[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.28 by root, Sat Jul 12 20:45:27 2008 UTC vs.
Revision 1.48 by root, Sun Jul 26 00:17:24 2009 UTC

…		…
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, IO::Async, Qt and POE are
5	loops	5	various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# file descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		12
		13	# one-shot or repeating timers
		14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		16
		17	print AnyEvent->now; # prints current event loop time
		18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		19
		20	# POSIX signal
		21	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		22
		23	# child process exit
		24	my $w = AnyEvent->child (pid => $pid, cb => sub {
		25	my ($pid, $status) = @_;
11	...	26	...
12	});	27	});
13		28
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	29	# called when event loop idle (if applicable)
15	...	30	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		31
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	32	my $w = AnyEvent->condvar; # stores whether a condition was flagged
19	$w->send; # wake up current and all future recv's	33	$w->send; # wake up current and all future recv's
20	$w->recv; # enters "main loop" till $condvar gets ->send	34	$w->recv; # enters "main loop" till $condvar gets ->send
		35	# use a condvar in callback mode:
		36	$w->cb (sub { $_[0]->recv });
21		37
22	INTRODUCTION/TUTORIAL	38	INTRODUCTION/TUTORIAL
23	This manpage is mainly a reference manual. If you are interested in a	39	This manpage is mainly a reference manual. If you are interested in a
24	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
25	manpage.	41	manpage.
		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	Repository, at <http://anyevent.schmorp.de>, for more info.
26		49
27	WHY YOU SHOULD USE THIS MODULE (OR NOT)	50	WHY YOU SHOULD USE THIS MODULE (OR NOT)
28	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
29	nowadays. So what is different about AnyEvent?	52	nowadays. So what is different about AnyEvent?
30		53
123	These watchers are normal Perl objects with normal Perl lifetime. After	146	These watchers are normal Perl objects with normal Perl lifetime. After
124	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
125	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
126	in control).	149	in control).
127		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
128	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
129	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
130	to it).	159	to it).
131		160
132	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.
…		…
147		176
148	I/O WATCHERS	177	I/O WATCHERS
149	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
150	the following mandatory key-value pairs as arguments:	179	the following mandatory key-value pairs as arguments:
151		180
152	"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
153	(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
154	"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
155	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	189	watcher waiting for "r"eadable or "w"ritable events, respectively.
		190
156	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.
157		192
158	Although the callback might get passed parameters, their value and	193	Although the callback might get passed parameters, their value and
159	presence is undefined and you cannot rely on them. Portable AnyEvent	194	presence is undefined and you cannot rely on them. Portable AnyEvent
160	callbacks cannot use arguments passed to I/O watcher callbacks.	195	callbacks cannot use arguments passed to I/O watcher callbacks.
161		196
…		…
293	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
294	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
295	the difference between "AnyEvent->time" and "AnyEvent->now" into	330	the difference between "AnyEvent->time" and "AnyEvent->now" into
296	account.	331	account.
297		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
298	SIGNAL WATCHERS	347	SIGNAL WATCHERS
299	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
300	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
301	callback to be invoked whenever a signal occurs.	350	callback to be invoked whenever a signal occurs.
302		351
…		…
308	invocation, and callback invocation will be synchronous. Synchronous	357	invocation, and callback invocation will be synchronous. Synchronous
309	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
310	process, but it is guaranteed not to interrupt any other callbacks.	359	process, but it is guaranteed not to interrupt any other callbacks.
311		360
312	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
313	signal between multiple watchers.	362	signal between multiple watchers, and AnyEvent will ensure that signals
		363	will not interrupt your program at bad times.
314		364
315	This watcher might use %SIG, so programs overwriting those signals	365	This watcher might use %SIG (depending on the event loop used), so
316	directly will likely not work correctly.	366	programs overwriting those signals directly will likely not work
		367	correctly.
317		368
318	Example: exit on SIGINT	369	Example: exit on SIGINT
319		370
320	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.
321		387
322	CHILD PROCESS WATCHERS	388	CHILD PROCESS WATCHERS
323	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.
324		390
325	The child process is specified by the "pid" argument (if set to 0, it	391	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	392	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	393	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	394	and an exit status is available, not on any trace events
329	and exit status (as returned by waitpid), so unlike other watcher types,	395	(stopped/continued).
330	you can rely on child watcher callback arguments.	396
		397	The callback will be called with the pid and exit status (as returned by
		398	waitpid), so unlike other watcher types, you can rely on child watcher
		399	callback arguments.
		400
		401	This watcher type works by installing a signal handler for "SIGCHLD",
		402	and since it cannot be shared, nothing else should use SIGCHLD or reap
		403	random child processes (waiting for specific child processes, e.g.
		404	inside "system", is just fine).
331		405
332	There is a slight catch to child watchers, however: you usually start	406	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	407	them after the child process was created, and this means the process
334	could have exited already (and no SIGCHLD will be sent anymore).	408	could have exited already (and no SIGCHLD will be sent anymore).
335		409
336	Not all event models handle this correctly (POE doesn't), but even for	410	Not all event models handle this correctly (neither POE nor IO::Async
		411	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	412	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	413	before the process exits (i.e. before you fork in the first place).
339	place).	414	AnyEvent's pure perl event loop handles all cases correctly regardless
		415	of when you start the watcher.
340		416
341	This means you cannot create a child watcher as the very first thing in	417	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	418	an AnyEvent program, you have to create at least one watcher before
343	you "fork" the child (alternatively, you can call "AnyEvent::detect").	419	you "fork" the child (alternatively, you can call "AnyEvent::detect").
344		420
		421	As most event loops do not support waiting for child events, they will
		422	be emulated by AnyEvent in most cases, in which the latency and race
		423	problems mentioned in the description of signal watchers apply.
		424
345	Example: fork a process and wait for it	425	Example: fork a process and wait for it
346		426
347	my $done = AnyEvent->condvar;	427	my $done = AnyEvent->condvar;
348		428
349	my $pid = fork or exit 5;	429	my $pid = fork or exit 5;
350		430
351	my $w = AnyEvent->child (	431	my $w = AnyEvent->child (
352	pid => $pid,	432	pid => $pid,
353	cb => sub {	433	cb => sub {
354	my ($pid, $status) = @_;	434	my ($pid, $status) = @_;
355	warn "pid $pid exited with status $status";	435	warn "pid $pid exited with status $status";
356	$done->send;	436	$done->send;
357	},	437	},
358	);	438	);
359		439
360	# do something else, then wait for process exit	440	# do something else, then wait for process exit
361	$done->recv;	441	$done->recv;
		442
		443	IDLE WATCHERS
		444	Sometimes there is a need to do something, but it is not so important to
		445	do it instantly, but only when there is nothing better to do. This
		446	"nothing better to do" is usually defined to be "no other events need
		447	attention by the event loop".
		448
		449	Idle watchers ideally get invoked when the event loop has nothing better
		450	to do, just before it would block the process to wait for new events.
		451	Instead of blocking, the idle watcher is invoked.
		452
		453	Most event loops unfortunately do not really support idle watchers (only
		454	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		455	will simply call the callback "from time to time".
		456
		457	Example: read lines from STDIN, but only process them when the program
		458	is otherwise idle:
		459
		460	my @lines; # read data
		461	my $idle_w;
		462	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		463	push @lines, scalar <STDIN>;
		464
		465	# start an idle watcher, if not already done
		466	$idle_w \|\|= AnyEvent->idle (cb => sub {
		467	# handle only one line, when there are lines left
		468	if (my $line = shift @lines) {
		469	print "handled when idle: $line";
		470	} else {
		471	# otherwise disable the idle watcher again
		472	undef $idle_w;
		473	}
		474	});
		475	});
362		476
363	CONDITION VARIABLES	477	CONDITION VARIABLES
364	If you are familiar with some event loops you will know that all of them	478	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	479	require you to run some blocking "loop", "run" or similar function that
366	will actively watch for new events and call your callbacks.	480	will actively watch for new events and call your callbacks.
367		481
368	AnyEvent is different, it expects somebody else to run the event loop	482	AnyEvent is slightly different: it expects somebody else to run the
369	and will only block when necessary (usually when told by the user).	483	event loop and will only block when necessary (usually when told by the
		484	user).
370		485
371	The instrument to do that is called a "condition variable", so called	486	The instrument to do that is called a "condition variable", so called
372	because they represent a condition that must become true.	487	because they represent a condition that must become true.
		488
		489	Now is probably a good time to look at the examples further below.
373		490
374	Condition variables can be created by calling the "AnyEvent->condvar"	491	Condition variables can be created by calling the "AnyEvent->condvar"
375	method, usually without arguments. The only argument pair allowed is	492	method, usually without arguments. The only argument pair allowed is
376	"cb", which specifies a callback to be called when the condition	493	"cb", which specifies a callback to be called when the condition
377	variable becomes true.	494	variable becomes true, with the condition variable as the first argument
		495	(but not the results).
378		496
379	After creation, the condition variable is "false" until it becomes	497	After creation, the condition variable is "false" until it becomes
380	"true" by calling the "send" method (or calling the condition variable	498	"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	499	as if it were a callback, read about the caveats in the description for
382	the "->send" method).	500	the "->send" method).
…		…
384	Condition variables are similar to callbacks, except that you can	502	Condition variables are similar to callbacks, except that you can
385	optionally wait for them. They can also be called merge points - points	503	optionally wait for them. They can also be called merge points - points
386	in time where multiple outstanding events have been processed. And yet	504	in time where multiple outstanding events have been processed. And yet
387	another way to call them is transactions - each condition variable can	505	another way to call them is transactions - each condition variable can
388	be used to represent a transaction, which finishes at some point and	506	be used to represent a transaction, which finishes at some point and
389	delivers a result.	507	delivers a result. And yet some people know them as "futures" - a
		508	promise to compute/deliver something that you can wait for.
390		509
391	Condition variables are very useful to signal that something has	510	Condition variables are very useful to signal that something has
392	finished, for example, if you write a module that does asynchronous http	511	finished, for example, if you write a module that does asynchronous http
393	requests, then a condition variable would be the ideal candidate to	512	requests, then a condition variable would be the ideal candidate to
394	signal the availability of results. The user can either act when the	513	signal the availability of results. The user can either act when the
…		…
428	after => 1,	547	after => 1,
429	cb => sub { $result_ready->send },	548	cb => sub { $result_ready->send },
430	);	549	);
431		550
432	# this "blocks" (while handling events) till the callback	551	# this "blocks" (while handling events) till the callback
433	# calls send	552	# calls -<send
434	$result_ready->recv;	553	$result_ready->recv;
435		554
436	Example: wait for a timer, but take advantage of the fact that condition	555	Example: wait for a timer, but take advantage of the fact that condition
437	variables are also code references.	556	variables are also callable directly.
438		557
439	my $done = AnyEvent->condvar;	558	my $done = AnyEvent->condvar;
440	my $delay = AnyEvent->timer (after => 5, cb => $done);	559	my $delay = AnyEvent->timer (after => 5, cb => $done);
441	$done->recv;	560	$done->recv;
		561
		562	Example: Imagine an API that returns a condvar and doesn't support
		563	callbacks. This is how you make a synchronous call, for example from the
		564	main program:
		565
		566	use AnyEvent::CouchDB;
		567
		568	...
		569
		570	my @info = $couchdb->info->recv;
		571
		572	And this is how you would just set a callback to be called whenever the
		573	results are available:
		574
		575	$couchdb->info->cb (sub {
		576	my @info = $_[0]->recv;
		577	});
442		578
443	METHODS FOR PRODUCERS	579	METHODS FOR PRODUCERS
444	These methods should only be used by the producing side, i.e. the	580	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	581	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	582	producer side which creates the condvar in most cases, but it isn't
…		…
456		592
457	Any arguments passed to the "send" call will be returned by all	593	Any arguments passed to the "send" call will be returned by all
458	future "->recv" calls.	594	future "->recv" calls.
459		595
460	Condition variables are overloaded so one can call them directly (as	596	Condition variables are overloaded so one can call them directly (as
461	a code reference). Calling them directly is the same as calling	597	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	598	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		599
469	$cv->croak ($error)	600	$cv->croak ($error)
470	Similar to send, but causes all call's to "->recv" to invoke	601	Similar to send, but causes all call's to "->recv" to invoke
471	"Carp::croak" with the given error message/object/scalar.	602	"Carp::croak" with the given error message/object/scalar.
472		603
473	This can be used to signal any errors to the condition variable	604	This can be used to signal any errors to the condition variable
474	user/consumer.	605	user/consumer. Doing it this way instead of calling "croak" directly
		606	delays the error detetcion, but has the overwhelmign advantage that
		607	it diagnoses the error at the place where the result is expected,
		608	and not deep in some event clalback without connection to the actual
		609	code causing the problem.
475		610
476	$cv->begin ([group callback])	611	$cv->begin ([group callback])
477	$cv->end	612	$cv->end
478	These two methods are EXPERIMENTAL and MIGHT CHANGE.
479
480	These two methods can be used to combine many transactions/events	613	These two methods can be used to combine many transactions/events
481	into one. For example, a function that pings many hosts in parallel	614	into one. For example, a function that pings many hosts in parallel
482	might want to use a condition variable for the whole process.	615	might want to use a condition variable for the whole process.
483		616
484	Every call to "->begin" will increment a counter, and every call to	617	Every call to "->begin" will increment a counter, and every call to
485	"->end" will decrement it. If the counter reaches 0 in "->end", the	618	"->end" will decrement it. If the counter reaches 0 in "->end", the
486	(last) callback passed to "begin" will be executed. That callback is	619	(last) callback passed to "begin" will be executed. That callback is
487	supposed to call "->send", but that is not required. If no	620	supposed to call "->send", but that is not required. If no
488	callback was set, "send" will be called without any arguments.	621	callback was set, "send" will be called without any arguments.
489		622
490	Let's clarify this with the ping example:	623	You can think of "$cv->send" giving you an OR condition (one call
		624	sends), while "$cv->begin" and "$cv->end" giving you an AND
		625	condition (all "begin" calls must be "end"'ed before the condvar
		626	sends).
		627
		628	Let's start with a simple example: you have two I/O watchers (for
		629	example, STDOUT and STDERR for a program), and you want to wait for
		630	both streams to close before activating a condvar:
		631
		632	my $cv = AnyEvent->condvar;
		633
		634	$cv->begin; # first watcher
		635	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		636	defined sysread $fh1, my $buf, 4096
		637	or $cv->end;
		638	});
		639
		640	$cv->begin; # second watcher
		641	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		642	defined sysread $fh2, my $buf, 4096
		643	or $cv->end;
		644	});
		645
		646	$cv->recv;
		647
		648	This works because for every event source (EOF on file handle),
		649	there is one call to "begin", so the condvar waits for all calls to
		650	"end" before sending.
		651
		652	The ping example mentioned above is slightly more complicated, as
		653	the there are results to be passwd back, and the number of tasks
		654	that are begung can potentially be zero:
491		655
492	my $cv = AnyEvent->condvar;	656	my $cv = AnyEvent->condvar;
493		657
494	my %result;	658	my %result;
495	$cv->begin (sub { $cv->send (\%result) });	659	$cv->begin (sub { $cv->send (\%result) });
…		…
515	the loop, which serves two important purposes: first, it sets the	679	the loop, which serves two important purposes: first, it sets the
516	callback to be called once the counter reaches 0, and second, it	680	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	681	ensures that "send" is called even when "no" hosts are being pinged
518	(the loop doesn't execute once).	682	(the loop doesn't execute once).
519		683
520	This is the general pattern when you "fan out" into multiple	684	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	685	potentially none) subrequests: use an outer "begin"/"end" pair to
522	ensure "end" is called at least once, and then, for each subrequest	686	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	687	for each subrequest you start, call "begin" and for each subrequest
524	"end".	688	you finish, call "end".
525		689
526	METHODS FOR CONSUMERS	690	METHODS FOR CONSUMERS
527	These methods should only be used by the consuming side, i.e. the code	691	These methods should only be used by the consuming side, i.e. the code
528	awaits the condition.	692	awaits the condition.
529		693
…		…
538	function will call "croak".	702	function will call "croak".
539		703
540	In list context, all parameters passed to "send" will be returned,	704	In list context, all parameters passed to "send" will be returned,
541	in scalar context only the first one will be returned.	705	in scalar context only the first one will be returned.
542		706
		707	Note that doing a blocking wait in a callback is not supported by
		708	any event loop, that is, recursive invocation of a blocking "->recv"
		709	is not allowed, and the "recv" call will "croak" if such a condition
		710	is detected. This condition can be slightly loosened by using
		711	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		712	thread that doesn't run the event loop itself.
		713
543	Not all event models support a blocking wait - some die in that case	714	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	715	(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	716	using this from a module, never require a blocking wait*. Instead,
546	the caller decide whether the call will block or not (for example,	717	let the caller decide whether the call will block or not (for
547	by coupling condition variables with some kind of request results	718	example, by coupling condition variables with some kind of request
548	and supporting callbacks so the caller knows that getting the result	719	results and supporting callbacks so the caller knows that getting
549	will not block, while still supporting blocking waits if the caller	720	the result will not block, while still supporting blocking waits if
550	so desires).	721	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		722
563	You can ensure that "-recv" never blocks by setting a callback and	723	You can ensure that "-recv" never blocks by setting a callback and
564	only calling "->recv" from within that callback (or at a later	724	only calling "->recv" from within that callback (or at a later
565	time). This will work even when the event loop does not support	725	time). This will work even when the event loop does not support
566	blocking waits otherwise.	726	blocking waits otherwise.
567		727
568	$bool = $cv->ready	728	$bool = $cv->ready
569	Returns true when the condition is "true", i.e. whether "send" or	729	Returns true when the condition is "true", i.e. whether "send" or
570	"croak" have been called.	730	"croak" have been called.
571		731
572	$cb = $cv->cb ([new callback])	732	$cb = $cv->cb ($cb->($cv))
573	This is a mutator function that returns the callback set and	733	This is a mutator function that returns the callback set and
574	optionally replaces it before doing so.	734	optionally replaces it before doing so.
575		735
576	The callback will be called when the condition becomes "true", i.e.	736	The callback will be called when the condition becomes "true", i.e.
577	when "send" or "croak" are called, with the only argument being the	737	when "send" or "croak" are called, with the only argument being the
578	condition variable itself. Calling "recv" inside the callback or at	738	condition variable itself. Calling "recv" inside the callback or at
579	any later time is guaranteed not to block.	739	any later time is guaranteed not to block.
580		740
		741	SUPPORTED EVENT LOOPS/BACKENDS
		742	The available backend classes are (every class has its own manpage):
		743
		744	Backends that are autoprobed when no other event loop can be found.
		745	EV is the preferred backend when no other event loop seems to be in
		746	use. If EV is not installed, then AnyEvent will try Event, and,
		747	failing that, will fall back to its own pure-perl implementation,
		748	which is available everywhere as it comes with AnyEvent itself.
		749
		750	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		751	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		752	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		753
		754	Backends that are transparently being picked up when they are used.
		755	These will be used when they are currently loaded when the first
		756	watcher is created, in which case it is assumed that the application
		757	is using them. This means that AnyEvent will automatically pick the
		758	right backend when the main program loads an event module before
		759	anything starts to create watchers. Nothing special needs to be done
		760	by the main program.
		761
		762	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		763	AnyEvent::Impl::Tk based on Tk, very broken.
		764	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		765	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		766	AnyEvent::Impl::Irssi used when running within irssi.
		767
		768	Backends with special needs.
		769	Qt requires the Qt::Application to be instantiated first, but will
		770	otherwise be picked up automatically. As long as the main program
		771	instantiates the application before any AnyEvent watchers are
		772	created, everything should just work.
		773
		774	AnyEvent::Impl::Qt based on Qt.
		775
		776	Support for IO::Async can only be partial, as it is too broken and
		777	architecturally limited to even support the AnyEvent API. It also is
		778	the only event loop that needs the loop to be set explicitly, so it
		779	can only be used by a main program knowing about AnyEvent. See
		780	AnyEvent::Impl::Async for the gory details.
		781
		782	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		783
		784	Event loops that are indirectly supported via other backends.
		785	Some event loops can be supported via other modules:
		786
		787	There is no direct support for WxWidgets (Wx) or Prima.
		788
		789	WxWidgets has no support for watching file handles. However, you can
		790	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		791	simply polls 20 times per second, which was considered to be too
		792	horrible to even consider for AnyEvent.
		793
		794	Prima is not supported as nobody seems to be using it, but it has a
		795	POE backend, so it can be supported through POE.
		796
		797	AnyEvent knows about both Prima and Wx, however, and will try to
		798	load POE when detecting them, in the hope that POE will pick them
		799	up, in which case everything will be automatic.
		800
581	GLOBAL VARIABLES AND FUNCTIONS	801	GLOBAL VARIABLES AND FUNCTIONS
		802	These are not normally required to use AnyEvent, but can be useful to
		803	write AnyEvent extension modules.
		804
582	$AnyEvent::MODEL	805	$AnyEvent::MODEL
583	Contains "undef" until the first watcher is being created. Then it	806	Contains "undef" until the first watcher is being created, before
		807	the backend has been autodetected.
		808
584	contains the event model that is being used, which is the name of	809	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	810	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	811	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).	812	other class in the case AnyEvent has been extended at runtime (e.g.
588		813	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		814
610	AnyEvent::detect	815	AnyEvent::detect
611	Returns $AnyEvent::MODEL, forcing autodetection of the event model	816	Returns $AnyEvent::MODEL, forcing autodetection of the event model
612	if necessary. You should only call this function right before you	817	if necessary. You should only call this function right before you
613	would have created an AnyEvent watcher anyway, that is, as late as	818	would have created an AnyEvent watcher anyway, that is, as late as
614	possible at runtime.	819	possible at runtime, and not e.g. while initialising of your module.
		820
		821	If you need to do some initialisation before AnyEvent watchers are
		822	created, use "post_detect".
615		823
616	$guard = AnyEvent::post_detect { BLOCK }	824	$guard = AnyEvent::post_detect { BLOCK }
617	Arranges for the code block to be executed as soon as the event	825	Arranges for the code block to be executed as soon as the event
618	model is autodetected (or immediately if this has already happened).	826	model is autodetected (or immediately if this has already happened).
619		827
		828	The block will be executed after the actual backend has been
		829	detected ($AnyEvent::MODEL is set), but before any watchers have
		830	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		831	other initialisations - see the sources of AnyEvent::Strict or
		832	AnyEvent::AIO to see how this is used.
		833
		834	The most common usage is to create some global watchers, without
		835	forcing event module detection too early, for example, AnyEvent::AIO
		836	creates and installs the global IO::AIO watcher in a "post_detect"
		837	block to avoid autodetecting the event module at load time.
		838
620	If called in scalar or list context, then it creates and returns an	839	If called in scalar or list context, then it creates and returns an
621	object that automatically removes the callback again when it is	840	object that automatically removes the callback again when it is
		841	destroyed (or "undef" when the hook was immediately executed). See
622	destroyed. See Coro::BDB for a case where this is useful.	842	AnyEvent::AIO for a case where this is useful.
		843
		844	Example: Create a watcher for the IO::AIO module and store it in
		845	$WATCHER. Only do so after the event loop is initialised, though.
		846
		847	our WATCHER;
		848
		849	my $guard = AnyEvent::post_detect {
		850	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		851	};
		852
		853	# the \|\|= is important in case post_detect immediately runs the block,
		854	# as to not clobber the newly-created watcher. assigning both watcher and
		855	# post_detect guard to the same variable has the advantage of users being
		856	# able to just C<undef $WATCHER> if the watcher causes them grief.
		857
		858	$WATCHER \|\|= $guard;
623		859
624	@AnyEvent::post_detect	860	@AnyEvent::post_detect
625	If there are any code references in this array (you can "push" to it	861	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	862	before or after loading AnyEvent), then they will called directly
627	after the event loop has been chosen.	863	after the event loop has been chosen.
628		864
629	You should check $AnyEvent::MODEL before adding to this array,	865	You should check $AnyEvent::MODEL before adding to this array,
630	though: if it contains a true value then the event loop has already	866	though: if it is defined then the event loop has already been
631	been detected, and the array will be ignored.	867	detected, and the array will be ignored.
632		868
633	Best use "AnyEvent::post_detect { BLOCK }" instead.	869	Best use "AnyEvent::post_detect { BLOCK }" when your application
		870	allows it,as it takes care of these details.
		871
		872	This variable is mainly useful for modules that can do something
		873	useful when AnyEvent is used and thus want to know when it is
		874	initialised, but do not need to even load it by default. This array
		875	provides the means to hook into AnyEvent passively, without loading
		876	it.
634		877
635	WHAT TO DO IN A MODULE	878	WHAT TO DO IN A MODULE
636	As a module author, you should "use AnyEvent" and call AnyEvent methods	879	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.	880	freely, but you should not load a specific event module or rely on it.
638		881
…		…
689	variable somewhere, waiting for it, and sending it when the program	932	variable somewhere, waiting for it, and sending it when the program
690	should exit cleanly.	933	should exit cleanly.
691		934
692	OTHER MODULES	935	OTHER MODULES
693	The following is a non-exhaustive list of additional modules that use	936	The following is a non-exhaustive list of additional modules that use
694	AnyEvent and can therefore be mixed easily with other AnyEvent modules	937	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	938	AnyEvent modules and other event loops in the same program. Some of the
696	available via CPAN.	939	modules come with AnyEvent, most are available via CPAN.
697		940
698	AnyEvent::Util	941	AnyEvent::Util
699	Contains various utility functions that replace often-used but	942	Contains various utility functions that replace often-used but
700	blocking functions such as "inet_aton" by event-/callback-based	943	blocking functions such as "inet_aton" by event-/callback-based
701	versions.	944	versions.
…		…
707	more.	950	more.
708		951
709	AnyEvent::Handle	952	AnyEvent::Handle
710	Provide read and write buffers, manages watchers for reads and	953	Provide read and write buffers, manages watchers for reads and
711	writes, supports raw and formatted I/O, I/O queued and fully	954	writes, supports raw and formatted I/O, I/O queued and fully
712	transparent and non-blocking SSL/TLS.	955	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
713		956
714	AnyEvent::DNS	957	AnyEvent::DNS
715	Provides rich asynchronous DNS resolver capabilities.	958	Provides rich asynchronous DNS resolver capabilities.
716		959
717	AnyEvent::HTTP	960	AnyEvent::HTTP
…		…
738		981
739	AnyEvent::GPSD	982	AnyEvent::GPSD
740	A non-blocking interface to gpsd, a daemon delivering GPS	983	A non-blocking interface to gpsd, a daemon delivering GPS
741	information.	984	information.
742		985
		986	AnyEvent::IRC
		987	AnyEvent based IRC client module family (replacing the older
		988	Net::IRC3).
		989
		990	AnyEvent::XMPP
		991	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		992	older Net::XMPP2>.
		993
743	AnyEvent::IGS	994	AnyEvent::IGS
744	A non-blocking interface to the Internet Go Server protocol (used by	995	A non-blocking interface to the Internet Go Server protocol (used by
745	App::IGS).	996	App::IGS).
746		997
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	998	Net::FCP
754	AnyEvent-based implementation of the Freenet Client Protocol,	999	AnyEvent-based implementation of the Freenet Client Protocol,
755	birthplace of AnyEvent.	1000	birthplace of AnyEvent.
756		1001
757	Event::ExecFlow	1002	Event::ExecFlow
758	High level API for event-based execution flow control.	1003	High level API for event-based execution flow control.
759		1004
760	Coro	1005	Coro
761	Has special support for AnyEvent via Coro::AnyEvent.	1006	Has special support for AnyEvent via Coro::AnyEvent.
762		1007
763	IO::Lambda	1008	ERROR AND EXCEPTION HANDLING
764	The lambda approach to I/O - don't ask, look there. Can use	1009	In general, AnyEvent does not do any error handling - it relies on the
765	AnyEvent.	1010	caller to do that if required. The AnyEvent::Strict module (see also the
		1011	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1012	checking of all AnyEvent methods, however, which is highly useful during
		1013	development.
766		1014
767	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1015	As for exception handling (i.e. runtime errors and exceptions thrown
768	This is an advanced topic that you do not normally need to use AnyEvent	1016	while executing a callback), this is not only highly event-loop
769	in a module. This section is only of use to event loop authors who want	1017	specific, but also not in any way wrapped by this module, as this is the
770	to provide AnyEvent compatibility.	1018	job of the main program.
771		1019
772	If you need to support another event library which isn't directly	1020	The pure perl event loop simply re-throws the exception (usually within
773	supported by AnyEvent, you can supply your own interface to it by	1021	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
774	pushing, before the first watcher gets created, the package name of the	1022	Glib uses "install_exception_handler" and so on.
775	event module and the package name of the interface to use onto
776	@AnyEvent::REGISTRY. You can do that before and even without loading
777	AnyEvent, so it is reasonably cheap.
778
779	Example:
780
781	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
782
783	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
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		1023
810	ENVIRONMENT VARIABLES	1024	ENVIRONMENT VARIABLES
811	The following environment variables are used by this module:	1025	The following environment variables are used by this module or its
		1026	submodules.
		1027
		1028	Note that AnyEvent will remove all environment variables starting with
		1029	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1030	enabled.
812		1031
813	"PERL_ANYEVENT_VERBOSE"	1032	"PERL_ANYEVENT_VERBOSE"
814	By default, AnyEvent will be completely silent except in fatal	1033	By default, AnyEvent will be completely silent except in fatal
815	conditions. You can set this environment variable to make AnyEvent	1034	conditions. You can set this environment variable to make AnyEvent
816	more talkative.	1035	more talkative.
…		…
819	conditions, such as not being able to load the event model specified	1038	conditions, such as not being able to load the event model specified
820	by "PERL_ANYEVENT_MODEL".	1039	by "PERL_ANYEVENT_MODEL".
821		1040
822	When set to 2 or higher, cause AnyEvent to report to STDERR which	1041	When set to 2 or higher, cause AnyEvent to report to STDERR which
823	event model it chooses.	1042	event model it chooses.
		1043
		1044	When set to 8 or higher, then AnyEvent will report extra information
		1045	on which optional modules it loads and how it implements certain
		1046	features.
824		1047
825	"PERL_ANYEVENT_STRICT"	1048	"PERL_ANYEVENT_STRICT"
826	AnyEvent does not do much argument checking by default, as thorough	1049	AnyEvent does not do much argument checking by default, as thorough
827	argument checking is very costly. Setting this variable to a true	1050	argument checking is very costly. Setting this variable to a true
828	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1051	value will cause AnyEvent to load "AnyEvent::Strict" and then to
829	thoroughly check the arguments passed to most method calls. If it	1052	thoroughly check the arguments passed to most method calls. If it
830	finds any problems it will croak.	1053	finds any problems, it will croak.
831		1054
832	In other words, enables "strict" mode.	1055	In other words, enables "strict" mode.
833		1056
834	Unlike "use strict" it is definitely recommended ot keep it off in	1057	Unlike "use strict" (or it's modern cousin, "use common::sense", it
835	production.	1058	is definitely recommended to keep it off in production. Keeping
		1059	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1060	programs can be very useful, however.
836		1061
837	"PERL_ANYEVENT_MODEL"	1062	"PERL_ANYEVENT_MODEL"
838	This can be used to specify the event model to be used by AnyEvent,	1063	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	1064	before auto detection and -probing kicks in. It must be a string
840	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1065	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
859	mentioned will be used, and preference will be given to protocols	1084	mentioned will be used, and preference will be given to protocols
860	mentioned earlier in the list.	1085	mentioned earlier in the list.
861		1086
862	This variable can effectively be used for denial-of-service attacks	1087	This variable can effectively be used for denial-of-service attacks
863	against local programs (e.g. when setuid), although the impact is	1088	against local programs (e.g. when setuid), although the impact is
864	likely small, as the program has to handle connection errors	1089	likely small, as the program has to handle conenction and other
865	already-	1090	failures anyways.
866		1091
867	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1092	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
868	IPv6, but support both and try to use both.	1093	IPv6, but support both and try to use both.
869	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1094	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
870	resolve or contact IPv6 addresses.	1095	resolve or contact IPv6 addresses.
…		…
881	EDNS0 in its DNS requests.	1106	EDNS0 in its DNS requests.
882		1107
883	"PERL_ANYEVENT_MAX_FORKS"	1108	"PERL_ANYEVENT_MAX_FORKS"
884	The maximum number of child processes that	1109	The maximum number of child processes that
885	"AnyEvent::Util::fork_call" will create in parallel.	1110	"AnyEvent::Util::fork_call" will create in parallel.
		1111
		1112	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1113	The default value for the "max_outstanding" parameter for the
		1114	default DNS resolver - this is the maximum number of parallel DNS
		1115	requests that are sent to the DNS server.
		1116
		1117	"PERL_ANYEVENT_RESOLV_CONF"
		1118	The file to use instead of /etc/resolv.conf (or OS-specific
		1119	configuration) in the default resolver. When set to the empty
		1120	string, no default config will be used.
		1121
		1122	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1123	When neither "ca_file" nor "ca_path" was specified during
		1124	AnyEvent::TLS context creation, and either of these environment
		1125	variables exist, they will be used to specify CA certificate
		1126	locations instead of a system-dependent default.
		1127
		1128	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1129	When these are set to 1, then the respective modules are not loaded.
		1130	Mostly good for testing AnyEvent itself.
		1131
		1132	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1133	This is an advanced topic that you do not normally need to use AnyEvent
		1134	in a module. This section is only of use to event loop authors who want
		1135	to provide AnyEvent compatibility.
		1136
		1137	If you need to support another event library which isn't directly
		1138	supported by AnyEvent, you can supply your own interface to it by
		1139	pushing, before the first watcher gets created, the package name of the
		1140	event module and the package name of the interface to use onto
		1141	@AnyEvent::REGISTRY. You can do that before and even without loading
		1142	AnyEvent, so it is reasonably cheap.
		1143
		1144	Example:
		1145
		1146	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1147
		1148	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
		1149	package/class when it finds the "urxvt" package/module is already
		1150	loaded.
		1151
		1152	When AnyEvent is loaded and asked to find a suitable event model, it
		1153	will first check for the presence of urxvt by trying to "use" the
		1154	"urxvt::anyevent" module.
		1155
		1156	The class should provide implementations for all watcher types. See
		1157	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
		1158	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
		1159	the sources.
		1160
		1161	If you don't provide "signal" and "child" watchers than AnyEvent will
		1162	provide suitable (hopefully) replacements.
		1163
		1164	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
		1165	terminal emulator uses the above line as-is. An interface isn't included
		1166	in AnyEvent because it doesn't make sense outside the embedded
		1167	interpreter inside rxvt-unicode, and it is updated and maintained as
		1168	part of the rxvt-unicode distribution.
		1169
		1170	rxvt-unicode also cheats a bit by not providing blocking access to
		1171	condition variables: code blocking while waiting for a condition will
		1172	"die". This still works with most modules/usages, and blocking calls
		1173	must not be done in an interactive application, so it makes sense.
886		1174
887	EXAMPLE PROGRAM	1175	EXAMPLE PROGRAM
888	The following program uses an I/O watcher to read data from STDIN, a	1176	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	1177	timer to display a message once per second, and a condition variable to
890	quit the program when the user enters quit:	1178	quit the program when the user enters quit:
…		…
1077	destroy is the time, in microseconds, that it takes to destroy a	1365	destroy is the time, in microseconds, that it takes to destroy a
1078	single watcher.	1366	single watcher.
1079		1367
1080	Results	1368	Results
1081	name watchers bytes create invoke destroy comment	1369	name watchers bytes create invoke destroy comment
1082	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1370	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
1083	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1371	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
1084	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1372	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
1085	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1373	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
1086	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1374	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
1087	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1375	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1376	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1377	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
1088	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1378	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
1089	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1379	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
1090	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1380	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
1091	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1381	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
1092		1382
1093	Discussion	1383	Discussion
1094	The benchmark does not measure scalability of the event loop very	1384	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)	1385	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	1386	can never compete with an event loop that uses epoll when the number of
…		…
1121	few of them active), of course, but this was not subject of this	1411	few of them active), of course, but this was not subject of this
1122	benchmark.	1412	benchmark.
1123		1413
1124	The "Event" module has a relatively high setup and callback invocation	1414	The "Event" module has a relatively high setup and callback invocation
1125	cost, but overall scores in on the third place.	1415	cost, but overall scores in on the third place.
		1416
		1417	"IO::Async" performs admirably well, about on par with "Event", even
		1418	when using its pure perl backend.
1126		1419
1127	"Glib"'s memory usage is quite a bit higher, but it features a faster	1420	"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".	1421	callback invocation and overall ends up in the same class as "Event".
1129	However, Glib scales extremely badly, doubling the number of watchers	1422	However, Glib scales extremely badly, doubling the number of watchers
1130	increases the processing time by more than a factor of four, making it	1423	increases the processing time by more than a factor of four, making it
…		…
1201	single "request", that is, reading the token from the pipe and	1494	single "request", that is, reading the token from the pipe and
1202	forwarding it to another server. This includes deleting the old timeout	1495	forwarding it to another server. This includes deleting the old timeout
1203	and creating a new one that moves the timeout into the future.	1496	and creating a new one that moves the timeout into the future.
1204		1497
1205	Results	1498	Results
1206	name sockets create request	1499	name sockets create request
1207	EV 20000 69.01 11.16	1500	EV 20000 69.01 11.16
1208	Perl 20000 73.32 35.87	1501	Perl 20000 73.32 35.87
		1502	IOAsync 20000 157.00 98.14 epoll
		1503	IOAsync 20000 159.31 616.06 poll
1209	Event 20000 212.62 257.32	1504	Event 20000 212.62 257.32
1210	Glib 20000 651.16 1896.30	1505	Glib 20000 651.16 1896.30
1211	POE 20000 349.67 12317.24 uses POE::Loop::Event	1506	POE 20000 349.67 12317.24 uses POE::Loop::Event
1212		1507
1213	Discussion	1508	Discussion
1214	This benchmark does measure scalability and overall performance of the	1509	This benchmark does measure scalability and overall performance of the
1215	particular event loop.	1510	particular event loop.
1216		1511
1217	EV is again fastest. Since it is using epoll on my system, the setup	1512	EV is again fastest. Since it is using epoll on my system, the setup
1218	time is relatively high, though.	1513	time is relatively high, though.
1219		1514
1220	Perl surprisingly comes second. It is much faster than the C-based event	1515	Perl surprisingly comes second. It is much faster than the C-based event
1221	loops Event and Glib.	1516	loops Event and Glib.
		1517
		1518	IO::Async performs very well when using its epoll backend, and still
		1519	quite good compared to Glib when using its pure perl backend.
1222		1520
1223	Event suffers from high setup time as well (look at its code and you	1521	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	1522	will understand why). Callback invocation also has a high overhead
1225	compared to the "$_->() for .."-style loop that the Perl event loop	1523	compared to the "$_->() for .."-style loop that the Perl event loop
1226	uses. Event uses select or poll in basically all documented	1524	uses. Event uses select or poll in basically all documented
…		…
1277		1575
1278	Summary	1576	Summary
1279	* C-based event loops perform very well with small number of watchers,	1577	* C-based event loops perform very well with small number of watchers,
1280	as the management overhead dominates.	1578	as the management overhead dominates.
1281		1579
		1580	THE IO::Lambda BENCHMARK
		1581	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1582	could be misinterpreted to make AnyEvent look bad. In fact, the
		1583	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1584	better (which shouldn't come as a surprise to anybody). As such, the
		1585	benchmark is fine, and mostly shows that the AnyEvent backend from
		1586	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1587	without the extra baggage? To explore this, I wrote the equivalent
		1588	benchmark for AnyEvent.
		1589
		1590	The benchmark itself creates an echo-server, and then, for 500 times,
		1591	connects to the echo server, sends a line, waits for the reply, and then
		1592	creates the next connection. This is a rather bad benchmark, as it
		1593	doesn't test the efficiency of the framework or much non-blocking I/O,
		1594	but it is a benchmark nevertheless.
		1595
		1596	name runtime
		1597	Lambda/select 0.330 sec
		1598	+ optimized 0.122 sec
		1599	Lambda/AnyEvent 0.327 sec
		1600	+ optimized 0.138 sec
		1601	Raw sockets/select 0.077 sec
		1602	POE/select, components 0.662 sec
		1603	POE/select, raw sockets 0.226 sec
		1604	POE/select, optimized 0.404 sec
		1605
		1606	AnyEvent/select/nb 0.085 sec
		1607	AnyEvent/EV/nb 0.068 sec
		1608	+state machine 0.134 sec
		1609
		1610	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1611	benchmarks actually make blocking connects and use 100% blocking I/O,
		1612	defeating the purpose of an event-based solution. All of the newly
		1613	written AnyEvent benchmarks use 100% non-blocking connects (using
		1614	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1615	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1616	connects generally require a lot more bookkeeping and event handling
		1617	than blocking connects (which involve a single syscall only).
		1618
		1619	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1620	offers similar expressive power as POE and IO::Lambda, using
		1621	conventional Perl syntax. This means that both the echo server and the
		1622	client are 100% non-blocking, further placing it at a disadvantage.
		1623
		1624	As you can see, the AnyEvent + EV combination even beats the
		1625	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1626	backend easily beats IO::Lambda and POE.
		1627
		1628	And even the 100% non-blocking version written using the high-level (and
		1629	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a
		1630	large margin, even though it does all of DNS, tcp-connect and socket I/O
		1631	in a non-blocking way.
		1632
		1633	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1634	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1635	part of the IO::lambda distribution and were used without any changes.
		1636
		1637	SIGNALS
		1638	AnyEvent currently installs handlers for these signals:
		1639
		1640	SIGCHLD
		1641	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1642	emulation for event loops that do not support them natively. Also,
		1643	some event loops install a similar handler.
		1644
		1645	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1646	then AnyEvent will reset it to default, to avoid losing child exit
		1647	statuses.
		1648
		1649	SIGPIPE
		1650	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1651	"undef" when AnyEvent gets loaded.
		1652
		1653	The rationale for this is that AnyEvent users usually do not really
		1654	depend on SIGPIPE delivery (which is purely an optimisation for
		1655	shell use, or badly-written programs), but "SIGPIPE" can cause
		1656	spurious and rare program exits as a lot of people do not expect
		1657	"SIGPIPE" when writing to some random socket.
		1658
		1659	The rationale for installing a no-op handler as opposed to ignoring
		1660	it is that this way, the handler will be restored to defaults on
		1661	exec.
		1662
		1663	Feel free to install your own handler, or reset it to defaults.
		1664
		1665	RECOMMENDED/OPTIONAL MODULES
		1666	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1667	it's built-in modules) are required to use it.
		1668
		1669	That does not mean that AnyEvent won't take advantage of some additional
		1670	modules if they are installed.
		1671
		1672	This section epxlains which additional modules will be used, and how
		1673	they affect AnyEvent's operetion.
		1674
		1675	Async::Interrupt
		1676	This slightly arcane module is used to implement fast signal
		1677	handling: To my knowledge, there is no way to do completely
		1678	race-free and quick signal handling in pure perl. To ensure that
		1679	signals still get delivered, AnyEvent will start an interval timer
		1680	to wake up perl (and catch the signals) with some delay (default is
		1681	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1682
		1683	If this module is available, then it will be used to implement
		1684	signal catching, which means that signals will not be delayed, and
		1685	the event loop will not be interrupted regularly, which is more
		1686	efficient (And good for battery life on laptops).
		1687
		1688	This affects not just the pure-perl event loop, but also other event
		1689	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1690
		1691	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1692	natively, and either employ their own workarounds (POE) or use
		1693	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1694	Installing Async::Interrupt does nothing for those backends.
		1695
		1696	EV This module isn't really "optional", as it is simply one of the
		1697	backend event loops that AnyEvent can use. However, it is simply the
		1698	best event loop available in terms of features, speed and stability:
		1699	It supports the AnyEvent API optimally, implements all the watcher
		1700	types in XS, does automatic timer adjustments even when no monotonic
		1701	clock is available, can take avdantage of advanced kernel interfaces
		1702	such as "epoll" and "kqueue", and is the fastest backend by far.
		1703	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1704	Glib::EV).
		1705
		1706	Guard
		1707	The guard module, when used, will be used to implement
		1708	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1709	uses a lot less memory), but otherwise doesn't affect guard
		1710	operation much. It is purely used for performance.
		1711
		1712	JSON and JSON::XS
		1713	This module is required when you want to read or write JSON data via
		1714	AnyEvent::Handle. It is also written in pure-perl, but can take
		1715	advantage of the ultra-high-speed JSON::XS module when it is
		1716	installed.
		1717
		1718	In fact, AnyEvent::Handle will use JSON::XS by default if it is
		1719	installed.
		1720
		1721	Net::SSLeay
		1722	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1723	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1724	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1725
		1726	Time::HiRes
		1727	This module is part of perl since release 5.008. It will be used
		1728	when the chosen event library does not come with a timing source on
		1729	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1730	additionally use it to try to use a monotonic clock for timing
		1731	stability.
		1732
1282	FORK	1733	FORK
1283	Most event libraries are not fork-safe. The ones who are usually are	1734	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.	1735	because they rely on inefficient but fork-safe "select" or "poll" calls.
1285	Only EV is fully fork-aware.	1736	Only EV is fully fork-aware.
1286		1737
1287	If you have to fork, you must either do so before creating your first	1738	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.	1739	watcher OR you must not use AnyEvent at all in the child OR you must do
		1740	something completely out of the scope of AnyEvent.
1289		1741
1290	SECURITY CONSIDERATIONS	1742	SECURITY CONSIDERATIONS
1291	AnyEvent can be forced to load any event model via	1743	AnyEvent can be forced to load any event model via
1292	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1744	$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	1745	to execute arbitrary code or directly gain access, it can easily be used
…		…
1297		1749
1298	You can make AnyEvent completely ignore this variable by deleting it	1750	You can make AnyEvent completely ignore this variable by deleting it
1299	before the first watcher gets created, e.g. with a "BEGIN" block:	1751	before the first watcher gets created, e.g. with a "BEGIN" block:
1300		1752
1301	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1753	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1302		1754
1303	use AnyEvent;	1755	use AnyEvent;
1304		1756
1305	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1757	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	1758	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),	1759	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1308	and $ENV{PERL_ANYEGENT_STRICT}.	1760	and $ENV{PERL_ANYEVENT_STRICT}.
		1761
		1762	Note that AnyEvent will remove all environment variables starting with
		1763	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1764	enabled.
1309		1765
1310	BUGS	1766	BUGS
1311	Perl 5.8 has numerous memleaks that sometimes hit this module and are	1767	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	1768	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	1769	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	1770	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1315	not as pronounced).	1771	not as pronounced).
1316		1772
1317	SEE ALSO	1773	SEE ALSO
1318	Utility functions: AnyEvent::Util.	1774	Utility functions: AnyEvent::Util.
1319		1775
1320	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1776	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1321	Event::Lib, Qt, POE.	1777	Event::Lib, Qt, POE.
1322		1778
1323	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1779	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1324	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1780	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1325	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1781	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1782	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
1326		1783
1327	Non-blocking file handles, sockets, TCP clients and servers:	1784	Non-blocking file handles, sockets, TCP clients and servers:
1328	AnyEvent::Handle, AnyEvent::Socket.	1785	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1329		1786
1330	Asynchronous DNS: AnyEvent::DNS.	1787	Asynchronous DNS: AnyEvent::DNS.
1331		1788
1332	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1789	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1333		1790
1334	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1791	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1792	AnyEvent::HTTP.
1335		1793
1336	AUTHOR	1794	AUTHOR
1337	Marc Lehmann <schmorp@schmorp.de>	1795	Marc Lehmann <schmorp@schmorp.de>
1338	http://home.schmorp.de/	1796	http://home.schmorp.de/
1339		1797

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Comparing AnyEvent/README (file contents):
Revision 1.28 by root, Sat Jul 12 20:45:27 2008 UTC vs.
Revision 1.48 by root, Sun Jul 26 00:17:24 2009 UTC