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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 - various supported	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
5	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, Tk. The first one found is used. If none are found, the module	109	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82	tries to load these modules in the stated order. The first one that can	110	used. If none are found, the module tries to load these modules
		111	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
		112	always succeed) in the order given. The first one that can be
83	be 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
84	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
85	very efficient, but should work everywhere.	115	very efficient, but should work everywhere.
86		116
87	Because AnyEvent first checks for modules that are already loaded,	117	Because AnyEvent first checks for modules that are already loaded,
88	loading an event model explicitly before first using AnyEvent will	118	loading an event model explicitly before first using AnyEvent will
…		…
97	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
98	to use AnyEvent so their modules work together with others seamlessly...	128	to use AnyEvent so their modules work together with others seamlessly...
99		129
100	The pure-perl implementation of AnyEvent is called	130	The pure-perl implementation of AnyEvent is called
101	"AnyEvent::Impl::Perl". Like other event modules you can load it	131	"AnyEvent::Impl::Perl". Like other event modules you can load it
102	explicitly.	132	explicitly and enjoy the high availability of that event loop :)
103		133
104	WATCHERS	134	WATCHERS
105	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
106	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
107	the callback to call, the filehandle to watch, etc.	137	the callback to call, the file handle to watch, etc.
108		138
109	These watchers are normal Perl objects with normal Perl lifetime. After	139	These watchers are normal Perl objects with normal Perl lifetime. After
110	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
111	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
112	in control).	142	in control).
113		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
114	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
115	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
116	to it).	152	to it).
117		153
118	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.
…		…
120	Many watchers either are used with "recursion" (repeating timers for	156	Many watchers either are used with "recursion" (repeating timers for
121	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.
122		158
123	An any way to achieve that is this pattern:	159	An any way to achieve that is this pattern:
124		160
125	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	161	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
126	# you can use $w here, for example to undef it	162	# you can use $w here, for example to undef it
127	undef $w;	163	undef $w;
128	});	164	});
129		165
130	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,
131	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
132	declared.	168	declared.
133		169
134	IO WATCHERS	170	I/O WATCHERS
135	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
136	the following mandatory key-value pairs as arguments:	172	the following mandatory key-value pairs as arguments:
137		173
138	"fh" the Perl *file handle* (*not* file descriptor) to watch for events.	174	"fh" is the Perl *file handle* (*not* 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
139	"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
140	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	182	watcher waiting for "r"eadable or "w"ritable events, respectively.
		183
141	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.
142		185
143	File handles will be kept alive, so as long as the watcher exists, the	186	Although the callback might get passed parameters, their value and
144	file handle exists, too.	187	presence is undefined and you cannot rely on them. Portable AnyEvent
		188	callbacks cannot use arguments passed to I/O watcher callbacks.
145		189
		190	The I/O watcher might use the underlying file descriptor or a copy of
146	It is not allowed to close a file handle as long as any watcher is	191	it. You must not close a file handle as long as any watcher is active on
147	active on the underlying file descriptor.	192	the underlying file descriptor.
148		193
149	Some event loops issue spurious readyness notifications, so you should	194	Some event loops issue spurious readyness notifications, so you should
150	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
151	handles.	196	handles.
152		197
153	Example:
154
155	# 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
156	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	201	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
157	chomp (my $input = <STDIN>);	202	chomp (my $input = <STDIN>);
158	warn "read: $input\n";	203	warn "read: $input\n";
159	undef $w;	204	undef $w;
160	});	205	});
…		…
162	TIME WATCHERS	207	TIME WATCHERS
163	You can create a time watcher by calling the "AnyEvent->timer" method	208	You can create a time watcher by calling the "AnyEvent->timer" method
164	with the following mandatory arguments:	209	with the following mandatory arguments:
165		210
166	"after" specifies after how many seconds (fractional values are	211	"after" specifies after how many seconds (fractional values are
167	supported) should the timer activate. "cb" the callback to invoke in	212	supported) the callback should be invoked. "cb" is the callback to
168	that case.	213	invoke in that case.
169		214
170	The timer callback will be invoked at most once: if you want a repeating	215	Although the callback might get passed parameters, their value and
171	timer you have to create a new watcher (this is a limitation by both Tk	216	presence is undefined and you cannot rely on them. Portable AnyEvent
172	and Glib).	217	callbacks cannot use arguments passed to time watcher callbacks.
173		218
174	Example:	219	The callback will normally be invoked once only. If you specify another
		220	parameter, "interval", as a strictly positive number (> 0), then the
		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.
175		224
		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.
		228
176	# fire an event after 7.7 seconds	229	Example: fire an event after 7.7 seconds.
		230
177	my $w = AnyEvent->timer (after => 7.7, cb => sub {	231	my $w = AnyEvent->timer (after => 7.7, cb => sub {
178	warn "timeout\n";	232	warn "timeout\n";
179	});	233	});
180		234
181	# to cancel the timer:	235	# to cancel the timer:
182	undef $w;	236	undef $w;
183		237
184	Example 2:
185
186	# 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.
187	my $w;
188		239
189	my $cb = sub {
190	# cancel the old timer while creating a new one
191	$w = AnyEvent->timer (after => 1, cb => $cb);	240	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		241	warn "timeout\n";
192	};	242	};
193
194	# start the "loop" by creating the first watcher
195	$w = AnyEvent->timer (after => 0.5, cb => $cb);
196		243
197	TIMING ISSUES	244	TIMING ISSUES
198	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
199	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
200	o'clock").	247	o'clock").
201		248
202	While most event loops expect timers to specified in a relative way,	249	While most event loops expect timers to specified in a relative way,
203	they use absolute time internally. This makes a difference when your	250	they use absolute time internally. This makes a difference when your
204	clock "jumps", for example, when ntp decides to set your clock backwards	251	clock "jumps", for example, when ntp decides to set your clock backwards
205	from the wrong 2014-01-01 to 2008-01-01, a watcher that you created to	252	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
206	fire "after" a second might actually take six years to finally fire.	253	supposed to fire "after" a second might actually take six years to
		254	finally fire.
207		255
208	AnyEvent cannot compensate for this. The only event loop that is	256	AnyEvent cannot compensate for this. The only event loop that is
209	conscious about these issues is EV, which offers both relative	257	conscious about these issues is EV, which offers both relative
210	(ev_timer) and absolute (ev_periodic) timers.	258	(ev_timer, based on true relative time) and absolute (ev_periodic, based
		259	on wallclock time) timers.
211		260
212	AnyEvent always prefers relative timers, if available, matching the	261	AnyEvent always prefers relative timers, if available, matching the
213	AnyEvent API.	262	AnyEvent API.
214		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
215	SIGNAL WATCHERS	340	SIGNAL WATCHERS
216	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
217	*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
218	whenever a signal occurs.	343	callback to be invoked whenever a signal occurs.
219		344
		345	Although the callback might get passed parameters, their value and
		346	presence is undefined and you cannot rely on them. Portable AnyEvent
		347	callbacks cannot use arguments passed to signal watcher callbacks.
		348
220	Multiple signals occurances can be clumped together into one callback	349	Multiple signal occurrences can be clumped together into one callback
221	invocation, and callback invocation will be synchronous. synchronous	350	invocation, and callback invocation will be synchronous. Synchronous
222	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
223	process, but it is guarenteed not to interrupt any other callbacks.	352	process, but it is guaranteed not to interrupt any other callbacks.
224		353
225	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
226	signal between multiple watchers.	355	signal between multiple watchers.
227		356
228	This watcher might use %SIG, so programs overwriting those signals	357	This watcher might use %SIG, so programs overwriting those signals
…		…
234		363
235	CHILD PROCESS WATCHERS	364	CHILD PROCESS WATCHERS
236	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.
237		366
238	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
239	watches for any child process exit). The watcher will trigger as often	368	watches for any child process exit). The watcher will triggered only
240	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
241	signal handler for "SIGCHLD". The callback will be called with the pid	370	on any trace events (stopped/continued).
242	and exit status (as returned by waitpid).
243		371
244	Example: wait for pid 1333	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.
245		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).
		380
		381	There is a slight catch to child watchers, however: you usually start
		382	them *after* the child process was created, and this means the process
		383	could have exited already (and no SIGCHLD will be sent anymore).
		384
		385	Not all event models handle this correctly (POE doesn't), but even for
		386	event models that *do* handle this correctly, they usually need to be
		387	loaded before the process exits (i.e. before you fork in the first
		388	place).
		389
		390	This means you cannot create a child watcher as the very first thing in
		391	an AnyEvent program, you *have* to create at least one watcher before
		392	you "fork" the child (alternatively, you can call "AnyEvent::detect").
		393
		394	Example: fork a process and wait for it
		395
		396	my $done = AnyEvent->condvar;
		397
		398	my $pid = fork or exit 5;
		399
246	my $w = AnyEvent->child (	400	my $w = AnyEvent->child (
247	pid => 1333,	401	pid => $pid,
248	cb => sub {	402	cb => sub {
249	my ($pid, $status) = @_;	403	my ($pid, $status) = @_;
250	warn "pid $pid exited with status $status";	404	warn "pid $pid exited with status $status";
		405	$done->send;
251	},	406	},
252	);	407	);
		408
		409	# do something else, then wait for process exit
		410	$done->recv;
		411
		412	IDLE WATCHERS
		413	Sometimes there is a need to do something, but it is not so important to
		414	do it instantly, but only when there is nothing better to do. This
		415	"nothing better to do" is usually defined to be "no other events need
		416	attention by the event loop".
		417
		418	Idle watchers ideally get invoked when the event loop has nothing better
		419	to do, just before it would block the process to wait for new events.
		420	Instead of blocking, the idle watcher is invoked.
		421
		422	Most event loops unfortunately do not really support idle watchers (only
		423	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		424	will simply call the callback "from time to time".
		425
		426	Example: read lines from STDIN, but only process them when the program
		427	is otherwise idle:
		428
		429	my @lines; # read data
		430	my $idle_w;
		431	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		432	push @lines, scalar <STDIN>;
		433
		434	# start an idle watcher, if not already done
		435	$idle_w ||= AnyEvent->idle (cb => sub {
		436	# handle only one line, when there are lines left
		437	if (my $line = shift @lines) {
		438	print "handled when idle: $line";
		439	} else {
		440	# otherwise disable the idle watcher again
		441	undef $idle_w;
		442	}
		443	});
		444	});
253		445
254	CONDITION VARIABLES	446	CONDITION VARIABLES
		447	If you are familiar with some event loops you will know that all of them
		448	require you to run some blocking "loop", "run" or similar function that
		449	will actively watch for new events and call your callbacks.
		450
		451	AnyEvent is different, it expects somebody else to run the event loop
		452	and will only block when necessary (usually when told by the user).
		453
		454	The instrument to do that is called a "condition variable", so called
		455	because they represent a condition that must become true.
		456
255	Condition variables can be created by calling the "AnyEvent->condvar"	457	Condition variables can be created by calling the "AnyEvent->condvar"
256	method without any arguments.	458	method, usually without arguments. The only argument pair allowed is
257		459
258	A condition variable waits for a condition - precisely that the	460	"cb", which specifies a callback to be called when the condition
259	"->broadcast" method has been called.	461	variable becomes true, with the condition variable as the first argument
		462	(but not the results).
260		463
261	They are very useful to signal that a condition has been fulfilled, for	464	After creation, the condition variable is "false" until it becomes
		465	"true" by calling the "send" method (or calling the condition variable
		466	as if it were a callback, read about the caveats in the description for
		467	the "->send" method).
		468
		469	Condition variables are similar to callbacks, except that you can
		470	optionally wait for them. They can also be called merge points - points
		471	in time where multiple outstanding events have been processed. And yet
		472	another way to call them is transactions - each condition variable can
		473	be used to represent a transaction, which finishes at some point and
		474	delivers a result.
		475
		476	Condition variables are very useful to signal that something has
262	example, if you write a module that does asynchronous http requests,	477	finished, for example, if you write a module that does asynchronous http
263	then a condition variable would be the ideal candidate to signal the	478	requests, then a condition variable would be the ideal candidate to
264	availability of results.	479	signal the availability of results. The user can either act when the
		480	callback is called or can synchronously "->recv" for the results.
265		481
266	You can also use condition variables to block your main program until an	482	You can also use them to simulate traditional event loops - for example,
267	event occurs - for example, you could "->wait" in your main program	483	you can block your main program until an event occurs - for example, you
268	until the user clicks the Quit button in your app, which would	484	could "->recv" in your main program until the user clicks the Quit
269	"->broadcast" the "quit" event.	485	button of your app, which would "->send" the "quit" event.
270		486
271	Note that condition variables recurse into the event loop - if you have	487	Note that condition variables recurse into the event loop - if you have
272	two pirces of code that call "->wait" in a round-robbin fashion, you	488	two pieces of code that call "->recv" in a round-robin fashion, you
273	lose. Therefore, condition variables are good to export to your caller,	489	lose. Therefore, condition variables are good to export to your caller,
274	but you should avoid making a blocking wait yourself, at least in	490	but you should avoid making a blocking wait yourself, at least in
275	callbacks, as this asks for trouble.	491	callbacks, as this asks for trouble.
276		492
277	This object has two methods:	493	Condition variables are represented by hash refs in perl, and the keys
		494	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		495	(it is often useful to build your own transaction class on top of
		496	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		497	it's "new" method in your own "new" method.
278		498
279	$cv->wait	499	There are two "sides" to a condition variable - the "producer side"
		500	which eventually calls "-> send", and the "consumer side", which waits
		501	for the send to occur.
		502
		503	Example: wait for a timer.
		504
		505	# wait till the result is ready
		506	my $result_ready = AnyEvent->condvar;
		507
		508	# do something such as adding a timer
		509	# or socket watcher the calls $result_ready->send
		510	# when the "result" is ready.
		511	# in this case, we simply use a timer:
		512	my $w = AnyEvent->timer (
		513	after => 1,
		514	cb => sub { $result_ready->send },
		515	);
		516
		517	# this "blocks" (while handling events) till the callback
		518	# calls send
		519	$result_ready->recv;
		520
		521	Example: wait for a timer, but take advantage of the fact that condition
		522	variables are also code references.
		523
		524	my $done = AnyEvent->condvar;
		525	my $delay = AnyEvent->timer (after => 5, cb => $done);
		526	$done->recv;
		527
		528	Example: Imagine an API that returns a condvar and doesn't support
		529	callbacks. This is how you make a synchronous call, for example from the
		530	main program:
		531
		532	use AnyEvent::CouchDB;
		533
		534	...
		535
		536	my @info = $couchdb->info->recv;
		537
		538	And this is how you would just ste a callback to be called whenever the
		539	results are available:
		540
		541	$couchdb->info->cb (sub {
		542	my @info = $_[0]->recv;
		543	});
		544
		545	METHODS FOR PRODUCERS
		546	These methods should only be used by the producing side, i.e. the
		547	code/module that eventually sends the signal. Note that it is also the
		548	producer side which creates the condvar in most cases, but it isn't
		549	uncommon for the consumer to create it as well.
		550
		551	$cv->send (...)
		552	Flag the condition as ready - a running "->recv" and all further
		553	calls to "recv" will (eventually) return after this method has been
		554	called. If nobody is waiting the send will be remembered.
		555
		556	If a callback has been set on the condition variable, it is called
		557	immediately from within send.
		558
		559	Any arguments passed to the "send" call will be returned by all
		560	future "->recv" calls.
		561
		562	Condition variables are overloaded so one can call them directly (as
		563	a code reference). Calling them directly is the same as calling
		564	"send". Note, however, that many C-based event loops do not handle
		565	overloading, so as tempting as it may be, passing a condition
		566	variable instead of a callback does not work. Both the pure perl and
		567	EV loops support overloading, however, as well as all functions that
		568	use perl to invoke a callback (as in AnyEvent::Socket and
		569	AnyEvent::DNS for example).
		570
		571	$cv->croak ($error)
		572	Similar to send, but causes all call's to "->recv" to invoke
		573	"Carp::croak" with the given error message/object/scalar.
		574
		575	This can be used to signal any errors to the condition variable
		576	user/consumer.
		577
		578	$cv->begin ([group callback])
		579	$cv->end
		580	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		581
		582	These two methods can be used to combine many transactions/events
		583	into one. For example, a function that pings many hosts in parallel
		584	might want to use a condition variable for the whole process.
		585
		586	Every call to "->begin" will increment a counter, and every call to
		587	"->end" will decrement it. If the counter reaches 0 in "->end", the
		588	(last) callback passed to "begin" will be executed. That callback is
		589	*supposed* to call "->send", but that is not required. If no
		590	callback was set, "send" will be called without any arguments.
		591
		592	Let's clarify this with the ping example:
		593
		594	my $cv = AnyEvent->condvar;
		595
		596	my %result;
		597	$cv->begin (sub { $cv->send (\%result) });
		598
		599	for my $host (@list_of_hosts) {
		600	$cv->begin;
		601	ping_host_then_call_callback $host, sub {
		602	$result{$host} = ...;
		603	$cv->end;
		604	};
		605	}
		606
		607	$cv->end;
		608
		609	This code fragment supposedly pings a number of hosts and calls
		610	"send" after results for all then have have been gathered - in any
		611	order. To achieve this, the code issues a call to "begin" when it
		612	starts each ping request and calls "end" when it has received some
		613	result for it. Since "begin" and "end" only maintain a counter, the
		614	order in which results arrive is not relevant.
		615
		616	There is an additional bracketing call to "begin" and "end" outside
		617	the loop, which serves two important purposes: first, it sets the
		618	callback to be called once the counter reaches 0, and second, it
		619	ensures that "send" is called even when "no" hosts are being pinged
		620	(the loop doesn't execute once).
		621
		622	This is the general pattern when you "fan out" into multiple
		623	subrequests: use an outer "begin"/"end" pair to set the callback and
		624	ensure "end" is called at least once, and then, for each subrequest
		625	you start, call "begin" and for each subrequest you finish, call
		626	"end".
		627
		628	METHODS FOR CONSUMERS
		629	These methods should only be used by the consuming side, i.e. the code
		630	awaits the condition.
		631
		632	$cv->recv
280	Wait (blocking if necessary) until the "->broadcast" method has been	633	Wait (blocking if necessary) until the "->send" or "->croak" methods
281	called on c<$cv>, while servicing other watchers normally.	634	have been called on c<$cv>, while servicing other watchers normally.
282		635
283	You can only wait once on a condition - additional calls will return	636	You can only wait once on a condition - additional calls are valid
284	immediately.	637	but will return immediately.
		638
		639	If an error condition has been set by calling "->croak", then this
		640	function will call "croak".
		641
		642	In list context, all parameters passed to "send" will be returned,
		643	in scalar context only the first one will be returned.
285		644
286	Not all event models support a blocking wait - some die in that case	645	Not all event models support a blocking wait - some die in that case
287	(programs might want to do that to stay interactive), so *if you are	646	(programs might want to do that to stay interactive), so *if you are
288	using this from a module, never require a blocking wait*, but let	647	using this from a module, never require a blocking wait*, but let
289	the caller decide whether the call will block or not (for example,	648	the caller decide whether the call will block or not (for example,
290	by coupling condition variables with some kind of request results	649	by coupling condition variables with some kind of request results
291	and supporting callbacks so the caller knows that getting the result	650	and supporting callbacks so the caller knows that getting the result
292	will not block, while still suppporting blocking waits if the caller	651	will not block, while still supporting blocking waits if the caller
293	so desires).	652	so desires).
294		653
295	Another reason *never* to "->wait" in a module is that you cannot	654	Another reason *never* to "->recv" in a module is that you cannot
296	sensibly have two "->wait"'s in parallel, as that would require	655	sensibly have two "->recv"'s in parallel, as that would require
297	multiple interpreters or coroutines/threads, none of which	656	multiple interpreters or coroutines/threads, none of which
298	"AnyEvent" can supply (the coroutine-aware backends	657	"AnyEvent" can supply.
299	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
300	support concurrent "->wait"'s from different coroutines, however).
301		658
302	$cv->broadcast	659	The Coro module, however, *can* and *does* supply coroutines and, in
303	Flag the condition as ready - a running "->wait" and all further	660	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
304	calls to "wait" will (eventually) return after this method has been	661	versions and also integrates coroutines into AnyEvent, making
305	called. If nobody is waiting the broadcast will be remembered..	662	blocking "->recv" calls perfectly safe as long as they are done from
		663	another coroutine (one that doesn't run the event loop).
306		664
307	Example:	665	You can ensure that "-recv" never blocks by setting a callback and
		666	only calling "->recv" from within that callback (or at a later
		667	time). This will work even when the event loop does not support
		668	blocking waits otherwise.
308		669
309	# wait till the result is ready	670	$bool = $cv->ready
310	my $result_ready = AnyEvent->condvar;	671	Returns true when the condition is "true", i.e. whether "send" or
		672	"croak" have been called.
311		673
312	# do something such as adding a timer	674	$cb = $cv->cb ($cb->($cv))
313	# or socket watcher the calls $result_ready->broadcast	675	This is a mutator function that returns the callback set and
314	# when the "result" is ready.	676	optionally replaces it before doing so.
315	# in this case, we simply use a timer:
316	my $w = AnyEvent->timer (
317	after => 1,
318	cb => sub { $result_ready->broadcast },
319	);
320		677
321	# this "blocks" (while handling events) till the watcher	678	The callback will be called when the condition becomes "true", i.e.
322	# calls broadcast	679	when "send" or "croak" are called, with the only argument being the
323	$result_ready->wait;	680	condition variable itself. Calling "recv" inside the callback or at
		681	any later time is guaranteed not to block.
324		682
325	GLOBAL VARIABLES AND FUNCTIONS	683	GLOBAL VARIABLES AND FUNCTIONS
326	$AnyEvent::MODEL	684	$AnyEvent::MODEL
327	Contains "undef" until the first watcher is being created. Then it	685	Contains "undef" until the first watcher is being created. Then it
328	contains the event model that is being used, which is the name of	686	contains the event model that is being used, which is the name of
…		…
330	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	688	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
331	case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*).	689	case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*).
332		690
333	The known classes so far are:	691	The known classes so far are:
334		692
335	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
336	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
337	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	693	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
338	AnyEvent::Impl::Event based on Event, also second best choice :)	694	AnyEvent::Impl::Event based on Event, second best choice.
		695	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
339	AnyEvent::Impl::Glib based on Glib, third-best choice.	696	AnyEvent::Impl::Glib based on Glib, third-best choice.
340	AnyEvent::Impl::Tk based on Tk, very bad choice.	697	AnyEvent::Impl::Tk based on Tk, very bad choice.
341	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	698	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		699	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		700	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		701
		702	There is no support for WxWidgets, as WxWidgets has no support for
		703	watching file handles. However, you can use WxWidgets through the
		704	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		705	second, which was considered to be too horrible to even consider for
		706	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
		707	using it's adaptor.
		708
		709	AnyEvent knows about Prima and Wx and will try to use POE when
		710	autodetecting them.
342		711
343	AnyEvent::detect	712	AnyEvent::detect
344	Returns $AnyEvent::MODEL, forcing autodetection of the event model	713	Returns $AnyEvent::MODEL, forcing autodetection of the event model
345	if necessary. You should only call this function right before you	714	if necessary. You should only call this function right before you
346	would have created an AnyEvent watcher anyway, that is, as late as	715	would have created an AnyEvent watcher anyway, that is, as late as
347	possible at runtime.	716	possible at runtime.
348		717
		718	$guard = AnyEvent::post_detect { BLOCK }
		719	Arranges for the code block to be executed as soon as the event
		720	model is autodetected (or immediately if this has already happened).
		721
		722	If called in scalar or list context, then it creates and returns an
		723	object that automatically removes the callback again when it is
		724	destroyed. See Coro::BDB for a case where this is useful.
		725
		726	@AnyEvent::post_detect
		727	If there are any code references in this array (you can "push" to it
		728	before or after loading AnyEvent), then they will called directly
		729	after the event loop has been chosen.
		730
		731	You should check $AnyEvent::MODEL before adding to this array,
		732	though: if it contains a true value then the event loop has already
		733	been detected, and the array will be ignored.
		734
		735	Best use "AnyEvent::post_detect { BLOCK }" instead.
		736
349	WHAT TO DO IN A MODULE	737	WHAT TO DO IN A MODULE
350	As a module author, you should "use AnyEvent" and call AnyEvent methods	738	As a module author, you should "use AnyEvent" and call AnyEvent methods
351	freely, but you should not load a specific event module or rely on it.	739	freely, but you should not load a specific event module or rely on it.
352		740
353	Be careful when you create watchers in the module body - AnyEvent will	741	Be careful when you create watchers in the module body - AnyEvent will
354	decide which event module to use as soon as the first method is called,	742	decide which event module to use as soon as the first method is called,
355	so by calling AnyEvent in your module body you force the user of your	743	so by calling AnyEvent in your module body you force the user of your
356	module to load the event module first.	744	module to load the event module first.
357		745
358	Never call "->wait" on a condition variable unless you *know* that the	746	Never call "->recv" on a condition variable unless you *know* that the
359	"->broadcast" method has been called on it already. This is because it	747	"->send" method has been called on it already. This is because it will
360	will stall the whole program, and the whole point of using events is to	748	stall the whole program, and the whole point of using events is to stay
361	stay interactive.	749	interactive.
362		750
363	It is fine, however, to call "->wait" when the user of your module	751	It is fine, however, to call "->recv" when the user of your module
364	requests it (i.e. if you create a http request object ad have a method	752	requests it (i.e. if you create a http request object ad have a method
365	called "results" that returns the results, it should call "->wait"	753	called "results" that returns the results, it should call "->recv"
366	freely, as the user of your module knows what she is doing. always).	754	freely, as the user of your module knows what she is doing. always).
367		755
368	WHAT TO DO IN THE MAIN PROGRAM	756	WHAT TO DO IN THE MAIN PROGRAM
369	There will always be a single main program - the only place that should	757	There will always be a single main program - the only place that should
370	dictate which event model to use.	758	dictate which event model to use.
…		…
372	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	760	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
373	do anything special (it does not need to be event-based) and let	761	do anything special (it does not need to be event-based) and let
374	AnyEvent decide which implementation to chose if some module relies on	762	AnyEvent decide which implementation to chose if some module relies on
375	it.	763	it.
376		764
377	If the main program relies on a specific event model. For example, in	765	If the main program relies on a specific event model - for example, in
378	Gtk2 programs you have to rely on the Glib module. You should load the	766	Gtk2 programs you have to rely on the Glib module - you should load the
379	event module before loading AnyEvent or any module that uses it:	767	event module before loading AnyEvent or any module that uses it:
380	generally speaking, you should load it as early as possible. The reason	768	generally speaking, you should load it as early as possible. The reason
381	is that modules might create watchers when they are loaded, and AnyEvent	769	is that modules might create watchers when they are loaded, and AnyEvent
382	will decide on the event model to use as soon as it creates watchers,	770	will decide on the event model to use as soon as it creates watchers,
383	and it might chose the wrong one unless you load the correct one	771	and it might chose the wrong one unless you load the correct one
384	yourself.	772	yourself.
385		773
386	You can chose to use a rather inefficient pure-perl implementation by	774	You can chose to use a pure-perl implementation by loading the
387	loading the "AnyEvent::Impl::Perl" module, which gives you similar	775	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
388	behaviour everywhere, but letting AnyEvent chose is generally better.	776	everywhere, but letting AnyEvent chose the model is generally better.
		777
		778	MAINLOOP EMULATION
		779	Sometimes (often for short test scripts, or even standalone programs who
		780	only want to use AnyEvent), you do not want to run a specific event
		781	loop.
		782
		783	In that case, you can use a condition variable like this:
		784
		785	AnyEvent->condvar->recv;
		786
		787	This has the effect of entering the event loop and looping forever.
		788
		789	Note that usually your program has some exit condition, in which case it
		790	is better to use the "traditional" approach of storing a condition
		791	variable somewhere, waiting for it, and sending it when the program
		792	should exit cleanly.
		793
		794	OTHER MODULES
		795	The following is a non-exhaustive list of additional modules that use
		796	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		797	in the same program. Some of the modules come with AnyEvent, some are
		798	available via CPAN.
		799
		800	AnyEvent::Util
		801	Contains various utility functions that replace often-used but
		802	blocking functions such as "inet_aton" by event-/callback-based
		803	versions.
		804
		805	AnyEvent::Socket
		806	Provides various utility functions for (internet protocol) sockets,
		807	addresses and name resolution. Also functions to create non-blocking
		808	tcp connections or tcp servers, with IPv6 and SRV record support and
		809	more.
		810
		811	AnyEvent::Handle
		812	Provide read and write buffers, manages watchers for reads and
		813	writes, supports raw and formatted I/O, I/O queued and fully
		814	transparent and non-blocking SSL/TLS.
		815
		816	AnyEvent::DNS
		817	Provides rich asynchronous DNS resolver capabilities.
		818
		819	AnyEvent::HTTP
		820	A simple-to-use HTTP library that is capable of making a lot of
		821	concurrent HTTP requests.
		822
		823	AnyEvent::HTTPD
		824	Provides a simple web application server framework.
		825
		826	AnyEvent::FastPing
		827	The fastest ping in the west.
		828
		829	AnyEvent::DBI
		830	Executes DBI requests asynchronously in a proxy process.
		831
		832	AnyEvent::AIO
		833	Truly asynchronous I/O, should be in the toolbox of every event
		834	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		835	together.
		836
		837	AnyEvent::BDB
		838	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		839	fuses BDB and AnyEvent together.
		840
		841	AnyEvent::GPSD
		842	A non-blocking interface to gpsd, a daemon delivering GPS
		843	information.
		844
		845	AnyEvent::IGS
		846	A non-blocking interface to the Internet Go Server protocol (used by
		847	App::IGS).
		848
		849	AnyEvent::IRC
		850	AnyEvent based IRC client module family (replacing the older
		851	Net::IRC3).
		852
		853	Net::XMPP2
		854	AnyEvent based XMPP (Jabber protocol) module family.
		855
		856	Net::FCP
		857	AnyEvent-based implementation of the Freenet Client Protocol,
		858	birthplace of AnyEvent.
		859
		860	Event::ExecFlow
		861	High level API for event-based execution flow control.
		862
		863	Coro
		864	Has special support for AnyEvent via Coro::AnyEvent.
		865
		866	IO::Lambda
		867	The lambda approach to I/O - don't ask, look there. Can use
		868	AnyEvent.
		869
		870	ERROR AND EXCEPTION HANDLING
		871	In general, AnyEvent does not do any error handling - it relies on the
		872	caller to do that if required. The AnyEvent::Strict module (see also the
		873	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		874	checking of all AnyEvent methods, however, which is highly useful during
		875	development.
		876
		877	As for exception handling (i.e. runtime errors and exceptions thrown
		878	while executing a callback), this is not only highly event-loop
		879	specific, but also not in any way wrapped by this module, as this is the
		880	job of the main program.
		881
		882	The pure perl event loop simply re-throws the exception (usually within
		883	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		884	Glib uses "install_exception_handler" and so on.
		885
		886	ENVIRONMENT VARIABLES
		887	The following environment variables are used by this module or its
		888	submodules:
		889
		890	"PERL_ANYEVENT_VERBOSE"
		891	By default, AnyEvent will be completely silent except in fatal
		892	conditions. You can set this environment variable to make AnyEvent
		893	more talkative.
		894
		895	When set to 1 or higher, causes AnyEvent to warn about unexpected
		896	conditions, such as not being able to load the event model specified
		897	by "PERL_ANYEVENT_MODEL".
		898
		899	When set to 2 or higher, cause AnyEvent to report to STDERR which
		900	event model it chooses.
		901
		902	"PERL_ANYEVENT_STRICT"
		903	AnyEvent does not do much argument checking by default, as thorough
		904	argument checking is very costly. Setting this variable to a true
		905	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		906	thoroughly check the arguments passed to most method calls. If it
		907	finds any problems it will croak.
		908
		909	In other words, enables "strict" mode.
		910
		911	Unlike "use strict", it is definitely recommended ot keep it off in
		912	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment
		913	while developing programs can be very useful, however.
		914
		915	"PERL_ANYEVENT_MODEL"
		916	This can be used to specify the event model to be used by AnyEvent,
		917	before auto detection and -probing kicks in. It must be a string
		918	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		919	gets prepended and the resulting module name is loaded and if the
		920	load was successful, used as event model. If it fails to load
		921	AnyEvent will proceed with auto detection and -probing.
		922
		923	This functionality might change in future versions.
		924
		925	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		926	could start your program like this:
		927
		928	PERL_ANYEVENT_MODEL=Perl perl ...
		929
		930	"PERL_ANYEVENT_PROTOCOLS"
		931	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		932	preferences for IPv4 or IPv6. The default is unspecified (and might
		933	change, or be the result of auto probing).
		934
		935	Must be set to a comma-separated list of protocols or address
		936	families, current supported: "ipv4" and "ipv6". Only protocols
		937	mentioned will be used, and preference will be given to protocols
		938	mentioned earlier in the list.
		939
		940	This variable can effectively be used for denial-of-service attacks
		941	against local programs (e.g. when setuid), although the impact is
		942	likely small, as the program has to handle conenction and other
		943	failures anyways.
		944
		945	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		946	IPv6, but support both and try to use both.
		947	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		948	resolve or contact IPv6 addresses.
		949	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		950	prefer IPv6 over IPv4.
		951
		952	"PERL_ANYEVENT_EDNS0"
		953	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		954	for DNS. This extension is generally useful to reduce DNS traffic,
		955	but some (broken) firewalls drop such DNS packets, which is why it
		956	is off by default.
		957
		958	Setting this variable to 1 will cause AnyEvent::DNS to announce
		959	EDNS0 in its DNS requests.
		960
		961	"PERL_ANYEVENT_MAX_FORKS"
		962	The maximum number of child processes that
		963	"AnyEvent::Util::fork_call" will create in parallel.
389		964
390	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	965	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
391	This is an advanced topic that you do not normally need to use AnyEvent	966	This is an advanced topic that you do not normally need to use AnyEvent
392	in a module. This section is only of use to event loop authors who want	967	in a module. This section is only of use to event loop authors who want
393	to provide AnyEvent compatibility.	968	to provide AnyEvent compatibility.
…		…
428	*rxvt-unicode* also cheats a bit by not providing blocking access to	1003	*rxvt-unicode* also cheats a bit by not providing blocking access to
429	condition variables: code blocking while waiting for a condition will	1004	condition variables: code blocking while waiting for a condition will
430	"die". This still works with most modules/usages, and blocking calls	1005	"die". This still works with most modules/usages, and blocking calls
431	must not be done in an interactive application, so it makes sense.	1006	must not be done in an interactive application, so it makes sense.
432		1007
433	ENVIRONMENT VARIABLES
434	The following environment variables are used by this module:
435
436	"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, cause AnyEvent to
437	report to STDERR which event model it chooses.
438
439	EXAMPLE PROGRAM	1008	EXAMPLE PROGRAM
440	The following program uses an IO watcher to read data from STDIN, a	1009	The following program uses an I/O watcher to read data from STDIN, a
441	timer to display a message once per second, and a condition variable to	1010	timer to display a message once per second, and a condition variable to
442	quit the program when the user enters quit:	1011	quit the program when the user enters quit:
443		1012
444	use AnyEvent;	1013	use AnyEvent;
445		1014
…		…
450	poll => 'r',	1019	poll => 'r',
451	cb => sub {	1020	cb => sub {
452	warn "io event <$_[0]>\n"; # will always output <r>	1021	warn "io event <$_[0]>\n"; # will always output <r>
453	chomp (my $input = <STDIN>); # read a line	1022	chomp (my $input = <STDIN>); # read a line
454	warn "read: $input\n"; # output what has been read	1023	warn "read: $input\n"; # output what has been read
455	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1024	$cv->send if $input =~ /^q/i; # quit program if /^q/i
456	},	1025	},
457	);	1026	);
458		1027
459	my $time_watcher; # can only be used once	1028	my $time_watcher; # can only be used once
460		1029
…		…
465	});	1034	});
466	}	1035	}
467		1036
468	new_timer; # create first timer	1037	new_timer; # create first timer
469		1038
470	$cv->wait; # wait until user enters /^q/i	1039	$cv->recv; # wait until user enters /^q/i
471		1040
472	REAL-WORLD EXAMPLE	1041	REAL-WORLD EXAMPLE
473	Consider the Net::FCP module. It features (among others) the following	1042	Consider the Net::FCP module. It features (among others) the following
474	API calls, which are to freenet what HTTP GET requests are to http:	1043	API calls, which are to freenet what HTTP GET requests are to http:
475		1044
…		…
524	syswrite $txn->{fh}, $txn->{request}	1093	syswrite $txn->{fh}, $txn->{request}
525	or die "connection or write error";	1094	or die "connection or write error";
526	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1095	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
527		1096
528	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1097	Again, "fh_ready_r" waits till all data has arrived, and then stores the
529	result and signals any possible waiters that the request ahs finished:	1098	result and signals any possible waiters that the request has finished:
530		1099
531	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1100	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
532		1101
533	if (end-of-file or data complete) {	1102	if (end-of-file or data complete) {
534	$txn->{result} = $txn->{buf};	1103	$txn->{result} = $txn->{buf};
535	$txn->{finished}->broadcast;	1104	$txn->{finished}->send;
536	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1105	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
537	}	1106	}
538		1107
539	The "result" method, finally, just waits for the finished signal (if the	1108	The "result" method, finally, just waits for the finished signal (if the
540	request was already finished, it doesn't wait, of course, and returns	1109	request was already finished, it doesn't wait, of course, and returns
541	the data:	1110	the data:
542		1111
543	$txn->{finished}->wait;	1112	$txn->{finished}->recv;
544	return $txn->{result};	1113	return $txn->{result};
545		1114
546	The actual code goes further and collects all errors ("die"s,	1115	The actual code goes further and collects all errors ("die"s,
547	exceptions) that occured during request processing. The "result" method	1116	exceptions) that occurred during request processing. The "result" method
548	detects whether an exception as thrown (it is stored inside the $txn	1117	detects whether an exception as thrown (it is stored inside the $txn
549	object) and just throws the exception, which means connection errors and	1118	object) and just throws the exception, which means connection errors and
550	other problems get reported tot he code that tries to use the result,	1119	other problems get reported tot he code that tries to use the result,
551	not in a random callback.	1120	not in a random callback.
552		1121
…		…
583		1152
584	my $quit = AnyEvent->condvar;	1153	my $quit = AnyEvent->condvar;
585		1154
586	$fcp->txn_client_get ($url)->cb (sub {	1155	$fcp->txn_client_get ($url)->cb (sub {
587	...	1156	...
588	$quit->broadcast;	1157	$quit->send;
589	});	1158	});
590		1159
591	$quit->wait;	1160	$quit->recv;
		1161
		1162	BENCHMARKS
		1163	To give you an idea of the performance and overheads that AnyEvent adds
		1164	over the event loops themselves and to give you an impression of the
		1165	speed of various event loops I prepared some benchmarks.
		1166
		1167	BENCHMARKING ANYEVENT OVERHEAD
		1168	Here is a benchmark of various supported event models used natively and
		1169	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1170	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1171	which it is), lets them fire exactly once and destroys them again.
		1172
		1173	Source code for this benchmark is found as eg/bench in the AnyEvent
		1174	distribution.
		1175
		1176	Explanation of the columns
		1177	*watcher* is the number of event watchers created/destroyed. Since
		1178	different event models feature vastly different performances, each event
		1179	loop was given a number of watchers so that overall runtime is
		1180	acceptable and similar between tested event loop (and keep them from
		1181	crashing): Glib would probably take thousands of years if asked to
		1182	process the same number of watchers as EV in this benchmark.
		1183
		1184	*bytes* is the number of bytes (as measured by the resident set size,
		1185	RSS) consumed by each watcher. This method of measuring captures both C
		1186	and Perl-based overheads.
		1187
		1188	*create* is the time, in microseconds (millionths of seconds), that it
		1189	takes to create a single watcher. The callback is a closure shared
		1190	between all watchers, to avoid adding memory overhead. That means
		1191	closure creation and memory usage is not included in the figures.
		1192
		1193	*invoke* is the time, in microseconds, used to invoke a simple callback.
		1194	The callback simply counts down a Perl variable and after it was invoked
		1195	"watcher" times, it would "->send" a condvar once to signal the end of
		1196	this phase.
		1197
		1198	*destroy* is the time, in microseconds, that it takes to destroy a
		1199	single watcher.
		1200
		1201	Results
		1202	name watchers bytes create invoke destroy comment
		1203	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1204	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1205	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1206	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1207	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1208	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1209	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1210	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1211	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1212	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1213
		1214	Discussion
		1215	The benchmark does *not* measure scalability of the event loop very
		1216	well. For example, a select-based event loop (such as the pure perl one)
		1217	can never compete with an event loop that uses epoll when the number of
		1218	file descriptors grows high. In this benchmark, all events become ready
		1219	at the same time, so select/poll-based implementations get an unnatural
		1220	speed boost.
		1221
		1222	Also, note that the number of watchers usually has a nonlinear effect on
		1223	overall speed, that is, creating twice as many watchers doesn't take
		1224	twice the time - usually it takes longer. This puts event loops tested
		1225	with a higher number of watchers at a disadvantage.
		1226
		1227	To put the range of results into perspective, consider that on the
		1228	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1229	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
		1230	CPU cycles with POE.
		1231
		1232	"EV" is the sole leader regarding speed and memory use, which are both
		1233	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1234	far less memory than any other event loop and is still faster than Event
		1235	natively.
		1236
		1237	The pure perl implementation is hit in a few sweet spots (both the
		1238	constant timeout and the use of a single fd hit optimisations in the
		1239	perl interpreter and the backend itself). Nevertheless this shows that
		1240	it adds very little overhead in itself. Like any select-based backend
		1241	its performance becomes really bad with lots of file descriptors (and
		1242	few of them active), of course, but this was not subject of this
		1243	benchmark.
		1244
		1245	The "Event" module has a relatively high setup and callback invocation
		1246	cost, but overall scores in on the third place.
		1247
		1248	"Glib"'s memory usage is quite a bit higher, but it features a faster
		1249	callback invocation and overall ends up in the same class as "Event".
		1250	However, Glib scales extremely badly, doubling the number of watchers
		1251	increases the processing time by more than a factor of four, making it
		1252	completely unusable when using larger numbers of watchers (note that
		1253	only a single file descriptor was used in the benchmark, so
		1254	inefficiencies of "poll" do not account for this).
		1255
		1256	The "Tk" adaptor works relatively well. The fact that it crashes with
		1257	more than 2000 watchers is a big setback, however, as correctness takes
		1258	precedence over speed. Nevertheless, its performance is surprising, as
		1259	the file descriptor is dup()ed for each watcher. This shows that the
		1260	dup() employed by some adaptors is not a big performance issue (it does
		1261	incur a hidden memory cost inside the kernel which is not reflected in
		1262	the figures above).
		1263
		1264	"POE", regardless of underlying event loop (whether using its pure perl
		1265	select-based backend or the Event module, the POE-EV backend couldn't be
		1266	tested because it wasn't working) shows abysmal performance and memory
		1267	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
		1268	watchers, and 10 times as much memory as Event (the high memory
		1269	requirements are caused by requiring a session for each watcher).
		1270	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1271	pure perl implementation.
		1272
		1273	The design of the POE adaptor class in AnyEvent can not really account
		1274	for the performance issues, though, as session creation overhead is
		1275	small compared to execution of the state machine, which is coded pretty
		1276	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1277	using multiple sessions is not a good approach, especially regarding
		1278	memory usage, even the author of POE could not come up with a faster
		1279	design).
		1280
		1281	Summary
		1282	* Using EV through AnyEvent is faster than any other event loop (even
		1283	when used without AnyEvent), but most event loops have acceptable
		1284	performance with or without AnyEvent.
		1285
		1286	* The overhead AnyEvent adds is usually much smaller than the overhead
		1287	of the actual event loop, only with extremely fast event loops such
		1288	as EV adds AnyEvent significant overhead.
		1289
		1290	* You should avoid POE like the plague if you want performance or
		1291	reasonable memory usage.
		1292
		1293	BENCHMARKING THE LARGE SERVER CASE
		1294	This benchmark actually benchmarks the event loop itself. It works by
		1295	creating a number of "servers": each server consists of a socket pair, a
		1296	timeout watcher that gets reset on activity (but never fires), and an
		1297	I/O watcher waiting for input on one side of the socket. Each time the
		1298	socket watcher reads a byte it will write that byte to a random other
		1299	"server".
		1300
		1301	The effect is that there will be a lot of I/O watchers, only part of
		1302	which are active at any one point (so there is a constant number of
		1303	active fds for each loop iteration, but which fds these are is random).
		1304	The timeout is reset each time something is read because that reflects
		1305	how most timeouts work (and puts extra pressure on the event loops).
		1306
		1307	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
		1308	100 (1%) are active. This mirrors the activity of large servers with
		1309	many connections, most of which are idle at any one point in time.
		1310
		1311	Source code for this benchmark is found as eg/bench2 in the AnyEvent
		1312	distribution.
		1313
		1314	Explanation of the columns
		1315	*sockets* is the number of sockets, and twice the number of "servers"
		1316	(as each server has a read and write socket end).
		1317
		1318	*create* is the time it takes to create a socket pair (which is
		1319	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1320
		1321	*request*, the most important value, is the time it takes to handle a
		1322	single "request", that is, reading the token from the pipe and
		1323	forwarding it to another server. This includes deleting the old timeout
		1324	and creating a new one that moves the timeout into the future.
		1325
		1326	Results
		1327	name sockets create request
		1328	EV 20000 69.01 11.16
		1329	Perl 20000 73.32 35.87
		1330	Event 20000 212.62 257.32
		1331	Glib 20000 651.16 1896.30
		1332	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1333
		1334	Discussion
		1335	This benchmark *does* measure scalability and overall performance of the
		1336	particular event loop.
		1337
		1338	EV is again fastest. Since it is using epoll on my system, the setup
		1339	time is relatively high, though.
		1340
		1341	Perl surprisingly comes second. It is much faster than the C-based event
		1342	loops Event and Glib.
		1343
		1344	Event suffers from high setup time as well (look at its code and you
		1345	will understand why). Callback invocation also has a high overhead
		1346	compared to the "$_->() for .."-style loop that the Perl event loop
		1347	uses. Event uses select or poll in basically all documented
		1348	configurations.
		1349
		1350	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1351	clearly fails to perform with many filehandles or in busy servers.
		1352
		1353	POE is still completely out of the picture, taking over 1000 times as
		1354	long as EV, and over 100 times as long as the Perl implementation, even
		1355	though it uses a C-based event loop in this case.
		1356
		1357	Summary
		1358	* The pure perl implementation performs extremely well.
		1359
		1360	* Avoid Glib or POE in large projects where performance matters.
		1361
		1362	BENCHMARKING SMALL SERVERS
		1363	While event loops should scale (and select-based ones do not...) even to
		1364	large servers, most programs we (or I :) actually write have only a few
		1365	I/O watchers.
		1366
		1367	In this benchmark, I use the same benchmark program as in the large
		1368	server case, but it uses only eight "servers", of which three are active
		1369	at any one time. This should reflect performance for a small server
		1370	relatively well.
		1371
		1372	The columns are identical to the previous table.
		1373
		1374	Results
		1375	name sockets create request
		1376	EV 16 20.00 6.54
		1377	Perl 16 25.75 12.62
		1378	Event 16 81.27 35.86
		1379	Glib 16 32.63 15.48
		1380	POE 16 261.87 276.28 uses POE::Loop::Event
		1381
		1382	Discussion
		1383	The benchmark tries to test the performance of a typical small server.
		1384	While knowing how various event loops perform is interesting, keep in
		1385	mind that their overhead in this case is usually not as important, due
		1386	to the small absolute number of watchers (that is, you need efficiency
		1387	and speed most when you have lots of watchers, not when you only have a
		1388	few of them).
		1389
		1390	EV is again fastest.
		1391
		1392	Perl again comes second. It is noticeably faster than the C-based event
		1393	loops Event and Glib, although the difference is too small to really
		1394	matter.
		1395
		1396	POE also performs much better in this case, but is is still far behind
		1397	the others.
		1398
		1399	Summary
		1400	* C-based event loops perform very well with small number of watchers,
		1401	as the management overhead dominates.
		1402
		1403	SIGNALS
		1404	AnyEvent currently installs handlers for these signals:
		1405
		1406	SIGCHLD
		1407	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1408	emulation for event loops that do not support them natively. Also,
		1409	some event loops install a similar handler.
		1410
		1411	SIGPIPE
		1412	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1413	"undef" when AnyEvent gets loaded.
		1414
		1415	The rationale for this is that AnyEvent users usually do not really
		1416	depend on SIGPIPE delivery (which is purely an optimisation for
		1417	shell use, or badly-written programs), but "SIGPIPE" can cause
		1418	spurious and rare program exits as a lot of people do not expect
		1419	"SIGPIPE" when writing to some random socket.
		1420
		1421	The rationale for installing a no-op handler as opposed to ignoring
		1422	it is that this way, the handler will be restored to defaults on
		1423	exec.
		1424
		1425	Feel free to install your own handler, or reset it to defaults.
		1426
		1427	FORK
		1428	Most event libraries are not fork-safe. The ones who are usually are
		1429	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1430	Only EV is fully fork-aware.
		1431
		1432	If you have to fork, you must either do so *before* creating your first
		1433	watcher OR you must not use AnyEvent at all in the child.
		1434
		1435	SECURITY CONSIDERATIONS
		1436	AnyEvent can be forced to load any event model via
		1437	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
		1438	to execute arbitrary code or directly gain access, it can easily be used
		1439	to make the program hang or malfunction in subtle ways, as AnyEvent
		1440	watchers will not be active when the program uses a different event
		1441	model than specified in the variable.
		1442
		1443	You can make AnyEvent completely ignore this variable by deleting it
		1444	before the first watcher gets created, e.g. with a "BEGIN" block:
		1445
		1446	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1447
		1448	use AnyEvent;
		1449
		1450	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1451	be used to probe what backend is used and gain other information (which
		1452	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1453	and $ENV{PERL_ANYEGENT_STRICT}.
		1454
		1455	BUGS
		1456	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1457	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1458	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1459	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1460	not as pronounced).
592		1461
593	SEE ALSO	1462	SEE ALSO
594	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1463	Utility functions: AnyEvent::Util.
595	Glib::Event, Glib, Coro, Tk.
596		1464
597	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1465	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
598	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1466	Event::Lib, Qt, POE.
		1467
		1468	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
599	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl.	1469	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
		1470	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
600		1471
		1472	Non-blocking file handles, sockets, TCP clients and servers:
		1473	AnyEvent::Handle, AnyEvent::Socket.
		1474
		1475	Asynchronous DNS: AnyEvent::DNS.
		1476
		1477	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1478
601	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1479	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
602		1480
		1481	AUTHOR
		1482	Marc Lehmann <schmorp@schmorp.de>
		1483	http://home.schmorp.de/
603		1484

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