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Comparing AnyEvent/README (file contents):
Revision 1.24 by root, Thu May 29 03:46:04 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 });
		37
		38	INTRODUCTION/TUTORIAL
		39	This manpage is mainly a reference manual. If you are interested in a
		40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		41	manpage.
21		42
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	43	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	44	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	45	nowadays. So what is different about AnyEvent?
25		46
26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	47	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
27	policy* and AnyEvent is small and efficient.	48	policy* and AnyEvent is small and efficient.
28		49
29	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
30	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
31	pragmatic way. For event models and certain classes of immortals alike,	52	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,	53	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.	54	only one event loop can be active at the same time in a process.
34	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.
35		57
36	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
37	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
38	religion, a way of living, and most importantly: without forcing your	60	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	61	module users into the same thing by forcing them to use the same event
40	model you use.	62	model you use.
41		63
42	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
43	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
44	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
45	cannot use anything else, as it is simply incompatible to everything	67	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	68	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.	69	are also forced to use the same event loop you use.
48		70
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	71	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	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
51	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
52	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.
53	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
54	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
55	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
56	event loops to AnyEvent, too, so it is future-proof).	78	to AnyEvent, too, so it is future-proof).
57		79
58	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
59	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
60	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
61	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
117	These watchers are normal Perl objects with normal Perl lifetime. After	139	These watchers are normal Perl objects with normal Perl lifetime. After
118	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
119	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
120	in control).	142	in control).
121		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
122	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
123	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
124	to it).	152	to it).
125		153
126	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.
…		…
128	Many watchers either are used with "recursion" (repeating timers for	156	Many watchers either are used with "recursion" (repeating timers for
129	example), or need to refer to their watcher object in other ways.	157	example), or need to refer to their watcher object in other ways.
130		158
131	An any way to achieve that is this pattern:	159	An any way to achieve that is this pattern:
132		160
133	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	161	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
134	# you can use $w here, for example to undef it	162	# you can use $w here, for example to undef it
135	undef $w;	163	undef $w;
136	});	164	});
137		165
138	Note that "my $w; $w =" combination. This is necessary because in Perl,	166	Note that "my $w; $w =" combination. This is necessary because in Perl,
139	my variables are only visible after the statement in which they are	167	my variables are only visible after the statement in which they are
140	declared.	168	declared.
141		169
142	I/O WATCHERS	170	I/O WATCHERS
143	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
144	the following mandatory key-value pairs as arguments:	172	the following mandatory key-value pairs as arguments:
145		173
146	"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
147	"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
148	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	182	watcher waiting for "r"eadable or "w"ritable events, respectively.
		183
149	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.
150		185
151	Although the callback might get passed parameters, their value and	186	Although the callback might get passed parameters, their value and
152	presence is undefined and you cannot rely on them. Portable AnyEvent	187	presence is undefined and you cannot rely on them. Portable AnyEvent
153	callbacks cannot use arguments passed to I/O watcher callbacks.	188	callbacks cannot use arguments passed to I/O watcher callbacks.
154		189
…		…
158		193
159	Some event loops issue spurious readyness notifications, so you should	194	Some event loops issue spurious readyness notifications, so you should
160	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
161	handles.	196	handles.
162		197
163	Example:
164
165	# 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
166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	201	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
167	chomp (my $input = <STDIN>);	202	chomp (my $input = <STDIN>);
168	warn "read: $input\n";	203	warn "read: $input\n";
169	undef $w;	204	undef $w;
170	});	205	});
…		…
179		214
180	Although the callback might get passed parameters, their value and	215	Although the callback might get passed parameters, their value and
181	presence is undefined and you cannot rely on them. Portable AnyEvent	216	presence is undefined and you cannot rely on them. Portable AnyEvent
182	callbacks cannot use arguments passed to time watcher callbacks.	217	callbacks cannot use arguments passed to time watcher callbacks.
183		218
184	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
185	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
186	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.
187		224
188	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.
189		228
190	# fire an event after 7.7 seconds	229	Example: fire an event after 7.7 seconds.
		230
191	my $w = AnyEvent->timer (after => 7.7, cb => sub {	231	my $w = AnyEvent->timer (after => 7.7, cb => sub {
192	warn "timeout\n";	232	warn "timeout\n";
193	});	233	});
194		234
195	# to cancel the timer:	235	# to cancel the timer:
196	undef $w;	236	undef $w;
197		237
198	Example 2:
199
200	# 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.
201	my $w;
202		239
203	my $cb = sub {
204	# cancel the old timer while creating a new one
205	$w = AnyEvent->timer (after => 1, cb => $cb);	240	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		241	warn "timeout\n";
206	};	242	};
207
208	# start the "loop" by creating the first watcher
209	$w = AnyEvent->timer (after => 0.5, cb => $cb);
210		243
211	TIMING ISSUES	244	TIMING ISSUES
212	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
213	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
214	o'clock").	247	o'clock").
…		…
288	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
289	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
290	the difference between "AnyEvent->time" and "AnyEvent->now" into	323	the difference between "AnyEvent->time" and "AnyEvent->now" into
291	account.	324	account.
292		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
293	SIGNAL WATCHERS	340	SIGNAL WATCHERS
294	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
295	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
296	whenever a signal occurs.	343	callback to be invoked whenever a signal occurs.
297		344
298	Although the callback might get passed parameters, their value and	345	Although the callback might get passed parameters, their value and
299	presence is undefined and you cannot rely on them. Portable AnyEvent	346	presence is undefined and you cannot rely on them. Portable AnyEvent
300	callbacks cannot use arguments passed to signal watcher callbacks.	347	callbacks cannot use arguments passed to signal watcher callbacks.
301		348
…		…
316		363
317	CHILD PROCESS WATCHERS	364	CHILD PROCESS WATCHERS
318	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.
319		366
320	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
321	watches for any child process exit). The watcher will trigger as often	368	watches for any child process exit). The watcher will triggered only
322	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
323	signal handler for "SIGCHLD". The callback will be called with the pid	370	on any trace events (stopped/continued).
324	and exit status (as returned by waitpid), so unlike other watcher types,	371
325	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).
326		380
327	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
328	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
329	could have exited already (and no SIGCHLD will be sent anymore).	383	could have exited already (and no SIGCHLD will be sent anymore).
330		384
331	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
332	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
333	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).
334	place).	389	AnyEvent's pure perl event loop handles all cases correctly regardless
		390	of when you start the watcher.
335		391
336	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
337	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
338	you "fork" the child (alternatively, you can call "AnyEvent::detect").	394	you "fork" the child (alternatively, you can call "AnyEvent::detect").
339		395
340	Example: fork a process and wait for it	396	Example: fork a process and wait for it
341		397
342	my $done = AnyEvent->condvar;	398	my $done = AnyEvent->condvar;
343		399
344	my $pid = fork or exit 5;	400	my $pid = fork or exit 5;
345		401
346	my $w = AnyEvent->child (	402	my $w = AnyEvent->child (
347	pid => $pid,	403	pid => $pid,
348	cb => sub {	404	cb => sub {
349	my ($pid, $status) = @_;	405	my ($pid, $status) = @_;
350	warn "pid $pid exited with status $status";	406	warn "pid $pid exited with status $status";
351	$done->send;	407	$done->send;
352	},	408	},
353	);	409	);
354		410
355	# do something else, then wait for process exit	411	# do something else, then wait for process exit
356	$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	});
357		447
358	CONDITION VARIABLES	448	CONDITION VARIABLES
359	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
360	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
361	will actively watch for new events and call your callbacks.	451	will actively watch for new events and call your callbacks.
362		452
363	AnyEvent is different, it expects somebody else to run the event loop	453	AnyEvent is slightly different: it expects somebody else to run the
364	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).
365		456
366	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
367	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.
368		461
369	Condition variables can be created by calling the "AnyEvent->condvar"	462	Condition variables can be created by calling the "AnyEvent->condvar"
370	method, usually without arguments. The only argument pair allowed is	463	method, usually without arguments. The only argument pair allowed is
371	"cb", which specifies a callback to be called when the condition	464	"cb", which specifies a callback to be called when the condition
372	variable becomes true.	465	variable becomes true, with the condition variable as the first argument
		466	(but not the results).
373		467
374	After creation, the condition variable is "false" until it becomes	468	After creation, the condition variable is "false" until it becomes
375	"true" by calling the "send" method (or calling the condition variable	469	"true" by calling the "send" method (or calling the condition variable
376	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
377	the "->send" method).	471	the "->send" method).
…		…
423	after => 1,	517	after => 1,
424	cb => sub { $result_ready->send },	518	cb => sub { $result_ready->send },
425	);	519	);
426		520
427	# this "blocks" (while handling events) till the callback	521	# this "blocks" (while handling events) till the callback
428	# calls send	522	# calls -<send
429	$result_ready->recv;	523	$result_ready->recv;
430		524
431	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
432	variables are also code references.	526	variables are also callable directly.
433		527
434	my $done = AnyEvent->condvar;	528	my $done = AnyEvent->condvar;
435	my $delay = AnyEvent->timer (after => 5, cb => $done);	529	my $delay = AnyEvent->timer (after => 5, cb => $done);
436	$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	});
437		548
438	METHODS FOR PRODUCERS	549	METHODS FOR PRODUCERS
439	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
440	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
441	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
…		…
451		562
452	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
453	future "->recv" calls.	564	future "->recv" calls.
454		565
455	Condition variables are overloaded so one can call them directly (as	566	Condition variables are overloaded so one can call them directly (as
456	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
457	"send". Note, however, that many C-based event loops do not handle	568	calling "send".
458	overloading, so as tempting as it may be, passing a condition
459	variable instead of a callback does not work. Both the pure perl and
460	EV loops support overloading, however, as well as all functions that
461	use perl to invoke a callback (as in AnyEvent::Socket and
462	AnyEvent::DNS for example).
463		569
464	$cv->croak ($error)	570	$cv->croak ($error)
465	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
466	"Carp::croak" with the given error message/object/scalar.	572	"Carp::croak" with the given error message/object/scalar.
467		573
468	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
469	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.
470		580
471	$cv->begin ([group callback])	581	$cv->begin ([group callback])
472	$cv->end	582	$cv->end
473	These two methods are EXPERIMENTAL and MIGHT CHANGE.
474
475	These two methods can be used to combine many transactions/events	583	These two methods can be used to combine many transactions/events
476	into one. For example, a function that pings many hosts in parallel	584	into one. For example, a function that pings many hosts in parallel
477	might want to use a condition variable for the whole process.	585	might want to use a condition variable for the whole process.
478		586
479	Every call to "->begin" will increment a counter, and every call to	587	Every call to "->begin" will increment a counter, and every call to
480	"->end" will decrement it. If the counter reaches 0 in "->end", the	588	"->end" will decrement it. If the counter reaches 0 in "->end", the
481	(last) callback passed to "begin" will be executed. That callback is	589	(last) callback passed to "begin" will be executed. That callback is
482	supposed to call "->send", but that is not required. If no	590	supposed to call "->send", but that is not required. If no
483	callback was set, "send" will be called without any arguments.	591	callback was set, "send" will be called without any arguments.
484		592
485	Let's clarify this with the ping example:	593	You can think of "$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:
486		625
487	my $cv = AnyEvent->condvar;	626	my $cv = AnyEvent->condvar;
488		627
489	my %result;	628	my %result;
490	$cv->begin (sub { $cv->send (\%result) });	629	$cv->begin (sub { $cv->send (\%result) });
…		…
510	the loop, which serves two important purposes: first, it sets the	649	the loop, which serves two important purposes: first, it sets the
511	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
512	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
513	(the loop doesn't execute once).	652	(the loop doesn't execute once).
514		653
515	This is the general pattern when you "fan out" into multiple	654	This is the general pattern when you "fan out" into multiple (but
516	subrequests: use an outer "begin"/"end" pair to set the callback and	655	potentially none) subrequests: use an outer "begin"/"end" pair to
517	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,
518	you start, call "begin" and for each subrequest you finish, call	657	for each subrequest you start, call "begin" and for each subrequest
519	"end".	658	you finish, call "end".
520		659
521	METHODS FOR CONSUMERS	660	METHODS FOR CONSUMERS
522	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
523	awaits the condition.	662	awaits the condition.
524		663
…		…
533	function will call "croak".	672	function will call "croak".
534		673
535	In list context, all parameters passed to "send" will be returned,	674	In list context, all parameters passed to "send" will be returned,
536	in scalar context only the first one will be returned.	675	in scalar context only the first one will be returned.
537		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
538	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
539	(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
540	using this from a module, never require a blocking wait*, but let	686	using this from a module, never require a blocking wait*. Instead,
541	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
542	by coupling condition variables with some kind of request results	688	example, by coupling condition variables with some kind of request
543	and supporting callbacks so the caller knows that getting the result	689	results and supporting callbacks so the caller knows that getting
544	will not block, while still supporting blocking waits if the caller	690	the result will not block, while still supporting blocking waits if
545	so desires).	691	the caller so desires).
546
547	Another reason never to "->recv" in a module is that you cannot
548	sensibly have two "->recv"'s in parallel, as that would require
549	multiple interpreters or coroutines/threads, none of which
550	"AnyEvent" can supply.
551
552	The Coro module, however, can and does supply coroutines and, in
553	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
554	versions and also integrates coroutines into AnyEvent, making
555	blocking "->recv" calls perfectly safe as long as they are done from
556	another coroutine (one that doesn't run the event loop).
557		692
558	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
559	only calling "->recv" from within that callback (or at a later	694	only calling "->recv" from within that callback (or at a later
560	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
561	blocking waits otherwise.	696	blocking waits otherwise.
562		697
563	$bool = $cv->ready	698	$bool = $cv->ready
564	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
565	"croak" have been called.	700	"croak" have been called.
566		701
567	$cb = $cv->cb ([new callback])	702	$cb = $cv->cb ($cb->($cv))
568	This is a mutator function that returns the callback set and	703	This is a mutator function that returns the callback set and
569	optionally replaces it before doing so.	704	optionally replaces it before doing so.
570		705
571	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.
572	when "send" or "croak" are called. Calling "recv" inside the	707	when "send" or "croak" are called, with the only argument being the
		708	condition variable itself. Calling "recv" inside the callback or at
573	callback or at any later time is guaranteed not to block.	709	any later time is guaranteed not to block.
		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.
574		769
575	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
576	$AnyEvent::MODEL	774	$AnyEvent::MODEL
577	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
578	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
579	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
580	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
581	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.
582		782	in rxvt-unicode it will be "urxvt::anyevent").
583	The known classes so far are:
584
585	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
586	AnyEvent::Impl::Event based on Event, second best choice.
587	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
588	AnyEvent::Impl::Glib based on Glib, third-best choice.
589	AnyEvent::Impl::Tk based on Tk, very bad choice.
590	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
591	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
592	AnyEvent::Impl::POE based on POE, not generic enough for full support.
593
594	There is no support for WxWidgets, as WxWidgets has no support for
595	watching file handles. However, you can use WxWidgets through the
596	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
597	second, which was considered to be too horrible to even consider for
598	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
599	using it's adaptor.
600
601	AnyEvent knows about Prima and Wx and will try to use POE when
602	autodetecting them.
603		783
604	AnyEvent::detect	784	AnyEvent::detect
605	Returns $AnyEvent::MODEL, forcing autodetection of the event model	785	Returns $AnyEvent::MODEL, forcing autodetection of the event model
606	if necessary. You should only call this function right before you	786	if necessary. You should only call this function right before you
607	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
608	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".
609		792
610	$guard = AnyEvent::post_detect { BLOCK }	793	$guard = AnyEvent::post_detect { BLOCK }
611	Arranges for the code block to be executed as soon as the event	794	Arranges for the code block to be executed as soon as the event
612	model is autodetected (or immediately if this has already happened).	795	model is autodetected (or immediately if this has already happened).
		796
		797	The block will be executed after the actual backend has been
		798	detected ($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.
613		807
614	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
615	object that automatically removes the callback again when it is	809	object that automatically removes the callback again when it is
616	destroyed. See Coro::BDB for a case where this is useful.	810	destroyed. See Coro::BDB for a case where this is useful.
617		811
…		…
619	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
620	before or after loading AnyEvent), then they will called directly	814	before or after loading AnyEvent), then they will called directly
621	after the event loop has been chosen.	815	after the event loop has been chosen.
622		816
623	You should check $AnyEvent::MODEL before adding to this array,	817	You should check $AnyEvent::MODEL before adding to this array,
624	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
625	been detected, and the array will be ignored.	819	detected, and the array will be ignored.
626		820
627	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.
628		829
629	WHAT TO DO IN A MODULE	830	WHAT TO DO IN A MODULE
630	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
631	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.
632		833
…		…
683	variable somewhere, waiting for it, and sending it when the program	884	variable somewhere, waiting for it, and sending it when the program
684	should exit cleanly.	885	should exit cleanly.
685		886
686	OTHER MODULES	887	OTHER MODULES
687	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
688	AnyEvent and can therefore be mixed easily with other AnyEvent modules	889	AnyEvent as a client and can therefore be mixed easily with other
689	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
690	available via CPAN.	891	modules come with AnyEvent, most are available via CPAN.
691		892
692	AnyEvent::Util	893	AnyEvent::Util
693	Contains various utility functions that replace often-used but	894	Contains various utility functions that replace often-used but
694	blocking functions such as "inet_aton" by event-/callback-based	895	blocking functions such as "inet_aton" by event-/callback-based
695	versions.	896	versions.
696
697	AnyEvent::Handle
698	Provide read and write buffers and manages watchers for reads and
699	writes.
700		897
701	AnyEvent::Socket	898	AnyEvent::Socket
702	Provides various utility functions for (internet protocol) sockets,	899	Provides various utility functions for (internet protocol) sockets,
703	addresses and name resolution. Also functions to create non-blocking	900	addresses and name resolution. Also functions to create non-blocking
704	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
705	more.	902	more.
706		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
707	AnyEvent::DNS	909	AnyEvent::DNS
708	Provides rich asynchronous DNS resolver capabilities.	910	Provides rich asynchronous DNS resolver capabilities.
709		911
		912	AnyEvent::HTTP
		913	A simple-to-use HTTP library that is capable of making a lot of
		914	concurrent HTTP requests.
		915
710	AnyEvent::HTTPD	916	AnyEvent::HTTPD
711	Provides a simple web application server framework.	917	Provides a simple web application server framework.
712		918
713	AnyEvent::FastPing	919	AnyEvent::FastPing
714	The fastest ping in the west.	920	The fastest ping in the west.
715		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
716	Net::IRC3	940	Net::IRC3).
717	AnyEvent based IRC client module family.
718		941
719	Net::XMPP2	942	AnyEvent::XMPP
720	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).
721		949
722	Net::FCP	950	Net::FCP
723	AnyEvent-based implementation of the Freenet Client Protocol,	951	AnyEvent-based implementation of the Freenet Client Protocol,
724	birthplace of AnyEvent.	952	birthplace of AnyEvent.
725		953
…		…
727	High level API for event-based execution flow control.	955	High level API for event-based execution flow control.
728		956
729	Coro	957	Coro
730	Has special support for AnyEvent via Coro::AnyEvent.	958	Has special support for AnyEvent via Coro::AnyEvent.
731		959
732	AnyEvent::AIO, IO::AIO	960	ERROR AND EXCEPTION HANDLING
733	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
734	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	962	caller to do that if required. The AnyEvent::Strict module (see also the
735	together.	963	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		964	checking of all AnyEvent methods, however, which is highly useful during
		965	development.
736		966
737	AnyEvent::BDB, BDB	967	As for exception handling (i.e. runtime errors and exceptions thrown
738	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently	968	while executing a callback), this is not only highly event-loop
739	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.
740		971
741	IO::Lambda	972	The pure perl event loop simply re-throws the exception (usually within
742	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->()",
743	AnyEvent.	974	Glib uses "install_exception_handler" and so on.
744
745	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
746	This is an advanced topic that you do not normally need to use AnyEvent
747	in a module. This section is only of use to event loop authors who want
748	to provide AnyEvent compatibility.
749
750	If you need to support another event library which isn't directly
751	supported by AnyEvent, you can supply your own interface to it by
752	pushing, before the first watcher gets created, the package name of the
753	event module and the package name of the interface to use onto
754	@AnyEvent::REGISTRY. You can do that before and even without loading
755	AnyEvent, so it is reasonably cheap.
756
757	Example:
758
759	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
760
761	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
762	package/class when it finds the "urxvt" package/module is already
763	loaded.
764
765	When AnyEvent is loaded and asked to find a suitable event model, it
766	will first check for the presence of urxvt by trying to "use" the
767	"urxvt::anyevent" module.
768
769	The class should provide implementations for all watcher types. See
770	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
771	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
772	the sources.
773
774	If you don't provide "signal" and "child" watchers than AnyEvent will
775	provide suitable (hopefully) replacements.
776
777	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
778	terminal emulator uses the above line as-is. An interface isn't included
779	in AnyEvent because it doesn't make sense outside the embedded
780	interpreter inside rxvt-unicode, and it is updated and maintained as
781	part of the rxvt-unicode distribution.
782
783	rxvt-unicode also cheats a bit by not providing blocking access to
784	condition variables: code blocking while waiting for a condition will
785	"die". This still works with most modules/usages, and blocking calls
786	must not be done in an interactive application, so it makes sense.
787		975
788	ENVIRONMENT VARIABLES	976	ENVIRONMENT VARIABLES
789	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.
790		983
791	"PERL_ANYEVENT_VERBOSE"	984	"PERL_ANYEVENT_VERBOSE"
792	By default, AnyEvent will be completely silent except in fatal	985	By default, AnyEvent will be completely silent except in fatal
793	conditions. You can set this environment variable to make AnyEvent	986	conditions. You can set this environment variable to make AnyEvent
794	more talkative.	987	more talkative.
…		…
797	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
798	by "PERL_ANYEVENT_MODEL".	991	by "PERL_ANYEVENT_MODEL".
799		992
800	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
801	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.
802		1008
803	"PERL_ANYEVENT_MODEL"	1009	"PERL_ANYEVENT_MODEL"
804	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,
805	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
806	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1012	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
811	This functionality might change in future versions.	1017	This functionality might change in future versions.
812		1018
813	For example, to force the pure perl model (AnyEvent::Impl::Perl) you	1019	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
814	could start your program like this:	1020	could start your program like this:
815		1021
816	PERL_ANYEVENT_MODEL=Perl perl ...	1022	PERL_ANYEVENT_MODEL=Perl perl ...
817		1023
818	"PERL_ANYEVENT_PROTOCOLS"	1024	"PERL_ANYEVENT_PROTOCOLS"
819	Used by both AnyEvent::DNS and AnyEvent::Socket to determine	1025	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
820	preferences for IPv4 or IPv6. The default is unspecified (and might	1026	preferences for IPv4 or IPv6. The default is unspecified (and might
821	change, or be the result of auto probing).	1027	change, or be the result of auto probing).
…		…
825	mentioned will be used, and preference will be given to protocols	1031	mentioned will be used, and preference will be given to protocols
826	mentioned earlier in the list.	1032	mentioned earlier in the list.
827		1033
828	This variable can effectively be used for denial-of-service attacks	1034	This variable can effectively be used for denial-of-service attacks
829	against local programs (e.g. when setuid), although the impact is	1035	against local programs (e.g. when setuid), although the impact is
830	likely small, as the program has to handle connection errors	1036	likely small, as the program has to handle conenction and other
831	already-	1037	failures anyways.
832		1038
833	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1039	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
834	IPv6, but support both and try to use both.	1040	IPv6, but support both and try to use both.
835	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1041	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
836	resolve or contact IPv6 addresses.	1042	resolve or contact IPv6 addresses.
…		…
847	EDNS0 in its DNS requests.	1053	EDNS0 in its DNS requests.
848		1054
849	"PERL_ANYEVENT_MAX_FORKS"	1055	"PERL_ANYEVENT_MAX_FORKS"
850	The maximum number of child processes that	1056	The maximum number of child processes that
851	"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.
852		1117
853	EXAMPLE PROGRAM	1118	EXAMPLE PROGRAM
854	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
855	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
856	quit the program when the user enters quit:	1121	quit the program when the user enters quit:
…		…
1043	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
1044	single watcher.	1309	single watcher.
1045		1310
1046	Results	1311	Results
1047	name watchers bytes create invoke destroy comment	1312	name watchers bytes create invoke destroy comment
1048	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
1049	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
1050	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
1051	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
1052	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
1053	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
1054	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
1055	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
1056	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
1057	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
1058		1325
1059	Discussion	1326	Discussion
1060	The benchmark does not measure scalability of the event loop very	1327	The benchmark does not measure scalability of the event loop very
1061	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)
1062	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
…		…
1087	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
1088	benchmark.	1355	benchmark.
1089		1356
1090	The "Event" module has a relatively high setup and callback invocation	1357	The "Event" module has a relatively high setup and callback invocation
1091	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.
1092		1362
1093	"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
1094	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".
1095	However, Glib scales extremely badly, doubling the number of watchers	1365	However, Glib scales extremely badly, doubling the number of watchers
1096	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
…		…
1167	single "request", that is, reading the token from the pipe and	1437	single "request", that is, reading the token from the pipe and
1168	forwarding it to another server. This includes deleting the old timeout	1438	forwarding it to another server. This includes deleting the old timeout
1169	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.
1170		1440
1171	Results	1441	Results
1172	name sockets create request	1442	name sockets create request
1173	EV 20000 69.01 11.16	1443	EV 20000 69.01 11.16
1174	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
1175	Event 20000 212.62 257.32	1447	Event 20000 212.62 257.32
1176	Glib 20000 651.16 1896.30	1448	Glib 20000 651.16 1896.30
1177	POE 20000 349.67 12317.24 uses POE::Loop::Event	1449	POE 20000 349.67 12317.24 uses POE::Loop::Event
1178		1450
1179	Discussion	1451	Discussion
1180	This benchmark does measure scalability and overall performance of the	1452	This benchmark does measure scalability and overall performance of the
1181	particular event loop.	1453	particular event loop.
1182		1454
1183	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
1184	time is relatively high, though.	1456	time is relatively high, though.
1185		1457
1186	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
1187	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.
1188		1463
1189	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
1190	will understand why). Callback invocation also has a high overhead	1465	will understand why). Callback invocation also has a high overhead
1191	compared to the "$_->() for .."-style loop that the Perl event loop	1466	compared to the "$_->() for .."-style loop that the Perl event loop
1192	uses. Event uses select or poll in basically all documented	1467	uses. Event uses select or poll in basically all documented
…		…
1243		1518
1244	Summary	1519	Summary
1245	* 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,
1246	as the management overhead dominates.	1521	as the management overhead dominates.
1247		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
1248	FORK	1608	FORK
1249	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
1250	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.
1251	Only EV is fully fork-aware.	1611	Only EV is fully fork-aware.
1252		1612
…		…
1262	model than specified in the variable.	1622	model than specified in the variable.
1263		1623
1264	You can make AnyEvent completely ignore this variable by deleting it	1624	You can make AnyEvent completely ignore this variable by deleting it
1265	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:
1266		1626
1267	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1627	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1268		1628
1269	use AnyEvent;	1629	use AnyEvent;
1270		1630
1271	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1631	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1272	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
1273	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).
1274		1646
1275	SEE ALSO	1647	SEE ALSO
1276	Utility functions: AnyEvent::Util.	1648	Utility functions: AnyEvent::Util.
1277		1649
1278	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,
1279	Event::Lib, Qt, POE.	1651	Event::Lib, Qt, POE.
1280		1652
1281	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1653	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1282	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1654	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1283	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1655	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1656	AnyEvent::Impl::IOAsync.
1284		1657
1285	Non-blocking file handles, sockets, TCP clients and servers:	1658	Non-blocking file handles, sockets, TCP clients and servers:
1286	AnyEvent::Handle, AnyEvent::Socket.	1659	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1287		1660
1288	Asynchronous DNS: AnyEvent::DNS.	1661	Asynchronous DNS: AnyEvent::DNS.
1289		1662
1290	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1663	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1291		1664
1292	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1665	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1666	AnyEvent::HTTP.
1293		1667
1294	AUTHOR	1668	AUTHOR
1295	Marc Lehmann <schmorp@schmorp.de>	1669	Marc Lehmann <schmorp@schmorp.de>
1296	http://home.schmorp.de/	1670	http://home.schmorp.de/
1297		1671

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Revision 1.24 by root, Thu May 29 03:46:04 2008 UTC vs.
Revision 1.45 by root, Fri Jul 17 14:57:03 2009 UTC