completely ignore this variable by deleting it
		1271	before the first watcher gets created, e.g. with a "BEGIN" block:
		1272
		1273	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1274
		1275	use AnyEvent;
		1276
		1277	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1278	be used to probe what backend is used and gain other information (which
		1279	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
411		1280
412	SEE ALSO	1281	SEE ALSO
413	Event modules: Coro::Event, Coro, Event, Glib::Event, Glib.	1282	Utility functions: AnyEvent::Util.
414		1283
		1284	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
		1285	Event::Lib, Qt, POE.
		1286
415	Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event,	1287	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
416	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk.	1288	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
		1289	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
417		1290
418	Nontrivial usage example: Net::FCP.	1291	Non-blocking file handles, sockets, TCP clients and servers:
		1292	AnyEvent::Handle, AnyEvent::Socket.
419		1293
		1294	Asynchronous DNS: AnyEvent::DNS.
420		1295
		1296	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1297
		1298	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
		1299
		1300	AUTHOR
		1301	Marc Lehmann <schmorp@schmorp.de>
		1302	http://home.schmorp.de/
		1303

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Comparing AnyEvent/README (file contents): Revision 1.10 by root, Mon Jul 16 19:36:36 2007 UTC vs. Revision 1.25 by root, Tue Jun 3 09:02:46 2008 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.10 by root, Mon Jul 16 19:36:36 2007 UTC vs.
Revision 1.25 by root, Tue Jun 3 09:02:46 2008 UTC