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Revision 1.69 by root, Tue Oct 4 17:45:04 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 });
		40
		41	INTRODUCTION/TUTORIAL
		42	This manpage is mainly a reference manual. If you are interested in a
		43	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		44	manpage.
		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.
21		54
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	55	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	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
24	nowadays. So what is different about AnyEvent?	57	nowadays. So what is different about AnyEvent?
25		58
26	Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of	59	Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of
27	policy* and AnyEvent is *small and efficient*.	60	policy* and AnyEvent is *small and efficient*.
28		61
29	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
30	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
31	pragmatic way. For event models and certain classes of immortals alike,	64	pragmatic way. For event models and certain classes of immortals alike,
32	the statement "there can only be one" is a bitter reality: In general,	65	the statement "there can only be one" is a bitter reality: In general,
33	only one event loop can be active at the same time in a process.	66	only one event loop can be active at the same time in a process.
34	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.
35		69
36	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
37	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
38	religion, a way of living, and most importantly: without forcing your	72	religion, a way of living, and most importantly: without forcing your
39	module users into the same thing by forcing them to use the same event	73	module users into the same thing by forcing them to use the same event
40	model you use.	74	model you use.
41		75
42	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
43	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
44	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
45	cannot use anything else, as it is simply incompatible to everything	79	cannot use anything else, as they are simply incompatible to everything
46	that isn't itself. What's worse, all the potential users of your module	80	that isn't them. What's worse, all the potential users of your module
47	are *also* forced to use the same event loop you use.	81	are *also* forced to use the same event loop you use.
48		82
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	83	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	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
51	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
52	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
53	But if your module uses AnyEvent, it works transparently with all event	87	your module uses AnyEvent, it works transparently with all event models
54	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
55	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
56	event loops to AnyEvent, too, so it is future-proof).	90	AnyEvent, too, so it is future-proof).
57		91
58	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
59	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
60	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
61	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
62	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
63	wrapper as technically possible.	97	technically possible.
64		98
65	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
66	useful functionality, such as an asynchronous DNS resolver, 100%	100	useful functionality, such as an asynchronous DNS resolver, 100%
67	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
68	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
…		…
71	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
72	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
73	model, you should *not* use this module.	107	model, you should *not* use this module.
74		108
75	DESCRIPTION	109	DESCRIPTION
76	AnyEvent provides an identical interface to multiple event loops. This	110	AnyEvent provides a uniform interface to various event loops. This
77	allows module authors to utilise an event loop without forcing module	111	allows module authors to use event loop functionality without forcing
78	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
79	coexist peacefully at any one time).	113	than one event loop cannot coexist peacefully).
80		114
81	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
82	module.	116	module.
83		117
84	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
85	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
86	following modules is already loaded: EV, Event, Glib,	120	following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
87	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
88	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
89	(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
90	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
91	successfully loaded will be used. If, after this, still none could be	125	tried.
92	found, AnyEvent will fall back to a pure-perl event loop, which is not
93	very efficient, but should work everywhere.
94		126
95	Because AnyEvent first checks for modules that are already loaded,	127	Because AnyEvent first checks for modules that are already loaded,
96	loading an event model explicitly before first using AnyEvent will	128	loading an event model explicitly before first using AnyEvent will
97	likely make that model the default. For example:	129	likely make that model the default. For example:
98		130
…		…
100	use AnyEvent;	132	use AnyEvent;
101		133
102	# .. AnyEvent will likely default to Tk	134	# .. AnyEvent will likely default to Tk
103		135
104	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
105	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
106	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.
107		140
108	The pure-perl implementation of AnyEvent is called	141	The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
109	"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
110	explicitly and enjoy the high availability of that event loop :)	143	availability of that event loop :)
111		144
112	WATCHERS	145	WATCHERS
113	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
114	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
115	the callback to call, the file handle to watch, etc.	148	the callback to call, the file handle to watch, etc.
…		…
117	These watchers are normal Perl objects with normal Perl lifetime. After	150	These watchers are normal Perl objects with normal Perl lifetime. After
118	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
119	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
120	in control).	153	in control).
121		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
122	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
123	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
124	to it).	163	to it).
125		164
126	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.
127		166
128	Many watchers either are used with "recursion" (repeating timers for	167	Many watchers either are used with "recursion" (repeating timers for
129	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.
130		169
131	An any way to achieve that is this pattern:	170	One way to achieve that is this pattern:
132		171
133	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	172	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
134	# you can use $w here, for example to undef it	173	# you can use $w here, for example to undef it
135	undef $w;	174	undef $w;
136	});	175	});
137		176
138	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,
139	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
140	declared.	179	declared.
141		180
142	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
143	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
144	the following mandatory key-value pairs as arguments:	189	the following mandatory key-value pairs as arguments:
145		190
146	"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
147	"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
148	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	199	watcher waiting for "r"eadable or "w"ritable events, respectively.
		200
149	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.
150		202
151	Although the callback might get passed parameters, their value and	203	Although the callback might get passed parameters, their value and
152	presence is undefined and you cannot rely on them. Portable AnyEvent	204	presence is undefined and you cannot rely on them. Portable AnyEvent
153	callbacks cannot use arguments passed to I/O watcher callbacks.	205	callbacks cannot use arguments passed to I/O watcher callbacks.
154		206
155	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
156	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
157	the underlying file descriptor.	209	the underlying file descriptor.
158		210
159	Some event loops issue spurious readyness notifications, so you should	211	Some event loops issue spurious readiness notifications, so you should
160	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
161	handles.	213	handles.
162		214
163	Example:
164
165	# 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
166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	218	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
167	chomp (my $input = <STDIN>);	219	chomp (my $input = <STDIN>);
168	warn "read: $input\n";	220	warn "read: $input\n";
169	undef $w;	221	undef $w;
170	});	222	});
171		223
172	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
173	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
174	with the following mandatory arguments:	234	with the following mandatory arguments:
175		235
176	"after" specifies after how many seconds (fractional values are	236	"after" specifies after how many seconds (fractional values are
177	supported) the callback should be invoked. "cb" is the callback to	237	supported) the callback should be invoked. "cb" is the callback to
…		…
179		239
180	Although the callback might get passed parameters, their value and	240	Although the callback might get passed parameters, their value and
181	presence is undefined and you cannot rely on them. Portable AnyEvent	241	presence is undefined and you cannot rely on them. Portable AnyEvent
182	callbacks cannot use arguments passed to time watcher callbacks.	242	callbacks cannot use arguments passed to time watcher callbacks.
183		243
184	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
185	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
186	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.
187		249
188	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.
189		253
190	# fire an event after 7.7 seconds	254	Example: fire an event after 7.7 seconds.
		255
191	my $w = AnyEvent->timer (after => 7.7, cb => sub {	256	my $w = AnyEvent->timer (after => 7.7, cb => sub {
192	warn "timeout\n";	257	warn "timeout\n";
193	});	258	});
194		259
195	# to cancel the timer:	260	# to cancel the timer:
196	undef $w;	261	undef $w;
197		262
198	Example 2:
199
200	# 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.
201	my $w;
202		264
203	my $cb = sub {
204	# cancel the old timer while creating a new one
205	$w = AnyEvent->timer (after => 1, cb => $cb);	265	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		266	warn "timeout\n";
206	};	267	};
207
208	# start the "loop" by creating the first watcher
209	$w = AnyEvent->timer (after => 0.5, cb => $cb);
210		268
211	TIMING ISSUES	269	TIMING ISSUES
212	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
213	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
214	o'clock").	272	o'clock").
215		273
216	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,
217	they use absolute time internally. This makes a difference when your	275	they use absolute time internally. This makes a difference when your
218	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
219	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
220	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
221	finally fire.	279	finally fire.
222		280
223	AnyEvent cannot compensate for this. The only event loop that is	281	AnyEvent cannot compensate for this. The only event loop that is
224	conscious about these issues is EV, which offers both relative	282	conscious of these issues is EV, which offers both relative (ev_timer,
225	(ev_timer, based on true relative time) and absolute (ev_periodic, based	283	based on true relative time) and absolute (ev_periodic, based on
226	on wallclock time) timers.	284	wallclock time) timers.
227		285
228	AnyEvent always prefers relative timers, if available, matching the	286	AnyEvent always prefers relative timers, if available, matching the
229	AnyEvent API.	287	AnyEvent API.
230		288
231	AnyEvent has two additional methods that return the "current time":	289	AnyEvent has two additional methods that return the "current time":
…		…
250	*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
251	function to call when you want to know the current time.*	309	function to call when you want to know the current time.*
252		310
253	This function is also often faster then "AnyEvent->time", and thus	311	This function is also often faster then "AnyEvent->time", and thus
254	the preferred method if you want some timestamp (for example,	312	the preferred method if you want some timestamp (for example,
255	AnyEvent::Handle uses this to update it's activity timeouts).	313	AnyEvent::Handle uses this to update its activity timeouts).
256		314
257	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
258	exact with your timing, you can skip it without bad conscience.	316	exact with your timing; you can skip it without a bad conscience.
259		317
260	For a practical example of when these times differ, consider	318	For a practical example of when these times differ, consider
261	Event::Lib and EV and the following set-up:	319	Event::Lib and EV and the following set-up:
262		320
263	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
264	at time=500 (assume no other callbacks delay processing). In your	322	at time=500 (assume no other callbacks delay processing). In your
265	callback, you wait a second by executing "sleep 1" (blocking the	323	callback, you wait a second by executing "sleep 1" (blocking the
266	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
267	timer that fires after three seconds.	325	timer that fires after three seconds.
268		326
…		…
288	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
289	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
290	the difference between "AnyEvent->time" and "AnyEvent->now" into	348	the difference between "AnyEvent->time" and "AnyEvent->now" into
291	account.	349	account.
292		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
293	SIGNAL WATCHERS	373	SIGNAL WATCHERS
		374	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		375
294	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
295	*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
296	whenever a signal occurs.	378	callback to be invoked whenever a signal occurs.
297		379
298	Although the callback might get passed parameters, their value and	380	Although the callback might get passed parameters, their value and
299	presence is undefined and you cannot rely on them. Portable AnyEvent	381	presence is undefined and you cannot rely on them. Portable AnyEvent
300	callbacks cannot use arguments passed to signal watcher callbacks.	382	callbacks cannot use arguments passed to signal watcher callbacks.
301		383
…		…
303	invocation, and callback invocation will be synchronous. Synchronous	385	invocation, and callback invocation will be synchronous. Synchronous
304	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
305	process, but it is guaranteed not to interrupt any other callbacks.	387	process, but it is guaranteed not to interrupt any other callbacks.
306		388
307	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
308	signal between multiple watchers.	390	signal between multiple watchers, and AnyEvent will ensure that signals
		391	will not interrupt your program at bad times.
309		392
310	This watcher might use %SIG, so programs overwriting those signals	393	This watcher might use %SIG (depending on the event loop used), so
311	directly will likely not work correctly.	394	programs overwriting those signals directly will likely not work
		395	correctly.
312		396
313	Example: exit on SIGINT	397	Example: exit on SIGINT
314		398
315	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	399	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
316		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 delay signal delivery
		409	indefinitely, the 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 10
		422	seconds by default, but can be overriden via
		423	$ENV{PERL_ANYEVENT_MAX_SIGNAL_LATENCY} or $AnyEvent::MAX_SIGNAL_LATENCY
		424	- see the Ö<ENVIRONMENT VARIABLES> section for details.
		425
		426	All these problems can be avoided by installing the optional
		427	Async::Interrupt module, which works with most event loops. It will not
		428	work with inherently broken event loops such as Event or Event::Lib (and
		429	not with POE currently). For those, you just have to suffer the delays.
		430
317	CHILD PROCESS WATCHERS	431	CHILD PROCESS WATCHERS
		432	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		433
318	You can also watch on a child process exit and catch its exit status.	434	You can also watch for a child process exit and catch its exit status.
319		435
320	The child process is specified by the "pid" argument (if set to 0, it	436	The child process is specified by the "pid" argument (on some backends,
321	watches for any child process exit). The watcher will trigger as often	437	using 0 watches for any child process exit, on others this will croak).
322	as status change for the child are received. This works by installing a	438	The watcher will be triggered only when the child process has finished
323	signal handler for "SIGCHLD". The callback will be called with the pid	439	and an exit status is available, not on any trace events
324	and exit status (as returned by waitpid), so unlike other watcher types,	440	(stopped/continued).
325	you *can* rely on child watcher callback arguments.	441
		442	The callback will be called with the pid and exit status (as returned by
		443	waitpid), so unlike other watcher types, you *can* rely on child watcher
		444	callback arguments.
		445
		446	This watcher type works by installing a signal handler for "SIGCHLD",
		447	and since it cannot be shared, nothing else should use SIGCHLD or reap
		448	random child processes (waiting for specific child processes, e.g.
		449	inside "system", is just fine).
326		450
327	There is a slight catch to child watchers, however: you usually start	451	There is a slight catch to child watchers, however: you usually start
328	them *after* the child process was created, and this means the process	452	them *after* the child process was created, and this means the process
329	could have exited already (and no SIGCHLD will be sent anymore).	453	could have exited already (and no SIGCHLD will be sent anymore).
330		454
331	Not all event models handle this correctly (POE doesn't), but even for	455	Not all event models handle this correctly (neither POE nor IO::Async
		456	do, see their AnyEvent::Impl manpages for details), but even for event
332	event models that *do* handle this correctly, they usually need to be	457	models that *do* handle this correctly, they usually need to be loaded
333	loaded before the process exits (i.e. before you fork in the first	458	before the process exits (i.e. before you fork in the first place).
334	place).	459	AnyEvent's pure perl event loop handles all cases correctly regardless
		460	of when you start the watcher.
335		461
336	This means you cannot create a child watcher as the very first thing in	462	This means you cannot create a child watcher as the very first thing in
337	an AnyEvent program, you *have* to create at least one watcher before	463	an AnyEvent program, you *have* to create at least one watcher before
338	you "fork" the child (alternatively, you can call "AnyEvent::detect").	464	you "fork" the child (alternatively, you can call "AnyEvent::detect").
339		465
		466	As most event loops do not support waiting for child events, they will
		467	be emulated by AnyEvent in most cases, in which case the latency and
		468	race problems mentioned in the description of signal watchers apply.
		469
340	Example: fork a process and wait for it	470	Example: fork a process and wait for it
341		471
342	my $done = AnyEvent->condvar;	472	my $done = AnyEvent->condvar;
343		473
344	my $pid = fork or exit 5;	474	my $pid = fork or exit 5;
345		475
346	my $w = AnyEvent->child (	476	my $w = AnyEvent->child (
347	pid => $pid,	477	pid => $pid,
348	cb => sub {	478	cb => sub {
349	my ($pid, $status) = @_;	479	my ($pid, $status) = @_;
350	warn "pid $pid exited with status $status";	480	warn "pid $pid exited with status $status";
351	$done->send;	481	$done->send;
352	},	482	},
353	);	483	);
354		484
355	# do something else, then wait for process exit	485	# do something else, then wait for process exit
356	$done->recv;	486	$done->recv;
		487
		488	IDLE WATCHERS
		489	$w = AnyEvent->idle (cb => <callback>);
		490
		491	This will repeatedly invoke the callback after the process becomes idle,
		492	until either the watcher is destroyed or new events have been detected.
		493
		494	Idle watchers are useful when there is a need to do something, but it is
		495	not so important (or wise) to do it instantly. The callback will be
		496	invoked only when there is "nothing better to do", which is usually
		497	defined as "all outstanding events have been handled and no new events
		498	have been detected". That means that idle watchers ideally get invoked
		499	when the event loop has just polled for new events but none have been
		500	detected. Instead of blocking to wait for more events, the idle watchers
		501	will be invoked.
		502
		503	Unfortunately, most event loops do not really support idle watchers
		504	(only EV, Event and Glib do it in a usable fashion) - for the rest,
		505	AnyEvent will simply call the callback "from time to time".
		506
		507	Example: read lines from STDIN, but only process them when the program
		508	is otherwise idle:
		509
		510	my @lines; # read data
		511	my $idle_w;
		512	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		513	push @lines, scalar <STDIN>;
		514
		515	# start an idle watcher, if not already done
		516	$idle_w ||= AnyEvent->idle (cb => sub {
		517	# handle only one line, when there are lines left
		518	if (my $line = shift @lines) {
		519	print "handled when idle: $line";
		520	} else {
		521	# otherwise disable the idle watcher again
		522	undef $idle_w;
		523	}
		524	});
		525	});
357		526
358	CONDITION VARIABLES	527	CONDITION VARIABLES
		528	$cv = AnyEvent->condvar;
		529
		530	$cv->send (<list>);
		531	my @res = $cv->recv;
		532
359	If you are familiar with some event loops you will know that all of them	533	If you are familiar with some event loops you will know that all of them
360	require you to run some blocking "loop", "run" or similar function that	534	require you to run some blocking "loop", "run" or similar function that
361	will actively watch for new events and call your callbacks.	535	will actively watch for new events and call your callbacks.
362		536
363	AnyEvent is different, it expects somebody else to run the event loop	537	AnyEvent is slightly different: it expects somebody else to run the
364	and will only block when necessary (usually when told by the user).	538	event loop and will only block when necessary (usually when told by the
		539	user).
365		540
366	The instrument to do that is called a "condition variable", so called	541	The tool to do that is called a "condition variable", so called because
367	because they represent a condition that must become true.	542	they represent a condition that must become true.
		543
		544	Now is probably a good time to look at the examples further below.
368		545
369	Condition variables can be created by calling the "AnyEvent->condvar"	546	Condition variables can be created by calling the "AnyEvent->condvar"
370	method, usually without arguments. The only argument pair allowed is	547	method, usually without arguments. The only argument pair allowed is
371	"cb", which specifies a callback to be called when the condition	548	"cb", which specifies a callback to be called when the condition
372	variable becomes true.	549	variable becomes true, with the condition variable as the first argument
		550	(but not the results).
373		551
374	After creation, the condition variable is "false" until it becomes	552	After creation, the condition variable is "false" until it becomes
375	"true" by calling the "send" method (or calling the condition variable	553	"true" by calling the "send" method (or calling the condition variable
376	as if it were a callback, read about the caveats in the description for	554	as if it were a callback, read about the caveats in the description for
377	the "->send" method).	555	the "->send" method).
378		556
379	Condition variables are similar to callbacks, except that you can	557	Since condition variables are the most complex part of the AnyEvent API,
380	optionally wait for them. They can also be called merge points - points	558	here are some different mental models of what they are - pick the ones
381	in time where multiple outstanding events have been processed. And yet	559	you can connect to:
382	another way to call them is transactions - each condition variable can	560
383	be used to represent a transaction, which finishes at some point and	561	* Condition variables are like callbacks - you can call them (and pass
384	delivers a result.	562	them instead of callbacks). Unlike callbacks however, you can also
		563	wait for them to be called.
		564
		565	* Condition variables are signals - one side can emit or send them,
		566	the other side can wait for them, or install a handler that is
		567	called when the signal fires.
		568
		569	* Condition variables are like "Merge Points" - points in your program
		570	where you merge multiple independent results/control flows into one.
		571
		572	* Condition variables represent a transaction - functions that start
		573	some kind of transaction can return them, leaving the caller the
		574	choice between waiting in a blocking fashion, or setting a callback.
		575
		576	* Condition variables represent future values, or promises to deliver
		577	some result, long before the result is available.
385		578
386	Condition variables are very useful to signal that something has	579	Condition variables are very useful to signal that something has
387	finished, for example, if you write a module that does asynchronous http	580	finished, for example, if you write a module that does asynchronous http
388	requests, then a condition variable would be the ideal candidate to	581	requests, then a condition variable would be the ideal candidate to
389	signal the availability of results. The user can either act when the	582	signal the availability of results. The user can either act when the
…		…
402		595
403	Condition variables are represented by hash refs in perl, and the keys	596	Condition variables are represented by hash refs in perl, and the keys
404	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy	597	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
405	(it is often useful to build your own transaction class on top of	598	(it is often useful to build your own transaction class on top of
406	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call	599	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
407	it's "new" method in your own "new" method.	600	its "new" method in your own "new" method.
408		601
409	There are two "sides" to a condition variable - the "producer side"	602	There are two "sides" to a condition variable - the "producer side"
410	which eventually calls "-> send", and the "consumer side", which waits	603	which eventually calls "-> send", and the "consumer side", which waits
411	for the send to occur.	604	for the send to occur.
412		605
413	Example: wait for a timer.	606	Example: wait for a timer.
414		607
415	# wait till the result is ready	608	# condition: "wait till the timer is fired"
416	my $result_ready = AnyEvent->condvar;	609	my $timer_fired = AnyEvent->condvar;
417		610
418	# do something such as adding a timer	611	# create the timer - we could wait for, say
419	# or socket watcher the calls $result_ready->send	612	# a handle becomign ready, or even an
420	# when the "result" is ready.	613	# AnyEvent::HTTP request to finish, but
421	# in this case, we simply use a timer:	614	# in this case, we simply use a timer:
422	my $w = AnyEvent->timer (	615	my $w = AnyEvent->timer (
423	after => 1,	616	after => 1,
424	cb => sub { $result_ready->send },	617	cb => sub { $timer_fired->send },
425	);	618	);
426		619
427	# this "blocks" (while handling events) till the callback	620	# this "blocks" (while handling events) till the callback
428	# calls send	621	# calls ->send
429	$result_ready->recv;	622	$timer_fired->recv;
430		623
431	Example: wait for a timer, but take advantage of the fact that condition	624	Example: wait for a timer, but take advantage of the fact that condition
432	variables are also code references.	625	variables are also callable directly.
433		626
434	my $done = AnyEvent->condvar;	627	my $done = AnyEvent->condvar;
435	my $delay = AnyEvent->timer (after => 5, cb => $done);	628	my $delay = AnyEvent->timer (after => 5, cb => $done);
436	$done->recv;	629	$done->recv;
		630
		631	Example: Imagine an API that returns a condvar and doesn't support
		632	callbacks. This is how you make a synchronous call, for example from the
		633	main program:
		634
		635	use AnyEvent::CouchDB;
		636
		637	...
		638
		639	my @info = $couchdb->info->recv;
		640
		641	And this is how you would just set a callback to be called whenever the
		642	results are available:
		643
		644	$couchdb->info->cb (sub {
		645	my @info = $_[0]->recv;
		646	});
437		647
438	METHODS FOR PRODUCERS	648	METHODS FOR PRODUCERS
439	These methods should only be used by the producing side, i.e. the	649	These methods should only be used by the producing side, i.e. the
440	code/module that eventually sends the signal. Note that it is also the	650	code/module that eventually sends the signal. Note that it is also the
441	producer side which creates the condvar in most cases, but it isn't	651	producer side which creates the condvar in most cases, but it isn't
…		…
451		661
452	Any arguments passed to the "send" call will be returned by all	662	Any arguments passed to the "send" call will be returned by all
453	future "->recv" calls.	663	future "->recv" calls.
454		664
455	Condition variables are overloaded so one can call them directly (as	665	Condition variables are overloaded so one can call them directly (as
456	a code reference). Calling them directly is the same as calling	666	if they were a code reference). Calling them directly is the same as
457	"send". Note, however, that many C-based event loops do not handle	667	calling "send".
458	overloading, so as tempting as it may be, passing a condition
459	variable instead of a callback does not work. Both the pure perl and
460	EV loops support overloading, however, as well as all functions that
461	use perl to invoke a callback (as in AnyEvent::Socket and
462	AnyEvent::DNS for example).
463		668
464	$cv->croak ($error)	669	$cv->croak ($error)
465	Similar to send, but causes all call's to "->recv" to invoke	670	Similar to send, but causes all calls to "->recv" to invoke
466	"Carp::croak" with the given error message/object/scalar.	671	"Carp::croak" with the given error message/object/scalar.
467		672
468	This can be used to signal any errors to the condition variable	673	This can be used to signal any errors to the condition variable
469	user/consumer.	674	user/consumer. Doing it this way instead of calling "croak" directly
		675	delays the error detection, but has the overwhelming advantage that
		676	it diagnoses the error at the place where the result is expected,
		677	and not deep in some event callback with no connection to the actual
		678	code causing the problem.
470		679
471	$cv->begin ([group callback])	680	$cv->begin ([group callback])
472	$cv->end	681	$cv->end
473	These two methods are EXPERIMENTAL and MIGHT CHANGE.
474
475	These two methods can be used to combine many transactions/events	682	These two methods can be used to combine many transactions/events
476	into one. For example, a function that pings many hosts in parallel	683	into one. For example, a function that pings many hosts in parallel
477	might want to use a condition variable for the whole process.	684	might want to use a condition variable for the whole process.
478		685
479	Every call to "->begin" will increment a counter, and every call to	686	Every call to "->begin" will increment a counter, and every call to
480	"->end" will decrement it. If the counter reaches 0 in "->end", the	687	"->end" will decrement it. If the counter reaches 0 in "->end", the
481	(last) callback passed to "begin" will be executed. That callback is	688	(last) callback passed to "begin" will be executed, passing the
482	*supposed* to call "->send", but that is not required. If no	689	condvar as first argument. That callback is *supposed* to call
		690	"->send", but that is not required. If no group callback was set,
483	callback was set, "send" will be called without any arguments.	691	"send" will be called without any arguments.
484		692
485	Let's clarify this with the ping example:	693	You can think of "$cv->send" giving you an OR condition (one call
		694	sends), while "$cv->begin" and "$cv->end" giving you an AND
		695	condition (all "begin" calls must be "end"'ed before the condvar
		696	sends).
		697
		698	Let's start with a simple example: you have two I/O watchers (for
		699	example, STDOUT and STDERR for a program), and you want to wait for
		700	both streams to close before activating a condvar:
486		701
487	my $cv = AnyEvent->condvar;	702	my $cv = AnyEvent->condvar;
488		703
		704	$cv->begin; # first watcher
		705	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		706	defined sysread $fh1, my $buf, 4096
		707	or $cv->end;
		708	});
		709
		710	$cv->begin; # second watcher
		711	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		712	defined sysread $fh2, my $buf, 4096
		713	or $cv->end;
		714	});
		715
		716	$cv->recv;
		717
		718	This works because for every event source (EOF on file handle),
		719	there is one call to "begin", so the condvar waits for all calls to
		720	"end" before sending.
		721
		722	The ping example mentioned above is slightly more complicated, as
		723	the there are results to be passwd back, and the number of tasks
		724	that are begun can potentially be zero:
		725
		726	my $cv = AnyEvent->condvar;
		727
489	my %result;	728	my %result;
490	$cv->begin (sub { $cv->send (\%result) });	729	$cv->begin (sub { shift->send (\%result) });
491		730
492	for my $host (@list_of_hosts) {	731	for my $host (@list_of_hosts) {
493	$cv->begin;	732	$cv->begin;
494	ping_host_then_call_callback $host, sub {	733	ping_host_then_call_callback $host, sub {
495	$result{$host} = ...;	734	$result{$host} = ...;
…		…
510	the loop, which serves two important purposes: first, it sets the	749	the loop, which serves two important purposes: first, it sets the
511	callback to be called once the counter reaches 0, and second, it	750	callback to be called once the counter reaches 0, and second, it
512	ensures that "send" is called even when "no" hosts are being pinged	751	ensures that "send" is called even when "no" hosts are being pinged
513	(the loop doesn't execute once).	752	(the loop doesn't execute once).
514		753
515	This is the general pattern when you "fan out" into multiple	754	This is the general pattern when you "fan out" into multiple (but
516	subrequests: use an outer "begin"/"end" pair to set the callback and	755	potentially zero) subrequests: use an outer "begin"/"end" pair to
517	ensure "end" is called at least once, and then, for each subrequest	756	set the callback and ensure "end" is called at least once, and then,
518	you start, call "begin" and for each subrequest you finish, call	757	for each subrequest you start, call "begin" and for each subrequest
519	"end".	758	you finish, call "end".
520		759
521	METHODS FOR CONSUMERS	760	METHODS FOR CONSUMERS
522	These methods should only be used by the consuming side, i.e. the code	761	These methods should only be used by the consuming side, i.e. the code
523	awaits the condition.	762	awaits the condition.
524		763
525	$cv->recv	764	$cv->recv
526	Wait (blocking if necessary) until the "->send" or "->croak" methods	765	Wait (blocking if necessary) until the "->send" or "->croak" methods
527	have been called on c<$cv>, while servicing other watchers normally.	766	have been called on $cv, while servicing other watchers normally.
528		767
529	You can only wait once on a condition - additional calls are valid	768	You can only wait once on a condition - additional calls are valid
530	but will return immediately.	769	but will return immediately.
531		770
532	If an error condition has been set by calling "->croak", then this	771	If an error condition has been set by calling "->croak", then this
533	function will call "croak".	772	function will call "croak".
534		773
535	In list context, all parameters passed to "send" will be returned,	774	In list context, all parameters passed to "send" will be returned,
536	in scalar context only the first one will be returned.	775	in scalar context only the first one will be returned.
537		776
		777	Note that doing a blocking wait in a callback is not supported by
		778	any event loop, that is, recursive invocation of a blocking "->recv"
		779	is not allowed, and the "recv" call will "croak" if such a condition
		780	is detected. This condition can be slightly loosened by using
		781	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		782	thread that doesn't run the event loop itself.
		783
538	Not all event models support a blocking wait - some die in that case	784	Not all event models support a blocking wait - some die in that case
539	(programs might want to do that to stay interactive), so *if you are	785	(programs might want to do that to stay interactive), so *if you are
540	using this from a module, never require a blocking wait*, but let	786	using this from a module, never require a blocking wait*. Instead,
541	the caller decide whether the call will block or not (for example,	787	let the caller decide whether the call will block or not (for
542	by coupling condition variables with some kind of request results	788	example, by coupling condition variables with some kind of request
543	and supporting callbacks so the caller knows that getting the result	789	results and supporting callbacks so the caller knows that getting
544	will not block, while still supporting blocking waits if the caller	790	the result will not block, while still supporting blocking waits if
545	so desires).	791	the caller so desires).
546		792
547	Another reason *never* to "->recv" in a module is that you cannot
548	sensibly have two "->recv"'s in parallel, as that would require
549	multiple interpreters or coroutines/threads, none of which
550	"AnyEvent" can supply.
551
552	The Coro module, however, *can* and *does* supply coroutines and, in
553	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
554	versions and also integrates coroutines into AnyEvent, making
555	blocking "->recv" calls perfectly safe as long as they are done from
556	another coroutine (one that doesn't run the event loop).
557
558	You can ensure that "-recv" never blocks by setting a callback and	793	You can ensure that "->recv" never blocks by setting a callback and
559	only calling "->recv" from within that callback (or at a later	794	only calling "->recv" from within that callback (or at a later
560	time). This will work even when the event loop does not support	795	time). This will work even when the event loop does not support
561	blocking waits otherwise.	796	blocking waits otherwise.
562		797
563	$bool = $cv->ready	798	$bool = $cv->ready
564	Returns true when the condition is "true", i.e. whether "send" or	799	Returns true when the condition is "true", i.e. whether "send" or
565	"croak" have been called.	800	"croak" have been called.
566		801
567	$cb = $cv->cb ([new callback])	802	$cb = $cv->cb ($cb->($cv))
568	This is a mutator function that returns the callback set and	803	This is a mutator function that returns the callback set and
569	optionally replaces it before doing so.	804	optionally replaces it before doing so.
570		805
571	The callback will be called when the condition becomes "true", i.e.	806	The callback will be called when the condition becomes "true", i.e.
572	when "send" or "croak" are called. Calling "recv" inside the	807	when "send" or "croak" are called, with the only argument being the
		808	condition variable itself. If the condition is already true, the
		809	callback is called immediately when it is set. Calling "recv" inside
573	callback or at any later time is guaranteed not to block.	810	the callback or at any later time is guaranteed not to block.
		811
		812	SUPPORTED EVENT LOOPS/BACKENDS
		813	The available backend classes are (every class has its own manpage):
		814
		815	Backends that are autoprobed when no other event loop can be found.
		816	EV is the preferred backend when no other event loop seems to be in
		817	use. If EV is not installed, then AnyEvent will fall back to its own
		818	pure-perl implementation, which is available everywhere as it comes
		819	with AnyEvent itself.
		820
		821	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		822	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
		823
		824	Backends that are transparently being picked up when they are used.
		825	These will be used if they are already loaded when the first watcher
		826	is created, in which case it is assumed that the application is
		827	using them. This means that AnyEvent will automatically pick the
		828	right backend when the main program loads an event module before
		829	anything starts to create watchers. Nothing special needs to be done
		830	by the main program.
		831
		832	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		833	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		834	AnyEvent::Impl::Tk based on Tk, very broken.
		835	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		836	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		837	AnyEvent::Impl::Irssi used when running within irssi.
		838	AnyEvent::Impl::IOAsync based on IO::Async.
		839	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		840	AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
		841
		842	Backends with special needs.
		843	Qt requires the Qt::Application to be instantiated first, but will
		844	otherwise be picked up automatically. As long as the main program
		845	instantiates the application before any AnyEvent watchers are
		846	created, everything should just work.
		847
		848	AnyEvent::Impl::Qt based on Qt.
		849
		850	Event loops that are indirectly supported via other backends.
		851	Some event loops can be supported via other modules:
		852
		853	There is no direct support for WxWidgets (Wx) or Prima.
		854
		855	WxWidgets has no support for watching file handles. However, you can
		856	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		857	simply polls 20 times per second, which was considered to be too
		858	horrible to even consider for AnyEvent.
		859
		860	Prima is not supported as nobody seems to be using it, but it has a
		861	POE backend, so it can be supported through POE.
		862
		863	AnyEvent knows about both Prima and Wx, however, and will try to
		864	load POE when detecting them, in the hope that POE will pick them
		865	up, in which case everything will be automatic.
574		866
575	GLOBAL VARIABLES AND FUNCTIONS	867	GLOBAL VARIABLES AND FUNCTIONS
		868	These are not normally required to use AnyEvent, but can be useful to
		869	write AnyEvent extension modules.
		870
576	$AnyEvent::MODEL	871	$AnyEvent::MODEL
577	Contains "undef" until the first watcher is being created. Then it	872	Contains "undef" until the first watcher is being created, before
		873	the backend has been autodetected.
		874
578	contains the event model that is being used, which is the name of	875	Afterwards it contains the event model that is being used, which is
579	the Perl class implementing the model. This class is usually one of	876	the name of the Perl class implementing the model. This class is
580	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	877	usually one of the "AnyEvent::Impl::xxx" modules, but can be any
581	case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*).	878	other class in the case AnyEvent has been extended at runtime (e.g.
582		879	in *rxvt-unicode* it will be "urxvt::anyevent").
583	The known classes so far are:
584
585	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
586	AnyEvent::Impl::Event based on Event, second best choice.
587	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
588	AnyEvent::Impl::Glib based on Glib, third-best choice.
589	AnyEvent::Impl::Tk based on Tk, very bad choice.
590	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
591	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
592	AnyEvent::Impl::POE based on POE, not generic enough for full support.
593
594	There is no support for WxWidgets, as WxWidgets has no support for
595	watching file handles. However, you can use WxWidgets through the
596	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
597	second, which was considered to be too horrible to even consider for
598	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
599	using it's adaptor.
600
601	AnyEvent knows about Prima and Wx and will try to use POE when
602	autodetecting them.
603		880
604	AnyEvent::detect	881	AnyEvent::detect
605	Returns $AnyEvent::MODEL, forcing autodetection of the event model	882	Returns $AnyEvent::MODEL, forcing autodetection of the event model
606	if necessary. You should only call this function right before you	883	if necessary. You should only call this function right before you
607	would have created an AnyEvent watcher anyway, that is, as late as	884	would have created an AnyEvent watcher anyway, that is, as late as
608	possible at runtime.	885	possible at runtime, and not e.g. during initialisation of your
		886	module.
		887
		888	The effect of calling this function is as if a watcher had been
		889	created (specifically, actions that happen "when the first watcher
		890	is created" happen when calling detetc as well).
		891
		892	If you need to do some initialisation before AnyEvent watchers are
		893	created, use "post_detect".
609		894
610	$guard = AnyEvent::post_detect { BLOCK }	895	$guard = AnyEvent::post_detect { BLOCK }
611	Arranges for the code block to be executed as soon as the event	896	Arranges for the code block to be executed as soon as the event
612	model is autodetected (or immediately if this has already happened).	897	model is autodetected (or immediately if that has already happened).
		898
		899	The block will be executed *after* the actual backend has been
		900	detected ($AnyEvent::MODEL is set), but *before* any watchers have
		901	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		902	other initialisations - see the sources of AnyEvent::Strict or
		903	AnyEvent::AIO to see how this is used.
		904
		905	The most common usage is to create some global watchers, without
		906	forcing event module detection too early, for example, AnyEvent::AIO
		907	creates and installs the global IO::AIO watcher in a "post_detect"
		908	block to avoid autodetecting the event module at load time.
613		909
614	If called in scalar or list context, then it creates and returns an	910	If called in scalar or list context, then it creates and returns an
615	object that automatically removes the callback again when it is	911	object that automatically removes the callback again when it is
		912	destroyed (or "undef" when the hook was immediately executed). See
616	destroyed. See Coro::BDB for a case where this is useful.	913	AnyEvent::AIO for a case where this is useful.
		914
		915	Example: Create a watcher for the IO::AIO module and store it in
		916	$WATCHER, but do so only do so after the event loop is initialised.
		917
		918	our WATCHER;
		919
		920	my $guard = AnyEvent::post_detect {
		921	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		922	};
		923
		924	# the ||= is important in case post_detect immediately runs the block,
		925	# as to not clobber the newly-created watcher. assigning both watcher and
		926	# post_detect guard to the same variable has the advantage of users being
		927	# able to just C<undef $WATCHER> if the watcher causes them grief.
		928
		929	$WATCHER ||= $guard;
617		930
618	@AnyEvent::post_detect	931	@AnyEvent::post_detect
619	If there are any code references in this array (you can "push" to it	932	If there are any code references in this array (you can "push" to it
620	before or after loading AnyEvent), then they will called directly	933	before or after loading AnyEvent), then they will be called directly
621	after the event loop has been chosen.	934	after the event loop has been chosen.
622		935
623	You should check $AnyEvent::MODEL before adding to this array,	936	You should check $AnyEvent::MODEL before adding to this array,
624	though: if it contains a true value then the event loop has already	937	though: if it is defined then the event loop has already been
625	been detected, and the array will be ignored.	938	detected, and the array will be ignored.
626		939
627	Best use "AnyEvent::post_detect { BLOCK }" instead.	940	Best use "AnyEvent::post_detect { BLOCK }" when your application
		941	allows it, as it takes care of these details.
		942
		943	This variable is mainly useful for modules that can do something
		944	useful when AnyEvent is used and thus want to know when it is
		945	initialised, but do not need to even load it by default. This array
		946	provides the means to hook into AnyEvent passively, without loading
		947	it.
		948
		949	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		950	together, you could put this into Coro (this is the actual code used
		951	by Coro to accomplish this):
		952
		953	if (defined $AnyEvent::MODEL) {
		954	# AnyEvent already initialised, so load Coro::AnyEvent
		955	require Coro::AnyEvent;
		956	} else {
		957	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		958	# as soon as it is
		959	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		960	}
		961
		962	AnyEvent::postpone { BLOCK }
		963	Arranges for the block to be executed as soon as possible, but not
		964	before the call itself returns. In practise, the block will be
		965	executed just before the event loop polls for new events, or shortly
		966	afterwards.
		967
		968	This function never returns anything (to make the "return postpone {
		969	... }" idiom more useful.
		970
		971	To understand the usefulness of this function, consider a function
		972	that asynchronously does something for you and returns some
		973	transaction object or guard to let you cancel the operation. For
		974	example, "AnyEvent::Socket::tcp_connect":
		975
		976	# start a conenction attempt unless one is active
		977	$self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		978	delete $self->{connect_guard};
		979	...
		980	};
		981
		982	Imagine that this function could instantly call the callback, for
		983	example, because it detects an obvious error such as a negative port
		984	number. Invoking the callback before the function returns causes
		985	problems however: the callback will be called and will try to delete
		986	the guard object. But since the function hasn't returned yet, there
		987	is nothing to delete. When the function eventually returns it will
		988	assign the guard object to "$self->{connect_guard}", where it will
		989	likely never be deleted, so the program thinks it is still trying to
		990	connect.
		991
		992	This is where "AnyEvent::postpone" should be used. Instead of
		993	calling the callback directly on error:
		994
		995	$cb->(undef), return # signal error to callback, BAD!
		996	if $some_error_condition;
		997
		998	It should use "postpone":
		999
		1000	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1001	if $some_error_condition;
		1002
		1003	AnyEvent::log $level, $msg[, @args]
		1004	Log the given $msg at the given $level.
		1005
		1006	If AnyEvent::Log is not loaded then this function makes a simple
		1007	test to see whether the message will be logged. If the test succeeds
		1008	it will load AnyEvent::Log and call "AnyEvent::Log::log" -
		1009	consequently, look at the AnyEvent::Log documentation for details.
		1010
		1011	If the test fails it will simply return. Right now this happens when
		1012	a numerical loglevel is used and it is larger than the level
		1013	specified via $ENV{PERL_ANYEVENT_VERBOSE}.
		1014
		1015	If you want to sprinkle loads of logging calls around your code,
		1016	consider creating a logger callback with the "AnyEvent::Log::logger"
		1017	function, which can reduce typing, codesize and can reduce the
		1018	logging overhead enourmously.
628		1019
629	WHAT TO DO IN A MODULE	1020	WHAT TO DO IN A MODULE
630	As a module author, you should "use AnyEvent" and call AnyEvent methods	1021	As a module author, you should "use AnyEvent" and call AnyEvent methods
631	freely, but you should not load a specific event module or rely on it.	1022	freely, but you should not load a specific event module or rely on it.
632		1023
…		…
640	stall the whole program, and the whole point of using events is to stay	1031	stall the whole program, and the whole point of using events is to stay
641	interactive.	1032	interactive.
642		1033
643	It is fine, however, to call "->recv" when the user of your module	1034	It is fine, however, to call "->recv" when the user of your module
644	requests it (i.e. if you create a http request object ad have a method	1035	requests it (i.e. if you create a http request object ad have a method
645	called "results" that returns the results, it should call "->recv"	1036	called "results" that returns the results, it may call "->recv" freely,
646	freely, as the user of your module knows what she is doing. always).	1037	as the user of your module knows what she is doing. Always).
647		1038
648	WHAT TO DO IN THE MAIN PROGRAM	1039	WHAT TO DO IN THE MAIN PROGRAM
649	There will always be a single main program - the only place that should	1040	There will always be a single main program - the only place that should
650	dictate which event model to use.	1041	dictate which event model to use.
651		1042
652	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	1043	If the program is not event-based, it need not do anything special, even
653	do anything special (it does not need to be event-based) and let	1044	when it depends on a module that uses an AnyEvent. If the program itself
654	AnyEvent decide which implementation to chose if some module relies on	1045	uses AnyEvent, but does not care which event loop is used, all it needs
655	it.	1046	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		1047	available loop implementation.
656		1048
657	If the main program relies on a specific event model - for example, in	1049	If the main program relies on a specific event model - for example, in
658	Gtk2 programs you have to rely on the Glib module - you should load the	1050	Gtk2 programs you have to rely on the Glib module - you should load the
659	event module before loading AnyEvent or any module that uses it:	1051	event module before loading AnyEvent or any module that uses it:
660	generally speaking, you should load it as early as possible. The reason	1052	generally speaking, you should load it as early as possible. The reason
661	is that modules might create watchers when they are loaded, and AnyEvent	1053	is that modules might create watchers when they are loaded, and AnyEvent
662	will decide on the event model to use as soon as it creates watchers,	1054	will decide on the event model to use as soon as it creates watchers,
663	and it might chose the wrong one unless you load the correct one	1055	and it might choose the wrong one unless you load the correct one
664	yourself.	1056	yourself.
665		1057
666	You can chose to use a pure-perl implementation by loading the	1058	You can chose to use a pure-perl implementation by loading the
667	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1059	"AnyEvent::Loop" module, which gives you similar behaviour everywhere,
668	everywhere, but letting AnyEvent chose the model is generally better.	1060	but letting AnyEvent chose the model is generally better.
669		1061
670	MAINLOOP EMULATION	1062	MAINLOOP EMULATION
671	Sometimes (often for short test scripts, or even standalone programs who	1063	Sometimes (often for short test scripts, or even standalone programs who
672	only want to use AnyEvent), you do not want to run a specific event	1064	only want to use AnyEvent), you do not want to run a specific event
673	loop.	1065	loop.
…		…
683	variable somewhere, waiting for it, and sending it when the program	1075	variable somewhere, waiting for it, and sending it when the program
684	should exit cleanly.	1076	should exit cleanly.
685		1077
686	OTHER MODULES	1078	OTHER MODULES
687	The following is a non-exhaustive list of additional modules that use	1079	The following is a non-exhaustive list of additional modules that use
688	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1080	AnyEvent as a client and can therefore be mixed easily with other
689	in the same program. Some of the modules come with AnyEvent, some are	1081	AnyEvent modules and other event loops in the same program. Some of the
690	available via CPAN.	1082	modules come as part of AnyEvent, the others are available via CPAN (see
		1083	<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
		1084	non-exhaustive list), and the list is heavily biased towards modules of
		1085	the AnyEvent author himself :)
691		1086
692	AnyEvent::Util	1087	AnyEvent::Util
693	Contains various utility functions that replace often-used but	1088	Contains various utility functions that replace often-used blocking
694	blocking functions such as "inet_aton" by event-/callback-based	1089	functions such as "inet_aton" with event/callback-based versions.
695	versions.
696
697	AnyEvent::Handle
698	Provide read and write buffers and manages watchers for reads and
699	writes.
700		1090
701	AnyEvent::Socket	1091	AnyEvent::Socket
702	Provides various utility functions for (internet protocol) sockets,	1092	Provides various utility functions for (internet protocol) sockets,
703	addresses and name resolution. Also functions to create non-blocking	1093	addresses and name resolution. Also functions to create non-blocking
704	tcp connections or tcp servers, with IPv6 and SRV record support and	1094	tcp connections or tcp servers, with IPv6 and SRV record support and
705	more.	1095	more.
706		1096
		1097	AnyEvent::Handle
		1098	Provide read and write buffers, manages watchers for reads and
		1099	writes, supports raw and formatted I/O, I/O queued and fully
		1100	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
		1101
707	AnyEvent::DNS	1102	AnyEvent::DNS
708	Provides rich asynchronous DNS resolver capabilities.	1103	Provides rich asynchronous DNS resolver capabilities.
709		1104
		1105	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
		1106	AnyEvent::IGS, AnyEvent::FCP
		1107	Implement event-based interfaces to the protocols of the same name
		1108	(for the curious, IGS is the International Go Server and FCP is the
		1109	Freenet Client Protocol).
		1110
		1111	AnyEvent::AIO
		1112	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1113	the toolbox of every event programmer. AnyEvent::AIO transparently
		1114	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1115	event-based file I/O, and much more.
		1116
		1117	AnyEvent::Filesys::Notify
		1118	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1119	path changes (e.g. "watch this directory for new files", "watch this
		1120	file for changes"). The AnyEvent::Filesys::Notify module promises to
		1121	do just that in a portbale fashion, supporting inotify on GNU/Linux
		1122	and some weird, without doubt broken, stuff on OS X to monitor
		1123	files. It can fall back to blocking scans at regular intervals
		1124	transparently on other platforms, so it's about as portable as it
		1125	gets.
		1126
		1127	(I haven't used it myself, but I haven't heard anybody complaining
		1128	about it yet).
		1129
		1130	AnyEvent::DBI
		1131	Executes DBI requests asynchronously in a proxy process for you,
		1132	notifying you in an event-based way when the operation is finished.
		1133
710	AnyEvent::HTTPD	1134	AnyEvent::HTTPD
711	Provides a simple web application server framework.	1135	A simple embedded webserver.
712		1136
713	AnyEvent::FastPing	1137	AnyEvent::FastPing
714	The fastest ping in the west.	1138	The fastest ping in the west.
715		1139
716	Net::IRC3
717	AnyEvent based IRC client module family.
718
719	Net::XMPP2
720	AnyEvent based XMPP (Jabber protocol) module family.
721
722	Net::FCP
723	AnyEvent-based implementation of the Freenet Client Protocol,
724	birthplace of AnyEvent.
725
726	Event::ExecFlow
727	High level API for event-based execution flow control.
728
729	Coro	1140	Coro
730	Has special support for AnyEvent via Coro::AnyEvent.	1141	Has special support for AnyEvent via Coro::AnyEvent, which allows
		1142	you to simply invert the flow control - don't call us, we will call
		1143	you:
731		1144
732	AnyEvent::AIO, IO::AIO	1145	async {
733	Truly asynchronous I/O, should be in the toolbox of every event	1146	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
734	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	1147	print "5 seconds later!\n";
735	together.
736		1148
737	AnyEvent::BDB, BDB	1149	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
738	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently	1150	my $line = <STDIN>; # works for ttys
739	fuses IO::AIO and AnyEvent together.
740		1151
741	IO::Lambda	1152	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
742	The lambda approach to I/O - don't ask, look there. Can use	1153	my ($body, $hdr) = Coro::rouse_wait;
743	AnyEvent.	1154	};
		1155
		1156	SIMPLIFIED AE API
		1157	Starting with version 5.0, AnyEvent officially supports a second, much
		1158	simpler, API that is designed to reduce the calling, typing and memory
		1159	overhead by using function call syntax and a fixed number of parameters.
		1160
		1161	See the AE manpage for details.
		1162
		1163	ERROR AND EXCEPTION HANDLING
		1164	In general, AnyEvent does not do any error handling - it relies on the
		1165	caller to do that if required. The AnyEvent::Strict module (see also the
		1166	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1167	checking of all AnyEvent methods, however, which is highly useful during
		1168	development.
		1169
		1170	As for exception handling (i.e. runtime errors and exceptions thrown
		1171	while executing a callback), this is not only highly event-loop
		1172	specific, but also not in any way wrapped by this module, as this is the
		1173	job of the main program.
		1174
		1175	The pure perl event loop simply re-throws the exception (usually within
		1176	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		1177	Glib uses "install_exception_handler" and so on.
		1178
		1179	ENVIRONMENT VARIABLES
		1180	AnyEvent supports a number of environment variables that tune the
		1181	runtime behaviour. They are usually evaluated when AnyEvent is loaded,
		1182	initialised, or a submodule that uses them is loaded. Many of them also
		1183	cause AnyEvent to load additional modules - for example,
		1184	"PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
		1185	loaded.
		1186
		1187	All the environment variables documented here start with
		1188	"PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
		1189	Other modules are encouraged (but by no means required) to use
		1190	"PERL_ANYEVENT_SUBMODULE" if they have registered the
		1191	AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
		1192	AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
		1193	should not access env variables starting with "AE_", see below).
		1194
		1195	All variables can also be set via the "AE_" prefix, that is, instead of
		1196	setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
		1197	there is a clash btween anyevent and another program that uses
		1198	"AE_something" you can set the corresponding "PERL_ANYEVENT_something"
		1199	variable to the empty string, as those variables take precedence.
		1200
		1201	When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
		1202	their "PERL_ANYEVENT_xxx" counterpart unless that variable already
		1203	exists. If taint mode is on, then AnyEvent will remove *all* environment
		1204	variables starting with "PERL_ANYEVENT_" from %ENV (or replace them with
		1205	"undef" or the empty string, if the corresaponding "AE_" variable is
		1206	set).
		1207
		1208	The exact algorithm is currently:
		1209
		1210	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		1211	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		1212	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		1213
		1214	This ensures that child processes will not see the "AE_" variables.
		1215
		1216	The following environment variables are currently known to AnyEvent:
		1217
		1218	"PERL_ANYEVENT_VERBOSE"
		1219	By default, AnyEvent will only log messages with loglevel 3
		1220	("critical") or higher (see AnyEvent::Log). You can set this
		1221	environment variable to a numerical loglevel to make AnyEvent more
		1222	(or less) talkative.
		1223
		1224	If you want to do more than just set the global logging level you
		1225	should have a look at "PERL_ANYEVENT_LOG", which allows much more
		1226	complex specifications.
		1227
		1228	When set to 0 ("off"), then no messages whatsoever will be logged
		1229	with the default logging settings.
		1230
		1231	When set to 5 or higher ("warn"), causes AnyEvent to warn about
		1232	unexpected conditions, such as not being able to load the event
		1233	model specified by "PERL_ANYEVENT_MODEL", or a guard callback
		1234	throwing an exception - this is the minimum recommended level.
		1235
		1236	When set to 7 or higher (info), cause AnyEvent to report which event
		1237	model it chooses.
		1238
		1239	When set to 8 or higher (debug), then AnyEvent will report extra
		1240	information on which optional modules it loads and how it implements
		1241	certain features.
		1242
		1243	"PERL_ANYEVENT_LOG"
		1244	Accepts rather complex logging specifications. For example, you
		1245	could log all "debug" messages of some module to stderr, warnings
		1246	and above to stderr, and errors and above to syslog, with:
		1247
		1248	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		1249
		1250	For the rather extensive details, see AnyEvent::Log.
		1251
		1252	This variable is evaluated when AnyEvent (or AnyEvent::Log) is
		1253	loaded, so will take effect even before AnyEvent has initialised
		1254	itself.
		1255
		1256	Note that specifying this environment variable causes the
		1257	AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
		1258	does not, so only using the latter saves a few hundred kB of memory
		1259	until the first message is being logged.
		1260
		1261	"PERL_ANYEVENT_STRICT"
		1262	AnyEvent does not do much argument checking by default, as thorough
		1263	argument checking is very costly. Setting this variable to a true
		1264	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1265	thoroughly check the arguments passed to most method calls. If it
		1266	finds any problems, it will croak.
		1267
		1268	In other words, enables "strict" mode.
		1269
		1270	Unlike "use strict" (or its modern cousin, "use common::sense", it
		1271	is definitely recommended to keep it off in production. Keeping
		1272	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1273	programs can be very useful, however.
		1274
		1275	"PERL_ANYEVENT_DEBUG_SHELL"
		1276	If this env variable is nonempty, then its contents will be
		1277	interpreted by "AnyEvent::Socket::parse_hostport" and
		1278	"AnyEvent::Debug::shell" (after replacing every occurance of $$ by
		1279	the process pid). The shell object is saved in
		1280	$AnyEvent::Debug::SHELL.
		1281
		1282	This happens when the first watcher is created.
		1283
		1284	For example, to bind a debug shell on a unix domain socket in
		1285	/tmp/debug<pid>.sock, you could use this:
		1286
		1287	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		1288	# connect with e.g.: socat readline /tmp/debug123.sock
		1289
		1290	Or to bind to tcp port 4545 on localhost:
		1291
		1292	PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
		1293	# connect with e.g.: telnet localhost 4545
		1294
		1295	Note that creating sockets in /tmp or on localhost is very unsafe on
		1296	multiuser systems.
		1297
		1298	"PERL_ANYEVENT_DEBUG_WRAP"
		1299	Can be set to 0, 1 or 2 and enables wrapping of all watchers for
		1300	debugging purposes. See "AnyEvent::Debug::wrap" for details.
		1301
		1302	"PERL_ANYEVENT_MODEL"
		1303	This can be used to specify the event model to be used by AnyEvent,
		1304	before auto detection and -probing kicks in.
		1305
		1306	It normally is a string consisting entirely of ASCII letters (e.g.
		1307	"EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
		1308	the resulting module name is loaded and - if the load was successful
		1309	- used as event model backend. If it fails to load then AnyEvent
		1310	will proceed with auto detection and -probing.
		1311
		1312	If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
		1313	then nothing gets prepended and the module name is used as-is (hint:
		1314	"::" at the end of a string designates a module name and quotes it
		1315	appropriately).
		1316
		1317	For example, to force the pure perl model (AnyEvent::Loop::Perl) you
		1318	could start your program like this:
		1319
		1320	PERL_ANYEVENT_MODEL=Perl perl ...
		1321
		1322	"PERL_ANYEVENT_PROTOCOLS"
		1323	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		1324	preferences for IPv4 or IPv6. The default is unspecified (and might
		1325	change, or be the result of auto probing).
		1326
		1327	Must be set to a comma-separated list of protocols or address
		1328	families, current supported: "ipv4" and "ipv6". Only protocols
		1329	mentioned will be used, and preference will be given to protocols
		1330	mentioned earlier in the list.
		1331
		1332	This variable can effectively be used for denial-of-service attacks
		1333	against local programs (e.g. when setuid), although the impact is
		1334	likely small, as the program has to handle conenction and other
		1335	failures anyways.
		1336
		1337	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		1338	IPv6, but support both and try to use both.
		1339	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		1340	resolve or contact IPv6 addresses.
		1341	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		1342	prefer IPv6 over IPv4.
		1343
		1344	"PERL_ANYEVENT_HOSTS"
		1345	This variable, if specified, overrides the /etc/hosts file used by
		1346	AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
		1347	read from that file instead.
		1348
		1349	"PERL_ANYEVENT_EDNS0"
		1350	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		1351	for DNS. This extension is generally useful to reduce DNS traffic,
		1352	especially when DNSSEC is involved, but some (broken) firewalls drop
		1353	such DNS packets, which is why it is off by default.
		1354
		1355	Setting this variable to 1 will cause AnyEvent::DNS to announce
		1356	EDNS0 in its DNS requests.
		1357
		1358	"PERL_ANYEVENT_MAX_FORKS"
		1359	The maximum number of child processes that
		1360	"AnyEvent::Util::fork_call" will create in parallel.
		1361
		1362	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1363	The default value for the "max_outstanding" parameter for the
		1364	default DNS resolver - this is the maximum number of parallel DNS
		1365	requests that are sent to the DNS server.
		1366
		1367	"PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
		1368	Perl has inherently racy signal handling (you can basically choose
		1369	between losing signals and memory corruption) - pure perl event
		1370	loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
		1371	available) therefore have to poll regularly to avoid losing signals.
		1372
		1373	Some event loops are racy, but don't poll regularly, and some event
		1374	loops are written in C but are still racy. For those event loops,
		1375	AnyEvent installs a timer that regularly wakes up the event loop.
		1376
		1377	By default, the interval for this timer is 10 seconds, but you can
		1378	override this delay with this environment variable (or by setting
		1379	the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
		1380	watchers).
		1381
		1382	Lower values increase CPU (and energy) usage, higher values can
		1383	introduce long delays when reaping children or waiting for signals.
		1384
		1385	The AnyEvent::Async module, if available, will be used to avoid this
		1386	polling (with most event loops).
		1387
		1388	"PERL_ANYEVENT_RESOLV_CONF"
		1389	The absolute path to a resolv.conf-style file to use instead of
		1390	/etc/resolv.conf (or the OS-specific configuration) in the default
		1391	resolver, or the empty string to select the default configuration.
		1392
		1393	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1394	When neither "ca_file" nor "ca_path" was specified during
		1395	AnyEvent::TLS context creation, and either of these environment
		1396	variables are nonempty, they will be used to specify CA certificate
		1397	locations instead of a system-dependent default.
		1398
		1399	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1400	When these are set to 1, then the respective modules are not loaded.
		1401	Mostly good for testing AnyEvent itself.
744		1402
745	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1403	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
746	This is an advanced topic that you do not normally need to use AnyEvent	1404	This is an advanced topic that you do not normally need to use AnyEvent
747	in a module. This section is only of use to event loop authors who want	1405	in a module. This section is only of use to event loop authors who want
748	to provide AnyEvent compatibility.	1406	to provide AnyEvent compatibility.
…		…
782		1440
783	*rxvt-unicode* also cheats a bit by not providing blocking access to	1441	*rxvt-unicode* also cheats a bit by not providing blocking access to
784	condition variables: code blocking while waiting for a condition will	1442	condition variables: code blocking while waiting for a condition will
785	"die". This still works with most modules/usages, and blocking calls	1443	"die". This still works with most modules/usages, and blocking calls
786	must not be done in an interactive application, so it makes sense.	1444	must not be done in an interactive application, so it makes sense.
787
788	ENVIRONMENT VARIABLES
789	The following environment variables are used by this module:
790
791	"PERL_ANYEVENT_VERBOSE"
792	By default, AnyEvent will be completely silent except in fatal
793	conditions. You can set this environment variable to make AnyEvent
794	more talkative.
795
796	When set to 1 or higher, causes AnyEvent to warn about unexpected
797	conditions, such as not being able to load the event model specified
798	by "PERL_ANYEVENT_MODEL".
799
800	When set to 2 or higher, cause AnyEvent to report to STDERR which
801	event model it chooses.
802
803	"PERL_ANYEVENT_MODEL"
804	This can be used to specify the event model to be used by AnyEvent,
805	before auto detection and -probing kicks in. It must be a string
806	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
807	gets prepended and the resulting module name is loaded and if the
808	load was successful, used as event model. If it fails to load
809	AnyEvent will proceed with auto detection and -probing.
810
811	This functionality might change in future versions.
812
813	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
814	could start your program like this:
815
816	PERL_ANYEVENT_MODEL=Perl perl ...
817
818	"PERL_ANYEVENT_PROTOCOLS"
819	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
820	preferences for IPv4 or IPv6. The default is unspecified (and might
821	change, or be the result of auto probing).
822
823	Must be set to a comma-separated list of protocols or address
824	families, current supported: "ipv4" and "ipv6". Only protocols
825	mentioned will be used, and preference will be given to protocols
826	mentioned earlier in the list.
827
828	This variable can effectively be used for denial-of-service attacks
829	against local programs (e.g. when setuid), although the impact is
830	likely small, as the program has to handle connection errors
831	already-
832
833	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
834	IPv6, but support both and try to use both.
835	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
836	resolve or contact IPv6 addresses.
837	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
838	prefer IPv6 over IPv4.
839
840	"PERL_ANYEVENT_EDNS0"
841	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
842	for DNS. This extension is generally useful to reduce DNS traffic,
843	but some (broken) firewalls drop such DNS packets, which is why it
844	is off by default.
845
846	Setting this variable to 1 will cause AnyEvent::DNS to announce
847	EDNS0 in its DNS requests.
848
849	"PERL_ANYEVENT_MAX_FORKS"
850	The maximum number of child processes that
851	"AnyEvent::Util::fork_call" will create in parallel.
852		1445
853	EXAMPLE PROGRAM	1446	EXAMPLE PROGRAM
854	The following program uses an I/O watcher to read data from STDIN, a	1447	The following program uses an I/O watcher to read data from STDIN, a
855	timer to display a message once per second, and a condition variable to	1448	timer to display a message once per second, and a condition variable to
856	quit the program when the user enters quit:	1449	quit the program when the user enters quit:
…		…
868	warn "read: $input\n"; # output what has been read	1461	warn "read: $input\n"; # output what has been read
869	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1462	$cv->send if $input =~ /^q/i; # quit program if /^q/i
870	},	1463	},
871	);	1464	);
872		1465
873	my $time_watcher; # can only be used once
874
875	sub new_timer {
876	$timer = AnyEvent->timer (after => 1, cb => sub {	1466	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
877	warn "timeout\n"; # print 'timeout' about every second	1467	warn "timeout\n"; # print 'timeout' at most every second
878	&new_timer; # and restart the time
879	});
880	}	1468	});
881
882	new_timer; # create first timer
883		1469
884	$cv->recv; # wait until user enters /^q/i	1470	$cv->recv; # wait until user enters /^q/i
885		1471
886	REAL-WORLD EXAMPLE	1472	REAL-WORLD EXAMPLE
887	Consider the Net::FCP module. It features (among others) the following	1473	Consider the Net::FCP module. It features (among others) the following
…		…
959		1545
960	The actual code goes further and collects all errors ("die"s,	1546	The actual code goes further and collects all errors ("die"s,
961	exceptions) that occurred during request processing. The "result" method	1547	exceptions) that occurred during request processing. The "result" method
962	detects whether an exception as thrown (it is stored inside the $txn	1548	detects whether an exception as thrown (it is stored inside the $txn
963	object) and just throws the exception, which means connection errors and	1549	object) and just throws the exception, which means connection errors and
964	other problems get reported tot he code that tries to use the result,	1550	other problems get reported to the code that tries to use the result,
965	not in a random callback.	1551	not in a random callback.
966		1552
967	All of this enables the following usage styles:	1553	All of this enables the following usage styles:
968		1554
969	1. Blocking:	1555	1. Blocking:
…		…
1014	through AnyEvent. The benchmark creates a lot of timers (with a zero	1600	through AnyEvent. The benchmark creates a lot of timers (with a zero
1015	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1601	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1016	which it is), lets them fire exactly once and destroys them again.	1602	which it is), lets them fire exactly once and destroys them again.
1017		1603
1018	Source code for this benchmark is found as eg/bench in the AnyEvent	1604	Source code for this benchmark is found as eg/bench in the AnyEvent
1019	distribution.	1605	distribution. It uses the AE interface, which makes a real difference
		1606	for the EV and Perl backends only.
1020		1607
1021	Explanation of the columns	1608	Explanation of the columns
1022	*watcher* is the number of event watchers created/destroyed. Since	1609	*watcher* is the number of event watchers created/destroyed. Since
1023	different event models feature vastly different performances, each event	1610	different event models feature vastly different performances, each event
1024	loop was given a number of watchers so that overall runtime is	1611	loop was given a number of watchers so that overall runtime is
…		…
1043	*destroy* is the time, in microseconds, that it takes to destroy a	1630	*destroy* is the time, in microseconds, that it takes to destroy a
1044	single watcher.	1631	single watcher.
1045		1632
1046	Results	1633	Results
1047	name watchers bytes create invoke destroy comment	1634	name watchers bytes create invoke destroy comment
1048	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1635	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1049	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1636	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1050	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1637	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1051	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1638	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1052	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1639	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1053	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1640	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1641	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1642	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1054	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1643	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1055	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1644	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1056	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1645	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1057	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1646	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1058		1647
1059	Discussion	1648	Discussion
1060	The benchmark does *not* measure scalability of the event loop very	1649	The benchmark does *not* measure scalability of the event loop very
1061	well. For example, a select-based event loop (such as the pure perl one)	1650	well. For example, a select-based event loop (such as the pure perl one)
1062	can never compete with an event loop that uses epoll when the number of	1651	can never compete with an event loop that uses epoll when the number of
…		…
1073	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1662	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1074	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1663	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1075	CPU cycles with POE.	1664	CPU cycles with POE.
1076		1665
1077	"EV" is the sole leader regarding speed and memory use, which are both	1666	"EV" is the sole leader regarding speed and memory use, which are both
1078	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1667	maximal/minimal, respectively. When using the AE API there is zero
		1668	overhead (when going through the AnyEvent API create is about 5-6 times
		1669	slower, with other times being equal, so still uses far less memory than
1079	far less memory than any other event loop and is still faster than Event	1670	any other event loop and is still faster than Event natively).
1080	natively.
1081		1671
1082	The pure perl implementation is hit in a few sweet spots (both the	1672	The pure perl implementation is hit in a few sweet spots (both the
1083	constant timeout and the use of a single fd hit optimisations in the	1673	constant timeout and the use of a single fd hit optimisations in the
1084	perl interpreter and the backend itself). Nevertheless this shows that	1674	perl interpreter and the backend itself). Nevertheless this shows that
1085	it adds very little overhead in itself. Like any select-based backend	1675	it adds very little overhead in itself. Like any select-based backend
…		…
1087	few of them active), of course, but this was not subject of this	1677	few of them active), of course, but this was not subject of this
1088	benchmark.	1678	benchmark.
1089		1679
1090	The "Event" module has a relatively high setup and callback invocation	1680	The "Event" module has a relatively high setup and callback invocation
1091	cost, but overall scores in on the third place.	1681	cost, but overall scores in on the third place.
		1682
		1683	"IO::Async" performs admirably well, about on par with "Event", even
		1684	when using its pure perl backend.
1092		1685
1093	"Glib"'s memory usage is quite a bit higher, but it features a faster	1686	"Glib"'s memory usage is quite a bit higher, but it features a faster
1094	callback invocation and overall ends up in the same class as "Event".	1687	callback invocation and overall ends up in the same class as "Event".
1095	However, Glib scales extremely badly, doubling the number of watchers	1688	However, Glib scales extremely badly, doubling the number of watchers
1096	increases the processing time by more than a factor of four, making it	1689	increases the processing time by more than a factor of four, making it
…		…
1128	when used without AnyEvent), but most event loops have acceptable	1721	when used without AnyEvent), but most event loops have acceptable
1129	performance with or without AnyEvent.	1722	performance with or without AnyEvent.
1130		1723
1131	* The overhead AnyEvent adds is usually much smaller than the overhead	1724	* The overhead AnyEvent adds is usually much smaller than the overhead
1132	of the actual event loop, only with extremely fast event loops such	1725	of the actual event loop, only with extremely fast event loops such
1133	as EV adds AnyEvent significant overhead.	1726	as EV does AnyEvent add significant overhead.
1134		1727
1135	* You should avoid POE like the plague if you want performance or	1728	* You should avoid POE like the plague if you want performance or
1136	reasonable memory usage.	1729	reasonable memory usage.
1137		1730
1138	BENCHMARKING THE LARGE SERVER CASE	1731	BENCHMARKING THE LARGE SERVER CASE
…		…
1152	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1745	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1153	100 (1%) are active. This mirrors the activity of large servers with	1746	100 (1%) are active. This mirrors the activity of large servers with
1154	many connections, most of which are idle at any one point in time.	1747	many connections, most of which are idle at any one point in time.
1155		1748
1156	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1749	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1157	distribution.	1750	distribution. It uses the AE interface, which makes a real difference
		1751	for the EV and Perl backends only.
1158		1752
1159	Explanation of the columns	1753	Explanation of the columns
1160	*sockets* is the number of sockets, and twice the number of "servers"	1754	*sockets* is the number of sockets, and twice the number of "servers"
1161	(as each server has a read and write socket end).	1755	(as each server has a read and write socket end).
1162		1756
…		…
1167	single "request", that is, reading the token from the pipe and	1761	single "request", that is, reading the token from the pipe and
1168	forwarding it to another server. This includes deleting the old timeout	1762	forwarding it to another server. This includes deleting the old timeout
1169	and creating a new one that moves the timeout into the future.	1763	and creating a new one that moves the timeout into the future.
1170		1764
1171	Results	1765	Results
1172	name sockets create request	1766	name sockets create request
1173	EV 20000 69.01 11.16	1767	EV 20000 62.66 7.99
1174	Perl 20000 73.32 35.87	1768	Perl 20000 68.32 32.64
1175	Event 20000 212.62 257.32	1769	IOAsync 20000 174.06 101.15 epoll
1176	Glib 20000 651.16 1896.30	1770	IOAsync 20000 174.67 610.84 poll
		1771	Event 20000 202.69 242.91
		1772	Glib 20000 557.01 1689.52
1177	POE 20000 349.67 12317.24 uses POE::Loop::Event	1773	POE 20000 341.54 12086.32 uses POE::Loop::Event
1178		1774
1179	Discussion	1775	Discussion
1180	This benchmark *does* measure scalability and overall performance of the	1776	This benchmark *does* measure scalability and overall performance of the
1181	particular event loop.	1777	particular event loop.
1182		1778
1183	EV is again fastest. Since it is using epoll on my system, the setup	1779	EV is again fastest. Since it is using epoll on my system, the setup
1184	time is relatively high, though.	1780	time is relatively high, though.
1185		1781
1186	Perl surprisingly comes second. It is much faster than the C-based event	1782	Perl surprisingly comes second. It is much faster than the C-based event
1187	loops Event and Glib.	1783	loops Event and Glib.
		1784
		1785	IO::Async performs very well when using its epoll backend, and still
		1786	quite good compared to Glib when using its pure perl backend.
1188		1787
1189	Event suffers from high setup time as well (look at its code and you	1788	Event suffers from high setup time as well (look at its code and you
1190	will understand why). Callback invocation also has a high overhead	1789	will understand why). Callback invocation also has a high overhead
1191	compared to the "$_->() for .."-style loop that the Perl event loop	1790	compared to the "$_->() for .."-style loop that the Perl event loop
1192	uses. Event uses select or poll in basically all documented	1791	uses. Event uses select or poll in basically all documented
…		…
1243		1842
1244	Summary	1843	Summary
1245	* C-based event loops perform very well with small number of watchers,	1844	* C-based event loops perform very well with small number of watchers,
1246	as the management overhead dominates.	1845	as the management overhead dominates.
1247		1846
		1847	THE IO::Lambda BENCHMARK
		1848	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1849	could be misinterpreted to make AnyEvent look bad. In fact, the
		1850	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1851	better (which shouldn't come as a surprise to anybody). As such, the
		1852	benchmark is fine, and mostly shows that the AnyEvent backend from
		1853	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1854	without the extra baggage? To explore this, I wrote the equivalent
		1855	benchmark for AnyEvent.
		1856
		1857	The benchmark itself creates an echo-server, and then, for 500 times,
		1858	connects to the echo server, sends a line, waits for the reply, and then
		1859	creates the next connection. This is a rather bad benchmark, as it
		1860	doesn't test the efficiency of the framework or much non-blocking I/O,
		1861	but it is a benchmark nevertheless.
		1862
		1863	name runtime
		1864	Lambda/select 0.330 sec
		1865	+ optimized 0.122 sec
		1866	Lambda/AnyEvent 0.327 sec
		1867	+ optimized 0.138 sec
		1868	Raw sockets/select 0.077 sec
		1869	POE/select, components 0.662 sec
		1870	POE/select, raw sockets 0.226 sec
		1871	POE/select, optimized 0.404 sec
		1872
		1873	AnyEvent/select/nb 0.085 sec
		1874	AnyEvent/EV/nb 0.068 sec
		1875	+state machine 0.134 sec
		1876
		1877	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1878	benchmarks actually make blocking connects and use 100% blocking I/O,
		1879	defeating the purpose of an event-based solution. All of the newly
		1880	written AnyEvent benchmarks use 100% non-blocking connects (using
		1881	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1882	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1883	connects generally require a lot more bookkeeping and event handling
		1884	than blocking connects (which involve a single syscall only).
		1885
		1886	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1887	offers similar expressive power as POE and IO::Lambda, using
		1888	conventional Perl syntax. This means that both the echo server and the
		1889	client are 100% non-blocking, further placing it at a disadvantage.
		1890
		1891	As you can see, the AnyEvent + EV combination even beats the
		1892	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1893	backend easily beats IO::Lambda and POE.
		1894
		1895	And even the 100% non-blocking version written using the high-level (and
		1896	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1897	higher level ("unoptimised") abstractions by a large margin, even though
		1898	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1899
		1900	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1901	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1902	part of the IO::Lambda distribution and were used without any changes.
		1903
		1904	SIGNALS
		1905	AnyEvent currently installs handlers for these signals:
		1906
		1907	SIGCHLD
		1908	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1909	emulation for event loops that do not support them natively. Also,
		1910	some event loops install a similar handler.
		1911
		1912	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1913	then AnyEvent will reset it to default, to avoid losing child exit
		1914	statuses.
		1915
		1916	SIGPIPE
		1917	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1918	"undef" when AnyEvent gets loaded.
		1919
		1920	The rationale for this is that AnyEvent users usually do not really
		1921	depend on SIGPIPE delivery (which is purely an optimisation for
		1922	shell use, or badly-written programs), but "SIGPIPE" can cause
		1923	spurious and rare program exits as a lot of people do not expect
		1924	"SIGPIPE" when writing to some random socket.
		1925
		1926	The rationale for installing a no-op handler as opposed to ignoring
		1927	it is that this way, the handler will be restored to defaults on
		1928	exec.
		1929
		1930	Feel free to install your own handler, or reset it to defaults.
		1931
		1932	RECOMMENDED/OPTIONAL MODULES
		1933	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1934	its built-in modules) are required to use it.
		1935
		1936	That does not mean that AnyEvent won't take advantage of some additional
		1937	modules if they are installed.
		1938
		1939	This section explains which additional modules will be used, and how
		1940	they affect AnyEvent's operation.
		1941
		1942	Async::Interrupt
		1943	This slightly arcane module is used to implement fast signal
		1944	handling: To my knowledge, there is no way to do completely
		1945	race-free and quick signal handling in pure perl. To ensure that
		1946	signals still get delivered, AnyEvent will start an interval timer
		1947	to wake up perl (and catch the signals) with some delay (default is
		1948	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1949
		1950	If this module is available, then it will be used to implement
		1951	signal catching, which means that signals will not be delayed, and
		1952	the event loop will not be interrupted regularly, which is more
		1953	efficient (and good for battery life on laptops).
		1954
		1955	This affects not just the pure-perl event loop, but also other event
		1956	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1957
		1958	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1959	natively, and either employ their own workarounds (POE) or use
		1960	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1961	Installing Async::Interrupt does nothing for those backends.
		1962
		1963	EV This module isn't really "optional", as it is simply one of the
		1964	backend event loops that AnyEvent can use. However, it is simply the
		1965	best event loop available in terms of features, speed and stability:
		1966	It supports the AnyEvent API optimally, implements all the watcher
		1967	types in XS, does automatic timer adjustments even when no monotonic
		1968	clock is available, can take avdantage of advanced kernel interfaces
		1969	such as "epoll" and "kqueue", and is the fastest backend *by far*.
		1970	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1971	Glib::EV).
		1972
		1973	If you only use backends that rely on another event loop (e.g.
		1974	"Tk"), then this module will do nothing for you.
		1975
		1976	Guard
		1977	The guard module, when used, will be used to implement
		1978	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1979	uses a lot less memory), but otherwise doesn't affect guard
		1980	operation much. It is purely used for performance.
		1981
		1982	JSON and JSON::XS
		1983	One of these modules is required when you want to read or write JSON
		1984	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		1985	can take advantage of the ultra-high-speed JSON::XS module when it
		1986	is installed.
		1987
		1988	Net::SSLeay
		1989	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1990	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1991	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1992
		1993	Time::HiRes
		1994	This module is part of perl since release 5.008. It will be used
		1995	when the chosen event library does not come with a timing source of
		1996	its own. The pure-perl event loop (AnyEvent::Loop) will additionally
		1997	load it to try to use a monotonic clock for timing stability.
		1998
1248	FORK	1999	FORK
1249	Most event libraries are not fork-safe. The ones who are usually are	2000	Most event libraries are not fork-safe. The ones who are usually are
1250	because they rely on inefficient but fork-safe "select" or "poll" calls.	2001	because they rely on inefficient but fork-safe "select" or "poll" calls
1251	Only EV is fully fork-aware.	2002	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		2003	epoll are usually badly thought-out hacks that are incompatible with
		2004	fork in one way or another. Only EV is fully fork-aware and ensures that
		2005	you continue event-processing in both parent and child (or both, if you
		2006	know what you are doing).
		2007
		2008	This means that, in general, you cannot fork and do event processing in
		2009	the child if the event library was initialised before the fork (which
		2010	usually happens when the first AnyEvent watcher is created, or the
		2011	library is loaded).
1252		2012
1253	If you have to fork, you must either do so *before* creating your first	2013	If you have to fork, you must either do so *before* creating your first
1254	watcher OR you must not use AnyEvent at all in the child.	2014	watcher OR you must not use AnyEvent at all in the child OR you must do
		2015	something completely out of the scope of AnyEvent.
		2016
		2017	The problem of doing event processing in the parent *and* the child is
		2018	much more complicated: even for backends that *are* fork-aware or
		2019	fork-safe, their behaviour is not usually what you want: fork clones all
		2020	watchers, that means all timers, I/O watchers etc. are active in both
		2021	parent and child, which is almost never what you want. USing "exec" to
		2022	start worker children from some kind of manage rprocess is usually
		2023	preferred, because it is much easier and cleaner, at the expense of
		2024	having to have another binary.
1255		2025
1256	SECURITY CONSIDERATIONS	2026	SECURITY CONSIDERATIONS
1257	AnyEvent can be forced to load any event model via	2027	AnyEvent can be forced to load any event model via
1258	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	2028	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1259	to execute arbitrary code or directly gain access, it can easily be used	2029	to execute arbitrary code or directly gain access, it can easily be used
…		…
1262	model than specified in the variable.	2032	model than specified in the variable.
1263		2033
1264	You can make AnyEvent completely ignore this variable by deleting it	2034	You can make AnyEvent completely ignore this variable by deleting it
1265	before the first watcher gets created, e.g. with a "BEGIN" block:	2035	before the first watcher gets created, e.g. with a "BEGIN" block:
1266		2036
1267	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	2037	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1268		2038
1269	use AnyEvent;	2039	use AnyEvent;
1270		2040
1271	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	2041	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1272	be used to probe what backend is used and gain other information (which	2042	be used to probe what backend is used and gain other information (which
1273	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).	2043	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		2044	and $ENV{PERL_ANYEVENT_STRICT}.
		2045
		2046	Note that AnyEvent will remove *all* environment variables starting with
		2047	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		2048	enabled.
		2049
		2050	BUGS
		2051	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		2052	hard to work around. If you suffer from memleaks, first upgrade to Perl
		2053	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		2054	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		2055	not as pronounced).
1274		2056
1275	SEE ALSO	2057	SEE ALSO
1276	Utility functions: AnyEvent::Util.	2058	Tutorial/Introduction: AnyEvent::Intro.
1277		2059
1278	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	2060	FAQ: AnyEvent::FAQ.
1279	Event::Lib, Qt, POE.	2061
		2062	Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
		2063	(simply logging).
		2064
		2065	Development/Debugging: AnyEvent::Strict (stricter checking),
		2066	AnyEvent::Debug (interactive shell, watcher tracing).
		2067
		2068	Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
		2069	Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK.
1280		2070
1281	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	2071	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1282	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	2072	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1283	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	2073	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		2074	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi, AnyEvent::Impl::FLTK.
1284		2075
1285	Non-blocking file handles, sockets, TCP clients and servers:	2076	Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1286	AnyEvent::Handle, AnyEvent::Socket.	2077	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1287		2078
1288	Asynchronous DNS: AnyEvent::DNS.	2079	Asynchronous DNS: AnyEvent::DNS.
1289		2080
1290	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	2081	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1291		2082
1292	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	2083	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
		2084	AnyEvent::HTTP.
1293		2085
1294	AUTHOR	2086	AUTHOR
1295	Marc Lehmann <schmorp@schmorp.de>	2087	Marc Lehmann <schmorp@schmorp.de>
1296	http://home.schmorp.de/	2088	http://home.schmorp.de/
1297		2089

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