ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.26 by root, Fri Jun 6 11:13:07 2008 UTC vs.
Revision 1.66 by root, Sun Aug 21 03:02:32 2011 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, FLTK and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# if you prefer function calls, look at the AE manpage for
		11	# an alternative API.
		12
		13	# file handle or descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {	14	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		15
		16	# one-shot or repeating timers
		17	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		18	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
		19
		20	print AnyEvent->now; # prints current event loop time
		21	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		22
		23	# POSIX signal
		24	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		25
		26	# child process exit
		27	my $w = AnyEvent->child (pid => $pid, cb => sub {
		28	my ($pid, $status) = @_;
11	...	29	...
12	});	30	});
13		31
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	32	# called when event loop idle (if applicable)
15	...	33	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		34
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	35	my $w = AnyEvent->condvar; # stores whether a condition was flagged
19	$w->send; # wake up current and all future recv's	36	$w->send; # wake up current and all future recv's
20	$w->recv; # enters "main loop" till $condvar gets ->send	37	$w->recv; # enters "main loop" till $condvar gets ->send
		38	# use a condvar in callback mode:
		39	$w->cb (sub { $_[0]->recv });
21		40
22	INTRODUCTION/TUTORIAL	41	INTRODUCTION/TUTORIAL
23	This manpage is mainly a reference manual. If you are interested in a	42	This manpage is mainly a reference manual. If you are interested in a
24	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	43	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
25	manpage.	44	manpage.
26		45
		46	SUPPORT
		47	An FAQ document is available as AnyEvent::FAQ.
		48
		49	There also is a mailinglist for discussing all things AnyEvent, and an
		50	IRC channel, too.
		51
		52	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		53	Repository, at <http://anyevent.schmorp.de>, for more info.
		54
27	WHY YOU SHOULD USE THIS MODULE (OR NOT)	55	WHY YOU SHOULD USE THIS MODULE (OR NOT)
28	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	56	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
29	nowadays. So what is different about AnyEvent?	57	nowadays. So what is different about AnyEvent?
30		58
31	Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of	59	Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of
32	policy* and AnyEvent is *small and efficient*.	60	policy* and AnyEvent is *small and efficient*.
33		61
34	First and foremost, *AnyEvent is not an event model* itself, it only	62	First and foremost, *AnyEvent is not an event model* itself, it only
35	interfaces to whatever event model the main program happens to use in a	63	interfaces to whatever event model the main program happens to use, in a
36	pragmatic way. For event models and certain classes of immortals alike,	64	pragmatic way. For event models and certain classes of immortals alike,
37	the statement "there can only be one" is a bitter reality: In general,	65	the statement "there can only be one" is a bitter reality: In general,
38	only one event loop can be active at the same time in a process.	66	only one event loop can be active at the same time in a process.
39	AnyEvent helps hiding the differences between those event loops.	67	AnyEvent cannot change this, but it can hide the differences between
		68	those event loops.
40		69
41	The goal of AnyEvent is to offer module authors the ability to do event	70	The goal of AnyEvent is to offer module authors the ability to do event
42	programming (waiting for I/O or timer events) without subscribing to a	71	programming (waiting for I/O or timer events) without subscribing to a
43	religion, a way of living, and most importantly: without forcing your	72	religion, a way of living, and most importantly: without forcing your
44	module users into the same thing by forcing them to use the same event	73	module users into the same thing by forcing them to use the same event
45	model you use.	74	model you use.
46		75
47	For modules like POE or IO::Async (which is a total misnomer as it is	76	For modules like POE or IO::Async (which is a total misnomer as it is
48	actually doing all I/O *synchronously*...), using them in your module is	77	actually doing all I/O *synchronously*...), using them in your module is
49	like joining a cult: After you joined, you are dependent on them and you	78	like joining a cult: After you join, you are dependent on them and you
50	cannot use anything else, as it is simply incompatible to everything	79	cannot use anything else, as they are simply incompatible to everything
51	that isn't itself. What's worse, all the potential users of your module	80	that isn't them. What's worse, all the potential users of your module
52	are *also* forced to use the same event loop you use.	81	are *also* forced to use the same event loop you use.
53		82
54	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	83	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
55	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	84	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
56	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your	85	with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
57	module uses one of those, every user of your module has to use it, too.	86	uses one of those, every user of your module has to use it, too. But if
58	But if your module uses AnyEvent, it works transparently with all event	87	your module uses AnyEvent, it works transparently with all event models
59	models it supports (including stuff like POE and IO::Async, as long as	88	it supports (including stuff like IO::Async, as long as those use one of
60	those use one of the supported event loops. It is trivial to add new	89	the supported event loops. It is easy to add new event loops to
61	event loops to AnyEvent, too, so it is future-proof).	90	AnyEvent, too, so it is future-proof).
62		91
63	In addition to being free of having to use *the one and only true event	92	In addition to being free of having to use *the one and only true event
64	model*, AnyEvent also is free of bloat and policy: with POE or similar	93	model*, AnyEvent also is free of bloat and policy: with POE or similar
65	modules, you get an enormous amount of code and strict rules you have to	94	modules, you get an enormous amount of code and strict rules you have to
66	follow. AnyEvent, on the other hand, is lean and up to the point, by	95	follow. AnyEvent, on the other hand, is lean and to the point, by only
67	only offering the functionality that is necessary, in as thin as a	96	offering the functionality that is necessary, in as thin as a wrapper as
68	wrapper as technically possible.	97	technically possible.
69		98
70	Of course, AnyEvent comes with a big (and fully optional!) toolbox of	99	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
71	useful functionality, such as an asynchronous DNS resolver, 100%	100	useful functionality, such as an asynchronous DNS resolver, 100%
72	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms	101	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
73	such as Windows) and lots of real-world knowledge and workarounds for	102	such as Windows) and lots of real-world knowledge and workarounds for
…		…
76	Now, if you *do want* lots of policy (this can arguably be somewhat	105	Now, if you *do want* lots of policy (this can arguably be somewhat
77	useful) and you want to force your users to use the one and only event	106	useful) and you want to force your users to use the one and only event
78	model, you should *not* use this module.	107	model, you should *not* use this module.
79		108
80	DESCRIPTION	109	DESCRIPTION
81	AnyEvent provides an identical interface to multiple event loops. This	110	AnyEvent provides a uniform interface to various event loops. This
82	allows module authors to utilise an event loop without forcing module	111	allows module authors to use event loop functionality without forcing
83	users to use the same event loop (as only a single event loop can	112	module users to use a specific event loop implementation (since more
84	coexist peacefully at any one time).	113	than one event loop cannot coexist peacefully).
85		114
86	The interface itself is vaguely similar, but not identical to the Event	115	The interface itself is vaguely similar, but not identical to the Event
87	module.	116	module.
88		117
89	During the first call of any watcher-creation method, the module tries	118	During the first call of any watcher-creation method, the module tries
90	to detect the currently loaded event loop by probing whether one of the	119	to detect the currently loaded event loop by probing whether one of the
91	following modules is already loaded: EV, Event, Glib,	120	following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
92	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is	121	Tk, Event::Lib, Qt, POE. The first one found is used. If none are
93	used. If none are found, the module tries to load these modules	122	detected, the module tries to load the first four modules in the order
94	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	123	given; but note that if EV is not available, the pure-perl
95	always succeed) in the order given. The first one that can be	124	AnyEvent::Loop should always work, so the other two are not normally
96	successfully loaded will be used. If, after this, still none could be	125	tried.
97	found, AnyEvent will fall back to a pure-perl event loop, which is not
98	very efficient, but should work everywhere.
99		126
100	Because AnyEvent first checks for modules that are already loaded,	127	Because AnyEvent first checks for modules that are already loaded,
101	loading an event model explicitly before first using AnyEvent will	128	loading an event model explicitly before first using AnyEvent will
102	likely make that model the default. For example:	129	likely make that model the default. For example:
103		130
…		…
105	use AnyEvent;	132	use AnyEvent;
106		133
107	# .. AnyEvent will likely default to Tk	134	# .. AnyEvent will likely default to Tk
108		135
109	The *likely* means that, if any module loads another event model and	136	The *likely* means that, if any module loads another event model and
110	starts using it, all bets are off. Maybe you should tell their authors	137	starts using it, all bets are off - this case should be very rare
111	to use AnyEvent so their modules work together with others seamlessly...	138	though, as very few modules hardcode event loops without announcing this
		139	very loudly.
112		140
113	The pure-perl implementation of AnyEvent is called	141	The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
114	"AnyEvent::Impl::Perl". Like other event modules you can load it	142	Like other event modules you can load it explicitly and enjoy the high
115	explicitly and enjoy the high availability of that event loop :)	143	availability of that event loop :)
116		144
117	WATCHERS	145	WATCHERS
118	AnyEvent has the central concept of a *watcher*, which is an object that	146	AnyEvent has the central concept of a *watcher*, which is an object that
119	stores relevant data for each kind of event you are waiting for, such as	147	stores relevant data for each kind of event you are waiting for, such as
120	the callback to call, the file handle to watch, etc.	148	the callback to call, the file handle to watch, etc.
…		…
122	These watchers are normal Perl objects with normal Perl lifetime. After	150	These watchers are normal Perl objects with normal Perl lifetime. After
123	creating a watcher it will immediately "watch" for events and invoke the	151	creating a watcher it will immediately "watch" for events and invoke the
124	callback when the event occurs (of course, only when the event model is	152	callback when the event occurs (of course, only when the event model is
125	in control).	153	in control).
126		154
		155	Note that callbacks must not permanently change global variables
		156	potentially in use by the event loop (such as $_ or $[) and that
		157	callbacks must not "die". The former is good programming practice in
		158	Perl and the latter stems from the fact that exception handling differs
		159	widely between event loops.
		160
127	To disable the watcher you have to destroy it (e.g. by setting the	161	To disable a watcher you have to destroy it (e.g. by setting the
128	variable you store it in to "undef" or otherwise deleting all references	162	variable you store it in to "undef" or otherwise deleting all references
129	to it).	163	to it).
130		164
131	All watchers are created by calling a method on the "AnyEvent" class.	165	All watchers are created by calling a method on the "AnyEvent" class.
132		166
133	Many watchers either are used with "recursion" (repeating timers for	167	Many watchers either are used with "recursion" (repeating timers for
134	example), or need to refer to their watcher object in other ways.	168	example), or need to refer to their watcher object in other ways.
135		169
136	An any way to achieve that is this pattern:	170	One way to achieve that is this pattern:
137		171
138	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	172	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
139	# you can use $w here, for example to undef it	173	# you can use $w here, for example to undef it
140	undef $w;	174	undef $w;
141	});	175	});
…		…
143	Note that "my $w; $w =" combination. This is necessary because in Perl,	177	Note that "my $w; $w =" combination. This is necessary because in Perl,
144	my variables are only visible after the statement in which they are	178	my variables are only visible after the statement in which they are
145	declared.	179	declared.
146		180
147	I/O WATCHERS	181	I/O WATCHERS
		182	$w = AnyEvent->io (
		183	fh => <filehandle_or_fileno>,
		184	poll => <"r" or "w">,
		185	cb => <callback>,
		186	);
		187
148	You can create an I/O watcher by calling the "AnyEvent->io" method with	188	You can create an I/O watcher by calling the "AnyEvent->io" method with
149	the following mandatory key-value pairs as arguments:	189	the following mandatory key-value pairs as arguments:
150		190
151	"fh" the Perl *file handle* (*not* file descriptor) to watch for events.	191	"fh" is the Perl *file handle* (or a naked file descriptor) to watch for
		192	events (AnyEvent might or might not keep a reference to this file
		193	handle). Note that only file handles pointing to things for which
		194	non-blocking operation makes sense are allowed. This includes sockets,
		195	most character devices, pipes, fifos and so on, but not for example
		196	files or block devices.
		197
152	"poll" must be a string that is either "r" or "w", which creates a	198	"poll" must be a string that is either "r" or "w", which creates a
153	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	199	watcher waiting for "r"eadable or "w"ritable events, respectively.
		200
154	is the callback to invoke each time the file handle becomes ready.	201	"cb" is the callback to invoke each time the file handle becomes ready.
155		202
156	Although the callback might get passed parameters, their value and	203	Although the callback might get passed parameters, their value and
157	presence is undefined and you cannot rely on them. Portable AnyEvent	204	presence is undefined and you cannot rely on them. Portable AnyEvent
158	callbacks cannot use arguments passed to I/O watcher callbacks.	205	callbacks cannot use arguments passed to I/O watcher callbacks.
159		206
160	The I/O watcher might use the underlying file descriptor or a copy of	207	The I/O watcher might use the underlying file descriptor or a copy of
161	it. You must not close a file handle as long as any watcher is active on	208	it. You must not close a file handle as long as any watcher is active on
162	the underlying file descriptor.	209	the underlying file descriptor.
163		210
164	Some event loops issue spurious readyness notifications, so you should	211	Some event loops issue spurious readiness notifications, so you should
165	always use non-blocking calls when reading/writing from/to your file	212	always use non-blocking calls when reading/writing from/to your file
166	handles.	213	handles.
167		214
168	Example:
169
170	# wait for readability of STDIN, then read a line and disable the watcher	215	Example: wait for readability of STDIN, then read a line and disable the
		216	watcher.
		217
171	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	218	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
172	chomp (my $input = <STDIN>);	219	chomp (my $input = <STDIN>);
173	warn "read: $input\n";	220	warn "read: $input\n";
174	undef $w;	221	undef $w;
175	});	222	});
176		223
177	TIME WATCHERS	224	TIME WATCHERS
		225	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		226
		227	$w = AnyEvent->timer (
		228	after => <fractional_seconds>,
		229	interval => <fractional_seconds>,
		230	cb => <callback>,
		231	);
		232
178	You can create a time watcher by calling the "AnyEvent->timer" method	233	You can create a time watcher by calling the "AnyEvent->timer" method
179	with the following mandatory arguments:	234	with the following mandatory arguments:
180		235
181	"after" specifies after how many seconds (fractional values are	236	"after" specifies after how many seconds (fractional values are
182	supported) the callback should be invoked. "cb" is the callback to	237	supported) the callback should be invoked. "cb" is the callback to
…		…
184		239
185	Although the callback might get passed parameters, their value and	240	Although the callback might get passed parameters, their value and
186	presence is undefined and you cannot rely on them. Portable AnyEvent	241	presence is undefined and you cannot rely on them. Portable AnyEvent
187	callbacks cannot use arguments passed to time watcher callbacks.	242	callbacks cannot use arguments passed to time watcher callbacks.
188		243
189	The timer callback will be invoked at most once: if you want a repeating	244	The callback will normally be invoked only once. If you specify another
190	timer you have to create a new watcher (this is a limitation by both Tk	245	parameter, "interval", as a strictly positive number (> 0), then the
191	and Glib).	246	callback will be invoked regularly at that interval (in fractional
		247	seconds) after the first invocation. If "interval" is specified with a
		248	false value, then it is treated as if it were not specified at all.
192		249
193	Example:	250	The callback will be rescheduled before invoking the callback, but no
		251	attempt is made to avoid timer drift in most backends, so the interval
		252	is only approximate.
194		253
195	# fire an event after 7.7 seconds	254	Example: fire an event after 7.7 seconds.
		255
196	my $w = AnyEvent->timer (after => 7.7, cb => sub {	256	my $w = AnyEvent->timer (after => 7.7, cb => sub {
197	warn "timeout\n";	257	warn "timeout\n";
198	});	258	});
199		259
200	# to cancel the timer:	260	# to cancel the timer:
201	undef $w;	261	undef $w;
202		262
203	Example 2:
204
205	# fire an event after 0.5 seconds, then roughly every second	263	Example 2: fire an event after 0.5 seconds, then roughly every second.
206	my $w;
207		264
208	my $cb = sub {
209	# cancel the old timer while creating a new one
210	$w = AnyEvent->timer (after => 1, cb => $cb);	265	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		266	warn "timeout\n";
211	};	267	};
212
213	# start the "loop" by creating the first watcher
214	$w = AnyEvent->timer (after => 0.5, cb => $cb);
215		268
216	TIMING ISSUES	269	TIMING ISSUES
217	There are two ways to handle timers: based on real time (relative, "fire	270	There are two ways to handle timers: based on real time (relative, "fire
218	in 10 seconds") and based on wallclock time (absolute, "fire at 12	271	in 10 seconds") and based on wallclock time (absolute, "fire at 12
219	o'clock").	272	o'clock").
220		273
221	While most event loops expect timers to specified in a relative way,	274	While most event loops expect timers to specified in a relative way,
222	they use absolute time internally. This makes a difference when your	275	they use absolute time internally. This makes a difference when your
223	clock "jumps", for example, when ntp decides to set your clock backwards	276	clock "jumps", for example, when ntp decides to set your clock backwards
224	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is	277	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
225	supposed to fire "after" a second might actually take six years to	278	supposed to fire "after a second" might actually take six years to
226	finally fire.	279	finally fire.
227		280
228	AnyEvent cannot compensate for this. The only event loop that is	281	AnyEvent cannot compensate for this. The only event loop that is
229	conscious about these issues is EV, which offers both relative	282	conscious of these issues is EV, which offers both relative (ev_timer,
230	(ev_timer, based on true relative time) and absolute (ev_periodic, based	283	based on true relative time) and absolute (ev_periodic, based on
231	on wallclock time) timers.	284	wallclock time) timers.
232		285
233	AnyEvent always prefers relative timers, if available, matching the	286	AnyEvent always prefers relative timers, if available, matching the
234	AnyEvent API.	287	AnyEvent API.
235		288
236	AnyEvent has two additional methods that return the "current time":	289	AnyEvent has two additional methods that return the "current time":
…		…
255	*In almost all cases (in all cases if you don't care), this is the	308	*In almost all cases (in all cases if you don't care), this is the
256	function to call when you want to know the current time.*	309	function to call when you want to know the current time.*
257		310
258	This function is also often faster then "AnyEvent->time", and thus	311	This function is also often faster then "AnyEvent->time", and thus
259	the preferred method if you want some timestamp (for example,	312	the preferred method if you want some timestamp (for example,
260	AnyEvent::Handle uses this to update it's activity timeouts).	313	AnyEvent::Handle uses this to update its activity timeouts).
261		314
262	The rest of this section is only of relevance if you try to be very	315	The rest of this section is only of relevance if you try to be very
263	exact with your timing, you can skip it without bad conscience.	316	exact with your timing; you can skip it without a bad conscience.
264		317
265	For a practical example of when these times differ, consider	318	For a practical example of when these times differ, consider
266	Event::Lib and EV and the following set-up:	319	Event::Lib and EV and the following set-up:
267		320
268	The event loop is running and has just invoked one of your callback	321	The event loop is running and has just invoked one of your callbacks
269	at time=500 (assume no other callbacks delay processing). In your	322	at time=500 (assume no other callbacks delay processing). In your
270	callback, you wait a second by executing "sleep 1" (blocking the	323	callback, you wait a second by executing "sleep 1" (blocking the
271	process for a second) and then (at time=501) you create a relative	324	process for a second) and then (at time=501) you create a relative
272	timer that fires after three seconds.	325	timer that fires after three seconds.
273		326
…		…
293	In either case, if you care (and in most cases, you don't), then you	346	In either case, if you care (and in most cases, you don't), then you
294	can get whatever behaviour you want with any event loop, by taking	347	can get whatever behaviour you want with any event loop, by taking
295	the difference between "AnyEvent->time" and "AnyEvent->now" into	348	the difference between "AnyEvent->time" and "AnyEvent->now" into
296	account.	349	account.
297		350
		351	AnyEvent->now_update
		352	Some event loops (such as EV or AnyEvent::Loop) cache the current
		353	time for each loop iteration (see the discussion of AnyEvent->now,
		354	above).
		355
		356	When a callback runs for a long time (or when the process sleeps),
		357	then this "current" time will differ substantially from the real
		358	time, which might affect timers and time-outs.
		359
		360	When this is the case, you can call this method, which will update
		361	the event loop's idea of "current time".
		362
		363	A typical example would be a script in a web server (e.g.
		364	"mod_perl") - when mod_perl executes the script, then the event loop
		365	will have the wrong idea about the "current time" (being potentially
		366	far in the past, when the script ran the last time). In that case
		367	you should arrange a call to "AnyEvent->now_update" each time the
		368	web server process wakes up again (e.g. at the start of your script,
		369	or in a handler).
		370
		371	Note that updating the time *might* cause some events to be handled.
		372
298	SIGNAL WATCHERS	373	SIGNAL WATCHERS
		374	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		375
299	You can watch for signals using a signal watcher, "signal" is the signal	376	You can watch for signals using a signal watcher, "signal" is the signal
300	*name* without any "SIG" prefix, "cb" is the Perl callback to be invoked	377	*name* in uppercase and without any "SIG" prefix, "cb" is the Perl
301	whenever a signal occurs.	378	callback to be invoked whenever a signal occurs.
302		379
303	Although the callback might get passed parameters, their value and	380	Although the callback might get passed parameters, their value and
304	presence is undefined and you cannot rely on them. Portable AnyEvent	381	presence is undefined and you cannot rely on them. Portable AnyEvent
305	callbacks cannot use arguments passed to signal watcher callbacks.	382	callbacks cannot use arguments passed to signal watcher callbacks.
306		383
…		…
308	invocation, and callback invocation will be synchronous. Synchronous	385	invocation, and callback invocation will be synchronous. Synchronous
309	means that it might take a while until the signal gets handled by the	386	means that it might take a while until the signal gets handled by the
310	process, but it is guaranteed not to interrupt any other callbacks.	387	process, but it is guaranteed not to interrupt any other callbacks.
311		388
312	The main advantage of using these watchers is that you can share a	389	The main advantage of using these watchers is that you can share a
313	signal between multiple watchers.	390	signal between multiple watchers, and AnyEvent will ensure that signals
		391	will not interrupt your program at bad times.
314		392
315	This watcher might use %SIG, so programs overwriting those signals	393	This watcher might use %SIG (depending on the event loop used), so
316	directly will likely not work correctly.	394	programs overwriting those signals directly will likely not work
		395	correctly.
317		396
318	Example: exit on SIGINT	397	Example: exit on SIGINT
319		398
320	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	399	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
321		400
		401	Restart Behaviour
		402	While restart behaviour is up to the event loop implementation, most
		403	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		404	pure perl implementation).
		405
		406	Safe/Unsafe Signals
		407	Perl signals can be either "safe" (synchronous to opcode handling) or
		408	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		409	latter might corrupt your memory.
		410
		411	AnyEvent signal handlers are, in addition, synchronous to the event
		412	loop, i.e. they will not interrupt your running perl program but will
		413	only be called as part of the normal event handling (just like timer,
		414	I/O etc. callbacks, too).
		415
		416	Signal Races, Delays and Workarounds
		417	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		418	callbacks to signals in a generic way, which is a pity, as you cannot do
		419	race-free signal handling in perl, requiring C libraries for this.
		420	AnyEvent will try to do its best, which means in some cases, signals
		421	will be delayed. The maximum time a signal might be delayed is specified
		422	in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
		423	can be changed only before the first signal watcher is created, and
		424	should be left alone otherwise. This variable determines how often
		425	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		426	will cause fewer spurious wake-ups, which is better for power and CPU
		427	saving.
		428
		429	All these problems can be avoided by installing the optional
		430	Async::Interrupt module, which works with most event loops. It will not
		431	work with inherently broken event loops such as Event or Event::Lib (and
		432	not with POE currently, as POE does its own workaround with one-second
		433	latency). For those, you just have to suffer the delays.
		434
322	CHILD PROCESS WATCHERS	435	CHILD PROCESS WATCHERS
		436	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		437
323	You can also watch on a child process exit and catch its exit status.	438	You can also watch for a child process exit and catch its exit status.
324		439
325	The child process is specified by the "pid" argument (if set to 0, it	440	The child process is specified by the "pid" argument (on some backends,
326	watches for any child process exit). The watcher will trigger as often	441	using 0 watches for any child process exit, on others this will croak).
327	as status change for the child are received. This works by installing a	442	The watcher will be triggered only when the child process has finished
328	signal handler for "SIGCHLD". The callback will be called with the pid	443	and an exit status is available, not on any trace events
329	and exit status (as returned by waitpid), so unlike other watcher types,	444	(stopped/continued).
330	you *can* rely on child watcher callback arguments.	445
		446	The callback will be called with the pid and exit status (as returned by
		447	waitpid), so unlike other watcher types, you *can* rely on child watcher
		448	callback arguments.
		449
		450	This watcher type works by installing a signal handler for "SIGCHLD",
		451	and since it cannot be shared, nothing else should use SIGCHLD or reap
		452	random child processes (waiting for specific child processes, e.g.
		453	inside "system", is just fine).
331		454
332	There is a slight catch to child watchers, however: you usually start	455	There is a slight catch to child watchers, however: you usually start
333	them *after* the child process was created, and this means the process	456	them *after* the child process was created, and this means the process
334	could have exited already (and no SIGCHLD will be sent anymore).	457	could have exited already (and no SIGCHLD will be sent anymore).
335		458
336	Not all event models handle this correctly (POE doesn't), but even for	459	Not all event models handle this correctly (neither POE nor IO::Async
		460	do, see their AnyEvent::Impl manpages for details), but even for event
337	event models that *do* handle this correctly, they usually need to be	461	models that *do* handle this correctly, they usually need to be loaded
338	loaded before the process exits (i.e. before you fork in the first	462	before the process exits (i.e. before you fork in the first place).
339	place).	463	AnyEvent's pure perl event loop handles all cases correctly regardless
		464	of when you start the watcher.
340		465
341	This means you cannot create a child watcher as the very first thing in	466	This means you cannot create a child watcher as the very first thing in
342	an AnyEvent program, you *have* to create at least one watcher before	467	an AnyEvent program, you *have* to create at least one watcher before
343	you "fork" the child (alternatively, you can call "AnyEvent::detect").	468	you "fork" the child (alternatively, you can call "AnyEvent::detect").
344		469
		470	As most event loops do not support waiting for child events, they will
		471	be emulated by AnyEvent in most cases, in which case the latency and
		472	race problems mentioned in the description of signal watchers apply.
		473
345	Example: fork a process and wait for it	474	Example: fork a process and wait for it
346		475
347	my $done = AnyEvent->condvar;	476	my $done = AnyEvent->condvar;
348		477
349	my $pid = fork or exit 5;	478	my $pid = fork or exit 5;
350		479
351	my $w = AnyEvent->child (	480	my $w = AnyEvent->child (
352	pid => $pid,	481	pid => $pid,
353	cb => sub {	482	cb => sub {
354	my ($pid, $status) = @_;	483	my ($pid, $status) = @_;
355	warn "pid $pid exited with status $status";	484	warn "pid $pid exited with status $status";
356	$done->send;	485	$done->send;
357	},	486	},
358	);	487	);
359		488
360	# do something else, then wait for process exit	489	# do something else, then wait for process exit
361	$done->recv;	490	$done->recv;
362		491
		492	IDLE WATCHERS
		493	$w = AnyEvent->idle (cb => <callback>);
		494
		495	This will repeatedly invoke the callback after the process becomes idle,
		496	until either the watcher is destroyed or new events have been detected.
		497
		498	Idle watchers are useful when there is a need to do something, but it is
		499	not so important (or wise) to do it instantly. The callback will be
		500	invoked only when there is "nothing better to do", which is usually
		501	defined as "all outstanding events have been handled and no new events
		502	have been detected". That means that idle watchers ideally get invoked
		503	when the event loop has just polled for new events but none have been
		504	detected. Instead of blocking to wait for more events, the idle watchers
		505	will be invoked.
		506
		507	Unfortunately, most event loops do not really support idle watchers
		508	(only EV, Event and Glib do it in a usable fashion) - for the rest,
		509	AnyEvent will simply call the callback "from time to time".
		510
		511	Example: read lines from STDIN, but only process them when the program
		512	is otherwise idle:
		513
		514	my @lines; # read data
		515	my $idle_w;
		516	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		517	push @lines, scalar <STDIN>;
		518
		519	# start an idle watcher, if not already done
		520	$idle_w ||= AnyEvent->idle (cb => sub {
		521	# handle only one line, when there are lines left
		522	if (my $line = shift @lines) {
		523	print "handled when idle: $line";
		524	} else {
		525	# otherwise disable the idle watcher again
		526	undef $idle_w;
		527	}
		528	});
		529	});
		530
363	CONDITION VARIABLES	531	CONDITION VARIABLES
		532	$cv = AnyEvent->condvar;
		533
		534	$cv->send (<list>);
		535	my @res = $cv->recv;
		536
364	If you are familiar with some event loops you will know that all of them	537	If you are familiar with some event loops you will know that all of them
365	require you to run some blocking "loop", "run" or similar function that	538	require you to run some blocking "loop", "run" or similar function that
366	will actively watch for new events and call your callbacks.	539	will actively watch for new events and call your callbacks.
367		540
368	AnyEvent is different, it expects somebody else to run the event loop	541	AnyEvent is slightly different: it expects somebody else to run the
369	and will only block when necessary (usually when told by the user).	542	event loop and will only block when necessary (usually when told by the
		543	user).
370		544
371	The instrument to do that is called a "condition variable", so called	545	The tool to do that is called a "condition variable", so called because
372	because they represent a condition that must become true.	546	they represent a condition that must become true.
		547
		548	Now is probably a good time to look at the examples further below.
373		549
374	Condition variables can be created by calling the "AnyEvent->condvar"	550	Condition variables can be created by calling the "AnyEvent->condvar"
375	method, usually without arguments. The only argument pair allowed is	551	method, usually without arguments. The only argument pair allowed is
376	"cb", which specifies a callback to be called when the condition	552	"cb", which specifies a callback to be called when the condition
377	variable becomes true.	553	variable becomes true, with the condition variable as the first argument
		554	(but not the results).
378		555
379	After creation, the condition variable is "false" until it becomes	556	After creation, the condition variable is "false" until it becomes
380	"true" by calling the "send" method (or calling the condition variable	557	"true" by calling the "send" method (or calling the condition variable
381	as if it were a callback, read about the caveats in the description for	558	as if it were a callback, read about the caveats in the description for
382	the "->send" method).	559	the "->send" method).
383		560
384	Condition variables are similar to callbacks, except that you can	561	Since condition variables are the most complex part of the AnyEvent API,
385	optionally wait for them. They can also be called merge points - points	562	here are some different mental models of what they are - pick the ones
386	in time where multiple outstanding events have been processed. And yet	563	you can connect to:
387	another way to call them is transactions - each condition variable can	564
388	be used to represent a transaction, which finishes at some point and	565	* Condition variables are like callbacks - you can call them (and pass
389	delivers a result.	566	them instead of callbacks). Unlike callbacks however, you can also
		567	wait for them to be called.
		568
		569	* Condition variables are signals - one side can emit or send them,
		570	the other side can wait for them, or install a handler that is
		571	called when the signal fires.
		572
		573	* Condition variables are like "Merge Points" - points in your program
		574	where you merge multiple independent results/control flows into one.
		575
		576	* Condition variables represent a transaction - functions that start
		577	some kind of transaction can return them, leaving the caller the
		578	choice between waiting in a blocking fashion, or setting a callback.
		579
		580	* Condition variables represent future values, or promises to deliver
		581	some result, long before the result is available.
390		582
391	Condition variables are very useful to signal that something has	583	Condition variables are very useful to signal that something has
392	finished, for example, if you write a module that does asynchronous http	584	finished, for example, if you write a module that does asynchronous http
393	requests, then a condition variable would be the ideal candidate to	585	requests, then a condition variable would be the ideal candidate to
394	signal the availability of results. The user can either act when the	586	signal the availability of results. The user can either act when the
…		…
407		599
408	Condition variables are represented by hash refs in perl, and the keys	600	Condition variables are represented by hash refs in perl, and the keys
409	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy	601	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
410	(it is often useful to build your own transaction class on top of	602	(it is often useful to build your own transaction class on top of
411	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call	603	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
412	it's "new" method in your own "new" method.	604	its "new" method in your own "new" method.
413		605
414	There are two "sides" to a condition variable - the "producer side"	606	There are two "sides" to a condition variable - the "producer side"
415	which eventually calls "-> send", and the "consumer side", which waits	607	which eventually calls "-> send", and the "consumer side", which waits
416	for the send to occur.	608	for the send to occur.
417		609
418	Example: wait for a timer.	610	Example: wait for a timer.
419		611
420	# wait till the result is ready	612	# condition: "wait till the timer is fired"
421	my $result_ready = AnyEvent->condvar;	613	my $timer_fired = AnyEvent->condvar;
422		614
423	# do something such as adding a timer	615	# create the timer - we could wait for, say
424	# or socket watcher the calls $result_ready->send	616	# a handle becomign ready, or even an
425	# when the "result" is ready.	617	# AnyEvent::HTTP request to finish, but
426	# in this case, we simply use a timer:	618	# in this case, we simply use a timer:
427	my $w = AnyEvent->timer (	619	my $w = AnyEvent->timer (
428	after => 1,	620	after => 1,
429	cb => sub { $result_ready->send },	621	cb => sub { $timer_fired->send },
430	);	622	);
431		623
432	# this "blocks" (while handling events) till the callback	624	# this "blocks" (while handling events) till the callback
433	# calls send	625	# calls ->send
434	$result_ready->recv;	626	$timer_fired->recv;
435		627
436	Example: wait for a timer, but take advantage of the fact that condition	628	Example: wait for a timer, but take advantage of the fact that condition
437	variables are also code references.	629	variables are also callable directly.
438		630
439	my $done = AnyEvent->condvar;	631	my $done = AnyEvent->condvar;
440	my $delay = AnyEvent->timer (after => 5, cb => $done);	632	my $delay = AnyEvent->timer (after => 5, cb => $done);
441	$done->recv;	633	$done->recv;
		634
		635	Example: Imagine an API that returns a condvar and doesn't support
		636	callbacks. This is how you make a synchronous call, for example from the
		637	main program:
		638
		639	use AnyEvent::CouchDB;
		640
		641	...
		642
		643	my @info = $couchdb->info->recv;
		644
		645	And this is how you would just set a callback to be called whenever the
		646	results are available:
		647
		648	$couchdb->info->cb (sub {
		649	my @info = $_[0]->recv;
		650	});
442		651
443	METHODS FOR PRODUCERS	652	METHODS FOR PRODUCERS
444	These methods should only be used by the producing side, i.e. the	653	These methods should only be used by the producing side, i.e. the
445	code/module that eventually sends the signal. Note that it is also the	654	code/module that eventually sends the signal. Note that it is also the
446	producer side which creates the condvar in most cases, but it isn't	655	producer side which creates the condvar in most cases, but it isn't
…		…
456		665
457	Any arguments passed to the "send" call will be returned by all	666	Any arguments passed to the "send" call will be returned by all
458	future "->recv" calls.	667	future "->recv" calls.
459		668
460	Condition variables are overloaded so one can call them directly (as	669	Condition variables are overloaded so one can call them directly (as
461	a code reference). Calling them directly is the same as calling	670	if they were a code reference). Calling them directly is the same as
462	"send". Note, however, that many C-based event loops do not handle	671	calling "send".
463	overloading, so as tempting as it may be, passing a condition
464	variable instead of a callback does not work. Both the pure perl and
465	EV loops support overloading, however, as well as all functions that
466	use perl to invoke a callback (as in AnyEvent::Socket and
467	AnyEvent::DNS for example).
468		672
469	$cv->croak ($error)	673	$cv->croak ($error)
470	Similar to send, but causes all call's to "->recv" to invoke	674	Similar to send, but causes all calls to "->recv" to invoke
471	"Carp::croak" with the given error message/object/scalar.	675	"Carp::croak" with the given error message/object/scalar.
472		676
473	This can be used to signal any errors to the condition variable	677	This can be used to signal any errors to the condition variable
474	user/consumer.	678	user/consumer. Doing it this way instead of calling "croak" directly
		679	delays the error detection, but has the overwhelming advantage that
		680	it diagnoses the error at the place where the result is expected,
		681	and not deep in some event callback with no connection to the actual
		682	code causing the problem.
475		683
476	$cv->begin ([group callback])	684	$cv->begin ([group callback])
477	$cv->end	685	$cv->end
478	These two methods are EXPERIMENTAL and MIGHT CHANGE.
479
480	These two methods can be used to combine many transactions/events	686	These two methods can be used to combine many transactions/events
481	into one. For example, a function that pings many hosts in parallel	687	into one. For example, a function that pings many hosts in parallel
482	might want to use a condition variable for the whole process.	688	might want to use a condition variable for the whole process.
483		689
484	Every call to "->begin" will increment a counter, and every call to	690	Every call to "->begin" will increment a counter, and every call to
485	"->end" will decrement it. If the counter reaches 0 in "->end", the	691	"->end" will decrement it. If the counter reaches 0 in "->end", the
486	(last) callback passed to "begin" will be executed. That callback is	692	(last) callback passed to "begin" will be executed, passing the
487	*supposed* to call "->send", but that is not required. If no	693	condvar as first argument. That callback is *supposed* to call
		694	"->send", but that is not required. If no group callback was set,
488	callback was set, "send" will be called without any arguments.	695	"send" will be called without any arguments.
489		696
490	Let's clarify this with the ping example:	697	You can think of "$cv->send" giving you an OR condition (one call
		698	sends), while "$cv->begin" and "$cv->end" giving you an AND
		699	condition (all "begin" calls must be "end"'ed before the condvar
		700	sends).
		701
		702	Let's start with a simple example: you have two I/O watchers (for
		703	example, STDOUT and STDERR for a program), and you want to wait for
		704	both streams to close before activating a condvar:
491		705
492	my $cv = AnyEvent->condvar;	706	my $cv = AnyEvent->condvar;
493		707
		708	$cv->begin; # first watcher
		709	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		710	defined sysread $fh1, my $buf, 4096
		711	or $cv->end;
		712	});
		713
		714	$cv->begin; # second watcher
		715	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		716	defined sysread $fh2, my $buf, 4096
		717	or $cv->end;
		718	});
		719
		720	$cv->recv;
		721
		722	This works because for every event source (EOF on file handle),
		723	there is one call to "begin", so the condvar waits for all calls to
		724	"end" before sending.
		725
		726	The ping example mentioned above is slightly more complicated, as
		727	the there are results to be passwd back, and the number of tasks
		728	that are begun can potentially be zero:
		729
		730	my $cv = AnyEvent->condvar;
		731
494	my %result;	732	my %result;
495	$cv->begin (sub { $cv->send (\%result) });	733	$cv->begin (sub { shift->send (\%result) });
496		734
497	for my $host (@list_of_hosts) {	735	for my $host (@list_of_hosts) {
498	$cv->begin;	736	$cv->begin;
499	ping_host_then_call_callback $host, sub {	737	ping_host_then_call_callback $host, sub {
500	$result{$host} = ...;	738	$result{$host} = ...;
…		…
515	the loop, which serves two important purposes: first, it sets the	753	the loop, which serves two important purposes: first, it sets the
516	callback to be called once the counter reaches 0, and second, it	754	callback to be called once the counter reaches 0, and second, it
517	ensures that "send" is called even when "no" hosts are being pinged	755	ensures that "send" is called even when "no" hosts are being pinged
518	(the loop doesn't execute once).	756	(the loop doesn't execute once).
519		757
520	This is the general pattern when you "fan out" into multiple	758	This is the general pattern when you "fan out" into multiple (but
521	subrequests: use an outer "begin"/"end" pair to set the callback and	759	potentially zero) subrequests: use an outer "begin"/"end" pair to
522	ensure "end" is called at least once, and then, for each subrequest	760	set the callback and ensure "end" is called at least once, and then,
523	you start, call "begin" and for each subrequest you finish, call	761	for each subrequest you start, call "begin" and for each subrequest
524	"end".	762	you finish, call "end".
525		763
526	METHODS FOR CONSUMERS	764	METHODS FOR CONSUMERS
527	These methods should only be used by the consuming side, i.e. the code	765	These methods should only be used by the consuming side, i.e. the code
528	awaits the condition.	766	awaits the condition.
529		767
530	$cv->recv	768	$cv->recv
531	Wait (blocking if necessary) until the "->send" or "->croak" methods	769	Wait (blocking if necessary) until the "->send" or "->croak" methods
532	have been called on c<$cv>, while servicing other watchers normally.	770	have been called on $cv, while servicing other watchers normally.
533		771
534	You can only wait once on a condition - additional calls are valid	772	You can only wait once on a condition - additional calls are valid
535	but will return immediately.	773	but will return immediately.
536		774
537	If an error condition has been set by calling "->croak", then this	775	If an error condition has been set by calling "->croak", then this
538	function will call "croak".	776	function will call "croak".
539		777
540	In list context, all parameters passed to "send" will be returned,	778	In list context, all parameters passed to "send" will be returned,
541	in scalar context only the first one will be returned.	779	in scalar context only the first one will be returned.
542		780
		781	Note that doing a blocking wait in a callback is not supported by
		782	any event loop, that is, recursive invocation of a blocking "->recv"
		783	is not allowed, and the "recv" call will "croak" if such a condition
		784	is detected. This condition can be slightly loosened by using
		785	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		786	thread that doesn't run the event loop itself.
		787
543	Not all event models support a blocking wait - some die in that case	788	Not all event models support a blocking wait - some die in that case
544	(programs might want to do that to stay interactive), so *if you are	789	(programs might want to do that to stay interactive), so *if you are
545	using this from a module, never require a blocking wait*, but let	790	using this from a module, never require a blocking wait*. Instead,
546	the caller decide whether the call will block or not (for example,	791	let the caller decide whether the call will block or not (for
547	by coupling condition variables with some kind of request results	792	example, by coupling condition variables with some kind of request
548	and supporting callbacks so the caller knows that getting the result	793	results and supporting callbacks so the caller knows that getting
549	will not block, while still supporting blocking waits if the caller	794	the result will not block, while still supporting blocking waits if
550	so desires).	795	the caller so desires).
551		796
552	Another reason *never* to "->recv" in a module is that you cannot
553	sensibly have two "->recv"'s in parallel, as that would require
554	multiple interpreters or coroutines/threads, none of which
555	"AnyEvent" can supply.
556
557	The Coro module, however, *can* and *does* supply coroutines and, in
558	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
559	versions and also integrates coroutines into AnyEvent, making
560	blocking "->recv" calls perfectly safe as long as they are done from
561	another coroutine (one that doesn't run the event loop).
562
563	You can ensure that "-recv" never blocks by setting a callback and	797	You can ensure that "->recv" never blocks by setting a callback and
564	only calling "->recv" from within that callback (or at a later	798	only calling "->recv" from within that callback (or at a later
565	time). This will work even when the event loop does not support	799	time). This will work even when the event loop does not support
566	blocking waits otherwise.	800	blocking waits otherwise.
567		801
568	$bool = $cv->ready	802	$bool = $cv->ready
569	Returns true when the condition is "true", i.e. whether "send" or	803	Returns true when the condition is "true", i.e. whether "send" or
570	"croak" have been called.	804	"croak" have been called.
571		805
572	$cb = $cv->cb ([new callback])	806	$cb = $cv->cb ($cb->($cv))
573	This is a mutator function that returns the callback set and	807	This is a mutator function that returns the callback set and
574	optionally replaces it before doing so.	808	optionally replaces it before doing so.
575		809
576	The callback will be called when the condition becomes "true", i.e.	810	The callback will be called when the condition becomes "true", i.e.
577	when "send" or "croak" are called, with the only argument being the	811	when "send" or "croak" are called, with the only argument being the
578	condition variable itself. Calling "recv" inside the callback or at	812	condition variable itself. If the condition is already true, the
		813	callback is called immediately when it is set. Calling "recv" inside
579	any later time is guaranteed not to block.	814	the callback or at any later time is guaranteed not to block.
		815
		816	SUPPORTED EVENT LOOPS/BACKENDS
		817	The available backend classes are (every class has its own manpage):
		818
		819	Backends that are autoprobed when no other event loop can be found.
		820	EV is the preferred backend when no other event loop seems to be in
		821	use. If EV is not installed, then AnyEvent will fall back to its own
		822	pure-perl implementation, which is available everywhere as it comes
		823	with AnyEvent itself.
		824
		825	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		826	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
		827
		828	Backends that are transparently being picked up when they are used.
		829	These will be used if they are already loaded when the first watcher
		830	is created, in which case it is assumed that the application is
		831	using them. This means that AnyEvent will automatically pick the
		832	right backend when the main program loads an event module before
		833	anything starts to create watchers. Nothing special needs to be done
		834	by the main program.
		835
		836	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		837	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		838	AnyEvent::Impl::Tk based on Tk, very broken.
		839	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		840	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		841	AnyEvent::Impl::Irssi used when running within irssi.
		842	AnyEvent::Impl::IOAsync based on IO::Async.
		843	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		844	AnyEvent::Impl::FLTK2 based on FLTK (fltk 2 binding).
		845
		846	Backends with special needs.
		847	Qt requires the Qt::Application to be instantiated first, but will
		848	otherwise be picked up automatically. As long as the main program
		849	instantiates the application before any AnyEvent watchers are
		850	created, everything should just work.
		851
		852	AnyEvent::Impl::Qt based on Qt.
		853
		854	Event loops that are indirectly supported via other backends.
		855	Some event loops can be supported via other modules:
		856
		857	There is no direct support for WxWidgets (Wx) or Prima.
		858
		859	WxWidgets has no support for watching file handles. However, you can
		860	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		861	simply polls 20 times per second, which was considered to be too
		862	horrible to even consider for AnyEvent.
		863
		864	Prima is not supported as nobody seems to be using it, but it has a
		865	POE backend, so it can be supported through POE.
		866
		867	AnyEvent knows about both Prima and Wx, however, and will try to
		868	load POE when detecting them, in the hope that POE will pick them
		869	up, in which case everything will be automatic.
580		870
581	GLOBAL VARIABLES AND FUNCTIONS	871	GLOBAL VARIABLES AND FUNCTIONS
		872	These are not normally required to use AnyEvent, but can be useful to
		873	write AnyEvent extension modules.
		874
582	$AnyEvent::MODEL	875	$AnyEvent::MODEL
583	Contains "undef" until the first watcher is being created. Then it	876	Contains "undef" until the first watcher is being created, before
		877	the backend has been autodetected.
		878
584	contains the event model that is being used, which is the name of	879	Afterwards it contains the event model that is being used, which is
585	the Perl class implementing the model. This class is usually one of	880	the name of the Perl class implementing the model. This class is
586	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	881	usually one of the "AnyEvent::Impl::xxx" modules, but can be any
587	case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*).	882	other class in the case AnyEvent has been extended at runtime (e.g.
588		883	in *rxvt-unicode* it will be "urxvt::anyevent").
589	The known classes so far are:
590
591	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
592	AnyEvent::Impl::Event based on Event, second best choice.
593	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
594	AnyEvent::Impl::Glib based on Glib, third-best choice.
595	AnyEvent::Impl::Tk based on Tk, very bad choice.
596	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
597	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
598	AnyEvent::Impl::POE based on POE, not generic enough for full support.
599
600	There is no support for WxWidgets, as WxWidgets has no support for
601	watching file handles. However, you can use WxWidgets through the
602	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
603	second, which was considered to be too horrible to even consider for
604	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
605	using it's adaptor.
606
607	AnyEvent knows about Prima and Wx and will try to use POE when
608	autodetecting them.
609		884
610	AnyEvent::detect	885	AnyEvent::detect
611	Returns $AnyEvent::MODEL, forcing autodetection of the event model	886	Returns $AnyEvent::MODEL, forcing autodetection of the event model
612	if necessary. You should only call this function right before you	887	if necessary. You should only call this function right before you
613	would have created an AnyEvent watcher anyway, that is, as late as	888	would have created an AnyEvent watcher anyway, that is, as late as
614	possible at runtime.	889	possible at runtime, and not e.g. during initialisation of your
		890	module.
		891
		892	The effect of calling this function is as if a watcher had been
		893	created (specifically, actions that happen "when the first watcher
		894	is created" happen when calling detetc as well).
		895
		896	If you need to do some initialisation before AnyEvent watchers are
		897	created, use "post_detect".
615		898
616	$guard = AnyEvent::post_detect { BLOCK }	899	$guard = AnyEvent::post_detect { BLOCK }
617	Arranges for the code block to be executed as soon as the event	900	Arranges for the code block to be executed as soon as the event
618	model is autodetected (or immediately if this has already happened).	901	model is autodetected (or immediately if that has already happened).
		902
		903	The block will be executed *after* the actual backend has been
		904	detected ($AnyEvent::MODEL is set), but *before* any watchers have
		905	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		906	other initialisations - see the sources of AnyEvent::Strict or
		907	AnyEvent::AIO to see how this is used.
		908
		909	The most common usage is to create some global watchers, without
		910	forcing event module detection too early, for example, AnyEvent::AIO
		911	creates and installs the global IO::AIO watcher in a "post_detect"
		912	block to avoid autodetecting the event module at load time.
619		913
620	If called in scalar or list context, then it creates and returns an	914	If called in scalar or list context, then it creates and returns an
621	object that automatically removes the callback again when it is	915	object that automatically removes the callback again when it is
		916	destroyed (or "undef" when the hook was immediately executed). See
622	destroyed. See Coro::BDB for a case where this is useful.	917	AnyEvent::AIO for a case where this is useful.
		918
		919	Example: Create a watcher for the IO::AIO module and store it in
		920	$WATCHER, but do so only do so after the event loop is initialised.
		921
		922	our WATCHER;
		923
		924	my $guard = AnyEvent::post_detect {
		925	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		926	};
		927
		928	# the ||= is important in case post_detect immediately runs the block,
		929	# as to not clobber the newly-created watcher. assigning both watcher and
		930	# post_detect guard to the same variable has the advantage of users being
		931	# able to just C<undef $WATCHER> if the watcher causes them grief.
		932
		933	$WATCHER ||= $guard;
623		934
624	@AnyEvent::post_detect	935	@AnyEvent::post_detect
625	If there are any code references in this array (you can "push" to it	936	If there are any code references in this array (you can "push" to it
626	before or after loading AnyEvent), then they will called directly	937	before or after loading AnyEvent), then they will be called directly
627	after the event loop has been chosen.	938	after the event loop has been chosen.
628		939
629	You should check $AnyEvent::MODEL before adding to this array,	940	You should check $AnyEvent::MODEL before adding to this array,
630	though: if it contains a true value then the event loop has already	941	though: if it is defined then the event loop has already been
631	been detected, and the array will be ignored.	942	detected, and the array will be ignored.
632		943
633	Best use "AnyEvent::post_detect { BLOCK }" instead.	944	Best use "AnyEvent::post_detect { BLOCK }" when your application
		945	allows it, as it takes care of these details.
		946
		947	This variable is mainly useful for modules that can do something
		948	useful when AnyEvent is used and thus want to know when it is
		949	initialised, but do not need to even load it by default. This array
		950	provides the means to hook into AnyEvent passively, without loading
		951	it.
		952
		953	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		954	together, you could put this into Coro (this is the actual code used
		955	by Coro to accomplish this):
		956
		957	if (defined $AnyEvent::MODEL) {
		958	# AnyEvent already initialised, so load Coro::AnyEvent
		959	require Coro::AnyEvent;
		960	} else {
		961	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		962	# as soon as it is
		963	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		964	}
		965
		966	AnyEvent::postpone { BLOCK }
		967	Arranges for the block to be executed as soon as possible, but not
		968	before the call itself returns. In practise, the block will be
		969	executed just before the event loop polls for new events, or shortly
		970	afterwards.
		971
		972	This function never returns anything (to make the "return postpone {
		973	... }" idiom more useful.
		974
		975	To understand the usefulness of this function, consider a function
		976	that asynchronously does something for you and returns some
		977	transaction object or guard to let you cancel the operation. For
		978	example, "AnyEvent::Socket::tcp_connect":
		979
		980	# start a conenction attempt unless one is active
		981	$self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		982	delete $self->{connect_guard};
		983	...
		984	};
		985
		986	Imagine that this function could instantly call the callback, for
		987	example, because it detects an obvious error such as a negative port
		988	number. Invoking the callback before the function returns causes
		989	problems however: the callback will be called and will try to delete
		990	the guard object. But since the function hasn't returned yet, there
		991	is nothing to delete. When the function eventually returns it will
		992	assign the guard object to "$self->{connect_guard}", where it will
		993	likely never be deleted, so the program thinks it is still trying to
		994	connect.
		995
		996	This is where "AnyEvent::postpone" should be used. Instead of
		997	calling the callback directly on error:
		998
		999	$cb->(undef), return # signal error to callback, BAD!
		1000	if $some_error_condition;
		1001
		1002	It should use "postpone":
		1003
		1004	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1005	if $some_error_condition;
		1006
		1007	AnyEvent::log $level, $msg[, @args]
		1008	Log the given $msg at the given $level.
		1009
		1010	Loads AnyEvent::Log on first use and calls "AnyEvent::Log::log" -
		1011	consequently, look at the AnyEvent::Log documentation for details.
		1012
		1013	If you want to sprinkle loads of logging calls around your code,
		1014	consider creating a logger callback with the "AnyEvent::Log::logger"
		1015	function.
634		1016
635	WHAT TO DO IN A MODULE	1017	WHAT TO DO IN A MODULE
636	As a module author, you should "use AnyEvent" and call AnyEvent methods	1018	As a module author, you should "use AnyEvent" and call AnyEvent methods
637	freely, but you should not load a specific event module or rely on it.	1019	freely, but you should not load a specific event module or rely on it.
638		1020
…		…
646	stall the whole program, and the whole point of using events is to stay	1028	stall the whole program, and the whole point of using events is to stay
647	interactive.	1029	interactive.
648		1030
649	It is fine, however, to call "->recv" when the user of your module	1031	It is fine, however, to call "->recv" when the user of your module
650	requests it (i.e. if you create a http request object ad have a method	1032	requests it (i.e. if you create a http request object ad have a method
651	called "results" that returns the results, it should call "->recv"	1033	called "results" that returns the results, it may call "->recv" freely,
652	freely, as the user of your module knows what she is doing. always).	1034	as the user of your module knows what she is doing. Always).
653		1035
654	WHAT TO DO IN THE MAIN PROGRAM	1036	WHAT TO DO IN THE MAIN PROGRAM
655	There will always be a single main program - the only place that should	1037	There will always be a single main program - the only place that should
656	dictate which event model to use.	1038	dictate which event model to use.
657		1039
658	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	1040	If the program is not event-based, it need not do anything special, even
659	do anything special (it does not need to be event-based) and let	1041	when it depends on a module that uses an AnyEvent. If the program itself
660	AnyEvent decide which implementation to chose if some module relies on	1042	uses AnyEvent, but does not care which event loop is used, all it needs
661	it.	1043	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		1044	available loop implementation.
662		1045
663	If the main program relies on a specific event model - for example, in	1046	If the main program relies on a specific event model - for example, in
664	Gtk2 programs you have to rely on the Glib module - you should load the	1047	Gtk2 programs you have to rely on the Glib module - you should load the
665	event module before loading AnyEvent or any module that uses it:	1048	event module before loading AnyEvent or any module that uses it:
666	generally speaking, you should load it as early as possible. The reason	1049	generally speaking, you should load it as early as possible. The reason
667	is that modules might create watchers when they are loaded, and AnyEvent	1050	is that modules might create watchers when they are loaded, and AnyEvent
668	will decide on the event model to use as soon as it creates watchers,	1051	will decide on the event model to use as soon as it creates watchers,
669	and it might chose the wrong one unless you load the correct one	1052	and it might choose the wrong one unless you load the correct one
670	yourself.	1053	yourself.
671		1054
672	You can chose to use a pure-perl implementation by loading the	1055	You can chose to use a pure-perl implementation by loading the
673	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1056	"AnyEvent::Loop" module, which gives you similar behaviour everywhere,
674	everywhere, but letting AnyEvent chose the model is generally better.	1057	but letting AnyEvent chose the model is generally better.
675		1058
676	MAINLOOP EMULATION	1059	MAINLOOP EMULATION
677	Sometimes (often for short test scripts, or even standalone programs who	1060	Sometimes (often for short test scripts, or even standalone programs who
678	only want to use AnyEvent), you do not want to run a specific event	1061	only want to use AnyEvent), you do not want to run a specific event
679	loop.	1062	loop.
…		…
689	variable somewhere, waiting for it, and sending it when the program	1072	variable somewhere, waiting for it, and sending it when the program
690	should exit cleanly.	1073	should exit cleanly.
691		1074
692	OTHER MODULES	1075	OTHER MODULES
693	The following is a non-exhaustive list of additional modules that use	1076	The following is a non-exhaustive list of additional modules that use
694	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1077	AnyEvent as a client and can therefore be mixed easily with other
695	in the same program. Some of the modules come with AnyEvent, some are	1078	AnyEvent modules and other event loops in the same program. Some of the
696	available via CPAN.	1079	modules come as part of AnyEvent, the others are available via CPAN (see
		1080	<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
		1081	non-exhaustive list), and the list is heavily biased towards modules of
		1082	the AnyEvent author himself :)
697		1083
698	AnyEvent::Util	1084	AnyEvent::Util
699	Contains various utility functions that replace often-used but	1085	Contains various utility functions that replace often-used blocking
700	blocking functions such as "inet_aton" by event-/callback-based	1086	functions such as "inet_aton" with event/callback-based versions.
701	versions.
702
703	AnyEvent::Handle
704	Provide read and write buffers and manages watchers for reads and
705	writes.
706		1087
707	AnyEvent::Socket	1088	AnyEvent::Socket
708	Provides various utility functions for (internet protocol) sockets,	1089	Provides various utility functions for (internet protocol) sockets,
709	addresses and name resolution. Also functions to create non-blocking	1090	addresses and name resolution. Also functions to create non-blocking
710	tcp connections or tcp servers, with IPv6 and SRV record support and	1091	tcp connections or tcp servers, with IPv6 and SRV record support and
711	more.	1092	more.
712		1093
		1094	AnyEvent::Handle
		1095	Provide read and write buffers, manages watchers for reads and
		1096	writes, supports raw and formatted I/O, I/O queued and fully
		1097	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
		1098
713	AnyEvent::DNS	1099	AnyEvent::DNS
714	Provides rich asynchronous DNS resolver capabilities.	1100	Provides rich asynchronous DNS resolver capabilities.
715		1101
		1102	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
		1103	AnyEvent::IGS, AnyEvent::FCP
		1104	Implement event-based interfaces to the protocols of the same name
		1105	(for the curious, IGS is the International Go Server and FCP is the
		1106	Freenet Client Protocol).
		1107
		1108	AnyEvent::Handle::UDP
		1109	Here be danger!
		1110
		1111	As Pauli would put it, "Not only is it not right, it's not even
		1112	wrong!" - there are so many things wrong with AnyEvent::Handle::UDP,
		1113	most notably its use of a stream-based API with a protocol that
		1114	isn't streamable, that the only way to improve it is to delete it.
		1115
		1116	It features data corruption (but typically only under load) and
		1117	general confusion. On top, the author is not only clueless about UDP
		1118	but also fact-resistant - some gems of his understanding: "connect
		1119	doesn't work with UDP", "UDP packets are not IP packets", "UDP only
		1120	has datagrams, not packets", "I don't need to implement proper error
		1121	checking as UDP doesn't support error checking" and so on - he
		1122	doesn't even understand what's wrong with his module when it is
		1123	explained to him.
		1124
716	AnyEvent::HTTP	1125	AnyEvent::DBI
717	A simple-to-use HTTP library that is capable of making a lot of	1126	Executes DBI requests asynchronously in a proxy process for you,
718	concurrent HTTP requests.	1127	notifying you in an event-based way when the operation is finished.
		1128
		1129	AnyEvent::AIO
		1130	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1131	the toolbox of every event programmer. AnyEvent::AIO transparently
		1132	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1133	event-based file I/O, and much more.
719		1134
720	AnyEvent::HTTPD	1135	AnyEvent::HTTPD
721	Provides a simple web application server framework.	1136	A simple embedded webserver.
722		1137
723	AnyEvent::FastPing	1138	AnyEvent::FastPing
724	The fastest ping in the west.	1139	The fastest ping in the west.
725		1140
726	Net::IRC3
727	AnyEvent based IRC client module family.
728
729	Net::XMPP2
730	AnyEvent based XMPP (Jabber protocol) module family.
731
732	Net::FCP
733	AnyEvent-based implementation of the Freenet Client Protocol,
734	birthplace of AnyEvent.
735
736	Event::ExecFlow
737	High level API for event-based execution flow control.
738
739	Coro	1141	Coro
740	Has special support for AnyEvent via Coro::AnyEvent.	1142	Has special support for AnyEvent via Coro::AnyEvent.
741		1143
742	AnyEvent::AIO, IO::AIO	1144	SIMPLIFIED AE API
743	Truly asynchronous I/O, should be in the toolbox of every event	1145	Starting with version 5.0, AnyEvent officially supports a second, much
744	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	1146	simpler, API that is designed to reduce the calling, typing and memory
745	together.	1147	overhead by using function call syntax and a fixed number of parameters.
746		1148
747	AnyEvent::BDB, BDB	1149	See the AE manpage for details.
748	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
749	fuses IO::AIO and AnyEvent together.
750		1150
751	IO::Lambda	1151	ERROR AND EXCEPTION HANDLING
752	The lambda approach to I/O - don't ask, look there. Can use	1152	In general, AnyEvent does not do any error handling - it relies on the
753	AnyEvent.	1153	caller to do that if required. The AnyEvent::Strict module (see also the
		1154	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1155	checking of all AnyEvent methods, however, which is highly useful during
		1156	development.
		1157
		1158	As for exception handling (i.e. runtime errors and exceptions thrown
		1159	while executing a callback), this is not only highly event-loop
		1160	specific, but also not in any way wrapped by this module, as this is the
		1161	job of the main program.
		1162
		1163	The pure perl event loop simply re-throws the exception (usually within
		1164	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		1165	Glib uses "install_exception_handler" and so on.
		1166
		1167	ENVIRONMENT VARIABLES
		1168	The following environment variables are used by this module or its
		1169	submodules.
		1170
		1171	Note that AnyEvent will remove *all* environment variables starting with
		1172	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1173	enabled.
		1174
		1175	"PERL_ANYEVENT_VERBOSE"
		1176	By default, AnyEvent will be completely silent except in fatal
		1177	conditions. You can set this environment variable to make AnyEvent
		1178	more talkative.
		1179
		1180	When set to 5 or higher, causes AnyEvent to warn about unexpected
		1181	conditions, such as not being able to load the event model specified
		1182	by "PERL_ANYEVENT_MODEL".
		1183
		1184	When set to 7 or higher, cause AnyEvent to report to STDERR which
		1185	event model it chooses.
		1186
		1187	When set to 8 or higher, then AnyEvent will report extra information
		1188	on which optional modules it loads and how it implements certain
		1189	features.
		1190
		1191	"PERL_ANYEVENT_STRICT"
		1192	AnyEvent does not do much argument checking by default, as thorough
		1193	argument checking is very costly. Setting this variable to a true
		1194	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1195	thoroughly check the arguments passed to most method calls. If it
		1196	finds any problems, it will croak.
		1197
		1198	In other words, enables "strict" mode.
		1199
		1200	Unlike "use strict" (or its modern cousin, "use common::sense", it
		1201	is definitely recommended to keep it off in production. Keeping
		1202	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1203	programs can be very useful, however.
		1204
		1205	"PERL_ANYEVENT_DEBUG_SHELL"
		1206	If this env variable is set, then its contents will be interpreted
		1207	by "AnyEvent::Socket::parse_hostport" (after replacing every
		1208	occurance of $$ by the process pid) and an "AnyEvent::Debug::shell"
		1209	is bound on that port. The shell object is saved in
		1210	$AnyEvent::Debug::SHELL.
		1211
		1212	This takes place when the first watcher is created.
		1213
		1214	For example, to bind a debug shell on a unix domain socket in
		1215	/tmp/debug<pid>.sock, you could use this:
		1216
		1217	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		1218
		1219	Note that creating sockets in /tmp is very unsafe on multiuser
		1220	systems.
		1221
		1222	"PERL_ANYEVENT_DEBUG_WRAP"
		1223	Can be set to 0, 1 or 2 and enables wrapping of all watchers for
		1224	debugging purposes. See "AnyEvent::Debug::wrap" for details.
		1225
		1226	"PERL_ANYEVENT_MODEL"
		1227	This can be used to specify the event model to be used by AnyEvent,
		1228	before auto detection and -probing kicks in.
		1229
		1230	It normally is a string consisting entirely of ASCII letters (e.g.
		1231	"EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
		1232	the resulting module name is loaded and - if the load was successful
		1233	- used as event model backend. If it fails to load then AnyEvent
		1234	will proceed with auto detection and -probing.
		1235
		1236	If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
		1237	then nothing gets prepended and the module name is used as-is (hint:
		1238	"::" at the end of a string designates a module name and quotes it
		1239	appropriately).
		1240
		1241	For example, to force the pure perl model (AnyEvent::Loop::Perl) you
		1242	could start your program like this:
		1243
		1244	PERL_ANYEVENT_MODEL=Perl perl ...
		1245
		1246	"PERL_ANYEVENT_PROTOCOLS"
		1247	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		1248	preferences for IPv4 or IPv6. The default is unspecified (and might
		1249	change, or be the result of auto probing).
		1250
		1251	Must be set to a comma-separated list of protocols or address
		1252	families, current supported: "ipv4" and "ipv6". Only protocols
		1253	mentioned will be used, and preference will be given to protocols
		1254	mentioned earlier in the list.
		1255
		1256	This variable can effectively be used for denial-of-service attacks
		1257	against local programs (e.g. when setuid), although the impact is
		1258	likely small, as the program has to handle conenction and other
		1259	failures anyways.
		1260
		1261	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		1262	IPv6, but support both and try to use both.
		1263	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		1264	resolve or contact IPv6 addresses.
		1265	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		1266	prefer IPv6 over IPv4.
		1267
		1268	"PERL_ANYEVENT_EDNS0"
		1269	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		1270	for DNS. This extension is generally useful to reduce DNS traffic,
		1271	but some (broken) firewalls drop such DNS packets, which is why it
		1272	is off by default.
		1273
		1274	Setting this variable to 1 will cause AnyEvent::DNS to announce
		1275	EDNS0 in its DNS requests.
		1276
		1277	"PERL_ANYEVENT_MAX_FORKS"
		1278	The maximum number of child processes that
		1279	"AnyEvent::Util::fork_call" will create in parallel.
		1280
		1281	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1282	The default value for the "max_outstanding" parameter for the
		1283	default DNS resolver - this is the maximum number of parallel DNS
		1284	requests that are sent to the DNS server.
		1285
		1286	"PERL_ANYEVENT_RESOLV_CONF"
		1287	The file to use instead of /etc/resolv.conf (or OS-specific
		1288	configuration) in the default resolver. When set to the empty
		1289	string, no default config will be used.
		1290
		1291	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1292	When neither "ca_file" nor "ca_path" was specified during
		1293	AnyEvent::TLS context creation, and either of these environment
		1294	variables exist, they will be used to specify CA certificate
		1295	locations instead of a system-dependent default.
		1296
		1297	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1298	When these are set to 1, then the respective modules are not loaded.
		1299	Mostly good for testing AnyEvent itself.
754		1300
755	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1301	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
756	This is an advanced topic that you do not normally need to use AnyEvent	1302	This is an advanced topic that you do not normally need to use AnyEvent
757	in a module. This section is only of use to event loop authors who want	1303	in a module. This section is only of use to event loop authors who want
758	to provide AnyEvent compatibility.	1304	to provide AnyEvent compatibility.
…		…
792		1338
793	*rxvt-unicode* also cheats a bit by not providing blocking access to	1339	*rxvt-unicode* also cheats a bit by not providing blocking access to
794	condition variables: code blocking while waiting for a condition will	1340	condition variables: code blocking while waiting for a condition will
795	"die". This still works with most modules/usages, and blocking calls	1341	"die". This still works with most modules/usages, and blocking calls
796	must not be done in an interactive application, so it makes sense.	1342	must not be done in an interactive application, so it makes sense.
797
798	ENVIRONMENT VARIABLES
799	The following environment variables are used by this module:
800
801	"PERL_ANYEVENT_VERBOSE"
802	By default, AnyEvent will be completely silent except in fatal
803	conditions. You can set this environment variable to make AnyEvent
804	more talkative.
805
806	When set to 1 or higher, causes AnyEvent to warn about unexpected
807	conditions, such as not being able to load the event model specified
808	by "PERL_ANYEVENT_MODEL".
809
810	When set to 2 or higher, cause AnyEvent to report to STDERR which
811	event model it chooses.
812
813	"PERL_ANYEVENT_MODEL"
814	This can be used to specify the event model to be used by AnyEvent,
815	before auto detection and -probing kicks in. It must be a string
816	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
817	gets prepended and the resulting module name is loaded and if the
818	load was successful, used as event model. If it fails to load
819	AnyEvent will proceed with auto detection and -probing.
820
821	This functionality might change in future versions.
822
823	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
824	could start your program like this:
825
826	PERL_ANYEVENT_MODEL=Perl perl ...
827
828	"PERL_ANYEVENT_PROTOCOLS"
829	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
830	preferences for IPv4 or IPv6. The default is unspecified (and might
831	change, or be the result of auto probing).
832
833	Must be set to a comma-separated list of protocols or address
834	families, current supported: "ipv4" and "ipv6". Only protocols
835	mentioned will be used, and preference will be given to protocols
836	mentioned earlier in the list.
837
838	This variable can effectively be used for denial-of-service attacks
839	against local programs (e.g. when setuid), although the impact is
840	likely small, as the program has to handle connection errors
841	already-
842
843	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
844	IPv6, but support both and try to use both.
845	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
846	resolve or contact IPv6 addresses.
847	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
848	prefer IPv6 over IPv4.
849
850	"PERL_ANYEVENT_EDNS0"
851	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
852	for DNS. This extension is generally useful to reduce DNS traffic,
853	but some (broken) firewalls drop such DNS packets, which is why it
854	is off by default.
855
856	Setting this variable to 1 will cause AnyEvent::DNS to announce
857	EDNS0 in its DNS requests.
858
859	"PERL_ANYEVENT_MAX_FORKS"
860	The maximum number of child processes that
861	"AnyEvent::Util::fork_call" will create in parallel.
862		1343
863	EXAMPLE PROGRAM	1344	EXAMPLE PROGRAM
864	The following program uses an I/O watcher to read data from STDIN, a	1345	The following program uses an I/O watcher to read data from STDIN, a
865	timer to display a message once per second, and a condition variable to	1346	timer to display a message once per second, and a condition variable to
866	quit the program when the user enters quit:	1347	quit the program when the user enters quit:
…		…
878	warn "read: $input\n"; # output what has been read	1359	warn "read: $input\n"; # output what has been read
879	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1360	$cv->send if $input =~ /^q/i; # quit program if /^q/i
880	},	1361	},
881	);	1362	);
882		1363
883	my $time_watcher; # can only be used once
884
885	sub new_timer {
886	$timer = AnyEvent->timer (after => 1, cb => sub {	1364	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
887	warn "timeout\n"; # print 'timeout' about every second	1365	warn "timeout\n"; # print 'timeout' at most every second
888	&new_timer; # and restart the time
889	});
890	}	1366	});
891
892	new_timer; # create first timer
893		1367
894	$cv->recv; # wait until user enters /^q/i	1368	$cv->recv; # wait until user enters /^q/i
895		1369
896	REAL-WORLD EXAMPLE	1370	REAL-WORLD EXAMPLE
897	Consider the Net::FCP module. It features (among others) the following	1371	Consider the Net::FCP module. It features (among others) the following
…		…
969		1443
970	The actual code goes further and collects all errors ("die"s,	1444	The actual code goes further and collects all errors ("die"s,
971	exceptions) that occurred during request processing. The "result" method	1445	exceptions) that occurred during request processing. The "result" method
972	detects whether an exception as thrown (it is stored inside the $txn	1446	detects whether an exception as thrown (it is stored inside the $txn
973	object) and just throws the exception, which means connection errors and	1447	object) and just throws the exception, which means connection errors and
974	other problems get reported tot he code that tries to use the result,	1448	other problems get reported to the code that tries to use the result,
975	not in a random callback.	1449	not in a random callback.
976		1450
977	All of this enables the following usage styles:	1451	All of this enables the following usage styles:
978		1452
979	1. Blocking:	1453	1. Blocking:
…		…
1024	through AnyEvent. The benchmark creates a lot of timers (with a zero	1498	through AnyEvent. The benchmark creates a lot of timers (with a zero
1025	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1499	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1026	which it is), lets them fire exactly once and destroys them again.	1500	which it is), lets them fire exactly once and destroys them again.
1027		1501
1028	Source code for this benchmark is found as eg/bench in the AnyEvent	1502	Source code for this benchmark is found as eg/bench in the AnyEvent
1029	distribution.	1503	distribution. It uses the AE interface, which makes a real difference
		1504	for the EV and Perl backends only.
1030		1505
1031	Explanation of the columns	1506	Explanation of the columns
1032	*watcher* is the number of event watchers created/destroyed. Since	1507	*watcher* is the number of event watchers created/destroyed. Since
1033	different event models feature vastly different performances, each event	1508	different event models feature vastly different performances, each event
1034	loop was given a number of watchers so that overall runtime is	1509	loop was given a number of watchers so that overall runtime is
…		…
1053	*destroy* is the time, in microseconds, that it takes to destroy a	1528	*destroy* is the time, in microseconds, that it takes to destroy a
1054	single watcher.	1529	single watcher.
1055		1530
1056	Results	1531	Results
1057	name watchers bytes create invoke destroy comment	1532	name watchers bytes create invoke destroy comment
1058	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1533	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1059	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1534	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1060	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1535	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1061	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1536	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1062	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1537	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1063	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1538	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1539	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1540	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1064	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1541	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1065	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1542	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1066	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1543	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1067	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1544	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1068		1545
1069	Discussion	1546	Discussion
1070	The benchmark does *not* measure scalability of the event loop very	1547	The benchmark does *not* measure scalability of the event loop very
1071	well. For example, a select-based event loop (such as the pure perl one)	1548	well. For example, a select-based event loop (such as the pure perl one)
1072	can never compete with an event loop that uses epoll when the number of	1549	can never compete with an event loop that uses epoll when the number of
…		…
1083	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1560	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1084	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1561	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1085	CPU cycles with POE.	1562	CPU cycles with POE.
1086		1563
1087	"EV" is the sole leader regarding speed and memory use, which are both	1564	"EV" is the sole leader regarding speed and memory use, which are both
1088	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1565	maximal/minimal, respectively. When using the AE API there is zero
		1566	overhead (when going through the AnyEvent API create is about 5-6 times
		1567	slower, with other times being equal, so still uses far less memory than
1089	far less memory than any other event loop and is still faster than Event	1568	any other event loop and is still faster than Event natively).
1090	natively.
1091		1569
1092	The pure perl implementation is hit in a few sweet spots (both the	1570	The pure perl implementation is hit in a few sweet spots (both the
1093	constant timeout and the use of a single fd hit optimisations in the	1571	constant timeout and the use of a single fd hit optimisations in the
1094	perl interpreter and the backend itself). Nevertheless this shows that	1572	perl interpreter and the backend itself). Nevertheless this shows that
1095	it adds very little overhead in itself. Like any select-based backend	1573	it adds very little overhead in itself. Like any select-based backend
…		…
1097	few of them active), of course, but this was not subject of this	1575	few of them active), of course, but this was not subject of this
1098	benchmark.	1576	benchmark.
1099		1577
1100	The "Event" module has a relatively high setup and callback invocation	1578	The "Event" module has a relatively high setup and callback invocation
1101	cost, but overall scores in on the third place.	1579	cost, but overall scores in on the third place.
		1580
		1581	"IO::Async" performs admirably well, about on par with "Event", even
		1582	when using its pure perl backend.
1102		1583
1103	"Glib"'s memory usage is quite a bit higher, but it features a faster	1584	"Glib"'s memory usage is quite a bit higher, but it features a faster
1104	callback invocation and overall ends up in the same class as "Event".	1585	callback invocation and overall ends up in the same class as "Event".
1105	However, Glib scales extremely badly, doubling the number of watchers	1586	However, Glib scales extremely badly, doubling the number of watchers
1106	increases the processing time by more than a factor of four, making it	1587	increases the processing time by more than a factor of four, making it
…		…
1138	when used without AnyEvent), but most event loops have acceptable	1619	when used without AnyEvent), but most event loops have acceptable
1139	performance with or without AnyEvent.	1620	performance with or without AnyEvent.
1140		1621
1141	* The overhead AnyEvent adds is usually much smaller than the overhead	1622	* The overhead AnyEvent adds is usually much smaller than the overhead
1142	of the actual event loop, only with extremely fast event loops such	1623	of the actual event loop, only with extremely fast event loops such
1143	as EV adds AnyEvent significant overhead.	1624	as EV does AnyEvent add significant overhead.
1144		1625
1145	* You should avoid POE like the plague if you want performance or	1626	* You should avoid POE like the plague if you want performance or
1146	reasonable memory usage.	1627	reasonable memory usage.
1147		1628
1148	BENCHMARKING THE LARGE SERVER CASE	1629	BENCHMARKING THE LARGE SERVER CASE
…		…
1162	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1643	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1163	100 (1%) are active. This mirrors the activity of large servers with	1644	100 (1%) are active. This mirrors the activity of large servers with
1164	many connections, most of which are idle at any one point in time.	1645	many connections, most of which are idle at any one point in time.
1165		1646
1166	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1647	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1167	distribution.	1648	distribution. It uses the AE interface, which makes a real difference
		1649	for the EV and Perl backends only.
1168		1650
1169	Explanation of the columns	1651	Explanation of the columns
1170	*sockets* is the number of sockets, and twice the number of "servers"	1652	*sockets* is the number of sockets, and twice the number of "servers"
1171	(as each server has a read and write socket end).	1653	(as each server has a read and write socket end).
1172		1654
…		…
1177	single "request", that is, reading the token from the pipe and	1659	single "request", that is, reading the token from the pipe and
1178	forwarding it to another server. This includes deleting the old timeout	1660	forwarding it to another server. This includes deleting the old timeout
1179	and creating a new one that moves the timeout into the future.	1661	and creating a new one that moves the timeout into the future.
1180		1662
1181	Results	1663	Results
1182	name sockets create request	1664	name sockets create request
1183	EV 20000 69.01 11.16	1665	EV 20000 62.66 7.99
1184	Perl 20000 73.32 35.87	1666	Perl 20000 68.32 32.64
1185	Event 20000 212.62 257.32	1667	IOAsync 20000 174.06 101.15 epoll
1186	Glib 20000 651.16 1896.30	1668	IOAsync 20000 174.67 610.84 poll
		1669	Event 20000 202.69 242.91
		1670	Glib 20000 557.01 1689.52
1187	POE 20000 349.67 12317.24 uses POE::Loop::Event	1671	POE 20000 341.54 12086.32 uses POE::Loop::Event
1188		1672
1189	Discussion	1673	Discussion
1190	This benchmark *does* measure scalability and overall performance of the	1674	This benchmark *does* measure scalability and overall performance of the
1191	particular event loop.	1675	particular event loop.
1192		1676
1193	EV is again fastest. Since it is using epoll on my system, the setup	1677	EV is again fastest. Since it is using epoll on my system, the setup
1194	time is relatively high, though.	1678	time is relatively high, though.
1195		1679
1196	Perl surprisingly comes second. It is much faster than the C-based event	1680	Perl surprisingly comes second. It is much faster than the C-based event
1197	loops Event and Glib.	1681	loops Event and Glib.
		1682
		1683	IO::Async performs very well when using its epoll backend, and still
		1684	quite good compared to Glib when using its pure perl backend.
1198		1685
1199	Event suffers from high setup time as well (look at its code and you	1686	Event suffers from high setup time as well (look at its code and you
1200	will understand why). Callback invocation also has a high overhead	1687	will understand why). Callback invocation also has a high overhead
1201	compared to the "$_->() for .."-style loop that the Perl event loop	1688	compared to the "$_->() for .."-style loop that the Perl event loop
1202	uses. Event uses select or poll in basically all documented	1689	uses. Event uses select or poll in basically all documented
…		…
1253		1740
1254	Summary	1741	Summary
1255	* C-based event loops perform very well with small number of watchers,	1742	* C-based event loops perform very well with small number of watchers,
1256	as the management overhead dominates.	1743	as the management overhead dominates.
1257		1744
		1745	THE IO::Lambda BENCHMARK
		1746	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1747	could be misinterpreted to make AnyEvent look bad. In fact, the
		1748	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1749	better (which shouldn't come as a surprise to anybody). As such, the
		1750	benchmark is fine, and mostly shows that the AnyEvent backend from
		1751	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1752	without the extra baggage? To explore this, I wrote the equivalent
		1753	benchmark for AnyEvent.
		1754
		1755	The benchmark itself creates an echo-server, and then, for 500 times,
		1756	connects to the echo server, sends a line, waits for the reply, and then
		1757	creates the next connection. This is a rather bad benchmark, as it
		1758	doesn't test the efficiency of the framework or much non-blocking I/O,
		1759	but it is a benchmark nevertheless.
		1760
		1761	name runtime
		1762	Lambda/select 0.330 sec
		1763	+ optimized 0.122 sec
		1764	Lambda/AnyEvent 0.327 sec
		1765	+ optimized 0.138 sec
		1766	Raw sockets/select 0.077 sec
		1767	POE/select, components 0.662 sec
		1768	POE/select, raw sockets 0.226 sec
		1769	POE/select, optimized 0.404 sec
		1770
		1771	AnyEvent/select/nb 0.085 sec
		1772	AnyEvent/EV/nb 0.068 sec
		1773	+state machine 0.134 sec
		1774
		1775	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1776	benchmarks actually make blocking connects and use 100% blocking I/O,
		1777	defeating the purpose of an event-based solution. All of the newly
		1778	written AnyEvent benchmarks use 100% non-blocking connects (using
		1779	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1780	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1781	connects generally require a lot more bookkeeping and event handling
		1782	than blocking connects (which involve a single syscall only).
		1783
		1784	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1785	offers similar expressive power as POE and IO::Lambda, using
		1786	conventional Perl syntax. This means that both the echo server and the
		1787	client are 100% non-blocking, further placing it at a disadvantage.
		1788
		1789	As you can see, the AnyEvent + EV combination even beats the
		1790	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1791	backend easily beats IO::Lambda and POE.
		1792
		1793	And even the 100% non-blocking version written using the high-level (and
		1794	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1795	higher level ("unoptimised") abstractions by a large margin, even though
		1796	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1797
		1798	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1799	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1800	part of the IO::Lambda distribution and were used without any changes.
		1801
		1802	SIGNALS
		1803	AnyEvent currently installs handlers for these signals:
		1804
		1805	SIGCHLD
		1806	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1807	emulation for event loops that do not support them natively. Also,
		1808	some event loops install a similar handler.
		1809
		1810	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1811	then AnyEvent will reset it to default, to avoid losing child exit
		1812	statuses.
		1813
		1814	SIGPIPE
		1815	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1816	"undef" when AnyEvent gets loaded.
		1817
		1818	The rationale for this is that AnyEvent users usually do not really
		1819	depend on SIGPIPE delivery (which is purely an optimisation for
		1820	shell use, or badly-written programs), but "SIGPIPE" can cause
		1821	spurious and rare program exits as a lot of people do not expect
		1822	"SIGPIPE" when writing to some random socket.
		1823
		1824	The rationale for installing a no-op handler as opposed to ignoring
		1825	it is that this way, the handler will be restored to defaults on
		1826	exec.
		1827
		1828	Feel free to install your own handler, or reset it to defaults.
		1829
		1830	RECOMMENDED/OPTIONAL MODULES
		1831	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1832	its built-in modules) are required to use it.
		1833
		1834	That does not mean that AnyEvent won't take advantage of some additional
		1835	modules if they are installed.
		1836
		1837	This section explains which additional modules will be used, and how
		1838	they affect AnyEvent's operation.
		1839
		1840	Async::Interrupt
		1841	This slightly arcane module is used to implement fast signal
		1842	handling: To my knowledge, there is no way to do completely
		1843	race-free and quick signal handling in pure perl. To ensure that
		1844	signals still get delivered, AnyEvent will start an interval timer
		1845	to wake up perl (and catch the signals) with some delay (default is
		1846	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1847
		1848	If this module is available, then it will be used to implement
		1849	signal catching, which means that signals will not be delayed, and
		1850	the event loop will not be interrupted regularly, which is more
		1851	efficient (and good for battery life on laptops).
		1852
		1853	This affects not just the pure-perl event loop, but also other event
		1854	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1855
		1856	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1857	natively, and either employ their own workarounds (POE) or use
		1858	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1859	Installing Async::Interrupt does nothing for those backends.
		1860
		1861	EV This module isn't really "optional", as it is simply one of the
		1862	backend event loops that AnyEvent can use. However, it is simply the
		1863	best event loop available in terms of features, speed and stability:
		1864	It supports the AnyEvent API optimally, implements all the watcher
		1865	types in XS, does automatic timer adjustments even when no monotonic
		1866	clock is available, can take avdantage of advanced kernel interfaces
		1867	such as "epoll" and "kqueue", and is the fastest backend *by far*.
		1868	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1869	Glib::EV).
		1870
		1871	If you only use backends that rely on another event loop (e.g.
		1872	"Tk"), then this module will do nothing for you.
		1873
		1874	Guard
		1875	The guard module, when used, will be used to implement
		1876	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1877	uses a lot less memory), but otherwise doesn't affect guard
		1878	operation much. It is purely used for performance.
		1879
		1880	JSON and JSON::XS
		1881	One of these modules is required when you want to read or write JSON
		1882	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		1883	can take advantage of the ultra-high-speed JSON::XS module when it
		1884	is installed.
		1885
		1886	Net::SSLeay
		1887	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1888	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1889	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1890
		1891	Time::HiRes
		1892	This module is part of perl since release 5.008. It will be used
		1893	when the chosen event library does not come with a timing source of
		1894	its own. The pure-perl event loop (AnyEvent::Loop) will additionally
		1895	load it to try to use a monotonic clock for timing stability.
		1896
1258	FORK	1897	FORK
1259	Most event libraries are not fork-safe. The ones who are usually are	1898	Most event libraries are not fork-safe. The ones who are usually are
1260	because they rely on inefficient but fork-safe "select" or "poll" calls.	1899	because they rely on inefficient but fork-safe "select" or "poll" calls
1261	Only EV is fully fork-aware.	1900	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		1901	epoll are usually badly thought-out hacks that are incompatible with
		1902	fork in one way or another. Only EV is fully fork-aware and ensures that
		1903	you continue event-processing in both parent and child (or both, if you
		1904	know what you are doing).
		1905
		1906	This means that, in general, you cannot fork and do event processing in
		1907	the child if the event library was initialised before the fork (which
		1908	usually happens when the first AnyEvent watcher is created, or the
		1909	library is loaded).
1262		1910
1263	If you have to fork, you must either do so *before* creating your first	1911	If you have to fork, you must either do so *before* creating your first
1264	watcher OR you must not use AnyEvent at all in the child.	1912	watcher OR you must not use AnyEvent at all in the child OR you must do
		1913	something completely out of the scope of AnyEvent.
		1914
		1915	The problem of doing event processing in the parent *and* the child is
		1916	much more complicated: even for backends that *are* fork-aware or
		1917	fork-safe, their behaviour is not usually what you want: fork clones all
		1918	watchers, that means all timers, I/O watchers etc. are active in both
		1919	parent and child, which is almost never what you want. USing "exec" to
		1920	start worker children from some kind of manage rprocess is usually
		1921	preferred, because it is much easier and cleaner, at the expense of
		1922	having to have another binary.
1265		1923
1266	SECURITY CONSIDERATIONS	1924	SECURITY CONSIDERATIONS
1267	AnyEvent can be forced to load any event model via	1925	AnyEvent can be forced to load any event model via
1268	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1926	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1269	to execute arbitrary code or directly gain access, it can easily be used	1927	to execute arbitrary code or directly gain access, it can easily be used
…		…
1273		1931
1274	You can make AnyEvent completely ignore this variable by deleting it	1932	You can make AnyEvent completely ignore this variable by deleting it
1275	before the first watcher gets created, e.g. with a "BEGIN" block:	1933	before the first watcher gets created, e.g. with a "BEGIN" block:
1276		1934
1277	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1935	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1278		1936
1279	use AnyEvent;	1937	use AnyEvent;
1280		1938
1281	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1939	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1282	be used to probe what backend is used and gain other information (which	1940	be used to probe what backend is used and gain other information (which
1283	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).	1941	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1942	and $ENV{PERL_ANYEVENT_STRICT}.
		1943
		1944	Note that AnyEvent will remove *all* environment variables starting with
		1945	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1946	enabled.
1284		1947
1285	BUGS	1948	BUGS
1286	Perl 5.8 has numerous memleaks that sometimes hit this module and are	1949	Perl 5.8 has numerous memleaks that sometimes hit this module and are
1287	hard to work around. If you suffer from memleaks, first upgrade to Perl	1950	hard to work around. If you suffer from memleaks, first upgrade to Perl
1288	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	1951	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1289	annoying mamleaks, such as leaking on "map" and "grep" but it is usually	1952	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1290	not as pronounced).	1953	not as pronounced).
1291		1954
1292	SEE ALSO	1955	SEE ALSO
1293	Utility functions: AnyEvent::Util.	1956	Tutorial/Introduction: AnyEvent::Intro.
1294		1957
1295	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1958	FAQ: AnyEvent::FAQ.
1296	Event::Lib, Qt, POE.	1959
		1960	Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
		1961	(simply logging).
		1962
		1963	Development/Debugging: AnyEvent::Strict (stricter checking),
		1964	AnyEvent::Debug (interactive shell, watcher tracing).
		1965
		1966	Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
		1967	Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK.
1297		1968
1298	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1969	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1299	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1970	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1300	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1971	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1972	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi, AnyEvent::Impl::FLTK.
1301		1973
1302	Non-blocking file handles, sockets, TCP clients and servers:	1974	Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1303	AnyEvent::Handle, AnyEvent::Socket.	1975	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1304		1976
1305	Asynchronous DNS: AnyEvent::DNS.	1977	Asynchronous DNS: AnyEvent::DNS.
1306		1978
1307	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1979	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1308		1980
1309	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1981	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
		1982	AnyEvent::HTTP.
1310		1983
1311	AUTHOR	1984	AUTHOR
1312	Marc Lehmann <schmorp@schmorp.de>	1985	Marc Lehmann <schmorp@schmorp.de>
1313	http://home.schmorp.de/	1986	http://home.schmorp.de/
1314		1987

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines