[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.43 by root, Thu Jul 9 08:37:06 2009 UTC vs.
Revision 1.73 by root, Fri Sep 5 22:24:12 2014 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 (or a naked 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
…		…
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
…		…
706	This is a mutator function that returns the callback set and	817	This is a mutator function that returns the callback set and
707	optionally replaces it before doing so.	818	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.
713		825
714	SUPPORTED EVENT LOOPS/BACKENDS	826	SUPPORTED EVENT LOOPS/BACKENDS
715	The available backend classes are (every class has its own manpage):	827	The available backend classes are (every class has its own manpage):
716		828
717	Backends that are autoprobed when no other event loop can be found.	829	Backends that are autoprobed when no other event loop can be found.
718	EV is the preferred backend when no other event loop seems to be in	830	EV is the preferred backend when no other event loop seems to be in
719	use. If EV is not installed, then AnyEvent will try Event, and,	831	use. If EV is not installed, then AnyEvent will fall back to its own
720	failing that, will fall back to its own pure-perl implementation,	832	pure-perl implementation, which is available everywhere as it comes
721	which is available everywhere as it comes with AnyEvent itself.	833	with AnyEvent itself.
722		834
723	AnyEvent::Impl::EV based on EV (interface to libev, best choice).	835	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
724	AnyEvent::Impl::Event based on Event, very stable, few glitches.
725	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.	836	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
726		837
727	Backends that are transparently being picked up when they are used.	838	Backends that are transparently being picked up when they are used.
728	These will be used when they are currently loaded when the first	839	These will be used if they are already loaded when the first watcher
729	watcher is created, in which case it is assumed that the application	840	is created, in which case it is assumed that the application is
730	is using them. This means that AnyEvent will automatically pick the	841	using them. This means that AnyEvent will automatically pick the
731	right backend when the main program loads an event module before	842	right backend when the main program loads an event module before
732	anything starts to create watchers. Nothing special needs to be done	843	anything starts to create watchers. Nothing special needs to be done
733	by the main program.	844	by the main program.
734		845
		846	AnyEvent::Impl::Event based on Event, very stable, few glitches.
735	AnyEvent::Impl::Glib based on Glib, slow but very stable.	847	AnyEvent::Impl::Glib based on Glib, slow but very stable.
736	AnyEvent::Impl::Tk based on Tk, very broken.	848	AnyEvent::Impl::Tk based on Tk, very broken.
		849	AnyEvent::Impl::UV based on UV, innovated square wheels.
737	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	850	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
738	AnyEvent::Impl::POE based on POE, very slow, some limitations.	851	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		852	AnyEvent::Impl::Irssi used when running within irssi.
		853	AnyEvent::Impl::IOAsync based on IO::Async.
		854	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		855	AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
739		856
740	Backends with special needs.	857	Backends with special needs.
741	Qt requires the Qt::Application to be instantiated first, but will	858	Qt requires the Qt::Application to be instantiated first, but will
742	otherwise be picked up automatically. As long as the main program	859	otherwise be picked up automatically. As long as the main program
743	instantiates the application before any AnyEvent watchers are	860	instantiates the application before any AnyEvent watchers are
744	created, everything should just work.	861	created, everything should just work.
745		862
746	AnyEvent::Impl::Qt based on Qt.	863	AnyEvent::Impl::Qt based on Qt.
747		864
748	Support for IO::Async can only be partial, as it is too broken and
749	architecturally limited to even support the AnyEvent API. It also is
750	the only event loop that needs the loop to be set explicitly, so it
751	can only be used by a main program knowing about AnyEvent. See
752	AnyEvent::Impl::Async for the gory details.
753
754	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
755
756	Event loops that are indirectly supported via other backends.	865	Event loops that are indirectly supported via other backends.
757	Some event loops can be supported via other modules:	866	Some event loops can be supported via other modules:
758		867
759	There is no direct support for WxWidgets (Wx) or Prima.	868	There is no direct support for WxWidgets (Wx) or Prima.
760		869
…		…
778	Contains "undef" until the first watcher is being created, before	887	Contains "undef" until the first watcher is being created, before
779	the backend has been autodetected.	888	the backend has been autodetected.
780		889
781	Afterwards it contains the event model that is being used, which is	890	Afterwards it contains the event model that is being used, which is
782	the name of the Perl class implementing the model. This class is	891	the name of the Perl class implementing the model. This class is
783	usually one of the "AnyEvent::Impl:xxx" modules, but can be any	892	usually one of the "AnyEvent::Impl::xxx" modules, but can be any
784	other class in the case AnyEvent has been extended at runtime (e.g.	893	other class in the case AnyEvent has been extended at runtime (e.g.
785	in rxvt-unicode it will be "urxvt::anyevent").	894	in rxvt-unicode it will be "urxvt::anyevent").
786		895
787	AnyEvent::detect	896	AnyEvent::detect
788	Returns $AnyEvent::MODEL, forcing autodetection of the event model	897	Returns $AnyEvent::MODEL, forcing autodetection of the event model
789	if necessary. You should only call this function right before you	898	if necessary. You should only call this function right before you
790	would have created an AnyEvent watcher anyway, that is, as late as	899	would have created an AnyEvent watcher anyway, that is, as late as
791	possible at runtime, and not e.g. while initialising of your module.	900	possible at runtime, and not e.g. during initialisation of your
		901	module.
		902
		903	The effect of calling this function is as if a watcher had been
		904	created (specifically, actions that happen "when the first watcher
		905	is created" happen when calling detetc as well).
792		906
793	If you need to do some initialisation before AnyEvent watchers are	907	If you need to do some initialisation before AnyEvent watchers are
794	created, use "post_detect".	908	created, use "post_detect".
795		909
796	$guard = AnyEvent::post_detect { BLOCK }	910	$guard = AnyEvent::post_detect { BLOCK }
797	Arranges for the code block to be executed as soon as the event	911	Arranges for the code block to be executed as soon as the event
798	model is autodetected (or immediately if this has already happened).	912	model is autodetected (or immediately if that has already happened).
799		913
800	The block will be executed after the actual backend has been	914	The block will be executed after the actual backend has been
801	detected ($AnyEvent::MODEL is set), but before any watchers have	915	detected ($AnyEvent::MODEL is set), but before any watchers have
802	been created, so it is possible to e.g. patch @AnyEvent::ISA or do	916	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
803	other initialisations - see the sources of AnyEvent::Strict or	917	other initialisations - see the sources of AnyEvent::Strict or
…		…
808	creates and installs the global IO::AIO watcher in a "post_detect"	922	creates and installs the global IO::AIO watcher in a "post_detect"
809	block to avoid autodetecting the event module at load time.	923	block to avoid autodetecting the event module at load time.
810		924
811	If called in scalar or list context, then it creates and returns an	925	If called in scalar or list context, then it creates and returns an
812	object that automatically removes the callback again when it is	926	object that automatically removes the callback again when it is
		927	destroyed (or "undef" when the hook was immediately executed). See
813	destroyed. See Coro::BDB for a case where this is useful.	928	AnyEvent::AIO for a case where this is useful.
		929
		930	Example: Create a watcher for the IO::AIO module and store it in
		931	$WATCHER, but do so only do so after the event loop is initialised.
		932
		933	our WATCHER;
		934
		935	my $guard = AnyEvent::post_detect {
		936	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		937	};
		938
		939	# the \|\|= is important in case post_detect immediately runs the block,
		940	# as to not clobber the newly-created watcher. assigning both watcher and
		941	# post_detect guard to the same variable has the advantage of users being
		942	# able to just C<undef $WATCHER> if the watcher causes them grief.
		943
		944	$WATCHER \|\|= $guard;
814		945
815	@AnyEvent::post_detect	946	@AnyEvent::post_detect
816	If there are any code references in this array (you can "push" to it	947	If there are any code references in this array (you can "push" to it
817	before or after loading AnyEvent), then they will called directly	948	before or after loading AnyEvent), then they will be called directly
818	after the event loop has been chosen.	949	after the event loop has been chosen.
819		950
820	You should check $AnyEvent::MODEL before adding to this array,	951	You should check $AnyEvent::MODEL before adding to this array,
821	though: if it is defined then the event loop has already been	952	though: if it is defined then the event loop has already been
822	detected, and the array will be ignored.	953	detected, and the array will be ignored.
823		954
824	Best use "AnyEvent::post_detect { BLOCK }" when your application	955	Best use "AnyEvent::post_detect { BLOCK }" when your application
825	allows it,as it takes care of these details.	956	allows it, as it takes care of these details.
826		957
827	This variable is mainly useful for modules that can do something	958	This variable is mainly useful for modules that can do something
828	useful when AnyEvent is used and thus want to know when it is	959	useful when AnyEvent is used and thus want to know when it is
829	initialised, but do not need to even load it by default. This array	960	initialised, but do not need to even load it by default. This array
830	provides the means to hook into AnyEvent passively, without loading	961	provides the means to hook into AnyEvent passively, without loading
831	it.	962	it.
832		963
		964	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		965	together, you could put this into Coro (this is the actual code used
		966	by Coro to accomplish this):
		967
		968	if (defined $AnyEvent::MODEL) {
		969	# AnyEvent already initialised, so load Coro::AnyEvent
		970	require Coro::AnyEvent;
		971	} else {
		972	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		973	# as soon as it is
		974	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		975	}
		976
		977	AnyEvent::postpone { BLOCK }
		978	Arranges for the block to be executed as soon as possible, but not
		979	before the call itself returns. In practise, the block will be
		980	executed just before the event loop polls for new events, or shortly
		981	afterwards.
		982
		983	This function never returns anything (to make the "return postpone {
		984	... }" idiom more useful.
		985
		986	To understand the usefulness of this function, consider a function
		987	that asynchronously does something for you and returns some
		988	transaction object or guard to let you cancel the operation. For
		989	example, "AnyEvent::Socket::tcp_connect":
		990
		991	# start a connection attempt unless one is active
		992	$self->{connect_guard} \|\|= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		993	delete $self->{connect_guard};
		994	...
		995	};
		996
		997	Imagine that this function could instantly call the callback, for
		998	example, because it detects an obvious error such as a negative port
		999	number. Invoking the callback before the function returns causes
		1000	problems however: the callback will be called and will try to delete
		1001	the guard object. But since the function hasn't returned yet, there
		1002	is nothing to delete. When the function eventually returns it will
		1003	assign the guard object to "$self->{connect_guard}", where it will
		1004	likely never be deleted, so the program thinks it is still trying to
		1005	connect.
		1006
		1007	This is where "AnyEvent::postpone" should be used. Instead of
		1008	calling the callback directly on error:
		1009
		1010	$cb->(undef), return # signal error to callback, BAD!
		1011	if $some_error_condition;
		1012
		1013	It should use "postpone":
		1014
		1015	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1016	if $some_error_condition;
		1017
		1018	AnyEvent::log $level, $msg[, @args]
		1019	Log the given $msg at the given $level.
		1020
		1021	If AnyEvent::Log is not loaded then this function makes a simple
		1022	test to see whether the message will be logged. If the test succeeds
		1023	it will load AnyEvent::Log and call "AnyEvent::Log::log" -
		1024	consequently, look at the AnyEvent::Log documentation for details.
		1025
		1026	If the test fails it will simply return. Right now this happens when
		1027	a numerical loglevel is used and it is larger than the level
		1028	specified via $ENV{PERL_ANYEVENT_VERBOSE}.
		1029
		1030	If you want to sprinkle loads of logging calls around your code,
		1031	consider creating a logger callback with the "AnyEvent::Log::logger"
		1032	function, which can reduce typing, codesize and can reduce the
		1033	logging overhead enourmously.
		1034
833	WHAT TO DO IN A MODULE	1035	WHAT TO DO IN A MODULE
834	As a module author, you should "use AnyEvent" and call AnyEvent methods	1036	As a module author, you should "use AnyEvent" and call AnyEvent methods
835	freely, but you should not load a specific event module or rely on it.	1037	freely, but you should not load a specific event module or rely on it.
836		1038
837	Be careful when you create watchers in the module body - AnyEvent will	1039	Be careful when you create watchers in the module body - AnyEvent will
…		…
844	stall the whole program, and the whole point of using events is to stay	1046	stall the whole program, and the whole point of using events is to stay
845	interactive.	1047	interactive.
846		1048
847	It is fine, however, to call "->recv" when the user of your module	1049	It is fine, however, to call "->recv" when the user of your module
848	requests it (i.e. if you create a http request object ad have a method	1050	requests it (i.e. if you create a http request object ad have a method
849	called "results" that returns the results, it should call "->recv"	1051	called "results" that returns the results, it may call "->recv" freely,
850	freely, as the user of your module knows what she is doing. always).	1052	as the user of your module knows what she is doing. Always).
851		1053
852	WHAT TO DO IN THE MAIN PROGRAM	1054	WHAT TO DO IN THE MAIN PROGRAM
853	There will always be a single main program - the only place that should	1055	There will always be a single main program - the only place that should
854	dictate which event model to use.	1056	dictate which event model to use.
855		1057
856	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	1058	If the program is not event-based, it need not do anything special, even
857	do anything special (it does not need to be event-based) and let	1059	when it depends on a module that uses an AnyEvent. If the program itself
858	AnyEvent decide which implementation to chose if some module relies on	1060	uses AnyEvent, but does not care which event loop is used, all it needs
859	it.	1061	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		1062	available loop implementation.
860		1063
861	If the main program relies on a specific event model - for example, in	1064	If the main program relies on a specific event model - for example, in
862	Gtk2 programs you have to rely on the Glib module - you should load the	1065	Gtk2 programs you have to rely on the Glib module - you should load the
863	event module before loading AnyEvent or any module that uses it:	1066	event module before loading AnyEvent or any module that uses it:
864	generally speaking, you should load it as early as possible. The reason	1067	generally speaking, you should load it as early as possible. The reason
865	is that modules might create watchers when they are loaded, and AnyEvent	1068	is that modules might create watchers when they are loaded, and AnyEvent
866	will decide on the event model to use as soon as it creates watchers,	1069	will decide on the event model to use as soon as it creates watchers,
867	and it might chose the wrong one unless you load the correct one	1070	and it might choose the wrong one unless you load the correct one
868	yourself.	1071	yourself.
869		1072
870	You can chose to use a pure-perl implementation by loading the	1073	You can chose to use a pure-perl implementation by loading the
871	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1074	"AnyEvent::Loop" module, which gives you similar behaviour everywhere,
872	everywhere, but letting AnyEvent chose the model is generally better.	1075	but letting AnyEvent chose the model is generally better.
873		1076
874	MAINLOOP EMULATION	1077	MAINLOOP EMULATION
875	Sometimes (often for short test scripts, or even standalone programs who	1078	Sometimes (often for short test scripts, or even standalone programs who
876	only want to use AnyEvent), you do not want to run a specific event	1079	only want to use AnyEvent), you do not want to run a specific event
877	loop.	1080	loop.
…		…
889		1092
890	OTHER MODULES	1093	OTHER MODULES
891	The following is a non-exhaustive list of additional modules that use	1094	The following is a non-exhaustive list of additional modules that use
892	AnyEvent as a client and can therefore be mixed easily with other	1095	AnyEvent as a client and can therefore be mixed easily with other
893	AnyEvent modules and other event loops in the same program. Some of the	1096	AnyEvent modules and other event loops in the same program. Some of the
894	modules come with AnyEvent, most are available via CPAN.	1097	modules come as part of AnyEvent, the others are available via CPAN (see
		1098	<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
		1099	non-exhaustive list), and the list is heavily biased towards modules of
		1100	the AnyEvent author himself :)
895		1101
896	AnyEvent::Util	1102	AnyEvent::Util (part of the AnyEvent distribution)
897	Contains various utility functions that replace often-used but	1103	Contains various utility functions that replace often-used blocking
898	blocking functions such as "inet_aton" by event-/callback-based	1104	functions such as "inet_aton" with event/callback-based versions.
899	versions.
900		1105
901	AnyEvent::Socket	1106	AnyEvent::Socket (part of the AnyEvent distribution)
902	Provides various utility functions for (internet protocol) sockets,	1107	Provides various utility functions for (internet protocol) sockets,
903	addresses and name resolution. Also functions to create non-blocking	1108	addresses and name resolution. Also functions to create non-blocking
904	tcp connections or tcp servers, with IPv6 and SRV record support and	1109	tcp connections or tcp servers, with IPv6 and SRV record support and
905	more.	1110	more.
906		1111
907	AnyEvent::Handle	1112	AnyEvent::Handle (part of the AnyEvent distribution)
908	Provide read and write buffers, manages watchers for reads and	1113	Provide read and write buffers, manages watchers for reads and
909	writes, supports raw and formatted I/O, I/O queued and fully	1114	writes, supports raw and formatted I/O, I/O queued and fully
910	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.	1115	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
911		1116
912	AnyEvent::DNS	1117	AnyEvent::DNS (part of the AnyEvent distribution)
913	Provides rich asynchronous DNS resolver capabilities.	1118	Provides rich asynchronous DNS resolver capabilities.
914		1119
915	AnyEvent::HTTP	1120	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
916	A simple-to-use HTTP library that is capable of making a lot of	1121	AnyEvent::IGS, AnyEvent::FCP
917	concurrent HTTP requests.	1122	Implement event-based interfaces to the protocols of the same name
		1123	(for the curious, IGS is the International Go Server and FCP is the
		1124	Freenet Client Protocol).
918		1125
		1126	AnyEvent::AIO (part of the AnyEvent distribution)
		1127	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1128	the toolbox of every event programmer. AnyEvent::AIO transparently
		1129	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1130	event-based file I/O, and much more.
		1131
		1132	AnyEvent::Fork, AnyEvent::Fork::RPC, AnyEvent::Fork::Pool,
		1133	AnyEvent::Fork::Remote
		1134	These let you safely fork new subprocesses, either locally or
		1135	remotely (e.g.v ia ssh), using some RPC protocol or not, without the
		1136	limitations normally imposed by fork (AnyEvent works fine for
		1137	example). Dynamically-resized worker pools are obviously included as
		1138	well.
		1139
		1140	And they are quite tiny and fast as well - "abusing" AnyEvent::Fork
		1141	just to exec external programs can easily beat using "fork" and
		1142	"exec" (or even "system") in most programs.
		1143
		1144	AnyEvent::Filesys::Notify
		1145	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1146	path changes (e.g. "watch this directory for new files", "watch this
		1147	file for changes"). The AnyEvent::Filesys::Notify module promises to
		1148	do just that in a portbale fashion, supporting inotify on GNU/Linux
		1149	and some weird, without doubt broken, stuff on OS X to monitor
		1150	files. It can fall back to blocking scans at regular intervals
		1151	transparently on other platforms, so it's about as portable as it
		1152	gets.
		1153
		1154	(I haven't used it myself, but it seems the biggest problem with it
		1155	is it quite bad performance).
		1156
919	AnyEvent::HTTPD	1157	AnyEvent::DBI
920	Provides a simple web application server framework.	1158	Executes DBI requests asynchronously in a proxy process for you,
		1159	notifying you in an event-based way when the operation is finished.
921		1160
922	AnyEvent::FastPing	1161	AnyEvent::FastPing
923	The fastest ping in the west.	1162	The fastest ping in the west.
924		1163
925	AnyEvent::DBI
926	Executes DBI requests asynchronously in a proxy process.
927
928	AnyEvent::AIO
929	Truly asynchronous I/O, should be in the toolbox of every event
930	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
931	together.
932
933	AnyEvent::BDB
934	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
935	fuses BDB and AnyEvent together.
936
937	AnyEvent::GPSD
938	A non-blocking interface to gpsd, a daemon delivering GPS
939	information.
940
941	AnyEvent::IRC
942	AnyEvent based IRC client module family (replacing the older
943	Net::IRC3).
944
945	AnyEvent::XMPP
946	AnyEvent based XMPP (Jabber protocol) module family (replacing the
947	older Net::XMPP2>.
948
949	AnyEvent::IGS
950	A non-blocking interface to the Internet Go Server protocol (used by
951	App::IGS).
952
953	Net::FCP
954	AnyEvent-based implementation of the Freenet Client Protocol,
955	birthplace of AnyEvent.
956
957	Event::ExecFlow
958	High level API for event-based execution flow control.
959
960	Coro	1164	Coro
961	Has special support for AnyEvent via Coro::AnyEvent.	1165	Has special support for AnyEvent via Coro::AnyEvent, which allows
		1166	you to simply invert the flow control - don't call us, we will call
		1167	you:
		1168
		1169	async {
		1170	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
		1171	print "5 seconds later!\n";
		1172
		1173	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
		1174	my $line = <STDIN>; # works for ttys
		1175
		1176	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
		1177	my ($body, $hdr) = Coro::rouse_wait;
		1178	};
		1179
		1180	SIMPLIFIED AE API
		1181	Starting with version 5.0, AnyEvent officially supports a second, much
		1182	simpler, API that is designed to reduce the calling, typing and memory
		1183	overhead by using function call syntax and a fixed number of parameters.
		1184
		1185	See the AE manpage for details.
962		1186
963	ERROR AND EXCEPTION HANDLING	1187	ERROR AND EXCEPTION HANDLING
964	In general, AnyEvent does not do any error handling - it relies on the	1188	In general, AnyEvent does not do any error handling - it relies on the
965	caller to do that if required. The AnyEvent::Strict module (see also the	1189	caller to do that if required. The AnyEvent::Strict module (see also the
966	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	1190	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
975	The pure perl event loop simply re-throws the exception (usually within	1199	The pure perl event loop simply re-throws the exception (usually within
976	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1200	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
977	Glib uses "install_exception_handler" and so on.	1201	Glib uses "install_exception_handler" and so on.
978		1202
979	ENVIRONMENT VARIABLES	1203	ENVIRONMENT VARIABLES
980	The following environment variables are used by this module or its	1204	AnyEvent supports a number of environment variables that tune the
981	submodules.	1205	runtime behaviour. They are usually evaluated when AnyEvent is loaded,
		1206	initialised, or a submodule that uses them is loaded. Many of them also
		1207	cause AnyEvent to load additional modules - for example,
		1208	"PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
		1209	loaded.
982		1210
983	Note that AnyEvent will remove all environment variables starting with	1211	All the environment variables documented here start with
984	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is	1212	"PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
985	enabled.	1213	Other modules are encouraged (but by no means required) to use
		1214	"PERL_ANYEVENT_SUBMODULE" if they have registered the
		1215	AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
		1216	AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
		1217	should not access env variables starting with "AE_", see below).
		1218
		1219	All variables can also be set via the "AE_" prefix, that is, instead of
		1220	setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
		1221	there is a clash btween anyevent and another program that uses
		1222	"AE_something" you can set the corresponding "PERL_ANYEVENT_something"
		1223	variable to the empty string, as those variables take precedence.
		1224
		1225	When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
		1226	their "PERL_ANYEVENT_xxx" counterpart unless that variable already
		1227	exists. If taint mode is on, then AnyEvent will remove all environment
		1228	variables starting with "PERL_ANYEVENT_" from %ENV (or replace them with
		1229	"undef" or the empty string, if the corresaponding "AE_" variable is
		1230	set).
		1231
		1232	The exact algorithm is currently:
		1233
		1234	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		1235	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		1236	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		1237
		1238	This ensures that child processes will not see the "AE_" variables.
		1239
		1240	The following environment variables are currently known to AnyEvent:
986		1241
987	"PERL_ANYEVENT_VERBOSE"	1242	"PERL_ANYEVENT_VERBOSE"
988	By default, AnyEvent will be completely silent except in fatal	1243	By default, AnyEvent will log messages with loglevel 4 ("error") or
989	conditions. You can set this environment variable to make AnyEvent	1244	higher (see AnyEvent::Log). You can set this environment variable to
990	more talkative.	1245	a numerical loglevel to make AnyEvent more (or less) talkative.
991		1246
		1247	If you want to do more than just set the global logging level you
		1248	should have a look at "PERL_ANYEVENT_LOG", which allows much more
		1249	complex specifications.
		1250
		1251	When set to 0 ("off"), then no messages whatsoever will be logged
		1252	with everything else at defaults.
		1253
992	When set to 1 or higher, causes AnyEvent to warn about unexpected	1254	When set to 5 or higher ("warn"), AnyEvent warns about unexpected
993	conditions, such as not being able to load the event model specified	1255	conditions, such as not being able to load the event model specified
994	by "PERL_ANYEVENT_MODEL".	1256	by "PERL_ANYEVENT_MODEL", or a guard callback throwing an exception
		1257	- this is the minimum recommended level for use during development.
995		1258
996	When set to 2 or higher, cause AnyEvent to report to STDERR which	1259	When set to 7 or higher (info), AnyEvent reports which event model
997	event model it chooses.	1260	it chooses.
		1261
		1262	When set to 8 or higher (debug), then AnyEvent will report extra
		1263	information on which optional modules it loads and how it implements
		1264	certain features.
		1265
		1266	"PERL_ANYEVENT_LOG"
		1267	Accepts rather complex logging specifications. For example, you
		1268	could log all "debug" messages of some module to stderr, warnings
		1269	and above to stderr, and errors and above to syslog, with:
		1270
		1271	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		1272
		1273	For the rather extensive details, see AnyEvent::Log.
		1274
		1275	This variable is evaluated when AnyEvent (or AnyEvent::Log) is
		1276	loaded, so will take effect even before AnyEvent has initialised
		1277	itself.
		1278
		1279	Note that specifying this environment variable causes the
		1280	AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
		1281	does not, so only using the latter saves a few hundred kB of memory
		1282	unless a module explicitly needs the extra features of
		1283	AnyEvent::Log.
998		1284
999	"PERL_ANYEVENT_STRICT"	1285	"PERL_ANYEVENT_STRICT"
1000	AnyEvent does not do much argument checking by default, as thorough	1286	AnyEvent does not do much argument checking by default, as thorough
1001	argument checking is very costly. Setting this variable to a true	1287	argument checking is very costly. Setting this variable to a true
1002	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1288	value will cause AnyEvent to load "AnyEvent::Strict" and then to
1003	thoroughly check the arguments passed to most method calls. If it	1289	thoroughly check the arguments passed to most method calls. If it
1004	finds any problems, it will croak.	1290	finds any problems, it will croak.
1005		1291
1006	In other words, enables "strict" mode.	1292	In other words, enables "strict" mode.
1007		1293
1008	Unlike "use strict", it is definitely recommended to keep it off in	1294	Unlike "use strict" (or its modern cousin, "use common::sense", it
1009	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment	1295	is definitely recommended to keep it off in production. Keeping
		1296	"PERL_ANYEVENT_STRICT=1" in your environment while developing
1010	while developing programs can be very useful, however.	1297	programs can be very useful, however.
		1298
		1299	"PERL_ANYEVENT_DEBUG_SHELL"
		1300	If this env variable is nonempty, then its contents will be
		1301	interpreted by "AnyEvent::Socket::parse_hostport" and
		1302	"AnyEvent::Debug::shell" (after replacing every occurance of $$ by
		1303	the process pid). The shell object is saved in
		1304	$AnyEvent::Debug::SHELL.
		1305
		1306	This happens when the first watcher is created.
		1307
		1308	For example, to bind a debug shell on a unix domain socket in
		1309	/tmp/debug<pid>.sock, you could use this:
		1310
		1311	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		1312	# connect with e.g.: socat readline /tmp/debug123.sock
		1313
		1314	Or to bind to tcp port 4545 on localhost:
		1315
		1316	PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
		1317	# connect with e.g.: telnet localhost 4545
		1318
		1319	Note that creating sockets in /tmp or on localhost is very unsafe on
		1320	multiuser systems.
		1321
		1322	"PERL_ANYEVENT_DEBUG_WRAP"
		1323	Can be set to 0, 1 or 2 and enables wrapping of all watchers for
		1324	debugging purposes. See "AnyEvent::Debug::wrap" for details.
1011		1325
1012	"PERL_ANYEVENT_MODEL"	1326	"PERL_ANYEVENT_MODEL"
1013	This can be used to specify the event model to be used by AnyEvent,	1327	This can be used to specify the event model to be used by AnyEvent,
1014	before auto detection and -probing kicks in. It must be a string	1328	before auto detection and -probing kicks in.
1015	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1329
1016	gets prepended and the resulting module name is loaded and if the	1330	It normally is a string consisting entirely of ASCII letters (e.g.
1017	load was successful, used as event model. If it fails to load	1331	"EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
		1332	the resulting module name is loaded and - if the load was successful
		1333	- used as event model backend. If it fails to load then AnyEvent
1018	AnyEvent will proceed with auto detection and -probing.	1334	will proceed with auto detection and -probing.
1019		1335
1020	This functionality might change in future versions.	1336	If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
		1337	then nothing gets prepended and the module name is used as-is (hint:
		1338	"::" at the end of a string designates a module name and quotes it
		1339	appropriately).
1021		1340
1022	For example, to force the pure perl model (AnyEvent::Impl::Perl) you	1341	For example, to force the pure perl model (AnyEvent::Loop::Perl) you
1023	could start your program like this:	1342	could start your program like this:
1024		1343
1025	PERL_ANYEVENT_MODEL=Perl perl ...	1344	PERL_ANYEVENT_MODEL=Perl perl ...
		1345
		1346	"PERL_ANYEVENT_IO_MODEL"
		1347	The current file I/O model - see AnyEvent::IO for more info.
		1348
		1349	At the moment, only "Perl" (small, pure-perl, synchronous) and
		1350	"IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
		1351	if AnyEvent::AIO can be loaded, otherwise it is "Perl".
1026		1352
1027	"PERL_ANYEVENT_PROTOCOLS"	1353	"PERL_ANYEVENT_PROTOCOLS"
1028	Used by both AnyEvent::DNS and AnyEvent::Socket to determine	1354	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
1029	preferences for IPv4 or IPv6. The default is unspecified (and might	1355	preferences for IPv4 or IPv6. The default is unspecified (and might
1030	change, or be the result of auto probing).	1356	change, or be the result of auto probing).
…		…
1034	mentioned will be used, and preference will be given to protocols	1360	mentioned will be used, and preference will be given to protocols
1035	mentioned earlier in the list.	1361	mentioned earlier in the list.
1036		1362
1037	This variable can effectively be used for denial-of-service attacks	1363	This variable can effectively be used for denial-of-service attacks
1038	against local programs (e.g. when setuid), although the impact is	1364	against local programs (e.g. when setuid), although the impact is
1039	likely small, as the program has to handle conenction and other	1365	likely small, as the program has to handle connection and other
1040	failures anyways.	1366	failures anyways.
1041		1367
1042	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1368	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
1043	IPv6, but support both and try to use both.	1369	IPv6, but support both and try to use both.
1044	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1370	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
1045	resolve or contact IPv6 addresses.	1371	resolve or contact IPv6 addresses.
1046	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but	1372	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
1047	prefer IPv6 over IPv4.	1373	prefer IPv6 over IPv4.
1048		1374
		1375	"PERL_ANYEVENT_HOSTS"
		1376	This variable, if specified, overrides the /etc/hosts file used by
		1377	AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
		1378	read from that file instead.
		1379
1049	"PERL_ANYEVENT_EDNS0"	1380	"PERL_ANYEVENT_EDNS0"
1050	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension	1381	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
1051	for DNS. This extension is generally useful to reduce DNS traffic,	1382	for DNS. This extension is generally useful to reduce DNS traffic,
1052	but some (broken) firewalls drop such DNS packets, which is why it	1383	especially when DNSSEC is involved, but some (broken) firewalls drop
1053	is off by default.	1384	such DNS packets, which is why it is off by default.
1054		1385
1055	Setting this variable to 1 will cause AnyEvent::DNS to announce	1386	Setting this variable to 1 will cause AnyEvent::DNS to announce
1056	EDNS0 in its DNS requests.	1387	EDNS0 in its DNS requests.
1057		1388
1058	"PERL_ANYEVENT_MAX_FORKS"	1389	"PERL_ANYEVENT_MAX_FORKS"
…		…
1062	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"	1393	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
1063	The default value for the "max_outstanding" parameter for the	1394	The default value for the "max_outstanding" parameter for the
1064	default DNS resolver - this is the maximum number of parallel DNS	1395	default DNS resolver - this is the maximum number of parallel DNS
1065	requests that are sent to the DNS server.	1396	requests that are sent to the DNS server.
1066		1397
		1398	"PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
		1399	Perl has inherently racy signal handling (you can basically choose
		1400	between losing signals and memory corruption) - pure perl event
		1401	loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
		1402	available) therefore have to poll regularly to avoid losing signals.
		1403
		1404	Some event loops are racy, but don't poll regularly, and some event
		1405	loops are written in C but are still racy. For those event loops,
		1406	AnyEvent installs a timer that regularly wakes up the event loop.
		1407
		1408	By default, the interval for this timer is 10 seconds, but you can
		1409	override this delay with this environment variable (or by setting
		1410	the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
		1411	watchers).
		1412
		1413	Lower values increase CPU (and energy) usage, higher values can
		1414	introduce long delays when reaping children or waiting for signals.
		1415
		1416	The AnyEvent::Async module, if available, will be used to avoid this
		1417	polling (with most event loops).
		1418
1067	"PERL_ANYEVENT_RESOLV_CONF"	1419	"PERL_ANYEVENT_RESOLV_CONF"
1068	The file to use instead of /etc/resolv.conf (or OS-specific	1420	The absolute path to a resolv.conf-style file to use instead of
1069	configuration) in the default resolver. When set to the empty	1421	/etc/resolv.conf (or the OS-specific configuration) in the default
1070	string, no default config will be used.	1422	resolver, or the empty string to select the default configuration.
1071		1423
1072	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".	1424	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
1073	When neither "ca_file" nor "ca_path" was specified during	1425	When neither "ca_file" nor "ca_path" was specified during
1074	AnyEvent::TLS context creation, and either of these environment	1426	AnyEvent::TLS context creation, and either of these environment
1075	variables exist, they will be used to specify CA certificate	1427	variables are nonempty, they will be used to specify CA certificate
1076	locations instead of a system-dependent default.	1428	locations instead of a system-dependent default.
		1429
		1430	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1431	When these are set to 1, then the respective modules are not loaded.
		1432	Mostly good for testing AnyEvent itself.
1077		1433
1078	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1434	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
1079	This is an advanced topic that you do not normally need to use AnyEvent	1435	This is an advanced topic that you do not normally need to use AnyEvent
1080	in a module. This section is only of use to event loop authors who want	1436	in a module. This section is only of use to event loop authors who want
1081	to provide AnyEvent compatibility.	1437	to provide AnyEvent compatibility.
…		…
1136	warn "read: $input\n"; # output what has been read	1492	warn "read: $input\n"; # output what has been read
1137	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1493	$cv->send if $input =~ /^q/i; # quit program if /^q/i
1138	},	1494	},
1139	);	1495	);
1140		1496
1141	my $time_watcher; # can only be used once
1142
1143	sub new_timer {
1144	$timer = AnyEvent->timer (after => 1, cb => sub {	1497	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
1145	warn "timeout\n"; # print 'timeout' about every second	1498	warn "timeout\n"; # print 'timeout' at most every second
1146	&new_timer; # and restart the time
1147	});
1148	}	1499	});
1149
1150	new_timer; # create first timer
1151		1500
1152	$cv->recv; # wait until user enters /^q/i	1501	$cv->recv; # wait until user enters /^q/i
1153		1502
1154	REAL-WORLD EXAMPLE	1503	REAL-WORLD EXAMPLE
1155	Consider the Net::FCP module. It features (among others) the following	1504	Consider the Net::FCP module. It features (among others) the following
…		…
1227		1576
1228	The actual code goes further and collects all errors ("die"s,	1577	The actual code goes further and collects all errors ("die"s,
1229	exceptions) that occurred during request processing. The "result" method	1578	exceptions) that occurred during request processing. The "result" method
1230	detects whether an exception as thrown (it is stored inside the $txn	1579	detects whether an exception as thrown (it is stored inside the $txn
1231	object) and just throws the exception, which means connection errors and	1580	object) and just throws the exception, which means connection errors and
1232	other problems get reported tot he code that tries to use the result,	1581	other problems get reported to the code that tries to use the result,
1233	not in a random callback.	1582	not in a random callback.
1234		1583
1235	All of this enables the following usage styles:	1584	All of this enables the following usage styles:
1236		1585
1237	1. Blocking:	1586	1. Blocking:
…		…
1282	through AnyEvent. The benchmark creates a lot of timers (with a zero	1631	through AnyEvent. The benchmark creates a lot of timers (with a zero
1283	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1632	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1284	which it is), lets them fire exactly once and destroys them again.	1633	which it is), lets them fire exactly once and destroys them again.
1285		1634
1286	Source code for this benchmark is found as eg/bench in the AnyEvent	1635	Source code for this benchmark is found as eg/bench in the AnyEvent
1287	distribution.	1636	distribution. It uses the AE interface, which makes a real difference
		1637	for the EV and Perl backends only.
1288		1638
1289	Explanation of the columns	1639	Explanation of the columns
1290	watcher is the number of event watchers created/destroyed. Since	1640	watcher is the number of event watchers created/destroyed. Since
1291	different event models feature vastly different performances, each event	1641	different event models feature vastly different performances, each event
1292	loop was given a number of watchers so that overall runtime is	1642	loop was given a number of watchers so that overall runtime is
…		…
1311	destroy is the time, in microseconds, that it takes to destroy a	1661	destroy is the time, in microseconds, that it takes to destroy a
1312	single watcher.	1662	single watcher.
1313		1663
1314	Results	1664	Results
1315	name watchers bytes create invoke destroy comment	1665	name watchers bytes create invoke destroy comment
1316	EV/EV 400000 224 0.47 0.35 0.27 EV native interface	1666	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1317	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers	1667	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1318	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal	1668	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1319	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation	1669	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1320	Event/Event 16000 517 32.20 31.80 0.81 Event native interface	1670	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1321	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers	1671	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
1322	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll	1672	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
1323	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll	1673	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1324	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour	1674	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1325	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers	1675	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1326	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event	1676	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1327	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select	1677	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1328		1678
1329	Discussion	1679	Discussion
1330	The benchmark does not measure scalability of the event loop very	1680	The benchmark does not measure scalability of the event loop very
1331	well. For example, a select-based event loop (such as the pure perl one)	1681	well. For example, a select-based event loop (such as the pure perl one)
1332	can never compete with an event loop that uses epoll when the number of	1682	can never compete with an event loop that uses epoll when the number of
…		…
1343	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1693	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1344	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1694	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1345	CPU cycles with POE.	1695	CPU cycles with POE.
1346		1696
1347	"EV" is the sole leader regarding speed and memory use, which are both	1697	"EV" is the sole leader regarding speed and memory use, which are both
1348	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1698	maximal/minimal, respectively. When using the AE API there is zero
		1699	overhead (when going through the AnyEvent API create is about 5-6 times
		1700	slower, with other times being equal, so still uses far less memory than
1349	far less memory than any other event loop and is still faster than Event	1701	any other event loop and is still faster than Event natively).
1350	natively.
1351		1702
1352	The pure perl implementation is hit in a few sweet spots (both the	1703	The pure perl implementation is hit in a few sweet spots (both the
1353	constant timeout and the use of a single fd hit optimisations in the	1704	constant timeout and the use of a single fd hit optimisations in the
1354	perl interpreter and the backend itself). Nevertheless this shows that	1705	perl interpreter and the backend itself). Nevertheless this shows that
1355	it adds very little overhead in itself. Like any select-based backend	1706	it adds very little overhead in itself. Like any select-based backend
…		…
1401	when used without AnyEvent), but most event loops have acceptable	1752	when used without AnyEvent), but most event loops have acceptable
1402	performance with or without AnyEvent.	1753	performance with or without AnyEvent.
1403		1754
1404	* The overhead AnyEvent adds is usually much smaller than the overhead	1755	* The overhead AnyEvent adds is usually much smaller than the overhead
1405	of the actual event loop, only with extremely fast event loops such	1756	of the actual event loop, only with extremely fast event loops such
1406	as EV adds AnyEvent significant overhead.	1757	as EV does AnyEvent add significant overhead.
1407		1758
1408	* You should avoid POE like the plague if you want performance or	1759	* You should avoid POE like the plague if you want performance or
1409	reasonable memory usage.	1760	reasonable memory usage.
1410		1761
1411	BENCHMARKING THE LARGE SERVER CASE	1762	BENCHMARKING THE LARGE SERVER CASE
…		…
1425	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1776	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1426	100 (1%) are active. This mirrors the activity of large servers with	1777	100 (1%) are active. This mirrors the activity of large servers with
1427	many connections, most of which are idle at any one point in time.	1778	many connections, most of which are idle at any one point in time.
1428		1779
1429	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1780	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1430	distribution.	1781	distribution. It uses the AE interface, which makes a real difference
		1782	for the EV and Perl backends only.
1431		1783
1432	Explanation of the columns	1784	Explanation of the columns
1433	sockets is the number of sockets, and twice the number of "servers"	1785	sockets is the number of sockets, and twice the number of "servers"
1434	(as each server has a read and write socket end).	1786	(as each server has a read and write socket end).
1435		1787
…		…
1441	forwarding it to another server. This includes deleting the old timeout	1793	forwarding it to another server. This includes deleting the old timeout
1442	and creating a new one that moves the timeout into the future.	1794	and creating a new one that moves the timeout into the future.
1443		1795
1444	Results	1796	Results
1445	name sockets create request	1797	name sockets create request
1446	EV 20000 69.01 11.16	1798	EV 20000 62.66 7.99
1447	Perl 20000 73.32 35.87	1799	Perl 20000 68.32 32.64
1448	IOAsync 20000 157.00 98.14 epoll	1800	IOAsync 20000 174.06 101.15 epoll
1449	IOAsync 20000 159.31 616.06 poll	1801	IOAsync 20000 174.67 610.84 poll
1450	Event 20000 212.62 257.32	1802	Event 20000 202.69 242.91
1451	Glib 20000 651.16 1896.30	1803	Glib 20000 557.01 1689.52
1452	POE 20000 349.67 12317.24 uses POE::Loop::Event	1804	POE 20000 341.54 12086.32 uses POE::Loop::Event
1453		1805
1454	Discussion	1806	Discussion
1455	This benchmark does measure scalability and overall performance of the	1807	This benchmark does measure scalability and overall performance of the
1456	particular event loop.	1808	particular event loop.
1457		1809
…		…
1570	As you can see, the AnyEvent + EV combination even beats the	1922	As you can see, the AnyEvent + EV combination even beats the
1571	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl	1923	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
1572	backend easily beats IO::Lambda and POE.	1924	backend easily beats IO::Lambda and POE.
1573		1925
1574	And even the 100% non-blocking version written using the high-level (and	1926	And even the 100% non-blocking version written using the high-level (and
1575	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a	1927	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
1576	large margin, even though it does all of DNS, tcp-connect and socket I/O	1928	higher level ("unoptimised") abstractions by a large margin, even though
1577	in a non-blocking way.	1929	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
1578		1930
1579	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and	1931	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
1580	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are	1932	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
1581	part of the IO::lambda distribution and were used without any changes.	1933	part of the IO::Lambda distribution and were used without any changes.
1582		1934
1583	SIGNALS	1935	SIGNALS
1584	AnyEvent currently installs handlers for these signals:	1936	AnyEvent currently installs handlers for these signals:
1585		1937
1586	SIGCHLD	1938	SIGCHLD
1587	A handler for "SIGCHLD" is installed by AnyEvent's child watcher	1939	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1588	emulation for event loops that do not support them natively. Also,	1940	emulation for event loops that do not support them natively. Also,
1589	some event loops install a similar handler.	1941	some event loops install a similar handler.
1590		1942
1591	If, when AnyEvent is loaded, SIGCHLD is set to IGNORE, then AnyEvent	1943	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
1592	will reset it to default, to avoid losing child exit statuses.	1944	then AnyEvent will reset it to default, to avoid losing child exit
		1945	statuses.
1593		1946
1594	SIGPIPE	1947	SIGPIPE
1595	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is	1948	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1596	"undef" when AnyEvent gets loaded.	1949	"undef" when AnyEvent gets loaded.
1597		1950
…		…
1605	it is that this way, the handler will be restored to defaults on	1958	it is that this way, the handler will be restored to defaults on
1606	exec.	1959	exec.
1607		1960
1608	Feel free to install your own handler, or reset it to defaults.	1961	Feel free to install your own handler, or reset it to defaults.
1609		1962
		1963	RECOMMENDED/OPTIONAL MODULES
		1964	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1965	its built-in modules) are required to use it.
		1966
		1967	That does not mean that AnyEvent won't take advantage of some additional
		1968	modules if they are installed.
		1969
		1970	This section explains which additional modules will be used, and how
		1971	they affect AnyEvent's operation.
		1972
		1973	Async::Interrupt
		1974	This slightly arcane module is used to implement fast signal
		1975	handling: To my knowledge, there is no way to do completely
		1976	race-free and quick signal handling in pure perl. To ensure that
		1977	signals still get delivered, AnyEvent will start an interval timer
		1978	to wake up perl (and catch the signals) with some delay (default is
		1979	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1980
		1981	If this module is available, then it will be used to implement
		1982	signal catching, which means that signals will not be delayed, and
		1983	the event loop will not be interrupted regularly, which is more
		1984	efficient (and good for battery life on laptops).
		1985
		1986	This affects not just the pure-perl event loop, but also other event
		1987	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1988
		1989	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1990	natively, and either employ their own workarounds (POE) or use
		1991	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1992	Installing Async::Interrupt does nothing for those backends.
		1993
		1994	EV This module isn't really "optional", as it is simply one of the
		1995	backend event loops that AnyEvent can use. However, it is simply the
		1996	best event loop available in terms of features, speed and stability:
		1997	It supports the AnyEvent API optimally, implements all the watcher
		1998	types in XS, does automatic timer adjustments even when no monotonic
		1999	clock is available, can take avdantage of advanced kernel interfaces
		2000	such as "epoll" and "kqueue", and is the fastest backend by far.
		2001	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		2002	Glib::EV).
		2003
		2004	If you only use backends that rely on another event loop (e.g.
		2005	"Tk"), then this module will do nothing for you.
		2006
		2007	Guard
		2008	The guard module, when used, will be used to implement
		2009	"AnyEvent::Util::guard". This speeds up guards considerably (and
		2010	uses a lot less memory), but otherwise doesn't affect guard
		2011	operation much. It is purely used for performance.
		2012
		2013	JSON and JSON::XS
		2014	One of these modules is required when you want to read or write JSON
		2015	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		2016	can take advantage of the ultra-high-speed JSON::XS module when it
		2017	is installed.
		2018
		2019	Net::SSLeay
		2020	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2021	worthwhile: If this module is installed, then AnyEvent::Handle (with
		2022	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		2023
		2024	Time::HiRes
		2025	This module is part of perl since release 5.008. It will be used
		2026	when the chosen event library does not come with a timing source of
		2027	its own. The pure-perl event loop (AnyEvent::Loop) will additionally
		2028	load it to try to use a monotonic clock for timing stability.
		2029
		2030	AnyEvent::AIO (and IO::AIO)
		2031	The default implementation of AnyEvent::IO is to do I/O
		2032	synchronously, stopping programs while they access the disk, which
		2033	is fine for a lot of programs.
		2034
		2035	Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
		2036	switch to a true asynchronous implementation, so event processing
		2037	can continue even while waiting for disk I/O.
		2038
1610	FORK	2039	FORK
1611	Most event libraries are not fork-safe. The ones who are usually are	2040	Most event libraries are not fork-safe. The ones who are usually are
1612	because they rely on inefficient but fork-safe "select" or "poll" calls.	2041	because they rely on inefficient but fork-safe "select" or "poll" calls
1613	Only EV is fully fork-aware.	2042	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		2043	epoll are usually badly thought-out hacks that are incompatible with
		2044	fork in one way or another. Only EV is fully fork-aware and ensures that
		2045	you continue event-processing in both parent and child (or both, if you
		2046	know what you are doing).
		2047
		2048	This means that, in general, you cannot fork and do event processing in
		2049	the child if the event library was initialised before the fork (which
		2050	usually happens when the first AnyEvent watcher is created, or the
		2051	library is loaded).
1614		2052
1615	If you have to fork, you must either do so before creating your first	2053	If you have to fork, you must either do so before creating your first
1616	watcher OR you must not use AnyEvent at all in the child.	2054	watcher OR you must not use AnyEvent at all in the child OR you must do
		2055	something completely out of the scope of AnyEvent (see below).
		2056
		2057	The problem of doing event processing in the parent and the child is
		2058	much more complicated: even for backends that are fork-aware or
		2059	fork-safe, their behaviour is not usually what you want: fork clones all
		2060	watchers, that means all timers, I/O watchers etc. are active in both
		2061	parent and child, which is almost never what you want. Using "exec" to
		2062	start worker children from some kind of manage prrocess is usually
		2063	preferred, because it is much easier and cleaner, at the expense of
		2064	having to have another binary.
		2065
		2066	In addition to logical problems with fork, there are also implementation
		2067	problems. For example, on POSIX systems, you cannot fork at all in Perl
		2068	code if a thread (I am talking of pthreads here) was ever created in the
		2069	process, and this is just the tip of the iceberg. In general, using fork
		2070	from Perl is difficult, and attempting to use fork without an exec to
		2071	implement some kind of parallel processing is almost certainly doomed.
		2072
		2073	To safely fork and exec, you should use a module such as Proc::FastSpawn
		2074	that let's you safely fork and exec new processes.
		2075
		2076	If you want to do multiprocessing using processes, you can look at the
		2077	AnyEvent::Fork module (and some related modules such as
		2078	AnyEvent::Fork::RPC, AnyEvent::Fork::Pool and AnyEvent::Fork::Remote).
		2079	This module allows you to safely create subprocesses without any
		2080	limitations - you can use X11 toolkits or AnyEvent in the children
		2081	created by AnyEvent::Fork safely and without any special precautions.
1617		2082
1618	SECURITY CONSIDERATIONS	2083	SECURITY CONSIDERATIONS
1619	AnyEvent can be forced to load any event model via	2084	AnyEvent can be forced to load any event model via
1620	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	2085	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1621	to execute arbitrary code or directly gain access, it can easily be used	2086	to execute arbitrary code or directly gain access, it can easily be used
…		…
1645	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	2110	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1646	annoying memleaks, such as leaking on "map" and "grep" but it is usually	2111	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1647	not as pronounced).	2112	not as pronounced).
1648		2113
1649	SEE ALSO	2114	SEE ALSO
1650	Utility functions: AnyEvent::Util.	2115	Tutorial/Introduction: AnyEvent::Intro.
1651		2116
1652	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	2117	FAQ: AnyEvent::FAQ.
1653	Event::Lib, Qt, POE.	2118
		2119	Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
		2120	(simply logging).
		2121
		2122	Development/Debugging: AnyEvent::Strict (stricter checking),
		2123	AnyEvent::Debug (interactive shell, watcher tracing).
		2124
		2125	Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
		2126	Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK.
1654		2127
1655	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	2128	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1656	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	2129	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1657	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,	2130	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
1658	AnyEvent::Impl::IOAsync.	2131	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi, AnyEvent::Impl::FLTK.
1659		2132
1660	Non-blocking file handles, sockets, TCP clients and servers:	2133	Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1661	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.	2134	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1662		2135
		2136	Asynchronous File I/O: AnyEvent::IO.
		2137
1663	Asynchronous DNS: AnyEvent::DNS.	2138	Asynchronous DNS: AnyEvent::DNS.
1664		2139
1665	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	2140	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1666		2141
1667	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,	2142	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
1668	AnyEvent::HTTP.	2143	AnyEvent::HTTP.
1669		2144
1670	AUTHOR	2145	AUTHOR
1671	Marc Lehmann <schmorp@schmorp.de>	2146	Marc Lehmann <schmorp@schmorp.de>
1672	http://home.schmorp.de/	2147	http://anyevent.schmorp.de
1673		2148

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Revision 1.73 by root, Fri Sep 5 22:24:12 2014 UTC