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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.
		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.
26		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
…		…
45	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
46	model you use.	75	model you use.
47		76
48	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
49	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
50	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
51	cannot use anything else, as they are simply incompatible to everything	80	cannot use anything else, as they are simply incompatible to everything
52	that isn't them. 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
53	are *also* forced to use the same event loop you use.	82	are *also* forced to use the same event loop you use.
54		83
55	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	84	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
56	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
57	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
58	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
59	But if your module uses AnyEvent, it works transparently with all event	88	your module uses AnyEvent, it works transparently with all event models
60	models it supports (including stuff like IO::Async, as long as those use	89	it supports (including stuff like IO::Async, as long as those use one of
61	one of the supported event loops. It is trivial to add new event loops	90	the supported event loops. It is easy to add new event loops to
62	to AnyEvent, too, so it is future-proof).	91	AnyEvent, too, so it is future-proof).
63		92
64	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
65	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
66	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
67	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
68	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
69	wrapper as technically possible.	98	technically possible.
70		99
71	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
72	useful functionality, such as an asynchronous DNS resolver, 100%	101	useful functionality, such as an asynchronous DNS resolver, 100%
73	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
74	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
…		…
77	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
78	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
79	model, you should *not* use this module.	108	model, you should *not* use this module.
80		109
81	DESCRIPTION	110	DESCRIPTION
82	AnyEvent provides an identical interface to multiple event loops. This	111	AnyEvent provides a uniform interface to various event loops. This
83	allows module authors to utilise an event loop without forcing module	112	allows module authors to use event loop functionality without forcing
84	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
85	coexist peacefully at any one time).	114	than one event loop cannot coexist peacefully).
86		115
87	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
88	module.	117	module.
89		118
90	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
91	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
92	following modules is already loaded: EV, Event, Glib,	121	following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
93	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
94	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
95	(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
96	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
97	successfully loaded will be used. If, after this, still none could be	126	tried.
98	found, AnyEvent will fall back to a pure-perl event loop, which is not
99	very efficient, but should work everywhere.
100		127
101	Because AnyEvent first checks for modules that are already loaded,	128	Because AnyEvent first checks for modules that are already loaded,
102	loading an event model explicitly before first using AnyEvent will	129	loading an event model explicitly before first using AnyEvent will
103	likely make that model the default. For example:	130	likely make that model the default. For example:
104		131
…		…
106	use AnyEvent;	133	use AnyEvent;
107		134
108	# .. AnyEvent will likely default to Tk	135	# .. AnyEvent will likely default to Tk
109		136
110	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
111	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
112	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.
113		141
114	The pure-perl implementation of AnyEvent is called	142	The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
115	"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
116	explicitly and enjoy the high availability of that event loop :)	144	availability of that event loop :)
117		145
118	WATCHERS	146	WATCHERS
119	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
120	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
121	the callback to call, the file handle to watch, etc.	149	the callback to call, the file handle to watch, etc.
…		…
123	These watchers are normal Perl objects with normal Perl lifetime. After	151	These watchers are normal Perl objects with normal Perl lifetime. After
124	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
125	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
126	in control).	154	in control).
127		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
128	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
129	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
130	to it).	164	to it).
131		165
132	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.
133		167
134	Many watchers either are used with "recursion" (repeating timers for	168	Many watchers either are used with "recursion" (repeating timers for
135	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.
136		170
137	An any way to achieve that is this pattern:	171	One way to achieve that is this pattern:
138		172
139	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	173	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
140	# you can use $w here, for example to undef it	174	# you can use $w here, for example to undef it
141	undef $w;	175	undef $w;
142	});	176	});
…		…
144	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,
145	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
146	declared.	180	declared.
147		181
148	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
149	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
150	the following mandatory key-value pairs as arguments:	190	the following mandatory key-value pairs as arguments:
151		191
152	"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
153	(AnyEvent might or might not keep a reference to this file handle).	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
154	"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
155	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	200	watcher waiting for "r"eadable or "w"ritable events, respectively.
		201
156	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.
157		203
158	Although the callback might get passed parameters, their value and	204	Although the callback might get passed parameters, their value and
159	presence is undefined and you cannot rely on them. Portable AnyEvent	205	presence is undefined and you cannot rely on them. Portable AnyEvent
160	callbacks cannot use arguments passed to I/O watcher callbacks.	206	callbacks cannot use arguments passed to I/O watcher callbacks.
161		207
162	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
163	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
164	the underlying file descriptor.	210	the underlying file descriptor.
165		211
166	Some event loops issue spurious readyness notifications, so you should	212	Some event loops issue spurious readiness notifications, so you should
167	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
168	handles.	214	handles.
169		215
170	Example: wait for readability of STDIN, then read a line and disable the	216	Example: wait for readability of STDIN, then read a line and disable the
171	watcher.	217	watcher.
…		…
175	warn "read: $input\n";	221	warn "read: $input\n";
176	undef $w;	222	undef $w;
177	});	223	});
178		224
179	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
180	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
181	with the following mandatory arguments:	235	with the following mandatory arguments:
182		236
183	"after" specifies after how many seconds (fractional values are	237	"after" specifies after how many seconds (fractional values are
184	supported) the callback should be invoked. "cb" is the callback to	238	supported) the callback should be invoked. "cb" is the callback to
…		…
186		240
187	Although the callback might get passed parameters, their value and	241	Although the callback might get passed parameters, their value and
188	presence is undefined and you cannot rely on them. Portable AnyEvent	242	presence is undefined and you cannot rely on them. Portable AnyEvent
189	callbacks cannot use arguments passed to time watcher callbacks.	243	callbacks cannot use arguments passed to time watcher callbacks.
190		244
191	The callback will normally be invoked once only. If you specify another	245	The callback will normally be invoked only once. If you specify another
192	parameter, "interval", as a strictly positive number (> 0), then the	246	parameter, "interval", as a strictly positive number (> 0), then the
193	callback will be invoked regularly at that interval (in fractional	247	callback will be invoked regularly at that interval (in fractional
194	seconds) after the first invocation. If "interval" is specified with a	248	seconds) after the first invocation. If "interval" is specified with a
195	false value, then it is treated as if it were missing.	249	false value, then it is treated as if it were not specified at all.
196		250
197	The callback will be rescheduled before invoking the callback, but no	251	The callback will be rescheduled before invoking the callback, but no
198	attempt is done to avoid timer drift in most backends, so the interval	252	attempt is made to avoid timer drift in most backends, so the interval
199	is only approximate.	253	is only approximate.
200		254
201	Example: fire an event after 7.7 seconds.	255	Example: fire an event after 7.7 seconds.
202		256
203	my $w = AnyEvent->timer (after => 7.7, cb => sub {	257	my $w = AnyEvent->timer (after => 7.7, cb => sub {
…		…
209		263
210	Example 2: 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.
211		265
212	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {	266	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
213	warn "timeout\n";	267	warn "timeout\n";
214	};	268	});
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* in uppercase and without any "SIG" prefix, "cb" is the Perl	378	*name* in uppercase and without any "SIG" prefix, "cb" is the Perl
301	callback to be invoked 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
…		…
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 (or "undef"
574	optionally replaces it before doing so.	818	if not) and 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	Additionally, when the callback is invoked, it is also removed from
		827	the condvar (reset to "undef"), so the condvar does not keep a
		828	reference to the callback after invocation.
		829
		830	SUPPORTED EVENT LOOPS/BACKENDS
		831	The following backend classes are part of the AnyEvent distribution
		832	(every class has its own manpage):
		833
		834	Backends that are autoprobed when no other event loop can be found.
		835	EV is the preferred backend when no other event loop seems to be in
		836	use. If EV is not installed, then AnyEvent will fall back to its own
		837	pure-perl implementation, which is available everywhere as it comes
		838	with AnyEvent itself.
		839
		840	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		841	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
		842
		843	Backends that are transparently being picked up when they are used.
		844	These will be used if they are already loaded when the first watcher
		845	is created, in which case it is assumed that the application is
		846	using them. This means that AnyEvent will automatically pick the
		847	right backend when the main program loads an event module before
		848	anything starts to create watchers. Nothing special needs to be done
		849	by the main program.
		850
		851	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		852	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		853	AnyEvent::Impl::Tk based on Tk, very broken.
		854	AnyEvent::Impl::UV based on UV, innovated square wheels.
		855	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		856	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		857	AnyEvent::Impl::Irssi used when running within irssi.
		858	AnyEvent::Impl::IOAsync based on IO::Async.
		859	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		860	AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
		861
		862	Backends with special needs.
		863	Qt requires the Qt::Application to be instantiated first, but will
		864	otherwise be picked up automatically. As long as the main program
		865	instantiates the application before any AnyEvent watchers are
		866	created, everything should just work.
		867
		868	AnyEvent::Impl::Qt based on Qt.
		869
		870	Event loops that are indirectly supported via other backends.
		871	Some event loops can be supported via other modules:
		872
		873	There is no direct support for WxWidgets (Wx) or Prima.
		874
		875	WxWidgets has no support for watching file handles. However, you can
		876	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		877	simply polls 20 times per second, which was considered to be too
		878	horrible to even consider for AnyEvent.
		879
		880	Prima is not supported as nobody seems to be using it, but it has a
		881	POE backend, so it can be supported through POE.
		882
		883	AnyEvent knows about both Prima and Wx, however, and will try to
		884	load POE when detecting them, in the hope that POE will pick them
		885	up, in which case everything will be automatic.
		886
		887	Known event loops outside the AnyEvent distribution
		888	The following event loops or programs support AnyEvent by providing
		889	their own AnyEvent backend. They will be picked up automatically.
		890
		891	urxvt::anyevent available to rxvt-unicode extensions
580		892
581	GLOBAL VARIABLES AND FUNCTIONS	893	GLOBAL VARIABLES AND FUNCTIONS
		894	These are not normally required to use AnyEvent, but can be useful to
		895	write AnyEvent extension modules.
		896
582	$AnyEvent::MODEL	897	$AnyEvent::MODEL
583	Contains "undef" until the first watcher is being created. Then it	898	Contains "undef" until the first watcher is being created, before
		899	the backend has been autodetected.
		900
584	contains the event model that is being used, which is the name of	901	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	902	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	903	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*).	904	other class in the case AnyEvent has been extended at runtime (e.g.
588		905	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		906
610	AnyEvent::detect	907	AnyEvent::detect
611	Returns $AnyEvent::MODEL, forcing autodetection of the event model	908	Returns $AnyEvent::MODEL, forcing autodetection of the event model
612	if necessary. You should only call this function right before you	909	if necessary. You should only call this function right before you
613	would have created an AnyEvent watcher anyway, that is, as late as	910	would have created an AnyEvent watcher anyway, that is, as late as
614	possible at runtime.	911	possible at runtime, and not e.g. during initialisation of your
		912	module.
		913
		914	The effect of calling this function is as if a watcher had been
		915	created (specifically, actions that happen "when the first watcher
		916	is created" happen when calling detetc as well).
		917
		918	If you need to do some initialisation before AnyEvent watchers are
		919	created, use "post_detect".
615		920
616	$guard = AnyEvent::post_detect { BLOCK }	921	$guard = AnyEvent::post_detect { BLOCK }
617	Arranges for the code block to be executed as soon as the event	922	Arranges for the code block to be executed as soon as the event
618	model is autodetected (or immediately if this has already happened).	923	model is autodetected (or immediately if that has already happened).
		924
		925	The block will be executed *after* the actual backend has been
		926	detected ($AnyEvent::MODEL is set), so it is possible to do some
		927	initialisation only when AnyEvent is actually initialised - see the
		928	sources of AnyEvent::AIO to see how this is used.
		929
		930	The most common usage is to create some global watchers, without
		931	forcing event module detection too early. For example, AnyEvent::AIO
		932	creates and installs the global IO::AIO watcher in a "post_detect"
		933	block to avoid autodetecting the event module at load time.
619		934
620	If called in scalar or list context, then it creates and returns an	935	If called in scalar or list context, then it creates and returns an
621	object that automatically removes the callback again when it is	936	object that automatically removes the callback again when it is
		937	destroyed (or "undef" when the hook was immediately executed). See
622	destroyed. See Coro::BDB for a case where this is useful.	938	AnyEvent::AIO for a case where this is useful.
		939
		940	Example: Create a watcher for the IO::AIO module and store it in
		941	$WATCHER, but do so only do so after the event loop is initialised.
		942
		943	our WATCHER;
		944
		945	my $guard = AnyEvent::post_detect {
		946	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		947	};
		948
		949	# the ||= is important in case post_detect immediately runs the block,
		950	# as to not clobber the newly-created watcher. assigning both watcher and
		951	# post_detect guard to the same variable has the advantage of users being
		952	# able to just C<undef $WATCHER> if the watcher causes them grief.
		953
		954	$WATCHER ||= $guard;
623		955
624	@AnyEvent::post_detect	956	@AnyEvent::post_detect
625	If there are any code references in this array (you can "push" to it	957	This is a lower level interface then "AnyEvent::post_detect" (the
626	before or after loading AnyEvent), then they will called directly	958	function). This variable is mainly useful for modules that can do
		959	something useful when AnyEvent is used and thus want to know when it
		960	is initialised, but do not need to even load it by default. This
		961	array provides the means to hook into AnyEvent passively, without
		962	loading it.
		963
		964	Here is how it works: If there are any code references in this array
		965	(you can "push" to it before or after loading AnyEvent), then they
627	after the event loop has been chosen.	966	will be called directly after the event loop has been chosen.
628		967
629	You should check $AnyEvent::MODEL before adding to this array,	968	You should check $AnyEvent::MODEL before adding to this array,
630	though: if it contains a true value then the event loop has already	969	though: if it is defined then the event loop has already been
631	been detected, and the array will be ignored.	970	detected, and the array will be ignored.
632		971
633	Best use "AnyEvent::post_detect { BLOCK }" instead.	972	Best use "AnyEvent::post_detect { BLOCK }" when your application
		973	allows it, as it takes care of these details.
		974
		975	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		976	together, you could put this into Coro (this is the actual code used
		977	by Coro to accomplish this):
		978
		979	if (defined $AnyEvent::MODEL) {
		980	# AnyEvent already initialised, so load Coro::AnyEvent
		981	require Coro::AnyEvent;
		982	} else {
		983	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		984	# as soon as it is
		985	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		986	}
		987
		988	AnyEvent::postpone { BLOCK }
		989	Arranges for the block to be executed as soon as possible, but not
		990	before the call itself returns. In practise, the block will be
		991	executed just before the event loop polls for new events, or shortly
		992	afterwards.
		993
		994	This function never returns anything (to make the "return postpone {
		995	... }" idiom more useful.
		996
		997	To understand the usefulness of this function, consider a function
		998	that asynchronously does something for you and returns some
		999	transaction object or guard to let you cancel the operation. For
		1000	example, "AnyEvent::Socket::tcp_connect":
		1001
		1002	# start a connection attempt unless one is active
		1003	$self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		1004	delete $self->{connect_guard};
		1005	...
		1006	};
		1007
		1008	Imagine that this function could instantly call the callback, for
		1009	example, because it detects an obvious error such as a negative port
		1010	number. Invoking the callback before the function returns causes
		1011	problems however: the callback will be called and will try to delete
		1012	the guard object. But since the function hasn't returned yet, there
		1013	is nothing to delete. When the function eventually returns it will
		1014	assign the guard object to "$self->{connect_guard}", where it will
		1015	likely never be deleted, so the program thinks it is still trying to
		1016	connect.
		1017
		1018	This is where "AnyEvent::postpone" should be used. Instead of
		1019	calling the callback directly on error:
		1020
		1021	$cb->(undef), return # signal error to callback, BAD!
		1022	if $some_error_condition;
		1023
		1024	It should use "postpone":
		1025
		1026	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1027	if $some_error_condition;
		1028
		1029	AnyEvent::log $level, $msg[, @args]
		1030	Log the given $msg at the given $level.
		1031
		1032	If AnyEvent::Log is not loaded then this function makes a simple
		1033	test to see whether the message will be logged. If the test succeeds
		1034	it will load AnyEvent::Log and call "AnyEvent::Log::log" -
		1035	consequently, look at the AnyEvent::Log documentation for details.
		1036
		1037	If the test fails it will simply return. Right now this happens when
		1038	a numerical loglevel is used and it is larger than the level
		1039	specified via $ENV{PERL_ANYEVENT_VERBOSE}.
		1040
		1041	If you want to sprinkle loads of logging calls around your code,
		1042	consider creating a logger callback with the "AnyEvent::Log::logger"
		1043	function, which can reduce typing, codesize and can reduce the
		1044	logging overhead enourmously.
		1045
		1046	AnyEvent::fh_block $filehandle
		1047	AnyEvent::fh_unblock $filehandle
		1048	Sets blocking or non-blocking behaviour for the given filehandle.
634		1049
635	WHAT TO DO IN A MODULE	1050	WHAT TO DO IN A MODULE
636	As a module author, you should "use AnyEvent" and call AnyEvent methods	1051	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.	1052	freely, but you should not load a specific event module or rely on it.
638		1053
…		…
646	stall the whole program, and the whole point of using events is to stay	1061	stall the whole program, and the whole point of using events is to stay
647	interactive.	1062	interactive.
648		1063
649	It is fine, however, to call "->recv" when the user of your module	1064	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	1065	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"	1066	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).	1067	as the user of your module knows what she is doing. Always).
653		1068
654	WHAT TO DO IN THE MAIN PROGRAM	1069	WHAT TO DO IN THE MAIN PROGRAM
655	There will always be a single main program - the only place that should	1070	There will always be a single main program - the only place that should
656	dictate which event model to use.	1071	dictate which event model to use.
657		1072
658	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	1073	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	1074	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	1075	uses AnyEvent, but does not care which event loop is used, all it needs
661	it.	1076	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		1077	available loop implementation.
662		1078
663	If the main program relies on a specific event model - for example, in	1079	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	1080	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:	1081	event module before loading AnyEvent or any module that uses it:
666	generally speaking, you should load it as early as possible. The reason	1082	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	1083	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,	1084	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	1085	and it might choose the wrong one unless you load the correct one
670	yourself.	1086	yourself.
671		1087
672	You can chose to use a pure-perl implementation by loading the	1088	You can chose to use a pure-perl implementation by loading the
673	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1089	"AnyEvent::Loop" module, which gives you similar behaviour everywhere,
674	everywhere, but letting AnyEvent chose the model is generally better.	1090	but letting AnyEvent chose the model is generally better.
675		1091
676	MAINLOOP EMULATION	1092	MAINLOOP EMULATION
677	Sometimes (often for short test scripts, or even standalone programs who	1093	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	1094	only want to use AnyEvent), you do not want to run a specific event
679	loop.	1095	loop.
…		…
689	variable somewhere, waiting for it, and sending it when the program	1105	variable somewhere, waiting for it, and sending it when the program
690	should exit cleanly.	1106	should exit cleanly.
691		1107
692	OTHER MODULES	1108	OTHER MODULES
693	The following is a non-exhaustive list of additional modules that use	1109	The following is a non-exhaustive list of additional modules that use
694	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1110	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	1111	AnyEvent modules and other event loops in the same program. Some of the
696	available via CPAN.	1112	modules come as part of AnyEvent, the others are available via CPAN (see
		1113	<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
		1114	non-exhaustive list), and the list is heavily biased towards modules of
		1115	the AnyEvent author himself :)
697		1116
698	AnyEvent::Util	1117	AnyEvent::Util (part of the AnyEvent distribution)
699	Contains various utility functions that replace often-used but	1118	Contains various utility functions that replace often-used blocking
700	blocking functions such as "inet_aton" by event-/callback-based	1119	functions such as "inet_aton" with event/callback-based versions.
701	versions.
702		1120
703	AnyEvent::Socket	1121	AnyEvent::Socket (part of the AnyEvent distribution)
704	Provides various utility functions for (internet protocol) sockets,	1122	Provides various utility functions for (internet protocol) sockets,
705	addresses and name resolution. Also functions to create non-blocking	1123	addresses and name resolution. Also functions to create non-blocking
706	tcp connections or tcp servers, with IPv6 and SRV record support and	1124	tcp connections or tcp servers, with IPv6 and SRV record support and
707	more.	1125	more.
708		1126
709	AnyEvent::Handle	1127	AnyEvent::Handle (part of the AnyEvent distribution)
710	Provide read and write buffers, manages watchers for reads and	1128	Provide read and write buffers, manages watchers for reads and
711	writes, supports raw and formatted I/O, I/O queued and fully	1129	writes, supports raw and formatted I/O, I/O queued and fully
712	transparent and non-blocking SSL/TLS.	1130	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
713		1131
714	AnyEvent::DNS	1132	AnyEvent::DNS (part of the AnyEvent distribution)
715	Provides rich asynchronous DNS resolver capabilities.	1133	Provides rich asynchronous DNS resolver capabilities.
716		1134
717	AnyEvent::HTTP	1135	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
718	A simple-to-use HTTP library that is capable of making a lot of	1136	AnyEvent::IGS, AnyEvent::FCP
719	concurrent HTTP requests.	1137	Implement event-based interfaces to the protocols of the same name
		1138	(for the curious, IGS is the International Go Server and FCP is the
		1139	Freenet Client Protocol).
720		1140
		1141	AnyEvent::AIO (part of the AnyEvent distribution)
		1142	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1143	the toolbox of every event programmer. AnyEvent::AIO transparently
		1144	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1145	event-based file I/O, and much more.
		1146
		1147	AnyEvent::Fork, AnyEvent::Fork::RPC, AnyEvent::Fork::Pool,
		1148	AnyEvent::Fork::Remote
		1149	These let you safely fork new subprocesses, either locally or
		1150	remotely (e.g.v ia ssh), using some RPC protocol or not, without the
		1151	limitations normally imposed by fork (AnyEvent works fine for
		1152	example). Dynamically-resized worker pools are obviously included as
		1153	well.
		1154
		1155	And they are quite tiny and fast as well - "abusing" AnyEvent::Fork
		1156	just to exec external programs can easily beat using "fork" and
		1157	"exec" (or even "system") in most programs.
		1158
		1159	AnyEvent::Filesys::Notify
		1160	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1161	path changes (e.g. "watch this directory for new files", "watch this
		1162	file for changes"). The AnyEvent::Filesys::Notify module promises to
		1163	do just that in a portbale fashion, supporting inotify on GNU/Linux
		1164	and some weird, without doubt broken, stuff on OS X to monitor
		1165	files. It can fall back to blocking scans at regular intervals
		1166	transparently on other platforms, so it's about as portable as it
		1167	gets.
		1168
		1169	(I haven't used it myself, but it seems the biggest problem with it
		1170	is it quite bad performance).
		1171
721	AnyEvent::HTTPD	1172	AnyEvent::DBI
722	Provides a simple web application server framework.	1173	Executes DBI requests asynchronously in a proxy process for you,
		1174	notifying you in an event-based way when the operation is finished.
723		1175
724	AnyEvent::FastPing	1176	AnyEvent::FastPing
725	The fastest ping in the west.	1177	The fastest ping in the west.
726		1178
727	AnyEvent::DBI
728	Executes DBI requests asynchronously in a proxy process.
729
730	AnyEvent::AIO
731	Truly asynchronous I/O, should be in the toolbox of every event
732	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
733	together.
734
735	AnyEvent::BDB
736	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
737	fuses BDB and AnyEvent together.
738
739	AnyEvent::GPSD
740	A non-blocking interface to gpsd, a daemon delivering GPS
741	information.
742
743	AnyEvent::IGS
744	A non-blocking interface to the Internet Go Server protocol (used by
745	App::IGS).
746
747	Net::IRC3
748	AnyEvent based IRC client module family.
749
750	Net::XMPP2
751	AnyEvent based XMPP (Jabber protocol) module family.
752
753	Net::FCP
754	AnyEvent-based implementation of the Freenet Client Protocol,
755	birthplace of AnyEvent.
756
757	Event::ExecFlow
758	High level API for event-based execution flow control.
759
760	Coro	1179	Coro
761	Has special support for AnyEvent via Coro::AnyEvent.	1180	Has special support for AnyEvent via Coro::AnyEvent, which allows
		1181	you to simply invert the flow control - don't call us, we will call
		1182	you:
762		1183
763	IO::Lambda	1184	async {
764	The lambda approach to I/O - don't ask, look there. Can use	1185	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
		1186	print "5 seconds later!\n";
		1187
		1188	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
		1189	my $line = <STDIN>; # works for ttys
		1190
		1191	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
		1192	my ($body, $hdr) = Coro::rouse_wait;
		1193	};
		1194
		1195	SIMPLIFIED AE API
		1196	Starting with version 5.0, AnyEvent officially supports a second, much
		1197	simpler, API that is designed to reduce the calling, typing and memory
		1198	overhead by using function call syntax and a fixed number of parameters.
		1199
		1200	See the AE manpage for details.
		1201
		1202	ERROR AND EXCEPTION HANDLING
		1203	In general, AnyEvent does not do any error handling - it relies on the
		1204	caller to do that if required. The AnyEvent::Strict module (see also the
		1205	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1206	checking of all AnyEvent methods, however, which is highly useful during
		1207	development.
		1208
		1209	As for exception handling (i.e. runtime errors and exceptions thrown
		1210	while executing a callback), this is not only highly event-loop
		1211	specific, but also not in any way wrapped by this module, as this is the
		1212	job of the main program.
		1213
		1214	The pure perl event loop simply re-throws the exception (usually within
		1215	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		1216	Glib uses "install_exception_handler" and so on.
		1217
		1218	ENVIRONMENT VARIABLES
		1219	AnyEvent supports a number of environment variables that tune the
		1220	runtime behaviour. They are usually evaluated when AnyEvent is loaded,
		1221	initialised, or a submodule that uses them is loaded. Many of them also
		1222	cause AnyEvent to load additional modules - for example,
		1223	"PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
		1224	loaded.
		1225
		1226	All the environment variables documented here start with
		1227	"PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
		1228	Other modules are encouraged (but by no means required) to use
		1229	"PERL_ANYEVENT_SUBMODULE" if they have registered the
		1230	AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
		1231	AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
		1232	should not access env variables starting with "AE_", see below).
		1233
		1234	All variables can also be set via the "AE_" prefix, that is, instead of
		1235	setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
		1236	there is a clash btween anyevent and another program that uses
		1237	"AE_something" you can set the corresponding "PERL_ANYEVENT_something"
		1238	variable to the empty string, as those variables take precedence.
		1239
		1240	When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
		1241	their "PERL_ANYEVENT_xxx" counterpart unless that variable already
		1242	exists. If taint mode is on, then AnyEvent will remove *all* environment
		1243	variables starting with "PERL_ANYEVENT_" from %ENV (or replace them with
		1244	"undef" or the empty string, if the corresaponding "AE_" variable is
		1245	set).
		1246
		1247	The exact algorithm is currently:
		1248
		1249	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		1250	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		1251	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		1252
		1253	This ensures that child processes will not see the "AE_" variables.
		1254
		1255	The following environment variables are currently known to AnyEvent:
		1256
		1257	"PERL_ANYEVENT_VERBOSE"
		1258	By default, AnyEvent will log messages with loglevel 4 ("error") or
		1259	higher (see AnyEvent::Log). You can set this environment variable to
		1260	a numerical loglevel to make AnyEvent more (or less) talkative.
		1261
		1262	If you want to do more than just set the global logging level you
		1263	should have a look at "PERL_ANYEVENT_LOG", which allows much more
		1264	complex specifications.
		1265
		1266	When set to 0 ("off"), then no messages whatsoever will be logged
		1267	with everything else at defaults.
		1268
		1269	When set to 5 or higher ("warn"), AnyEvent warns about unexpected
		1270	conditions, such as not being able to load the event model specified
		1271	by "PERL_ANYEVENT_MODEL", or a guard callback throwing an exception
		1272	- this is the minimum recommended level for use during development.
		1273
		1274	When set to 7 or higher (info), AnyEvent reports which event model
		1275	it chooses.
		1276
		1277	When set to 8 or higher (debug), then AnyEvent will report extra
		1278	information on which optional modules it loads and how it implements
		1279	certain features.
		1280
		1281	"PERL_ANYEVENT_LOG"
		1282	Accepts rather complex logging specifications. For example, you
		1283	could log all "debug" messages of some module to stderr, warnings
		1284	and above to stderr, and errors and above to syslog, with:
		1285
		1286	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		1287
		1288	For the rather extensive details, see AnyEvent::Log.
		1289
		1290	This variable is evaluated when AnyEvent (or AnyEvent::Log) is
		1291	loaded, so will take effect even before AnyEvent has initialised
		1292	itself.
		1293
		1294	Note that specifying this environment variable causes the
		1295	AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
		1296	does not, so only using the latter saves a few hundred kB of memory
		1297	unless a module explicitly needs the extra features of
765	AnyEvent.	1298	AnyEvent::Log.
		1299
		1300	"PERL_ANYEVENT_STRICT"
		1301	AnyEvent does not do much argument checking by default, as thorough
		1302	argument checking is very costly. Setting this variable to a true
		1303	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1304	thoroughly check the arguments passed to most method calls. If it
		1305	finds any problems, it will croak.
		1306
		1307	In other words, enables "strict" mode.
		1308
		1309	Unlike "use strict" (or its modern cousin, "use common::sense", it
		1310	is definitely recommended to keep it off in production. Keeping
		1311	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1312	programs can be very useful, however.
		1313
		1314	"PERL_ANYEVENT_DEBUG_SHELL"
		1315	If this env variable is nonempty, then its contents will be
		1316	interpreted by "AnyEvent::Socket::parse_hostport" and
		1317	"AnyEvent::Debug::shell" (after replacing every occurance of $$ by
		1318	the process pid). The shell object is saved in
		1319	$AnyEvent::Debug::SHELL.
		1320
		1321	This happens when the first watcher is created.
		1322
		1323	For example, to bind a debug shell on a unix domain socket in
		1324	/tmp/debug<pid>.sock, you could use this:
		1325
		1326	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		1327	# connect with e.g.: socat readline /tmp/debug123.sock
		1328
		1329	Or to bind to tcp port 4545 on localhost:
		1330
		1331	PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
		1332	# connect with e.g.: telnet localhost 4545
		1333
		1334	Note that creating sockets in /tmp or on localhost is very unsafe on
		1335	multiuser systems.
		1336
		1337	"PERL_ANYEVENT_DEBUG_WRAP"
		1338	Can be set to 0, 1 or 2 and enables wrapping of all watchers for
		1339	debugging purposes. See "AnyEvent::Debug::wrap" for details.
		1340
		1341	"PERL_ANYEVENT_MODEL"
		1342	This can be used to specify the event model to be used by AnyEvent,
		1343	before auto detection and -probing kicks in.
		1344
		1345	It normally is a string consisting entirely of ASCII letters (e.g.
		1346	"EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
		1347	the resulting module name is loaded and - if the load was successful
		1348	- used as event model backend. If it fails to load then AnyEvent
		1349	will proceed with auto detection and -probing.
		1350
		1351	If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
		1352	then nothing gets prepended and the module name is used as-is (hint:
		1353	"::" at the end of a string designates a module name and quotes it
		1354	appropriately).
		1355
		1356	For example, to force the pure perl model (AnyEvent::Loop::Perl) you
		1357	could start your program like this:
		1358
		1359	PERL_ANYEVENT_MODEL=Perl perl ...
		1360
		1361	"PERL_ANYEVENT_IO_MODEL"
		1362	The current file I/O model - see AnyEvent::IO for more info.
		1363
		1364	At the moment, only "Perl" (small, pure-perl, synchronous) and
		1365	"IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
		1366	if AnyEvent::AIO can be loaded, otherwise it is "Perl".
		1367
		1368	"PERL_ANYEVENT_PROTOCOLS"
		1369	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		1370	preferences for IPv4 or IPv6. The default is unspecified (and might
		1371	change, or be the result of auto probing).
		1372
		1373	Must be set to a comma-separated list of protocols or address
		1374	families, current supported: "ipv4" and "ipv6". Only protocols
		1375	mentioned will be used, and preference will be given to protocols
		1376	mentioned earlier in the list.
		1377
		1378	This variable can effectively be used for denial-of-service attacks
		1379	against local programs (e.g. when setuid), although the impact is
		1380	likely small, as the program has to handle connection and other
		1381	failures anyways.
		1382
		1383	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		1384	IPv6, but support both and try to use both.
		1385	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		1386	resolve or contact IPv6 addresses.
		1387	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		1388	prefer IPv6 over IPv4.
		1389
		1390	"PERL_ANYEVENT_HOSTS"
		1391	This variable, if specified, overrides the /etc/hosts file used by
		1392	AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
		1393	read from that file instead.
		1394
		1395	"PERL_ANYEVENT_EDNS0"
		1396	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		1397	for DNS. This extension is generally useful to reduce DNS traffic,
		1398	especially when DNSSEC is involved, but some (broken) firewalls drop
		1399	such DNS packets, which is why it is off by default.
		1400
		1401	Setting this variable to 1 will cause AnyEvent::DNS to announce
		1402	EDNS0 in its DNS requests.
		1403
		1404	"PERL_ANYEVENT_MAX_FORKS"
		1405	The maximum number of child processes that
		1406	"AnyEvent::Util::fork_call" will create in parallel.
		1407
		1408	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1409	The default value for the "max_outstanding" parameter for the
		1410	default DNS resolver - this is the maximum number of parallel DNS
		1411	requests that are sent to the DNS server.
		1412
		1413	"PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
		1414	Perl has inherently racy signal handling (you can basically choose
		1415	between losing signals and memory corruption) - pure perl event
		1416	loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
		1417	available) therefore have to poll regularly to avoid losing signals.
		1418
		1419	Some event loops are racy, but don't poll regularly, and some event
		1420	loops are written in C but are still racy. For those event loops,
		1421	AnyEvent installs a timer that regularly wakes up the event loop.
		1422
		1423	By default, the interval for this timer is 10 seconds, but you can
		1424	override this delay with this environment variable (or by setting
		1425	the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
		1426	watchers).
		1427
		1428	Lower values increase CPU (and energy) usage, higher values can
		1429	introduce long delays when reaping children or waiting for signals.
		1430
		1431	The AnyEvent::Async module, if available, will be used to avoid this
		1432	polling (with most event loops).
		1433
		1434	"PERL_ANYEVENT_RESOLV_CONF"
		1435	The absolute path to a resolv.conf-style file to use instead of
		1436	/etc/resolv.conf (or the OS-specific configuration) in the default
		1437	resolver, or the empty string to select the default configuration.
		1438
		1439	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1440	When neither "ca_file" nor "ca_path" was specified during
		1441	AnyEvent::TLS context creation, and either of these environment
		1442	variables are nonempty, they will be used to specify CA certificate
		1443	locations instead of a system-dependent default.
		1444
		1445	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1446	When these are set to 1, then the respective modules are not loaded.
		1447	Mostly good for testing AnyEvent itself.
766		1448
767	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1449	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
768	This is an advanced topic that you do not normally need to use AnyEvent	1450	This is an advanced topic that you do not normally need to use AnyEvent
769	in a module. This section is only of use to event loop authors who want	1451	in a module. This section is only of use to event loop authors who want
770	to provide AnyEvent compatibility.	1452	to provide AnyEvent compatibility.
…		…
804		1486
805	*rxvt-unicode* also cheats a bit by not providing blocking access to	1487	*rxvt-unicode* also cheats a bit by not providing blocking access to
806	condition variables: code blocking while waiting for a condition will	1488	condition variables: code blocking while waiting for a condition will
807	"die". This still works with most modules/usages, and blocking calls	1489	"die". This still works with most modules/usages, and blocking calls
808	must not be done in an interactive application, so it makes sense.	1490	must not be done in an interactive application, so it makes sense.
809
810	ENVIRONMENT VARIABLES
811	The following environment variables are used by this module:
812
813	"PERL_ANYEVENT_VERBOSE"
814	By default, AnyEvent will be completely silent except in fatal
815	conditions. You can set this environment variable to make AnyEvent
816	more talkative.
817
818	When set to 1 or higher, causes AnyEvent to warn about unexpected
819	conditions, such as not being able to load the event model specified
820	by "PERL_ANYEVENT_MODEL".
821
822	When set to 2 or higher, cause AnyEvent to report to STDERR which
823	event model it chooses.
824
825	"PERL_ANYEVENT_STRICT"
826	AnyEvent does not do much argument checking by default, as thorough
827	argument checking is very costly. Setting this variable to a true
828	value will cause AnyEvent to load "AnyEvent::Strict" and then to
829	thoroughly check the arguments passed to most method calls. If it
830	finds any problems it will croak.
831
832	In other words, enables "strict" mode.
833
834	Unlike "use strict" it is definitely recommended ot keep it off in
835	production.
836
837	"PERL_ANYEVENT_MODEL"
838	This can be used to specify the event model to be used by AnyEvent,
839	before auto detection and -probing kicks in. It must be a string
840	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
841	gets prepended and the resulting module name is loaded and if the
842	load was successful, used as event model. If it fails to load
843	AnyEvent will proceed with auto detection and -probing.
844
845	This functionality might change in future versions.
846
847	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
848	could start your program like this:
849
850	PERL_ANYEVENT_MODEL=Perl perl ...
851
852	"PERL_ANYEVENT_PROTOCOLS"
853	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
854	preferences for IPv4 or IPv6. The default is unspecified (and might
855	change, or be the result of auto probing).
856
857	Must be set to a comma-separated list of protocols or address
858	families, current supported: "ipv4" and "ipv6". Only protocols
859	mentioned will be used, and preference will be given to protocols
860	mentioned earlier in the list.
861
862	This variable can effectively be used for denial-of-service attacks
863	against local programs (e.g. when setuid), although the impact is
864	likely small, as the program has to handle connection errors
865	already-
866
867	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
868	IPv6, but support both and try to use both.
869	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
870	resolve or contact IPv6 addresses.
871	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
872	prefer IPv6 over IPv4.
873
874	"PERL_ANYEVENT_EDNS0"
875	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
876	for DNS. This extension is generally useful to reduce DNS traffic,
877	but some (broken) firewalls drop such DNS packets, which is why it
878	is off by default.
879
880	Setting this variable to 1 will cause AnyEvent::DNS to announce
881	EDNS0 in its DNS requests.
882
883	"PERL_ANYEVENT_MAX_FORKS"
884	The maximum number of child processes that
885	"AnyEvent::Util::fork_call" will create in parallel.
886		1491
887	EXAMPLE PROGRAM	1492	EXAMPLE PROGRAM
888	The following program uses an I/O watcher to read data from STDIN, a	1493	The following program uses an I/O watcher to read data from STDIN, a
889	timer to display a message once per second, and a condition variable to	1494	timer to display a message once per second, and a condition variable to
890	quit the program when the user enters quit:	1495	quit the program when the user enters quit:
…		…
902	warn "read: $input\n"; # output what has been read	1507	warn "read: $input\n"; # output what has been read
903	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1508	$cv->send if $input =~ /^q/i; # quit program if /^q/i
904	},	1509	},
905	);	1510	);
906		1511
907	my $time_watcher; # can only be used once
908
909	sub new_timer {
910	$timer = AnyEvent->timer (after => 1, cb => sub {	1512	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
911	warn "timeout\n"; # print 'timeout' about every second	1513	warn "timeout\n"; # print 'timeout' at most every second
912	&new_timer; # and restart the time
913	});
914	}	1514	});
915
916	new_timer; # create first timer
917		1515
918	$cv->recv; # wait until user enters /^q/i	1516	$cv->recv; # wait until user enters /^q/i
919		1517
920	REAL-WORLD EXAMPLE	1518	REAL-WORLD EXAMPLE
921	Consider the Net::FCP module. It features (among others) the following	1519	Consider the Net::FCP module. It features (among others) the following
…		…
993		1591
994	The actual code goes further and collects all errors ("die"s,	1592	The actual code goes further and collects all errors ("die"s,
995	exceptions) that occurred during request processing. The "result" method	1593	exceptions) that occurred during request processing. The "result" method
996	detects whether an exception as thrown (it is stored inside the $txn	1594	detects whether an exception as thrown (it is stored inside the $txn
997	object) and just throws the exception, which means connection errors and	1595	object) and just throws the exception, which means connection errors and
998	other problems get reported tot he code that tries to use the result,	1596	other problems get reported to the code that tries to use the result,
999	not in a random callback.	1597	not in a random callback.
1000		1598
1001	All of this enables the following usage styles:	1599	All of this enables the following usage styles:
1002		1600
1003	1. Blocking:	1601	1. Blocking:
…		…
1021	my $txn = shift;	1619	my $txn = shift;
1022	my $data = $txn->result;	1620	my $data = $txn->result;
1023	...	1621	...
1024	});	1622	});
1025		1623
1026	EV::loop;	1624	EV::run;
1027		1625
1028	3b. The module user could use AnyEvent, too:	1626	3b. The module user could use AnyEvent, too:
1029		1627
1030	use AnyEvent;	1628	use AnyEvent;
1031		1629
…		…
1048	through AnyEvent. The benchmark creates a lot of timers (with a zero	1646	through AnyEvent. The benchmark creates a lot of timers (with a zero
1049	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1647	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1050	which it is), lets them fire exactly once and destroys them again.	1648	which it is), lets them fire exactly once and destroys them again.
1051		1649
1052	Source code for this benchmark is found as eg/bench in the AnyEvent	1650	Source code for this benchmark is found as eg/bench in the AnyEvent
1053	distribution.	1651	distribution. It uses the AE interface, which makes a real difference
		1652	for the EV and Perl backends only.
1054		1653
1055	Explanation of the columns	1654	Explanation of the columns
1056	*watcher* is the number of event watchers created/destroyed. Since	1655	*watcher* is the number of event watchers created/destroyed. Since
1057	different event models feature vastly different performances, each event	1656	different event models feature vastly different performances, each event
1058	loop was given a number of watchers so that overall runtime is	1657	loop was given a number of watchers so that overall runtime is
…		…
1077	*destroy* is the time, in microseconds, that it takes to destroy a	1676	*destroy* is the time, in microseconds, that it takes to destroy a
1078	single watcher.	1677	single watcher.
1079		1678
1080	Results	1679	Results
1081	name watchers bytes create invoke destroy comment	1680	name watchers bytes create invoke destroy comment
1082	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1681	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1083	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1682	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1084	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1683	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1085	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1684	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1086	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1685	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1087	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1686	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1687	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1688	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1088	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1689	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1089	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1690	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1090	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1691	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1091	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1692	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1092		1693
1093	Discussion	1694	Discussion
1094	The benchmark does *not* measure scalability of the event loop very	1695	The benchmark does *not* measure scalability of the event loop very
1095	well. For example, a select-based event loop (such as the pure perl one)	1696	well. For example, a select-based event loop (such as the pure perl one)
1096	can never compete with an event loop that uses epoll when the number of	1697	can never compete with an event loop that uses epoll when the number of
…		…
1107	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1708	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1108	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1709	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1109	CPU cycles with POE.	1710	CPU cycles with POE.
1110		1711
1111	"EV" is the sole leader regarding speed and memory use, which are both	1712	"EV" is the sole leader regarding speed and memory use, which are both
1112	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1713	maximal/minimal, respectively. When using the AE API there is zero
		1714	overhead (when going through the AnyEvent API create is about 5-6 times
		1715	slower, with other times being equal, so still uses far less memory than
1113	far less memory than any other event loop and is still faster than Event	1716	any other event loop and is still faster than Event natively).
1114	natively.
1115		1717
1116	The pure perl implementation is hit in a few sweet spots (both the	1718	The pure perl implementation is hit in a few sweet spots (both the
1117	constant timeout and the use of a single fd hit optimisations in the	1719	constant timeout and the use of a single fd hit optimisations in the
1118	perl interpreter and the backend itself). Nevertheless this shows that	1720	perl interpreter and the backend itself). Nevertheless this shows that
1119	it adds very little overhead in itself. Like any select-based backend	1721	it adds very little overhead in itself. Like any select-based backend
…		…
1121	few of them active), of course, but this was not subject of this	1723	few of them active), of course, but this was not subject of this
1122	benchmark.	1724	benchmark.
1123		1725
1124	The "Event" module has a relatively high setup and callback invocation	1726	The "Event" module has a relatively high setup and callback invocation
1125	cost, but overall scores in on the third place.	1727	cost, but overall scores in on the third place.
		1728
		1729	"IO::Async" performs admirably well, about on par with "Event", even
		1730	when using its pure perl backend.
1126		1731
1127	"Glib"'s memory usage is quite a bit higher, but it features a faster	1732	"Glib"'s memory usage is quite a bit higher, but it features a faster
1128	callback invocation and overall ends up in the same class as "Event".	1733	callback invocation and overall ends up in the same class as "Event".
1129	However, Glib scales extremely badly, doubling the number of watchers	1734	However, Glib scales extremely badly, doubling the number of watchers
1130	increases the processing time by more than a factor of four, making it	1735	increases the processing time by more than a factor of four, making it
…		…
1162	when used without AnyEvent), but most event loops have acceptable	1767	when used without AnyEvent), but most event loops have acceptable
1163	performance with or without AnyEvent.	1768	performance with or without AnyEvent.
1164		1769
1165	* The overhead AnyEvent adds is usually much smaller than the overhead	1770	* The overhead AnyEvent adds is usually much smaller than the overhead
1166	of the actual event loop, only with extremely fast event loops such	1771	of the actual event loop, only with extremely fast event loops such
1167	as EV adds AnyEvent significant overhead.	1772	as EV does AnyEvent add significant overhead.
1168		1773
1169	* You should avoid POE like the plague if you want performance or	1774	* You should avoid POE like the plague if you want performance or
1170	reasonable memory usage.	1775	reasonable memory usage.
1171		1776
1172	BENCHMARKING THE LARGE SERVER CASE	1777	BENCHMARKING THE LARGE SERVER CASE
…		…
1186	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1791	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1187	100 (1%) are active. This mirrors the activity of large servers with	1792	100 (1%) are active. This mirrors the activity of large servers with
1188	many connections, most of which are idle at any one point in time.	1793	many connections, most of which are idle at any one point in time.
1189		1794
1190	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1795	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1191	distribution.	1796	distribution. It uses the AE interface, which makes a real difference
		1797	for the EV and Perl backends only.
1192		1798
1193	Explanation of the columns	1799	Explanation of the columns
1194	*sockets* is the number of sockets, and twice the number of "servers"	1800	*sockets* is the number of sockets, and twice the number of "servers"
1195	(as each server has a read and write socket end).	1801	(as each server has a read and write socket end).
1196		1802
…		…
1201	single "request", that is, reading the token from the pipe and	1807	single "request", that is, reading the token from the pipe and
1202	forwarding it to another server. This includes deleting the old timeout	1808	forwarding it to another server. This includes deleting the old timeout
1203	and creating a new one that moves the timeout into the future.	1809	and creating a new one that moves the timeout into the future.
1204		1810
1205	Results	1811	Results
1206	name sockets create request	1812	name sockets create request
1207	EV 20000 69.01 11.16	1813	EV 20000 62.66 7.99
1208	Perl 20000 73.32 35.87	1814	Perl 20000 68.32 32.64
1209	Event 20000 212.62 257.32	1815	IOAsync 20000 174.06 101.15 epoll
1210	Glib 20000 651.16 1896.30	1816	IOAsync 20000 174.67 610.84 poll
		1817	Event 20000 202.69 242.91
		1818	Glib 20000 557.01 1689.52
1211	POE 20000 349.67 12317.24 uses POE::Loop::Event	1819	POE 20000 341.54 12086.32 uses POE::Loop::Event
1212		1820
1213	Discussion	1821	Discussion
1214	This benchmark *does* measure scalability and overall performance of the	1822	This benchmark *does* measure scalability and overall performance of the
1215	particular event loop.	1823	particular event loop.
1216		1824
1217	EV is again fastest. Since it is using epoll on my system, the setup	1825	EV is again fastest. Since it is using epoll on my system, the setup
1218	time is relatively high, though.	1826	time is relatively high, though.
1219		1827
1220	Perl surprisingly comes second. It is much faster than the C-based event	1828	Perl surprisingly comes second. It is much faster than the C-based event
1221	loops Event and Glib.	1829	loops Event and Glib.
		1830
		1831	IO::Async performs very well when using its epoll backend, and still
		1832	quite good compared to Glib when using its pure perl backend.
1222		1833
1223	Event suffers from high setup time as well (look at its code and you	1834	Event suffers from high setup time as well (look at its code and you
1224	will understand why). Callback invocation also has a high overhead	1835	will understand why). Callback invocation also has a high overhead
1225	compared to the "$_->() for .."-style loop that the Perl event loop	1836	compared to the "$_->() for .."-style loop that the Perl event loop
1226	uses. Event uses select or poll in basically all documented	1837	uses. Event uses select or poll in basically all documented
…		…
1277		1888
1278	Summary	1889	Summary
1279	* C-based event loops perform very well with small number of watchers,	1890	* C-based event loops perform very well with small number of watchers,
1280	as the management overhead dominates.	1891	as the management overhead dominates.
1281		1892
		1893	THE IO::Lambda BENCHMARK
		1894	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1895	could be misinterpreted to make AnyEvent look bad. In fact, the
		1896	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1897	better (which shouldn't come as a surprise to anybody). As such, the
		1898	benchmark is fine, and mostly shows that the AnyEvent backend from
		1899	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1900	without the extra baggage? To explore this, I wrote the equivalent
		1901	benchmark for AnyEvent.
		1902
		1903	The benchmark itself creates an echo-server, and then, for 500 times,
		1904	connects to the echo server, sends a line, waits for the reply, and then
		1905	creates the next connection. This is a rather bad benchmark, as it
		1906	doesn't test the efficiency of the framework or much non-blocking I/O,
		1907	but it is a benchmark nevertheless.
		1908
		1909	name runtime
		1910	Lambda/select 0.330 sec
		1911	+ optimized 0.122 sec
		1912	Lambda/AnyEvent 0.327 sec
		1913	+ optimized 0.138 sec
		1914	Raw sockets/select 0.077 sec
		1915	POE/select, components 0.662 sec
		1916	POE/select, raw sockets 0.226 sec
		1917	POE/select, optimized 0.404 sec
		1918
		1919	AnyEvent/select/nb 0.085 sec
		1920	AnyEvent/EV/nb 0.068 sec
		1921	+state machine 0.134 sec
		1922
		1923	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1924	benchmarks actually make blocking connects and use 100% blocking I/O,
		1925	defeating the purpose of an event-based solution. All of the newly
		1926	written AnyEvent benchmarks use 100% non-blocking connects (using
		1927	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1928	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1929	connects generally require a lot more bookkeeping and event handling
		1930	than blocking connects (which involve a single syscall only).
		1931
		1932	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1933	offers similar expressive power as POE and IO::Lambda, using
		1934	conventional Perl syntax. This means that both the echo server and the
		1935	client are 100% non-blocking, further placing it at a disadvantage.
		1936
		1937	As you can see, the AnyEvent + EV combination even beats the
		1938	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1939	backend easily beats IO::Lambda and POE.
		1940
		1941	And even the 100% non-blocking version written using the high-level (and
		1942	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1943	higher level ("unoptimised") abstractions by a large margin, even though
		1944	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1945
		1946	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1947	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1948	part of the IO::Lambda distribution and were used without any changes.
		1949
		1950	SIGNALS
		1951	AnyEvent currently installs handlers for these signals:
		1952
		1953	SIGCHLD
		1954	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1955	emulation for event loops that do not support them natively. Also,
		1956	some event loops install a similar handler.
		1957
		1958	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1959	then AnyEvent will reset it to default, to avoid losing child exit
		1960	statuses.
		1961
		1962	SIGPIPE
		1963	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1964	"undef" when AnyEvent gets loaded.
		1965
		1966	The rationale for this is that AnyEvent users usually do not really
		1967	depend on SIGPIPE delivery (which is purely an optimisation for
		1968	shell use, or badly-written programs), but "SIGPIPE" can cause
		1969	spurious and rare program exits as a lot of people do not expect
		1970	"SIGPIPE" when writing to some random socket.
		1971
		1972	The rationale for installing a no-op handler as opposed to ignoring
		1973	it is that this way, the handler will be restored to defaults on
		1974	exec.
		1975
		1976	Feel free to install your own handler, or reset it to defaults.
		1977
		1978	RECOMMENDED/OPTIONAL MODULES
		1979	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1980	its built-in modules) are required to use it.
		1981
		1982	That does not mean that AnyEvent won't take advantage of some additional
		1983	modules if they are installed.
		1984
		1985	This section explains which additional modules will be used, and how
		1986	they affect AnyEvent's operation.
		1987
		1988	Async::Interrupt
		1989	This slightly arcane module is used to implement fast signal
		1990	handling: To my knowledge, there is no way to do completely
		1991	race-free and quick signal handling in pure perl. To ensure that
		1992	signals still get delivered, AnyEvent will start an interval timer
		1993	to wake up perl (and catch the signals) with some delay (default is
		1994	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1995
		1996	If this module is available, then it will be used to implement
		1997	signal catching, which means that signals will not be delayed, and
		1998	the event loop will not be interrupted regularly, which is more
		1999	efficient (and good for battery life on laptops).
		2000
		2001	This affects not just the pure-perl event loop, but also other event
		2002	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2003
		2004	Some event loops (POE, Event, Event::Lib) offer signal watchers
		2005	natively, and either employ their own workarounds (POE) or use
		2006	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		2007	Installing Async::Interrupt does nothing for those backends.
		2008
		2009	EV This module isn't really "optional", as it is simply one of the
		2010	backend event loops that AnyEvent can use. However, it is simply the
		2011	best event loop available in terms of features, speed and stability:
		2012	It supports the AnyEvent API optimally, implements all the watcher
		2013	types in XS, does automatic timer adjustments even when no monotonic
		2014	clock is available, can take avdantage of advanced kernel interfaces
		2015	such as "epoll" and "kqueue", and is the fastest backend *by far*.
		2016	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		2017	Glib::EV).
		2018
		2019	If you only use backends that rely on another event loop (e.g.
		2020	"Tk"), then this module will do nothing for you.
		2021
		2022	Guard
		2023	The guard module, when used, will be used to implement
		2024	"AnyEvent::Util::guard". This speeds up guards considerably (and
		2025	uses a lot less memory), but otherwise doesn't affect guard
		2026	operation much. It is purely used for performance.
		2027
		2028	JSON and JSON::XS
		2029	One of these modules is required when you want to read or write JSON
		2030	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		2031	can take advantage of the ultra-high-speed JSON::XS module when it
		2032	is installed.
		2033
		2034	Net::SSLeay
		2035	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2036	worthwhile: If this module is installed, then AnyEvent::Handle (with
		2037	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		2038
		2039	Time::HiRes
		2040	This module is part of perl since release 5.008. It will be used
		2041	when the chosen event library does not come with a timing source of
		2042	its own. The pure-perl event loop (AnyEvent::Loop) will additionally
		2043	load it to try to use a monotonic clock for timing stability.
		2044
		2045	AnyEvent::AIO (and IO::AIO)
		2046	The default implementation of AnyEvent::IO is to do I/O
		2047	synchronously, stopping programs while they access the disk, which
		2048	is fine for a lot of programs.
		2049
		2050	Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
		2051	switch to a true asynchronous implementation, so event processing
		2052	can continue even while waiting for disk I/O.
		2053
1282	FORK	2054	FORK
1283	Most event libraries are not fork-safe. The ones who are usually are	2055	Most event libraries are not fork-safe. The ones who are usually are
1284	because they rely on inefficient but fork-safe "select" or "poll" calls.	2056	because they rely on inefficient but fork-safe "select" or "poll" calls
1285	Only EV is fully fork-aware.	2057	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		2058	epoll are usually badly thought-out hacks that are incompatible with
		2059	fork in one way or another. Only EV is fully fork-aware and ensures that
		2060	you continue event-processing in both parent and child (or both, if you
		2061	know what you are doing).
		2062
		2063	This means that, in general, you cannot fork and do event processing in
		2064	the child if the event library was initialised before the fork (which
		2065	usually happens when the first AnyEvent watcher is created, or the
		2066	library is loaded).
1286		2067
1287	If you have to fork, you must either do so *before* creating your first	2068	If you have to fork, you must either do so *before* creating your first
1288	watcher OR you must not use AnyEvent at all in the child.	2069	watcher OR you must not use AnyEvent at all in the child OR you must do
		2070	something completely out of the scope of AnyEvent (see below).
		2071
		2072	The problem of doing event processing in the parent *and* the child is
		2073	much more complicated: even for backends that *are* fork-aware or
		2074	fork-safe, their behaviour is not usually what you want: fork clones all
		2075	watchers, that means all timers, I/O watchers etc. are active in both
		2076	parent and child, which is almost never what you want. Using "exec" to
		2077	start worker children from some kind of manage prrocess is usually
		2078	preferred, because it is much easier and cleaner, at the expense of
		2079	having to have another binary.
		2080
		2081	In addition to logical problems with fork, there are also implementation
		2082	problems. For example, on POSIX systems, you cannot fork at all in Perl
		2083	code if a thread (I am talking of pthreads here) was ever created in the
		2084	process, and this is just the tip of the iceberg. In general, using fork
		2085	from Perl is difficult, and attempting to use fork without an exec to
		2086	implement some kind of parallel processing is almost certainly doomed.
		2087
		2088	To safely fork and exec, you should use a module such as Proc::FastSpawn
		2089	that let's you safely fork and exec new processes.
		2090
		2091	If you want to do multiprocessing using processes, you can look at the
		2092	AnyEvent::Fork module (and some related modules such as
		2093	AnyEvent::Fork::RPC, AnyEvent::Fork::Pool and AnyEvent::Fork::Remote).
		2094	This module allows you to safely create subprocesses without any
		2095	limitations - you can use X11 toolkits or AnyEvent in the children
		2096	created by AnyEvent::Fork safely and without any special precautions.
1289		2097
1290	SECURITY CONSIDERATIONS	2098	SECURITY CONSIDERATIONS
1291	AnyEvent can be forced to load any event model via	2099	AnyEvent can be forced to load any event model via
1292	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	2100	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1293	to execute arbitrary code or directly gain access, it can easily be used	2101	to execute arbitrary code or directly gain access, it can easily be used
…		…
1297		2105
1298	You can make AnyEvent completely ignore this variable by deleting it	2106	You can make AnyEvent completely ignore this variable by deleting it
1299	before the first watcher gets created, e.g. with a "BEGIN" block:	2107	before the first watcher gets created, e.g. with a "BEGIN" block:
1300		2108
1301	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	2109	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1302		2110
1303	use AnyEvent;	2111	use AnyEvent;
1304		2112
1305	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	2113	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1306	be used to probe what backend is used and gain other information (which	2114	be used to probe what backend is used and gain other information (which
1307	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),	2115	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1308	and $ENV{PERL_ANYEGENT_STRICT}.	2116	and $ENV{PERL_ANYEVENT_STRICT}.
		2117
		2118	Note that AnyEvent will remove *all* environment variables starting with
		2119	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		2120	enabled.
1309		2121
1310	BUGS	2122	BUGS
1311	Perl 5.8 has numerous memleaks that sometimes hit this module and are	2123	Perl 5.8 has numerous memleaks that sometimes hit this module and are
1312	hard to work around. If you suffer from memleaks, first upgrade to Perl	2124	hard to work around. If you suffer from memleaks, first upgrade to Perl
1313	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	2125	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1314	annoying mamleaks, such as leaking on "map" and "grep" but it is usually	2126	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1315	not as pronounced).	2127	not as pronounced).
1316		2128
1317	SEE ALSO	2129	SEE ALSO
1318	Utility functions: AnyEvent::Util.	2130	Tutorial/Introduction: AnyEvent::Intro.
1319		2131
1320	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	2132	FAQ: AnyEvent::FAQ.
1321	Event::Lib, Qt, POE.	2133
		2134	Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
		2135	(simply logging).
		2136
		2137	Development/Debugging: AnyEvent::Strict (stricter checking),
		2138	AnyEvent::Debug (interactive shell, watcher tracing).
		2139
		2140	Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
		2141	Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK, Cocoa::EventLoop, UV.
1322		2142
1323	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	2143	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1324	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	2144	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1325	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	2145	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		2146	AnyEvent::Impl::IOAsync, AnyEvent::Impl::Irssi, AnyEvent::Impl::FLTK,
		2147	AnyEvent::Impl::Cocoa, AnyEvent::Impl::UV.
1326		2148
1327	Non-blocking file handles, sockets, TCP clients and servers:	2149	Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1328	AnyEvent::Handle, AnyEvent::Socket.	2150	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		2151
		2152	Asynchronous File I/O: AnyEvent::IO.
1329		2153
1330	Asynchronous DNS: AnyEvent::DNS.	2154	Asynchronous DNS: AnyEvent::DNS.
1331		2155
1332	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	2156	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1333		2157
1334	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	2158	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
		2159	AnyEvent::HTTP.
1335		2160
1336	AUTHOR	2161	AUTHOR
1337	Marc Lehmann <schmorp@schmorp.de>	2162	Marc Lehmann <schmorp@schmorp.de>
1338	http://home.schmorp.de/	2163	http://anyevent.schmorp.de
1339		2164

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