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Comparing AnyEvent/README (file contents):
Revision 1.21 by root, Sat May 17 21:34:15 2008 UTC vs.
Revision 1.58 by root, Sun Dec 20 22:49:52 2009 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - the DBI of event loop programming
3		3
4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	loops	5	Qt and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# file descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		12
		13	# one-shot or repeating timers
		14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		16
		17	print AnyEvent->now; # prints current event loop time
		18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		19
		20	# POSIX signal
		21	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		22
		23	# child process exit
		24	my $w = AnyEvent->child (pid => $pid, cb => sub {
		25	my ($pid, $status) = @_;
11	...	26	...
12	});	27	});
13		28
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	29	# called when event loop idle (if applicable)
15	...	30	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		31
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	32	my $w = AnyEvent->condvar; # stores whether a condition was flagged
19	$w->send; # wake up current and all future recv's	33	$w->send; # wake up current and all future recv's
20	$w->recv; # enters "main loop" till $condvar gets ->send	34	$w->recv; # enters "main loop" till $condvar gets ->send
		35	# use a condvar in callback mode:
		36	$w->cb (sub { $_[0]->recv });
		37
		38	INTRODUCTION/TUTORIAL
		39	This manpage is mainly a reference manual. If you are interested in a
		40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		41	manpage.
		42
		43	SUPPORT
		44	There is a mailinglist for discussing all things AnyEvent, and an IRC
		45	channel, too.
		46
		47	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		48	Repository, at <http://anyevent.schmorp.de>, for more info.
21		49
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	50	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	51	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	52	nowadays. So what is different about AnyEvent?
25		53
26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	54	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
27	policy* and AnyEvent is small and efficient.	55	policy* and AnyEvent is small and efficient.
28		56
29	First and foremost, AnyEvent is not an event model itself, it only	57	First and foremost, AnyEvent is not an event model itself, it only
30	interfaces to whatever event model the main program happens to use in a	58	interfaces to whatever event model the main program happens to use, in a
31	pragmatic way. For event models and certain classes of immortals alike,	59	pragmatic way. For event models and certain classes of immortals alike,
32	the statement "there can only be one" is a bitter reality: In general,	60	the statement "there can only be one" is a bitter reality: In general,
33	only one event loop can be active at the same time in a process.	61	only one event loop can be active at the same time in a process.
34	AnyEvent helps hiding the differences between those event loops.	62	AnyEvent cannot change this, but it can hide the differences between
		63	those event loops.
35		64
36	The goal of AnyEvent is to offer module authors the ability to do event	65	The goal of AnyEvent is to offer module authors the ability to do event
37	programming (waiting for I/O or timer events) without subscribing to a	66	programming (waiting for I/O or timer events) without subscribing to a
38	religion, a way of living, and most importantly: without forcing your	67	religion, a way of living, and most importantly: without forcing your
39	module users into the same thing by forcing them to use the same event	68	module users into the same thing by forcing them to use the same event
40	model you use.	69	model you use.
41		70
42	For modules like POE or IO::Async (which is a total misnomer as it is	71	For modules like POE or IO::Async (which is a total misnomer as it is
43	actually doing all I/O synchronously...), using them in your module is	72	actually doing all I/O synchronously...), using them in your module is
44	like joining a cult: After you joined, you are dependent on them and you	73	like joining a cult: After you joined, you are dependent on them and you
45	cannot use anything else, as it is simply incompatible to everything	74	cannot use anything else, as they are simply incompatible to everything
46	that isn't itself. What's worse, all the potential users of your module	75	that isn't them. What's worse, all the potential users of your module
47	are also forced to use the same event loop you use.	76	are also forced to use the same event loop you use.
48		77
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	78	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	79	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your	80	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
52	module uses one of those, every user of your module has to use it, too.	81	module uses one of those, every user of your module has to use it, too.
53	But if your module uses AnyEvent, it works transparently with all event	82	But if your module uses AnyEvent, it works transparently with all event
54	models it supports (including stuff like POE and IO::Async, as long as	83	models it supports (including stuff like IO::Async, as long as those use
55	those use one of the supported event loops. It is trivial to add new	84	one of the supported event loops. It is trivial to add new event loops
56	event loops to AnyEvent, too, so it is future-proof).	85	to AnyEvent, too, so it is future-proof).
57		86
58	In addition to being free of having to use *the one and only true event	87	In addition to being free of having to use *the one and only true event
59	model*, AnyEvent also is free of bloat and policy: with POE or similar	88	model*, AnyEvent also is free of bloat and policy: with POE or similar
60	modules, you get an 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
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	A typical example would be a script in a web server (e.g.
		360	"mod_perl") - when mod_perl executes the script, then the event loop
		361	will have the wrong idea about the "current time" (being potentially
		362	far in the past, when the script ran the last time). In that case
		363	you should arrange a call to "AnyEvent->now_update" each time the
		364	web server process wakes up again (e.g. at the start of your script,
		365	or in a handler).
		366
		367	Note that updating the time might cause some events to be handled.
		368
225	SIGNAL WATCHERS	369	SIGNAL WATCHERS
		370	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		371
226	You can watch for signals using a signal watcher, "signal" is the signal	372	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	373	name in uppercase and without any "SIG" prefix, "cb" is the Perl
228	whenever a signal occurs.	374	callback to be invoked whenever a signal occurs.
229		375
230	Although the callback might get passed parameters, their value and	376	Although the callback might get passed parameters, their value and
231	presence is undefined and you cannot rely on them. Portable AnyEvent	377	presence is undefined and you cannot rely on them. Portable AnyEvent
232	callbacks cannot use arguments passed to signal watcher callbacks.	378	callbacks cannot use arguments passed to signal watcher callbacks.
233		379
234	Multiple signal occurances can be clumped together into one callback	380	Multiple signal occurrences can be clumped together into one callback
235	invocation, and callback invocation will be synchronous. synchronous	381	invocation, and callback invocation will be synchronous. Synchronous
236	means that it might take a while until the signal gets handled by the	382	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.	383	process, but it is guaranteed not to interrupt any other callbacks.
238		384
239	The main advantage of using these watchers is that you can share a	385	The main advantage of using these watchers is that you can share a
240	signal between multiple watchers.	386	signal between multiple watchers, and AnyEvent will ensure that signals
		387	will not interrupt your program at bad times.
241		388
242	This watcher might use %SIG, so programs overwriting those signals	389	This watcher might use %SIG (depending on the event loop used), so
243	directly will likely not work correctly.	390	programs overwriting those signals directly will likely not work
		391	correctly.
244		392
245	Example: exit on SIGINT	393	Example: exit on SIGINT
246		394
247	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	395	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
248		396
		397	Restart Behaviour
		398	While restart behaviour is up to the event loop implementation, most
		399	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		400	pure perl implementation).
		401
		402	Safe/Unsafe Signals
		403	Perl signals can be either "safe" (synchronous to opcode handling) or
		404	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		405	latter might corrupt your memory.
		406
		407	AnyEvent signal handlers are, in addition, synchronous to the event
		408	loop, i.e. they will not interrupt your running perl program but will
		409	only be called as part of the normal event handling (just like timer,
		410	I/O etc. callbacks, too).
		411
		412	Signal Races, Delays and Workarounds
		413	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		414	callbacks to signals in a generic way, which is a pity, as you cannot do
		415	race-free signal handling in perl, requiring C libraries for this.
		416	AnyEvent will try to do it's best, which means in some cases, signals
		417	will be delayed. The maximum time a signal might be delayed is specified
		418	in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
		419	can be changed only before the first signal watcher is created, and
		420	should be left alone otherwise. This variable determines how often
		421	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		422	will cause fewer spurious wake-ups, which is better for power and CPU
		423	saving.
		424
		425	All these problems can be avoided by installing the optional
		426	Async::Interrupt module, which works with most event loops. It will not
		427	work with inherently broken event loops such as Event or Event::Lib (and
		428	not with POE currently, as POE does it's own workaround with one-second
		429	latency). For those, you just have to suffer the delays.
		430
249	CHILD PROCESS WATCHERS	431	CHILD PROCESS WATCHERS
		432	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		433
250	You can also watch on a child process exit and catch its exit status.	434	You can also watch on a child process exit and catch its exit status.
251		435
252	The child process is specified by the "pid" argument (if set to 0, it	436	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	437	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	438	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	439	and an exit status is available, not on any trace events
256	and exit status (as returned by waitpid), so unlike other watcher types,	440	(stopped/continued).
257	you can rely on child watcher callback arguments.	441
		442	The callback will be called with the pid and exit status (as returned by
		443	waitpid), so unlike other watcher types, you can rely on child watcher
		444	callback arguments.
		445
		446	This watcher type works by installing a signal handler for "SIGCHLD",
		447	and since it cannot be shared, nothing else should use SIGCHLD or reap
		448	random child processes (waiting for specific child processes, e.g.
		449	inside "system", is just fine).
258		450
259	There is a slight catch to child watchers, however: you usually start	451	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	452	them after the child process was created, and this means the process
261	could have exited already (and no SIGCHLD will be sent anymore).	453	could have exited already (and no SIGCHLD will be sent anymore).
262		454
263	Not all event models handle this correctly (POE doesn't), but even for	455	Not all event models handle this correctly (neither POE nor IO::Async
		456	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	457	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	458	before the process exits (i.e. before you fork in the first place).
266	place).	459	AnyEvent's pure perl event loop handles all cases correctly regardless
		460	of when you start the watcher.
267		461
268	This means you cannot create a child watcher as the very first thing in	462	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	463	an AnyEvent program, you have to create at least one watcher before
270	you "fork" the child (alternatively, you can call "AnyEvent::detect").	464	you "fork" the child (alternatively, you can call "AnyEvent::detect").
271		465
		466	As most event loops do not support waiting for child events, they will
		467	be emulated by AnyEvent in most cases, in which the latency and race
		468	problems mentioned in the description of signal watchers apply.
		469
272	Example: fork a process and wait for it	470	Example: fork a process and wait for it
273		471
274	my $done = AnyEvent->condvar;	472	my $done = AnyEvent->condvar;
275		473
276	my $pid = fork or exit 5;	474	my $pid = fork or exit 5;
277		475
278	my $w = AnyEvent->child (	476	my $w = AnyEvent->child (
279	pid => $pid,	477	pid => $pid,
280	cb => sub {	478	cb => sub {
281	my ($pid, $status) = @_;	479	my ($pid, $status) = @_;
282	warn "pid $pid exited with status $status";	480	warn "pid $pid exited with status $status";
283	$done->send;	481	$done->send;
284	},	482	},
285	);	483	);
286		484
287	# do something else, then wait for process exit	485	# do something else, then wait for process exit
288	$done->recv;	486	$done->recv;
		487
		488	IDLE WATCHERS
		489	$w = AnyEvent->idle (cb => <callback>);
		490
		491	Sometimes there is a need to do something, but it is not so important to
		492	do it instantly, but only when there is nothing better to do. This
		493	"nothing better to do" is usually defined to be "no other events need
		494	attention by the event loop".
		495
		496	Idle watchers ideally get invoked when the event loop has nothing better
		497	to do, just before it would block the process to wait for new events.
		498	Instead of blocking, the idle watcher is invoked.
		499
		500	Most event loops unfortunately do not really support idle watchers (only
		501	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		502	will simply call the callback "from time to time".
		503
		504	Example: read lines from STDIN, but only process them when the program
		505	is otherwise idle:
		506
		507	my @lines; # read data
		508	my $idle_w;
		509	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		510	push @lines, scalar <STDIN>;
		511
		512	# start an idle watcher, if not already done
		513	$idle_w \|\|= AnyEvent->idle (cb => sub {
		514	# handle only one line, when there are lines left
		515	if (my $line = shift @lines) {
		516	print "handled when idle: $line";
		517	} else {
		518	# otherwise disable the idle watcher again
		519	undef $idle_w;
		520	}
		521	});
		522	});
289		523
290	CONDITION VARIABLES	524	CONDITION VARIABLES
		525	$cv = AnyEvent->condvar;
		526
		527	$cv->send (<list>);
		528	my @res = $cv->recv;
		529
291	If you are familiar with some event loops you will know that all of them	530	If you are familiar with some event loops you will know that all of them
292	require you to run some blocking "loop", "run" or similar function that	531	require you to run some blocking "loop", "run" or similar function that
293	will actively watch for new events and call your callbacks.	532	will actively watch for new events and call your callbacks.
294		533
295	AnyEvent is different, it expects somebody else to run the event loop	534	AnyEvent is slightly different: it expects somebody else to run the
296	and will only block when necessary (usually when told by the user).	535	event loop and will only block when necessary (usually when told by the
		536	user).
297		537
298	The instrument to do that is called a "condition variable", so called	538	The instrument to do that is called a "condition variable", so called
299	because they represent a condition that must become true.	539	because they represent a condition that must become true.
		540
		541	Now is probably a good time to look at the examples further below.
300		542
301	Condition variables can be created by calling the "AnyEvent->condvar"	543	Condition variables can be created by calling the "AnyEvent->condvar"
302	method, usually without arguments. The only argument pair allowed is	544	method, usually without arguments. The only argument pair allowed is
303	"cb", which specifies a callback to be called when the condition	545	"cb", which specifies a callback to be called when the condition
304	variable becomes true.	546	variable becomes true, with the condition variable as the first argument
		547	(but not the results).
305		548
306	After creation, the conditon variable is "false" until it becomes "true"	549	After creation, the condition variable is "false" until it becomes
		550	"true" by calling the "send" method (or calling the condition variable
		551	as if it were a callback, read about the caveats in the description for
307	by calling the "send" method.	552	the "->send" method).
308		553
309	Condition variables are similar to callbacks, except that you can	554	Condition variables are similar to callbacks, except that you can
310	optionally wait for them. They can also be called merge points - points	555	optionally wait for them. They can also be called merge points - points
311	in time where multiple outstandign events have been processed. And yet	556	in time where multiple outstanding events have been processed. And yet
312	another way to call them is transations - each condition variable can be	557	another way to call them is transactions - each condition variable can
313	used to represent a transaction, which finishes at some point and	558	be used to represent a transaction, which finishes at some point and
314	delivers a result.	559	delivers a result. And yet some people know them as "futures" - a
		560	promise to compute/deliver something that you can wait for.
315		561
316	Condition variables are very useful to signal that something has	562	Condition variables are very useful to signal that something has
317	finished, for example, if you write a module that does asynchronous http	563	finished, for example, if you write a module that does asynchronous http
318	requests, then a condition variable would be the ideal candidate to	564	requests, then a condition variable would be the ideal candidate to
319	signal the availability of results. The user can either act when the	565	signal the availability of results. The user can either act when the
…		…
323	you can block your main program until an event occurs - for example, you	569	you can block your main program until an event occurs - for example, you
324	could "->recv" in your main program until the user clicks the Quit	570	could "->recv" in your main program until the user clicks the Quit
325	button of your app, which would "->send" the "quit" event.	571	button of your app, which would "->send" the "quit" event.
326		572
327	Note that condition variables recurse into the event loop - if you have	573	Note that condition variables recurse into the event loop - if you have
328	two pieces of code that call "->recv" in a round-robbin fashion, you	574	two pieces of code that call "->recv" in a round-robin fashion, you
329	lose. Therefore, condition variables are good to export to your caller,	575	lose. Therefore, condition variables are good to export to your caller,
330	but you should avoid making a blocking wait yourself, at least in	576	but you should avoid making a blocking wait yourself, at least in
331	callbacks, as this asks for trouble.	577	callbacks, as this asks for trouble.
332		578
333	Condition variables are represented by hash refs in perl, and the keys	579	Condition variables are represented by hash refs in perl, and the keys
…		…
338		584
339	There are two "sides" to a condition variable - the "producer side"	585	There are two "sides" to a condition variable - the "producer side"
340	which eventually calls "-> send", and the "consumer side", which waits	586	which eventually calls "-> send", and the "consumer side", which waits
341	for the send to occur.	587	for the send to occur.
342		588
343	Example:	589	Example: wait for a timer.
344		590
345	# wait till the result is ready	591	# wait till the result is ready
346	my $result_ready = AnyEvent->condvar;	592	my $result_ready = AnyEvent->condvar;
347		593
348	# do something such as adding a timer	594	# do something such as adding a timer
…		…
353	after => 1,	599	after => 1,
354	cb => sub { $result_ready->send },	600	cb => sub { $result_ready->send },
355	);	601	);
356		602
357	# this "blocks" (while handling events) till the callback	603	# this "blocks" (while handling events) till the callback
358	# calls send	604	# calls ->send
359	$result_ready->recv;	605	$result_ready->recv;
		606
		607	Example: wait for a timer, but take advantage of the fact that condition
		608	variables are also callable directly.
		609
		610	my $done = AnyEvent->condvar;
		611	my $delay = AnyEvent->timer (after => 5, cb => $done);
		612	$done->recv;
		613
		614	Example: Imagine an API that returns a condvar and doesn't support
		615	callbacks. This is how you make a synchronous call, for example from the
		616	main program:
		617
		618	use AnyEvent::CouchDB;
		619
		620	...
		621
		622	my @info = $couchdb->info->recv;
		623
		624	And this is how you would just set a callback to be called whenever the
		625	results are available:
		626
		627	$couchdb->info->cb (sub {
		628	my @info = $_[0]->recv;
		629	});
360		630
361	METHODS FOR PRODUCERS	631	METHODS FOR PRODUCERS
362	These methods should only be used by the producing side, i.e. the	632	These methods should only be used by the producing side, i.e. the
363	code/module that eventually sends the signal. Note that it is also the	633	code/module that eventually sends the signal. Note that it is also the
364	producer side which creates the condvar in most cases, but it isn't	634	producer side which creates the condvar in most cases, but it isn't
…		…
373	immediately from within send.	643	immediately from within send.
374		644
375	Any arguments passed to the "send" call will be returned by all	645	Any arguments passed to the "send" call will be returned by all
376	future "->recv" calls.	646	future "->recv" calls.
377		647
		648	Condition variables are overloaded so one can call them directly (as
		649	if they were a code reference). Calling them directly is the same as
		650	calling "send".
		651
378	$cv->croak ($error)	652	$cv->croak ($error)
379	Similar to send, but causes all call's to "->recv" to invoke	653	Similar to send, but causes all call's to "->recv" to invoke
380	"Carp::croak" with the given error message/object/scalar.	654	"Carp::croak" with the given error message/object/scalar.
381		655
382	This can be used to signal any errors to the condition variable	656	This can be used to signal any errors to the condition variable
383	user/consumer.	657	user/consumer. Doing it this way instead of calling "croak" directly
		658	delays the error detetcion, but has the overwhelmign advantage that
		659	it diagnoses the error at the place where the result is expected,
		660	and not deep in some event clalback without connection to the actual
		661	code causing the problem.
384		662
385	$cv->begin ([group callback])	663	$cv->begin ([group callback])
386	$cv->end	664	$cv->end
387	These two methods are EXPERIMENTAL and MIGHT CHANGE.
388
389	These two methods can be used to combine many transactions/events	665	These two methods can be used to combine many transactions/events
390	into one. For example, a function that pings many hosts in parallel	666	into one. For example, a function that pings many hosts in parallel
391	might want to use a condition variable for the whole process.	667	might want to use a condition variable for the whole process.
392		668
393	Every call to "->begin" will increment a counter, and every call to	669	Every call to "->begin" will increment a counter, and every call to
394	"->end" will decrement it. If the counter reaches 0 in "->end", the	670	"->end" will decrement it. If the counter reaches 0 in "->end", the
395	(last) callback passed to "begin" will be executed. That callback is	671	(last) callback passed to "begin" will be executed, passing the
396	supposed to call "->send", but that is not required. If no	672	condvar as first argument. That callback is supposed to call
		673	"->send", but that is not required. If no group callback was set,
397	callback was set, "send" will be called without any arguments.	674	"send" will be called without any arguments.
398		675
399	Let's clarify this with the ping example:	676	You can think of "$cv->send" giving you an OR condition (one call
		677	sends), while "$cv->begin" and "$cv->end" giving you an AND
		678	condition (all "begin" calls must be "end"'ed before the condvar
		679	sends).
		680
		681	Let's start with a simple example: you have two I/O watchers (for
		682	example, STDOUT and STDERR for a program), and you want to wait for
		683	both streams to close before activating a condvar:
400		684
401	my $cv = AnyEvent->condvar;	685	my $cv = AnyEvent->condvar;
402		686
		687	$cv->begin; # first watcher
		688	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		689	defined sysread $fh1, my $buf, 4096
		690	or $cv->end;
		691	});
		692
		693	$cv->begin; # second watcher
		694	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		695	defined sysread $fh2, my $buf, 4096
		696	or $cv->end;
		697	});
		698
		699	$cv->recv;
		700
		701	This works because for every event source (EOF on file handle),
		702	there is one call to "begin", so the condvar waits for all calls to
		703	"end" before sending.
		704
		705	The ping example mentioned above is slightly more complicated, as
		706	the there are results to be passwd back, and the number of tasks
		707	that are begung can potentially be zero:
		708
		709	my $cv = AnyEvent->condvar;
		710
403	my %result;	711	my %result;
404	$cv->begin (sub { $cv->send (\%result) });	712	$cv->begin (sub { shift->send (\%result) });
405		713
406	for my $host (@list_of_hosts) {	714	for my $host (@list_of_hosts) {
407	$cv->begin;	715	$cv->begin;
408	ping_host_then_call_callback $host, sub {	716	ping_host_then_call_callback $host, sub {
409	$result{$host} = ...;	717	$result{$host} = ...;
…		…
424	the loop, which serves two important purposes: first, it sets the	732	the loop, which serves two important purposes: first, it sets the
425	callback to be called once the counter reaches 0, and second, it	733	callback to be called once the counter reaches 0, and second, it
426	ensures that "send" is called even when "no" hosts are being pinged	734	ensures that "send" is called even when "no" hosts are being pinged
427	(the loop doesn't execute once).	735	(the loop doesn't execute once).
428		736
429	This is the general pattern when you "fan out" into multiple	737	This is the general pattern when you "fan out" into multiple (but
430	subrequests: use an outer "begin"/"end" pair to set the callback and	738	potentially none) subrequests: use an outer "begin"/"end" pair to
431	ensure "end" is called at least once, and then, for each subrequest	739	set the callback and ensure "end" is called at least once, and then,
432	you start, call "begin" and for eahc subrequest you finish, call	740	for each subrequest you start, call "begin" and for each subrequest
433	"end".	741	you finish, call "end".
434		742
435	METHODS FOR CONSUMERS	743	METHODS FOR CONSUMERS
436	These methods should only be used by the consuming side, i.e. the code	744	These methods should only be used by the consuming side, i.e. the code
437	awaits the condition.	745	awaits the condition.
438		746
…		…
447	function will call "croak".	755	function will call "croak".
448		756
449	In list context, all parameters passed to "send" will be returned,	757	In list context, all parameters passed to "send" will be returned,
450	in scalar context only the first one will be returned.	758	in scalar context only the first one will be returned.
451		759
		760	Note that doing a blocking wait in a callback is not supported by
		761	any event loop, that is, recursive invocation of a blocking "->recv"
		762	is not allowed, and the "recv" call will "croak" if such a condition
		763	is detected. This condition can be slightly loosened by using
		764	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		765	thread that doesn't run the event loop itself.
		766
452	Not all event models support a blocking wait - some die in that case	767	Not all event models support a blocking wait - some die in that case
453	(programs might want to do that to stay interactive), so *if you are	768	(programs might want to do that to stay interactive), so *if you are
454	using this from a module, never require a blocking wait*, but let	769	using this from a module, never require a blocking wait*. Instead,
455	the caller decide whether the call will block or not (for example,	770	let the caller decide whether the call will block or not (for
456	by coupling condition variables with some kind of request results	771	example, by coupling condition variables with some kind of request
457	and supporting callbacks so the caller knows that getting the result	772	results and supporting callbacks so the caller knows that getting
458	will not block, while still suppporting blocking waits if the caller	773	the result will not block, while still supporting blocking waits if
459	so desires).	774	the caller so desires).
460
461	Another reason never to "->recv" in a module is that you cannot
462	sensibly have two "->recv"'s in parallel, as that would require
463	multiple interpreters or coroutines/threads, none of which
464	"AnyEvent" can supply.
465
466	The Coro module, however, can and does supply coroutines and, in
467	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
468	versions and also integrates coroutines into AnyEvent, making
469	blocking "->recv" calls perfectly safe as long as they are done from
470	another coroutine (one that doesn't run the event loop).
471		775
472	You can ensure that "-recv" never blocks by setting a callback and	776	You can ensure that "-recv" never blocks by setting a callback and
473	only calling "->recv" from within that callback (or at a later	777	only calling "->recv" from within that callback (or at a later
474	time). This will work even when the event loop does not support	778	time). This will work even when the event loop does not support
475	blocking waits otherwise.	779	blocking waits otherwise.
476		780
477	$bool = $cv->ready	781	$bool = $cv->ready
478	Returns true when the condition is "true", i.e. whether "send" or	782	Returns true when the condition is "true", i.e. whether "send" or
479	"croak" have been called.	783	"croak" have been called.
480		784
481	$cb = $cv->cb ([new callback])	785	$cb = $cv->cb ($cb->($cv))
482	This is a mutator function that returns the callback set and	786	This is a mutator function that returns the callback set and
483	optionally replaces it before doing so.	787	optionally replaces it before doing so.
484		788
485	The callback will be called when the condition becomes "true", i.e.	789	The callback will be called when the condition becomes (or already
486	when "send" or "croak" are called. Calling "recv" inside the	790	was) "true", i.e. when "send" or "croak" are called (or were
487	callback or at any later time is guaranteed not to block.	791	called), with the only argument being the condition variable itself.
		792	Calling "recv" inside the callback or at any later time is
		793	guaranteed not to block.
		794
		795	SUPPORTED EVENT LOOPS/BACKENDS
		796	The available backend classes are (every class has its own manpage):
		797
		798	Backends that are autoprobed when no other event loop can be found.
		799	EV is the preferred backend when no other event loop seems to be in
		800	use. If EV is not installed, then AnyEvent will fall back to its own
		801	pure-perl implementation, which is available everywhere as it comes
		802	with AnyEvent itself.
		803
		804	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		805	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		806
		807	Backends that are transparently being picked up when they are used.
		808	These will be used when they are currently loaded when the first
		809	watcher is created, in which case it is assumed that the application
		810	is using them. This means that AnyEvent will automatically pick the
		811	right backend when the main program loads an event module before
		812	anything starts to create watchers. Nothing special needs to be done
		813	by the main program.
		814
		815	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		816	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		817	AnyEvent::Impl::Tk based on Tk, very broken.
		818	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		819	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		820	AnyEvent::Impl::Irssi used when running within irssi.
		821
		822	Backends with special needs.
		823	Qt requires the Qt::Application to be instantiated first, but will
		824	otherwise be picked up automatically. As long as the main program
		825	instantiates the application before any AnyEvent watchers are
		826	created, everything should just work.
		827
		828	AnyEvent::Impl::Qt based on Qt.
		829
		830	Support for IO::Async can only be partial, as it is too broken and
		831	architecturally limited to even support the AnyEvent API. It also is
		832	the only event loop that needs the loop to be set explicitly, so it
		833	can only be used by a main program knowing about AnyEvent. See
		834	AnyEvent::Impl::Async for the gory details.
		835
		836	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		837
		838	Event loops that are indirectly supported via other backends.
		839	Some event loops can be supported via other modules:
		840
		841	There is no direct support for WxWidgets (Wx) or Prima.
		842
		843	WxWidgets has no support for watching file handles. However, you can
		844	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		845	simply polls 20 times per second, which was considered to be too
		846	horrible to even consider for AnyEvent.
		847
		848	Prima is not supported as nobody seems to be using it, but it has a
		849	POE backend, so it can be supported through POE.
		850
		851	AnyEvent knows about both Prima and Wx, however, and will try to
		852	load POE when detecting them, in the hope that POE will pick them
		853	up, in which case everything will be automatic.
488		854
489	GLOBAL VARIABLES AND FUNCTIONS	855	GLOBAL VARIABLES AND FUNCTIONS
		856	These are not normally required to use AnyEvent, but can be useful to
		857	write AnyEvent extension modules.
		858
490	$AnyEvent::MODEL	859	$AnyEvent::MODEL
491	Contains "undef" until the first watcher is being created. Then it	860	Contains "undef" until the first watcher is being created, before
		861	the backend has been autodetected.
		862
492	contains the event model that is being used, which is the name of	863	Afterwards it contains the event model that is being used, which is
493	the Perl class implementing the model. This class is usually one of	864	the name of the Perl class implementing the model. This class is
494	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	865	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
495	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	866	other class in the case AnyEvent has been extended at runtime (e.g.
496		867	in rxvt-unicode it will be "urxvt::anyevent").
497	The known classes so far are:
498
499	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
500	AnyEvent::Impl::Event based on Event, second best choice.
501	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
502	AnyEvent::Impl::Glib based on Glib, third-best choice.
503	AnyEvent::Impl::Tk based on Tk, very bad choice.
504	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
505	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
506	AnyEvent::Impl::POE based on POE, not generic enough for full support.
507
508	There is no support for WxWidgets, as WxWidgets has no support for
509	watching file handles. However, you can use WxWidgets through the
510	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
511	second, which was considered to be too horrible to even consider for
512	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
513	using it's adaptor.
514
515	AnyEvent knows about Prima and Wx and will try to use POE when
516	autodetecting them.
517		868
518	AnyEvent::detect	869	AnyEvent::detect
519	Returns $AnyEvent::MODEL, forcing autodetection of the event model	870	Returns $AnyEvent::MODEL, forcing autodetection of the event model
520	if necessary. You should only call this function right before you	871	if necessary. You should only call this function right before you
521	would have created an AnyEvent watcher anyway, that is, as late as	872	would have created an AnyEvent watcher anyway, that is, as late as
522	possible at runtime.	873	possible at runtime, and not e.g. while initialising of your module.
		874
		875	If you need to do some initialisation before AnyEvent watchers are
		876	created, use "post_detect".
523		877
524	$guard = AnyEvent::post_detect { BLOCK }	878	$guard = AnyEvent::post_detect { BLOCK }
525	Arranges for the code block to be executed as soon as the event	879	Arranges for the code block to be executed as soon as the event
526	model is autodetected (or immediately if this has already happened).	880	model is autodetected (or immediately if this has already happened).
527		881
		882	The block will be executed after the actual backend has been
		883	detected ($AnyEvent::MODEL is set), but before any watchers have
		884	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		885	other initialisations - see the sources of AnyEvent::Strict or
		886	AnyEvent::AIO to see how this is used.
		887
		888	The most common usage is to create some global watchers, without
		889	forcing event module detection too early, for example, AnyEvent::AIO
		890	creates and installs the global IO::AIO watcher in a "post_detect"
		891	block to avoid autodetecting the event module at load time.
		892
528	If called in scalar or list context, then it creates and returns an	893	If called in scalar or list context, then it creates and returns an
529	object that automatically removes the callback again when it is	894	object that automatically removes the callback again when it is
		895	destroyed (or "undef" when the hook was immediately executed). See
530	destroyed. See Coro::BDB for a case where this is useful.	896	AnyEvent::AIO for a case where this is useful.
		897
		898	Example: Create a watcher for the IO::AIO module and store it in
		899	$WATCHER. Only do so after the event loop is initialised, though.
		900
		901	our WATCHER;
		902
		903	my $guard = AnyEvent::post_detect {
		904	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		905	};
		906
		907	# the \|\|= is important in case post_detect immediately runs the block,
		908	# as to not clobber the newly-created watcher. assigning both watcher and
		909	# post_detect guard to the same variable has the advantage of users being
		910	# able to just C<undef $WATCHER> if the watcher causes them grief.
		911
		912	$WATCHER \|\|= $guard;
531		913
532	@AnyEvent::post_detect	914	@AnyEvent::post_detect
533	If there are any code references in this array (you can "push" to it	915	If there are any code references in this array (you can "push" to it
534	before or after loading AnyEvent), then they will called directly	916	before or after loading AnyEvent), then they will called directly
535	after the event loop has been chosen.	917	after the event loop has been chosen.
536		918
537	You should check $AnyEvent::MODEL before adding to this array,	919	You should check $AnyEvent::MODEL before adding to this array,
538	though: if it contains a true value then the event loop has already	920	though: if it is defined then the event loop has already been
539	been detected, and the array will be ignored.	921	detected, and the array will be ignored.
540		922
541	Best use "AnyEvent::post_detect { BLOCK }" instead.	923	Best use "AnyEvent::post_detect { BLOCK }" when your application
		924	allows it, as it takes care of these details.
		925
		926	This variable is mainly useful for modules that can do something
		927	useful when AnyEvent is used and thus want to know when it is
		928	initialised, but do not need to even load it by default. This array
		929	provides the means to hook into AnyEvent passively, without loading
		930	it.
		931
		932	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		933	together, you could put this into Coro (this is the actual code used
		934	by Coro to accomplish this):
		935
		936	if (defined $AnyEvent::MODEL) {
		937	# AnyEvent already initialised, so load Coro::AnyEvent
		938	require Coro::AnyEvent;
		939	} else {
		940	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		941	# as soon as it is
		942	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		943	}
542		944
543	WHAT TO DO IN A MODULE	945	WHAT TO DO IN A MODULE
544	As a module author, you should "use AnyEvent" and call AnyEvent methods	946	As a module author, you should "use AnyEvent" and call AnyEvent methods
545	freely, but you should not load a specific event module or rely on it.	947	freely, but you should not load a specific event module or rely on it.
546		948
…		…
566	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	968	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
567	do anything special (it does not need to be event-based) and let	969	do anything special (it does not need to be event-based) and let
568	AnyEvent decide which implementation to chose if some module relies on	970	AnyEvent decide which implementation to chose if some module relies on
569	it.	971	it.
570		972
571	If the main program relies on a specific event model. For example, in	973	If the main program relies on a specific event model - for example, in
572	Gtk2 programs you have to rely on the Glib module. You should load the	974	Gtk2 programs you have to rely on the Glib module - you should load the
573	event module before loading AnyEvent or any module that uses it:	975	event module before loading AnyEvent or any module that uses it:
574	generally speaking, you should load it as early as possible. The reason	976	generally speaking, you should load it as early as possible. The reason
575	is that modules might create watchers when they are loaded, and AnyEvent	977	is that modules might create watchers when they are loaded, and AnyEvent
576	will decide on the event model to use as soon as it creates watchers,	978	will decide on the event model to use as soon as it creates watchers,
577	and it might chose the wrong one unless you load the correct one	979	and it might chose the wrong one unless you load the correct one
578	yourself.	980	yourself.
579		981
580	You can chose to use a rather inefficient pure-perl implementation by	982	You can chose to use a pure-perl implementation by loading the
581	loading the "AnyEvent::Impl::Perl" module, which gives you similar	983	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
582	behaviour everywhere, but letting AnyEvent chose is generally better.	984	everywhere, but letting AnyEvent chose the model is generally better.
		985
		986	MAINLOOP EMULATION
		987	Sometimes (often for short test scripts, or even standalone programs who
		988	only want to use AnyEvent), you do not want to run a specific event
		989	loop.
		990
		991	In that case, you can use a condition variable like this:
		992
		993	AnyEvent->condvar->recv;
		994
		995	This has the effect of entering the event loop and looping forever.
		996
		997	Note that usually your program has some exit condition, in which case it
		998	is better to use the "traditional" approach of storing a condition
		999	variable somewhere, waiting for it, and sending it when the program
		1000	should exit cleanly.
583		1001
584	OTHER MODULES	1002	OTHER MODULES
585	The following is a non-exhaustive list of additional modules that use	1003	The following is a non-exhaustive list of additional modules that use
586	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1004	AnyEvent as a client and can therefore be mixed easily with other
587	in the same program. Some of the modules come with AnyEvent, some are	1005	AnyEvent modules and other event loops in the same program. Some of the
588	available via CPAN.	1006	modules come with AnyEvent, most are available via CPAN.
589		1007
590	AnyEvent::Util	1008	AnyEvent::Util
591	Contains various utility functions that replace often-used but	1009	Contains various utility functions that replace often-used but
592	blocking functions such as "inet_aton" by event-/callback-based	1010	blocking functions such as "inet_aton" by event-/callback-based
593	versions.	1011	versions.
594		1012
		1013	AnyEvent::Socket
		1014	Provides various utility functions for (internet protocol) sockets,
		1015	addresses and name resolution. Also functions to create non-blocking
		1016	tcp connections or tcp servers, with IPv6 and SRV record support and
		1017	more.
		1018
595	AnyEvent::Handle	1019	AnyEvent::Handle
596	Provide read and write buffers and manages watchers for reads and	1020	Provide read and write buffers, manages watchers for reads and
597	writes.	1021	writes, supports raw and formatted I/O, I/O queued and fully
		1022	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
		1023
		1024	AnyEvent::DNS
		1025	Provides rich asynchronous DNS resolver capabilities.
		1026
		1027	AnyEvent::HTTP
		1028	A simple-to-use HTTP library that is capable of making a lot of
		1029	concurrent HTTP requests.
598		1030
599	AnyEvent::HTTPD	1031	AnyEvent::HTTPD
600	Provides a simple web application server framework.	1032	Provides a simple web application server framework.
601		1033
602	AnyEvent::DNS
603	Provides asynchronous DNS resolver capabilities, beyond what
604	AnyEvent::Util offers.
605
606	AnyEvent::FastPing	1034	AnyEvent::FastPing
607	The fastest ping in the west.	1035	The fastest ping in the west.
608		1036
		1037	AnyEvent::DBI
		1038	Executes DBI requests asynchronously in a proxy process.
		1039
		1040	AnyEvent::AIO
		1041	Truly asynchronous I/O, should be in the toolbox of every event
		1042	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		1043	together.
		1044
		1045	AnyEvent::BDB
		1046	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		1047	fuses BDB and AnyEvent together.
		1048
		1049	AnyEvent::GPSD
		1050	A non-blocking interface to gpsd, a daemon delivering GPS
		1051	information.
		1052
		1053	AnyEvent::IRC
		1054	AnyEvent based IRC client module family (replacing the older
609	Net::IRC3	1055	Net::IRC3).
610	AnyEvent based IRC client module family.
611		1056
612	Net::XMPP2	1057	AnyEvent::XMPP
613	AnyEvent based XMPP (Jabber protocol) module family.	1058	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		1059	older Net::XMPP2>.
		1060
		1061	AnyEvent::IGS
		1062	A non-blocking interface to the Internet Go Server protocol (used by
		1063	App::IGS).
614		1064
615	Net::FCP	1065	Net::FCP
616	AnyEvent-based implementation of the Freenet Client Protocol,	1066	AnyEvent-based implementation of the Freenet Client Protocol,
617	birthplace of AnyEvent.	1067	birthplace of AnyEvent.
618		1068
…		…
620	High level API for event-based execution flow control.	1070	High level API for event-based execution flow control.
621		1071
622	Coro	1072	Coro
623	Has special support for AnyEvent via Coro::AnyEvent.	1073	Has special support for AnyEvent via Coro::AnyEvent.
624		1074
625	AnyEvent::AIO, IO::AIO	1075	SIMPLIFIED AE API
626	Truly asynchronous I/O, should be in the toolbox of every event	1076	Starting with version 5.0, AnyEvent officially supports a second, much
627	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	1077	simpler, API that is designed to reduce the calling, typing and memory
628	together.	1078	overhead.
629		1079
630	AnyEvent::BDB, BDB	1080	See the AE manpage for details.
631	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
632	fuses IO::AIO and AnyEvent together.
633		1081
634	IO::Lambda	1082	ERROR AND EXCEPTION HANDLING
635	The lambda approach to I/O - don't ask, look there. Can use	1083	In general, AnyEvent does not do any error handling - it relies on the
636	AnyEvent.	1084	caller to do that if required. The AnyEvent::Strict module (see also the
		1085	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1086	checking of all AnyEvent methods, however, which is highly useful during
		1087	development.
		1088
		1089	As for exception handling (i.e. runtime errors and exceptions thrown
		1090	while executing a callback), this is not only highly event-loop
		1091	specific, but also not in any way wrapped by this module, as this is the
		1092	job of the main program.
		1093
		1094	The pure perl event loop simply re-throws the exception (usually within
		1095	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		1096	Glib uses "install_exception_handler" and so on.
		1097
		1098	ENVIRONMENT VARIABLES
		1099	The following environment variables are used by this module or its
		1100	submodules.
		1101
		1102	Note that AnyEvent will remove all environment variables starting with
		1103	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1104	enabled.
		1105
		1106	"PERL_ANYEVENT_VERBOSE"
		1107	By default, AnyEvent will be completely silent except in fatal
		1108	conditions. You can set this environment variable to make AnyEvent
		1109	more talkative.
		1110
		1111	When set to 1 or higher, causes AnyEvent to warn about unexpected
		1112	conditions, such as not being able to load the event model specified
		1113	by "PERL_ANYEVENT_MODEL".
		1114
		1115	When set to 2 or higher, cause AnyEvent to report to STDERR which
		1116	event model it chooses.
		1117
		1118	When set to 8 or higher, then AnyEvent will report extra information
		1119	on which optional modules it loads and how it implements certain
		1120	features.
		1121
		1122	"PERL_ANYEVENT_STRICT"
		1123	AnyEvent does not do much argument checking by default, as thorough
		1124	argument checking is very costly. Setting this variable to a true
		1125	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1126	thoroughly check the arguments passed to most method calls. If it
		1127	finds any problems, it will croak.
		1128
		1129	In other words, enables "strict" mode.
		1130
		1131	Unlike "use strict" (or it's modern cousin, "use common::sense", it
		1132	is definitely recommended to keep it off in production. Keeping
		1133	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1134	programs can be very useful, however.
		1135
		1136	"PERL_ANYEVENT_MODEL"
		1137	This can be used to specify the event model to be used by AnyEvent,
		1138	before auto detection and -probing kicks in. It must be a string
		1139	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		1140	gets prepended and the resulting module name is loaded and if the
		1141	load was successful, used as event model. If it fails to load
		1142	AnyEvent will proceed with auto detection and -probing.
		1143
		1144	This functionality might change in future versions.
		1145
		1146	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		1147	could start your program like this:
		1148
		1149	PERL_ANYEVENT_MODEL=Perl perl ...
		1150
		1151	"PERL_ANYEVENT_PROTOCOLS"
		1152	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		1153	preferences for IPv4 or IPv6. The default is unspecified (and might
		1154	change, or be the result of auto probing).
		1155
		1156	Must be set to a comma-separated list of protocols or address
		1157	families, current supported: "ipv4" and "ipv6". Only protocols
		1158	mentioned will be used, and preference will be given to protocols
		1159	mentioned earlier in the list.
		1160
		1161	This variable can effectively be used for denial-of-service attacks
		1162	against local programs (e.g. when setuid), although the impact is
		1163	likely small, as the program has to handle conenction and other
		1164	failures anyways.
		1165
		1166	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		1167	IPv6, but support both and try to use both.
		1168	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		1169	resolve or contact IPv6 addresses.
		1170	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		1171	prefer IPv6 over IPv4.
		1172
		1173	"PERL_ANYEVENT_EDNS0"
		1174	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		1175	for DNS. This extension is generally useful to reduce DNS traffic,
		1176	but some (broken) firewalls drop such DNS packets, which is why it
		1177	is off by default.
		1178
		1179	Setting this variable to 1 will cause AnyEvent::DNS to announce
		1180	EDNS0 in its DNS requests.
		1181
		1182	"PERL_ANYEVENT_MAX_FORKS"
		1183	The maximum number of child processes that
		1184	"AnyEvent::Util::fork_call" will create in parallel.
		1185
		1186	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1187	The default value for the "max_outstanding" parameter for the
		1188	default DNS resolver - this is the maximum number of parallel DNS
		1189	requests that are sent to the DNS server.
		1190
		1191	"PERL_ANYEVENT_RESOLV_CONF"
		1192	The file to use instead of /etc/resolv.conf (or OS-specific
		1193	configuration) in the default resolver. When set to the empty
		1194	string, no default config will be used.
		1195
		1196	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1197	When neither "ca_file" nor "ca_path" was specified during
		1198	AnyEvent::TLS context creation, and either of these environment
		1199	variables exist, they will be used to specify CA certificate
		1200	locations instead of a system-dependent default.
		1201
		1202	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1203	When these are set to 1, then the respective modules are not loaded.
		1204	Mostly good for testing AnyEvent itself.
637		1205
638	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1206	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
639	This is an advanced topic that you do not normally need to use AnyEvent	1207	This is an advanced topic that you do not normally need to use AnyEvent
640	in a module. This section is only of use to event loop authors who want	1208	in a module. This section is only of use to event loop authors who want
641	to provide AnyEvent compatibility.	1209	to provide AnyEvent compatibility.
…		…
675		1243
676	rxvt-unicode also cheats a bit by not providing blocking access to	1244	rxvt-unicode also cheats a bit by not providing blocking access to
677	condition variables: code blocking while waiting for a condition will	1245	condition variables: code blocking while waiting for a condition will
678	"die". This still works with most modules/usages, and blocking calls	1246	"die". This still works with most modules/usages, and blocking calls
679	must not be done in an interactive application, so it makes sense.	1247	must not be done in an interactive application, so it makes sense.
680
681	ENVIRONMENT VARIABLES
682	The following environment variables are used by this module:
683
684	"PERL_ANYEVENT_VERBOSE"
685	By default, AnyEvent will be completely silent except in fatal
686	conditions. You can set this environment variable to make AnyEvent
687	more talkative.
688
689	When set to 1 or higher, causes AnyEvent to warn about unexpected
690	conditions, such as not being able to load the event model specified
691	by "PERL_ANYEVENT_MODEL".
692
693	When set to 2 or higher, cause AnyEvent to report to STDERR which
694	event model it chooses.
695
696	"PERL_ANYEVENT_MODEL"
697	This can be used to specify the event model to be used by AnyEvent,
698	before autodetection and -probing kicks in. It must be a string
699	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
700	gets prepended and the resulting module name is loaded and if the
701	load was successful, used as event model. If it fails to load
702	AnyEvent will proceed with autodetection and -probing.
703
704	This functionality might change in future versions.
705
706	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
707	could start your program like this:
708
709	PERL_ANYEVENT_MODEL=Perl perl ...
710		1248
711	EXAMPLE PROGRAM	1249	EXAMPLE PROGRAM
712	The following program uses an I/O watcher to read data from STDIN, a	1250	The following program uses an I/O watcher to read data from STDIN, a
713	timer to display a message once per second, and a condition variable to	1251	timer to display a message once per second, and a condition variable to
714	quit the program when the user enters quit:	1252	quit the program when the user enters quit:
…		…
726	warn "read: $input\n"; # output what has been read	1264	warn "read: $input\n"; # output what has been read
727	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1265	$cv->send if $input =~ /^q/i; # quit program if /^q/i
728	},	1266	},
729	);	1267	);
730		1268
731	my $time_watcher; # can only be used once
732
733	sub new_timer {
734	$timer = AnyEvent->timer (after => 1, cb => sub {	1269	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
735	warn "timeout\n"; # print 'timeout' about every second	1270	warn "timeout\n"; # print 'timeout' at most every second
736	&new_timer; # and restart the time
737	});
738	}	1271	});
739
740	new_timer; # create first timer
741		1272
742	$cv->recv; # wait until user enters /^q/i	1273	$cv->recv; # wait until user enters /^q/i
743		1274
744	REAL-WORLD EXAMPLE	1275	REAL-WORLD EXAMPLE
745	Consider the Net::FCP module. It features (among others) the following	1276	Consider the Net::FCP module. It features (among others) the following
…		…
796	syswrite $txn->{fh}, $txn->{request}	1327	syswrite $txn->{fh}, $txn->{request}
797	or die "connection or write error";	1328	or die "connection or write error";
798	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1329	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
799		1330
800	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1331	Again, "fh_ready_r" waits till all data has arrived, and then stores the
801	result and signals any possible waiters that the request ahs finished:	1332	result and signals any possible waiters that the request has finished:
802		1333
803	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1334	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
804		1335
805	if (end-of-file or data complete) {	1336	if (end-of-file or data complete) {
806	$txn->{result} = $txn->{buf};	1337	$txn->{result} = $txn->{buf};
…		…
814		1345
815	$txn->{finished}->recv;	1346	$txn->{finished}->recv;
816	return $txn->{result};	1347	return $txn->{result};
817		1348
818	The actual code goes further and collects all errors ("die"s,	1349	The actual code goes further and collects all errors ("die"s,
819	exceptions) that occured during request processing. The "result" method	1350	exceptions) that occurred during request processing. The "result" method
820	detects whether an exception as thrown (it is stored inside the $txn	1351	detects whether an exception as thrown (it is stored inside the $txn
821	object) and just throws the exception, which means connection errors and	1352	object) and just throws the exception, which means connection errors and
822	other problems get reported tot he code that tries to use the result,	1353	other problems get reported tot he code that tries to use the result,
823	not in a random callback.	1354	not in a random callback.
824		1355
…		…
867	over the event loops themselves and to give you an impression of the	1398	over the event loops themselves and to give you an impression of the
868	speed of various event loops I prepared some benchmarks.	1399	speed of various event loops I prepared some benchmarks.
869		1400
870	BENCHMARKING ANYEVENT OVERHEAD	1401	BENCHMARKING ANYEVENT OVERHEAD
871	Here is a benchmark of various supported event models used natively and	1402	Here is a benchmark of various supported event models used natively and
872	through anyevent. The benchmark creates a lot of timers (with a zero	1403	through AnyEvent. The benchmark creates a lot of timers (with a zero
873	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1404	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
874	which it is), lets them fire exactly once and destroys them again.	1405	which it is), lets them fire exactly once and destroys them again.
875		1406
876	Source code for this benchmark is found as eg/bench in the AnyEvent	1407	Source code for this benchmark is found as eg/bench in the AnyEvent
877	distribution.	1408	distribution. It uses the AE interface, which makes a real difference
		1409	for the EV and Perl backends only.
878		1410
879	Explanation of the columns	1411	Explanation of the columns
880	watcher is the number of event watchers created/destroyed. Since	1412	watcher is the number of event watchers created/destroyed. Since
881	different event models feature vastly different performances, each event	1413	different event models feature vastly different performances, each event
882	loop was given a number of watchers so that overall runtime is	1414	loop was given a number of watchers so that overall runtime is
…		…
901	destroy is the time, in microseconds, that it takes to destroy a	1433	destroy is the time, in microseconds, that it takes to destroy a
902	single watcher.	1434	single watcher.
903		1435
904	Results	1436	Results
905	name watchers bytes create invoke destroy comment	1437	name watchers bytes create invoke destroy comment
906	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1438	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
907	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1439	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
908	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1440	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
909	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1441	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
910	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1442	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
911	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1443	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1444	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1445	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
912	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1446	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
913	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1447	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
914	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1448	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
915	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1449	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
916		1450
917	Discussion	1451	Discussion
918	The benchmark does not measure scalability of the event loop very	1452	The benchmark does not measure scalability of the event loop very
919	well. For example, a select-based event loop (such as the pure perl one)	1453	well. For example, a select-based event loop (such as the pure perl one)
920	can never compete with an event loop that uses epoll when the number of	1454	can never compete with an event loop that uses epoll when the number of
…		…
931	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1465	benchmark machine, handling an event takes roughly 1600 CPU cycles with
932	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1466	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
933	CPU cycles with POE.	1467	CPU cycles with POE.
934		1468
935	"EV" is the sole leader regarding speed and memory use, which are both	1469	"EV" is the sole leader regarding speed and memory use, which are both
936	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1470	maximal/minimal, respectively. When using the AE API there is zero
		1471	overhead (when going through the AnyEvent API create is about 5-6 times
		1472	slower, with other times being equal, so still uses far less memory than
937	far less memory than any other event loop and is still faster than Event	1473	any other event loop and is still faster than Event natively).
938	natively.
939		1474
940	The pure perl implementation is hit in a few sweet spots (both the	1475	The pure perl implementation is hit in a few sweet spots (both the
941	constant timeout and the use of a single fd hit optimisations in the	1476	constant timeout and the use of a single fd hit optimisations in the
942	perl interpreter and the backend itself). Nevertheless this shows that	1477	perl interpreter and the backend itself). Nevertheless this shows that
943	it adds very little overhead in itself. Like any select-based backend	1478	it adds very little overhead in itself. Like any select-based backend
…		…
945	few of them active), of course, but this was not subject of this	1480	few of them active), of course, but this was not subject of this
946	benchmark.	1481	benchmark.
947		1482
948	The "Event" module has a relatively high setup and callback invocation	1483	The "Event" module has a relatively high setup and callback invocation
949	cost, but overall scores in on the third place.	1484	cost, but overall scores in on the third place.
		1485
		1486	"IO::Async" performs admirably well, about on par with "Event", even
		1487	when using its pure perl backend.
950		1488
951	"Glib"'s memory usage is quite a bit higher, but it features a faster	1489	"Glib"'s memory usage is quite a bit higher, but it features a faster
952	callback invocation and overall ends up in the same class as "Event".	1490	callback invocation and overall ends up in the same class as "Event".
953	However, Glib scales extremely badly, doubling the number of watchers	1491	However, Glib scales extremely badly, doubling the number of watchers
954	increases the processing time by more than a factor of four, making it	1492	increases the processing time by more than a factor of four, making it
…		…
992		1530
993	* You should avoid POE like the plague if you want performance or	1531	* You should avoid POE like the plague if you want performance or
994	reasonable memory usage.	1532	reasonable memory usage.
995		1533
996	BENCHMARKING THE LARGE SERVER CASE	1534	BENCHMARKING THE LARGE SERVER CASE
997	This benchmark atcually benchmarks the event loop itself. It works by	1535	This benchmark actually benchmarks the event loop itself. It works by
998	creating a number of "servers": each server consists of a socketpair, a	1536	creating a number of "servers": each server consists of a socket pair, a
999	timeout watcher that gets reset on activity (but never fires), and an	1537	timeout watcher that gets reset on activity (but never fires), and an
1000	I/O watcher waiting for input on one side of the socket. Each time the	1538	I/O watcher waiting for input on one side of the socket. Each time the
1001	socket watcher reads a byte it will write that byte to a random other	1539	socket watcher reads a byte it will write that byte to a random other
1002	"server".	1540	"server".
1003		1541
1004	The effect is that there will be a lot of I/O watchers, only part of	1542	The effect is that there will be a lot of I/O watchers, only part of
1005	which are active at any one point (so there is a constant number of	1543	which are active at any one point (so there is a constant number of
1006	active fds for each loop iterstaion, but which fds these are is random).	1544	active fds for each loop iteration, but which fds these are is random).
1007	The timeout is reset each time something is read because that reflects	1545	The timeout is reset each time something is read because that reflects
1008	how most timeouts work (and puts extra pressure on the event loops).	1546	how most timeouts work (and puts extra pressure on the event loops).
1009		1547
1010	In this benchmark, we use 10000 socketpairs (20000 sockets), of which	1548	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1011	100 (1%) are active. This mirrors the activity of large servers with	1549	100 (1%) are active. This mirrors the activity of large servers with
1012	many connections, most of which are idle at any one point in time.	1550	many connections, most of which are idle at any one point in time.
1013		1551
1014	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1552	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1015	distribution.	1553	distribution. It uses the AE interface, which makes a real difference
		1554	for the EV and Perl backends only.
1016		1555
1017	Explanation of the columns	1556	Explanation of the columns
1018	sockets is the number of sockets, and twice the number of "servers"	1557	sockets is the number of sockets, and twice the number of "servers"
1019	(as each server has a read and write socket end).	1558	(as each server has a read and write socket end).
1020		1559
1021	create is the time it takes to create a socketpair (which is	1560	create is the time it takes to create a socket pair (which is
1022	nontrivial) and two watchers: an I/O watcher and a timeout watcher.	1561	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
1023		1562
1024	request, the most important value, is the time it takes to handle a	1563	request, the most important value, is the time it takes to handle a
1025	single "request", that is, reading the token from the pipe and	1564	single "request", that is, reading the token from the pipe and
1026	forwarding it to another server. This includes deleting the old timeout	1565	forwarding it to another server. This includes deleting the old timeout
1027	and creating a new one that moves the timeout into the future.	1566	and creating a new one that moves the timeout into the future.
1028		1567
1029	Results	1568	Results
1030	name sockets create request	1569	name sockets create request
1031	EV 20000 69.01 11.16	1570	EV 20000 62.66 7.99
1032	Perl 20000 73.32 35.87	1571	Perl 20000 68.32 32.64
1033	Event 20000 212.62 257.32	1572	IOAsync 20000 174.06 101.15 epoll
1034	Glib 20000 651.16 1896.30	1573	IOAsync 20000 174.67 610.84 poll
		1574	Event 20000 202.69 242.91
		1575	Glib 20000 557.01 1689.52
1035	POE 20000 349.67 12317.24 uses POE::Loop::Event	1576	POE 20000 341.54 12086.32 uses POE::Loop::Event
1036		1577
1037	Discussion	1578	Discussion
1038	This benchmark does measure scalability and overall performance of the	1579	This benchmark does measure scalability and overall performance of the
1039	particular event loop.	1580	particular event loop.
1040		1581
1041	EV is again fastest. Since it is using epoll on my system, the setup	1582	EV is again fastest. Since it is using epoll on my system, the setup
1042	time is relatively high, though.	1583	time is relatively high, though.
1043		1584
1044	Perl surprisingly comes second. It is much faster than the C-based event	1585	Perl surprisingly comes second. It is much faster than the C-based event
1045	loops Event and Glib.	1586	loops Event and Glib.
		1587
		1588	IO::Async performs very well when using its epoll backend, and still
		1589	quite good compared to Glib when using its pure perl backend.
1046		1590
1047	Event suffers from high setup time as well (look at its code and you	1591	Event suffers from high setup time as well (look at its code and you
1048	will understand why). Callback invocation also has a high overhead	1592	will understand why). Callback invocation also has a high overhead
1049	compared to the "$_->() for .."-style loop that the Perl event loop	1593	compared to the "$_->() for .."-style loop that the Perl event loop
1050	uses. Event uses select or poll in basically all documented	1594	uses. Event uses select or poll in basically all documented
…		…
1090	and speed most when you have lots of watchers, not when you only have a	1634	and speed most when you have lots of watchers, not when you only have a
1091	few of them).	1635	few of them).
1092		1636
1093	EV is again fastest.	1637	EV is again fastest.
1094		1638
1095	Perl again comes second. It is noticably faster than the C-based event	1639	Perl again comes second. It is noticeably faster than the C-based event
1096	loops Event and Glib, although the difference is too small to really	1640	loops Event and Glib, although the difference is too small to really
1097	matter.	1641	matter.
1098		1642
1099	POE also performs much better in this case, but is is still far behind	1643	POE also performs much better in this case, but is is still far behind
1100	the others.	1644	the others.
1101		1645
1102	Summary	1646	Summary
1103	* C-based event loops perform very well with small number of watchers,	1647	* C-based event loops perform very well with small number of watchers,
1104	as the management overhead dominates.	1648	as the management overhead dominates.
		1649
		1650	THE IO::Lambda BENCHMARK
		1651	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1652	could be misinterpreted to make AnyEvent look bad. In fact, the
		1653	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1654	better (which shouldn't come as a surprise to anybody). As such, the
		1655	benchmark is fine, and mostly shows that the AnyEvent backend from
		1656	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1657	without the extra baggage? To explore this, I wrote the equivalent
		1658	benchmark for AnyEvent.
		1659
		1660	The benchmark itself creates an echo-server, and then, for 500 times,
		1661	connects to the echo server, sends a line, waits for the reply, and then
		1662	creates the next connection. This is a rather bad benchmark, as it
		1663	doesn't test the efficiency of the framework or much non-blocking I/O,
		1664	but it is a benchmark nevertheless.
		1665
		1666	name runtime
		1667	Lambda/select 0.330 sec
		1668	+ optimized 0.122 sec
		1669	Lambda/AnyEvent 0.327 sec
		1670	+ optimized 0.138 sec
		1671	Raw sockets/select 0.077 sec
		1672	POE/select, components 0.662 sec
		1673	POE/select, raw sockets 0.226 sec
		1674	POE/select, optimized 0.404 sec
		1675
		1676	AnyEvent/select/nb 0.085 sec
		1677	AnyEvent/EV/nb 0.068 sec
		1678	+state machine 0.134 sec
		1679
		1680	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1681	benchmarks actually make blocking connects and use 100% blocking I/O,
		1682	defeating the purpose of an event-based solution. All of the newly
		1683	written AnyEvent benchmarks use 100% non-blocking connects (using
		1684	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1685	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1686	connects generally require a lot more bookkeeping and event handling
		1687	than blocking connects (which involve a single syscall only).
		1688
		1689	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1690	offers similar expressive power as POE and IO::Lambda, using
		1691	conventional Perl syntax. This means that both the echo server and the
		1692	client are 100% non-blocking, further placing it at a disadvantage.
		1693
		1694	As you can see, the AnyEvent + EV combination even beats the
		1695	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1696	backend easily beats IO::Lambda and POE.
		1697
		1698	And even the 100% non-blocking version written using the high-level (and
		1699	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1700	higher level ("unoptimised") abstractions by a large margin, even though
		1701	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1702
		1703	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1704	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1705	part of the IO::Lambda distribution and were used without any changes.
		1706
		1707	SIGNALS
		1708	AnyEvent currently installs handlers for these signals:
		1709
		1710	SIGCHLD
		1711	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1712	emulation for event loops that do not support them natively. Also,
		1713	some event loops install a similar handler.
		1714
		1715	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1716	then AnyEvent will reset it to default, to avoid losing child exit
		1717	statuses.
		1718
		1719	SIGPIPE
		1720	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1721	"undef" when AnyEvent gets loaded.
		1722
		1723	The rationale for this is that AnyEvent users usually do not really
		1724	depend on SIGPIPE delivery (which is purely an optimisation for
		1725	shell use, or badly-written programs), but "SIGPIPE" can cause
		1726	spurious and rare program exits as a lot of people do not expect
		1727	"SIGPIPE" when writing to some random socket.
		1728
		1729	The rationale for installing a no-op handler as opposed to ignoring
		1730	it is that this way, the handler will be restored to defaults on
		1731	exec.
		1732
		1733	Feel free to install your own handler, or reset it to defaults.
		1734
		1735	RECOMMENDED/OPTIONAL MODULES
		1736	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1737	it's built-in modules) are required to use it.
		1738
		1739	That does not mean that AnyEvent won't take advantage of some additional
		1740	modules if they are installed.
		1741
		1742	This section explains which additional modules will be used, and how
		1743	they affect AnyEvent's operation.
		1744
		1745	Async::Interrupt
		1746	This slightly arcane module is used to implement fast signal
		1747	handling: To my knowledge, there is no way to do completely
		1748	race-free and quick signal handling in pure perl. To ensure that
		1749	signals still get delivered, AnyEvent will start an interval timer
		1750	to wake up perl (and catch the signals) with some delay (default is
		1751	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1752
		1753	If this module is available, then it will be used to implement
		1754	signal catching, which means that signals will not be delayed, and
		1755	the event loop will not be interrupted regularly, which is more
		1756	efficient (and good for battery life on laptops).
		1757
		1758	This affects not just the pure-perl event loop, but also other event
		1759	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1760
		1761	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1762	natively, and either employ their own workarounds (POE) or use
		1763	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1764	Installing Async::Interrupt does nothing for those backends.
		1765
		1766	EV This module isn't really "optional", as it is simply one of the
		1767	backend event loops that AnyEvent can use. However, it is simply the
		1768	best event loop available in terms of features, speed and stability:
		1769	It supports the AnyEvent API optimally, implements all the watcher
		1770	types in XS, does automatic timer adjustments even when no monotonic
		1771	clock is available, can take avdantage of advanced kernel interfaces
		1772	such as "epoll" and "kqueue", and is the fastest backend by far.
		1773	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1774	Glib::EV).
		1775
		1776	Guard
		1777	The guard module, when used, will be used to implement
		1778	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1779	uses a lot less memory), but otherwise doesn't affect guard
		1780	operation much. It is purely used for performance.
		1781
		1782	JSON and JSON::XS
		1783	One of these modules is required when you want to read or write JSON
		1784	data via AnyEvent::Handle. It is also written in pure-perl, but can
		1785	take advantage of the ultra-high-speed JSON::XS module when it is
		1786	installed.
		1787
		1788	In fact, AnyEvent::Handle will use JSON::XS by default if it is
		1789	installed.
		1790
		1791	Net::SSLeay
		1792	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1793	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1794	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1795
		1796	Time::HiRes
		1797	This module is part of perl since release 5.008. It will be used
		1798	when the chosen event library does not come with a timing source on
		1799	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1800	additionally use it to try to use a monotonic clock for timing
		1801	stability.
1105		1802
1106	FORK	1803	FORK
1107	Most event libraries are not fork-safe. The ones who are usually are	1804	Most event libraries are not fork-safe. The ones who are usually are
1108	because they rely on inefficient but fork-safe "select" or "poll" calls.	1805	because they rely on inefficient but fork-safe "select" or "poll" calls.
1109	Only EV is fully fork-aware.	1806	Only EV is fully fork-aware.
1110		1807
		1808	This means that, in general, you cannot fork and do event processing in
		1809	the child if a watcher was created before the fork (which in turn
		1810	initialises the event library).
		1811
1111	If you have to fork, you must either do so before creating your first	1812	If you have to fork, you must either do so before creating your first
1112	watcher OR you must not use AnyEvent at all in the child.	1813	watcher OR you must not use AnyEvent at all in the child OR you must do
		1814	something completely out of the scope of AnyEvent.
		1815
		1816	The problem of doing event processing in the parent and the child is
		1817	much more complicated: even for backends that are fork-aware or
		1818	fork-safe, their behaviour is not usually what you want: fork clones all
		1819	watchers, that means all timers, I/O watchers etc. are active in both
		1820	parent and child, which is almost never what you want.
1113		1821
1114	SECURITY CONSIDERATIONS	1822	SECURITY CONSIDERATIONS
1115	AnyEvent can be forced to load any event model via	1823	AnyEvent can be forced to load any event model via
1116	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1824	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1117	to execute arbitrary code or directly gain access, it can easily be used	1825	to execute arbitrary code or directly gain access, it can easily be used
…		…
1120	model than specified in the variable.	1828	model than specified in the variable.
1121		1829
1122	You can make AnyEvent completely ignore this variable by deleting it	1830	You can make AnyEvent completely ignore this variable by deleting it
1123	before the first watcher gets created, e.g. with a "BEGIN" block:	1831	before the first watcher gets created, e.g. with a "BEGIN" block:
1124		1832
1125	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1833	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1126		1834
1127	use AnyEvent;	1835	use AnyEvent;
1128		1836
1129	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1837	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1130	be used to probe what backend is used and gain other information (which	1838	be used to probe what backend is used and gain other information (which
1131	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).	1839	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1840	and $ENV{PERL_ANYEVENT_STRICT}.
		1841
		1842	Note that AnyEvent will remove all environment variables starting with
		1843	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1844	enabled.
		1845
		1846	BUGS
		1847	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1848	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1849	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1850	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1851	not as pronounced).
1132		1852
1133	SEE ALSO	1853	SEE ALSO
		1854	Utility functions: AnyEvent::Util.
		1855
1134	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1856	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1135	Event::Lib, Qt, POE.	1857	Event::Lib, Qt, POE.
1136		1858
1137	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1859	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1138	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1860	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1139	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1861	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1862	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
		1863
		1864	Non-blocking file handles, sockets, TCP clients and servers:
		1865	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		1866
		1867	Asynchronous DNS: AnyEvent::DNS.
1140		1868
1141	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1869	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1142		1870
1143	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1871	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1872	AnyEvent::HTTP.
1144		1873
1145	AUTHOR	1874	AUTHOR
1146	Marc Lehmann <schmorp@schmorp.de>	1875	Marc Lehmann <schmorp@schmorp.de>
1147	http://home.schmorp.de/	1876	http://home.schmorp.de/
1148		1877

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Comparing AnyEvent/README (file contents): Revision 1.21 by root, Sat May 17 21:34:15 2008 UTC vs. Revision 1.58 by root, Sun Dec 20 22:49:52 2009 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.21 by root, Sat May 17 21:34:15 2008 UTC vs.
Revision 1.58 by root, Sun Dec 20 22:49:52 2009 UTC