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Comparing AnyEvent/README (file contents):
Revision 1.25 by root, Tue Jun 3 09:02:46 2008 UTC vs.
Revision 1.45 by root, Fri Jul 17 14:57:03 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, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
5	loops	5	event loops.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# file descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		12
		13	# one-shot or repeating timers
		14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		16
		17	print AnyEvent->now; # prints current event loop time
		18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		19
		20	# POSIX signal
		21	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		22
		23	# child process exit
		24	my $w = AnyEvent->child (pid => $pid, cb => sub {
		25	my ($pid, $status) = @_;
11	...	26	...
12	});	27	});
13		28
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	29	# called when event loop idle (if applicable)
15	...	30	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		31
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	32	my $w = AnyEvent->condvar; # stores whether a condition was flagged
19	$w->send; # wake up current and all future recv's	33	$w->send; # wake up current and all future recv's
20	$w->recv; # enters "main loop" till $condvar gets ->send	34	$w->recv; # enters "main loop" till $condvar gets ->send
		35	# use a condvar in callback mode:
		36	$w->cb (sub { $_[0]->recv });
21		37
22	INTRODUCTION/TUTORIAL	38	INTRODUCTION/TUTORIAL
23	This manpage is mainly a reference manual. If you are interested in a	39	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	40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
25	manpage.	41	manpage.
30		46
31	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	47	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
32	policy* and AnyEvent is small and efficient.	48	policy* and AnyEvent is small and efficient.
33		49
34	First and foremost, AnyEvent is not an event model itself, it only	50	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	51	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,	52	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,	53	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.	54	only one event loop can be active at the same time in a process.
39	AnyEvent helps hiding the differences between those event loops.	55	AnyEvent cannot change this, but it can hide the differences between
		56	those event loops.
40		57
41	The goal of AnyEvent is to offer module authors the ability to do event	58	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	59	programming (waiting for I/O or timer events) without subscribing to a
43	religion, a way of living, and most importantly: without forcing your	60	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	61	module users into the same thing by forcing them to use the same event
45	model you use.	62	model you use.
46		63
47	For modules like POE or IO::Async (which is a total misnomer as it is	64	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	65	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	66	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	67	cannot use anything else, as they are simply incompatible to everything
51	that isn't itself. What's worse, all the potential users of your module	68	that isn't them. What's worse, all the potential users of your module
52	are also forced to use the same event loop you use.	69	are also forced to use the same event loop you use.
53		70
54	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	71	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
55	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	72	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	73	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.	74	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	75	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	76	models it supports (including stuff like IO::Async, as long as those use
60	those use one of the supported event loops. It is trivial to add new	77	one of the supported event loops. It is trivial to add new event loops
61	event loops to AnyEvent, too, so it is future-proof).	78	to AnyEvent, too, so it is future-proof).
62		79
63	In addition to being free of having to use *the one and only true event	80	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	81	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	82	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	83	follow. AnyEvent, on the other hand, is lean and up to the point, by
…		…
122	These watchers are normal Perl objects with normal Perl lifetime. After	139	These watchers are normal Perl objects with normal Perl lifetime. After
123	creating a watcher it will immediately "watch" for events and invoke the	140	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	141	callback when the event occurs (of course, only when the event model is
125	in control).	142	in control).
126		143
		144	Note that callbacks must not permanently change global variables
		145	potentially in use by the event loop (such as $_ or $[) and that
		146	callbacks must not "die". The former is good programming practise in
		147	Perl and the latter stems from the fact that exception handling differs
		148	widely between event loops.
		149
127	To disable the watcher you have to destroy it (e.g. by setting the	150	To disable the watcher you have to destroy it (e.g. by setting the
128	variable you store it in to "undef" or otherwise deleting all references	151	variable you store it in to "undef" or otherwise deleting all references
129	to it).	152	to it).
130		153
131	All watchers are created by calling a method on the "AnyEvent" class.	154	All watchers are created by calling a method on the "AnyEvent" class.
…		…
146		169
147	I/O WATCHERS	170	I/O WATCHERS
148	You can create an I/O watcher by calling the "AnyEvent->io" method with	171	You can create an I/O watcher by calling the "AnyEvent->io" method with
149	the following mandatory key-value pairs as arguments:	172	the following mandatory key-value pairs as arguments:
150		173
151	"fh" the Perl file handle (not file descriptor) to watch for events.	174	"fh" is the Perl file handle (or a naked file descriptor) to watch for
		175	events (AnyEvent might or might not keep a reference to this file
		176	handle). Note that only file handles pointing to things for which
		177	non-blocking operation makes sense are allowed. This includes sockets,
		178	most character devices, pipes, fifos and so on, but not for example
		179	files or block devices.
		180
152	"poll" must be a string that is either "r" or "w", which creates a	181	"poll" must be a string that is either "r" or "w", which creates a
153	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	182	watcher waiting for "r"eadable or "w"ritable events, respectively.
		183
154	is the callback to invoke each time the file handle becomes ready.	184	"cb" is the callback to invoke each time the file handle becomes ready.
155		185
156	Although the callback might get passed parameters, their value and	186	Although the callback might get passed parameters, their value and
157	presence is undefined and you cannot rely on them. Portable AnyEvent	187	presence is undefined and you cannot rely on them. Portable AnyEvent
158	callbacks cannot use arguments passed to I/O watcher callbacks.	188	callbacks cannot use arguments passed to I/O watcher callbacks.
159		189
…		…
163		193
164	Some event loops issue spurious readyness notifications, so you should	194	Some event loops issue spurious readyness notifications, so you should
165	always use non-blocking calls when reading/writing from/to your file	195	always use non-blocking calls when reading/writing from/to your file
166	handles.	196	handles.
167		197
168	Example:
169
170	# wait for readability of STDIN, then read a line and disable the watcher	198	Example: wait for readability of STDIN, then read a line and disable the
		199	watcher.
		200
171	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	201	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
172	chomp (my $input = <STDIN>);	202	chomp (my $input = <STDIN>);
173	warn "read: $input\n";	203	warn "read: $input\n";
174	undef $w;	204	undef $w;
175	});	205	});
…		…
184		214
185	Although the callback might get passed parameters, their value and	215	Although the callback might get passed parameters, their value and
186	presence is undefined and you cannot rely on them. Portable AnyEvent	216	presence is undefined and you cannot rely on them. Portable AnyEvent
187	callbacks cannot use arguments passed to time watcher callbacks.	217	callbacks cannot use arguments passed to time watcher callbacks.
188		218
189	The timer callback will be invoked at most once: if you want a repeating	219	The callback will normally be invoked once only. If you specify another
190	timer you have to create a new watcher (this is a limitation by both Tk	220	parameter, "interval", as a strictly positive number (> 0), then the
191	and Glib).	221	callback will be invoked regularly at that interval (in fractional
		222	seconds) after the first invocation. If "interval" is specified with a
		223	false value, then it is treated as if it were missing.
192		224
193	Example:	225	The callback will be rescheduled before invoking the callback, but no
		226	attempt is done to avoid timer drift in most backends, so the interval
		227	is only approximate.
194		228
195	# fire an event after 7.7 seconds	229	Example: fire an event after 7.7 seconds.
		230
196	my $w = AnyEvent->timer (after => 7.7, cb => sub {	231	my $w = AnyEvent->timer (after => 7.7, cb => sub {
197	warn "timeout\n";	232	warn "timeout\n";
198	});	233	});
199		234
200	# to cancel the timer:	235	# to cancel the timer:
201	undef $w;	236	undef $w;
202		237
203	Example 2:
204
205	# fire an event after 0.5 seconds, then roughly every second	238	Example 2: fire an event after 0.5 seconds, then roughly every second.
206	my $w;
207		239
208	my $cb = sub {
209	# cancel the old timer while creating a new one
210	$w = AnyEvent->timer (after => 1, cb => $cb);	240	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		241	warn "timeout\n";
211	};	242	};
212
213	# start the "loop" by creating the first watcher
214	$w = AnyEvent->timer (after => 0.5, cb => $cb);
215		243
216	TIMING ISSUES	244	TIMING ISSUES
217	There are two ways to handle timers: based on real time (relative, "fire	245	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	246	in 10 seconds") and based on wallclock time (absolute, "fire at 12
219	o'clock").	247	o'clock").
…		…
293	In either case, if you care (and in most cases, you don't), then you	321	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	322	can get whatever behaviour you want with any event loop, by taking
295	the difference between "AnyEvent->time" and "AnyEvent->now" into	323	the difference between "AnyEvent->time" and "AnyEvent->now" into
296	account.	324	account.
297		325
		326	AnyEvent->now_update
		327	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		328	current time for each loop iteration (see the discussion of
		329	AnyEvent->now, above).
		330
		331	When a callback runs for a long time (or when the process sleeps),
		332	then this "current" time will differ substantially from the real
		333	time, which might affect timers and time-outs.
		334
		335	When this is the case, you can call this method, which will update
		336	the event loop's idea of "current time".
		337
		338	Note that updating the time might cause some events to be handled.
		339
298	SIGNAL WATCHERS	340	SIGNAL WATCHERS
299	You can watch for signals using a signal watcher, "signal" is the signal	341	You can watch for signals using a signal watcher, "signal" is the signal
300	name without any "SIG" prefix, "cb" is the Perl callback to be invoked	342	name in uppercase and without any "SIG" prefix, "cb" is the Perl
301	whenever a signal occurs.	343	callback to be invoked whenever a signal occurs.
302		344
303	Although the callback might get passed parameters, their value and	345	Although the callback might get passed parameters, their value and
304	presence is undefined and you cannot rely on them. Portable AnyEvent	346	presence is undefined and you cannot rely on them. Portable AnyEvent
305	callbacks cannot use arguments passed to signal watcher callbacks.	347	callbacks cannot use arguments passed to signal watcher callbacks.
306		348
…		…
321		363
322	CHILD PROCESS WATCHERS	364	CHILD PROCESS WATCHERS
323	You can also watch on a child process exit and catch its exit status.	365	You can also watch on a child process exit and catch its exit status.
324		366
325	The child process is specified by the "pid" argument (if set to 0, it	367	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	368	watches for any child process exit). The watcher will triggered only
327	as status change for the child are received. This works by installing a	369	when the child process has finished and an exit status is available, not
328	signal handler for "SIGCHLD". The callback will be called with the pid	370	on any trace events (stopped/continued).
329	and exit status (as returned by waitpid), so unlike other watcher types,	371
330	you can rely on child watcher callback arguments.	372	The callback will be called with the pid and exit status (as returned by
		373	waitpid), so unlike other watcher types, you can rely on child watcher
		374	callback arguments.
		375
		376	This watcher type works by installing a signal handler for "SIGCHLD",
		377	and since it cannot be shared, nothing else should use SIGCHLD or reap
		378	random child processes (waiting for specific child processes, e.g.
		379	inside "system", is just fine).
331		380
332	There is a slight catch to child watchers, however: you usually start	381	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	382	them after the child process was created, and this means the process
334	could have exited already (and no SIGCHLD will be sent anymore).	383	could have exited already (and no SIGCHLD will be sent anymore).
335		384
336	Not all event models handle this correctly (POE doesn't), but even for	385	Not all event models handle this correctly (neither POE nor IO::Async
		386	do, see their AnyEvent::Impl manpages for details), but even for event
337	event models that do handle this correctly, they usually need to be	387	models that do handle this correctly, they usually need to be loaded
338	loaded before the process exits (i.e. before you fork in the first	388	before the process exits (i.e. before you fork in the first place).
339	place).	389	AnyEvent's pure perl event loop handles all cases correctly regardless
		390	of when you start the watcher.
340		391
341	This means you cannot create a child watcher as the very first thing in	392	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	393	an AnyEvent program, you have to create at least one watcher before
343	you "fork" the child (alternatively, you can call "AnyEvent::detect").	394	you "fork" the child (alternatively, you can call "AnyEvent::detect").
344		395
345	Example: fork a process and wait for it	396	Example: fork a process and wait for it
346		397
347	my $done = AnyEvent->condvar;	398	my $done = AnyEvent->condvar;
348		399
349	my $pid = fork or exit 5;	400	my $pid = fork or exit 5;
350		401
351	my $w = AnyEvent->child (	402	my $w = AnyEvent->child (
352	pid => $pid,	403	pid => $pid,
353	cb => sub {	404	cb => sub {
354	my ($pid, $status) = @_;	405	my ($pid, $status) = @_;
355	warn "pid $pid exited with status $status";	406	warn "pid $pid exited with status $status";
356	$done->send;	407	$done->send;
357	},	408	},
358	);	409	);
359		410
360	# do something else, then wait for process exit	411	# do something else, then wait for process exit
361	$done->recv;	412	$done->recv;
		413
		414	IDLE WATCHERS
		415	Sometimes there is a need to do something, but it is not so important to
		416	do it instantly, but only when there is nothing better to do. This
		417	"nothing better to do" is usually defined to be "no other events need
		418	attention by the event loop".
		419
		420	Idle watchers ideally get invoked when the event loop has nothing better
		421	to do, just before it would block the process to wait for new events.
		422	Instead of blocking, the idle watcher is invoked.
		423
		424	Most event loops unfortunately do not really support idle watchers (only
		425	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		426	will simply call the callback "from time to time".
		427
		428	Example: read lines from STDIN, but only process them when the program
		429	is otherwise idle:
		430
		431	my @lines; # read data
		432	my $idle_w;
		433	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		434	push @lines, scalar <STDIN>;
		435
		436	# start an idle watcher, if not already done
		437	$idle_w \|\|= AnyEvent->idle (cb => sub {
		438	# handle only one line, when there are lines left
		439	if (my $line = shift @lines) {
		440	print "handled when idle: $line";
		441	} else {
		442	# otherwise disable the idle watcher again
		443	undef $idle_w;
		444	}
		445	});
		446	});
362		447
363	CONDITION VARIABLES	448	CONDITION VARIABLES
364	If you are familiar with some event loops you will know that all of them	449	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	450	require you to run some blocking "loop", "run" or similar function that
366	will actively watch for new events and call your callbacks.	451	will actively watch for new events and call your callbacks.
367		452
368	AnyEvent is different, it expects somebody else to run the event loop	453	AnyEvent is slightly different: it expects somebody else to run the
369	and will only block when necessary (usually when told by the user).	454	event loop and will only block when necessary (usually when told by the
		455	user).
370		456
371	The instrument to do that is called a "condition variable", so called	457	The instrument to do that is called a "condition variable", so called
372	because they represent a condition that must become true.	458	because they represent a condition that must become true.
		459
		460	Now is probably a good time to look at the examples further below.
373		461
374	Condition variables can be created by calling the "AnyEvent->condvar"	462	Condition variables can be created by calling the "AnyEvent->condvar"
375	method, usually without arguments. The only argument pair allowed is	463	method, usually without arguments. The only argument pair allowed is
376	"cb", which specifies a callback to be called when the condition	464	"cb", which specifies a callback to be called when the condition
377	variable becomes true.	465	variable becomes true, with the condition variable as the first argument
		466	(but not the results).
378		467
379	After creation, the condition variable is "false" until it becomes	468	After creation, the condition variable is "false" until it becomes
380	"true" by calling the "send" method (or calling the condition variable	469	"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	470	as if it were a callback, read about the caveats in the description for
382	the "->send" method).	471	the "->send" method).
…		…
428	after => 1,	517	after => 1,
429	cb => sub { $result_ready->send },	518	cb => sub { $result_ready->send },
430	);	519	);
431		520
432	# this "blocks" (while handling events) till the callback	521	# this "blocks" (while handling events) till the callback
433	# calls send	522	# calls -<send
434	$result_ready->recv;	523	$result_ready->recv;
435		524
436	Example: wait for a timer, but take advantage of the fact that condition	525	Example: wait for a timer, but take advantage of the fact that condition
437	variables are also code references.	526	variables are also callable directly.
438		527
439	my $done = AnyEvent->condvar;	528	my $done = AnyEvent->condvar;
440	my $delay = AnyEvent->timer (after => 5, cb => $done);	529	my $delay = AnyEvent->timer (after => 5, cb => $done);
441	$done->recv;	530	$done->recv;
		531
		532	Example: Imagine an API that returns a condvar and doesn't support
		533	callbacks. This is how you make a synchronous call, for example from the
		534	main program:
		535
		536	use AnyEvent::CouchDB;
		537
		538	...
		539
		540	my @info = $couchdb->info->recv;
		541
		542	And this is how you would just set a callback to be called whenever the
		543	results are available:
		544
		545	$couchdb->info->cb (sub {
		546	my @info = $_[0]->recv;
		547	});
442		548
443	METHODS FOR PRODUCERS	549	METHODS FOR PRODUCERS
444	These methods should only be used by the producing side, i.e. the	550	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	551	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	552	producer side which creates the condvar in most cases, but it isn't
…		…
456		562
457	Any arguments passed to the "send" call will be returned by all	563	Any arguments passed to the "send" call will be returned by all
458	future "->recv" calls.	564	future "->recv" calls.
459		565
460	Condition variables are overloaded so one can call them directly (as	566	Condition variables are overloaded so one can call them directly (as
461	a code reference). Calling them directly is the same as calling	567	if they were a code reference). Calling them directly is the same as
462	"send". Note, however, that many C-based event loops do not handle	568	calling "send".
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		569
469	$cv->croak ($error)	570	$cv->croak ($error)
470	Similar to send, but causes all call's to "->recv" to invoke	571	Similar to send, but causes all call's to "->recv" to invoke
471	"Carp::croak" with the given error message/object/scalar.	572	"Carp::croak" with the given error message/object/scalar.
472		573
473	This can be used to signal any errors to the condition variable	574	This can be used to signal any errors to the condition variable
474	user/consumer.	575	user/consumer. Doing it this way instead of calling "croak" directly
		576	delays the error detetcion, but has the overwhelmign advantage that
		577	it diagnoses the error at the place where the result is expected,
		578	and not deep in some event clalback without connection to the actual
		579	code causing the problem.
475		580
476	$cv->begin ([group callback])	581	$cv->begin ([group callback])
477	$cv->end	582	$cv->end
478	These two methods are EXPERIMENTAL and MIGHT CHANGE.
479
480	These two methods can be used to combine many transactions/events	583	These two methods can be used to combine many transactions/events
481	into one. For example, a function that pings many hosts in parallel	584	into one. For example, a function that pings many hosts in parallel
482	might want to use a condition variable for the whole process.	585	might want to use a condition variable for the whole process.
483		586
484	Every call to "->begin" will increment a counter, and every call to	587	Every call to "->begin" will increment a counter, and every call to
485	"->end" will decrement it. If the counter reaches 0 in "->end", the	588	"->end" will decrement it. If the counter reaches 0 in "->end", the
486	(last) callback passed to "begin" will be executed. That callback is	589	(last) callback passed to "begin" will be executed. That callback is
487	supposed to call "->send", but that is not required. If no	590	supposed to call "->send", but that is not required. If no
488	callback was set, "send" will be called without any arguments.	591	callback was set, "send" will be called without any arguments.
489		592
490	Let's clarify this with the ping example:	593	You can think of "$cv->send" giving you an OR condition (one call
		594	sends), while "$cv->begin" and "$cv->end" giving you an AND
		595	condition (all "begin" calls must be "end"'ed before the condvar
		596	sends).
		597
		598	Let's start with a simple example: you have two I/O watchers (for
		599	example, STDOUT and STDERR for a program), and you want to wait for
		600	both streams to close before activating a condvar:
		601
		602	my $cv = AnyEvent->condvar;
		603
		604	$cv->begin; # first watcher
		605	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		606	defined sysread $fh1, my $buf, 4096
		607	or $cv->end;
		608	});
		609
		610	$cv->begin; # second watcher
		611	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		612	defined sysread $fh2, my $buf, 4096
		613	or $cv->end;
		614	});
		615
		616	$cv->recv;
		617
		618	This works because for every event source (EOF on file handle),
		619	there is one call to "begin", so the condvar waits for all calls to
		620	"end" before sending.
		621
		622	The ping example mentioned above is slightly more complicated, as
		623	the there are results to be passwd back, and the number of tasks
		624	that are begung can potentially be zero:
491		625
492	my $cv = AnyEvent->condvar;	626	my $cv = AnyEvent->condvar;
493		627
494	my %result;	628	my %result;
495	$cv->begin (sub { $cv->send (\%result) });	629	$cv->begin (sub { $cv->send (\%result) });
…		…
515	the loop, which serves two important purposes: first, it sets the	649	the loop, which serves two important purposes: first, it sets the
516	callback to be called once the counter reaches 0, and second, it	650	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	651	ensures that "send" is called even when "no" hosts are being pinged
518	(the loop doesn't execute once).	652	(the loop doesn't execute once).
519		653
520	This is the general pattern when you "fan out" into multiple	654	This is the general pattern when you "fan out" into multiple (but
521	subrequests: use an outer "begin"/"end" pair to set the callback and	655	potentially none) subrequests: use an outer "begin"/"end" pair to
522	ensure "end" is called at least once, and then, for each subrequest	656	set the callback and ensure "end" is called at least once, and then,
523	you start, call "begin" and for each subrequest you finish, call	657	for each subrequest you start, call "begin" and for each subrequest
524	"end".	658	you finish, call "end".
525		659
526	METHODS FOR CONSUMERS	660	METHODS FOR CONSUMERS
527	These methods should only be used by the consuming side, i.e. the code	661	These methods should only be used by the consuming side, i.e. the code
528	awaits the condition.	662	awaits the condition.
529		663
…		…
538	function will call "croak".	672	function will call "croak".
539		673
540	In list context, all parameters passed to "send" will be returned,	674	In list context, all parameters passed to "send" will be returned,
541	in scalar context only the first one will be returned.	675	in scalar context only the first one will be returned.
542		676
		677	Note that doing a blocking wait in a callback is not supported by
		678	any event loop, that is, recursive invocation of a blocking "->recv"
		679	is not allowed, and the "recv" call will "croak" if such a condition
		680	is detected. This condition can be slightly loosened by using
		681	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		682	thread that doesn't run the event loop itself.
		683
543	Not all event models support a blocking wait - some die in that case	684	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	685	(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	686	using this from a module, never require a blocking wait*. Instead,
546	the caller decide whether the call will block or not (for example,	687	let the caller decide whether the call will block or not (for
547	by coupling condition variables with some kind of request results	688	example, by coupling condition variables with some kind of request
548	and supporting callbacks so the caller knows that getting the result	689	results and supporting callbacks so the caller knows that getting
549	will not block, while still supporting blocking waits if the caller	690	the result will not block, while still supporting blocking waits if
550	so desires).	691	the caller 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		692
563	You can ensure that "-recv" never blocks by setting a callback and	693	You can ensure that "-recv" never blocks by setting a callback and
564	only calling "->recv" from within that callback (or at a later	694	only calling "->recv" from within that callback (or at a later
565	time). This will work even when the event loop does not support	695	time). This will work even when the event loop does not support
566	blocking waits otherwise.	696	blocking waits otherwise.
567		697
568	$bool = $cv->ready	698	$bool = $cv->ready
569	Returns true when the condition is "true", i.e. whether "send" or	699	Returns true when the condition is "true", i.e. whether "send" or
570	"croak" have been called.	700	"croak" have been called.
571		701
572	$cb = $cv->cb ([new callback])	702	$cb = $cv->cb ($cb->($cv))
573	This is a mutator function that returns the callback set and	703	This is a mutator function that returns the callback set and
574	optionally replaces it before doing so.	704	optionally replaces it before doing so.
575		705
576	The callback will be called when the condition becomes "true", i.e.	706	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	707	when "send" or "croak" are called, with the only argument being the
578	condition variable itself. Calling "recv" inside the callback or at	708	condition variable itself. Calling "recv" inside the callback or at
579	any later time is guaranteed not to block.	709	any later time is guaranteed not to block.
580		710
		711	SUPPORTED EVENT LOOPS/BACKENDS
		712	The available backend classes are (every class has its own manpage):
		713
		714	Backends that are autoprobed when no other event loop can be found.
		715	EV is the preferred backend when no other event loop seems to be in
		716	use. If EV is not installed, then AnyEvent will try Event, and,
		717	failing that, will fall back to its own pure-perl implementation,
		718	which is available everywhere as it comes with AnyEvent itself.
		719
		720	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		721	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		722	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		723
		724	Backends that are transparently being picked up when they are used.
		725	These will be used when they are currently loaded when the first
		726	watcher is created, in which case it is assumed that the application
		727	is using them. This means that AnyEvent will automatically pick the
		728	right backend when the main program loads an event module before
		729	anything starts to create watchers. Nothing special needs to be done
		730	by the main program.
		731
		732	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		733	AnyEvent::Impl::Tk based on Tk, very broken.
		734	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		735	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		736
		737	Backends with special needs.
		738	Qt requires the Qt::Application to be instantiated first, but will
		739	otherwise be picked up automatically. As long as the main program
		740	instantiates the application before any AnyEvent watchers are
		741	created, everything should just work.
		742
		743	AnyEvent::Impl::Qt based on Qt.
		744
		745	Support for IO::Async can only be partial, as it is too broken and
		746	architecturally limited to even support the AnyEvent API. It also is
		747	the only event loop that needs the loop to be set explicitly, so it
		748	can only be used by a main program knowing about AnyEvent. See
		749	AnyEvent::Impl::Async for the gory details.
		750
		751	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		752
		753	Event loops that are indirectly supported via other backends.
		754	Some event loops can be supported via other modules:
		755
		756	There is no direct support for WxWidgets (Wx) or Prima.
		757
		758	WxWidgets has no support for watching file handles. However, you can
		759	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		760	simply polls 20 times per second, which was considered to be too
		761	horrible to even consider for AnyEvent.
		762
		763	Prima is not supported as nobody seems to be using it, but it has a
		764	POE backend, so it can be supported through POE.
		765
		766	AnyEvent knows about both Prima and Wx, however, and will try to
		767	load POE when detecting them, in the hope that POE will pick them
		768	up, in which case everything will be automatic.
		769
581	GLOBAL VARIABLES AND FUNCTIONS	770	GLOBAL VARIABLES AND FUNCTIONS
		771	These are not normally required to use AnyEvent, but can be useful to
		772	write AnyEvent extension modules.
		773
582	$AnyEvent::MODEL	774	$AnyEvent::MODEL
583	Contains "undef" until the first watcher is being created. Then it	775	Contains "undef" until the first watcher is being created, before
		776	the backend has been autodetected.
		777
584	contains the event model that is being used, which is the name of	778	Afterwards it contains the event model that is being used, which is
585	the Perl class implementing the model. This class is usually one of	779	the name of the Perl class implementing the model. This class is
586	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	780	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
587	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	781	other class in the case AnyEvent has been extended at runtime (e.g.
588		782	in rxvt-unicode it will be "urxvt::anyevent").
589	The known classes so far are:
590
591	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
592	AnyEvent::Impl::Event based on Event, second best choice.
593	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
594	AnyEvent::Impl::Glib based on Glib, third-best choice.
595	AnyEvent::Impl::Tk based on Tk, very bad choice.
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.
609		783
610	AnyEvent::detect	784	AnyEvent::detect
611	Returns $AnyEvent::MODEL, forcing autodetection of the event model	785	Returns $AnyEvent::MODEL, forcing autodetection of the event model
612	if necessary. You should only call this function right before you	786	if necessary. You should only call this function right before you
613	would have created an AnyEvent watcher anyway, that is, as late as	787	would have created an AnyEvent watcher anyway, that is, as late as
614	possible at runtime.	788	possible at runtime, and not e.g. while initialising of your module.
		789
		790	If you need to do some initialisation before AnyEvent watchers are
		791	created, use "post_detect".
615		792
616	$guard = AnyEvent::post_detect { BLOCK }	793	$guard = AnyEvent::post_detect { BLOCK }
617	Arranges for the code block to be executed as soon as the event	794	Arranges for the code block to be executed as soon as the event
618	model is autodetected (or immediately if this has already happened).	795	model is autodetected (or immediately if this has already happened).
		796
		797	The block will be executed after the actual backend has been
		798	detected ($AnyEvent::MODEL is set), but before any watchers have
		799	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		800	other initialisations - see the sources of AnyEvent::Strict or
		801	AnyEvent::AIO to see how this is used.
		802
		803	The most common usage is to create some global watchers, without
		804	forcing event module detection too early, for example, AnyEvent::AIO
		805	creates and installs the global IO::AIO watcher in a "post_detect"
		806	block to avoid autodetecting the event module at load time.
619		807
620	If called in scalar or list context, then it creates and returns an	808	If called in scalar or list context, then it creates and returns an
621	object that automatically removes the callback again when it is	809	object that automatically removes the callback again when it is
622	destroyed. See Coro::BDB for a case where this is useful.	810	destroyed. See Coro::BDB for a case where this is useful.
623		811
…		…
625	If there are any code references in this array (you can "push" to it	813	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	814	before or after loading AnyEvent), then they will called directly
627	after the event loop has been chosen.	815	after the event loop has been chosen.
628		816
629	You should check $AnyEvent::MODEL before adding to this array,	817	You should check $AnyEvent::MODEL before adding to this array,
630	though: if it contains a true value then the event loop has already	818	though: if it is defined then the event loop has already been
631	been detected, and the array will be ignored.	819	detected, and the array will be ignored.
632		820
633	Best use "AnyEvent::post_detect { BLOCK }" instead.	821	Best use "AnyEvent::post_detect { BLOCK }" when your application
		822	allows it,as it takes care of these details.
		823
		824	This variable is mainly useful for modules that can do something
		825	useful when AnyEvent is used and thus want to know when it is
		826	initialised, but do not need to even load it by default. This array
		827	provides the means to hook into AnyEvent passively, without loading
		828	it.
634		829
635	WHAT TO DO IN A MODULE	830	WHAT TO DO IN A MODULE
636	As a module author, you should "use AnyEvent" and call AnyEvent methods	831	As a module author, you should "use AnyEvent" and call AnyEvent methods
637	freely, but you should not load a specific event module or rely on it.	832	freely, but you should not load a specific event module or rely on it.
638		833
…		…
689	variable somewhere, waiting for it, and sending it when the program	884	variable somewhere, waiting for it, and sending it when the program
690	should exit cleanly.	885	should exit cleanly.
691		886
692	OTHER MODULES	887	OTHER MODULES
693	The following is a non-exhaustive list of additional modules that use	888	The following is a non-exhaustive list of additional modules that use
694	AnyEvent and can therefore be mixed easily with other AnyEvent modules	889	AnyEvent as a client and can therefore be mixed easily with other
695	in the same program. Some of the modules come with AnyEvent, some are	890	AnyEvent modules and other event loops in the same program. Some of the
696	available via CPAN.	891	modules come with AnyEvent, most are available via CPAN.
697		892
698	AnyEvent::Util	893	AnyEvent::Util
699	Contains various utility functions that replace often-used but	894	Contains various utility functions that replace often-used but
700	blocking functions such as "inet_aton" by event-/callback-based	895	blocking functions such as "inet_aton" by event-/callback-based
701	versions.	896	versions.
702
703	AnyEvent::Handle
704	Provide read and write buffers and manages watchers for reads and
705	writes.
706		897
707	AnyEvent::Socket	898	AnyEvent::Socket
708	Provides various utility functions for (internet protocol) sockets,	899	Provides various utility functions for (internet protocol) sockets,
709	addresses and name resolution. Also functions to create non-blocking	900	addresses and name resolution. Also functions to create non-blocking
710	tcp connections or tcp servers, with IPv6 and SRV record support and	901	tcp connections or tcp servers, with IPv6 and SRV record support and
711	more.	902	more.
712		903
		904	AnyEvent::Handle
		905	Provide read and write buffers, manages watchers for reads and
		906	writes, supports raw and formatted I/O, I/O queued and fully
		907	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
		908
713	AnyEvent::DNS	909	AnyEvent::DNS
714	Provides rich asynchronous DNS resolver capabilities.	910	Provides rich asynchronous DNS resolver capabilities.
715		911
		912	AnyEvent::HTTP
		913	A simple-to-use HTTP library that is capable of making a lot of
		914	concurrent HTTP requests.
		915
716	AnyEvent::HTTPD	916	AnyEvent::HTTPD
717	Provides a simple web application server framework.	917	Provides a simple web application server framework.
718		918
719	AnyEvent::FastPing	919	AnyEvent::FastPing
720	The fastest ping in the west.	920	The fastest ping in the west.
721		921
		922	AnyEvent::DBI
		923	Executes DBI requests asynchronously in a proxy process.
		924
		925	AnyEvent::AIO
		926	Truly asynchronous I/O, should be in the toolbox of every event
		927	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		928	together.
		929
		930	AnyEvent::BDB
		931	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		932	fuses BDB and AnyEvent together.
		933
		934	AnyEvent::GPSD
		935	A non-blocking interface to gpsd, a daemon delivering GPS
		936	information.
		937
		938	AnyEvent::IRC
		939	AnyEvent based IRC client module family (replacing the older
722	Net::IRC3	940	Net::IRC3).
723	AnyEvent based IRC client module family.
724		941
725	Net::XMPP2	942	AnyEvent::XMPP
726	AnyEvent based XMPP (Jabber protocol) module family.	943	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		944	older Net::XMPP2>.
		945
		946	AnyEvent::IGS
		947	A non-blocking interface to the Internet Go Server protocol (used by
		948	App::IGS).
727		949
728	Net::FCP	950	Net::FCP
729	AnyEvent-based implementation of the Freenet Client Protocol,	951	AnyEvent-based implementation of the Freenet Client Protocol,
730	birthplace of AnyEvent.	952	birthplace of AnyEvent.
731		953
…		…
733	High level API for event-based execution flow control.	955	High level API for event-based execution flow control.
734		956
735	Coro	957	Coro
736	Has special support for AnyEvent via Coro::AnyEvent.	958	Has special support for AnyEvent via Coro::AnyEvent.
737		959
738	AnyEvent::AIO, IO::AIO	960	ERROR AND EXCEPTION HANDLING
739	Truly asynchronous I/O, should be in the toolbox of every event	961	In general, AnyEvent does not do any error handling - it relies on the
740	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	962	caller to do that if required. The AnyEvent::Strict module (see also the
741	together.	963	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		964	checking of all AnyEvent methods, however, which is highly useful during
		965	development.
742		966
743	AnyEvent::BDB, BDB	967	As for exception handling (i.e. runtime errors and exceptions thrown
744	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently	968	while executing a callback), this is not only highly event-loop
745	fuses IO::AIO and AnyEvent together.	969	specific, but also not in any way wrapped by this module, as this is the
		970	job of the main program.
746		971
747	IO::Lambda	972	The pure perl event loop simply re-throws the exception (usually within
748	The lambda approach to I/O - don't ask, look there. Can use	973	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
749	AnyEvent.	974	Glib uses "install_exception_handler" and so on.
750
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
756	If you need to support another event library which isn't directly
757	supported by AnyEvent, you can supply your own interface to it by
758	pushing, before the first watcher gets created, the package name of the
759	event module and the package name of the interface to use onto
760	@AnyEvent::REGISTRY. You can do that before and even without loading
761	AnyEvent, so it is reasonably cheap.
762
763	Example:
764
765	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
766
767	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
768	package/class when it finds the "urxvt" package/module is already
769	loaded.
770
771	When AnyEvent is loaded and asked to find a suitable event model, it
772	will first check for the presence of urxvt by trying to "use" the
773	"urxvt::anyevent" module.
774
775	The class should provide implementations for all watcher types. See
776	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
777	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
778	the sources.
779
780	If you don't provide "signal" and "child" watchers than AnyEvent will
781	provide suitable (hopefully) replacements.
782
783	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
784	terminal emulator uses the above line as-is. An interface isn't included
785	in AnyEvent because it doesn't make sense outside the embedded
786	interpreter inside rxvt-unicode, and it is updated and maintained as
787	part of the rxvt-unicode distribution.
788
789	rxvt-unicode also cheats a bit by not providing blocking access to
790	condition variables: code blocking while waiting for a condition will
791	"die". This still works with most modules/usages, and blocking calls
792	must not be done in an interactive application, so it makes sense.
793		975
794	ENVIRONMENT VARIABLES	976	ENVIRONMENT VARIABLES
795	The following environment variables are used by this module:	977	The following environment variables are used by this module or its
		978	submodules.
		979
		980	Note that AnyEvent will remove all environment variables starting with
		981	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		982	enabled.
796		983
797	"PERL_ANYEVENT_VERBOSE"	984	"PERL_ANYEVENT_VERBOSE"
798	By default, AnyEvent will be completely silent except in fatal	985	By default, AnyEvent will be completely silent except in fatal
799	conditions. You can set this environment variable to make AnyEvent	986	conditions. You can set this environment variable to make AnyEvent
800	more talkative.	987	more talkative.
…		…
803	conditions, such as not being able to load the event model specified	990	conditions, such as not being able to load the event model specified
804	by "PERL_ANYEVENT_MODEL".	991	by "PERL_ANYEVENT_MODEL".
805		992
806	When set to 2 or higher, cause AnyEvent to report to STDERR which	993	When set to 2 or higher, cause AnyEvent to report to STDERR which
807	event model it chooses.	994	event model it chooses.
		995
		996	"PERL_ANYEVENT_STRICT"
		997	AnyEvent does not do much argument checking by default, as thorough
		998	argument checking is very costly. Setting this variable to a true
		999	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1000	thoroughly check the arguments passed to most method calls. If it
		1001	finds any problems, it will croak.
		1002
		1003	In other words, enables "strict" mode.
		1004
		1005	Unlike "use strict", it is definitely recommended to keep it off in
		1006	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment
		1007	while developing programs can be very useful, however.
808		1008
809	"PERL_ANYEVENT_MODEL"	1009	"PERL_ANYEVENT_MODEL"
810	This can be used to specify the event model to be used by AnyEvent,	1010	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	1011	before auto detection and -probing kicks in. It must be a string
812	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1012	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
831	mentioned will be used, and preference will be given to protocols	1031	mentioned will be used, and preference will be given to protocols
832	mentioned earlier in the list.	1032	mentioned earlier in the list.
833		1033
834	This variable can effectively be used for denial-of-service attacks	1034	This variable can effectively be used for denial-of-service attacks
835	against local programs (e.g. when setuid), although the impact is	1035	against local programs (e.g. when setuid), although the impact is
836	likely small, as the program has to handle connection errors	1036	likely small, as the program has to handle conenction and other
837	already-	1037	failures anyways.
838		1038
839	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1039	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
840	IPv6, but support both and try to use both.	1040	IPv6, but support both and try to use both.
841	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1041	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
842	resolve or contact IPv6 addresses.	1042	resolve or contact IPv6 addresses.
…		…
853	EDNS0 in its DNS requests.	1053	EDNS0 in its DNS requests.
854		1054
855	"PERL_ANYEVENT_MAX_FORKS"	1055	"PERL_ANYEVENT_MAX_FORKS"
856	The maximum number of child processes that	1056	The maximum number of child processes that
857	"AnyEvent::Util::fork_call" will create in parallel.	1057	"AnyEvent::Util::fork_call" will create in parallel.
		1058
		1059	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1060	The default value for the "max_outstanding" parameter for the
		1061	default DNS resolver - this is the maximum number of parallel DNS
		1062	requests that are sent to the DNS server.
		1063
		1064	"PERL_ANYEVENT_RESOLV_CONF"
		1065	The file to use instead of /etc/resolv.conf (or OS-specific
		1066	configuration) in the default resolver. When set to the empty
		1067	string, no default config will be used.
		1068
		1069	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1070	When neither "ca_file" nor "ca_path" was specified during
		1071	AnyEvent::TLS context creation, and either of these environment
		1072	variables exist, they will be used to specify CA certificate
		1073	locations instead of a system-dependent default.
		1074
		1075	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1076	This is an advanced topic that you do not normally need to use AnyEvent
		1077	in a module. This section is only of use to event loop authors who want
		1078	to provide AnyEvent compatibility.
		1079
		1080	If you need to support another event library which isn't directly
		1081	supported by AnyEvent, you can supply your own interface to it by
		1082	pushing, before the first watcher gets created, the package name of the
		1083	event module and the package name of the interface to use onto
		1084	@AnyEvent::REGISTRY. You can do that before and even without loading
		1085	AnyEvent, so it is reasonably cheap.
		1086
		1087	Example:
		1088
		1089	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1090
		1091	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
		1092	package/class when it finds the "urxvt" package/module is already
		1093	loaded.
		1094
		1095	When AnyEvent is loaded and asked to find a suitable event model, it
		1096	will first check for the presence of urxvt by trying to "use" the
		1097	"urxvt::anyevent" module.
		1098
		1099	The class should provide implementations for all watcher types. See
		1100	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
		1101	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
		1102	the sources.
		1103
		1104	If you don't provide "signal" and "child" watchers than AnyEvent will
		1105	provide suitable (hopefully) replacements.
		1106
		1107	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
		1108	terminal emulator uses the above line as-is. An interface isn't included
		1109	in AnyEvent because it doesn't make sense outside the embedded
		1110	interpreter inside rxvt-unicode, and it is updated and maintained as
		1111	part of the rxvt-unicode distribution.
		1112
		1113	rxvt-unicode also cheats a bit by not providing blocking access to
		1114	condition variables: code blocking while waiting for a condition will
		1115	"die". This still works with most modules/usages, and blocking calls
		1116	must not be done in an interactive application, so it makes sense.
858		1117
859	EXAMPLE PROGRAM	1118	EXAMPLE PROGRAM
860	The following program uses an I/O watcher to read data from STDIN, a	1119	The following program uses an I/O watcher to read data from STDIN, a
861	timer to display a message once per second, and a condition variable to	1120	timer to display a message once per second, and a condition variable to
862	quit the program when the user enters quit:	1121	quit the program when the user enters quit:
…		…
1049	destroy is the time, in microseconds, that it takes to destroy a	1308	destroy is the time, in microseconds, that it takes to destroy a
1050	single watcher.	1309	single watcher.
1051		1310
1052	Results	1311	Results
1053	name watchers bytes create invoke destroy comment	1312	name watchers bytes create invoke destroy comment
1054	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1313	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
1055	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1314	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
1056	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1315	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
1057	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1316	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
1058	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1317	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
1059	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1318	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1319	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1320	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
1060	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1321	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
1061	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1322	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
1062	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1323	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
1063	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1324	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
1064		1325
1065	Discussion	1326	Discussion
1066	The benchmark does not measure scalability of the event loop very	1327	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)	1328	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	1329	can never compete with an event loop that uses epoll when the number of
…		…
1093	few of them active), of course, but this was not subject of this	1354	few of them active), of course, but this was not subject of this
1094	benchmark.	1355	benchmark.
1095		1356
1096	The "Event" module has a relatively high setup and callback invocation	1357	The "Event" module has a relatively high setup and callback invocation
1097	cost, but overall scores in on the third place.	1358	cost, but overall scores in on the third place.
		1359
		1360	"IO::Async" performs admirably well, about on par with "Event", even
		1361	when using its pure perl backend.
1098		1362
1099	"Glib"'s memory usage is quite a bit higher, but it features a faster	1363	"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".	1364	callback invocation and overall ends up in the same class as "Event".
1101	However, Glib scales extremely badly, doubling the number of watchers	1365	However, Glib scales extremely badly, doubling the number of watchers
1102	increases the processing time by more than a factor of four, making it	1366	increases the processing time by more than a factor of four, making it
…		…
1173	single "request", that is, reading the token from the pipe and	1437	single "request", that is, reading the token from the pipe and
1174	forwarding it to another server. This includes deleting the old timeout	1438	forwarding it to another server. This includes deleting the old timeout
1175	and creating a new one that moves the timeout into the future.	1439	and creating a new one that moves the timeout into the future.
1176		1440
1177	Results	1441	Results
1178	name sockets create request	1442	name sockets create request
1179	EV 20000 69.01 11.16	1443	EV 20000 69.01 11.16
1180	Perl 20000 73.32 35.87	1444	Perl 20000 73.32 35.87
		1445	IOAsync 20000 157.00 98.14 epoll
		1446	IOAsync 20000 159.31 616.06 poll
1181	Event 20000 212.62 257.32	1447	Event 20000 212.62 257.32
1182	Glib 20000 651.16 1896.30	1448	Glib 20000 651.16 1896.30
1183	POE 20000 349.67 12317.24 uses POE::Loop::Event	1449	POE 20000 349.67 12317.24 uses POE::Loop::Event
1184		1450
1185	Discussion	1451	Discussion
1186	This benchmark does measure scalability and overall performance of the	1452	This benchmark does measure scalability and overall performance of the
1187	particular event loop.	1453	particular event loop.
1188		1454
1189	EV is again fastest. Since it is using epoll on my system, the setup	1455	EV is again fastest. Since it is using epoll on my system, the setup
1190	time is relatively high, though.	1456	time is relatively high, though.
1191		1457
1192	Perl surprisingly comes second. It is much faster than the C-based event	1458	Perl surprisingly comes second. It is much faster than the C-based event
1193	loops Event and Glib.	1459	loops Event and Glib.
		1460
		1461	IO::Async performs very well when using its epoll backend, and still
		1462	quite good compared to Glib when using its pure perl backend.
1194		1463
1195	Event suffers from high setup time as well (look at its code and you	1464	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	1465	will understand why). Callback invocation also has a high overhead
1197	compared to the "$_->() for .."-style loop that the Perl event loop	1466	compared to the "$_->() for .."-style loop that the Perl event loop
1198	uses. Event uses select or poll in basically all documented	1467	uses. Event uses select or poll in basically all documented
…		…
1249		1518
1250	Summary	1519	Summary
1251	* C-based event loops perform very well with small number of watchers,	1520	* C-based event loops perform very well with small number of watchers,
1252	as the management overhead dominates.	1521	as the management overhead dominates.
1253		1522
		1523	THE IO::Lambda BENCHMARK
		1524	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1525	could be misinterpreted to make AnyEvent look bad. In fact, the
		1526	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1527	better (which shouldn't come as a surprise to anybody). As such, the
		1528	benchmark is fine, and mostly shows that the AnyEvent backend from
		1529	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1530	without the extra baggage? To explore this, I wrote the equivalent
		1531	benchmark for AnyEvent.
		1532
		1533	The benchmark itself creates an echo-server, and then, for 500 times,
		1534	connects to the echo server, sends a line, waits for the reply, and then
		1535	creates the next connection. This is a rather bad benchmark, as it
		1536	doesn't test the efficiency of the framework or much non-blocking I/O,
		1537	but it is a benchmark nevertheless.
		1538
		1539	name runtime
		1540	Lambda/select 0.330 sec
		1541	+ optimized 0.122 sec
		1542	Lambda/AnyEvent 0.327 sec
		1543	+ optimized 0.138 sec
		1544	Raw sockets/select 0.077 sec
		1545	POE/select, components 0.662 sec
		1546	POE/select, raw sockets 0.226 sec
		1547	POE/select, optimized 0.404 sec
		1548
		1549	AnyEvent/select/nb 0.085 sec
		1550	AnyEvent/EV/nb 0.068 sec
		1551	+state machine 0.134 sec
		1552
		1553	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1554	benchmarks actually make blocking connects and use 100% blocking I/O,
		1555	defeating the purpose of an event-based solution. All of the newly
		1556	written AnyEvent benchmarks use 100% non-blocking connects (using
		1557	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1558	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1559	connects generally require a lot more bookkeeping and event handling
		1560	than blocking connects (which involve a single syscall only).
		1561
		1562	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1563	offers similar expressive power as POE and IO::Lambda, using
		1564	conventional Perl syntax. This means that both the echo server and the
		1565	client are 100% non-blocking, further placing it at a disadvantage.
		1566
		1567	As you can see, the AnyEvent + EV combination even beats the
		1568	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1569	backend easily beats IO::Lambda and POE.
		1570
		1571	And even the 100% non-blocking version written using the high-level (and
		1572	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a
		1573	large margin, even though it does all of DNS, tcp-connect and socket I/O
		1574	in a non-blocking way.
		1575
		1576	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1577	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1578	part of the IO::lambda distribution and were used without any changes.
		1579
		1580	SIGNALS
		1581	AnyEvent currently installs handlers for these signals:
		1582
		1583	SIGCHLD
		1584	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1585	emulation for event loops that do not support them natively. Also,
		1586	some event loops install a similar handler.
		1587
		1588	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1589	then AnyEvent will reset it to default, to avoid losing child exit
		1590	statuses.
		1591
		1592	SIGPIPE
		1593	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1594	"undef" when AnyEvent gets loaded.
		1595
		1596	The rationale for this is that AnyEvent users usually do not really
		1597	depend on SIGPIPE delivery (which is purely an optimisation for
		1598	shell use, or badly-written programs), but "SIGPIPE" can cause
		1599	spurious and rare program exits as a lot of people do not expect
		1600	"SIGPIPE" when writing to some random socket.
		1601
		1602	The rationale for installing a no-op handler as opposed to ignoring
		1603	it is that this way, the handler will be restored to defaults on
		1604	exec.
		1605
		1606	Feel free to install your own handler, or reset it to defaults.
		1607
1254	FORK	1608	FORK
1255	Most event libraries are not fork-safe. The ones who are usually are	1609	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.	1610	because they rely on inefficient but fork-safe "select" or "poll" calls.
1257	Only EV is fully fork-aware.	1611	Only EV is fully fork-aware.
1258		1612
…		…
1269		1623
1270	You can make AnyEvent completely ignore this variable by deleting it	1624	You can make AnyEvent completely ignore this variable by deleting it
1271	before the first watcher gets created, e.g. with a "BEGIN" block:	1625	before the first watcher gets created, e.g. with a "BEGIN" block:
1272		1626
1273	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1627	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1274		1628
1275	use AnyEvent;	1629	use AnyEvent;
1276		1630
1277	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1631	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	1632	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).	1633	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1634	and $ENV{PERL_ANYEVENT_STRICT}.
		1635
		1636	Note that AnyEvent will remove all environment variables starting with
		1637	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1638	enabled.
		1639
		1640	BUGS
		1641	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1642	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1643	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1644	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1645	not as pronounced).
1280		1646
1281	SEE ALSO	1647	SEE ALSO
1282	Utility functions: AnyEvent::Util.	1648	Utility functions: AnyEvent::Util.
1283		1649
1284	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1650	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1285	Event::Lib, Qt, POE.	1651	Event::Lib, Qt, POE.
1286		1652
1287	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1653	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1288	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1654	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1289	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1655	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1656	AnyEvent::Impl::IOAsync.
1290		1657
1291	Non-blocking file handles, sockets, TCP clients and servers:	1658	Non-blocking file handles, sockets, TCP clients and servers:
1292	AnyEvent::Handle, AnyEvent::Socket.	1659	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1293		1660
1294	Asynchronous DNS: AnyEvent::DNS.	1661	Asynchronous DNS: AnyEvent::DNS.
1295		1662
1296	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1663	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1297		1664
1298	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1665	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1666	AnyEvent::HTTP.
1299		1667
1300	AUTHOR	1668	AUTHOR
1301	Marc Lehmann <schmorp@schmorp.de>	1669	Marc Lehmann <schmorp@schmorp.de>
1302	http://home.schmorp.de/	1670	http://home.schmorp.de/
1303		1671

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Revision 1.25 by root, Tue Jun 3 09:02:46 2008 UTC vs.
Revision 1.45 by root, Fri Jul 17 14:57:03 2009 UTC