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Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs.
Revision 1.45 by root, Fri Jul 17 14:57:03 2009 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - provide framework for multiple event loops
3		3
4	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE -	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
5	various supported event loops	5	event loops.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# file descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		12
		13	# one-shot or repeating timers
		14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		16
		17	print AnyEvent->now; # prints current event loop time
		18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		19
		20	# POSIX signal
		21	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		22
		23	# child process exit
		24	my $w = AnyEvent->child (pid => $pid, cb => sub {
		25	my ($pid, $status) = @_;
11	...	26	...
12	});	27	});
13		28
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	29	# called when event loop idle (if applicable)
15	...	30	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		31
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	32	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		33	$w->send; # wake up current and all future recv's
19	$w->wait; # enters "main loop" till $condvar gets ->broadcast	34	$w->recv; # enters "main loop" till $condvar gets ->send
20	$w->broadcast; # wake up current and all future wait's	35	# use a condvar in callback mode:
		36	$w->cb (sub { $_[0]->recv });
		37
		38	INTRODUCTION/TUTORIAL
		39	This manpage is mainly a reference manual. If you are interested in a
		40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		41	manpage.
21		42
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	43	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	44	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	45	nowadays. So what is different about AnyEvent?
25		46
26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	47	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
27	policy* and AnyEvent is small and efficient.	48	policy* and AnyEvent is small and efficient.
28		49
29	First and foremost, AnyEvent is not an event model itself, it only	50	First and foremost, AnyEvent is not an event model itself, it only
30	interfaces to whatever event model the main program happens to use in a	51	interfaces to whatever event model the main program happens to use, in a
31	pragmatic way. For event models and certain classes of immortals alike,	52	pragmatic way. For event models and certain classes of immortals alike,
32	the statement "there can only be one" is a bitter reality: In general,	53	the statement "there can only be one" is a bitter reality: In general,
33	only one event loop can be active at the same time in a process.	54	only one event loop can be active at the same time in a process.
34	AnyEvent helps hiding the differences between those event loops.	55	AnyEvent cannot change this, but it can hide the differences between
		56	those event loops.
35		57
36	The goal of AnyEvent is to offer module authors the ability to do event	58	The goal of AnyEvent is to offer module authors the ability to do event
37	programming (waiting for I/O or timer events) without subscribing to a	59	programming (waiting for I/O or timer events) without subscribing to a
38	religion, a way of living, and most importantly: without forcing your	60	religion, a way of living, and most importantly: without forcing your
39	module users into the same thing by forcing them to use the same event	61	module users into the same thing by forcing them to use the same event
40	model you use.	62	model you use.
41		63
42	For modules like POE or IO::Async (which is a total misnomer as it is	64	For modules like POE or IO::Async (which is a total misnomer as it is
43	actually doing all I/O synchronously...), using them in your module is	65	actually doing all I/O synchronously...), using them in your module is
44	like joining a cult: After you joined, you are dependent on them and you	66	like joining a cult: After you joined, you are dependent on them and you
45	cannot use anything else, as it is simply incompatible to everything	67	cannot use anything else, as they are simply incompatible to everything
46	that isn't itself. What's worse, all the potential users of your module	68	that isn't them. What's worse, all the potential users of your module
47	are also forced to use the same event loop you use.	69	are also forced to use the same event loop you use.
48		70
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	71	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	72	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your	73	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
52	module uses one of those, every user of your module has to use it, too.	74	module uses one of those, every user of your module has to use it, too.
53	But if your module uses AnyEvent, it works transparently with all event	75	But if your module uses AnyEvent, it works transparently with all event
54	models it supports (including stuff like POE and IO::Async, as long as	76	models it supports (including stuff like IO::Async, as long as those use
55	those use one of the supported event loops. It is trivial to add new	77	one of the supported event loops. It is trivial to add new event loops
56	event loops to AnyEvent, too, so it is future-proof).	78	to AnyEvent, too, so it is future-proof).
57		79
58	In addition to being free of having to use *the one and only true event	80	In addition to being free of having to use *the one and only true event
59	model*, AnyEvent also is free of bloat and policy: with POE or similar	81	model*, AnyEvent also is free of bloat and policy: with POE or similar
60	modules, you get an enourmous amount of code and strict rules you have	82	modules, you get an enormous amount of code and strict rules you have to
61	to follow. AnyEvent, on the other hand, is lean and up to the point, by	83	follow. AnyEvent, on the other hand, is lean and up to the point, by
62	only offering the functionality that is necessary, in as thin as a	84	only offering the functionality that is necessary, in as thin as a
63	wrapper as technically possible.	85	wrapper as technically possible.
64		86
		87	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
		88	useful functionality, such as an asynchronous DNS resolver, 100%
		89	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		90	such as Windows) and lots of real-world knowledge and workarounds for
		91	platform bugs and differences.
		92
65	Of course, if you want lots of policy (this can arguably be somewhat	93	Now, if you do want lots of policy (this can arguably be somewhat
66	useful) and you want to force your users to use the one and only event	94	useful) and you want to force your users to use the one and only event
67	model, you should not use this module.	95	model, you should not use this module.
68		96
69	DESCRIPTION	97	DESCRIPTION
70	AnyEvent provides an identical interface to multiple event loops. This	98	AnyEvent provides an identical interface to multiple event loops. This
75	The interface itself is vaguely similar, but not identical to the Event	103	The interface itself is vaguely similar, but not identical to the Event
76	module.	104	module.
77		105
78	During the first call of any watcher-creation method, the module tries	106	During the first call of any watcher-creation method, the module tries
79	to detect the currently loaded event loop by probing whether one of the	107	to detect the currently loaded event loop by probing whether one of the
80	following modules is already loaded: Coro::EV, Coro::Event, EV, Event,	108	following modules is already loaded: EV, Event, Glib,
81	Glib, AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found	109	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82	is used. If none are found, the module tries to load these modules	110	used. If none are found, the module tries to load these modules
83	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	111	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
84	always succeed) in the order given. The first one that can be	112	always succeed) in the order given. The first one that can be
85	successfully loaded will be used. If, after this, still none could be	113	successfully loaded will be used. If, after this, still none could be
86	found, AnyEvent will fall back to a pure-perl event loop, which is not	114	found, AnyEvent will fall back to a pure-perl event loop, which is not
87	very efficient, but should work everywhere.	115	very efficient, but should work everywhere.
…		…
99	starts using it, all bets are off. Maybe you should tell their authors	127	starts using it, all bets are off. Maybe you should tell their authors
100	to use AnyEvent so their modules work together with others seamlessly...	128	to use AnyEvent so their modules work together with others seamlessly...
101		129
102	The pure-perl implementation of AnyEvent is called	130	The pure-perl implementation of AnyEvent is called
103	"AnyEvent::Impl::Perl". Like other event modules you can load it	131	"AnyEvent::Impl::Perl". Like other event modules you can load it
104	explicitly.	132	explicitly and enjoy the high availability of that event loop :)
105		133
106	WATCHERS	134	WATCHERS
107	AnyEvent has the central concept of a watcher, which is an object that	135	AnyEvent has the central concept of a watcher, which is an object that
108	stores relevant data for each kind of event you are waiting for, such as	136	stores relevant data for each kind of event you are waiting for, such as
109	the callback to call, the filehandle to watch, etc.	137	the callback to call, the file handle to watch, etc.
110		138
111	These watchers are normal Perl objects with normal Perl lifetime. After	139	These watchers are normal Perl objects with normal Perl lifetime. After
112	creating a watcher it will immediately "watch" for events and invoke the	140	creating a watcher it will immediately "watch" for events and invoke the
113	callback when the event occurs (of course, only when the event model is	141	callback when the event occurs (of course, only when the event model is
114	in control).	142	in control).
115		143
		144	Note that callbacks must not permanently change global variables
		145	potentially in use by the event loop (such as $_ or $[) and that
		146	callbacks must not "die". The former is good programming practise in
		147	Perl and the latter stems from the fact that exception handling differs
		148	widely between event loops.
		149
116	To disable the watcher you have to destroy it (e.g. by setting the	150	To disable the watcher you have to destroy it (e.g. by setting the
117	variable you store it in to "undef" or otherwise deleting all references	151	variable you store it in to "undef" or otherwise deleting all references
118	to it).	152	to it).
119		153
120	All watchers are created by calling a method on the "AnyEvent" class.	154	All watchers are created by calling a method on the "AnyEvent" class.
…		…
122	Many watchers either are used with "recursion" (repeating timers for	156	Many watchers either are used with "recursion" (repeating timers for
123	example), or need to refer to their watcher object in other ways.	157	example), or need to refer to their watcher object in other ways.
124		158
125	An any way to achieve that is this pattern:	159	An any way to achieve that is this pattern:
126		160
127	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	161	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
128	# you can use $w here, for example to undef it	162	# you can use $w here, for example to undef it
129	undef $w;	163	undef $w;
130	});	164	});
131		165
132	Note that "my $w; $w =" combination. This is necessary because in Perl,	166	Note that "my $w; $w =" combination. This is necessary because in Perl,
133	my variables are only visible after the statement in which they are	167	my variables are only visible after the statement in which they are
134	declared.	168	declared.
135		169
136	I/O WATCHERS	170	I/O WATCHERS
137	You can create an I/O watcher by calling the "AnyEvent->io" method with	171	You can create an I/O watcher by calling the "AnyEvent->io" method with
138	the following mandatory key-value pairs as arguments:	172	the following mandatory key-value pairs as arguments:
139		173
140	"fh" the Perl file handle (not file descriptor) to watch for events.	174	"fh" is the Perl file handle (or a naked file descriptor) to watch for
		175	events (AnyEvent might or might not keep a reference to this file
		176	handle). Note that only file handles pointing to things for which
		177	non-blocking operation makes sense are allowed. This includes sockets,
		178	most character devices, pipes, fifos and so on, but not for example
		179	files or block devices.
		180
141	"poll" must be a string that is either "r" or "w", which creates a	181	"poll" must be a string that is either "r" or "w", which creates a
142	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	182	watcher waiting for "r"eadable or "w"ritable events, respectively.
		183
143	is the callback to invoke each time the file handle becomes ready.	184	"cb" is the callback to invoke each time the file handle becomes ready.
144		185
145	Although the callback might get passed parameters, their value and	186	Although the callback might get passed parameters, their value and
146	presence is undefined and you cannot rely on them. Portable AnyEvent	187	presence is undefined and you cannot rely on them. Portable AnyEvent
147	callbacks cannot use arguments passed to I/O watcher callbacks.	188	callbacks cannot use arguments passed to I/O watcher callbacks.
148		189
…		…
152		193
153	Some event loops issue spurious readyness notifications, so you should	194	Some event loops issue spurious readyness notifications, so you should
154	always use non-blocking calls when reading/writing from/to your file	195	always use non-blocking calls when reading/writing from/to your file
155	handles.	196	handles.
156		197
157	Example:
158
159	# wait for readability of STDIN, then read a line and disable the watcher	198	Example: wait for readability of STDIN, then read a line and disable the
		199	watcher.
		200
160	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	201	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
161	chomp (my $input = <STDIN>);	202	chomp (my $input = <STDIN>);
162	warn "read: $input\n";	203	warn "read: $input\n";
163	undef $w;	204	undef $w;
164	});	205	});
…		…
173		214
174	Although the callback might get passed parameters, their value and	215	Although the callback might get passed parameters, their value and
175	presence is undefined and you cannot rely on them. Portable AnyEvent	216	presence is undefined and you cannot rely on them. Portable AnyEvent
176	callbacks cannot use arguments passed to time watcher callbacks.	217	callbacks cannot use arguments passed to time watcher callbacks.
177		218
178	The timer callback will be invoked at most once: if you want a repeating	219	The callback will normally be invoked once only. If you specify another
179	timer you have to create a new watcher (this is a limitation by both Tk	220	parameter, "interval", as a strictly positive number (> 0), then the
180	and Glib).	221	callback will be invoked regularly at that interval (in fractional
		222	seconds) after the first invocation. If "interval" is specified with a
		223	false value, then it is treated as if it were missing.
181		224
182	Example:	225	The callback will be rescheduled before invoking the callback, but no
		226	attempt is done to avoid timer drift in most backends, so the interval
		227	is only approximate.
183		228
184	# fire an event after 7.7 seconds	229	Example: fire an event after 7.7 seconds.
		230
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	231	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	232	warn "timeout\n";
187	});	233	});
188		234
189	# to cancel the timer:	235	# to cancel the timer:
190	undef $w;	236	undef $w;
191		237
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	238	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		239
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	240	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		241	warn "timeout\n";
200	};	242	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		243
205	TIMING ISSUES	244	TIMING ISSUES
206	There are two ways to handle timers: based on real time (relative, "fire	245	There are two ways to handle timers: based on real time (relative, "fire
207	in 10 seconds") and based on wallclock time (absolute, "fire at 12	246	in 10 seconds") and based on wallclock time (absolute, "fire at 12
208	o'clock").	247	o'clock").
…		…
220	on wallclock time) timers.	259	on wallclock time) timers.
221		260
222	AnyEvent always prefers relative timers, if available, matching the	261	AnyEvent always prefers relative timers, if available, matching the
223	AnyEvent API.	262	AnyEvent API.
224		263
		264	AnyEvent has two additional methods that return the "current time":
		265
		266	AnyEvent->time
		267	This returns the "current wallclock time" as a fractional number of
		268	seconds since the Epoch (the same thing as "time" or
		269	"Time::HiRes::time" return, and the result is guaranteed to be
		270	compatible with those).
		271
		272	It progresses independently of any event loop processing, i.e. each
		273	call will check the system clock, which usually gets updated
		274	frequently.
		275
		276	AnyEvent->now
		277	This also returns the "current wallclock time", but unlike "time",
		278	above, this value might change only once per event loop iteration,
		279	depending on the event loop (most return the same time as "time",
		280	above). This is the time that AnyEvent's timers get scheduled
		281	against.
		282
		283	*In almost all cases (in all cases if you don't care), this is the
		284	function to call when you want to know the current time.*
		285
		286	This function is also often faster then "AnyEvent->time", and thus
		287	the preferred method if you want some timestamp (for example,
		288	AnyEvent::Handle uses this to update it's activity timeouts).
		289
		290	The rest of this section is only of relevance if you try to be very
		291	exact with your timing, you can skip it without bad conscience.
		292
		293	For a practical example of when these times differ, consider
		294	Event::Lib and EV and the following set-up:
		295
		296	The event loop is running and has just invoked one of your callback
		297	at time=500 (assume no other callbacks delay processing). In your
		298	callback, you wait a second by executing "sleep 1" (blocking the
		299	process for a second) and then (at time=501) you create a relative
		300	timer that fires after three seconds.
		301
		302	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		303	return 501, because that is the current time, and the timer will be
		304	scheduled to fire at time=504 (501 + 3).
		305
		306	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		307	but "AnyEvent->now" returns 500, as that is the time the last event
		308	processing phase started. With EV, your timer gets scheduled to run
		309	at time=503 (500 + 3).
		310
		311	In one sense, Event::Lib is more exact, as it uses the current time
		312	regardless of any delays introduced by event processing. However,
		313	most callbacks do not expect large delays in processing, so this
		314	causes a higher drift (and a lot more system calls to get the
		315	current time).
		316
		317	In another sense, EV is more exact, as your timer will be scheduled
		318	at the same time, regardless of how long event processing actually
		319	took.
		320
		321	In either case, if you care (and in most cases, you don't), then you
		322	can get whatever behaviour you want with any event loop, by taking
		323	the difference between "AnyEvent->time" and "AnyEvent->now" into
		324	account.
		325
		326	AnyEvent->now_update
		327	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		328	current time for each loop iteration (see the discussion of
		329	AnyEvent->now, above).
		330
		331	When a callback runs for a long time (or when the process sleeps),
		332	then this "current" time will differ substantially from the real
		333	time, which might affect timers and time-outs.
		334
		335	When this is the case, you can call this method, which will update
		336	the event loop's idea of "current time".
		337
		338	Note that updating the time might cause some events to be handled.
		339
225	SIGNAL WATCHERS	340	SIGNAL WATCHERS
226	You can watch for signals using a signal watcher, "signal" is the signal	341	You can watch for signals using a signal watcher, "signal" is the signal
227	name without any "SIG" prefix, "cb" is the Perl callback to be invoked	342	name in uppercase and without any "SIG" prefix, "cb" is the Perl
228	whenever a signal occurs.	343	callback to be invoked whenever a signal occurs.
229		344
230	Although the callback might get passed parameters, their value and	345	Although the callback might get passed parameters, their value and
231	presence is undefined and you cannot rely on them. Portable AnyEvent	346	presence is undefined and you cannot rely on them. Portable AnyEvent
232	callbacks cannot use arguments passed to signal watcher callbacks.	347	callbacks cannot use arguments passed to signal watcher callbacks.
233		348
234	Multiple signal occurances can be clumped together into one callback	349	Multiple signal occurrences can be clumped together into one callback
235	invocation, and callback invocation will be synchronous. synchronous	350	invocation, and callback invocation will be synchronous. Synchronous
236	means that it might take a while until the signal gets handled by the	351	means that it might take a while until the signal gets handled by the
237	process, but it is guarenteed not to interrupt any other callbacks.	352	process, but it is guaranteed not to interrupt any other callbacks.
238		353
239	The main advantage of using these watchers is that you can share a	354	The main advantage of using these watchers is that you can share a
240	signal between multiple watchers.	355	signal between multiple watchers.
241		356
242	This watcher might use %SIG, so programs overwriting those signals	357	This watcher might use %SIG, so programs overwriting those signals
…		…
248		363
249	CHILD PROCESS WATCHERS	364	CHILD PROCESS WATCHERS
250	You can also watch on a child process exit and catch its exit status.	365	You can also watch on a child process exit and catch its exit status.
251		366
252	The child process is specified by the "pid" argument (if set to 0, it	367	The child process is specified by the "pid" argument (if set to 0, it
253	watches for any child process exit). The watcher will trigger as often	368	watches for any child process exit). The watcher will triggered only
254	as status change for the child are received. This works by installing a	369	when the child process has finished and an exit status is available, not
255	signal handler for "SIGCHLD". The callback will be called with the pid	370	on any trace events (stopped/continued).
256	and exit status (as returned by waitpid), so unlike other watcher types,	371
257	you can rely on child watcher callback arguments.	372	The callback will be called with the pid and exit status (as returned by
		373	waitpid), so unlike other watcher types, you can rely on child watcher
		374	callback arguments.
		375
		376	This watcher type works by installing a signal handler for "SIGCHLD",
		377	and since it cannot be shared, nothing else should use SIGCHLD or reap
		378	random child processes (waiting for specific child processes, e.g.
		379	inside "system", is just fine).
258		380
259	There is a slight catch to child watchers, however: you usually start	381	There is a slight catch to child watchers, however: you usually start
260	them after the child process was created, and this means the process	382	them after the child process was created, and this means the process
261	could have exited already (and no SIGCHLD will be sent anymore).	383	could have exited already (and no SIGCHLD will be sent anymore).
262		384
263	Not all event models handle this correctly (POE doesn't), but even for	385	Not all event models handle this correctly (neither POE nor IO::Async
		386	do, see their AnyEvent::Impl manpages for details), but even for event
264	event models that do handle this correctly, they usually need to be	387	models that do handle this correctly, they usually need to be loaded
265	loaded before the process exits (i.e. before you fork in the first	388	before the process exits (i.e. before you fork in the first place).
266	place).	389	AnyEvent's pure perl event loop handles all cases correctly regardless
		390	of when you start the watcher.
267		391
268	This means you cannot create a child watcher as the very first thing in	392	This means you cannot create a child watcher as the very first thing in
269	an AnyEvent program, you have to create at least one watcher before	393	an AnyEvent program, you have to create at least one watcher before
270	you "fork" the child (alternatively, you can call "AnyEvent::detect").	394	you "fork" the child (alternatively, you can call "AnyEvent::detect").
271		395
272	Example: fork a process and wait for it	396	Example: fork a process and wait for it
273		397
274	my $done = AnyEvent->condvar;	398	my $done = AnyEvent->condvar;
275		399
276	AnyEvent::detect; # force event module to be initialised
277
278	my $pid = fork or exit 5;	400	my $pid = fork or exit 5;
279		401
280	my $w = AnyEvent->child (	402	my $w = AnyEvent->child (
281	pid => $pid,	403	pid => $pid,
282	cb => sub {	404	cb => sub {
283	my ($pid, $status) = @_;	405	my ($pid, $status) = @_;
284	warn "pid $pid exited with status $status";	406	warn "pid $pid exited with status $status";
285	$done->broadcast;	407	$done->send;
286	},	408	},
287	);	409	);
288		410
289	# do something else, then wait for process exit	411	# do something else, then wait for process exit
290	$done->wait;	412	$done->recv;
		413
		414	IDLE WATCHERS
		415	Sometimes there is a need to do something, but it is not so important to
		416	do it instantly, but only when there is nothing better to do. This
		417	"nothing better to do" is usually defined to be "no other events need
		418	attention by the event loop".
		419
		420	Idle watchers ideally get invoked when the event loop has nothing better
		421	to do, just before it would block the process to wait for new events.
		422	Instead of blocking, the idle watcher is invoked.
		423
		424	Most event loops unfortunately do not really support idle watchers (only
		425	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		426	will simply call the callback "from time to time".
		427
		428	Example: read lines from STDIN, but only process them when the program
		429	is otherwise idle:
		430
		431	my @lines; # read data
		432	my $idle_w;
		433	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		434	push @lines, scalar <STDIN>;
		435
		436	# start an idle watcher, if not already done
		437	$idle_w \|\|= AnyEvent->idle (cb => sub {
		438	# handle only one line, when there are lines left
		439	if (my $line = shift @lines) {
		440	print "handled when idle: $line";
		441	} else {
		442	# otherwise disable the idle watcher again
		443	undef $idle_w;
		444	}
		445	});
		446	});
291		447
292	CONDITION VARIABLES	448	CONDITION VARIABLES
		449	If you are familiar with some event loops you will know that all of them
		450	require you to run some blocking "loop", "run" or similar function that
		451	will actively watch for new events and call your callbacks.
		452
		453	AnyEvent is slightly different: it expects somebody else to run the
		454	event loop and will only block when necessary (usually when told by the
		455	user).
		456
		457	The instrument to do that is called a "condition variable", so called
		458	because they represent a condition that must become true.
		459
		460	Now is probably a good time to look at the examples further below.
		461
293	Condition variables can be created by calling the "AnyEvent->condvar"	462	Condition variables can be created by calling the "AnyEvent->condvar"
294	method without any arguments.	463	method, usually without arguments. The only argument pair allowed is
		464	"cb", which specifies a callback to be called when the condition
		465	variable becomes true, with the condition variable as the first argument
		466	(but not the results).
295		467
296	A condition variable waits for a condition - precisely that the	468	After creation, the condition variable is "false" until it becomes
297	"->broadcast" method has been called.	469	"true" by calling the "send" method (or calling the condition variable
		470	as if it were a callback, read about the caveats in the description for
		471	the "->send" method).
298		472
299	They are very useful to signal that a condition has been fulfilled, for	473	Condition variables are similar to callbacks, except that you can
		474	optionally wait for them. They can also be called merge points - points
		475	in time where multiple outstanding events have been processed. And yet
		476	another way to call them is transactions - each condition variable can
		477	be used to represent a transaction, which finishes at some point and
		478	delivers a result.
		479
		480	Condition variables are very useful to signal that something has
300	example, if you write a module that does asynchronous http requests,	481	finished, for example, if you write a module that does asynchronous http
301	then a condition variable would be the ideal candidate to signal the	482	requests, then a condition variable would be the ideal candidate to
302	availability of results.	483	signal the availability of results. The user can either act when the
		484	callback is called or can synchronously "->recv" for the results.
303		485
304	You can also use condition variables to block your main program until an	486	You can also use them to simulate traditional event loops - for example,
305	event occurs - for example, you could "->wait" in your main program	487	you can block your main program until an event occurs - for example, you
306	until the user clicks the Quit button in your app, which would	488	could "->recv" in your main program until the user clicks the Quit
307	"->broadcast" the "quit" event.	489	button of your app, which would "->send" the "quit" event.
308		490
309	Note that condition variables recurse into the event loop - if you have	491	Note that condition variables recurse into the event loop - if you have
310	two pirces of code that call "->wait" in a round-robbin fashion, you	492	two pieces of code that call "->recv" in a round-robin fashion, you
311	lose. Therefore, condition variables are good to export to your caller,	493	lose. Therefore, condition variables are good to export to your caller,
312	but you should avoid making a blocking wait yourself, at least in	494	but you should avoid making a blocking wait yourself, at least in
313	callbacks, as this asks for trouble.	495	callbacks, as this asks for trouble.
314		496
315	This object has two methods:	497	Condition variables are represented by hash refs in perl, and the keys
		498	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		499	(it is often useful to build your own transaction class on top of
		500	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		501	it's "new" method in your own "new" method.
316		502
317	$cv->wait	503	There are two "sides" to a condition variable - the "producer side"
318	Wait (blocking if necessary) until the "->broadcast" method has been	504	which eventually calls "-> send", and the "consumer side", which waits
319	called on c<$cv>, while servicing other watchers normally.	505	for the send to occur.
320		506
321	You can only wait once on a condition - additional calls will return	507	Example: wait for a timer.
322	immediately.
323
324	Not all event models support a blocking wait - some die in that case
325	(programs might want to do that to stay interactive), so *if you are
326	using this from a module, never require a blocking wait*, but let
327	the caller decide whether the call will block or not (for example,
328	by coupling condition variables with some kind of request results
329	and supporting callbacks so the caller knows that getting the result
330	will not block, while still suppporting blocking waits if the caller
331	so desires).
332
333	Another reason never to "->wait" in a module is that you cannot
334	sensibly have two "->wait"'s in parallel, as that would require
335	multiple interpreters or coroutines/threads, none of which
336	"AnyEvent" can supply (the coroutine-aware backends
337	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
338	support concurrent "->wait"'s from different coroutines, however).
339
340	$cv->broadcast
341	Flag the condition as ready - a running "->wait" and all further
342	calls to "wait" will (eventually) return after this method has been
343	called. If nobody is waiting the broadcast will be remembered..
344
345	Example:
346		508
347	# wait till the result is ready	509	# wait till the result is ready
348	my $result_ready = AnyEvent->condvar;	510	my $result_ready = AnyEvent->condvar;
349		511
350	# do something such as adding a timer	512	# do something such as adding a timer
351	# or socket watcher the calls $result_ready->broadcast	513	# or socket watcher the calls $result_ready->send
352	# when the "result" is ready.	514	# when the "result" is ready.
353	# in this case, we simply use a timer:	515	# in this case, we simply use a timer:
354	my $w = AnyEvent->timer (	516	my $w = AnyEvent->timer (
355	after => 1,	517	after => 1,
356	cb => sub { $result_ready->broadcast },	518	cb => sub { $result_ready->send },
357	);	519	);
358		520
359	# this "blocks" (while handling events) till the watcher	521	# this "blocks" (while handling events) till the callback
360	# calls broadcast	522	# calls -<send
361	$result_ready->wait;	523	$result_ready->recv;
		524
		525	Example: wait for a timer, but take advantage of the fact that condition
		526	variables are also callable directly.
		527
		528	my $done = AnyEvent->condvar;
		529	my $delay = AnyEvent->timer (after => 5, cb => $done);
		530	$done->recv;
		531
		532	Example: Imagine an API that returns a condvar and doesn't support
		533	callbacks. This is how you make a synchronous call, for example from the
		534	main program:
		535
		536	use AnyEvent::CouchDB;
		537
		538	...
		539
		540	my @info = $couchdb->info->recv;
		541
		542	And this is how you would just set a callback to be called whenever the
		543	results are available:
		544
		545	$couchdb->info->cb (sub {
		546	my @info = $_[0]->recv;
		547	});
		548
		549	METHODS FOR PRODUCERS
		550	These methods should only be used by the producing side, i.e. the
		551	code/module that eventually sends the signal. Note that it is also the
		552	producer side which creates the condvar in most cases, but it isn't
		553	uncommon for the consumer to create it as well.
		554
		555	$cv->send (...)
		556	Flag the condition as ready - a running "->recv" and all further
		557	calls to "recv" will (eventually) return after this method has been
		558	called. If nobody is waiting the send will be remembered.
		559
		560	If a callback has been set on the condition variable, it is called
		561	immediately from within send.
		562
		563	Any arguments passed to the "send" call will be returned by all
		564	future "->recv" calls.
		565
		566	Condition variables are overloaded so one can call them directly (as
		567	if they were a code reference). Calling them directly is the same as
		568	calling "send".
		569
		570	$cv->croak ($error)
		571	Similar to send, but causes all call's to "->recv" to invoke
		572	"Carp::croak" with the given error message/object/scalar.
		573
		574	This can be used to signal any errors to the condition variable
		575	user/consumer. Doing it this way instead of calling "croak" directly
		576	delays the error detetcion, but has the overwhelmign advantage that
		577	it diagnoses the error at the place where the result is expected,
		578	and not deep in some event clalback without connection to the actual
		579	code causing the problem.
		580
		581	$cv->begin ([group callback])
		582	$cv->end
		583	These two methods can be used to combine many transactions/events
		584	into one. For example, a function that pings many hosts in parallel
		585	might want to use a condition variable for the whole process.
		586
		587	Every call to "->begin" will increment a counter, and every call to
		588	"->end" will decrement it. If the counter reaches 0 in "->end", the
		589	(last) callback passed to "begin" will be executed. That callback is
		590	supposed to call "->send", but that is not required. If no
		591	callback was set, "send" will be called without any arguments.
		592
		593	You can think of "$cv->send" giving you an OR condition (one call
		594	sends), while "$cv->begin" and "$cv->end" giving you an AND
		595	condition (all "begin" calls must be "end"'ed before the condvar
		596	sends).
		597
		598	Let's start with a simple example: you have two I/O watchers (for
		599	example, STDOUT and STDERR for a program), and you want to wait for
		600	both streams to close before activating a condvar:
		601
		602	my $cv = AnyEvent->condvar;
		603
		604	$cv->begin; # first watcher
		605	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		606	defined sysread $fh1, my $buf, 4096
		607	or $cv->end;
		608	});
		609
		610	$cv->begin; # second watcher
		611	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		612	defined sysread $fh2, my $buf, 4096
		613	or $cv->end;
		614	});
		615
		616	$cv->recv;
		617
		618	This works because for every event source (EOF on file handle),
		619	there is one call to "begin", so the condvar waits for all calls to
		620	"end" before sending.
		621
		622	The ping example mentioned above is slightly more complicated, as
		623	the there are results to be passwd back, and the number of tasks
		624	that are begung can potentially be zero:
		625
		626	my $cv = AnyEvent->condvar;
		627
		628	my %result;
		629	$cv->begin (sub { $cv->send (\%result) });
		630
		631	for my $host (@list_of_hosts) {
		632	$cv->begin;
		633	ping_host_then_call_callback $host, sub {
		634	$result{$host} = ...;
		635	$cv->end;
		636	};
		637	}
		638
		639	$cv->end;
		640
		641	This code fragment supposedly pings a number of hosts and calls
		642	"send" after results for all then have have been gathered - in any
		643	order. To achieve this, the code issues a call to "begin" when it
		644	starts each ping request and calls "end" when it has received some
		645	result for it. Since "begin" and "end" only maintain a counter, the
		646	order in which results arrive is not relevant.
		647
		648	There is an additional bracketing call to "begin" and "end" outside
		649	the loop, which serves two important purposes: first, it sets the
		650	callback to be called once the counter reaches 0, and second, it
		651	ensures that "send" is called even when "no" hosts are being pinged
		652	(the loop doesn't execute once).
		653
		654	This is the general pattern when you "fan out" into multiple (but
		655	potentially none) subrequests: use an outer "begin"/"end" pair to
		656	set the callback and ensure "end" is called at least once, and then,
		657	for each subrequest you start, call "begin" and for each subrequest
		658	you finish, call "end".
		659
		660	METHODS FOR CONSUMERS
		661	These methods should only be used by the consuming side, i.e. the code
		662	awaits the condition.
		663
		664	$cv->recv
		665	Wait (blocking if necessary) until the "->send" or "->croak" methods
		666	have been called on c<$cv>, while servicing other watchers normally.
		667
		668	You can only wait once on a condition - additional calls are valid
		669	but will return immediately.
		670
		671	If an error condition has been set by calling "->croak", then this
		672	function will call "croak".
		673
		674	In list context, all parameters passed to "send" will be returned,
		675	in scalar context only the first one will be returned.
		676
		677	Note that doing a blocking wait in a callback is not supported by
		678	any event loop, that is, recursive invocation of a blocking "->recv"
		679	is not allowed, and the "recv" call will "croak" if such a condition
		680	is detected. This condition can be slightly loosened by using
		681	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		682	thread that doesn't run the event loop itself.
		683
		684	Not all event models support a blocking wait - some die in that case
		685	(programs might want to do that to stay interactive), so *if you are
		686	using this from a module, never require a blocking wait*. Instead,
		687	let the caller decide whether the call will block or not (for
		688	example, by coupling condition variables with some kind of request
		689	results and supporting callbacks so the caller knows that getting
		690	the result will not block, while still supporting blocking waits if
		691	the caller so desires).
		692
		693	You can ensure that "-recv" never blocks by setting a callback and
		694	only calling "->recv" from within that callback (or at a later
		695	time). This will work even when the event loop does not support
		696	blocking waits otherwise.
		697
		698	$bool = $cv->ready
		699	Returns true when the condition is "true", i.e. whether "send" or
		700	"croak" have been called.
		701
		702	$cb = $cv->cb ($cb->($cv))
		703	This is a mutator function that returns the callback set and
		704	optionally replaces it before doing so.
		705
		706	The callback will be called when the condition becomes "true", i.e.
		707	when "send" or "croak" are called, with the only argument being the
		708	condition variable itself. Calling "recv" inside the callback or at
		709	any later time is guaranteed not to block.
		710
		711	SUPPORTED EVENT LOOPS/BACKENDS
		712	The available backend classes are (every class has its own manpage):
		713
		714	Backends that are autoprobed when no other event loop can be found.
		715	EV is the preferred backend when no other event loop seems to be in
		716	use. If EV is not installed, then AnyEvent will try Event, and,
		717	failing that, will fall back to its own pure-perl implementation,
		718	which is available everywhere as it comes with AnyEvent itself.
		719
		720	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		721	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		722	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		723
		724	Backends that are transparently being picked up when they are used.
		725	These will be used when they are currently loaded when the first
		726	watcher is created, in which case it is assumed that the application
		727	is using them. This means that AnyEvent will automatically pick the
		728	right backend when the main program loads an event module before
		729	anything starts to create watchers. Nothing special needs to be done
		730	by the main program.
		731
		732	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		733	AnyEvent::Impl::Tk based on Tk, very broken.
		734	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		735	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		736
		737	Backends with special needs.
		738	Qt requires the Qt::Application to be instantiated first, but will
		739	otherwise be picked up automatically. As long as the main program
		740	instantiates the application before any AnyEvent watchers are
		741	created, everything should just work.
		742
		743	AnyEvent::Impl::Qt based on Qt.
		744
		745	Support for IO::Async can only be partial, as it is too broken and
		746	architecturally limited to even support the AnyEvent API. It also is
		747	the only event loop that needs the loop to be set explicitly, so it
		748	can only be used by a main program knowing about AnyEvent. See
		749	AnyEvent::Impl::Async for the gory details.
		750
		751	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		752
		753	Event loops that are indirectly supported via other backends.
		754	Some event loops can be supported via other modules:
		755
		756	There is no direct support for WxWidgets (Wx) or Prima.
		757
		758	WxWidgets has no support for watching file handles. However, you can
		759	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		760	simply polls 20 times per second, which was considered to be too
		761	horrible to even consider for AnyEvent.
		762
		763	Prima is not supported as nobody seems to be using it, but it has a
		764	POE backend, so it can be supported through POE.
		765
		766	AnyEvent knows about both Prima and Wx, however, and will try to
		767	load POE when detecting them, in the hope that POE will pick them
		768	up, in which case everything will be automatic.
362		769
363	GLOBAL VARIABLES AND FUNCTIONS	770	GLOBAL VARIABLES AND FUNCTIONS
		771	These are not normally required to use AnyEvent, but can be useful to
		772	write AnyEvent extension modules.
		773
364	$AnyEvent::MODEL	774	$AnyEvent::MODEL
365	Contains "undef" until the first watcher is being created. Then it	775	Contains "undef" until the first watcher is being created, before
		776	the backend has been autodetected.
		777
366	contains the event model that is being used, which is the name of	778	Afterwards it contains the event model that is being used, which is
367	the Perl class implementing the model. This class is usually one of	779	the name of the Perl class implementing the model. This class is
368	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	780	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
369	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	781	other class in the case AnyEvent has been extended at runtime (e.g.
370		782	in rxvt-unicode it will be "urxvt::anyevent").
371	The known classes so far are:
372
373	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
374	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
375	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
376	AnyEvent::Impl::Event based on Event, second best choice.
377	AnyEvent::Impl::Glib based on Glib, third-best choice.
378	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
379	AnyEvent::Impl::Tk based on Tk, very bad choice.
380	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
381	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
382	AnyEvent::Impl::POE based on POE, not generic enough for full support.
383
384	There is no support for WxWidgets, as WxWidgets has no support for
385	watching file handles. However, you can use WxWidgets through the
386	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
387	second, which was considered to be too horrible to even consider for
388	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
389	using it's adaptor.
390
391	AnyEvent knows about Prima and Wx and will try to use POE when
392	autodetecting them.
393		783
394	AnyEvent::detect	784	AnyEvent::detect
395	Returns $AnyEvent::MODEL, forcing autodetection of the event model	785	Returns $AnyEvent::MODEL, forcing autodetection of the event model
396	if necessary. You should only call this function right before you	786	if necessary. You should only call this function right before you
397	would have created an AnyEvent watcher anyway, that is, as late as	787	would have created an AnyEvent watcher anyway, that is, as late as
398	possible at runtime.	788	possible at runtime, and not e.g. while initialising of your module.
		789
		790	If you need to do some initialisation before AnyEvent watchers are
		791	created, use "post_detect".
		792
		793	$guard = AnyEvent::post_detect { BLOCK }
		794	Arranges for the code block to be executed as soon as the event
		795	model is autodetected (or immediately if this has already happened).
		796
		797	The block will be executed after the actual backend has been
		798	detected ($AnyEvent::MODEL is set), but before any watchers have
		799	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		800	other initialisations - see the sources of AnyEvent::Strict or
		801	AnyEvent::AIO to see how this is used.
		802
		803	The most common usage is to create some global watchers, without
		804	forcing event module detection too early, for example, AnyEvent::AIO
		805	creates and installs the global IO::AIO watcher in a "post_detect"
		806	block to avoid autodetecting the event module at load time.
		807
		808	If called in scalar or list context, then it creates and returns an
		809	object that automatically removes the callback again when it is
		810	destroyed. See Coro::BDB for a case where this is useful.
		811
		812	@AnyEvent::post_detect
		813	If there are any code references in this array (you can "push" to it
		814	before or after loading AnyEvent), then they will called directly
		815	after the event loop has been chosen.
		816
		817	You should check $AnyEvent::MODEL before adding to this array,
		818	though: if it is defined then the event loop has already been
		819	detected, and the array will be ignored.
		820
		821	Best use "AnyEvent::post_detect { BLOCK }" when your application
		822	allows it,as it takes care of these details.
		823
		824	This variable is mainly useful for modules that can do something
		825	useful when AnyEvent is used and thus want to know when it is
		826	initialised, but do not need to even load it by default. This array
		827	provides the means to hook into AnyEvent passively, without loading
		828	it.
399		829
400	WHAT TO DO IN A MODULE	830	WHAT TO DO IN A MODULE
401	As a module author, you should "use AnyEvent" and call AnyEvent methods	831	As a module author, you should "use AnyEvent" and call AnyEvent methods
402	freely, but you should not load a specific event module or rely on it.	832	freely, but you should not load a specific event module or rely on it.
403		833
404	Be careful when you create watchers in the module body - AnyEvent will	834	Be careful when you create watchers in the module body - AnyEvent will
405	decide which event module to use as soon as the first method is called,	835	decide which event module to use as soon as the first method is called,
406	so by calling AnyEvent in your module body you force the user of your	836	so by calling AnyEvent in your module body you force the user of your
407	module to load the event module first.	837	module to load the event module first.
408		838
409	Never call "->wait" on a condition variable unless you know that the	839	Never call "->recv" on a condition variable unless you know that the
410	"->broadcast" method has been called on it already. This is because it	840	"->send" method has been called on it already. This is because it will
411	will stall the whole program, and the whole point of using events is to	841	stall the whole program, and the whole point of using events is to stay
412	stay interactive.	842	interactive.
413		843
414	It is fine, however, to call "->wait" when the user of your module	844	It is fine, however, to call "->recv" when the user of your module
415	requests it (i.e. if you create a http request object ad have a method	845	requests it (i.e. if you create a http request object ad have a method
416	called "results" that returns the results, it should call "->wait"	846	called "results" that returns the results, it should call "->recv"
417	freely, as the user of your module knows what she is doing. always).	847	freely, as the user of your module knows what she is doing. always).
418		848
419	WHAT TO DO IN THE MAIN PROGRAM	849	WHAT TO DO IN THE MAIN PROGRAM
420	There will always be a single main program - the only place that should	850	There will always be a single main program - the only place that should
421	dictate which event model to use.	851	dictate which event model to use.
…		…
423	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	853	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
424	do anything special (it does not need to be event-based) and let	854	do anything special (it does not need to be event-based) and let
425	AnyEvent decide which implementation to chose if some module relies on	855	AnyEvent decide which implementation to chose if some module relies on
426	it.	856	it.
427		857
428	If the main program relies on a specific event model. For example, in	858	If the main program relies on a specific event model - for example, in
429	Gtk2 programs you have to rely on the Glib module. You should load the	859	Gtk2 programs you have to rely on the Glib module - you should load the
430	event module before loading AnyEvent or any module that uses it:	860	event module before loading AnyEvent or any module that uses it:
431	generally speaking, you should load it as early as possible. The reason	861	generally speaking, you should load it as early as possible. The reason
432	is that modules might create watchers when they are loaded, and AnyEvent	862	is that modules might create watchers when they are loaded, and AnyEvent
433	will decide on the event model to use as soon as it creates watchers,	863	will decide on the event model to use as soon as it creates watchers,
434	and it might chose the wrong one unless you load the correct one	864	and it might chose the wrong one unless you load the correct one
435	yourself.	865	yourself.
436		866
437	You can chose to use a rather inefficient pure-perl implementation by	867	You can chose to use a pure-perl implementation by loading the
438	loading the "AnyEvent::Impl::Perl" module, which gives you similar	868	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
439	behaviour everywhere, but letting AnyEvent chose is generally better.	869	everywhere, but letting AnyEvent chose the model is generally better.
		870
		871	MAINLOOP EMULATION
		872	Sometimes (often for short test scripts, or even standalone programs who
		873	only want to use AnyEvent), you do not want to run a specific event
		874	loop.
		875
		876	In that case, you can use a condition variable like this:
		877
		878	AnyEvent->condvar->recv;
		879
		880	This has the effect of entering the event loop and looping forever.
		881
		882	Note that usually your program has some exit condition, in which case it
		883	is better to use the "traditional" approach of storing a condition
		884	variable somewhere, waiting for it, and sending it when the program
		885	should exit cleanly.
440		886
441	OTHER MODULES	887	OTHER MODULES
442	The following is a non-exhaustive list of additional modules that use	888	The following is a non-exhaustive list of additional modules that use
443	AnyEvent and can therefore be mixed easily with other AnyEvent modules	889	AnyEvent as a client and can therefore be mixed easily with other
444	in the same program. Some of the modules come with AnyEvent, some are	890	AnyEvent modules and other event loops in the same program. Some of the
445	available via CPAN.	891	modules come with AnyEvent, most are available via CPAN.
446		892
447	AnyEvent::Util	893	AnyEvent::Util
448	Contains various utility functions that replace often-used but	894	Contains various utility functions that replace often-used but
449	blocking functions such as "inet_aton" by event-/callback-based	895	blocking functions such as "inet_aton" by event-/callback-based
450	versions.	896	versions.
451		897
		898	AnyEvent::Socket
		899	Provides various utility functions for (internet protocol) sockets,
		900	addresses and name resolution. Also functions to create non-blocking
		901	tcp connections or tcp servers, with IPv6 and SRV record support and
		902	more.
		903
452	AnyEvent::Handle	904	AnyEvent::Handle
453	Provide read and write buffers and manages watchers for reads and	905	Provide read and write buffers, manages watchers for reads and
454	writes.	906	writes, supports raw and formatted I/O, I/O queued and fully
		907	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
455		908
456	AnyEvent::Socket	909	AnyEvent::DNS
457	Provides a means to do non-blocking connects, accepts etc.	910	Provides rich asynchronous DNS resolver capabilities.
		911
		912	AnyEvent::HTTP
		913	A simple-to-use HTTP library that is capable of making a lot of
		914	concurrent HTTP requests.
458		915
459	AnyEvent::HTTPD	916	AnyEvent::HTTPD
460	Provides a simple web application server framework.	917	Provides a simple web application server framework.
461		918
462	AnyEvent::DNS
463	Provides asynchronous DNS resolver capabilities, beyond what
464	AnyEvent::Util offers.
465
466	AnyEvent::FastPing	919	AnyEvent::FastPing
467	The fastest ping in the west.	920	The fastest ping in the west.
468		921
		922	AnyEvent::DBI
		923	Executes DBI requests asynchronously in a proxy process.
		924
		925	AnyEvent::AIO
		926	Truly asynchronous I/O, should be in the toolbox of every event
		927	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		928	together.
		929
		930	AnyEvent::BDB
		931	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		932	fuses BDB and AnyEvent together.
		933
		934	AnyEvent::GPSD
		935	A non-blocking interface to gpsd, a daemon delivering GPS
		936	information.
		937
		938	AnyEvent::IRC
		939	AnyEvent based IRC client module family (replacing the older
469	Net::IRC3	940	Net::IRC3).
470	AnyEvent based IRC client module family.
471		941
472	Net::XMPP2	942	AnyEvent::XMPP
473	AnyEvent based XMPP (Jabber protocol) module family.	943	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		944	older Net::XMPP2>.
		945
		946	AnyEvent::IGS
		947	A non-blocking interface to the Internet Go Server protocol (used by
		948	App::IGS).
474		949
475	Net::FCP	950	Net::FCP
476	AnyEvent-based implementation of the Freenet Client Protocol,	951	AnyEvent-based implementation of the Freenet Client Protocol,
477	birthplace of AnyEvent.	952	birthplace of AnyEvent.
478		953
479	Event::ExecFlow	954	Event::ExecFlow
480	High level API for event-based execution flow control.	955	High level API for event-based execution flow control.
481		956
482	Coro	957	Coro
483	Has special support for AnyEvent.	958	Has special support for AnyEvent via Coro::AnyEvent.
484		959
485	IO::Lambda	960	ERROR AND EXCEPTION HANDLING
486	The lambda approach to I/O - don't ask, look there. Can use	961	In general, AnyEvent does not do any error handling - it relies on the
487	AnyEvent.	962	caller to do that if required. The AnyEvent::Strict module (see also the
		963	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		964	checking of all AnyEvent methods, however, which is highly useful during
		965	development.
488		966
489	IO::AIO	967	As for exception handling (i.e. runtime errors and exceptions thrown
490	Truly asynchronous I/O, should be in the toolbox of every event	968	while executing a callback), this is not only highly event-loop
491	programmer. Can be trivially made to use AnyEvent.	969	specific, but also not in any way wrapped by this module, as this is the
		970	job of the main program.
492		971
493	BDB Truly asynchronous Berkeley DB access. Can be trivially made to use	972	The pure perl event loop simply re-throws the exception (usually within
494	AnyEvent.	973	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		974	Glib uses "install_exception_handler" and so on.
		975
		976	ENVIRONMENT VARIABLES
		977	The following environment variables are used by this module or its
		978	submodules.
		979
		980	Note that AnyEvent will remove all environment variables starting with
		981	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		982	enabled.
		983
		984	"PERL_ANYEVENT_VERBOSE"
		985	By default, AnyEvent will be completely silent except in fatal
		986	conditions. You can set this environment variable to make AnyEvent
		987	more talkative.
		988
		989	When set to 1 or higher, causes AnyEvent to warn about unexpected
		990	conditions, such as not being able to load the event model specified
		991	by "PERL_ANYEVENT_MODEL".
		992
		993	When set to 2 or higher, cause AnyEvent to report to STDERR which
		994	event model it chooses.
		995
		996	"PERL_ANYEVENT_STRICT"
		997	AnyEvent does not do much argument checking by default, as thorough
		998	argument checking is very costly. Setting this variable to a true
		999	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1000	thoroughly check the arguments passed to most method calls. If it
		1001	finds any problems, it will croak.
		1002
		1003	In other words, enables "strict" mode.
		1004
		1005	Unlike "use strict", it is definitely recommended to keep it off in
		1006	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment
		1007	while developing programs can be very useful, however.
		1008
		1009	"PERL_ANYEVENT_MODEL"
		1010	This can be used to specify the event model to be used by AnyEvent,
		1011	before auto detection and -probing kicks in. It must be a string
		1012	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		1013	gets prepended and the resulting module name is loaded and if the
		1014	load was successful, used as event model. If it fails to load
		1015	AnyEvent will proceed with auto detection and -probing.
		1016
		1017	This functionality might change in future versions.
		1018
		1019	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		1020	could start your program like this:
		1021
		1022	PERL_ANYEVENT_MODEL=Perl perl ...
		1023
		1024	"PERL_ANYEVENT_PROTOCOLS"
		1025	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		1026	preferences for IPv4 or IPv6. The default is unspecified (and might
		1027	change, or be the result of auto probing).
		1028
		1029	Must be set to a comma-separated list of protocols or address
		1030	families, current supported: "ipv4" and "ipv6". Only protocols
		1031	mentioned will be used, and preference will be given to protocols
		1032	mentioned earlier in the list.
		1033
		1034	This variable can effectively be used for denial-of-service attacks
		1035	against local programs (e.g. when setuid), although the impact is
		1036	likely small, as the program has to handle conenction and other
		1037	failures anyways.
		1038
		1039	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		1040	IPv6, but support both and try to use both.
		1041	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		1042	resolve or contact IPv6 addresses.
		1043	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		1044	prefer IPv6 over IPv4.
		1045
		1046	"PERL_ANYEVENT_EDNS0"
		1047	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		1048	for DNS. This extension is generally useful to reduce DNS traffic,
		1049	but some (broken) firewalls drop such DNS packets, which is why it
		1050	is off by default.
		1051
		1052	Setting this variable to 1 will cause AnyEvent::DNS to announce
		1053	EDNS0 in its DNS requests.
		1054
		1055	"PERL_ANYEVENT_MAX_FORKS"
		1056	The maximum number of child processes that
		1057	"AnyEvent::Util::fork_call" will create in parallel.
		1058
		1059	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1060	The default value for the "max_outstanding" parameter for the
		1061	default DNS resolver - this is the maximum number of parallel DNS
		1062	requests that are sent to the DNS server.
		1063
		1064	"PERL_ANYEVENT_RESOLV_CONF"
		1065	The file to use instead of /etc/resolv.conf (or OS-specific
		1066	configuration) in the default resolver. When set to the empty
		1067	string, no default config will be used.
		1068
		1069	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1070	When neither "ca_file" nor "ca_path" was specified during
		1071	AnyEvent::TLS context creation, and either of these environment
		1072	variables exist, they will be used to specify CA certificate
		1073	locations instead of a system-dependent default.
495		1074
496	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1075	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
497	This is an advanced topic that you do not normally need to use AnyEvent	1076	This is an advanced topic that you do not normally need to use AnyEvent
498	in a module. This section is only of use to event loop authors who want	1077	in a module. This section is only of use to event loop authors who want
499	to provide AnyEvent compatibility.	1078	to provide AnyEvent compatibility.
…		…
533		1112
534	rxvt-unicode also cheats a bit by not providing blocking access to	1113	rxvt-unicode also cheats a bit by not providing blocking access to
535	condition variables: code blocking while waiting for a condition will	1114	condition variables: code blocking while waiting for a condition will
536	"die". This still works with most modules/usages, and blocking calls	1115	"die". This still works with most modules/usages, and blocking calls
537	must not be done in an interactive application, so it makes sense.	1116	must not be done in an interactive application, so it makes sense.
538
539	ENVIRONMENT VARIABLES
540	The following environment variables are used by this module:
541
542	"PERL_ANYEVENT_VERBOSE"
543	By default, AnyEvent will be completely silent except in fatal
544	conditions. You can set this environment variable to make AnyEvent
545	more talkative.
546
547	When set to 1 or higher, causes AnyEvent to warn about unexpected
548	conditions, such as not being able to load the event model specified
549	by "PERL_ANYEVENT_MODEL".
550
551	When set to 2 or higher, cause AnyEvent to report to STDERR which
552	event model it chooses.
553
554	"PERL_ANYEVENT_MODEL"
555	This can be used to specify the event model to be used by AnyEvent,
556	before autodetection and -probing kicks in. It must be a string
557	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
558	gets prepended and the resulting module name is loaded and if the
559	load was successful, used as event model. If it fails to load
560	AnyEvent will proceed with autodetection and -probing.
561
562	This functionality might change in future versions.
563
564	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
565	could start your program like this:
566
567	PERL_ANYEVENT_MODEL=Perl perl ...
568		1117
569	EXAMPLE PROGRAM	1118	EXAMPLE PROGRAM
570	The following program uses an I/O watcher to read data from STDIN, a	1119	The following program uses an I/O watcher to read data from STDIN, a
571	timer to display a message once per second, and a condition variable to	1120	timer to display a message once per second, and a condition variable to
572	quit the program when the user enters quit:	1121	quit the program when the user enters quit:
…		…
580	poll => 'r',	1129	poll => 'r',
581	cb => sub {	1130	cb => sub {
582	warn "io event <$_[0]>\n"; # will always output <r>	1131	warn "io event <$_[0]>\n"; # will always output <r>
583	chomp (my $input = <STDIN>); # read a line	1132	chomp (my $input = <STDIN>); # read a line
584	warn "read: $input\n"; # output what has been read	1133	warn "read: $input\n"; # output what has been read
585	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1134	$cv->send if $input =~ /^q/i; # quit program if /^q/i
586	},	1135	},
587	);	1136	);
588		1137
589	my $time_watcher; # can only be used once	1138	my $time_watcher; # can only be used once
590		1139
…		…
595	});	1144	});
596	}	1145	}
597		1146
598	new_timer; # create first timer	1147	new_timer; # create first timer
599		1148
600	$cv->wait; # wait until user enters /^q/i	1149	$cv->recv; # wait until user enters /^q/i
601		1150
602	REAL-WORLD EXAMPLE	1151	REAL-WORLD EXAMPLE
603	Consider the Net::FCP module. It features (among others) the following	1152	Consider the Net::FCP module. It features (among others) the following
604	API calls, which are to freenet what HTTP GET requests are to http:	1153	API calls, which are to freenet what HTTP GET requests are to http:
605		1154
…		…
654	syswrite $txn->{fh}, $txn->{request}	1203	syswrite $txn->{fh}, $txn->{request}
655	or die "connection or write error";	1204	or die "connection or write error";
656	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1205	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
657		1206
658	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1207	Again, "fh_ready_r" waits till all data has arrived, and then stores the
659	result and signals any possible waiters that the request ahs finished:	1208	result and signals any possible waiters that the request has finished:
660		1209
661	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1210	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
662		1211
663	if (end-of-file or data complete) {	1212	if (end-of-file or data complete) {
664	$txn->{result} = $txn->{buf};	1213	$txn->{result} = $txn->{buf};
665	$txn->{finished}->broadcast;	1214	$txn->{finished}->send;
666	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1215	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
667	}	1216	}
668		1217
669	The "result" method, finally, just waits for the finished signal (if the	1218	The "result" method, finally, just waits for the finished signal (if the
670	request was already finished, it doesn't wait, of course, and returns	1219	request was already finished, it doesn't wait, of course, and returns
671	the data:	1220	the data:
672		1221
673	$txn->{finished}->wait;	1222	$txn->{finished}->recv;
674	return $txn->{result};	1223	return $txn->{result};
675		1224
676	The actual code goes further and collects all errors ("die"s,	1225	The actual code goes further and collects all errors ("die"s,
677	exceptions) that occured during request processing. The "result" method	1226	exceptions) that occurred during request processing. The "result" method
678	detects whether an exception as thrown (it is stored inside the $txn	1227	detects whether an exception as thrown (it is stored inside the $txn
679	object) and just throws the exception, which means connection errors and	1228	object) and just throws the exception, which means connection errors and
680	other problems get reported tot he code that tries to use the result,	1229	other problems get reported tot he code that tries to use the result,
681	not in a random callback.	1230	not in a random callback.
682		1231
…		…
713		1262
714	my $quit = AnyEvent->condvar;	1263	my $quit = AnyEvent->condvar;
715		1264
716	$fcp->txn_client_get ($url)->cb (sub {	1265	$fcp->txn_client_get ($url)->cb (sub {
717	...	1266	...
718	$quit->broadcast;	1267	$quit->send;
719	});	1268	});
720		1269
721	$quit->wait;	1270	$quit->recv;
722		1271
723	BENCHMARKS	1272	BENCHMARKS
724	To give you an idea of the performance and overheads that AnyEvent adds	1273	To give you an idea of the performance and overheads that AnyEvent adds
725	over the event loops themselves and to give you an impression of the	1274	over the event loops themselves and to give you an impression of the
726	speed of various event loops I prepared some benchmarks.	1275	speed of various event loops I prepared some benchmarks.
727		1276
728	BENCHMARKING ANYEVENT OVERHEAD	1277	BENCHMARKING ANYEVENT OVERHEAD
729	Here is a benchmark of various supported event models used natively and	1278	Here is a benchmark of various supported event models used natively and
730	through anyevent. The benchmark creates a lot of timers (with a zero	1279	through AnyEvent. The benchmark creates a lot of timers (with a zero
731	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1280	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
732	which it is), lets them fire exactly once and destroys them again.	1281	which it is), lets them fire exactly once and destroys them again.
733		1282
734	Source code for this benchmark is found as eg/bench in the AnyEvent	1283	Source code for this benchmark is found as eg/bench in the AnyEvent
735	distribution.	1284	distribution.
…		…
751	between all watchers, to avoid adding memory overhead. That means	1300	between all watchers, to avoid adding memory overhead. That means
752	closure creation and memory usage is not included in the figures.	1301	closure creation and memory usage is not included in the figures.
753		1302
754	invoke is the time, in microseconds, used to invoke a simple callback.	1303	invoke is the time, in microseconds, used to invoke a simple callback.
755	The callback simply counts down a Perl variable and after it was invoked	1304	The callback simply counts down a Perl variable and after it was invoked
756	"watcher" times, it would "->broadcast" a condvar once to signal the end	1305	"watcher" times, it would "->send" a condvar once to signal the end of
757	of this phase.	1306	this phase.
758		1307
759	destroy is the time, in microseconds, that it takes to destroy a	1308	destroy is the time, in microseconds, that it takes to destroy a
760	single watcher.	1309	single watcher.
761		1310
762	Results	1311	Results
763	name watchers bytes create invoke destroy comment	1312	name watchers bytes create invoke destroy comment
764	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1313	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
765	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1314	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
766	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1315	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
767	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1316	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
768	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1317	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
769	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1318	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1319	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1320	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
770	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1321	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
771	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1322	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
772	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1323	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
773	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1324	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
774		1325
775	Discussion	1326	Discussion
776	The benchmark does not measure scalability of the event loop very	1327	The benchmark does not measure scalability of the event loop very
777	well. For example, a select-based event loop (such as the pure perl one)	1328	well. For example, a select-based event loop (such as the pure perl one)
778	can never compete with an event loop that uses epoll when the number of	1329	can never compete with an event loop that uses epoll when the number of
…		…
804	benchmark.	1355	benchmark.
805		1356
806	The "Event" module has a relatively high setup and callback invocation	1357	The "Event" module has a relatively high setup and callback invocation
807	cost, but overall scores in on the third place.	1358	cost, but overall scores in on the third place.
808		1359
		1360	"IO::Async" performs admirably well, about on par with "Event", even
		1361	when using its pure perl backend.
		1362
809	"Glib"'s memory usage is quite a bit higher, but it features a faster	1363	"Glib"'s memory usage is quite a bit higher, but it features a faster
810	callback invocation and overall ends up in the same class as "Event".	1364	callback invocation and overall ends up in the same class as "Event".
811	However, Glib scales extremely badly, doubling the number of watchers	1365	However, Glib scales extremely badly, doubling the number of watchers
812	increases the processing time by more than a factor of four, making it	1366	increases the processing time by more than a factor of four, making it
813	completely unusable when using larger numbers of watchers (note that	1367	completely unusable when using larger numbers of watchers (note that
…		…
823	the figures above).	1377	the figures above).
824		1378
825	"POE", regardless of underlying event loop (whether using its pure perl	1379	"POE", regardless of underlying event loop (whether using its pure perl
826	select-based backend or the Event module, the POE-EV backend couldn't be	1380	select-based backend or the Event module, the POE-EV backend couldn't be
827	tested because it wasn't working) shows abysmal performance and memory	1381	tested because it wasn't working) shows abysmal performance and memory
828	usage: Watchers use almost 30 times as much memory as EV watchers, and	1382	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
829	10 times as much memory as Event (the high memory requirements are	1383	watchers, and 10 times as much memory as Event (the high memory
830	caused by requiring a session for each watcher). Watcher invocation	1384	requirements are caused by requiring a session for each watcher).
831	speed is almost 900 times slower than with AnyEvent's pure perl	1385	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1386	pure perl implementation.
		1387
832	implementation. The design of the POE adaptor class in AnyEvent can not	1388	The design of the POE adaptor class in AnyEvent can not really account
833	really account for this, as session creation overhead is small compared	1389	for the performance issues, though, as session creation overhead is
834	to execution of the state machine, which is coded pretty optimally	1390	small compared to execution of the state machine, which is coded pretty
835	within AnyEvent::Impl::POE. POE simply seems to be abysmally slow.	1391	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1392	using multiple sessions is not a good approach, especially regarding
		1393	memory usage, even the author of POE could not come up with a faster
		1394	design).
836		1395
837	Summary	1396	Summary
838	* Using EV through AnyEvent is faster than any other event loop (even	1397	* Using EV through AnyEvent is faster than any other event loop (even
839	when used without AnyEvent), but most event loops have acceptable	1398	when used without AnyEvent), but most event loops have acceptable
840	performance with or without AnyEvent.	1399	performance with or without AnyEvent.
…		…
845		1404
846	* You should avoid POE like the plague if you want performance or	1405	* You should avoid POE like the plague if you want performance or
847	reasonable memory usage.	1406	reasonable memory usage.
848		1407
849	BENCHMARKING THE LARGE SERVER CASE	1408	BENCHMARKING THE LARGE SERVER CASE
850	This benchmark atcually benchmarks the event loop itself. It works by	1409	This benchmark actually benchmarks the event loop itself. It works by
851	creating a number of "servers": each server consists of a socketpair, a	1410	creating a number of "servers": each server consists of a socket pair, a
852	timeout watcher that gets reset on activity (but never fires), and an	1411	timeout watcher that gets reset on activity (but never fires), and an
853	I/O watcher waiting for input on one side of the socket. Each time the	1412	I/O watcher waiting for input on one side of the socket. Each time the
854	socket watcher reads a byte it will write that byte to a random other	1413	socket watcher reads a byte it will write that byte to a random other
855	"server".	1414	"server".
856		1415
857	The effect is that there will be a lot of I/O watchers, only part of	1416	The effect is that there will be a lot of I/O watchers, only part of
858	which are active at any one point (so there is a constant number of	1417	which are active at any one point (so there is a constant number of
859	active fds for each loop iterstaion, but which fds these are is random).	1418	active fds for each loop iteration, but which fds these are is random).
860	The timeout is reset each time something is read because that reflects	1419	The timeout is reset each time something is read because that reflects
861	how most timeouts work (and puts extra pressure on the event loops).	1420	how most timeouts work (and puts extra pressure on the event loops).
862		1421
863	In this benchmark, we use 10000 socketpairs (20000 sockets), of which	1422	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
864	100 (1%) are active. This mirrors the activity of large servers with	1423	100 (1%) are active. This mirrors the activity of large servers with
865	many connections, most of which are idle at any one point in time.	1424	many connections, most of which are idle at any one point in time.
866		1425
867	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1426	Source code for this benchmark is found as eg/bench2 in the AnyEvent
868	distribution.	1427	distribution.
869		1428
870	Explanation of the columns	1429	Explanation of the columns
871	sockets is the number of sockets, and twice the number of "servers"	1430	sockets is the number of sockets, and twice the number of "servers"
872	(as each server has a read and write socket end).	1431	(as each server has a read and write socket end).
873		1432
874	create is the time it takes to create a socketpair (which is	1433	create is the time it takes to create a socket pair (which is
875	nontrivial) and two watchers: an I/O watcher and a timeout watcher.	1434	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
876		1435
877	request, the most important value, is the time it takes to handle a	1436	request, the most important value, is the time it takes to handle a
878	single "request", that is, reading the token from the pipe and	1437	single "request", that is, reading the token from the pipe and
879	forwarding it to another server. This includes deleting the old timeout	1438	forwarding it to another server. This includes deleting the old timeout
880	and creating a new one that moves the timeout into the future.	1439	and creating a new one that moves the timeout into the future.
881		1440
882	Results	1441	Results
883	name sockets create request	1442	name sockets create request
884	EV 20000 69.01 11.16	1443	EV 20000 69.01 11.16
885	Perl 20000 73.32 35.87	1444	Perl 20000 73.32 35.87
		1445	IOAsync 20000 157.00 98.14 epoll
		1446	IOAsync 20000 159.31 616.06 poll
886	Event 20000 212.62 257.32	1447	Event 20000 212.62 257.32
887	Glib 20000 651.16 1896.30	1448	Glib 20000 651.16 1896.30
888	POE 20000 349.67 12317.24 uses POE::Loop::Event	1449	POE 20000 349.67 12317.24 uses POE::Loop::Event
889		1450
890	Discussion	1451	Discussion
891	This benchmark does measure scalability and overall performance of the	1452	This benchmark does measure scalability and overall performance of the
892	particular event loop.	1453	particular event loop.
893		1454
894	EV is again fastest. Since it is using epoll on my system, the setup	1455	EV is again fastest. Since it is using epoll on my system, the setup
895	time is relatively high, though.	1456	time is relatively high, though.
896		1457
897	Perl surprisingly comes second. It is much faster than the C-based event	1458	Perl surprisingly comes second. It is much faster than the C-based event
898	loops Event and Glib.	1459	loops Event and Glib.
		1460
		1461	IO::Async performs very well when using its epoll backend, and still
		1462	quite good compared to Glib when using its pure perl backend.
899		1463
900	Event suffers from high setup time as well (look at its code and you	1464	Event suffers from high setup time as well (look at its code and you
901	will understand why). Callback invocation also has a high overhead	1465	will understand why). Callback invocation also has a high overhead
902	compared to the "$_->() for .."-style loop that the Perl event loop	1466	compared to the "$_->() for .."-style loop that the Perl event loop
903	uses. Event uses select or poll in basically all documented	1467	uses. Event uses select or poll in basically all documented
…		…
909	POE is still completely out of the picture, taking over 1000 times as	1473	POE is still completely out of the picture, taking over 1000 times as
910	long as EV, and over 100 times as long as the Perl implementation, even	1474	long as EV, and over 100 times as long as the Perl implementation, even
911	though it uses a C-based event loop in this case.	1475	though it uses a C-based event loop in this case.
912		1476
913	Summary	1477	Summary
914	* The pure perl implementation performs extremely well, considering	1478	* The pure perl implementation performs extremely well.
915	that it uses select.
916		1479
917	* Avoid Glib or POE in large projects where performance matters.	1480	* Avoid Glib or POE in large projects where performance matters.
918		1481
919	BENCHMARKING SMALL SERVERS	1482	BENCHMARKING SMALL SERVERS
920	While event loops should scale (and select-based ones do not...) even to	1483	While event loops should scale (and select-based ones do not...) even to
…		…
944	and speed most when you have lots of watchers, not when you only have a	1507	and speed most when you have lots of watchers, not when you only have a
945	few of them).	1508	few of them).
946		1509
947	EV is again fastest.	1510	EV is again fastest.
948		1511
949	Perl again comes second. It is noticably faster than the C-based event	1512	Perl again comes second. It is noticeably faster than the C-based event
950	loops Event and Glib, although the difference is too small to really	1513	loops Event and Glib, although the difference is too small to really
951	matter.	1514	matter.
952		1515
953	POE also performs much better in this case, but is is still far behind	1516	POE also performs much better in this case, but is is still far behind
954	the others.	1517	the others.
955		1518
956	Summary	1519	Summary
957	* C-based event loops perform very well with small number of watchers,	1520	* C-based event loops perform very well with small number of watchers,
958	as the management overhead dominates.	1521	as the management overhead dominates.
959		1522
		1523	THE IO::Lambda BENCHMARK
		1524	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1525	could be misinterpreted to make AnyEvent look bad. In fact, the
		1526	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1527	better (which shouldn't come as a surprise to anybody). As such, the
		1528	benchmark is fine, and mostly shows that the AnyEvent backend from
		1529	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1530	without the extra baggage? To explore this, I wrote the equivalent
		1531	benchmark for AnyEvent.
		1532
		1533	The benchmark itself creates an echo-server, and then, for 500 times,
		1534	connects to the echo server, sends a line, waits for the reply, and then
		1535	creates the next connection. This is a rather bad benchmark, as it
		1536	doesn't test the efficiency of the framework or much non-blocking I/O,
		1537	but it is a benchmark nevertheless.
		1538
		1539	name runtime
		1540	Lambda/select 0.330 sec
		1541	+ optimized 0.122 sec
		1542	Lambda/AnyEvent 0.327 sec
		1543	+ optimized 0.138 sec
		1544	Raw sockets/select 0.077 sec
		1545	POE/select, components 0.662 sec
		1546	POE/select, raw sockets 0.226 sec
		1547	POE/select, optimized 0.404 sec
		1548
		1549	AnyEvent/select/nb 0.085 sec
		1550	AnyEvent/EV/nb 0.068 sec
		1551	+state machine 0.134 sec
		1552
		1553	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1554	benchmarks actually make blocking connects and use 100% blocking I/O,
		1555	defeating the purpose of an event-based solution. All of the newly
		1556	written AnyEvent benchmarks use 100% non-blocking connects (using
		1557	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1558	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1559	connects generally require a lot more bookkeeping and event handling
		1560	than blocking connects (which involve a single syscall only).
		1561
		1562	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1563	offers similar expressive power as POE and IO::Lambda, using
		1564	conventional Perl syntax. This means that both the echo server and the
		1565	client are 100% non-blocking, further placing it at a disadvantage.
		1566
		1567	As you can see, the AnyEvent + EV combination even beats the
		1568	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1569	backend easily beats IO::Lambda and POE.
		1570
		1571	And even the 100% non-blocking version written using the high-level (and
		1572	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a
		1573	large margin, even though it does all of DNS, tcp-connect and socket I/O
		1574	in a non-blocking way.
		1575
		1576	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1577	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1578	part of the IO::lambda distribution and were used without any changes.
		1579
		1580	SIGNALS
		1581	AnyEvent currently installs handlers for these signals:
		1582
		1583	SIGCHLD
		1584	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1585	emulation for event loops that do not support them natively. Also,
		1586	some event loops install a similar handler.
		1587
		1588	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1589	then AnyEvent will reset it to default, to avoid losing child exit
		1590	statuses.
		1591
		1592	SIGPIPE
		1593	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1594	"undef" when AnyEvent gets loaded.
		1595
		1596	The rationale for this is that AnyEvent users usually do not really
		1597	depend on SIGPIPE delivery (which is purely an optimisation for
		1598	shell use, or badly-written programs), but "SIGPIPE" can cause
		1599	spurious and rare program exits as a lot of people do not expect
		1600	"SIGPIPE" when writing to some random socket.
		1601
		1602	The rationale for installing a no-op handler as opposed to ignoring
		1603	it is that this way, the handler will be restored to defaults on
		1604	exec.
		1605
		1606	Feel free to install your own handler, or reset it to defaults.
		1607
960	FORK	1608	FORK
961	Most event libraries are not fork-safe. The ones who are usually are	1609	Most event libraries are not fork-safe. The ones who are usually are
962	because they are so inefficient. Only EV is fully fork-aware.	1610	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1611	Only EV is fully fork-aware.
963		1612
964	If you have to fork, you must either do so before creating your first	1613	If you have to fork, you must either do so before creating your first
965	watcher OR you must not use AnyEvent at all in the child.	1614	watcher OR you must not use AnyEvent at all in the child.
966		1615
967	SECURITY CONSIDERATIONS	1616	SECURITY CONSIDERATIONS
…		…
973	model than specified in the variable.	1622	model than specified in the variable.
974		1623
975	You can make AnyEvent completely ignore this variable by deleting it	1624	You can make AnyEvent completely ignore this variable by deleting it
976	before the first watcher gets created, e.g. with a "BEGIN" block:	1625	before the first watcher gets created, e.g. with a "BEGIN" block:
977		1626
978	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1627	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
979		1628
980	use AnyEvent;	1629	use AnyEvent;
		1630
		1631	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1632	be used to probe what backend is used and gain other information (which
		1633	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1634	and $ENV{PERL_ANYEVENT_STRICT}.
		1635
		1636	Note that AnyEvent will remove all environment variables starting with
		1637	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1638	enabled.
		1639
		1640	BUGS
		1641	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1642	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1643	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1644	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1645	not as pronounced).
981		1646
982	SEE ALSO	1647	SEE ALSO
983	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1648	Utility functions: AnyEvent::Util.
984	Glib::Event, Glib, Coro, Tk, Event::Lib, Qt, POE.
985		1649
986	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1650	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
987	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1651	Event::Lib, Qt, POE.
988	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib,	1652
		1653	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
		1654	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
989	AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1655	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1656	AnyEvent::Impl::IOAsync.
990		1657
		1658	Non-blocking file handles, sockets, TCP clients and servers:
		1659	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		1660
		1661	Asynchronous DNS: AnyEvent::DNS.
		1662
		1663	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1664
991	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1665	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1666	AnyEvent::HTTP.
992		1667
993	AUTHOR	1668	AUTHOR
994	Marc Lehmann <schmorp@schmorp.de>	1669	Marc Lehmann <schmorp@schmorp.de>
995	http://home.schmorp.de/	1670	http://home.schmorp.de/
996		1671

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Comparing AnyEvent/README (file contents): Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs. Revision 1.45 by root, Fri Jul 17 14:57:03 2009 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs.
Revision 1.45 by root, Fri Jul 17 14:57:03 2009 UTC