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Comparing AnyEvent/README (file contents):
Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs.
Revision 1.50 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, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE -	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	various supported event 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
		33	$w->send; # wake up current and all future recv's
19	$w->wait; # enters "main loop" till $condvar gets ->broadcast	34	$w->recv; # enters "main loop" till $condvar gets ->send
20	$w->broadcast; # wake up current and all future wait's	35	# use a condvar in callback mode:
		36	$w->cb (sub { $_[0]->recv });
		37
		38	INTRODUCTION/TUTORIAL
		39	This manpage is mainly a reference manual. If you are interested in a
		40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		41	manpage.
		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 enourmous amount of code and strict rules you have	89	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	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
75	The interface itself is vaguely similar, but not identical to the Event	110	The interface itself is vaguely similar, but not identical to the Event
76	module.	111	module.
77		112
78	During the first call of any watcher-creation method, the module tries	113	During the first call of any watcher-creation method, the module tries
79	to detect the currently loaded event loop by probing whether one of the	114	to detect the currently loaded event loop by probing whether one of the
80	following modules is already loaded: Coro::EV, Coro::Event, EV, Event,	115	following modules is already loaded: EV, Event, Glib,
81	Glib, AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found	116	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82	is used. If none are found, the module tries to load these modules	117	used. If none are found, the module tries to load these modules
83	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	118	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
84	always succeed) in the order given. The first one that can be	119	always succeed) in the order given. The first one that can be
85	successfully loaded will be used. If, after this, still none could be	120	successfully loaded will be used. If, after this, still none could be
86	found, AnyEvent will fall back to a pure-perl event loop, which is not	121	found, AnyEvent will fall back to a pure-perl event loop, which is not
87	very efficient, but should work everywhere.	122	very efficient, but should work everywhere.
…		…
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 filehandle to watch, etc.	144	the callback to call, the file handle to watch, etc.
110		145
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
234	Multiple signal occurances can be clumped together into one callback	372	Multiple signal occurrences can be clumped together into one callback
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 guarenteed 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	AnyEvent::detect; # force event module to be initialised
277
278	my $pid = fork or exit 5;	451	my $pid = fork or exit 5;
279		452
280	my $w = AnyEvent->child (	453	my $w = AnyEvent->child (
281	pid => $pid,	454	pid => $pid,
282	cb => sub {	455	cb => sub {
283	my ($pid, $status) = @_;	456	my ($pid, $status) = @_;
284	warn "pid $pid exited with status $status";	457	warn "pid $pid exited with status $status";
285	$done->broadcast;	458	$done->send;
286	},	459	},
287	);	460	);
288		461
289	# do something else, then wait for process exit	462	# do something else, then wait for process exit
290	$done->wait;	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	});
291		500
292	CONDITION VARIABLES	501	CONDITION VARIABLES
		502	$cv = AnyEvent->condvar;
		503
		504	$cv->send (<list>);
		505	my @res = $cv->recv;
		506
		507	If you are familiar with some event loops you will know that all of them
		508	require you to run some blocking "loop", "run" or similar function that
		509	will actively watch for new events and call your callbacks.
		510
		511	AnyEvent is slightly different: it expects somebody else to run the
		512	event loop and will only block when necessary (usually when told by the
		513	user).
		514
		515	The instrument to do that is called a "condition variable", so called
		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.
		519
293	Condition variables can be created by calling the "AnyEvent->condvar"	520	Condition variables can be created by calling the "AnyEvent->condvar"
294	method without any arguments.	521	method, usually without arguments. The only argument pair allowed is
		522	"cb", which specifies a callback to be called when the condition
		523	variable becomes true, with the condition variable as the first argument
		524	(but not the results).
295		525
296	A condition variable waits for a condition - precisely that the	526	After creation, the condition variable is "false" until it becomes
297	"->broadcast" method has been called.	527	"true" by calling the "send" method (or calling the condition variable
		528	as if it were a callback, read about the caveats in the description for
		529	the "->send" method).
298		530
299	They are very useful to signal that a condition has been fulfilled, for	531	Condition variables are similar to callbacks, except that you can
		532	optionally wait for them. They can also be called merge points - points
		533	in time where multiple outstanding events have been processed. And yet
		534	another way to call them is transactions - each condition variable can
		535	be used to represent a transaction, which finishes at some point and
		536	delivers a result. And yet some people know them as "futures" - a
		537	promise to compute/deliver something that you can wait for.
		538
		539	Condition variables are very useful to signal that something has
300	example, if you write a module that does asynchronous http requests,	540	finished, for example, if you write a module that does asynchronous http
301	then a condition variable would be the ideal candidate to signal the	541	requests, then a condition variable would be the ideal candidate to
302	availability of results.	542	signal the availability of results. The user can either act when the
		543	callback is called or can synchronously "->recv" for the results.
303		544
304	You can also use condition variables to block your main program until an	545	You can also use them to simulate traditional event loops - for example,
305	event occurs - for example, you could "->wait" in your main program	546	you can block your main program until an event occurs - for example, you
306	until the user clicks the Quit button in your app, which would	547	could "->recv" in your main program until the user clicks the Quit
307	"->broadcast" the "quit" event.	548	button of your app, which would "->send" the "quit" event.
308		549
309	Note that condition variables recurse into the event loop - if you have	550	Note that condition variables recurse into the event loop - if you have
310	two pirces of code that call "->wait" in a round-robbin fashion, you	551	two pieces of code that call "->recv" in a round-robin fashion, you
311	lose. Therefore, condition variables are good to export to your caller,	552	lose. Therefore, condition variables are good to export to your caller,
312	but you should avoid making a blocking wait yourself, at least in	553	but you should avoid making a blocking wait yourself, at least in
313	callbacks, as this asks for trouble.	554	callbacks, as this asks for trouble.
314		555
315	This object has two methods:	556	Condition variables are represented by hash refs in perl, and the keys
		557	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		558	(it is often useful to build your own transaction class on top of
		559	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		560	it's "new" method in your own "new" method.
316		561
317	$cv->wait	562	There are two "sides" to a condition variable - the "producer side"
318	Wait (blocking if necessary) until the "->broadcast" method has been	563	which eventually calls "-> send", and the "consumer side", which waits
319	called on c<$cv>, while servicing other watchers normally.	564	for the send to occur.
320		565
321	You can only wait once on a condition - additional calls will return	566	Example: wait for a timer.
322	immediately.
323
324	Not all event models support a blocking wait - some die in that case
325	(programs might want to do that to stay interactive), so *if you are
326	using this from a module, never require a blocking wait*, but let
327	the caller decide whether the call will block or not (for example,
328	by coupling condition variables with some kind of request results
329	and supporting callbacks so the caller knows that getting the result
330	will not block, while still suppporting blocking waits if the caller
331	so desires).
332
333	Another reason never to "->wait" in a module is that you cannot
334	sensibly have two "->wait"'s in parallel, as that would require
335	multiple interpreters or coroutines/threads, none of which
336	"AnyEvent" can supply (the coroutine-aware backends
337	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
338	support concurrent "->wait"'s from different coroutines, however).
339
340	$cv->broadcast
341	Flag the condition as ready - a running "->wait" and all further
342	calls to "wait" will (eventually) return after this method has been
343	called. If nobody is waiting the broadcast will be remembered..
344
345	Example:
346		567
347	# wait till the result is ready	568	# wait till the result is ready
348	my $result_ready = AnyEvent->condvar;	569	my $result_ready = AnyEvent->condvar;
349		570
350	# do something such as adding a timer	571	# do something such as adding a timer
351	# or socket watcher the calls $result_ready->broadcast	572	# or socket watcher the calls $result_ready->send
352	# when the "result" is ready.	573	# when the "result" is ready.
353	# in this case, we simply use a timer:	574	# in this case, we simply use a timer:
354	my $w = AnyEvent->timer (	575	my $w = AnyEvent->timer (
355	after => 1,	576	after => 1,
356	cb => sub { $result_ready->broadcast },	577	cb => sub { $result_ready->send },
357	);	578	);
358		579
359	# this "blocks" (while handling events) till the watcher	580	# this "blocks" (while handling events) till the callback
360	# calls broadcast	581	# calls -<send
361	$result_ready->wait;	582	$result_ready->recv;
		583
		584	Example: wait for a timer, but take advantage of the fact that condition
		585	variables are also callable directly.
		586
		587	my $done = AnyEvent->condvar;
		588	my $delay = AnyEvent->timer (after => 5, cb => $done);
		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	});
		607
		608	METHODS FOR PRODUCERS
		609	These methods should only be used by the producing side, i.e. the
		610	code/module that eventually sends the signal. Note that it is also the
		611	producer side which creates the condvar in most cases, but it isn't
		612	uncommon for the consumer to create it as well.
		613
		614	$cv->send (...)
		615	Flag the condition as ready - a running "->recv" and all further
		616	calls to "recv" will (eventually) return after this method has been
		617	called. If nobody is waiting the send will be remembered.
		618
		619	If a callback has been set on the condition variable, it is called
		620	immediately from within send.
		621
		622	Any arguments passed to the "send" call will be returned by all
		623	future "->recv" calls.
		624
		625	Condition variables are overloaded so one can call them directly (as
		626	if they were a code reference). Calling them directly is the same as
		627	calling "send".
		628
		629	$cv->croak ($error)
		630	Similar to send, but causes all call's to "->recv" to invoke
		631	"Carp::croak" with the given error message/object/scalar.
		632
		633	This can be used to signal any errors to the condition variable
		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.
		639
		640	$cv->begin ([group callback])
		641	$cv->end
		642	These two methods can be used to combine many transactions/events
		643	into one. For example, a function that pings many hosts in parallel
		644	might want to use a condition variable for the whole process.
		645
		646	Every call to "->begin" will increment a counter, and every call to
		647	"->end" will decrement it. If the counter reaches 0 in "->end", the
		648	(last) callback passed to "begin" will be executed. That callback is
		649	supposed to call "->send", but that is not required. If no
		650	callback was set, "send" will be called without any arguments.
		651
		652	You can think of "$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:
		684
		685	my $cv = AnyEvent->condvar;
		686
		687	my %result;
		688	$cv->begin (sub { $cv->send (\%result) });
		689
		690	for my $host (@list_of_hosts) {
		691	$cv->begin;
		692	ping_host_then_call_callback $host, sub {
		693	$result{$host} = ...;
		694	$cv->end;
		695	};
		696	}
		697
		698	$cv->end;
		699
		700	This code fragment supposedly pings a number of hosts and calls
		701	"send" after results for all then have have been gathered - in any
		702	order. To achieve this, the code issues a call to "begin" when it
		703	starts each ping request and calls "end" when it has received some
		704	result for it. Since "begin" and "end" only maintain a counter, the
		705	order in which results arrive is not relevant.
		706
		707	There is an additional bracketing call to "begin" and "end" outside
		708	the loop, which serves two important purposes: first, it sets the
		709	callback to be called once the counter reaches 0, and second, it
		710	ensures that "send" is called even when "no" hosts are being pinged
		711	(the loop doesn't execute once).
		712
		713	This is the general pattern when you "fan out" into multiple (but
		714	potentially none) subrequests: use an outer "begin"/"end" pair to
		715	set the callback and ensure "end" is called at least once, and then,
		716	for each subrequest you start, call "begin" and for each subrequest
		717	you finish, call "end".
		718
		719	METHODS FOR CONSUMERS
		720	These methods should only be used by the consuming side, i.e. the code
		721	awaits the condition.
		722
		723	$cv->recv
		724	Wait (blocking if necessary) until the "->send" or "->croak" methods
		725	have been called on c<$cv>, while servicing other watchers normally.
		726
		727	You can only wait once on a condition - additional calls are valid
		728	but will return immediately.
		729
		730	If an error condition has been set by calling "->croak", then this
		731	function will call "croak".
		732
		733	In list context, all parameters passed to "send" will be returned,
		734	in scalar context only the first one will be returned.
		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
		743	Not all event models support a blocking wait - some die in that case
		744	(programs might want to do that to stay interactive), so *if you are
		745	using this from a module, never require a blocking wait*. Instead,
		746	let the caller decide whether the call will block or not (for
		747	example, by coupling condition variables with some kind of request
		748	results and supporting callbacks so the caller knows that getting
		749	the result will not block, while still supporting blocking waits if
		750	the caller so desires).
		751
		752	You can ensure that "-recv" never blocks by setting a callback and
		753	only calling "->recv" from within that callback (or at a later
		754	time). This will work even when the event loop does not support
		755	blocking waits otherwise.
		756
		757	$bool = $cv->ready
		758	Returns true when the condition is "true", i.e. whether "send" or
		759	"croak" have been called.
		760
		761	$cb = $cv->cb ($cb->($cv))
		762	This is a mutator function that returns the callback set and
		763	optionally replaces it before doing so.
		764
		765	The callback will be called when the condition becomes (or already
		766	was) "true", i.e. when "send" or "croak" are called (or were
		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.
362		830
363	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
364	$AnyEvent::MODEL	835	$AnyEvent::MODEL
365	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
366	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
367	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
368	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
369	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.
370		843	in rxvt-unicode it will be "urxvt::anyevent").
371	The known classes so far are:
372
373	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
374	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
375	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
376	AnyEvent::Impl::Event based on Event, second best choice.
377	AnyEvent::Impl::Glib based on Glib, third-best choice.
378	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
379	AnyEvent::Impl::Tk based on Tk, very bad choice.
380	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
381	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
382	AnyEvent::Impl::POE based on POE, not generic enough for full support.
383
384	There is no support for WxWidgets, as WxWidgets has no support for
385	watching file handles. However, you can use WxWidgets through the
386	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
387	second, which was considered to be too horrible to even consider for
388	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
389	using it's adaptor.
390
391	AnyEvent knows about Prima and Wx and will try to use POE when
392	autodetecting them.
393		844
394	AnyEvent::detect	845	AnyEvent::detect
395	Returns $AnyEvent::MODEL, forcing autodetection of the event model	846	Returns $AnyEvent::MODEL, forcing autodetection of the event model
396	if necessary. You should only call this function right before you	847	if necessary. You should only call this function right before you
397	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
398	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".
		853
		854	$guard = AnyEvent::post_detect { BLOCK }
		855	Arranges for the code block to be executed as soon as the event
		856	model is autodetected (or immediately if this has already happened).
		857
		858	The block will be executed after the actual backend has been
		859	detected ($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
		869	If called in scalar or list context, then it creates and returns an
		870	object that automatically removes the callback again when it is
		871	destroyed (or "undef" when the hook was immediately executed). See
		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;
		889
		890	@AnyEvent::post_detect
		891	If there are any code references in this array (you can "push" to it
		892	before or after loading AnyEvent), then they will called directly
		893	after the event loop has been chosen.
		894
		895	You should check $AnyEvent::MODEL before adding to this array,
		896	though: if it is defined then the event loop has already been
		897	detected, and the array will be ignored.
		898
		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.
399		907
400	WHAT TO DO IN A MODULE	908	WHAT TO DO IN A MODULE
401	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
402	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.
403		911
404	Be careful when you create watchers in the module body - AnyEvent will	912	Be careful when you create watchers in the module body - AnyEvent will
405	decide which event module to use as soon as the first method is called,	913	decide which event module to use as soon as the first method is called,
406	so by calling AnyEvent in your module body you force the user of your	914	so by calling AnyEvent in your module body you force the user of your
407	module to load the event module first.	915	module to load the event module first.
408		916
409	Never call "->wait" on a condition variable unless you know that the	917	Never call "->recv" on a condition variable unless you know that the
410	"->broadcast" method has been called on it already. This is because it	918	"->send" method has been called on it already. This is because it will
411	will stall the whole program, and the whole point of using events is to	919	stall the whole program, and the whole point of using events is to stay
412	stay interactive.	920	interactive.
413		921
414	It is fine, however, to call "->wait" when the user of your module	922	It is fine, however, to call "->recv" when the user of your module
415	requests it (i.e. if you create a http request object ad have a method	923	requests it (i.e. if you create a http request object ad have a method
416	called "results" that returns the results, it should call "->wait"	924	called "results" that returns the results, it should call "->recv"
417	freely, as the user of your module knows what she is doing. always).	925	freely, as the user of your module knows what she is doing. always).
418		926
419	WHAT TO DO IN THE MAIN PROGRAM	927	WHAT TO DO IN THE MAIN PROGRAM
420	There will always be a single main program - the only place that should	928	There will always be a single main program - the only place that should
421	dictate which event model to use.	929	dictate which event model to use.
…		…
423	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
424	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
425	AnyEvent decide which implementation to chose if some module relies on	933	AnyEvent decide which implementation to chose if some module relies on
426	it.	934	it.
427		935
428	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
429	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
430	event module before loading AnyEvent or any module that uses it:	938	event module before loading AnyEvent or any module that uses it:
431	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
432	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
433	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,
434	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
435	yourself.	943	yourself.
436		944
437	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
438	loading the "AnyEvent::Impl::Perl" module, which gives you similar	946	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
439	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.
440		964
441	OTHER MODULES	965	OTHER MODULES
442	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
443	AnyEvent and can therefore be mixed easily with other AnyEvent modules	967	AnyEvent as a client and can therefore be mixed easily with other
444	in the same program. Some of the modules come with AnyEvent, some are	968	AnyEvent modules and other event loops in the same program. Some of the
445	available via CPAN.	969	modules come with AnyEvent, most are available via CPAN.
446		970
447	AnyEvent::Util	971	AnyEvent::Util
448	Contains various utility functions that replace often-used but	972	Contains various utility functions that replace often-used but
449	blocking functions such as "inet_aton" by event-/callback-based	973	blocking functions such as "inet_aton" by event-/callback-based
450	versions.	974	versions.
451		975
		976	AnyEvent::Socket
		977	Provides various utility functions for (internet protocol) sockets,
		978	addresses and name resolution. Also functions to create non-blocking
		979	tcp connections or tcp servers, with IPv6 and SRV record support and
		980	more.
		981
452	AnyEvent::Handle	982	AnyEvent::Handle
453	Provide read and write buffers and manages watchers for reads and	983	Provide read and write buffers, manages watchers for reads and
454	writes.	984	writes, supports raw and formatted I/O, I/O queued and fully
		985	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
455		986
456	AnyEvent::Socket	987	AnyEvent::DNS
457	Provides a means to do non-blocking connects, accepts etc.	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.
458		993
459	AnyEvent::HTTPD	994	AnyEvent::HTTPD
460	Provides a simple web application server framework.	995	Provides a simple web application server framework.
461		996
462	AnyEvent::DNS
463	Provides asynchronous DNS resolver capabilities, beyond what
464	AnyEvent::Util offers.
465
466	AnyEvent::FastPing	997	AnyEvent::FastPing
467	The fastest ping in the west.	998	The fastest ping in the west.
468		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
469	Net::IRC3	1018	Net::IRC3).
470	AnyEvent based IRC client module family.
471		1019
472	Net::XMPP2	1020	AnyEvent::XMPP
473	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).
474		1027
475	Net::FCP	1028	Net::FCP
476	AnyEvent-based implementation of the Freenet Client Protocol,	1029	AnyEvent-based implementation of the Freenet Client Protocol,
477	birthplace of AnyEvent.	1030	birthplace of AnyEvent.
478		1031
479	Event::ExecFlow	1032	Event::ExecFlow
480	High level API for event-based execution flow control.	1033	High level API for event-based execution flow control.
481		1034
482	Coro	1035	Coro
483	Has special support for AnyEvent.	1036	Has special support for AnyEvent via Coro::AnyEvent.
484		1037
485	IO::Lambda	1038	ERROR AND EXCEPTION HANDLING
486	The lambda approach to I/O - don't ask, look there. Can use	1039	In general, AnyEvent does not do any error handling - it relies on the
487	AnyEvent.	1040	caller to do that if required. The AnyEvent::Strict module (see also the
		1041	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1042	checking of all AnyEvent methods, however, which is highly useful during
		1043	development.
488		1044
489	IO::AIO	1045	As for exception handling (i.e. runtime errors and exceptions thrown
490	Truly asynchronous I/O, should be in the toolbox of every event	1046	while executing a callback), this is not only highly event-loop
491	programmer. Can be trivially made to use AnyEvent.	1047	specific, but also not in any way wrapped by this module, as this is the
		1048	job of the main program.
492		1049
493	BDB Truly asynchronous Berkeley DB access. Can be trivially made to use	1050	The pure perl event loop simply re-throws the exception (usually within
494	AnyEvent.	1051	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		1052	Glib uses "install_exception_handler" and so on.
		1053
		1054	ENVIRONMENT VARIABLES
		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.
		1061
		1062	"PERL_ANYEVENT_VERBOSE"
		1063	By default, AnyEvent will be completely silent except in fatal
		1064	conditions. You can set this environment variable to make AnyEvent
		1065	more talkative.
		1066
		1067	When set to 1 or higher, causes AnyEvent to warn about unexpected
		1068	conditions, such as not being able to load the event model specified
		1069	by "PERL_ANYEVENT_MODEL".
		1070
		1071	When set to 2 or higher, cause AnyEvent to report to STDERR which
		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.
		1091
		1092	"PERL_ANYEVENT_MODEL"
		1093	This can be used to specify the event model to be used by AnyEvent,
		1094	before auto detection and -probing kicks in. It must be a string
		1095	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		1096	gets prepended and the resulting module name is loaded and if the
		1097	load was successful, used as event model. If it fails to load
		1098	AnyEvent will proceed with auto detection and -probing.
		1099
		1100	This functionality might change in future versions.
		1101
		1102	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		1103	could start your program like this:
		1104
		1105	PERL_ANYEVENT_MODEL=Perl perl ...
		1106
		1107	"PERL_ANYEVENT_PROTOCOLS"
		1108	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		1109	preferences for IPv4 or IPv6. The default is unspecified (and might
		1110	change, or be the result of auto probing).
		1111
		1112	Must be set to a comma-separated list of protocols or address
		1113	families, current supported: "ipv4" and "ipv6". Only protocols
		1114	mentioned will be used, and preference will be given to protocols
		1115	mentioned earlier in the list.
		1116
		1117	This variable can effectively be used for denial-of-service attacks
		1118	against local programs (e.g. when setuid), although the impact is
		1119	likely small, as the program has to handle conenction and other
		1120	failures anyways.
		1121
		1122	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		1123	IPv6, but support both and try to use both.
		1124	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		1125	resolve or contact IPv6 addresses.
		1126	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		1127	prefer IPv6 over IPv4.
		1128
		1129	"PERL_ANYEVENT_EDNS0"
		1130	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		1131	for DNS. This extension is generally useful to reduce DNS traffic,
		1132	but some (broken) firewalls drop such DNS packets, which is why it
		1133	is off by default.
		1134
		1135	Setting this variable to 1 will cause AnyEvent::DNS to announce
		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.
495		1161
496	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1162	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
497	This is an advanced topic that you do not normally need to use AnyEvent	1163	This is an advanced topic that you do not normally need to use AnyEvent
498	in a module. This section is only of use to event loop authors who want	1164	in a module. This section is only of use to event loop authors who want
499	to provide AnyEvent compatibility.	1165	to provide AnyEvent compatibility.
…		…
533		1199
534	rxvt-unicode also cheats a bit by not providing blocking access to	1200	rxvt-unicode also cheats a bit by not providing blocking access to
535	condition variables: code blocking while waiting for a condition will	1201	condition variables: code blocking while waiting for a condition will
536	"die". This still works with most modules/usages, and blocking calls	1202	"die". This still works with most modules/usages, and blocking calls
537	must not be done in an interactive application, so it makes sense.	1203	must not be done in an interactive application, so it makes sense.
538
539	ENVIRONMENT VARIABLES
540	The following environment variables are used by this module:
541
542	"PERL_ANYEVENT_VERBOSE"
543	By default, AnyEvent will be completely silent except in fatal
544	conditions. You can set this environment variable to make AnyEvent
545	more talkative.
546
547	When set to 1 or higher, causes AnyEvent to warn about unexpected
548	conditions, such as not being able to load the event model specified
549	by "PERL_ANYEVENT_MODEL".
550
551	When set to 2 or higher, cause AnyEvent to report to STDERR which
552	event model it chooses.
553
554	"PERL_ANYEVENT_MODEL"
555	This can be used to specify the event model to be used by AnyEvent,
556	before autodetection and -probing kicks in. It must be a string
557	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
558	gets prepended and the resulting module name is loaded and if the
559	load was successful, used as event model. If it fails to load
560	AnyEvent will proceed with autodetection and -probing.
561
562	This functionality might change in future versions.
563
564	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
565	could start your program like this:
566
567	PERL_ANYEVENT_MODEL=Perl perl ...
568		1204
569	EXAMPLE PROGRAM	1205	EXAMPLE PROGRAM
570	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
571	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
572	quit the program when the user enters quit:	1208	quit the program when the user enters quit:
…		…
580	poll => 'r',	1216	poll => 'r',
581	cb => sub {	1217	cb => sub {
582	warn "io event <$_[0]>\n"; # will always output <r>	1218	warn "io event <$_[0]>\n"; # will always output <r>
583	chomp (my $input = <STDIN>); # read a line	1219	chomp (my $input = <STDIN>); # read a line
584	warn "read: $input\n"; # output what has been read	1220	warn "read: $input\n"; # output what has been read
585	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1221	$cv->send if $input =~ /^q/i; # quit program if /^q/i
586	},	1222	},
587	);	1223	);
588		1224
589	my $time_watcher; # can only be used once	1225	my $time_watcher; # can only be used once
590		1226
…		…
595	});	1231	});
596	}	1232	}
597		1233
598	new_timer; # create first timer	1234	new_timer; # create first timer
599		1235
600	$cv->wait; # wait until user enters /^q/i	1236	$cv->recv; # wait until user enters /^q/i
601		1237
602	REAL-WORLD EXAMPLE	1238	REAL-WORLD EXAMPLE
603	Consider the Net::FCP module. It features (among others) the following	1239	Consider the Net::FCP module. It features (among others) the following
604	API calls, which are to freenet what HTTP GET requests are to http:	1240	API calls, which are to freenet what HTTP GET requests are to http:
605		1241
…		…
654	syswrite $txn->{fh}, $txn->{request}	1290	syswrite $txn->{fh}, $txn->{request}
655	or die "connection or write error";	1291	or die "connection or write error";
656	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1292	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
657		1293
658	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1294	Again, "fh_ready_r" waits till all data has arrived, and then stores the
659	result and signals any possible waiters that the request ahs finished:	1295	result and signals any possible waiters that the request has finished:
660		1296
661	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1297	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
662		1298
663	if (end-of-file or data complete) {	1299	if (end-of-file or data complete) {
664	$txn->{result} = $txn->{buf};	1300	$txn->{result} = $txn->{buf};
665	$txn->{finished}->broadcast;	1301	$txn->{finished}->send;
666	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1302	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
667	}	1303	}
668		1304
669	The "result" method, finally, just waits for the finished signal (if the	1305	The "result" method, finally, just waits for the finished signal (if the
670	request was already finished, it doesn't wait, of course, and returns	1306	request was already finished, it doesn't wait, of course, and returns
671	the data:	1307	the data:
672		1308
673	$txn->{finished}->wait;	1309	$txn->{finished}->recv;
674	return $txn->{result};	1310	return $txn->{result};
675		1311
676	The actual code goes further and collects all errors ("die"s,	1312	The actual code goes further and collects all errors ("die"s,
677	exceptions) that occured during request processing. The "result" method	1313	exceptions) that occurred during request processing. The "result" method
678	detects whether an exception as thrown (it is stored inside the $txn	1314	detects whether an exception as thrown (it is stored inside the $txn
679	object) and just throws the exception, which means connection errors and	1315	object) and just throws the exception, which means connection errors and
680	other problems get reported tot he code that tries to use the result,	1316	other problems get reported tot he code that tries to use the result,
681	not in a random callback.	1317	not in a random callback.
682		1318
…		…
713		1349
714	my $quit = AnyEvent->condvar;	1350	my $quit = AnyEvent->condvar;
715		1351
716	$fcp->txn_client_get ($url)->cb (sub {	1352	$fcp->txn_client_get ($url)->cb (sub {
717	...	1353	...
718	$quit->broadcast;	1354	$quit->send;
719	});	1355	});
720		1356
721	$quit->wait;	1357	$quit->recv;
722		1358
723	BENCHMARKS	1359	BENCHMARKS
724	To give you an idea of the performance and overheads that AnyEvent adds	1360	To give you an idea of the performance and overheads that AnyEvent adds
725	over the event loops themselves and to give you an impression of the	1361	over the event loops themselves and to give you an impression of the
726	speed of various event loops I prepared some benchmarks.	1362	speed of various event loops I prepared some benchmarks.
727		1363
728	BENCHMARKING ANYEVENT OVERHEAD	1364	BENCHMARKING ANYEVENT OVERHEAD
729	Here is a benchmark of various supported event models used natively and	1365	Here is a benchmark of various supported event models used natively and
730	through anyevent. The benchmark creates a lot of timers (with a zero	1366	through AnyEvent. The benchmark creates a lot of timers (with a zero
731	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1367	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
732	which it is), lets them fire exactly once and destroys them again.	1368	which it is), lets them fire exactly once and destroys them again.
733		1369
734	Source code for this benchmark is found as eg/bench in the AnyEvent	1370	Source code for this benchmark is found as eg/bench in the AnyEvent
735	distribution.	1371	distribution.
…		…
751	between all watchers, to avoid adding memory overhead. That means	1387	between all watchers, to avoid adding memory overhead. That means
752	closure creation and memory usage is not included in the figures.	1388	closure creation and memory usage is not included in the figures.
753		1389
754	invoke is the time, in microseconds, used to invoke a simple callback.	1390	invoke is the time, in microseconds, used to invoke a simple callback.
755	The callback simply counts down a Perl variable and after it was invoked	1391	The callback simply counts down a Perl variable and after it was invoked
756	"watcher" times, it would "->broadcast" a condvar once to signal the end	1392	"watcher" times, it would "->send" a condvar once to signal the end of
757	of this phase.	1393	this phase.
758		1394
759	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
760	single watcher.	1396	single watcher.
761		1397
762	Results	1398	Results
763	name watchers bytes create invoke destroy comment	1399	name watchers bytes create invoke destroy comment
764	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
765	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
766	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
767	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
768	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
769	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
770	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
771	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
772	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
773	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
774		1412
775	Discussion	1413	Discussion
776	The benchmark does not measure scalability of the event loop very	1414	The benchmark does not measure scalability of the event loop very
777	well. For example, a select-based event loop (such as the pure perl one)	1415	well. For example, a select-based event loop (such as the pure perl one)
778	can never compete with an event loop that uses epoll when the number of	1416	can never compete with an event loop that uses epoll when the number of
…		…
804	benchmark.	1442	benchmark.
805		1443
806	The "Event" module has a relatively high setup and callback invocation	1444	The "Event" module has a relatively high setup and callback invocation
807	cost, but overall scores in on the third place.	1445	cost, but overall scores in on the third place.
808		1446
		1447	"IO::Async" performs admirably well, about on par with "Event", even
		1448	when using its pure perl backend.
		1449
809	"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
810	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".
811	However, Glib scales extremely badly, doubling the number of watchers	1452	However, Glib scales extremely badly, doubling the number of watchers
812	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
813	completely unusable when using larger numbers of watchers (note that	1454	completely unusable when using larger numbers of watchers (note that
…		…
823	the figures above).	1464	the figures above).
824		1465
825	"POE", regardless of underlying event loop (whether using its pure perl	1466	"POE", regardless of underlying event loop (whether using its pure perl
826	select-based backend or the Event module, the POE-EV backend couldn't be	1467	select-based backend or the Event module, the POE-EV backend couldn't be
827	tested because it wasn't working) shows abysmal performance and memory	1468	tested because it wasn't working) shows abysmal performance and memory
828	usage: Watchers use almost 30 times as much memory as EV watchers, and	1469	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
829	10 times as much memory as Event (the high memory requirements are	1470	watchers, and 10 times as much memory as Event (the high memory
830	caused by requiring a session for each watcher). Watcher invocation	1471	requirements are caused by requiring a session for each watcher).
831	speed is almost 900 times slower than with AnyEvent's pure perl	1472	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1473	pure perl implementation.
		1474
832	implementation. The design of the POE adaptor class in AnyEvent can not	1475	The design of the POE adaptor class in AnyEvent can not really account
833	really account for this, as session creation overhead is small compared	1476	for the performance issues, though, as session creation overhead is
834	to execution of the state machine, which is coded pretty optimally	1477	small compared to execution of the state machine, which is coded pretty
835	within AnyEvent::Impl::POE. POE simply seems to be abysmally slow.	1478	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1479	using multiple sessions is not a good approach, especially regarding
		1480	memory usage, even the author of POE could not come up with a faster
		1481	design).
836		1482
837	Summary	1483	Summary
838	* Using EV through AnyEvent is faster than any other event loop (even	1484	* Using EV through AnyEvent is faster than any other event loop (even
839	when used without AnyEvent), but most event loops have acceptable	1485	when used without AnyEvent), but most event loops have acceptable
840	performance with or without AnyEvent.	1486	performance with or without AnyEvent.
…		…
845		1491
846	* You should avoid POE like the plague if you want performance or	1492	* You should avoid POE like the plague if you want performance or
847	reasonable memory usage.	1493	reasonable memory usage.
848		1494
849	BENCHMARKING THE LARGE SERVER CASE	1495	BENCHMARKING THE LARGE SERVER CASE
850	This benchmark atcually benchmarks the event loop itself. It works by	1496	This benchmark actually benchmarks the event loop itself. It works by
851	creating a number of "servers": each server consists of a socketpair, a	1497	creating a number of "servers": each server consists of a socket pair, a
852	timeout watcher that gets reset on activity (but never fires), and an	1498	timeout watcher that gets reset on activity (but never fires), and an
853	I/O watcher waiting for input on one side of the socket. Each time the	1499	I/O watcher waiting for input on one side of the socket. Each time the
854	socket watcher reads a byte it will write that byte to a random other	1500	socket watcher reads a byte it will write that byte to a random other
855	"server".	1501	"server".
856		1502
857	The effect is that there will be a lot of I/O watchers, only part of	1503	The effect is that there will be a lot of I/O watchers, only part of
858	which are active at any one point (so there is a constant number of	1504	which are active at any one point (so there is a constant number of
859	active fds for each loop iterstaion, but which fds these are is random).	1505	active fds for each loop iteration, but which fds these are is random).
860	The timeout is reset each time something is read because that reflects	1506	The timeout is reset each time something is read because that reflects
861	how most timeouts work (and puts extra pressure on the event loops).	1507	how most timeouts work (and puts extra pressure on the event loops).
862		1508
863	In this benchmark, we use 10000 socketpairs (20000 sockets), of which	1509	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
864	100 (1%) are active. This mirrors the activity of large servers with	1510	100 (1%) are active. This mirrors the activity of large servers with
865	many connections, most of which are idle at any one point in time.	1511	many connections, most of which are idle at any one point in time.
866		1512
867	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1513	Source code for this benchmark is found as eg/bench2 in the AnyEvent
868	distribution.	1514	distribution.
869		1515
870	Explanation of the columns	1516	Explanation of the columns
871	sockets is the number of sockets, and twice the number of "servers"	1517	sockets is the number of sockets, and twice the number of "servers"
872	(as each server has a read and write socket end).	1518	(as each server has a read and write socket end).
873		1519
874	create is the time it takes to create a socketpair (which is	1520	create is the time it takes to create a socket pair (which is
875	nontrivial) and two watchers: an I/O watcher and a timeout watcher.	1521	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
876		1522
877	request, the most important value, is the time it takes to handle a	1523	request, the most important value, is the time it takes to handle a
878	single "request", that is, reading the token from the pipe and	1524	single "request", that is, reading the token from the pipe and
879	forwarding it to another server. This includes deleting the old timeout	1525	forwarding it to another server. This includes deleting the old timeout
880	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.
881		1527
882	Results	1528	Results
883	name sockets create request	1529	name sockets create request
884	EV 20000 69.01 11.16	1530	EV 20000 69.01 11.16
885	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
886	Event 20000 212.62 257.32	1534	Event 20000 212.62 257.32
887	Glib 20000 651.16 1896.30	1535	Glib 20000 651.16 1896.30
888	POE 20000 349.67 12317.24 uses POE::Loop::Event	1536	POE 20000 349.67 12317.24 uses POE::Loop::Event
889		1537
890	Discussion	1538	Discussion
891	This benchmark does measure scalability and overall performance of the	1539	This benchmark does measure scalability and overall performance of the
892	particular event loop.	1540	particular event loop.
893		1541
894	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
895	time is relatively high, though.	1543	time is relatively high, though.
896		1544
897	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
898	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.
899		1550
900	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
901	will understand why). Callback invocation also has a high overhead	1552	will understand why). Callback invocation also has a high overhead
902	compared to the "$_->() for .."-style loop that the Perl event loop	1553	compared to the "$_->() for .."-style loop that the Perl event loop
903	uses. Event uses select or poll in basically all documented	1554	uses. Event uses select or poll in basically all documented
…		…
909	POE is still completely out of the picture, taking over 1000 times as	1560	POE is still completely out of the picture, taking over 1000 times as
910	long as EV, and over 100 times as long as the Perl implementation, even	1561	long as EV, and over 100 times as long as the Perl implementation, even
911	though it uses a C-based event loop in this case.	1562	though it uses a C-based event loop in this case.
912		1563
913	Summary	1564	Summary
914	* The pure perl implementation performs extremely well, considering	1565	* The pure perl implementation performs extremely well.
915	that it uses select.
916		1566
917	* Avoid Glib or POE in large projects where performance matters.	1567	* Avoid Glib or POE in large projects where performance matters.
918		1568
919	BENCHMARKING SMALL SERVERS	1569	BENCHMARKING SMALL SERVERS
920	While event loops should scale (and select-based ones do not...) even to	1570	While event loops should scale (and select-based ones do not...) even to
…		…
944	and speed most when you have lots of watchers, not when you only have a	1594	and speed most when you have lots of watchers, not when you only have a
945	few of them).	1595	few of them).
946		1596
947	EV is again fastest.	1597	EV is again fastest.
948		1598
949	Perl again comes second. It is noticably faster than the C-based event	1599	Perl again comes second. It is noticeably faster than the C-based event
950	loops Event and Glib, although the difference is too small to really	1600	loops Event and Glib, although the difference is too small to really
951	matter.	1601	matter.
952		1602
953	POE also performs much better in this case, but is is still far behind	1603	POE also performs much better in this case, but is is still far behind
954	the others.	1604	the others.
955		1605
956	Summary	1606	Summary
957	* 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,
958	as the management overhead dominates.	1608	as the management overhead dominates.
959		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
960	FORK	1763	FORK
961	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
962	because they are so inefficient. Only EV is fully fork-aware.	1765	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1766	Only EV is fully fork-aware.
963		1767
964	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
965	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.
966		1771
967	SECURITY CONSIDERATIONS	1772	SECURITY CONSIDERATIONS
968	AnyEvent can be forced to load any event model via	1773	AnyEvent can be forced to load any event model via
969	$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
970	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
…		…
973	model than specified in the variable.	1778	model than specified in the variable.
974		1779
975	You can make AnyEvent completely ignore this variable by deleting it	1780	You can make AnyEvent completely ignore this variable by deleting it
976	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:
977		1782
978	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1783	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
979		1784
980	use AnyEvent;	1785	use AnyEvent;
		1786
		1787	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1788	be used to probe what backend is used and gain other information (which
		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).
981		1802
982	SEE ALSO	1803	SEE ALSO
983	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1804	Utility functions: AnyEvent::Util.
984	Glib::Event, Glib, Coro, Tk, Event::Lib, Qt, POE.
985		1805
986	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1806	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
987	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1807	Event::Lib, Qt, POE.
988	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib,	1808
		1809	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
		1810	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
		1811	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
989	AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1812	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
990		1813
		1814	Non-blocking file handles, sockets, TCP clients and servers:
		1815	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		1816
		1817	Asynchronous DNS: AnyEvent::DNS.
		1818
		1819	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1820
991	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1821	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1822	AnyEvent::HTTP.
992		1823
993	AUTHOR	1824	AUTHOR
994	Marc Lehmann <schmorp@schmorp.de>	1825	Marc Lehmann <schmorp@schmorp.de>
995	http://home.schmorp.de/	1826	http://home.schmorp.de/
996		1827

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Comparing AnyEvent/README (file contents): Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs. Revision 1.50 by root, Sat Aug 1 09:14:54 2009 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs.
Revision 1.50 by root, Sat Aug 1 09:14:54 2009 UTC