[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.31 by root, Thu Oct 2 06:42:39 2008 UTC vs.
Revision 1.47 by root, Mon Jul 20 22:39:57 2009 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - events independent of event loop implementation
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 { ... });
11		12
		13	# one-shot or repeating timers
12	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });	14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
13	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...	15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
14		16
15	print AnyEvent->now; # prints current event loop time	17	print AnyEvent->now; # prints current event loop time
16	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.	18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
17		19
		20	# POSIX signal
18	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });	21	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
19		22
		23	# child process exit
20	my $w = AnyEvent->child (pid => $pid, cb => sub {	24	my $w = AnyEvent->child (pid => $pid, cb => sub {
21	my ($pid, $status) = @_;	25	my ($pid, $status) = @_;
22	...	26	...
23	});	27	});
		28
		29	# called when event loop idle (if applicable)
		30	my $w = AnyEvent->idle (cb => sub { ... });
24		31
25	my $w = AnyEvent->condvar; # stores whether a condition was flagged	32	my $w = AnyEvent->condvar; # stores whether a condition was flagged
26	$w->send; # wake up current and all future recv's	33	$w->send; # wake up current and all future recv's
27	$w->recv; # enters "main loop" till $condvar gets ->send	34	$w->recv; # enters "main loop" till $condvar gets ->send
28	# use a condvar in callback mode:	35	# use a condvar in callback mode:
30		37
31	INTRODUCTION/TUTORIAL	38	INTRODUCTION/TUTORIAL
32	This manpage is mainly a reference manual. If you are interested in a	39	This manpage is mainly a reference manual. If you are interested in a
33	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
34	manpage.	41	manpage.
		42
		43	SUPPORT
		44	There is a mailinglist for discussing all things AnyEvent, and an IRC
		45	channel, too.
		46
		47	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		48	Respository, at <http://anyevent.schmorp.de>, for more info.
35		49
36	WHY YOU SHOULD USE THIS MODULE (OR NOT)	50	WHY YOU SHOULD USE THIS MODULE (OR NOT)
37	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	51	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
38	nowadays. So what is different about AnyEvent?	52	nowadays. So what is different about AnyEvent?
39		53
…		…
132	These watchers are normal Perl objects with normal Perl lifetime. After	146	These watchers are normal Perl objects with normal Perl lifetime. After
133	creating a watcher it will immediately "watch" for events and invoke the	147	creating a watcher it will immediately "watch" for events and invoke the
134	callback when the event occurs (of course, only when the event model is	148	callback when the event occurs (of course, only when the event model is
135	in control).	149	in control).
136		150
		151	Note that callbacks must not permanently change global variables
		152	potentially in use by the event loop (such as $_ or $[) and that
		153	callbacks must not "die". The former is good programming practise in
		154	Perl and the latter stems from the fact that exception handling differs
		155	widely between event loops.
		156
137	To disable the watcher you have to destroy it (e.g. by setting the	157	To disable the watcher you have to destroy it (e.g. by setting the
138	variable you store it in to "undef" or otherwise deleting all references	158	variable you store it in to "undef" or otherwise deleting all references
139	to it).	159	to it).
140		160
141	All watchers are created by calling a method on the "AnyEvent" class.	161	All watchers are created by calling a method on the "AnyEvent" class.
…		…
156		176
157	I/O WATCHERS	177	I/O WATCHERS
158	You can create an I/O watcher by calling the "AnyEvent->io" method with	178	You can create an I/O watcher by calling the "AnyEvent->io" method with
159	the following mandatory key-value pairs as arguments:	179	the following mandatory key-value pairs as arguments:
160		180
161	"fh" the Perl file handle (not file descriptor) to watch for events	181	"fh" is the Perl file handle (or a naked file descriptor) to watch for
162	(AnyEvent might or might not keep a reference to this file handle).	182	events (AnyEvent might or might not keep a reference to this file
		183	handle). Note that only file handles pointing to things for which
		184	non-blocking operation makes sense are allowed. This includes sockets,
		185	most character devices, pipes, fifos and so on, but not for example
		186	files or block devices.
		187
163	"poll" must be a string that is either "r" or "w", which creates a	188	"poll" must be a string that is either "r" or "w", which creates a
164	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	189	watcher waiting for "r"eadable or "w"ritable events, respectively.
		190
165	is the callback to invoke each time the file handle becomes ready.	191	"cb" is the callback to invoke each time the file handle becomes ready.
166		192
167	Although the callback might get passed parameters, their value and	193	Although the callback might get passed parameters, their value and
168	presence is undefined and you cannot rely on them. Portable AnyEvent	194	presence is undefined and you cannot rely on them. Portable AnyEvent
169	callbacks cannot use arguments passed to I/O watcher callbacks.	195	callbacks cannot use arguments passed to I/O watcher callbacks.
170		196
…		…
302	In either case, if you care (and in most cases, you don't), then you	328	In either case, if you care (and in most cases, you don't), then you
303	can get whatever behaviour you want with any event loop, by taking	329	can get whatever behaviour you want with any event loop, by taking
304	the difference between "AnyEvent->time" and "AnyEvent->now" into	330	the difference between "AnyEvent->time" and "AnyEvent->now" into
305	account.	331	account.
306		332
		333	AnyEvent->now_update
		334	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		335	current time for each loop iteration (see the discussion of
		336	AnyEvent->now, above).
		337
		338	When a callback runs for a long time (or when the process sleeps),
		339	then this "current" time will differ substantially from the real
		340	time, which might affect timers and time-outs.
		341
		342	When this is the case, you can call this method, which will update
		343	the event loop's idea of "current time".
		344
		345	Note that updating the time might cause some events to be handled.
		346
307	SIGNAL WATCHERS	347	SIGNAL WATCHERS
308	You can watch for signals using a signal watcher, "signal" is the signal	348	You can watch for signals using a signal watcher, "signal" is the signal
309	name in uppercase and without any "SIG" prefix, "cb" is the Perl	349	name in uppercase and without any "SIG" prefix, "cb" is the Perl
310	callback to be invoked whenever a signal occurs.	350	callback to be invoked whenever a signal occurs.
311		351
…		…
317	invocation, and callback invocation will be synchronous. Synchronous	357	invocation, and callback invocation will be synchronous. Synchronous
318	means that it might take a while until the signal gets handled by the	358	means that it might take a while until the signal gets handled by the
319	process, but it is guaranteed not to interrupt any other callbacks.	359	process, but it is guaranteed not to interrupt any other callbacks.
320		360
321	The main advantage of using these watchers is that you can share a	361	The main advantage of using these watchers is that you can share a
322	signal between multiple watchers.	362	signal between multiple watchers, and AnyEvent will ensure that signals
		363	will not interrupt your program at bad times.
323		364
324	This watcher might use %SIG, so programs overwriting those signals	365	This watcher might use %SIG (depending on the event loop used), so
325	directly will likely not work correctly.	366	programs overwriting those signals directly will likely not work
		367	correctly.
326		368
327	Example: exit on SIGINT	369	Example: exit on SIGINT
328		370
329	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	371	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		372
		373	Signal Races, Delays and Workarounds
		374	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		375	callbacks to signals in a generic way, which is a pity, as you cannot do
		376	race-free signal handling in perl. AnyEvent will try to do it's best,
		377	but in some cases, signals will be delayed. The maximum time a signal
		378	might be delayed is specified in $AnyEvent::MAX_SIGNAL_LATENCY (default:
		379	10 seconds). This variable can be changed only before the first signal
		380	watcher is created, and should be left alone otherwise. Higher values
		381	will cause fewer spurious wake-ups, which is better for power and CPU
		382	saving. All these problems can be avoided by installing the optional
		383	Async::Interrupt module. This will not work with inherently broken event
		384	loops such as Event or Event::Lib (and not with POE currently, as POE
		385	does it's own workaround with one-second latency). With those, you just
		386	have to suffer the delays.
330		387
331	CHILD PROCESS WATCHERS	388	CHILD PROCESS WATCHERS
332	You can also watch on a child process exit and catch its exit status.	389	You can also watch on a child process exit and catch its exit status.
333		390
334	The child process is specified by the "pid" argument (if set to 0, it	391	The child process is specified by the "pid" argument (if set to 0, it
…		…
347		404
348	There is a slight catch to child watchers, however: you usually start	405	There is a slight catch to child watchers, however: you usually start
349	them after the child process was created, and this means the process	406	them after the child process was created, and this means the process
350	could have exited already (and no SIGCHLD will be sent anymore).	407	could have exited already (and no SIGCHLD will be sent anymore).
351		408
352	Not all event models handle this correctly (POE doesn't), but even for	409	Not all event models handle this correctly (neither POE nor IO::Async
		410	do, see their AnyEvent::Impl manpages for details), but even for event
353	event models that do handle this correctly, they usually need to be	411	models that do handle this correctly, they usually need to be loaded
354	loaded before the process exits (i.e. before you fork in the first	412	before the process exits (i.e. before you fork in the first place).
355	place).	413	AnyEvent's pure perl event loop handles all cases correctly regardless
		414	of when you start the watcher.
356		415
357	This means you cannot create a child watcher as the very first thing in	416	This means you cannot create a child watcher as the very first thing in
358	an AnyEvent program, you have to create at least one watcher before	417	an AnyEvent program, you have to create at least one watcher before
359	you "fork" the child (alternatively, you can call "AnyEvent::detect").	418	you "fork" the child (alternatively, you can call "AnyEvent::detect").
360		419
		420	As most event loops do not support waiting for child events, they will
		421	be emulated by AnyEvent in most cases, in which the latency and race
		422	problems mentioned in the description of signal watchers apply.
		423
361	Example: fork a process and wait for it	424	Example: fork a process and wait for it
362		425
363	my $done = AnyEvent->condvar;	426	my $done = AnyEvent->condvar;
364		427
365	my $pid = fork or exit 5;	428	my $pid = fork or exit 5;
366		429
367	my $w = AnyEvent->child (	430	my $w = AnyEvent->child (
368	pid => $pid,	431	pid => $pid,
369	cb => sub {	432	cb => sub {
370	my ($pid, $status) = @_;	433	my ($pid, $status) = @_;
371	warn "pid $pid exited with status $status";	434	warn "pid $pid exited with status $status";
372	$done->send;	435	$done->send;
373	},	436	},
374	);	437	);
375		438
376	# do something else, then wait for process exit	439	# do something else, then wait for process exit
377	$done->recv;	440	$done->recv;
		441
		442	IDLE WATCHERS
		443	Sometimes there is a need to do something, but it is not so important to
		444	do it instantly, but only when there is nothing better to do. This
		445	"nothing better to do" is usually defined to be "no other events need
		446	attention by the event loop".
		447
		448	Idle watchers ideally get invoked when the event loop has nothing better
		449	to do, just before it would block the process to wait for new events.
		450	Instead of blocking, the idle watcher is invoked.
		451
		452	Most event loops unfortunately do not really support idle watchers (only
		453	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		454	will simply call the callback "from time to time".
		455
		456	Example: read lines from STDIN, but only process them when the program
		457	is otherwise idle:
		458
		459	my @lines; # read data
		460	my $idle_w;
		461	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		462	push @lines, scalar <STDIN>;
		463
		464	# start an idle watcher, if not already done
		465	$idle_w \|\|= AnyEvent->idle (cb => sub {
		466	# handle only one line, when there are lines left
		467	if (my $line = shift @lines) {
		468	print "handled when idle: $line";
		469	} else {
		470	# otherwise disable the idle watcher again
		471	undef $idle_w;
		472	}
		473	});
		474	});
378		475
379	CONDITION VARIABLES	476	CONDITION VARIABLES
380	If you are familiar with some event loops you will know that all of them	477	If you are familiar with some event loops you will know that all of them
381	require you to run some blocking "loop", "run" or similar function that	478	require you to run some blocking "loop", "run" or similar function that
382	will actively watch for new events and call your callbacks.	479	will actively watch for new events and call your callbacks.
383		480
384	AnyEvent is different, it expects somebody else to run the event loop	481	AnyEvent is slightly different: it expects somebody else to run the
385	and will only block when necessary (usually when told by the user).	482	event loop and will only block when necessary (usually when told by the
		483	user).
386		484
387	The instrument to do that is called a "condition variable", so called	485	The instrument to do that is called a "condition variable", so called
388	because they represent a condition that must become true.	486	because they represent a condition that must become true.
389		487
		488	Now is probably a good time to look at the examples further below.
		489
390	Condition variables can be created by calling the "AnyEvent->condvar"	490	Condition variables can be created by calling the "AnyEvent->condvar"
391	method, usually without arguments. The only argument pair allowed is	491	method, usually without arguments. The only argument pair allowed is
392
393	"cb", which specifies a callback to be called when the condition	492	"cb", which specifies a callback to be called when the condition
394	variable becomes true, with the condition variable as the first argument	493	variable becomes true, with the condition variable as the first argument
395	(but not the results).	494	(but not the results).
396		495
397	After creation, the condition variable is "false" until it becomes	496	After creation, the condition variable is "false" until it becomes
…		…
402	Condition variables are similar to callbacks, except that you can	501	Condition variables are similar to callbacks, except that you can
403	optionally wait for them. They can also be called merge points - points	502	optionally wait for them. They can also be called merge points - points
404	in time where multiple outstanding events have been processed. And yet	503	in time where multiple outstanding events have been processed. And yet
405	another way to call them is transactions - each condition variable can	504	another way to call them is transactions - each condition variable can
406	be used to represent a transaction, which finishes at some point and	505	be used to represent a transaction, which finishes at some point and
407	delivers a result.	506	delivers a result. And yet some people know them as "futures" - a
		507	promise to compute/deliver something that you can wait for.
408		508
409	Condition variables are very useful to signal that something has	509	Condition variables are very useful to signal that something has
410	finished, for example, if you write a module that does asynchronous http	510	finished, for example, if you write a module that does asynchronous http
411	requests, then a condition variable would be the ideal candidate to	511	requests, then a condition variable would be the ideal candidate to
412	signal the availability of results. The user can either act when the	512	signal the availability of results. The user can either act when the
…		…
446	after => 1,	546	after => 1,
447	cb => sub { $result_ready->send },	547	cb => sub { $result_ready->send },
448	);	548	);
449		549
450	# this "blocks" (while handling events) till the callback	550	# this "blocks" (while handling events) till the callback
451	# calls send	551	# calls -<send
452	$result_ready->recv;	552	$result_ready->recv;
453		553
454	Example: wait for a timer, but take advantage of the fact that condition	554	Example: wait for a timer, but take advantage of the fact that condition
455	variables are also code references.	555	variables are also callable directly.
456		556
457	my $done = AnyEvent->condvar;	557	my $done = AnyEvent->condvar;
458	my $delay = AnyEvent->timer (after => 5, cb => $done);	558	my $delay = AnyEvent->timer (after => 5, cb => $done);
459	$done->recv;	559	$done->recv;
460		560
…		…
466		566
467	...	567	...
468		568
469	my @info = $couchdb->info->recv;	569	my @info = $couchdb->info->recv;
470		570
471	And this is how you would just ste a callback to be called whenever the	571	And this is how you would just set a callback to be called whenever the
472	results are available:	572	results are available:
473		573
474	$couchdb->info->cb (sub {	574	$couchdb->info->cb (sub {
475	my @info = $_[0]->recv;	575	my @info = $_[0]->recv;
476	});	576	});
…		…
491		591
492	Any arguments passed to the "send" call will be returned by all	592	Any arguments passed to the "send" call will be returned by all
493	future "->recv" calls.	593	future "->recv" calls.
494		594
495	Condition variables are overloaded so one can call them directly (as	595	Condition variables are overloaded so one can call them directly (as
496	a code reference). Calling them directly is the same as calling	596	if they were a code reference). Calling them directly is the same as
497	"send". Note, however, that many C-based event loops do not handle	597	calling "send".
498	overloading, so as tempting as it may be, passing a condition
499	variable instead of a callback does not work. Both the pure perl and
500	EV loops support overloading, however, as well as all functions that
501	use perl to invoke a callback (as in AnyEvent::Socket and
502	AnyEvent::DNS for example).
503		598
504	$cv->croak ($error)	599	$cv->croak ($error)
505	Similar to send, but causes all call's to "->recv" to invoke	600	Similar to send, but causes all call's to "->recv" to invoke
506	"Carp::croak" with the given error message/object/scalar.	601	"Carp::croak" with the given error message/object/scalar.
507		602
508	This can be used to signal any errors to the condition variable	603	This can be used to signal any errors to the condition variable
509	user/consumer.	604	user/consumer. Doing it this way instead of calling "croak" directly
		605	delays the error detetcion, but has the overwhelmign advantage that
		606	it diagnoses the error at the place where the result is expected,
		607	and not deep in some event clalback without connection to the actual
		608	code causing the problem.
510		609
511	$cv->begin ([group callback])	610	$cv->begin ([group callback])
512	$cv->end	611	$cv->end
513	These two methods are EXPERIMENTAL and MIGHT CHANGE.
514
515	These two methods can be used to combine many transactions/events	612	These two methods can be used to combine many transactions/events
516	into one. For example, a function that pings many hosts in parallel	613	into one. For example, a function that pings many hosts in parallel
517	might want to use a condition variable for the whole process.	614	might want to use a condition variable for the whole process.
518		615
519	Every call to "->begin" will increment a counter, and every call to	616	Every call to "->begin" will increment a counter, and every call to
520	"->end" will decrement it. If the counter reaches 0 in "->end", the	617	"->end" will decrement it. If the counter reaches 0 in "->end", the
521	(last) callback passed to "begin" will be executed. That callback is	618	(last) callback passed to "begin" will be executed. That callback is
522	supposed to call "->send", but that is not required. If no	619	supposed to call "->send", but that is not required. If no
523	callback was set, "send" will be called without any arguments.	620	callback was set, "send" will be called without any arguments.
524		621
525	Let's clarify this with the ping example:	622	You can think of "$cv->send" giving you an OR condition (one call
		623	sends), while "$cv->begin" and "$cv->end" giving you an AND
		624	condition (all "begin" calls must be "end"'ed before the condvar
		625	sends).
		626
		627	Let's start with a simple example: you have two I/O watchers (for
		628	example, STDOUT and STDERR for a program), and you want to wait for
		629	both streams to close before activating a condvar:
		630
		631	my $cv = AnyEvent->condvar;
		632
		633	$cv->begin; # first watcher
		634	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		635	defined sysread $fh1, my $buf, 4096
		636	or $cv->end;
		637	});
		638
		639	$cv->begin; # second watcher
		640	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		641	defined sysread $fh2, my $buf, 4096
		642	or $cv->end;
		643	});
		644
		645	$cv->recv;
		646
		647	This works because for every event source (EOF on file handle),
		648	there is one call to "begin", so the condvar waits for all calls to
		649	"end" before sending.
		650
		651	The ping example mentioned above is slightly more complicated, as
		652	the there are results to be passwd back, and the number of tasks
		653	that are begung can potentially be zero:
526		654
527	my $cv = AnyEvent->condvar;	655	my $cv = AnyEvent->condvar;
528		656
529	my %result;	657	my %result;
530	$cv->begin (sub { $cv->send (\%result) });	658	$cv->begin (sub { $cv->send (\%result) });
…		…
550	the loop, which serves two important purposes: first, it sets the	678	the loop, which serves two important purposes: first, it sets the
551	callback to be called once the counter reaches 0, and second, it	679	callback to be called once the counter reaches 0, and second, it
552	ensures that "send" is called even when "no" hosts are being pinged	680	ensures that "send" is called even when "no" hosts are being pinged
553	(the loop doesn't execute once).	681	(the loop doesn't execute once).
554		682
555	This is the general pattern when you "fan out" into multiple	683	This is the general pattern when you "fan out" into multiple (but
556	subrequests: use an outer "begin"/"end" pair to set the callback and	684	potentially none) subrequests: use an outer "begin"/"end" pair to
557	ensure "end" is called at least once, and then, for each subrequest	685	set the callback and ensure "end" is called at least once, and then,
558	you start, call "begin" and for each subrequest you finish, call	686	for each subrequest you start, call "begin" and for each subrequest
559	"end".	687	you finish, call "end".
560		688
561	METHODS FOR CONSUMERS	689	METHODS FOR CONSUMERS
562	These methods should only be used by the consuming side, i.e. the code	690	These methods should only be used by the consuming side, i.e. the code
563	awaits the condition.	691	awaits the condition.
564		692
…		…
573	function will call "croak".	701	function will call "croak".
574		702
575	In list context, all parameters passed to "send" will be returned,	703	In list context, all parameters passed to "send" will be returned,
576	in scalar context only the first one will be returned.	704	in scalar context only the first one will be returned.
577		705
		706	Note that doing a blocking wait in a callback is not supported by
		707	any event loop, that is, recursive invocation of a blocking "->recv"
		708	is not allowed, and the "recv" call will "croak" if such a condition
		709	is detected. This condition can be slightly loosened by using
		710	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		711	thread that doesn't run the event loop itself.
		712
578	Not all event models support a blocking wait - some die in that case	713	Not all event models support a blocking wait - some die in that case
579	(programs might want to do that to stay interactive), so *if you are	714	(programs might want to do that to stay interactive), so *if you are
580	using this from a module, never require a blocking wait*, but let	715	using this from a module, never require a blocking wait*. Instead,
581	the caller decide whether the call will block or not (for example,	716	let the caller decide whether the call will block or not (for
582	by coupling condition variables with some kind of request results	717	example, by coupling condition variables with some kind of request
583	and supporting callbacks so the caller knows that getting the result	718	results and supporting callbacks so the caller knows that getting
584	will not block, while still supporting blocking waits if the caller	719	the result will not block, while still supporting blocking waits if
585	so desires).	720	the caller so desires).
586
587	Another reason never to "->recv" in a module is that you cannot
588	sensibly have two "->recv"'s in parallel, as that would require
589	multiple interpreters or coroutines/threads, none of which
590	"AnyEvent" can supply.
591
592	The Coro module, however, can and does supply coroutines and, in
593	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
594	versions and also integrates coroutines into AnyEvent, making
595	blocking "->recv" calls perfectly safe as long as they are done from
596	another coroutine (one that doesn't run the event loop).
597		721
598	You can ensure that "-recv" never blocks by setting a callback and	722	You can ensure that "-recv" never blocks by setting a callback and
599	only calling "->recv" from within that callback (or at a later	723	only calling "->recv" from within that callback (or at a later
600	time). This will work even when the event loop does not support	724	time). This will work even when the event loop does not support
601	blocking waits otherwise.	725	blocking waits otherwise.
…		…
611	The callback will be called when the condition becomes "true", i.e.	735	The callback will be called when the condition becomes "true", i.e.
612	when "send" or "croak" are called, with the only argument being the	736	when "send" or "croak" are called, with the only argument being the
613	condition variable itself. Calling "recv" inside the callback or at	737	condition variable itself. Calling "recv" inside the callback or at
614	any later time is guaranteed not to block.	738	any later time is guaranteed not to block.
615		739
		740	SUPPORTED EVENT LOOPS/BACKENDS
		741	The available backend classes are (every class has its own manpage):
		742
		743	Backends that are autoprobed when no other event loop can be found.
		744	EV is the preferred backend when no other event loop seems to be in
		745	use. If EV is not installed, then AnyEvent will try Event, and,
		746	failing that, will fall back to its own pure-perl implementation,
		747	which is available everywhere as it comes with AnyEvent itself.
		748
		749	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		750	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		751	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		752
		753	Backends that are transparently being picked up when they are used.
		754	These will be used when they are currently loaded when the first
		755	watcher is created, in which case it is assumed that the application
		756	is using them. This means that AnyEvent will automatically pick the
		757	right backend when the main program loads an event module before
		758	anything starts to create watchers. Nothing special needs to be done
		759	by the main program.
		760
		761	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		762	AnyEvent::Impl::Tk based on Tk, very broken.
		763	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		764	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		765
		766	Backends with special needs.
		767	Qt requires the Qt::Application to be instantiated first, but will
		768	otherwise be picked up automatically. As long as the main program
		769	instantiates the application before any AnyEvent watchers are
		770	created, everything should just work.
		771
		772	AnyEvent::Impl::Qt based on Qt.
		773
		774	Support for IO::Async can only be partial, as it is too broken and
		775	architecturally limited to even support the AnyEvent API. It also is
		776	the only event loop that needs the loop to be set explicitly, so it
		777	can only be used by a main program knowing about AnyEvent. See
		778	AnyEvent::Impl::Async for the gory details.
		779
		780	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		781
		782	Event loops that are indirectly supported via other backends.
		783	Some event loops can be supported via other modules:
		784
		785	There is no direct support for WxWidgets (Wx) or Prima.
		786
		787	WxWidgets has no support for watching file handles. However, you can
		788	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		789	simply polls 20 times per second, which was considered to be too
		790	horrible to even consider for AnyEvent.
		791
		792	Prima is not supported as nobody seems to be using it, but it has a
		793	POE backend, so it can be supported through POE.
		794
		795	AnyEvent knows about both Prima and Wx, however, and will try to
		796	load POE when detecting them, in the hope that POE will pick them
		797	up, in which case everything will be automatic.
		798
616	GLOBAL VARIABLES AND FUNCTIONS	799	GLOBAL VARIABLES AND FUNCTIONS
		800	These are not normally required to use AnyEvent, but can be useful to
		801	write AnyEvent extension modules.
		802
617	$AnyEvent::MODEL	803	$AnyEvent::MODEL
618	Contains "undef" until the first watcher is being created. Then it	804	Contains "undef" until the first watcher is being created, before
		805	the backend has been autodetected.
		806
619	contains the event model that is being used, which is the name of	807	Afterwards it contains the event model that is being used, which is
620	the Perl class implementing the model. This class is usually one of	808	the name of the Perl class implementing the model. This class is
621	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	809	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
622	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	810	other class in the case AnyEvent has been extended at runtime (e.g.
623		811	in rxvt-unicode it will be "urxvt::anyevent").
624	The known classes so far are:
625
626	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
627	AnyEvent::Impl::Event based on Event, second best choice.
628	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
629	AnyEvent::Impl::Glib based on Glib, third-best choice.
630	AnyEvent::Impl::Tk based on Tk, very bad choice.
631	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
632	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
633	AnyEvent::Impl::POE based on POE, not generic enough for full support.
634
635	There is no support for WxWidgets, as WxWidgets has no support for
636	watching file handles. However, you can use WxWidgets through the
637	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
638	second, which was considered to be too horrible to even consider for
639	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
640	using it's adaptor.
641
642	AnyEvent knows about Prima and Wx and will try to use POE when
643	autodetecting them.
644		812
645	AnyEvent::detect	813	AnyEvent::detect
646	Returns $AnyEvent::MODEL, forcing autodetection of the event model	814	Returns $AnyEvent::MODEL, forcing autodetection of the event model
647	if necessary. You should only call this function right before you	815	if necessary. You should only call this function right before you
648	would have created an AnyEvent watcher anyway, that is, as late as	816	would have created an AnyEvent watcher anyway, that is, as late as
649	possible at runtime.	817	possible at runtime, and not e.g. while initialising of your module.
		818
		819	If you need to do some initialisation before AnyEvent watchers are
		820	created, use "post_detect".
650		821
651	$guard = AnyEvent::post_detect { BLOCK }	822	$guard = AnyEvent::post_detect { BLOCK }
652	Arranges for the code block to be executed as soon as the event	823	Arranges for the code block to be executed as soon as the event
653	model is autodetected (or immediately if this has already happened).	824	model is autodetected (or immediately if this has already happened).
		825
		826	The block will be executed after the actual backend has been
		827	detected ($AnyEvent::MODEL is set), but before any watchers have
		828	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		829	other initialisations - see the sources of AnyEvent::Strict or
		830	AnyEvent::AIO to see how this is used.
		831
		832	The most common usage is to create some global watchers, without
		833	forcing event module detection too early, for example, AnyEvent::AIO
		834	creates and installs the global IO::AIO watcher in a "post_detect"
		835	block to avoid autodetecting the event module at load time.
654		836
655	If called in scalar or list context, then it creates and returns an	837	If called in scalar or list context, then it creates and returns an
656	object that automatically removes the callback again when it is	838	object that automatically removes the callback again when it is
657	destroyed. See Coro::BDB for a case where this is useful.	839	destroyed. See Coro::BDB for a case where this is useful.
658		840
…		…
660	If there are any code references in this array (you can "push" to it	842	If there are any code references in this array (you can "push" to it
661	before or after loading AnyEvent), then they will called directly	843	before or after loading AnyEvent), then they will called directly
662	after the event loop has been chosen.	844	after the event loop has been chosen.
663		845
664	You should check $AnyEvent::MODEL before adding to this array,	846	You should check $AnyEvent::MODEL before adding to this array,
665	though: if it contains a true value then the event loop has already	847	though: if it is defined then the event loop has already been
666	been detected, and the array will be ignored.	848	detected, and the array will be ignored.
667		849
668	Best use "AnyEvent::post_detect { BLOCK }" instead.	850	Best use "AnyEvent::post_detect { BLOCK }" when your application
		851	allows it,as it takes care of these details.
		852
		853	This variable is mainly useful for modules that can do something
		854	useful when AnyEvent is used and thus want to know when it is
		855	initialised, but do not need to even load it by default. This array
		856	provides the means to hook into AnyEvent passively, without loading
		857	it.
669		858
670	WHAT TO DO IN A MODULE	859	WHAT TO DO IN A MODULE
671	As a module author, you should "use AnyEvent" and call AnyEvent methods	860	As a module author, you should "use AnyEvent" and call AnyEvent methods
672	freely, but you should not load a specific event module or rely on it.	861	freely, but you should not load a specific event module or rely on it.
673		862
…		…
724	variable somewhere, waiting for it, and sending it when the program	913	variable somewhere, waiting for it, and sending it when the program
725	should exit cleanly.	914	should exit cleanly.
726		915
727	OTHER MODULES	916	OTHER MODULES
728	The following is a non-exhaustive list of additional modules that use	917	The following is a non-exhaustive list of additional modules that use
729	AnyEvent and can therefore be mixed easily with other AnyEvent modules	918	AnyEvent as a client and can therefore be mixed easily with other
730	in the same program. Some of the modules come with AnyEvent, some are	919	AnyEvent modules and other event loops in the same program. Some of the
731	available via CPAN.	920	modules come with AnyEvent, most are available via CPAN.
732		921
733	AnyEvent::Util	922	AnyEvent::Util
734	Contains various utility functions that replace often-used but	923	Contains various utility functions that replace often-used but
735	blocking functions such as "inet_aton" by event-/callback-based	924	blocking functions such as "inet_aton" by event-/callback-based
736	versions.	925	versions.
…		…
742	more.	931	more.
743		932
744	AnyEvent::Handle	933	AnyEvent::Handle
745	Provide read and write buffers, manages watchers for reads and	934	Provide read and write buffers, manages watchers for reads and
746	writes, supports raw and formatted I/O, I/O queued and fully	935	writes, supports raw and formatted I/O, I/O queued and fully
747	transparent and non-blocking SSL/TLS.	936	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
748		937
749	AnyEvent::DNS	938	AnyEvent::DNS
750	Provides rich asynchronous DNS resolver capabilities.	939	Provides rich asynchronous DNS resolver capabilities.
751		940
752	AnyEvent::HTTP	941	AnyEvent::HTTP
…		…
773		962
774	AnyEvent::GPSD	963	AnyEvent::GPSD
775	A non-blocking interface to gpsd, a daemon delivering GPS	964	A non-blocking interface to gpsd, a daemon delivering GPS
776	information.	965	information.
777		966
		967	AnyEvent::IRC
		968	AnyEvent based IRC client module family (replacing the older
		969	Net::IRC3).
		970
		971	AnyEvent::XMPP
		972	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		973	older Net::XMPP2>.
		974
778	AnyEvent::IGS	975	AnyEvent::IGS
779	A non-blocking interface to the Internet Go Server protocol (used by	976	A non-blocking interface to the Internet Go Server protocol (used by
780	App::IGS).	977	App::IGS).
781		978
782	AnyEvent::IRC
783	AnyEvent based IRC client module family (replacing the older
784	Net::IRC3).
785
786	Net::XMPP2
787	AnyEvent based XMPP (Jabber protocol) module family.
788
789	Net::FCP	979	Net::FCP
790	AnyEvent-based implementation of the Freenet Client Protocol,	980	AnyEvent-based implementation of the Freenet Client Protocol,
791	birthplace of AnyEvent.	981	birthplace of AnyEvent.
792		982
793	Event::ExecFlow	983	Event::ExecFlow
794	High level API for event-based execution flow control.	984	High level API for event-based execution flow control.
795		985
796	Coro	986	Coro
797	Has special support for AnyEvent via Coro::AnyEvent.	987	Has special support for AnyEvent via Coro::AnyEvent.
798
799	IO::Lambda
800	The lambda approach to I/O - don't ask, look there. Can use
801	AnyEvent.
802		988
803	ERROR AND EXCEPTION HANDLING	989	ERROR AND EXCEPTION HANDLING
804	In general, AnyEvent does not do any error handling - it relies on the	990	In general, AnyEvent does not do any error handling - it relies on the
805	caller to do that if required. The AnyEvent::Strict module (see also the	991	caller to do that if required. The AnyEvent::Strict module (see also the
806	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	992	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
816	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1002	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
817	Glib uses "install_exception_handler" and so on.	1003	Glib uses "install_exception_handler" and so on.
818		1004
819	ENVIRONMENT VARIABLES	1005	ENVIRONMENT VARIABLES
820	The following environment variables are used by this module or its	1006	The following environment variables are used by this module or its
821	submodules:	1007	submodules.
		1008
		1009	Note that AnyEvent will remove all environment variables starting with
		1010	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1011	enabled.
822		1012
823	"PERL_ANYEVENT_VERBOSE"	1013	"PERL_ANYEVENT_VERBOSE"
824	By default, AnyEvent will be completely silent except in fatal	1014	By default, AnyEvent will be completely silent except in fatal
825	conditions. You can set this environment variable to make AnyEvent	1015	conditions. You can set this environment variable to make AnyEvent
826	more talkative.	1016	more talkative.
…		…
829	conditions, such as not being able to load the event model specified	1019	conditions, such as not being able to load the event model specified
830	by "PERL_ANYEVENT_MODEL".	1020	by "PERL_ANYEVENT_MODEL".
831		1021
832	When set to 2 or higher, cause AnyEvent to report to STDERR which	1022	When set to 2 or higher, cause AnyEvent to report to STDERR which
833	event model it chooses.	1023	event model it chooses.
		1024
		1025	When set to 8 or higher, then AnyEvent will report extra information
		1026	on which optional modules it loads and how it implements certain
		1027	features.
834		1028
835	"PERL_ANYEVENT_STRICT"	1029	"PERL_ANYEVENT_STRICT"
836	AnyEvent does not do much argument checking by default, as thorough	1030	AnyEvent does not do much argument checking by default, as thorough
837	argument checking is very costly. Setting this variable to a true	1031	argument checking is very costly. Setting this variable to a true
838	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1032	value will cause AnyEvent to load "AnyEvent::Strict" and then to
839	thoroughly check the arguments passed to most method calls. If it	1033	thoroughly check the arguments passed to most method calls. If it
840	finds any problems it will croak.	1034	finds any problems, it will croak.
841		1035
842	In other words, enables "strict" mode.	1036	In other words, enables "strict" mode.
843		1037
844	Unlike "use strict", it is definitely recommended ot keep it off in	1038	Unlike "use strict" (or it's modern cousin, "use common::sense", it
845	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment	1039	is definitely recommended to keep it off in production. Keeping
		1040	"PERL_ANYEVENT_STRICT=1" in your environment while developing
846	while developing programs can be very useful, however.	1041	programs can be very useful, however.
847		1042
848	"PERL_ANYEVENT_MODEL"	1043	"PERL_ANYEVENT_MODEL"
849	This can be used to specify the event model to be used by AnyEvent,	1044	This can be used to specify the event model to be used by AnyEvent,
850	before auto detection and -probing kicks in. It must be a string	1045	before auto detection and -probing kicks in. It must be a string
851	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1046	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
870	mentioned will be used, and preference will be given to protocols	1065	mentioned will be used, and preference will be given to protocols
871	mentioned earlier in the list.	1066	mentioned earlier in the list.
872		1067
873	This variable can effectively be used for denial-of-service attacks	1068	This variable can effectively be used for denial-of-service attacks
874	against local programs (e.g. when setuid), although the impact is	1069	against local programs (e.g. when setuid), although the impact is
875	likely small, as the program has to handle connection errors	1070	likely small, as the program has to handle conenction and other
876	already-	1071	failures anyways.
877		1072
878	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1073	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
879	IPv6, but support both and try to use both.	1074	IPv6, but support both and try to use both.
880	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1075	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
881	resolve or contact IPv6 addresses.	1076	resolve or contact IPv6 addresses.
…		…
892	EDNS0 in its DNS requests.	1087	EDNS0 in its DNS requests.
893		1088
894	"PERL_ANYEVENT_MAX_FORKS"	1089	"PERL_ANYEVENT_MAX_FORKS"
895	The maximum number of child processes that	1090	The maximum number of child processes that
896	"AnyEvent::Util::fork_call" will create in parallel.	1091	"AnyEvent::Util::fork_call" will create in parallel.
		1092
		1093	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1094	The default value for the "max_outstanding" parameter for the
		1095	default DNS resolver - this is the maximum number of parallel DNS
		1096	requests that are sent to the DNS server.
		1097
		1098	"PERL_ANYEVENT_RESOLV_CONF"
		1099	The file to use instead of /etc/resolv.conf (or OS-specific
		1100	configuration) in the default resolver. When set to the empty
		1101	string, no default config will be used.
		1102
		1103	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1104	When neither "ca_file" nor "ca_path" was specified during
		1105	AnyEvent::TLS context creation, and either of these environment
		1106	variables exist, they will be used to specify CA certificate
		1107	locations instead of a system-dependent default.
		1108
		1109	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1110	When these are set to 1, then the respective modules are not loaded.
		1111	Mostly good for testing AnyEvent itself.
897		1112
898	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1113	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
899	This is an advanced topic that you do not normally need to use AnyEvent	1114	This is an advanced topic that you do not normally need to use AnyEvent
900	in a module. This section is only of use to event loop authors who want	1115	in a module. This section is only of use to event loop authors who want
901	to provide AnyEvent compatibility.	1116	to provide AnyEvent compatibility.
…		…
1131	destroy is the time, in microseconds, that it takes to destroy a	1346	destroy is the time, in microseconds, that it takes to destroy a
1132	single watcher.	1347	single watcher.
1133		1348
1134	Results	1349	Results
1135	name watchers bytes create invoke destroy comment	1350	name watchers bytes create invoke destroy comment
1136	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1351	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
1137	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1352	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
1138	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1353	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
1139	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1354	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
1140	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1355	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
1141	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1356	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1357	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1358	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
1142	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1359	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
1143	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1360	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
1144	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1361	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
1145	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1362	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
1146		1363
1147	Discussion	1364	Discussion
1148	The benchmark does not measure scalability of the event loop very	1365	The benchmark does not measure scalability of the event loop very
1149	well. For example, a select-based event loop (such as the pure perl one)	1366	well. For example, a select-based event loop (such as the pure perl one)
1150	can never compete with an event loop that uses epoll when the number of	1367	can never compete with an event loop that uses epoll when the number of
…		…
1175	few of them active), of course, but this was not subject of this	1392	few of them active), of course, but this was not subject of this
1176	benchmark.	1393	benchmark.
1177		1394
1178	The "Event" module has a relatively high setup and callback invocation	1395	The "Event" module has a relatively high setup and callback invocation
1179	cost, but overall scores in on the third place.	1396	cost, but overall scores in on the third place.
		1397
		1398	"IO::Async" performs admirably well, about on par with "Event", even
		1399	when using its pure perl backend.
1180		1400
1181	"Glib"'s memory usage is quite a bit higher, but it features a faster	1401	"Glib"'s memory usage is quite a bit higher, but it features a faster
1182	callback invocation and overall ends up in the same class as "Event".	1402	callback invocation and overall ends up in the same class as "Event".
1183	However, Glib scales extremely badly, doubling the number of watchers	1403	However, Glib scales extremely badly, doubling the number of watchers
1184	increases the processing time by more than a factor of four, making it	1404	increases the processing time by more than a factor of four, making it
…		…
1255	single "request", that is, reading the token from the pipe and	1475	single "request", that is, reading the token from the pipe and
1256	forwarding it to another server. This includes deleting the old timeout	1476	forwarding it to another server. This includes deleting the old timeout
1257	and creating a new one that moves the timeout into the future.	1477	and creating a new one that moves the timeout into the future.
1258		1478
1259	Results	1479	Results
1260	name sockets create request	1480	name sockets create request
1261	EV 20000 69.01 11.16	1481	EV 20000 69.01 11.16
1262	Perl 20000 73.32 35.87	1482	Perl 20000 73.32 35.87
		1483	IOAsync 20000 157.00 98.14 epoll
		1484	IOAsync 20000 159.31 616.06 poll
1263	Event 20000 212.62 257.32	1485	Event 20000 212.62 257.32
1264	Glib 20000 651.16 1896.30	1486	Glib 20000 651.16 1896.30
1265	POE 20000 349.67 12317.24 uses POE::Loop::Event	1487	POE 20000 349.67 12317.24 uses POE::Loop::Event
1266		1488
1267	Discussion	1489	Discussion
1268	This benchmark does measure scalability and overall performance of the	1490	This benchmark does measure scalability and overall performance of the
1269	particular event loop.	1491	particular event loop.
1270		1492
1271	EV is again fastest. Since it is using epoll on my system, the setup	1493	EV is again fastest. Since it is using epoll on my system, the setup
1272	time is relatively high, though.	1494	time is relatively high, though.
1273		1495
1274	Perl surprisingly comes second. It is much faster than the C-based event	1496	Perl surprisingly comes second. It is much faster than the C-based event
1275	loops Event and Glib.	1497	loops Event and Glib.
		1498
		1499	IO::Async performs very well when using its epoll backend, and still
		1500	quite good compared to Glib when using its pure perl backend.
1276		1501
1277	Event suffers from high setup time as well (look at its code and you	1502	Event suffers from high setup time as well (look at its code and you
1278	will understand why). Callback invocation also has a high overhead	1503	will understand why). Callback invocation also has a high overhead
1279	compared to the "$_->() for .."-style loop that the Perl event loop	1504	compared to the "$_->() for .."-style loop that the Perl event loop
1280	uses. Event uses select or poll in basically all documented	1505	uses. Event uses select or poll in basically all documented
…		…
1331		1556
1332	Summary	1557	Summary
1333	* C-based event loops perform very well with small number of watchers,	1558	* C-based event loops perform very well with small number of watchers,
1334	as the management overhead dominates.	1559	as the management overhead dominates.
1335		1560
		1561	THE IO::Lambda BENCHMARK
		1562	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1563	could be misinterpreted to make AnyEvent look bad. In fact, the
		1564	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1565	better (which shouldn't come as a surprise to anybody). As such, the
		1566	benchmark is fine, and mostly shows that the AnyEvent backend from
		1567	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1568	without the extra baggage? To explore this, I wrote the equivalent
		1569	benchmark for AnyEvent.
		1570
		1571	The benchmark itself creates an echo-server, and then, for 500 times,
		1572	connects to the echo server, sends a line, waits for the reply, and then
		1573	creates the next connection. This is a rather bad benchmark, as it
		1574	doesn't test the efficiency of the framework or much non-blocking I/O,
		1575	but it is a benchmark nevertheless.
		1576
		1577	name runtime
		1578	Lambda/select 0.330 sec
		1579	+ optimized 0.122 sec
		1580	Lambda/AnyEvent 0.327 sec
		1581	+ optimized 0.138 sec
		1582	Raw sockets/select 0.077 sec
		1583	POE/select, components 0.662 sec
		1584	POE/select, raw sockets 0.226 sec
		1585	POE/select, optimized 0.404 sec
		1586
		1587	AnyEvent/select/nb 0.085 sec
		1588	AnyEvent/EV/nb 0.068 sec
		1589	+state machine 0.134 sec
		1590
		1591	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1592	benchmarks actually make blocking connects and use 100% blocking I/O,
		1593	defeating the purpose of an event-based solution. All of the newly
		1594	written AnyEvent benchmarks use 100% non-blocking connects (using
		1595	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1596	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1597	connects generally require a lot more bookkeeping and event handling
		1598	than blocking connects (which involve a single syscall only).
		1599
		1600	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1601	offers similar expressive power as POE and IO::Lambda, using
		1602	conventional Perl syntax. This means that both the echo server and the
		1603	client are 100% non-blocking, further placing it at a disadvantage.
		1604
		1605	As you can see, the AnyEvent + EV combination even beats the
		1606	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1607	backend easily beats IO::Lambda and POE.
		1608
		1609	And even the 100% non-blocking version written using the high-level (and
		1610	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a
		1611	large margin, even though it does all of DNS, tcp-connect and socket I/O
		1612	in a non-blocking way.
		1613
		1614	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1615	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1616	part of the IO::lambda distribution and were used without any changes.
		1617
		1618	SIGNALS
		1619	AnyEvent currently installs handlers for these signals:
		1620
		1621	SIGCHLD
		1622	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1623	emulation for event loops that do not support them natively. Also,
		1624	some event loops install a similar handler.
		1625
		1626	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1627	then AnyEvent will reset it to default, to avoid losing child exit
		1628	statuses.
		1629
		1630	SIGPIPE
		1631	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1632	"undef" when AnyEvent gets loaded.
		1633
		1634	The rationale for this is that AnyEvent users usually do not really
		1635	depend on SIGPIPE delivery (which is purely an optimisation for
		1636	shell use, or badly-written programs), but "SIGPIPE" can cause
		1637	spurious and rare program exits as a lot of people do not expect
		1638	"SIGPIPE" when writing to some random socket.
		1639
		1640	The rationale for installing a no-op handler as opposed to ignoring
		1641	it is that this way, the handler will be restored to defaults on
		1642	exec.
		1643
		1644	Feel free to install your own handler, or reset it to defaults.
		1645
		1646	RECOMMENDED/OPTIONAL MODULES
		1647	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1648	it's built-in modules) are required to use it.
		1649
		1650	That does not mean that AnyEvent won't take advantage of some additional
		1651	modules if they are installed.
		1652
		1653	This section epxlains which additional modules will be used, and how
		1654	they affect AnyEvent's operetion.
		1655
		1656	Async::Interrupt
		1657	This slightly arcane module is used to implement fast signal
		1658	handling: To my knowledge, there is no way to do completely
		1659	race-free and quick signal handling in pure perl. To ensure that
		1660	signals still get delivered, AnyEvent will start an interval timer
		1661	to wake up perl (and catch the signals) with some delay (default is
		1662	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1663
		1664	If this module is available, then it will be used to implement
		1665	signal catching, which means that signals will not be delayed, and
		1666	the event loop will not be interrupted regularly, which is more
		1667	efficient (And good for battery life on laptops).
		1668
		1669	This affects not just the pure-perl event loop, but also other event
		1670	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1671
		1672	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1673	natively, and either employ their own workarounds (POE) or use
		1674	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1675	Installing Async::Interrupt does nothing for those backends.
		1676
		1677	EV This module isn't really "optional", as it is simply one of the
		1678	backend event loops that AnyEvent can use. However, it is simply the
		1679	best event loop available in terms of features, speed and stability:
		1680	It supports the AnyEvent API optimally, implements all the watcher
		1681	types in XS, does automatic timer adjustments even when no monotonic
		1682	clock is available, can take avdantage of advanced kernel interfaces
		1683	such as "epoll" and "kqueue", and is the fastest backend by far.
		1684	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1685	Glib::EV).
		1686
		1687	Guard
		1688	The guard module, when used, will be used to implement
		1689	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1690	uses a lot less memory), but otherwise doesn't affect guard
		1691	operation much. It is purely used for performance.
		1692
		1693	JSON and JSON::XS
		1694	This module is required when you want to read or write JSON data via
		1695	AnyEvent::Handle. It is also written in pure-perl, but can take
		1696	advantage of the ultra-high-speed JSON::XS module when it is
		1697	installed.
		1698
		1699	In fact, AnyEvent::Handle will use JSON::XS by default if it is
		1700	installed.
		1701
		1702	Net::SSLeay
		1703	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1704	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1705	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1706
		1707	Time::HiRes
		1708	This module is part of perl since release 5.008. It will be used
		1709	when the chosen event library does not come with a timing source on
		1710	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1711	additionally use it to try to use a monotonic clock for timing
		1712	stability.
		1713
1336	FORK	1714	FORK
1337	Most event libraries are not fork-safe. The ones who are usually are	1715	Most event libraries are not fork-safe. The ones who are usually are
1338	because they rely on inefficient but fork-safe "select" or "poll" calls.	1716	because they rely on inefficient but fork-safe "select" or "poll" calls.
1339	Only EV is fully fork-aware.	1717	Only EV is fully fork-aware.
1340		1718
1341	If you have to fork, you must either do so before creating your first	1719	If you have to fork, you must either do so before creating your first
1342	watcher OR you must not use AnyEvent at all in the child.	1720	watcher OR you must not use AnyEvent at all in the child OR you must do
		1721	something completely out of the scope of AnyEvent.
1343		1722
1344	SECURITY CONSIDERATIONS	1723	SECURITY CONSIDERATIONS
1345	AnyEvent can be forced to load any event model via	1724	AnyEvent can be forced to load any event model via
1346	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1725	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1347	to execute arbitrary code or directly gain access, it can easily be used	1726	to execute arbitrary code or directly gain access, it can easily be used
…		…
1351		1730
1352	You can make AnyEvent completely ignore this variable by deleting it	1731	You can make AnyEvent completely ignore this variable by deleting it
1353	before the first watcher gets created, e.g. with a "BEGIN" block:	1732	before the first watcher gets created, e.g. with a "BEGIN" block:
1354		1733
1355	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1734	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1356		1735
1357	use AnyEvent;	1736	use AnyEvent;
1358		1737
1359	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1738	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1360	be used to probe what backend is used and gain other information (which	1739	be used to probe what backend is used and gain other information (which
1361	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),	1740	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1362	and $ENV{PERL_ANYEGENT_STRICT}.	1741	and $ENV{PERL_ANYEVENT_STRICT}.
		1742
		1743	Note that AnyEvent will remove all environment variables starting with
		1744	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1745	enabled.
1363		1746
1364	BUGS	1747	BUGS
1365	Perl 5.8 has numerous memleaks that sometimes hit this module and are	1748	Perl 5.8 has numerous memleaks that sometimes hit this module and are
1366	hard to work around. If you suffer from memleaks, first upgrade to Perl	1749	hard to work around. If you suffer from memleaks, first upgrade to Perl
1367	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	1750	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1368	annoying mamleaks, such as leaking on "map" and "grep" but it is usually	1751	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1369	not as pronounced).	1752	not as pronounced).
1370		1753
1371	SEE ALSO	1754	SEE ALSO
1372	Utility functions: AnyEvent::Util.	1755	Utility functions: AnyEvent::Util.
1373		1756
1374	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1757	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1375	Event::Lib, Qt, POE.	1758	Event::Lib, Qt, POE.
1376		1759
1377	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1760	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1378	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1761	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1379	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1762	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1763	AnyEvent::Impl::IOAsync.
1380		1764
1381	Non-blocking file handles, sockets, TCP clients and servers:	1765	Non-blocking file handles, sockets, TCP clients and servers:
1382	AnyEvent::Handle, AnyEvent::Socket.	1766	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1383		1767
1384	Asynchronous DNS: AnyEvent::DNS.	1768	Asynchronous DNS: AnyEvent::DNS.
1385		1769
1386	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1770	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1387		1771
1388	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1772	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1773	AnyEvent::HTTP.
1389		1774
1390	AUTHOR	1775	AUTHOR
1391	Marc Lehmann <schmorp@schmorp.de>	1776	Marc Lehmann <schmorp@schmorp.de>
1392	http://home.schmorp.de/	1777	http://home.schmorp.de/
1393		1778

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Comparing AnyEvent/README (file contents): Revision 1.31 by root, Thu Oct 2 06:42:39 2008 UTC vs. Revision 1.47 by root, Mon Jul 20 22:39:57 2009 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.31 by root, Thu Oct 2 06:42:39 2008 UTC vs.
Revision 1.47 by root, Mon Jul 20 22:39:57 2009 UTC