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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, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	loops	5	Qt, FLTK and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# if you prefer function calls, look at the AE manpage for
		11	# an alternative API.
		12
		13	# file handle or descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { ... });	14	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
11		15
		16	# one-shot or repeating timers
12	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });	17	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
13	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...	18	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
14		19
15	print AnyEvent->now; # prints current event loop time	20	print AnyEvent->now; # prints current event loop time
16	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.	21	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
17		22
		23	# POSIX signal
18	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });	24	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
19		25
		26	# child process exit
20	my $w = AnyEvent->child (pid => $pid, cb => sub {	27	my $w = AnyEvent->child (pid => $pid, cb => sub {
21	my ($pid, $status) = @_;	28	my ($pid, $status) = @_;
22	...	29	...
23	});	30	});
		31
		32	# called when event loop idle (if applicable)
		33	my $w = AnyEvent->idle (cb => sub { ... });
24		34
25	my $w = AnyEvent->condvar; # stores whether a condition was flagged	35	my $w = AnyEvent->condvar; # stores whether a condition was flagged
26	$w->send; # wake up current and all future recv's	36	$w->send; # wake up current and all future recv's
27	$w->recv; # enters "main loop" till $condvar gets ->send	37	$w->recv; # enters "main loop" till $condvar gets ->send
28	# use a condvar in callback mode:	38	# use a condvar in callback mode:
…		…
30		40
31	INTRODUCTION/TUTORIAL	41	INTRODUCTION/TUTORIAL
32	This manpage is mainly a reference manual. If you are interested in a	42	This manpage is mainly a reference manual. If you are interested in a
33	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	43	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
34	manpage.	44	manpage.
		45
		46	SUPPORT
		47	An FAQ document is available as AnyEvent::FAQ.
		48
		49	There also is a mailinglist for discussing all things AnyEvent, and an
		50	IRC channel, too.
		51
		52	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		53	Repository, at <http://anyevent.schmorp.de>, for more info.
35		54
36	WHY YOU SHOULD USE THIS MODULE (OR NOT)	55	WHY YOU SHOULD USE THIS MODULE (OR NOT)
37	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	56	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
38	nowadays. So what is different about AnyEvent?	57	nowadays. So what is different about AnyEvent?
39		58
…		…
54	module users into the same thing by forcing them to use the same event	73	module users into the same thing by forcing them to use the same event
55	model you use.	74	model you use.
56		75
57	For modules like POE or IO::Async (which is a total misnomer as it is	76	For modules like POE or IO::Async (which is a total misnomer as it is
58	actually doing all I/O *synchronously*...), using them in your module is	77	actually doing all I/O *synchronously*...), using them in your module is
59	like joining a cult: After you joined, you are dependent on them and you	78	like joining a cult: After you join, you are dependent on them and you
60	cannot use anything else, as they are simply incompatible to everything	79	cannot use anything else, as they are simply incompatible to everything
61	that isn't them. What's worse, all the potential users of your module	80	that isn't them. What's worse, all the potential users of your module
62	are *also* forced to use the same event loop you use.	81	are *also* forced to use the same event loop you use.
63		82
64	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	83	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
65	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	84	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
66	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your	85	with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
67	module uses one of those, every user of your module has to use it, too.	86	uses one of those, every user of your module has to use it, too. But if
68	But if your module uses AnyEvent, it works transparently with all event	87	your module uses AnyEvent, it works transparently with all event models
69	models it supports (including stuff like IO::Async, as long as those use	88	it supports (including stuff like IO::Async, as long as those use one of
70	one of the supported event loops. It is trivial to add new event loops	89	the supported event loops. It is easy to add new event loops to
71	to AnyEvent, too, so it is future-proof).	90	AnyEvent, too, so it is future-proof).
72		91
73	In addition to being free of having to use *the one and only true event	92	In addition to being free of having to use *the one and only true event
74	model*, AnyEvent also is free of bloat and policy: with POE or similar	93	model*, AnyEvent also is free of bloat and policy: with POE or similar
75	modules, you get an enormous amount of code and strict rules you have to	94	modules, you get an enormous amount of code and strict rules you have to
76	follow. AnyEvent, on the other hand, is lean and up to the point, by	95	follow. AnyEvent, on the other hand, is lean and to the point, by only
77	only offering the functionality that is necessary, in as thin as a	96	offering the functionality that is necessary, in as thin as a wrapper as
78	wrapper as technically possible.	97	technically possible.
79		98
80	Of course, AnyEvent comes with a big (and fully optional!) toolbox of	99	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
81	useful functionality, such as an asynchronous DNS resolver, 100%	100	useful functionality, such as an asynchronous DNS resolver, 100%
82	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms	101	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
83	such as Windows) and lots of real-world knowledge and workarounds for	102	such as Windows) and lots of real-world knowledge and workarounds for
…		…
86	Now, if you *do want* lots of policy (this can arguably be somewhat	105	Now, if you *do want* lots of policy (this can arguably be somewhat
87	useful) and you want to force your users to use the one and only event	106	useful) and you want to force your users to use the one and only event
88	model, you should *not* use this module.	107	model, you should *not* use this module.
89		108
90	DESCRIPTION	109	DESCRIPTION
91	AnyEvent provides an identical interface to multiple event loops. This	110	AnyEvent provides a uniform interface to various event loops. This
92	allows module authors to utilise an event loop without forcing module	111	allows module authors to use event loop functionality without forcing
93	users to use the same event loop (as only a single event loop can	112	module users to use a specific event loop implementation (since more
94	coexist peacefully at any one time).	113	than one event loop cannot coexist peacefully).
95		114
96	The interface itself is vaguely similar, but not identical to the Event	115	The interface itself is vaguely similar, but not identical to the Event
97	module.	116	module.
98		117
99	During the first call of any watcher-creation method, the module tries	118	During the first call of any watcher-creation method, the module tries
100	to detect the currently loaded event loop by probing whether one of the	119	to detect the currently loaded event loop by probing whether one of the
101	following modules is already loaded: EV, Event, Glib,	120	following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
102	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is	121	Tk, Event::Lib, Qt, POE. The first one found is used. If none are
103	used. If none are found, the module tries to load these modules	122	detected, the module tries to load the first four modules in the order
104	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	123	given; but note that if EV is not available, the pure-perl
105	always succeed) in the order given. The first one that can be	124	AnyEvent::Loop should always work, so the other two are not normally
106	successfully loaded will be used. If, after this, still none could be	125	tried.
107	found, AnyEvent will fall back to a pure-perl event loop, which is not
108	very efficient, but should work everywhere.
109		126
110	Because AnyEvent first checks for modules that are already loaded,	127	Because AnyEvent first checks for modules that are already loaded,
111	loading an event model explicitly before first using AnyEvent will	128	loading an event model explicitly before first using AnyEvent will
112	likely make that model the default. For example:	129	likely make that model the default. For example:
113		130
…		…
115	use AnyEvent;	132	use AnyEvent;
116		133
117	# .. AnyEvent will likely default to Tk	134	# .. AnyEvent will likely default to Tk
118		135
119	The *likely* means that, if any module loads another event model and	136	The *likely* means that, if any module loads another event model and
120	starts using it, all bets are off. Maybe you should tell their authors	137	starts using it, all bets are off - this case should be very rare
121	to use AnyEvent so their modules work together with others seamlessly...	138	though, as very few modules hardcode event loops without announcing this
		139	very loudly.
122		140
123	The pure-perl implementation of AnyEvent is called	141	The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
124	"AnyEvent::Impl::Perl". Like other event modules you can load it	142	Like other event modules you can load it explicitly and enjoy the high
125	explicitly and enjoy the high availability of that event loop :)	143	availability of that event loop :)
126		144
127	WATCHERS	145	WATCHERS
128	AnyEvent has the central concept of a *watcher*, which is an object that	146	AnyEvent has the central concept of a *watcher*, which is an object that
129	stores relevant data for each kind of event you are waiting for, such as	147	stores relevant data for each kind of event you are waiting for, such as
130	the callback to call, the file handle to watch, etc.	148	the callback to call, the file handle to watch, etc.
…		…
132	These watchers are normal Perl objects with normal Perl lifetime. After	150	These watchers are normal Perl objects with normal Perl lifetime. After
133	creating a watcher it will immediately "watch" for events and invoke the	151	creating a watcher it will immediately "watch" for events and invoke the
134	callback when the event occurs (of course, only when the event model is	152	callback when the event occurs (of course, only when the event model is
135	in control).	153	in control).
136		154
		155	Note that callbacks must not permanently change global variables
		156	potentially in use by the event loop (such as $_ or $[) and that
		157	callbacks must not "die". The former is good programming practice in
		158	Perl and the latter stems from the fact that exception handling differs
		159	widely between event loops.
		160
137	To disable the watcher you have to destroy it (e.g. by setting the	161	To disable a watcher you have to destroy it (e.g. by setting the
138	variable you store it in to "undef" or otherwise deleting all references	162	variable you store it in to "undef" or otherwise deleting all references
139	to it).	163	to it).
140		164
141	All watchers are created by calling a method on the "AnyEvent" class.	165	All watchers are created by calling a method on the "AnyEvent" class.
142		166
143	Many watchers either are used with "recursion" (repeating timers for	167	Many watchers either are used with "recursion" (repeating timers for
144	example), or need to refer to their watcher object in other ways.	168	example), or need to refer to their watcher object in other ways.
145		169
146	An any way to achieve that is this pattern:	170	One way to achieve that is this pattern:
147		171
148	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	172	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
149	# you can use $w here, for example to undef it	173	# you can use $w here, for example to undef it
150	undef $w;	174	undef $w;
151	});	175	});
…		…
153	Note that "my $w; $w =" combination. This is necessary because in Perl,	177	Note that "my $w; $w =" combination. This is necessary because in Perl,
154	my variables are only visible after the statement in which they are	178	my variables are only visible after the statement in which they are
155	declared.	179	declared.
156		180
157	I/O WATCHERS	181	I/O WATCHERS
		182	$w = AnyEvent->io (
		183	fh => <filehandle_or_fileno>,
		184	poll => <"r" or "w">,
		185	cb => <callback>,
		186	);
		187
158	You can create an I/O watcher by calling the "AnyEvent->io" method with	188	You can create an I/O watcher by calling the "AnyEvent->io" method with
159	the following mandatory key-value pairs as arguments:	189	the following mandatory key-value pairs as arguments:
160		190
161	"fh" the Perl *file handle* (*not* file descriptor) to watch for events	191	"fh" is the Perl *file handle* (or a naked file descriptor) to watch for
162	(AnyEvent might or might not keep a reference to this file handle).	192	events (AnyEvent might or might not keep a reference to this file
		193	handle). Note that only file handles pointing to things for which
		194	non-blocking operation makes sense are allowed. This includes sockets,
		195	most character devices, pipes, fifos and so on, but not for example
		196	files or block devices.
		197
163	"poll" must be a string that is either "r" or "w", which creates a	198	"poll" must be a string that is either "r" or "w", which creates a
164	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	199	watcher waiting for "r"eadable or "w"ritable events, respectively.
		200
165	is the callback to invoke each time the file handle becomes ready.	201	"cb" is the callback to invoke each time the file handle becomes ready.
166		202
167	Although the callback might get passed parameters, their value and	203	Although the callback might get passed parameters, their value and
168	presence is undefined and you cannot rely on them. Portable AnyEvent	204	presence is undefined and you cannot rely on them. Portable AnyEvent
169	callbacks cannot use arguments passed to I/O watcher callbacks.	205	callbacks cannot use arguments passed to I/O watcher callbacks.
170		206
171	The I/O watcher might use the underlying file descriptor or a copy of	207	The I/O watcher might use the underlying file descriptor or a copy of
172	it. You must not close a file handle as long as any watcher is active on	208	it. You must not close a file handle as long as any watcher is active on
173	the underlying file descriptor.	209	the underlying file descriptor.
174		210
175	Some event loops issue spurious readyness notifications, so you should	211	Some event loops issue spurious readiness notifications, so you should
176	always use non-blocking calls when reading/writing from/to your file	212	always use non-blocking calls when reading/writing from/to your file
177	handles.	213	handles.
178		214
179	Example: wait for readability of STDIN, then read a line and disable the	215	Example: wait for readability of STDIN, then read a line and disable the
180	watcher.	216	watcher.
…		…
184	warn "read: $input\n";	220	warn "read: $input\n";
185	undef $w;	221	undef $w;
186	});	222	});
187		223
188	TIME WATCHERS	224	TIME WATCHERS
		225	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		226
		227	$w = AnyEvent->timer (
		228	after => <fractional_seconds>,
		229	interval => <fractional_seconds>,
		230	cb => <callback>,
		231	);
		232
189	You can create a time watcher by calling the "AnyEvent->timer" method	233	You can create a time watcher by calling the "AnyEvent->timer" method
190	with the following mandatory arguments:	234	with the following mandatory arguments:
191		235
192	"after" specifies after how many seconds (fractional values are	236	"after" specifies after how many seconds (fractional values are
193	supported) the callback should be invoked. "cb" is the callback to	237	supported) the callback should be invoked. "cb" is the callback to
…		…
195		239
196	Although the callback might get passed parameters, their value and	240	Although the callback might get passed parameters, their value and
197	presence is undefined and you cannot rely on them. Portable AnyEvent	241	presence is undefined and you cannot rely on them. Portable AnyEvent
198	callbacks cannot use arguments passed to time watcher callbacks.	242	callbacks cannot use arguments passed to time watcher callbacks.
199		243
200	The callback will normally be invoked once only. If you specify another	244	The callback will normally be invoked only once. If you specify another
201	parameter, "interval", as a strictly positive number (> 0), then the	245	parameter, "interval", as a strictly positive number (> 0), then the
202	callback will be invoked regularly at that interval (in fractional	246	callback will be invoked regularly at that interval (in fractional
203	seconds) after the first invocation. If "interval" is specified with a	247	seconds) after the first invocation. If "interval" is specified with a
204	false value, then it is treated as if it were missing.	248	false value, then it is treated as if it were not specified at all.
205		249
206	The callback will be rescheduled before invoking the callback, but no	250	The callback will be rescheduled before invoking the callback, but no
207	attempt is done to avoid timer drift in most backends, so the interval	251	attempt is made to avoid timer drift in most backends, so the interval
208	is only approximate.	252	is only approximate.
209		253
210	Example: fire an event after 7.7 seconds.	254	Example: fire an event after 7.7 seconds.
211		255
212	my $w = AnyEvent->timer (after => 7.7, cb => sub {	256	my $w = AnyEvent->timer (after => 7.7, cb => sub {
…		…
218		262
219	Example 2: fire an event after 0.5 seconds, then roughly every second.	263	Example 2: fire an event after 0.5 seconds, then roughly every second.
220		264
221	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {	265	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
222	warn "timeout\n";	266	warn "timeout\n";
223	};	267	});
224		268
225	TIMING ISSUES	269	TIMING ISSUES
226	There are two ways to handle timers: based on real time (relative, "fire	270	There are two ways to handle timers: based on real time (relative, "fire
227	in 10 seconds") and based on wallclock time (absolute, "fire at 12	271	in 10 seconds") and based on wallclock time (absolute, "fire at 12
228	o'clock").	272	o'clock").
229		273
230	While most event loops expect timers to specified in a relative way,	274	While most event loops expect timers to specified in a relative way,
231	they use absolute time internally. This makes a difference when your	275	they use absolute time internally. This makes a difference when your
232	clock "jumps", for example, when ntp decides to set your clock backwards	276	clock "jumps", for example, when ntp decides to set your clock backwards
233	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is	277	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
234	supposed to fire "after" a second might actually take six years to	278	supposed to fire "after a second" might actually take six years to
235	finally fire.	279	finally fire.
236		280
237	AnyEvent cannot compensate for this. The only event loop that is	281	AnyEvent cannot compensate for this. The only event loop that is
238	conscious about these issues is EV, which offers both relative	282	conscious of these issues is EV, which offers both relative (ev_timer,
239	(ev_timer, based on true relative time) and absolute (ev_periodic, based	283	based on true relative time) and absolute (ev_periodic, based on
240	on wallclock time) timers.	284	wallclock time) timers.
241		285
242	AnyEvent always prefers relative timers, if available, matching the	286	AnyEvent always prefers relative timers, if available, matching the
243	AnyEvent API.	287	AnyEvent API.
244		288
245	AnyEvent has two additional methods that return the "current time":	289	AnyEvent has two additional methods that return the "current time":
…		…
264	*In almost all cases (in all cases if you don't care), this is the	308	*In almost all cases (in all cases if you don't care), this is the
265	function to call when you want to know the current time.*	309	function to call when you want to know the current time.*
266		310
267	This function is also often faster then "AnyEvent->time", and thus	311	This function is also often faster then "AnyEvent->time", and thus
268	the preferred method if you want some timestamp (for example,	312	the preferred method if you want some timestamp (for example,
269	AnyEvent::Handle uses this to update it's activity timeouts).	313	AnyEvent::Handle uses this to update its activity timeouts).
270		314
271	The rest of this section is only of relevance if you try to be very	315	The rest of this section is only of relevance if you try to be very
272	exact with your timing, you can skip it without bad conscience.	316	exact with your timing; you can skip it without a bad conscience.
273		317
274	For a practical example of when these times differ, consider	318	For a practical example of when these times differ, consider
275	Event::Lib and EV and the following set-up:	319	Event::Lib and EV and the following set-up:
276		320
277	The event loop is running and has just invoked one of your callback	321	The event loop is running and has just invoked one of your callbacks
278	at time=500 (assume no other callbacks delay processing). In your	322	at time=500 (assume no other callbacks delay processing). In your
279	callback, you wait a second by executing "sleep 1" (blocking the	323	callback, you wait a second by executing "sleep 1" (blocking the
280	process for a second) and then (at time=501) you create a relative	324	process for a second) and then (at time=501) you create a relative
281	timer that fires after three seconds.	325	timer that fires after three seconds.
282		326
…		…
302	In either case, if you care (and in most cases, you don't), then you	346	In either case, if you care (and in most cases, you don't), then you
303	can get whatever behaviour you want with any event loop, by taking	347	can get whatever behaviour you want with any event loop, by taking
304	the difference between "AnyEvent->time" and "AnyEvent->now" into	348	the difference between "AnyEvent->time" and "AnyEvent->now" into
305	account.	349	account.
306		350
		351	AnyEvent->now_update
		352	Some event loops (such as EV or AnyEvent::Loop) cache the current
		353	time for each loop iteration (see the discussion of AnyEvent->now,
		354	above).
		355
		356	When a callback runs for a long time (or when the process sleeps),
		357	then this "current" time will differ substantially from the real
		358	time, which might affect timers and time-outs.
		359
		360	When this is the case, you can call this method, which will update
		361	the event loop's idea of "current time".
		362
		363	A typical example would be a script in a web server (e.g.
		364	"mod_perl") - when mod_perl executes the script, then the event loop
		365	will have the wrong idea about the "current time" (being potentially
		366	far in the past, when the script ran the last time). In that case
		367	you should arrange a call to "AnyEvent->now_update" each time the
		368	web server process wakes up again (e.g. at the start of your script,
		369	or in a handler).
		370
		371	Note that updating the time *might* cause some events to be handled.
		372
307	SIGNAL WATCHERS	373	SIGNAL WATCHERS
		374	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		375
308	You can watch for signals using a signal watcher, "signal" is the signal	376	You can watch for signals using a signal watcher, "signal" is the signal
309	*name* in uppercase and without any "SIG" prefix, "cb" is the Perl	377	*name* in uppercase and without any "SIG" prefix, "cb" is the Perl
310	callback to be invoked whenever a signal occurs.	378	callback to be invoked whenever a signal occurs.
311		379
312	Although the callback might get passed parameters, their value and	380	Although the callback might get passed parameters, their value and
…		…
317	invocation, and callback invocation will be synchronous. Synchronous	385	invocation, and callback invocation will be synchronous. Synchronous
318	means that it might take a while until the signal gets handled by the	386	means that it might take a while until the signal gets handled by the
319	process, but it is guaranteed not to interrupt any other callbacks.	387	process, but it is guaranteed not to interrupt any other callbacks.
320		388
321	The main advantage of using these watchers is that you can share a	389	The main advantage of using these watchers is that you can share a
322	signal between multiple watchers.	390	signal between multiple watchers, and AnyEvent will ensure that signals
		391	will not interrupt your program at bad times.
323		392
324	This watcher might use %SIG, so programs overwriting those signals	393	This watcher might use %SIG (depending on the event loop used), so
325	directly will likely not work correctly.	394	programs overwriting those signals directly will likely not work
		395	correctly.
326		396
327	Example: exit on SIGINT	397	Example: exit on SIGINT
328		398
329	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	399	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
330		400
		401	Restart Behaviour
		402	While restart behaviour is up to the event loop implementation, most
		403	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		404	pure perl implementation).
		405
		406	Safe/Unsafe Signals
		407	Perl signals can be either "safe" (synchronous to opcode handling) or
		408	"unsafe" (asynchronous) - the former might delay signal delivery
		409	indefinitely, the latter might corrupt your memory.
		410
		411	AnyEvent signal handlers are, in addition, synchronous to the event
		412	loop, i.e. they will not interrupt your running perl program but will
		413	only be called as part of the normal event handling (just like timer,
		414	I/O etc. callbacks, too).
		415
		416	Signal Races, Delays and Workarounds
		417	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		418	callbacks to signals in a generic way, which is a pity, as you cannot do
		419	race-free signal handling in perl, requiring C libraries for this.
		420	AnyEvent will try to do its best, which means in some cases, signals
		421	will be delayed. The maximum time a signal might be delayed is 10
		422	seconds by default, but can be overriden via
		423	$ENV{PERL_ANYEVENT_MAX_SIGNAL_LATENCY} or $AnyEvent::MAX_SIGNAL_LATENCY
		424	- see the "ENVIRONMENT VARIABLES" section for details.
		425
		426	All these problems can be avoided by installing the optional
		427	Async::Interrupt module, which works with most event loops. It will not
		428	work with inherently broken event loops such as Event or Event::Lib (and
		429	not with POE currently). For those, you just have to suffer the delays.
		430
331	CHILD PROCESS WATCHERS	431	CHILD PROCESS WATCHERS
		432	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		433
332	You can also watch on a child process exit and catch its exit status.	434	You can also watch for a child process exit and catch its exit status.
333		435
334	The child process is specified by the "pid" argument (if set to 0, it	436	The child process is specified by the "pid" argument (on some backends,
335	watches for any child process exit). The watcher will triggered only	437	using 0 watches for any child process exit, on others this will croak).
336	when the child process has finished and an exit status is available, not	438	The watcher will be triggered only when the child process has finished
337	on any trace events (stopped/continued).	439	and an exit status is available, not on any trace events
		440	(stopped/continued).
338		441
339	The callback will be called with the pid and exit status (as returned by	442	The callback will be called with the pid and exit status (as returned by
340	waitpid), so unlike other watcher types, you *can* rely on child watcher	443	waitpid), so unlike other watcher types, you *can* rely on child watcher
341	callback arguments.	444	callback arguments.
342		445
…		…
347		450
348	There is a slight catch to child watchers, however: you usually start	451	There is a slight catch to child watchers, however: you usually start
349	them *after* the child process was created, and this means the process	452	them *after* the child process was created, and this means the process
350	could have exited already (and no SIGCHLD will be sent anymore).	453	could have exited already (and no SIGCHLD will be sent anymore).
351		454
352	Not all event models handle this correctly (POE doesn't), but even for	455	Not all event models handle this correctly (neither POE nor IO::Async
		456	do, see their AnyEvent::Impl manpages for details), but even for event
353	event models that *do* handle this correctly, they usually need to be	457	models that *do* handle this correctly, they usually need to be loaded
354	loaded before the process exits (i.e. before you fork in the first	458	before the process exits (i.e. before you fork in the first place).
355	place).	459	AnyEvent's pure perl event loop handles all cases correctly regardless
		460	of when you start the watcher.
356		461
357	This means you cannot create a child watcher as the very first thing in	462	This means you cannot create a child watcher as the very first thing in
358	an AnyEvent program, you *have* to create at least one watcher before	463	an AnyEvent program, you *have* to create at least one watcher before
359	you "fork" the child (alternatively, you can call "AnyEvent::detect").	464	you "fork" the child (alternatively, you can call "AnyEvent::detect").
360		465
		466	As most event loops do not support waiting for child events, they will
		467	be emulated by AnyEvent in most cases, in which case the latency and
		468	race problems mentioned in the description of signal watchers apply.
		469
361	Example: fork a process and wait for it	470	Example: fork a process and wait for it
362		471
363	my $done = AnyEvent->condvar;	472	my $done = AnyEvent->condvar;
364		473
365	my $pid = fork or exit 5;	474	my $pid = fork or exit 5;
366		475
367	my $w = AnyEvent->child (	476	my $w = AnyEvent->child (
368	pid => $pid,	477	pid => $pid,
369	cb => sub {	478	cb => sub {
370	my ($pid, $status) = @_;	479	my ($pid, $status) = @_;
371	warn "pid $pid exited with status $status";	480	warn "pid $pid exited with status $status";
372	$done->send;	481	$done->send;
373	},	482	},
374	);	483	);
375		484
376	# do something else, then wait for process exit	485	# do something else, then wait for process exit
377	$done->recv;	486	$done->recv;
378		487
		488	IDLE WATCHERS
		489	$w = AnyEvent->idle (cb => <callback>);
		490
		491	This will repeatedly invoke the callback after the process becomes idle,
		492	until either the watcher is destroyed or new events have been detected.
		493
		494	Idle watchers are useful when there is a need to do something, but it is
		495	not so important (or wise) to do it instantly. The callback will be
		496	invoked only when there is "nothing better to do", which is usually
		497	defined as "all outstanding events have been handled and no new events
		498	have been detected". That means that idle watchers ideally get invoked
		499	when the event loop has just polled for new events but none have been
		500	detected. Instead of blocking to wait for more events, the idle watchers
		501	will be invoked.
		502
		503	Unfortunately, most event loops do not really support idle watchers
		504	(only EV, Event and Glib do it in a usable fashion) - for the rest,
		505	AnyEvent will simply call the callback "from time to time".
		506
		507	Example: read lines from STDIN, but only process them when the program
		508	is otherwise idle:
		509
		510	my @lines; # read data
		511	my $idle_w;
		512	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		513	push @lines, scalar <STDIN>;
		514
		515	# start an idle watcher, if not already done
		516	$idle_w ||= AnyEvent->idle (cb => sub {
		517	# handle only one line, when there are lines left
		518	if (my $line = shift @lines) {
		519	print "handled when idle: $line";
		520	} else {
		521	# otherwise disable the idle watcher again
		522	undef $idle_w;
		523	}
		524	});
		525	});
		526
379	CONDITION VARIABLES	527	CONDITION VARIABLES
		528	$cv = AnyEvent->condvar;
		529
		530	$cv->send (<list>);
		531	my @res = $cv->recv;
		532
380	If you are familiar with some event loops you will know that all of them	533	If you are familiar with some event loops you will know that all of them
381	require you to run some blocking "loop", "run" or similar function that	534	require you to run some blocking "loop", "run" or similar function that
382	will actively watch for new events and call your callbacks.	535	will actively watch for new events and call your callbacks.
383		536
384	AnyEvent is different, it expects somebody else to run the event loop	537	AnyEvent is slightly different: it expects somebody else to run the
385	and will only block when necessary (usually when told by the user).	538	event loop and will only block when necessary (usually when told by the
		539	user).
386		540
387	The instrument to do that is called a "condition variable", so called	541	The tool to do that is called a "condition variable", so called because
388	because they represent a condition that must become true.	542	they represent a condition that must become true.
		543
		544	Now is probably a good time to look at the examples further below.
389		545
390	Condition variables can be created by calling the "AnyEvent->condvar"	546	Condition variables can be created by calling the "AnyEvent->condvar"
391	method, usually without arguments. The only argument pair allowed is	547	method, usually without arguments. The only argument pair allowed is
392
393	"cb", which specifies a callback to be called when the condition	548	"cb", which specifies a callback to be called when the condition
394	variable becomes true, with the condition variable as the first argument	549	variable becomes true, with the condition variable as the first argument
395	(but not the results).	550	(but not the results).
396		551
397	After creation, the condition variable is "false" until it becomes	552	After creation, the condition variable is "false" until it becomes
398	"true" by calling the "send" method (or calling the condition variable	553	"true" by calling the "send" method (or calling the condition variable
399	as if it were a callback, read about the caveats in the description for	554	as if it were a callback, read about the caveats in the description for
400	the "->send" method).	555	the "->send" method).
401		556
402	Condition variables are similar to callbacks, except that you can	557	Since condition variables are the most complex part of the AnyEvent API,
403	optionally wait for them. They can also be called merge points - points	558	here are some different mental models of what they are - pick the ones
404	in time where multiple outstanding events have been processed. And yet	559	you can connect to:
405	another way to call them is transactions - each condition variable can	560
406	be used to represent a transaction, which finishes at some point and	561	* Condition variables are like callbacks - you can call them (and pass
407	delivers a result.	562	them instead of callbacks). Unlike callbacks however, you can also
		563	wait for them to be called.
		564
		565	* Condition variables are signals - one side can emit or send them,
		566	the other side can wait for them, or install a handler that is
		567	called when the signal fires.
		568
		569	* Condition variables are like "Merge Points" - points in your program
		570	where you merge multiple independent results/control flows into one.
		571
		572	* Condition variables represent a transaction - functions that start
		573	some kind of transaction can return them, leaving the caller the
		574	choice between waiting in a blocking fashion, or setting a callback.
		575
		576	* Condition variables represent future values, or promises to deliver
		577	some result, long before the result is available.
408		578
409	Condition variables are very useful to signal that something has	579	Condition variables are very useful to signal that something has
410	finished, for example, if you write a module that does asynchronous http	580	finished, for example, if you write a module that does asynchronous http
411	requests, then a condition variable would be the ideal candidate to	581	requests, then a condition variable would be the ideal candidate to
412	signal the availability of results. The user can either act when the	582	signal the availability of results. The user can either act when the
…		…
425		595
426	Condition variables are represented by hash refs in perl, and the keys	596	Condition variables are represented by hash refs in perl, and the keys
427	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy	597	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
428	(it is often useful to build your own transaction class on top of	598	(it is often useful to build your own transaction class on top of
429	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call	599	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
430	it's "new" method in your own "new" method.	600	its "new" method in your own "new" method.
431		601
432	There are two "sides" to a condition variable - the "producer side"	602	There are two "sides" to a condition variable - the "producer side"
433	which eventually calls "-> send", and the "consumer side", which waits	603	which eventually calls "-> send", and the "consumer side", which waits
434	for the send to occur.	604	for the send to occur.
435		605
436	Example: wait for a timer.	606	Example: wait for a timer.
437		607
438	# wait till the result is ready	608	# condition: "wait till the timer is fired"
439	my $result_ready = AnyEvent->condvar;	609	my $timer_fired = AnyEvent->condvar;
440		610
441	# do something such as adding a timer	611	# create the timer - we could wait for, say
442	# or socket watcher the calls $result_ready->send	612	# a handle becomign ready, or even an
443	# when the "result" is ready.	613	# AnyEvent::HTTP request to finish, but
444	# in this case, we simply use a timer:	614	# in this case, we simply use a timer:
445	my $w = AnyEvent->timer (	615	my $w = AnyEvent->timer (
446	after => 1,	616	after => 1,
447	cb => sub { $result_ready->send },	617	cb => sub { $timer_fired->send },
448	);	618	);
449		619
450	# this "blocks" (while handling events) till the callback	620	# this "blocks" (while handling events) till the callback
451	# calls send	621	# calls ->send
452	$result_ready->recv;	622	$timer_fired->recv;
453		623
454	Example: wait for a timer, but take advantage of the fact that condition	624	Example: wait for a timer, but take advantage of the fact that condition
455	variables are also code references.	625	variables are also callable directly.
456		626
457	my $done = AnyEvent->condvar;	627	my $done = AnyEvent->condvar;
458	my $delay = AnyEvent->timer (after => 5, cb => $done);	628	my $delay = AnyEvent->timer (after => 5, cb => $done);
459	$done->recv;	629	$done->recv;
460		630
…		…
466		636
467	...	637	...
468		638
469	my @info = $couchdb->info->recv;	639	my @info = $couchdb->info->recv;
470		640
471	And this is how you would just ste a callback to be called whenever the	641	And this is how you would just set a callback to be called whenever the
472	results are available:	642	results are available:
473		643
474	$couchdb->info->cb (sub {	644	$couchdb->info->cb (sub {
475	my @info = $_[0]->recv;	645	my @info = $_[0]->recv;
476	});	646	});
…		…
491		661
492	Any arguments passed to the "send" call will be returned by all	662	Any arguments passed to the "send" call will be returned by all
493	future "->recv" calls.	663	future "->recv" calls.
494		664
495	Condition variables are overloaded so one can call them directly (as	665	Condition variables are overloaded so one can call them directly (as
496	a code reference). Calling them directly is the same as calling	666	if they were a code reference). Calling them directly is the same as
497	"send". Note, however, that many C-based event loops do not handle	667	calling "send".
498	overloading, so as tempting as it may be, passing a condition
499	variable instead of a callback does not work. Both the pure perl and
500	EV loops support overloading, however, as well as all functions that
501	use perl to invoke a callback (as in AnyEvent::Socket and
502	AnyEvent::DNS for example).
503		668
504	$cv->croak ($error)	669	$cv->croak ($error)
505	Similar to send, but causes all call's to "->recv" to invoke	670	Similar to send, but causes all calls to "->recv" to invoke
506	"Carp::croak" with the given error message/object/scalar.	671	"Carp::croak" with the given error message/object/scalar.
507		672
508	This can be used to signal any errors to the condition variable	673	This can be used to signal any errors to the condition variable
509	user/consumer.	674	user/consumer. Doing it this way instead of calling "croak" directly
		675	delays the error detection, but has the overwhelming advantage that
		676	it diagnoses the error at the place where the result is expected,
		677	and not deep in some event callback with no connection to the actual
		678	code causing the problem.
510		679
511	$cv->begin ([group callback])	680	$cv->begin ([group callback])
512	$cv->end	681	$cv->end
513	These two methods are EXPERIMENTAL and MIGHT CHANGE.
514
515	These two methods can be used to combine many transactions/events	682	These two methods can be used to combine many transactions/events
516	into one. For example, a function that pings many hosts in parallel	683	into one. For example, a function that pings many hosts in parallel
517	might want to use a condition variable for the whole process.	684	might want to use a condition variable for the whole process.
518		685
519	Every call to "->begin" will increment a counter, and every call to	686	Every call to "->begin" will increment a counter, and every call to
520	"->end" will decrement it. If the counter reaches 0 in "->end", the	687	"->end" will decrement it. If the counter reaches 0 in "->end", the
521	(last) callback passed to "begin" will be executed. That callback is	688	(last) callback passed to "begin" will be executed, passing the
522	*supposed* to call "->send", but that is not required. If no	689	condvar as first argument. That callback is *supposed* to call
		690	"->send", but that is not required. If no group callback was set,
523	callback was set, "send" will be called without any arguments.	691	"send" will be called without any arguments.
524		692
525	Let's clarify this with the ping example:	693	You can think of "$cv->send" giving you an OR condition (one call
		694	sends), while "$cv->begin" and "$cv->end" giving you an AND
		695	condition (all "begin" calls must be "end"'ed before the condvar
		696	sends).
		697
		698	Let's start with a simple example: you have two I/O watchers (for
		699	example, STDOUT and STDERR for a program), and you want to wait for
		700	both streams to close before activating a condvar:
526		701
527	my $cv = AnyEvent->condvar;	702	my $cv = AnyEvent->condvar;
528		703
		704	$cv->begin; # first watcher
		705	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		706	defined sysread $fh1, my $buf, 4096
		707	or $cv->end;
		708	});
		709
		710	$cv->begin; # second watcher
		711	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		712	defined sysread $fh2, my $buf, 4096
		713	or $cv->end;
		714	});
		715
		716	$cv->recv;
		717
		718	This works because for every event source (EOF on file handle),
		719	there is one call to "begin", so the condvar waits for all calls to
		720	"end" before sending.
		721
		722	The ping example mentioned above is slightly more complicated, as
		723	the there are results to be passwd back, and the number of tasks
		724	that are begun can potentially be zero:
		725
		726	my $cv = AnyEvent->condvar;
		727
529	my %result;	728	my %result;
530	$cv->begin (sub { $cv->send (\%result) });	729	$cv->begin (sub { shift->send (\%result) });
531		730
532	for my $host (@list_of_hosts) {	731	for my $host (@list_of_hosts) {
533	$cv->begin;	732	$cv->begin;
534	ping_host_then_call_callback $host, sub {	733	ping_host_then_call_callback $host, sub {
535	$result{$host} = ...;	734	$result{$host} = ...;
…		…
537	};	736	};
538	}	737	}
539		738
540	$cv->end;	739	$cv->end;
541		740
		741	...
		742
		743	my $results = $cv->recv;
		744
542	This code fragment supposedly pings a number of hosts and calls	745	This code fragment supposedly pings a number of hosts and calls
543	"send" after results for all then have have been gathered - in any	746	"send" after results for all then have have been gathered - in any
544	order. To achieve this, the code issues a call to "begin" when it	747	order. To achieve this, the code issues a call to "begin" when it
545	starts each ping request and calls "end" when it has received some	748	starts each ping request and calls "end" when it has received some
546	result for it. Since "begin" and "end" only maintain a counter, the	749	result for it. Since "begin" and "end" only maintain a counter, the
…		…
550	the loop, which serves two important purposes: first, it sets the	753	the loop, which serves two important purposes: first, it sets the
551	callback to be called once the counter reaches 0, and second, it	754	callback to be called once the counter reaches 0, and second, it
552	ensures that "send" is called even when "no" hosts are being pinged	755	ensures that "send" is called even when "no" hosts are being pinged
553	(the loop doesn't execute once).	756	(the loop doesn't execute once).
554		757
555	This is the general pattern when you "fan out" into multiple	758	This is the general pattern when you "fan out" into multiple (but
556	subrequests: use an outer "begin"/"end" pair to set the callback and	759	potentially zero) subrequests: use an outer "begin"/"end" pair to
557	ensure "end" is called at least once, and then, for each subrequest	760	set the callback and ensure "end" is called at least once, and then,
558	you start, call "begin" and for each subrequest you finish, call	761	for each subrequest you start, call "begin" and for each subrequest
559	"end".	762	you finish, call "end".
560		763
561	METHODS FOR CONSUMERS	764	METHODS FOR CONSUMERS
562	These methods should only be used by the consuming side, i.e. the code	765	These methods should only be used by the consuming side, i.e. the code
563	awaits the condition.	766	awaits the condition.
564		767
565	$cv->recv	768	$cv->recv
566	Wait (blocking if necessary) until the "->send" or "->croak" methods	769	Wait (blocking if necessary) until the "->send" or "->croak" methods
567	have been called on c<$cv>, while servicing other watchers normally.	770	have been called on $cv, while servicing other watchers normally.
568		771
569	You can only wait once on a condition - additional calls are valid	772	You can only wait once on a condition - additional calls are valid
570	but will return immediately.	773	but will return immediately.
571		774
572	If an error condition has been set by calling "->croak", then this	775	If an error condition has been set by calling "->croak", then this
573	function will call "croak".	776	function will call "croak".
574		777
575	In list context, all parameters passed to "send" will be returned,	778	In list context, all parameters passed to "send" will be returned,
576	in scalar context only the first one will be returned.	779	in scalar context only the first one will be returned.
577		780
		781	Note that doing a blocking wait in a callback is not supported by
		782	any event loop, that is, recursive invocation of a blocking "->recv"
		783	is not allowed and the "recv" call will "croak" if such a condition
		784	is detected. This requirement can be dropped by relying on
		785	Coro::AnyEvent , which allows you to do a blocking "->recv" from any
		786	thread that doesn't run the event loop itself. Coro::AnyEvent is
		787	loaded automatically when Coro is used with AnyEvent, so code does
		788	not need to do anything special to take advantage of that: any code
		789	that would normally block your program because it calls "recv", be
		790	executed in an "async" thread instead without blocking other
		791	threads.
		792
578	Not all event models support a blocking wait - some die in that case	793	Not all event models support a blocking wait - some die in that case
579	(programs might want to do that to stay interactive), so *if you are	794	(programs might want to do that to stay interactive), so *if you are
580	using this from a module, never require a blocking wait*, but let	795	using this from a module, never require a blocking wait*. Instead,
581	the caller decide whether the call will block or not (for example,	796	let the caller decide whether the call will block or not (for
582	by coupling condition variables with some kind of request results	797	example, by coupling condition variables with some kind of request
583	and supporting callbacks so the caller knows that getting the result	798	results and supporting callbacks so the caller knows that getting
584	will not block, while still supporting blocking waits if the caller	799	the result will not block, while still supporting blocking waits if
585	so desires).	800	the caller so desires).
586		801
587	Another reason *never* to "->recv" in a module is that you cannot
588	sensibly have two "->recv"'s in parallel, as that would require
589	multiple interpreters or coroutines/threads, none of which
590	"AnyEvent" can supply.
591
592	The Coro module, however, *can* and *does* supply coroutines and, in
593	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
594	versions and also integrates coroutines into AnyEvent, making
595	blocking "->recv" calls perfectly safe as long as they are done from
596	another coroutine (one that doesn't run the event loop).
597
598	You can ensure that "-recv" never blocks by setting a callback and	802	You can ensure that "->recv" never blocks by setting a callback and
599	only calling "->recv" from within that callback (or at a later	803	only calling "->recv" from within that callback (or at a later
600	time). This will work even when the event loop does not support	804	time). This will work even when the event loop does not support
601	blocking waits otherwise.	805	blocking waits otherwise.
602		806
603	$bool = $cv->ready	807	$bool = $cv->ready
…		…
608	This is a mutator function that returns the callback set and	812	This is a mutator function that returns the callback set and
609	optionally replaces it before doing so.	813	optionally replaces it before doing so.
610		814
611	The callback will be called when the condition becomes "true", i.e.	815	The callback will be called when the condition becomes "true", i.e.
612	when "send" or "croak" are called, with the only argument being the	816	when "send" or "croak" are called, with the only argument being the
613	condition variable itself. Calling "recv" inside the callback or at	817	condition variable itself. If the condition is already true, the
		818	callback is called immediately when it is set. Calling "recv" inside
614	any later time is guaranteed not to block.	819	the callback or at any later time is guaranteed not to block.
		820
		821	SUPPORTED EVENT LOOPS/BACKENDS
		822	The available backend classes are (every class has its own manpage):
		823
		824	Backends that are autoprobed when no other event loop can be found.
		825	EV is the preferred backend when no other event loop seems to be in
		826	use. If EV is not installed, then AnyEvent will fall back to its own
		827	pure-perl implementation, which is available everywhere as it comes
		828	with AnyEvent itself.
		829
		830	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		831	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
		832
		833	Backends that are transparently being picked up when they are used.
		834	These will be used if they are already loaded when the first watcher
		835	is created, in which case it is assumed that the application is
		836	using them. This means that AnyEvent will automatically pick the
		837	right backend when the main program loads an event module before
		838	anything starts to create watchers. Nothing special needs to be done
		839	by the main program.
		840
		841	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		842	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		843	AnyEvent::Impl::Tk based on Tk, very broken.
		844	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		845	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		846	AnyEvent::Impl::Irssi used when running within irssi.
		847	AnyEvent::Impl::IOAsync based on IO::Async.
		848	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		849	AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
		850
		851	Backends with special needs.
		852	Qt requires the Qt::Application to be instantiated first, but will
		853	otherwise be picked up automatically. As long as the main program
		854	instantiates the application before any AnyEvent watchers are
		855	created, everything should just work.
		856
		857	AnyEvent::Impl::Qt based on Qt.
		858
		859	Event loops that are indirectly supported via other backends.
		860	Some event loops can be supported via other modules:
		861
		862	There is no direct support for WxWidgets (Wx) or Prima.
		863
		864	WxWidgets has no support for watching file handles. However, you can
		865	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		866	simply polls 20 times per second, which was considered to be too
		867	horrible to even consider for AnyEvent.
		868
		869	Prima is not supported as nobody seems to be using it, but it has a
		870	POE backend, so it can be supported through POE.
		871
		872	AnyEvent knows about both Prima and Wx, however, and will try to
		873	load POE when detecting them, in the hope that POE will pick them
		874	up, in which case everything will be automatic.
615		875
616	GLOBAL VARIABLES AND FUNCTIONS	876	GLOBAL VARIABLES AND FUNCTIONS
		877	These are not normally required to use AnyEvent, but can be useful to
		878	write AnyEvent extension modules.
		879
617	$AnyEvent::MODEL	880	$AnyEvent::MODEL
618	Contains "undef" until the first watcher is being created. Then it	881	Contains "undef" until the first watcher is being created, before
		882	the backend has been autodetected.
		883
619	contains the event model that is being used, which is the name of	884	Afterwards it contains the event model that is being used, which is
620	the Perl class implementing the model. This class is usually one of	885	the name of the Perl class implementing the model. This class is
621	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	886	usually one of the "AnyEvent::Impl::xxx" modules, but can be any
622	case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*).	887	other class in the case AnyEvent has been extended at runtime (e.g.
623		888	in *rxvt-unicode* it will be "urxvt::anyevent").
624	The known classes so far are:
625
626	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
627	AnyEvent::Impl::Event based on Event, second best choice.
628	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
629	AnyEvent::Impl::Glib based on Glib, third-best choice.
630	AnyEvent::Impl::Tk based on Tk, very bad choice.
631	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
632	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
633	AnyEvent::Impl::POE based on POE, not generic enough for full support.
634
635	There is no support for WxWidgets, as WxWidgets has no support for
636	watching file handles. However, you can use WxWidgets through the
637	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
638	second, which was considered to be too horrible to even consider for
639	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
640	using it's adaptor.
641
642	AnyEvent knows about Prima and Wx and will try to use POE when
643	autodetecting them.
644		889
645	AnyEvent::detect	890	AnyEvent::detect
646	Returns $AnyEvent::MODEL, forcing autodetection of the event model	891	Returns $AnyEvent::MODEL, forcing autodetection of the event model
647	if necessary. You should only call this function right before you	892	if necessary. You should only call this function right before you
648	would have created an AnyEvent watcher anyway, that is, as late as	893	would have created an AnyEvent watcher anyway, that is, as late as
649	possible at runtime.	894	possible at runtime, and not e.g. during initialisation of your
		895	module.
		896
		897	The effect of calling this function is as if a watcher had been
		898	created (specifically, actions that happen "when the first watcher
		899	is created" happen when calling detetc as well).
		900
		901	If you need to do some initialisation before AnyEvent watchers are
		902	created, use "post_detect".
650		903
651	$guard = AnyEvent::post_detect { BLOCK }	904	$guard = AnyEvent::post_detect { BLOCK }
652	Arranges for the code block to be executed as soon as the event	905	Arranges for the code block to be executed as soon as the event
653	model is autodetected (or immediately if this has already happened).	906	model is autodetected (or immediately if that has already happened).
		907
		908	The block will be executed *after* the actual backend has been
		909	detected ($AnyEvent::MODEL is set), but *before* any watchers have
		910	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		911	other initialisations - see the sources of AnyEvent::Strict or
		912	AnyEvent::AIO to see how this is used.
		913
		914	The most common usage is to create some global watchers, without
		915	forcing event module detection too early, for example, AnyEvent::AIO
		916	creates and installs the global IO::AIO watcher in a "post_detect"
		917	block to avoid autodetecting the event module at load time.
654		918
655	If called in scalar or list context, then it creates and returns an	919	If called in scalar or list context, then it creates and returns an
656	object that automatically removes the callback again when it is	920	object that automatically removes the callback again when it is
		921	destroyed (or "undef" when the hook was immediately executed). See
657	destroyed. See Coro::BDB for a case where this is useful.	922	AnyEvent::AIO for a case where this is useful.
		923
		924	Example: Create a watcher for the IO::AIO module and store it in
		925	$WATCHER, but do so only do so after the event loop is initialised.
		926
		927	our WATCHER;
		928
		929	my $guard = AnyEvent::post_detect {
		930	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		931	};
		932
		933	# the ||= is important in case post_detect immediately runs the block,
		934	# as to not clobber the newly-created watcher. assigning both watcher and
		935	# post_detect guard to the same variable has the advantage of users being
		936	# able to just C<undef $WATCHER> if the watcher causes them grief.
		937
		938	$WATCHER ||= $guard;
658		939
659	@AnyEvent::post_detect	940	@AnyEvent::post_detect
660	If there are any code references in this array (you can "push" to it	941	If there are any code references in this array (you can "push" to it
661	before or after loading AnyEvent), then they will called directly	942	before or after loading AnyEvent), then they will be called directly
662	after the event loop has been chosen.	943	after the event loop has been chosen.
663		944
664	You should check $AnyEvent::MODEL before adding to this array,	945	You should check $AnyEvent::MODEL before adding to this array,
665	though: if it contains a true value then the event loop has already	946	though: if it is defined then the event loop has already been
666	been detected, and the array will be ignored.	947	detected, and the array will be ignored.
667		948
668	Best use "AnyEvent::post_detect { BLOCK }" instead.	949	Best use "AnyEvent::post_detect { BLOCK }" when your application
		950	allows it, as it takes care of these details.
		951
		952	This variable is mainly useful for modules that can do something
		953	useful when AnyEvent is used and thus want to know when it is
		954	initialised, but do not need to even load it by default. This array
		955	provides the means to hook into AnyEvent passively, without loading
		956	it.
		957
		958	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		959	together, you could put this into Coro (this is the actual code used
		960	by Coro to accomplish this):
		961
		962	if (defined $AnyEvent::MODEL) {
		963	# AnyEvent already initialised, so load Coro::AnyEvent
		964	require Coro::AnyEvent;
		965	} else {
		966	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		967	# as soon as it is
		968	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		969	}
		970
		971	AnyEvent::postpone { BLOCK }
		972	Arranges for the block to be executed as soon as possible, but not
		973	before the call itself returns. In practise, the block will be
		974	executed just before the event loop polls for new events, or shortly
		975	afterwards.
		976
		977	This function never returns anything (to make the "return postpone {
		978	... }" idiom more useful.
		979
		980	To understand the usefulness of this function, consider a function
		981	that asynchronously does something for you and returns some
		982	transaction object or guard to let you cancel the operation. For
		983	example, "AnyEvent::Socket::tcp_connect":
		984
		985	# start a conenction attempt unless one is active
		986	$self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		987	delete $self->{connect_guard};
		988	...
		989	};
		990
		991	Imagine that this function could instantly call the callback, for
		992	example, because it detects an obvious error such as a negative port
		993	number. Invoking the callback before the function returns causes
		994	problems however: the callback will be called and will try to delete
		995	the guard object. But since the function hasn't returned yet, there
		996	is nothing to delete. When the function eventually returns it will
		997	assign the guard object to "$self->{connect_guard}", where it will
		998	likely never be deleted, so the program thinks it is still trying to
		999	connect.
		1000
		1001	This is where "AnyEvent::postpone" should be used. Instead of
		1002	calling the callback directly on error:
		1003
		1004	$cb->(undef), return # signal error to callback, BAD!
		1005	if $some_error_condition;
		1006
		1007	It should use "postpone":
		1008
		1009	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1010	if $some_error_condition;
		1011
		1012	AnyEvent::log $level, $msg[, @args]
		1013	Log the given $msg at the given $level.
		1014
		1015	If AnyEvent::Log is not loaded then this function makes a simple
		1016	test to see whether the message will be logged. If the test succeeds
		1017	it will load AnyEvent::Log and call "AnyEvent::Log::log" -
		1018	consequently, look at the AnyEvent::Log documentation for details.
		1019
		1020	If the test fails it will simply return. Right now this happens when
		1021	a numerical loglevel is used and it is larger than the level
		1022	specified via $ENV{PERL_ANYEVENT_VERBOSE}.
		1023
		1024	If you want to sprinkle loads of logging calls around your code,
		1025	consider creating a logger callback with the "AnyEvent::Log::logger"
		1026	function, which can reduce typing, codesize and can reduce the
		1027	logging overhead enourmously.
669		1028
670	WHAT TO DO IN A MODULE	1029	WHAT TO DO IN A MODULE
671	As a module author, you should "use AnyEvent" and call AnyEvent methods	1030	As a module author, you should "use AnyEvent" and call AnyEvent methods
672	freely, but you should not load a specific event module or rely on it.	1031	freely, but you should not load a specific event module or rely on it.
673		1032
…		…
681	stall the whole program, and the whole point of using events is to stay	1040	stall the whole program, and the whole point of using events is to stay
682	interactive.	1041	interactive.
683		1042
684	It is fine, however, to call "->recv" when the user of your module	1043	It is fine, however, to call "->recv" when the user of your module
685	requests it (i.e. if you create a http request object ad have a method	1044	requests it (i.e. if you create a http request object ad have a method
686	called "results" that returns the results, it should call "->recv"	1045	called "results" that returns the results, it may call "->recv" freely,
687	freely, as the user of your module knows what she is doing. always).	1046	as the user of your module knows what she is doing. Always).
688		1047
689	WHAT TO DO IN THE MAIN PROGRAM	1048	WHAT TO DO IN THE MAIN PROGRAM
690	There will always be a single main program - the only place that should	1049	There will always be a single main program - the only place that should
691	dictate which event model to use.	1050	dictate which event model to use.
692		1051
693	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	1052	If the program is not event-based, it need not do anything special, even
694	do anything special (it does not need to be event-based) and let	1053	when it depends on a module that uses an AnyEvent. If the program itself
695	AnyEvent decide which implementation to chose if some module relies on	1054	uses AnyEvent, but does not care which event loop is used, all it needs
696	it.	1055	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		1056	available loop implementation.
697		1057
698	If the main program relies on a specific event model - for example, in	1058	If the main program relies on a specific event model - for example, in
699	Gtk2 programs you have to rely on the Glib module - you should load the	1059	Gtk2 programs you have to rely on the Glib module - you should load the
700	event module before loading AnyEvent or any module that uses it:	1060	event module before loading AnyEvent or any module that uses it:
701	generally speaking, you should load it as early as possible. The reason	1061	generally speaking, you should load it as early as possible. The reason
702	is that modules might create watchers when they are loaded, and AnyEvent	1062	is that modules might create watchers when they are loaded, and AnyEvent
703	will decide on the event model to use as soon as it creates watchers,	1063	will decide on the event model to use as soon as it creates watchers,
704	and it might chose the wrong one unless you load the correct one	1064	and it might choose the wrong one unless you load the correct one
705	yourself.	1065	yourself.
706		1066
707	You can chose to use a pure-perl implementation by loading the	1067	You can chose to use a pure-perl implementation by loading the
708	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1068	"AnyEvent::Loop" module, which gives you similar behaviour everywhere,
709	everywhere, but letting AnyEvent chose the model is generally better.	1069	but letting AnyEvent chose the model is generally better.
710		1070
711	MAINLOOP EMULATION	1071	MAINLOOP EMULATION
712	Sometimes (often for short test scripts, or even standalone programs who	1072	Sometimes (often for short test scripts, or even standalone programs who
713	only want to use AnyEvent), you do not want to run a specific event	1073	only want to use AnyEvent), you do not want to run a specific event
714	loop.	1074	loop.
…		…
724	variable somewhere, waiting for it, and sending it when the program	1084	variable somewhere, waiting for it, and sending it when the program
725	should exit cleanly.	1085	should exit cleanly.
726		1086
727	OTHER MODULES	1087	OTHER MODULES
728	The following is a non-exhaustive list of additional modules that use	1088	The following is a non-exhaustive list of additional modules that use
729	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1089	AnyEvent as a client and can therefore be mixed easily with other
730	in the same program. Some of the modules come with AnyEvent, some are	1090	AnyEvent modules and other event loops in the same program. Some of the
731	available via CPAN.	1091	modules come as part of AnyEvent, the others are available via CPAN (see
		1092	<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
		1093	non-exhaustive list), and the list is heavily biased towards modules of
		1094	the AnyEvent author himself :)
732		1095
733	AnyEvent::Util	1096	AnyEvent::Util (part of the AnyEvent distribution)
734	Contains various utility functions that replace often-used but	1097	Contains various utility functions that replace often-used blocking
735	blocking functions such as "inet_aton" by event-/callback-based	1098	functions such as "inet_aton" with event/callback-based versions.
736	versions.
737		1099
738	AnyEvent::Socket	1100	AnyEvent::Socket (part of the AnyEvent distribution)
739	Provides various utility functions for (internet protocol) sockets,	1101	Provides various utility functions for (internet protocol) sockets,
740	addresses and name resolution. Also functions to create non-blocking	1102	addresses and name resolution. Also functions to create non-blocking
741	tcp connections or tcp servers, with IPv6 and SRV record support and	1103	tcp connections or tcp servers, with IPv6 and SRV record support and
742	more.	1104	more.
743		1105
744	AnyEvent::Handle	1106	AnyEvent::Handle (part of the AnyEvent distribution)
745	Provide read and write buffers, manages watchers for reads and	1107	Provide read and write buffers, manages watchers for reads and
746	writes, supports raw and formatted I/O, I/O queued and fully	1108	writes, supports raw and formatted I/O, I/O queued and fully
747	transparent and non-blocking SSL/TLS.	1109	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
748		1110
749	AnyEvent::DNS	1111	AnyEvent::DNS (part of the AnyEvent distribution)
750	Provides rich asynchronous DNS resolver capabilities.	1112	Provides rich asynchronous DNS resolver capabilities.
751		1113
		1114	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
		1115	AnyEvent::IGS, AnyEvent::FCP
		1116	Implement event-based interfaces to the protocols of the same name
		1117	(for the curious, IGS is the International Go Server and FCP is the
		1118	Freenet Client Protocol).
		1119
		1120	AnyEvent::AIO (part of the AnyEvent distribution)
		1121	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1122	the toolbox of every event programmer. AnyEvent::AIO transparently
		1123	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1124	event-based file I/O, and much more.
		1125
		1126	AnyEvent::Filesys::Notify
		1127	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1128	path changes (e.g. "watch this directory for new files", "watch this
		1129	file for changes"). The AnyEvent::Filesys::Notify module promises to
		1130	do just that in a portbale fashion, supporting inotify on GNU/Linux
		1131	and some weird, without doubt broken, stuff on OS X to monitor
		1132	files. It can fall back to blocking scans at regular intervals
		1133	transparently on other platforms, so it's about as portable as it
		1134	gets.
		1135
		1136	(I haven't used it myself, but I haven't heard anybody complaining
		1137	about it yet).
		1138
752	AnyEvent::HTTP	1139	AnyEvent::DBI
753	A simple-to-use HTTP library that is capable of making a lot of	1140	Executes DBI requests asynchronously in a proxy process for you,
754	concurrent HTTP requests.	1141	notifying you in an event-based way when the operation is finished.
755		1142
756	AnyEvent::HTTPD	1143	AnyEvent::HTTPD
757	Provides a simple web application server framework.	1144	A simple embedded webserver.
758		1145
759	AnyEvent::FastPing	1146	AnyEvent::FastPing
760	The fastest ping in the west.	1147	The fastest ping in the west.
761		1148
762	AnyEvent::DBI
763	Executes DBI requests asynchronously in a proxy process.
764
765	AnyEvent::AIO
766	Truly asynchronous I/O, should be in the toolbox of every event
767	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
768	together.
769
770	AnyEvent::BDB
771	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
772	fuses BDB and AnyEvent together.
773
774	AnyEvent::GPSD
775	A non-blocking interface to gpsd, a daemon delivering GPS
776	information.
777
778	AnyEvent::IGS
779	A non-blocking interface to the Internet Go Server protocol (used by
780	App::IGS).
781
782	Net::IRC3
783	AnyEvent based IRC client module family.
784
785	Net::XMPP2
786	AnyEvent based XMPP (Jabber protocol) module family.
787
788	Net::FCP
789	AnyEvent-based implementation of the Freenet Client Protocol,
790	birthplace of AnyEvent.
791
792	Event::ExecFlow
793	High level API for event-based execution flow control.
794
795	Coro	1149	Coro
796	Has special support for AnyEvent via Coro::AnyEvent.	1150	Has special support for AnyEvent via Coro::AnyEvent, which allows
		1151	you to simply invert the flow control - don't call us, we will call
		1152	you:
797		1153
798	IO::Lambda	1154	async {
799	The lambda approach to I/O - don't ask, look there. Can use	1155	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
800	AnyEvent.	1156	print "5 seconds later!\n";
		1157
		1158	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
		1159	my $line = <STDIN>; # works for ttys
		1160
		1161	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
		1162	my ($body, $hdr) = Coro::rouse_wait;
		1163	};
		1164
		1165	SIMPLIFIED AE API
		1166	Starting with version 5.0, AnyEvent officially supports a second, much
		1167	simpler, API that is designed to reduce the calling, typing and memory
		1168	overhead by using function call syntax and a fixed number of parameters.
		1169
		1170	See the AE manpage for details.
801		1171
802	ERROR AND EXCEPTION HANDLING	1172	ERROR AND EXCEPTION HANDLING
803	In general, AnyEvent does not do any error handling - it relies on the	1173	In general, AnyEvent does not do any error handling - it relies on the
804	caller to do that if required. The AnyEvent::Strict module (see also the	1174	caller to do that if required. The AnyEvent::Strict module (see also the
805	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	1175	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
814	The pure perl event loop simply re-throws the exception (usually within	1184	The pure perl event loop simply re-throws the exception (usually within
815	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1185	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
816	Glib uses "install_exception_handler" and so on.	1186	Glib uses "install_exception_handler" and so on.
817		1187
818	ENVIRONMENT VARIABLES	1188	ENVIRONMENT VARIABLES
819	The following environment variables are used by this module or its	1189	AnyEvent supports a number of environment variables that tune the
820	submodules:	1190	runtime behaviour. They are usually evaluated when AnyEvent is loaded,
		1191	initialised, or a submodule that uses them is loaded. Many of them also
		1192	cause AnyEvent to load additional modules - for example,
		1193	"PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
		1194	loaded.
		1195
		1196	All the environment variables documented here start with
		1197	"PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
		1198	Other modules are encouraged (but by no means required) to use
		1199	"PERL_ANYEVENT_SUBMODULE" if they have registered the
		1200	AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
		1201	AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
		1202	should not access env variables starting with "AE_", see below).
		1203
		1204	All variables can also be set via the "AE_" prefix, that is, instead of
		1205	setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
		1206	there is a clash btween anyevent and another program that uses
		1207	"AE_something" you can set the corresponding "PERL_ANYEVENT_something"
		1208	variable to the empty string, as those variables take precedence.
		1209
		1210	When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
		1211	their "PERL_ANYEVENT_xxx" counterpart unless that variable already
		1212	exists. If taint mode is on, then AnyEvent will remove *all* environment
		1213	variables starting with "PERL_ANYEVENT_" from %ENV (or replace them with
		1214	"undef" or the empty string, if the corresaponding "AE_" variable is
		1215	set).
		1216
		1217	The exact algorithm is currently:
		1218
		1219	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		1220	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		1221	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		1222
		1223	This ensures that child processes will not see the "AE_" variables.
		1224
		1225	The following environment variables are currently known to AnyEvent:
821		1226
822	"PERL_ANYEVENT_VERBOSE"	1227	"PERL_ANYEVENT_VERBOSE"
823	By default, AnyEvent will be completely silent except in fatal	1228	By default, AnyEvent will log messages with loglevel 4 ("error") or
824	conditions. You can set this environment variable to make AnyEvent	1229	higher (see AnyEvent::Log). You can set this environment variable to
825	more talkative.	1230	a numerical loglevel to make AnyEvent more (or less) talkative.
826		1231
		1232	If you want to do more than just set the global logging level you
		1233	should have a look at "PERL_ANYEVENT_LOG", which allows much more
		1234	complex specifications.
		1235
		1236	When set to 0 ("off"), then no messages whatsoever will be logged
		1237	with everything else at defaults.
		1238
827	When set to 1 or higher, causes AnyEvent to warn about unexpected	1239	When set to 5 or higher ("warn"), AnyEvent warns about unexpected
828	conditions, such as not being able to load the event model specified	1240	conditions, such as not being able to load the event model specified
829	by "PERL_ANYEVENT_MODEL".	1241	by "PERL_ANYEVENT_MODEL", or a guard callback throwing an exception
		1242	- this is the minimum recommended level for use during development.
830		1243
831	When set to 2 or higher, cause AnyEvent to report to STDERR which	1244	When set to 7 or higher (info), AnyEvent reports which event model
832	event model it chooses.	1245	it chooses.
		1246
		1247	When set to 8 or higher (debug), then AnyEvent will report extra
		1248	information on which optional modules it loads and how it implements
		1249	certain features.
		1250
		1251	"PERL_ANYEVENT_LOG"
		1252	Accepts rather complex logging specifications. For example, you
		1253	could log all "debug" messages of some module to stderr, warnings
		1254	and above to stderr, and errors and above to syslog, with:
		1255
		1256	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		1257
		1258	For the rather extensive details, see AnyEvent::Log.
		1259
		1260	This variable is evaluated when AnyEvent (or AnyEvent::Log) is
		1261	loaded, so will take effect even before AnyEvent has initialised
		1262	itself.
		1263
		1264	Note that specifying this environment variable causes the
		1265	AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
		1266	does not, so only using the latter saves a few hundred kB of memory
		1267	unless a module explicitly needs the extra features of
		1268	AnyEvent::Log.
833		1269
834	"PERL_ANYEVENT_STRICT"	1270	"PERL_ANYEVENT_STRICT"
835	AnyEvent does not do much argument checking by default, as thorough	1271	AnyEvent does not do much argument checking by default, as thorough
836	argument checking is very costly. Setting this variable to a true	1272	argument checking is very costly. Setting this variable to a true
837	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1273	value will cause AnyEvent to load "AnyEvent::Strict" and then to
838	thoroughly check the arguments passed to most method calls. If it	1274	thoroughly check the arguments passed to most method calls. If it
839	finds any problems it will croak.	1275	finds any problems, it will croak.
840		1276
841	In other words, enables "strict" mode.	1277	In other words, enables "strict" mode.
842		1278
843	Unlike "use strict", it is definitely recommended ot keep it off in	1279	Unlike "use strict" (or its modern cousin, "use common::sense", it
844	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment	1280	is definitely recommended to keep it off in production. Keeping
		1281	"PERL_ANYEVENT_STRICT=1" in your environment while developing
845	while developing programs can be very useful, however.	1282	programs can be very useful, however.
		1283
		1284	"PERL_ANYEVENT_DEBUG_SHELL"
		1285	If this env variable is nonempty, then its contents will be
		1286	interpreted by "AnyEvent::Socket::parse_hostport" and
		1287	"AnyEvent::Debug::shell" (after replacing every occurance of $$ by
		1288	the process pid). The shell object is saved in
		1289	$AnyEvent::Debug::SHELL.
		1290
		1291	This happens when the first watcher is created.
		1292
		1293	For example, to bind a debug shell on a unix domain socket in
		1294	/tmp/debug<pid>.sock, you could use this:
		1295
		1296	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		1297	# connect with e.g.: socat readline /tmp/debug123.sock
		1298
		1299	Or to bind to tcp port 4545 on localhost:
		1300
		1301	PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
		1302	# connect with e.g.: telnet localhost 4545
		1303
		1304	Note that creating sockets in /tmp or on localhost is very unsafe on
		1305	multiuser systems.
		1306
		1307	"PERL_ANYEVENT_DEBUG_WRAP"
		1308	Can be set to 0, 1 or 2 and enables wrapping of all watchers for
		1309	debugging purposes. See "AnyEvent::Debug::wrap" for details.
846		1310
847	"PERL_ANYEVENT_MODEL"	1311	"PERL_ANYEVENT_MODEL"
848	This can be used to specify the event model to be used by AnyEvent,	1312	This can be used to specify the event model to be used by AnyEvent,
849	before auto detection and -probing kicks in. It must be a string	1313	before auto detection and -probing kicks in.
850	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1314
851	gets prepended and the resulting module name is loaded and if the	1315	It normally is a string consisting entirely of ASCII letters (e.g.
852	load was successful, used as event model. If it fails to load	1316	"EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
		1317	the resulting module name is loaded and - if the load was successful
		1318	- used as event model backend. If it fails to load then AnyEvent
853	AnyEvent will proceed with auto detection and -probing.	1319	will proceed with auto detection and -probing.
854		1320
855	This functionality might change in future versions.	1321	If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
		1322	then nothing gets prepended and the module name is used as-is (hint:
		1323	"::" at the end of a string designates a module name and quotes it
		1324	appropriately).
856		1325
857	For example, to force the pure perl model (AnyEvent::Impl::Perl) you	1326	For example, to force the pure perl model (AnyEvent::Loop::Perl) you
858	could start your program like this:	1327	could start your program like this:
859		1328
860	PERL_ANYEVENT_MODEL=Perl perl ...	1329	PERL_ANYEVENT_MODEL=Perl perl ...
		1330
		1331	"PERL_ANYEVENT_IO_MODEL"
		1332	The current file I/O model - see AnyEvent::IO for more info.
		1333
		1334	At the moment, only "Perl" (small, pure-perl, synchronous) and
		1335	"IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
		1336	if AnyEvent::AIO can be loaded, otherwise it is "Perl".
861		1337
862	"PERL_ANYEVENT_PROTOCOLS"	1338	"PERL_ANYEVENT_PROTOCOLS"
863	Used by both AnyEvent::DNS and AnyEvent::Socket to determine	1339	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
864	preferences for IPv4 or IPv6. The default is unspecified (and might	1340	preferences for IPv4 or IPv6. The default is unspecified (and might
865	change, or be the result of auto probing).	1341	change, or be the result of auto probing).
…		…
869	mentioned will be used, and preference will be given to protocols	1345	mentioned will be used, and preference will be given to protocols
870	mentioned earlier in the list.	1346	mentioned earlier in the list.
871		1347
872	This variable can effectively be used for denial-of-service attacks	1348	This variable can effectively be used for denial-of-service attacks
873	against local programs (e.g. when setuid), although the impact is	1349	against local programs (e.g. when setuid), although the impact is
874	likely small, as the program has to handle connection errors	1350	likely small, as the program has to handle conenction and other
875	already-	1351	failures anyways.
876		1352
877	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1353	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
878	IPv6, but support both and try to use both.	1354	IPv6, but support both and try to use both.
879	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1355	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
880	resolve or contact IPv6 addresses.	1356	resolve or contact IPv6 addresses.
881	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but	1357	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
882	prefer IPv6 over IPv4.	1358	prefer IPv6 over IPv4.
883		1359
		1360	"PERL_ANYEVENT_HOSTS"
		1361	This variable, if specified, overrides the /etc/hosts file used by
		1362	AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
		1363	read from that file instead.
		1364
884	"PERL_ANYEVENT_EDNS0"	1365	"PERL_ANYEVENT_EDNS0"
885	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension	1366	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
886	for DNS. This extension is generally useful to reduce DNS traffic,	1367	for DNS. This extension is generally useful to reduce DNS traffic,
887	but some (broken) firewalls drop such DNS packets, which is why it	1368	especially when DNSSEC is involved, but some (broken) firewalls drop
888	is off by default.	1369	such DNS packets, which is why it is off by default.
889		1370
890	Setting this variable to 1 will cause AnyEvent::DNS to announce	1371	Setting this variable to 1 will cause AnyEvent::DNS to announce
891	EDNS0 in its DNS requests.	1372	EDNS0 in its DNS requests.
892		1373
893	"PERL_ANYEVENT_MAX_FORKS"	1374	"PERL_ANYEVENT_MAX_FORKS"
894	The maximum number of child processes that	1375	The maximum number of child processes that
895	"AnyEvent::Util::fork_call" will create in parallel.	1376	"AnyEvent::Util::fork_call" will create in parallel.
		1377
		1378	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1379	The default value for the "max_outstanding" parameter for the
		1380	default DNS resolver - this is the maximum number of parallel DNS
		1381	requests that are sent to the DNS server.
		1382
		1383	"PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
		1384	Perl has inherently racy signal handling (you can basically choose
		1385	between losing signals and memory corruption) - pure perl event
		1386	loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
		1387	available) therefore have to poll regularly to avoid losing signals.
		1388
		1389	Some event loops are racy, but don't poll regularly, and some event
		1390	loops are written in C but are still racy. For those event loops,
		1391	AnyEvent installs a timer that regularly wakes up the event loop.
		1392
		1393	By default, the interval for this timer is 10 seconds, but you can
		1394	override this delay with this environment variable (or by setting
		1395	the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
		1396	watchers).
		1397
		1398	Lower values increase CPU (and energy) usage, higher values can
		1399	introduce long delays when reaping children or waiting for signals.
		1400
		1401	The AnyEvent::Async module, if available, will be used to avoid this
		1402	polling (with most event loops).
		1403
		1404	"PERL_ANYEVENT_RESOLV_CONF"
		1405	The absolute path to a resolv.conf-style file to use instead of
		1406	/etc/resolv.conf (or the OS-specific configuration) in the default
		1407	resolver, or the empty string to select the default configuration.
		1408
		1409	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1410	When neither "ca_file" nor "ca_path" was specified during
		1411	AnyEvent::TLS context creation, and either of these environment
		1412	variables are nonempty, they will be used to specify CA certificate
		1413	locations instead of a system-dependent default.
		1414
		1415	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1416	When these are set to 1, then the respective modules are not loaded.
		1417	Mostly good for testing AnyEvent itself.
896		1418
897	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1419	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
898	This is an advanced topic that you do not normally need to use AnyEvent	1420	This is an advanced topic that you do not normally need to use AnyEvent
899	in a module. This section is only of use to event loop authors who want	1421	in a module. This section is only of use to event loop authors who want
900	to provide AnyEvent compatibility.	1422	to provide AnyEvent compatibility.
…		…
955	warn "read: $input\n"; # output what has been read	1477	warn "read: $input\n"; # output what has been read
956	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1478	$cv->send if $input =~ /^q/i; # quit program if /^q/i
957	},	1479	},
958	);	1480	);
959		1481
960	my $time_watcher; # can only be used once
961
962	sub new_timer {
963	$timer = AnyEvent->timer (after => 1, cb => sub {	1482	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
964	warn "timeout\n"; # print 'timeout' about every second	1483	warn "timeout\n"; # print 'timeout' at most every second
965	&new_timer; # and restart the time
966	});
967	}	1484	});
968
969	new_timer; # create first timer
970		1485
971	$cv->recv; # wait until user enters /^q/i	1486	$cv->recv; # wait until user enters /^q/i
972		1487
973	REAL-WORLD EXAMPLE	1488	REAL-WORLD EXAMPLE
974	Consider the Net::FCP module. It features (among others) the following	1489	Consider the Net::FCP module. It features (among others) the following
…		…
1046		1561
1047	The actual code goes further and collects all errors ("die"s,	1562	The actual code goes further and collects all errors ("die"s,
1048	exceptions) that occurred during request processing. The "result" method	1563	exceptions) that occurred during request processing. The "result" method
1049	detects whether an exception as thrown (it is stored inside the $txn	1564	detects whether an exception as thrown (it is stored inside the $txn
1050	object) and just throws the exception, which means connection errors and	1565	object) and just throws the exception, which means connection errors and
1051	other problems get reported tot he code that tries to use the result,	1566	other problems get reported to the code that tries to use the result,
1052	not in a random callback.	1567	not in a random callback.
1053		1568
1054	All of this enables the following usage styles:	1569	All of this enables the following usage styles:
1055		1570
1056	1. Blocking:	1571	1. Blocking:
…		…
1101	through AnyEvent. The benchmark creates a lot of timers (with a zero	1616	through AnyEvent. The benchmark creates a lot of timers (with a zero
1102	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1617	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1103	which it is), lets them fire exactly once and destroys them again.	1618	which it is), lets them fire exactly once and destroys them again.
1104		1619
1105	Source code for this benchmark is found as eg/bench in the AnyEvent	1620	Source code for this benchmark is found as eg/bench in the AnyEvent
1106	distribution.	1621	distribution. It uses the AE interface, which makes a real difference
		1622	for the EV and Perl backends only.
1107		1623
1108	Explanation of the columns	1624	Explanation of the columns
1109	*watcher* is the number of event watchers created/destroyed. Since	1625	*watcher* is the number of event watchers created/destroyed. Since
1110	different event models feature vastly different performances, each event	1626	different event models feature vastly different performances, each event
1111	loop was given a number of watchers so that overall runtime is	1627	loop was given a number of watchers so that overall runtime is
…		…
1130	*destroy* is the time, in microseconds, that it takes to destroy a	1646	*destroy* is the time, in microseconds, that it takes to destroy a
1131	single watcher.	1647	single watcher.
1132		1648
1133	Results	1649	Results
1134	name watchers bytes create invoke destroy comment	1650	name watchers bytes create invoke destroy comment
1135	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1651	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1136	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1652	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1137	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1653	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1138	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1654	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1139	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1655	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1140	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1656	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1657	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1658	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1141	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1659	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1142	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1660	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1143	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1661	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1144	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1662	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1145		1663
1146	Discussion	1664	Discussion
1147	The benchmark does *not* measure scalability of the event loop very	1665	The benchmark does *not* measure scalability of the event loop very
1148	well. For example, a select-based event loop (such as the pure perl one)	1666	well. For example, a select-based event loop (such as the pure perl one)
1149	can never compete with an event loop that uses epoll when the number of	1667	can never compete with an event loop that uses epoll when the number of
…		…
1160	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1678	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1161	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1679	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1162	CPU cycles with POE.	1680	CPU cycles with POE.
1163		1681
1164	"EV" is the sole leader regarding speed and memory use, which are both	1682	"EV" is the sole leader regarding speed and memory use, which are both
1165	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1683	maximal/minimal, respectively. When using the AE API there is zero
		1684	overhead (when going through the AnyEvent API create is about 5-6 times
		1685	slower, with other times being equal, so still uses far less memory than
1166	far less memory than any other event loop and is still faster than Event	1686	any other event loop and is still faster than Event natively).
1167	natively.
1168		1687
1169	The pure perl implementation is hit in a few sweet spots (both the	1688	The pure perl implementation is hit in a few sweet spots (both the
1170	constant timeout and the use of a single fd hit optimisations in the	1689	constant timeout and the use of a single fd hit optimisations in the
1171	perl interpreter and the backend itself). Nevertheless this shows that	1690	perl interpreter and the backend itself). Nevertheless this shows that
1172	it adds very little overhead in itself. Like any select-based backend	1691	it adds very little overhead in itself. Like any select-based backend
…		…
1174	few of them active), of course, but this was not subject of this	1693	few of them active), of course, but this was not subject of this
1175	benchmark.	1694	benchmark.
1176		1695
1177	The "Event" module has a relatively high setup and callback invocation	1696	The "Event" module has a relatively high setup and callback invocation
1178	cost, but overall scores in on the third place.	1697	cost, but overall scores in on the third place.
		1698
		1699	"IO::Async" performs admirably well, about on par with "Event", even
		1700	when using its pure perl backend.
1179		1701
1180	"Glib"'s memory usage is quite a bit higher, but it features a faster	1702	"Glib"'s memory usage is quite a bit higher, but it features a faster
1181	callback invocation and overall ends up in the same class as "Event".	1703	callback invocation and overall ends up in the same class as "Event".
1182	However, Glib scales extremely badly, doubling the number of watchers	1704	However, Glib scales extremely badly, doubling the number of watchers
1183	increases the processing time by more than a factor of four, making it	1705	increases the processing time by more than a factor of four, making it
…		…
1215	when used without AnyEvent), but most event loops have acceptable	1737	when used without AnyEvent), but most event loops have acceptable
1216	performance with or without AnyEvent.	1738	performance with or without AnyEvent.
1217		1739
1218	* The overhead AnyEvent adds is usually much smaller than the overhead	1740	* The overhead AnyEvent adds is usually much smaller than the overhead
1219	of the actual event loop, only with extremely fast event loops such	1741	of the actual event loop, only with extremely fast event loops such
1220	as EV adds AnyEvent significant overhead.	1742	as EV does AnyEvent add significant overhead.
1221		1743
1222	* You should avoid POE like the plague if you want performance or	1744	* You should avoid POE like the plague if you want performance or
1223	reasonable memory usage.	1745	reasonable memory usage.
1224		1746
1225	BENCHMARKING THE LARGE SERVER CASE	1747	BENCHMARKING THE LARGE SERVER CASE
…		…
1239	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1761	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1240	100 (1%) are active. This mirrors the activity of large servers with	1762	100 (1%) are active. This mirrors the activity of large servers with
1241	many connections, most of which are idle at any one point in time.	1763	many connections, most of which are idle at any one point in time.
1242		1764
1243	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1765	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1244	distribution.	1766	distribution. It uses the AE interface, which makes a real difference
		1767	for the EV and Perl backends only.
1245		1768
1246	Explanation of the columns	1769	Explanation of the columns
1247	*sockets* is the number of sockets, and twice the number of "servers"	1770	*sockets* is the number of sockets, and twice the number of "servers"
1248	(as each server has a read and write socket end).	1771	(as each server has a read and write socket end).
1249		1772
…		…
1254	single "request", that is, reading the token from the pipe and	1777	single "request", that is, reading the token from the pipe and
1255	forwarding it to another server. This includes deleting the old timeout	1778	forwarding it to another server. This includes deleting the old timeout
1256	and creating a new one that moves the timeout into the future.	1779	and creating a new one that moves the timeout into the future.
1257		1780
1258	Results	1781	Results
1259	name sockets create request	1782	name sockets create request
1260	EV 20000 69.01 11.16	1783	EV 20000 62.66 7.99
1261	Perl 20000 73.32 35.87	1784	Perl 20000 68.32 32.64
1262	Event 20000 212.62 257.32	1785	IOAsync 20000 174.06 101.15 epoll
1263	Glib 20000 651.16 1896.30	1786	IOAsync 20000 174.67 610.84 poll
		1787	Event 20000 202.69 242.91
		1788	Glib 20000 557.01 1689.52
1264	POE 20000 349.67 12317.24 uses POE::Loop::Event	1789	POE 20000 341.54 12086.32 uses POE::Loop::Event
1265		1790
1266	Discussion	1791	Discussion
1267	This benchmark *does* measure scalability and overall performance of the	1792	This benchmark *does* measure scalability and overall performance of the
1268	particular event loop.	1793	particular event loop.
1269		1794
1270	EV is again fastest. Since it is using epoll on my system, the setup	1795	EV is again fastest. Since it is using epoll on my system, the setup
1271	time is relatively high, though.	1796	time is relatively high, though.
1272		1797
1273	Perl surprisingly comes second. It is much faster than the C-based event	1798	Perl surprisingly comes second. It is much faster than the C-based event
1274	loops Event and Glib.	1799	loops Event and Glib.
		1800
		1801	IO::Async performs very well when using its epoll backend, and still
		1802	quite good compared to Glib when using its pure perl backend.
1275		1803
1276	Event suffers from high setup time as well (look at its code and you	1804	Event suffers from high setup time as well (look at its code and you
1277	will understand why). Callback invocation also has a high overhead	1805	will understand why). Callback invocation also has a high overhead
1278	compared to the "$_->() for .."-style loop that the Perl event loop	1806	compared to the "$_->() for .."-style loop that the Perl event loop
1279	uses. Event uses select or poll in basically all documented	1807	uses. Event uses select or poll in basically all documented
…		…
1330		1858
1331	Summary	1859	Summary
1332	* C-based event loops perform very well with small number of watchers,	1860	* C-based event loops perform very well with small number of watchers,
1333	as the management overhead dominates.	1861	as the management overhead dominates.
1334		1862
		1863	THE IO::Lambda BENCHMARK
		1864	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1865	could be misinterpreted to make AnyEvent look bad. In fact, the
		1866	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1867	better (which shouldn't come as a surprise to anybody). As such, the
		1868	benchmark is fine, and mostly shows that the AnyEvent backend from
		1869	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1870	without the extra baggage? To explore this, I wrote the equivalent
		1871	benchmark for AnyEvent.
		1872
		1873	The benchmark itself creates an echo-server, and then, for 500 times,
		1874	connects to the echo server, sends a line, waits for the reply, and then
		1875	creates the next connection. This is a rather bad benchmark, as it
		1876	doesn't test the efficiency of the framework or much non-blocking I/O,
		1877	but it is a benchmark nevertheless.
		1878
		1879	name runtime
		1880	Lambda/select 0.330 sec
		1881	+ optimized 0.122 sec
		1882	Lambda/AnyEvent 0.327 sec
		1883	+ optimized 0.138 sec
		1884	Raw sockets/select 0.077 sec
		1885	POE/select, components 0.662 sec
		1886	POE/select, raw sockets 0.226 sec
		1887	POE/select, optimized 0.404 sec
		1888
		1889	AnyEvent/select/nb 0.085 sec
		1890	AnyEvent/EV/nb 0.068 sec
		1891	+state machine 0.134 sec
		1892
		1893	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1894	benchmarks actually make blocking connects and use 100% blocking I/O,
		1895	defeating the purpose of an event-based solution. All of the newly
		1896	written AnyEvent benchmarks use 100% non-blocking connects (using
		1897	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1898	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1899	connects generally require a lot more bookkeeping and event handling
		1900	than blocking connects (which involve a single syscall only).
		1901
		1902	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1903	offers similar expressive power as POE and IO::Lambda, using
		1904	conventional Perl syntax. This means that both the echo server and the
		1905	client are 100% non-blocking, further placing it at a disadvantage.
		1906
		1907	As you can see, the AnyEvent + EV combination even beats the
		1908	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1909	backend easily beats IO::Lambda and POE.
		1910
		1911	And even the 100% non-blocking version written using the high-level (and
		1912	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1913	higher level ("unoptimised") abstractions by a large margin, even though
		1914	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1915
		1916	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1917	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1918	part of the IO::Lambda distribution and were used without any changes.
		1919
		1920	SIGNALS
		1921	AnyEvent currently installs handlers for these signals:
		1922
		1923	SIGCHLD
		1924	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1925	emulation for event loops that do not support them natively. Also,
		1926	some event loops install a similar handler.
		1927
		1928	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1929	then AnyEvent will reset it to default, to avoid losing child exit
		1930	statuses.
		1931
		1932	SIGPIPE
		1933	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1934	"undef" when AnyEvent gets loaded.
		1935
		1936	The rationale for this is that AnyEvent users usually do not really
		1937	depend on SIGPIPE delivery (which is purely an optimisation for
		1938	shell use, or badly-written programs), but "SIGPIPE" can cause
		1939	spurious and rare program exits as a lot of people do not expect
		1940	"SIGPIPE" when writing to some random socket.
		1941
		1942	The rationale for installing a no-op handler as opposed to ignoring
		1943	it is that this way, the handler will be restored to defaults on
		1944	exec.
		1945
		1946	Feel free to install your own handler, or reset it to defaults.
		1947
		1948	RECOMMENDED/OPTIONAL MODULES
		1949	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1950	its built-in modules) are required to use it.
		1951
		1952	That does not mean that AnyEvent won't take advantage of some additional
		1953	modules if they are installed.
		1954
		1955	This section explains which additional modules will be used, and how
		1956	they affect AnyEvent's operation.
		1957
		1958	Async::Interrupt
		1959	This slightly arcane module is used to implement fast signal
		1960	handling: To my knowledge, there is no way to do completely
		1961	race-free and quick signal handling in pure perl. To ensure that
		1962	signals still get delivered, AnyEvent will start an interval timer
		1963	to wake up perl (and catch the signals) with some delay (default is
		1964	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1965
		1966	If this module is available, then it will be used to implement
		1967	signal catching, which means that signals will not be delayed, and
		1968	the event loop will not be interrupted regularly, which is more
		1969	efficient (and good for battery life on laptops).
		1970
		1971	This affects not just the pure-perl event loop, but also other event
		1972	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1973
		1974	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1975	natively, and either employ their own workarounds (POE) or use
		1976	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1977	Installing Async::Interrupt does nothing for those backends.
		1978
		1979	EV This module isn't really "optional", as it is simply one of the
		1980	backend event loops that AnyEvent can use. However, it is simply the
		1981	best event loop available in terms of features, speed and stability:
		1982	It supports the AnyEvent API optimally, implements all the watcher
		1983	types in XS, does automatic timer adjustments even when no monotonic
		1984	clock is available, can take avdantage of advanced kernel interfaces
		1985	such as "epoll" and "kqueue", and is the fastest backend *by far*.
		1986	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1987	Glib::EV).
		1988
		1989	If you only use backends that rely on another event loop (e.g.
		1990	"Tk"), then this module will do nothing for you.
		1991
		1992	Guard
		1993	The guard module, when used, will be used to implement
		1994	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1995	uses a lot less memory), but otherwise doesn't affect guard
		1996	operation much. It is purely used for performance.
		1997
		1998	JSON and JSON::XS
		1999	One of these modules is required when you want to read or write JSON
		2000	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		2001	can take advantage of the ultra-high-speed JSON::XS module when it
		2002	is installed.
		2003
		2004	Net::SSLeay
		2005	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2006	worthwhile: If this module is installed, then AnyEvent::Handle (with
		2007	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		2008
		2009	Time::HiRes
		2010	This module is part of perl since release 5.008. It will be used
		2011	when the chosen event library does not come with a timing source of
		2012	its own. The pure-perl event loop (AnyEvent::Loop) will additionally
		2013	load it to try to use a monotonic clock for timing stability.
		2014
		2015	AnyEvent::AIO (and IO::AIO)
		2016	The default implementation of AnyEvent::IO is to do I/O
		2017	synchronously, stopping programs while they access the disk, which
		2018	is fine for a lot of programs.
		2019
		2020	Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
		2021	switch to a true asynchronous implementation, so event processing
		2022	can continue even while waiting for disk I/O.
		2023
1335	FORK	2024	FORK
1336	Most event libraries are not fork-safe. The ones who are usually are	2025	Most event libraries are not fork-safe. The ones who are usually are
1337	because they rely on inefficient but fork-safe "select" or "poll" calls.	2026	because they rely on inefficient but fork-safe "select" or "poll" calls
1338	Only EV is fully fork-aware.	2027	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		2028	epoll are usually badly thought-out hacks that are incompatible with
		2029	fork in one way or another. Only EV is fully fork-aware and ensures that
		2030	you continue event-processing in both parent and child (or both, if you
		2031	know what you are doing).
		2032
		2033	This means that, in general, you cannot fork and do event processing in
		2034	the child if the event library was initialised before the fork (which
		2035	usually happens when the first AnyEvent watcher is created, or the
		2036	library is loaded).
1339		2037
1340	If you have to fork, you must either do so *before* creating your first	2038	If you have to fork, you must either do so *before* creating your first
1341	watcher OR you must not use AnyEvent at all in the child.	2039	watcher OR you must not use AnyEvent at all in the child OR you must do
		2040	something completely out of the scope of AnyEvent.
		2041
		2042	The problem of doing event processing in the parent *and* the child is
		2043	much more complicated: even for backends that *are* fork-aware or
		2044	fork-safe, their behaviour is not usually what you want: fork clones all
		2045	watchers, that means all timers, I/O watchers etc. are active in both
		2046	parent and child, which is almost never what you want. USing "exec" to
		2047	start worker children from some kind of manage rprocess is usually
		2048	preferred, because it is much easier and cleaner, at the expense of
		2049	having to have another binary.
1342		2050
1343	SECURITY CONSIDERATIONS	2051	SECURITY CONSIDERATIONS
1344	AnyEvent can be forced to load any event model via	2052	AnyEvent can be forced to load any event model via
1345	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	2053	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1346	to execute arbitrary code or directly gain access, it can easily be used	2054	to execute arbitrary code or directly gain access, it can easily be used
…		…
1350		2058
1351	You can make AnyEvent completely ignore this variable by deleting it	2059	You can make AnyEvent completely ignore this variable by deleting it
1352	before the first watcher gets created, e.g. with a "BEGIN" block:	2060	before the first watcher gets created, e.g. with a "BEGIN" block:
1353		2061
1354	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	2062	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1355		2063
1356	use AnyEvent;	2064	use AnyEvent;
1357		2065
1358	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	2066	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1359	be used to probe what backend is used and gain other information (which	2067	be used to probe what backend is used and gain other information (which
1360	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),	2068	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1361	and $ENV{PERL_ANYEGENT_STRICT}.	2069	and $ENV{PERL_ANYEVENT_STRICT}.
		2070
		2071	Note that AnyEvent will remove *all* environment variables starting with
		2072	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		2073	enabled.
1362		2074
1363	BUGS	2075	BUGS
1364	Perl 5.8 has numerous memleaks that sometimes hit this module and are	2076	Perl 5.8 has numerous memleaks that sometimes hit this module and are
1365	hard to work around. If you suffer from memleaks, first upgrade to Perl	2077	hard to work around. If you suffer from memleaks, first upgrade to Perl
1366	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	2078	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1367	annoying mamleaks, such as leaking on "map" and "grep" but it is usually	2079	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1368	not as pronounced).	2080	not as pronounced).
1369		2081
1370	SEE ALSO	2082	SEE ALSO
1371	Utility functions: AnyEvent::Util.	2083	Tutorial/Introduction: AnyEvent::Intro.
1372		2084
1373	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	2085	FAQ: AnyEvent::FAQ.
1374	Event::Lib, Qt, POE.	2086
		2087	Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
		2088	(simply logging).
		2089
		2090	Development/Debugging: AnyEvent::Strict (stricter checking),
		2091	AnyEvent::Debug (interactive shell, watcher tracing).
		2092
		2093	Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
		2094	Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK.
1375		2095
1376	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	2096	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1377	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	2097	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1378	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	2098	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		2099	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi, AnyEvent::Impl::FLTK.
1379		2100
1380	Non-blocking file handles, sockets, TCP clients and servers:	2101	Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1381	AnyEvent::Handle, AnyEvent::Socket.	2102	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		2103
		2104	Asynchronous File I/O: AnyEvent::IO.
1382		2105
1383	Asynchronous DNS: AnyEvent::DNS.	2106	Asynchronous DNS: AnyEvent::DNS.
1384		2107
1385	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	2108	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1386		2109
1387	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	2110	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
		2111	AnyEvent::HTTP.
1388		2112
1389	AUTHOR	2113	AUTHOR
1390	Marc Lehmann <schmorp@schmorp.de>	2114	Marc Lehmann <schmorp@schmorp.de>
1391	http://home.schmorp.de/	2115	http://anyevent.schmorp.de
1392		2116

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