[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.38 by root, Sun Apr 26 18:12:53 2009 UTC vs.
Revision 1.72 by root, Tue Dec 17 16:43:15 2013 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, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	loops	5	Qt, FLTK and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# if you prefer function calls, look at the AE manpage for
		11	# an alternative API.
		12
10	# file descriptor readable	13	# file handle or descriptor readable
11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });	14	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12		15
13	# one-shot or repeating timers	16	# one-shot or repeating timers
14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });	17	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...	18	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
16		19
17	print AnyEvent->now; # prints current event loop time	20	print AnyEvent->now; # prints current event loop time
18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.	21	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
19		22
20	# POSIX signal	23	# POSIX signal
37		40
38	INTRODUCTION/TUTORIAL	41	INTRODUCTION/TUTORIAL
39	This manpage is mainly a reference manual. If you are interested in a	42	This manpage is mainly a reference manual. If you are interested in a
40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	43	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
41	manpage.	44	manpage.
		45
		46	SUPPORT
		47	An FAQ document is available as AnyEvent::FAQ.
		48
		49	There also is a mailinglist for discussing all things AnyEvent, and an
		50	IRC channel, too.
		51
		52	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		53	Repository, at <http://anyevent.schmorp.de>, for more info.
42		54
43	WHY YOU SHOULD USE THIS MODULE (OR NOT)	55	WHY YOU SHOULD USE THIS MODULE (OR NOT)
44	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	56	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
45	nowadays. So what is different about AnyEvent?	57	nowadays. So what is different about AnyEvent?
46		58
…		…
61	module users into the same thing by forcing them to use the same event	73	module users into the same thing by forcing them to use the same event
62	model you use.	74	model you use.
63		75
64	For modules like POE or IO::Async (which is a total misnomer as it is	76	For modules like POE or IO::Async (which is a total misnomer as it is
65	actually doing all I/O synchronously...), using them in your module is	77	actually doing all I/O synchronously...), using them in your module is
66	like joining a cult: After you joined, you are dependent on them and you	78	like joining a cult: After you join, you are dependent on them and you
67	cannot use anything else, as they are simply incompatible to everything	79	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	80	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.	81	are also forced to use the same event loop you use.
70		82
71	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	83	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
72	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	84	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
73	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your	85	with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
74	module uses one of those, every user of your module has to use it, too.	86	uses one of those, every user of your module has to use it, too. But if
75	But if your module uses AnyEvent, it works transparently with all event	87	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	88	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	89	the supported event loops. It is easy to add new event loops to
78	to AnyEvent, too, so it is future-proof).	90	AnyEvent, too, so it is future-proof).
79		91
80	In addition to being free of having to use *the one and only true event	92	In addition to being free of having to use *the one and only true event
81	model*, AnyEvent also is free of bloat and policy: with POE or similar	93	model*, AnyEvent also is free of bloat and policy: with POE or similar
82	modules, you get an enormous amount of code and strict rules you have to	94	modules, you get an enormous amount of code and strict rules you have to
83	follow. AnyEvent, on the other hand, is lean and up to the point, by	95	follow. AnyEvent, on the other hand, is lean and to the point, by only
84	only offering the functionality that is necessary, in as thin as a	96	offering the functionality that is necessary, in as thin as a wrapper as
85	wrapper as technically possible.	97	technically possible.
86		98
87	Of course, AnyEvent comes with a big (and fully optional!) toolbox of	99	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
88	useful functionality, such as an asynchronous DNS resolver, 100%	100	useful functionality, such as an asynchronous DNS resolver, 100%
89	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms	101	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
90	such as Windows) and lots of real-world knowledge and workarounds for	102	such as Windows) and lots of real-world knowledge and workarounds for
…		…
93	Now, if you do want lots of policy (this can arguably be somewhat	105	Now, if you do want lots of policy (this can arguably be somewhat
94	useful) and you want to force your users to use the one and only event	106	useful) and you want to force your users to use the one and only event
95	model, you should not use this module.	107	model, you should not use this module.
96		108
97	DESCRIPTION	109	DESCRIPTION
98	AnyEvent provides an identical interface to multiple event loops. This	110	AnyEvent provides a uniform interface to various event loops. This
99	allows module authors to utilise an event loop without forcing module	111	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	112	module users to use a specific event loop implementation (since more
101	coexist peacefully at any one time).	113	than one event loop cannot coexist peacefully).
102		114
103	The interface itself is vaguely similar, but not identical to the Event	115	The interface itself is vaguely similar, but not identical to the Event
104	module.	116	module.
105		117
106	During the first call of any watcher-creation method, the module tries	118	During the first call of any watcher-creation method, the module tries
107	to detect the currently loaded event loop by probing whether one of the	119	to detect the currently loaded event loop by probing whether one of the
108	following modules is already loaded: EV, Event, Glib,	120	following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
109	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is	121	Tk, Event::Lib, Qt, POE. The first one found is used. If none are
110	used. If none are found, the module tries to load these modules	122	detected, the module tries to load the first four modules in the order
111	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	123	given; but note that if EV is not available, the pure-perl
112	always succeed) in the order given. The first one that can be	124	AnyEvent::Loop should always work, so the other two are not normally
113	successfully loaded will be used. If, after this, still none could be	125	tried.
114	found, AnyEvent will fall back to a pure-perl event loop, which is not
115	very efficient, but should work everywhere.
116		126
117	Because AnyEvent first checks for modules that are already loaded,	127	Because AnyEvent first checks for modules that are already loaded,
118	loading an event model explicitly before first using AnyEvent will	128	loading an event model explicitly before first using AnyEvent will
119	likely make that model the default. For example:	129	likely make that model the default. For example:
120		130
…		…
122	use AnyEvent;	132	use AnyEvent;
123		133
124	# .. AnyEvent will likely default to Tk	134	# .. AnyEvent will likely default to Tk
125		135
126	The likely means that, if any module loads another event model and	136	The likely means that, if any module loads another event model and
127	starts using it, all bets are off. Maybe you should tell their authors	137	starts using it, all bets are off - this case should be very rare
128	to use AnyEvent so their modules work together with others seamlessly...	138	though, as very few modules hardcode event loops without announcing this
		139	very loudly.
129		140
130	The pure-perl implementation of AnyEvent is called	141	The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
131	"AnyEvent::Impl::Perl". Like other event modules you can load it	142	Like other event modules you can load it explicitly and enjoy the high
132	explicitly and enjoy the high availability of that event loop :)	143	availability of that event loop :)
133		144
134	WATCHERS	145	WATCHERS
135	AnyEvent has the central concept of a watcher, which is an object that	146	AnyEvent has the central concept of a watcher, which is an object that
136	stores relevant data for each kind of event you are waiting for, such as	147	stores relevant data for each kind of event you are waiting for, such as
137	the callback to call, the file handle to watch, etc.	148	the callback to call, the file handle to watch, etc.
…		…
141	callback when the event occurs (of course, only when the event model is	152	callback when the event occurs (of course, only when the event model is
142	in control).	153	in control).
143		154
144	Note that callbacks must not permanently change global variables	155	Note that callbacks must not permanently change global variables
145	potentially in use by the event loop (such as $_ or $[) and that	156	potentially in use by the event loop (such as $_ or $[) and that
146	callbacks must not "die". The former is good programming practise in	157	callbacks must not "die". The former is good programming practice in
147	Perl and the latter stems from the fact that exception handling differs	158	Perl and the latter stems from the fact that exception handling differs
148	widely between event loops.	159	widely between event loops.
149		160
150	To disable the watcher you have to destroy it (e.g. by setting the	161	To disable a watcher you have to destroy it (e.g. by setting the
151	variable you store it in to "undef" or otherwise deleting all references	162	variable you store it in to "undef" or otherwise deleting all references
152	to it).	163	to it).
153		164
154	All watchers are created by calling a method on the "AnyEvent" class.	165	All watchers are created by calling a method on the "AnyEvent" class.
155		166
156	Many watchers either are used with "recursion" (repeating timers for	167	Many watchers either are used with "recursion" (repeating timers for
157	example), or need to refer to their watcher object in other ways.	168	example), or need to refer to their watcher object in other ways.
158		169
159	An any way to achieve that is this pattern:	170	One way to achieve that is this pattern:
160		171
161	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	172	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
162	# you can use $w here, for example to undef it	173	# you can use $w here, for example to undef it
163	undef $w;	174	undef $w;
164	});	175	});
…		…
166	Note that "my $w; $w =" combination. This is necessary because in Perl,	177	Note that "my $w; $w =" combination. This is necessary because in Perl,
167	my variables are only visible after the statement in which they are	178	my variables are only visible after the statement in which they are
168	declared.	179	declared.
169		180
170	I/O WATCHERS	181	I/O WATCHERS
		182	$w = AnyEvent->io (
		183	fh => <filehandle_or_fileno>,
		184	poll => <"r" or "w">,
		185	cb => <callback>,
		186	);
		187
171	You can create an I/O watcher by calling the "AnyEvent->io" method with	188	You can create an I/O watcher by calling the "AnyEvent->io" method with
172	the following mandatory key-value pairs as arguments:	189	the following mandatory key-value pairs as arguments:
173		190
174	"fh" is the Perl file handle (not file descriptor) to watch for	191	"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	192	events (AnyEvent might or might not keep a reference to this file
176	handle). Note that only file handles pointing to things for which	193	handle). Note that only file handles pointing to things for which
177	non-blocking operation makes sense are allowed. This includes sockets,	194	non-blocking operation makes sense are allowed. This includes sockets,
178	most character devices, pipes, fifos and so on, but not for example	195	most character devices, pipes, fifos and so on, but not for example
179	files or block devices.	196	files or block devices.
…		…
189		206
190	The I/O watcher might use the underlying file descriptor or a copy of	207	The I/O watcher might use the underlying file descriptor or a copy of
191	it. You must not close a file handle as long as any watcher is active on	208	it. You must not close a file handle as long as any watcher is active on
192	the underlying file descriptor.	209	the underlying file descriptor.
193		210
194	Some event loops issue spurious readyness notifications, so you should	211	Some event loops issue spurious readiness notifications, so you should
195	always use non-blocking calls when reading/writing from/to your file	212	always use non-blocking calls when reading/writing from/to your file
196	handles.	213	handles.
197		214
198	Example: wait for readability of STDIN, then read a line and disable the	215	Example: wait for readability of STDIN, then read a line and disable the
199	watcher.	216	watcher.
…		…
203	warn "read: $input\n";	220	warn "read: $input\n";
204	undef $w;	221	undef $w;
205	});	222	});
206		223
207	TIME WATCHERS	224	TIME WATCHERS
		225	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		226
		227	$w = AnyEvent->timer (
		228	after => <fractional_seconds>,
		229	interval => <fractional_seconds>,
		230	cb => <callback>,
		231	);
		232
208	You can create a time watcher by calling the "AnyEvent->timer" method	233	You can create a time watcher by calling the "AnyEvent->timer" method
209	with the following mandatory arguments:	234	with the following mandatory arguments:
210		235
211	"after" specifies after how many seconds (fractional values are	236	"after" specifies after how many seconds (fractional values are
212	supported) the callback should be invoked. "cb" is the callback to	237	supported) the callback should be invoked. "cb" is the callback to
…		…
214		239
215	Although the callback might get passed parameters, their value and	240	Although the callback might get passed parameters, their value and
216	presence is undefined and you cannot rely on them. Portable AnyEvent	241	presence is undefined and you cannot rely on them. Portable AnyEvent
217	callbacks cannot use arguments passed to time watcher callbacks.	242	callbacks cannot use arguments passed to time watcher callbacks.
218		243
219	The callback will normally be invoked once only. If you specify another	244	The callback will normally be invoked only once. If you specify another
220	parameter, "interval", as a strictly positive number (> 0), then the	245	parameter, "interval", as a strictly positive number (> 0), then the
221	callback will be invoked regularly at that interval (in fractional	246	callback will be invoked regularly at that interval (in fractional
222	seconds) after the first invocation. If "interval" is specified with a	247	seconds) after the first invocation. If "interval" is specified with a
223	false value, then it is treated as if it were missing.	248	false value, then it is treated as if it were not specified at all.
224		249
225	The callback will be rescheduled before invoking the callback, but no	250	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	251	attempt is made to avoid timer drift in most backends, so the interval
227	is only approximate.	252	is only approximate.
228		253
229	Example: fire an event after 7.7 seconds.	254	Example: fire an event after 7.7 seconds.
230		255
231	my $w = AnyEvent->timer (after => 7.7, cb => sub {	256	my $w = AnyEvent->timer (after => 7.7, cb => sub {
…		…
237		262
238	Example 2: fire an event after 0.5 seconds, then roughly every second.	263	Example 2: fire an event after 0.5 seconds, then roughly every second.
239		264
240	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {	265	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
241	warn "timeout\n";	266	warn "timeout\n";
242	};	267	});
243		268
244	TIMING ISSUES	269	TIMING ISSUES
245	There are two ways to handle timers: based on real time (relative, "fire	270	There are two ways to handle timers: based on real time (relative, "fire
246	in 10 seconds") and based on wallclock time (absolute, "fire at 12	271	in 10 seconds") and based on wallclock time (absolute, "fire at 12
247	o'clock").	272	o'clock").
248		273
249	While most event loops expect timers to specified in a relative way,	274	While most event loops expect timers to specified in a relative way,
250	they use absolute time internally. This makes a difference when your	275	they use absolute time internally. This makes a difference when your
251	clock "jumps", for example, when ntp decides to set your clock backwards	276	clock "jumps", for example, when ntp decides to set your clock backwards
252	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is	277	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
253	supposed to fire "after" a second might actually take six years to	278	supposed to fire "after a second" might actually take six years to
254	finally fire.	279	finally fire.
255		280
256	AnyEvent cannot compensate for this. The only event loop that is	281	AnyEvent cannot compensate for this. The only event loop that is
257	conscious about these issues is EV, which offers both relative	282	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	283	based on true relative time) and absolute (ev_periodic, based on
259	on wallclock time) timers.	284	wallclock time) timers.
260		285
261	AnyEvent always prefers relative timers, if available, matching the	286	AnyEvent always prefers relative timers, if available, matching the
262	AnyEvent API.	287	AnyEvent API.
263		288
264	AnyEvent has two additional methods that return the "current time":	289	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	308	*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.*	309	function to call when you want to know the current time.*
285		310
286	This function is also often faster then "AnyEvent->time", and thus	311	This function is also often faster then "AnyEvent->time", and thus
287	the preferred method if you want some timestamp (for example,	312	the preferred method if you want some timestamp (for example,
288	AnyEvent::Handle uses this to update it's activity timeouts).	313	AnyEvent::Handle uses this to update its activity timeouts).
289		314
290	The rest of this section is only of relevance if you try to be very	315	The rest of this section is only of relevance if you try to be very
291	exact with your timing, you can skip it without bad conscience.	316	exact with your timing; you can skip it without a bad conscience.
292		317
293	For a practical example of when these times differ, consider	318	For a practical example of when these times differ, consider
294	Event::Lib and EV and the following set-up:	319	Event::Lib and EV and the following set-up:
295		320
296	The event loop is running and has just invoked one of your callback	321	The event loop is running and has just invoked one of your callbacks
297	at time=500 (assume no other callbacks delay processing). In your	322	at time=500 (assume no other callbacks delay processing). In your
298	callback, you wait a second by executing "sleep 1" (blocking the	323	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	324	process for a second) and then (at time=501) you create a relative
300	timer that fires after three seconds.	325	timer that fires after three seconds.
301		326
…		…
322	can get whatever behaviour you want with any event loop, by taking	347	can get whatever behaviour you want with any event loop, by taking
323	the difference between "AnyEvent->time" and "AnyEvent->now" into	348	the difference between "AnyEvent->time" and "AnyEvent->now" into
324	account.	349	account.
325		350
326	AnyEvent->now_update	351	AnyEvent->now_update
327	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the	352	Some event loops (such as EV or AnyEvent::Loop) cache the current
328	current time for each loop iteration (see the discussion of	353	time for each loop iteration (see the discussion of AnyEvent->now,
329	AnyEvent->now, above).	354	above).
330		355
331	When a callback runs for a long time (or when the process sleeps),	356	When a callback runs for a long time (or when the process sleeps),
332	then this "current" time will differ substantially from the real	357	then this "current" time will differ substantially from the real
333	time, which might affect timers and time-outs.	358	time, which might affect timers and time-outs.
334		359
335	When this is the case, you can call this method, which will update	360	When this is the case, you can call this method, which will update
336	the event loop's idea of "current time".	361	the event loop's idea of "current time".
337		362
		363	A typical example would be a script in a web server (e.g.
		364	"mod_perl") - when mod_perl executes the script, then the event loop
		365	will have the wrong idea about the "current time" (being potentially
		366	far in the past, when the script ran the last time). In that case
		367	you should arrange a call to "AnyEvent->now_update" each time the
		368	web server process wakes up again (e.g. at the start of your script,
		369	or in a handler).
		370
338	Note that updating the time might cause some events to be handled.	371	Note that updating the time might cause some events to be handled.
339		372
340	SIGNAL WATCHERS	373	SIGNAL WATCHERS
		374	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		375
341	You can watch for signals using a signal watcher, "signal" is the signal	376	You can watch for signals using a signal watcher, "signal" is the signal
342	name in uppercase and without any "SIG" prefix, "cb" is the Perl	377	name in uppercase and without any "SIG" prefix, "cb" is the Perl
343	callback to be invoked whenever a signal occurs.	378	callback to be invoked whenever a signal occurs.
344		379
345	Although the callback might get passed parameters, their value and	380	Although the callback might get passed parameters, their value and
…		…
350	invocation, and callback invocation will be synchronous. Synchronous	385	invocation, and callback invocation will be synchronous. Synchronous
351	means that it might take a while until the signal gets handled by the	386	means that it might take a while until the signal gets handled by the
352	process, but it is guaranteed not to interrupt any other callbacks.	387	process, but it is guaranteed not to interrupt any other callbacks.
353		388
354	The main advantage of using these watchers is that you can share a	389	The main advantage of using these watchers is that you can share a
355	signal between multiple watchers.	390	signal between multiple watchers, and AnyEvent will ensure that signals
		391	will not interrupt your program at bad times.
356		392
357	This watcher might use %SIG, so programs overwriting those signals	393	This watcher might use %SIG (depending on the event loop used), so
358	directly will likely not work correctly.	394	programs overwriting those signals directly will likely not work
		395	correctly.
359		396
360	Example: exit on SIGINT	397	Example: exit on SIGINT
361		398
362	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	399	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
363		400
		401	Restart Behaviour
		402	While restart behaviour is up to the event loop implementation, most
		403	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		404	pure perl implementation).
		405
		406	Safe/Unsafe Signals
		407	Perl signals can be either "safe" (synchronous to opcode handling) or
		408	"unsafe" (asynchronous) - the former might delay signal delivery
		409	indefinitely, the latter might corrupt your memory.
		410
		411	AnyEvent signal handlers are, in addition, synchronous to the event
		412	loop, i.e. they will not interrupt your running perl program but will
		413	only be called as part of the normal event handling (just like timer,
		414	I/O etc. callbacks, too).
		415
		416	Signal Races, Delays and Workarounds
		417	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		418	callbacks to signals in a generic way, which is a pity, as you cannot do
		419	race-free signal handling in perl, requiring C libraries for this.
		420	AnyEvent will try to do its best, which means in some cases, signals
		421	will be delayed. The maximum time a signal might be delayed is 10
		422	seconds by default, but can be overriden via
		423	$ENV{PERL_ANYEVENT_MAX_SIGNAL_LATENCY} or $AnyEvent::MAX_SIGNAL_LATENCY
		424	- see the "ENVIRONMENT VARIABLES" section for details.
		425
		426	All these problems can be avoided by installing the optional
		427	Async::Interrupt module, which works with most event loops. It will not
		428	work with inherently broken event loops such as Event or Event::Lib (and
		429	not with POE currently). For those, you just have to suffer the delays.
		430
364	CHILD PROCESS WATCHERS	431	CHILD PROCESS WATCHERS
		432	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		433
365	You can also watch on a child process exit and catch its exit status.	434	You can also watch for a child process exit and catch its exit status.
366		435
367	The child process is specified by the "pid" argument (if set to 0, it	436	The child process is specified by the "pid" argument (on some backends,
368	watches for any child process exit). The watcher will triggered only	437	using 0 watches for any child process exit, on others this will croak).
369	when the child process has finished and an exit status is available, not	438	The watcher will be triggered only when the child process has finished
370	on any trace events (stopped/continued).	439	and an exit status is available, not on any trace events
		440	(stopped/continued).
371		441
372	The callback will be called with the pid and exit status (as returned by	442	The callback will be called with the pid and exit status (as returned by
373	waitpid), so unlike other watcher types, you can rely on child watcher	443	waitpid), so unlike other watcher types, you can rely on child watcher
374	callback arguments.	444	callback arguments.
375		445
…		…
380		450
381	There is a slight catch to child watchers, however: you usually start	451	There is a slight catch to child watchers, however: you usually start
382	them after the child process was created, and this means the process	452	them after the child process was created, and this means the process
383	could have exited already (and no SIGCHLD will be sent anymore).	453	could have exited already (and no SIGCHLD will be sent anymore).
384		454
385	Not all event models handle this correctly (POE doesn't), but even for	455	Not all event models handle this correctly (neither POE nor IO::Async
		456	do, see their AnyEvent::Impl manpages for details), but even for event
386	event models that do handle this correctly, they usually need to be	457	models that do handle this correctly, they usually need to be loaded
387	loaded before the process exits (i.e. before you fork in the first	458	before the process exits (i.e. before you fork in the first place).
388	place).	459	AnyEvent's pure perl event loop handles all cases correctly regardless
		460	of when you start the watcher.
389		461
390	This means you cannot create a child watcher as the very first thing in	462	This means you cannot create a child watcher as the very first thing in
391	an AnyEvent program, you have to create at least one watcher before	463	an AnyEvent program, you have to create at least one watcher before
392	you "fork" the child (alternatively, you can call "AnyEvent::detect").	464	you "fork" the child (alternatively, you can call "AnyEvent::detect").
393		465
		466	As most event loops do not support waiting for child events, they will
		467	be emulated by AnyEvent in most cases, in which case the latency and
		468	race problems mentioned in the description of signal watchers apply.
		469
394	Example: fork a process and wait for it	470	Example: fork a process and wait for it
395		471
396	my $done = AnyEvent->condvar;	472	my $done = AnyEvent->condvar;
397		473
		474	# this forks and immediately calls exit in the child. this
		475	# normally has all sorts of bad consequences for your parent,
		476	# so take this as an example only. always fork and exec,
		477	# or call POSIX::_exit, in real code.
398	my $pid = fork or exit 5;	478	my $pid = fork or exit 5;
399		479
400	my $w = AnyEvent->child (	480	my $w = AnyEvent->child (
401	pid => $pid,	481	pid => $pid,
402	cb => sub {	482	cb => sub {
403	my ($pid, $status) = @_;	483	my ($pid, $status) = @_;
404	warn "pid $pid exited with status $status";	484	warn "pid $pid exited with status $status";
405	$done->send;	485	$done->send;
406	},	486	},
407	);	487	);
408		488
409	# do something else, then wait for process exit	489	# do something else, then wait for process exit
410	$done->recv;	490	$done->recv;
411		491
412	IDLE WATCHERS	492	IDLE WATCHERS
413	Sometimes there is a need to do something, but it is not so important to	493	$w = AnyEvent->idle (cb => <callback>);
414	do it instantly, but only when there is nothing better to do. This
415	"nothing better to do" is usually defined to be "no other events need
416	attention by the event loop".
417		494
418	Idle watchers ideally get invoked when the event loop has nothing better	495	This will repeatedly invoke the callback after the process becomes idle,
419	to do, just before it would block the process to wait for new events.	496	until either the watcher is destroyed or new events have been detected.
420	Instead of blocking, the idle watcher is invoked.
421		497
422	Most event loops unfortunately do not really support idle watchers (only	498	Idle watchers are useful when there is a need to do something, but it is
		499	not so important (or wise) to do it instantly. The callback will be
		500	invoked only when there is "nothing better to do", which is usually
		501	defined as "all outstanding events have been handled and no new events
		502	have been detected". That means that idle watchers ideally get invoked
		503	when the event loop has just polled for new events but none have been
		504	detected. Instead of blocking to wait for more events, the idle watchers
		505	will be invoked.
		506
		507	Unfortunately, most event loops do not really support idle watchers
423	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent	508	(only EV, Event and Glib do it in a usable fashion) - for the rest,
424	will simply call the callback "from time to time".	509	AnyEvent will simply call the callback "from time to time".
425		510
426	Example: read lines from STDIN, but only process them when the program	511	Example: read lines from STDIN, but only process them when the program
427	is otherwise idle:	512	is otherwise idle:
428		513
429	my @lines; # read data	514	my @lines; # read data
…		…
442	}	527	}
443	});	528	});
444	});	529	});
445		530
446	CONDITION VARIABLES	531	CONDITION VARIABLES
		532	$cv = AnyEvent->condvar;
		533
		534	$cv->send (<list>);
		535	my @res = $cv->recv;
		536
447	If you are familiar with some event loops you will know that all of them	537	If you are familiar with some event loops you will know that all of them
448	require you to run some blocking "loop", "run" or similar function that	538	require you to run some blocking "loop", "run" or similar function that
449	will actively watch for new events and call your callbacks.	539	will actively watch for new events and call your callbacks.
450		540
451	AnyEvent is different, it expects somebody else to run the event loop	541	AnyEvent is slightly different: it expects somebody else to run the
452	and will only block when necessary (usually when told by the user).	542	event loop and will only block when necessary (usually when told by the
		543	user).
453		544
454	The instrument to do that is called a "condition variable", so called	545	The tool to do that is called a "condition variable", so called because
455	because they represent a condition that must become true.	546	they represent a condition that must become true.
		547
		548	Now is probably a good time to look at the examples further below.
456		549
457	Condition variables can be created by calling the "AnyEvent->condvar"	550	Condition variables can be created by calling the "AnyEvent->condvar"
458	method, usually without arguments. The only argument pair allowed is	551	method, usually without arguments. The only argument pair allowed is
459
460	"cb", which specifies a callback to be called when the condition	552	"cb", which specifies a callback to be called when the condition
461	variable becomes true, with the condition variable as the first argument	553	variable becomes true, with the condition variable as the first argument
462	(but not the results).	554	(but not the results).
463		555
464	After creation, the condition variable is "false" until it becomes	556	After creation, the condition variable is "false" until it becomes
465	"true" by calling the "send" method (or calling the condition variable	557	"true" by calling the "send" method (or calling the condition variable
466	as if it were a callback, read about the caveats in the description for	558	as if it were a callback, read about the caveats in the description for
467	the "->send" method).	559	the "->send" method).
468		560
469	Condition variables are similar to callbacks, except that you can	561	Since condition variables are the most complex part of the AnyEvent API,
470	optionally wait for them. They can also be called merge points - points	562	here are some different mental models of what they are - pick the ones
471	in time where multiple outstanding events have been processed. And yet	563	you can connect to:
472	another way to call them is transactions - each condition variable can	564
473	be used to represent a transaction, which finishes at some point and	565	* Condition variables are like callbacks - you can call them (and pass
474	delivers a result.	566	them instead of callbacks). Unlike callbacks however, you can also
		567	wait for them to be called.
		568
		569	* Condition variables are signals - one side can emit or send them,
		570	the other side can wait for them, or install a handler that is
		571	called when the signal fires.
		572
		573	* Condition variables are like "Merge Points" - points in your program
		574	where you merge multiple independent results/control flows into one.
		575
		576	* Condition variables represent a transaction - functions that start
		577	some kind of transaction can return them, leaving the caller the
		578	choice between waiting in a blocking fashion, or setting a callback.
		579
		580	* Condition variables represent future values, or promises to deliver
		581	some result, long before the result is available.
475		582
476	Condition variables are very useful to signal that something has	583	Condition variables are very useful to signal that something has
477	finished, for example, if you write a module that does asynchronous http	584	finished, for example, if you write a module that does asynchronous http
478	requests, then a condition variable would be the ideal candidate to	585	requests, then a condition variable would be the ideal candidate to
479	signal the availability of results. The user can either act when the	586	signal the availability of results. The user can either act when the
…		…
492		599
493	Condition variables are represented by hash refs in perl, and the keys	600	Condition variables are represented by hash refs in perl, and the keys
494	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy	601	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
495	(it is often useful to build your own transaction class on top of	602	(it is often useful to build your own transaction class on top of
496	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call	603	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
497	it's "new" method in your own "new" method.	604	its "new" method in your own "new" method.
498		605
499	There are two "sides" to a condition variable - the "producer side"	606	There are two "sides" to a condition variable - the "producer side"
500	which eventually calls "-> send", and the "consumer side", which waits	607	which eventually calls "-> send", and the "consumer side", which waits
501	for the send to occur.	608	for the send to occur.
502		609
503	Example: wait for a timer.	610	Example: wait for a timer.
504		611
505	# wait till the result is ready	612	# condition: "wait till the timer is fired"
506	my $result_ready = AnyEvent->condvar;	613	my $timer_fired = AnyEvent->condvar;
507		614
508	# do something such as adding a timer	615	# create the timer - we could wait for, say
509	# or socket watcher the calls $result_ready->send	616	# a handle becomign ready, or even an
510	# when the "result" is ready.	617	# AnyEvent::HTTP request to finish, but
511	# in this case, we simply use a timer:	618	# in this case, we simply use a timer:
512	my $w = AnyEvent->timer (	619	my $w = AnyEvent->timer (
513	after => 1,	620	after => 1,
514	cb => sub { $result_ready->send },	621	cb => sub { $timer_fired->send },
515	);	622	);
516		623
517	# this "blocks" (while handling events) till the callback	624	# this "blocks" (while handling events) till the callback
518	# calls send	625	# calls ->send
519	$result_ready->recv;	626	$timer_fired->recv;
520		627
521	Example: wait for a timer, but take advantage of the fact that condition	628	Example: wait for a timer, but take advantage of the fact that condition
522	variables are also code references.	629	variables are also callable directly.
523		630
524	my $done = AnyEvent->condvar;	631	my $done = AnyEvent->condvar;
525	my $delay = AnyEvent->timer (after => 5, cb => $done);	632	my $delay = AnyEvent->timer (after => 5, cb => $done);
526	$done->recv;	633	$done->recv;
527		634
…		…
533		640
534	...	641	...
535		642
536	my @info = $couchdb->info->recv;	643	my @info = $couchdb->info->recv;
537		644
538	And this is how you would just ste a callback to be called whenever the	645	And this is how you would just set a callback to be called whenever the
539	results are available:	646	results are available:
540		647
541	$couchdb->info->cb (sub {	648	$couchdb->info->cb (sub {
542	my @info = $_[0]->recv;	649	my @info = $_[0]->recv;
543	});	650	});
…		…
558		665
559	Any arguments passed to the "send" call will be returned by all	666	Any arguments passed to the "send" call will be returned by all
560	future "->recv" calls.	667	future "->recv" calls.
561		668
562	Condition variables are overloaded so one can call them directly (as	669	Condition variables are overloaded so one can call them directly (as
563	a code reference). Calling them directly is the same as calling	670	if they were a code reference). Calling them directly is the same as
564	"send". Note, however, that many C-based event loops do not handle	671	calling "send".
565	overloading, so as tempting as it may be, passing a condition
566	variable instead of a callback does not work. Both the pure perl and
567	EV loops support overloading, however, as well as all functions that
568	use perl to invoke a callback (as in AnyEvent::Socket and
569	AnyEvent::DNS for example).
570		672
571	$cv->croak ($error)	673	$cv->croak ($error)
572	Similar to send, but causes all call's to "->recv" to invoke	674	Similar to send, but causes all calls to "->recv" to invoke
573	"Carp::croak" with the given error message/object/scalar.	675	"Carp::croak" with the given error message/object/scalar.
574		676
575	This can be used to signal any errors to the condition variable	677	This can be used to signal any errors to the condition variable
576	user/consumer.	678	user/consumer. Doing it this way instead of calling "croak" directly
		679	delays the error detection, but has the overwhelming advantage that
		680	it diagnoses the error at the place where the result is expected,
		681	and not deep in some event callback with no connection to the actual
		682	code causing the problem.
577		683
578	$cv->begin ([group callback])	684	$cv->begin ([group callback])
579	$cv->end	685	$cv->end
580	These two methods are EXPERIMENTAL and MIGHT CHANGE.
581
582	These two methods can be used to combine many transactions/events	686	These two methods can be used to combine many transactions/events
583	into one. For example, a function that pings many hosts in parallel	687	into one. For example, a function that pings many hosts in parallel
584	might want to use a condition variable for the whole process.	688	might want to use a condition variable for the whole process.
585		689
586	Every call to "->begin" will increment a counter, and every call to	690	Every call to "->begin" will increment a counter, and every call to
587	"->end" will decrement it. If the counter reaches 0 in "->end", the	691	"->end" will decrement it. If the counter reaches 0 in "->end", the
588	(last) callback passed to "begin" will be executed. That callback is	692	(last) callback passed to "begin" will be executed, passing the
589	supposed to call "->send", but that is not required. If no	693	condvar as first argument. That callback is supposed to call
		694	"->send", but that is not required. If no group callback was set,
590	callback was set, "send" will be called without any arguments.	695	"send" will be called without any arguments.
591		696
592	Let's clarify this with the ping example:	697	You can think of "$cv->send" giving you an OR condition (one call
		698	sends), while "$cv->begin" and "$cv->end" giving you an AND
		699	condition (all "begin" calls must be "end"'ed before the condvar
		700	sends).
		701
		702	Let's start with a simple example: you have two I/O watchers (for
		703	example, STDOUT and STDERR for a program), and you want to wait for
		704	both streams to close before activating a condvar:
593		705
594	my $cv = AnyEvent->condvar;	706	my $cv = AnyEvent->condvar;
595		707
		708	$cv->begin; # first watcher
		709	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		710	defined sysread $fh1, my $buf, 4096
		711	or $cv->end;
		712	});
		713
		714	$cv->begin; # second watcher
		715	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		716	defined sysread $fh2, my $buf, 4096
		717	or $cv->end;
		718	});
		719
		720	$cv->recv;
		721
		722	This works because for every event source (EOF on file handle),
		723	there is one call to "begin", so the condvar waits for all calls to
		724	"end" before sending.
		725
		726	The ping example mentioned above is slightly more complicated, as
		727	the there are results to be passed back, and the number of tasks
		728	that are begun can potentially be zero:
		729
		730	my $cv = AnyEvent->condvar;
		731
596	my %result;	732	my %result;
597	$cv->begin (sub { $cv->send (\%result) });	733	$cv->begin (sub { shift->send (\%result) });
598		734
599	for my $host (@list_of_hosts) {	735	for my $host (@list_of_hosts) {
600	$cv->begin;	736	$cv->begin;
601	ping_host_then_call_callback $host, sub {	737	ping_host_then_call_callback $host, sub {
602	$result{$host} = ...;	738	$result{$host} = ...;
…		…
604	};	740	};
605	}	741	}
606		742
607	$cv->end;	743	$cv->end;
608		744
		745	...
		746
		747	my $results = $cv->recv;
		748
609	This code fragment supposedly pings a number of hosts and calls	749	This code fragment supposedly pings a number of hosts and calls
610	"send" after results for all then have have been gathered - in any	750	"send" after results for all then have have been gathered - in any
611	order. To achieve this, the code issues a call to "begin" when it	751	order. To achieve this, the code issues a call to "begin" when it
612	starts each ping request and calls "end" when it has received some	752	starts each ping request and calls "end" when it has received some
613	result for it. Since "begin" and "end" only maintain a counter, the	753	result for it. Since "begin" and "end" only maintain a counter, the
…		…
617	the loop, which serves two important purposes: first, it sets the	757	the loop, which serves two important purposes: first, it sets the
618	callback to be called once the counter reaches 0, and second, it	758	callback to be called once the counter reaches 0, and second, it
619	ensures that "send" is called even when "no" hosts are being pinged	759	ensures that "send" is called even when "no" hosts are being pinged
620	(the loop doesn't execute once).	760	(the loop doesn't execute once).
621		761
622	This is the general pattern when you "fan out" into multiple	762	This is the general pattern when you "fan out" into multiple (but
623	subrequests: use an outer "begin"/"end" pair to set the callback and	763	potentially zero) subrequests: use an outer "begin"/"end" pair to
624	ensure "end" is called at least once, and then, for each subrequest	764	set the callback and ensure "end" is called at least once, and then,
625	you start, call "begin" and for each subrequest you finish, call	765	for each subrequest you start, call "begin" and for each subrequest
626	"end".	766	you finish, call "end".
627		767
628	METHODS FOR CONSUMERS	768	METHODS FOR CONSUMERS
629	These methods should only be used by the consuming side, i.e. the code	769	These methods should only be used by the consuming side, i.e. the code
630	awaits the condition.	770	awaits the condition.
631		771
632	$cv->recv	772	$cv->recv
633	Wait (blocking if necessary) until the "->send" or "->croak" methods	773	Wait (blocking if necessary) until the "->send" or "->croak" methods
634	have been called on c<$cv>, while servicing other watchers normally.	774	have been called on $cv, while servicing other watchers normally.
635		775
636	You can only wait once on a condition - additional calls are valid	776	You can only wait once on a condition - additional calls are valid
637	but will return immediately.	777	but will return immediately.
638		778
639	If an error condition has been set by calling "->croak", then this	779	If an error condition has been set by calling "->croak", then this
640	function will call "croak".	780	function will call "croak".
641		781
642	In list context, all parameters passed to "send" will be returned,	782	In list context, all parameters passed to "send" will be returned,
643	in scalar context only the first one will be returned.	783	in scalar context only the first one will be returned.
644		784
		785	Note that doing a blocking wait in a callback is not supported by
		786	any event loop, that is, recursive invocation of a blocking "->recv"
		787	is not allowed and the "recv" call will "croak" if such a condition
		788	is detected. This requirement can be dropped by relying on
		789	Coro::AnyEvent , which allows you to do a blocking "->recv" from any
		790	thread that doesn't run the event loop itself. Coro::AnyEvent is
		791	loaded automatically when Coro is used with AnyEvent, so code does
		792	not need to do anything special to take advantage of that: any code
		793	that would normally block your program because it calls "recv", be
		794	executed in an "async" thread instead without blocking other
		795	threads.
		796
645	Not all event models support a blocking wait - some die in that case	797	Not all event models support a blocking wait - some die in that case
646	(programs might want to do that to stay interactive), so *if you are	798	(programs might want to do that to stay interactive), so *if you are
647	using this from a module, never require a blocking wait*, but let	799	using this from a module, never require a blocking wait*. Instead,
648	the caller decide whether the call will block or not (for example,	800	let the caller decide whether the call will block or not (for
649	by coupling condition variables with some kind of request results	801	example, by coupling condition variables with some kind of request
650	and supporting callbacks so the caller knows that getting the result	802	results and supporting callbacks so the caller knows that getting
651	will not block, while still supporting blocking waits if the caller	803	the result will not block, while still supporting blocking waits if
652	so desires).	804	the caller so desires).
653		805
654	Another reason never to "->recv" in a module is that you cannot
655	sensibly have two "->recv"'s in parallel, as that would require
656	multiple interpreters or coroutines/threads, none of which
657	"AnyEvent" can supply.
658
659	The Coro module, however, can and does supply coroutines and, in
660	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
661	versions and also integrates coroutines into AnyEvent, making
662	blocking "->recv" calls perfectly safe as long as they are done from
663	another coroutine (one that doesn't run the event loop).
664
665	You can ensure that "-recv" never blocks by setting a callback and	806	You can ensure that "->recv" never blocks by setting a callback and
666	only calling "->recv" from within that callback (or at a later	807	only calling "->recv" from within that callback (or at a later
667	time). This will work even when the event loop does not support	808	time). This will work even when the event loop does not support
668	blocking waits otherwise.	809	blocking waits otherwise.
669		810
670	$bool = $cv->ready	811	$bool = $cv->ready
…		…
675	This is a mutator function that returns the callback set and	816	This is a mutator function that returns the callback set and
676	optionally replaces it before doing so.	817	optionally replaces it before doing so.
677		818
678	The callback will be called when the condition becomes "true", i.e.	819	The callback will be called when the condition becomes "true", i.e.
679	when "send" or "croak" are called, with the only argument being the	820	when "send" or "croak" are called, with the only argument being the
680	condition variable itself. Calling "recv" inside the callback or at	821	condition variable itself. If the condition is already true, the
		822	callback is called immediately when it is set. Calling "recv" inside
681	any later time is guaranteed not to block.	823	the callback or at any later time is guaranteed not to block.
		824
		825	SUPPORTED EVENT LOOPS/BACKENDS
		826	The available backend classes are (every class has its own manpage):
		827
		828	Backends that are autoprobed when no other event loop can be found.
		829	EV is the preferred backend when no other event loop seems to be in
		830	use. If EV is not installed, then AnyEvent will fall back to its own
		831	pure-perl implementation, which is available everywhere as it comes
		832	with AnyEvent itself.
		833
		834	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		835	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
		836
		837	Backends that are transparently being picked up when they are used.
		838	These will be used if they are already loaded when the first watcher
		839	is created, in which case it is assumed that the application is
		840	using them. This means that AnyEvent will automatically pick the
		841	right backend when the main program loads an event module before
		842	anything starts to create watchers. Nothing special needs to be done
		843	by the main program.
		844
		845	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		846	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		847	AnyEvent::Impl::Tk based on Tk, very broken.
		848	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		849	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		850	AnyEvent::Impl::Irssi used when running within irssi.
		851	AnyEvent::Impl::IOAsync based on IO::Async.
		852	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		853	AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
		854
		855	Backends with special needs.
		856	Qt requires the Qt::Application to be instantiated first, but will
		857	otherwise be picked up automatically. As long as the main program
		858	instantiates the application before any AnyEvent watchers are
		859	created, everything should just work.
		860
		861	AnyEvent::Impl::Qt based on Qt.
		862
		863	Event loops that are indirectly supported via other backends.
		864	Some event loops can be supported via other modules:
		865
		866	There is no direct support for WxWidgets (Wx) or Prima.
		867
		868	WxWidgets has no support for watching file handles. However, you can
		869	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		870	simply polls 20 times per second, which was considered to be too
		871	horrible to even consider for AnyEvent.
		872
		873	Prima is not supported as nobody seems to be using it, but it has a
		874	POE backend, so it can be supported through POE.
		875
		876	AnyEvent knows about both Prima and Wx, however, and will try to
		877	load POE when detecting them, in the hope that POE will pick them
		878	up, in which case everything will be automatic.
682		879
683	GLOBAL VARIABLES AND FUNCTIONS	880	GLOBAL VARIABLES AND FUNCTIONS
		881	These are not normally required to use AnyEvent, but can be useful to
		882	write AnyEvent extension modules.
		883
684	$AnyEvent::MODEL	884	$AnyEvent::MODEL
685	Contains "undef" until the first watcher is being created. Then it	885	Contains "undef" until the first watcher is being created, before
		886	the backend has been autodetected.
		887
686	contains the event model that is being used, which is the name of	888	Afterwards it contains the event model that is being used, which is
687	the Perl class implementing the model. This class is usually one of	889	the name of the Perl class implementing the model. This class is
688	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	890	usually one of the "AnyEvent::Impl::xxx" modules, but can be any
689	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	891	other class in the case AnyEvent has been extended at runtime (e.g.
690		892	in rxvt-unicode it will be "urxvt::anyevent").
691	The known classes so far are:
692
693	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
694	AnyEvent::Impl::Event based on Event, second best choice.
695	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
696	AnyEvent::Impl::Glib based on Glib, third-best choice.
697	AnyEvent::Impl::Tk based on Tk, very bad choice.
698	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
699	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
700	AnyEvent::Impl::POE based on POE, not generic enough for full support.
701
702	There is no support for WxWidgets, as WxWidgets has no support for
703	watching file handles. However, you can use WxWidgets through the
704	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
705	second, which was considered to be too horrible to even consider for
706	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
707	using it's adaptor.
708
709	AnyEvent knows about Prima and Wx and will try to use POE when
710	autodetecting them.
711		893
712	AnyEvent::detect	894	AnyEvent::detect
713	Returns $AnyEvent::MODEL, forcing autodetection of the event model	895	Returns $AnyEvent::MODEL, forcing autodetection of the event model
714	if necessary. You should only call this function right before you	896	if necessary. You should only call this function right before you
715	would have created an AnyEvent watcher anyway, that is, as late as	897	would have created an AnyEvent watcher anyway, that is, as late as
716	possible at runtime.	898	possible at runtime, and not e.g. during initialisation of your
		899	module.
		900
		901	The effect of calling this function is as if a watcher had been
		902	created (specifically, actions that happen "when the first watcher
		903	is created" happen when calling detetc as well).
		904
		905	If you need to do some initialisation before AnyEvent watchers are
		906	created, use "post_detect".
717		907
718	$guard = AnyEvent::post_detect { BLOCK }	908	$guard = AnyEvent::post_detect { BLOCK }
719	Arranges for the code block to be executed as soon as the event	909	Arranges for the code block to be executed as soon as the event
720	model is autodetected (or immediately if this has already happened).	910	model is autodetected (or immediately if that has already happened).
		911
		912	The block will be executed after the actual backend has been
		913	detected ($AnyEvent::MODEL is set), but before any watchers have
		914	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		915	other initialisations - see the sources of AnyEvent::Strict or
		916	AnyEvent::AIO to see how this is used.
		917
		918	The most common usage is to create some global watchers, without
		919	forcing event module detection too early, for example, AnyEvent::AIO
		920	creates and installs the global IO::AIO watcher in a "post_detect"
		921	block to avoid autodetecting the event module at load time.
721		922
722	If called in scalar or list context, then it creates and returns an	923	If called in scalar or list context, then it creates and returns an
723	object that automatically removes the callback again when it is	924	object that automatically removes the callback again when it is
		925	destroyed (or "undef" when the hook was immediately executed). See
724	destroyed. See Coro::BDB for a case where this is useful.	926	AnyEvent::AIO for a case where this is useful.
		927
		928	Example: Create a watcher for the IO::AIO module and store it in
		929	$WATCHER, but do so only do so after the event loop is initialised.
		930
		931	our WATCHER;
		932
		933	my $guard = AnyEvent::post_detect {
		934	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		935	};
		936
		937	# the \|\|= is important in case post_detect immediately runs the block,
		938	# as to not clobber the newly-created watcher. assigning both watcher and
		939	# post_detect guard to the same variable has the advantage of users being
		940	# able to just C<undef $WATCHER> if the watcher causes them grief.
		941
		942	$WATCHER \|\|= $guard;
725		943
726	@AnyEvent::post_detect	944	@AnyEvent::post_detect
727	If there are any code references in this array (you can "push" to it	945	If there are any code references in this array (you can "push" to it
728	before or after loading AnyEvent), then they will called directly	946	before or after loading AnyEvent), then they will be called directly
729	after the event loop has been chosen.	947	after the event loop has been chosen.
730		948
731	You should check $AnyEvent::MODEL before adding to this array,	949	You should check $AnyEvent::MODEL before adding to this array,
732	though: if it contains a true value then the event loop has already	950	though: if it is defined then the event loop has already been
733	been detected, and the array will be ignored.	951	detected, and the array will be ignored.
734		952
735	Best use "AnyEvent::post_detect { BLOCK }" instead.	953	Best use "AnyEvent::post_detect { BLOCK }" when your application
		954	allows it, as it takes care of these details.
		955
		956	This variable is mainly useful for modules that can do something
		957	useful when AnyEvent is used and thus want to know when it is
		958	initialised, but do not need to even load it by default. This array
		959	provides the means to hook into AnyEvent passively, without loading
		960	it.
		961
		962	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		963	together, you could put this into Coro (this is the actual code used
		964	by Coro to accomplish this):
		965
		966	if (defined $AnyEvent::MODEL) {
		967	# AnyEvent already initialised, so load Coro::AnyEvent
		968	require Coro::AnyEvent;
		969	} else {
		970	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		971	# as soon as it is
		972	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		973	}
		974
		975	AnyEvent::postpone { BLOCK }
		976	Arranges for the block to be executed as soon as possible, but not
		977	before the call itself returns. In practise, the block will be
		978	executed just before the event loop polls for new events, or shortly
		979	afterwards.
		980
		981	This function never returns anything (to make the "return postpone {
		982	... }" idiom more useful.
		983
		984	To understand the usefulness of this function, consider a function
		985	that asynchronously does something for you and returns some
		986	transaction object or guard to let you cancel the operation. For
		987	example, "AnyEvent::Socket::tcp_connect":
		988
		989	# start a conenction attempt unless one is active
		990	$self->{connect_guard} \|\|= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		991	delete $self->{connect_guard};
		992	...
		993	};
		994
		995	Imagine that this function could instantly call the callback, for
		996	example, because it detects an obvious error such as a negative port
		997	number. Invoking the callback before the function returns causes
		998	problems however: the callback will be called and will try to delete
		999	the guard object. But since the function hasn't returned yet, there
		1000	is nothing to delete. When the function eventually returns it will
		1001	assign the guard object to "$self->{connect_guard}", where it will
		1002	likely never be deleted, so the program thinks it is still trying to
		1003	connect.
		1004
		1005	This is where "AnyEvent::postpone" should be used. Instead of
		1006	calling the callback directly on error:
		1007
		1008	$cb->(undef), return # signal error to callback, BAD!
		1009	if $some_error_condition;
		1010
		1011	It should use "postpone":
		1012
		1013	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1014	if $some_error_condition;
		1015
		1016	AnyEvent::log $level, $msg[, @args]
		1017	Log the given $msg at the given $level.
		1018
		1019	If AnyEvent::Log is not loaded then this function makes a simple
		1020	test to see whether the message will be logged. If the test succeeds
		1021	it will load AnyEvent::Log and call "AnyEvent::Log::log" -
		1022	consequently, look at the AnyEvent::Log documentation for details.
		1023
		1024	If the test fails it will simply return. Right now this happens when
		1025	a numerical loglevel is used and it is larger than the level
		1026	specified via $ENV{PERL_ANYEVENT_VERBOSE}.
		1027
		1028	If you want to sprinkle loads of logging calls around your code,
		1029	consider creating a logger callback with the "AnyEvent::Log::logger"
		1030	function, which can reduce typing, codesize and can reduce the
		1031	logging overhead enourmously.
736		1032
737	WHAT TO DO IN A MODULE	1033	WHAT TO DO IN A MODULE
738	As a module author, you should "use AnyEvent" and call AnyEvent methods	1034	As a module author, you should "use AnyEvent" and call AnyEvent methods
739	freely, but you should not load a specific event module or rely on it.	1035	freely, but you should not load a specific event module or rely on it.
740		1036
…		…
748	stall the whole program, and the whole point of using events is to stay	1044	stall the whole program, and the whole point of using events is to stay
749	interactive.	1045	interactive.
750		1046
751	It is fine, however, to call "->recv" when the user of your module	1047	It is fine, however, to call "->recv" when the user of your module
752	requests it (i.e. if you create a http request object ad have a method	1048	requests it (i.e. if you create a http request object ad have a method
753	called "results" that returns the results, it should call "->recv"	1049	called "results" that returns the results, it may call "->recv" freely,
754	freely, as the user of your module knows what she is doing. always).	1050	as the user of your module knows what she is doing. Always).
755		1051
756	WHAT TO DO IN THE MAIN PROGRAM	1052	WHAT TO DO IN THE MAIN PROGRAM
757	There will always be a single main program - the only place that should	1053	There will always be a single main program - the only place that should
758	dictate which event model to use.	1054	dictate which event model to use.
759		1055
760	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	1056	If the program is not event-based, it need not do anything special, even
761	do anything special (it does not need to be event-based) and let	1057	when it depends on a module that uses an AnyEvent. If the program itself
762	AnyEvent decide which implementation to chose if some module relies on	1058	uses AnyEvent, but does not care which event loop is used, all it needs
763	it.	1059	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		1060	available loop implementation.
764		1061
765	If the main program relies on a specific event model - for example, in	1062	If the main program relies on a specific event model - for example, in
766	Gtk2 programs you have to rely on the Glib module - you should load the	1063	Gtk2 programs you have to rely on the Glib module - you should load the
767	event module before loading AnyEvent or any module that uses it:	1064	event module before loading AnyEvent or any module that uses it:
768	generally speaking, you should load it as early as possible. The reason	1065	generally speaking, you should load it as early as possible. The reason
769	is that modules might create watchers when they are loaded, and AnyEvent	1066	is that modules might create watchers when they are loaded, and AnyEvent
770	will decide on the event model to use as soon as it creates watchers,	1067	will decide on the event model to use as soon as it creates watchers,
771	and it might chose the wrong one unless you load the correct one	1068	and it might choose the wrong one unless you load the correct one
772	yourself.	1069	yourself.
773		1070
774	You can chose to use a pure-perl implementation by loading the	1071	You can chose to use a pure-perl implementation by loading the
775	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1072	"AnyEvent::Loop" module, which gives you similar behaviour everywhere,
776	everywhere, but letting AnyEvent chose the model is generally better.	1073	but letting AnyEvent chose the model is generally better.
777		1074
778	MAINLOOP EMULATION	1075	MAINLOOP EMULATION
779	Sometimes (often for short test scripts, or even standalone programs who	1076	Sometimes (often for short test scripts, or even standalone programs who
780	only want to use AnyEvent), you do not want to run a specific event	1077	only want to use AnyEvent), you do not want to run a specific event
781	loop.	1078	loop.
…		…
791	variable somewhere, waiting for it, and sending it when the program	1088	variable somewhere, waiting for it, and sending it when the program
792	should exit cleanly.	1089	should exit cleanly.
793		1090
794	OTHER MODULES	1091	OTHER MODULES
795	The following is a non-exhaustive list of additional modules that use	1092	The following is a non-exhaustive list of additional modules that use
796	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1093	AnyEvent as a client and can therefore be mixed easily with other
797	in the same program. Some of the modules come with AnyEvent, some are	1094	AnyEvent modules and other event loops in the same program. Some of the
798	available via CPAN.	1095	modules come as part of AnyEvent, the others are available via CPAN (see
		1096	<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
		1097	non-exhaustive list), and the list is heavily biased towards modules of
		1098	the AnyEvent author himself :)
799		1099
800	AnyEvent::Util	1100	AnyEvent::Util (part of the AnyEvent distribution)
801	Contains various utility functions that replace often-used but	1101	Contains various utility functions that replace often-used blocking
802	blocking functions such as "inet_aton" by event-/callback-based	1102	functions such as "inet_aton" with event/callback-based versions.
803	versions.
804		1103
805	AnyEvent::Socket	1104	AnyEvent::Socket (part of the AnyEvent distribution)
806	Provides various utility functions for (internet protocol) sockets,	1105	Provides various utility functions for (internet protocol) sockets,
807	addresses and name resolution. Also functions to create non-blocking	1106	addresses and name resolution. Also functions to create non-blocking
808	tcp connections or tcp servers, with IPv6 and SRV record support and	1107	tcp connections or tcp servers, with IPv6 and SRV record support and
809	more.	1108	more.
810		1109
811	AnyEvent::Handle	1110	AnyEvent::Handle (part of the AnyEvent distribution)
812	Provide read and write buffers, manages watchers for reads and	1111	Provide read and write buffers, manages watchers for reads and
813	writes, supports raw and formatted I/O, I/O queued and fully	1112	writes, supports raw and formatted I/O, I/O queued and fully
814	transparent and non-blocking SSL/TLS.	1113	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
815		1114
816	AnyEvent::DNS	1115	AnyEvent::DNS (part of the AnyEvent distribution)
817	Provides rich asynchronous DNS resolver capabilities.	1116	Provides rich asynchronous DNS resolver capabilities.
818		1117
819	AnyEvent::HTTP	1118	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
820	A simple-to-use HTTP library that is capable of making a lot of	1119	AnyEvent::IGS, AnyEvent::FCP
821	concurrent HTTP requests.	1120	Implement event-based interfaces to the protocols of the same name
		1121	(for the curious, IGS is the International Go Server and FCP is the
		1122	Freenet Client Protocol).
822		1123
		1124	AnyEvent::AIO (part of the AnyEvent distribution)
		1125	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1126	the toolbox of every event programmer. AnyEvent::AIO transparently
		1127	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1128	event-based file I/O, and much more.
		1129
		1130	AnyEvent::Fork, AnyEvent::Fork::RPC, AnyEvent::Fork::Pool,
		1131	AnyEvent::Fork::Remote
		1132	These let you safely fork new subprocesses, either locally or
		1133	remotely (e.g.v ia ssh), using some RPC protocol or not, without the
		1134	limitations normally imposed by fork (AnyEvent works fine for
		1135	example). Dynamically-resized worker pools are obviously included as
		1136	well.
		1137
		1138	And they are quite tiny and fast as well - "abusing" AnyEvent::Fork
		1139	just to exec external programs can easily beat using "fork" and
		1140	"exec" (or even "system") in most programs.
		1141
		1142	AnyEvent::Filesys::Notify
		1143	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1144	path changes (e.g. "watch this directory for new files", "watch this
		1145	file for changes"). The AnyEvent::Filesys::Notify module promises to
		1146	do just that in a portbale fashion, supporting inotify on GNU/Linux
		1147	and some weird, without doubt broken, stuff on OS X to monitor
		1148	files. It can fall back to blocking scans at regular intervals
		1149	transparently on other platforms, so it's about as portable as it
		1150	gets.
		1151
		1152	(I haven't used it myself, but it seems the biggest problem with it
		1153	is it quite bad performance).
		1154
823	AnyEvent::HTTPD	1155	AnyEvent::DBI
824	Provides a simple web application server framework.	1156	Executes DBI requests asynchronously in a proxy process for you,
		1157	notifying you in an event-based way when the operation is finished.
825		1158
826	AnyEvent::FastPing	1159	AnyEvent::FastPing
827	The fastest ping in the west.	1160	The fastest ping in the west.
828		1161
829	AnyEvent::DBI
830	Executes DBI requests asynchronously in a proxy process.
831
832	AnyEvent::AIO
833	Truly asynchronous I/O, should be in the toolbox of every event
834	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
835	together.
836
837	AnyEvent::BDB
838	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
839	fuses BDB and AnyEvent together.
840
841	AnyEvent::GPSD
842	A non-blocking interface to gpsd, a daemon delivering GPS
843	information.
844
845	AnyEvent::IGS
846	A non-blocking interface to the Internet Go Server protocol (used by
847	App::IGS).
848
849	AnyEvent::IRC
850	AnyEvent based IRC client module family (replacing the older
851	Net::IRC3).
852
853	Net::XMPP2
854	AnyEvent based XMPP (Jabber protocol) module family.
855
856	Net::FCP
857	AnyEvent-based implementation of the Freenet Client Protocol,
858	birthplace of AnyEvent.
859
860	Event::ExecFlow
861	High level API for event-based execution flow control.
862
863	Coro	1162	Coro
864	Has special support for AnyEvent via Coro::AnyEvent.	1163	Has special support for AnyEvent via Coro::AnyEvent, which allows
		1164	you to simply invert the flow control - don't call us, we will call
		1165	you:
865		1166
866	IO::Lambda	1167	async {
867	The lambda approach to I/O - don't ask, look there. Can use	1168	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
868	AnyEvent.	1169	print "5 seconds later!\n";
		1170
		1171	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
		1172	my $line = <STDIN>; # works for ttys
		1173
		1174	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
		1175	my ($body, $hdr) = Coro::rouse_wait;
		1176	};
		1177
		1178	SIMPLIFIED AE API
		1179	Starting with version 5.0, AnyEvent officially supports a second, much
		1180	simpler, API that is designed to reduce the calling, typing and memory
		1181	overhead by using function call syntax and a fixed number of parameters.
		1182
		1183	See the AE manpage for details.
869		1184
870	ERROR AND EXCEPTION HANDLING	1185	ERROR AND EXCEPTION HANDLING
871	In general, AnyEvent does not do any error handling - it relies on the	1186	In general, AnyEvent does not do any error handling - it relies on the
872	caller to do that if required. The AnyEvent::Strict module (see also the	1187	caller to do that if required. The AnyEvent::Strict module (see also the
873	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	1188	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
882	The pure perl event loop simply re-throws the exception (usually within	1197	The pure perl event loop simply re-throws the exception (usually within
883	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1198	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
884	Glib uses "install_exception_handler" and so on.	1199	Glib uses "install_exception_handler" and so on.
885		1200
886	ENVIRONMENT VARIABLES	1201	ENVIRONMENT VARIABLES
887	The following environment variables are used by this module or its	1202	AnyEvent supports a number of environment variables that tune the
888	submodules:	1203	runtime behaviour. They are usually evaluated when AnyEvent is loaded,
		1204	initialised, or a submodule that uses them is loaded. Many of them also
		1205	cause AnyEvent to load additional modules - for example,
		1206	"PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
		1207	loaded.
		1208
		1209	All the environment variables documented here start with
		1210	"PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
		1211	Other modules are encouraged (but by no means required) to use
		1212	"PERL_ANYEVENT_SUBMODULE" if they have registered the
		1213	AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
		1214	AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
		1215	should not access env variables starting with "AE_", see below).
		1216
		1217	All variables can also be set via the "AE_" prefix, that is, instead of
		1218	setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
		1219	there is a clash btween anyevent and another program that uses
		1220	"AE_something" you can set the corresponding "PERL_ANYEVENT_something"
		1221	variable to the empty string, as those variables take precedence.
		1222
		1223	When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
		1224	their "PERL_ANYEVENT_xxx" counterpart unless that variable already
		1225	exists. If taint mode is on, then AnyEvent will remove all environment
		1226	variables starting with "PERL_ANYEVENT_" from %ENV (or replace them with
		1227	"undef" or the empty string, if the corresaponding "AE_" variable is
		1228	set).
		1229
		1230	The exact algorithm is currently:
		1231
		1232	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		1233	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		1234	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		1235
		1236	This ensures that child processes will not see the "AE_" variables.
		1237
		1238	The following environment variables are currently known to AnyEvent:
889		1239
890	"PERL_ANYEVENT_VERBOSE"	1240	"PERL_ANYEVENT_VERBOSE"
891	By default, AnyEvent will be completely silent except in fatal	1241	By default, AnyEvent will log messages with loglevel 4 ("error") or
892	conditions. You can set this environment variable to make AnyEvent	1242	higher (see AnyEvent::Log). You can set this environment variable to
893	more talkative.	1243	a numerical loglevel to make AnyEvent more (or less) talkative.
894		1244
		1245	If you want to do more than just set the global logging level you
		1246	should have a look at "PERL_ANYEVENT_LOG", which allows much more
		1247	complex specifications.
		1248
		1249	When set to 0 ("off"), then no messages whatsoever will be logged
		1250	with everything else at defaults.
		1251
895	When set to 1 or higher, causes AnyEvent to warn about unexpected	1252	When set to 5 or higher ("warn"), AnyEvent warns about unexpected
896	conditions, such as not being able to load the event model specified	1253	conditions, such as not being able to load the event model specified
897	by "PERL_ANYEVENT_MODEL".	1254	by "PERL_ANYEVENT_MODEL", or a guard callback throwing an exception
		1255	- this is the minimum recommended level for use during development.
898		1256
899	When set to 2 or higher, cause AnyEvent to report to STDERR which	1257	When set to 7 or higher (info), AnyEvent reports which event model
900	event model it chooses.	1258	it chooses.
		1259
		1260	When set to 8 or higher (debug), then AnyEvent will report extra
		1261	information on which optional modules it loads and how it implements
		1262	certain features.
		1263
		1264	"PERL_ANYEVENT_LOG"
		1265	Accepts rather complex logging specifications. For example, you
		1266	could log all "debug" messages of some module to stderr, warnings
		1267	and above to stderr, and errors and above to syslog, with:
		1268
		1269	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		1270
		1271	For the rather extensive details, see AnyEvent::Log.
		1272
		1273	This variable is evaluated when AnyEvent (or AnyEvent::Log) is
		1274	loaded, so will take effect even before AnyEvent has initialised
		1275	itself.
		1276
		1277	Note that specifying this environment variable causes the
		1278	AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
		1279	does not, so only using the latter saves a few hundred kB of memory
		1280	unless a module explicitly needs the extra features of
		1281	AnyEvent::Log.
901		1282
902	"PERL_ANYEVENT_STRICT"	1283	"PERL_ANYEVENT_STRICT"
903	AnyEvent does not do much argument checking by default, as thorough	1284	AnyEvent does not do much argument checking by default, as thorough
904	argument checking is very costly. Setting this variable to a true	1285	argument checking is very costly. Setting this variable to a true
905	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1286	value will cause AnyEvent to load "AnyEvent::Strict" and then to
906	thoroughly check the arguments passed to most method calls. If it	1287	thoroughly check the arguments passed to most method calls. If it
907	finds any problems it will croak.	1288	finds any problems, it will croak.
908		1289
909	In other words, enables "strict" mode.	1290	In other words, enables "strict" mode.
910		1291
911	Unlike "use strict", it is definitely recommended ot keep it off in	1292	Unlike "use strict" (or its modern cousin, "use common::sense", it
912	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment	1293	is definitely recommended to keep it off in production. Keeping
		1294	"PERL_ANYEVENT_STRICT=1" in your environment while developing
913	while developing programs can be very useful, however.	1295	programs can be very useful, however.
		1296
		1297	"PERL_ANYEVENT_DEBUG_SHELL"
		1298	If this env variable is nonempty, then its contents will be
		1299	interpreted by "AnyEvent::Socket::parse_hostport" and
		1300	"AnyEvent::Debug::shell" (after replacing every occurance of $$ by
		1301	the process pid). The shell object is saved in
		1302	$AnyEvent::Debug::SHELL.
		1303
		1304	This happens when the first watcher is created.
		1305
		1306	For example, to bind a debug shell on a unix domain socket in
		1307	/tmp/debug<pid>.sock, you could use this:
		1308
		1309	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		1310	# connect with e.g.: socat readline /tmp/debug123.sock
		1311
		1312	Or to bind to tcp port 4545 on localhost:
		1313
		1314	PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
		1315	# connect with e.g.: telnet localhost 4545
		1316
		1317	Note that creating sockets in /tmp or on localhost is very unsafe on
		1318	multiuser systems.
		1319
		1320	"PERL_ANYEVENT_DEBUG_WRAP"
		1321	Can be set to 0, 1 or 2 and enables wrapping of all watchers for
		1322	debugging purposes. See "AnyEvent::Debug::wrap" for details.
914		1323
915	"PERL_ANYEVENT_MODEL"	1324	"PERL_ANYEVENT_MODEL"
916	This can be used to specify the event model to be used by AnyEvent,	1325	This can be used to specify the event model to be used by AnyEvent,
917	before auto detection and -probing kicks in. It must be a string	1326	before auto detection and -probing kicks in.
918	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1327
919	gets prepended and the resulting module name is loaded and if the	1328	It normally is a string consisting entirely of ASCII letters (e.g.
920	load was successful, used as event model. If it fails to load	1329	"EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
		1330	the resulting module name is loaded and - if the load was successful
		1331	- used as event model backend. If it fails to load then AnyEvent
921	AnyEvent will proceed with auto detection and -probing.	1332	will proceed with auto detection and -probing.
922		1333
923	This functionality might change in future versions.	1334	If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
		1335	then nothing gets prepended and the module name is used as-is (hint:
		1336	"::" at the end of a string designates a module name and quotes it
		1337	appropriately).
924		1338
925	For example, to force the pure perl model (AnyEvent::Impl::Perl) you	1339	For example, to force the pure perl model (AnyEvent::Loop::Perl) you
926	could start your program like this:	1340	could start your program like this:
927		1341
928	PERL_ANYEVENT_MODEL=Perl perl ...	1342	PERL_ANYEVENT_MODEL=Perl perl ...
		1343
		1344	"PERL_ANYEVENT_IO_MODEL"
		1345	The current file I/O model - see AnyEvent::IO for more info.
		1346
		1347	At the moment, only "Perl" (small, pure-perl, synchronous) and
		1348	"IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
		1349	if AnyEvent::AIO can be loaded, otherwise it is "Perl".
929		1350
930	"PERL_ANYEVENT_PROTOCOLS"	1351	"PERL_ANYEVENT_PROTOCOLS"
931	Used by both AnyEvent::DNS and AnyEvent::Socket to determine	1352	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
932	preferences for IPv4 or IPv6. The default is unspecified (and might	1353	preferences for IPv4 or IPv6. The default is unspecified (and might
933	change, or be the result of auto probing).	1354	change, or be the result of auto probing).
…		…
947	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1368	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
948	resolve or contact IPv6 addresses.	1369	resolve or contact IPv6 addresses.
949	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but	1370	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
950	prefer IPv6 over IPv4.	1371	prefer IPv6 over IPv4.
951		1372
		1373	"PERL_ANYEVENT_HOSTS"
		1374	This variable, if specified, overrides the /etc/hosts file used by
		1375	AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
		1376	read from that file instead.
		1377
952	"PERL_ANYEVENT_EDNS0"	1378	"PERL_ANYEVENT_EDNS0"
953	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension	1379	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
954	for DNS. This extension is generally useful to reduce DNS traffic,	1380	for DNS. This extension is generally useful to reduce DNS traffic,
955	but some (broken) firewalls drop such DNS packets, which is why it	1381	especially when DNSSEC is involved, but some (broken) firewalls drop
956	is off by default.	1382	such DNS packets, which is why it is off by default.
957		1383
958	Setting this variable to 1 will cause AnyEvent::DNS to announce	1384	Setting this variable to 1 will cause AnyEvent::DNS to announce
959	EDNS0 in its DNS requests.	1385	EDNS0 in its DNS requests.
960		1386
961	"PERL_ANYEVENT_MAX_FORKS"	1387	"PERL_ANYEVENT_MAX_FORKS"
962	The maximum number of child processes that	1388	The maximum number of child processes that
963	"AnyEvent::Util::fork_call" will create in parallel.	1389	"AnyEvent::Util::fork_call" will create in parallel.
		1390
		1391	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1392	The default value for the "max_outstanding" parameter for the
		1393	default DNS resolver - this is the maximum number of parallel DNS
		1394	requests that are sent to the DNS server.
		1395
		1396	"PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
		1397	Perl has inherently racy signal handling (you can basically choose
		1398	between losing signals and memory corruption) - pure perl event
		1399	loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
		1400	available) therefore have to poll regularly to avoid losing signals.
		1401
		1402	Some event loops are racy, but don't poll regularly, and some event
		1403	loops are written in C but are still racy. For those event loops,
		1404	AnyEvent installs a timer that regularly wakes up the event loop.
		1405
		1406	By default, the interval for this timer is 10 seconds, but you can
		1407	override this delay with this environment variable (or by setting
		1408	the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
		1409	watchers).
		1410
		1411	Lower values increase CPU (and energy) usage, higher values can
		1412	introduce long delays when reaping children or waiting for signals.
		1413
		1414	The AnyEvent::Async module, if available, will be used to avoid this
		1415	polling (with most event loops).
		1416
		1417	"PERL_ANYEVENT_RESOLV_CONF"
		1418	The absolute path to a resolv.conf-style file to use instead of
		1419	/etc/resolv.conf (or the OS-specific configuration) in the default
		1420	resolver, or the empty string to select the default configuration.
		1421
		1422	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1423	When neither "ca_file" nor "ca_path" was specified during
		1424	AnyEvent::TLS context creation, and either of these environment
		1425	variables are nonempty, they will be used to specify CA certificate
		1426	locations instead of a system-dependent default.
		1427
		1428	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1429	When these are set to 1, then the respective modules are not loaded.
		1430	Mostly good for testing AnyEvent itself.
964		1431
965	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1432	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
966	This is an advanced topic that you do not normally need to use AnyEvent	1433	This is an advanced topic that you do not normally need to use AnyEvent
967	in a module. This section is only of use to event loop authors who want	1434	in a module. This section is only of use to event loop authors who want
968	to provide AnyEvent compatibility.	1435	to provide AnyEvent compatibility.
…		…
1023	warn "read: $input\n"; # output what has been read	1490	warn "read: $input\n"; # output what has been read
1024	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1491	$cv->send if $input =~ /^q/i; # quit program if /^q/i
1025	},	1492	},
1026	);	1493	);
1027		1494
1028	my $time_watcher; # can only be used once
1029
1030	sub new_timer {
1031	$timer = AnyEvent->timer (after => 1, cb => sub {	1495	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
1032	warn "timeout\n"; # print 'timeout' about every second	1496	warn "timeout\n"; # print 'timeout' at most every second
1033	&new_timer; # and restart the time
1034	});
1035	}	1497	});
1036
1037	new_timer; # create first timer
1038		1498
1039	$cv->recv; # wait until user enters /^q/i	1499	$cv->recv; # wait until user enters /^q/i
1040		1500
1041	REAL-WORLD EXAMPLE	1501	REAL-WORLD EXAMPLE
1042	Consider the Net::FCP module. It features (among others) the following	1502	Consider the Net::FCP module. It features (among others) the following
…		…
1114		1574
1115	The actual code goes further and collects all errors ("die"s,	1575	The actual code goes further and collects all errors ("die"s,
1116	exceptions) that occurred during request processing. The "result" method	1576	exceptions) that occurred during request processing. The "result" method
1117	detects whether an exception as thrown (it is stored inside the $txn	1577	detects whether an exception as thrown (it is stored inside the $txn
1118	object) and just throws the exception, which means connection errors and	1578	object) and just throws the exception, which means connection errors and
1119	other problems get reported tot he code that tries to use the result,	1579	other problems get reported to the code that tries to use the result,
1120	not in a random callback.	1580	not in a random callback.
1121		1581
1122	All of this enables the following usage styles:	1582	All of this enables the following usage styles:
1123		1583
1124	1. Blocking:	1584	1. Blocking:
…		…
1169	through AnyEvent. The benchmark creates a lot of timers (with a zero	1629	through AnyEvent. The benchmark creates a lot of timers (with a zero
1170	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1630	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1171	which it is), lets them fire exactly once and destroys them again.	1631	which it is), lets them fire exactly once and destroys them again.
1172		1632
1173	Source code for this benchmark is found as eg/bench in the AnyEvent	1633	Source code for this benchmark is found as eg/bench in the AnyEvent
1174	distribution.	1634	distribution. It uses the AE interface, which makes a real difference
		1635	for the EV and Perl backends only.
1175		1636
1176	Explanation of the columns	1637	Explanation of the columns
1177	watcher is the number of event watchers created/destroyed. Since	1638	watcher is the number of event watchers created/destroyed. Since
1178	different event models feature vastly different performances, each event	1639	different event models feature vastly different performances, each event
1179	loop was given a number of watchers so that overall runtime is	1640	loop was given a number of watchers so that overall runtime is
…		…
1198	destroy is the time, in microseconds, that it takes to destroy a	1659	destroy is the time, in microseconds, that it takes to destroy a
1199	single watcher.	1660	single watcher.
1200		1661
1201	Results	1662	Results
1202	name watchers bytes create invoke destroy comment	1663	name watchers bytes create invoke destroy comment
1203	EV/EV 400000 224 0.47 0.35 0.27 EV native interface	1664	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1204	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers	1665	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1205	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal	1666	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1206	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation	1667	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1207	Event/Event 16000 517 32.20 31.80 0.81 Event native interface	1668	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1208	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers	1669	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1670	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1671	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1209	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour	1672	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1210	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers	1673	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1211	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event	1674	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1212	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select	1675	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1213		1676
1214	Discussion	1677	Discussion
1215	The benchmark does not measure scalability of the event loop very	1678	The benchmark does not measure scalability of the event loop very
1216	well. For example, a select-based event loop (such as the pure perl one)	1679	well. For example, a select-based event loop (such as the pure perl one)
1217	can never compete with an event loop that uses epoll when the number of	1680	can never compete with an event loop that uses epoll when the number of
…		…
1228	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1691	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1229	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1692	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1230	CPU cycles with POE.	1693	CPU cycles with POE.
1231		1694
1232	"EV" is the sole leader regarding speed and memory use, which are both	1695	"EV" is the sole leader regarding speed and memory use, which are both
1233	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1696	maximal/minimal, respectively. When using the AE API there is zero
		1697	overhead (when going through the AnyEvent API create is about 5-6 times
		1698	slower, with other times being equal, so still uses far less memory than
1234	far less memory than any other event loop and is still faster than Event	1699	any other event loop and is still faster than Event natively).
1235	natively.
1236		1700
1237	The pure perl implementation is hit in a few sweet spots (both the	1701	The pure perl implementation is hit in a few sweet spots (both the
1238	constant timeout and the use of a single fd hit optimisations in the	1702	constant timeout and the use of a single fd hit optimisations in the
1239	perl interpreter and the backend itself). Nevertheless this shows that	1703	perl interpreter and the backend itself). Nevertheless this shows that
1240	it adds very little overhead in itself. Like any select-based backend	1704	it adds very little overhead in itself. Like any select-based backend
…		…
1242	few of them active), of course, but this was not subject of this	1706	few of them active), of course, but this was not subject of this
1243	benchmark.	1707	benchmark.
1244		1708
1245	The "Event" module has a relatively high setup and callback invocation	1709	The "Event" module has a relatively high setup and callback invocation
1246	cost, but overall scores in on the third place.	1710	cost, but overall scores in on the third place.
		1711
		1712	"IO::Async" performs admirably well, about on par with "Event", even
		1713	when using its pure perl backend.
1247		1714
1248	"Glib"'s memory usage is quite a bit higher, but it features a faster	1715	"Glib"'s memory usage is quite a bit higher, but it features a faster
1249	callback invocation and overall ends up in the same class as "Event".	1716	callback invocation and overall ends up in the same class as "Event".
1250	However, Glib scales extremely badly, doubling the number of watchers	1717	However, Glib scales extremely badly, doubling the number of watchers
1251	increases the processing time by more than a factor of four, making it	1718	increases the processing time by more than a factor of four, making it
…		…
1283	when used without AnyEvent), but most event loops have acceptable	1750	when used without AnyEvent), but most event loops have acceptable
1284	performance with or without AnyEvent.	1751	performance with or without AnyEvent.
1285		1752
1286	* The overhead AnyEvent adds is usually much smaller than the overhead	1753	* The overhead AnyEvent adds is usually much smaller than the overhead
1287	of the actual event loop, only with extremely fast event loops such	1754	of the actual event loop, only with extremely fast event loops such
1288	as EV adds AnyEvent significant overhead.	1755	as EV does AnyEvent add significant overhead.
1289		1756
1290	* You should avoid POE like the plague if you want performance or	1757	* You should avoid POE like the plague if you want performance or
1291	reasonable memory usage.	1758	reasonable memory usage.
1292		1759
1293	BENCHMARKING THE LARGE SERVER CASE	1760	BENCHMARKING THE LARGE SERVER CASE
…		…
1307	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1774	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1308	100 (1%) are active. This mirrors the activity of large servers with	1775	100 (1%) are active. This mirrors the activity of large servers with
1309	many connections, most of which are idle at any one point in time.	1776	many connections, most of which are idle at any one point in time.
1310		1777
1311	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1778	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1312	distribution.	1779	distribution. It uses the AE interface, which makes a real difference
		1780	for the EV and Perl backends only.
1313		1781
1314	Explanation of the columns	1782	Explanation of the columns
1315	sockets is the number of sockets, and twice the number of "servers"	1783	sockets is the number of sockets, and twice the number of "servers"
1316	(as each server has a read and write socket end).	1784	(as each server has a read and write socket end).
1317		1785
…		…
1322	single "request", that is, reading the token from the pipe and	1790	single "request", that is, reading the token from the pipe and
1323	forwarding it to another server. This includes deleting the old timeout	1791	forwarding it to another server. This includes deleting the old timeout
1324	and creating a new one that moves the timeout into the future.	1792	and creating a new one that moves the timeout into the future.
1325		1793
1326	Results	1794	Results
1327	name sockets create request	1795	name sockets create request
1328	EV 20000 69.01 11.16	1796	EV 20000 62.66 7.99
1329	Perl 20000 73.32 35.87	1797	Perl 20000 68.32 32.64
1330	Event 20000 212.62 257.32	1798	IOAsync 20000 174.06 101.15 epoll
1331	Glib 20000 651.16 1896.30	1799	IOAsync 20000 174.67 610.84 poll
		1800	Event 20000 202.69 242.91
		1801	Glib 20000 557.01 1689.52
1332	POE 20000 349.67 12317.24 uses POE::Loop::Event	1802	POE 20000 341.54 12086.32 uses POE::Loop::Event
1333		1803
1334	Discussion	1804	Discussion
1335	This benchmark does measure scalability and overall performance of the	1805	This benchmark does measure scalability and overall performance of the
1336	particular event loop.	1806	particular event loop.
1337		1807
1338	EV is again fastest. Since it is using epoll on my system, the setup	1808	EV is again fastest. Since it is using epoll on my system, the setup
1339	time is relatively high, though.	1809	time is relatively high, though.
1340		1810
1341	Perl surprisingly comes second. It is much faster than the C-based event	1811	Perl surprisingly comes second. It is much faster than the C-based event
1342	loops Event and Glib.	1812	loops Event and Glib.
		1813
		1814	IO::Async performs very well when using its epoll backend, and still
		1815	quite good compared to Glib when using its pure perl backend.
1343		1816
1344	Event suffers from high setup time as well (look at its code and you	1817	Event suffers from high setup time as well (look at its code and you
1345	will understand why). Callback invocation also has a high overhead	1818	will understand why). Callback invocation also has a high overhead
1346	compared to the "$_->() for .."-style loop that the Perl event loop	1819	compared to the "$_->() for .."-style loop that the Perl event loop
1347	uses. Event uses select or poll in basically all documented	1820	uses. Event uses select or poll in basically all documented
…		…
1398		1871
1399	Summary	1872	Summary
1400	* C-based event loops perform very well with small number of watchers,	1873	* C-based event loops perform very well with small number of watchers,
1401	as the management overhead dominates.	1874	as the management overhead dominates.
1402		1875
		1876	THE IO::Lambda BENCHMARK
		1877	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1878	could be misinterpreted to make AnyEvent look bad. In fact, the
		1879	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1880	better (which shouldn't come as a surprise to anybody). As such, the
		1881	benchmark is fine, and mostly shows that the AnyEvent backend from
		1882	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1883	without the extra baggage? To explore this, I wrote the equivalent
		1884	benchmark for AnyEvent.
		1885
		1886	The benchmark itself creates an echo-server, and then, for 500 times,
		1887	connects to the echo server, sends a line, waits for the reply, and then
		1888	creates the next connection. This is a rather bad benchmark, as it
		1889	doesn't test the efficiency of the framework or much non-blocking I/O,
		1890	but it is a benchmark nevertheless.
		1891
		1892	name runtime
		1893	Lambda/select 0.330 sec
		1894	+ optimized 0.122 sec
		1895	Lambda/AnyEvent 0.327 sec
		1896	+ optimized 0.138 sec
		1897	Raw sockets/select 0.077 sec
		1898	POE/select, components 0.662 sec
		1899	POE/select, raw sockets 0.226 sec
		1900	POE/select, optimized 0.404 sec
		1901
		1902	AnyEvent/select/nb 0.085 sec
		1903	AnyEvent/EV/nb 0.068 sec
		1904	+state machine 0.134 sec
		1905
		1906	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1907	benchmarks actually make blocking connects and use 100% blocking I/O,
		1908	defeating the purpose of an event-based solution. All of the newly
		1909	written AnyEvent benchmarks use 100% non-blocking connects (using
		1910	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1911	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1912	connects generally require a lot more bookkeeping and event handling
		1913	than blocking connects (which involve a single syscall only).
		1914
		1915	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1916	offers similar expressive power as POE and IO::Lambda, using
		1917	conventional Perl syntax. This means that both the echo server and the
		1918	client are 100% non-blocking, further placing it at a disadvantage.
		1919
		1920	As you can see, the AnyEvent + EV combination even beats the
		1921	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1922	backend easily beats IO::Lambda and POE.
		1923
		1924	And even the 100% non-blocking version written using the high-level (and
		1925	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1926	higher level ("unoptimised") abstractions by a large margin, even though
		1927	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1928
		1929	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1930	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1931	part of the IO::Lambda distribution and were used without any changes.
		1932
1403	SIGNALS	1933	SIGNALS
1404	AnyEvent currently installs handlers for these signals:	1934	AnyEvent currently installs handlers for these signals:
1405		1935
1406	SIGCHLD	1936	SIGCHLD
1407	A handler for "SIGCHLD" is installed by AnyEvent's child watcher	1937	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1408	emulation for event loops that do not support them natively. Also,	1938	emulation for event loops that do not support them natively. Also,
1409	some event loops install a similar handler.	1939	some event loops install a similar handler.
		1940
		1941	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1942	then AnyEvent will reset it to default, to avoid losing child exit
		1943	statuses.
1410		1944
1411	SIGPIPE	1945	SIGPIPE
1412	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is	1946	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1413	"undef" when AnyEvent gets loaded.	1947	"undef" when AnyEvent gets loaded.
1414		1948
…		…
1422	it is that this way, the handler will be restored to defaults on	1956	it is that this way, the handler will be restored to defaults on
1423	exec.	1957	exec.
1424		1958
1425	Feel free to install your own handler, or reset it to defaults.	1959	Feel free to install your own handler, or reset it to defaults.
1426		1960
		1961	RECOMMENDED/OPTIONAL MODULES
		1962	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1963	its built-in modules) are required to use it.
		1964
		1965	That does not mean that AnyEvent won't take advantage of some additional
		1966	modules if they are installed.
		1967
		1968	This section explains which additional modules will be used, and how
		1969	they affect AnyEvent's operation.
		1970
		1971	Async::Interrupt
		1972	This slightly arcane module is used to implement fast signal
		1973	handling: To my knowledge, there is no way to do completely
		1974	race-free and quick signal handling in pure perl. To ensure that
		1975	signals still get delivered, AnyEvent will start an interval timer
		1976	to wake up perl (and catch the signals) with some delay (default is
		1977	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1978
		1979	If this module is available, then it will be used to implement
		1980	signal catching, which means that signals will not be delayed, and
		1981	the event loop will not be interrupted regularly, which is more
		1982	efficient (and good for battery life on laptops).
		1983
		1984	This affects not just the pure-perl event loop, but also other event
		1985	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1986
		1987	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1988	natively, and either employ their own workarounds (POE) or use
		1989	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1990	Installing Async::Interrupt does nothing for those backends.
		1991
		1992	EV This module isn't really "optional", as it is simply one of the
		1993	backend event loops that AnyEvent can use. However, it is simply the
		1994	best event loop available in terms of features, speed and stability:
		1995	It supports the AnyEvent API optimally, implements all the watcher
		1996	types in XS, does automatic timer adjustments even when no monotonic
		1997	clock is available, can take avdantage of advanced kernel interfaces
		1998	such as "epoll" and "kqueue", and is the fastest backend by far.
		1999	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		2000	Glib::EV).
		2001
		2002	If you only use backends that rely on another event loop (e.g.
		2003	"Tk"), then this module will do nothing for you.
		2004
		2005	Guard
		2006	The guard module, when used, will be used to implement
		2007	"AnyEvent::Util::guard". This speeds up guards considerably (and
		2008	uses a lot less memory), but otherwise doesn't affect guard
		2009	operation much. It is purely used for performance.
		2010
		2011	JSON and JSON::XS
		2012	One of these modules is required when you want to read or write JSON
		2013	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		2014	can take advantage of the ultra-high-speed JSON::XS module when it
		2015	is installed.
		2016
		2017	Net::SSLeay
		2018	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2019	worthwhile: If this module is installed, then AnyEvent::Handle (with
		2020	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		2021
		2022	Time::HiRes
		2023	This module is part of perl since release 5.008. It will be used
		2024	when the chosen event library does not come with a timing source of
		2025	its own. The pure-perl event loop (AnyEvent::Loop) will additionally
		2026	load it to try to use a monotonic clock for timing stability.
		2027
		2028	AnyEvent::AIO (and IO::AIO)
		2029	The default implementation of AnyEvent::IO is to do I/O
		2030	synchronously, stopping programs while they access the disk, which
		2031	is fine for a lot of programs.
		2032
		2033	Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
		2034	switch to a true asynchronous implementation, so event processing
		2035	can continue even while waiting for disk I/O.
		2036
1427	FORK	2037	FORK
1428	Most event libraries are not fork-safe. The ones who are usually are	2038	Most event libraries are not fork-safe. The ones who are usually are
1429	because they rely on inefficient but fork-safe "select" or "poll" calls.	2039	because they rely on inefficient but fork-safe "select" or "poll" calls
1430	Only EV is fully fork-aware.	2040	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		2041	epoll are usually badly thought-out hacks that are incompatible with
		2042	fork in one way or another. Only EV is fully fork-aware and ensures that
		2043	you continue event-processing in both parent and child (or both, if you
		2044	know what you are doing).
		2045
		2046	This means that, in general, you cannot fork and do event processing in
		2047	the child if the event library was initialised before the fork (which
		2048	usually happens when the first AnyEvent watcher is created, or the
		2049	library is loaded).
1431		2050
1432	If you have to fork, you must either do so before creating your first	2051	If you have to fork, you must either do so before creating your first
1433	watcher OR you must not use AnyEvent at all in the child.	2052	watcher OR you must not use AnyEvent at all in the child OR you must do
		2053	something completely out of the scope of AnyEvent (see below).
		2054
		2055	The problem of doing event processing in the parent and the child is
		2056	much more complicated: even for backends that are fork-aware or
		2057	fork-safe, their behaviour is not usually what you want: fork clones all
		2058	watchers, that means all timers, I/O watchers etc. are active in both
		2059	parent and child, which is almost never what you want. Using "exec" to
		2060	start worker children from some kind of manage prrocess is usually
		2061	preferred, because it is much easier and cleaner, at the expense of
		2062	having to have another binary.
		2063
		2064	In addition to logical problems with fork, there are also implementation
		2065	problems. For example, on POSIX systems, you cannot fork at all in Perl
		2066	code if a thread (I am talking of pthreads here) was ever created in the
		2067	process, and this is just the tip of the iceberg. In general, using fork
		2068	from Perl is difficult, and attempting to use fork without an exec to
		2069	implement some kind of parallel processing is almost certainly doomed.
		2070
		2071	To safely fork and exec, you should use a module such as Proc::FastSpawn
		2072	that let's you safely fork and exec new processes.
		2073
		2074	If you want to do multiprocessing using processes, you can look at the
		2075	AnyEvent::Fork module (and some related modules such as
		2076	AnyEvent::Fork::RPC, AnyEvent::Fork::Pool and AnyEvent::Fork::Remote).
		2077	This module allows you to safely create subprocesses without any
		2078	limitations - you can use X11 toolkits or AnyEvent in the children
		2079	created by AnyEvent::Fork safely and without any special precautions.
1434		2080
1435	SECURITY CONSIDERATIONS	2081	SECURITY CONSIDERATIONS
1436	AnyEvent can be forced to load any event model via	2082	AnyEvent can be forced to load any event model via
1437	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	2083	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1438	to execute arbitrary code or directly gain access, it can easily be used	2084	to execute arbitrary code or directly gain access, it can easily be used
…		…
1442		2088
1443	You can make AnyEvent completely ignore this variable by deleting it	2089	You can make AnyEvent completely ignore this variable by deleting it
1444	before the first watcher gets created, e.g. with a "BEGIN" block:	2090	before the first watcher gets created, e.g. with a "BEGIN" block:
1445		2091
1446	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	2092	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1447		2093
1448	use AnyEvent;	2094	use AnyEvent;
1449		2095
1450	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	2096	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1451	be used to probe what backend is used and gain other information (which	2097	be used to probe what backend is used and gain other information (which
1452	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),	2098	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1453	and $ENV{PERL_ANYEGENT_STRICT}.	2099	and $ENV{PERL_ANYEVENT_STRICT}.
		2100
		2101	Note that AnyEvent will remove all environment variables starting with
		2102	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		2103	enabled.
1454		2104
1455	BUGS	2105	BUGS
1456	Perl 5.8 has numerous memleaks that sometimes hit this module and are	2106	Perl 5.8 has numerous memleaks that sometimes hit this module and are
1457	hard to work around. If you suffer from memleaks, first upgrade to Perl	2107	hard to work around. If you suffer from memleaks, first upgrade to Perl
1458	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	2108	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1459	annoying memleaks, such as leaking on "map" and "grep" but it is usually	2109	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1460	not as pronounced).	2110	not as pronounced).
1461		2111
1462	SEE ALSO	2112	SEE ALSO
1463	Utility functions: AnyEvent::Util.	2113	Tutorial/Introduction: AnyEvent::Intro.
1464		2114
1465	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	2115	FAQ: AnyEvent::FAQ.
1466	Event::Lib, Qt, POE.	2116
		2117	Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
		2118	(simply logging).
		2119
		2120	Development/Debugging: AnyEvent::Strict (stricter checking),
		2121	AnyEvent::Debug (interactive shell, watcher tracing).
		2122
		2123	Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
		2124	Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK.
1467		2125
1468	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	2126	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1469	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	2127	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1470	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	2128	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		2129	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi, AnyEvent::Impl::FLTK.
1471		2130
1472	Non-blocking file handles, sockets, TCP clients and servers:	2131	Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1473	AnyEvent::Handle, AnyEvent::Socket.	2132	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		2133
		2134	Asynchronous File I/O: AnyEvent::IO.
1474		2135
1475	Asynchronous DNS: AnyEvent::DNS.	2136	Asynchronous DNS: AnyEvent::DNS.
1476		2137
1477	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	2138	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1478		2139
1479	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	2140	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
		2141	AnyEvent::HTTP.
1480		2142
1481	AUTHOR	2143	AUTHOR
1482	Marc Lehmann <schmorp@schmorp.de>	2144	Marc Lehmann <schmorp@schmorp.de>
1483	http://home.schmorp.de/	2145	http://anyevent.schmorp.de
1484		2146

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing AnyEvent/README (file contents): Revision 1.38 by root, Sun Apr 26 18:12:53 2009 UTC vs. Revision 1.72 by root, Tue Dec 17 16:43:15 2013 UTC

Diff Legend

Comparing AnyEvent/README (file contents):
Revision 1.38 by root, Sun Apr 26 18:12:53 2009 UTC vs.
Revision 1.72 by root, Tue Dec 17 16:43:15 2013 UTC