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Revision 1.21 by root, Sat May 17 21:34:15 2008 UTC vs.
Revision 1.46 by root, Sat Jul 18 05:19:09 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, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
5	loops	5	event loops.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# file descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		12
		13	# one-shot or repeating timers
		14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		16
		17	print AnyEvent->now; # prints current event loop time
		18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		19
		20	# POSIX signal
		21	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		22
		23	# child process exit
		24	my $w = AnyEvent->child (pid => $pid, cb => sub {
		25	my ($pid, $status) = @_;
11	...	26	...
12	});	27	});
13		28
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	29	# called when event loop idle (if applicable)
15	...	30	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		31
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	32	my $w = AnyEvent->condvar; # stores whether a condition was flagged
19	$w->send; # wake up current and all future recv's	33	$w->send; # wake up current and all future recv's
20	$w->recv; # enters "main loop" till $condvar gets ->send	34	$w->recv; # enters "main loop" till $condvar gets ->send
		35	# use a condvar in callback mode:
		36	$w->cb (sub { $_[0]->recv });
		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
99	starts using it, all bets are off. Maybe you should tell their authors	127	starts using it, all bets are off. Maybe you should tell their authors
100	to use AnyEvent so their modules work together with others seamlessly...	128	to use AnyEvent so their modules work together with others seamlessly...
101		129
102	The pure-perl implementation of AnyEvent is called	130	The pure-perl implementation of AnyEvent is called
103	"AnyEvent::Impl::Perl". Like other event modules you can load it	131	"AnyEvent::Impl::Perl". Like other event modules you can load it
104	explicitly.	132	explicitly and enjoy the high availability of that event loop :)
105		133
106	WATCHERS	134	WATCHERS
107	AnyEvent has the central concept of a watcher, which is an object that	135	AnyEvent has the central concept of a watcher, which is an object that
108	stores relevant data for each kind of event you are waiting for, such as	136	stores relevant data for each kind of event you are waiting for, such as
109	the callback to call, the filehandle to watch, etc.	137	the callback to call, the file handle to watch, etc.
110		138
111	These watchers are normal Perl objects with normal Perl lifetime. After	139	These watchers are normal Perl objects with normal Perl lifetime. After
112	creating a watcher it will immediately "watch" for events and invoke the	140	creating a watcher it will immediately "watch" for events and invoke the
113	callback when the event occurs (of course, only when the event model is	141	callback when the event occurs (of course, only when the event model is
114	in control).	142	in control).
115		143
		144	Note that callbacks must not permanently change global variables
		145	potentially in use by the event loop (such as $_ or $[) and that
		146	callbacks must not "die". The former is good programming practise in
		147	Perl and the latter stems from the fact that exception handling differs
		148	widely between event loops.
		149
116	To disable the watcher you have to destroy it (e.g. by setting the	150	To disable the watcher you have to destroy it (e.g. by setting the
117	variable you store it in to "undef" or otherwise deleting all references	151	variable you store it in to "undef" or otherwise deleting all references
118	to it).	152	to it).
119		153
120	All watchers are created by calling a method on the "AnyEvent" class.	154	All watchers are created by calling a method on the "AnyEvent" class.
…		…
122	Many watchers either are used with "recursion" (repeating timers for	156	Many watchers either are used with "recursion" (repeating timers for
123	example), or need to refer to their watcher object in other ways.	157	example), or need to refer to their watcher object in other ways.
124		158
125	An any way to achieve that is this pattern:	159	An any way to achieve that is this pattern:
126		160
127	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	161	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
128	# you can use $w here, for example to undef it	162	# you can use $w here, for example to undef it
129	undef $w;	163	undef $w;
130	});	164	});
131		165
132	Note that "my $w; $w =" combination. This is necessary because in Perl,	166	Note that "my $w; $w =" combination. This is necessary because in Perl,
133	my variables are only visible after the statement in which they are	167	my variables are only visible after the statement in which they are
134	declared.	168	declared.
135		169
136	I/O WATCHERS	170	I/O WATCHERS
137	You can create an I/O watcher by calling the "AnyEvent->io" method with	171	You can create an I/O watcher by calling the "AnyEvent->io" method with
138	the following mandatory key-value pairs as arguments:	172	the following mandatory key-value pairs as arguments:
139		173
140	"fh" the Perl file handle (not file descriptor) to watch for events.	174	"fh" is the Perl file handle (or a naked file descriptor) to watch for
		175	events (AnyEvent might or might not keep a reference to this file
		176	handle). Note that only file handles pointing to things for which
		177	non-blocking operation makes sense are allowed. This includes sockets,
		178	most character devices, pipes, fifos and so on, but not for example
		179	files or block devices.
		180
141	"poll" must be a string that is either "r" or "w", which creates a	181	"poll" must be a string that is either "r" or "w", which creates a
142	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	182	watcher waiting for "r"eadable or "w"ritable events, respectively.
		183
143	is the callback to invoke each time the file handle becomes ready.	184	"cb" is the callback to invoke each time the file handle becomes ready.
144		185
145	Although the callback might get passed parameters, their value and	186	Although the callback might get passed parameters, their value and
146	presence is undefined and you cannot rely on them. Portable AnyEvent	187	presence is undefined and you cannot rely on them. Portable AnyEvent
147	callbacks cannot use arguments passed to I/O watcher callbacks.	188	callbacks cannot use arguments passed to I/O watcher callbacks.
148		189
…		…
152		193
153	Some event loops issue spurious readyness notifications, so you should	194	Some event loops issue spurious readyness notifications, so you should
154	always use non-blocking calls when reading/writing from/to your file	195	always use non-blocking calls when reading/writing from/to your file
155	handles.	196	handles.
156		197
157	Example:
158
159	# wait for readability of STDIN, then read a line and disable the watcher	198	Example: wait for readability of STDIN, then read a line and disable the
		199	watcher.
		200
160	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	201	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
161	chomp (my $input = <STDIN>);	202	chomp (my $input = <STDIN>);
162	warn "read: $input\n";	203	warn "read: $input\n";
163	undef $w;	204	undef $w;
164	});	205	});
…		…
173		214
174	Although the callback might get passed parameters, their value and	215	Although the callback might get passed parameters, their value and
175	presence is undefined and you cannot rely on them. Portable AnyEvent	216	presence is undefined and you cannot rely on them. Portable AnyEvent
176	callbacks cannot use arguments passed to time watcher callbacks.	217	callbacks cannot use arguments passed to time watcher callbacks.
177		218
178	The timer callback will be invoked at most once: if you want a repeating	219	The callback will normally be invoked once only. If you specify another
179	timer you have to create a new watcher (this is a limitation by both Tk	220	parameter, "interval", as a strictly positive number (> 0), then the
180	and Glib).	221	callback will be invoked regularly at that interval (in fractional
		222	seconds) after the first invocation. If "interval" is specified with a
		223	false value, then it is treated as if it were missing.
181		224
182	Example:	225	The callback will be rescheduled before invoking the callback, but no
		226	attempt is done to avoid timer drift in most backends, so the interval
		227	is only approximate.
183		228
184	# fire an event after 7.7 seconds	229	Example: fire an event after 7.7 seconds.
		230
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	231	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	232	warn "timeout\n";
187	});	233	});
188		234
189	# to cancel the timer:	235	# to cancel the timer:
190	undef $w;	236	undef $w;
191		237
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	238	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		239
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	240	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		241	warn "timeout\n";
200	};	242	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		243
205	TIMING ISSUES	244	TIMING ISSUES
206	There are two ways to handle timers: based on real time (relative, "fire	245	There are two ways to handle timers: based on real time (relative, "fire
207	in 10 seconds") and based on wallclock time (absolute, "fire at 12	246	in 10 seconds") and based on wallclock time (absolute, "fire at 12
208	o'clock").	247	o'clock").
…		…
220	on wallclock time) timers.	259	on wallclock time) timers.
221		260
222	AnyEvent always prefers relative timers, if available, matching the	261	AnyEvent always prefers relative timers, if available, matching the
223	AnyEvent API.	262	AnyEvent API.
224		263
		264	AnyEvent has two additional methods that return the "current time":
		265
		266	AnyEvent->time
		267	This returns the "current wallclock time" as a fractional number of
		268	seconds since the Epoch (the same thing as "time" or
		269	"Time::HiRes::time" return, and the result is guaranteed to be
		270	compatible with those).
		271
		272	It progresses independently of any event loop processing, i.e. each
		273	call will check the system clock, which usually gets updated
		274	frequently.
		275
		276	AnyEvent->now
		277	This also returns the "current wallclock time", but unlike "time",
		278	above, this value might change only once per event loop iteration,
		279	depending on the event loop (most return the same time as "time",
		280	above). This is the time that AnyEvent's timers get scheduled
		281	against.
		282
		283	*In almost all cases (in all cases if you don't care), this is the
		284	function to call when you want to know the current time.*
		285
		286	This function is also often faster then "AnyEvent->time", and thus
		287	the preferred method if you want some timestamp (for example,
		288	AnyEvent::Handle uses this to update it's activity timeouts).
		289
		290	The rest of this section is only of relevance if you try to be very
		291	exact with your timing, you can skip it without bad conscience.
		292
		293	For a practical example of when these times differ, consider
		294	Event::Lib and EV and the following set-up:
		295
		296	The event loop is running and has just invoked one of your callback
		297	at time=500 (assume no other callbacks delay processing). In your
		298	callback, you wait a second by executing "sleep 1" (blocking the
		299	process for a second) and then (at time=501) you create a relative
		300	timer that fires after three seconds.
		301
		302	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		303	return 501, because that is the current time, and the timer will be
		304	scheduled to fire at time=504 (501 + 3).
		305
		306	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		307	but "AnyEvent->now" returns 500, as that is the time the last event
		308	processing phase started. With EV, your timer gets scheduled to run
		309	at time=503 (500 + 3).
		310
		311	In one sense, Event::Lib is more exact, as it uses the current time
		312	regardless of any delays introduced by event processing. However,
		313	most callbacks do not expect large delays in processing, so this
		314	causes a higher drift (and a lot more system calls to get the
		315	current time).
		316
		317	In another sense, EV is more exact, as your timer will be scheduled
		318	at the same time, regardless of how long event processing actually
		319	took.
		320
		321	In either case, if you care (and in most cases, you don't), then you
		322	can get whatever behaviour you want with any event loop, by taking
		323	the difference between "AnyEvent->time" and "AnyEvent->now" into
		324	account.
		325
		326	AnyEvent->now_update
		327	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		328	current time for each loop iteration (see the discussion of
		329	AnyEvent->now, above).
		330
		331	When a callback runs for a long time (or when the process sleeps),
		332	then this "current" time will differ substantially from the real
		333	time, which might affect timers and time-outs.
		334
		335	When this is the case, you can call this method, which will update
		336	the event loop's idea of "current time".
		337
		338	Note that updating the time might cause some events to be handled.
		339
225	SIGNAL WATCHERS	340	SIGNAL WATCHERS
226	You can watch for signals using a signal watcher, "signal" is the signal	341	You can watch for signals using a signal watcher, "signal" is the signal
227	name without any "SIG" prefix, "cb" is the Perl callback to be invoked	342	name in uppercase and without any "SIG" prefix, "cb" is the Perl
228	whenever a signal occurs.	343	callback to be invoked whenever a signal occurs.
229		344
230	Although the callback might get passed parameters, their value and	345	Although the callback might get passed parameters, their value and
231	presence is undefined and you cannot rely on them. Portable AnyEvent	346	presence is undefined and you cannot rely on them. Portable AnyEvent
232	callbacks cannot use arguments passed to signal watcher callbacks.	347	callbacks cannot use arguments passed to signal watcher callbacks.
233		348
234	Multiple signal occurances can be clumped together into one callback	349	Multiple signal occurrences can be clumped together into one callback
235	invocation, and callback invocation will be synchronous. synchronous	350	invocation, and callback invocation will be synchronous. Synchronous
236	means that it might take a while until the signal gets handled by the	351	means that it might take a while until the signal gets handled by the
237	process, but it is guarenteed not to interrupt any other callbacks.	352	process, but it is guaranteed not to interrupt any other callbacks.
238		353
239	The main advantage of using these watchers is that you can share a	354	The main advantage of using these watchers is that you can share a
240	signal between multiple watchers.	355	signal between multiple watchers, and AnyEvent will ensure that signals
		356	will not interrupt your program at bad times.
241		357
242	This watcher might use %SIG, so programs overwriting those signals	358	This watcher might use %SIG (depending on the event loop used), so
243	directly will likely not work correctly.	359	programs overwriting those signals directly will likely not work
		360	correctly.
		361
		362	Also note that many event loops (e.g. Glib, Tk, Qt, IO::Async) do not
		363	support attaching callbacks to signals, which is a pity, as you cannot
		364	do race-free signal handling in perl. AnyEvent will try to do it's best,
		365	but in some cases, signals will be delayed. The maximum time a signal
		366	might be delayed is specified in $AnyEvent::MAX_SIGNAL_LATENCY (default:
		367	10 seconds). This variable can be changed only before the first signal
		368	watcher is created, and should be left alone otherwise. Higher values
		369	will cause fewer spurious wake-ups, which is better for power and CPU
		370	saving. All these problems can be avoided by installing the optional
		371	Async::Interrupt module.
244		372
245	Example: exit on SIGINT	373	Example: exit on SIGINT
246		374
247	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	375	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
248		376
249	CHILD PROCESS WATCHERS	377	CHILD PROCESS WATCHERS
250	You can also watch on a child process exit and catch its exit status.	378	You can also watch on a child process exit and catch its exit status.
251		379
252	The child process is specified by the "pid" argument (if set to 0, it	380	The child process is specified by the "pid" argument (if set to 0, it
253	watches for any child process exit). The watcher will trigger as often	381	watches for any child process exit). The watcher will triggered only
254	as status change for the child are received. This works by installing a	382	when the child process has finished and an exit status is available, not
255	signal handler for "SIGCHLD". The callback will be called with the pid	383	on any trace events (stopped/continued).
256	and exit status (as returned by waitpid), so unlike other watcher types,	384
257	you can rely on child watcher callback arguments.	385	The callback will be called with the pid and exit status (as returned by
		386	waitpid), so unlike other watcher types, you can rely on child watcher
		387	callback arguments.
		388
		389	This watcher type works by installing a signal handler for "SIGCHLD",
		390	and since it cannot be shared, nothing else should use SIGCHLD or reap
		391	random child processes (waiting for specific child processes, e.g.
		392	inside "system", is just fine).
258		393
259	There is a slight catch to child watchers, however: you usually start	394	There is a slight catch to child watchers, however: you usually start
260	them after the child process was created, and this means the process	395	them after the child process was created, and this means the process
261	could have exited already (and no SIGCHLD will be sent anymore).	396	could have exited already (and no SIGCHLD will be sent anymore).
262		397
263	Not all event models handle this correctly (POE doesn't), but even for	398	Not all event models handle this correctly (neither POE nor IO::Async
		399	do, see their AnyEvent::Impl manpages for details), but even for event
264	event models that do handle this correctly, they usually need to be	400	models that do handle this correctly, they usually need to be loaded
265	loaded before the process exits (i.e. before you fork in the first	401	before the process exits (i.e. before you fork in the first place).
266	place).	402	AnyEvent's pure perl event loop handles all cases correctly regardless
		403	of when you start the watcher.
267		404
268	This means you cannot create a child watcher as the very first thing in	405	This means you cannot create a child watcher as the very first thing in
269	an AnyEvent program, you have to create at least one watcher before	406	an AnyEvent program, you have to create at least one watcher before
270	you "fork" the child (alternatively, you can call "AnyEvent::detect").	407	you "fork" the child (alternatively, you can call "AnyEvent::detect").
271		408
		409	As most event loops do not support waiting for child events, they will
		410	be emulated by AnyEvent in most cases, in which the latency and race
		411	problems mentioned in the description of signal watchers apply.
		412
272	Example: fork a process and wait for it	413	Example: fork a process and wait for it
273		414
274	my $done = AnyEvent->condvar;	415	my $done = AnyEvent->condvar;
275		416
276	my $pid = fork or exit 5;	417	my $pid = fork or exit 5;
277		418
278	my $w = AnyEvent->child (	419	my $w = AnyEvent->child (
279	pid => $pid,	420	pid => $pid,
280	cb => sub {	421	cb => sub {
281	my ($pid, $status) = @_;	422	my ($pid, $status) = @_;
282	warn "pid $pid exited with status $status";	423	warn "pid $pid exited with status $status";
283	$done->send;	424	$done->send;
284	},	425	},
285	);	426	);
286		427
287	# do something else, then wait for process exit	428	# do something else, then wait for process exit
288	$done->recv;	429	$done->recv;
		430
		431	IDLE WATCHERS
		432	Sometimes there is a need to do something, but it is not so important to
		433	do it instantly, but only when there is nothing better to do. This
		434	"nothing better to do" is usually defined to be "no other events need
		435	attention by the event loop".
		436
		437	Idle watchers ideally get invoked when the event loop has nothing better
		438	to do, just before it would block the process to wait for new events.
		439	Instead of blocking, the idle watcher is invoked.
		440
		441	Most event loops unfortunately do not really support idle watchers (only
		442	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		443	will simply call the callback "from time to time".
		444
		445	Example: read lines from STDIN, but only process them when the program
		446	is otherwise idle:
		447
		448	my @lines; # read data
		449	my $idle_w;
		450	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		451	push @lines, scalar <STDIN>;
		452
		453	# start an idle watcher, if not already done
		454	$idle_w \|\|= AnyEvent->idle (cb => sub {
		455	# handle only one line, when there are lines left
		456	if (my $line = shift @lines) {
		457	print "handled when idle: $line";
		458	} else {
		459	# otherwise disable the idle watcher again
		460	undef $idle_w;
		461	}
		462	});
		463	});
289		464
290	CONDITION VARIABLES	465	CONDITION VARIABLES
291	If you are familiar with some event loops you will know that all of them	466	If you are familiar with some event loops you will know that all of them
292	require you to run some blocking "loop", "run" or similar function that	467	require you to run some blocking "loop", "run" or similar function that
293	will actively watch for new events and call your callbacks.	468	will actively watch for new events and call your callbacks.
294		469
295	AnyEvent is different, it expects somebody else to run the event loop	470	AnyEvent is slightly different: it expects somebody else to run the
296	and will only block when necessary (usually when told by the user).	471	event loop and will only block when necessary (usually when told by the
		472	user).
297		473
298	The instrument to do that is called a "condition variable", so called	474	The instrument to do that is called a "condition variable", so called
299	because they represent a condition that must become true.	475	because they represent a condition that must become true.
		476
		477	Now is probably a good time to look at the examples further below.
300		478
301	Condition variables can be created by calling the "AnyEvent->condvar"	479	Condition variables can be created by calling the "AnyEvent->condvar"
302	method, usually without arguments. The only argument pair allowed is	480	method, usually without arguments. The only argument pair allowed is
303	"cb", which specifies a callback to be called when the condition	481	"cb", which specifies a callback to be called when the condition
304	variable becomes true.	482	variable becomes true, with the condition variable as the first argument
		483	(but not the results).
305		484
306	After creation, the conditon variable is "false" until it becomes "true"	485	After creation, the condition variable is "false" until it becomes
		486	"true" by calling the "send" method (or calling the condition variable
		487	as if it were a callback, read about the caveats in the description for
307	by calling the "send" method.	488	the "->send" method).
308		489
309	Condition variables are similar to callbacks, except that you can	490	Condition variables are similar to callbacks, except that you can
310	optionally wait for them. They can also be called merge points - points	491	optionally wait for them. They can also be called merge points - points
311	in time where multiple outstandign events have been processed. And yet	492	in time where multiple outstanding events have been processed. And yet
312	another way to call them is transations - each condition variable can be	493	another way to call them is transactions - each condition variable can
313	used to represent a transaction, which finishes at some point and	494	be used to represent a transaction, which finishes at some point and
314	delivers a result.	495	delivers a result.
315		496
316	Condition variables are very useful to signal that something has	497	Condition variables are very useful to signal that something has
317	finished, for example, if you write a module that does asynchronous http	498	finished, for example, if you write a module that does asynchronous http
318	requests, then a condition variable would be the ideal candidate to	499	requests, then a condition variable would be the ideal candidate to
…		…
323	you can block your main program until an event occurs - for example, you	504	you can block your main program until an event occurs - for example, you
324	could "->recv" in your main program until the user clicks the Quit	505	could "->recv" in your main program until the user clicks the Quit
325	button of your app, which would "->send" the "quit" event.	506	button of your app, which would "->send" the "quit" event.
326		507
327	Note that condition variables recurse into the event loop - if you have	508	Note that condition variables recurse into the event loop - if you have
328	two pieces of code that call "->recv" in a round-robbin fashion, you	509	two pieces of code that call "->recv" in a round-robin fashion, you
329	lose. Therefore, condition variables are good to export to your caller,	510	lose. Therefore, condition variables are good to export to your caller,
330	but you should avoid making a blocking wait yourself, at least in	511	but you should avoid making a blocking wait yourself, at least in
331	callbacks, as this asks for trouble.	512	callbacks, as this asks for trouble.
332		513
333	Condition variables are represented by hash refs in perl, and the keys	514	Condition variables are represented by hash refs in perl, and the keys
…		…
338		519
339	There are two "sides" to a condition variable - the "producer side"	520	There are two "sides" to a condition variable - the "producer side"
340	which eventually calls "-> send", and the "consumer side", which waits	521	which eventually calls "-> send", and the "consumer side", which waits
341	for the send to occur.	522	for the send to occur.
342		523
343	Example:	524	Example: wait for a timer.
344		525
345	# wait till the result is ready	526	# wait till the result is ready
346	my $result_ready = AnyEvent->condvar;	527	my $result_ready = AnyEvent->condvar;
347		528
348	# do something such as adding a timer	529	# do something such as adding a timer
…		…
353	after => 1,	534	after => 1,
354	cb => sub { $result_ready->send },	535	cb => sub { $result_ready->send },
355	);	536	);
356		537
357	# this "blocks" (while handling events) till the callback	538	# this "blocks" (while handling events) till the callback
358	# calls send	539	# calls -<send
359	$result_ready->recv;	540	$result_ready->recv;
		541
		542	Example: wait for a timer, but take advantage of the fact that condition
		543	variables are also callable directly.
		544
		545	my $done = AnyEvent->condvar;
		546	my $delay = AnyEvent->timer (after => 5, cb => $done);
		547	$done->recv;
		548
		549	Example: Imagine an API that returns a condvar and doesn't support
		550	callbacks. This is how you make a synchronous call, for example from the
		551	main program:
		552
		553	use AnyEvent::CouchDB;
		554
		555	...
		556
		557	my @info = $couchdb->info->recv;
		558
		559	And this is how you would just set a callback to be called whenever the
		560	results are available:
		561
		562	$couchdb->info->cb (sub {
		563	my @info = $_[0]->recv;
		564	});
360		565
361	METHODS FOR PRODUCERS	566	METHODS FOR PRODUCERS
362	These methods should only be used by the producing side, i.e. the	567	These methods should only be used by the producing side, i.e. the
363	code/module that eventually sends the signal. Note that it is also the	568	code/module that eventually sends the signal. Note that it is also the
364	producer side which creates the condvar in most cases, but it isn't	569	producer side which creates the condvar in most cases, but it isn't
…		…
373	immediately from within send.	578	immediately from within send.
374		579
375	Any arguments passed to the "send" call will be returned by all	580	Any arguments passed to the "send" call will be returned by all
376	future "->recv" calls.	581	future "->recv" calls.
377		582
		583	Condition variables are overloaded so one can call them directly (as
		584	if they were a code reference). Calling them directly is the same as
		585	calling "send".
		586
378	$cv->croak ($error)	587	$cv->croak ($error)
379	Similar to send, but causes all call's to "->recv" to invoke	588	Similar to send, but causes all call's to "->recv" to invoke
380	"Carp::croak" with the given error message/object/scalar.	589	"Carp::croak" with the given error message/object/scalar.
381		590
382	This can be used to signal any errors to the condition variable	591	This can be used to signal any errors to the condition variable
383	user/consumer.	592	user/consumer. Doing it this way instead of calling "croak" directly
		593	delays the error detetcion, but has the overwhelmign advantage that
		594	it diagnoses the error at the place where the result is expected,
		595	and not deep in some event clalback without connection to the actual
		596	code causing the problem.
384		597
385	$cv->begin ([group callback])	598	$cv->begin ([group callback])
386	$cv->end	599	$cv->end
387	These two methods are EXPERIMENTAL and MIGHT CHANGE.
388
389	These two methods can be used to combine many transactions/events	600	These two methods can be used to combine many transactions/events
390	into one. For example, a function that pings many hosts in parallel	601	into one. For example, a function that pings many hosts in parallel
391	might want to use a condition variable for the whole process.	602	might want to use a condition variable for the whole process.
392		603
393	Every call to "->begin" will increment a counter, and every call to	604	Every call to "->begin" will increment a counter, and every call to
394	"->end" will decrement it. If the counter reaches 0 in "->end", the	605	"->end" will decrement it. If the counter reaches 0 in "->end", the
395	(last) callback passed to "begin" will be executed. That callback is	606	(last) callback passed to "begin" will be executed. That callback is
396	supposed to call "->send", but that is not required. If no	607	supposed to call "->send", but that is not required. If no
397	callback was set, "send" will be called without any arguments.	608	callback was set, "send" will be called without any arguments.
398		609
399	Let's clarify this with the ping example:	610	You can think of "$cv->send" giving you an OR condition (one call
		611	sends), while "$cv->begin" and "$cv->end" giving you an AND
		612	condition (all "begin" calls must be "end"'ed before the condvar
		613	sends).
		614
		615	Let's start with a simple example: you have two I/O watchers (for
		616	example, STDOUT and STDERR for a program), and you want to wait for
		617	both streams to close before activating a condvar:
		618
		619	my $cv = AnyEvent->condvar;
		620
		621	$cv->begin; # first watcher
		622	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		623	defined sysread $fh1, my $buf, 4096
		624	or $cv->end;
		625	});
		626
		627	$cv->begin; # second watcher
		628	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		629	defined sysread $fh2, my $buf, 4096
		630	or $cv->end;
		631	});
		632
		633	$cv->recv;
		634
		635	This works because for every event source (EOF on file handle),
		636	there is one call to "begin", so the condvar waits for all calls to
		637	"end" before sending.
		638
		639	The ping example mentioned above is slightly more complicated, as
		640	the there are results to be passwd back, and the number of tasks
		641	that are begung can potentially be zero:
400		642
401	my $cv = AnyEvent->condvar;	643	my $cv = AnyEvent->condvar;
402		644
403	my %result;	645	my %result;
404	$cv->begin (sub { $cv->send (\%result) });	646	$cv->begin (sub { $cv->send (\%result) });
…		…
424	the loop, which serves two important purposes: first, it sets the	666	the loop, which serves two important purposes: first, it sets the
425	callback to be called once the counter reaches 0, and second, it	667	callback to be called once the counter reaches 0, and second, it
426	ensures that "send" is called even when "no" hosts are being pinged	668	ensures that "send" is called even when "no" hosts are being pinged
427	(the loop doesn't execute once).	669	(the loop doesn't execute once).
428		670
429	This is the general pattern when you "fan out" into multiple	671	This is the general pattern when you "fan out" into multiple (but
430	subrequests: use an outer "begin"/"end" pair to set the callback and	672	potentially none) subrequests: use an outer "begin"/"end" pair to
431	ensure "end" is called at least once, and then, for each subrequest	673	set the callback and ensure "end" is called at least once, and then,
432	you start, call "begin" and for eahc subrequest you finish, call	674	for each subrequest you start, call "begin" and for each subrequest
433	"end".	675	you finish, call "end".
434		676
435	METHODS FOR CONSUMERS	677	METHODS FOR CONSUMERS
436	These methods should only be used by the consuming side, i.e. the code	678	These methods should only be used by the consuming side, i.e. the code
437	awaits the condition.	679	awaits the condition.
438		680
…		…
447	function will call "croak".	689	function will call "croak".
448		690
449	In list context, all parameters passed to "send" will be returned,	691	In list context, all parameters passed to "send" will be returned,
450	in scalar context only the first one will be returned.	692	in scalar context only the first one will be returned.
451		693
		694	Note that doing a blocking wait in a callback is not supported by
		695	any event loop, that is, recursive invocation of a blocking "->recv"
		696	is not allowed, and the "recv" call will "croak" if such a condition
		697	is detected. This condition can be slightly loosened by using
		698	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		699	thread that doesn't run the event loop itself.
		700
452	Not all event models support a blocking wait - some die in that case	701	Not all event models support a blocking wait - some die in that case
453	(programs might want to do that to stay interactive), so *if you are	702	(programs might want to do that to stay interactive), so *if you are
454	using this from a module, never require a blocking wait*, but let	703	using this from a module, never require a blocking wait*. Instead,
455	the caller decide whether the call will block or not (for example,	704	let the caller decide whether the call will block or not (for
456	by coupling condition variables with some kind of request results	705	example, by coupling condition variables with some kind of request
457	and supporting callbacks so the caller knows that getting the result	706	results and supporting callbacks so the caller knows that getting
458	will not block, while still suppporting blocking waits if the caller	707	the result will not block, while still supporting blocking waits if
459	so desires).	708	the caller so desires).
460
461	Another reason never to "->recv" in a module is that you cannot
462	sensibly have two "->recv"'s in parallel, as that would require
463	multiple interpreters or coroutines/threads, none of which
464	"AnyEvent" can supply.
465
466	The Coro module, however, can and does supply coroutines and, in
467	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
468	versions and also integrates coroutines into AnyEvent, making
469	blocking "->recv" calls perfectly safe as long as they are done from
470	another coroutine (one that doesn't run the event loop).
471		709
472	You can ensure that "-recv" never blocks by setting a callback and	710	You can ensure that "-recv" never blocks by setting a callback and
473	only calling "->recv" from within that callback (or at a later	711	only calling "->recv" from within that callback (or at a later
474	time). This will work even when the event loop does not support	712	time). This will work even when the event loop does not support
475	blocking waits otherwise.	713	blocking waits otherwise.
476		714
477	$bool = $cv->ready	715	$bool = $cv->ready
478	Returns true when the condition is "true", i.e. whether "send" or	716	Returns true when the condition is "true", i.e. whether "send" or
479	"croak" have been called.	717	"croak" have been called.
480		718
481	$cb = $cv->cb ([new callback])	719	$cb = $cv->cb ($cb->($cv))
482	This is a mutator function that returns the callback set and	720	This is a mutator function that returns the callback set and
483	optionally replaces it before doing so.	721	optionally replaces it before doing so.
484		722
485	The callback will be called when the condition becomes "true", i.e.	723	The callback will be called when the condition becomes "true", i.e.
486	when "send" or "croak" are called. Calling "recv" inside the	724	when "send" or "croak" are called, with the only argument being the
		725	condition variable itself. Calling "recv" inside the callback or at
487	callback or at any later time is guaranteed not to block.	726	any later time is guaranteed not to block.
		727
		728	SUPPORTED EVENT LOOPS/BACKENDS
		729	The available backend classes are (every class has its own manpage):
		730
		731	Backends that are autoprobed when no other event loop can be found.
		732	EV is the preferred backend when no other event loop seems to be in
		733	use. If EV is not installed, then AnyEvent will try Event, and,
		734	failing that, will fall back to its own pure-perl implementation,
		735	which is available everywhere as it comes with AnyEvent itself.
		736
		737	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		738	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		739	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		740
		741	Backends that are transparently being picked up when they are used.
		742	These will be used when they are currently loaded when the first
		743	watcher is created, in which case it is assumed that the application
		744	is using them. This means that AnyEvent will automatically pick the
		745	right backend when the main program loads an event module before
		746	anything starts to create watchers. Nothing special needs to be done
		747	by the main program.
		748
		749	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		750	AnyEvent::Impl::Tk based on Tk, very broken.
		751	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		752	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		753
		754	Backends with special needs.
		755	Qt requires the Qt::Application to be instantiated first, but will
		756	otherwise be picked up automatically. As long as the main program
		757	instantiates the application before any AnyEvent watchers are
		758	created, everything should just work.
		759
		760	AnyEvent::Impl::Qt based on Qt.
		761
		762	Support for IO::Async can only be partial, as it is too broken and
		763	architecturally limited to even support the AnyEvent API. It also is
		764	the only event loop that needs the loop to be set explicitly, so it
		765	can only be used by a main program knowing about AnyEvent. See
		766	AnyEvent::Impl::Async for the gory details.
		767
		768	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		769
		770	Event loops that are indirectly supported via other backends.
		771	Some event loops can be supported via other modules:
		772
		773	There is no direct support for WxWidgets (Wx) or Prima.
		774
		775	WxWidgets has no support for watching file handles. However, you can
		776	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		777	simply polls 20 times per second, which was considered to be too
		778	horrible to even consider for AnyEvent.
		779
		780	Prima is not supported as nobody seems to be using it, but it has a
		781	POE backend, so it can be supported through POE.
		782
		783	AnyEvent knows about both Prima and Wx, however, and will try to
		784	load POE when detecting them, in the hope that POE will pick them
		785	up, in which case everything will be automatic.
488		786
489	GLOBAL VARIABLES AND FUNCTIONS	787	GLOBAL VARIABLES AND FUNCTIONS
		788	These are not normally required to use AnyEvent, but can be useful to
		789	write AnyEvent extension modules.
		790
490	$AnyEvent::MODEL	791	$AnyEvent::MODEL
491	Contains "undef" until the first watcher is being created. Then it	792	Contains "undef" until the first watcher is being created, before
		793	the backend has been autodetected.
		794
492	contains the event model that is being used, which is the name of	795	Afterwards it contains the event model that is being used, which is
493	the Perl class implementing the model. This class is usually one of	796	the name of the Perl class implementing the model. This class is
494	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	797	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
495	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	798	other class in the case AnyEvent has been extended at runtime (e.g.
496		799	in rxvt-unicode it will be "urxvt::anyevent").
497	The known classes so far are:
498
499	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
500	AnyEvent::Impl::Event based on Event, second best choice.
501	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
502	AnyEvent::Impl::Glib based on Glib, third-best choice.
503	AnyEvent::Impl::Tk based on Tk, very bad choice.
504	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
505	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
506	AnyEvent::Impl::POE based on POE, not generic enough for full support.
507
508	There is no support for WxWidgets, as WxWidgets has no support for
509	watching file handles. However, you can use WxWidgets through the
510	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
511	second, which was considered to be too horrible to even consider for
512	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
513	using it's adaptor.
514
515	AnyEvent knows about Prima and Wx and will try to use POE when
516	autodetecting them.
517		800
518	AnyEvent::detect	801	AnyEvent::detect
519	Returns $AnyEvent::MODEL, forcing autodetection of the event model	802	Returns $AnyEvent::MODEL, forcing autodetection of the event model
520	if necessary. You should only call this function right before you	803	if necessary. You should only call this function right before you
521	would have created an AnyEvent watcher anyway, that is, as late as	804	would have created an AnyEvent watcher anyway, that is, as late as
522	possible at runtime.	805	possible at runtime, and not e.g. while initialising of your module.
		806
		807	If you need to do some initialisation before AnyEvent watchers are
		808	created, use "post_detect".
523		809
524	$guard = AnyEvent::post_detect { BLOCK }	810	$guard = AnyEvent::post_detect { BLOCK }
525	Arranges for the code block to be executed as soon as the event	811	Arranges for the code block to be executed as soon as the event
526	model is autodetected (or immediately if this has already happened).	812	model is autodetected (or immediately if this has already happened).
		813
		814	The block will be executed after the actual backend has been
		815	detected ($AnyEvent::MODEL is set), but before any watchers have
		816	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		817	other initialisations - see the sources of AnyEvent::Strict or
		818	AnyEvent::AIO to see how this is used.
		819
		820	The most common usage is to create some global watchers, without
		821	forcing event module detection too early, for example, AnyEvent::AIO
		822	creates and installs the global IO::AIO watcher in a "post_detect"
		823	block to avoid autodetecting the event module at load time.
527		824
528	If called in scalar or list context, then it creates and returns an	825	If called in scalar or list context, then it creates and returns an
529	object that automatically removes the callback again when it is	826	object that automatically removes the callback again when it is
530	destroyed. See Coro::BDB for a case where this is useful.	827	destroyed. See Coro::BDB for a case where this is useful.
531		828
…		…
533	If there are any code references in this array (you can "push" to it	830	If there are any code references in this array (you can "push" to it
534	before or after loading AnyEvent), then they will called directly	831	before or after loading AnyEvent), then they will called directly
535	after the event loop has been chosen.	832	after the event loop has been chosen.
536		833
537	You should check $AnyEvent::MODEL before adding to this array,	834	You should check $AnyEvent::MODEL before adding to this array,
538	though: if it contains a true value then the event loop has already	835	though: if it is defined then the event loop has already been
539	been detected, and the array will be ignored.	836	detected, and the array will be ignored.
540		837
541	Best use "AnyEvent::post_detect { BLOCK }" instead.	838	Best use "AnyEvent::post_detect { BLOCK }" when your application
		839	allows it,as it takes care of these details.
		840
		841	This variable is mainly useful for modules that can do something
		842	useful when AnyEvent is used and thus want to know when it is
		843	initialised, but do not need to even load it by default. This array
		844	provides the means to hook into AnyEvent passively, without loading
		845	it.
542		846
543	WHAT TO DO IN A MODULE	847	WHAT TO DO IN A MODULE
544	As a module author, you should "use AnyEvent" and call AnyEvent methods	848	As a module author, you should "use AnyEvent" and call AnyEvent methods
545	freely, but you should not load a specific event module or rely on it.	849	freely, but you should not load a specific event module or rely on it.
546		850
…		…
566	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	870	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
567	do anything special (it does not need to be event-based) and let	871	do anything special (it does not need to be event-based) and let
568	AnyEvent decide which implementation to chose if some module relies on	872	AnyEvent decide which implementation to chose if some module relies on
569	it.	873	it.
570		874
571	If the main program relies on a specific event model. For example, in	875	If the main program relies on a specific event model - for example, in
572	Gtk2 programs you have to rely on the Glib module. You should load the	876	Gtk2 programs you have to rely on the Glib module - you should load the
573	event module before loading AnyEvent or any module that uses it:	877	event module before loading AnyEvent or any module that uses it:
574	generally speaking, you should load it as early as possible. The reason	878	generally speaking, you should load it as early as possible. The reason
575	is that modules might create watchers when they are loaded, and AnyEvent	879	is that modules might create watchers when they are loaded, and AnyEvent
576	will decide on the event model to use as soon as it creates watchers,	880	will decide on the event model to use as soon as it creates watchers,
577	and it might chose the wrong one unless you load the correct one	881	and it might chose the wrong one unless you load the correct one
578	yourself.	882	yourself.
579		883
580	You can chose to use a rather inefficient pure-perl implementation by	884	You can chose to use a pure-perl implementation by loading the
581	loading the "AnyEvent::Impl::Perl" module, which gives you similar	885	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
582	behaviour everywhere, but letting AnyEvent chose is generally better.	886	everywhere, but letting AnyEvent chose the model is generally better.
		887
		888	MAINLOOP EMULATION
		889	Sometimes (often for short test scripts, or even standalone programs who
		890	only want to use AnyEvent), you do not want to run a specific event
		891	loop.
		892
		893	In that case, you can use a condition variable like this:
		894
		895	AnyEvent->condvar->recv;
		896
		897	This has the effect of entering the event loop and looping forever.
		898
		899	Note that usually your program has some exit condition, in which case it
		900	is better to use the "traditional" approach of storing a condition
		901	variable somewhere, waiting for it, and sending it when the program
		902	should exit cleanly.
583		903
584	OTHER MODULES	904	OTHER MODULES
585	The following is a non-exhaustive list of additional modules that use	905	The following is a non-exhaustive list of additional modules that use
586	AnyEvent and can therefore be mixed easily with other AnyEvent modules	906	AnyEvent as a client and can therefore be mixed easily with other
587	in the same program. Some of the modules come with AnyEvent, some are	907	AnyEvent modules and other event loops in the same program. Some of the
588	available via CPAN.	908	modules come with AnyEvent, most are available via CPAN.
589		909
590	AnyEvent::Util	910	AnyEvent::Util
591	Contains various utility functions that replace often-used but	911	Contains various utility functions that replace often-used but
592	blocking functions such as "inet_aton" by event-/callback-based	912	blocking functions such as "inet_aton" by event-/callback-based
593	versions.	913	versions.
594		914
		915	AnyEvent::Socket
		916	Provides various utility functions for (internet protocol) sockets,
		917	addresses and name resolution. Also functions to create non-blocking
		918	tcp connections or tcp servers, with IPv6 and SRV record support and
		919	more.
		920
595	AnyEvent::Handle	921	AnyEvent::Handle
596	Provide read and write buffers and manages watchers for reads and	922	Provide read and write buffers, manages watchers for reads and
597	writes.	923	writes, supports raw and formatted I/O, I/O queued and fully
		924	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
		925
		926	AnyEvent::DNS
		927	Provides rich asynchronous DNS resolver capabilities.
		928
		929	AnyEvent::HTTP
		930	A simple-to-use HTTP library that is capable of making a lot of
		931	concurrent HTTP requests.
598		932
599	AnyEvent::HTTPD	933	AnyEvent::HTTPD
600	Provides a simple web application server framework.	934	Provides a simple web application server framework.
601		935
602	AnyEvent::DNS
603	Provides asynchronous DNS resolver capabilities, beyond what
604	AnyEvent::Util offers.
605
606	AnyEvent::FastPing	936	AnyEvent::FastPing
607	The fastest ping in the west.	937	The fastest ping in the west.
608		938
		939	AnyEvent::DBI
		940	Executes DBI requests asynchronously in a proxy process.
		941
		942	AnyEvent::AIO
		943	Truly asynchronous I/O, should be in the toolbox of every event
		944	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		945	together.
		946
		947	AnyEvent::BDB
		948	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		949	fuses BDB and AnyEvent together.
		950
		951	AnyEvent::GPSD
		952	A non-blocking interface to gpsd, a daemon delivering GPS
		953	information.
		954
		955	AnyEvent::IRC
		956	AnyEvent based IRC client module family (replacing the older
609	Net::IRC3	957	Net::IRC3).
610	AnyEvent based IRC client module family.
611		958
612	Net::XMPP2	959	AnyEvent::XMPP
613	AnyEvent based XMPP (Jabber protocol) module family.	960	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		961	older Net::XMPP2>.
		962
		963	AnyEvent::IGS
		964	A non-blocking interface to the Internet Go Server protocol (used by
		965	App::IGS).
614		966
615	Net::FCP	967	Net::FCP
616	AnyEvent-based implementation of the Freenet Client Protocol,	968	AnyEvent-based implementation of the Freenet Client Protocol,
617	birthplace of AnyEvent.	969	birthplace of AnyEvent.
618		970
…		…
620	High level API for event-based execution flow control.	972	High level API for event-based execution flow control.
621		973
622	Coro	974	Coro
623	Has special support for AnyEvent via Coro::AnyEvent.	975	Has special support for AnyEvent via Coro::AnyEvent.
624		976
625	AnyEvent::AIO, IO::AIO	977	ERROR AND EXCEPTION HANDLING
626	Truly asynchronous I/O, should be in the toolbox of every event	978	In general, AnyEvent does not do any error handling - it relies on the
627	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	979	caller to do that if required. The AnyEvent::Strict module (see also the
628	together.	980	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		981	checking of all AnyEvent methods, however, which is highly useful during
		982	development.
629		983
630	AnyEvent::BDB, BDB	984	As for exception handling (i.e. runtime errors and exceptions thrown
631	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently	985	while executing a callback), this is not only highly event-loop
632	fuses IO::AIO and AnyEvent together.	986	specific, but also not in any way wrapped by this module, as this is the
		987	job of the main program.
633		988
634	IO::Lambda	989	The pure perl event loop simply re-throws the exception (usually within
635	The lambda approach to I/O - don't ask, look there. Can use	990	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
636	AnyEvent.	991	Glib uses "install_exception_handler" and so on.
		992
		993	ENVIRONMENT VARIABLES
		994	The following environment variables are used by this module or its
		995	submodules.
		996
		997	Note that AnyEvent will remove all environment variables starting with
		998	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		999	enabled.
		1000
		1001	"PERL_ANYEVENT_VERBOSE"
		1002	By default, AnyEvent will be completely silent except in fatal
		1003	conditions. You can set this environment variable to make AnyEvent
		1004	more talkative.
		1005
		1006	When set to 1 or higher, causes AnyEvent to warn about unexpected
		1007	conditions, such as not being able to load the event model specified
		1008	by "PERL_ANYEVENT_MODEL".
		1009
		1010	When set to 2 or higher, cause AnyEvent to report to STDERR which
		1011	event model it chooses.
		1012
		1013	When set to 8 or higher, then AnyEvent will report extra information
		1014	on which optional modules it loads and how it implements certain
		1015	features.
		1016
		1017	"PERL_ANYEVENT_STRICT"
		1018	AnyEvent does not do much argument checking by default, as thorough
		1019	argument checking is very costly. Setting this variable to a true
		1020	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1021	thoroughly check the arguments passed to most method calls. If it
		1022	finds any problems, it will croak.
		1023
		1024	In other words, enables "strict" mode.
		1025
		1026	Unlike "use strict" (or it's modern cousin, "use common::sense", it
		1027	is definitely recommended to keep it off in production. Keeping
		1028	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1029	programs can be very useful, however.
		1030
		1031	"PERL_ANYEVENT_MODEL"
		1032	This can be used to specify the event model to be used by AnyEvent,
		1033	before auto detection and -probing kicks in. It must be a string
		1034	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		1035	gets prepended and the resulting module name is loaded and if the
		1036	load was successful, used as event model. If it fails to load
		1037	AnyEvent will proceed with auto detection and -probing.
		1038
		1039	This functionality might change in future versions.
		1040
		1041	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		1042	could start your program like this:
		1043
		1044	PERL_ANYEVENT_MODEL=Perl perl ...
		1045
		1046	"PERL_ANYEVENT_PROTOCOLS"
		1047	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		1048	preferences for IPv4 or IPv6. The default is unspecified (and might
		1049	change, or be the result of auto probing).
		1050
		1051	Must be set to a comma-separated list of protocols or address
		1052	families, current supported: "ipv4" and "ipv6". Only protocols
		1053	mentioned will be used, and preference will be given to protocols
		1054	mentioned earlier in the list.
		1055
		1056	This variable can effectively be used for denial-of-service attacks
		1057	against local programs (e.g. when setuid), although the impact is
		1058	likely small, as the program has to handle conenction and other
		1059	failures anyways.
		1060
		1061	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		1062	IPv6, but support both and try to use both.
		1063	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		1064	resolve or contact IPv6 addresses.
		1065	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		1066	prefer IPv6 over IPv4.
		1067
		1068	"PERL_ANYEVENT_EDNS0"
		1069	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		1070	for DNS. This extension is generally useful to reduce DNS traffic,
		1071	but some (broken) firewalls drop such DNS packets, which is why it
		1072	is off by default.
		1073
		1074	Setting this variable to 1 will cause AnyEvent::DNS to announce
		1075	EDNS0 in its DNS requests.
		1076
		1077	"PERL_ANYEVENT_MAX_FORKS"
		1078	The maximum number of child processes that
		1079	"AnyEvent::Util::fork_call" will create in parallel.
		1080
		1081	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1082	The default value for the "max_outstanding" parameter for the
		1083	default DNS resolver - this is the maximum number of parallel DNS
		1084	requests that are sent to the DNS server.
		1085
		1086	"PERL_ANYEVENT_RESOLV_CONF"
		1087	The file to use instead of /etc/resolv.conf (or OS-specific
		1088	configuration) in the default resolver. When set to the empty
		1089	string, no default config will be used.
		1090
		1091	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1092	When neither "ca_file" nor "ca_path" was specified during
		1093	AnyEvent::TLS context creation, and either of these environment
		1094	variables exist, they will be used to specify CA certificate
		1095	locations instead of a system-dependent default.
		1096
		1097	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1098	When these are set to 1, then the respective modules are not loaded.
		1099	Mostly good for testing AnyEvent itself.
637		1100
638	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1101	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
639	This is an advanced topic that you do not normally need to use AnyEvent	1102	This is an advanced topic that you do not normally need to use AnyEvent
640	in a module. This section is only of use to event loop authors who want	1103	in a module. This section is only of use to event loop authors who want
641	to provide AnyEvent compatibility.	1104	to provide AnyEvent compatibility.
…		…
675		1138
676	rxvt-unicode also cheats a bit by not providing blocking access to	1139	rxvt-unicode also cheats a bit by not providing blocking access to
677	condition variables: code blocking while waiting for a condition will	1140	condition variables: code blocking while waiting for a condition will
678	"die". This still works with most modules/usages, and blocking calls	1141	"die". This still works with most modules/usages, and blocking calls
679	must not be done in an interactive application, so it makes sense.	1142	must not be done in an interactive application, so it makes sense.
680
681	ENVIRONMENT VARIABLES
682	The following environment variables are used by this module:
683
684	"PERL_ANYEVENT_VERBOSE"
685	By default, AnyEvent will be completely silent except in fatal
686	conditions. You can set this environment variable to make AnyEvent
687	more talkative.
688
689	When set to 1 or higher, causes AnyEvent to warn about unexpected
690	conditions, such as not being able to load the event model specified
691	by "PERL_ANYEVENT_MODEL".
692
693	When set to 2 or higher, cause AnyEvent to report to STDERR which
694	event model it chooses.
695
696	"PERL_ANYEVENT_MODEL"
697	This can be used to specify the event model to be used by AnyEvent,
698	before autodetection and -probing kicks in. It must be a string
699	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
700	gets prepended and the resulting module name is loaded and if the
701	load was successful, used as event model. If it fails to load
702	AnyEvent will proceed with autodetection and -probing.
703
704	This functionality might change in future versions.
705
706	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
707	could start your program like this:
708
709	PERL_ANYEVENT_MODEL=Perl perl ...
710		1143
711	EXAMPLE PROGRAM	1144	EXAMPLE PROGRAM
712	The following program uses an I/O watcher to read data from STDIN, a	1145	The following program uses an I/O watcher to read data from STDIN, a
713	timer to display a message once per second, and a condition variable to	1146	timer to display a message once per second, and a condition variable to
714	quit the program when the user enters quit:	1147	quit the program when the user enters quit:
…		…
796	syswrite $txn->{fh}, $txn->{request}	1229	syswrite $txn->{fh}, $txn->{request}
797	or die "connection or write error";	1230	or die "connection or write error";
798	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1231	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
799		1232
800	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1233	Again, "fh_ready_r" waits till all data has arrived, and then stores the
801	result and signals any possible waiters that the request ahs finished:	1234	result and signals any possible waiters that the request has finished:
802		1235
803	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1236	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
804		1237
805	if (end-of-file or data complete) {	1238	if (end-of-file or data complete) {
806	$txn->{result} = $txn->{buf};	1239	$txn->{result} = $txn->{buf};
…		…
814		1247
815	$txn->{finished}->recv;	1248	$txn->{finished}->recv;
816	return $txn->{result};	1249	return $txn->{result};
817		1250
818	The actual code goes further and collects all errors ("die"s,	1251	The actual code goes further and collects all errors ("die"s,
819	exceptions) that occured during request processing. The "result" method	1252	exceptions) that occurred during request processing. The "result" method
820	detects whether an exception as thrown (it is stored inside the $txn	1253	detects whether an exception as thrown (it is stored inside the $txn
821	object) and just throws the exception, which means connection errors and	1254	object) and just throws the exception, which means connection errors and
822	other problems get reported tot he code that tries to use the result,	1255	other problems get reported tot he code that tries to use the result,
823	not in a random callback.	1256	not in a random callback.
824		1257
…		…
867	over the event loops themselves and to give you an impression of the	1300	over the event loops themselves and to give you an impression of the
868	speed of various event loops I prepared some benchmarks.	1301	speed of various event loops I prepared some benchmarks.
869		1302
870	BENCHMARKING ANYEVENT OVERHEAD	1303	BENCHMARKING ANYEVENT OVERHEAD
871	Here is a benchmark of various supported event models used natively and	1304	Here is a benchmark of various supported event models used natively and
872	through anyevent. The benchmark creates a lot of timers (with a zero	1305	through AnyEvent. The benchmark creates a lot of timers (with a zero
873	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1306	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
874	which it is), lets them fire exactly once and destroys them again.	1307	which it is), lets them fire exactly once and destroys them again.
875		1308
876	Source code for this benchmark is found as eg/bench in the AnyEvent	1309	Source code for this benchmark is found as eg/bench in the AnyEvent
877	distribution.	1310	distribution.
…		…
901	destroy is the time, in microseconds, that it takes to destroy a	1334	destroy is the time, in microseconds, that it takes to destroy a
902	single watcher.	1335	single watcher.
903		1336
904	Results	1337	Results
905	name watchers bytes create invoke destroy comment	1338	name watchers bytes create invoke destroy comment
906	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1339	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
907	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1340	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
908	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1341	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
909	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1342	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
910	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1343	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
911	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1344	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1345	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1346	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
912	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1347	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
913	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1348	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
914	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1349	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
915	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1350	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
916		1351
917	Discussion	1352	Discussion
918	The benchmark does not measure scalability of the event loop very	1353	The benchmark does not measure scalability of the event loop very
919	well. For example, a select-based event loop (such as the pure perl one)	1354	well. For example, a select-based event loop (such as the pure perl one)
920	can never compete with an event loop that uses epoll when the number of	1355	can never compete with an event loop that uses epoll when the number of
…		…
945	few of them active), of course, but this was not subject of this	1380	few of them active), of course, but this was not subject of this
946	benchmark.	1381	benchmark.
947		1382
948	The "Event" module has a relatively high setup and callback invocation	1383	The "Event" module has a relatively high setup and callback invocation
949	cost, but overall scores in on the third place.	1384	cost, but overall scores in on the third place.
		1385
		1386	"IO::Async" performs admirably well, about on par with "Event", even
		1387	when using its pure perl backend.
950		1388
951	"Glib"'s memory usage is quite a bit higher, but it features a faster	1389	"Glib"'s memory usage is quite a bit higher, but it features a faster
952	callback invocation and overall ends up in the same class as "Event".	1390	callback invocation and overall ends up in the same class as "Event".
953	However, Glib scales extremely badly, doubling the number of watchers	1391	However, Glib scales extremely badly, doubling the number of watchers
954	increases the processing time by more than a factor of four, making it	1392	increases the processing time by more than a factor of four, making it
…		…
992		1430
993	* You should avoid POE like the plague if you want performance or	1431	* You should avoid POE like the plague if you want performance or
994	reasonable memory usage.	1432	reasonable memory usage.
995		1433
996	BENCHMARKING THE LARGE SERVER CASE	1434	BENCHMARKING THE LARGE SERVER CASE
997	This benchmark atcually benchmarks the event loop itself. It works by	1435	This benchmark actually benchmarks the event loop itself. It works by
998	creating a number of "servers": each server consists of a socketpair, a	1436	creating a number of "servers": each server consists of a socket pair, a
999	timeout watcher that gets reset on activity (but never fires), and an	1437	timeout watcher that gets reset on activity (but never fires), and an
1000	I/O watcher waiting for input on one side of the socket. Each time the	1438	I/O watcher waiting for input on one side of the socket. Each time the
1001	socket watcher reads a byte it will write that byte to a random other	1439	socket watcher reads a byte it will write that byte to a random other
1002	"server".	1440	"server".
1003		1441
1004	The effect is that there will be a lot of I/O watchers, only part of	1442	The effect is that there will be a lot of I/O watchers, only part of
1005	which are active at any one point (so there is a constant number of	1443	which are active at any one point (so there is a constant number of
1006	active fds for each loop iterstaion, but which fds these are is random).	1444	active fds for each loop iteration, but which fds these are is random).
1007	The timeout is reset each time something is read because that reflects	1445	The timeout is reset each time something is read because that reflects
1008	how most timeouts work (and puts extra pressure on the event loops).	1446	how most timeouts work (and puts extra pressure on the event loops).
1009		1447
1010	In this benchmark, we use 10000 socketpairs (20000 sockets), of which	1448	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1011	100 (1%) are active. This mirrors the activity of large servers with	1449	100 (1%) are active. This mirrors the activity of large servers with
1012	many connections, most of which are idle at any one point in time.	1450	many connections, most of which are idle at any one point in time.
1013		1451
1014	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1452	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1015	distribution.	1453	distribution.
1016		1454
1017	Explanation of the columns	1455	Explanation of the columns
1018	sockets is the number of sockets, and twice the number of "servers"	1456	sockets is the number of sockets, and twice the number of "servers"
1019	(as each server has a read and write socket end).	1457	(as each server has a read and write socket end).
1020		1458
1021	create is the time it takes to create a socketpair (which is	1459	create is the time it takes to create a socket pair (which is
1022	nontrivial) and two watchers: an I/O watcher and a timeout watcher.	1460	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
1023		1461
1024	request, the most important value, is the time it takes to handle a	1462	request, the most important value, is the time it takes to handle a
1025	single "request", that is, reading the token from the pipe and	1463	single "request", that is, reading the token from the pipe and
1026	forwarding it to another server. This includes deleting the old timeout	1464	forwarding it to another server. This includes deleting the old timeout
1027	and creating a new one that moves the timeout into the future.	1465	and creating a new one that moves the timeout into the future.
1028		1466
1029	Results	1467	Results
1030	name sockets create request	1468	name sockets create request
1031	EV 20000 69.01 11.16	1469	EV 20000 69.01 11.16
1032	Perl 20000 73.32 35.87	1470	Perl 20000 73.32 35.87
		1471	IOAsync 20000 157.00 98.14 epoll
		1472	IOAsync 20000 159.31 616.06 poll
1033	Event 20000 212.62 257.32	1473	Event 20000 212.62 257.32
1034	Glib 20000 651.16 1896.30	1474	Glib 20000 651.16 1896.30
1035	POE 20000 349.67 12317.24 uses POE::Loop::Event	1475	POE 20000 349.67 12317.24 uses POE::Loop::Event
1036		1476
1037	Discussion	1477	Discussion
1038	This benchmark does measure scalability and overall performance of the	1478	This benchmark does measure scalability and overall performance of the
1039	particular event loop.	1479	particular event loop.
1040		1480
1041	EV is again fastest. Since it is using epoll on my system, the setup	1481	EV is again fastest. Since it is using epoll on my system, the setup
1042	time is relatively high, though.	1482	time is relatively high, though.
1043		1483
1044	Perl surprisingly comes second. It is much faster than the C-based event	1484	Perl surprisingly comes second. It is much faster than the C-based event
1045	loops Event and Glib.	1485	loops Event and Glib.
		1486
		1487	IO::Async performs very well when using its epoll backend, and still
		1488	quite good compared to Glib when using its pure perl backend.
1046		1489
1047	Event suffers from high setup time as well (look at its code and you	1490	Event suffers from high setup time as well (look at its code and you
1048	will understand why). Callback invocation also has a high overhead	1491	will understand why). Callback invocation also has a high overhead
1049	compared to the "$_->() for .."-style loop that the Perl event loop	1492	compared to the "$_->() for .."-style loop that the Perl event loop
1050	uses. Event uses select or poll in basically all documented	1493	uses. Event uses select or poll in basically all documented
…		…
1090	and speed most when you have lots of watchers, not when you only have a	1533	and speed most when you have lots of watchers, not when you only have a
1091	few of them).	1534	few of them).
1092		1535
1093	EV is again fastest.	1536	EV is again fastest.
1094		1537
1095	Perl again comes second. It is noticably faster than the C-based event	1538	Perl again comes second. It is noticeably faster than the C-based event
1096	loops Event and Glib, although the difference is too small to really	1539	loops Event and Glib, although the difference is too small to really
1097	matter.	1540	matter.
1098		1541
1099	POE also performs much better in this case, but is is still far behind	1542	POE also performs much better in this case, but is is still far behind
1100	the others.	1543	the others.
1101		1544
1102	Summary	1545	Summary
1103	* C-based event loops perform very well with small number of watchers,	1546	* C-based event loops perform very well with small number of watchers,
1104	as the management overhead dominates.	1547	as the management overhead dominates.
		1548
		1549	THE IO::Lambda BENCHMARK
		1550	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1551	could be misinterpreted to make AnyEvent look bad. In fact, the
		1552	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1553	better (which shouldn't come as a surprise to anybody). As such, the
		1554	benchmark is fine, and mostly shows that the AnyEvent backend from
		1555	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1556	without the extra baggage? To explore this, I wrote the equivalent
		1557	benchmark for AnyEvent.
		1558
		1559	The benchmark itself creates an echo-server, and then, for 500 times,
		1560	connects to the echo server, sends a line, waits for the reply, and then
		1561	creates the next connection. This is a rather bad benchmark, as it
		1562	doesn't test the efficiency of the framework or much non-blocking I/O,
		1563	but it is a benchmark nevertheless.
		1564
		1565	name runtime
		1566	Lambda/select 0.330 sec
		1567	+ optimized 0.122 sec
		1568	Lambda/AnyEvent 0.327 sec
		1569	+ optimized 0.138 sec
		1570	Raw sockets/select 0.077 sec
		1571	POE/select, components 0.662 sec
		1572	POE/select, raw sockets 0.226 sec
		1573	POE/select, optimized 0.404 sec
		1574
		1575	AnyEvent/select/nb 0.085 sec
		1576	AnyEvent/EV/nb 0.068 sec
		1577	+state machine 0.134 sec
		1578
		1579	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1580	benchmarks actually make blocking connects and use 100% blocking I/O,
		1581	defeating the purpose of an event-based solution. All of the newly
		1582	written AnyEvent benchmarks use 100% non-blocking connects (using
		1583	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1584	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1585	connects generally require a lot more bookkeeping and event handling
		1586	than blocking connects (which involve a single syscall only).
		1587
		1588	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1589	offers similar expressive power as POE and IO::Lambda, using
		1590	conventional Perl syntax. This means that both the echo server and the
		1591	client are 100% non-blocking, further placing it at a disadvantage.
		1592
		1593	As you can see, the AnyEvent + EV combination even beats the
		1594	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1595	backend easily beats IO::Lambda and POE.
		1596
		1597	And even the 100% non-blocking version written using the high-level (and
		1598	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a
		1599	large margin, even though it does all of DNS, tcp-connect and socket I/O
		1600	in a non-blocking way.
		1601
		1602	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1603	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1604	part of the IO::lambda distribution and were used without any changes.
		1605
		1606	SIGNALS
		1607	AnyEvent currently installs handlers for these signals:
		1608
		1609	SIGCHLD
		1610	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1611	emulation for event loops that do not support them natively. Also,
		1612	some event loops install a similar handler.
		1613
		1614	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1615	then AnyEvent will reset it to default, to avoid losing child exit
		1616	statuses.
		1617
		1618	SIGPIPE
		1619	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1620	"undef" when AnyEvent gets loaded.
		1621
		1622	The rationale for this is that AnyEvent users usually do not really
		1623	depend on SIGPIPE delivery (which is purely an optimisation for
		1624	shell use, or badly-written programs), but "SIGPIPE" can cause
		1625	spurious and rare program exits as a lot of people do not expect
		1626	"SIGPIPE" when writing to some random socket.
		1627
		1628	The rationale for installing a no-op handler as opposed to ignoring
		1629	it is that this way, the handler will be restored to defaults on
		1630	exec.
		1631
		1632	Feel free to install your own handler, or reset it to defaults.
		1633
		1634	RECOMMENDED/OPTIONAL MODULES
		1635	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1636	it's built-in modules) are required to use it.
		1637
		1638	That does not mean that AnyEvent won't take advantage of some additional
		1639	modules if they are installed.
		1640
		1641	This section epxlains which additional modules will be used, and how
		1642	they affect AnyEvent's operetion.
		1643
		1644	Async::Interrupt
		1645	This slightly arcane module is used to implement fast signal
		1646	handling: To my knowledge, there is no way to do completely
		1647	race-free and quick signal handling in pure perl. To ensure that
		1648	signals still get delivered, AnyEvent will start an interval timer
		1649	to wake up perl (and catch the signals) with soemd elay (default is
		1650	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1651
		1652	If this module is available, then it will be used to implement
		1653	signal catching, which means that signals will not be delayed, and
		1654	the event loop will not be interrupted regularly, which is more
		1655	efficient (And good for battery life on laptops).
		1656
		1657	This affects not just the pure-perl event loop, but also other event
		1658	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1659
		1660	EV This module isn't really "optional", as it is simply one of the
		1661	backend event loops that AnyEvent can use. However, it is simply the
		1662	best event loop available in terms of features, speed and stability:
		1663	It supports the AnyEvent API optimally, implements all the watcher
		1664	types in XS, does automatic timer adjustments even when no monotonic
		1665	clock is available, can take avdantage of advanced kernel interfaces
		1666	such as "epoll" and "kqueue", and is the fastest backend by far.
		1667	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1668	Glib::EV).
		1669
		1670	Guard
		1671	The guard module, when used, will be used to implement
		1672	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1673	uses a lot less memory), but otherwise doesn't affect guard
		1674	operation much. It is purely used for performance.
		1675
		1676	JSON and JSON::XS
		1677	This module is required when you want to read or write JSON data via
		1678	AnyEvent::Handle. It is also written in pure-perl, but can take
		1679	advantage of the ulta-high-speed JSON::XS module when it is
		1680	installed.
		1681
		1682	In fact, AnyEvent::Handle will use JSON::XS by default if it is
		1683	installed.
		1684
		1685	Net::SSLeay
		1686	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1687	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1688	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1689
		1690	Time::HiRes
		1691	This module is part of perl since release 5.008. It will be used
		1692	when the chosen event library does not come with a timing source on
		1693	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1694	additionally use it to try to use a monotonic clock for timing
		1695	stability.
1105		1696
1106	FORK	1697	FORK
1107	Most event libraries are not fork-safe. The ones who are usually are	1698	Most event libraries are not fork-safe. The ones who are usually are
1108	because they rely on inefficient but fork-safe "select" or "poll" calls.	1699	because they rely on inefficient but fork-safe "select" or "poll" calls.
1109	Only EV is fully fork-aware.	1700	Only EV is fully fork-aware.
1110		1701
1111	If you have to fork, you must either do so before creating your first	1702	If you have to fork, you must either do so before creating your first
1112	watcher OR you must not use AnyEvent at all in the child.	1703	watcher OR you must not use AnyEvent at all in the child OR you must do
		1704	something completely out of the scope of AnyEvent.
1113		1705
1114	SECURITY CONSIDERATIONS	1706	SECURITY CONSIDERATIONS
1115	AnyEvent can be forced to load any event model via	1707	AnyEvent can be forced to load any event model via
1116	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1708	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1117	to execute arbitrary code or directly gain access, it can easily be used	1709	to execute arbitrary code or directly gain access, it can easily be used
…		…
1120	model than specified in the variable.	1712	model than specified in the variable.
1121		1713
1122	You can make AnyEvent completely ignore this variable by deleting it	1714	You can make AnyEvent completely ignore this variable by deleting it
1123	before the first watcher gets created, e.g. with a "BEGIN" block:	1715	before the first watcher gets created, e.g. with a "BEGIN" block:
1124		1716
1125	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1717	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1126		1718
1127	use AnyEvent;	1719	use AnyEvent;
1128		1720
1129	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1721	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1130	be used to probe what backend is used and gain other information (which	1722	be used to probe what backend is used and gain other information (which
1131	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).	1723	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1724	and $ENV{PERL_ANYEVENT_STRICT}.
		1725
		1726	Note that AnyEvent will remove all environment variables starting with
		1727	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1728	enabled.
		1729
		1730	BUGS
		1731	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1732	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1733	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1734	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1735	not as pronounced).
1132		1736
1133	SEE ALSO	1737	SEE ALSO
		1738	Utility functions: AnyEvent::Util.
		1739
1134	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1740	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1135	Event::Lib, Qt, POE.	1741	Event::Lib, Qt, POE.
1136		1742
1137	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1743	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1138	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1744	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1139	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1745	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1746	AnyEvent::Impl::IOAsync.
		1747
		1748	Non-blocking file handles, sockets, TCP clients and servers:
		1749	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		1750
		1751	Asynchronous DNS: AnyEvent::DNS.
1140		1752
1141	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1753	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1142		1754
1143	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1755	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1756	AnyEvent::HTTP.
1144		1757
1145	AUTHOR	1758	AUTHOR
1146	Marc Lehmann <schmorp@schmorp.de>	1759	Marc Lehmann <schmorp@schmorp.de>
1147	http://home.schmorp.de/	1760	http://home.schmorp.de/
1148		1761

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Comparing AnyEvent/README (file contents): Revision 1.21 by root, Sat May 17 21:34:15 2008 UTC vs. Revision 1.46 by root, Sat Jul 18 05:19:09 2009 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.21 by root, Sat May 17 21:34:15 2008 UTC vs.
Revision 1.46 by root, Sat Jul 18 05:19:09 2009 UTC