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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, UV, Perl, Event::Lib, Irssi, rxvt-unicode,
5	loops	5	IO::Async, Qt, FLTK and POE are various supported event
		6	loops/environments.
6		7
7	SYNOPSIS	8	SYNOPSIS
8	use AnyEvent;	9	use AnyEvent;
9		10
		11	# if you prefer function calls, look at the AE manpage for
		12	# an alternative API.
		13
		14	# file handle or descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {	15	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		16
		17	# one-shot or repeating timers
		18	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		19	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
		20
		21	print AnyEvent->now; # prints current event loop time
		22	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		23
		24	# POSIX signal
		25	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		26
		27	# child process exit
		28	my $w = AnyEvent->child (pid => $pid, cb => sub {
		29	my ($pid, $status) = @_;
11	...	30	...
12	});	31	});
13		32
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	33	# called when event loop idle (if applicable)
15	...	34	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		35
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	36	my $w = AnyEvent->condvar; # stores whether a condition was flagged
19	$w->send; # wake up current and all future recv's	37	$w->send; # wake up current and all future recv's
20	$w->recv; # enters "main loop" till $condvar gets ->send	38	$w->recv; # enters "main loop" till $condvar gets ->send
		39	# use a condvar in callback mode:
		40	$w->cb (sub { $_[0]->recv });
21		41
22	INTRODUCTION/TUTORIAL	42	INTRODUCTION/TUTORIAL
23	This manpage is mainly a reference manual. If you are interested in a	43	This manpage is mainly a reference manual. If you are interested in a
24	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	44	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
25	manpage.	45	manpage.
26		46
		47	SUPPORT
		48	An FAQ document is available as AnyEvent::FAQ.
		49
		50	There also is a mailinglist for discussing all things AnyEvent, and an
		51	IRC channel, too.
		52
		53	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		54	Repository, at <http://anyevent.schmorp.de>, for more info.
		55
27	WHY YOU SHOULD USE THIS MODULE (OR NOT)	56	WHY YOU SHOULD USE THIS MODULE (OR NOT)
28	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	57	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
29	nowadays. So what is different about AnyEvent?	58	nowadays. So what is different about AnyEvent?
30		59
31	Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of	60	Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of
32	policy* and AnyEvent is *small and efficient*.	61	policy* and AnyEvent is *small and efficient*.
33		62
34	First and foremost, *AnyEvent is not an event model* itself, it only	63	First and foremost, *AnyEvent is not an event model* itself, it only
35	interfaces to whatever event model the main program happens to use in a	64	interfaces to whatever event model the main program happens to use, in a
36	pragmatic way. For event models and certain classes of immortals alike,	65	pragmatic way. For event models and certain classes of immortals alike,
37	the statement "there can only be one" is a bitter reality: In general,	66	the statement "there can only be one" is a bitter reality: In general,
38	only one event loop can be active at the same time in a process.	67	only one event loop can be active at the same time in a process.
39	AnyEvent helps hiding the differences between those event loops.	68	AnyEvent cannot change this, but it can hide the differences between
		69	those event loops.
40		70
41	The goal of AnyEvent is to offer module authors the ability to do event	71	The goal of AnyEvent is to offer module authors the ability to do event
42	programming (waiting for I/O or timer events) without subscribing to a	72	programming (waiting for I/O or timer events) without subscribing to a
43	religion, a way of living, and most importantly: without forcing your	73	religion, a way of living, and most importantly: without forcing your
44	module users into the same thing by forcing them to use the same event	74	module users into the same thing by forcing them to use the same event
45	model you use.	75	model you use.
46		76
47	For modules like POE or IO::Async (which is a total misnomer as it is	77	For modules like POE or IO::Async (which is a total misnomer as it is
48	actually doing all I/O *synchronously*...), using them in your module is	78	actually doing all I/O *synchronously*...), using them in your module is
49	like joining a cult: After you joined, you are dependent on them and you	79	like joining a cult: After you join, you are dependent on them and you
50	cannot use anything else, as it is simply incompatible to everything	80	cannot use anything else, as they are simply incompatible to everything
51	that isn't itself. What's worse, all the potential users of your module	81	that isn't them. What's worse, all the potential users of your module
52	are *also* forced to use the same event loop you use.	82	are *also* forced to use the same event loop you use.
53		83
54	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	84	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
55	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	85	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
56	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your	86	with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
57	module uses one of those, every user of your module has to use it, too.	87	uses one of those, every user of your module has to use it, too. But if
58	But if your module uses AnyEvent, it works transparently with all event	88	your module uses AnyEvent, it works transparently with all event models
59	models it supports (including stuff like POE and IO::Async, as long as	89	it supports (including stuff like IO::Async, as long as those use one of
60	those use one of the supported event loops. It is trivial to add new	90	the supported event loops. It is easy to add new event loops to
61	event loops to AnyEvent, too, so it is future-proof).	91	AnyEvent, too, so it is future-proof).
62		92
63	In addition to being free of having to use *the one and only true event	93	In addition to being free of having to use *the one and only true event
64	model*, AnyEvent also is free of bloat and policy: with POE or similar	94	model*, AnyEvent also is free of bloat and policy: with POE or similar
65	modules, you get an enormous amount of code and strict rules you have to	95	modules, you get an enormous amount of code and strict rules you have to
66	follow. AnyEvent, on the other hand, is lean and up to the point, by	96	follow. AnyEvent, on the other hand, is lean and to the point, by only
67	only offering the functionality that is necessary, in as thin as a	97	offering the functionality that is necessary, in as thin as a wrapper as
68	wrapper as technically possible.	98	technically possible.
69		99
70	Of course, AnyEvent comes with a big (and fully optional!) toolbox of	100	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
71	useful functionality, such as an asynchronous DNS resolver, 100%	101	useful functionality, such as an asynchronous DNS resolver, 100%
72	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms	102	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
73	such as Windows) and lots of real-world knowledge and workarounds for	103	such as Windows) and lots of real-world knowledge and workarounds for
…		…
76	Now, if you *do want* lots of policy (this can arguably be somewhat	106	Now, if you *do want* lots of policy (this can arguably be somewhat
77	useful) and you want to force your users to use the one and only event	107	useful) and you want to force your users to use the one and only event
78	model, you should *not* use this module.	108	model, you should *not* use this module.
79		109
80	DESCRIPTION	110	DESCRIPTION
81	AnyEvent provides an identical interface to multiple event loops. This	111	AnyEvent provides a uniform interface to various event loops. This
82	allows module authors to utilise an event loop without forcing module	112	allows module authors to use event loop functionality without forcing
83	users to use the same event loop (as only a single event loop can	113	module users to use a specific event loop implementation (since more
84	coexist peacefully at any one time).	114	than one event loop cannot coexist peacefully).
85		115
86	The interface itself is vaguely similar, but not identical to the Event	116	The interface itself is vaguely similar, but not identical to the Event
87	module.	117	module.
88		118
89	During the first call of any watcher-creation method, the module tries	119	During the first call of any watcher-creation method, the module tries
90	to detect the currently loaded event loop by probing whether one of the	120	to detect the currently loaded event loop by probing whether one of the
91	following modules is already loaded: EV, Event, Glib,	121	following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
92	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is	122	Tk, Event::Lib, Qt, POE. The first one found is used. If none are
93	used. If none are found, the module tries to load these modules	123	detected, the module tries to load the first four modules in the order
94	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	124	given; but note that if EV is not available, the pure-perl
95	always succeed) in the order given. The first one that can be	125	AnyEvent::Loop should always work, so the other two are not normally
96	successfully loaded will be used. If, after this, still none could be	126	tried.
97	found, AnyEvent will fall back to a pure-perl event loop, which is not
98	very efficient, but should work everywhere.
99		127
100	Because AnyEvent first checks for modules that are already loaded,	128	Because AnyEvent first checks for modules that are already loaded,
101	loading an event model explicitly before first using AnyEvent will	129	loading an event model explicitly before first using AnyEvent will
102	likely make that model the default. For example:	130	likely make that model the default. For example:
103		131
…		…
105	use AnyEvent;	133	use AnyEvent;
106		134
107	# .. AnyEvent will likely default to Tk	135	# .. AnyEvent will likely default to Tk
108		136
109	The *likely* means that, if any module loads another event model and	137	The *likely* means that, if any module loads another event model and
110	starts using it, all bets are off. Maybe you should tell their authors	138	starts using it, all bets are off - this case should be very rare
111	to use AnyEvent so their modules work together with others seamlessly...	139	though, as very few modules hardcode event loops without announcing this
		140	very loudly.
112		141
113	The pure-perl implementation of AnyEvent is called	142	The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
114	"AnyEvent::Impl::Perl". Like other event modules you can load it	143	Like other event modules you can load it explicitly and enjoy the high
115	explicitly and enjoy the high availability of that event loop :)	144	availability of that event loop :)
116		145
117	WATCHERS	146	WATCHERS
118	AnyEvent has the central concept of a *watcher*, which is an object that	147	AnyEvent has the central concept of a *watcher*, which is an object that
119	stores relevant data for each kind of event you are waiting for, such as	148	stores relevant data for each kind of event you are waiting for, such as
120	the callback to call, the file handle to watch, etc.	149	the callback to call, the file handle to watch, etc.
…		…
122	These watchers are normal Perl objects with normal Perl lifetime. After	151	These watchers are normal Perl objects with normal Perl lifetime. After
123	creating a watcher it will immediately "watch" for events and invoke the	152	creating a watcher it will immediately "watch" for events and invoke the
124	callback when the event occurs (of course, only when the event model is	153	callback when the event occurs (of course, only when the event model is
125	in control).	154	in control).
126		155
		156	Note that callbacks must not permanently change global variables
		157	potentially in use by the event loop (such as $_ or $[) and that
		158	callbacks must not "die". The former is good programming practice in
		159	Perl and the latter stems from the fact that exception handling differs
		160	widely between event loops.
		161
127	To disable the watcher you have to destroy it (e.g. by setting the	162	To disable a watcher you have to destroy it (e.g. by setting the
128	variable you store it in to "undef" or otherwise deleting all references	163	variable you store it in to "undef" or otherwise deleting all references
129	to it).	164	to it).
130		165
131	All watchers are created by calling a method on the "AnyEvent" class.	166	All watchers are created by calling a method on the "AnyEvent" class.
132		167
133	Many watchers either are used with "recursion" (repeating timers for	168	Many watchers either are used with "recursion" (repeating timers for
134	example), or need to refer to their watcher object in other ways.	169	example), or need to refer to their watcher object in other ways.
135		170
136	An any way to achieve that is this pattern:	171	One way to achieve that is this pattern:
137		172
138	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	173	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
139	# you can use $w here, for example to undef it	174	# you can use $w here, for example to undef it
140	undef $w;	175	undef $w;
141	});	176	});
…		…
143	Note that "my $w; $w =" combination. This is necessary because in Perl,	178	Note that "my $w; $w =" combination. This is necessary because in Perl,
144	my variables are only visible after the statement in which they are	179	my variables are only visible after the statement in which they are
145	declared.	180	declared.
146		181
147	I/O WATCHERS	182	I/O WATCHERS
		183	$w = AnyEvent->io (
		184	fh => <filehandle_or_fileno>,
		185	poll => <"r" or "w">,
		186	cb => <callback>,
		187	);
		188
148	You can create an I/O watcher by calling the "AnyEvent->io" method with	189	You can create an I/O watcher by calling the "AnyEvent->io" method with
149	the following mandatory key-value pairs as arguments:	190	the following mandatory key-value pairs as arguments:
150		191
151	"fh" the Perl *file handle* (*not* file descriptor) to watch for events.	192	"fh" is the Perl *file handle* (or a naked file descriptor) to watch for
		193	events (AnyEvent might or might not keep a reference to this file
		194	handle). Note that only file handles pointing to things for which
		195	non-blocking operation makes sense are allowed. This includes sockets,
		196	most character devices, pipes, fifos and so on, but not for example
		197	files or block devices.
		198
152	"poll" must be a string that is either "r" or "w", which creates a	199	"poll" must be a string that is either "r" or "w", which creates a
153	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	200	watcher waiting for "r"eadable or "w"ritable events, respectively.
		201
154	is the callback to invoke each time the file handle becomes ready.	202	"cb" is the callback to invoke each time the file handle becomes ready.
155		203
156	Although the callback might get passed parameters, their value and	204	Although the callback might get passed parameters, their value and
157	presence is undefined and you cannot rely on them. Portable AnyEvent	205	presence is undefined and you cannot rely on them. Portable AnyEvent
158	callbacks cannot use arguments passed to I/O watcher callbacks.	206	callbacks cannot use arguments passed to I/O watcher callbacks.
159		207
160	The I/O watcher might use the underlying file descriptor or a copy of	208	The I/O watcher might use the underlying file descriptor or a copy of
161	it. You must not close a file handle as long as any watcher is active on	209	it. You must not close a file handle as long as any watcher is active on
162	the underlying file descriptor.	210	the underlying file descriptor.
163		211
164	Some event loops issue spurious readyness notifications, so you should	212	Some event loops issue spurious readiness notifications, so you should
165	always use non-blocking calls when reading/writing from/to your file	213	always use non-blocking calls when reading/writing from/to your file
166	handles.	214	handles.
167		215
168	Example:
169
170	# wait for readability of STDIN, then read a line and disable the watcher	216	Example: wait for readability of STDIN, then read a line and disable the
		217	watcher.
		218
171	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	219	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
172	chomp (my $input = <STDIN>);	220	chomp (my $input = <STDIN>);
173	warn "read: $input\n";	221	warn "read: $input\n";
174	undef $w;	222	undef $w;
175	});	223	});
176		224
177	TIME WATCHERS	225	TIME WATCHERS
		226	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		227
		228	$w = AnyEvent->timer (
		229	after => <fractional_seconds>,
		230	interval => <fractional_seconds>,
		231	cb => <callback>,
		232	);
		233
178	You can create a time watcher by calling the "AnyEvent->timer" method	234	You can create a time watcher by calling the "AnyEvent->timer" method
179	with the following mandatory arguments:	235	with the following mandatory arguments:
180		236
181	"after" specifies after how many seconds (fractional values are	237	"after" specifies after how many seconds (fractional values are
182	supported) the callback should be invoked. "cb" is the callback to	238	supported) the callback should be invoked. "cb" is the callback to
…		…
184		240
185	Although the callback might get passed parameters, their value and	241	Although the callback might get passed parameters, their value and
186	presence is undefined and you cannot rely on them. Portable AnyEvent	242	presence is undefined and you cannot rely on them. Portable AnyEvent
187	callbacks cannot use arguments passed to time watcher callbacks.	243	callbacks cannot use arguments passed to time watcher callbacks.
188		244
189	The timer callback will be invoked at most once: if you want a repeating	245	The callback will normally be invoked only once. If you specify another
190	timer you have to create a new watcher (this is a limitation by both Tk	246	parameter, "interval", as a strictly positive number (> 0), then the
191	and Glib).	247	callback will be invoked regularly at that interval (in fractional
		248	seconds) after the first invocation. If "interval" is specified with a
		249	false value, then it is treated as if it were not specified at all.
192		250
193	Example:	251	The callback will be rescheduled before invoking the callback, but no
		252	attempt is made to avoid timer drift in most backends, so the interval
		253	is only approximate.
194		254
195	# fire an event after 7.7 seconds	255	Example: fire an event after 7.7 seconds.
		256
196	my $w = AnyEvent->timer (after => 7.7, cb => sub {	257	my $w = AnyEvent->timer (after => 7.7, cb => sub {
197	warn "timeout\n";	258	warn "timeout\n";
198	});	259	});
199		260
200	# to cancel the timer:	261	# to cancel the timer:
201	undef $w;	262	undef $w;
202		263
203	Example 2:
204
205	# fire an event after 0.5 seconds, then roughly every second	264	Example 2: fire an event after 0.5 seconds, then roughly every second.
206	my $w;
207		265
208	my $cb = sub {
209	# cancel the old timer while creating a new one
210	$w = AnyEvent->timer (after => 1, cb => $cb);	266	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		267	warn "timeout\n";
211	};	268	});
212
213	# start the "loop" by creating the first watcher
214	$w = AnyEvent->timer (after => 0.5, cb => $cb);
215		269
216	TIMING ISSUES	270	TIMING ISSUES
217	There are two ways to handle timers: based on real time (relative, "fire	271	There are two ways to handle timers: based on real time (relative, "fire
218	in 10 seconds") and based on wallclock time (absolute, "fire at 12	272	in 10 seconds") and based on wallclock time (absolute, "fire at 12
219	o'clock").	273	o'clock").
220		274
221	While most event loops expect timers to specified in a relative way,	275	While most event loops expect timers to specified in a relative way,
222	they use absolute time internally. This makes a difference when your	276	they use absolute time internally. This makes a difference when your
223	clock "jumps", for example, when ntp decides to set your clock backwards	277	clock "jumps", for example, when ntp decides to set your clock backwards
224	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is	278	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
225	supposed to fire "after" a second might actually take six years to	279	supposed to fire "after a second" might actually take six years to
226	finally fire.	280	finally fire.
227		281
228	AnyEvent cannot compensate for this. The only event loop that is	282	AnyEvent cannot compensate for this. The only event loop that is
229	conscious about these issues is EV, which offers both relative	283	conscious of these issues is EV, which offers both relative (ev_timer,
230	(ev_timer, based on true relative time) and absolute (ev_periodic, based	284	based on true relative time) and absolute (ev_periodic, based on
231	on wallclock time) timers.	285	wallclock time) timers.
232		286
233	AnyEvent always prefers relative timers, if available, matching the	287	AnyEvent always prefers relative timers, if available, matching the
234	AnyEvent API.	288	AnyEvent API.
235		289
236	AnyEvent has two additional methods that return the "current time":	290	AnyEvent has two additional methods that return the "current time":
…		…
255	*In almost all cases (in all cases if you don't care), this is the	309	*In almost all cases (in all cases if you don't care), this is the
256	function to call when you want to know the current time.*	310	function to call when you want to know the current time.*
257		311
258	This function is also often faster then "AnyEvent->time", and thus	312	This function is also often faster then "AnyEvent->time", and thus
259	the preferred method if you want some timestamp (for example,	313	the preferred method if you want some timestamp (for example,
260	AnyEvent::Handle uses this to update it's activity timeouts).	314	AnyEvent::Handle uses this to update its activity timeouts).
261		315
262	The rest of this section is only of relevance if you try to be very	316	The rest of this section is only of relevance if you try to be very
263	exact with your timing, you can skip it without bad conscience.	317	exact with your timing; you can skip it without a bad conscience.
264		318
265	For a practical example of when these times differ, consider	319	For a practical example of when these times differ, consider
266	Event::Lib and EV and the following set-up:	320	Event::Lib and EV and the following set-up:
267		321
268	The event loop is running and has just invoked one of your callback	322	The event loop is running and has just invoked one of your callbacks
269	at time=500 (assume no other callbacks delay processing). In your	323	at time=500 (assume no other callbacks delay processing). In your
270	callback, you wait a second by executing "sleep 1" (blocking the	324	callback, you wait a second by executing "sleep 1" (blocking the
271	process for a second) and then (at time=501) you create a relative	325	process for a second) and then (at time=501) you create a relative
272	timer that fires after three seconds.	326	timer that fires after three seconds.
273		327
…		…
293	In either case, if you care (and in most cases, you don't), then you	347	In either case, if you care (and in most cases, you don't), then you
294	can get whatever behaviour you want with any event loop, by taking	348	can get whatever behaviour you want with any event loop, by taking
295	the difference between "AnyEvent->time" and "AnyEvent->now" into	349	the difference between "AnyEvent->time" and "AnyEvent->now" into
296	account.	350	account.
297		351
		352	AnyEvent->now_update
		353	Some event loops (such as EV or AnyEvent::Loop) cache the current
		354	time for each loop iteration (see the discussion of AnyEvent->now,
		355	above).
		356
		357	When a callback runs for a long time (or when the process sleeps),
		358	then this "current" time will differ substantially from the real
		359	time, which might affect timers and time-outs.
		360
		361	When this is the case, you can call this method, which will update
		362	the event loop's idea of "current time".
		363
		364	A typical example would be a script in a web server (e.g.
		365	"mod_perl") - when mod_perl executes the script, then the event loop
		366	will have the wrong idea about the "current time" (being potentially
		367	far in the past, when the script ran the last time). In that case
		368	you should arrange a call to "AnyEvent->now_update" each time the
		369	web server process wakes up again (e.g. at the start of your script,
		370	or in a handler).
		371
		372	Note that updating the time *might* cause some events to be handled.
		373
298	SIGNAL WATCHERS	374	SIGNAL WATCHERS
		375	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		376
299	You can watch for signals using a signal watcher, "signal" is the signal	377	You can watch for signals using a signal watcher, "signal" is the signal
300	*name* without any "SIG" prefix, "cb" is the Perl callback to be invoked	378	*name* in uppercase and without any "SIG" prefix, "cb" is the Perl
301	whenever a signal occurs.	379	callback to be invoked whenever a signal occurs.
302		380
303	Although the callback might get passed parameters, their value and	381	Although the callback might get passed parameters, their value and
304	presence is undefined and you cannot rely on them. Portable AnyEvent	382	presence is undefined and you cannot rely on them. Portable AnyEvent
305	callbacks cannot use arguments passed to signal watcher callbacks.	383	callbacks cannot use arguments passed to signal watcher callbacks.
306		384
…		…
308	invocation, and callback invocation will be synchronous. Synchronous	386	invocation, and callback invocation will be synchronous. Synchronous
309	means that it might take a while until the signal gets handled by the	387	means that it might take a while until the signal gets handled by the
310	process, but it is guaranteed not to interrupt any other callbacks.	388	process, but it is guaranteed not to interrupt any other callbacks.
311		389
312	The main advantage of using these watchers is that you can share a	390	The main advantage of using these watchers is that you can share a
313	signal between multiple watchers.	391	signal between multiple watchers, and AnyEvent will ensure that signals
		392	will not interrupt your program at bad times.
314		393
315	This watcher might use %SIG, so programs overwriting those signals	394	This watcher might use %SIG (depending on the event loop used), so
316	directly will likely not work correctly.	395	programs overwriting those signals directly will likely not work
		396	correctly.
317		397
318	Example: exit on SIGINT	398	Example: exit on SIGINT
319		399
320	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	400	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
321		401
		402	Restart Behaviour
		403	While restart behaviour is up to the event loop implementation, most
		404	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		405	pure perl implementation).
		406
		407	Safe/Unsafe Signals
		408	Perl signals can be either "safe" (synchronous to opcode handling) or
		409	"unsafe" (asynchronous) - the former might delay signal delivery
		410	indefinitely, the latter might corrupt your memory.
		411
		412	AnyEvent signal handlers are, in addition, synchronous to the event
		413	loop, i.e. they will not interrupt your running perl program but will
		414	only be called as part of the normal event handling (just like timer,
		415	I/O etc. callbacks, too).
		416
		417	Signal Races, Delays and Workarounds
		418	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		419	callbacks to signals in a generic way, which is a pity, as you cannot do
		420	race-free signal handling in perl, requiring C libraries for this.
		421	AnyEvent will try to do its best, which means in some cases, signals
		422	will be delayed. The maximum time a signal might be delayed is 10
		423	seconds by default, but can be overriden via
		424	$ENV{PERL_ANYEVENT_MAX_SIGNAL_LATENCY} or $AnyEvent::MAX_SIGNAL_LATENCY
		425	- see the "ENVIRONMENT VARIABLES" section for details.
		426
		427	All these problems can be avoided by installing the optional
		428	Async::Interrupt module, which works with most event loops. It will not
		429	work with inherently broken event loops such as Event or Event::Lib (and
		430	not with POE currently). For those, you just have to suffer the delays.
		431
322	CHILD PROCESS WATCHERS	432	CHILD PROCESS WATCHERS
		433	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		434
323	You can also watch on a child process exit and catch its exit status.	435	You can also watch for a child process exit and catch its exit status.
324		436
325	The child process is specified by the "pid" argument (if set to 0, it	437	The child process is specified by the "pid" argument (on some backends,
326	watches for any child process exit). The watcher will trigger as often	438	using 0 watches for any child process exit, on others this will croak).
327	as status change for the child are received. This works by installing a	439	The watcher will be triggered only when the child process has finished
328	signal handler for "SIGCHLD". The callback will be called with the pid	440	and an exit status is available, not on any trace events
329	and exit status (as returned by waitpid), so unlike other watcher types,	441	(stopped/continued).
330	you *can* rely on child watcher callback arguments.	442
		443	The callback will be called with the pid and exit status (as returned by
		444	waitpid), so unlike other watcher types, you *can* rely on child watcher
		445	callback arguments.
		446
		447	This watcher type works by installing a signal handler for "SIGCHLD",
		448	and since it cannot be shared, nothing else should use SIGCHLD or reap
		449	random child processes (waiting for specific child processes, e.g.
		450	inside "system", is just fine).
331		451
332	There is a slight catch to child watchers, however: you usually start	452	There is a slight catch to child watchers, however: you usually start
333	them *after* the child process was created, and this means the process	453	them *after* the child process was created, and this means the process
334	could have exited already (and no SIGCHLD will be sent anymore).	454	could have exited already (and no SIGCHLD will be sent anymore).
335		455
336	Not all event models handle this correctly (POE doesn't), but even for	456	Not all event models handle this correctly (neither POE nor IO::Async
		457	do, see their AnyEvent::Impl manpages for details), but even for event
337	event models that *do* handle this correctly, they usually need to be	458	models that *do* handle this correctly, they usually need to be loaded
338	loaded before the process exits (i.e. before you fork in the first	459	before the process exits (i.e. before you fork in the first place).
339	place).	460	AnyEvent's pure perl event loop handles all cases correctly regardless
		461	of when you start the watcher.
340		462
341	This means you cannot create a child watcher as the very first thing in	463	This means you cannot create a child watcher as the very first thing in
342	an AnyEvent program, you *have* to create at least one watcher before	464	an AnyEvent program, you *have* to create at least one watcher before
343	you "fork" the child (alternatively, you can call "AnyEvent::detect").	465	you "fork" the child (alternatively, you can call "AnyEvent::detect").
344		466
		467	As most event loops do not support waiting for child events, they will
		468	be emulated by AnyEvent in most cases, in which case the latency and
		469	race problems mentioned in the description of signal watchers apply.
		470
345	Example: fork a process and wait for it	471	Example: fork a process and wait for it
346		472
347	my $done = AnyEvent->condvar;	473	my $done = AnyEvent->condvar;
348		474
		475	# this forks and immediately calls exit in the child. this
		476	# normally has all sorts of bad consequences for your parent,
		477	# so take this as an example only. always fork and exec,
		478	# or call POSIX::_exit, in real code.
349	my $pid = fork or exit 5;	479	my $pid = fork or exit 5;
350		480
351	my $w = AnyEvent->child (	481	my $w = AnyEvent->child (
352	pid => $pid,	482	pid => $pid,
353	cb => sub {	483	cb => sub {
354	my ($pid, $status) = @_;	484	my ($pid, $status) = @_;
355	warn "pid $pid exited with status $status";	485	warn "pid $pid exited with status $status";
356	$done->send;	486	$done->send;
357	},	487	},
358	);	488	);
359		489
360	# do something else, then wait for process exit	490	# do something else, then wait for process exit
361	$done->recv;	491	$done->recv;
362		492
		493	IDLE WATCHERS
		494	$w = AnyEvent->idle (cb => <callback>);
		495
		496	This will repeatedly invoke the callback after the process becomes idle,
		497	until either the watcher is destroyed or new events have been detected.
		498
		499	Idle watchers are useful when there is a need to do something, but it is
		500	not so important (or wise) to do it instantly. The callback will be
		501	invoked only when there is "nothing better to do", which is usually
		502	defined as "all outstanding events have been handled and no new events
		503	have been detected". That means that idle watchers ideally get invoked
		504	when the event loop has just polled for new events but none have been
		505	detected. Instead of blocking to wait for more events, the idle watchers
		506	will be invoked.
		507
		508	Unfortunately, most event loops do not really support idle watchers
		509	(only EV, Event and Glib do it in a usable fashion) - for the rest,
		510	AnyEvent will simply call the callback "from time to time".
		511
		512	Example: read lines from STDIN, but only process them when the program
		513	is otherwise idle:
		514
		515	my @lines; # read data
		516	my $idle_w;
		517	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		518	push @lines, scalar <STDIN>;
		519
		520	# start an idle watcher, if not already done
		521	$idle_w ||= AnyEvent->idle (cb => sub {
		522	# handle only one line, when there are lines left
		523	if (my $line = shift @lines) {
		524	print "handled when idle: $line";
		525	} else {
		526	# otherwise disable the idle watcher again
		527	undef $idle_w;
		528	}
		529	});
		530	});
		531
363	CONDITION VARIABLES	532	CONDITION VARIABLES
		533	$cv = AnyEvent->condvar;
		534
		535	$cv->send (<list>);
		536	my @res = $cv->recv;
		537
364	If you are familiar with some event loops you will know that all of them	538	If you are familiar with some event loops you will know that all of them
365	require you to run some blocking "loop", "run" or similar function that	539	require you to run some blocking "loop", "run" or similar function that
366	will actively watch for new events and call your callbacks.	540	will actively watch for new events and call your callbacks.
367		541
368	AnyEvent is different, it expects somebody else to run the event loop	542	AnyEvent is slightly different: it expects somebody else to run the
369	and will only block when necessary (usually when told by the user).	543	event loop and will only block when necessary (usually when told by the
		544	user).
370		545
371	The instrument to do that is called a "condition variable", so called	546	The tool to do that is called a "condition variable", so called because
372	because they represent a condition that must become true.	547	they represent a condition that must become true.
		548
		549	Now is probably a good time to look at the examples further below.
373		550
374	Condition variables can be created by calling the "AnyEvent->condvar"	551	Condition variables can be created by calling the "AnyEvent->condvar"
375	method, usually without arguments. The only argument pair allowed is	552	method, usually without arguments. The only argument pair allowed is
376	"cb", which specifies a callback to be called when the condition	553	"cb", which specifies a callback to be called when the condition
377	variable becomes true.	554	variable becomes true, with the condition variable as the first argument
		555	(but not the results).
378		556
379	After creation, the condition variable is "false" until it becomes	557	After creation, the condition variable is "false" until it becomes
380	"true" by calling the "send" method (or calling the condition variable	558	"true" by calling the "send" method (or calling the condition variable
381	as if it were a callback, read about the caveats in the description for	559	as if it were a callback, read about the caveats in the description for
382	the "->send" method).	560	the "->send" method).
383		561
384	Condition variables are similar to callbacks, except that you can	562	Since condition variables are the most complex part of the AnyEvent API,
385	optionally wait for them. They can also be called merge points - points	563	here are some different mental models of what they are - pick the ones
386	in time where multiple outstanding events have been processed. And yet	564	you can connect to:
387	another way to call them is transactions - each condition variable can	565
388	be used to represent a transaction, which finishes at some point and	566	* Condition variables are like callbacks - you can call them (and pass
389	delivers a result.	567	them instead of callbacks). Unlike callbacks however, you can also
		568	wait for them to be called.
		569
		570	* Condition variables are signals - one side can emit or send them,
		571	the other side can wait for them, or install a handler that is
		572	called when the signal fires.
		573
		574	* Condition variables are like "Merge Points" - points in your program
		575	where you merge multiple independent results/control flows into one.
		576
		577	* Condition variables represent a transaction - functions that start
		578	some kind of transaction can return them, leaving the caller the
		579	choice between waiting in a blocking fashion, or setting a callback.
		580
		581	* Condition variables represent future values, or promises to deliver
		582	some result, long before the result is available.
390		583
391	Condition variables are very useful to signal that something has	584	Condition variables are very useful to signal that something has
392	finished, for example, if you write a module that does asynchronous http	585	finished, for example, if you write a module that does asynchronous http
393	requests, then a condition variable would be the ideal candidate to	586	requests, then a condition variable would be the ideal candidate to
394	signal the availability of results. The user can either act when the	587	signal the availability of results. The user can either act when the
…		…
407		600
408	Condition variables are represented by hash refs in perl, and the keys	601	Condition variables are represented by hash refs in perl, and the keys
409	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy	602	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
410	(it is often useful to build your own transaction class on top of	603	(it is often useful to build your own transaction class on top of
411	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call	604	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
412	it's "new" method in your own "new" method.	605	its "new" method in your own "new" method.
413		606
414	There are two "sides" to a condition variable - the "producer side"	607	There are two "sides" to a condition variable - the "producer side"
415	which eventually calls "-> send", and the "consumer side", which waits	608	which eventually calls "-> send", and the "consumer side", which waits
416	for the send to occur.	609	for the send to occur.
417		610
418	Example: wait for a timer.	611	Example: wait for a timer.
419		612
420	# wait till the result is ready	613	# condition: "wait till the timer is fired"
421	my $result_ready = AnyEvent->condvar;	614	my $timer_fired = AnyEvent->condvar;
422		615
423	# do something such as adding a timer	616	# create the timer - we could wait for, say
424	# or socket watcher the calls $result_ready->send	617	# a handle becomign ready, or even an
425	# when the "result" is ready.	618	# AnyEvent::HTTP request to finish, but
426	# in this case, we simply use a timer:	619	# in this case, we simply use a timer:
427	my $w = AnyEvent->timer (	620	my $w = AnyEvent->timer (
428	after => 1,	621	after => 1,
429	cb => sub { $result_ready->send },	622	cb => sub { $timer_fired->send },
430	);	623	);
431		624
432	# this "blocks" (while handling events) till the callback	625	# this "blocks" (while handling events) till the callback
433	# calls send	626	# calls ->send
434	$result_ready->recv;	627	$timer_fired->recv;
435		628
436	Example: wait for a timer, but take advantage of the fact that condition	629	Example: wait for a timer, but take advantage of the fact that condition
437	variables are also code references.	630	variables are also callable directly.
438		631
439	my $done = AnyEvent->condvar;	632	my $done = AnyEvent->condvar;
440	my $delay = AnyEvent->timer (after => 5, cb => $done);	633	my $delay = AnyEvent->timer (after => 5, cb => $done);
441	$done->recv;	634	$done->recv;
		635
		636	Example: Imagine an API that returns a condvar and doesn't support
		637	callbacks. This is how you make a synchronous call, for example from the
		638	main program:
		639
		640	use AnyEvent::CouchDB;
		641
		642	...
		643
		644	my @info = $couchdb->info->recv;
		645
		646	And this is how you would just set a callback to be called whenever the
		647	results are available:
		648
		649	$couchdb->info->cb (sub {
		650	my @info = $_[0]->recv;
		651	});
442		652
443	METHODS FOR PRODUCERS	653	METHODS FOR PRODUCERS
444	These methods should only be used by the producing side, i.e. the	654	These methods should only be used by the producing side, i.e. the
445	code/module that eventually sends the signal. Note that it is also the	655	code/module that eventually sends the signal. Note that it is also the
446	producer side which creates the condvar in most cases, but it isn't	656	producer side which creates the condvar in most cases, but it isn't
…		…
456		666
457	Any arguments passed to the "send" call will be returned by all	667	Any arguments passed to the "send" call will be returned by all
458	future "->recv" calls.	668	future "->recv" calls.
459		669
460	Condition variables are overloaded so one can call them directly (as	670	Condition variables are overloaded so one can call them directly (as
461	a code reference). Calling them directly is the same as calling	671	if they were a code reference). Calling them directly is the same as
462	"send". Note, however, that many C-based event loops do not handle	672	calling "send".
463	overloading, so as tempting as it may be, passing a condition
464	variable instead of a callback does not work. Both the pure perl and
465	EV loops support overloading, however, as well as all functions that
466	use perl to invoke a callback (as in AnyEvent::Socket and
467	AnyEvent::DNS for example).
468		673
469	$cv->croak ($error)	674	$cv->croak ($error)
470	Similar to send, but causes all call's to "->recv" to invoke	675	Similar to send, but causes all calls to "->recv" to invoke
471	"Carp::croak" with the given error message/object/scalar.	676	"Carp::croak" with the given error message/object/scalar.
472		677
473	This can be used to signal any errors to the condition variable	678	This can be used to signal any errors to the condition variable
474	user/consumer.	679	user/consumer. Doing it this way instead of calling "croak" directly
		680	delays the error detection, but has the overwhelming advantage that
		681	it diagnoses the error at the place where the result is expected,
		682	and not deep in some event callback with no connection to the actual
		683	code causing the problem.
475		684
476	$cv->begin ([group callback])	685	$cv->begin ([group callback])
477	$cv->end	686	$cv->end
478	These two methods are EXPERIMENTAL and MIGHT CHANGE.
479
480	These two methods can be used to combine many transactions/events	687	These two methods can be used to combine many transactions/events
481	into one. For example, a function that pings many hosts in parallel	688	into one. For example, a function that pings many hosts in parallel
482	might want to use a condition variable for the whole process.	689	might want to use a condition variable for the whole process.
483		690
484	Every call to "->begin" will increment a counter, and every call to	691	Every call to "->begin" will increment a counter, and every call to
485	"->end" will decrement it. If the counter reaches 0 in "->end", the	692	"->end" will decrement it. If the counter reaches 0 in "->end", the
486	(last) callback passed to "begin" will be executed. That callback is	693	(last) callback passed to "begin" will be executed, passing the
487	*supposed* to call "->send", but that is not required. If no	694	condvar as first argument. That callback is *supposed* to call
		695	"->send", but that is not required. If no group callback was set,
488	callback was set, "send" will be called without any arguments.	696	"send" will be called without any arguments.
489		697
490	Let's clarify this with the ping example:	698	You can think of "$cv->send" giving you an OR condition (one call
		699	sends), while "$cv->begin" and "$cv->end" giving you an AND
		700	condition (all "begin" calls must be "end"'ed before the condvar
		701	sends).
		702
		703	Let's start with a simple example: you have two I/O watchers (for
		704	example, STDOUT and STDERR for a program), and you want to wait for
		705	both streams to close before activating a condvar:
491		706
492	my $cv = AnyEvent->condvar;	707	my $cv = AnyEvent->condvar;
493		708
		709	$cv->begin; # first watcher
		710	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		711	defined sysread $fh1, my $buf, 4096
		712	or $cv->end;
		713	});
		714
		715	$cv->begin; # second watcher
		716	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		717	defined sysread $fh2, my $buf, 4096
		718	or $cv->end;
		719	});
		720
		721	$cv->recv;
		722
		723	This works because for every event source (EOF on file handle),
		724	there is one call to "begin", so the condvar waits for all calls to
		725	"end" before sending.
		726
		727	The ping example mentioned above is slightly more complicated, as
		728	the there are results to be passed back, and the number of tasks
		729	that are begun can potentially be zero:
		730
		731	my $cv = AnyEvent->condvar;
		732
494	my %result;	733	my %result;
495	$cv->begin (sub { $cv->send (\%result) });	734	$cv->begin (sub { shift->send (\%result) });
496		735
497	for my $host (@list_of_hosts) {	736	for my $host (@list_of_hosts) {
498	$cv->begin;	737	$cv->begin;
499	ping_host_then_call_callback $host, sub {	738	ping_host_then_call_callback $host, sub {
500	$result{$host} = ...;	739	$result{$host} = ...;
…		…
502	};	741	};
503	}	742	}
504		743
505	$cv->end;	744	$cv->end;
506		745
		746	...
		747
		748	my $results = $cv->recv;
		749
507	This code fragment supposedly pings a number of hosts and calls	750	This code fragment supposedly pings a number of hosts and calls
508	"send" after results for all then have have been gathered - in any	751	"send" after results for all then have have been gathered - in any
509	order. To achieve this, the code issues a call to "begin" when it	752	order. To achieve this, the code issues a call to "begin" when it
510	starts each ping request and calls "end" when it has received some	753	starts each ping request and calls "end" when it has received some
511	result for it. Since "begin" and "end" only maintain a counter, the	754	result for it. Since "begin" and "end" only maintain a counter, the
…		…
515	the loop, which serves two important purposes: first, it sets the	758	the loop, which serves two important purposes: first, it sets the
516	callback to be called once the counter reaches 0, and second, it	759	callback to be called once the counter reaches 0, and second, it
517	ensures that "send" is called even when "no" hosts are being pinged	760	ensures that "send" is called even when "no" hosts are being pinged
518	(the loop doesn't execute once).	761	(the loop doesn't execute once).
519		762
520	This is the general pattern when you "fan out" into multiple	763	This is the general pattern when you "fan out" into multiple (but
521	subrequests: use an outer "begin"/"end" pair to set the callback and	764	potentially zero) subrequests: use an outer "begin"/"end" pair to
522	ensure "end" is called at least once, and then, for each subrequest	765	set the callback and ensure "end" is called at least once, and then,
523	you start, call "begin" and for each subrequest you finish, call	766	for each subrequest you start, call "begin" and for each subrequest
524	"end".	767	you finish, call "end".
525		768
526	METHODS FOR CONSUMERS	769	METHODS FOR CONSUMERS
527	These methods should only be used by the consuming side, i.e. the code	770	These methods should only be used by the consuming side, i.e. the code
528	awaits the condition.	771	awaits the condition.
529		772
530	$cv->recv	773	$cv->recv
531	Wait (blocking if necessary) until the "->send" or "->croak" methods	774	Wait (blocking if necessary) until the "->send" or "->croak" methods
532	have been called on c<$cv>, while servicing other watchers normally.	775	have been called on $cv, while servicing other watchers normally.
533		776
534	You can only wait once on a condition - additional calls are valid	777	You can only wait once on a condition - additional calls are valid
535	but will return immediately.	778	but will return immediately.
536		779
537	If an error condition has been set by calling "->croak", then this	780	If an error condition has been set by calling "->croak", then this
538	function will call "croak".	781	function will call "croak".
539		782
540	In list context, all parameters passed to "send" will be returned,	783	In list context, all parameters passed to "send" will be returned,
541	in scalar context only the first one will be returned.	784	in scalar context only the first one will be returned.
542		785
		786	Note that doing a blocking wait in a callback is not supported by
		787	any event loop, that is, recursive invocation of a blocking "->recv"
		788	is not allowed and the "recv" call will "croak" if such a condition
		789	is detected. This requirement can be dropped by relying on
		790	Coro::AnyEvent , which allows you to do a blocking "->recv" from any
		791	thread that doesn't run the event loop itself. Coro::AnyEvent is
		792	loaded automatically when Coro is used with AnyEvent, so code does
		793	not need to do anything special to take advantage of that: any code
		794	that would normally block your program because it calls "recv", be
		795	executed in an "async" thread instead without blocking other
		796	threads.
		797
543	Not all event models support a blocking wait - some die in that case	798	Not all event models support a blocking wait - some die in that case
544	(programs might want to do that to stay interactive), so *if you are	799	(programs might want to do that to stay interactive), so *if you are
545	using this from a module, never require a blocking wait*, but let	800	using this from a module, never require a blocking wait*. Instead,
546	the caller decide whether the call will block or not (for example,	801	let the caller decide whether the call will block or not (for
547	by coupling condition variables with some kind of request results	802	example, by coupling condition variables with some kind of request
548	and supporting callbacks so the caller knows that getting the result	803	results and supporting callbacks so the caller knows that getting
549	will not block, while still supporting blocking waits if the caller	804	the result will not block, while still supporting blocking waits if
550	so desires).	805	the caller so desires).
551		806
552	Another reason *never* to "->recv" in a module is that you cannot
553	sensibly have two "->recv"'s in parallel, as that would require
554	multiple interpreters or coroutines/threads, none of which
555	"AnyEvent" can supply.
556
557	The Coro module, however, *can* and *does* supply coroutines and, in
558	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
559	versions and also integrates coroutines into AnyEvent, making
560	blocking "->recv" calls perfectly safe as long as they are done from
561	another coroutine (one that doesn't run the event loop).
562
563	You can ensure that "-recv" never blocks by setting a callback and	807	You can ensure that "->recv" never blocks by setting a callback and
564	only calling "->recv" from within that callback (or at a later	808	only calling "->recv" from within that callback (or at a later
565	time). This will work even when the event loop does not support	809	time). This will work even when the event loop does not support
566	blocking waits otherwise.	810	blocking waits otherwise.
567		811
568	$bool = $cv->ready	812	$bool = $cv->ready
569	Returns true when the condition is "true", i.e. whether "send" or	813	Returns true when the condition is "true", i.e. whether "send" or
570	"croak" have been called.	814	"croak" have been called.
571		815
572	$cb = $cv->cb ([new callback])	816	$cb = $cv->cb ($cb->($cv))
573	This is a mutator function that returns the callback set and	817	This is a mutator function that returns the callback set and
574	optionally replaces it before doing so.	818	optionally replaces it before doing so.
575		819
576	The callback will be called when the condition becomes "true", i.e.	820	The callback will be called when the condition becomes "true", i.e.
577	when "send" or "croak" are called, with the only argument being the	821	when "send" or "croak" are called, with the only argument being the
578	condition variable itself. Calling "recv" inside the callback or at	822	condition variable itself. If the condition is already true, the
		823	callback is called immediately when it is set. Calling "recv" inside
579	any later time is guaranteed not to block.	824	the callback or at any later time is guaranteed not to block.
		825
		826	SUPPORTED EVENT LOOPS/BACKENDS
		827	The available backend classes are (every class has its own manpage):
		828
		829	Backends that are autoprobed when no other event loop can be found.
		830	EV is the preferred backend when no other event loop seems to be in
		831	use. If EV is not installed, then AnyEvent will fall back to its own
		832	pure-perl implementation, which is available everywhere as it comes
		833	with AnyEvent itself.
		834
		835	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		836	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
		837
		838	Backends that are transparently being picked up when they are used.
		839	These will be used if they are already loaded when the first watcher
		840	is created, in which case it is assumed that the application is
		841	using them. This means that AnyEvent will automatically pick the
		842	right backend when the main program loads an event module before
		843	anything starts to create watchers. Nothing special needs to be done
		844	by the main program.
		845
		846	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		847	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		848	AnyEvent::Impl::Tk based on Tk, very broken.
		849	AnyEvent::Impl::UV based on UV, innovated square wheels.
		850	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		851	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		852	AnyEvent::Impl::Irssi used when running within irssi.
		853	AnyEvent::Impl::IOAsync based on IO::Async.
		854	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		855	AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
		856
		857	Backends with special needs.
		858	Qt requires the Qt::Application to be instantiated first, but will
		859	otherwise be picked up automatically. As long as the main program
		860	instantiates the application before any AnyEvent watchers are
		861	created, everything should just work.
		862
		863	AnyEvent::Impl::Qt based on Qt.
		864
		865	Event loops that are indirectly supported via other backends.
		866	Some event loops can be supported via other modules:
		867
		868	There is no direct support for WxWidgets (Wx) or Prima.
		869
		870	WxWidgets has no support for watching file handles. However, you can
		871	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		872	simply polls 20 times per second, which was considered to be too
		873	horrible to even consider for AnyEvent.
		874
		875	Prima is not supported as nobody seems to be using it, but it has a
		876	POE backend, so it can be supported through POE.
		877
		878	AnyEvent knows about both Prima and Wx, however, and will try to
		879	load POE when detecting them, in the hope that POE will pick them
		880	up, in which case everything will be automatic.
580		881
581	GLOBAL VARIABLES AND FUNCTIONS	882	GLOBAL VARIABLES AND FUNCTIONS
		883	These are not normally required to use AnyEvent, but can be useful to
		884	write AnyEvent extension modules.
		885
582	$AnyEvent::MODEL	886	$AnyEvent::MODEL
583	Contains "undef" until the first watcher is being created. Then it	887	Contains "undef" until the first watcher is being created, before
		888	the backend has been autodetected.
		889
584	contains the event model that is being used, which is the name of	890	Afterwards it contains the event model that is being used, which is
585	the Perl class implementing the model. This class is usually one of	891	the name of the Perl class implementing the model. This class is
586	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	892	usually one of the "AnyEvent::Impl::xxx" modules, but can be any
587	case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*).	893	other class in the case AnyEvent has been extended at runtime (e.g.
588		894	in *rxvt-unicode* it will be "urxvt::anyevent").
589	The known classes so far are:
590
591	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
592	AnyEvent::Impl::Event based on Event, second best choice.
593	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
594	AnyEvent::Impl::Glib based on Glib, third-best choice.
595	AnyEvent::Impl::Tk based on Tk, very bad choice.
596	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
597	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
598	AnyEvent::Impl::POE based on POE, not generic enough for full support.
599
600	There is no support for WxWidgets, as WxWidgets has no support for
601	watching file handles. However, you can use WxWidgets through the
602	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
603	second, which was considered to be too horrible to even consider for
604	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
605	using it's adaptor.
606
607	AnyEvent knows about Prima and Wx and will try to use POE when
608	autodetecting them.
609		895
610	AnyEvent::detect	896	AnyEvent::detect
611	Returns $AnyEvent::MODEL, forcing autodetection of the event model	897	Returns $AnyEvent::MODEL, forcing autodetection of the event model
612	if necessary. You should only call this function right before you	898	if necessary. You should only call this function right before you
613	would have created an AnyEvent watcher anyway, that is, as late as	899	would have created an AnyEvent watcher anyway, that is, as late as
614	possible at runtime.	900	possible at runtime, and not e.g. during initialisation of your
		901	module.
		902
		903	The effect of calling this function is as if a watcher had been
		904	created (specifically, actions that happen "when the first watcher
		905	is created" happen when calling detetc as well).
		906
		907	If you need to do some initialisation before AnyEvent watchers are
		908	created, use "post_detect".
615		909
616	$guard = AnyEvent::post_detect { BLOCK }	910	$guard = AnyEvent::post_detect { BLOCK }
617	Arranges for the code block to be executed as soon as the event	911	Arranges for the code block to be executed as soon as the event
618	model is autodetected (or immediately if this has already happened).	912	model is autodetected (or immediately if that has already happened).
		913
		914	The block will be executed *after* the actual backend has been
		915	detected ($AnyEvent::MODEL is set), but *before* any watchers have
		916	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		917	other initialisations - see the sources of AnyEvent::Strict or
		918	AnyEvent::AIO to see how this is used.
		919
		920	The most common usage is to create some global watchers, without
		921	forcing event module detection too early, for example, AnyEvent::AIO
		922	creates and installs the global IO::AIO watcher in a "post_detect"
		923	block to avoid autodetecting the event module at load time.
619		924
620	If called in scalar or list context, then it creates and returns an	925	If called in scalar or list context, then it creates and returns an
621	object that automatically removes the callback again when it is	926	object that automatically removes the callback again when it is
		927	destroyed (or "undef" when the hook was immediately executed). See
622	destroyed. See Coro::BDB for a case where this is useful.	928	AnyEvent::AIO for a case where this is useful.
		929
		930	Example: Create a watcher for the IO::AIO module and store it in
		931	$WATCHER, but do so only do so after the event loop is initialised.
		932
		933	our WATCHER;
		934
		935	my $guard = AnyEvent::post_detect {
		936	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		937	};
		938
		939	# the ||= is important in case post_detect immediately runs the block,
		940	# as to not clobber the newly-created watcher. assigning both watcher and
		941	# post_detect guard to the same variable has the advantage of users being
		942	# able to just C<undef $WATCHER> if the watcher causes them grief.
		943
		944	$WATCHER ||= $guard;
623		945
624	@AnyEvent::post_detect	946	@AnyEvent::post_detect
625	If there are any code references in this array (you can "push" to it	947	If there are any code references in this array (you can "push" to it
626	before or after loading AnyEvent), then they will called directly	948	before or after loading AnyEvent), then they will be called directly
627	after the event loop has been chosen.	949	after the event loop has been chosen.
628		950
629	You should check $AnyEvent::MODEL before adding to this array,	951	You should check $AnyEvent::MODEL before adding to this array,
630	though: if it contains a true value then the event loop has already	952	though: if it is defined then the event loop has already been
631	been detected, and the array will be ignored.	953	detected, and the array will be ignored.
632		954
633	Best use "AnyEvent::post_detect { BLOCK }" instead.	955	Best use "AnyEvent::post_detect { BLOCK }" when your application
		956	allows it, as it takes care of these details.
		957
		958	This variable is mainly useful for modules that can do something
		959	useful when AnyEvent is used and thus want to know when it is
		960	initialised, but do not need to even load it by default. This array
		961	provides the means to hook into AnyEvent passively, without loading
		962	it.
		963
		964	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		965	together, you could put this into Coro (this is the actual code used
		966	by Coro to accomplish this):
		967
		968	if (defined $AnyEvent::MODEL) {
		969	# AnyEvent already initialised, so load Coro::AnyEvent
		970	require Coro::AnyEvent;
		971	} else {
		972	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		973	# as soon as it is
		974	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		975	}
		976
		977	AnyEvent::postpone { BLOCK }
		978	Arranges for the block to be executed as soon as possible, but not
		979	before the call itself returns. In practise, the block will be
		980	executed just before the event loop polls for new events, or shortly
		981	afterwards.
		982
		983	This function never returns anything (to make the "return postpone {
		984	... }" idiom more useful.
		985
		986	To understand the usefulness of this function, consider a function
		987	that asynchronously does something for you and returns some
		988	transaction object or guard to let you cancel the operation. For
		989	example, "AnyEvent::Socket::tcp_connect":
		990
		991	# start a connection attempt unless one is active
		992	$self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		993	delete $self->{connect_guard};
		994	...
		995	};
		996
		997	Imagine that this function could instantly call the callback, for
		998	example, because it detects an obvious error such as a negative port
		999	number. Invoking the callback before the function returns causes
		1000	problems however: the callback will be called and will try to delete
		1001	the guard object. But since the function hasn't returned yet, there
		1002	is nothing to delete. When the function eventually returns it will
		1003	assign the guard object to "$self->{connect_guard}", where it will
		1004	likely never be deleted, so the program thinks it is still trying to
		1005	connect.
		1006
		1007	This is where "AnyEvent::postpone" should be used. Instead of
		1008	calling the callback directly on error:
		1009
		1010	$cb->(undef), return # signal error to callback, BAD!
		1011	if $some_error_condition;
		1012
		1013	It should use "postpone":
		1014
		1015	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1016	if $some_error_condition;
		1017
		1018	AnyEvent::log $level, $msg[, @args]
		1019	Log the given $msg at the given $level.
		1020
		1021	If AnyEvent::Log is not loaded then this function makes a simple
		1022	test to see whether the message will be logged. If the test succeeds
		1023	it will load AnyEvent::Log and call "AnyEvent::Log::log" -
		1024	consequently, look at the AnyEvent::Log documentation for details.
		1025
		1026	If the test fails it will simply return. Right now this happens when
		1027	a numerical loglevel is used and it is larger than the level
		1028	specified via $ENV{PERL_ANYEVENT_VERBOSE}.
		1029
		1030	If you want to sprinkle loads of logging calls around your code,
		1031	consider creating a logger callback with the "AnyEvent::Log::logger"
		1032	function, which can reduce typing, codesize and can reduce the
		1033	logging overhead enourmously.
		1034
		1035	AnyEvent::fh_block $filehandle
		1036	AnyEvent::fh_unblock $filehandle
		1037	Sets blocking or non-blocking behaviour for the given filehandle.
634		1038
635	WHAT TO DO IN A MODULE	1039	WHAT TO DO IN A MODULE
636	As a module author, you should "use AnyEvent" and call AnyEvent methods	1040	As a module author, you should "use AnyEvent" and call AnyEvent methods
637	freely, but you should not load a specific event module or rely on it.	1041	freely, but you should not load a specific event module or rely on it.
638		1042
…		…
646	stall the whole program, and the whole point of using events is to stay	1050	stall the whole program, and the whole point of using events is to stay
647	interactive.	1051	interactive.
648		1052
649	It is fine, however, to call "->recv" when the user of your module	1053	It is fine, however, to call "->recv" when the user of your module
650	requests it (i.e. if you create a http request object ad have a method	1054	requests it (i.e. if you create a http request object ad have a method
651	called "results" that returns the results, it should call "->recv"	1055	called "results" that returns the results, it may call "->recv" freely,
652	freely, as the user of your module knows what she is doing. always).	1056	as the user of your module knows what she is doing. Always).
653		1057
654	WHAT TO DO IN THE MAIN PROGRAM	1058	WHAT TO DO IN THE MAIN PROGRAM
655	There will always be a single main program - the only place that should	1059	There will always be a single main program - the only place that should
656	dictate which event model to use.	1060	dictate which event model to use.
657		1061
658	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	1062	If the program is not event-based, it need not do anything special, even
659	do anything special (it does not need to be event-based) and let	1063	when it depends on a module that uses an AnyEvent. If the program itself
660	AnyEvent decide which implementation to chose if some module relies on	1064	uses AnyEvent, but does not care which event loop is used, all it needs
661	it.	1065	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		1066	available loop implementation.
662		1067
663	If the main program relies on a specific event model - for example, in	1068	If the main program relies on a specific event model - for example, in
664	Gtk2 programs you have to rely on the Glib module - you should load the	1069	Gtk2 programs you have to rely on the Glib module - you should load the
665	event module before loading AnyEvent or any module that uses it:	1070	event module before loading AnyEvent or any module that uses it:
666	generally speaking, you should load it as early as possible. The reason	1071	generally speaking, you should load it as early as possible. The reason
667	is that modules might create watchers when they are loaded, and AnyEvent	1072	is that modules might create watchers when they are loaded, and AnyEvent
668	will decide on the event model to use as soon as it creates watchers,	1073	will decide on the event model to use as soon as it creates watchers,
669	and it might chose the wrong one unless you load the correct one	1074	and it might choose the wrong one unless you load the correct one
670	yourself.	1075	yourself.
671		1076
672	You can chose to use a pure-perl implementation by loading the	1077	You can chose to use a pure-perl implementation by loading the
673	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1078	"AnyEvent::Loop" module, which gives you similar behaviour everywhere,
674	everywhere, but letting AnyEvent chose the model is generally better.	1079	but letting AnyEvent chose the model is generally better.
675		1080
676	MAINLOOP EMULATION	1081	MAINLOOP EMULATION
677	Sometimes (often for short test scripts, or even standalone programs who	1082	Sometimes (often for short test scripts, or even standalone programs who
678	only want to use AnyEvent), you do not want to run a specific event	1083	only want to use AnyEvent), you do not want to run a specific event
679	loop.	1084	loop.
…		…
689	variable somewhere, waiting for it, and sending it when the program	1094	variable somewhere, waiting for it, and sending it when the program
690	should exit cleanly.	1095	should exit cleanly.
691		1096
692	OTHER MODULES	1097	OTHER MODULES
693	The following is a non-exhaustive list of additional modules that use	1098	The following is a non-exhaustive list of additional modules that use
694	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1099	AnyEvent as a client and can therefore be mixed easily with other
695	in the same program. Some of the modules come with AnyEvent, some are	1100	AnyEvent modules and other event loops in the same program. Some of the
696	available via CPAN.	1101	modules come as part of AnyEvent, the others are available via CPAN (see
		1102	<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
		1103	non-exhaustive list), and the list is heavily biased towards modules of
		1104	the AnyEvent author himself :)
697		1105
698	AnyEvent::Util	1106	AnyEvent::Util (part of the AnyEvent distribution)
699	Contains various utility functions that replace often-used but	1107	Contains various utility functions that replace often-used blocking
700	blocking functions such as "inet_aton" by event-/callback-based	1108	functions such as "inet_aton" with event/callback-based versions.
701	versions.
702		1109
703	AnyEvent::Handle	1110	AnyEvent::Socket (part of the AnyEvent distribution)
704	Provide read and write buffers and manages watchers for reads and
705	writes.
706
707	AnyEvent::Socket
708	Provides various utility functions for (internet protocol) sockets,	1111	Provides various utility functions for (internet protocol) sockets,
709	addresses and name resolution. Also functions to create non-blocking	1112	addresses and name resolution. Also functions to create non-blocking
710	tcp connections or tcp servers, with IPv6 and SRV record support and	1113	tcp connections or tcp servers, with IPv6 and SRV record support and
711	more.	1114	more.
712		1115
713	AnyEvent::DNS	1116	AnyEvent::Handle (part of the AnyEvent distribution)
		1117	Provide read and write buffers, manages watchers for reads and
		1118	writes, supports raw and formatted I/O, I/O queued and fully
		1119	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
		1120
		1121	AnyEvent::DNS (part of the AnyEvent distribution)
714	Provides rich asynchronous DNS resolver capabilities.	1122	Provides rich asynchronous DNS resolver capabilities.
715		1123
		1124	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
		1125	AnyEvent::IGS, AnyEvent::FCP
		1126	Implement event-based interfaces to the protocols of the same name
		1127	(for the curious, IGS is the International Go Server and FCP is the
		1128	Freenet Client Protocol).
		1129
		1130	AnyEvent::AIO (part of the AnyEvent distribution)
		1131	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1132	the toolbox of every event programmer. AnyEvent::AIO transparently
		1133	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1134	event-based file I/O, and much more.
		1135
		1136	AnyEvent::Fork, AnyEvent::Fork::RPC, AnyEvent::Fork::Pool,
		1137	AnyEvent::Fork::Remote
		1138	These let you safely fork new subprocesses, either locally or
		1139	remotely (e.g.v ia ssh), using some RPC protocol or not, without the
		1140	limitations normally imposed by fork (AnyEvent works fine for
		1141	example). Dynamically-resized worker pools are obviously included as
		1142	well.
		1143
		1144	And they are quite tiny and fast as well - "abusing" AnyEvent::Fork
		1145	just to exec external programs can easily beat using "fork" and
		1146	"exec" (or even "system") in most programs.
		1147
		1148	AnyEvent::Filesys::Notify
		1149	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1150	path changes (e.g. "watch this directory for new files", "watch this
		1151	file for changes"). The AnyEvent::Filesys::Notify module promises to
		1152	do just that in a portbale fashion, supporting inotify on GNU/Linux
		1153	and some weird, without doubt broken, stuff on OS X to monitor
		1154	files. It can fall back to blocking scans at regular intervals
		1155	transparently on other platforms, so it's about as portable as it
		1156	gets.
		1157
		1158	(I haven't used it myself, but it seems the biggest problem with it
		1159	is it quite bad performance).
		1160
716	AnyEvent::HTTPD	1161	AnyEvent::DBI
717	Provides a simple web application server framework.	1162	Executes DBI requests asynchronously in a proxy process for you,
		1163	notifying you in an event-based way when the operation is finished.
718		1164
719	AnyEvent::FastPing	1165	AnyEvent::FastPing
720	The fastest ping in the west.	1166	The fastest ping in the west.
721		1167
722	Net::IRC3
723	AnyEvent based IRC client module family.
724
725	Net::XMPP2
726	AnyEvent based XMPP (Jabber protocol) module family.
727
728	Net::FCP
729	AnyEvent-based implementation of the Freenet Client Protocol,
730	birthplace of AnyEvent.
731
732	Event::ExecFlow
733	High level API for event-based execution flow control.
734
735	Coro	1168	Coro
736	Has special support for AnyEvent via Coro::AnyEvent.	1169	Has special support for AnyEvent via Coro::AnyEvent, which allows
		1170	you to simply invert the flow control - don't call us, we will call
		1171	you:
737		1172
738	AnyEvent::AIO, IO::AIO	1173	async {
739	Truly asynchronous I/O, should be in the toolbox of every event	1174	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
740	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	1175	print "5 seconds later!\n";
741	together.
742		1176
743	AnyEvent::BDB, BDB	1177	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
744	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently	1178	my $line = <STDIN>; # works for ttys
745	fuses IO::AIO and AnyEvent together.
746		1179
747	IO::Lambda	1180	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
748	The lambda approach to I/O - don't ask, look there. Can use	1181	my ($body, $hdr) = Coro::rouse_wait;
		1182	};
		1183
		1184	SIMPLIFIED AE API
		1185	Starting with version 5.0, AnyEvent officially supports a second, much
		1186	simpler, API that is designed to reduce the calling, typing and memory
		1187	overhead by using function call syntax and a fixed number of parameters.
		1188
		1189	See the AE manpage for details.
		1190
		1191	ERROR AND EXCEPTION HANDLING
		1192	In general, AnyEvent does not do any error handling - it relies on the
		1193	caller to do that if required. The AnyEvent::Strict module (see also the
		1194	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1195	checking of all AnyEvent methods, however, which is highly useful during
		1196	development.
		1197
		1198	As for exception handling (i.e. runtime errors and exceptions thrown
		1199	while executing a callback), this is not only highly event-loop
		1200	specific, but also not in any way wrapped by this module, as this is the
		1201	job of the main program.
		1202
		1203	The pure perl event loop simply re-throws the exception (usually within
		1204	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		1205	Glib uses "install_exception_handler" and so on.
		1206
		1207	ENVIRONMENT VARIABLES
		1208	AnyEvent supports a number of environment variables that tune the
		1209	runtime behaviour. They are usually evaluated when AnyEvent is loaded,
		1210	initialised, or a submodule that uses them is loaded. Many of them also
		1211	cause AnyEvent to load additional modules - for example,
		1212	"PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
		1213	loaded.
		1214
		1215	All the environment variables documented here start with
		1216	"PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
		1217	Other modules are encouraged (but by no means required) to use
		1218	"PERL_ANYEVENT_SUBMODULE" if they have registered the
		1219	AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
		1220	AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
		1221	should not access env variables starting with "AE_", see below).
		1222
		1223	All variables can also be set via the "AE_" prefix, that is, instead of
		1224	setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
		1225	there is a clash btween anyevent and another program that uses
		1226	"AE_something" you can set the corresponding "PERL_ANYEVENT_something"
		1227	variable to the empty string, as those variables take precedence.
		1228
		1229	When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
		1230	their "PERL_ANYEVENT_xxx" counterpart unless that variable already
		1231	exists. If taint mode is on, then AnyEvent will remove *all* environment
		1232	variables starting with "PERL_ANYEVENT_" from %ENV (or replace them with
		1233	"undef" or the empty string, if the corresaponding "AE_" variable is
		1234	set).
		1235
		1236	The exact algorithm is currently:
		1237
		1238	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		1239	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		1240	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		1241
		1242	This ensures that child processes will not see the "AE_" variables.
		1243
		1244	The following environment variables are currently known to AnyEvent:
		1245
		1246	"PERL_ANYEVENT_VERBOSE"
		1247	By default, AnyEvent will log messages with loglevel 4 ("error") or
		1248	higher (see AnyEvent::Log). You can set this environment variable to
		1249	a numerical loglevel to make AnyEvent more (or less) talkative.
		1250
		1251	If you want to do more than just set the global logging level you
		1252	should have a look at "PERL_ANYEVENT_LOG", which allows much more
		1253	complex specifications.
		1254
		1255	When set to 0 ("off"), then no messages whatsoever will be logged
		1256	with everything else at defaults.
		1257
		1258	When set to 5 or higher ("warn"), AnyEvent warns about unexpected
		1259	conditions, such as not being able to load the event model specified
		1260	by "PERL_ANYEVENT_MODEL", or a guard callback throwing an exception
		1261	- this is the minimum recommended level for use during development.
		1262
		1263	When set to 7 or higher (info), AnyEvent reports which event model
		1264	it chooses.
		1265
		1266	When set to 8 or higher (debug), then AnyEvent will report extra
		1267	information on which optional modules it loads and how it implements
		1268	certain features.
		1269
		1270	"PERL_ANYEVENT_LOG"
		1271	Accepts rather complex logging specifications. For example, you
		1272	could log all "debug" messages of some module to stderr, warnings
		1273	and above to stderr, and errors and above to syslog, with:
		1274
		1275	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		1276
		1277	For the rather extensive details, see AnyEvent::Log.
		1278
		1279	This variable is evaluated when AnyEvent (or AnyEvent::Log) is
		1280	loaded, so will take effect even before AnyEvent has initialised
		1281	itself.
		1282
		1283	Note that specifying this environment variable causes the
		1284	AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
		1285	does not, so only using the latter saves a few hundred kB of memory
		1286	unless a module explicitly needs the extra features of
749	AnyEvent.	1287	AnyEvent::Log.
		1288
		1289	"PERL_ANYEVENT_STRICT"
		1290	AnyEvent does not do much argument checking by default, as thorough
		1291	argument checking is very costly. Setting this variable to a true
		1292	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1293	thoroughly check the arguments passed to most method calls. If it
		1294	finds any problems, it will croak.
		1295
		1296	In other words, enables "strict" mode.
		1297
		1298	Unlike "use strict" (or its modern cousin, "use common::sense", it
		1299	is definitely recommended to keep it off in production. Keeping
		1300	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1301	programs can be very useful, however.
		1302
		1303	"PERL_ANYEVENT_DEBUG_SHELL"
		1304	If this env variable is nonempty, then its contents will be
		1305	interpreted by "AnyEvent::Socket::parse_hostport" and
		1306	"AnyEvent::Debug::shell" (after replacing every occurance of $$ by
		1307	the process pid). The shell object is saved in
		1308	$AnyEvent::Debug::SHELL.
		1309
		1310	This happens when the first watcher is created.
		1311
		1312	For example, to bind a debug shell on a unix domain socket in
		1313	/tmp/debug<pid>.sock, you could use this:
		1314
		1315	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		1316	# connect with e.g.: socat readline /tmp/debug123.sock
		1317
		1318	Or to bind to tcp port 4545 on localhost:
		1319
		1320	PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
		1321	# connect with e.g.: telnet localhost 4545
		1322
		1323	Note that creating sockets in /tmp or on localhost is very unsafe on
		1324	multiuser systems.
		1325
		1326	"PERL_ANYEVENT_DEBUG_WRAP"
		1327	Can be set to 0, 1 or 2 and enables wrapping of all watchers for
		1328	debugging purposes. See "AnyEvent::Debug::wrap" for details.
		1329
		1330	"PERL_ANYEVENT_MODEL"
		1331	This can be used to specify the event model to be used by AnyEvent,
		1332	before auto detection and -probing kicks in.
		1333
		1334	It normally is a string consisting entirely of ASCII letters (e.g.
		1335	"EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
		1336	the resulting module name is loaded and - if the load was successful
		1337	- used as event model backend. If it fails to load then AnyEvent
		1338	will proceed with auto detection and -probing.
		1339
		1340	If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
		1341	then nothing gets prepended and the module name is used as-is (hint:
		1342	"::" at the end of a string designates a module name and quotes it
		1343	appropriately).
		1344
		1345	For example, to force the pure perl model (AnyEvent::Loop::Perl) you
		1346	could start your program like this:
		1347
		1348	PERL_ANYEVENT_MODEL=Perl perl ...
		1349
		1350	"PERL_ANYEVENT_IO_MODEL"
		1351	The current file I/O model - see AnyEvent::IO for more info.
		1352
		1353	At the moment, only "Perl" (small, pure-perl, synchronous) and
		1354	"IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
		1355	if AnyEvent::AIO can be loaded, otherwise it is "Perl".
		1356
		1357	"PERL_ANYEVENT_PROTOCOLS"
		1358	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		1359	preferences for IPv4 or IPv6. The default is unspecified (and might
		1360	change, or be the result of auto probing).
		1361
		1362	Must be set to a comma-separated list of protocols or address
		1363	families, current supported: "ipv4" and "ipv6". Only protocols
		1364	mentioned will be used, and preference will be given to protocols
		1365	mentioned earlier in the list.
		1366
		1367	This variable can effectively be used for denial-of-service attacks
		1368	against local programs (e.g. when setuid), although the impact is
		1369	likely small, as the program has to handle connection and other
		1370	failures anyways.
		1371
		1372	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		1373	IPv6, but support both and try to use both.
		1374	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		1375	resolve or contact IPv6 addresses.
		1376	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		1377	prefer IPv6 over IPv4.
		1378
		1379	"PERL_ANYEVENT_HOSTS"
		1380	This variable, if specified, overrides the /etc/hosts file used by
		1381	AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
		1382	read from that file instead.
		1383
		1384	"PERL_ANYEVENT_EDNS0"
		1385	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		1386	for DNS. This extension is generally useful to reduce DNS traffic,
		1387	especially when DNSSEC is involved, but some (broken) firewalls drop
		1388	such DNS packets, which is why it is off by default.
		1389
		1390	Setting this variable to 1 will cause AnyEvent::DNS to announce
		1391	EDNS0 in its DNS requests.
		1392
		1393	"PERL_ANYEVENT_MAX_FORKS"
		1394	The maximum number of child processes that
		1395	"AnyEvent::Util::fork_call" will create in parallel.
		1396
		1397	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1398	The default value for the "max_outstanding" parameter for the
		1399	default DNS resolver - this is the maximum number of parallel DNS
		1400	requests that are sent to the DNS server.
		1401
		1402	"PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
		1403	Perl has inherently racy signal handling (you can basically choose
		1404	between losing signals and memory corruption) - pure perl event
		1405	loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
		1406	available) therefore have to poll regularly to avoid losing signals.
		1407
		1408	Some event loops are racy, but don't poll regularly, and some event
		1409	loops are written in C but are still racy. For those event loops,
		1410	AnyEvent installs a timer that regularly wakes up the event loop.
		1411
		1412	By default, the interval for this timer is 10 seconds, but you can
		1413	override this delay with this environment variable (or by setting
		1414	the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
		1415	watchers).
		1416
		1417	Lower values increase CPU (and energy) usage, higher values can
		1418	introduce long delays when reaping children or waiting for signals.
		1419
		1420	The AnyEvent::Async module, if available, will be used to avoid this
		1421	polling (with most event loops).
		1422
		1423	"PERL_ANYEVENT_RESOLV_CONF"
		1424	The absolute path to a resolv.conf-style file to use instead of
		1425	/etc/resolv.conf (or the OS-specific configuration) in the default
		1426	resolver, or the empty string to select the default configuration.
		1427
		1428	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1429	When neither "ca_file" nor "ca_path" was specified during
		1430	AnyEvent::TLS context creation, and either of these environment
		1431	variables are nonempty, they will be used to specify CA certificate
		1432	locations instead of a system-dependent default.
		1433
		1434	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1435	When these are set to 1, then the respective modules are not loaded.
		1436	Mostly good for testing AnyEvent itself.
750		1437
751	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1438	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
752	This is an advanced topic that you do not normally need to use AnyEvent	1439	This is an advanced topic that you do not normally need to use AnyEvent
753	in a module. This section is only of use to event loop authors who want	1440	in a module. This section is only of use to event loop authors who want
754	to provide AnyEvent compatibility.	1441	to provide AnyEvent compatibility.
…		…
788		1475
789	*rxvt-unicode* also cheats a bit by not providing blocking access to	1476	*rxvt-unicode* also cheats a bit by not providing blocking access to
790	condition variables: code blocking while waiting for a condition will	1477	condition variables: code blocking while waiting for a condition will
791	"die". This still works with most modules/usages, and blocking calls	1478	"die". This still works with most modules/usages, and blocking calls
792	must not be done in an interactive application, so it makes sense.	1479	must not be done in an interactive application, so it makes sense.
793
794	ENVIRONMENT VARIABLES
795	The following environment variables are used by this module:
796
797	"PERL_ANYEVENT_VERBOSE"
798	By default, AnyEvent will be completely silent except in fatal
799	conditions. You can set this environment variable to make AnyEvent
800	more talkative.
801
802	When set to 1 or higher, causes AnyEvent to warn about unexpected
803	conditions, such as not being able to load the event model specified
804	by "PERL_ANYEVENT_MODEL".
805
806	When set to 2 or higher, cause AnyEvent to report to STDERR which
807	event model it chooses.
808
809	"PERL_ANYEVENT_MODEL"
810	This can be used to specify the event model to be used by AnyEvent,
811	before auto detection and -probing kicks in. It must be a string
812	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
813	gets prepended and the resulting module name is loaded and if the
814	load was successful, used as event model. If it fails to load
815	AnyEvent will proceed with auto detection and -probing.
816
817	This functionality might change in future versions.
818
819	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
820	could start your program like this:
821
822	PERL_ANYEVENT_MODEL=Perl perl ...
823
824	"PERL_ANYEVENT_PROTOCOLS"
825	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
826	preferences for IPv4 or IPv6. The default is unspecified (and might
827	change, or be the result of auto probing).
828
829	Must be set to a comma-separated list of protocols or address
830	families, current supported: "ipv4" and "ipv6". Only protocols
831	mentioned will be used, and preference will be given to protocols
832	mentioned earlier in the list.
833
834	This variable can effectively be used for denial-of-service attacks
835	against local programs (e.g. when setuid), although the impact is
836	likely small, as the program has to handle connection errors
837	already-
838
839	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
840	IPv6, but support both and try to use both.
841	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
842	resolve or contact IPv6 addresses.
843	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
844	prefer IPv6 over IPv4.
845
846	"PERL_ANYEVENT_EDNS0"
847	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
848	for DNS. This extension is generally useful to reduce DNS traffic,
849	but some (broken) firewalls drop such DNS packets, which is why it
850	is off by default.
851
852	Setting this variable to 1 will cause AnyEvent::DNS to announce
853	EDNS0 in its DNS requests.
854
855	"PERL_ANYEVENT_MAX_FORKS"
856	The maximum number of child processes that
857	"AnyEvent::Util::fork_call" will create in parallel.
858		1480
859	EXAMPLE PROGRAM	1481	EXAMPLE PROGRAM
860	The following program uses an I/O watcher to read data from STDIN, a	1482	The following program uses an I/O watcher to read data from STDIN, a
861	timer to display a message once per second, and a condition variable to	1483	timer to display a message once per second, and a condition variable to
862	quit the program when the user enters quit:	1484	quit the program when the user enters quit:
…		…
874	warn "read: $input\n"; # output what has been read	1496	warn "read: $input\n"; # output what has been read
875	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1497	$cv->send if $input =~ /^q/i; # quit program if /^q/i
876	},	1498	},
877	);	1499	);
878		1500
879	my $time_watcher; # can only be used once
880
881	sub new_timer {
882	$timer = AnyEvent->timer (after => 1, cb => sub {	1501	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
883	warn "timeout\n"; # print 'timeout' about every second	1502	warn "timeout\n"; # print 'timeout' at most every second
884	&new_timer; # and restart the time
885	});
886	}	1503	});
887
888	new_timer; # create first timer
889		1504
890	$cv->recv; # wait until user enters /^q/i	1505	$cv->recv; # wait until user enters /^q/i
891		1506
892	REAL-WORLD EXAMPLE	1507	REAL-WORLD EXAMPLE
893	Consider the Net::FCP module. It features (among others) the following	1508	Consider the Net::FCP module. It features (among others) the following
…		…
965		1580
966	The actual code goes further and collects all errors ("die"s,	1581	The actual code goes further and collects all errors ("die"s,
967	exceptions) that occurred during request processing. The "result" method	1582	exceptions) that occurred during request processing. The "result" method
968	detects whether an exception as thrown (it is stored inside the $txn	1583	detects whether an exception as thrown (it is stored inside the $txn
969	object) and just throws the exception, which means connection errors and	1584	object) and just throws the exception, which means connection errors and
970	other problems get reported tot he code that tries to use the result,	1585	other problems get reported to the code that tries to use the result,
971	not in a random callback.	1586	not in a random callback.
972		1587
973	All of this enables the following usage styles:	1588	All of this enables the following usage styles:
974		1589
975	1. Blocking:	1590	1. Blocking:
…		…
1020	through AnyEvent. The benchmark creates a lot of timers (with a zero	1635	through AnyEvent. The benchmark creates a lot of timers (with a zero
1021	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1636	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1022	which it is), lets them fire exactly once and destroys them again.	1637	which it is), lets them fire exactly once and destroys them again.
1023		1638
1024	Source code for this benchmark is found as eg/bench in the AnyEvent	1639	Source code for this benchmark is found as eg/bench in the AnyEvent
1025	distribution.	1640	distribution. It uses the AE interface, which makes a real difference
		1641	for the EV and Perl backends only.
1026		1642
1027	Explanation of the columns	1643	Explanation of the columns
1028	*watcher* is the number of event watchers created/destroyed. Since	1644	*watcher* is the number of event watchers created/destroyed. Since
1029	different event models feature vastly different performances, each event	1645	different event models feature vastly different performances, each event
1030	loop was given a number of watchers so that overall runtime is	1646	loop was given a number of watchers so that overall runtime is
…		…
1049	*destroy* is the time, in microseconds, that it takes to destroy a	1665	*destroy* is the time, in microseconds, that it takes to destroy a
1050	single watcher.	1666	single watcher.
1051		1667
1052	Results	1668	Results
1053	name watchers bytes create invoke destroy comment	1669	name watchers bytes create invoke destroy comment
1054	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1670	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1055	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1671	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1056	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1672	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1057	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1673	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1058	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1674	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1059	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1675	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1676	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1677	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1060	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1678	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1061	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1679	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1062	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1680	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1063	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1681	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1064		1682
1065	Discussion	1683	Discussion
1066	The benchmark does *not* measure scalability of the event loop very	1684	The benchmark does *not* measure scalability of the event loop very
1067	well. For example, a select-based event loop (such as the pure perl one)	1685	well. For example, a select-based event loop (such as the pure perl one)
1068	can never compete with an event loop that uses epoll when the number of	1686	can never compete with an event loop that uses epoll when the number of
…		…
1079	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1697	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1080	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1698	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1081	CPU cycles with POE.	1699	CPU cycles with POE.
1082		1700
1083	"EV" is the sole leader regarding speed and memory use, which are both	1701	"EV" is the sole leader regarding speed and memory use, which are both
1084	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1702	maximal/minimal, respectively. When using the AE API there is zero
		1703	overhead (when going through the AnyEvent API create is about 5-6 times
		1704	slower, with other times being equal, so still uses far less memory than
1085	far less memory than any other event loop and is still faster than Event	1705	any other event loop and is still faster than Event natively).
1086	natively.
1087		1706
1088	The pure perl implementation is hit in a few sweet spots (both the	1707	The pure perl implementation is hit in a few sweet spots (both the
1089	constant timeout and the use of a single fd hit optimisations in the	1708	constant timeout and the use of a single fd hit optimisations in the
1090	perl interpreter and the backend itself). Nevertheless this shows that	1709	perl interpreter and the backend itself). Nevertheless this shows that
1091	it adds very little overhead in itself. Like any select-based backend	1710	it adds very little overhead in itself. Like any select-based backend
…		…
1093	few of them active), of course, but this was not subject of this	1712	few of them active), of course, but this was not subject of this
1094	benchmark.	1713	benchmark.
1095		1714
1096	The "Event" module has a relatively high setup and callback invocation	1715	The "Event" module has a relatively high setup and callback invocation
1097	cost, but overall scores in on the third place.	1716	cost, but overall scores in on the third place.
		1717
		1718	"IO::Async" performs admirably well, about on par with "Event", even
		1719	when using its pure perl backend.
1098		1720
1099	"Glib"'s memory usage is quite a bit higher, but it features a faster	1721	"Glib"'s memory usage is quite a bit higher, but it features a faster
1100	callback invocation and overall ends up in the same class as "Event".	1722	callback invocation and overall ends up in the same class as "Event".
1101	However, Glib scales extremely badly, doubling the number of watchers	1723	However, Glib scales extremely badly, doubling the number of watchers
1102	increases the processing time by more than a factor of four, making it	1724	increases the processing time by more than a factor of four, making it
…		…
1134	when used without AnyEvent), but most event loops have acceptable	1756	when used without AnyEvent), but most event loops have acceptable
1135	performance with or without AnyEvent.	1757	performance with or without AnyEvent.
1136		1758
1137	* The overhead AnyEvent adds is usually much smaller than the overhead	1759	* The overhead AnyEvent adds is usually much smaller than the overhead
1138	of the actual event loop, only with extremely fast event loops such	1760	of the actual event loop, only with extremely fast event loops such
1139	as EV adds AnyEvent significant overhead.	1761	as EV does AnyEvent add significant overhead.
1140		1762
1141	* You should avoid POE like the plague if you want performance or	1763	* You should avoid POE like the plague if you want performance or
1142	reasonable memory usage.	1764	reasonable memory usage.
1143		1765
1144	BENCHMARKING THE LARGE SERVER CASE	1766	BENCHMARKING THE LARGE SERVER CASE
…		…
1158	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1780	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1159	100 (1%) are active. This mirrors the activity of large servers with	1781	100 (1%) are active. This mirrors the activity of large servers with
1160	many connections, most of which are idle at any one point in time.	1782	many connections, most of which are idle at any one point in time.
1161		1783
1162	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1784	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1163	distribution.	1785	distribution. It uses the AE interface, which makes a real difference
		1786	for the EV and Perl backends only.
1164		1787
1165	Explanation of the columns	1788	Explanation of the columns
1166	*sockets* is the number of sockets, and twice the number of "servers"	1789	*sockets* is the number of sockets, and twice the number of "servers"
1167	(as each server has a read and write socket end).	1790	(as each server has a read and write socket end).
1168		1791
…		…
1173	single "request", that is, reading the token from the pipe and	1796	single "request", that is, reading the token from the pipe and
1174	forwarding it to another server. This includes deleting the old timeout	1797	forwarding it to another server. This includes deleting the old timeout
1175	and creating a new one that moves the timeout into the future.	1798	and creating a new one that moves the timeout into the future.
1176		1799
1177	Results	1800	Results
1178	name sockets create request	1801	name sockets create request
1179	EV 20000 69.01 11.16	1802	EV 20000 62.66 7.99
1180	Perl 20000 73.32 35.87	1803	Perl 20000 68.32 32.64
1181	Event 20000 212.62 257.32	1804	IOAsync 20000 174.06 101.15 epoll
1182	Glib 20000 651.16 1896.30	1805	IOAsync 20000 174.67 610.84 poll
		1806	Event 20000 202.69 242.91
		1807	Glib 20000 557.01 1689.52
1183	POE 20000 349.67 12317.24 uses POE::Loop::Event	1808	POE 20000 341.54 12086.32 uses POE::Loop::Event
1184		1809
1185	Discussion	1810	Discussion
1186	This benchmark *does* measure scalability and overall performance of the	1811	This benchmark *does* measure scalability and overall performance of the
1187	particular event loop.	1812	particular event loop.
1188		1813
1189	EV is again fastest. Since it is using epoll on my system, the setup	1814	EV is again fastest. Since it is using epoll on my system, the setup
1190	time is relatively high, though.	1815	time is relatively high, though.
1191		1816
1192	Perl surprisingly comes second. It is much faster than the C-based event	1817	Perl surprisingly comes second. It is much faster than the C-based event
1193	loops Event and Glib.	1818	loops Event and Glib.
		1819
		1820	IO::Async performs very well when using its epoll backend, and still
		1821	quite good compared to Glib when using its pure perl backend.
1194		1822
1195	Event suffers from high setup time as well (look at its code and you	1823	Event suffers from high setup time as well (look at its code and you
1196	will understand why). Callback invocation also has a high overhead	1824	will understand why). Callback invocation also has a high overhead
1197	compared to the "$_->() for .."-style loop that the Perl event loop	1825	compared to the "$_->() for .."-style loop that the Perl event loop
1198	uses. Event uses select or poll in basically all documented	1826	uses. Event uses select or poll in basically all documented
…		…
1249		1877
1250	Summary	1878	Summary
1251	* C-based event loops perform very well with small number of watchers,	1879	* C-based event loops perform very well with small number of watchers,
1252	as the management overhead dominates.	1880	as the management overhead dominates.
1253		1881
		1882	THE IO::Lambda BENCHMARK
		1883	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1884	could be misinterpreted to make AnyEvent look bad. In fact, the
		1885	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1886	better (which shouldn't come as a surprise to anybody). As such, the
		1887	benchmark is fine, and mostly shows that the AnyEvent backend from
		1888	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1889	without the extra baggage? To explore this, I wrote the equivalent
		1890	benchmark for AnyEvent.
		1891
		1892	The benchmark itself creates an echo-server, and then, for 500 times,
		1893	connects to the echo server, sends a line, waits for the reply, and then
		1894	creates the next connection. This is a rather bad benchmark, as it
		1895	doesn't test the efficiency of the framework or much non-blocking I/O,
		1896	but it is a benchmark nevertheless.
		1897
		1898	name runtime
		1899	Lambda/select 0.330 sec
		1900	+ optimized 0.122 sec
		1901	Lambda/AnyEvent 0.327 sec
		1902	+ optimized 0.138 sec
		1903	Raw sockets/select 0.077 sec
		1904	POE/select, components 0.662 sec
		1905	POE/select, raw sockets 0.226 sec
		1906	POE/select, optimized 0.404 sec
		1907
		1908	AnyEvent/select/nb 0.085 sec
		1909	AnyEvent/EV/nb 0.068 sec
		1910	+state machine 0.134 sec
		1911
		1912	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1913	benchmarks actually make blocking connects and use 100% blocking I/O,
		1914	defeating the purpose of an event-based solution. All of the newly
		1915	written AnyEvent benchmarks use 100% non-blocking connects (using
		1916	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1917	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1918	connects generally require a lot more bookkeeping and event handling
		1919	than blocking connects (which involve a single syscall only).
		1920
		1921	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1922	offers similar expressive power as POE and IO::Lambda, using
		1923	conventional Perl syntax. This means that both the echo server and the
		1924	client are 100% non-blocking, further placing it at a disadvantage.
		1925
		1926	As you can see, the AnyEvent + EV combination even beats the
		1927	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1928	backend easily beats IO::Lambda and POE.
		1929
		1930	And even the 100% non-blocking version written using the high-level (and
		1931	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1932	higher level ("unoptimised") abstractions by a large margin, even though
		1933	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1934
		1935	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1936	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1937	part of the IO::Lambda distribution and were used without any changes.
		1938
		1939	SIGNALS
		1940	AnyEvent currently installs handlers for these signals:
		1941
		1942	SIGCHLD
		1943	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1944	emulation for event loops that do not support them natively. Also,
		1945	some event loops install a similar handler.
		1946
		1947	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1948	then AnyEvent will reset it to default, to avoid losing child exit
		1949	statuses.
		1950
		1951	SIGPIPE
		1952	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1953	"undef" when AnyEvent gets loaded.
		1954
		1955	The rationale for this is that AnyEvent users usually do not really
		1956	depend on SIGPIPE delivery (which is purely an optimisation for
		1957	shell use, or badly-written programs), but "SIGPIPE" can cause
		1958	spurious and rare program exits as a lot of people do not expect
		1959	"SIGPIPE" when writing to some random socket.
		1960
		1961	The rationale for installing a no-op handler as opposed to ignoring
		1962	it is that this way, the handler will be restored to defaults on
		1963	exec.
		1964
		1965	Feel free to install your own handler, or reset it to defaults.
		1966
		1967	RECOMMENDED/OPTIONAL MODULES
		1968	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1969	its built-in modules) are required to use it.
		1970
		1971	That does not mean that AnyEvent won't take advantage of some additional
		1972	modules if they are installed.
		1973
		1974	This section explains which additional modules will be used, and how
		1975	they affect AnyEvent's operation.
		1976
		1977	Async::Interrupt
		1978	This slightly arcane module is used to implement fast signal
		1979	handling: To my knowledge, there is no way to do completely
		1980	race-free and quick signal handling in pure perl. To ensure that
		1981	signals still get delivered, AnyEvent will start an interval timer
		1982	to wake up perl (and catch the signals) with some delay (default is
		1983	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1984
		1985	If this module is available, then it will be used to implement
		1986	signal catching, which means that signals will not be delayed, and
		1987	the event loop will not be interrupted regularly, which is more
		1988	efficient (and good for battery life on laptops).
		1989
		1990	This affects not just the pure-perl event loop, but also other event
		1991	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1992
		1993	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1994	natively, and either employ their own workarounds (POE) or use
		1995	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1996	Installing Async::Interrupt does nothing for those backends.
		1997
		1998	EV This module isn't really "optional", as it is simply one of the
		1999	backend event loops that AnyEvent can use. However, it is simply the
		2000	best event loop available in terms of features, speed and stability:
		2001	It supports the AnyEvent API optimally, implements all the watcher
		2002	types in XS, does automatic timer adjustments even when no monotonic
		2003	clock is available, can take avdantage of advanced kernel interfaces
		2004	such as "epoll" and "kqueue", and is the fastest backend *by far*.
		2005	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		2006	Glib::EV).
		2007
		2008	If you only use backends that rely on another event loop (e.g.
		2009	"Tk"), then this module will do nothing for you.
		2010
		2011	Guard
		2012	The guard module, when used, will be used to implement
		2013	"AnyEvent::Util::guard". This speeds up guards considerably (and
		2014	uses a lot less memory), but otherwise doesn't affect guard
		2015	operation much. It is purely used for performance.
		2016
		2017	JSON and JSON::XS
		2018	One of these modules is required when you want to read or write JSON
		2019	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		2020	can take advantage of the ultra-high-speed JSON::XS module when it
		2021	is installed.
		2022
		2023	Net::SSLeay
		2024	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2025	worthwhile: If this module is installed, then AnyEvent::Handle (with
		2026	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		2027
		2028	Time::HiRes
		2029	This module is part of perl since release 5.008. It will be used
		2030	when the chosen event library does not come with a timing source of
		2031	its own. The pure-perl event loop (AnyEvent::Loop) will additionally
		2032	load it to try to use a monotonic clock for timing stability.
		2033
		2034	AnyEvent::AIO (and IO::AIO)
		2035	The default implementation of AnyEvent::IO is to do I/O
		2036	synchronously, stopping programs while they access the disk, which
		2037	is fine for a lot of programs.
		2038
		2039	Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
		2040	switch to a true asynchronous implementation, so event processing
		2041	can continue even while waiting for disk I/O.
		2042
1254	FORK	2043	FORK
1255	Most event libraries are not fork-safe. The ones who are usually are	2044	Most event libraries are not fork-safe. The ones who are usually are
1256	because they rely on inefficient but fork-safe "select" or "poll" calls.	2045	because they rely on inefficient but fork-safe "select" or "poll" calls
1257	Only EV is fully fork-aware.	2046	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		2047	epoll are usually badly thought-out hacks that are incompatible with
		2048	fork in one way or another. Only EV is fully fork-aware and ensures that
		2049	you continue event-processing in both parent and child (or both, if you
		2050	know what you are doing).
		2051
		2052	This means that, in general, you cannot fork and do event processing in
		2053	the child if the event library was initialised before the fork (which
		2054	usually happens when the first AnyEvent watcher is created, or the
		2055	library is loaded).
1258		2056
1259	If you have to fork, you must either do so *before* creating your first	2057	If you have to fork, you must either do so *before* creating your first
1260	watcher OR you must not use AnyEvent at all in the child.	2058	watcher OR you must not use AnyEvent at all in the child OR you must do
		2059	something completely out of the scope of AnyEvent (see below).
		2060
		2061	The problem of doing event processing in the parent *and* the child is
		2062	much more complicated: even for backends that *are* fork-aware or
		2063	fork-safe, their behaviour is not usually what you want: fork clones all
		2064	watchers, that means all timers, I/O watchers etc. are active in both
		2065	parent and child, which is almost never what you want. Using "exec" to
		2066	start worker children from some kind of manage prrocess is usually
		2067	preferred, because it is much easier and cleaner, at the expense of
		2068	having to have another binary.
		2069
		2070	In addition to logical problems with fork, there are also implementation
		2071	problems. For example, on POSIX systems, you cannot fork at all in Perl
		2072	code if a thread (I am talking of pthreads here) was ever created in the
		2073	process, and this is just the tip of the iceberg. In general, using fork
		2074	from Perl is difficult, and attempting to use fork without an exec to
		2075	implement some kind of parallel processing is almost certainly doomed.
		2076
		2077	To safely fork and exec, you should use a module such as Proc::FastSpawn
		2078	that let's you safely fork and exec new processes.
		2079
		2080	If you want to do multiprocessing using processes, you can look at the
		2081	AnyEvent::Fork module (and some related modules such as
		2082	AnyEvent::Fork::RPC, AnyEvent::Fork::Pool and AnyEvent::Fork::Remote).
		2083	This module allows you to safely create subprocesses without any
		2084	limitations - you can use X11 toolkits or AnyEvent in the children
		2085	created by AnyEvent::Fork safely and without any special precautions.
1261		2086
1262	SECURITY CONSIDERATIONS	2087	SECURITY CONSIDERATIONS
1263	AnyEvent can be forced to load any event model via	2088	AnyEvent can be forced to load any event model via
1264	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	2089	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1265	to execute arbitrary code or directly gain access, it can easily be used	2090	to execute arbitrary code or directly gain access, it can easily be used
…		…
1269		2094
1270	You can make AnyEvent completely ignore this variable by deleting it	2095	You can make AnyEvent completely ignore this variable by deleting it
1271	before the first watcher gets created, e.g. with a "BEGIN" block:	2096	before the first watcher gets created, e.g. with a "BEGIN" block:
1272		2097
1273	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	2098	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1274		2099
1275	use AnyEvent;	2100	use AnyEvent;
1276		2101
1277	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	2102	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1278	be used to probe what backend is used and gain other information (which	2103	be used to probe what backend is used and gain other information (which
1279	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).	2104	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		2105	and $ENV{PERL_ANYEVENT_STRICT}.
		2106
		2107	Note that AnyEvent will remove *all* environment variables starting with
		2108	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		2109	enabled.
		2110
		2111	BUGS
		2112	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		2113	hard to work around. If you suffer from memleaks, first upgrade to Perl
		2114	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		2115	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		2116	not as pronounced).
1280		2117
1281	SEE ALSO	2118	SEE ALSO
1282	Utility functions: AnyEvent::Util.	2119	Tutorial/Introduction: AnyEvent::Intro.
1283		2120
1284	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	2121	FAQ: AnyEvent::FAQ.
1285	Event::Lib, Qt, POE.	2122
		2123	Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
		2124	(simply logging).
		2125
		2126	Development/Debugging: AnyEvent::Strict (stricter checking),
		2127	AnyEvent::Debug (interactive shell, watcher tracing).
		2128
		2129	Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
		2130	Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK, Cocoa::EventLoop, UV.
1286		2131
1287	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	2132	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1288	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	2133	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1289	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	2134	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		2135	AnyEvent::Impl::IOAsync, AnyEvent::Impl::Irssi, AnyEvent::Impl::FLTK,
		2136	AnyEvent::Impl::Cocoa, AnyEvent::Impl::UV.
1290		2137
1291	Non-blocking file handles, sockets, TCP clients and servers:	2138	Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1292	AnyEvent::Handle, AnyEvent::Socket.	2139	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		2140
		2141	Asynchronous File I/O: AnyEvent::IO.
1293		2142
1294	Asynchronous DNS: AnyEvent::DNS.	2143	Asynchronous DNS: AnyEvent::DNS.
1295		2144
1296	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	2145	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1297		2146
1298	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	2147	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
		2148	AnyEvent::HTTP.
1299		2149
1300	AUTHOR	2150	AUTHOR
1301	Marc Lehmann <schmorp@schmorp.de>	2151	Marc Lehmann <schmorp@schmorp.de>
1302	http://home.schmorp.de/	2152	http://anyevent.schmorp.de
1303		2153

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