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Revision 1.18 by root, Thu Apr 24 09:13:26 2008 UTC vs.
Revision 1.41 by root, Fri Jun 26 06:33:17 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 -	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, Tk, Event::Lib, Qt. The first one found is used. If none are	109	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82	found, the module tries to load these modules (excluding Event::Lib and	110	used. If none are found, the module tries to load these modules
83	Qt) in the order given. The first one that can be successfully loaded	111	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
84	will be used. If, after this, still none could be found, AnyEvent will	112	always succeed) in the order given. The first one that can be
85	fall back to a pure-perl event loop, which is not very efficient, but	113	successfully loaded will be used. If, after this, still none could be
86	should work everywhere.	114	found, AnyEvent will fall back to a pure-perl event loop, which is not
		115	very efficient, but should work everywhere.
87		116
88	Because AnyEvent first checks for modules that are already loaded,	117	Because AnyEvent first checks for modules that are already loaded,
89	loading an event model explicitly before first using AnyEvent will	118	loading an event model explicitly before first using AnyEvent will
90	likely make that model the default. For example:	119	likely make that model the default. For example:
91		120
…		…
98	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
99	to use AnyEvent so their modules work together with others seamlessly...	128	to use AnyEvent so their modules work together with others seamlessly...
100		129
101	The pure-perl implementation of AnyEvent is called	130	The pure-perl implementation of AnyEvent is called
102	"AnyEvent::Impl::Perl". Like other event modules you can load it	131	"AnyEvent::Impl::Perl". Like other event modules you can load it
103	explicitly.	132	explicitly and enjoy the high availability of that event loop :)
104		133
105	WATCHERS	134	WATCHERS
106	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
107	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
108	the callback to call, the filehandle to watch, etc.	137	the callback to call, the file handle to watch, etc.
109		138
110	These watchers are normal Perl objects with normal Perl lifetime. After	139	These watchers are normal Perl objects with normal Perl lifetime. After
111	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
112	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
113	in control).	142	in control).
114		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
115	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
116	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
117	to it).	152	to it).
118		153
119	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.
…		…
121	Many watchers either are used with "recursion" (repeating timers for	156	Many watchers either are used with "recursion" (repeating timers for
122	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.
123		158
124	An any way to achieve that is this pattern:	159	An any way to achieve that is this pattern:
125		160
126	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	161	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
127	# you can use $w here, for example to undef it	162	# you can use $w here, for example to undef it
128	undef $w;	163	undef $w;
129	});	164	});
130		165
131	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,
132	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
133	declared.	168	declared.
134		169
135	IO WATCHERS	170	I/O WATCHERS
136	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
137	the following mandatory key-value pairs as arguments:	172	the following mandatory key-value pairs as arguments:
138		173
139	"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
140	"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
141	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	182	watcher waiting for "r"eadable or "w"ritable events, respectively.
		183
142	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.
143		185
144	As long as the I/O watcher exists it will keep the file descriptor or a	186	Although the callback might get passed parameters, their value and
145	copy of it alive/open.	187	presence is undefined and you cannot rely on them. Portable AnyEvent
		188	callbacks cannot use arguments passed to I/O watcher callbacks.
146		189
		190	The I/O watcher might use the underlying file descriptor or a copy of
147	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
148	active on the underlying file descriptor.	192	the underlying file descriptor.
149		193
150	Some event loops issue spurious readyness notifications, so you should	194	Some event loops issue spurious readyness notifications, so you should
151	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
152	handles.	196	handles.
153		197
154	Example:
155
156	# 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
157	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	201	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
158	chomp (my $input = <STDIN>);	202	chomp (my $input = <STDIN>);
159	warn "read: $input\n";	203	warn "read: $input\n";
160	undef $w;	204	undef $w;
161	});	205	});
…		…
163	TIME WATCHERS	207	TIME WATCHERS
164	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
165	with the following mandatory arguments:	209	with the following mandatory arguments:
166		210
167	"after" specifies after how many seconds (fractional values are	211	"after" specifies after how many seconds (fractional values are
168	supported) should the timer activate. "cb" the callback to invoke in	212	supported) the callback should be invoked. "cb" is the callback to
169	that case.	213	invoke in that case.
170		214
171	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
172	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
173	and Glib).	217	callbacks cannot use arguments passed to time watcher callbacks.
174		218
175	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.
176		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
177	# fire an event after 7.7 seconds	229	Example: fire an event after 7.7 seconds.
		230
178	my $w = AnyEvent->timer (after => 7.7, cb => sub {	231	my $w = AnyEvent->timer (after => 7.7, cb => sub {
179	warn "timeout\n";	232	warn "timeout\n";
180	});	233	});
181		234
182	# to cancel the timer:	235	# to cancel the timer:
183	undef $w;	236	undef $w;
184		237
185	Example 2:
186
187	# 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.
188	my $w;
189		239
190	my $cb = sub {
191	# cancel the old timer while creating a new one
192	$w = AnyEvent->timer (after => 1, cb => $cb);	240	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		241	warn "timeout\n";
193	};	242	};
194
195	# start the "loop" by creating the first watcher
196	$w = AnyEvent->timer (after => 0.5, cb => $cb);
197		243
198	TIMING ISSUES	244	TIMING ISSUES
199	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
200	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
201	o'clock").	247	o'clock").
…		…
213	on wallclock time) timers.	259	on wallclock time) timers.
214		260
215	AnyEvent always prefers relative timers, if available, matching the	261	AnyEvent always prefers relative timers, if available, matching the
216	AnyEvent API.	262	AnyEvent API.
217		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
218	SIGNAL WATCHERS	340	SIGNAL WATCHERS
219	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
220	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
221	whenever a signal occurs.	343	callback to be invoked whenever a signal occurs.
222		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
223	Multiple signal occurances can be clumped together into one callback	349	Multiple signal occurrences can be clumped together into one callback
224	invocation, and callback invocation will be synchronous. synchronous	350	invocation, and callback invocation will be synchronous. Synchronous
225	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
226	process, but it is guarenteed not to interrupt any other callbacks.	352	process, but it is guaranteed not to interrupt any other callbacks.
227		353
228	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
229	signal between multiple watchers.	355	signal between multiple watchers.
230		356
231	This watcher might use %SIG, so programs overwriting those signals	357	This watcher might use %SIG, so programs overwriting those signals
…		…
237		363
238	CHILD PROCESS WATCHERS	364	CHILD PROCESS WATCHERS
239	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.
240		366
241	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
242	watches for any child process exit). The watcher will trigger as often	368	watches for any child process exit). The watcher will triggered only
243	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
244	signal handler for "SIGCHLD". The callback will be called with the pid	370	on any trace events (stopped/continued).
245	and exit status (as returned by waitpid).
246		371
247	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.
248		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 (neither POE nor IO::Async
		386	do, see their AnyEvent::Impl manpages for details), but even for event
		387	models that do handle this correctly, they usually need to be loaded
		388	before the process exits (i.e. before you fork in the first place).
		389	AnyEvent's pure perl event loop handles all cases correctly regardless
		390	of when you start the watcher.
		391
		392	This means you cannot create a child watcher as the very first thing in
		393	an AnyEvent program, you have to create at least one watcher before
		394	you "fork" the child (alternatively, you can call "AnyEvent::detect").
		395
		396	Example: fork a process and wait for it
		397
		398	my $done = AnyEvent->condvar;
		399
		400	my $pid = fork or exit 5;
		401
249	my $w = AnyEvent->child (	402	my $w = AnyEvent->child (
250	pid => 1333,	403	pid => $pid,
251	cb => sub {	404	cb => sub {
252	my ($pid, $status) = @_;	405	my ($pid, $status) = @_;
253	warn "pid $pid exited with status $status";	406	warn "pid $pid exited with status $status";
		407	$done->send;
254	},	408	},
255	);	409	);
		410
		411	# do something else, then wait for process exit
		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	});
256		447
257	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 different, it expects somebody else to run the event loop
		454	and will only block when necessary (usually when told by the user).
		455
		456	The instrument to do that is called a "condition variable", so called
		457	because they represent a condition that must become true.
		458
258	Condition variables can be created by calling the "AnyEvent->condvar"	459	Condition variables can be created by calling the "AnyEvent->condvar"
259	method without any arguments.	460	method, usually without arguments. The only argument pair allowed is
260		461
261	A condition variable waits for a condition - precisely that the	462	"cb", which specifies a callback to be called when the condition
262	"->broadcast" method has been called.	463	variable becomes true, with the condition variable as the first argument
		464	(but not the results).
263		465
264	They are very useful to signal that a condition has been fulfilled, for	466	After creation, the condition variable is "false" until it becomes
		467	"true" by calling the "send" method (or calling the condition variable
		468	as if it were a callback, read about the caveats in the description for
		469	the "->send" method).
		470
		471	Condition variables are similar to callbacks, except that you can
		472	optionally wait for them. They can also be called merge points - points
		473	in time where multiple outstanding events have been processed. And yet
		474	another way to call them is transactions - each condition variable can
		475	be used to represent a transaction, which finishes at some point and
		476	delivers a result.
		477
		478	Condition variables are very useful to signal that something has
265	example, if you write a module that does asynchronous http requests,	479	finished, for example, if you write a module that does asynchronous http
266	then a condition variable would be the ideal candidate to signal the	480	requests, then a condition variable would be the ideal candidate to
267	availability of results.	481	signal the availability of results. The user can either act when the
		482	callback is called or can synchronously "->recv" for the results.
268		483
269	You can also use condition variables to block your main program until an	484	You can also use them to simulate traditional event loops - for example,
270	event occurs - for example, you could "->wait" in your main program	485	you can block your main program until an event occurs - for example, you
271	until the user clicks the Quit button in your app, which would	486	could "->recv" in your main program until the user clicks the Quit
272	"->broadcast" the "quit" event.	487	button of your app, which would "->send" the "quit" event.
273		488
274	Note that condition variables recurse into the event loop - if you have	489	Note that condition variables recurse into the event loop - if you have
275	two pirces of code that call "->wait" in a round-robbin fashion, you	490	two pieces of code that call "->recv" in a round-robin fashion, you
276	lose. Therefore, condition variables are good to export to your caller,	491	lose. Therefore, condition variables are good to export to your caller,
277	but you should avoid making a blocking wait yourself, at least in	492	but you should avoid making a blocking wait yourself, at least in
278	callbacks, as this asks for trouble.	493	callbacks, as this asks for trouble.
279		494
280	This object has two methods:	495	Condition variables are represented by hash refs in perl, and the keys
		496	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		497	(it is often useful to build your own transaction class on top of
		498	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		499	it's "new" method in your own "new" method.
281		500
282	$cv->wait	501	There are two "sides" to a condition variable - the "producer side"
		502	which eventually calls "-> send", and the "consumer side", which waits
		503	for the send to occur.
		504
		505	Example: wait for a timer.
		506
		507	# wait till the result is ready
		508	my $result_ready = AnyEvent->condvar;
		509
		510	# do something such as adding a timer
		511	# or socket watcher the calls $result_ready->send
		512	# when the "result" is ready.
		513	# in this case, we simply use a timer:
		514	my $w = AnyEvent->timer (
		515	after => 1,
		516	cb => sub { $result_ready->send },
		517	);
		518
		519	# this "blocks" (while handling events) till the callback
		520	# calls send
		521	$result_ready->recv;
		522
		523	Example: wait for a timer, but take advantage of the fact that condition
		524	variables are also code references.
		525
		526	my $done = AnyEvent->condvar;
		527	my $delay = AnyEvent->timer (after => 5, cb => $done);
		528	$done->recv;
		529
		530	Example: Imagine an API that returns a condvar and doesn't support
		531	callbacks. This is how you make a synchronous call, for example from the
		532	main program:
		533
		534	use AnyEvent::CouchDB;
		535
		536	...
		537
		538	my @info = $couchdb->info->recv;
		539
		540	And this is how you would just ste a callback to be called whenever the
		541	results are available:
		542
		543	$couchdb->info->cb (sub {
		544	my @info = $_[0]->recv;
		545	});
		546
		547	METHODS FOR PRODUCERS
		548	These methods should only be used by the producing side, i.e. the
		549	code/module that eventually sends the signal. Note that it is also the
		550	producer side which creates the condvar in most cases, but it isn't
		551	uncommon for the consumer to create it as well.
		552
		553	$cv->send (...)
		554	Flag the condition as ready - a running "->recv" and all further
		555	calls to "recv" will (eventually) return after this method has been
		556	called. If nobody is waiting the send will be remembered.
		557
		558	If a callback has been set on the condition variable, it is called
		559	immediately from within send.
		560
		561	Any arguments passed to the "send" call will be returned by all
		562	future "->recv" calls.
		563
		564	Condition variables are overloaded so one can call them directly (as
		565	a code reference). Calling them directly is the same as calling
		566	"send". Note, however, that many C-based event loops do not handle
		567	overloading, so as tempting as it may be, passing a condition
		568	variable instead of a callback does not work. Both the pure perl and
		569	EV loops support overloading, however, as well as all functions that
		570	use perl to invoke a callback (as in AnyEvent::Socket and
		571	AnyEvent::DNS for example).
		572
		573	$cv->croak ($error)
		574	Similar to send, but causes all call's to "->recv" to invoke
		575	"Carp::croak" with the given error message/object/scalar.
		576
		577	This can be used to signal any errors to the condition variable
		578	user/consumer.
		579
		580	$cv->begin ([group callback])
		581	$cv->end
		582	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		583
		584	These two methods can be used to combine many transactions/events
		585	into one. For example, a function that pings many hosts in parallel
		586	might want to use a condition variable for the whole process.
		587
		588	Every call to "->begin" will increment a counter, and every call to
		589	"->end" will decrement it. If the counter reaches 0 in "->end", the
		590	(last) callback passed to "begin" will be executed. That callback is
		591	supposed to call "->send", but that is not required. If no
		592	callback was set, "send" will be called without any arguments.
		593
		594	Let's clarify this with the ping example:
		595
		596	my $cv = AnyEvent->condvar;
		597
		598	my %result;
		599	$cv->begin (sub { $cv->send (\%result) });
		600
		601	for my $host (@list_of_hosts) {
		602	$cv->begin;
		603	ping_host_then_call_callback $host, sub {
		604	$result{$host} = ...;
		605	$cv->end;
		606	};
		607	}
		608
		609	$cv->end;
		610
		611	This code fragment supposedly pings a number of hosts and calls
		612	"send" after results for all then have have been gathered - in any
		613	order. To achieve this, the code issues a call to "begin" when it
		614	starts each ping request and calls "end" when it has received some
		615	result for it. Since "begin" and "end" only maintain a counter, the
		616	order in which results arrive is not relevant.
		617
		618	There is an additional bracketing call to "begin" and "end" outside
		619	the loop, which serves two important purposes: first, it sets the
		620	callback to be called once the counter reaches 0, and second, it
		621	ensures that "send" is called even when "no" hosts are being pinged
		622	(the loop doesn't execute once).
		623
		624	This is the general pattern when you "fan out" into multiple
		625	subrequests: use an outer "begin"/"end" pair to set the callback and
		626	ensure "end" is called at least once, and then, for each subrequest
		627	you start, call "begin" and for each subrequest you finish, call
		628	"end".
		629
		630	METHODS FOR CONSUMERS
		631	These methods should only be used by the consuming side, i.e. the code
		632	awaits the condition.
		633
		634	$cv->recv
283	Wait (blocking if necessary) until the "->broadcast" method has been	635	Wait (blocking if necessary) until the "->send" or "->croak" methods
284	called on c<$cv>, while servicing other watchers normally.	636	have been called on c<$cv>, while servicing other watchers normally.
285		637
286	You can only wait once on a condition - additional calls will return	638	You can only wait once on a condition - additional calls are valid
287	immediately.	639	but will return immediately.
		640
		641	If an error condition has been set by calling "->croak", then this
		642	function will call "croak".
		643
		644	In list context, all parameters passed to "send" will be returned,
		645	in scalar context only the first one will be returned.
288		646
289	Not all event models support a blocking wait - some die in that case	647	Not all event models support a blocking wait - some die in that case
290	(programs might want to do that to stay interactive), so *if you are	648	(programs might want to do that to stay interactive), so *if you are
291	using this from a module, never require a blocking wait*, but let	649	using this from a module, never require a blocking wait*, but let
292	the caller decide whether the call will block or not (for example,	650	the caller decide whether the call will block or not (for example,
293	by coupling condition variables with some kind of request results	651	by coupling condition variables with some kind of request results
294	and supporting callbacks so the caller knows that getting the result	652	and supporting callbacks so the caller knows that getting the result
295	will not block, while still suppporting blocking waits if the caller	653	will not block, while still supporting blocking waits if the caller
296	so desires).	654	so desires).
297		655
298	Another reason never to "->wait" in a module is that you cannot	656	Another reason never to "->recv" in a module is that you cannot
299	sensibly have two "->wait"'s in parallel, as that would require	657	sensibly have two "->recv"'s in parallel, as that would require
300	multiple interpreters or coroutines/threads, none of which	658	multiple interpreters or coroutines/threads, none of which
301	"AnyEvent" can supply (the coroutine-aware backends	659	"AnyEvent" can supply.
302	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
303	support concurrent "->wait"'s from different coroutines, however).
304		660
305	$cv->broadcast	661	The Coro module, however, can and does supply coroutines and, in
306	Flag the condition as ready - a running "->wait" and all further	662	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
307	calls to "wait" will (eventually) return after this method has been	663	versions and also integrates coroutines into AnyEvent, making
308	called. If nobody is waiting the broadcast will be remembered..	664	blocking "->recv" calls perfectly safe as long as they are done from
		665	another coroutine (one that doesn't run the event loop).
309		666
310	Example:	667	You can ensure that "-recv" never blocks by setting a callback and
		668	only calling "->recv" from within that callback (or at a later
		669	time). This will work even when the event loop does not support
		670	blocking waits otherwise.
311		671
312	# wait till the result is ready	672	$bool = $cv->ready
313	my $result_ready = AnyEvent->condvar;	673	Returns true when the condition is "true", i.e. whether "send" or
		674	"croak" have been called.
314		675
315	# do something such as adding a timer	676	$cb = $cv->cb ($cb->($cv))
316	# or socket watcher the calls $result_ready->broadcast	677	This is a mutator function that returns the callback set and
317	# when the "result" is ready.	678	optionally replaces it before doing so.
318	# in this case, we simply use a timer:
319	my $w = AnyEvent->timer (
320	after => 1,
321	cb => sub { $result_ready->broadcast },
322	);
323		679
324	# this "blocks" (while handling events) till the watcher	680	The callback will be called when the condition becomes "true", i.e.
325	# calls broadcast	681	when "send" or "croak" are called, with the only argument being the
326	$result_ready->wait;	682	condition variable itself. Calling "recv" inside the callback or at
		683	any later time is guaranteed not to block.
327		684
328	GLOBAL VARIABLES AND FUNCTIONS	685	GLOBAL VARIABLES AND FUNCTIONS
329	$AnyEvent::MODEL	686	$AnyEvent::MODEL
330	Contains "undef" until the first watcher is being created. Then it	687	Contains "undef" until the first watcher is being created. Then it
331	contains the event model that is being used, which is the name of	688	contains the event model that is being used, which is the name of
…		…
333	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	690	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
334	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	691	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
335		692
336	The known classes so far are:	693	The known classes so far are:
337		694
338	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
339	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
340	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	695	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
341	AnyEvent::Impl::Event based on Event, second best choice.	696	AnyEvent::Impl::Event based on Event, second best choice.
		697	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
342	AnyEvent::Impl::Glib based on Glib, third-best choice.	698	AnyEvent::Impl::Glib based on Glib, third-best choice.
343	AnyEvent::Impl::Tk based on Tk, very bad choice.	699	AnyEvent::Impl::Tk based on Tk, very bad choice.
344	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
345	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).	700	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
346	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	701	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		702	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		703
		704	# warning, support for IO::Async is only partial, as it is too broken
		705	# and limited toe ven support the AnyEvent API. See AnyEvent::Impl::Async.
		706	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed (see its docs).
		707
		708	There is no support for WxWidgets, as WxWidgets has no support for
		709	watching file handles. However, you can use WxWidgets through the
		710	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		711	second, which was considered to be too horrible to even consider for
		712	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
		713	using it's adaptor.
		714
		715	AnyEvent knows about Prima and Wx and will try to use POE when
		716	autodetecting them.
347		717
348	AnyEvent::detect	718	AnyEvent::detect
349	Returns $AnyEvent::MODEL, forcing autodetection of the event model	719	Returns $AnyEvent::MODEL, forcing autodetection of the event model
350	if necessary. You should only call this function right before you	720	if necessary. You should only call this function right before you
351	would have created an AnyEvent watcher anyway, that is, as late as	721	would have created an AnyEvent watcher anyway, that is, as late as
352	possible at runtime.	722	possible at runtime.
353		723
		724	$guard = AnyEvent::post_detect { BLOCK }
		725	Arranges for the code block to be executed as soon as the event
		726	model is autodetected (or immediately if this has already happened).
		727
		728	If called in scalar or list context, then it creates and returns an
		729	object that automatically removes the callback again when it is
		730	destroyed. See Coro::BDB for a case where this is useful.
		731
		732	@AnyEvent::post_detect
		733	If there are any code references in this array (you can "push" to it
		734	before or after loading AnyEvent), then they will called directly
		735	after the event loop has been chosen.
		736
		737	You should check $AnyEvent::MODEL before adding to this array,
		738	though: if it contains a true value then the event loop has already
		739	been detected, and the array will be ignored.
		740
		741	Best use "AnyEvent::post_detect { BLOCK }" instead.
		742
354	WHAT TO DO IN A MODULE	743	WHAT TO DO IN A MODULE
355	As a module author, you should "use AnyEvent" and call AnyEvent methods	744	As a module author, you should "use AnyEvent" and call AnyEvent methods
356	freely, but you should not load a specific event module or rely on it.	745	freely, but you should not load a specific event module or rely on it.
357		746
358	Be careful when you create watchers in the module body - AnyEvent will	747	Be careful when you create watchers in the module body - AnyEvent will
359	decide which event module to use as soon as the first method is called,	748	decide which event module to use as soon as the first method is called,
360	so by calling AnyEvent in your module body you force the user of your	749	so by calling AnyEvent in your module body you force the user of your
361	module to load the event module first.	750	module to load the event module first.
362		751
363	Never call "->wait" on a condition variable unless you know that the	752	Never call "->recv" on a condition variable unless you know that the
364	"->broadcast" method has been called on it already. This is because it	753	"->send" method has been called on it already. This is because it will
365	will stall the whole program, and the whole point of using events is to	754	stall the whole program, and the whole point of using events is to stay
366	stay interactive.	755	interactive.
367		756
368	It is fine, however, to call "->wait" when the user of your module	757	It is fine, however, to call "->recv" when the user of your module
369	requests it (i.e. if you create a http request object ad have a method	758	requests it (i.e. if you create a http request object ad have a method
370	called "results" that returns the results, it should call "->wait"	759	called "results" that returns the results, it should call "->recv"
371	freely, as the user of your module knows what she is doing. always).	760	freely, as the user of your module knows what she is doing. always).
372		761
373	WHAT TO DO IN THE MAIN PROGRAM	762	WHAT TO DO IN THE MAIN PROGRAM
374	There will always be a single main program - the only place that should	763	There will always be a single main program - the only place that should
375	dictate which event model to use.	764	dictate which event model to use.
…		…
377	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	766	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
378	do anything special (it does not need to be event-based) and let	767	do anything special (it does not need to be event-based) and let
379	AnyEvent decide which implementation to chose if some module relies on	768	AnyEvent decide which implementation to chose if some module relies on
380	it.	769	it.
381		770
382	If the main program relies on a specific event model. For example, in	771	If the main program relies on a specific event model - for example, in
383	Gtk2 programs you have to rely on the Glib module. You should load the	772	Gtk2 programs you have to rely on the Glib module - you should load the
384	event module before loading AnyEvent or any module that uses it:	773	event module before loading AnyEvent or any module that uses it:
385	generally speaking, you should load it as early as possible. The reason	774	generally speaking, you should load it as early as possible. The reason
386	is that modules might create watchers when they are loaded, and AnyEvent	775	is that modules might create watchers when they are loaded, and AnyEvent
387	will decide on the event model to use as soon as it creates watchers,	776	will decide on the event model to use as soon as it creates watchers,
388	and it might chose the wrong one unless you load the correct one	777	and it might chose the wrong one unless you load the correct one
389	yourself.	778	yourself.
390		779
391	You can chose to use a rather inefficient pure-perl implementation by	780	You can chose to use a pure-perl implementation by loading the
392	loading the "AnyEvent::Impl::Perl" module, which gives you similar	781	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
393	behaviour everywhere, but letting AnyEvent chose is generally better.	782	everywhere, but letting AnyEvent chose the model is generally better.
		783
		784	MAINLOOP EMULATION
		785	Sometimes (often for short test scripts, or even standalone programs who
		786	only want to use AnyEvent), you do not want to run a specific event
		787	loop.
		788
		789	In that case, you can use a condition variable like this:
		790
		791	AnyEvent->condvar->recv;
		792
		793	This has the effect of entering the event loop and looping forever.
		794
		795	Note that usually your program has some exit condition, in which case it
		796	is better to use the "traditional" approach of storing a condition
		797	variable somewhere, waiting for it, and sending it when the program
		798	should exit cleanly.
		799
		800	OTHER MODULES
		801	The following is a non-exhaustive list of additional modules that use
		802	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		803	in the same program. Some of the modules come with AnyEvent, some are
		804	available via CPAN.
		805
		806	AnyEvent::Util
		807	Contains various utility functions that replace often-used but
		808	blocking functions such as "inet_aton" by event-/callback-based
		809	versions.
		810
		811	AnyEvent::Socket
		812	Provides various utility functions for (internet protocol) sockets,
		813	addresses and name resolution. Also functions to create non-blocking
		814	tcp connections or tcp servers, with IPv6 and SRV record support and
		815	more.
		816
		817	AnyEvent::Handle
		818	Provide read and write buffers, manages watchers for reads and
		819	writes, supports raw and formatted I/O, I/O queued and fully
		820	transparent and non-blocking SSL/TLS.
		821
		822	AnyEvent::DNS
		823	Provides rich asynchronous DNS resolver capabilities.
		824
		825	AnyEvent::HTTP
		826	A simple-to-use HTTP library that is capable of making a lot of
		827	concurrent HTTP requests.
		828
		829	AnyEvent::HTTPD
		830	Provides a simple web application server framework.
		831
		832	AnyEvent::FastPing
		833	The fastest ping in the west.
		834
		835	AnyEvent::DBI
		836	Executes DBI requests asynchronously in a proxy process.
		837
		838	AnyEvent::AIO
		839	Truly asynchronous I/O, should be in the toolbox of every event
		840	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		841	together.
		842
		843	AnyEvent::BDB
		844	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		845	fuses BDB and AnyEvent together.
		846
		847	AnyEvent::GPSD
		848	A non-blocking interface to gpsd, a daemon delivering GPS
		849	information.
		850
		851	AnyEvent::IGS
		852	A non-blocking interface to the Internet Go Server protocol (used by
		853	App::IGS).
		854
		855	AnyEvent::IRC
		856	AnyEvent based IRC client module family (replacing the older
		857	Net::IRC3).
		858
		859	Net::XMPP2
		860	AnyEvent based XMPP (Jabber protocol) module family.
		861
		862	Net::FCP
		863	AnyEvent-based implementation of the Freenet Client Protocol,
		864	birthplace of AnyEvent.
		865
		866	Event::ExecFlow
		867	High level API for event-based execution flow control.
		868
		869	Coro
		870	Has special support for AnyEvent via Coro::AnyEvent.
		871
		872	IO::Lambda
		873	The lambda approach to I/O - don't ask, look there. Can use
		874	AnyEvent.
		875
		876	ERROR AND EXCEPTION HANDLING
		877	In general, AnyEvent does not do any error handling - it relies on the
		878	caller to do that if required. The AnyEvent::Strict module (see also the
		879	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		880	checking of all AnyEvent methods, however, which is highly useful during
		881	development.
		882
		883	As for exception handling (i.e. runtime errors and exceptions thrown
		884	while executing a callback), this is not only highly event-loop
		885	specific, but also not in any way wrapped by this module, as this is the
		886	job of the main program.
		887
		888	The pure perl event loop simply re-throws the exception (usually within
		889	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		890	Glib uses "install_exception_handler" and so on.
		891
		892	ENVIRONMENT VARIABLES
		893	The following environment variables are used by this module or its
		894	submodules.
		895
		896	Note that AnyEvent will remove all environment variables starting with
		897	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		898	enabled.
		899
		900	"PERL_ANYEVENT_VERBOSE"
		901	By default, AnyEvent will be completely silent except in fatal
		902	conditions. You can set this environment variable to make AnyEvent
		903	more talkative.
		904
		905	When set to 1 or higher, causes AnyEvent to warn about unexpected
		906	conditions, such as not being able to load the event model specified
		907	by "PERL_ANYEVENT_MODEL".
		908
		909	When set to 2 or higher, cause AnyEvent to report to STDERR which
		910	event model it chooses.
		911
		912	"PERL_ANYEVENT_STRICT"
		913	AnyEvent does not do much argument checking by default, as thorough
		914	argument checking is very costly. Setting this variable to a true
		915	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		916	thoroughly check the arguments passed to most method calls. If it
		917	finds any problems, it will croak.
		918
		919	In other words, enables "strict" mode.
		920
		921	Unlike "use strict", it is definitely recommended to keep it off in
		922	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment
		923	while developing programs can be very useful, however.
		924
		925	"PERL_ANYEVENT_MODEL"
		926	This can be used to specify the event model to be used by AnyEvent,
		927	before auto detection and -probing kicks in. It must be a string
		928	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		929	gets prepended and the resulting module name is loaded and if the
		930	load was successful, used as event model. If it fails to load
		931	AnyEvent will proceed with auto detection and -probing.
		932
		933	This functionality might change in future versions.
		934
		935	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		936	could start your program like this:
		937
		938	PERL_ANYEVENT_MODEL=Perl perl ...
		939
		940	"PERL_ANYEVENT_PROTOCOLS"
		941	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		942	preferences for IPv4 or IPv6. The default is unspecified (and might
		943	change, or be the result of auto probing).
		944
		945	Must be set to a comma-separated list of protocols or address
		946	families, current supported: "ipv4" and "ipv6". Only protocols
		947	mentioned will be used, and preference will be given to protocols
		948	mentioned earlier in the list.
		949
		950	This variable can effectively be used for denial-of-service attacks
		951	against local programs (e.g. when setuid), although the impact is
		952	likely small, as the program has to handle conenction and other
		953	failures anyways.
		954
		955	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		956	IPv6, but support both and try to use both.
		957	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		958	resolve or contact IPv6 addresses.
		959	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		960	prefer IPv6 over IPv4.
		961
		962	"PERL_ANYEVENT_EDNS0"
		963	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		964	for DNS. This extension is generally useful to reduce DNS traffic,
		965	but some (broken) firewalls drop such DNS packets, which is why it
		966	is off by default.
		967
		968	Setting this variable to 1 will cause AnyEvent::DNS to announce
		969	EDNS0 in its DNS requests.
		970
		971	"PERL_ANYEVENT_MAX_FORKS"
		972	The maximum number of child processes that
		973	"AnyEvent::Util::fork_call" will create in parallel.
394		974
395	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	975	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
396	This is an advanced topic that you do not normally need to use AnyEvent	976	This is an advanced topic that you do not normally need to use AnyEvent
397	in a module. This section is only of use to event loop authors who want	977	in a module. This section is only of use to event loop authors who want
398	to provide AnyEvent compatibility.	978	to provide AnyEvent compatibility.
…		…
433	rxvt-unicode also cheats a bit by not providing blocking access to	1013	rxvt-unicode also cheats a bit by not providing blocking access to
434	condition variables: code blocking while waiting for a condition will	1014	condition variables: code blocking while waiting for a condition will
435	"die". This still works with most modules/usages, and blocking calls	1015	"die". This still works with most modules/usages, and blocking calls
436	must not be done in an interactive application, so it makes sense.	1016	must not be done in an interactive application, so it makes sense.
437		1017
438	ENVIRONMENT VARIABLES
439	The following environment variables are used by this module:
440
441	"PERL_ANYEVENT_VERBOSE"
442	When set to 2 or higher, cause AnyEvent to report to STDERR which
443	event model it chooses.
444
445	"PERL_ANYEVENT_MODEL"
446	This can be used to specify the event model to be used by AnyEvent,
447	before autodetection and -probing kicks in. It must be a string
448	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
449	gets prepended and the resulting module name is loaded and if the
450	load was successful, used as event model. If it fails to load
451	AnyEvent will proceed with autodetection and -probing.
452
453	This functionality might change in future versions.
454
455	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
456	could start your program like this:
457
458	PERL_ANYEVENT_MODEL=Perl perl ...
459
460	EXAMPLE PROGRAM	1018	EXAMPLE PROGRAM
461	The following program uses an IO watcher to read data from STDIN, a	1019	The following program uses an I/O watcher to read data from STDIN, a
462	timer to display a message once per second, and a condition variable to	1020	timer to display a message once per second, and a condition variable to
463	quit the program when the user enters quit:	1021	quit the program when the user enters quit:
464		1022
465	use AnyEvent;	1023	use AnyEvent;
466		1024
…		…
471	poll => 'r',	1029	poll => 'r',
472	cb => sub {	1030	cb => sub {
473	warn "io event <$_[0]>\n"; # will always output <r>	1031	warn "io event <$_[0]>\n"; # will always output <r>
474	chomp (my $input = <STDIN>); # read a line	1032	chomp (my $input = <STDIN>); # read a line
475	warn "read: $input\n"; # output what has been read	1033	warn "read: $input\n"; # output what has been read
476	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1034	$cv->send if $input =~ /^q/i; # quit program if /^q/i
477	},	1035	},
478	);	1036	);
479		1037
480	my $time_watcher; # can only be used once	1038	my $time_watcher; # can only be used once
481		1039
…		…
486	});	1044	});
487	}	1045	}
488		1046
489	new_timer; # create first timer	1047	new_timer; # create first timer
490		1048
491	$cv->wait; # wait until user enters /^q/i	1049	$cv->recv; # wait until user enters /^q/i
492		1050
493	REAL-WORLD EXAMPLE	1051	REAL-WORLD EXAMPLE
494	Consider the Net::FCP module. It features (among others) the following	1052	Consider the Net::FCP module. It features (among others) the following
495	API calls, which are to freenet what HTTP GET requests are to http:	1053	API calls, which are to freenet what HTTP GET requests are to http:
496		1054
…		…
545	syswrite $txn->{fh}, $txn->{request}	1103	syswrite $txn->{fh}, $txn->{request}
546	or die "connection or write error";	1104	or die "connection or write error";
547	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1105	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
548		1106
549	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1107	Again, "fh_ready_r" waits till all data has arrived, and then stores the
550	result and signals any possible waiters that the request ahs finished:	1108	result and signals any possible waiters that the request has finished:
551		1109
552	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1110	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
553		1111
554	if (end-of-file or data complete) {	1112	if (end-of-file or data complete) {
555	$txn->{result} = $txn->{buf};	1113	$txn->{result} = $txn->{buf};
556	$txn->{finished}->broadcast;	1114	$txn->{finished}->send;
557	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1115	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
558	}	1116	}
559		1117
560	The "result" method, finally, just waits for the finished signal (if the	1118	The "result" method, finally, just waits for the finished signal (if the
561	request was already finished, it doesn't wait, of course, and returns	1119	request was already finished, it doesn't wait, of course, and returns
562	the data:	1120	the data:
563		1121
564	$txn->{finished}->wait;	1122	$txn->{finished}->recv;
565	return $txn->{result};	1123	return $txn->{result};
566		1124
567	The actual code goes further and collects all errors ("die"s,	1125	The actual code goes further and collects all errors ("die"s,
568	exceptions) that occured during request processing. The "result" method	1126	exceptions) that occurred during request processing. The "result" method
569	detects whether an exception as thrown (it is stored inside the $txn	1127	detects whether an exception as thrown (it is stored inside the $txn
570	object) and just throws the exception, which means connection errors and	1128	object) and just throws the exception, which means connection errors and
571	other problems get reported tot he code that tries to use the result,	1129	other problems get reported tot he code that tries to use the result,
572	not in a random callback.	1130	not in a random callback.
573		1131
…		…
604		1162
605	my $quit = AnyEvent->condvar;	1163	my $quit = AnyEvent->condvar;
606		1164
607	$fcp->txn_client_get ($url)->cb (sub {	1165	$fcp->txn_client_get ($url)->cb (sub {
608	...	1166	...
609	$quit->broadcast;	1167	$quit->send;
610	});	1168	});
611		1169
612	$quit->wait;	1170	$quit->recv;
		1171
		1172	BENCHMARKS
		1173	To give you an idea of the performance and overheads that AnyEvent adds
		1174	over the event loops themselves and to give you an impression of the
		1175	speed of various event loops I prepared some benchmarks.
		1176
		1177	BENCHMARKING ANYEVENT OVERHEAD
		1178	Here is a benchmark of various supported event models used natively and
		1179	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1180	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1181	which it is), lets them fire exactly once and destroys them again.
		1182
		1183	Source code for this benchmark is found as eg/bench in the AnyEvent
		1184	distribution.
		1185
		1186	Explanation of the columns
		1187	watcher is the number of event watchers created/destroyed. Since
		1188	different event models feature vastly different performances, each event
		1189	loop was given a number of watchers so that overall runtime is
		1190	acceptable and similar between tested event loop (and keep them from
		1191	crashing): Glib would probably take thousands of years if asked to
		1192	process the same number of watchers as EV in this benchmark.
		1193
		1194	bytes is the number of bytes (as measured by the resident set size,
		1195	RSS) consumed by each watcher. This method of measuring captures both C
		1196	and Perl-based overheads.
		1197
		1198	create is the time, in microseconds (millionths of seconds), that it
		1199	takes to create a single watcher. The callback is a closure shared
		1200	between all watchers, to avoid adding memory overhead. That means
		1201	closure creation and memory usage is not included in the figures.
		1202
		1203	invoke is the time, in microseconds, used to invoke a simple callback.
		1204	The callback simply counts down a Perl variable and after it was invoked
		1205	"watcher" times, it would "->send" a condvar once to signal the end of
		1206	this phase.
		1207
		1208	destroy is the time, in microseconds, that it takes to destroy a
		1209	single watcher.
		1210
		1211	Results
		1212	name watchers bytes create invoke destroy comment
		1213	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1214	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1215	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1216	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1217	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1218	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1219	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1220	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
		1221	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1222	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1223	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1224	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1225
		1226	Discussion
		1227	The benchmark does not measure scalability of the event loop very
		1228	well. For example, a select-based event loop (such as the pure perl one)
		1229	can never compete with an event loop that uses epoll when the number of
		1230	file descriptors grows high. In this benchmark, all events become ready
		1231	at the same time, so select/poll-based implementations get an unnatural
		1232	speed boost.
		1233
		1234	Also, note that the number of watchers usually has a nonlinear effect on
		1235	overall speed, that is, creating twice as many watchers doesn't take
		1236	twice the time - usually it takes longer. This puts event loops tested
		1237	with a higher number of watchers at a disadvantage.
		1238
		1239	To put the range of results into perspective, consider that on the
		1240	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1241	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
		1242	CPU cycles with POE.
		1243
		1244	"EV" is the sole leader regarding speed and memory use, which are both
		1245	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1246	far less memory than any other event loop and is still faster than Event
		1247	natively.
		1248
		1249	The pure perl implementation is hit in a few sweet spots (both the
		1250	constant timeout and the use of a single fd hit optimisations in the
		1251	perl interpreter and the backend itself). Nevertheless this shows that
		1252	it adds very little overhead in itself. Like any select-based backend
		1253	its performance becomes really bad with lots of file descriptors (and
		1254	few of them active), of course, but this was not subject of this
		1255	benchmark.
		1256
		1257	The "Event" module has a relatively high setup and callback invocation
		1258	cost, but overall scores in on the third place.
		1259
		1260	"IO::Async" performs admirably well, about on par with "Event", even
		1261	when using its pure perl backend.
		1262
		1263	"Glib"'s memory usage is quite a bit higher, but it features a faster
		1264	callback invocation and overall ends up in the same class as "Event".
		1265	However, Glib scales extremely badly, doubling the number of watchers
		1266	increases the processing time by more than a factor of four, making it
		1267	completely unusable when using larger numbers of watchers (note that
		1268	only a single file descriptor was used in the benchmark, so
		1269	inefficiencies of "poll" do not account for this).
		1270
		1271	The "Tk" adaptor works relatively well. The fact that it crashes with
		1272	more than 2000 watchers is a big setback, however, as correctness takes
		1273	precedence over speed. Nevertheless, its performance is surprising, as
		1274	the file descriptor is dup()ed for each watcher. This shows that the
		1275	dup() employed by some adaptors is not a big performance issue (it does
		1276	incur a hidden memory cost inside the kernel which is not reflected in
		1277	the figures above).
		1278
		1279	"POE", regardless of underlying event loop (whether using its pure perl
		1280	select-based backend or the Event module, the POE-EV backend couldn't be
		1281	tested because it wasn't working) shows abysmal performance and memory
		1282	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
		1283	watchers, and 10 times as much memory as Event (the high memory
		1284	requirements are caused by requiring a session for each watcher).
		1285	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1286	pure perl implementation.
		1287
		1288	The design of the POE adaptor class in AnyEvent can not really account
		1289	for the performance issues, though, as session creation overhead is
		1290	small compared to execution of the state machine, which is coded pretty
		1291	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1292	using multiple sessions is not a good approach, especially regarding
		1293	memory usage, even the author of POE could not come up with a faster
		1294	design).
		1295
		1296	Summary
		1297	* Using EV through AnyEvent is faster than any other event loop (even
		1298	when used without AnyEvent), but most event loops have acceptable
		1299	performance with or without AnyEvent.
		1300
		1301	* The overhead AnyEvent adds is usually much smaller than the overhead
		1302	of the actual event loop, only with extremely fast event loops such
		1303	as EV adds AnyEvent significant overhead.
		1304
		1305	* You should avoid POE like the plague if you want performance or
		1306	reasonable memory usage.
		1307
		1308	BENCHMARKING THE LARGE SERVER CASE
		1309	This benchmark actually benchmarks the event loop itself. It works by
		1310	creating a number of "servers": each server consists of a socket pair, a
		1311	timeout watcher that gets reset on activity (but never fires), and an
		1312	I/O watcher waiting for input on one side of the socket. Each time the
		1313	socket watcher reads a byte it will write that byte to a random other
		1314	"server".
		1315
		1316	The effect is that there will be a lot of I/O watchers, only part of
		1317	which are active at any one point (so there is a constant number of
		1318	active fds for each loop iteration, but which fds these are is random).
		1319	The timeout is reset each time something is read because that reflects
		1320	how most timeouts work (and puts extra pressure on the event loops).
		1321
		1322	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
		1323	100 (1%) are active. This mirrors the activity of large servers with
		1324	many connections, most of which are idle at any one point in time.
		1325
		1326	Source code for this benchmark is found as eg/bench2 in the AnyEvent
		1327	distribution.
		1328
		1329	Explanation of the columns
		1330	sockets is the number of sockets, and twice the number of "servers"
		1331	(as each server has a read and write socket end).
		1332
		1333	create is the time it takes to create a socket pair (which is
		1334	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1335
		1336	request, the most important value, is the time it takes to handle a
		1337	single "request", that is, reading the token from the pipe and
		1338	forwarding it to another server. This includes deleting the old timeout
		1339	and creating a new one that moves the timeout into the future.
		1340
		1341	Results
		1342	name sockets create request
		1343	EV 20000 69.01 11.16
		1344	Perl 20000 73.32 35.87
		1345	IOAsync 20000 157.00 98.14 epoll
		1346	IOAsync 20000 159.31 616.06 poll
		1347	Event 20000 212.62 257.32
		1348	Glib 20000 651.16 1896.30
		1349	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1350
		1351	Discussion
		1352	This benchmark does measure scalability and overall performance of the
		1353	particular event loop.
		1354
		1355	EV is again fastest. Since it is using epoll on my system, the setup
		1356	time is relatively high, though.
		1357
		1358	Perl surprisingly comes second. It is much faster than the C-based event
		1359	loops Event and Glib.
		1360
		1361	IO::Async performs very well when using its epoll backend, and still
		1362	quite good compared to Glib when using its pure perl backend.
		1363
		1364	Event suffers from high setup time as well (look at its code and you
		1365	will understand why). Callback invocation also has a high overhead
		1366	compared to the "$_->() for .."-style loop that the Perl event loop
		1367	uses. Event uses select or poll in basically all documented
		1368	configurations.
		1369
		1370	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1371	clearly fails to perform with many filehandles or in busy servers.
		1372
		1373	POE is still completely out of the picture, taking over 1000 times as
		1374	long as EV, and over 100 times as long as the Perl implementation, even
		1375	though it uses a C-based event loop in this case.
		1376
		1377	Summary
		1378	* The pure perl implementation performs extremely well.
		1379
		1380	* Avoid Glib or POE in large projects where performance matters.
		1381
		1382	BENCHMARKING SMALL SERVERS
		1383	While event loops should scale (and select-based ones do not...) even to
		1384	large servers, most programs we (or I :) actually write have only a few
		1385	I/O watchers.
		1386
		1387	In this benchmark, I use the same benchmark program as in the large
		1388	server case, but it uses only eight "servers", of which three are active
		1389	at any one time. This should reflect performance for a small server
		1390	relatively well.
		1391
		1392	The columns are identical to the previous table.
		1393
		1394	Results
		1395	name sockets create request
		1396	EV 16 20.00 6.54
		1397	Perl 16 25.75 12.62
		1398	Event 16 81.27 35.86
		1399	Glib 16 32.63 15.48
		1400	POE 16 261.87 276.28 uses POE::Loop::Event
		1401
		1402	Discussion
		1403	The benchmark tries to test the performance of a typical small server.
		1404	While knowing how various event loops perform is interesting, keep in
		1405	mind that their overhead in this case is usually not as important, due
		1406	to the small absolute number of watchers (that is, you need efficiency
		1407	and speed most when you have lots of watchers, not when you only have a
		1408	few of them).
		1409
		1410	EV is again fastest.
		1411
		1412	Perl again comes second. It is noticeably faster than the C-based event
		1413	loops Event and Glib, although the difference is too small to really
		1414	matter.
		1415
		1416	POE also performs much better in this case, but is is still far behind
		1417	the others.
		1418
		1419	Summary
		1420	* C-based event loops perform very well with small number of watchers,
		1421	as the management overhead dominates.
		1422
		1423	THE IO::Lambda BENCHMARK
		1424	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1425	could be misinterpreted to make AnyEvent look bad. In fact, the
		1426	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1427	better (which shouldn't come as a surprise to anybody). As such, the
		1428	benchmark is fine, and mostly shows that the AnyEvent backend from
		1429	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1430	without the extra baggage? To explore this, I wrote the equivalent
		1431	benchmark for AnyEvent.
		1432
		1433	The benchmark itself creates an echo-server, and then, for 500 times,
		1434	connects to the echo server, sends a line, waits for the reply, and then
		1435	creates the next connection. This is a rather bad benchmark, as it
		1436	doesn't test the efficiency of the framework or much non-blocking I/O,
		1437	but it is a benchmark nevertheless.
		1438
		1439	name runtime
		1440	Lambda/select 0.330 sec
		1441	+ optimized 0.122 sec
		1442	Lambda/AnyEvent 0.327 sec
		1443	+ optimized 0.138 sec
		1444	Raw sockets/select 0.077 sec
		1445	POE/select, components 0.662 sec
		1446	POE/select, raw sockets 0.226 sec
		1447	POE/select, optimized 0.404 sec
		1448
		1449	AnyEvent/select/nb 0.085 sec
		1450	AnyEvent/EV/nb 0.068 sec
		1451	+state machine 0.134 sec
		1452
		1453	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1454	benchmarks actually make blocking connects and use 100% blocking I/O,
		1455	defeating the purpose of an event-based solution. All of the newly
		1456	written AnyEvent benchmarks use 100% non-blocking connects (using
		1457	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1458	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1459	connects generally require a lot more bookkeeping and event handling
		1460	than blocking connects (which involve a single syscall only).
		1461
		1462	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1463	offers similar expressive power as POE and IO::Lambda, using
		1464	conventional Perl syntax. This means that both the echo server and the
		1465	client are 100% non-blocking, further placing it at a disadvantage.
		1466
		1467	As you can see, the AnyEvent + EV combination even beats the
		1468	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1469	backend easily beats IO::Lambda and POE.
		1470
		1471	And even the 100% non-blocking version written using the high-level (and
		1472	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a
		1473	large margin, even though it does all of DNS, tcp-connect and socket I/O
		1474	in a non-blocking way.
		1475
		1476	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1477	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1478	part of the IO::lambda distribution and were used without any changes.
		1479
		1480	SIGNALS
		1481	AnyEvent currently installs handlers for these signals:
		1482
		1483	SIGCHLD
		1484	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1485	emulation for event loops that do not support them natively. Also,
		1486	some event loops install a similar handler.
		1487
		1488	If, when AnyEvent is loaded, SIGCHLD is set to IGNORE, then AnyEvent
		1489	will reset it to default, to avoid losing child exit statuses.
		1490
		1491	SIGPIPE
		1492	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1493	"undef" when AnyEvent gets loaded.
		1494
		1495	The rationale for this is that AnyEvent users usually do not really
		1496	depend on SIGPIPE delivery (which is purely an optimisation for
		1497	shell use, or badly-written programs), but "SIGPIPE" can cause
		1498	spurious and rare program exits as a lot of people do not expect
		1499	"SIGPIPE" when writing to some random socket.
		1500
		1501	The rationale for installing a no-op handler as opposed to ignoring
		1502	it is that this way, the handler will be restored to defaults on
		1503	exec.
		1504
		1505	Feel free to install your own handler, or reset it to defaults.
613		1506
614	FORK	1507	FORK
615	Most event libraries are not fork-safe. The ones who are usually are	1508	Most event libraries are not fork-safe. The ones who are usually are
616	because they are so inefficient. Only EV is fully fork-aware.	1509	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1510	Only EV is fully fork-aware.
617		1511
618	If you have to fork, you must either do so before creating your first	1512	If you have to fork, you must either do so before creating your first
619	watcher OR you must not use AnyEvent at all in the child.	1513	watcher OR you must not use AnyEvent at all in the child.
620		1514
621	SECURITY CONSIDERATIONS	1515	SECURITY CONSIDERATIONS
…		…
627	model than specified in the variable.	1521	model than specified in the variable.
628		1522
629	You can make AnyEvent completely ignore this variable by deleting it	1523	You can make AnyEvent completely ignore this variable by deleting it
630	before the first watcher gets created, e.g. with a "BEGIN" block:	1524	before the first watcher gets created, e.g. with a "BEGIN" block:
631		1525
632	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1526	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
633		1527
634	use AnyEvent;	1528	use AnyEvent;
		1529
		1530	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1531	be used to probe what backend is used and gain other information (which
		1532	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1533	and $ENV{PERL_ANYEVENT_STRICT}.
		1534
		1535	Note that AnyEvent will remove all environment variables starting with
		1536	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1537	enabled.
		1538
		1539	BUGS
		1540	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1541	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1542	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1543	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1544	not as pronounced).
635		1545
636	SEE ALSO	1546	SEE ALSO
637	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1547	Utility functions: AnyEvent::Util.
638	Glib::Event, Glib, Coro, Tk, Event::Lib, Qt.
639		1548
640	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1549	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
641	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1550	Event::Lib, Qt, POE.
642	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib,
643	AnyEvent::Impl::Qt.
644		1551
		1552	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
		1553	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
		1554	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
		1555
		1556	Non-blocking file handles, sockets, TCP clients and servers:
		1557	AnyEvent::Handle, AnyEvent::Socket.
		1558
		1559	Asynchronous DNS: AnyEvent::DNS.
		1560
		1561	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1562
645	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1563	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
646		1564
647	AUTHOR	1565	AUTHOR
648	Marc Lehmann <schmorp@schmorp.de>	1566	Marc Lehmann <schmorp@schmorp.de>
649	http://home.schmorp.de/	1567	http://home.schmorp.de/
650		1568

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Comparing AnyEvent/README (file contents): Revision 1.18 by root, Thu Apr 24 09:13:26 2008 UTC vs. Revision 1.41 by root, Fri Jun 26 06:33:17 2009 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.18 by root, Thu Apr 24 09:13:26 2008 UTC vs.
Revision 1.41 by root, Fri Jun 26 06:33:17 2009 UTC