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Comparing AnyEvent/README (file contents):
Revision 1.22 by root, Sat May 24 17:58:33 2008 UTC vs.
Revision 1.50 by root, Sat Aug 1 09:14:54 2009 UTC

…		…
1	=> NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - the DBI of event loop programming
3		3
4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	loops	5	Qt and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# file descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		12
		13	# one-shot or repeating timers
		14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		16
		17	print AnyEvent->now; # prints current event loop time
		18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		19
		20	# POSIX signal
		21	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		22
		23	# child process exit
		24	my $w = AnyEvent->child (pid => $pid, cb => sub {
		25	my ($pid, $status) = @_;
11	...	26	...
12	});	27	});
13		28
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	29	# called when event loop idle (if applicable)
15	...	30	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		31
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	32	my $w = AnyEvent->condvar; # stores whether a condition was flagged
19	$w->send; # wake up current and all future recv's	33	$w->send; # wake up current and all future recv's
20	$w->recv; # enters "main loop" till $condvar gets ->send	34	$w->recv; # enters "main loop" till $condvar gets ->send
		35	# use a condvar in callback mode:
		36	$w->cb (sub { $_[0]->recv });
		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.
		42
		43	SUPPORT
		44	There is a mailinglist for discussing all things AnyEvent, and an IRC
		45	channel, too.
		46
		47	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		48	Repository, at <http://anyevent.schmorp.de>, for more info.
21		49
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	50	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	51	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	52	nowadays. So what is different about AnyEvent?
25		53
26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	54	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
27	policy* and AnyEvent is small and efficient.	55	policy* and AnyEvent is small and efficient.
28		56
29	First and foremost, AnyEvent is not an event model itself, it only	57	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	58	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,	59	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,	60	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.	61	only one event loop can be active at the same time in a process.
34	AnyEvent helps hiding the differences between those event loops.	62	AnyEvent cannot change this, but it can hide the differences between
		63	those event loops.
35		64
36	The goal of AnyEvent is to offer module authors the ability to do event	65	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	66	programming (waiting for I/O or timer events) without subscribing to a
38	religion, a way of living, and most importantly: without forcing your	67	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	68	module users into the same thing by forcing them to use the same event
40	model you use.	69	model you use.
41		70
42	For modules like POE or IO::Async (which is a total misnomer as it is	71	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	72	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	73	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	74	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	75	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.	76	are also forced to use the same event loop you use.
48		77
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	78	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	79	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	80	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.	81	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	82	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	83	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	84	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).	85	to AnyEvent, too, so it is future-proof).
57		86
58	In addition to being free of having to use *the one and only true event	87	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	88	model*, AnyEvent also is free of bloat and policy: with POE or similar
60	modules, you get an enormous amount of code and strict rules you have to	89	modules, you get an enormous amount of code and strict rules you have to
61	follow. AnyEvent, on the other hand, is lean and up to the point, by	90	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	91	only offering the functionality that is necessary, in as thin as a
63	wrapper as technically possible.	92	wrapper as technically possible.
64		93
		94	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
		95	useful functionality, such as an asynchronous DNS resolver, 100%
		96	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		97	such as Windows) and lots of real-world knowledge and workarounds for
		98	platform bugs and differences.
		99
65	Of course, if you want lots of policy (this can arguably be somewhat	100	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	101	useful) and you want to force your users to use the one and only event
67	model, you should not use this module.	102	model, you should not use this module.
68		103
69	DESCRIPTION	104	DESCRIPTION
70	AnyEvent provides an identical interface to multiple event loops. This	105	AnyEvent provides an identical interface to multiple event loops. This
99	starts using it, all bets are off. Maybe you should tell their authors	134	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...	135	to use AnyEvent so their modules work together with others seamlessly...
101		136
102	The pure-perl implementation of AnyEvent is called	137	The pure-perl implementation of AnyEvent is called
103	"AnyEvent::Impl::Perl". Like other event modules you can load it	138	"AnyEvent::Impl::Perl". Like other event modules you can load it
104	explicitly.	139	explicitly and enjoy the high availability of that event loop :)
105		140
106	WATCHERS	141	WATCHERS
107	AnyEvent has the central concept of a watcher, which is an object that	142	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	143	stores relevant data for each kind of event you are waiting for, such as
109	the callback to call, the file handle to watch, etc.	144	the callback to call, the file handle to watch, etc.
…		…
111	These watchers are normal Perl objects with normal Perl lifetime. After	146	These watchers are normal Perl objects with normal Perl lifetime. After
112	creating a watcher it will immediately "watch" for events and invoke the	147	creating a watcher it will immediately "watch" for events and invoke the
113	callback when the event occurs (of course, only when the event model is	148	callback when the event occurs (of course, only when the event model is
114	in control).	149	in control).
115		150
		151	Note that callbacks must not permanently change global variables
		152	potentially in use by the event loop (such as $_ or $[) and that
		153	callbacks must not "die". The former is good programming practise in
		154	Perl and the latter stems from the fact that exception handling differs
		155	widely between event loops.
		156
116	To disable the watcher you have to destroy it (e.g. by setting the	157	To disable the watcher you have to destroy it (e.g. by setting the
117	variable you store it in to "undef" or otherwise deleting all references	158	variable you store it in to "undef" or otherwise deleting all references
118	to it).	159	to it).
119		160
120	All watchers are created by calling a method on the "AnyEvent" class.	161	All watchers are created by calling a method on the "AnyEvent" class.
…		…
122	Many watchers either are used with "recursion" (repeating timers for	163	Many watchers either are used with "recursion" (repeating timers for
123	example), or need to refer to their watcher object in other ways.	164	example), or need to refer to their watcher object in other ways.
124		165
125	An any way to achieve that is this pattern:	166	An any way to achieve that is this pattern:
126		167
127	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	168	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
128	# you can use $w here, for example to undef it	169	# you can use $w here, for example to undef it
129	undef $w;	170	undef $w;
130	});	171	});
131		172
132	Note that "my $w; $w =" combination. This is necessary because in Perl,	173	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	174	my variables are only visible after the statement in which they are
134	declared.	175	declared.
135		176
136	I/O WATCHERS	177	I/O WATCHERS
		178	$w = AnyEvent->io (
		179	fh => <filehandle_or_fileno>,
		180	poll => <"r" or "w">,
		181	cb => <callback>,
		182	);
		183
137	You can create an I/O watcher by calling the "AnyEvent->io" method with	184	You can create an I/O watcher by calling the "AnyEvent->io" method with
138	the following mandatory key-value pairs as arguments:	185	the following mandatory key-value pairs as arguments:
139		186
140	"fh" the Perl file handle (not file descriptor) to watch for events.	187	"fh" is the Perl file handle (or a naked file descriptor) to watch for
		188	events (AnyEvent might or might not keep a reference to this file
		189	handle). Note that only file handles pointing to things for which
		190	non-blocking operation makes sense are allowed. This includes sockets,
		191	most character devices, pipes, fifos and so on, but not for example
		192	files or block devices.
		193
141	"poll" must be a string that is either "r" or "w", which creates a	194	"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"	195	watcher waiting for "r"eadable or "w"ritable events, respectively.
		196
143	is the callback to invoke each time the file handle becomes ready.	197	"cb" is the callback to invoke each time the file handle becomes ready.
144		198
145	Although the callback might get passed parameters, their value and	199	Although the callback might get passed parameters, their value and
146	presence is undefined and you cannot rely on them. Portable AnyEvent	200	presence is undefined and you cannot rely on them. Portable AnyEvent
147	callbacks cannot use arguments passed to I/O watcher callbacks.	201	callbacks cannot use arguments passed to I/O watcher callbacks.
148		202
…		…
152		206
153	Some event loops issue spurious readyness notifications, so you should	207	Some event loops issue spurious readyness notifications, so you should
154	always use non-blocking calls when reading/writing from/to your file	208	always use non-blocking calls when reading/writing from/to your file
155	handles.	209	handles.
156		210
157	Example:
158
159	# wait for readability of STDIN, then read a line and disable the watcher	211	Example: wait for readability of STDIN, then read a line and disable the
		212	watcher.
		213
160	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	214	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
161	chomp (my $input = <STDIN>);	215	chomp (my $input = <STDIN>);
162	warn "read: $input\n";	216	warn "read: $input\n";
163	undef $w;	217	undef $w;
164	});	218	});
165		219
166	TIME WATCHERS	220	TIME WATCHERS
		221	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		222
		223	$w = AnyEvent->timer (
		224	after => <fractional_seconds>,
		225	interval => <fractional_seconds>,
		226	cb => <callback>,
		227	);
		228
167	You can create a time watcher by calling the "AnyEvent->timer" method	229	You can create a time watcher by calling the "AnyEvent->timer" method
168	with the following mandatory arguments:	230	with the following mandatory arguments:
169		231
170	"after" specifies after how many seconds (fractional values are	232	"after" specifies after how many seconds (fractional values are
171	supported) the callback should be invoked. "cb" is the callback to	233	supported) the callback should be invoked. "cb" is the callback to
…		…
173		235
174	Although the callback might get passed parameters, their value and	236	Although the callback might get passed parameters, their value and
175	presence is undefined and you cannot rely on them. Portable AnyEvent	237	presence is undefined and you cannot rely on them. Portable AnyEvent
176	callbacks cannot use arguments passed to time watcher callbacks.	238	callbacks cannot use arguments passed to time watcher callbacks.
177		239
178	The timer callback will be invoked at most once: if you want a repeating	240	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	241	parameter, "interval", as a strictly positive number (> 0), then the
180	and Glib).	242	callback will be invoked regularly at that interval (in fractional
		243	seconds) after the first invocation. If "interval" is specified with a
		244	false value, then it is treated as if it were missing.
181		245
182	Example:	246	The callback will be rescheduled before invoking the callback, but no
		247	attempt is done to avoid timer drift in most backends, so the interval
		248	is only approximate.
183		249
184	# fire an event after 7.7 seconds	250	Example: fire an event after 7.7 seconds.
		251
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	252	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	253	warn "timeout\n";
187	});	254	});
188		255
189	# to cancel the timer:	256	# to cancel the timer:
190	undef $w;	257	undef $w;
191		258
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	259	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		260
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	261	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		262	warn "timeout\n";
200	};	263	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		264
205	TIMING ISSUES	265	TIMING ISSUES
206	There are two ways to handle timers: based on real time (relative, "fire	266	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	267	in 10 seconds") and based on wallclock time (absolute, "fire at 12
208	o'clock").	268	o'clock").
…		…
220	on wallclock time) timers.	280	on wallclock time) timers.
221		281
222	AnyEvent always prefers relative timers, if available, matching the	282	AnyEvent always prefers relative timers, if available, matching the
223	AnyEvent API.	283	AnyEvent API.
224		284
		285	AnyEvent has two additional methods that return the "current time":
		286
		287	AnyEvent->time
		288	This returns the "current wallclock time" as a fractional number of
		289	seconds since the Epoch (the same thing as "time" or
		290	"Time::HiRes::time" return, and the result is guaranteed to be
		291	compatible with those).
		292
		293	It progresses independently of any event loop processing, i.e. each
		294	call will check the system clock, which usually gets updated
		295	frequently.
		296
		297	AnyEvent->now
		298	This also returns the "current wallclock time", but unlike "time",
		299	above, this value might change only once per event loop iteration,
		300	depending on the event loop (most return the same time as "time",
		301	above). This is the time that AnyEvent's timers get scheduled
		302	against.
		303
		304	*In almost all cases (in all cases if you don't care), this is the
		305	function to call when you want to know the current time.*
		306
		307	This function is also often faster then "AnyEvent->time", and thus
		308	the preferred method if you want some timestamp (for example,
		309	AnyEvent::Handle uses this to update it's activity timeouts).
		310
		311	The rest of this section is only of relevance if you try to be very
		312	exact with your timing, you can skip it without bad conscience.
		313
		314	For a practical example of when these times differ, consider
		315	Event::Lib and EV and the following set-up:
		316
		317	The event loop is running and has just invoked one of your callback
		318	at time=500 (assume no other callbacks delay processing). In your
		319	callback, you wait a second by executing "sleep 1" (blocking the
		320	process for a second) and then (at time=501) you create a relative
		321	timer that fires after three seconds.
		322
		323	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		324	return 501, because that is the current time, and the timer will be
		325	scheduled to fire at time=504 (501 + 3).
		326
		327	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		328	but "AnyEvent->now" returns 500, as that is the time the last event
		329	processing phase started. With EV, your timer gets scheduled to run
		330	at time=503 (500 + 3).
		331
		332	In one sense, Event::Lib is more exact, as it uses the current time
		333	regardless of any delays introduced by event processing. However,
		334	most callbacks do not expect large delays in processing, so this
		335	causes a higher drift (and a lot more system calls to get the
		336	current time).
		337
		338	In another sense, EV is more exact, as your timer will be scheduled
		339	at the same time, regardless of how long event processing actually
		340	took.
		341
		342	In either case, if you care (and in most cases, you don't), then you
		343	can get whatever behaviour you want with any event loop, by taking
		344	the difference between "AnyEvent->time" and "AnyEvent->now" into
		345	account.
		346
		347	AnyEvent->now_update
		348	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		349	current time for each loop iteration (see the discussion of
		350	AnyEvent->now, above).
		351
		352	When a callback runs for a long time (or when the process sleeps),
		353	then this "current" time will differ substantially from the real
		354	time, which might affect timers and time-outs.
		355
		356	When this is the case, you can call this method, which will update
		357	the event loop's idea of "current time".
		358
		359	Note that updating the time might cause some events to be handled.
		360
225	SIGNAL WATCHERS	361	SIGNAL WATCHERS
		362	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		363
226	You can watch for signals using a signal watcher, "signal" is the signal	364	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	365	name in uppercase and without any "SIG" prefix, "cb" is the Perl
228	whenever a signal occurs.	366	callback to be invoked whenever a signal occurs.
229		367
230	Although the callback might get passed parameters, their value and	368	Although the callback might get passed parameters, their value and
231	presence is undefined and you cannot rely on them. Portable AnyEvent	369	presence is undefined and you cannot rely on them. Portable AnyEvent
232	callbacks cannot use arguments passed to signal watcher callbacks.	370	callbacks cannot use arguments passed to signal watcher callbacks.
233		371
…		…
235	invocation, and callback invocation will be synchronous. Synchronous	373	invocation, and callback invocation will be synchronous. Synchronous
236	means that it might take a while until the signal gets handled by the	374	means that it might take a while until the signal gets handled by the
237	process, but it is guaranteed not to interrupt any other callbacks.	375	process, but it is guaranteed not to interrupt any other callbacks.
238		376
239	The main advantage of using these watchers is that you can share a	377	The main advantage of using these watchers is that you can share a
240	signal between multiple watchers.	378	signal between multiple watchers, and AnyEvent will ensure that signals
		379	will not interrupt your program at bad times.
241		380
242	This watcher might use %SIG, so programs overwriting those signals	381	This watcher might use %SIG (depending on the event loop used), so
243	directly will likely not work correctly.	382	programs overwriting those signals directly will likely not work
		383	correctly.
244		384
245	Example: exit on SIGINT	385	Example: exit on SIGINT
246		386
247	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	387	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
248		388
		389	Signal Races, Delays and Workarounds
		390	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		391	callbacks to signals in a generic way, which is a pity, as you cannot do
		392	race-free signal handling in perl, requiring C libraries for this.
		393	AnyEvent will try to do it's best, which means in some cases, signals
		394	will be delayed. The maximum time a signal might be delayed is specified
		395	in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
		396	can be changed only before the first signal watcher is created, and
		397	should be left alone otherwise. This variable determines how often
		398	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		399	will cause fewer spurious wake-ups, which is better for power and CPU
		400	saving.
		401
		402	All these problems can be avoided by installing the optional
		403	Async::Interrupt module, which works with most event loops. It will not
		404	work with inherently broken event loops such as Event or Event::Lib (and
		405	not with POE currently, as POE does it's own workaround with one-second
		406	latency). For those, you just have to suffer the delays.
		407
249	CHILD PROCESS WATCHERS	408	CHILD PROCESS WATCHERS
		409	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		410
250	You can also watch on a child process exit and catch its exit status.	411	You can also watch on a child process exit and catch its exit status.
251		412
252	The child process is specified by the "pid" argument (if set to 0, it	413	The child process is specified by the "pid" argument (one some backends,
253	watches for any child process exit). The watcher will trigger as often	414	using 0 watches for any child process exit, on others this will croak).
254	as status change for the child are received. This works by installing a	415	The watcher will be triggered only when the child process has finished
255	signal handler for "SIGCHLD". The callback will be called with the pid	416	and an exit status is available, not on any trace events
256	and exit status (as returned by waitpid), so unlike other watcher types,	417	(stopped/continued).
257	you can rely on child watcher callback arguments.	418
		419	The callback will be called with the pid and exit status (as returned by
		420	waitpid), so unlike other watcher types, you can rely on child watcher
		421	callback arguments.
		422
		423	This watcher type works by installing a signal handler for "SIGCHLD",
		424	and since it cannot be shared, nothing else should use SIGCHLD or reap
		425	random child processes (waiting for specific child processes, e.g.
		426	inside "system", is just fine).
258		427
259	There is a slight catch to child watchers, however: you usually start	428	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	429	them after the child process was created, and this means the process
261	could have exited already (and no SIGCHLD will be sent anymore).	430	could have exited already (and no SIGCHLD will be sent anymore).
262		431
263	Not all event models handle this correctly (POE doesn't), but even for	432	Not all event models handle this correctly (neither POE nor IO::Async
		433	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	434	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	435	before the process exits (i.e. before you fork in the first place).
266	place).	436	AnyEvent's pure perl event loop handles all cases correctly regardless
		437	of when you start the watcher.
267		438
268	This means you cannot create a child watcher as the very first thing in	439	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	440	an AnyEvent program, you have to create at least one watcher before
270	you "fork" the child (alternatively, you can call "AnyEvent::detect").	441	you "fork" the child (alternatively, you can call "AnyEvent::detect").
271		442
		443	As most event loops do not support waiting for child events, they will
		444	be emulated by AnyEvent in most cases, in which the latency and race
		445	problems mentioned in the description of signal watchers apply.
		446
272	Example: fork a process and wait for it	447	Example: fork a process and wait for it
273		448
274	my $done = AnyEvent->condvar;	449	my $done = AnyEvent->condvar;
275		450
276	my $pid = fork or exit 5;	451	my $pid = fork or exit 5;
277		452
278	my $w = AnyEvent->child (	453	my $w = AnyEvent->child (
279	pid => $pid,	454	pid => $pid,
280	cb => sub {	455	cb => sub {
281	my ($pid, $status) = @_;	456	my ($pid, $status) = @_;
282	warn "pid $pid exited with status $status";	457	warn "pid $pid exited with status $status";
283	$done->send;	458	$done->send;
284	},	459	},
285	);	460	);
286		461
287	# do something else, then wait for process exit	462	# do something else, then wait for process exit
288	$done->recv;	463	$done->recv;
		464
		465	IDLE WATCHERS
		466	$w = AnyEvent->idle (cb => <callback>);
		467
		468	Sometimes there is a need to do something, but it is not so important to
		469	do it instantly, but only when there is nothing better to do. This
		470	"nothing better to do" is usually defined to be "no other events need
		471	attention by the event loop".
		472
		473	Idle watchers ideally get invoked when the event loop has nothing better
		474	to do, just before it would block the process to wait for new events.
		475	Instead of blocking, the idle watcher is invoked.
		476
		477	Most event loops unfortunately do not really support idle watchers (only
		478	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		479	will simply call the callback "from time to time".
		480
		481	Example: read lines from STDIN, but only process them when the program
		482	is otherwise idle:
		483
		484	my @lines; # read data
		485	my $idle_w;
		486	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		487	push @lines, scalar <STDIN>;
		488
		489	# start an idle watcher, if not already done
		490	$idle_w \|\|= AnyEvent->idle (cb => sub {
		491	# handle only one line, when there are lines left
		492	if (my $line = shift @lines) {
		493	print "handled when idle: $line";
		494	} else {
		495	# otherwise disable the idle watcher again
		496	undef $idle_w;
		497	}
		498	});
		499	});
289		500
290	CONDITION VARIABLES	501	CONDITION VARIABLES
		502	$cv = AnyEvent->condvar;
		503
		504	$cv->send (<list>);
		505	my @res = $cv->recv;
		506
291	If you are familiar with some event loops you will know that all of them	507	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	508	require you to run some blocking "loop", "run" or similar function that
293	will actively watch for new events and call your callbacks.	509	will actively watch for new events and call your callbacks.
294		510
295	AnyEvent is different, it expects somebody else to run the event loop	511	AnyEvent is slightly different: it expects somebody else to run the
296	and will only block when necessary (usually when told by the user).	512	event loop and will only block when necessary (usually when told by the
		513	user).
297		514
298	The instrument to do that is called a "condition variable", so called	515	The instrument to do that is called a "condition variable", so called
299	because they represent a condition that must become true.	516	because they represent a condition that must become true.
		517
		518	Now is probably a good time to look at the examples further below.
300		519
301	Condition variables can be created by calling the "AnyEvent->condvar"	520	Condition variables can be created by calling the "AnyEvent->condvar"
302	method, usually without arguments. The only argument pair allowed is	521	method, usually without arguments. The only argument pair allowed is
303	"cb", which specifies a callback to be called when the condition	522	"cb", which specifies a callback to be called when the condition
304	variable becomes true.	523	variable becomes true, with the condition variable as the first argument
		524	(but not the results).
305		525
306	After creation, the condition variable is "false" until it becomes	526	After creation, the condition variable is "false" until it becomes
307	"true" by calling the "send" method (or calling the condition variable	527	"true" by calling the "send" method (or calling the condition variable
308	as if it were a callback).	528	as if it were a callback, read about the caveats in the description for
		529	the "->send" method).
309		530
310	Condition variables are similar to callbacks, except that you can	531	Condition variables are similar to callbacks, except that you can
311	optionally wait for them. They can also be called merge points - points	532	optionally wait for them. They can also be called merge points - points
312	in time where multiple outstanding events have been processed. And yet	533	in time where multiple outstanding events have been processed. And yet
313	another way to call them is transactions - each condition variable can	534	another way to call them is transactions - each condition variable can
314	be used to represent a transaction, which finishes at some point and	535	be used to represent a transaction, which finishes at some point and
315	delivers a result.	536	delivers a result. And yet some people know them as "futures" - a
		537	promise to compute/deliver something that you can wait for.
316		538
317	Condition variables are very useful to signal that something has	539	Condition variables are very useful to signal that something has
318	finished, for example, if you write a module that does asynchronous http	540	finished, for example, if you write a module that does asynchronous http
319	requests, then a condition variable would be the ideal candidate to	541	requests, then a condition variable would be the ideal candidate to
320	signal the availability of results. The user can either act when the	542	signal the availability of results. The user can either act when the
…		…
354	after => 1,	576	after => 1,
355	cb => sub { $result_ready->send },	577	cb => sub { $result_ready->send },
356	);	578	);
357		579
358	# this "blocks" (while handling events) till the callback	580	# this "blocks" (while handling events) till the callback
359	# calls send	581	# calls -<send
360	$result_ready->recv;	582	$result_ready->recv;
361		583
362	Example: wait for a timer, but take advantage of the fact that condition	584	Example: wait for a timer, but take advantage of the fact that condition
363	variables are also code references.	585	variables are also callable directly.
364		586
365	my $done = AnyEvent->condvar;	587	my $done = AnyEvent->condvar;
366	my $delay = AnyEvent->timer (after => 5, cb => $done);	588	my $delay = AnyEvent->timer (after => 5, cb => $done);
367	$done->recv;	589	$done->recv;
		590
		591	Example: Imagine an API that returns a condvar and doesn't support
		592	callbacks. This is how you make a synchronous call, for example from the
		593	main program:
		594
		595	use AnyEvent::CouchDB;
		596
		597	...
		598
		599	my @info = $couchdb->info->recv;
		600
		601	And this is how you would just set a callback to be called whenever the
		602	results are available:
		603
		604	$couchdb->info->cb (sub {
		605	my @info = $_[0]->recv;
		606	});
368		607
369	METHODS FOR PRODUCERS	608	METHODS FOR PRODUCERS
370	These methods should only be used by the producing side, i.e. the	609	These methods should only be used by the producing side, i.e. the
371	code/module that eventually sends the signal. Note that it is also the	610	code/module that eventually sends the signal. Note that it is also the
372	producer side which creates the condvar in most cases, but it isn't	611	producer side which creates the condvar in most cases, but it isn't
…		…
382		621
383	Any arguments passed to the "send" call will be returned by all	622	Any arguments passed to the "send" call will be returned by all
384	future "->recv" calls.	623	future "->recv" calls.
385		624
386	Condition variables are overloaded so one can call them directly (as	625	Condition variables are overloaded so one can call them directly (as
387	a code reference). Calling them directly is the same as calling	626	if they were a code reference). Calling them directly is the same as
388	"send".	627	calling "send".
389		628
390	$cv->croak ($error)	629	$cv->croak ($error)
391	Similar to send, but causes all call's to "->recv" to invoke	630	Similar to send, but causes all call's to "->recv" to invoke
392	"Carp::croak" with the given error message/object/scalar.	631	"Carp::croak" with the given error message/object/scalar.
393		632
394	This can be used to signal any errors to the condition variable	633	This can be used to signal any errors to the condition variable
395	user/consumer.	634	user/consumer. Doing it this way instead of calling "croak" directly
		635	delays the error detetcion, but has the overwhelmign advantage that
		636	it diagnoses the error at the place where the result is expected,
		637	and not deep in some event clalback without connection to the actual
		638	code causing the problem.
396		639
397	$cv->begin ([group callback])	640	$cv->begin ([group callback])
398	$cv->end	641	$cv->end
399	These two methods are EXPERIMENTAL and MIGHT CHANGE.
400
401	These two methods can be used to combine many transactions/events	642	These two methods can be used to combine many transactions/events
402	into one. For example, a function that pings many hosts in parallel	643	into one. For example, a function that pings many hosts in parallel
403	might want to use a condition variable for the whole process.	644	might want to use a condition variable for the whole process.
404		645
405	Every call to "->begin" will increment a counter, and every call to	646	Every call to "->begin" will increment a counter, and every call to
406	"->end" will decrement it. If the counter reaches 0 in "->end", the	647	"->end" will decrement it. If the counter reaches 0 in "->end", the
407	(last) callback passed to "begin" will be executed. That callback is	648	(last) callback passed to "begin" will be executed. That callback is
408	supposed to call "->send", but that is not required. If no	649	supposed to call "->send", but that is not required. If no
409	callback was set, "send" will be called without any arguments.	650	callback was set, "send" will be called without any arguments.
410		651
411	Let's clarify this with the ping example:	652	You can think of "$cv->send" giving you an OR condition (one call
		653	sends), while "$cv->begin" and "$cv->end" giving you an AND
		654	condition (all "begin" calls must be "end"'ed before the condvar
		655	sends).
		656
		657	Let's start with a simple example: you have two I/O watchers (for
		658	example, STDOUT and STDERR for a program), and you want to wait for
		659	both streams to close before activating a condvar:
		660
		661	my $cv = AnyEvent->condvar;
		662
		663	$cv->begin; # first watcher
		664	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		665	defined sysread $fh1, my $buf, 4096
		666	or $cv->end;
		667	});
		668
		669	$cv->begin; # second watcher
		670	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		671	defined sysread $fh2, my $buf, 4096
		672	or $cv->end;
		673	});
		674
		675	$cv->recv;
		676
		677	This works because for every event source (EOF on file handle),
		678	there is one call to "begin", so the condvar waits for all calls to
		679	"end" before sending.
		680
		681	The ping example mentioned above is slightly more complicated, as
		682	the there are results to be passwd back, and the number of tasks
		683	that are begung can potentially be zero:
412		684
413	my $cv = AnyEvent->condvar;	685	my $cv = AnyEvent->condvar;
414		686
415	my %result;	687	my %result;
416	$cv->begin (sub { $cv->send (\%result) });	688	$cv->begin (sub { $cv->send (\%result) });
…		…
436	the loop, which serves two important purposes: first, it sets the	708	the loop, which serves two important purposes: first, it sets the
437	callback to be called once the counter reaches 0, and second, it	709	callback to be called once the counter reaches 0, and second, it
438	ensures that "send" is called even when "no" hosts are being pinged	710	ensures that "send" is called even when "no" hosts are being pinged
439	(the loop doesn't execute once).	711	(the loop doesn't execute once).
440		712
441	This is the general pattern when you "fan out" into multiple	713	This is the general pattern when you "fan out" into multiple (but
442	subrequests: use an outer "begin"/"end" pair to set the callback and	714	potentially none) subrequests: use an outer "begin"/"end" pair to
443	ensure "end" is called at least once, and then, for each subrequest	715	set the callback and ensure "end" is called at least once, and then,
444	you start, call "begin" and for each subrequest you finish, call	716	for each subrequest you start, call "begin" and for each subrequest
445	"end".	717	you finish, call "end".
446		718
447	METHODS FOR CONSUMERS	719	METHODS FOR CONSUMERS
448	These methods should only be used by the consuming side, i.e. the code	720	These methods should only be used by the consuming side, i.e. the code
449	awaits the condition.	721	awaits the condition.
450		722
…		…
459	function will call "croak".	731	function will call "croak".
460		732
461	In list context, all parameters passed to "send" will be returned,	733	In list context, all parameters passed to "send" will be returned,
462	in scalar context only the first one will be returned.	734	in scalar context only the first one will be returned.
463		735
		736	Note that doing a blocking wait in a callback is not supported by
		737	any event loop, that is, recursive invocation of a blocking "->recv"
		738	is not allowed, and the "recv" call will "croak" if such a condition
		739	is detected. This condition can be slightly loosened by using
		740	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		741	thread that doesn't run the event loop itself.
		742
464	Not all event models support a blocking wait - some die in that case	743	Not all event models support a blocking wait - some die in that case
465	(programs might want to do that to stay interactive), so *if you are	744	(programs might want to do that to stay interactive), so *if you are
466	using this from a module, never require a blocking wait*, but let	745	using this from a module, never require a blocking wait*. Instead,
467	the caller decide whether the call will block or not (for example,	746	let the caller decide whether the call will block or not (for
468	by coupling condition variables with some kind of request results	747	example, by coupling condition variables with some kind of request
469	and supporting callbacks so the caller knows that getting the result	748	results and supporting callbacks so the caller knows that getting
470	will not block, while still supporting blocking waits if the caller	749	the result will not block, while still supporting blocking waits if
471	so desires).	750	the caller so desires).
472
473	Another reason never to "->recv" in a module is that you cannot
474	sensibly have two "->recv"'s in parallel, as that would require
475	multiple interpreters or coroutines/threads, none of which
476	"AnyEvent" can supply.
477
478	The Coro module, however, can and does supply coroutines and, in
479	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
480	versions and also integrates coroutines into AnyEvent, making
481	blocking "->recv" calls perfectly safe as long as they are done from
482	another coroutine (one that doesn't run the event loop).
483		751
484	You can ensure that "-recv" never blocks by setting a callback and	752	You can ensure that "-recv" never blocks by setting a callback and
485	only calling "->recv" from within that callback (or at a later	753	only calling "->recv" from within that callback (or at a later
486	time). This will work even when the event loop does not support	754	time). This will work even when the event loop does not support
487	blocking waits otherwise.	755	blocking waits otherwise.
488		756
489	$bool = $cv->ready	757	$bool = $cv->ready
490	Returns true when the condition is "true", i.e. whether "send" or	758	Returns true when the condition is "true", i.e. whether "send" or
491	"croak" have been called.	759	"croak" have been called.
492		760
493	$cb = $cv->cb ([new callback])	761	$cb = $cv->cb ($cb->($cv))
494	This is a mutator function that returns the callback set and	762	This is a mutator function that returns the callback set and
495	optionally replaces it before doing so.	763	optionally replaces it before doing so.
496		764
497	The callback will be called when the condition becomes "true", i.e.	765	The callback will be called when the condition becomes (or already
498	when "send" or "croak" are called. Calling "recv" inside the	766	was) "true", i.e. when "send" or "croak" are called (or were
499	callback or at any later time is guaranteed not to block.	767	called), with the only argument being the condition variable itself.
		768	Calling "recv" inside the callback or at any later time is
		769	guaranteed not to block.
		770
		771	SUPPORTED EVENT LOOPS/BACKENDS
		772	The available backend classes are (every class has its own manpage):
		773
		774	Backends that are autoprobed when no other event loop can be found.
		775	EV is the preferred backend when no other event loop seems to be in
		776	use. If EV is not installed, then AnyEvent will try Event, and,
		777	failing that, will fall back to its own pure-perl implementation,
		778	which is available everywhere as it comes with AnyEvent itself.
		779
		780	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		781	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		782	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		783
		784	Backends that are transparently being picked up when they are used.
		785	These will be used when they are currently loaded when the first
		786	watcher is created, in which case it is assumed that the application
		787	is using them. This means that AnyEvent will automatically pick the
		788	right backend when the main program loads an event module before
		789	anything starts to create watchers. Nothing special needs to be done
		790	by the main program.
		791
		792	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		793	AnyEvent::Impl::Tk based on Tk, very broken.
		794	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		795	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		796	AnyEvent::Impl::Irssi used when running within irssi.
		797
		798	Backends with special needs.
		799	Qt requires the Qt::Application to be instantiated first, but will
		800	otherwise be picked up automatically. As long as the main program
		801	instantiates the application before any AnyEvent watchers are
		802	created, everything should just work.
		803
		804	AnyEvent::Impl::Qt based on Qt.
		805
		806	Support for IO::Async can only be partial, as it is too broken and
		807	architecturally limited to even support the AnyEvent API. It also is
		808	the only event loop that needs the loop to be set explicitly, so it
		809	can only be used by a main program knowing about AnyEvent. See
		810	AnyEvent::Impl::Async for the gory details.
		811
		812	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		813
		814	Event loops that are indirectly supported via other backends.
		815	Some event loops can be supported via other modules:
		816
		817	There is no direct support for WxWidgets (Wx) or Prima.
		818
		819	WxWidgets has no support for watching file handles. However, you can
		820	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		821	simply polls 20 times per second, which was considered to be too
		822	horrible to even consider for AnyEvent.
		823
		824	Prima is not supported as nobody seems to be using it, but it has a
		825	POE backend, so it can be supported through POE.
		826
		827	AnyEvent knows about both Prima and Wx, however, and will try to
		828	load POE when detecting them, in the hope that POE will pick them
		829	up, in which case everything will be automatic.
500		830
501	GLOBAL VARIABLES AND FUNCTIONS	831	GLOBAL VARIABLES AND FUNCTIONS
		832	These are not normally required to use AnyEvent, but can be useful to
		833	write AnyEvent extension modules.
		834
502	$AnyEvent::MODEL	835	$AnyEvent::MODEL
503	Contains "undef" until the first watcher is being created. Then it	836	Contains "undef" until the first watcher is being created, before
		837	the backend has been autodetected.
		838
504	contains the event model that is being used, which is the name of	839	Afterwards it contains the event model that is being used, which is
505	the Perl class implementing the model. This class is usually one of	840	the name of the Perl class implementing the model. This class is
506	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	841	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
507	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	842	other class in the case AnyEvent has been extended at runtime (e.g.
508		843	in rxvt-unicode it will be "urxvt::anyevent").
509	The known classes so far are:
510
511	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
512	AnyEvent::Impl::Event based on Event, second best choice.
513	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
514	AnyEvent::Impl::Glib based on Glib, third-best choice.
515	AnyEvent::Impl::Tk based on Tk, very bad choice.
516	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
517	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
518	AnyEvent::Impl::POE based on POE, not generic enough for full support.
519
520	There is no support for WxWidgets, as WxWidgets has no support for
521	watching file handles. However, you can use WxWidgets through the
522	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
523	second, which was considered to be too horrible to even consider for
524	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
525	using it's adaptor.
526
527	AnyEvent knows about Prima and Wx and will try to use POE when
528	autodetecting them.
529		844
530	AnyEvent::detect	845	AnyEvent::detect
531	Returns $AnyEvent::MODEL, forcing autodetection of the event model	846	Returns $AnyEvent::MODEL, forcing autodetection of the event model
532	if necessary. You should only call this function right before you	847	if necessary. You should only call this function right before you
533	would have created an AnyEvent watcher anyway, that is, as late as	848	would have created an AnyEvent watcher anyway, that is, as late as
534	possible at runtime.	849	possible at runtime, and not e.g. while initialising of your module.
		850
		851	If you need to do some initialisation before AnyEvent watchers are
		852	created, use "post_detect".
535		853
536	$guard = AnyEvent::post_detect { BLOCK }	854	$guard = AnyEvent::post_detect { BLOCK }
537	Arranges for the code block to be executed as soon as the event	855	Arranges for the code block to be executed as soon as the event
538	model is autodetected (or immediately if this has already happened).	856	model is autodetected (or immediately if this has already happened).
539		857
		858	The block will be executed after the actual backend has been
		859	detected ($AnyEvent::MODEL is set), but before any watchers have
		860	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		861	other initialisations - see the sources of AnyEvent::Strict or
		862	AnyEvent::AIO to see how this is used.
		863
		864	The most common usage is to create some global watchers, without
		865	forcing event module detection too early, for example, AnyEvent::AIO
		866	creates and installs the global IO::AIO watcher in a "post_detect"
		867	block to avoid autodetecting the event module at load time.
		868
540	If called in scalar or list context, then it creates and returns an	869	If called in scalar or list context, then it creates and returns an
541	object that automatically removes the callback again when it is	870	object that automatically removes the callback again when it is
		871	destroyed (or "undef" when the hook was immediately executed). See
542	destroyed. See Coro::BDB for a case where this is useful.	872	AnyEvent::AIO for a case where this is useful.
		873
		874	Example: Create a watcher for the IO::AIO module and store it in
		875	$WATCHER. Only do so after the event loop is initialised, though.
		876
		877	our WATCHER;
		878
		879	my $guard = AnyEvent::post_detect {
		880	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		881	};
		882
		883	# the \|\|= is important in case post_detect immediately runs the block,
		884	# as to not clobber the newly-created watcher. assigning both watcher and
		885	# post_detect guard to the same variable has the advantage of users being
		886	# able to just C<undef $WATCHER> if the watcher causes them grief.
		887
		888	$WATCHER \|\|= $guard;
543		889
544	@AnyEvent::post_detect	890	@AnyEvent::post_detect
545	If there are any code references in this array (you can "push" to it	891	If there are any code references in this array (you can "push" to it
546	before or after loading AnyEvent), then they will called directly	892	before or after loading AnyEvent), then they will called directly
547	after the event loop has been chosen.	893	after the event loop has been chosen.
548		894
549	You should check $AnyEvent::MODEL before adding to this array,	895	You should check $AnyEvent::MODEL before adding to this array,
550	though: if it contains a true value then the event loop has already	896	though: if it is defined then the event loop has already been
551	been detected, and the array will be ignored.	897	detected, and the array will be ignored.
552		898
553	Best use "AnyEvent::post_detect { BLOCK }" instead.	899	Best use "AnyEvent::post_detect { BLOCK }" when your application
		900	allows it,as it takes care of these details.
		901
		902	This variable is mainly useful for modules that can do something
		903	useful when AnyEvent is used and thus want to know when it is
		904	initialised, but do not need to even load it by default. This array
		905	provides the means to hook into AnyEvent passively, without loading
		906	it.
554		907
555	WHAT TO DO IN A MODULE	908	WHAT TO DO IN A MODULE
556	As a module author, you should "use AnyEvent" and call AnyEvent methods	909	As a module author, you should "use AnyEvent" and call AnyEvent methods
557	freely, but you should not load a specific event module or rely on it.	910	freely, but you should not load a specific event module or rely on it.
558		911
…		…
578	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	931	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
579	do anything special (it does not need to be event-based) and let	932	do anything special (it does not need to be event-based) and let
580	AnyEvent decide which implementation to chose if some module relies on	933	AnyEvent decide which implementation to chose if some module relies on
581	it.	934	it.
582		935
583	If the main program relies on a specific event model. For example, in	936	If the main program relies on a specific event model - for example, in
584	Gtk2 programs you have to rely on the Glib module. You should load the	937	Gtk2 programs you have to rely on the Glib module - you should load the
585	event module before loading AnyEvent or any module that uses it:	938	event module before loading AnyEvent or any module that uses it:
586	generally speaking, you should load it as early as possible. The reason	939	generally speaking, you should load it as early as possible. The reason
587	is that modules might create watchers when they are loaded, and AnyEvent	940	is that modules might create watchers when they are loaded, and AnyEvent
588	will decide on the event model to use as soon as it creates watchers,	941	will decide on the event model to use as soon as it creates watchers,
589	and it might chose the wrong one unless you load the correct one	942	and it might chose the wrong one unless you load the correct one
590	yourself.	943	yourself.
591		944
592	You can chose to use a rather inefficient pure-perl implementation by	945	You can chose to use a pure-perl implementation by loading the
593	loading the "AnyEvent::Impl::Perl" module, which gives you similar	946	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
594	behaviour everywhere, but letting AnyEvent chose is generally better.	947	everywhere, but letting AnyEvent chose the model is generally better.
		948
		949	MAINLOOP EMULATION
		950	Sometimes (often for short test scripts, or even standalone programs who
		951	only want to use AnyEvent), you do not want to run a specific event
		952	loop.
		953
		954	In that case, you can use a condition variable like this:
		955
		956	AnyEvent->condvar->recv;
		957
		958	This has the effect of entering the event loop and looping forever.
		959
		960	Note that usually your program has some exit condition, in which case it
		961	is better to use the "traditional" approach of storing a condition
		962	variable somewhere, waiting for it, and sending it when the program
		963	should exit cleanly.
595		964
596	OTHER MODULES	965	OTHER MODULES
597	The following is a non-exhaustive list of additional modules that use	966	The following is a non-exhaustive list of additional modules that use
598	AnyEvent and can therefore be mixed easily with other AnyEvent modules	967	AnyEvent as a client and can therefore be mixed easily with other
599	in the same program. Some of the modules come with AnyEvent, some are	968	AnyEvent modules and other event loops in the same program. Some of the
600	available via CPAN.	969	modules come with AnyEvent, most are available via CPAN.
601		970
602	AnyEvent::Util	971	AnyEvent::Util
603	Contains various utility functions that replace often-used but	972	Contains various utility functions that replace often-used but
604	blocking functions such as "inet_aton" by event-/callback-based	973	blocking functions such as "inet_aton" by event-/callback-based
605	versions.	974	versions.
606
607	AnyEvent::Handle
608	Provide read and write buffers and manages watchers for reads and
609	writes.
610		975
611	AnyEvent::Socket	976	AnyEvent::Socket
612	Provides various utility functions for (internet protocol) sockets,	977	Provides various utility functions for (internet protocol) sockets,
613	addresses and name resolution. Also functions to create non-blocking	978	addresses and name resolution. Also functions to create non-blocking
614	tcp connections or tcp servers, with IPv6 and SRV record support and	979	tcp connections or tcp servers, with IPv6 and SRV record support and
615	more.	980	more.
616		981
		982	AnyEvent::Handle
		983	Provide read and write buffers, manages watchers for reads and
		984	writes, supports raw and formatted I/O, I/O queued and fully
		985	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
		986
		987	AnyEvent::DNS
		988	Provides rich asynchronous DNS resolver capabilities.
		989
		990	AnyEvent::HTTP
		991	A simple-to-use HTTP library that is capable of making a lot of
		992	concurrent HTTP requests.
		993
617	AnyEvent::HTTPD	994	AnyEvent::HTTPD
618	Provides a simple web application server framework.	995	Provides a simple web application server framework.
619		996
620	AnyEvent::DNS
621	Provides rich asynchronous DNS resolver capabilities.
622
623	AnyEvent::FastPing	997	AnyEvent::FastPing
624	The fastest ping in the west.	998	The fastest ping in the west.
625		999
		1000	AnyEvent::DBI
		1001	Executes DBI requests asynchronously in a proxy process.
		1002
		1003	AnyEvent::AIO
		1004	Truly asynchronous I/O, should be in the toolbox of every event
		1005	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		1006	together.
		1007
		1008	AnyEvent::BDB
		1009	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		1010	fuses BDB and AnyEvent together.
		1011
		1012	AnyEvent::GPSD
		1013	A non-blocking interface to gpsd, a daemon delivering GPS
		1014	information.
		1015
		1016	AnyEvent::IRC
		1017	AnyEvent based IRC client module family (replacing the older
626	Net::IRC3	1018	Net::IRC3).
627	AnyEvent based IRC client module family.
628		1019
629	Net::XMPP2	1020	AnyEvent::XMPP
630	AnyEvent based XMPP (Jabber protocol) module family.	1021	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		1022	older Net::XMPP2>.
		1023
		1024	AnyEvent::IGS
		1025	A non-blocking interface to the Internet Go Server protocol (used by
		1026	App::IGS).
631		1027
632	Net::FCP	1028	Net::FCP
633	AnyEvent-based implementation of the Freenet Client Protocol,	1029	AnyEvent-based implementation of the Freenet Client Protocol,
634	birthplace of AnyEvent.	1030	birthplace of AnyEvent.
635		1031
…		…
637	High level API for event-based execution flow control.	1033	High level API for event-based execution flow control.
638		1034
639	Coro	1035	Coro
640	Has special support for AnyEvent via Coro::AnyEvent.	1036	Has special support for AnyEvent via Coro::AnyEvent.
641		1037
642	AnyEvent::AIO, IO::AIO	1038	ERROR AND EXCEPTION HANDLING
643	Truly asynchronous I/O, should be in the toolbox of every event	1039	In general, AnyEvent does not do any error handling - it relies on the
644	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	1040	caller to do that if required. The AnyEvent::Strict module (see also the
645	together.	1041	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1042	checking of all AnyEvent methods, however, which is highly useful during
		1043	development.
646		1044
647	AnyEvent::BDB, BDB	1045	As for exception handling (i.e. runtime errors and exceptions thrown
648	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently	1046	while executing a callback), this is not only highly event-loop
649	fuses IO::AIO and AnyEvent together.	1047	specific, but also not in any way wrapped by this module, as this is the
		1048	job of the main program.
650		1049
651	IO::Lambda	1050	The pure perl event loop simply re-throws the exception (usually within
652	The lambda approach to I/O - don't ask, look there. Can use	1051	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
653	AnyEvent.	1052	Glib uses "install_exception_handler" and so on.
654
655	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
656	This is an advanced topic that you do not normally need to use AnyEvent
657	in a module. This section is only of use to event loop authors who want
658	to provide AnyEvent compatibility.
659
660	If you need to support another event library which isn't directly
661	supported by AnyEvent, you can supply your own interface to it by
662	pushing, before the first watcher gets created, the package name of the
663	event module and the package name of the interface to use onto
664	@AnyEvent::REGISTRY. You can do that before and even without loading
665	AnyEvent, so it is reasonably cheap.
666
667	Example:
668
669	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
670
671	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
672	package/class when it finds the "urxvt" package/module is already
673	loaded.
674
675	When AnyEvent is loaded and asked to find a suitable event model, it
676	will first check for the presence of urxvt by trying to "use" the
677	"urxvt::anyevent" module.
678
679	The class should provide implementations for all watcher types. See
680	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
681	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
682	the sources.
683
684	If you don't provide "signal" and "child" watchers than AnyEvent will
685	provide suitable (hopefully) replacements.
686
687	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
688	terminal emulator uses the above line as-is. An interface isn't included
689	in AnyEvent because it doesn't make sense outside the embedded
690	interpreter inside rxvt-unicode, and it is updated and maintained as
691	part of the rxvt-unicode distribution.
692
693	rxvt-unicode also cheats a bit by not providing blocking access to
694	condition variables: code blocking while waiting for a condition will
695	"die". This still works with most modules/usages, and blocking calls
696	must not be done in an interactive application, so it makes sense.
697		1053
698	ENVIRONMENT VARIABLES	1054	ENVIRONMENT VARIABLES
699	The following environment variables are used by this module:	1055	The following environment variables are used by this module or its
		1056	submodules.
		1057
		1058	Note that AnyEvent will remove all environment variables starting with
		1059	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1060	enabled.
700		1061
701	"PERL_ANYEVENT_VERBOSE"	1062	"PERL_ANYEVENT_VERBOSE"
702	By default, AnyEvent will be completely silent except in fatal	1063	By default, AnyEvent will be completely silent except in fatal
703	conditions. You can set this environment variable to make AnyEvent	1064	conditions. You can set this environment variable to make AnyEvent
704	more talkative.	1065	more talkative.
…		…
707	conditions, such as not being able to load the event model specified	1068	conditions, such as not being able to load the event model specified
708	by "PERL_ANYEVENT_MODEL".	1069	by "PERL_ANYEVENT_MODEL".
709		1070
710	When set to 2 or higher, cause AnyEvent to report to STDERR which	1071	When set to 2 or higher, cause AnyEvent to report to STDERR which
711	event model it chooses.	1072	event model it chooses.
		1073
		1074	When set to 8 or higher, then AnyEvent will report extra information
		1075	on which optional modules it loads and how it implements certain
		1076	features.
		1077
		1078	"PERL_ANYEVENT_STRICT"
		1079	AnyEvent does not do much argument checking by default, as thorough
		1080	argument checking is very costly. Setting this variable to a true
		1081	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1082	thoroughly check the arguments passed to most method calls. If it
		1083	finds any problems, it will croak.
		1084
		1085	In other words, enables "strict" mode.
		1086
		1087	Unlike "use strict" (or it's modern cousin, "use common::sense", it
		1088	is definitely recommended to keep it off in production. Keeping
		1089	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1090	programs can be very useful, however.
712		1091
713	"PERL_ANYEVENT_MODEL"	1092	"PERL_ANYEVENT_MODEL"
714	This can be used to specify the event model to be used by AnyEvent,	1093	This can be used to specify the event model to be used by AnyEvent,
715	before auto detection and -probing kicks in. It must be a string	1094	before auto detection and -probing kicks in. It must be a string
716	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1095	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
721	This functionality might change in future versions.	1100	This functionality might change in future versions.
722		1101
723	For example, to force the pure perl model (AnyEvent::Impl::Perl) you	1102	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
724	could start your program like this:	1103	could start your program like this:
725		1104
726	PERL_ANYEVENT_MODEL=Perl perl ...	1105	PERL_ANYEVENT_MODEL=Perl perl ...
727		1106
728	"PERL_ANYEVENT_PROTOCOLS"	1107	"PERL_ANYEVENT_PROTOCOLS"
729	Used by both AnyEvent::DNS and AnyEvent::Socket to determine	1108	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
730	preferences for IPv4 or IPv6. The default is unspecified (and might	1109	preferences for IPv4 or IPv6. The default is unspecified (and might
731	change, or be the result of auto probing).	1110	change, or be the result of auto probing).
…		…
735	mentioned will be used, and preference will be given to protocols	1114	mentioned will be used, and preference will be given to protocols
736	mentioned earlier in the list.	1115	mentioned earlier in the list.
737		1116
738	This variable can effectively be used for denial-of-service attacks	1117	This variable can effectively be used for denial-of-service attacks
739	against local programs (e.g. when setuid), although the impact is	1118	against local programs (e.g. when setuid), although the impact is
740	likely small, as the program has to handle connection errors	1119	likely small, as the program has to handle conenction and other
741	already-	1120	failures anyways.
742		1121
743	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1122	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
744	IPv6, but support both and try to use both.	1123	IPv6, but support both and try to use both.
745	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1124	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
746	resolve or contact IPv6 addresses.	1125	resolve or contact IPv6 addresses.
…		…
753	but some (broken) firewalls drop such DNS packets, which is why it	1132	but some (broken) firewalls drop such DNS packets, which is why it
754	is off by default.	1133	is off by default.
755		1134
756	Setting this variable to 1 will cause AnyEvent::DNS to announce	1135	Setting this variable to 1 will cause AnyEvent::DNS to announce
757	EDNS0 in its DNS requests.	1136	EDNS0 in its DNS requests.
		1137
		1138	"PERL_ANYEVENT_MAX_FORKS"
		1139	The maximum number of child processes that
		1140	"AnyEvent::Util::fork_call" will create in parallel.
		1141
		1142	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1143	The default value for the "max_outstanding" parameter for the
		1144	default DNS resolver - this is the maximum number of parallel DNS
		1145	requests that are sent to the DNS server.
		1146
		1147	"PERL_ANYEVENT_RESOLV_CONF"
		1148	The file to use instead of /etc/resolv.conf (or OS-specific
		1149	configuration) in the default resolver. When set to the empty
		1150	string, no default config will be used.
		1151
		1152	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1153	When neither "ca_file" nor "ca_path" was specified during
		1154	AnyEvent::TLS context creation, and either of these environment
		1155	variables exist, they will be used to specify CA certificate
		1156	locations instead of a system-dependent default.
		1157
		1158	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1159	When these are set to 1, then the respective modules are not loaded.
		1160	Mostly good for testing AnyEvent itself.
		1161
		1162	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1163	This is an advanced topic that you do not normally need to use AnyEvent
		1164	in a module. This section is only of use to event loop authors who want
		1165	to provide AnyEvent compatibility.
		1166
		1167	If you need to support another event library which isn't directly
		1168	supported by AnyEvent, you can supply your own interface to it by
		1169	pushing, before the first watcher gets created, the package name of the
		1170	event module and the package name of the interface to use onto
		1171	@AnyEvent::REGISTRY. You can do that before and even without loading
		1172	AnyEvent, so it is reasonably cheap.
		1173
		1174	Example:
		1175
		1176	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1177
		1178	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
		1179	package/class when it finds the "urxvt" package/module is already
		1180	loaded.
		1181
		1182	When AnyEvent is loaded and asked to find a suitable event model, it
		1183	will first check for the presence of urxvt by trying to "use" the
		1184	"urxvt::anyevent" module.
		1185
		1186	The class should provide implementations for all watcher types. See
		1187	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
		1188	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
		1189	the sources.
		1190
		1191	If you don't provide "signal" and "child" watchers than AnyEvent will
		1192	provide suitable (hopefully) replacements.
		1193
		1194	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
		1195	terminal emulator uses the above line as-is. An interface isn't included
		1196	in AnyEvent because it doesn't make sense outside the embedded
		1197	interpreter inside rxvt-unicode, and it is updated and maintained as
		1198	part of the rxvt-unicode distribution.
		1199
		1200	rxvt-unicode also cheats a bit by not providing blocking access to
		1201	condition variables: code blocking while waiting for a condition will
		1202	"die". This still works with most modules/usages, and blocking calls
		1203	must not be done in an interactive application, so it makes sense.
758		1204
759	EXAMPLE PROGRAM	1205	EXAMPLE PROGRAM
760	The following program uses an I/O watcher to read data from STDIN, a	1206	The following program uses an I/O watcher to read data from STDIN, a
761	timer to display a message once per second, and a condition variable to	1207	timer to display a message once per second, and a condition variable to
762	quit the program when the user enters quit:	1208	quit the program when the user enters quit:
…		…
949	destroy is the time, in microseconds, that it takes to destroy a	1395	destroy is the time, in microseconds, that it takes to destroy a
950	single watcher.	1396	single watcher.
951		1397
952	Results	1398	Results
953	name watchers bytes create invoke destroy comment	1399	name watchers bytes create invoke destroy comment
954	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1400	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
955	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1401	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
956	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1402	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
957	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1403	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
958	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1404	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
959	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1405	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1406	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1407	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
960	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1408	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
961	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1409	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
962	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1410	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
963	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1411	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
964		1412
965	Discussion	1413	Discussion
966	The benchmark does not measure scalability of the event loop very	1414	The benchmark does not measure scalability of the event loop very
967	well. For example, a select-based event loop (such as the pure perl one)	1415	well. For example, a select-based event loop (such as the pure perl one)
968	can never compete with an event loop that uses epoll when the number of	1416	can never compete with an event loop that uses epoll when the number of
…		…
993	few of them active), of course, but this was not subject of this	1441	few of them active), of course, but this was not subject of this
994	benchmark.	1442	benchmark.
995		1443
996	The "Event" module has a relatively high setup and callback invocation	1444	The "Event" module has a relatively high setup and callback invocation
997	cost, but overall scores in on the third place.	1445	cost, but overall scores in on the third place.
		1446
		1447	"IO::Async" performs admirably well, about on par with "Event", even
		1448	when using its pure perl backend.
998		1449
999	"Glib"'s memory usage is quite a bit higher, but it features a faster	1450	"Glib"'s memory usage is quite a bit higher, but it features a faster
1000	callback invocation and overall ends up in the same class as "Event".	1451	callback invocation and overall ends up in the same class as "Event".
1001	However, Glib scales extremely badly, doubling the number of watchers	1452	However, Glib scales extremely badly, doubling the number of watchers
1002	increases the processing time by more than a factor of four, making it	1453	increases the processing time by more than a factor of four, making it
…		…
1073	single "request", that is, reading the token from the pipe and	1524	single "request", that is, reading the token from the pipe and
1074	forwarding it to another server. This includes deleting the old timeout	1525	forwarding it to another server. This includes deleting the old timeout
1075	and creating a new one that moves the timeout into the future.	1526	and creating a new one that moves the timeout into the future.
1076		1527
1077	Results	1528	Results
1078	name sockets create request	1529	name sockets create request
1079	EV 20000 69.01 11.16	1530	EV 20000 69.01 11.16
1080	Perl 20000 73.32 35.87	1531	Perl 20000 73.32 35.87
		1532	IOAsync 20000 157.00 98.14 epoll
		1533	IOAsync 20000 159.31 616.06 poll
1081	Event 20000 212.62 257.32	1534	Event 20000 212.62 257.32
1082	Glib 20000 651.16 1896.30	1535	Glib 20000 651.16 1896.30
1083	POE 20000 349.67 12317.24 uses POE::Loop::Event	1536	POE 20000 349.67 12317.24 uses POE::Loop::Event
1084		1537
1085	Discussion	1538	Discussion
1086	This benchmark does measure scalability and overall performance of the	1539	This benchmark does measure scalability and overall performance of the
1087	particular event loop.	1540	particular event loop.
1088		1541
1089	EV is again fastest. Since it is using epoll on my system, the setup	1542	EV is again fastest. Since it is using epoll on my system, the setup
1090	time is relatively high, though.	1543	time is relatively high, though.
1091		1544
1092	Perl surprisingly comes second. It is much faster than the C-based event	1545	Perl surprisingly comes second. It is much faster than the C-based event
1093	loops Event and Glib.	1546	loops Event and Glib.
		1547
		1548	IO::Async performs very well when using its epoll backend, and still
		1549	quite good compared to Glib when using its pure perl backend.
1094		1550
1095	Event suffers from high setup time as well (look at its code and you	1551	Event suffers from high setup time as well (look at its code and you
1096	will understand why). Callback invocation also has a high overhead	1552	will understand why). Callback invocation also has a high overhead
1097	compared to the "$_->() for .."-style loop that the Perl event loop	1553	compared to the "$_->() for .."-style loop that the Perl event loop
1098	uses. Event uses select or poll in basically all documented	1554	uses. Event uses select or poll in basically all documented
…		…
1149		1605
1150	Summary	1606	Summary
1151	* C-based event loops perform very well with small number of watchers,	1607	* C-based event loops perform very well with small number of watchers,
1152	as the management overhead dominates.	1608	as the management overhead dominates.
1153		1609
		1610	THE IO::Lambda BENCHMARK
		1611	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1612	could be misinterpreted to make AnyEvent look bad. In fact, the
		1613	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1614	better (which shouldn't come as a surprise to anybody). As such, the
		1615	benchmark is fine, and mostly shows that the AnyEvent backend from
		1616	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1617	without the extra baggage? To explore this, I wrote the equivalent
		1618	benchmark for AnyEvent.
		1619
		1620	The benchmark itself creates an echo-server, and then, for 500 times,
		1621	connects to the echo server, sends a line, waits for the reply, and then
		1622	creates the next connection. This is a rather bad benchmark, as it
		1623	doesn't test the efficiency of the framework or much non-blocking I/O,
		1624	but it is a benchmark nevertheless.
		1625
		1626	name runtime
		1627	Lambda/select 0.330 sec
		1628	+ optimized 0.122 sec
		1629	Lambda/AnyEvent 0.327 sec
		1630	+ optimized 0.138 sec
		1631	Raw sockets/select 0.077 sec
		1632	POE/select, components 0.662 sec
		1633	POE/select, raw sockets 0.226 sec
		1634	POE/select, optimized 0.404 sec
		1635
		1636	AnyEvent/select/nb 0.085 sec
		1637	AnyEvent/EV/nb 0.068 sec
		1638	+state machine 0.134 sec
		1639
		1640	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1641	benchmarks actually make blocking connects and use 100% blocking I/O,
		1642	defeating the purpose of an event-based solution. All of the newly
		1643	written AnyEvent benchmarks use 100% non-blocking connects (using
		1644	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1645	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1646	connects generally require a lot more bookkeeping and event handling
		1647	than blocking connects (which involve a single syscall only).
		1648
		1649	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1650	offers similar expressive power as POE and IO::Lambda, using
		1651	conventional Perl syntax. This means that both the echo server and the
		1652	client are 100% non-blocking, further placing it at a disadvantage.
		1653
		1654	As you can see, the AnyEvent + EV combination even beats the
		1655	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1656	backend easily beats IO::Lambda and POE.
		1657
		1658	And even the 100% non-blocking version written using the high-level (and
		1659	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a
		1660	large margin, even though it does all of DNS, tcp-connect and socket I/O
		1661	in a non-blocking way.
		1662
		1663	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1664	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1665	part of the IO::lambda distribution and were used without any changes.
		1666
		1667	SIGNALS
		1668	AnyEvent currently installs handlers for these signals:
		1669
		1670	SIGCHLD
		1671	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1672	emulation for event loops that do not support them natively. Also,
		1673	some event loops install a similar handler.
		1674
		1675	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1676	then AnyEvent will reset it to default, to avoid losing child exit
		1677	statuses.
		1678
		1679	SIGPIPE
		1680	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1681	"undef" when AnyEvent gets loaded.
		1682
		1683	The rationale for this is that AnyEvent users usually do not really
		1684	depend on SIGPIPE delivery (which is purely an optimisation for
		1685	shell use, or badly-written programs), but "SIGPIPE" can cause
		1686	spurious and rare program exits as a lot of people do not expect
		1687	"SIGPIPE" when writing to some random socket.
		1688
		1689	The rationale for installing a no-op handler as opposed to ignoring
		1690	it is that this way, the handler will be restored to defaults on
		1691	exec.
		1692
		1693	Feel free to install your own handler, or reset it to defaults.
		1694
		1695	RECOMMENDED/OPTIONAL MODULES
		1696	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1697	it's built-in modules) are required to use it.
		1698
		1699	That does not mean that AnyEvent won't take advantage of some additional
		1700	modules if they are installed.
		1701
		1702	This section epxlains which additional modules will be used, and how
		1703	they affect AnyEvent's operetion.
		1704
		1705	Async::Interrupt
		1706	This slightly arcane module is used to implement fast signal
		1707	handling: To my knowledge, there is no way to do completely
		1708	race-free and quick signal handling in pure perl. To ensure that
		1709	signals still get delivered, AnyEvent will start an interval timer
		1710	to wake up perl (and catch the signals) with some delay (default is
		1711	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1712
		1713	If this module is available, then it will be used to implement
		1714	signal catching, which means that signals will not be delayed, and
		1715	the event loop will not be interrupted regularly, which is more
		1716	efficient (And good for battery life on laptops).
		1717
		1718	This affects not just the pure-perl event loop, but also other event
		1719	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1720
		1721	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1722	natively, and either employ their own workarounds (POE) or use
		1723	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1724	Installing Async::Interrupt does nothing for those backends.
		1725
		1726	EV This module isn't really "optional", as it is simply one of the
		1727	backend event loops that AnyEvent can use. However, it is simply the
		1728	best event loop available in terms of features, speed and stability:
		1729	It supports the AnyEvent API optimally, implements all the watcher
		1730	types in XS, does automatic timer adjustments even when no monotonic
		1731	clock is available, can take avdantage of advanced kernel interfaces
		1732	such as "epoll" and "kqueue", and is the fastest backend by far.
		1733	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1734	Glib::EV).
		1735
		1736	Guard
		1737	The guard module, when used, will be used to implement
		1738	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1739	uses a lot less memory), but otherwise doesn't affect guard
		1740	operation much. It is purely used for performance.
		1741
		1742	JSON and JSON::XS
		1743	This module is required when you want to read or write JSON data via
		1744	AnyEvent::Handle. It is also written in pure-perl, but can take
		1745	advantage of the ultra-high-speed JSON::XS module when it is
		1746	installed.
		1747
		1748	In fact, AnyEvent::Handle will use JSON::XS by default if it is
		1749	installed.
		1750
		1751	Net::SSLeay
		1752	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1753	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1754	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1755
		1756	Time::HiRes
		1757	This module is part of perl since release 5.008. It will be used
		1758	when the chosen event library does not come with a timing source on
		1759	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1760	additionally use it to try to use a monotonic clock for timing
		1761	stability.
		1762
1154	FORK	1763	FORK
1155	Most event libraries are not fork-safe. The ones who are usually are	1764	Most event libraries are not fork-safe. The ones who are usually are
1156	because they rely on inefficient but fork-safe "select" or "poll" calls.	1765	because they rely on inefficient but fork-safe "select" or "poll" calls.
1157	Only EV is fully fork-aware.	1766	Only EV is fully fork-aware.
1158		1767
1159	If you have to fork, you must either do so before creating your first	1768	If you have to fork, you must either do so before creating your first
1160	watcher OR you must not use AnyEvent at all in the child.	1769	watcher OR you must not use AnyEvent at all in the child OR you must do
		1770	something completely out of the scope of AnyEvent.
1161		1771
1162	SECURITY CONSIDERATIONS	1772	SECURITY CONSIDERATIONS
1163	AnyEvent can be forced to load any event model via	1773	AnyEvent can be forced to load any event model via
1164	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1774	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1165	to execute arbitrary code or directly gain access, it can easily be used	1775	to execute arbitrary code or directly gain access, it can easily be used
…		…
1168	model than specified in the variable.	1778	model than specified in the variable.
1169		1779
1170	You can make AnyEvent completely ignore this variable by deleting it	1780	You can make AnyEvent completely ignore this variable by deleting it
1171	before the first watcher gets created, e.g. with a "BEGIN" block:	1781	before the first watcher gets created, e.g. with a "BEGIN" block:
1172		1782
1173	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1783	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1174		1784
1175	use AnyEvent;	1785	use AnyEvent;
1176		1786
1177	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1787	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1178	be used to probe what backend is used and gain other information (which	1788	be used to probe what backend is used and gain other information (which
1179	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).	1789	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1790	and $ENV{PERL_ANYEVENT_STRICT}.
		1791
		1792	Note that AnyEvent will remove all environment variables starting with
		1793	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1794	enabled.
		1795
		1796	BUGS
		1797	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1798	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1799	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1800	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1801	not as pronounced).
1180		1802
1181	SEE ALSO	1803	SEE ALSO
1182	Utility functions: AnyEvent::Util.	1804	Utility functions: AnyEvent::Util.
1183		1805
1184	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1806	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1185	Event::Lib, Qt, POE.	1807	Event::Lib, Qt, POE.
1186		1808
1187	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1809	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1188	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1810	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1189	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1811	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1812	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
1190		1813
1191	Non-blocking file handles, sockets, TCP clients and servers:	1814	Non-blocking file handles, sockets, TCP clients and servers:
1192	AnyEvent::Handle, AnyEvent::Socket.	1815	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1193		1816
1194	Asynchronous DNS: AnyEvent::DNS.	1817	Asynchronous DNS: AnyEvent::DNS.
1195		1818
1196	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1819	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1197		1820
1198	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1821	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1822	AnyEvent::HTTP.
1199		1823
1200	AUTHOR	1824	AUTHOR
1201	Marc Lehmann <schmorp@schmorp.de>	1825	Marc Lehmann <schmorp@schmorp.de>
1202	http://home.schmorp.de/	1826	http://home.schmorp.de/
1203		1827

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Comparing AnyEvent/README (file contents): Revision 1.22 by root, Sat May 24 17:58:33 2008 UTC vs. Revision 1.50 by root, Sat Aug 1 09:14:54 2009 UTC

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Revision 1.22 by root, Sat May 24 17:58:33 2008 UTC vs.
Revision 1.50 by root, Sat Aug 1 09:14:54 2009 UTC