[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.42 by root, Mon Jun 29 21:00:32 2009 UTC vs.
Revision 1.77 by root, Sat Sep 17 02:33:54 2016 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - the DBI of event loop programming
3		3
4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported	4	EV, Event, Glib, Tk, UV, Perl, Event::Lib, Irssi, rxvt-unicode,
5	event loops.	5	IO::Async, Qt, FLTK and POE are various supported event
		6	loops/environments.
6		7
7	SYNOPSIS	8	SYNOPSIS
8	use AnyEvent;	9	use AnyEvent;
9		10
		11	# if you prefer function calls, look at the AE manpage for
		12	# an alternative API.
		13
10	# file descriptor readable	14	# file handle or descriptor readable
11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });	15	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12		16
13	# one-shot or repeating timers	17	# one-shot or repeating timers
14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });	18	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...	19	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
16		20
17	print AnyEvent->now; # prints current event loop time	21	print AnyEvent->now; # prints current event loop time
18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.	22	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
19		23
20	# POSIX signal	24	# POSIX signal
37		41
38	INTRODUCTION/TUTORIAL	42	INTRODUCTION/TUTORIAL
39	This manpage is mainly a reference manual. If you are interested in a	43	This manpage is mainly a reference manual. If you are interested in a
40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	44	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
41	manpage.	45	manpage.
		46
		47	SUPPORT
		48	An FAQ document is available as AnyEvent::FAQ.
		49
		50	There also is a mailinglist for discussing all things AnyEvent, and an
		51	IRC channel, too.
		52
		53	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		54	Repository, at <http://anyevent.schmorp.de>, for more info.
42		55
43	WHY YOU SHOULD USE THIS MODULE (OR NOT)	56	WHY YOU SHOULD USE THIS MODULE (OR NOT)
44	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	57	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
45	nowadays. So what is different about AnyEvent?	58	nowadays. So what is different about AnyEvent?
46		59
…		…
61	module users into the same thing by forcing them to use the same event	74	module users into the same thing by forcing them to use the same event
62	model you use.	75	model you use.
63		76
64	For modules like POE or IO::Async (which is a total misnomer as it is	77	For modules like POE or IO::Async (which is a total misnomer as it is
65	actually doing all I/O synchronously...), using them in your module is	78	actually doing all I/O synchronously...), using them in your module is
66	like joining a cult: After you joined, you are dependent on them and you	79	like joining a cult: After you join, you are dependent on them and you
67	cannot use anything else, as they are simply incompatible to everything	80	cannot use anything else, as they are simply incompatible to everything
68	that isn't them. What's worse, all the potential users of your module	81	that isn't them. What's worse, all the potential users of your module
69	are also forced to use the same event loop you use.	82	are also forced to use the same event loop you use.
70		83
71	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	84	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
72	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	85	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
73	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your	86	with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
74	module uses one of those, every user of your module has to use it, too.	87	uses one of those, every user of your module has to use it, too. But if
75	But if your module uses AnyEvent, it works transparently with all event	88	your module uses AnyEvent, it works transparently with all event models
76	models it supports (including stuff like IO::Async, as long as those use	89	it supports (including stuff like IO::Async, as long as those use one of
77	one of the supported event loops. It is trivial to add new event loops	90	the supported event loops. It is easy to add new event loops to
78	to AnyEvent, too, so it is future-proof).	91	AnyEvent, too, so it is future-proof).
79		92
80	In addition to being free of having to use *the one and only true event	93	In addition to being free of having to use *the one and only true event
81	model*, AnyEvent also is free of bloat and policy: with POE or similar	94	model*, AnyEvent also is free of bloat and policy: with POE or similar
82	modules, you get an enormous amount of code and strict rules you have to	95	modules, you get an enormous amount of code and strict rules you have to
83	follow. AnyEvent, on the other hand, is lean and up to the point, by	96	follow. AnyEvent, on the other hand, is lean and to the point, by only
84	only offering the functionality that is necessary, in as thin as a	97	offering the functionality that is necessary, in as thin as a wrapper as
85	wrapper as technically possible.	98	technically possible.
86		99
87	Of course, AnyEvent comes with a big (and fully optional!) toolbox of	100	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
88	useful functionality, such as an asynchronous DNS resolver, 100%	101	useful functionality, such as an asynchronous DNS resolver, 100%
89	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms	102	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
90	such as Windows) and lots of real-world knowledge and workarounds for	103	such as Windows) and lots of real-world knowledge and workarounds for
…		…
93	Now, if you do want lots of policy (this can arguably be somewhat	106	Now, if you do want lots of policy (this can arguably be somewhat
94	useful) and you want to force your users to use the one and only event	107	useful) and you want to force your users to use the one and only event
95	model, you should not use this module.	108	model, you should not use this module.
96		109
97	DESCRIPTION	110	DESCRIPTION
98	AnyEvent provides an identical interface to multiple event loops. This	111	AnyEvent provides a uniform interface to various event loops. This
99	allows module authors to utilise an event loop without forcing module	112	allows module authors to use event loop functionality without forcing
100	users to use the same event loop (as only a single event loop can	113	module users to use a specific event loop implementation (since more
101	coexist peacefully at any one time).	114	than one event loop cannot coexist peacefully).
102		115
103	The interface itself is vaguely similar, but not identical to the Event	116	The interface itself is vaguely similar, but not identical to the Event
104	module.	117	module.
105		118
106	During the first call of any watcher-creation method, the module tries	119	During the first call of any watcher-creation method, the module tries
107	to detect the currently loaded event loop by probing whether one of the	120	to detect the currently loaded event loop by probing whether one of the
108	following modules is already loaded: EV, Event, Glib,	121	following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
109	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is	122	Tk, Event::Lib, Qt, POE. The first one found is used. If none are
110	used. If none are found, the module tries to load these modules	123	detected, the module tries to load the first four modules in the order
111	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	124	given; but note that if EV is not available, the pure-perl
112	always succeed) in the order given. The first one that can be	125	AnyEvent::Loop should always work, so the other two are not normally
113	successfully loaded will be used. If, after this, still none could be	126	tried.
114	found, AnyEvent will fall back to a pure-perl event loop, which is not
115	very efficient, but should work everywhere.
116		127
117	Because AnyEvent first checks for modules that are already loaded,	128	Because AnyEvent first checks for modules that are already loaded,
118	loading an event model explicitly before first using AnyEvent will	129	loading an event model explicitly before first using AnyEvent will
119	likely make that model the default. For example:	130	likely make that model the default. For example:
120		131
…		…
122	use AnyEvent;	133	use AnyEvent;
123		134
124	# .. AnyEvent will likely default to Tk	135	# .. AnyEvent will likely default to Tk
125		136
126	The likely means that, if any module loads another event model and	137	The likely means that, if any module loads another event model and
127	starts using it, all bets are off. Maybe you should tell their authors	138	starts using it, all bets are off - this case should be very rare
128	to use AnyEvent so their modules work together with others seamlessly...	139	though, as very few modules hardcode event loops without announcing this
		140	very loudly.
129		141
130	The pure-perl implementation of AnyEvent is called	142	The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
131	"AnyEvent::Impl::Perl". Like other event modules you can load it	143	Like other event modules you can load it explicitly and enjoy the high
132	explicitly and enjoy the high availability of that event loop :)	144	availability of that event loop :)
133		145
134	WATCHERS	146	WATCHERS
135	AnyEvent has the central concept of a watcher, which is an object that	147	AnyEvent has the central concept of a watcher, which is an object that
136	stores relevant data for each kind of event you are waiting for, such as	148	stores relevant data for each kind of event you are waiting for, such as
137	the callback to call, the file handle to watch, etc.	149	the callback to call, the file handle to watch, etc.
…		…
141	callback when the event occurs (of course, only when the event model is	153	callback when the event occurs (of course, only when the event model is
142	in control).	154	in control).
143		155
144	Note that callbacks must not permanently change global variables	156	Note that callbacks must not permanently change global variables
145	potentially in use by the event loop (such as $_ or $[) and that	157	potentially in use by the event loop (such as $_ or $[) and that
146	callbacks must not "die". The former is good programming practise in	158	callbacks must not "die". The former is good programming practice in
147	Perl and the latter stems from the fact that exception handling differs	159	Perl and the latter stems from the fact that exception handling differs
148	widely between event loops.	160	widely between event loops.
149		161
150	To disable the watcher you have to destroy it (e.g. by setting the	162	To disable a watcher you have to destroy it (e.g. by setting the
151	variable you store it in to "undef" or otherwise deleting all references	163	variable you store it in to "undef" or otherwise deleting all references
152	to it).	164	to it).
153		165
154	All watchers are created by calling a method on the "AnyEvent" class.	166	All watchers are created by calling a method on the "AnyEvent" class.
155		167
156	Many watchers either are used with "recursion" (repeating timers for	168	Many watchers either are used with "recursion" (repeating timers for
157	example), or need to refer to their watcher object in other ways.	169	example), or need to refer to their watcher object in other ways.
158		170
159	An any way to achieve that is this pattern:	171	One way to achieve that is this pattern:
160		172
161	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	173	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
162	# you can use $w here, for example to undef it	174	# you can use $w here, for example to undef it
163	undef $w;	175	undef $w;
164	});	176	});
…		…
166	Note that "my $w; $w =" combination. This is necessary because in Perl,	178	Note that "my $w; $w =" combination. This is necessary because in Perl,
167	my variables are only visible after the statement in which they are	179	my variables are only visible after the statement in which they are
168	declared.	180	declared.
169		181
170	I/O WATCHERS	182	I/O WATCHERS
		183	$w = AnyEvent->io (
		184	fh => <filehandle_or_fileno>,
		185	poll => <"r" or "w">,
		186	cb => <callback>,
		187	);
		188
171	You can create an I/O watcher by calling the "AnyEvent->io" method with	189	You can create an I/O watcher by calling the "AnyEvent->io" method with
172	the following mandatory key-value pairs as arguments:	190	the following mandatory key-value pairs as arguments:
173		191
174	"fh" is the Perl file handle (not file descriptor) to watch for	192	"fh" is the Perl file handle (or a naked file descriptor) to watch for
175	events (AnyEvent might or might not keep a reference to this file	193	events (AnyEvent might or might not keep a reference to this file
176	handle). Note that only file handles pointing to things for which	194	handle). Note that only file handles pointing to things for which
177	non-blocking operation makes sense are allowed. This includes sockets,	195	non-blocking operation makes sense are allowed. This includes sockets,
178	most character devices, pipes, fifos and so on, but not for example	196	most character devices, pipes, fifos and so on, but not for example
179	files or block devices.	197	files or block devices.
…		…
189		207
190	The I/O watcher might use the underlying file descriptor or a copy of	208	The I/O watcher might use the underlying file descriptor or a copy of
191	it. You must not close a file handle as long as any watcher is active on	209	it. You must not close a file handle as long as any watcher is active on
192	the underlying file descriptor.	210	the underlying file descriptor.
193		211
194	Some event loops issue spurious readyness notifications, so you should	212	Some event loops issue spurious readiness notifications, so you should
195	always use non-blocking calls when reading/writing from/to your file	213	always use non-blocking calls when reading/writing from/to your file
196	handles.	214	handles.
197		215
198	Example: wait for readability of STDIN, then read a line and disable the	216	Example: wait for readability of STDIN, then read a line and disable the
199	watcher.	217	watcher.
…		…
203	warn "read: $input\n";	221	warn "read: $input\n";
204	undef $w;	222	undef $w;
205	});	223	});
206		224
207	TIME WATCHERS	225	TIME WATCHERS
		226	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		227
		228	$w = AnyEvent->timer (
		229	after => <fractional_seconds>,
		230	interval => <fractional_seconds>,
		231	cb => <callback>,
		232	);
		233
208	You can create a time watcher by calling the "AnyEvent->timer" method	234	You can create a time watcher by calling the "AnyEvent->timer" method
209	with the following mandatory arguments:	235	with the following mandatory arguments:
210		236
211	"after" specifies after how many seconds (fractional values are	237	"after" specifies after how many seconds (fractional values are
212	supported) the callback should be invoked. "cb" is the callback to	238	supported) the callback should be invoked. "cb" is the callback to
…		…
214		240
215	Although the callback might get passed parameters, their value and	241	Although the callback might get passed parameters, their value and
216	presence is undefined and you cannot rely on them. Portable AnyEvent	242	presence is undefined and you cannot rely on them. Portable AnyEvent
217	callbacks cannot use arguments passed to time watcher callbacks.	243	callbacks cannot use arguments passed to time watcher callbacks.
218		244
219	The callback will normally be invoked once only. If you specify another	245	The callback will normally be invoked only once. If you specify another
220	parameter, "interval", as a strictly positive number (> 0), then the	246	parameter, "interval", as a strictly positive number (> 0), then the
221	callback will be invoked regularly at that interval (in fractional	247	callback will be invoked regularly at that interval (in fractional
222	seconds) after the first invocation. If "interval" is specified with a	248	seconds) after the first invocation. If "interval" is specified with a
223	false value, then it is treated as if it were missing.	249	false value, then it is treated as if it were not specified at all.
224		250
225	The callback will be rescheduled before invoking the callback, but no	251	The callback will be rescheduled before invoking the callback, but no
226	attempt is done to avoid timer drift in most backends, so the interval	252	attempt is made to avoid timer drift in most backends, so the interval
227	is only approximate.	253	is only approximate.
228		254
229	Example: fire an event after 7.7 seconds.	255	Example: fire an event after 7.7 seconds.
230		256
231	my $w = AnyEvent->timer (after => 7.7, cb => sub {	257	my $w = AnyEvent->timer (after => 7.7, cb => sub {
…		…
237		263
238	Example 2: fire an event after 0.5 seconds, then roughly every second.	264	Example 2: fire an event after 0.5 seconds, then roughly every second.
239		265
240	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {	266	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
241	warn "timeout\n";	267	warn "timeout\n";
242	};	268	});
243		269
244	TIMING ISSUES	270	TIMING ISSUES
245	There are two ways to handle timers: based on real time (relative, "fire	271	There are two ways to handle timers: based on real time (relative, "fire
246	in 10 seconds") and based on wallclock time (absolute, "fire at 12	272	in 10 seconds") and based on wallclock time (absolute, "fire at 12
247	o'clock").	273	o'clock").
248		274
249	While most event loops expect timers to specified in a relative way,	275	While most event loops expect timers to specified in a relative way,
250	they use absolute time internally. This makes a difference when your	276	they use absolute time internally. This makes a difference when your
251	clock "jumps", for example, when ntp decides to set your clock backwards	277	clock "jumps", for example, when ntp decides to set your clock backwards
252	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is	278	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
253	supposed to fire "after" a second might actually take six years to	279	supposed to fire "after a second" might actually take six years to
254	finally fire.	280	finally fire.
255		281
256	AnyEvent cannot compensate for this. The only event loop that is	282	AnyEvent cannot compensate for this. The only event loop that is
257	conscious about these issues is EV, which offers both relative	283	conscious of these issues is EV, which offers both relative (ev_timer,
258	(ev_timer, based on true relative time) and absolute (ev_periodic, based	284	based on true relative time) and absolute (ev_periodic, based on
259	on wallclock time) timers.	285	wallclock time) timers.
260		286
261	AnyEvent always prefers relative timers, if available, matching the	287	AnyEvent always prefers relative timers, if available, matching the
262	AnyEvent API.	288	AnyEvent API.
263		289
264	AnyEvent has two additional methods that return the "current time":	290	AnyEvent has two additional methods that return the "current time":
…		…
283	*In almost all cases (in all cases if you don't care), this is the	309	*In almost all cases (in all cases if you don't care), this is the
284	function to call when you want to know the current time.*	310	function to call when you want to know the current time.*
285		311
286	This function is also often faster then "AnyEvent->time", and thus	312	This function is also often faster then "AnyEvent->time", and thus
287	the preferred method if you want some timestamp (for example,	313	the preferred method if you want some timestamp (for example,
288	AnyEvent::Handle uses this to update it's activity timeouts).	314	AnyEvent::Handle uses this to update its activity timeouts).
289		315
290	The rest of this section is only of relevance if you try to be very	316	The rest of this section is only of relevance if you try to be very
291	exact with your timing, you can skip it without bad conscience.	317	exact with your timing; you can skip it without a bad conscience.
292		318
293	For a practical example of when these times differ, consider	319	For a practical example of when these times differ, consider
294	Event::Lib and EV and the following set-up:	320	Event::Lib and EV and the following set-up:
295		321
296	The event loop is running and has just invoked one of your callback	322	The event loop is running and has just invoked one of your callbacks
297	at time=500 (assume no other callbacks delay processing). In your	323	at time=500 (assume no other callbacks delay processing). In your
298	callback, you wait a second by executing "sleep 1" (blocking the	324	callback, you wait a second by executing "sleep 1" (blocking the
299	process for a second) and then (at time=501) you create a relative	325	process for a second) and then (at time=501) you create a relative
300	timer that fires after three seconds.	326	timer that fires after three seconds.
301		327
…		…
322	can get whatever behaviour you want with any event loop, by taking	348	can get whatever behaviour you want with any event loop, by taking
323	the difference between "AnyEvent->time" and "AnyEvent->now" into	349	the difference between "AnyEvent->time" and "AnyEvent->now" into
324	account.	350	account.
325		351
326	AnyEvent->now_update	352	AnyEvent->now_update
327	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the	353	Some event loops (such as EV or AnyEvent::Loop) cache the current
328	current time for each loop iteration (see the discussion of	354	time for each loop iteration (see the discussion of AnyEvent->now,
329	AnyEvent->now, above).	355	above).
330		356
331	When a callback runs for a long time (or when the process sleeps),	357	When a callback runs for a long time (or when the process sleeps),
332	then this "current" time will differ substantially from the real	358	then this "current" time will differ substantially from the real
333	time, which might affect timers and time-outs.	359	time, which might affect timers and time-outs.
334		360
335	When this is the case, you can call this method, which will update	361	When this is the case, you can call this method, which will update
336	the event loop's idea of "current time".	362	the event loop's idea of "current time".
337		363
		364	A typical example would be a script in a web server (e.g.
		365	"mod_perl") - when mod_perl executes the script, then the event loop
		366	will have the wrong idea about the "current time" (being potentially
		367	far in the past, when the script ran the last time). In that case
		368	you should arrange a call to "AnyEvent->now_update" each time the
		369	web server process wakes up again (e.g. at the start of your script,
		370	or in a handler).
		371
338	Note that updating the time might cause some events to be handled.	372	Note that updating the time might cause some events to be handled.
339		373
340	SIGNAL WATCHERS	374	SIGNAL WATCHERS
		375	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		376
341	You can watch for signals using a signal watcher, "signal" is the signal	377	You can watch for signals using a signal watcher, "signal" is the signal
342	name in uppercase and without any "SIG" prefix, "cb" is the Perl	378	name in uppercase and without any "SIG" prefix, "cb" is the Perl
343	callback to be invoked whenever a signal occurs.	379	callback to be invoked whenever a signal occurs.
344		380
345	Although the callback might get passed parameters, their value and	381	Although the callback might get passed parameters, their value and
…		…
350	invocation, and callback invocation will be synchronous. Synchronous	386	invocation, and callback invocation will be synchronous. Synchronous
351	means that it might take a while until the signal gets handled by the	387	means that it might take a while until the signal gets handled by the
352	process, but it is guaranteed not to interrupt any other callbacks.	388	process, but it is guaranteed not to interrupt any other callbacks.
353		389
354	The main advantage of using these watchers is that you can share a	390	The main advantage of using these watchers is that you can share a
355	signal between multiple watchers.	391	signal between multiple watchers, and AnyEvent will ensure that signals
		392	will not interrupt your program at bad times.
356		393
357	This watcher might use %SIG, so programs overwriting those signals	394	This watcher might use %SIG (depending on the event loop used), so
358	directly will likely not work correctly.	395	programs overwriting those signals directly will likely not work
		396	correctly.
359		397
360	Example: exit on SIGINT	398	Example: exit on SIGINT
361		399
362	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	400	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
363		401
		402	Restart Behaviour
		403	While restart behaviour is up to the event loop implementation, most
		404	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		405	pure perl implementation).
		406
		407	Safe/Unsafe Signals
		408	Perl signals can be either "safe" (synchronous to opcode handling) or
		409	"unsafe" (asynchronous) - the former might delay signal delivery
		410	indefinitely, the latter might corrupt your memory.
		411
		412	AnyEvent signal handlers are, in addition, synchronous to the event
		413	loop, i.e. they will not interrupt your running perl program but will
		414	only be called as part of the normal event handling (just like timer,
		415	I/O etc. callbacks, too).
		416
		417	Signal Races, Delays and Workarounds
		418	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		419	callbacks to signals in a generic way, which is a pity, as you cannot do
		420	race-free signal handling in perl, requiring C libraries for this.
		421	AnyEvent will try to do its best, which means in some cases, signals
		422	will be delayed. The maximum time a signal might be delayed is 10
		423	seconds by default, but can be overriden via
		424	$ENV{PERL_ANYEVENT_MAX_SIGNAL_LATENCY} or $AnyEvent::MAX_SIGNAL_LATENCY
		425	- see the "ENVIRONMENT VARIABLES" section for details.
		426
		427	All these problems can be avoided by installing the optional
		428	Async::Interrupt module, which works with most event loops. It will not
		429	work with inherently broken event loops such as Event or Event::Lib (and
		430	not with POE currently). For those, you just have to suffer the delays.
		431
364	CHILD PROCESS WATCHERS	432	CHILD PROCESS WATCHERS
		433	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		434
365	You can also watch on a child process exit and catch its exit status.	435	You can also watch for a child process exit and catch its exit status.
366		436
367	The child process is specified by the "pid" argument (if set to 0, it	437	The child process is specified by the "pid" argument (on some backends,
368	watches for any child process exit). The watcher will triggered only	438	using 0 watches for any child process exit, on others this will croak).
369	when the child process has finished and an exit status is available, not	439	The watcher will be triggered only when the child process has finished
370	on any trace events (stopped/continued).	440	and an exit status is available, not on any trace events
		441	(stopped/continued).
371		442
372	The callback will be called with the pid and exit status (as returned by	443	The callback will be called with the pid and exit status (as returned by
373	waitpid), so unlike other watcher types, you can rely on child watcher	444	waitpid), so unlike other watcher types, you can rely on child watcher
374	callback arguments.	445	callback arguments.
375		446
…		…
391		462
392	This means you cannot create a child watcher as the very first thing in	463	This means you cannot create a child watcher as the very first thing in
393	an AnyEvent program, you have to create at least one watcher before	464	an AnyEvent program, you have to create at least one watcher before
394	you "fork" the child (alternatively, you can call "AnyEvent::detect").	465	you "fork" the child (alternatively, you can call "AnyEvent::detect").
395		466
		467	As most event loops do not support waiting for child events, they will
		468	be emulated by AnyEvent in most cases, in which case the latency and
		469	race problems mentioned in the description of signal watchers apply.
		470
396	Example: fork a process and wait for it	471	Example: fork a process and wait for it
397		472
398	my $done = AnyEvent->condvar;	473	my $done = AnyEvent->condvar;
399		474
		475	# this forks and immediately calls exit in the child. this
		476	# normally has all sorts of bad consequences for your parent,
		477	# so take this as an example only. always fork and exec,
		478	# or call POSIX::_exit, in real code.
400	my $pid = fork or exit 5;	479	my $pid = fork or exit 5;
401		480
402	my $w = AnyEvent->child (	481	my $w = AnyEvent->child (
403	pid => $pid,	482	pid => $pid,
404	cb => sub {	483	cb => sub {
…		…
410		489
411	# do something else, then wait for process exit	490	# do something else, then wait for process exit
412	$done->recv;	491	$done->recv;
413		492
414	IDLE WATCHERS	493	IDLE WATCHERS
415	Sometimes there is a need to do something, but it is not so important to	494	$w = AnyEvent->idle (cb => <callback>);
416	do it instantly, but only when there is nothing better to do. This
417	"nothing better to do" is usually defined to be "no other events need
418	attention by the event loop".
419		495
420	Idle watchers ideally get invoked when the event loop has nothing better	496	This will repeatedly invoke the callback after the process becomes idle,
421	to do, just before it would block the process to wait for new events.	497	until either the watcher is destroyed or new events have been detected.
422	Instead of blocking, the idle watcher is invoked.
423		498
424	Most event loops unfortunately do not really support idle watchers (only	499	Idle watchers are useful when there is a need to do something, but it is
		500	not so important (or wise) to do it instantly. The callback will be
		501	invoked only when there is "nothing better to do", which is usually
		502	defined as "all outstanding events have been handled and no new events
		503	have been detected". That means that idle watchers ideally get invoked
		504	when the event loop has just polled for new events but none have been
		505	detected. Instead of blocking to wait for more events, the idle watchers
		506	will be invoked.
		507
		508	Unfortunately, most event loops do not really support idle watchers
425	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent	509	(only EV, Event and Glib do it in a usable fashion) - for the rest,
426	will simply call the callback "from time to time".	510	AnyEvent will simply call the callback "from time to time".
427		511
428	Example: read lines from STDIN, but only process them when the program	512	Example: read lines from STDIN, but only process them when the program
429	is otherwise idle:	513	is otherwise idle:
430		514
431	my @lines; # read data	515	my @lines; # read data
…		…
444	}	528	}
445	});	529	});
446	});	530	});
447		531
448	CONDITION VARIABLES	532	CONDITION VARIABLES
		533	$cv = AnyEvent->condvar;
		534
		535	$cv->send (<list>);
		536	my @res = $cv->recv;
		537
449	If you are familiar with some event loops you will know that all of them	538	If you are familiar with some event loops you will know that all of them
450	require you to run some blocking "loop", "run" or similar function that	539	require you to run some blocking "loop", "run" or similar function that
451	will actively watch for new events and call your callbacks.	540	will actively watch for new events and call your callbacks.
452		541
453	AnyEvent is different, it expects somebody else to run the event loop	542	AnyEvent is slightly different: it expects somebody else to run the
454	and will only block when necessary (usually when told by the user).	543	event loop and will only block when necessary (usually when told by the
		544	user).
455		545
456	The instrument to do that is called a "condition variable", so called	546	The tool to do that is called a "condition variable", so called because
457	because they represent a condition that must become true.	547	they represent a condition that must become true.
		548
		549	Now is probably a good time to look at the examples further below.
458		550
459	Condition variables can be created by calling the "AnyEvent->condvar"	551	Condition variables can be created by calling the "AnyEvent->condvar"
460	method, usually without arguments. The only argument pair allowed is	552	method, usually without arguments. The only argument pair allowed is
461
462	"cb", which specifies a callback to be called when the condition	553	"cb", which specifies a callback to be called when the condition
463	variable becomes true, with the condition variable as the first argument	554	variable becomes true, with the condition variable as the first argument
464	(but not the results).	555	(but not the results).
465		556
466	After creation, the condition variable is "false" until it becomes	557	After creation, the condition variable is "false" until it becomes
467	"true" by calling the "send" method (or calling the condition variable	558	"true" by calling the "send" method (or calling the condition variable
468	as if it were a callback, read about the caveats in the description for	559	as if it were a callback, read about the caveats in the description for
469	the "->send" method).	560	the "->send" method).
470		561
471	Condition variables are similar to callbacks, except that you can	562	Since condition variables are the most complex part of the AnyEvent API,
472	optionally wait for them. They can also be called merge points - points	563	here are some different mental models of what they are - pick the ones
473	in time where multiple outstanding events have been processed. And yet	564	you can connect to:
474	another way to call them is transactions - each condition variable can	565
475	be used to represent a transaction, which finishes at some point and	566	* Condition variables are like callbacks - you can call them (and pass
476	delivers a result.	567	them instead of callbacks). Unlike callbacks however, you can also
		568	wait for them to be called.
		569
		570	* Condition variables are signals - one side can emit or send them,
		571	the other side can wait for them, or install a handler that is
		572	called when the signal fires.
		573
		574	* Condition variables are like "Merge Points" - points in your program
		575	where you merge multiple independent results/control flows into one.
		576
		577	* Condition variables represent a transaction - functions that start
		578	some kind of transaction can return them, leaving the caller the
		579	choice between waiting in a blocking fashion, or setting a callback.
		580
		581	* Condition variables represent future values, or promises to deliver
		582	some result, long before the result is available.
477		583
478	Condition variables are very useful to signal that something has	584	Condition variables are very useful to signal that something has
479	finished, for example, if you write a module that does asynchronous http	585	finished, for example, if you write a module that does asynchronous http
480	requests, then a condition variable would be the ideal candidate to	586	requests, then a condition variable would be the ideal candidate to
481	signal the availability of results. The user can either act when the	587	signal the availability of results. The user can either act when the
…		…
494		600
495	Condition variables are represented by hash refs in perl, and the keys	601	Condition variables are represented by hash refs in perl, and the keys
496	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy	602	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
497	(it is often useful to build your own transaction class on top of	603	(it is often useful to build your own transaction class on top of
498	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call	604	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
499	it's "new" method in your own "new" method.	605	its "new" method in your own "new" method.
500		606
501	There are two "sides" to a condition variable - the "producer side"	607	There are two "sides" to a condition variable - the "producer side"
502	which eventually calls "-> send", and the "consumer side", which waits	608	which eventually calls "-> send", and the "consumer side", which waits
503	for the send to occur.	609	for the send to occur.
504		610
505	Example: wait for a timer.	611	Example: wait for a timer.
506		612
507	# wait till the result is ready	613	# condition: "wait till the timer is fired"
508	my $result_ready = AnyEvent->condvar;	614	my $timer_fired = AnyEvent->condvar;
509		615
510	# do something such as adding a timer	616	# create the timer - we could wait for, say
511	# or socket watcher the calls $result_ready->send	617	# a handle becomign ready, or even an
512	# when the "result" is ready.	618	# AnyEvent::HTTP request to finish, but
513	# in this case, we simply use a timer:	619	# in this case, we simply use a timer:
514	my $w = AnyEvent->timer (	620	my $w = AnyEvent->timer (
515	after => 1,	621	after => 1,
516	cb => sub { $result_ready->send },	622	cb => sub { $timer_fired->send },
517	);	623	);
518		624
519	# this "blocks" (while handling events) till the callback	625	# this "blocks" (while handling events) till the callback
520	# calls send	626	# calls ->send
521	$result_ready->recv;	627	$timer_fired->recv;
522		628
523	Example: wait for a timer, but take advantage of the fact that condition	629	Example: wait for a timer, but take advantage of the fact that condition
524	variables are also code references.	630	variables are also callable directly.
525		631
526	my $done = AnyEvent->condvar;	632	my $done = AnyEvent->condvar;
527	my $delay = AnyEvent->timer (after => 5, cb => $done);	633	my $delay = AnyEvent->timer (after => 5, cb => $done);
528	$done->recv;	634	$done->recv;
529		635
…		…
535		641
536	...	642	...
537		643
538	my @info = $couchdb->info->recv;	644	my @info = $couchdb->info->recv;
539		645
540	And this is how you would just ste a callback to be called whenever the	646	And this is how you would just set a callback to be called whenever the
541	results are available:	647	results are available:
542		648
543	$couchdb->info->cb (sub {	649	$couchdb->info->cb (sub {
544	my @info = $_[0]->recv;	650	my @info = $_[0]->recv;
545	});	651	});
…		…
560		666
561	Any arguments passed to the "send" call will be returned by all	667	Any arguments passed to the "send" call will be returned by all
562	future "->recv" calls.	668	future "->recv" calls.
563		669
564	Condition variables are overloaded so one can call them directly (as	670	Condition variables are overloaded so one can call them directly (as
565	a code reference). Calling them directly is the same as calling	671	if they were a code reference). Calling them directly is the same as
566	"send". Note, however, that many C-based event loops do not handle	672	calling "send".
567	overloading, so as tempting as it may be, passing a condition
568	variable instead of a callback does not work. Both the pure perl and
569	EV loops support overloading, however, as well as all functions that
570	use perl to invoke a callback (as in AnyEvent::Socket and
571	AnyEvent::DNS for example).
572		673
573	$cv->croak ($error)	674	$cv->croak ($error)
574	Similar to send, but causes all call's to "->recv" to invoke	675	Similar to send, but causes all calls to "->recv" to invoke
575	"Carp::croak" with the given error message/object/scalar.	676	"Carp::croak" with the given error message/object/scalar.
576		677
577	This can be used to signal any errors to the condition variable	678	This can be used to signal any errors to the condition variable
578	user/consumer.	679	user/consumer. Doing it this way instead of calling "croak" directly
		680	delays the error detection, but has the overwhelming advantage that
		681	it diagnoses the error at the place where the result is expected,
		682	and not deep in some event callback with no connection to the actual
		683	code causing the problem.
579		684
580	$cv->begin ([group callback])	685	$cv->begin ([group callback])
581	$cv->end	686	$cv->end
582	These two methods can be used to combine many transactions/events	687	These two methods can be used to combine many transactions/events
583	into one. For example, a function that pings many hosts in parallel	688	into one. For example, a function that pings many hosts in parallel
584	might want to use a condition variable for the whole process.	689	might want to use a condition variable for the whole process.
585		690
586	Every call to "->begin" will increment a counter, and every call to	691	Every call to "->begin" will increment a counter, and every call to
587	"->end" will decrement it. If the counter reaches 0 in "->end", the	692	"->end" will decrement it. If the counter reaches 0 in "->end", the
588	(last) callback passed to "begin" will be executed. That callback is	693	(last) callback passed to "begin" will be executed, passing the
589	supposed to call "->send", but that is not required. If no	694	condvar as first argument. That callback is supposed to call
		695	"->send", but that is not required. If no group callback was set,
590	callback was set, "send" will be called without any arguments.	696	"send" will be called without any arguments.
591		697
592	You can think of "$cv->send" giving you an OR condition (one call	698	You can think of "$cv->send" giving you an OR condition (one call
593	sends), while "$cv->begin" and "$cv->end" giving you an AND	699	sends), while "$cv->begin" and "$cv->end" giving you an AND
594	condition (all "begin" calls must be "end"'ed before the condvar	700	condition (all "begin" calls must be "end"'ed before the condvar
595	sends).	701	sends).
…		…
617	This works because for every event source (EOF on file handle),	723	This works because for every event source (EOF on file handle),
618	there is one call to "begin", so the condvar waits for all calls to	724	there is one call to "begin", so the condvar waits for all calls to
619	"end" before sending.	725	"end" before sending.
620		726
621	The ping example mentioned above is slightly more complicated, as	727	The ping example mentioned above is slightly more complicated, as
622	the there are results to be passwd back, and the number of tasks	728	the there are results to be passed back, and the number of tasks
623	that are begung can potentially be zero:	729	that are begun can potentially be zero:
624		730
625	my $cv = AnyEvent->condvar;	731	my $cv = AnyEvent->condvar;
626		732
627	my %result;	733	my %result;
628	$cv->begin (sub { $cv->send (\%result) });	734	$cv->begin (sub { shift->send (\%result) });
629		735
630	for my $host (@list_of_hosts) {	736	for my $host (@list_of_hosts) {
631	$cv->begin;	737	$cv->begin;
632	ping_host_then_call_callback $host, sub {	738	ping_host_then_call_callback $host, sub {
633	$result{$host} = ...;	739	$result{$host} = ...;
…		…
635	};	741	};
636	}	742	}
637		743
638	$cv->end;	744	$cv->end;
639		745
		746	...
		747
		748	my $results = $cv->recv;
		749
640	This code fragment supposedly pings a number of hosts and calls	750	This code fragment supposedly pings a number of hosts and calls
641	"send" after results for all then have have been gathered - in any	751	"send" after results for all then have have been gathered - in any
642	order. To achieve this, the code issues a call to "begin" when it	752	order. To achieve this, the code issues a call to "begin" when it
643	starts each ping request and calls "end" when it has received some	753	starts each ping request and calls "end" when it has received some
644	result for it. Since "begin" and "end" only maintain a counter, the	754	result for it. Since "begin" and "end" only maintain a counter, the
…		…
649	callback to be called once the counter reaches 0, and second, it	759	callback to be called once the counter reaches 0, and second, it
650	ensures that "send" is called even when "no" hosts are being pinged	760	ensures that "send" is called even when "no" hosts are being pinged
651	(the loop doesn't execute once).	761	(the loop doesn't execute once).
652		762
653	This is the general pattern when you "fan out" into multiple (but	763	This is the general pattern when you "fan out" into multiple (but
654	potentially none) subrequests: use an outer "begin"/"end" pair to	764	potentially zero) subrequests: use an outer "begin"/"end" pair to
655	set the callback and ensure "end" is called at least once, and then,	765	set the callback and ensure "end" is called at least once, and then,
656	for each subrequest you start, call "begin" and for each subrequest	766	for each subrequest you start, call "begin" and for each subrequest
657	you finish, call "end".	767	you finish, call "end".
658		768
659	METHODS FOR CONSUMERS	769	METHODS FOR CONSUMERS
660	These methods should only be used by the consuming side, i.e. the code	770	These methods should only be used by the consuming side, i.e. the code
661	awaits the condition.	771	awaits the condition.
662		772
663	$cv->recv	773	$cv->recv
664	Wait (blocking if necessary) until the "->send" or "->croak" methods	774	Wait (blocking if necessary) until the "->send" or "->croak" methods
665	have been called on c<$cv>, while servicing other watchers normally.	775	have been called on $cv, while servicing other watchers normally.
666		776
667	You can only wait once on a condition - additional calls are valid	777	You can only wait once on a condition - additional calls are valid
668	but will return immediately.	778	but will return immediately.
669		779
670	If an error condition has been set by calling "->croak", then this	780	If an error condition has been set by calling "->croak", then this
671	function will call "croak".	781	function will call "croak".
672		782
673	In list context, all parameters passed to "send" will be returned,	783	In list context, all parameters passed to "send" will be returned,
674	in scalar context only the first one will be returned.	784	in scalar context only the first one will be returned.
675		785
		786	Note that doing a blocking wait in a callback is not supported by
		787	any event loop, that is, recursive invocation of a blocking "->recv"
		788	is not allowed and the "recv" call will "croak" if such a condition
		789	is detected. This requirement can be dropped by relying on
		790	Coro::AnyEvent , which allows you to do a blocking "->recv" from any
		791	thread that doesn't run the event loop itself. Coro::AnyEvent is
		792	loaded automatically when Coro is used with AnyEvent, so code does
		793	not need to do anything special to take advantage of that: any code
		794	that would normally block your program because it calls "recv", be
		795	executed in an "async" thread instead without blocking other
		796	threads.
		797
676	Not all event models support a blocking wait - some die in that case	798	Not all event models support a blocking wait - some die in that case
677	(programs might want to do that to stay interactive), so *if you are	799	(programs might want to do that to stay interactive), so *if you are
678	using this from a module, never require a blocking wait*, but let	800	using this from a module, never require a blocking wait*. Instead,
679	the caller decide whether the call will block or not (for example,	801	let the caller decide whether the call will block or not (for
680	by coupling condition variables with some kind of request results	802	example, by coupling condition variables with some kind of request
681	and supporting callbacks so the caller knows that getting the result	803	results and supporting callbacks so the caller knows that getting
682	will not block, while still supporting blocking waits if the caller	804	the result will not block, while still supporting blocking waits if
683	so desires).	805	the caller so desires).
684		806
685	Another reason never to "->recv" in a module is that you cannot
686	sensibly have two "->recv"'s in parallel, as that would require
687	multiple interpreters or coroutines/threads, none of which
688	"AnyEvent" can supply.
689
690	The Coro module, however, can and does supply coroutines and, in
691	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
692	versions and also integrates coroutines into AnyEvent, making
693	blocking "->recv" calls perfectly safe as long as they are done from
694	another coroutine (one that doesn't run the event loop).
695
696	You can ensure that "-recv" never blocks by setting a callback and	807	You can ensure that "->recv" never blocks by setting a callback and
697	only calling "->recv" from within that callback (or at a later	808	only calling "->recv" from within that callback (or at a later
698	time). This will work even when the event loop does not support	809	time). This will work even when the event loop does not support
699	blocking waits otherwise.	810	blocking waits otherwise.
700		811
701	$bool = $cv->ready	812	$bool = $cv->ready
702	Returns true when the condition is "true", i.e. whether "send" or	813	Returns true when the condition is "true", i.e. whether "send" or
703	"croak" have been called.	814	"croak" have been called.
704		815
705	$cb = $cv->cb ($cb->($cv))	816	$cb = $cv->cb ($cb->($cv))
706	This is a mutator function that returns the callback set and	817	This is a mutator function that returns the callback set (or "undef"
707	optionally replaces it before doing so.	818	if not) and optionally replaces it before doing so.
708		819
709	The callback will be called when the condition becomes "true", i.e.	820	The callback will be called when the condition becomes "true", i.e.
710	when "send" or "croak" are called, with the only argument being the	821	when "send" or "croak" are called, with the only argument being the
711	condition variable itself. Calling "recv" inside the callback or at	822	condition variable itself. If the condition is already true, the
		823	callback is called immediately when it is set. Calling "recv" inside
712	any later time is guaranteed not to block.	824	the callback or at any later time is guaranteed not to block.
		825
		826	Additionally, when the callback is invoked, it is also removed from
		827	the condvar (reset to "undef"), so the condvar does not keep a
		828	reference to the callback after invocation.
		829
		830	SUPPORTED EVENT LOOPS/BACKENDS
		831	The available backend classes are (every class has its own manpage):
		832
		833	Backends that are autoprobed when no other event loop can be found.
		834	EV is the preferred backend when no other event loop seems to be in
		835	use. If EV is not installed, then AnyEvent will fall back to its own
		836	pure-perl implementation, which is available everywhere as it comes
		837	with AnyEvent itself.
		838
		839	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		840	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
		841
		842	Backends that are transparently being picked up when they are used.
		843	These will be used if they are already loaded when the first watcher
		844	is created, in which case it is assumed that the application is
		845	using them. This means that AnyEvent will automatically pick the
		846	right backend when the main program loads an event module before
		847	anything starts to create watchers. Nothing special needs to be done
		848	by the main program.
		849
		850	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		851	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		852	AnyEvent::Impl::Tk based on Tk, very broken.
		853	AnyEvent::Impl::UV based on UV, innovated square wheels.
		854	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		855	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		856	AnyEvent::Impl::Irssi used when running within irssi.
		857	AnyEvent::Impl::IOAsync based on IO::Async.
		858	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		859	AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
		860
		861	Backends with special needs.
		862	Qt requires the Qt::Application to be instantiated first, but will
		863	otherwise be picked up automatically. As long as the main program
		864	instantiates the application before any AnyEvent watchers are
		865	created, everything should just work.
		866
		867	AnyEvent::Impl::Qt based on Qt.
		868
		869	Event loops that are indirectly supported via other backends.
		870	Some event loops can be supported via other modules:
		871
		872	There is no direct support for WxWidgets (Wx) or Prima.
		873
		874	WxWidgets has no support for watching file handles. However, you can
		875	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		876	simply polls 20 times per second, which was considered to be too
		877	horrible to even consider for AnyEvent.
		878
		879	Prima is not supported as nobody seems to be using it, but it has a
		880	POE backend, so it can be supported through POE.
		881
		882	AnyEvent knows about both Prima and Wx, however, and will try to
		883	load POE when detecting them, in the hope that POE will pick them
		884	up, in which case everything will be automatic.
713		885
714	GLOBAL VARIABLES AND FUNCTIONS	886	GLOBAL VARIABLES AND FUNCTIONS
		887	These are not normally required to use AnyEvent, but can be useful to
		888	write AnyEvent extension modules.
		889
715	$AnyEvent::MODEL	890	$AnyEvent::MODEL
716	Contains "undef" until the first watcher is being created. Then it	891	Contains "undef" until the first watcher is being created, before
		892	the backend has been autodetected.
		893
717	contains the event model that is being used, which is the name of	894	Afterwards it contains the event model that is being used, which is
718	the Perl class implementing the model. This class is usually one of	895	the name of the Perl class implementing the model. This class is
719	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	896	usually one of the "AnyEvent::Impl::xxx" modules, but can be any
720	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	897	other class in the case AnyEvent has been extended at runtime (e.g.
721		898	in rxvt-unicode it will be "urxvt::anyevent").
722	The known classes so far are:
723
724	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
725	AnyEvent::Impl::Event based on Event, second best choice.
726	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
727	AnyEvent::Impl::Glib based on Glib, third-best choice.
728	AnyEvent::Impl::Tk based on Tk, very bad choice.
729	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
730	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
731	AnyEvent::Impl::POE based on POE, not generic enough for full support.
732
733	# warning, support for IO::Async is only partial, as it is too broken
734	# and limited toe ven support the AnyEvent API. See AnyEvent::Impl::Async.
735	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed (see its docs).
736
737	There is no support for WxWidgets, as WxWidgets has no support for
738	watching file handles. However, you can use WxWidgets through the
739	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
740	second, which was considered to be too horrible to even consider for
741	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
742	using it's adaptor.
743
744	AnyEvent knows about Prima and Wx and will try to use POE when
745	autodetecting them.
746		899
747	AnyEvent::detect	900	AnyEvent::detect
748	Returns $AnyEvent::MODEL, forcing autodetection of the event model	901	Returns $AnyEvent::MODEL, forcing autodetection of the event model
749	if necessary. You should only call this function right before you	902	if necessary. You should only call this function right before you
750	would have created an AnyEvent watcher anyway, that is, as late as	903	would have created an AnyEvent watcher anyway, that is, as late as
751	possible at runtime.	904	possible at runtime, and not e.g. during initialisation of your
		905	module.
		906
		907	The effect of calling this function is as if a watcher had been
		908	created (specifically, actions that happen "when the first watcher
		909	is created" happen when calling detetc as well).
		910
		911	If you need to do some initialisation before AnyEvent watchers are
		912	created, use "post_detect".
752		913
753	$guard = AnyEvent::post_detect { BLOCK }	914	$guard = AnyEvent::post_detect { BLOCK }
754	Arranges for the code block to be executed as soon as the event	915	Arranges for the code block to be executed as soon as the event
755	model is autodetected (or immediately if this has already happened).	916	model is autodetected (or immediately if that has already happened).
		917
		918	The block will be executed after the actual backend has been
		919	detected ($AnyEvent::MODEL is set), but before any watchers have
		920	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		921	other initialisations - see the sources of AnyEvent::Strict or
		922	AnyEvent::AIO to see how this is used.
		923
		924	The most common usage is to create some global watchers, without
		925	forcing event module detection too early, for example, AnyEvent::AIO
		926	creates and installs the global IO::AIO watcher in a "post_detect"
		927	block to avoid autodetecting the event module at load time.
756		928
757	If called in scalar or list context, then it creates and returns an	929	If called in scalar or list context, then it creates and returns an
758	object that automatically removes the callback again when it is	930	object that automatically removes the callback again when it is
		931	destroyed (or "undef" when the hook was immediately executed). See
759	destroyed. See Coro::BDB for a case where this is useful.	932	AnyEvent::AIO for a case where this is useful.
		933
		934	Example: Create a watcher for the IO::AIO module and store it in
		935	$WATCHER, but do so only do so after the event loop is initialised.
		936
		937	our WATCHER;
		938
		939	my $guard = AnyEvent::post_detect {
		940	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		941	};
		942
		943	# the \|\|= is important in case post_detect immediately runs the block,
		944	# as to not clobber the newly-created watcher. assigning both watcher and
		945	# post_detect guard to the same variable has the advantage of users being
		946	# able to just C<undef $WATCHER> if the watcher causes them grief.
		947
		948	$WATCHER \|\|= $guard;
760		949
761	@AnyEvent::post_detect	950	@AnyEvent::post_detect
762	If there are any code references in this array (you can "push" to it	951	If there are any code references in this array (you can "push" to it
763	before or after loading AnyEvent), then they will called directly	952	before or after loading AnyEvent), then they will be called directly
764	after the event loop has been chosen.	953	after the event loop has been chosen.
765		954
766	You should check $AnyEvent::MODEL before adding to this array,	955	You should check $AnyEvent::MODEL before adding to this array,
767	though: if it contains a true value then the event loop has already	956	though: if it is defined then the event loop has already been
768	been detected, and the array will be ignored.	957	detected, and the array will be ignored.
769		958
770	Best use "AnyEvent::post_detect { BLOCK }" instead.	959	Best use "AnyEvent::post_detect { BLOCK }" when your application
		960	allows it, as it takes care of these details.
		961
		962	This variable is mainly useful for modules that can do something
		963	useful when AnyEvent is used and thus want to know when it is
		964	initialised, but do not need to even load it by default. This array
		965	provides the means to hook into AnyEvent passively, without loading
		966	it.
		967
		968	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		969	together, you could put this into Coro (this is the actual code used
		970	by Coro to accomplish this):
		971
		972	if (defined $AnyEvent::MODEL) {
		973	# AnyEvent already initialised, so load Coro::AnyEvent
		974	require Coro::AnyEvent;
		975	} else {
		976	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		977	# as soon as it is
		978	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		979	}
		980
		981	AnyEvent::postpone { BLOCK }
		982	Arranges for the block to be executed as soon as possible, but not
		983	before the call itself returns. In practise, the block will be
		984	executed just before the event loop polls for new events, or shortly
		985	afterwards.
		986
		987	This function never returns anything (to make the "return postpone {
		988	... }" idiom more useful.
		989
		990	To understand the usefulness of this function, consider a function
		991	that asynchronously does something for you and returns some
		992	transaction object or guard to let you cancel the operation. For
		993	example, "AnyEvent::Socket::tcp_connect":
		994
		995	# start a connection attempt unless one is active
		996	$self->{connect_guard} \|\|= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		997	delete $self->{connect_guard};
		998	...
		999	};
		1000
		1001	Imagine that this function could instantly call the callback, for
		1002	example, because it detects an obvious error such as a negative port
		1003	number. Invoking the callback before the function returns causes
		1004	problems however: the callback will be called and will try to delete
		1005	the guard object. But since the function hasn't returned yet, there
		1006	is nothing to delete. When the function eventually returns it will
		1007	assign the guard object to "$self->{connect_guard}", where it will
		1008	likely never be deleted, so the program thinks it is still trying to
		1009	connect.
		1010
		1011	This is where "AnyEvent::postpone" should be used. Instead of
		1012	calling the callback directly on error:
		1013
		1014	$cb->(undef), return # signal error to callback, BAD!
		1015	if $some_error_condition;
		1016
		1017	It should use "postpone":
		1018
		1019	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1020	if $some_error_condition;
		1021
		1022	AnyEvent::log $level, $msg[, @args]
		1023	Log the given $msg at the given $level.
		1024
		1025	If AnyEvent::Log is not loaded then this function makes a simple
		1026	test to see whether the message will be logged. If the test succeeds
		1027	it will load AnyEvent::Log and call "AnyEvent::Log::log" -
		1028	consequently, look at the AnyEvent::Log documentation for details.
		1029
		1030	If the test fails it will simply return. Right now this happens when
		1031	a numerical loglevel is used and it is larger than the level
		1032	specified via $ENV{PERL_ANYEVENT_VERBOSE}.
		1033
		1034	If you want to sprinkle loads of logging calls around your code,
		1035	consider creating a logger callback with the "AnyEvent::Log::logger"
		1036	function, which can reduce typing, codesize and can reduce the
		1037	logging overhead enourmously.
		1038
		1039	AnyEvent::fh_block $filehandle
		1040	AnyEvent::fh_unblock $filehandle
		1041	Sets blocking or non-blocking behaviour for the given filehandle.
771		1042
772	WHAT TO DO IN A MODULE	1043	WHAT TO DO IN A MODULE
773	As a module author, you should "use AnyEvent" and call AnyEvent methods	1044	As a module author, you should "use AnyEvent" and call AnyEvent methods
774	freely, but you should not load a specific event module or rely on it.	1045	freely, but you should not load a specific event module or rely on it.
775		1046
…		…
783	stall the whole program, and the whole point of using events is to stay	1054	stall the whole program, and the whole point of using events is to stay
784	interactive.	1055	interactive.
785		1056
786	It is fine, however, to call "->recv" when the user of your module	1057	It is fine, however, to call "->recv" when the user of your module
787	requests it (i.e. if you create a http request object ad have a method	1058	requests it (i.e. if you create a http request object ad have a method
788	called "results" that returns the results, it should call "->recv"	1059	called "results" that returns the results, it may call "->recv" freely,
789	freely, as the user of your module knows what she is doing. always).	1060	as the user of your module knows what she is doing. Always).
790		1061
791	WHAT TO DO IN THE MAIN PROGRAM	1062	WHAT TO DO IN THE MAIN PROGRAM
792	There will always be a single main program - the only place that should	1063	There will always be a single main program - the only place that should
793	dictate which event model to use.	1064	dictate which event model to use.
794		1065
795	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	1066	If the program is not event-based, it need not do anything special, even
796	do anything special (it does not need to be event-based) and let	1067	when it depends on a module that uses an AnyEvent. If the program itself
797	AnyEvent decide which implementation to chose if some module relies on	1068	uses AnyEvent, but does not care which event loop is used, all it needs
798	it.	1069	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		1070	available loop implementation.
799		1071
800	If the main program relies on a specific event model - for example, in	1072	If the main program relies on a specific event model - for example, in
801	Gtk2 programs you have to rely on the Glib module - you should load the	1073	Gtk2 programs you have to rely on the Glib module - you should load the
802	event module before loading AnyEvent or any module that uses it:	1074	event module before loading AnyEvent or any module that uses it:
803	generally speaking, you should load it as early as possible. The reason	1075	generally speaking, you should load it as early as possible. The reason
804	is that modules might create watchers when they are loaded, and AnyEvent	1076	is that modules might create watchers when they are loaded, and AnyEvent
805	will decide on the event model to use as soon as it creates watchers,	1077	will decide on the event model to use as soon as it creates watchers,
806	and it might chose the wrong one unless you load the correct one	1078	and it might choose the wrong one unless you load the correct one
807	yourself.	1079	yourself.
808		1080
809	You can chose to use a pure-perl implementation by loading the	1081	You can chose to use a pure-perl implementation by loading the
810	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1082	"AnyEvent::Loop" module, which gives you similar behaviour everywhere,
811	everywhere, but letting AnyEvent chose the model is generally better.	1083	but letting AnyEvent chose the model is generally better.
812		1084
813	MAINLOOP EMULATION	1085	MAINLOOP EMULATION
814	Sometimes (often for short test scripts, or even standalone programs who	1086	Sometimes (often for short test scripts, or even standalone programs who
815	only want to use AnyEvent), you do not want to run a specific event	1087	only want to use AnyEvent), you do not want to run a specific event
816	loop.	1088	loop.
…		…
826	variable somewhere, waiting for it, and sending it when the program	1098	variable somewhere, waiting for it, and sending it when the program
827	should exit cleanly.	1099	should exit cleanly.
828		1100
829	OTHER MODULES	1101	OTHER MODULES
830	The following is a non-exhaustive list of additional modules that use	1102	The following is a non-exhaustive list of additional modules that use
831	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1103	AnyEvent as a client and can therefore be mixed easily with other
832	in the same program. Some of the modules come with AnyEvent, some are	1104	AnyEvent modules and other event loops in the same program. Some of the
833	available via CPAN.	1105	modules come as part of AnyEvent, the others are available via CPAN (see
		1106	<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
		1107	non-exhaustive list), and the list is heavily biased towards modules of
		1108	the AnyEvent author himself :)
834		1109
835	AnyEvent::Util	1110	AnyEvent::Util (part of the AnyEvent distribution)
836	Contains various utility functions that replace often-used but	1111	Contains various utility functions that replace often-used blocking
837	blocking functions such as "inet_aton" by event-/callback-based	1112	functions such as "inet_aton" with event/callback-based versions.
838	versions.
839		1113
840	AnyEvent::Socket	1114	AnyEvent::Socket (part of the AnyEvent distribution)
841	Provides various utility functions for (internet protocol) sockets,	1115	Provides various utility functions for (internet protocol) sockets,
842	addresses and name resolution. Also functions to create non-blocking	1116	addresses and name resolution. Also functions to create non-blocking
843	tcp connections or tcp servers, with IPv6 and SRV record support and	1117	tcp connections or tcp servers, with IPv6 and SRV record support and
844	more.	1118	more.
845		1119
846	AnyEvent::Handle	1120	AnyEvent::Handle (part of the AnyEvent distribution)
847	Provide read and write buffers, manages watchers for reads and	1121	Provide read and write buffers, manages watchers for reads and
848	writes, supports raw and formatted I/O, I/O queued and fully	1122	writes, supports raw and formatted I/O, I/O queued and fully
849	transparent and non-blocking SSL/TLS.	1123	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
850		1124
851	AnyEvent::DNS	1125	AnyEvent::DNS (part of the AnyEvent distribution)
852	Provides rich asynchronous DNS resolver capabilities.	1126	Provides rich asynchronous DNS resolver capabilities.
853		1127
854	AnyEvent::HTTP	1128	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
855	A simple-to-use HTTP library that is capable of making a lot of	1129	AnyEvent::IGS, AnyEvent::FCP
856	concurrent HTTP requests.	1130	Implement event-based interfaces to the protocols of the same name
		1131	(for the curious, IGS is the International Go Server and FCP is the
		1132	Freenet Client Protocol).
857		1133
		1134	AnyEvent::AIO (part of the AnyEvent distribution)
		1135	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1136	the toolbox of every event programmer. AnyEvent::AIO transparently
		1137	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1138	event-based file I/O, and much more.
		1139
		1140	AnyEvent::Fork, AnyEvent::Fork::RPC, AnyEvent::Fork::Pool,
		1141	AnyEvent::Fork::Remote
		1142	These let you safely fork new subprocesses, either locally or
		1143	remotely (e.g.v ia ssh), using some RPC protocol or not, without the
		1144	limitations normally imposed by fork (AnyEvent works fine for
		1145	example). Dynamically-resized worker pools are obviously included as
		1146	well.
		1147
		1148	And they are quite tiny and fast as well - "abusing" AnyEvent::Fork
		1149	just to exec external programs can easily beat using "fork" and
		1150	"exec" (or even "system") in most programs.
		1151
		1152	AnyEvent::Filesys::Notify
		1153	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1154	path changes (e.g. "watch this directory for new files", "watch this
		1155	file for changes"). The AnyEvent::Filesys::Notify module promises to
		1156	do just that in a portbale fashion, supporting inotify on GNU/Linux
		1157	and some weird, without doubt broken, stuff on OS X to monitor
		1158	files. It can fall back to blocking scans at regular intervals
		1159	transparently on other platforms, so it's about as portable as it
		1160	gets.
		1161
		1162	(I haven't used it myself, but it seems the biggest problem with it
		1163	is it quite bad performance).
		1164
858	AnyEvent::HTTPD	1165	AnyEvent::DBI
859	Provides a simple web application server framework.	1166	Executes DBI requests asynchronously in a proxy process for you,
		1167	notifying you in an event-based way when the operation is finished.
860		1168
861	AnyEvent::FastPing	1169	AnyEvent::FastPing
862	The fastest ping in the west.	1170	The fastest ping in the west.
863		1171
864	AnyEvent::DBI
865	Executes DBI requests asynchronously in a proxy process.
866
867	AnyEvent::AIO
868	Truly asynchronous I/O, should be in the toolbox of every event
869	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
870	together.
871
872	AnyEvent::BDB
873	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
874	fuses BDB and AnyEvent together.
875
876	AnyEvent::GPSD
877	A non-blocking interface to gpsd, a daemon delivering GPS
878	information.
879
880	AnyEvent::IGS
881	A non-blocking interface to the Internet Go Server protocol (used by
882	App::IGS).
883
884	AnyEvent::IRC
885	AnyEvent based IRC client module family (replacing the older
886	Net::IRC3).
887
888	Net::XMPP2
889	AnyEvent based XMPP (Jabber protocol) module family.
890
891	Net::FCP
892	AnyEvent-based implementation of the Freenet Client Protocol,
893	birthplace of AnyEvent.
894
895	Event::ExecFlow
896	High level API for event-based execution flow control.
897
898	Coro	1172	Coro
899	Has special support for AnyEvent via Coro::AnyEvent.	1173	Has special support for AnyEvent via Coro::AnyEvent, which allows
		1174	you to simply invert the flow control - don't call us, we will call
		1175	you:
900		1176
901	IO::Lambda	1177	async {
902	The lambda approach to I/O - don't ask, look there. Can use	1178	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
903	AnyEvent.	1179	print "5 seconds later!\n";
		1180
		1181	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
		1182	my $line = <STDIN>; # works for ttys
		1183
		1184	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
		1185	my ($body, $hdr) = Coro::rouse_wait;
		1186	};
		1187
		1188	SIMPLIFIED AE API
		1189	Starting with version 5.0, AnyEvent officially supports a second, much
		1190	simpler, API that is designed to reduce the calling, typing and memory
		1191	overhead by using function call syntax and a fixed number of parameters.
		1192
		1193	See the AE manpage for details.
904		1194
905	ERROR AND EXCEPTION HANDLING	1195	ERROR AND EXCEPTION HANDLING
906	In general, AnyEvent does not do any error handling - it relies on the	1196	In general, AnyEvent does not do any error handling - it relies on the
907	caller to do that if required. The AnyEvent::Strict module (see also the	1197	caller to do that if required. The AnyEvent::Strict module (see also the
908	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	1198	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
917	The pure perl event loop simply re-throws the exception (usually within	1207	The pure perl event loop simply re-throws the exception (usually within
918	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1208	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
919	Glib uses "install_exception_handler" and so on.	1209	Glib uses "install_exception_handler" and so on.
920		1210
921	ENVIRONMENT VARIABLES	1211	ENVIRONMENT VARIABLES
922	The following environment variables are used by this module or its	1212	AnyEvent supports a number of environment variables that tune the
923	submodules.	1213	runtime behaviour. They are usually evaluated when AnyEvent is loaded,
		1214	initialised, or a submodule that uses them is loaded. Many of them also
		1215	cause AnyEvent to load additional modules - for example,
		1216	"PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
		1217	loaded.
924		1218
925	Note that AnyEvent will remove all environment variables starting with	1219	All the environment variables documented here start with
926	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is	1220	"PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
927	enabled.	1221	Other modules are encouraged (but by no means required) to use
		1222	"PERL_ANYEVENT_SUBMODULE" if they have registered the
		1223	AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
		1224	AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
		1225	should not access env variables starting with "AE_", see below).
		1226
		1227	All variables can also be set via the "AE_" prefix, that is, instead of
		1228	setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
		1229	there is a clash btween anyevent and another program that uses
		1230	"AE_something" you can set the corresponding "PERL_ANYEVENT_something"
		1231	variable to the empty string, as those variables take precedence.
		1232
		1233	When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
		1234	their "PERL_ANYEVENT_xxx" counterpart unless that variable already
		1235	exists. If taint mode is on, then AnyEvent will remove all environment
		1236	variables starting with "PERL_ANYEVENT_" from %ENV (or replace them with
		1237	"undef" or the empty string, if the corresaponding "AE_" variable is
		1238	set).
		1239
		1240	The exact algorithm is currently:
		1241
		1242	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		1243	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		1244	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		1245
		1246	This ensures that child processes will not see the "AE_" variables.
		1247
		1248	The following environment variables are currently known to AnyEvent:
928		1249
929	"PERL_ANYEVENT_VERBOSE"	1250	"PERL_ANYEVENT_VERBOSE"
930	By default, AnyEvent will be completely silent except in fatal	1251	By default, AnyEvent will log messages with loglevel 4 ("error") or
931	conditions. You can set this environment variable to make AnyEvent	1252	higher (see AnyEvent::Log). You can set this environment variable to
932	more talkative.	1253	a numerical loglevel to make AnyEvent more (or less) talkative.
933		1254
		1255	If you want to do more than just set the global logging level you
		1256	should have a look at "PERL_ANYEVENT_LOG", which allows much more
		1257	complex specifications.
		1258
		1259	When set to 0 ("off"), then no messages whatsoever will be logged
		1260	with everything else at defaults.
		1261
934	When set to 1 or higher, causes AnyEvent to warn about unexpected	1262	When set to 5 or higher ("warn"), AnyEvent warns about unexpected
935	conditions, such as not being able to load the event model specified	1263	conditions, such as not being able to load the event model specified
936	by "PERL_ANYEVENT_MODEL".	1264	by "PERL_ANYEVENT_MODEL", or a guard callback throwing an exception
		1265	- this is the minimum recommended level for use during development.
937		1266
938	When set to 2 or higher, cause AnyEvent to report to STDERR which	1267	When set to 7 or higher (info), AnyEvent reports which event model
939	event model it chooses.	1268	it chooses.
		1269
		1270	When set to 8 or higher (debug), then AnyEvent will report extra
		1271	information on which optional modules it loads and how it implements
		1272	certain features.
		1273
		1274	"PERL_ANYEVENT_LOG"
		1275	Accepts rather complex logging specifications. For example, you
		1276	could log all "debug" messages of some module to stderr, warnings
		1277	and above to stderr, and errors and above to syslog, with:
		1278
		1279	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		1280
		1281	For the rather extensive details, see AnyEvent::Log.
		1282
		1283	This variable is evaluated when AnyEvent (or AnyEvent::Log) is
		1284	loaded, so will take effect even before AnyEvent has initialised
		1285	itself.
		1286
		1287	Note that specifying this environment variable causes the
		1288	AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
		1289	does not, so only using the latter saves a few hundred kB of memory
		1290	unless a module explicitly needs the extra features of
		1291	AnyEvent::Log.
940		1292
941	"PERL_ANYEVENT_STRICT"	1293	"PERL_ANYEVENT_STRICT"
942	AnyEvent does not do much argument checking by default, as thorough	1294	AnyEvent does not do much argument checking by default, as thorough
943	argument checking is very costly. Setting this variable to a true	1295	argument checking is very costly. Setting this variable to a true
944	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1296	value will cause AnyEvent to load "AnyEvent::Strict" and then to
945	thoroughly check the arguments passed to most method calls. If it	1297	thoroughly check the arguments passed to most method calls. If it
946	finds any problems, it will croak.	1298	finds any problems, it will croak.
947		1299
948	In other words, enables "strict" mode.	1300	In other words, enables "strict" mode.
949		1301
950	Unlike "use strict", it is definitely recommended to keep it off in	1302	Unlike "use strict" (or its modern cousin, "use common::sense", it
951	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment	1303	is definitely recommended to keep it off in production. Keeping
		1304	"PERL_ANYEVENT_STRICT=1" in your environment while developing
952	while developing programs can be very useful, however.	1305	programs can be very useful, however.
		1306
		1307	"PERL_ANYEVENT_DEBUG_SHELL"
		1308	If this env variable is nonempty, then its contents will be
		1309	interpreted by "AnyEvent::Socket::parse_hostport" and
		1310	"AnyEvent::Debug::shell" (after replacing every occurance of $$ by
		1311	the process pid). The shell object is saved in
		1312	$AnyEvent::Debug::SHELL.
		1313
		1314	This happens when the first watcher is created.
		1315
		1316	For example, to bind a debug shell on a unix domain socket in
		1317	/tmp/debug<pid>.sock, you could use this:
		1318
		1319	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		1320	# connect with e.g.: socat readline /tmp/debug123.sock
		1321
		1322	Or to bind to tcp port 4545 on localhost:
		1323
		1324	PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
		1325	# connect with e.g.: telnet localhost 4545
		1326
		1327	Note that creating sockets in /tmp or on localhost is very unsafe on
		1328	multiuser systems.
		1329
		1330	"PERL_ANYEVENT_DEBUG_WRAP"
		1331	Can be set to 0, 1 or 2 and enables wrapping of all watchers for
		1332	debugging purposes. See "AnyEvent::Debug::wrap" for details.
953		1333
954	"PERL_ANYEVENT_MODEL"	1334	"PERL_ANYEVENT_MODEL"
955	This can be used to specify the event model to be used by AnyEvent,	1335	This can be used to specify the event model to be used by AnyEvent,
956	before auto detection and -probing kicks in. It must be a string	1336	before auto detection and -probing kicks in.
957	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1337
958	gets prepended and the resulting module name is loaded and if the	1338	It normally is a string consisting entirely of ASCII letters (e.g.
959	load was successful, used as event model. If it fails to load	1339	"EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
		1340	the resulting module name is loaded and - if the load was successful
		1341	- used as event model backend. If it fails to load then AnyEvent
960	AnyEvent will proceed with auto detection and -probing.	1342	will proceed with auto detection and -probing.
961		1343
962	This functionality might change in future versions.	1344	If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
		1345	then nothing gets prepended and the module name is used as-is (hint:
		1346	"::" at the end of a string designates a module name and quotes it
		1347	appropriately).
963		1348
964	For example, to force the pure perl model (AnyEvent::Impl::Perl) you	1349	For example, to force the pure perl model (AnyEvent::Loop::Perl) you
965	could start your program like this:	1350	could start your program like this:
966		1351
967	PERL_ANYEVENT_MODEL=Perl perl ...	1352	PERL_ANYEVENT_MODEL=Perl perl ...
		1353
		1354	"PERL_ANYEVENT_IO_MODEL"
		1355	The current file I/O model - see AnyEvent::IO for more info.
		1356
		1357	At the moment, only "Perl" (small, pure-perl, synchronous) and
		1358	"IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
		1359	if AnyEvent::AIO can be loaded, otherwise it is "Perl".
968		1360
969	"PERL_ANYEVENT_PROTOCOLS"	1361	"PERL_ANYEVENT_PROTOCOLS"
970	Used by both AnyEvent::DNS and AnyEvent::Socket to determine	1362	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
971	preferences for IPv4 or IPv6. The default is unspecified (and might	1363	preferences for IPv4 or IPv6. The default is unspecified (and might
972	change, or be the result of auto probing).	1364	change, or be the result of auto probing).
…		…
976	mentioned will be used, and preference will be given to protocols	1368	mentioned will be used, and preference will be given to protocols
977	mentioned earlier in the list.	1369	mentioned earlier in the list.
978		1370
979	This variable can effectively be used for denial-of-service attacks	1371	This variable can effectively be used for denial-of-service attacks
980	against local programs (e.g. when setuid), although the impact is	1372	against local programs (e.g. when setuid), although the impact is
981	likely small, as the program has to handle conenction and other	1373	likely small, as the program has to handle connection and other
982	failures anyways.	1374	failures anyways.
983		1375
984	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1376	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
985	IPv6, but support both and try to use both.	1377	IPv6, but support both and try to use both.
986	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1378	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
987	resolve or contact IPv6 addresses.	1379	resolve or contact IPv6 addresses.
988	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but	1380	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
989	prefer IPv6 over IPv4.	1381	prefer IPv6 over IPv4.
990		1382
		1383	"PERL_ANYEVENT_HOSTS"
		1384	This variable, if specified, overrides the /etc/hosts file used by
		1385	AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
		1386	read from that file instead.
		1387
991	"PERL_ANYEVENT_EDNS0"	1388	"PERL_ANYEVENT_EDNS0"
992	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension	1389	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
993	for DNS. This extension is generally useful to reduce DNS traffic,	1390	for DNS. This extension is generally useful to reduce DNS traffic,
994	but some (broken) firewalls drop such DNS packets, which is why it	1391	especially when DNSSEC is involved, but some (broken) firewalls drop
995	is off by default.	1392	such DNS packets, which is why it is off by default.
996		1393
997	Setting this variable to 1 will cause AnyEvent::DNS to announce	1394	Setting this variable to 1 will cause AnyEvent::DNS to announce
998	EDNS0 in its DNS requests.	1395	EDNS0 in its DNS requests.
999		1396
1000	"PERL_ANYEVENT_MAX_FORKS"	1397	"PERL_ANYEVENT_MAX_FORKS"
1001	The maximum number of child processes that	1398	The maximum number of child processes that
1002	"AnyEvent::Util::fork_call" will create in parallel.	1399	"AnyEvent::Util::fork_call" will create in parallel.
		1400
		1401	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1402	The default value for the "max_outstanding" parameter for the
		1403	default DNS resolver - this is the maximum number of parallel DNS
		1404	requests that are sent to the DNS server.
		1405
		1406	"PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
		1407	Perl has inherently racy signal handling (you can basically choose
		1408	between losing signals and memory corruption) - pure perl event
		1409	loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
		1410	available) therefore have to poll regularly to avoid losing signals.
		1411
		1412	Some event loops are racy, but don't poll regularly, and some event
		1413	loops are written in C but are still racy. For those event loops,
		1414	AnyEvent installs a timer that regularly wakes up the event loop.
		1415
		1416	By default, the interval for this timer is 10 seconds, but you can
		1417	override this delay with this environment variable (or by setting
		1418	the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
		1419	watchers).
		1420
		1421	Lower values increase CPU (and energy) usage, higher values can
		1422	introduce long delays when reaping children or waiting for signals.
		1423
		1424	The AnyEvent::Async module, if available, will be used to avoid this
		1425	polling (with most event loops).
		1426
		1427	"PERL_ANYEVENT_RESOLV_CONF"
		1428	The absolute path to a resolv.conf-style file to use instead of
		1429	/etc/resolv.conf (or the OS-specific configuration) in the default
		1430	resolver, or the empty string to select the default configuration.
		1431
		1432	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1433	When neither "ca_file" nor "ca_path" was specified during
		1434	AnyEvent::TLS context creation, and either of these environment
		1435	variables are nonempty, they will be used to specify CA certificate
		1436	locations instead of a system-dependent default.
		1437
		1438	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1439	When these are set to 1, then the respective modules are not loaded.
		1440	Mostly good for testing AnyEvent itself.
1003		1441
1004	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1442	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
1005	This is an advanced topic that you do not normally need to use AnyEvent	1443	This is an advanced topic that you do not normally need to use AnyEvent
1006	in a module. This section is only of use to event loop authors who want	1444	in a module. This section is only of use to event loop authors who want
1007	to provide AnyEvent compatibility.	1445	to provide AnyEvent compatibility.
…		…
1062	warn "read: $input\n"; # output what has been read	1500	warn "read: $input\n"; # output what has been read
1063	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1501	$cv->send if $input =~ /^q/i; # quit program if /^q/i
1064	},	1502	},
1065	);	1503	);
1066		1504
1067	my $time_watcher; # can only be used once
1068
1069	sub new_timer {
1070	$timer = AnyEvent->timer (after => 1, cb => sub {	1505	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
1071	warn "timeout\n"; # print 'timeout' about every second	1506	warn "timeout\n"; # print 'timeout' at most every second
1072	&new_timer; # and restart the time
1073	});
1074	}	1507	});
1075
1076	new_timer; # create first timer
1077		1508
1078	$cv->recv; # wait until user enters /^q/i	1509	$cv->recv; # wait until user enters /^q/i
1079		1510
1080	REAL-WORLD EXAMPLE	1511	REAL-WORLD EXAMPLE
1081	Consider the Net::FCP module. It features (among others) the following	1512	Consider the Net::FCP module. It features (among others) the following
…		…
1153		1584
1154	The actual code goes further and collects all errors ("die"s,	1585	The actual code goes further and collects all errors ("die"s,
1155	exceptions) that occurred during request processing. The "result" method	1586	exceptions) that occurred during request processing. The "result" method
1156	detects whether an exception as thrown (it is stored inside the $txn	1587	detects whether an exception as thrown (it is stored inside the $txn
1157	object) and just throws the exception, which means connection errors and	1588	object) and just throws the exception, which means connection errors and
1158	other problems get reported tot he code that tries to use the result,	1589	other problems get reported to the code that tries to use the result,
1159	not in a random callback.	1590	not in a random callback.
1160		1591
1161	All of this enables the following usage styles:	1592	All of this enables the following usage styles:
1162		1593
1163	1. Blocking:	1594	1. Blocking:
…		…
1181	my $txn = shift;	1612	my $txn = shift;
1182	my $data = $txn->result;	1613	my $data = $txn->result;
1183	...	1614	...
1184	});	1615	});
1185		1616
1186	EV::loop;	1617	EV::run;
1187		1618
1188	3b. The module user could use AnyEvent, too:	1619	3b. The module user could use AnyEvent, too:
1189		1620
1190	use AnyEvent;	1621	use AnyEvent;
1191		1622
…		…
1208	through AnyEvent. The benchmark creates a lot of timers (with a zero	1639	through AnyEvent. The benchmark creates a lot of timers (with a zero
1209	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1640	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1210	which it is), lets them fire exactly once and destroys them again.	1641	which it is), lets them fire exactly once and destroys them again.
1211		1642
1212	Source code for this benchmark is found as eg/bench in the AnyEvent	1643	Source code for this benchmark is found as eg/bench in the AnyEvent
1213	distribution.	1644	distribution. It uses the AE interface, which makes a real difference
		1645	for the EV and Perl backends only.
1214		1646
1215	Explanation of the columns	1647	Explanation of the columns
1216	watcher is the number of event watchers created/destroyed. Since	1648	watcher is the number of event watchers created/destroyed. Since
1217	different event models feature vastly different performances, each event	1649	different event models feature vastly different performances, each event
1218	loop was given a number of watchers so that overall runtime is	1650	loop was given a number of watchers so that overall runtime is
…		…
1237	destroy is the time, in microseconds, that it takes to destroy a	1669	destroy is the time, in microseconds, that it takes to destroy a
1238	single watcher.	1670	single watcher.
1239		1671
1240	Results	1672	Results
1241	name watchers bytes create invoke destroy comment	1673	name watchers bytes create invoke destroy comment
1242	EV/EV 400000 224 0.47 0.35 0.27 EV native interface	1674	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1243	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers	1675	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1244	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal	1676	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1245	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation	1677	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1246	Event/Event 16000 517 32.20 31.80 0.81 Event native interface	1678	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1247	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers	1679	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
1248	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll	1680	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
1249	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll	1681	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1250	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour	1682	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1251	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers	1683	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1252	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event	1684	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1253	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select	1685	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1254		1686
1255	Discussion	1687	Discussion
1256	The benchmark does not measure scalability of the event loop very	1688	The benchmark does not measure scalability of the event loop very
1257	well. For example, a select-based event loop (such as the pure perl one)	1689	well. For example, a select-based event loop (such as the pure perl one)
1258	can never compete with an event loop that uses epoll when the number of	1690	can never compete with an event loop that uses epoll when the number of
…		…
1269	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1701	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1270	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1702	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1271	CPU cycles with POE.	1703	CPU cycles with POE.
1272		1704
1273	"EV" is the sole leader regarding speed and memory use, which are both	1705	"EV" is the sole leader regarding speed and memory use, which are both
1274	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1706	maximal/minimal, respectively. When using the AE API there is zero
		1707	overhead (when going through the AnyEvent API create is about 5-6 times
		1708	slower, with other times being equal, so still uses far less memory than
1275	far less memory than any other event loop and is still faster than Event	1709	any other event loop and is still faster than Event natively).
1276	natively.
1277		1710
1278	The pure perl implementation is hit in a few sweet spots (both the	1711	The pure perl implementation is hit in a few sweet spots (both the
1279	constant timeout and the use of a single fd hit optimisations in the	1712	constant timeout and the use of a single fd hit optimisations in the
1280	perl interpreter and the backend itself). Nevertheless this shows that	1713	perl interpreter and the backend itself). Nevertheless this shows that
1281	it adds very little overhead in itself. Like any select-based backend	1714	it adds very little overhead in itself. Like any select-based backend
…		…
1327	when used without AnyEvent), but most event loops have acceptable	1760	when used without AnyEvent), but most event loops have acceptable
1328	performance with or without AnyEvent.	1761	performance with or without AnyEvent.
1329		1762
1330	* The overhead AnyEvent adds is usually much smaller than the overhead	1763	* The overhead AnyEvent adds is usually much smaller than the overhead
1331	of the actual event loop, only with extremely fast event loops such	1764	of the actual event loop, only with extremely fast event loops such
1332	as EV adds AnyEvent significant overhead.	1765	as EV does AnyEvent add significant overhead.
1333		1766
1334	* You should avoid POE like the plague if you want performance or	1767	* You should avoid POE like the plague if you want performance or
1335	reasonable memory usage.	1768	reasonable memory usage.
1336		1769
1337	BENCHMARKING THE LARGE SERVER CASE	1770	BENCHMARKING THE LARGE SERVER CASE
…		…
1351	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1784	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1352	100 (1%) are active. This mirrors the activity of large servers with	1785	100 (1%) are active. This mirrors the activity of large servers with
1353	many connections, most of which are idle at any one point in time.	1786	many connections, most of which are idle at any one point in time.
1354		1787
1355	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1788	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1356	distribution.	1789	distribution. It uses the AE interface, which makes a real difference
		1790	for the EV and Perl backends only.
1357		1791
1358	Explanation of the columns	1792	Explanation of the columns
1359	sockets is the number of sockets, and twice the number of "servers"	1793	sockets is the number of sockets, and twice the number of "servers"
1360	(as each server has a read and write socket end).	1794	(as each server has a read and write socket end).
1361		1795
…		…
1367	forwarding it to another server. This includes deleting the old timeout	1801	forwarding it to another server. This includes deleting the old timeout
1368	and creating a new one that moves the timeout into the future.	1802	and creating a new one that moves the timeout into the future.
1369		1803
1370	Results	1804	Results
1371	name sockets create request	1805	name sockets create request
1372	EV 20000 69.01 11.16	1806	EV 20000 62.66 7.99
1373	Perl 20000 73.32 35.87	1807	Perl 20000 68.32 32.64
1374	IOAsync 20000 157.00 98.14 epoll	1808	IOAsync 20000 174.06 101.15 epoll
1375	IOAsync 20000 159.31 616.06 poll	1809	IOAsync 20000 174.67 610.84 poll
1376	Event 20000 212.62 257.32	1810	Event 20000 202.69 242.91
1377	Glib 20000 651.16 1896.30	1811	Glib 20000 557.01 1689.52
1378	POE 20000 349.67 12317.24 uses POE::Loop::Event	1812	POE 20000 341.54 12086.32 uses POE::Loop::Event
1379		1813
1380	Discussion	1814	Discussion
1381	This benchmark does measure scalability and overall performance of the	1815	This benchmark does measure scalability and overall performance of the
1382	particular event loop.	1816	particular event loop.
1383		1817
…		…
1496	As you can see, the AnyEvent + EV combination even beats the	1930	As you can see, the AnyEvent + EV combination even beats the
1497	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl	1931	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
1498	backend easily beats IO::Lambda and POE.	1932	backend easily beats IO::Lambda and POE.
1499		1933
1500	And even the 100% non-blocking version written using the high-level (and	1934	And even the 100% non-blocking version written using the high-level (and
1501	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a	1935	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
1502	large margin, even though it does all of DNS, tcp-connect and socket I/O	1936	higher level ("unoptimised") abstractions by a large margin, even though
1503	in a non-blocking way.	1937	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
1504		1938
1505	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and	1939	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
1506	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are	1940	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
1507	part of the IO::lambda distribution and were used without any changes.	1941	part of the IO::Lambda distribution and were used without any changes.
1508		1942
1509	SIGNALS	1943	SIGNALS
1510	AnyEvent currently installs handlers for these signals:	1944	AnyEvent currently installs handlers for these signals:
1511		1945
1512	SIGCHLD	1946	SIGCHLD
1513	A handler for "SIGCHLD" is installed by AnyEvent's child watcher	1947	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1514	emulation for event loops that do not support them natively. Also,	1948	emulation for event loops that do not support them natively. Also,
1515	some event loops install a similar handler.	1949	some event loops install a similar handler.
1516		1950
1517	If, when AnyEvent is loaded, SIGCHLD is set to IGNORE, then AnyEvent	1951	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
1518	will reset it to default, to avoid losing child exit statuses.	1952	then AnyEvent will reset it to default, to avoid losing child exit
		1953	statuses.
1519		1954
1520	SIGPIPE	1955	SIGPIPE
1521	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is	1956	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1522	"undef" when AnyEvent gets loaded.	1957	"undef" when AnyEvent gets loaded.
1523		1958
…		…
1531	it is that this way, the handler will be restored to defaults on	1966	it is that this way, the handler will be restored to defaults on
1532	exec.	1967	exec.
1533		1968
1534	Feel free to install your own handler, or reset it to defaults.	1969	Feel free to install your own handler, or reset it to defaults.
1535		1970
		1971	RECOMMENDED/OPTIONAL MODULES
		1972	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1973	its built-in modules) are required to use it.
		1974
		1975	That does not mean that AnyEvent won't take advantage of some additional
		1976	modules if they are installed.
		1977
		1978	This section explains which additional modules will be used, and how
		1979	they affect AnyEvent's operation.
		1980
		1981	Async::Interrupt
		1982	This slightly arcane module is used to implement fast signal
		1983	handling: To my knowledge, there is no way to do completely
		1984	race-free and quick signal handling in pure perl. To ensure that
		1985	signals still get delivered, AnyEvent will start an interval timer
		1986	to wake up perl (and catch the signals) with some delay (default is
		1987	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1988
		1989	If this module is available, then it will be used to implement
		1990	signal catching, which means that signals will not be delayed, and
		1991	the event loop will not be interrupted regularly, which is more
		1992	efficient (and good for battery life on laptops).
		1993
		1994	This affects not just the pure-perl event loop, but also other event
		1995	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1996
		1997	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1998	natively, and either employ their own workarounds (POE) or use
		1999	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		2000	Installing Async::Interrupt does nothing for those backends.
		2001
		2002	EV This module isn't really "optional", as it is simply one of the
		2003	backend event loops that AnyEvent can use. However, it is simply the
		2004	best event loop available in terms of features, speed and stability:
		2005	It supports the AnyEvent API optimally, implements all the watcher
		2006	types in XS, does automatic timer adjustments even when no monotonic
		2007	clock is available, can take avdantage of advanced kernel interfaces
		2008	such as "epoll" and "kqueue", and is the fastest backend by far.
		2009	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		2010	Glib::EV).
		2011
		2012	If you only use backends that rely on another event loop (e.g.
		2013	"Tk"), then this module will do nothing for you.
		2014
		2015	Guard
		2016	The guard module, when used, will be used to implement
		2017	"AnyEvent::Util::guard". This speeds up guards considerably (and
		2018	uses a lot less memory), but otherwise doesn't affect guard
		2019	operation much. It is purely used for performance.
		2020
		2021	JSON and JSON::XS
		2022	One of these modules is required when you want to read or write JSON
		2023	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		2024	can take advantage of the ultra-high-speed JSON::XS module when it
		2025	is installed.
		2026
		2027	Net::SSLeay
		2028	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2029	worthwhile: If this module is installed, then AnyEvent::Handle (with
		2030	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		2031
		2032	Time::HiRes
		2033	This module is part of perl since release 5.008. It will be used
		2034	when the chosen event library does not come with a timing source of
		2035	its own. The pure-perl event loop (AnyEvent::Loop) will additionally
		2036	load it to try to use a monotonic clock for timing stability.
		2037
		2038	AnyEvent::AIO (and IO::AIO)
		2039	The default implementation of AnyEvent::IO is to do I/O
		2040	synchronously, stopping programs while they access the disk, which
		2041	is fine for a lot of programs.
		2042
		2043	Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
		2044	switch to a true asynchronous implementation, so event processing
		2045	can continue even while waiting for disk I/O.
		2046
1536	FORK	2047	FORK
1537	Most event libraries are not fork-safe. The ones who are usually are	2048	Most event libraries are not fork-safe. The ones who are usually are
1538	because they rely on inefficient but fork-safe "select" or "poll" calls.	2049	because they rely on inefficient but fork-safe "select" or "poll" calls
1539	Only EV is fully fork-aware.	2050	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		2051	epoll are usually badly thought-out hacks that are incompatible with
		2052	fork in one way or another. Only EV is fully fork-aware and ensures that
		2053	you continue event-processing in both parent and child (or both, if you
		2054	know what you are doing).
		2055
		2056	This means that, in general, you cannot fork and do event processing in
		2057	the child if the event library was initialised before the fork (which
		2058	usually happens when the first AnyEvent watcher is created, or the
		2059	library is loaded).
1540		2060
1541	If you have to fork, you must either do so before creating your first	2061	If you have to fork, you must either do so before creating your first
1542	watcher OR you must not use AnyEvent at all in the child.	2062	watcher OR you must not use AnyEvent at all in the child OR you must do
		2063	something completely out of the scope of AnyEvent (see below).
		2064
		2065	The problem of doing event processing in the parent and the child is
		2066	much more complicated: even for backends that are fork-aware or
		2067	fork-safe, their behaviour is not usually what you want: fork clones all
		2068	watchers, that means all timers, I/O watchers etc. are active in both
		2069	parent and child, which is almost never what you want. Using "exec" to
		2070	start worker children from some kind of manage prrocess is usually
		2071	preferred, because it is much easier and cleaner, at the expense of
		2072	having to have another binary.
		2073
		2074	In addition to logical problems with fork, there are also implementation
		2075	problems. For example, on POSIX systems, you cannot fork at all in Perl
		2076	code if a thread (I am talking of pthreads here) was ever created in the
		2077	process, and this is just the tip of the iceberg. In general, using fork
		2078	from Perl is difficult, and attempting to use fork without an exec to
		2079	implement some kind of parallel processing is almost certainly doomed.
		2080
		2081	To safely fork and exec, you should use a module such as Proc::FastSpawn
		2082	that let's you safely fork and exec new processes.
		2083
		2084	If you want to do multiprocessing using processes, you can look at the
		2085	AnyEvent::Fork module (and some related modules such as
		2086	AnyEvent::Fork::RPC, AnyEvent::Fork::Pool and AnyEvent::Fork::Remote).
		2087	This module allows you to safely create subprocesses without any
		2088	limitations - you can use X11 toolkits or AnyEvent in the children
		2089	created by AnyEvent::Fork safely and without any special precautions.
1543		2090
1544	SECURITY CONSIDERATIONS	2091	SECURITY CONSIDERATIONS
1545	AnyEvent can be forced to load any event model via	2092	AnyEvent can be forced to load any event model via
1546	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	2093	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1547	to execute arbitrary code or directly gain access, it can easily be used	2094	to execute arbitrary code or directly gain access, it can easily be used
…		…
1571	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	2118	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1572	annoying memleaks, such as leaking on "map" and "grep" but it is usually	2119	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1573	not as pronounced).	2120	not as pronounced).
1574		2121
1575	SEE ALSO	2122	SEE ALSO
1576	Utility functions: AnyEvent::Util.	2123	Tutorial/Introduction: AnyEvent::Intro.
1577		2124
1578	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	2125	FAQ: AnyEvent::FAQ.
1579	Event::Lib, Qt, POE.	2126
		2127	Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
		2128	(simply logging).
		2129
		2130	Development/Debugging: AnyEvent::Strict (stricter checking),
		2131	AnyEvent::Debug (interactive shell, watcher tracing).
		2132
		2133	Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
		2134	Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK, Cocoa::EventLoop, UV.
1580		2135
1581	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	2136	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1582	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	2137	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1583	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	2138	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		2139	AnyEvent::Impl::IOAsync, AnyEvent::Impl::Irssi, AnyEvent::Impl::FLTK,
		2140	AnyEvent::Impl::Cocoa, AnyEvent::Impl::UV.
1584		2141
1585	Non-blocking file handles, sockets, TCP clients and servers:	2142	Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1586	AnyEvent::Handle, AnyEvent::Socket.	2143	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		2144
		2145	Asynchronous File I/O: AnyEvent::IO.
1587		2146
1588	Asynchronous DNS: AnyEvent::DNS.	2147	Asynchronous DNS: AnyEvent::DNS.
1589		2148
1590	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	2149	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1591		2150
1592	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	2151	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
		2152	AnyEvent::HTTP.
1593		2153
1594	AUTHOR	2154	AUTHOR
1595	Marc Lehmann <schmorp@schmorp.de>	2155	Marc Lehmann <schmorp@schmorp.de>
1596	http://home.schmorp.de/	2156	http://anyevent.schmorp.de
1597		2157

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Comparing AnyEvent/README (file contents):
Revision 1.42 by root, Mon Jun 29 21:00:32 2009 UTC vs.
Revision 1.77 by root, Sat Sep 17 02:33:54 2016 UTC