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1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - the DBI of event loop programming
3		3
4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	loops	5	Qt and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# if you prefer function calls, look at the AE manpage for
		11	# an alternative API.
		12
		13	# file handle or descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {	14	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		15
		16	# one-shot or repeating timers
		17	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		18	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		19
		20	print AnyEvent->now; # prints current event loop time
		21	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		22
		23	# POSIX signal
		24	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		25
		26	# child process exit
		27	my $w = AnyEvent->child (pid => $pid, cb => sub {
		28	my ($pid, $status) = @_;
11	...	29	...
12	});	30	});
13		31
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	32	# called when event loop idle (if applicable)
15	...	33	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		34
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	35	my $w = AnyEvent->condvar; # stores whether a condition was flagged
19	$w->send; # wake up current and all future recv's	36	$w->send; # wake up current and all future recv's
20	$w->recv; # enters "main loop" till $condvar gets ->send	37	$w->recv; # enters "main loop" till $condvar gets ->send
		38	# use a condvar in callback mode:
		39	$w->cb (sub { $_[0]->recv });
21		40
22	INTRODUCTION/TUTORIAL	41	INTRODUCTION/TUTORIAL
23	This manpage is mainly a reference manual. If you are interested in a	42	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	43	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
25	manpage.	44	manpage.
		45
		46	SUPPORT
		47	There is a mailinglist for discussing all things AnyEvent, and an IRC
		48	channel, too.
		49
		50	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		51	Repository, at <http://anyevent.schmorp.de>, for more info.
26		52
27	WHY YOU SHOULD USE THIS MODULE (OR NOT)	53	WHY YOU SHOULD USE THIS MODULE (OR NOT)
28	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	54	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
29	nowadays. So what is different about AnyEvent?	55	nowadays. So what is different about AnyEvent?
30		56
…		…
123	These watchers are normal Perl objects with normal Perl lifetime. After	149	These watchers are normal Perl objects with normal Perl lifetime. After
124	creating a watcher it will immediately "watch" for events and invoke the	150	creating a watcher it will immediately "watch" for events and invoke the
125	callback when the event occurs (of course, only when the event model is	151	callback when the event occurs (of course, only when the event model is
126	in control).	152	in control).
127		153
		154	Note that callbacks must not permanently change global variables
		155	potentially in use by the event loop (such as $_ or $[) and that
		156	callbacks must not "die". The former is good programming practise in
		157	Perl and the latter stems from the fact that exception handling differs
		158	widely between event loops.
		159
128	To disable the watcher you have to destroy it (e.g. by setting the	160	To disable the watcher you have to destroy it (e.g. by setting the
129	variable you store it in to "undef" or otherwise deleting all references	161	variable you store it in to "undef" or otherwise deleting all references
130	to it).	162	to it).
131		163
132	All watchers are created by calling a method on the "AnyEvent" class.	164	All watchers are created by calling a method on the "AnyEvent" class.
…		…
144	Note that "my $w; $w =" combination. This is necessary because in Perl,	176	Note that "my $w; $w =" combination. This is necessary because in Perl,
145	my variables are only visible after the statement in which they are	177	my variables are only visible after the statement in which they are
146	declared.	178	declared.
147		179
148	I/O WATCHERS	180	I/O WATCHERS
		181	$w = AnyEvent->io (
		182	fh => <filehandle_or_fileno>,
		183	poll => <"r" or "w">,
		184	cb => <callback>,
		185	);
		186
149	You can create an I/O watcher by calling the "AnyEvent->io" method with	187	You can create an I/O watcher by calling the "AnyEvent->io" method with
150	the following mandatory key-value pairs as arguments:	188	the following mandatory key-value pairs as arguments:
151		189
152	"fh" the Perl *file handle* (*not* file descriptor) to watch for events	190	"fh" is the Perl *file handle* (or a naked file descriptor) to watch for
153	(AnyEvent might or might not keep a reference to this file handle).	191	events (AnyEvent might or might not keep a reference to this file
		192	handle). Note that only file handles pointing to things for which
		193	non-blocking operation makes sense are allowed. This includes sockets,
		194	most character devices, pipes, fifos and so on, but not for example
		195	files or block devices.
		196
154	"poll" must be a string that is either "r" or "w", which creates a	197	"poll" must be a string that is either "r" or "w", which creates a
155	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	198	watcher waiting for "r"eadable or "w"ritable events, respectively.
		199
156	is the callback to invoke each time the file handle becomes ready.	200	"cb" is the callback to invoke each time the file handle becomes ready.
157		201
158	Although the callback might get passed parameters, their value and	202	Although the callback might get passed parameters, their value and
159	presence is undefined and you cannot rely on them. Portable AnyEvent	203	presence is undefined and you cannot rely on them. Portable AnyEvent
160	callbacks cannot use arguments passed to I/O watcher callbacks.	204	callbacks cannot use arguments passed to I/O watcher callbacks.
161		205
…		…
175	warn "read: $input\n";	219	warn "read: $input\n";
176	undef $w;	220	undef $w;
177	});	221	});
178		222
179	TIME WATCHERS	223	TIME WATCHERS
		224	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		225
		226	$w = AnyEvent->timer (
		227	after => <fractional_seconds>,
		228	interval => <fractional_seconds>,
		229	cb => <callback>,
		230	);
		231
180	You can create a time watcher by calling the "AnyEvent->timer" method	232	You can create a time watcher by calling the "AnyEvent->timer" method
181	with the following mandatory arguments:	233	with the following mandatory arguments:
182		234
183	"after" specifies after how many seconds (fractional values are	235	"after" specifies after how many seconds (fractional values are
184	supported) the callback should be invoked. "cb" is the callback to	236	supported) the callback should be invoked. "cb" is the callback to
…		…
293	In either case, if you care (and in most cases, you don't), then you	345	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	346	can get whatever behaviour you want with any event loop, by taking
295	the difference between "AnyEvent->time" and "AnyEvent->now" into	347	the difference between "AnyEvent->time" and "AnyEvent->now" into
296	account.	348	account.
297		349
		350	AnyEvent->now_update
		351	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		352	current time for each loop iteration (see the discussion of
		353	AnyEvent->now, above).
		354
		355	When a callback runs for a long time (or when the process sleeps),
		356	then this "current" time will differ substantially from the real
		357	time, which might affect timers and time-outs.
		358
		359	When this is the case, you can call this method, which will update
		360	the event loop's idea of "current time".
		361
		362	A typical example would be a script in a web server (e.g.
		363	"mod_perl") - when mod_perl executes the script, then the event loop
		364	will have the wrong idea about the "current time" (being potentially
		365	far in the past, when the script ran the last time). In that case
		366	you should arrange a call to "AnyEvent->now_update" each time the
		367	web server process wakes up again (e.g. at the start of your script,
		368	or in a handler).
		369
		370	Note that updating the time *might* cause some events to be handled.
		371
298	SIGNAL WATCHERS	372	SIGNAL WATCHERS
		373	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		374
299	You can watch for signals using a signal watcher, "signal" is the signal	375	You can watch for signals using a signal watcher, "signal" is the signal
300	*name* in uppercase and without any "SIG" prefix, "cb" is the Perl	376	*name* in uppercase and without any "SIG" prefix, "cb" is the Perl
301	callback to be invoked whenever a signal occurs.	377	callback to be invoked whenever a signal occurs.
302		378
303	Although the callback might get passed parameters, their value and	379	Although the callback might get passed parameters, their value and
…		…
308	invocation, and callback invocation will be synchronous. Synchronous	384	invocation, and callback invocation will be synchronous. Synchronous
309	means that it might take a while until the signal gets handled by the	385	means that it might take a while until the signal gets handled by the
310	process, but it is guaranteed not to interrupt any other callbacks.	386	process, but it is guaranteed not to interrupt any other callbacks.
311		387
312	The main advantage of using these watchers is that you can share a	388	The main advantage of using these watchers is that you can share a
313	signal between multiple watchers.	389	signal between multiple watchers, and AnyEvent will ensure that signals
		390	will not interrupt your program at bad times.
314		391
315	This watcher might use %SIG, so programs overwriting those signals	392	This watcher might use %SIG (depending on the event loop used), so
316	directly will likely not work correctly.	393	programs overwriting those signals directly will likely not work
		394	correctly.
317		395
318	Example: exit on SIGINT	396	Example: exit on SIGINT
319		397
320	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	398	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
321		399
		400	Restart Behaviour
		401	While restart behaviour is up to the event loop implementation, most
		402	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		403	pure perl implementation).
		404
		405	Safe/Unsafe Signals
		406	Perl signals can be either "safe" (synchronous to opcode handling) or
		407	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		408	latter might corrupt your memory.
		409
		410	AnyEvent signal handlers are, in addition, synchronous to the event
		411	loop, i.e. they will not interrupt your running perl program but will
		412	only be called as part of the normal event handling (just like timer,
		413	I/O etc. callbacks, too).
		414
		415	Signal Races, Delays and Workarounds
		416	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		417	callbacks to signals in a generic way, which is a pity, as you cannot do
		418	race-free signal handling in perl, requiring C libraries for this.
		419	AnyEvent will try to do it's best, which means in some cases, signals
		420	will be delayed. The maximum time a signal might be delayed is specified
		421	in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
		422	can be changed only before the first signal watcher is created, and
		423	should be left alone otherwise. This variable determines how often
		424	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		425	will cause fewer spurious wake-ups, which is better for power and CPU
		426	saving.
		427
		428	All these problems can be avoided by installing the optional
		429	Async::Interrupt module, which works with most event loops. It will not
		430	work with inherently broken event loops such as Event or Event::Lib (and
		431	not with POE currently, as POE does it's own workaround with one-second
		432	latency). For those, you just have to suffer the delays.
		433
322	CHILD PROCESS WATCHERS	434	CHILD PROCESS WATCHERS
		435	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		436
323	You can also watch on a child process exit and catch its exit status.	437	You can also watch on a child process exit and catch its exit status.
324		438
325	The child process is specified by the "pid" argument (if set to 0, it	439	The child process is specified by the "pid" argument (one some backends,
326	watches for any child process exit). The watcher will trigger as often	440	using 0 watches for any child process exit, on others this will croak).
327	as status change for the child are received. This works by installing a	441	The watcher will be triggered only when the child process has finished
328	signal handler for "SIGCHLD". The callback will be called with the pid	442	and an exit status is available, not on any trace events
329	and exit status (as returned by waitpid), so unlike other watcher types,	443	(stopped/continued).
330	you *can* rely on child watcher callback arguments.	444
		445	The callback will be called with the pid and exit status (as returned by
		446	waitpid), so unlike other watcher types, you *can* rely on child watcher
		447	callback arguments.
		448
		449	This watcher type works by installing a signal handler for "SIGCHLD",
		450	and since it cannot be shared, nothing else should use SIGCHLD or reap
		451	random child processes (waiting for specific child processes, e.g.
		452	inside "system", is just fine).
331		453
332	There is a slight catch to child watchers, however: you usually start	454	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	455	them *after* the child process was created, and this means the process
334	could have exited already (and no SIGCHLD will be sent anymore).	456	could have exited already (and no SIGCHLD will be sent anymore).
335		457
336	Not all event models handle this correctly (POE doesn't), but even for	458	Not all event models handle this correctly (neither POE nor IO::Async
		459	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	460	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	461	before the process exits (i.e. before you fork in the first place).
339	place).	462	AnyEvent's pure perl event loop handles all cases correctly regardless
		463	of when you start the watcher.
340		464
341	This means you cannot create a child watcher as the very first thing in	465	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	466	an AnyEvent program, you *have* to create at least one watcher before
343	you "fork" the child (alternatively, you can call "AnyEvent::detect").	467	you "fork" the child (alternatively, you can call "AnyEvent::detect").
344		468
		469	As most event loops do not support waiting for child events, they will
		470	be emulated by AnyEvent in most cases, in which the latency and race
		471	problems mentioned in the description of signal watchers apply.
		472
345	Example: fork a process and wait for it	473	Example: fork a process and wait for it
346		474
347	my $done = AnyEvent->condvar;	475	my $done = AnyEvent->condvar;
348		476
349	my $pid = fork or exit 5;	477	my $pid = fork or exit 5;
350		478
351	my $w = AnyEvent->child (	479	my $w = AnyEvent->child (
352	pid => $pid,	480	pid => $pid,
353	cb => sub {	481	cb => sub {
354	my ($pid, $status) = @_;	482	my ($pid, $status) = @_;
355	warn "pid $pid exited with status $status";	483	warn "pid $pid exited with status $status";
356	$done->send;	484	$done->send;
357	},	485	},
358	);	486	);
359		487
360	# do something else, then wait for process exit	488	# do something else, then wait for process exit
361	$done->recv;	489	$done->recv;
362		490
		491	IDLE WATCHERS
		492	$w = AnyEvent->idle (cb => <callback>);
		493
		494	Repeatedly invoke the callback after the process becomes idle, until
		495	either the watcher is destroyed or new events have been detected.
		496
		497	Idle watchers are useful when there is a need to do something, but it is
		498	not so important (or wise) to do it instantly. The callback will be
		499	invoked only when there is "nothing better to do", which is usually
		500	defined as "all outstanding events have been handled and no new events
		501	have been detected". That means that idle watchers ideally get invoked
		502	when the event loop has just polled for new events but none have been
		503	detected. Instead of blocking to wait for more events, the idle watchers
		504	will be invoked.
		505
		506	Unfortunately, most event loops do not really support idle watchers
		507	(only EV, Event and Glib do it in a usable fashion) - for the rest,
		508	AnyEvent will simply call the callback "from time to time".
		509
		510	Example: read lines from STDIN, but only process them when the program
		511	is otherwise idle:
		512
		513	my @lines; # read data
		514	my $idle_w;
		515	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		516	push @lines, scalar <STDIN>;
		517
		518	# start an idle watcher, if not already done
		519	$idle_w ||= AnyEvent->idle (cb => sub {
		520	# handle only one line, when there are lines left
		521	if (my $line = shift @lines) {
		522	print "handled when idle: $line";
		523	} else {
		524	# otherwise disable the idle watcher again
		525	undef $idle_w;
		526	}
		527	});
		528	});
		529
363	CONDITION VARIABLES	530	CONDITION VARIABLES
		531	$cv = AnyEvent->condvar;
		532
		533	$cv->send (<list>);
		534	my @res = $cv->recv;
		535
364	If you are familiar with some event loops you will know that all of them	536	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	537	require you to run some blocking "loop", "run" or similar function that
366	will actively watch for new events and call your callbacks.	538	will actively watch for new events and call your callbacks.
367		539
368	AnyEvent is different, it expects somebody else to run the event loop	540	AnyEvent is slightly different: it expects somebody else to run the
369	and will only block when necessary (usually when told by the user).	541	event loop and will only block when necessary (usually when told by the
		542	user).
370		543
371	The instrument to do that is called a "condition variable", so called	544	The tool to do that is called a "condition variable", so called because
372	because they represent a condition that must become true.	545	they represent a condition that must become true.
		546
		547	Now is probably a good time to look at the examples further below.
373		548
374	Condition variables can be created by calling the "AnyEvent->condvar"	549	Condition variables can be created by calling the "AnyEvent->condvar"
375	method, usually without arguments. The only argument pair allowed is	550	method, usually without arguments. The only argument pair allowed is
376	"cb", which specifies a callback to be called when the condition	551	"cb", which specifies a callback to be called when the condition
377	variable becomes true.	552	variable becomes true, with the condition variable as the first argument
		553	(but not the results).
378		554
379	After creation, the condition variable is "false" until it becomes	555	After creation, the condition variable is "false" until it becomes
380	"true" by calling the "send" method (or calling the condition variable	556	"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	557	as if it were a callback, read about the caveats in the description for
382	the "->send" method).	558	the "->send" method).
383		559
384	Condition variables are similar to callbacks, except that you can	560	Since condition variables are the most complex part of the AnyEvent API,
385	optionally wait for them. They can also be called merge points - points	561	here are some different mental models of what they are - pick the ones
386	in time where multiple outstanding events have been processed. And yet	562	you can connect to:
387	another way to call them is transactions - each condition variable can	563
388	be used to represent a transaction, which finishes at some point and	564	* Condition variables are like callbacks - you can call them (and pass
389	delivers a result.	565	them instead of callbacks). Unlike callbacks however, you can also
		566	wait for them to be called.
		567
		568	* Condition variables are signals - one side can emit or send them,
		569	the other side can wait for them, or install a handler that is
		570	called when the signal fires.
		571
		572	* Condition variables are like "Merge Points" - points in your program
		573	where you merge multiple independent results/control flows into one.
		574
		575	* Condition variables represent a transaction - function that start
		576	some kind of transaction can return them, leaving the caller the
		577	choice between waiting in a blocking fashion, or setting a callback.
		578
		579	* Condition variables represent future values, or promises to deliver
		580	some result, long before the result is available.
390		581
391	Condition variables are very useful to signal that something has	582	Condition variables are very useful to signal that something has
392	finished, for example, if you write a module that does asynchronous http	583	finished, for example, if you write a module that does asynchronous http
393	requests, then a condition variable would be the ideal candidate to	584	requests, then a condition variable would be the ideal candidate to
394	signal the availability of results. The user can either act when the	585	signal the availability of results. The user can either act when the
…		…
415	which eventually calls "-> send", and the "consumer side", which waits	606	which eventually calls "-> send", and the "consumer side", which waits
416	for the send to occur.	607	for the send to occur.
417		608
418	Example: wait for a timer.	609	Example: wait for a timer.
419		610
420	# wait till the result is ready	611	# condition: "wait till the timer is fired"
421	my $result_ready = AnyEvent->condvar;	612	my $timer_fired = AnyEvent->condvar;
422		613
423	# do something such as adding a timer	614	# create the timer - we could wait for, say
424	# or socket watcher the calls $result_ready->send	615	# a handle becomign ready, or even an
425	# when the "result" is ready.	616	# AnyEvent::HTTP request to finish, but
426	# in this case, we simply use a timer:	617	# in this case, we simply use a timer:
427	my $w = AnyEvent->timer (	618	my $w = AnyEvent->timer (
428	after => 1,	619	after => 1,
429	cb => sub { $result_ready->send },	620	cb => sub { $timer_fired->send },
430	);	621	);
431		622
432	# this "blocks" (while handling events) till the callback	623	# this "blocks" (while handling events) till the callback
433	# calls send	624	# calls ->send
434	$result_ready->recv;	625	$timer_fired->recv;
435		626
436	Example: wait for a timer, but take advantage of the fact that condition	627	Example: wait for a timer, but take advantage of the fact that condition
437	variables are also code references.	628	variables are also callable directly.
438		629
439	my $done = AnyEvent->condvar;	630	my $done = AnyEvent->condvar;
440	my $delay = AnyEvent->timer (after => 5, cb => $done);	631	my $delay = AnyEvent->timer (after => 5, cb => $done);
441	$done->recv;	632	$done->recv;
		633
		634	Example: Imagine an API that returns a condvar and doesn't support
		635	callbacks. This is how you make a synchronous call, for example from the
		636	main program:
		637
		638	use AnyEvent::CouchDB;
		639
		640	...
		641
		642	my @info = $couchdb->info->recv;
		643
		644	And this is how you would just set a callback to be called whenever the
		645	results are available:
		646
		647	$couchdb->info->cb (sub {
		648	my @info = $_[0]->recv;
		649	});
442		650
443	METHODS FOR PRODUCERS	651	METHODS FOR PRODUCERS
444	These methods should only be used by the producing side, i.e. the	652	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	653	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	654	producer side which creates the condvar in most cases, but it isn't
…		…
456		664
457	Any arguments passed to the "send" call will be returned by all	665	Any arguments passed to the "send" call will be returned by all
458	future "->recv" calls.	666	future "->recv" calls.
459		667
460	Condition variables are overloaded so one can call them directly (as	668	Condition variables are overloaded so one can call them directly (as
461	a code reference). Calling them directly is the same as calling	669	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	670	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		671
469	$cv->croak ($error)	672	$cv->croak ($error)
470	Similar to send, but causes all call's to "->recv" to invoke	673	Similar to send, but causes all call's to "->recv" to invoke
471	"Carp::croak" with the given error message/object/scalar.	674	"Carp::croak" with the given error message/object/scalar.
472		675
473	This can be used to signal any errors to the condition variable	676	This can be used to signal any errors to the condition variable
474	user/consumer.	677	user/consumer. Doing it this way instead of calling "croak" directly
		678	delays the error detetcion, but has the overwhelmign advantage that
		679	it diagnoses the error at the place where the result is expected,
		680	and not deep in some event clalback without connection to the actual
		681	code causing the problem.
475		682
476	$cv->begin ([group callback])	683	$cv->begin ([group callback])
477	$cv->end	684	$cv->end
478	These two methods are EXPERIMENTAL and MIGHT CHANGE.
479
480	These two methods can be used to combine many transactions/events	685	These two methods can be used to combine many transactions/events
481	into one. For example, a function that pings many hosts in parallel	686	into one. For example, a function that pings many hosts in parallel
482	might want to use a condition variable for the whole process.	687	might want to use a condition variable for the whole process.
483		688
484	Every call to "->begin" will increment a counter, and every call to	689	Every call to "->begin" will increment a counter, and every call to
485	"->end" will decrement it. If the counter reaches 0 in "->end", the	690	"->end" will decrement it. If the counter reaches 0 in "->end", the
486	(last) callback passed to "begin" will be executed. That callback is	691	(last) callback passed to "begin" will be executed, passing the
487	*supposed* to call "->send", but that is not required. If no	692	condvar as first argument. That callback is *supposed* to call
		693	"->send", but that is not required. If no group callback was set,
488	callback was set, "send" will be called without any arguments.	694	"send" will be called without any arguments.
489		695
490	Let's clarify this with the ping example:	696	You can think of "$cv->send" giving you an OR condition (one call
		697	sends), while "$cv->begin" and "$cv->end" giving you an AND
		698	condition (all "begin" calls must be "end"'ed before the condvar
		699	sends).
		700
		701	Let's start with a simple example: you have two I/O watchers (for
		702	example, STDOUT and STDERR for a program), and you want to wait for
		703	both streams to close before activating a condvar:
491		704
492	my $cv = AnyEvent->condvar;	705	my $cv = AnyEvent->condvar;
493		706
		707	$cv->begin; # first watcher
		708	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		709	defined sysread $fh1, my $buf, 4096
		710	or $cv->end;
		711	});
		712
		713	$cv->begin; # second watcher
		714	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		715	defined sysread $fh2, my $buf, 4096
		716	or $cv->end;
		717	});
		718
		719	$cv->recv;
		720
		721	This works because for every event source (EOF on file handle),
		722	there is one call to "begin", so the condvar waits for all calls to
		723	"end" before sending.
		724
		725	The ping example mentioned above is slightly more complicated, as
		726	the there are results to be passwd back, and the number of tasks
		727	that are begung can potentially be zero:
		728
		729	my $cv = AnyEvent->condvar;
		730
494	my %result;	731	my %result;
495	$cv->begin (sub { $cv->send (\%result) });	732	$cv->begin (sub { shift->send (\%result) });
496		733
497	for my $host (@list_of_hosts) {	734	for my $host (@list_of_hosts) {
498	$cv->begin;	735	$cv->begin;
499	ping_host_then_call_callback $host, sub {	736	ping_host_then_call_callback $host, sub {
500	$result{$host} = ...;	737	$result{$host} = ...;
…		…
515	the loop, which serves two important purposes: first, it sets the	752	the loop, which serves two important purposes: first, it sets the
516	callback to be called once the counter reaches 0, and second, it	753	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	754	ensures that "send" is called even when "no" hosts are being pinged
518	(the loop doesn't execute once).	755	(the loop doesn't execute once).
519		756
520	This is the general pattern when you "fan out" into multiple	757	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	758	potentially none) subrequests: use an outer "begin"/"end" pair to
522	ensure "end" is called at least once, and then, for each subrequest	759	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	760	for each subrequest you start, call "begin" and for each subrequest
524	"end".	761	you finish, call "end".
525		762
526	METHODS FOR CONSUMERS	763	METHODS FOR CONSUMERS
527	These methods should only be used by the consuming side, i.e. the code	764	These methods should only be used by the consuming side, i.e. the code
528	awaits the condition.	765	awaits the condition.
529		766
…		…
538	function will call "croak".	775	function will call "croak".
539		776
540	In list context, all parameters passed to "send" will be returned,	777	In list context, all parameters passed to "send" will be returned,
541	in scalar context only the first one will be returned.	778	in scalar context only the first one will be returned.
542		779
		780	Note that doing a blocking wait in a callback is not supported by
		781	any event loop, that is, recursive invocation of a blocking "->recv"
		782	is not allowed, and the "recv" call will "croak" if such a condition
		783	is detected. This condition can be slightly loosened by using
		784	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		785	thread that doesn't run the event loop itself.
		786
543	Not all event models support a blocking wait - some die in that case	787	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	788	(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	789	using this from a module, never require a blocking wait*. Instead,
546	the caller decide whether the call will block or not (for example,	790	let the caller decide whether the call will block or not (for
547	by coupling condition variables with some kind of request results	791	example, by coupling condition variables with some kind of request
548	and supporting callbacks so the caller knows that getting the result	792	results and supporting callbacks so the caller knows that getting
549	will not block, while still supporting blocking waits if the caller	793	the result will not block, while still supporting blocking waits if
550	so desires).	794	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		795
563	You can ensure that "-recv" never blocks by setting a callback and	796	You can ensure that "-recv" never blocks by setting a callback and
564	only calling "->recv" from within that callback (or at a later	797	only calling "->recv" from within that callback (or at a later
565	time). This will work even when the event loop does not support	798	time). This will work even when the event loop does not support
566	blocking waits otherwise.	799	blocking waits otherwise.
567		800
568	$bool = $cv->ready	801	$bool = $cv->ready
569	Returns true when the condition is "true", i.e. whether "send" or	802	Returns true when the condition is "true", i.e. whether "send" or
570	"croak" have been called.	803	"croak" have been called.
571		804
572	$cb = $cv->cb ([new callback])	805	$cb = $cv->cb ($cb->($cv))
573	This is a mutator function that returns the callback set and	806	This is a mutator function that returns the callback set and
574	optionally replaces it before doing so.	807	optionally replaces it before doing so.
575		808
576	The callback will be called when the condition becomes "true", i.e.	809	The callback will be called when the condition becomes (or already
577	when "send" or "croak" are called, with the only argument being the	810	was) "true", i.e. when "send" or "croak" are called (or were
578	condition variable itself. Calling "recv" inside the callback or at	811	called), with the only argument being the condition variable itself.
		812	Calling "recv" inside the callback or at any later time is
579	any later time is guaranteed not to block.	813	guaranteed not to block.
		814
		815	SUPPORTED EVENT LOOPS/BACKENDS
		816	The available backend classes are (every class has its own manpage):
		817
		818	Backends that are autoprobed when no other event loop can be found.
		819	EV is the preferred backend when no other event loop seems to be in
		820	use. If EV is not installed, then AnyEvent will fall back to its own
		821	pure-perl implementation, which is available everywhere as it comes
		822	with AnyEvent itself.
		823
		824	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		825	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		826
		827	Backends that are transparently being picked up when they are used.
		828	These will be used when they are currently loaded when the first
		829	watcher is created, in which case it is assumed that the application
		830	is using them. This means that AnyEvent will automatically pick the
		831	right backend when the main program loads an event module before
		832	anything starts to create watchers. Nothing special needs to be done
		833	by the main program.
		834
		835	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		836	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		837	AnyEvent::Impl::Tk based on Tk, very broken.
		838	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		839	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		840	AnyEvent::Impl::Irssi used when running within irssi.
		841
		842	Backends with special needs.
		843	Qt requires the Qt::Application to be instantiated first, but will
		844	otherwise be picked up automatically. As long as the main program
		845	instantiates the application before any AnyEvent watchers are
		846	created, everything should just work.
		847
		848	AnyEvent::Impl::Qt based on Qt.
		849
		850	Support for IO::Async can only be partial, as it is too broken and
		851	architecturally limited to even support the AnyEvent API. It also is
		852	the only event loop that needs the loop to be set explicitly, so it
		853	can only be used by a main program knowing about AnyEvent. See
		854	AnyEvent::Impl::Async for the gory details.
		855
		856	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		857
		858	Event loops that are indirectly supported via other backends.
		859	Some event loops can be supported via other modules:
		860
		861	There is no direct support for WxWidgets (Wx) or Prima.
		862
		863	WxWidgets has no support for watching file handles. However, you can
		864	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		865	simply polls 20 times per second, which was considered to be too
		866	horrible to even consider for AnyEvent.
		867
		868	Prima is not supported as nobody seems to be using it, but it has a
		869	POE backend, so it can be supported through POE.
		870
		871	AnyEvent knows about both Prima and Wx, however, and will try to
		872	load POE when detecting them, in the hope that POE will pick them
		873	up, in which case everything will be automatic.
580		874
581	GLOBAL VARIABLES AND FUNCTIONS	875	GLOBAL VARIABLES AND FUNCTIONS
		876	These are not normally required to use AnyEvent, but can be useful to
		877	write AnyEvent extension modules.
		878
582	$AnyEvent::MODEL	879	$AnyEvent::MODEL
583	Contains "undef" until the first watcher is being created. Then it	880	Contains "undef" until the first watcher is being created, before
		881	the backend has been autodetected.
		882
584	contains the event model that is being used, which is the name of	883	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	884	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	885	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*).	886	other class in the case AnyEvent has been extended at runtime (e.g.
588		887	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		888
610	AnyEvent::detect	889	AnyEvent::detect
611	Returns $AnyEvent::MODEL, forcing autodetection of the event model	890	Returns $AnyEvent::MODEL, forcing autodetection of the event model
612	if necessary. You should only call this function right before you	891	if necessary. You should only call this function right before you
613	would have created an AnyEvent watcher anyway, that is, as late as	892	would have created an AnyEvent watcher anyway, that is, as late as
614	possible at runtime.	893	possible at runtime, and not e.g. while initialising of your module.
		894
		895	If you need to do some initialisation before AnyEvent watchers are
		896	created, use "post_detect".
615		897
616	$guard = AnyEvent::post_detect { BLOCK }	898	$guard = AnyEvent::post_detect { BLOCK }
617	Arranges for the code block to be executed as soon as the event	899	Arranges for the code block to be executed as soon as the event
618	model is autodetected (or immediately if this has already happened).	900	model is autodetected (or immediately if this has already happened).
619		901
		902	The block will be executed *after* the actual backend has been
		903	detected ($AnyEvent::MODEL is set), but *before* any watchers have
		904	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		905	other initialisations - see the sources of AnyEvent::Strict or
		906	AnyEvent::AIO to see how this is used.
		907
		908	The most common usage is to create some global watchers, without
		909	forcing event module detection too early, for example, AnyEvent::AIO
		910	creates and installs the global IO::AIO watcher in a "post_detect"
		911	block to avoid autodetecting the event module at load time.
		912
620	If called in scalar or list context, then it creates and returns an	913	If called in scalar or list context, then it creates and returns an
621	object that automatically removes the callback again when it is	914	object that automatically removes the callback again when it is
		915	destroyed (or "undef" when the hook was immediately executed). See
622	destroyed. See Coro::BDB for a case where this is useful.	916	AnyEvent::AIO for a case where this is useful.
		917
		918	Example: Create a watcher for the IO::AIO module and store it in
		919	$WATCHER. Only do so after the event loop is initialised, though.
		920
		921	our WATCHER;
		922
		923	my $guard = AnyEvent::post_detect {
		924	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		925	};
		926
		927	# the ||= is important in case post_detect immediately runs the block,
		928	# as to not clobber the newly-created watcher. assigning both watcher and
		929	# post_detect guard to the same variable has the advantage of users being
		930	# able to just C<undef $WATCHER> if the watcher causes them grief.
		931
		932	$WATCHER ||= $guard;
623		933
624	@AnyEvent::post_detect	934	@AnyEvent::post_detect
625	If there are any code references in this array (you can "push" to it	935	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	936	before or after loading AnyEvent), then they will called directly
627	after the event loop has been chosen.	937	after the event loop has been chosen.
628		938
629	You should check $AnyEvent::MODEL before adding to this array,	939	You should check $AnyEvent::MODEL before adding to this array,
630	though: if it contains a true value then the event loop has already	940	though: if it is defined then the event loop has already been
631	been detected, and the array will be ignored.	941	detected, and the array will be ignored.
632		942
633	Best use "AnyEvent::post_detect { BLOCK }" instead.	943	Best use "AnyEvent::post_detect { BLOCK }" when your application
		944	allows it, as it takes care of these details.
		945
		946	This variable is mainly useful for modules that can do something
		947	useful when AnyEvent is used and thus want to know when it is
		948	initialised, but do not need to even load it by default. This array
		949	provides the means to hook into AnyEvent passively, without loading
		950	it.
		951
		952	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		953	together, you could put this into Coro (this is the actual code used
		954	by Coro to accomplish this):
		955
		956	if (defined $AnyEvent::MODEL) {
		957	# AnyEvent already initialised, so load Coro::AnyEvent
		958	require Coro::AnyEvent;
		959	} else {
		960	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		961	# as soon as it is
		962	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		963	}
634		964
635	WHAT TO DO IN A MODULE	965	WHAT TO DO IN A MODULE
636	As a module author, you should "use AnyEvent" and call AnyEvent methods	966	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.	967	freely, but you should not load a specific event module or rely on it.
638		968
…		…
689	variable somewhere, waiting for it, and sending it when the program	1019	variable somewhere, waiting for it, and sending it when the program
690	should exit cleanly.	1020	should exit cleanly.
691		1021
692	OTHER MODULES	1022	OTHER MODULES
693	The following is a non-exhaustive list of additional modules that use	1023	The following is a non-exhaustive list of additional modules that use
694	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1024	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	1025	AnyEvent modules and other event loops in the same program. Some of the
696	available via CPAN.	1026	modules come as part of AnyEvent, the others are available via CPAN.
697		1027
698	AnyEvent::Util	1028	AnyEvent::Util
699	Contains various utility functions that replace often-used but	1029	Contains various utility functions that replace often-used but
700	blocking functions such as "inet_aton" by event-/callback-based	1030	blocking functions such as "inet_aton" by event-/callback-based
701	versions.	1031	versions.
…		…
707	more.	1037	more.
708		1038
709	AnyEvent::Handle	1039	AnyEvent::Handle
710	Provide read and write buffers, manages watchers for reads and	1040	Provide read and write buffers, manages watchers for reads and
711	writes, supports raw and formatted I/O, I/O queued and fully	1041	writes, supports raw and formatted I/O, I/O queued and fully
712	transparent and non-blocking SSL/TLS.	1042	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
713		1043
714	AnyEvent::DNS	1044	AnyEvent::DNS
715	Provides rich asynchronous DNS resolver capabilities.	1045	Provides rich asynchronous DNS resolver capabilities.
716		1046
		1047	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
		1048	AnyEvent::IGS, AnyEvent::FCP
		1049	Implement event-based interfaces to the protocols of the same name
		1050	(for the curious, IGS is the International Go Server and FCP is the
		1051	Freenet Client Protocol).
		1052
		1053	AnyEvent::Handle::UDP
		1054	Here be danger!
		1055
		1056	As Pauli would put it, "Not only is it not right, it's not even
		1057	wrong!" - there are so many things wrong with AnyEvent::Handle::UDP,
		1058	most notably it's use of a stream-based API with a protocol that
		1059	isn't streamable, that the only way to improve it is to delete it.
		1060
		1061	It features data corruption (but typically only under load) and
		1062	general confusion. On top, the author is not only clueless about UDP
		1063	but also fact-resistant - some gems of his understanding: "connect
		1064	doesn't work with UDP", "UDP packets are not IP packets", "UDP only
		1065	has datagrams, not packets", "I don't need to implement proper error
		1066	checking as UDP doesn't support error checking" and so on - he
		1067	doesn't even understand what's wrong with his module when it is
		1068	explained to him.
		1069
717	AnyEvent::HTTP	1070	AnyEvent::DBI
718	A simple-to-use HTTP library that is capable of making a lot of	1071	Executes DBI requests asynchronously in a proxy process for you,
719	concurrent HTTP requests.	1072	notifying you in an event-bnased way when the operation is finished.
		1073
		1074	AnyEvent::AIO
		1075	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1076	the toolbox of every event programmer. AnyEvent::AIO transparently
		1077	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1078	event-based file I/O, and much more.
720		1079
721	AnyEvent::HTTPD	1080	AnyEvent::HTTPD
722	Provides a simple web application server framework.	1081	A simple embedded webserver.
723		1082
724	AnyEvent::FastPing	1083	AnyEvent::FastPing
725	The fastest ping in the west.	1084	The fastest ping in the west.
726		1085
727	AnyEvent::DBI
728	Executes DBI requests asynchronously in a proxy process.
729
730	AnyEvent::AIO
731	Truly asynchronous I/O, should be in the toolbox of every event
732	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
733	together.
734
735	AnyEvent::BDB
736	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
737	fuses BDB and AnyEvent together.
738
739	AnyEvent::GPSD
740	A non-blocking interface to gpsd, a daemon delivering GPS
741	information.
742
743	AnyEvent::IGS
744	A non-blocking interface to the Internet Go Server protocol (used by
745	App::IGS).
746
747	Net::IRC3
748	AnyEvent based IRC client module family.
749
750	Net::XMPP2
751	AnyEvent based XMPP (Jabber protocol) module family.
752
753	Net::FCP
754	AnyEvent-based implementation of the Freenet Client Protocol,
755	birthplace of AnyEvent.
756
757	Event::ExecFlow
758	High level API for event-based execution flow control.
759
760	Coro	1086	Coro
761	Has special support for AnyEvent via Coro::AnyEvent.	1087	Has special support for AnyEvent via Coro::AnyEvent.
762		1088
763	IO::Lambda	1089	SIMPLIFIED AE API
764	The lambda approach to I/O - don't ask, look there. Can use	1090	Starting with version 5.0, AnyEvent officially supports a second, much
765	AnyEvent.	1091	simpler, API that is designed to reduce the calling, typing and memory
		1092	overhead by using function call syntax and a fixed number of parameters.
766		1093
767	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1094	See the AE manpage for details.
768	This is an advanced topic that you do not normally need to use AnyEvent
769	in a module. This section is only of use to event loop authors who want
770	to provide AnyEvent compatibility.
771		1095
772	If you need to support another event library which isn't directly	1096	ERROR AND EXCEPTION HANDLING
773	supported by AnyEvent, you can supply your own interface to it by	1097	In general, AnyEvent does not do any error handling - it relies on the
774	pushing, before the first watcher gets created, the package name of the	1098	caller to do that if required. The AnyEvent::Strict module (see also the
775	event module and the package name of the interface to use onto	1099	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
776	@AnyEvent::REGISTRY. You can do that before and even without loading	1100	checking of all AnyEvent methods, however, which is highly useful during
777	AnyEvent, so it is reasonably cheap.	1101	development.
778		1102
779	Example:	1103	As for exception handling (i.e. runtime errors and exceptions thrown
		1104	while executing a callback), this is not only highly event-loop
		1105	specific, but also not in any way wrapped by this module, as this is the
		1106	job of the main program.
780		1107
781	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	1108	The pure perl event loop simply re-throws the exception (usually within
782		1109	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
783	This tells AnyEvent to (literally) use the "urxvt::anyevent::"	1110	Glib uses "install_exception_handler" and so on.
784	package/class when it finds the "urxvt" package/module is already
785	loaded.
786
787	When AnyEvent is loaded and asked to find a suitable event model, it
788	will first check for the presence of urxvt by trying to "use" the
789	"urxvt::anyevent" module.
790
791	The class should provide implementations for all watcher types. See
792	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
793	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
794	the sources.
795
796	If you don't provide "signal" and "child" watchers than AnyEvent will
797	provide suitable (hopefully) replacements.
798
799	The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt)
800	terminal emulator uses the above line as-is. An interface isn't included
801	in AnyEvent because it doesn't make sense outside the embedded
802	interpreter inside *rxvt-unicode*, and it is updated and maintained as
803	part of the *rxvt-unicode* distribution.
804
805	*rxvt-unicode* also cheats a bit by not providing blocking access to
806	condition variables: code blocking while waiting for a condition will
807	"die". This still works with most modules/usages, and blocking calls
808	must not be done in an interactive application, so it makes sense.
809		1111
810	ENVIRONMENT VARIABLES	1112	ENVIRONMENT VARIABLES
811	The following environment variables are used by this module:	1113	The following environment variables are used by this module or its
		1114	submodules.
		1115
		1116	Note that AnyEvent will remove *all* environment variables starting with
		1117	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1118	enabled.
812		1119
813	"PERL_ANYEVENT_VERBOSE"	1120	"PERL_ANYEVENT_VERBOSE"
814	By default, AnyEvent will be completely silent except in fatal	1121	By default, AnyEvent will be completely silent except in fatal
815	conditions. You can set this environment variable to make AnyEvent	1122	conditions. You can set this environment variable to make AnyEvent
816	more talkative.	1123	more talkative.
…		…
819	conditions, such as not being able to load the event model specified	1126	conditions, such as not being able to load the event model specified
820	by "PERL_ANYEVENT_MODEL".	1127	by "PERL_ANYEVENT_MODEL".
821		1128
822	When set to 2 or higher, cause AnyEvent to report to STDERR which	1129	When set to 2 or higher, cause AnyEvent to report to STDERR which
823	event model it chooses.	1130	event model it chooses.
		1131
		1132	When set to 8 or higher, then AnyEvent will report extra information
		1133	on which optional modules it loads and how it implements certain
		1134	features.
824		1135
825	"PERL_ANYEVENT_STRICT"	1136	"PERL_ANYEVENT_STRICT"
826	AnyEvent does not do much argument checking by default, as thorough	1137	AnyEvent does not do much argument checking by default, as thorough
827	argument checking is very costly. Setting this variable to a true	1138	argument checking is very costly. Setting this variable to a true
828	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1139	value will cause AnyEvent to load "AnyEvent::Strict" and then to
829	thoroughly check the arguments passed to most method calls. If it	1140	thoroughly check the arguments passed to most method calls. If it
830	finds any problems it will croak.	1141	finds any problems, it will croak.
831		1142
832	In other words, enables "strict" mode.	1143	In other words, enables "strict" mode.
833		1144
834	Unlike "use strict" it is definitely recommended ot keep it off in	1145	Unlike "use strict" (or it's modern cousin, "use common::sense", it
835	production.	1146	is definitely recommended to keep it off in production. Keeping
		1147	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1148	programs can be very useful, however.
836		1149
837	"PERL_ANYEVENT_MODEL"	1150	"PERL_ANYEVENT_MODEL"
838	This can be used to specify the event model to be used by AnyEvent,	1151	This can be used to specify the event model to be used by AnyEvent,
839	before auto detection and -probing kicks in. It must be a string	1152	before auto detection and -probing kicks in. It must be a string
840	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1153	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
859	mentioned will be used, and preference will be given to protocols	1172	mentioned will be used, and preference will be given to protocols
860	mentioned earlier in the list.	1173	mentioned earlier in the list.
861		1174
862	This variable can effectively be used for denial-of-service attacks	1175	This variable can effectively be used for denial-of-service attacks
863	against local programs (e.g. when setuid), although the impact is	1176	against local programs (e.g. when setuid), although the impact is
864	likely small, as the program has to handle connection errors	1177	likely small, as the program has to handle conenction and other
865	already-	1178	failures anyways.
866		1179
867	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1180	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
868	IPv6, but support both and try to use both.	1181	IPv6, but support both and try to use both.
869	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1182	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
870	resolve or contact IPv6 addresses.	1183	resolve or contact IPv6 addresses.
…		…
881	EDNS0 in its DNS requests.	1194	EDNS0 in its DNS requests.
882		1195
883	"PERL_ANYEVENT_MAX_FORKS"	1196	"PERL_ANYEVENT_MAX_FORKS"
884	The maximum number of child processes that	1197	The maximum number of child processes that
885	"AnyEvent::Util::fork_call" will create in parallel.	1198	"AnyEvent::Util::fork_call" will create in parallel.
		1199
		1200	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1201	The default value for the "max_outstanding" parameter for the
		1202	default DNS resolver - this is the maximum number of parallel DNS
		1203	requests that are sent to the DNS server.
		1204
		1205	"PERL_ANYEVENT_RESOLV_CONF"
		1206	The file to use instead of /etc/resolv.conf (or OS-specific
		1207	configuration) in the default resolver. When set to the empty
		1208	string, no default config will be used.
		1209
		1210	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1211	When neither "ca_file" nor "ca_path" was specified during
		1212	AnyEvent::TLS context creation, and either of these environment
		1213	variables exist, they will be used to specify CA certificate
		1214	locations instead of a system-dependent default.
		1215
		1216	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1217	When these are set to 1, then the respective modules are not loaded.
		1218	Mostly good for testing AnyEvent itself.
		1219
		1220	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1221	This is an advanced topic that you do not normally need to use AnyEvent
		1222	in a module. This section is only of use to event loop authors who want
		1223	to provide AnyEvent compatibility.
		1224
		1225	If you need to support another event library which isn't directly
		1226	supported by AnyEvent, you can supply your own interface to it by
		1227	pushing, before the first watcher gets created, the package name of the
		1228	event module and the package name of the interface to use onto
		1229	@AnyEvent::REGISTRY. You can do that before and even without loading
		1230	AnyEvent, so it is reasonably cheap.
		1231
		1232	Example:
		1233
		1234	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1235
		1236	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
		1237	package/class when it finds the "urxvt" package/module is already
		1238	loaded.
		1239
		1240	When AnyEvent is loaded and asked to find a suitable event model, it
		1241	will first check for the presence of urxvt by trying to "use" the
		1242	"urxvt::anyevent" module.
		1243
		1244	The class should provide implementations for all watcher types. See
		1245	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
		1246	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
		1247	the sources.
		1248
		1249	If you don't provide "signal" and "child" watchers than AnyEvent will
		1250	provide suitable (hopefully) replacements.
		1251
		1252	The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt)
		1253	terminal emulator uses the above line as-is. An interface isn't included
		1254	in AnyEvent because it doesn't make sense outside the embedded
		1255	interpreter inside *rxvt-unicode*, and it is updated and maintained as
		1256	part of the *rxvt-unicode* distribution.
		1257
		1258	*rxvt-unicode* also cheats a bit by not providing blocking access to
		1259	condition variables: code blocking while waiting for a condition will
		1260	"die". This still works with most modules/usages, and blocking calls
		1261	must not be done in an interactive application, so it makes sense.
886		1262
887	EXAMPLE PROGRAM	1263	EXAMPLE PROGRAM
888	The following program uses an I/O watcher to read data from STDIN, a	1264	The following program uses an I/O watcher to read data from STDIN, a
889	timer to display a message once per second, and a condition variable to	1265	timer to display a message once per second, and a condition variable to
890	quit the program when the user enters quit:	1266	quit the program when the user enters quit:
…		…
902	warn "read: $input\n"; # output what has been read	1278	warn "read: $input\n"; # output what has been read
903	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1279	$cv->send if $input =~ /^q/i; # quit program if /^q/i
904	},	1280	},
905	);	1281	);
906		1282
907	my $time_watcher; # can only be used once
908
909	sub new_timer {
910	$timer = AnyEvent->timer (after => 1, cb => sub {	1283	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
911	warn "timeout\n"; # print 'timeout' about every second	1284	warn "timeout\n"; # print 'timeout' at most every second
912	&new_timer; # and restart the time
913	});
914	}	1285	});
915
916	new_timer; # create first timer
917		1286
918	$cv->recv; # wait until user enters /^q/i	1287	$cv->recv; # wait until user enters /^q/i
919		1288
920	REAL-WORLD EXAMPLE	1289	REAL-WORLD EXAMPLE
921	Consider the Net::FCP module. It features (among others) the following	1290	Consider the Net::FCP module. It features (among others) the following
…		…
993		1362
994	The actual code goes further and collects all errors ("die"s,	1363	The actual code goes further and collects all errors ("die"s,
995	exceptions) that occurred during request processing. The "result" method	1364	exceptions) that occurred during request processing. The "result" method
996	detects whether an exception as thrown (it is stored inside the $txn	1365	detects whether an exception as thrown (it is stored inside the $txn
997	object) and just throws the exception, which means connection errors and	1366	object) and just throws the exception, which means connection errors and
998	other problems get reported tot he code that tries to use the result,	1367	other problems get reported to the code that tries to use the result,
999	not in a random callback.	1368	not in a random callback.
1000		1369
1001	All of this enables the following usage styles:	1370	All of this enables the following usage styles:
1002		1371
1003	1. Blocking:	1372	1. Blocking:
…		…
1048	through AnyEvent. The benchmark creates a lot of timers (with a zero	1417	through AnyEvent. The benchmark creates a lot of timers (with a zero
1049	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1418	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1050	which it is), lets them fire exactly once and destroys them again.	1419	which it is), lets them fire exactly once and destroys them again.
1051		1420
1052	Source code for this benchmark is found as eg/bench in the AnyEvent	1421	Source code for this benchmark is found as eg/bench in the AnyEvent
1053	distribution.	1422	distribution. It uses the AE interface, which makes a real difference
		1423	for the EV and Perl backends only.
1054		1424
1055	Explanation of the columns	1425	Explanation of the columns
1056	*watcher* is the number of event watchers created/destroyed. Since	1426	*watcher* is the number of event watchers created/destroyed. Since
1057	different event models feature vastly different performances, each event	1427	different event models feature vastly different performances, each event
1058	loop was given a number of watchers so that overall runtime is	1428	loop was given a number of watchers so that overall runtime is
…		…
1077	*destroy* is the time, in microseconds, that it takes to destroy a	1447	*destroy* is the time, in microseconds, that it takes to destroy a
1078	single watcher.	1448	single watcher.
1079		1449
1080	Results	1450	Results
1081	name watchers bytes create invoke destroy comment	1451	name watchers bytes create invoke destroy comment
1082	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1452	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1083	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1453	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1084	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1454	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1085	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1455	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1086	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1456	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1087	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1457	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1458	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1459	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1088	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1460	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1089	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1461	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1090	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1462	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1091	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1463	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1092		1464
1093	Discussion	1465	Discussion
1094	The benchmark does *not* measure scalability of the event loop very	1466	The benchmark does *not* measure scalability of the event loop very
1095	well. For example, a select-based event loop (such as the pure perl one)	1467	well. For example, a select-based event loop (such as the pure perl one)
1096	can never compete with an event loop that uses epoll when the number of	1468	can never compete with an event loop that uses epoll when the number of
…		…
1107	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1479	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1108	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1480	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1109	CPU cycles with POE.	1481	CPU cycles with POE.
1110		1482
1111	"EV" is the sole leader regarding speed and memory use, which are both	1483	"EV" is the sole leader regarding speed and memory use, which are both
1112	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1484	maximal/minimal, respectively. When using the AE API there is zero
		1485	overhead (when going through the AnyEvent API create is about 5-6 times
		1486	slower, with other times being equal, so still uses far less memory than
1113	far less memory than any other event loop and is still faster than Event	1487	any other event loop and is still faster than Event natively).
1114	natively.
1115		1488
1116	The pure perl implementation is hit in a few sweet spots (both the	1489	The pure perl implementation is hit in a few sweet spots (both the
1117	constant timeout and the use of a single fd hit optimisations in the	1490	constant timeout and the use of a single fd hit optimisations in the
1118	perl interpreter and the backend itself). Nevertheless this shows that	1491	perl interpreter and the backend itself). Nevertheless this shows that
1119	it adds very little overhead in itself. Like any select-based backend	1492	it adds very little overhead in itself. Like any select-based backend
…		…
1121	few of them active), of course, but this was not subject of this	1494	few of them active), of course, but this was not subject of this
1122	benchmark.	1495	benchmark.
1123		1496
1124	The "Event" module has a relatively high setup and callback invocation	1497	The "Event" module has a relatively high setup and callback invocation
1125	cost, but overall scores in on the third place.	1498	cost, but overall scores in on the third place.
		1499
		1500	"IO::Async" performs admirably well, about on par with "Event", even
		1501	when using its pure perl backend.
1126		1502
1127	"Glib"'s memory usage is quite a bit higher, but it features a faster	1503	"Glib"'s memory usage is quite a bit higher, but it features a faster
1128	callback invocation and overall ends up in the same class as "Event".	1504	callback invocation and overall ends up in the same class as "Event".
1129	However, Glib scales extremely badly, doubling the number of watchers	1505	However, Glib scales extremely badly, doubling the number of watchers
1130	increases the processing time by more than a factor of four, making it	1506	increases the processing time by more than a factor of four, making it
…		…
1186	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1562	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1187	100 (1%) are active. This mirrors the activity of large servers with	1563	100 (1%) are active. This mirrors the activity of large servers with
1188	many connections, most of which are idle at any one point in time.	1564	many connections, most of which are idle at any one point in time.
1189		1565
1190	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1566	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1191	distribution.	1567	distribution. It uses the AE interface, which makes a real difference
		1568	for the EV and Perl backends only.
1192		1569
1193	Explanation of the columns	1570	Explanation of the columns
1194	*sockets* is the number of sockets, and twice the number of "servers"	1571	*sockets* is the number of sockets, and twice the number of "servers"
1195	(as each server has a read and write socket end).	1572	(as each server has a read and write socket end).
1196		1573
…		…
1201	single "request", that is, reading the token from the pipe and	1578	single "request", that is, reading the token from the pipe and
1202	forwarding it to another server. This includes deleting the old timeout	1579	forwarding it to another server. This includes deleting the old timeout
1203	and creating a new one that moves the timeout into the future.	1580	and creating a new one that moves the timeout into the future.
1204		1581
1205	Results	1582	Results
1206	name sockets create request	1583	name sockets create request
1207	EV 20000 69.01 11.16	1584	EV 20000 62.66 7.99
1208	Perl 20000 73.32 35.87	1585	Perl 20000 68.32 32.64
1209	Event 20000 212.62 257.32	1586	IOAsync 20000 174.06 101.15 epoll
1210	Glib 20000 651.16 1896.30	1587	IOAsync 20000 174.67 610.84 poll
		1588	Event 20000 202.69 242.91
		1589	Glib 20000 557.01 1689.52
1211	POE 20000 349.67 12317.24 uses POE::Loop::Event	1590	POE 20000 341.54 12086.32 uses POE::Loop::Event
1212		1591
1213	Discussion	1592	Discussion
1214	This benchmark *does* measure scalability and overall performance of the	1593	This benchmark *does* measure scalability and overall performance of the
1215	particular event loop.	1594	particular event loop.
1216		1595
1217	EV is again fastest. Since it is using epoll on my system, the setup	1596	EV is again fastest. Since it is using epoll on my system, the setup
1218	time is relatively high, though.	1597	time is relatively high, though.
1219		1598
1220	Perl surprisingly comes second. It is much faster than the C-based event	1599	Perl surprisingly comes second. It is much faster than the C-based event
1221	loops Event and Glib.	1600	loops Event and Glib.
		1601
		1602	IO::Async performs very well when using its epoll backend, and still
		1603	quite good compared to Glib when using its pure perl backend.
1222		1604
1223	Event suffers from high setup time as well (look at its code and you	1605	Event suffers from high setup time as well (look at its code and you
1224	will understand why). Callback invocation also has a high overhead	1606	will understand why). Callback invocation also has a high overhead
1225	compared to the "$_->() for .."-style loop that the Perl event loop	1607	compared to the "$_->() for .."-style loop that the Perl event loop
1226	uses. Event uses select or poll in basically all documented	1608	uses. Event uses select or poll in basically all documented
…		…
1277		1659
1278	Summary	1660	Summary
1279	* C-based event loops perform very well with small number of watchers,	1661	* C-based event loops perform very well with small number of watchers,
1280	as the management overhead dominates.	1662	as the management overhead dominates.
1281		1663
		1664	THE IO::Lambda BENCHMARK
		1665	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1666	could be misinterpreted to make AnyEvent look bad. In fact, the
		1667	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1668	better (which shouldn't come as a surprise to anybody). As such, the
		1669	benchmark is fine, and mostly shows that the AnyEvent backend from
		1670	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1671	without the extra baggage? To explore this, I wrote the equivalent
		1672	benchmark for AnyEvent.
		1673
		1674	The benchmark itself creates an echo-server, and then, for 500 times,
		1675	connects to the echo server, sends a line, waits for the reply, and then
		1676	creates the next connection. This is a rather bad benchmark, as it
		1677	doesn't test the efficiency of the framework or much non-blocking I/O,
		1678	but it is a benchmark nevertheless.
		1679
		1680	name runtime
		1681	Lambda/select 0.330 sec
		1682	+ optimized 0.122 sec
		1683	Lambda/AnyEvent 0.327 sec
		1684	+ optimized 0.138 sec
		1685	Raw sockets/select 0.077 sec
		1686	POE/select, components 0.662 sec
		1687	POE/select, raw sockets 0.226 sec
		1688	POE/select, optimized 0.404 sec
		1689
		1690	AnyEvent/select/nb 0.085 sec
		1691	AnyEvent/EV/nb 0.068 sec
		1692	+state machine 0.134 sec
		1693
		1694	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1695	benchmarks actually make blocking connects and use 100% blocking I/O,
		1696	defeating the purpose of an event-based solution. All of the newly
		1697	written AnyEvent benchmarks use 100% non-blocking connects (using
		1698	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1699	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1700	connects generally require a lot more bookkeeping and event handling
		1701	than blocking connects (which involve a single syscall only).
		1702
		1703	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1704	offers similar expressive power as POE and IO::Lambda, using
		1705	conventional Perl syntax. This means that both the echo server and the
		1706	client are 100% non-blocking, further placing it at a disadvantage.
		1707
		1708	As you can see, the AnyEvent + EV combination even beats the
		1709	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1710	backend easily beats IO::Lambda and POE.
		1711
		1712	And even the 100% non-blocking version written using the high-level (and
		1713	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1714	higher level ("unoptimised") abstractions by a large margin, even though
		1715	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1716
		1717	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1718	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1719	part of the IO::Lambda distribution and were used without any changes.
		1720
		1721	SIGNALS
		1722	AnyEvent currently installs handlers for these signals:
		1723
		1724	SIGCHLD
		1725	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1726	emulation for event loops that do not support them natively. Also,
		1727	some event loops install a similar handler.
		1728
		1729	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1730	then AnyEvent will reset it to default, to avoid losing child exit
		1731	statuses.
		1732
		1733	SIGPIPE
		1734	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1735	"undef" when AnyEvent gets loaded.
		1736
		1737	The rationale for this is that AnyEvent users usually do not really
		1738	depend on SIGPIPE delivery (which is purely an optimisation for
		1739	shell use, or badly-written programs), but "SIGPIPE" can cause
		1740	spurious and rare program exits as a lot of people do not expect
		1741	"SIGPIPE" when writing to some random socket.
		1742
		1743	The rationale for installing a no-op handler as opposed to ignoring
		1744	it is that this way, the handler will be restored to defaults on
		1745	exec.
		1746
		1747	Feel free to install your own handler, or reset it to defaults.
		1748
		1749	RECOMMENDED/OPTIONAL MODULES
		1750	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1751	it's built-in modules) are required to use it.
		1752
		1753	That does not mean that AnyEvent won't take advantage of some additional
		1754	modules if they are installed.
		1755
		1756	This section explains which additional modules will be used, and how
		1757	they affect AnyEvent's operation.
		1758
		1759	Async::Interrupt
		1760	This slightly arcane module is used to implement fast signal
		1761	handling: To my knowledge, there is no way to do completely
		1762	race-free and quick signal handling in pure perl. To ensure that
		1763	signals still get delivered, AnyEvent will start an interval timer
		1764	to wake up perl (and catch the signals) with some delay (default is
		1765	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1766
		1767	If this module is available, then it will be used to implement
		1768	signal catching, which means that signals will not be delayed, and
		1769	the event loop will not be interrupted regularly, which is more
		1770	efficient (and good for battery life on laptops).
		1771
		1772	This affects not just the pure-perl event loop, but also other event
		1773	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1774
		1775	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1776	natively, and either employ their own workarounds (POE) or use
		1777	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1778	Installing Async::Interrupt does nothing for those backends.
		1779
		1780	EV This module isn't really "optional", as it is simply one of the
		1781	backend event loops that AnyEvent can use. However, it is simply the
		1782	best event loop available in terms of features, speed and stability:
		1783	It supports the AnyEvent API optimally, implements all the watcher
		1784	types in XS, does automatic timer adjustments even when no monotonic
		1785	clock is available, can take avdantage of advanced kernel interfaces
		1786	such as "epoll" and "kqueue", and is the fastest backend *by far*.
		1787	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1788	Glib::EV).
		1789
		1790	If you only use backends that rely on another event loop (e.g.
		1791	"Tk"), then this module will do nothing for you.
		1792
		1793	Guard
		1794	The guard module, when used, will be used to implement
		1795	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1796	uses a lot less memory), but otherwise doesn't affect guard
		1797	operation much. It is purely used for performance.
		1798
		1799	JSON and JSON::XS
		1800	One of these modules is required when you want to read or write JSON
		1801	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		1802	can take advantage of the ultra-high-speed JSON::XS module when it
		1803	is installed.
		1804
		1805	Net::SSLeay
		1806	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1807	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1808	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1809
		1810	Time::HiRes
		1811	This module is part of perl since release 5.008. It will be used
		1812	when the chosen event library does not come with a timing source on
		1813	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1814	additionally use it to try to use a monotonic clock for timing
		1815	stability.
		1816
1282	FORK	1817	FORK
1283	Most event libraries are not fork-safe. The ones who are usually are	1818	Most event libraries are not fork-safe. The ones who are usually are
1284	because they rely on inefficient but fork-safe "select" or "poll" calls.	1819	because they rely on inefficient but fork-safe "select" or "poll" calls
1285	Only EV is fully fork-aware.	1820	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		1821	epoll are usually badly thought-out hacks that are incompatible with
		1822	fork in one way or another. Only EV is fully fork-aware and ensures that
		1823	you continue event-processing in both parent and child (or both, if you
		1824	know what you are doing).
		1825
		1826	This means that, in general, you cannot fork and do event processing in
		1827	the child if the event library was initialised before the fork (which
		1828	usually happens when the first AnyEvent watcher is created, or the
		1829	library is loaded).
1286		1830
1287	If you have to fork, you must either do so *before* creating your first	1831	If you have to fork, you must either do so *before* creating your first
1288	watcher OR you must not use AnyEvent at all in the child.	1832	watcher OR you must not use AnyEvent at all in the child OR you must do
		1833	something completely out of the scope of AnyEvent.
		1834
		1835	The problem of doing event processing in the parent *and* the child is
		1836	much more complicated: even for backends that *are* fork-aware or
		1837	fork-safe, their behaviour is not usually what you want: fork clones all
		1838	watchers, that means all timers, I/O watchers etc. are active in both
		1839	parent and child, which is almost never what you want. USing "exec" to
		1840	start worker children from some kind of manage rprocess is usually
		1841	preferred, because it is much easier and cleaner, at the expense of
		1842	having to have another binary.
1289		1843
1290	SECURITY CONSIDERATIONS	1844	SECURITY CONSIDERATIONS
1291	AnyEvent can be forced to load any event model via	1845	AnyEvent can be forced to load any event model via
1292	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1846	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1293	to execute arbitrary code or directly gain access, it can easily be used	1847	to execute arbitrary code or directly gain access, it can easily be used
…		…
1297		1851
1298	You can make AnyEvent completely ignore this variable by deleting it	1852	You can make AnyEvent completely ignore this variable by deleting it
1299	before the first watcher gets created, e.g. with a "BEGIN" block:	1853	before the first watcher gets created, e.g. with a "BEGIN" block:
1300		1854
1301	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1855	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1302		1856
1303	use AnyEvent;	1857	use AnyEvent;
1304		1858
1305	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1859	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1306	be used to probe what backend is used and gain other information (which	1860	be used to probe what backend is used and gain other information (which
1307	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),	1861	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1308	and $ENV{PERL_ANYEGENT_STRICT}.	1862	and $ENV{PERL_ANYEVENT_STRICT}.
		1863
		1864	Note that AnyEvent will remove *all* environment variables starting with
		1865	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1866	enabled.
1309		1867
1310	BUGS	1868	BUGS
1311	Perl 5.8 has numerous memleaks that sometimes hit this module and are	1869	Perl 5.8 has numerous memleaks that sometimes hit this module and are
1312	hard to work around. If you suffer from memleaks, first upgrade to Perl	1870	hard to work around. If you suffer from memleaks, first upgrade to Perl
1313	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	1871	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1314	annoying mamleaks, such as leaking on "map" and "grep" but it is usually	1872	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1315	not as pronounced).	1873	not as pronounced).
1316		1874
1317	SEE ALSO	1875	SEE ALSO
1318	Utility functions: AnyEvent::Util.	1876	Utility functions: AnyEvent::Util.
1319		1877
1320	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1878	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1321	Event::Lib, Qt, POE.	1879	Event::Lib, Qt, POE.
1322		1880
1323	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1881	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1324	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1882	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1325	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1883	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1884	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
1326		1885
1327	Non-blocking file handles, sockets, TCP clients and servers:	1886	Non-blocking file handles, sockets, TCP clients and servers:
1328	AnyEvent::Handle, AnyEvent::Socket.	1887	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1329		1888
1330	Asynchronous DNS: AnyEvent::DNS.	1889	Asynchronous DNS: AnyEvent::DNS.
1331		1890
1332	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1891	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1333		1892
1334	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1893	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1894	AnyEvent::HTTP.
1335		1895
1336	AUTHOR	1896	AUTHOR
1337	Marc Lehmann <schmorp@schmorp.de>	1897	Marc Lehmann <schmorp@schmorp.de>
1338	http://home.schmorp.de/	1898	http://home.schmorp.de/
1339		1899

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