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Comparing AnyEvent/README (file contents):
Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs.
Revision 1.36 by root, Fri Mar 27 10:49:50 2009 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - provide framework for multiple event loops
3		3
4	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE -	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
5	various supported event loops	5	loops
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub { ... });
		11
		12	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		13	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		14
		15	print AnyEvent->now; # prints current event loop time
		16	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		17
		18	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		19
		20	my $w = AnyEvent->child (pid => $pid, cb => sub {
		21	my ($pid, $status) = @_;
11	...	22	...
12	});	23	});
13		24
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {
15	...
16	});
17
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	25	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		26	$w->send; # wake up current and all future recv's
19	$w->wait; # enters "main loop" till $condvar gets ->broadcast	27	$w->recv; # enters "main loop" till $condvar gets ->send
20	$w->broadcast; # wake up current and all future wait's	28	# use a condvar in callback mode:
		29	$w->cb (sub { $_[0]->recv });
		30
		31	INTRODUCTION/TUTORIAL
		32	This manpage is mainly a reference manual. If you are interested in a
		33	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		34	manpage.
21		35
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	36	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	37	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	38	nowadays. So what is different about AnyEvent?
25		39
26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	40	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
27	policy* and AnyEvent is small and efficient.	41	policy* and AnyEvent is small and efficient.
28		42
29	First and foremost, AnyEvent is not an event model itself, it only	43	First and foremost, AnyEvent is not an event model itself, it only
30	interfaces to whatever event model the main program happens to use in a	44	interfaces to whatever event model the main program happens to use, in a
31	pragmatic way. For event models and certain classes of immortals alike,	45	pragmatic way. For event models and certain classes of immortals alike,
32	the statement "there can only be one" is a bitter reality: In general,	46	the statement "there can only be one" is a bitter reality: In general,
33	only one event loop can be active at the same time in a process.	47	only one event loop can be active at the same time in a process.
34	AnyEvent helps hiding the differences between those event loops.	48	AnyEvent cannot change this, but it can hide the differences between
		49	those event loops.
35		50
36	The goal of AnyEvent is to offer module authors the ability to do event	51	The goal of AnyEvent is to offer module authors the ability to do event
37	programming (waiting for I/O or timer events) without subscribing to a	52	programming (waiting for I/O or timer events) without subscribing to a
38	religion, a way of living, and most importantly: without forcing your	53	religion, a way of living, and most importantly: without forcing your
39	module users into the same thing by forcing them to use the same event	54	module users into the same thing by forcing them to use the same event
40	model you use.	55	model you use.
41		56
42	For modules like POE or IO::Async (which is a total misnomer as it is	57	For modules like POE or IO::Async (which is a total misnomer as it is
43	actually doing all I/O synchronously...), using them in your module is	58	actually doing all I/O synchronously...), using them in your module is
44	like joining a cult: After you joined, you are dependent on them and you	59	like joining a cult: After you joined, you are dependent on them and you
45	cannot use anything else, as it is simply incompatible to everything	60	cannot use anything else, as they are simply incompatible to everything
46	that isn't itself. What's worse, all the potential users of your module	61	that isn't them. What's worse, all the potential users of your module
47	are also forced to use the same event loop you use.	62	are also forced to use the same event loop you use.
48		63
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	64	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	65	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your	66	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
52	module uses one of those, every user of your module has to use it, too.	67	module uses one of those, every user of your module has to use it, too.
53	But if your module uses AnyEvent, it works transparently with all event	68	But if your module uses AnyEvent, it works transparently with all event
54	models it supports (including stuff like POE and IO::Async, as long as	69	models it supports (including stuff like IO::Async, as long as those use
55	those use one of the supported event loops. It is trivial to add new	70	one of the supported event loops. It is trivial to add new event loops
56	event loops to AnyEvent, too, so it is future-proof).	71	to AnyEvent, too, so it is future-proof).
57		72
58	In addition to being free of having to use *the one and only true event	73	In addition to being free of having to use *the one and only true event
59	model*, AnyEvent also is free of bloat and policy: with POE or similar	74	model*, AnyEvent also is free of bloat and policy: with POE or similar
60	modules, you get an enourmous amount of code and strict rules you have	75	modules, you get an enormous amount of code and strict rules you have to
61	to follow. AnyEvent, on the other hand, is lean and up to the point, by	76	follow. AnyEvent, on the other hand, is lean and up to the point, by
62	only offering the functionality that is necessary, in as thin as a	77	only offering the functionality that is necessary, in as thin as a
63	wrapper as technically possible.	78	wrapper as technically possible.
64		79
		80	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
		81	useful functionality, such as an asynchronous DNS resolver, 100%
		82	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		83	such as Windows) and lots of real-world knowledge and workarounds for
		84	platform bugs and differences.
		85
65	Of course, if you want lots of policy (this can arguably be somewhat	86	Now, if you do want lots of policy (this can arguably be somewhat
66	useful) and you want to force your users to use the one and only event	87	useful) and you want to force your users to use the one and only event
67	model, you should not use this module.	88	model, you should not use this module.
68		89
69	DESCRIPTION	90	DESCRIPTION
70	AnyEvent provides an identical interface to multiple event loops. This	91	AnyEvent provides an identical interface to multiple event loops. This
75	The interface itself is vaguely similar, but not identical to the Event	96	The interface itself is vaguely similar, but not identical to the Event
76	module.	97	module.
77		98
78	During the first call of any watcher-creation method, the module tries	99	During the first call of any watcher-creation method, the module tries
79	to detect the currently loaded event loop by probing whether one of the	100	to detect the currently loaded event loop by probing whether one of the
80	following modules is already loaded: Coro::EV, Coro::Event, EV, Event,	101	following modules is already loaded: EV, Event, Glib,
81	Glib, AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found	102	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82	is used. If none are found, the module tries to load these modules	103	used. If none are found, the module tries to load these modules
83	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	104	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
84	always succeed) in the order given. The first one that can be	105	always succeed) in the order given. The first one that can be
85	successfully loaded will be used. If, after this, still none could be	106	successfully loaded will be used. If, after this, still none could be
86	found, AnyEvent will fall back to a pure-perl event loop, which is not	107	found, AnyEvent will fall back to a pure-perl event loop, which is not
87	very efficient, but should work everywhere.	108	very efficient, but should work everywhere.
…		…
99	starts using it, all bets are off. Maybe you should tell their authors	120	starts using it, all bets are off. Maybe you should tell their authors
100	to use AnyEvent so their modules work together with others seamlessly...	121	to use AnyEvent so their modules work together with others seamlessly...
101		122
102	The pure-perl implementation of AnyEvent is called	123	The pure-perl implementation of AnyEvent is called
103	"AnyEvent::Impl::Perl". Like other event modules you can load it	124	"AnyEvent::Impl::Perl". Like other event modules you can load it
104	explicitly.	125	explicitly and enjoy the high availability of that event loop :)
105		126
106	WATCHERS	127	WATCHERS
107	AnyEvent has the central concept of a watcher, which is an object that	128	AnyEvent has the central concept of a watcher, which is an object that
108	stores relevant data for each kind of event you are waiting for, such as	129	stores relevant data for each kind of event you are waiting for, such as
109	the callback to call, the filehandle to watch, etc.	130	the callback to call, the file handle to watch, etc.
110		131
111	These watchers are normal Perl objects with normal Perl lifetime. After	132	These watchers are normal Perl objects with normal Perl lifetime. After
112	creating a watcher it will immediately "watch" for events and invoke the	133	creating a watcher it will immediately "watch" for events and invoke the
113	callback when the event occurs (of course, only when the event model is	134	callback when the event occurs (of course, only when the event model is
114	in control).	135	in control).
115		136
		137	Note that callbacks must not permanently change global variables
		138	potentially in use by the event loop (such as $_ or $[) and that
		139	callbacks must not "die". The former is good programming practise in
		140	Perl and the latter stems from the fact that exception handling differs
		141	widely between event loops.
		142
116	To disable the watcher you have to destroy it (e.g. by setting the	143	To disable the watcher you have to destroy it (e.g. by setting the
117	variable you store it in to "undef" or otherwise deleting all references	144	variable you store it in to "undef" or otherwise deleting all references
118	to it).	145	to it).
119		146
120	All watchers are created by calling a method on the "AnyEvent" class.	147	All watchers are created by calling a method on the "AnyEvent" class.
…		…
122	Many watchers either are used with "recursion" (repeating timers for	149	Many watchers either are used with "recursion" (repeating timers for
123	example), or need to refer to their watcher object in other ways.	150	example), or need to refer to their watcher object in other ways.
124		151
125	An any way to achieve that is this pattern:	152	An any way to achieve that is this pattern:
126		153
127	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	154	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
128	# you can use $w here, for example to undef it	155	# you can use $w here, for example to undef it
129	undef $w;	156	undef $w;
130	});	157	});
131		158
132	Note that "my $w; $w =" combination. This is necessary because in Perl,	159	Note that "my $w; $w =" combination. This is necessary because in Perl,
133	my variables are only visible after the statement in which they are	160	my variables are only visible after the statement in which they are
134	declared.	161	declared.
135		162
136	I/O WATCHERS	163	I/O WATCHERS
137	You can create an I/O watcher by calling the "AnyEvent->io" method with	164	You can create an I/O watcher by calling the "AnyEvent->io" method with
138	the following mandatory key-value pairs as arguments:	165	the following mandatory key-value pairs as arguments:
139		166
140	"fh" the Perl file handle (not file descriptor) to watch for events.	167	"fh" is the Perl file handle (not file descriptor) to watch for
		168	events (AnyEvent might or might not keep a reference to this file
		169	handle). Note that only file handles pointing to things for which
		170	non-blocking operation makes sense are allowed. This includes sockets,
		171	most character devices, pipes, fifos and so on, but not for example
		172	files or block devices.
		173
141	"poll" must be a string that is either "r" or "w", which creates a	174	"poll" must be a string that is either "r" or "w", which creates a
142	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	175	watcher waiting for "r"eadable or "w"ritable events, respectively.
		176
143	is the callback to invoke each time the file handle becomes ready.	177	"cb" is the callback to invoke each time the file handle becomes ready.
144		178
145	Although the callback might get passed parameters, their value and	179	Although the callback might get passed parameters, their value and
146	presence is undefined and you cannot rely on them. Portable AnyEvent	180	presence is undefined and you cannot rely on them. Portable AnyEvent
147	callbacks cannot use arguments passed to I/O watcher callbacks.	181	callbacks cannot use arguments passed to I/O watcher callbacks.
148		182
…		…
152		186
153	Some event loops issue spurious readyness notifications, so you should	187	Some event loops issue spurious readyness notifications, so you should
154	always use non-blocking calls when reading/writing from/to your file	188	always use non-blocking calls when reading/writing from/to your file
155	handles.	189	handles.
156		190
157	Example:
158
159	# wait for readability of STDIN, then read a line and disable the watcher	191	Example: wait for readability of STDIN, then read a line and disable the
		192	watcher.
		193
160	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	194	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
161	chomp (my $input = <STDIN>);	195	chomp (my $input = <STDIN>);
162	warn "read: $input\n";	196	warn "read: $input\n";
163	undef $w;	197	undef $w;
164	});	198	});
…		…
173		207
174	Although the callback might get passed parameters, their value and	208	Although the callback might get passed parameters, their value and
175	presence is undefined and you cannot rely on them. Portable AnyEvent	209	presence is undefined and you cannot rely on them. Portable AnyEvent
176	callbacks cannot use arguments passed to time watcher callbacks.	210	callbacks cannot use arguments passed to time watcher callbacks.
177		211
178	The timer callback will be invoked at most once: if you want a repeating	212	The callback will normally be invoked once only. If you specify another
179	timer you have to create a new watcher (this is a limitation by both Tk	213	parameter, "interval", as a strictly positive number (> 0), then the
180	and Glib).	214	callback will be invoked regularly at that interval (in fractional
		215	seconds) after the first invocation. If "interval" is specified with a
		216	false value, then it is treated as if it were missing.
181		217
182	Example:	218	The callback will be rescheduled before invoking the callback, but no
		219	attempt is done to avoid timer drift in most backends, so the interval
		220	is only approximate.
183		221
184	# fire an event after 7.7 seconds	222	Example: fire an event after 7.7 seconds.
		223
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	224	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	225	warn "timeout\n";
187	});	226	});
188		227
189	# to cancel the timer:	228	# to cancel the timer:
190	undef $w;	229	undef $w;
191		230
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	231	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		232
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	233	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		234	warn "timeout\n";
200	};	235	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		236
205	TIMING ISSUES	237	TIMING ISSUES
206	There are two ways to handle timers: based on real time (relative, "fire	238	There are two ways to handle timers: based on real time (relative, "fire
207	in 10 seconds") and based on wallclock time (absolute, "fire at 12	239	in 10 seconds") and based on wallclock time (absolute, "fire at 12
208	o'clock").	240	o'clock").
…		…
220	on wallclock time) timers.	252	on wallclock time) timers.
221		253
222	AnyEvent always prefers relative timers, if available, matching the	254	AnyEvent always prefers relative timers, if available, matching the
223	AnyEvent API.	255	AnyEvent API.
224		256
		257	AnyEvent has two additional methods that return the "current time":
		258
		259	AnyEvent->time
		260	This returns the "current wallclock time" as a fractional number of
		261	seconds since the Epoch (the same thing as "time" or
		262	"Time::HiRes::time" return, and the result is guaranteed to be
		263	compatible with those).
		264
		265	It progresses independently of any event loop processing, i.e. each
		266	call will check the system clock, which usually gets updated
		267	frequently.
		268
		269	AnyEvent->now
		270	This also returns the "current wallclock time", but unlike "time",
		271	above, this value might change only once per event loop iteration,
		272	depending on the event loop (most return the same time as "time",
		273	above). This is the time that AnyEvent's timers get scheduled
		274	against.
		275
		276	*In almost all cases (in all cases if you don't care), this is the
		277	function to call when you want to know the current time.*
		278
		279	This function is also often faster then "AnyEvent->time", and thus
		280	the preferred method if you want some timestamp (for example,
		281	AnyEvent::Handle uses this to update it's activity timeouts).
		282
		283	The rest of this section is only of relevance if you try to be very
		284	exact with your timing, you can skip it without bad conscience.
		285
		286	For a practical example of when these times differ, consider
		287	Event::Lib and EV and the following set-up:
		288
		289	The event loop is running and has just invoked one of your callback
		290	at time=500 (assume no other callbacks delay processing). In your
		291	callback, you wait a second by executing "sleep 1" (blocking the
		292	process for a second) and then (at time=501) you create a relative
		293	timer that fires after three seconds.
		294
		295	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		296	return 501, because that is the current time, and the timer will be
		297	scheduled to fire at time=504 (501 + 3).
		298
		299	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		300	but "AnyEvent->now" returns 500, as that is the time the last event
		301	processing phase started. With EV, your timer gets scheduled to run
		302	at time=503 (500 + 3).
		303
		304	In one sense, Event::Lib is more exact, as it uses the current time
		305	regardless of any delays introduced by event processing. However,
		306	most callbacks do not expect large delays in processing, so this
		307	causes a higher drift (and a lot more system calls to get the
		308	current time).
		309
		310	In another sense, EV is more exact, as your timer will be scheduled
		311	at the same time, regardless of how long event processing actually
		312	took.
		313
		314	In either case, if you care (and in most cases, you don't), then you
		315	can get whatever behaviour you want with any event loop, by taking
		316	the difference between "AnyEvent->time" and "AnyEvent->now" into
		317	account.
		318
225	SIGNAL WATCHERS	319	SIGNAL WATCHERS
226	You can watch for signals using a signal watcher, "signal" is the signal	320	You can watch for signals using a signal watcher, "signal" is the signal
227	name without any "SIG" prefix, "cb" is the Perl callback to be invoked	321	name in uppercase and without any "SIG" prefix, "cb" is the Perl
228	whenever a signal occurs.	322	callback to be invoked whenever a signal occurs.
229		323
230	Although the callback might get passed parameters, their value and	324	Although the callback might get passed parameters, their value and
231	presence is undefined and you cannot rely on them. Portable AnyEvent	325	presence is undefined and you cannot rely on them. Portable AnyEvent
232	callbacks cannot use arguments passed to signal watcher callbacks.	326	callbacks cannot use arguments passed to signal watcher callbacks.
233		327
234	Multiple signal occurances can be clumped together into one callback	328	Multiple signal occurrences can be clumped together into one callback
235	invocation, and callback invocation will be synchronous. synchronous	329	invocation, and callback invocation will be synchronous. Synchronous
236	means that it might take a while until the signal gets handled by the	330	means that it might take a while until the signal gets handled by the
237	process, but it is guarenteed not to interrupt any other callbacks.	331	process, but it is guaranteed not to interrupt any other callbacks.
238		332
239	The main advantage of using these watchers is that you can share a	333	The main advantage of using these watchers is that you can share a
240	signal between multiple watchers.	334	signal between multiple watchers.
241		335
242	This watcher might use %SIG, so programs overwriting those signals	336	This watcher might use %SIG, so programs overwriting those signals
…		…
248		342
249	CHILD PROCESS WATCHERS	343	CHILD PROCESS WATCHERS
250	You can also watch on a child process exit and catch its exit status.	344	You can also watch on a child process exit and catch its exit status.
251		345
252	The child process is specified by the "pid" argument (if set to 0, it	346	The child process is specified by the "pid" argument (if set to 0, it
253	watches for any child process exit). The watcher will trigger as often	347	watches for any child process exit). The watcher will triggered only
254	as status change for the child are received. This works by installing a	348	when the child process has finished and an exit status is available, not
255	signal handler for "SIGCHLD". The callback will be called with the pid	349	on any trace events (stopped/continued).
256	and exit status (as returned by waitpid), so unlike other watcher types,	350
257	you can rely on child watcher callback arguments.	351	The callback will be called with the pid and exit status (as returned by
		352	waitpid), so unlike other watcher types, you can rely on child watcher
		353	callback arguments.
		354
		355	This watcher type works by installing a signal handler for "SIGCHLD",
		356	and since it cannot be shared, nothing else should use SIGCHLD or reap
		357	random child processes (waiting for specific child processes, e.g.
		358	inside "system", is just fine).
258		359
259	There is a slight catch to child watchers, however: you usually start	360	There is a slight catch to child watchers, however: you usually start
260	them after the child process was created, and this means the process	361	them after the child process was created, and this means the process
261	could have exited already (and no SIGCHLD will be sent anymore).	362	could have exited already (and no SIGCHLD will be sent anymore).
262		363
…		…
269	an AnyEvent program, you have to create at least one watcher before	370	an AnyEvent program, you have to create at least one watcher before
270	you "fork" the child (alternatively, you can call "AnyEvent::detect").	371	you "fork" the child (alternatively, you can call "AnyEvent::detect").
271		372
272	Example: fork a process and wait for it	373	Example: fork a process and wait for it
273		374
274	my $done = AnyEvent->condvar;	375	my $done = AnyEvent->condvar;
275		376
276	AnyEvent::detect; # force event module to be initialised
277
278	my $pid = fork or exit 5;	377	my $pid = fork or exit 5;
279		378
280	my $w = AnyEvent->child (	379	my $w = AnyEvent->child (
281	pid => $pid,	380	pid => $pid,
282	cb => sub {	381	cb => sub {
283	my ($pid, $status) = @_;	382	my ($pid, $status) = @_;
284	warn "pid $pid exited with status $status";	383	warn "pid $pid exited with status $status";
285	$done->broadcast;	384	$done->send;
286	},	385	},
287	);	386	);
288		387
289	# do something else, then wait for process exit	388	# do something else, then wait for process exit
290	$done->wait;	389	$done->recv;
291		390
292	CONDITION VARIABLES	391	CONDITION VARIABLES
		392	If you are familiar with some event loops you will know that all of them
		393	require you to run some blocking "loop", "run" or similar function that
		394	will actively watch for new events and call your callbacks.
		395
		396	AnyEvent is different, it expects somebody else to run the event loop
		397	and will only block when necessary (usually when told by the user).
		398
		399	The instrument to do that is called a "condition variable", so called
		400	because they represent a condition that must become true.
		401
293	Condition variables can be created by calling the "AnyEvent->condvar"	402	Condition variables can be created by calling the "AnyEvent->condvar"
294	method without any arguments.	403	method, usually without arguments. The only argument pair allowed is
295		404
296	A condition variable waits for a condition - precisely that the	405	"cb", which specifies a callback to be called when the condition
297	"->broadcast" method has been called.	406	variable becomes true, with the condition variable as the first argument
		407	(but not the results).
298		408
299	They are very useful to signal that a condition has been fulfilled, for	409	After creation, the condition variable is "false" until it becomes
		410	"true" by calling the "send" method (or calling the condition variable
		411	as if it were a callback, read about the caveats in the description for
		412	the "->send" method).
		413
		414	Condition variables are similar to callbacks, except that you can
		415	optionally wait for them. They can also be called merge points - points
		416	in time where multiple outstanding events have been processed. And yet
		417	another way to call them is transactions - each condition variable can
		418	be used to represent a transaction, which finishes at some point and
		419	delivers a result.
		420
		421	Condition variables are very useful to signal that something has
300	example, if you write a module that does asynchronous http requests,	422	finished, for example, if you write a module that does asynchronous http
301	then a condition variable would be the ideal candidate to signal the	423	requests, then a condition variable would be the ideal candidate to
302	availability of results.	424	signal the availability of results. The user can either act when the
		425	callback is called or can synchronously "->recv" for the results.
303		426
304	You can also use condition variables to block your main program until an	427	You can also use them to simulate traditional event loops - for example,
305	event occurs - for example, you could "->wait" in your main program	428	you can block your main program until an event occurs - for example, you
306	until the user clicks the Quit button in your app, which would	429	could "->recv" in your main program until the user clicks the Quit
307	"->broadcast" the "quit" event.	430	button of your app, which would "->send" the "quit" event.
308		431
309	Note that condition variables recurse into the event loop - if you have	432	Note that condition variables recurse into the event loop - if you have
310	two pirces of code that call "->wait" in a round-robbin fashion, you	433	two pieces of code that call "->recv" in a round-robin fashion, you
311	lose. Therefore, condition variables are good to export to your caller,	434	lose. Therefore, condition variables are good to export to your caller,
312	but you should avoid making a blocking wait yourself, at least in	435	but you should avoid making a blocking wait yourself, at least in
313	callbacks, as this asks for trouble.	436	callbacks, as this asks for trouble.
314		437
315	This object has two methods:	438	Condition variables are represented by hash refs in perl, and the keys
		439	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		440	(it is often useful to build your own transaction class on top of
		441	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		442	it's "new" method in your own "new" method.
316		443
317	$cv->wait	444	There are two "sides" to a condition variable - the "producer side"
		445	which eventually calls "-> send", and the "consumer side", which waits
		446	for the send to occur.
		447
		448	Example: wait for a timer.
		449
		450	# wait till the result is ready
		451	my $result_ready = AnyEvent->condvar;
		452
		453	# do something such as adding a timer
		454	# or socket watcher the calls $result_ready->send
		455	# when the "result" is ready.
		456	# in this case, we simply use a timer:
		457	my $w = AnyEvent->timer (
		458	after => 1,
		459	cb => sub { $result_ready->send },
		460	);
		461
		462	# this "blocks" (while handling events) till the callback
		463	# calls send
		464	$result_ready->recv;
		465
		466	Example: wait for a timer, but take advantage of the fact that condition
		467	variables are also code references.
		468
		469	my $done = AnyEvent->condvar;
		470	my $delay = AnyEvent->timer (after => 5, cb => $done);
		471	$done->recv;
		472
		473	Example: Imagine an API that returns a condvar and doesn't support
		474	callbacks. This is how you make a synchronous call, for example from the
		475	main program:
		476
		477	use AnyEvent::CouchDB;
		478
		479	...
		480
		481	my @info = $couchdb->info->recv;
		482
		483	And this is how you would just ste a callback to be called whenever the
		484	results are available:
		485
		486	$couchdb->info->cb (sub {
		487	my @info = $_[0]->recv;
		488	});
		489
		490	METHODS FOR PRODUCERS
		491	These methods should only be used by the producing side, i.e. the
		492	code/module that eventually sends the signal. Note that it is also the
		493	producer side which creates the condvar in most cases, but it isn't
		494	uncommon for the consumer to create it as well.
		495
		496	$cv->send (...)
		497	Flag the condition as ready - a running "->recv" and all further
		498	calls to "recv" will (eventually) return after this method has been
		499	called. If nobody is waiting the send will be remembered.
		500
		501	If a callback has been set on the condition variable, it is called
		502	immediately from within send.
		503
		504	Any arguments passed to the "send" call will be returned by all
		505	future "->recv" calls.
		506
		507	Condition variables are overloaded so one can call them directly (as
		508	a code reference). Calling them directly is the same as calling
		509	"send". Note, however, that many C-based event loops do not handle
		510	overloading, so as tempting as it may be, passing a condition
		511	variable instead of a callback does not work. Both the pure perl and
		512	EV loops support overloading, however, as well as all functions that
		513	use perl to invoke a callback (as in AnyEvent::Socket and
		514	AnyEvent::DNS for example).
		515
		516	$cv->croak ($error)
		517	Similar to send, but causes all call's to "->recv" to invoke
		518	"Carp::croak" with the given error message/object/scalar.
		519
		520	This can be used to signal any errors to the condition variable
		521	user/consumer.
		522
		523	$cv->begin ([group callback])
		524	$cv->end
		525	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		526
		527	These two methods can be used to combine many transactions/events
		528	into one. For example, a function that pings many hosts in parallel
		529	might want to use a condition variable for the whole process.
		530
		531	Every call to "->begin" will increment a counter, and every call to
		532	"->end" will decrement it. If the counter reaches 0 in "->end", the
		533	(last) callback passed to "begin" will be executed. That callback is
		534	supposed to call "->send", but that is not required. If no
		535	callback was set, "send" will be called without any arguments.
		536
		537	Let's clarify this with the ping example:
		538
		539	my $cv = AnyEvent->condvar;
		540
		541	my %result;
		542	$cv->begin (sub { $cv->send (\%result) });
		543
		544	for my $host (@list_of_hosts) {
		545	$cv->begin;
		546	ping_host_then_call_callback $host, sub {
		547	$result{$host} = ...;
		548	$cv->end;
		549	};
		550	}
		551
		552	$cv->end;
		553
		554	This code fragment supposedly pings a number of hosts and calls
		555	"send" after results for all then have have been gathered - in any
		556	order. To achieve this, the code issues a call to "begin" when it
		557	starts each ping request and calls "end" when it has received some
		558	result for it. Since "begin" and "end" only maintain a counter, the
		559	order in which results arrive is not relevant.
		560
		561	There is an additional bracketing call to "begin" and "end" outside
		562	the loop, which serves two important purposes: first, it sets the
		563	callback to be called once the counter reaches 0, and second, it
		564	ensures that "send" is called even when "no" hosts are being pinged
		565	(the loop doesn't execute once).
		566
		567	This is the general pattern when you "fan out" into multiple
		568	subrequests: use an outer "begin"/"end" pair to set the callback and
		569	ensure "end" is called at least once, and then, for each subrequest
		570	you start, call "begin" and for each subrequest you finish, call
		571	"end".
		572
		573	METHODS FOR CONSUMERS
		574	These methods should only be used by the consuming side, i.e. the code
		575	awaits the condition.
		576
		577	$cv->recv
318	Wait (blocking if necessary) until the "->broadcast" method has been	578	Wait (blocking if necessary) until the "->send" or "->croak" methods
319	called on c<$cv>, while servicing other watchers normally.	579	have been called on c<$cv>, while servicing other watchers normally.
320		580
321	You can only wait once on a condition - additional calls will return	581	You can only wait once on a condition - additional calls are valid
322	immediately.	582	but will return immediately.
		583
		584	If an error condition has been set by calling "->croak", then this
		585	function will call "croak".
		586
		587	In list context, all parameters passed to "send" will be returned,
		588	in scalar context only the first one will be returned.
323		589
324	Not all event models support a blocking wait - some die in that case	590	Not all event models support a blocking wait - some die in that case
325	(programs might want to do that to stay interactive), so *if you are	591	(programs might want to do that to stay interactive), so *if you are
326	using this from a module, never require a blocking wait*, but let	592	using this from a module, never require a blocking wait*, but let
327	the caller decide whether the call will block or not (for example,	593	the caller decide whether the call will block or not (for example,
328	by coupling condition variables with some kind of request results	594	by coupling condition variables with some kind of request results
329	and supporting callbacks so the caller knows that getting the result	595	and supporting callbacks so the caller knows that getting the result
330	will not block, while still suppporting blocking waits if the caller	596	will not block, while still supporting blocking waits if the caller
331	so desires).	597	so desires).
332		598
333	Another reason never to "->wait" in a module is that you cannot	599	Another reason never to "->recv" in a module is that you cannot
334	sensibly have two "->wait"'s in parallel, as that would require	600	sensibly have two "->recv"'s in parallel, as that would require
335	multiple interpreters or coroutines/threads, none of which	601	multiple interpreters or coroutines/threads, none of which
336	"AnyEvent" can supply (the coroutine-aware backends	602	"AnyEvent" can supply.
337	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
338	support concurrent "->wait"'s from different coroutines, however).
339		603
340	$cv->broadcast	604	The Coro module, however, can and does supply coroutines and, in
341	Flag the condition as ready - a running "->wait" and all further	605	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
342	calls to "wait" will (eventually) return after this method has been	606	versions and also integrates coroutines into AnyEvent, making
343	called. If nobody is waiting the broadcast will be remembered..	607	blocking "->recv" calls perfectly safe as long as they are done from
		608	another coroutine (one that doesn't run the event loop).
344		609
345	Example:	610	You can ensure that "-recv" never blocks by setting a callback and
		611	only calling "->recv" from within that callback (or at a later
		612	time). This will work even when the event loop does not support
		613	blocking waits otherwise.
346		614
347	# wait till the result is ready	615	$bool = $cv->ready
348	my $result_ready = AnyEvent->condvar;	616	Returns true when the condition is "true", i.e. whether "send" or
		617	"croak" have been called.
349		618
350	# do something such as adding a timer	619	$cb = $cv->cb ($cb->($cv))
351	# or socket watcher the calls $result_ready->broadcast	620	This is a mutator function that returns the callback set and
352	# when the "result" is ready.	621	optionally replaces it before doing so.
353	# in this case, we simply use a timer:
354	my $w = AnyEvent->timer (
355	after => 1,
356	cb => sub { $result_ready->broadcast },
357	);
358		622
359	# this "blocks" (while handling events) till the watcher	623	The callback will be called when the condition becomes "true", i.e.
360	# calls broadcast	624	when "send" or "croak" are called, with the only argument being the
361	$result_ready->wait;	625	condition variable itself. Calling "recv" inside the callback or at
		626	any later time is guaranteed not to block.
362		627
363	GLOBAL VARIABLES AND FUNCTIONS	628	GLOBAL VARIABLES AND FUNCTIONS
364	$AnyEvent::MODEL	629	$AnyEvent::MODEL
365	Contains "undef" until the first watcher is being created. Then it	630	Contains "undef" until the first watcher is being created. Then it
366	contains the event model that is being used, which is the name of	631	contains the event model that is being used, which is the name of
…		…
368	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	633	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
369	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	634	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
370		635
371	The known classes so far are:	636	The known classes so far are:
372		637
373	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
374	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
375	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	638	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
376	AnyEvent::Impl::Event based on Event, second best choice.	639	AnyEvent::Impl::Event based on Event, second best choice.
		640	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
377	AnyEvent::Impl::Glib based on Glib, third-best choice.	641	AnyEvent::Impl::Glib based on Glib, third-best choice.
378	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
379	AnyEvent::Impl::Tk based on Tk, very bad choice.	642	AnyEvent::Impl::Tk based on Tk, very bad choice.
380	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).	643	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
381	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	644	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
382	AnyEvent::Impl::POE based on POE, not generic enough for full support.	645	AnyEvent::Impl::POE based on POE, not generic enough for full support.
383		646
…		…
395	Returns $AnyEvent::MODEL, forcing autodetection of the event model	658	Returns $AnyEvent::MODEL, forcing autodetection of the event model
396	if necessary. You should only call this function right before you	659	if necessary. You should only call this function right before you
397	would have created an AnyEvent watcher anyway, that is, as late as	660	would have created an AnyEvent watcher anyway, that is, as late as
398	possible at runtime.	661	possible at runtime.
399		662
		663	$guard = AnyEvent::post_detect { BLOCK }
		664	Arranges for the code block to be executed as soon as the event
		665	model is autodetected (or immediately if this has already happened).
		666
		667	If called in scalar or list context, then it creates and returns an
		668	object that automatically removes the callback again when it is
		669	destroyed. See Coro::BDB for a case where this is useful.
		670
		671	@AnyEvent::post_detect
		672	If there are any code references in this array (you can "push" to it
		673	before or after loading AnyEvent), then they will called directly
		674	after the event loop has been chosen.
		675
		676	You should check $AnyEvent::MODEL before adding to this array,
		677	though: if it contains a true value then the event loop has already
		678	been detected, and the array will be ignored.
		679
		680	Best use "AnyEvent::post_detect { BLOCK }" instead.
		681
400	WHAT TO DO IN A MODULE	682	WHAT TO DO IN A MODULE
401	As a module author, you should "use AnyEvent" and call AnyEvent methods	683	As a module author, you should "use AnyEvent" and call AnyEvent methods
402	freely, but you should not load a specific event module or rely on it.	684	freely, but you should not load a specific event module or rely on it.
403		685
404	Be careful when you create watchers in the module body - AnyEvent will	686	Be careful when you create watchers in the module body - AnyEvent will
405	decide which event module to use as soon as the first method is called,	687	decide which event module to use as soon as the first method is called,
406	so by calling AnyEvent in your module body you force the user of your	688	so by calling AnyEvent in your module body you force the user of your
407	module to load the event module first.	689	module to load the event module first.
408		690
409	Never call "->wait" on a condition variable unless you know that the	691	Never call "->recv" on a condition variable unless you know that the
410	"->broadcast" method has been called on it already. This is because it	692	"->send" method has been called on it already. This is because it will
411	will stall the whole program, and the whole point of using events is to	693	stall the whole program, and the whole point of using events is to stay
412	stay interactive.	694	interactive.
413		695
414	It is fine, however, to call "->wait" when the user of your module	696	It is fine, however, to call "->recv" when the user of your module
415	requests it (i.e. if you create a http request object ad have a method	697	requests it (i.e. if you create a http request object ad have a method
416	called "results" that returns the results, it should call "->wait"	698	called "results" that returns the results, it should call "->recv"
417	freely, as the user of your module knows what she is doing. always).	699	freely, as the user of your module knows what she is doing. always).
418		700
419	WHAT TO DO IN THE MAIN PROGRAM	701	WHAT TO DO IN THE MAIN PROGRAM
420	There will always be a single main program - the only place that should	702	There will always be a single main program - the only place that should
421	dictate which event model to use.	703	dictate which event model to use.
…		…
423	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	705	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
424	do anything special (it does not need to be event-based) and let	706	do anything special (it does not need to be event-based) and let
425	AnyEvent decide which implementation to chose if some module relies on	707	AnyEvent decide which implementation to chose if some module relies on
426	it.	708	it.
427		709
428	If the main program relies on a specific event model. For example, in	710	If the main program relies on a specific event model - for example, in
429	Gtk2 programs you have to rely on the Glib module. You should load the	711	Gtk2 programs you have to rely on the Glib module - you should load the
430	event module before loading AnyEvent or any module that uses it:	712	event module before loading AnyEvent or any module that uses it:
431	generally speaking, you should load it as early as possible. The reason	713	generally speaking, you should load it as early as possible. The reason
432	is that modules might create watchers when they are loaded, and AnyEvent	714	is that modules might create watchers when they are loaded, and AnyEvent
433	will decide on the event model to use as soon as it creates watchers,	715	will decide on the event model to use as soon as it creates watchers,
434	and it might chose the wrong one unless you load the correct one	716	and it might chose the wrong one unless you load the correct one
435	yourself.	717	yourself.
436		718
437	You can chose to use a rather inefficient pure-perl implementation by	719	You can chose to use a pure-perl implementation by loading the
438	loading the "AnyEvent::Impl::Perl" module, which gives you similar	720	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
439	behaviour everywhere, but letting AnyEvent chose is generally better.	721	everywhere, but letting AnyEvent chose the model is generally better.
		722
		723	MAINLOOP EMULATION
		724	Sometimes (often for short test scripts, or even standalone programs who
		725	only want to use AnyEvent), you do not want to run a specific event
		726	loop.
		727
		728	In that case, you can use a condition variable like this:
		729
		730	AnyEvent->condvar->recv;
		731
		732	This has the effect of entering the event loop and looping forever.
		733
		734	Note that usually your program has some exit condition, in which case it
		735	is better to use the "traditional" approach of storing a condition
		736	variable somewhere, waiting for it, and sending it when the program
		737	should exit cleanly.
440		738
441	OTHER MODULES	739	OTHER MODULES
442	The following is a non-exhaustive list of additional modules that use	740	The following is a non-exhaustive list of additional modules that use
443	AnyEvent and can therefore be mixed easily with other AnyEvent modules	741	AnyEvent and can therefore be mixed easily with other AnyEvent modules
444	in the same program. Some of the modules come with AnyEvent, some are	742	in the same program. Some of the modules come with AnyEvent, some are
…		…
447	AnyEvent::Util	745	AnyEvent::Util
448	Contains various utility functions that replace often-used but	746	Contains various utility functions that replace often-used but
449	blocking functions such as "inet_aton" by event-/callback-based	747	blocking functions such as "inet_aton" by event-/callback-based
450	versions.	748	versions.
451		749
		750	AnyEvent::Socket
		751	Provides various utility functions for (internet protocol) sockets,
		752	addresses and name resolution. Also functions to create non-blocking
		753	tcp connections or tcp servers, with IPv6 and SRV record support and
		754	more.
		755
452	AnyEvent::Handle	756	AnyEvent::Handle
453	Provide read and write buffers and manages watchers for reads and	757	Provide read and write buffers, manages watchers for reads and
454	writes.	758	writes, supports raw and formatted I/O, I/O queued and fully
		759	transparent and non-blocking SSL/TLS.
455		760
456	AnyEvent::Socket	761	AnyEvent::DNS
457	Provides a means to do non-blocking connects, accepts etc.	762	Provides rich asynchronous DNS resolver capabilities.
		763
		764	AnyEvent::HTTP
		765	A simple-to-use HTTP library that is capable of making a lot of
		766	concurrent HTTP requests.
458		767
459	AnyEvent::HTTPD	768	AnyEvent::HTTPD
460	Provides a simple web application server framework.	769	Provides a simple web application server framework.
461		770
462	AnyEvent::DNS
463	Provides asynchronous DNS resolver capabilities, beyond what
464	AnyEvent::Util offers.
465
466	AnyEvent::FastPing	771	AnyEvent::FastPing
467	The fastest ping in the west.	772	The fastest ping in the west.
468		773
		774	AnyEvent::DBI
		775	Executes DBI requests asynchronously in a proxy process.
		776
		777	AnyEvent::AIO
		778	Truly asynchronous I/O, should be in the toolbox of every event
		779	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		780	together.
		781
		782	AnyEvent::BDB
		783	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		784	fuses BDB and AnyEvent together.
		785
		786	AnyEvent::GPSD
		787	A non-blocking interface to gpsd, a daemon delivering GPS
		788	information.
		789
		790	AnyEvent::IGS
		791	A non-blocking interface to the Internet Go Server protocol (used by
		792	App::IGS).
		793
		794	AnyEvent::IRC
		795	AnyEvent based IRC client module family (replacing the older
469	Net::IRC3	796	Net::IRC3).
470	AnyEvent based IRC client module family.
471		797
472	Net::XMPP2	798	Net::XMPP2
473	AnyEvent based XMPP (Jabber protocol) module family.	799	AnyEvent based XMPP (Jabber protocol) module family.
474		800
475	Net::FCP	801	Net::FCP
…		…
478		804
479	Event::ExecFlow	805	Event::ExecFlow
480	High level API for event-based execution flow control.	806	High level API for event-based execution flow control.
481		807
482	Coro	808	Coro
483	Has special support for AnyEvent.	809	Has special support for AnyEvent via Coro::AnyEvent.
484		810
485	IO::Lambda	811	IO::Lambda
486	The lambda approach to I/O - don't ask, look there. Can use	812	The lambda approach to I/O - don't ask, look there. Can use
487	AnyEvent.	813	AnyEvent.
488		814
489	IO::AIO	815	ERROR AND EXCEPTION HANDLING
490	Truly asynchronous I/O, should be in the toolbox of every event	816	In general, AnyEvent does not do any error handling - it relies on the
491	programmer. Can be trivially made to use AnyEvent.	817	caller to do that if required. The AnyEvent::Strict module (see also the
		818	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		819	checking of all AnyEvent methods, however, which is highly useful during
		820	development.
492		821
493	BDB Truly asynchronous Berkeley DB access. Can be trivially made to use	822	As for exception handling (i.e. runtime errors and exceptions thrown
494	AnyEvent.	823	while executing a callback), this is not only highly event-loop
		824	specific, but also not in any way wrapped by this module, as this is the
		825	job of the main program.
		826
		827	The pure perl event loop simply re-throws the exception (usually within
		828	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		829	Glib uses "install_exception_handler" and so on.
		830
		831	ENVIRONMENT VARIABLES
		832	The following environment variables are used by this module or its
		833	submodules:
		834
		835	"PERL_ANYEVENT_VERBOSE"
		836	By default, AnyEvent will be completely silent except in fatal
		837	conditions. You can set this environment variable to make AnyEvent
		838	more talkative.
		839
		840	When set to 1 or higher, causes AnyEvent to warn about unexpected
		841	conditions, such as not being able to load the event model specified
		842	by "PERL_ANYEVENT_MODEL".
		843
		844	When set to 2 or higher, cause AnyEvent to report to STDERR which
		845	event model it chooses.
		846
		847	"PERL_ANYEVENT_STRICT"
		848	AnyEvent does not do much argument checking by default, as thorough
		849	argument checking is very costly. Setting this variable to a true
		850	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		851	thoroughly check the arguments passed to most method calls. If it
		852	finds any problems it will croak.
		853
		854	In other words, enables "strict" mode.
		855
		856	Unlike "use strict", it is definitely recommended ot keep it off in
		857	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment
		858	while developing programs can be very useful, however.
		859
		860	"PERL_ANYEVENT_MODEL"
		861	This can be used to specify the event model to be used by AnyEvent,
		862	before auto detection and -probing kicks in. It must be a string
		863	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		864	gets prepended and the resulting module name is loaded and if the
		865	load was successful, used as event model. If it fails to load
		866	AnyEvent will proceed with auto detection and -probing.
		867
		868	This functionality might change in future versions.
		869
		870	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		871	could start your program like this:
		872
		873	PERL_ANYEVENT_MODEL=Perl perl ...
		874
		875	"PERL_ANYEVENT_PROTOCOLS"
		876	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		877	preferences for IPv4 or IPv6. The default is unspecified (and might
		878	change, or be the result of auto probing).
		879
		880	Must be set to a comma-separated list of protocols or address
		881	families, current supported: "ipv4" and "ipv6". Only protocols
		882	mentioned will be used, and preference will be given to protocols
		883	mentioned earlier in the list.
		884
		885	This variable can effectively be used for denial-of-service attacks
		886	against local programs (e.g. when setuid), although the impact is
		887	likely small, as the program has to handle conenction and other
		888	failures anyways.
		889
		890	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		891	IPv6, but support both and try to use both.
		892	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		893	resolve or contact IPv6 addresses.
		894	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		895	prefer IPv6 over IPv4.
		896
		897	"PERL_ANYEVENT_EDNS0"
		898	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		899	for DNS. This extension is generally useful to reduce DNS traffic,
		900	but some (broken) firewalls drop such DNS packets, which is why it
		901	is off by default.
		902
		903	Setting this variable to 1 will cause AnyEvent::DNS to announce
		904	EDNS0 in its DNS requests.
		905
		906	"PERL_ANYEVENT_MAX_FORKS"
		907	The maximum number of child processes that
		908	"AnyEvent::Util::fork_call" will create in parallel.
495		909
496	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	910	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
497	This is an advanced topic that you do not normally need to use AnyEvent	911	This is an advanced topic that you do not normally need to use AnyEvent
498	in a module. This section is only of use to event loop authors who want	912	in a module. This section is only of use to event loop authors who want
499	to provide AnyEvent compatibility.	913	to provide AnyEvent compatibility.
…		…
533		947
534	rxvt-unicode also cheats a bit by not providing blocking access to	948	rxvt-unicode also cheats a bit by not providing blocking access to
535	condition variables: code blocking while waiting for a condition will	949	condition variables: code blocking while waiting for a condition will
536	"die". This still works with most modules/usages, and blocking calls	950	"die". This still works with most modules/usages, and blocking calls
537	must not be done in an interactive application, so it makes sense.	951	must not be done in an interactive application, so it makes sense.
538
539	ENVIRONMENT VARIABLES
540	The following environment variables are used by this module:
541
542	"PERL_ANYEVENT_VERBOSE"
543	By default, AnyEvent will be completely silent except in fatal
544	conditions. You can set this environment variable to make AnyEvent
545	more talkative.
546
547	When set to 1 or higher, causes AnyEvent to warn about unexpected
548	conditions, such as not being able to load the event model specified
549	by "PERL_ANYEVENT_MODEL".
550
551	When set to 2 or higher, cause AnyEvent to report to STDERR which
552	event model it chooses.
553
554	"PERL_ANYEVENT_MODEL"
555	This can be used to specify the event model to be used by AnyEvent,
556	before autodetection and -probing kicks in. It must be a string
557	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
558	gets prepended and the resulting module name is loaded and if the
559	load was successful, used as event model. If it fails to load
560	AnyEvent will proceed with autodetection and -probing.
561
562	This functionality might change in future versions.
563
564	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
565	could start your program like this:
566
567	PERL_ANYEVENT_MODEL=Perl perl ...
568		952
569	EXAMPLE PROGRAM	953	EXAMPLE PROGRAM
570	The following program uses an I/O watcher to read data from STDIN, a	954	The following program uses an I/O watcher to read data from STDIN, a
571	timer to display a message once per second, and a condition variable to	955	timer to display a message once per second, and a condition variable to
572	quit the program when the user enters quit:	956	quit the program when the user enters quit:
…		…
580	poll => 'r',	964	poll => 'r',
581	cb => sub {	965	cb => sub {
582	warn "io event <$_[0]>\n"; # will always output <r>	966	warn "io event <$_[0]>\n"; # will always output <r>
583	chomp (my $input = <STDIN>); # read a line	967	chomp (my $input = <STDIN>); # read a line
584	warn "read: $input\n"; # output what has been read	968	warn "read: $input\n"; # output what has been read
585	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	969	$cv->send if $input =~ /^q/i; # quit program if /^q/i
586	},	970	},
587	);	971	);
588		972
589	my $time_watcher; # can only be used once	973	my $time_watcher; # can only be used once
590		974
…		…
595	});	979	});
596	}	980	}
597		981
598	new_timer; # create first timer	982	new_timer; # create first timer
599		983
600	$cv->wait; # wait until user enters /^q/i	984	$cv->recv; # wait until user enters /^q/i
601		985
602	REAL-WORLD EXAMPLE	986	REAL-WORLD EXAMPLE
603	Consider the Net::FCP module. It features (among others) the following	987	Consider the Net::FCP module. It features (among others) the following
604	API calls, which are to freenet what HTTP GET requests are to http:	988	API calls, which are to freenet what HTTP GET requests are to http:
605		989
…		…
654	syswrite $txn->{fh}, $txn->{request}	1038	syswrite $txn->{fh}, $txn->{request}
655	or die "connection or write error";	1039	or die "connection or write error";
656	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1040	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
657		1041
658	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1042	Again, "fh_ready_r" waits till all data has arrived, and then stores the
659	result and signals any possible waiters that the request ahs finished:	1043	result and signals any possible waiters that the request has finished:
660		1044
661	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1045	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
662		1046
663	if (end-of-file or data complete) {	1047	if (end-of-file or data complete) {
664	$txn->{result} = $txn->{buf};	1048	$txn->{result} = $txn->{buf};
665	$txn->{finished}->broadcast;	1049	$txn->{finished}->send;
666	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1050	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
667	}	1051	}
668		1052
669	The "result" method, finally, just waits for the finished signal (if the	1053	The "result" method, finally, just waits for the finished signal (if the
670	request was already finished, it doesn't wait, of course, and returns	1054	request was already finished, it doesn't wait, of course, and returns
671	the data:	1055	the data:
672		1056
673	$txn->{finished}->wait;	1057	$txn->{finished}->recv;
674	return $txn->{result};	1058	return $txn->{result};
675		1059
676	The actual code goes further and collects all errors ("die"s,	1060	The actual code goes further and collects all errors ("die"s,
677	exceptions) that occured during request processing. The "result" method	1061	exceptions) that occurred during request processing. The "result" method
678	detects whether an exception as thrown (it is stored inside the $txn	1062	detects whether an exception as thrown (it is stored inside the $txn
679	object) and just throws the exception, which means connection errors and	1063	object) and just throws the exception, which means connection errors and
680	other problems get reported tot he code that tries to use the result,	1064	other problems get reported tot he code that tries to use the result,
681	not in a random callback.	1065	not in a random callback.
682		1066
…		…
713		1097
714	my $quit = AnyEvent->condvar;	1098	my $quit = AnyEvent->condvar;
715		1099
716	$fcp->txn_client_get ($url)->cb (sub {	1100	$fcp->txn_client_get ($url)->cb (sub {
717	...	1101	...
718	$quit->broadcast;	1102	$quit->send;
719	});	1103	});
720		1104
721	$quit->wait;	1105	$quit->recv;
722		1106
723	BENCHMARKS	1107	BENCHMARKS
724	To give you an idea of the performance and overheads that AnyEvent adds	1108	To give you an idea of the performance and overheads that AnyEvent adds
725	over the event loops themselves and to give you an impression of the	1109	over the event loops themselves and to give you an impression of the
726	speed of various event loops I prepared some benchmarks.	1110	speed of various event loops I prepared some benchmarks.
727		1111
728	BENCHMARKING ANYEVENT OVERHEAD	1112	BENCHMARKING ANYEVENT OVERHEAD
729	Here is a benchmark of various supported event models used natively and	1113	Here is a benchmark of various supported event models used natively and
730	through anyevent. The benchmark creates a lot of timers (with a zero	1114	through AnyEvent. The benchmark creates a lot of timers (with a zero
731	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1115	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
732	which it is), lets them fire exactly once and destroys them again.	1116	which it is), lets them fire exactly once and destroys them again.
733		1117
734	Source code for this benchmark is found as eg/bench in the AnyEvent	1118	Source code for this benchmark is found as eg/bench in the AnyEvent
735	distribution.	1119	distribution.
…		…
751	between all watchers, to avoid adding memory overhead. That means	1135	between all watchers, to avoid adding memory overhead. That means
752	closure creation and memory usage is not included in the figures.	1136	closure creation and memory usage is not included in the figures.
753		1137
754	invoke is the time, in microseconds, used to invoke a simple callback.	1138	invoke is the time, in microseconds, used to invoke a simple callback.
755	The callback simply counts down a Perl variable and after it was invoked	1139	The callback simply counts down a Perl variable and after it was invoked
756	"watcher" times, it would "->broadcast" a condvar once to signal the end	1140	"watcher" times, it would "->send" a condvar once to signal the end of
757	of this phase.	1141	this phase.
758		1142
759	destroy is the time, in microseconds, that it takes to destroy a	1143	destroy is the time, in microseconds, that it takes to destroy a
760	single watcher.	1144	single watcher.
761		1145
762	Results	1146	Results
763	name watchers bytes create invoke destroy comment	1147	name watchers bytes create invoke destroy comment
764	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1148	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
765	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1149	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
766	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1150	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
767	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1151	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
768	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1152	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
769	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1153	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
770	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1154	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
771	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1155	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
772	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1156	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
773	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1157	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
774		1158
775	Discussion	1159	Discussion
776	The benchmark does not measure scalability of the event loop very	1160	The benchmark does not measure scalability of the event loop very
777	well. For example, a select-based event loop (such as the pure perl one)	1161	well. For example, a select-based event loop (such as the pure perl one)
778	can never compete with an event loop that uses epoll when the number of	1162	can never compete with an event loop that uses epoll when the number of
…		…
823	the figures above).	1207	the figures above).
824		1208
825	"POE", regardless of underlying event loop (whether using its pure perl	1209	"POE", regardless of underlying event loop (whether using its pure perl
826	select-based backend or the Event module, the POE-EV backend couldn't be	1210	select-based backend or the Event module, the POE-EV backend couldn't be
827	tested because it wasn't working) shows abysmal performance and memory	1211	tested because it wasn't working) shows abysmal performance and memory
828	usage: Watchers use almost 30 times as much memory as EV watchers, and	1212	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
829	10 times as much memory as Event (the high memory requirements are	1213	watchers, and 10 times as much memory as Event (the high memory
830	caused by requiring a session for each watcher). Watcher invocation	1214	requirements are caused by requiring a session for each watcher).
831	speed is almost 900 times slower than with AnyEvent's pure perl	1215	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1216	pure perl implementation.
		1217
832	implementation. The design of the POE adaptor class in AnyEvent can not	1218	The design of the POE adaptor class in AnyEvent can not really account
833	really account for this, as session creation overhead is small compared	1219	for the performance issues, though, as session creation overhead is
834	to execution of the state machine, which is coded pretty optimally	1220	small compared to execution of the state machine, which is coded pretty
835	within AnyEvent::Impl::POE. POE simply seems to be abysmally slow.	1221	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1222	using multiple sessions is not a good approach, especially regarding
		1223	memory usage, even the author of POE could not come up with a faster
		1224	design).
836		1225
837	Summary	1226	Summary
838	* Using EV through AnyEvent is faster than any other event loop (even	1227	* Using EV through AnyEvent is faster than any other event loop (even
839	when used without AnyEvent), but most event loops have acceptable	1228	when used without AnyEvent), but most event loops have acceptable
840	performance with or without AnyEvent.	1229	performance with or without AnyEvent.
…		…
845		1234
846	* You should avoid POE like the plague if you want performance or	1235	* You should avoid POE like the plague if you want performance or
847	reasonable memory usage.	1236	reasonable memory usage.
848		1237
849	BENCHMARKING THE LARGE SERVER CASE	1238	BENCHMARKING THE LARGE SERVER CASE
850	This benchmark atcually benchmarks the event loop itself. It works by	1239	This benchmark actually benchmarks the event loop itself. It works by
851	creating a number of "servers": each server consists of a socketpair, a	1240	creating a number of "servers": each server consists of a socket pair, a
852	timeout watcher that gets reset on activity (but never fires), and an	1241	timeout watcher that gets reset on activity (but never fires), and an
853	I/O watcher waiting for input on one side of the socket. Each time the	1242	I/O watcher waiting for input on one side of the socket. Each time the
854	socket watcher reads a byte it will write that byte to a random other	1243	socket watcher reads a byte it will write that byte to a random other
855	"server".	1244	"server".
856		1245
857	The effect is that there will be a lot of I/O watchers, only part of	1246	The effect is that there will be a lot of I/O watchers, only part of
858	which are active at any one point (so there is a constant number of	1247	which are active at any one point (so there is a constant number of
859	active fds for each loop iterstaion, but which fds these are is random).	1248	active fds for each loop iteration, but which fds these are is random).
860	The timeout is reset each time something is read because that reflects	1249	The timeout is reset each time something is read because that reflects
861	how most timeouts work (and puts extra pressure on the event loops).	1250	how most timeouts work (and puts extra pressure on the event loops).
862		1251
863	In this benchmark, we use 10000 socketpairs (20000 sockets), of which	1252	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
864	100 (1%) are active. This mirrors the activity of large servers with	1253	100 (1%) are active. This mirrors the activity of large servers with
865	many connections, most of which are idle at any one point in time.	1254	many connections, most of which are idle at any one point in time.
866		1255
867	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1256	Source code for this benchmark is found as eg/bench2 in the AnyEvent
868	distribution.	1257	distribution.
869		1258
870	Explanation of the columns	1259	Explanation of the columns
871	sockets is the number of sockets, and twice the number of "servers"	1260	sockets is the number of sockets, and twice the number of "servers"
872	(as each server has a read and write socket end).	1261	(as each server has a read and write socket end).
873		1262
874	create is the time it takes to create a socketpair (which is	1263	create is the time it takes to create a socket pair (which is
875	nontrivial) and two watchers: an I/O watcher and a timeout watcher.	1264	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
876		1265
877	request, the most important value, is the time it takes to handle a	1266	request, the most important value, is the time it takes to handle a
878	single "request", that is, reading the token from the pipe and	1267	single "request", that is, reading the token from the pipe and
879	forwarding it to another server. This includes deleting the old timeout	1268	forwarding it to another server. This includes deleting the old timeout
…		…
909	POE is still completely out of the picture, taking over 1000 times as	1298	POE is still completely out of the picture, taking over 1000 times as
910	long as EV, and over 100 times as long as the Perl implementation, even	1299	long as EV, and over 100 times as long as the Perl implementation, even
911	though it uses a C-based event loop in this case.	1300	though it uses a C-based event loop in this case.
912		1301
913	Summary	1302	Summary
914	* The pure perl implementation performs extremely well, considering	1303	* The pure perl implementation performs extremely well.
915	that it uses select.
916		1304
917	* Avoid Glib or POE in large projects where performance matters.	1305	* Avoid Glib or POE in large projects where performance matters.
918		1306
919	BENCHMARKING SMALL SERVERS	1307	BENCHMARKING SMALL SERVERS
920	While event loops should scale (and select-based ones do not...) even to	1308	While event loops should scale (and select-based ones do not...) even to
…		…
944	and speed most when you have lots of watchers, not when you only have a	1332	and speed most when you have lots of watchers, not when you only have a
945	few of them).	1333	few of them).
946		1334
947	EV is again fastest.	1335	EV is again fastest.
948		1336
949	Perl again comes second. It is noticably faster than the C-based event	1337	Perl again comes second. It is noticeably faster than the C-based event
950	loops Event and Glib, although the difference is too small to really	1338	loops Event and Glib, although the difference is too small to really
951	matter.	1339	matter.
952		1340
953	POE also performs much better in this case, but is is still far behind	1341	POE also performs much better in this case, but is is still far behind
954	the others.	1342	the others.
955		1343
956	Summary	1344	Summary
957	* C-based event loops perform very well with small number of watchers,	1345	* C-based event loops perform very well with small number of watchers,
958	as the management overhead dominates.	1346	as the management overhead dominates.
959		1347
		1348	SIGNALS
		1349	AnyEvent currently installs handlers for these signals:
		1350
		1351	SIGCHLD
		1352	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1353	emulation for event loops that do not support them natively. Also,
		1354	some event loops install a similar handler.
		1355
		1356	SIGPIPE
		1357	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1358	"undef" when AnyEvent gets loaded.
		1359
		1360	The rationale for this is that AnyEvent users usually do not really
		1361	depend on SIGPIPE delivery (which is purely an optimisation for
		1362	shell use, or badly-written programs), but "SIGPIPE" can cause
		1363	spurious and rare program exits as a lot of people do not expect
		1364	"SIGPIPE" when writing to some random socket.
		1365
		1366	The rationale for installing a no-op handler as opposed to ignoring
		1367	it is that this way, the handler will be restored to defaults on
		1368	exec.
		1369
		1370	Feel free to install your own handler, or reset it to defaults.
		1371
960	FORK	1372	FORK
961	Most event libraries are not fork-safe. The ones who are usually are	1373	Most event libraries are not fork-safe. The ones who are usually are
962	because they are so inefficient. Only EV is fully fork-aware.	1374	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1375	Only EV is fully fork-aware.
963		1376
964	If you have to fork, you must either do so before creating your first	1377	If you have to fork, you must either do so before creating your first
965	watcher OR you must not use AnyEvent at all in the child.	1378	watcher OR you must not use AnyEvent at all in the child.
966		1379
967	SECURITY CONSIDERATIONS	1380	SECURITY CONSIDERATIONS
…		…
973	model than specified in the variable.	1386	model than specified in the variable.
974		1387
975	You can make AnyEvent completely ignore this variable by deleting it	1388	You can make AnyEvent completely ignore this variable by deleting it
976	before the first watcher gets created, e.g. with a "BEGIN" block:	1389	before the first watcher gets created, e.g. with a "BEGIN" block:
977		1390
978	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1391	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
979		1392
980	use AnyEvent;	1393	use AnyEvent;
		1394
		1395	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1396	be used to probe what backend is used and gain other information (which
		1397	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1398	and $ENV{PERL_ANYEGENT_STRICT}.
		1399
		1400	BUGS
		1401	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1402	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1403	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1404	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1405	not as pronounced).
981		1406
982	SEE ALSO	1407	SEE ALSO
983	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1408	Utility functions: AnyEvent::Util.
984	Glib::Event, Glib, Coro, Tk, Event::Lib, Qt, POE.
985		1409
986	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1410	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
987	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1411	Event::Lib, Qt, POE.
988	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib,	1412
		1413	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
		1414	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
989	AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1415	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
990		1416
		1417	Non-blocking file handles, sockets, TCP clients and servers:
		1418	AnyEvent::Handle, AnyEvent::Socket.
		1419
		1420	Asynchronous DNS: AnyEvent::DNS.
		1421
		1422	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1423
991	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1424	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
992		1425
993	AUTHOR	1426	AUTHOR
994	Marc Lehmann <schmorp@schmorp.de>	1427	Marc Lehmann <schmorp@schmorp.de>
995	http://home.schmorp.de/	1428	http://home.schmorp.de/
996		1429

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Comparing AnyEvent/README (file contents): Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs. Revision 1.36 by root, Fri Mar 27 10:49:50 2009 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs.
Revision 1.36 by root, Fri Mar 27 10:49:50 2009 UTC