[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.45 by root, Fri Jul 17 14:57:03 2009 UTC vs.
Revision 1.73 by root, Fri Sep 5 22:24:12 2014 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - the DBI of event loop programming
3		3
4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported	4	EV, Event, Glib, Tk, UV, Perl, Event::Lib, Irssi, rxvt-unicode,
5	event loops.	5	IO::Async, Qt, FLTK and POE are various supported event
		6	loops/environments.
6		7
7	SYNOPSIS	8	SYNOPSIS
8	use AnyEvent;	9	use AnyEvent;
9		10
		11	# if you prefer function calls, look at the AE manpage for
		12	# an alternative API.
		13
10	# file descriptor readable	14	# file handle or descriptor readable
11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });	15	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12		16
13	# one-shot or repeating timers	17	# one-shot or repeating timers
14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });	18	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...	19	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
16		20
17	print AnyEvent->now; # prints current event loop time	21	print AnyEvent->now; # prints current event loop time
18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.	22	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
19		23
20	# POSIX signal	24	# POSIX signal
37		41
38	INTRODUCTION/TUTORIAL	42	INTRODUCTION/TUTORIAL
39	This manpage is mainly a reference manual. If you are interested in a	43	This manpage is mainly a reference manual. If you are interested in a
40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	44	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
41	manpage.	45	manpage.
		46
		47	SUPPORT
		48	An FAQ document is available as AnyEvent::FAQ.
		49
		50	There also is a mailinglist for discussing all things AnyEvent, and an
		51	IRC channel, too.
		52
		53	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		54	Repository, at <http://anyevent.schmorp.de>, for more info.
42		55
43	WHY YOU SHOULD USE THIS MODULE (OR NOT)	56	WHY YOU SHOULD USE THIS MODULE (OR NOT)
44	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	57	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
45	nowadays. So what is different about AnyEvent?	58	nowadays. So what is different about AnyEvent?
46		59
…		…
61	module users into the same thing by forcing them to use the same event	74	module users into the same thing by forcing them to use the same event
62	model you use.	75	model you use.
63		76
64	For modules like POE or IO::Async (which is a total misnomer as it is	77	For modules like POE or IO::Async (which is a total misnomer as it is
65	actually doing all I/O synchronously...), using them in your module is	78	actually doing all I/O synchronously...), using them in your module is
66	like joining a cult: After you joined, you are dependent on them and you	79	like joining a cult: After you join, you are dependent on them and you
67	cannot use anything else, as they are simply incompatible to everything	80	cannot use anything else, as they are simply incompatible to everything
68	that isn't them. What's worse, all the potential users of your module	81	that isn't them. What's worse, all the potential users of your module
69	are also forced to use the same event loop you use.	82	are also forced to use the same event loop you use.
70		83
71	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	84	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
72	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	85	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
73	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your	86	with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
74	module uses one of those, every user of your module has to use it, too.	87	uses one of those, every user of your module has to use it, too. But if
75	But if your module uses AnyEvent, it works transparently with all event	88	your module uses AnyEvent, it works transparently with all event models
76	models it supports (including stuff like IO::Async, as long as those use	89	it supports (including stuff like IO::Async, as long as those use one of
77	one of the supported event loops. It is trivial to add new event loops	90	the supported event loops. It is easy to add new event loops to
78	to AnyEvent, too, so it is future-proof).	91	AnyEvent, too, so it is future-proof).
79		92
80	In addition to being free of having to use *the one and only true event	93	In addition to being free of having to use *the one and only true event
81	model*, AnyEvent also is free of bloat and policy: with POE or similar	94	model*, AnyEvent also is free of bloat and policy: with POE or similar
82	modules, you get an enormous amount of code and strict rules you have to	95	modules, you get an enormous amount of code and strict rules you have to
83	follow. AnyEvent, on the other hand, is lean and up to the point, by	96	follow. AnyEvent, on the other hand, is lean and to the point, by only
84	only offering the functionality that is necessary, in as thin as a	97	offering the functionality that is necessary, in as thin as a wrapper as
85	wrapper as technically possible.	98	technically possible.
86		99
87	Of course, AnyEvent comes with a big (and fully optional!) toolbox of	100	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
88	useful functionality, such as an asynchronous DNS resolver, 100%	101	useful functionality, such as an asynchronous DNS resolver, 100%
89	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms	102	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
90	such as Windows) and lots of real-world knowledge and workarounds for	103	such as Windows) and lots of real-world knowledge and workarounds for
…		…
93	Now, if you do want lots of policy (this can arguably be somewhat	106	Now, if you do want lots of policy (this can arguably be somewhat
94	useful) and you want to force your users to use the one and only event	107	useful) and you want to force your users to use the one and only event
95	model, you should not use this module.	108	model, you should not use this module.
96		109
97	DESCRIPTION	110	DESCRIPTION
98	AnyEvent provides an identical interface to multiple event loops. This	111	AnyEvent provides a uniform interface to various event loops. This
99	allows module authors to utilise an event loop without forcing module	112	allows module authors to use event loop functionality without forcing
100	users to use the same event loop (as only a single event loop can	113	module users to use a specific event loop implementation (since more
101	coexist peacefully at any one time).	114	than one event loop cannot coexist peacefully).
102		115
103	The interface itself is vaguely similar, but not identical to the Event	116	The interface itself is vaguely similar, but not identical to the Event
104	module.	117	module.
105		118
106	During the first call of any watcher-creation method, the module tries	119	During the first call of any watcher-creation method, the module tries
107	to detect the currently loaded event loop by probing whether one of the	120	to detect the currently loaded event loop by probing whether one of the
108	following modules is already loaded: EV, Event, Glib,	121	following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
109	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is	122	Tk, Event::Lib, Qt, POE. The first one found is used. If none are
110	used. If none are found, the module tries to load these modules	123	detected, the module tries to load the first four modules in the order
111	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	124	given; but note that if EV is not available, the pure-perl
112	always succeed) in the order given. The first one that can be	125	AnyEvent::Loop should always work, so the other two are not normally
113	successfully loaded will be used. If, after this, still none could be	126	tried.
114	found, AnyEvent will fall back to a pure-perl event loop, which is not
115	very efficient, but should work everywhere.
116		127
117	Because AnyEvent first checks for modules that are already loaded,	128	Because AnyEvent first checks for modules that are already loaded,
118	loading an event model explicitly before first using AnyEvent will	129	loading an event model explicitly before first using AnyEvent will
119	likely make that model the default. For example:	130	likely make that model the default. For example:
120		131
…		…
122	use AnyEvent;	133	use AnyEvent;
123		134
124	# .. AnyEvent will likely default to Tk	135	# .. AnyEvent will likely default to Tk
125		136
126	The likely means that, if any module loads another event model and	137	The likely means that, if any module loads another event model and
127	starts using it, all bets are off. Maybe you should tell their authors	138	starts using it, all bets are off - this case should be very rare
128	to use AnyEvent so their modules work together with others seamlessly...	139	though, as very few modules hardcode event loops without announcing this
		140	very loudly.
129		141
130	The pure-perl implementation of AnyEvent is called	142	The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
131	"AnyEvent::Impl::Perl". Like other event modules you can load it	143	Like other event modules you can load it explicitly and enjoy the high
132	explicitly and enjoy the high availability of that event loop :)	144	availability of that event loop :)
133		145
134	WATCHERS	146	WATCHERS
135	AnyEvent has the central concept of a watcher, which is an object that	147	AnyEvent has the central concept of a watcher, which is an object that
136	stores relevant data for each kind of event you are waiting for, such as	148	stores relevant data for each kind of event you are waiting for, such as
137	the callback to call, the file handle to watch, etc.	149	the callback to call, the file handle to watch, etc.
…		…
141	callback when the event occurs (of course, only when the event model is	153	callback when the event occurs (of course, only when the event model is
142	in control).	154	in control).
143		155
144	Note that callbacks must not permanently change global variables	156	Note that callbacks must not permanently change global variables
145	potentially in use by the event loop (such as $_ or $[) and that	157	potentially in use by the event loop (such as $_ or $[) and that
146	callbacks must not "die". The former is good programming practise in	158	callbacks must not "die". The former is good programming practice in
147	Perl and the latter stems from the fact that exception handling differs	159	Perl and the latter stems from the fact that exception handling differs
148	widely between event loops.	160	widely between event loops.
149		161
150	To disable the watcher you have to destroy it (e.g. by setting the	162	To disable a watcher you have to destroy it (e.g. by setting the
151	variable you store it in to "undef" or otherwise deleting all references	163	variable you store it in to "undef" or otherwise deleting all references
152	to it).	164	to it).
153		165
154	All watchers are created by calling a method on the "AnyEvent" class.	166	All watchers are created by calling a method on the "AnyEvent" class.
155		167
156	Many watchers either are used with "recursion" (repeating timers for	168	Many watchers either are used with "recursion" (repeating timers for
157	example), or need to refer to their watcher object in other ways.	169	example), or need to refer to their watcher object in other ways.
158		170
159	An any way to achieve that is this pattern:	171	One way to achieve that is this pattern:
160		172
161	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	173	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
162	# you can use $w here, for example to undef it	174	# you can use $w here, for example to undef it
163	undef $w;	175	undef $w;
164	});	176	});
…		…
166	Note that "my $w; $w =" combination. This is necessary because in Perl,	178	Note that "my $w; $w =" combination. This is necessary because in Perl,
167	my variables are only visible after the statement in which they are	179	my variables are only visible after the statement in which they are
168	declared.	180	declared.
169		181
170	I/O WATCHERS	182	I/O WATCHERS
		183	$w = AnyEvent->io (
		184	fh => <filehandle_or_fileno>,
		185	poll => <"r" or "w">,
		186	cb => <callback>,
		187	);
		188
171	You can create an I/O watcher by calling the "AnyEvent->io" method with	189	You can create an I/O watcher by calling the "AnyEvent->io" method with
172	the following mandatory key-value pairs as arguments:	190	the following mandatory key-value pairs as arguments:
173		191
174	"fh" is the Perl file handle (or a naked file descriptor) to watch for	192	"fh" is the Perl file handle (or a naked file descriptor) to watch for
175	events (AnyEvent might or might not keep a reference to this file	193	events (AnyEvent might or might not keep a reference to this file
…		…
189		207
190	The I/O watcher might use the underlying file descriptor or a copy of	208	The I/O watcher might use the underlying file descriptor or a copy of
191	it. You must not close a file handle as long as any watcher is active on	209	it. You must not close a file handle as long as any watcher is active on
192	the underlying file descriptor.	210	the underlying file descriptor.
193		211
194	Some event loops issue spurious readyness notifications, so you should	212	Some event loops issue spurious readiness notifications, so you should
195	always use non-blocking calls when reading/writing from/to your file	213	always use non-blocking calls when reading/writing from/to your file
196	handles.	214	handles.
197		215
198	Example: wait for readability of STDIN, then read a line and disable the	216	Example: wait for readability of STDIN, then read a line and disable the
199	watcher.	217	watcher.
…		…
203	warn "read: $input\n";	221	warn "read: $input\n";
204	undef $w;	222	undef $w;
205	});	223	});
206		224
207	TIME WATCHERS	225	TIME WATCHERS
		226	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		227
		228	$w = AnyEvent->timer (
		229	after => <fractional_seconds>,
		230	interval => <fractional_seconds>,
		231	cb => <callback>,
		232	);
		233
208	You can create a time watcher by calling the "AnyEvent->timer" method	234	You can create a time watcher by calling the "AnyEvent->timer" method
209	with the following mandatory arguments:	235	with the following mandatory arguments:
210		236
211	"after" specifies after how many seconds (fractional values are	237	"after" specifies after how many seconds (fractional values are
212	supported) the callback should be invoked. "cb" is the callback to	238	supported) the callback should be invoked. "cb" is the callback to
…		…
214		240
215	Although the callback might get passed parameters, their value and	241	Although the callback might get passed parameters, their value and
216	presence is undefined and you cannot rely on them. Portable AnyEvent	242	presence is undefined and you cannot rely on them. Portable AnyEvent
217	callbacks cannot use arguments passed to time watcher callbacks.	243	callbacks cannot use arguments passed to time watcher callbacks.
218		244
219	The callback will normally be invoked once only. If you specify another	245	The callback will normally be invoked only once. If you specify another
220	parameter, "interval", as a strictly positive number (> 0), then the	246	parameter, "interval", as a strictly positive number (> 0), then the
221	callback will be invoked regularly at that interval (in fractional	247	callback will be invoked regularly at that interval (in fractional
222	seconds) after the first invocation. If "interval" is specified with a	248	seconds) after the first invocation. If "interval" is specified with a
223	false value, then it is treated as if it were missing.	249	false value, then it is treated as if it were not specified at all.
224		250
225	The callback will be rescheduled before invoking the callback, but no	251	The callback will be rescheduled before invoking the callback, but no
226	attempt is done to avoid timer drift in most backends, so the interval	252	attempt is made to avoid timer drift in most backends, so the interval
227	is only approximate.	253	is only approximate.
228		254
229	Example: fire an event after 7.7 seconds.	255	Example: fire an event after 7.7 seconds.
230		256
231	my $w = AnyEvent->timer (after => 7.7, cb => sub {	257	my $w = AnyEvent->timer (after => 7.7, cb => sub {
…		…
237		263
238	Example 2: fire an event after 0.5 seconds, then roughly every second.	264	Example 2: fire an event after 0.5 seconds, then roughly every second.
239		265
240	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {	266	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
241	warn "timeout\n";	267	warn "timeout\n";
242	};	268	});
243		269
244	TIMING ISSUES	270	TIMING ISSUES
245	There are two ways to handle timers: based on real time (relative, "fire	271	There are two ways to handle timers: based on real time (relative, "fire
246	in 10 seconds") and based on wallclock time (absolute, "fire at 12	272	in 10 seconds") and based on wallclock time (absolute, "fire at 12
247	o'clock").	273	o'clock").
248		274
249	While most event loops expect timers to specified in a relative way,	275	While most event loops expect timers to specified in a relative way,
250	they use absolute time internally. This makes a difference when your	276	they use absolute time internally. This makes a difference when your
251	clock "jumps", for example, when ntp decides to set your clock backwards	277	clock "jumps", for example, when ntp decides to set your clock backwards
252	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is	278	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
253	supposed to fire "after" a second might actually take six years to	279	supposed to fire "after a second" might actually take six years to
254	finally fire.	280	finally fire.
255		281
256	AnyEvent cannot compensate for this. The only event loop that is	282	AnyEvent cannot compensate for this. The only event loop that is
257	conscious about these issues is EV, which offers both relative	283	conscious of these issues is EV, which offers both relative (ev_timer,
258	(ev_timer, based on true relative time) and absolute (ev_periodic, based	284	based on true relative time) and absolute (ev_periodic, based on
259	on wallclock time) timers.	285	wallclock time) timers.
260		286
261	AnyEvent always prefers relative timers, if available, matching the	287	AnyEvent always prefers relative timers, if available, matching the
262	AnyEvent API.	288	AnyEvent API.
263		289
264	AnyEvent has two additional methods that return the "current time":	290	AnyEvent has two additional methods that return the "current time":
…		…
283	*In almost all cases (in all cases if you don't care), this is the	309	*In almost all cases (in all cases if you don't care), this is the
284	function to call when you want to know the current time.*	310	function to call when you want to know the current time.*
285		311
286	This function is also often faster then "AnyEvent->time", and thus	312	This function is also often faster then "AnyEvent->time", and thus
287	the preferred method if you want some timestamp (for example,	313	the preferred method if you want some timestamp (for example,
288	AnyEvent::Handle uses this to update it's activity timeouts).	314	AnyEvent::Handle uses this to update its activity timeouts).
289		315
290	The rest of this section is only of relevance if you try to be very	316	The rest of this section is only of relevance if you try to be very
291	exact with your timing, you can skip it without bad conscience.	317	exact with your timing; you can skip it without a bad conscience.
292		318
293	For a practical example of when these times differ, consider	319	For a practical example of when these times differ, consider
294	Event::Lib and EV and the following set-up:	320	Event::Lib and EV and the following set-up:
295		321
296	The event loop is running and has just invoked one of your callback	322	The event loop is running and has just invoked one of your callbacks
297	at time=500 (assume no other callbacks delay processing). In your	323	at time=500 (assume no other callbacks delay processing). In your
298	callback, you wait a second by executing "sleep 1" (blocking the	324	callback, you wait a second by executing "sleep 1" (blocking the
299	process for a second) and then (at time=501) you create a relative	325	process for a second) and then (at time=501) you create a relative
300	timer that fires after three seconds.	326	timer that fires after three seconds.
301		327
…		…
322	can get whatever behaviour you want with any event loop, by taking	348	can get whatever behaviour you want with any event loop, by taking
323	the difference between "AnyEvent->time" and "AnyEvent->now" into	349	the difference between "AnyEvent->time" and "AnyEvent->now" into
324	account.	350	account.
325		351
326	AnyEvent->now_update	352	AnyEvent->now_update
327	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the	353	Some event loops (such as EV or AnyEvent::Loop) cache the current
328	current time for each loop iteration (see the discussion of	354	time for each loop iteration (see the discussion of AnyEvent->now,
329	AnyEvent->now, above).	355	above).
330		356
331	When a callback runs for a long time (or when the process sleeps),	357	When a callback runs for a long time (or when the process sleeps),
332	then this "current" time will differ substantially from the real	358	then this "current" time will differ substantially from the real
333	time, which might affect timers and time-outs.	359	time, which might affect timers and time-outs.
334		360
335	When this is the case, you can call this method, which will update	361	When this is the case, you can call this method, which will update
336	the event loop's idea of "current time".	362	the event loop's idea of "current time".
337		363
		364	A typical example would be a script in a web server (e.g.
		365	"mod_perl") - when mod_perl executes the script, then the event loop
		366	will have the wrong idea about the "current time" (being potentially
		367	far in the past, when the script ran the last time). In that case
		368	you should arrange a call to "AnyEvent->now_update" each time the
		369	web server process wakes up again (e.g. at the start of your script,
		370	or in a handler).
		371
338	Note that updating the time might cause some events to be handled.	372	Note that updating the time might cause some events to be handled.
339		373
340	SIGNAL WATCHERS	374	SIGNAL WATCHERS
		375	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		376
341	You can watch for signals using a signal watcher, "signal" is the signal	377	You can watch for signals using a signal watcher, "signal" is the signal
342	name in uppercase and without any "SIG" prefix, "cb" is the Perl	378	name in uppercase and without any "SIG" prefix, "cb" is the Perl
343	callback to be invoked whenever a signal occurs.	379	callback to be invoked whenever a signal occurs.
344		380
345	Although the callback might get passed parameters, their value and	381	Although the callback might get passed parameters, their value and
…		…
350	invocation, and callback invocation will be synchronous. Synchronous	386	invocation, and callback invocation will be synchronous. Synchronous
351	means that it might take a while until the signal gets handled by the	387	means that it might take a while until the signal gets handled by the
352	process, but it is guaranteed not to interrupt any other callbacks.	388	process, but it is guaranteed not to interrupt any other callbacks.
353		389
354	The main advantage of using these watchers is that you can share a	390	The main advantage of using these watchers is that you can share a
355	signal between multiple watchers.	391	signal between multiple watchers, and AnyEvent will ensure that signals
		392	will not interrupt your program at bad times.
356		393
357	This watcher might use %SIG, so programs overwriting those signals	394	This watcher might use %SIG (depending on the event loop used), so
358	directly will likely not work correctly.	395	programs overwriting those signals directly will likely not work
		396	correctly.
359		397
360	Example: exit on SIGINT	398	Example: exit on SIGINT
361		399
362	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	400	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
363		401
		402	Restart Behaviour
		403	While restart behaviour is up to the event loop implementation, most
		404	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		405	pure perl implementation).
		406
		407	Safe/Unsafe Signals
		408	Perl signals can be either "safe" (synchronous to opcode handling) or
		409	"unsafe" (asynchronous) - the former might delay signal delivery
		410	indefinitely, the latter might corrupt your memory.
		411
		412	AnyEvent signal handlers are, in addition, synchronous to the event
		413	loop, i.e. they will not interrupt your running perl program but will
		414	only be called as part of the normal event handling (just like timer,
		415	I/O etc. callbacks, too).
		416
		417	Signal Races, Delays and Workarounds
		418	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		419	callbacks to signals in a generic way, which is a pity, as you cannot do
		420	race-free signal handling in perl, requiring C libraries for this.
		421	AnyEvent will try to do its best, which means in some cases, signals
		422	will be delayed. The maximum time a signal might be delayed is 10
		423	seconds by default, but can be overriden via
		424	$ENV{PERL_ANYEVENT_MAX_SIGNAL_LATENCY} or $AnyEvent::MAX_SIGNAL_LATENCY
		425	- see the "ENVIRONMENT VARIABLES" section for details.
		426
		427	All these problems can be avoided by installing the optional
		428	Async::Interrupt module, which works with most event loops. It will not
		429	work with inherently broken event loops such as Event or Event::Lib (and
		430	not with POE currently). For those, you just have to suffer the delays.
		431
364	CHILD PROCESS WATCHERS	432	CHILD PROCESS WATCHERS
		433	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		434
365	You can also watch on a child process exit and catch its exit status.	435	You can also watch for a child process exit and catch its exit status.
366		436
367	The child process is specified by the "pid" argument (if set to 0, it	437	The child process is specified by the "pid" argument (on some backends,
368	watches for any child process exit). The watcher will triggered only	438	using 0 watches for any child process exit, on others this will croak).
369	when the child process has finished and an exit status is available, not	439	The watcher will be triggered only when the child process has finished
370	on any trace events (stopped/continued).	440	and an exit status is available, not on any trace events
		441	(stopped/continued).
371		442
372	The callback will be called with the pid and exit status (as returned by	443	The callback will be called with the pid and exit status (as returned by
373	waitpid), so unlike other watcher types, you can rely on child watcher	444	waitpid), so unlike other watcher types, you can rely on child watcher
374	callback arguments.	445	callback arguments.
375		446
…		…
391		462
392	This means you cannot create a child watcher as the very first thing in	463	This means you cannot create a child watcher as the very first thing in
393	an AnyEvent program, you have to create at least one watcher before	464	an AnyEvent program, you have to create at least one watcher before
394	you "fork" the child (alternatively, you can call "AnyEvent::detect").	465	you "fork" the child (alternatively, you can call "AnyEvent::detect").
395		466
		467	As most event loops do not support waiting for child events, they will
		468	be emulated by AnyEvent in most cases, in which case the latency and
		469	race problems mentioned in the description of signal watchers apply.
		470
396	Example: fork a process and wait for it	471	Example: fork a process and wait for it
397		472
398	my $done = AnyEvent->condvar;	473	my $done = AnyEvent->condvar;
399		474
		475	# this forks and immediately calls exit in the child. this
		476	# normally has all sorts of bad consequences for your parent,
		477	# so take this as an example only. always fork and exec,
		478	# or call POSIX::_exit, in real code.
400	my $pid = fork or exit 5;	479	my $pid = fork or exit 5;
401		480
402	my $w = AnyEvent->child (	481	my $w = AnyEvent->child (
403	pid => $pid,	482	pid => $pid,
404	cb => sub {	483	cb => sub {
…		…
410		489
411	# do something else, then wait for process exit	490	# do something else, then wait for process exit
412	$done->recv;	491	$done->recv;
413		492
414	IDLE WATCHERS	493	IDLE WATCHERS
415	Sometimes there is a need to do something, but it is not so important to	494	$w = AnyEvent->idle (cb => <callback>);
416	do it instantly, but only when there is nothing better to do. This
417	"nothing better to do" is usually defined to be "no other events need
418	attention by the event loop".
419		495
420	Idle watchers ideally get invoked when the event loop has nothing better	496	This will repeatedly invoke the callback after the process becomes idle,
421	to do, just before it would block the process to wait for new events.	497	until either the watcher is destroyed or new events have been detected.
422	Instead of blocking, the idle watcher is invoked.
423		498
424	Most event loops unfortunately do not really support idle watchers (only	499	Idle watchers are useful when there is a need to do something, but it is
		500	not so important (or wise) to do it instantly. The callback will be
		501	invoked only when there is "nothing better to do", which is usually
		502	defined as "all outstanding events have been handled and no new events
		503	have been detected". That means that idle watchers ideally get invoked
		504	when the event loop has just polled for new events but none have been
		505	detected. Instead of blocking to wait for more events, the idle watchers
		506	will be invoked.
		507
		508	Unfortunately, most event loops do not really support idle watchers
425	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent	509	(only EV, Event and Glib do it in a usable fashion) - for the rest,
426	will simply call the callback "from time to time".	510	AnyEvent will simply call the callback "from time to time".
427		511
428	Example: read lines from STDIN, but only process them when the program	512	Example: read lines from STDIN, but only process them when the program
429	is otherwise idle:	513	is otherwise idle:
430		514
431	my @lines; # read data	515	my @lines; # read data
…		…
444	}	528	}
445	});	529	});
446	});	530	});
447		531
448	CONDITION VARIABLES	532	CONDITION VARIABLES
		533	$cv = AnyEvent->condvar;
		534
		535	$cv->send (<list>);
		536	my @res = $cv->recv;
		537
449	If you are familiar with some event loops you will know that all of them	538	If you are familiar with some event loops you will know that all of them
450	require you to run some blocking "loop", "run" or similar function that	539	require you to run some blocking "loop", "run" or similar function that
451	will actively watch for new events and call your callbacks.	540	will actively watch for new events and call your callbacks.
452		541
453	AnyEvent is slightly different: it expects somebody else to run the	542	AnyEvent is slightly different: it expects somebody else to run the
454	event loop and will only block when necessary (usually when told by the	543	event loop and will only block when necessary (usually when told by the
455	user).	544	user).
456		545
457	The instrument to do that is called a "condition variable", so called	546	The tool to do that is called a "condition variable", so called because
458	because they represent a condition that must become true.	547	they represent a condition that must become true.
459		548
460	Now is probably a good time to look at the examples further below.	549	Now is probably a good time to look at the examples further below.
461		550
462	Condition variables can be created by calling the "AnyEvent->condvar"	551	Condition variables can be created by calling the "AnyEvent->condvar"
463	method, usually without arguments. The only argument pair allowed is	552	method, usually without arguments. The only argument pair allowed is
…		…
468	After creation, the condition variable is "false" until it becomes	557	After creation, the condition variable is "false" until it becomes
469	"true" by calling the "send" method (or calling the condition variable	558	"true" by calling the "send" method (or calling the condition variable
470	as if it were a callback, read about the caveats in the description for	559	as if it were a callback, read about the caveats in the description for
471	the "->send" method).	560	the "->send" method).
472		561
473	Condition variables are similar to callbacks, except that you can	562	Since condition variables are the most complex part of the AnyEvent API,
474	optionally wait for them. They can also be called merge points - points	563	here are some different mental models of what they are - pick the ones
475	in time where multiple outstanding events have been processed. And yet	564	you can connect to:
476	another way to call them is transactions - each condition variable can	565
477	be used to represent a transaction, which finishes at some point and	566	* Condition variables are like callbacks - you can call them (and pass
478	delivers a result.	567	them instead of callbacks). Unlike callbacks however, you can also
		568	wait for them to be called.
		569
		570	* Condition variables are signals - one side can emit or send them,
		571	the other side can wait for them, or install a handler that is
		572	called when the signal fires.
		573
		574	* Condition variables are like "Merge Points" - points in your program
		575	where you merge multiple independent results/control flows into one.
		576
		577	* Condition variables represent a transaction - functions that start
		578	some kind of transaction can return them, leaving the caller the
		579	choice between waiting in a blocking fashion, or setting a callback.
		580
		581	* Condition variables represent future values, or promises to deliver
		582	some result, long before the result is available.
479		583
480	Condition variables are very useful to signal that something has	584	Condition variables are very useful to signal that something has
481	finished, for example, if you write a module that does asynchronous http	585	finished, for example, if you write a module that does asynchronous http
482	requests, then a condition variable would be the ideal candidate to	586	requests, then a condition variable would be the ideal candidate to
483	signal the availability of results. The user can either act when the	587	signal the availability of results. The user can either act when the
…		…
496		600
497	Condition variables are represented by hash refs in perl, and the keys	601	Condition variables are represented by hash refs in perl, and the keys
498	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy	602	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
499	(it is often useful to build your own transaction class on top of	603	(it is often useful to build your own transaction class on top of
500	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call	604	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
501	it's "new" method in your own "new" method.	605	its "new" method in your own "new" method.
502		606
503	There are two "sides" to a condition variable - the "producer side"	607	There are two "sides" to a condition variable - the "producer side"
504	which eventually calls "-> send", and the "consumer side", which waits	608	which eventually calls "-> send", and the "consumer side", which waits
505	for the send to occur.	609	for the send to occur.
506		610
507	Example: wait for a timer.	611	Example: wait for a timer.
508		612
509	# wait till the result is ready	613	# condition: "wait till the timer is fired"
510	my $result_ready = AnyEvent->condvar;	614	my $timer_fired = AnyEvent->condvar;
511		615
512	# do something such as adding a timer	616	# create the timer - we could wait for, say
513	# or socket watcher the calls $result_ready->send	617	# a handle becomign ready, or even an
514	# when the "result" is ready.	618	# AnyEvent::HTTP request to finish, but
515	# in this case, we simply use a timer:	619	# in this case, we simply use a timer:
516	my $w = AnyEvent->timer (	620	my $w = AnyEvent->timer (
517	after => 1,	621	after => 1,
518	cb => sub { $result_ready->send },	622	cb => sub { $timer_fired->send },
519	);	623	);
520		624
521	# this "blocks" (while handling events) till the callback	625	# this "blocks" (while handling events) till the callback
522	# calls -<send	626	# calls ->send
523	$result_ready->recv;	627	$timer_fired->recv;
524		628
525	Example: wait for a timer, but take advantage of the fact that condition	629	Example: wait for a timer, but take advantage of the fact that condition
526	variables are also callable directly.	630	variables are also callable directly.
527		631
528	my $done = AnyEvent->condvar;	632	my $done = AnyEvent->condvar;
…		…
566	Condition variables are overloaded so one can call them directly (as	670	Condition variables are overloaded so one can call them directly (as
567	if they were a code reference). Calling them directly is the same as	671	if they were a code reference). Calling them directly is the same as
568	calling "send".	672	calling "send".
569		673
570	$cv->croak ($error)	674	$cv->croak ($error)
571	Similar to send, but causes all call's to "->recv" to invoke	675	Similar to send, but causes all calls to "->recv" to invoke
572	"Carp::croak" with the given error message/object/scalar.	676	"Carp::croak" with the given error message/object/scalar.
573		677
574	This can be used to signal any errors to the condition variable	678	This can be used to signal any errors to the condition variable
575	user/consumer. Doing it this way instead of calling "croak" directly	679	user/consumer. Doing it this way instead of calling "croak" directly
576	delays the error detetcion, but has the overwhelmign advantage that	680	delays the error detection, but has the overwhelming advantage that
577	it diagnoses the error at the place where the result is expected,	681	it diagnoses the error at the place where the result is expected,
578	and not deep in some event clalback without connection to the actual	682	and not deep in some event callback with no connection to the actual
579	code causing the problem.	683	code causing the problem.
580		684
581	$cv->begin ([group callback])	685	$cv->begin ([group callback])
582	$cv->end	686	$cv->end
583	These two methods can be used to combine many transactions/events	687	These two methods can be used to combine many transactions/events
584	into one. For example, a function that pings many hosts in parallel	688	into one. For example, a function that pings many hosts in parallel
585	might want to use a condition variable for the whole process.	689	might want to use a condition variable for the whole process.
586		690
587	Every call to "->begin" will increment a counter, and every call to	691	Every call to "->begin" will increment a counter, and every call to
588	"->end" will decrement it. If the counter reaches 0 in "->end", the	692	"->end" will decrement it. If the counter reaches 0 in "->end", the
589	(last) callback passed to "begin" will be executed. That callback is	693	(last) callback passed to "begin" will be executed, passing the
590	supposed to call "->send", but that is not required. If no	694	condvar as first argument. That callback is supposed to call
		695	"->send", but that is not required. If no group callback was set,
591	callback was set, "send" will be called without any arguments.	696	"send" will be called without any arguments.
592		697
593	You can think of "$cv->send" giving you an OR condition (one call	698	You can think of "$cv->send" giving you an OR condition (one call
594	sends), while "$cv->begin" and "$cv->end" giving you an AND	699	sends), while "$cv->begin" and "$cv->end" giving you an AND
595	condition (all "begin" calls must be "end"'ed before the condvar	700	condition (all "begin" calls must be "end"'ed before the condvar
596	sends).	701	sends).
…		…
618	This works because for every event source (EOF on file handle),	723	This works because for every event source (EOF on file handle),
619	there is one call to "begin", so the condvar waits for all calls to	724	there is one call to "begin", so the condvar waits for all calls to
620	"end" before sending.	725	"end" before sending.
621		726
622	The ping example mentioned above is slightly more complicated, as	727	The ping example mentioned above is slightly more complicated, as
623	the there are results to be passwd back, and the number of tasks	728	the there are results to be passed back, and the number of tasks
624	that are begung can potentially be zero:	729	that are begun can potentially be zero:
625		730
626	my $cv = AnyEvent->condvar;	731	my $cv = AnyEvent->condvar;
627		732
628	my %result;	733	my %result;
629	$cv->begin (sub { $cv->send (\%result) });	734	$cv->begin (sub { shift->send (\%result) });
630		735
631	for my $host (@list_of_hosts) {	736	for my $host (@list_of_hosts) {
632	$cv->begin;	737	$cv->begin;
633	ping_host_then_call_callback $host, sub {	738	ping_host_then_call_callback $host, sub {
634	$result{$host} = ...;	739	$result{$host} = ...;
…		…
636	};	741	};
637	}	742	}
638		743
639	$cv->end;	744	$cv->end;
640		745
		746	...
		747
		748	my $results = $cv->recv;
		749
641	This code fragment supposedly pings a number of hosts and calls	750	This code fragment supposedly pings a number of hosts and calls
642	"send" after results for all then have have been gathered - in any	751	"send" after results for all then have have been gathered - in any
643	order. To achieve this, the code issues a call to "begin" when it	752	order. To achieve this, the code issues a call to "begin" when it
644	starts each ping request and calls "end" when it has received some	753	starts each ping request and calls "end" when it has received some
645	result for it. Since "begin" and "end" only maintain a counter, the	754	result for it. Since "begin" and "end" only maintain a counter, the
…		…
650	callback to be called once the counter reaches 0, and second, it	759	callback to be called once the counter reaches 0, and second, it
651	ensures that "send" is called even when "no" hosts are being pinged	760	ensures that "send" is called even when "no" hosts are being pinged
652	(the loop doesn't execute once).	761	(the loop doesn't execute once).
653		762
654	This is the general pattern when you "fan out" into multiple (but	763	This is the general pattern when you "fan out" into multiple (but
655	potentially none) subrequests: use an outer "begin"/"end" pair to	764	potentially zero) subrequests: use an outer "begin"/"end" pair to
656	set the callback and ensure "end" is called at least once, and then,	765	set the callback and ensure "end" is called at least once, and then,
657	for each subrequest you start, call "begin" and for each subrequest	766	for each subrequest you start, call "begin" and for each subrequest
658	you finish, call "end".	767	you finish, call "end".
659		768
660	METHODS FOR CONSUMERS	769	METHODS FOR CONSUMERS
661	These methods should only be used by the consuming side, i.e. the code	770	These methods should only be used by the consuming side, i.e. the code
662	awaits the condition.	771	awaits the condition.
663		772
664	$cv->recv	773	$cv->recv
665	Wait (blocking if necessary) until the "->send" or "->croak" methods	774	Wait (blocking if necessary) until the "->send" or "->croak" methods
666	have been called on c<$cv>, while servicing other watchers normally.	775	have been called on $cv, while servicing other watchers normally.
667		776
668	You can only wait once on a condition - additional calls are valid	777	You can only wait once on a condition - additional calls are valid
669	but will return immediately.	778	but will return immediately.
670		779
671	If an error condition has been set by calling "->croak", then this	780	If an error condition has been set by calling "->croak", then this
…		…
674	In list context, all parameters passed to "send" will be returned,	783	In list context, all parameters passed to "send" will be returned,
675	in scalar context only the first one will be returned.	784	in scalar context only the first one will be returned.
676		785
677	Note that doing a blocking wait in a callback is not supported by	786	Note that doing a blocking wait in a callback is not supported by
678	any event loop, that is, recursive invocation of a blocking "->recv"	787	any event loop, that is, recursive invocation of a blocking "->recv"
679	is not allowed, and the "recv" call will "croak" if such a condition	788	is not allowed and the "recv" call will "croak" if such a condition
680	is detected. This condition can be slightly loosened by using	789	is detected. This requirement can be dropped by relying on
681	Coro::AnyEvent, which allows you to do a blocking "->recv" from any	790	Coro::AnyEvent , which allows you to do a blocking "->recv" from any
682	thread that doesn't run the event loop itself.	791	thread that doesn't run the event loop itself. Coro::AnyEvent is
		792	loaded automatically when Coro is used with AnyEvent, so code does
		793	not need to do anything special to take advantage of that: any code
		794	that would normally block your program because it calls "recv", be
		795	executed in an "async" thread instead without blocking other
		796	threads.
683		797
684	Not all event models support a blocking wait - some die in that case	798	Not all event models support a blocking wait - some die in that case
685	(programs might want to do that to stay interactive), so *if you are	799	(programs might want to do that to stay interactive), so *if you are
686	using this from a module, never require a blocking wait*. Instead,	800	using this from a module, never require a blocking wait*. Instead,
687	let the caller decide whether the call will block or not (for	801	let the caller decide whether the call will block or not (for
688	example, by coupling condition variables with some kind of request	802	example, by coupling condition variables with some kind of request
689	results and supporting callbacks so the caller knows that getting	803	results and supporting callbacks so the caller knows that getting
690	the result will not block, while still supporting blocking waits if	804	the result will not block, while still supporting blocking waits if
691	the caller so desires).	805	the caller so desires).
692		806
693	You can ensure that "-recv" never blocks by setting a callback and	807	You can ensure that "->recv" never blocks by setting a callback and
694	only calling "->recv" from within that callback (or at a later	808	only calling "->recv" from within that callback (or at a later
695	time). This will work even when the event loop does not support	809	time). This will work even when the event loop does not support
696	blocking waits otherwise.	810	blocking waits otherwise.
697		811
698	$bool = $cv->ready	812	$bool = $cv->ready
…		…
703	This is a mutator function that returns the callback set and	817	This is a mutator function that returns the callback set and
704	optionally replaces it before doing so.	818	optionally replaces it before doing so.
705		819
706	The callback will be called when the condition becomes "true", i.e.	820	The callback will be called when the condition becomes "true", i.e.
707	when "send" or "croak" are called, with the only argument being the	821	when "send" or "croak" are called, with the only argument being the
708	condition variable itself. Calling "recv" inside the callback or at	822	condition variable itself. If the condition is already true, the
		823	callback is called immediately when it is set. Calling "recv" inside
709	any later time is guaranteed not to block.	824	the callback or at any later time is guaranteed not to block.
710		825
711	SUPPORTED EVENT LOOPS/BACKENDS	826	SUPPORTED EVENT LOOPS/BACKENDS
712	The available backend classes are (every class has its own manpage):	827	The available backend classes are (every class has its own manpage):
713		828
714	Backends that are autoprobed when no other event loop can be found.	829	Backends that are autoprobed when no other event loop can be found.
715	EV is the preferred backend when no other event loop seems to be in	830	EV is the preferred backend when no other event loop seems to be in
716	use. If EV is not installed, then AnyEvent will try Event, and,	831	use. If EV is not installed, then AnyEvent will fall back to its own
717	failing that, will fall back to its own pure-perl implementation,	832	pure-perl implementation, which is available everywhere as it comes
718	which is available everywhere as it comes with AnyEvent itself.	833	with AnyEvent itself.
719		834
720	AnyEvent::Impl::EV based on EV (interface to libev, best choice).	835	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
721	AnyEvent::Impl::Event based on Event, very stable, few glitches.
722	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.	836	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
723		837
724	Backends that are transparently being picked up when they are used.	838	Backends that are transparently being picked up when they are used.
725	These will be used when they are currently loaded when the first	839	These will be used if they are already loaded when the first watcher
726	watcher is created, in which case it is assumed that the application	840	is created, in which case it is assumed that the application is
727	is using them. This means that AnyEvent will automatically pick the	841	using them. This means that AnyEvent will automatically pick the
728	right backend when the main program loads an event module before	842	right backend when the main program loads an event module before
729	anything starts to create watchers. Nothing special needs to be done	843	anything starts to create watchers. Nothing special needs to be done
730	by the main program.	844	by the main program.
731		845
		846	AnyEvent::Impl::Event based on Event, very stable, few glitches.
732	AnyEvent::Impl::Glib based on Glib, slow but very stable.	847	AnyEvent::Impl::Glib based on Glib, slow but very stable.
733	AnyEvent::Impl::Tk based on Tk, very broken.	848	AnyEvent::Impl::Tk based on Tk, very broken.
		849	AnyEvent::Impl::UV based on UV, innovated square wheels.
734	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	850	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
735	AnyEvent::Impl::POE based on POE, very slow, some limitations.	851	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		852	AnyEvent::Impl::Irssi used when running within irssi.
		853	AnyEvent::Impl::IOAsync based on IO::Async.
		854	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		855	AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
736		856
737	Backends with special needs.	857	Backends with special needs.
738	Qt requires the Qt::Application to be instantiated first, but will	858	Qt requires the Qt::Application to be instantiated first, but will
739	otherwise be picked up automatically. As long as the main program	859	otherwise be picked up automatically. As long as the main program
740	instantiates the application before any AnyEvent watchers are	860	instantiates the application before any AnyEvent watchers are
741	created, everything should just work.	861	created, everything should just work.
742		862
743	AnyEvent::Impl::Qt based on Qt.	863	AnyEvent::Impl::Qt based on Qt.
744		864
745	Support for IO::Async can only be partial, as it is too broken and
746	architecturally limited to even support the AnyEvent API. It also is
747	the only event loop that needs the loop to be set explicitly, so it
748	can only be used by a main program knowing about AnyEvent. See
749	AnyEvent::Impl::Async for the gory details.
750
751	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
752
753	Event loops that are indirectly supported via other backends.	865	Event loops that are indirectly supported via other backends.
754	Some event loops can be supported via other modules:	866	Some event loops can be supported via other modules:
755		867
756	There is no direct support for WxWidgets (Wx) or Prima.	868	There is no direct support for WxWidgets (Wx) or Prima.
757		869
…		…
775	Contains "undef" until the first watcher is being created, before	887	Contains "undef" until the first watcher is being created, before
776	the backend has been autodetected.	888	the backend has been autodetected.
777		889
778	Afterwards it contains the event model that is being used, which is	890	Afterwards it contains the event model that is being used, which is
779	the name of the Perl class implementing the model. This class is	891	the name of the Perl class implementing the model. This class is
780	usually one of the "AnyEvent::Impl:xxx" modules, but can be any	892	usually one of the "AnyEvent::Impl::xxx" modules, but can be any
781	other class in the case AnyEvent has been extended at runtime (e.g.	893	other class in the case AnyEvent has been extended at runtime (e.g.
782	in rxvt-unicode it will be "urxvt::anyevent").	894	in rxvt-unicode it will be "urxvt::anyevent").
783		895
784	AnyEvent::detect	896	AnyEvent::detect
785	Returns $AnyEvent::MODEL, forcing autodetection of the event model	897	Returns $AnyEvent::MODEL, forcing autodetection of the event model
786	if necessary. You should only call this function right before you	898	if necessary. You should only call this function right before you
787	would have created an AnyEvent watcher anyway, that is, as late as	899	would have created an AnyEvent watcher anyway, that is, as late as
788	possible at runtime, and not e.g. while initialising of your module.	900	possible at runtime, and not e.g. during initialisation of your
		901	module.
		902
		903	The effect of calling this function is as if a watcher had been
		904	created (specifically, actions that happen "when the first watcher
		905	is created" happen when calling detetc as well).
789		906
790	If you need to do some initialisation before AnyEvent watchers are	907	If you need to do some initialisation before AnyEvent watchers are
791	created, use "post_detect".	908	created, use "post_detect".
792		909
793	$guard = AnyEvent::post_detect { BLOCK }	910	$guard = AnyEvent::post_detect { BLOCK }
794	Arranges for the code block to be executed as soon as the event	911	Arranges for the code block to be executed as soon as the event
795	model is autodetected (or immediately if this has already happened).	912	model is autodetected (or immediately if that has already happened).
796		913
797	The block will be executed after the actual backend has been	914	The block will be executed after the actual backend has been
798	detected ($AnyEvent::MODEL is set), but before any watchers have	915	detected ($AnyEvent::MODEL is set), but before any watchers have
799	been created, so it is possible to e.g. patch @AnyEvent::ISA or do	916	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
800	other initialisations - see the sources of AnyEvent::Strict or	917	other initialisations - see the sources of AnyEvent::Strict or
…		…
805	creates and installs the global IO::AIO watcher in a "post_detect"	922	creates and installs the global IO::AIO watcher in a "post_detect"
806	block to avoid autodetecting the event module at load time.	923	block to avoid autodetecting the event module at load time.
807		924
808	If called in scalar or list context, then it creates and returns an	925	If called in scalar or list context, then it creates and returns an
809	object that automatically removes the callback again when it is	926	object that automatically removes the callback again when it is
		927	destroyed (or "undef" when the hook was immediately executed). See
810	destroyed. See Coro::BDB for a case where this is useful.	928	AnyEvent::AIO for a case where this is useful.
		929
		930	Example: Create a watcher for the IO::AIO module and store it in
		931	$WATCHER, but do so only do so after the event loop is initialised.
		932
		933	our WATCHER;
		934
		935	my $guard = AnyEvent::post_detect {
		936	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		937	};
		938
		939	# the \|\|= is important in case post_detect immediately runs the block,
		940	# as to not clobber the newly-created watcher. assigning both watcher and
		941	# post_detect guard to the same variable has the advantage of users being
		942	# able to just C<undef $WATCHER> if the watcher causes them grief.
		943
		944	$WATCHER \|\|= $guard;
811		945
812	@AnyEvent::post_detect	946	@AnyEvent::post_detect
813	If there are any code references in this array (you can "push" to it	947	If there are any code references in this array (you can "push" to it
814	before or after loading AnyEvent), then they will called directly	948	before or after loading AnyEvent), then they will be called directly
815	after the event loop has been chosen.	949	after the event loop has been chosen.
816		950
817	You should check $AnyEvent::MODEL before adding to this array,	951	You should check $AnyEvent::MODEL before adding to this array,
818	though: if it is defined then the event loop has already been	952	though: if it is defined then the event loop has already been
819	detected, and the array will be ignored.	953	detected, and the array will be ignored.
820		954
821	Best use "AnyEvent::post_detect { BLOCK }" when your application	955	Best use "AnyEvent::post_detect { BLOCK }" when your application
822	allows it,as it takes care of these details.	956	allows it, as it takes care of these details.
823		957
824	This variable is mainly useful for modules that can do something	958	This variable is mainly useful for modules that can do something
825	useful when AnyEvent is used and thus want to know when it is	959	useful when AnyEvent is used and thus want to know when it is
826	initialised, but do not need to even load it by default. This array	960	initialised, but do not need to even load it by default. This array
827	provides the means to hook into AnyEvent passively, without loading	961	provides the means to hook into AnyEvent passively, without loading
828	it.	962	it.
829		963
		964	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		965	together, you could put this into Coro (this is the actual code used
		966	by Coro to accomplish this):
		967
		968	if (defined $AnyEvent::MODEL) {
		969	# AnyEvent already initialised, so load Coro::AnyEvent
		970	require Coro::AnyEvent;
		971	} else {
		972	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		973	# as soon as it is
		974	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		975	}
		976
		977	AnyEvent::postpone { BLOCK }
		978	Arranges for the block to be executed as soon as possible, but not
		979	before the call itself returns. In practise, the block will be
		980	executed just before the event loop polls for new events, or shortly
		981	afterwards.
		982
		983	This function never returns anything (to make the "return postpone {
		984	... }" idiom more useful.
		985
		986	To understand the usefulness of this function, consider a function
		987	that asynchronously does something for you and returns some
		988	transaction object or guard to let you cancel the operation. For
		989	example, "AnyEvent::Socket::tcp_connect":
		990
		991	# start a connection attempt unless one is active
		992	$self->{connect_guard} \|\|= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		993	delete $self->{connect_guard};
		994	...
		995	};
		996
		997	Imagine that this function could instantly call the callback, for
		998	example, because it detects an obvious error such as a negative port
		999	number. Invoking the callback before the function returns causes
		1000	problems however: the callback will be called and will try to delete
		1001	the guard object. But since the function hasn't returned yet, there
		1002	is nothing to delete. When the function eventually returns it will
		1003	assign the guard object to "$self->{connect_guard}", where it will
		1004	likely never be deleted, so the program thinks it is still trying to
		1005	connect.
		1006
		1007	This is where "AnyEvent::postpone" should be used. Instead of
		1008	calling the callback directly on error:
		1009
		1010	$cb->(undef), return # signal error to callback, BAD!
		1011	if $some_error_condition;
		1012
		1013	It should use "postpone":
		1014
		1015	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1016	if $some_error_condition;
		1017
		1018	AnyEvent::log $level, $msg[, @args]
		1019	Log the given $msg at the given $level.
		1020
		1021	If AnyEvent::Log is not loaded then this function makes a simple
		1022	test to see whether the message will be logged. If the test succeeds
		1023	it will load AnyEvent::Log and call "AnyEvent::Log::log" -
		1024	consequently, look at the AnyEvent::Log documentation for details.
		1025
		1026	If the test fails it will simply return. Right now this happens when
		1027	a numerical loglevel is used and it is larger than the level
		1028	specified via $ENV{PERL_ANYEVENT_VERBOSE}.
		1029
		1030	If you want to sprinkle loads of logging calls around your code,
		1031	consider creating a logger callback with the "AnyEvent::Log::logger"
		1032	function, which can reduce typing, codesize and can reduce the
		1033	logging overhead enourmously.
		1034
830	WHAT TO DO IN A MODULE	1035	WHAT TO DO IN A MODULE
831	As a module author, you should "use AnyEvent" and call AnyEvent methods	1036	As a module author, you should "use AnyEvent" and call AnyEvent methods
832	freely, but you should not load a specific event module or rely on it.	1037	freely, but you should not load a specific event module or rely on it.
833		1038
834	Be careful when you create watchers in the module body - AnyEvent will	1039	Be careful when you create watchers in the module body - AnyEvent will
…		…
841	stall the whole program, and the whole point of using events is to stay	1046	stall the whole program, and the whole point of using events is to stay
842	interactive.	1047	interactive.
843		1048
844	It is fine, however, to call "->recv" when the user of your module	1049	It is fine, however, to call "->recv" when the user of your module
845	requests it (i.e. if you create a http request object ad have a method	1050	requests it (i.e. if you create a http request object ad have a method
846	called "results" that returns the results, it should call "->recv"	1051	called "results" that returns the results, it may call "->recv" freely,
847	freely, as the user of your module knows what she is doing. always).	1052	as the user of your module knows what she is doing. Always).
848		1053
849	WHAT TO DO IN THE MAIN PROGRAM	1054	WHAT TO DO IN THE MAIN PROGRAM
850	There will always be a single main program - the only place that should	1055	There will always be a single main program - the only place that should
851	dictate which event model to use.	1056	dictate which event model to use.
852		1057
853	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	1058	If the program is not event-based, it need not do anything special, even
854	do anything special (it does not need to be event-based) and let	1059	when it depends on a module that uses an AnyEvent. If the program itself
855	AnyEvent decide which implementation to chose if some module relies on	1060	uses AnyEvent, but does not care which event loop is used, all it needs
856	it.	1061	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		1062	available loop implementation.
857		1063
858	If the main program relies on a specific event model - for example, in	1064	If the main program relies on a specific event model - for example, in
859	Gtk2 programs you have to rely on the Glib module - you should load the	1065	Gtk2 programs you have to rely on the Glib module - you should load the
860	event module before loading AnyEvent or any module that uses it:	1066	event module before loading AnyEvent or any module that uses it:
861	generally speaking, you should load it as early as possible. The reason	1067	generally speaking, you should load it as early as possible. The reason
862	is that modules might create watchers when they are loaded, and AnyEvent	1068	is that modules might create watchers when they are loaded, and AnyEvent
863	will decide on the event model to use as soon as it creates watchers,	1069	will decide on the event model to use as soon as it creates watchers,
864	and it might chose the wrong one unless you load the correct one	1070	and it might choose the wrong one unless you load the correct one
865	yourself.	1071	yourself.
866		1072
867	You can chose to use a pure-perl implementation by loading the	1073	You can chose to use a pure-perl implementation by loading the
868	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1074	"AnyEvent::Loop" module, which gives you similar behaviour everywhere,
869	everywhere, but letting AnyEvent chose the model is generally better.	1075	but letting AnyEvent chose the model is generally better.
870		1076
871	MAINLOOP EMULATION	1077	MAINLOOP EMULATION
872	Sometimes (often for short test scripts, or even standalone programs who	1078	Sometimes (often for short test scripts, or even standalone programs who
873	only want to use AnyEvent), you do not want to run a specific event	1079	only want to use AnyEvent), you do not want to run a specific event
874	loop.	1080	loop.
…		…
886		1092
887	OTHER MODULES	1093	OTHER MODULES
888	The following is a non-exhaustive list of additional modules that use	1094	The following is a non-exhaustive list of additional modules that use
889	AnyEvent as a client and can therefore be mixed easily with other	1095	AnyEvent as a client and can therefore be mixed easily with other
890	AnyEvent modules and other event loops in the same program. Some of the	1096	AnyEvent modules and other event loops in the same program. Some of the
891	modules come with AnyEvent, most are available via CPAN.	1097	modules come as part of AnyEvent, the others are available via CPAN (see
		1098	<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
		1099	non-exhaustive list), and the list is heavily biased towards modules of
		1100	the AnyEvent author himself :)
892		1101
893	AnyEvent::Util	1102	AnyEvent::Util (part of the AnyEvent distribution)
894	Contains various utility functions that replace often-used but	1103	Contains various utility functions that replace often-used blocking
895	blocking functions such as "inet_aton" by event-/callback-based	1104	functions such as "inet_aton" with event/callback-based versions.
896	versions.
897		1105
898	AnyEvent::Socket	1106	AnyEvent::Socket (part of the AnyEvent distribution)
899	Provides various utility functions for (internet protocol) sockets,	1107	Provides various utility functions for (internet protocol) sockets,
900	addresses and name resolution. Also functions to create non-blocking	1108	addresses and name resolution. Also functions to create non-blocking
901	tcp connections or tcp servers, with IPv6 and SRV record support and	1109	tcp connections or tcp servers, with IPv6 and SRV record support and
902	more.	1110	more.
903		1111
904	AnyEvent::Handle	1112	AnyEvent::Handle (part of the AnyEvent distribution)
905	Provide read and write buffers, manages watchers for reads and	1113	Provide read and write buffers, manages watchers for reads and
906	writes, supports raw and formatted I/O, I/O queued and fully	1114	writes, supports raw and formatted I/O, I/O queued and fully
907	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.	1115	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
908		1116
909	AnyEvent::DNS	1117	AnyEvent::DNS (part of the AnyEvent distribution)
910	Provides rich asynchronous DNS resolver capabilities.	1118	Provides rich asynchronous DNS resolver capabilities.
911		1119
912	AnyEvent::HTTP	1120	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
913	A simple-to-use HTTP library that is capable of making a lot of	1121	AnyEvent::IGS, AnyEvent::FCP
914	concurrent HTTP requests.	1122	Implement event-based interfaces to the protocols of the same name
		1123	(for the curious, IGS is the International Go Server and FCP is the
		1124	Freenet Client Protocol).
915		1125
		1126	AnyEvent::AIO (part of the AnyEvent distribution)
		1127	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1128	the toolbox of every event programmer. AnyEvent::AIO transparently
		1129	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1130	event-based file I/O, and much more.
		1131
		1132	AnyEvent::Fork, AnyEvent::Fork::RPC, AnyEvent::Fork::Pool,
		1133	AnyEvent::Fork::Remote
		1134	These let you safely fork new subprocesses, either locally or
		1135	remotely (e.g.v ia ssh), using some RPC protocol or not, without the
		1136	limitations normally imposed by fork (AnyEvent works fine for
		1137	example). Dynamically-resized worker pools are obviously included as
		1138	well.
		1139
		1140	And they are quite tiny and fast as well - "abusing" AnyEvent::Fork
		1141	just to exec external programs can easily beat using "fork" and
		1142	"exec" (or even "system") in most programs.
		1143
		1144	AnyEvent::Filesys::Notify
		1145	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1146	path changes (e.g. "watch this directory for new files", "watch this
		1147	file for changes"). The AnyEvent::Filesys::Notify module promises to
		1148	do just that in a portbale fashion, supporting inotify on GNU/Linux
		1149	and some weird, without doubt broken, stuff on OS X to monitor
		1150	files. It can fall back to blocking scans at regular intervals
		1151	transparently on other platforms, so it's about as portable as it
		1152	gets.
		1153
		1154	(I haven't used it myself, but it seems the biggest problem with it
		1155	is it quite bad performance).
		1156
916	AnyEvent::HTTPD	1157	AnyEvent::DBI
917	Provides a simple web application server framework.	1158	Executes DBI requests asynchronously in a proxy process for you,
		1159	notifying you in an event-based way when the operation is finished.
918		1160
919	AnyEvent::FastPing	1161	AnyEvent::FastPing
920	The fastest ping in the west.	1162	The fastest ping in the west.
921		1163
922	AnyEvent::DBI
923	Executes DBI requests asynchronously in a proxy process.
924
925	AnyEvent::AIO
926	Truly asynchronous I/O, should be in the toolbox of every event
927	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
928	together.
929
930	AnyEvent::BDB
931	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
932	fuses BDB and AnyEvent together.
933
934	AnyEvent::GPSD
935	A non-blocking interface to gpsd, a daemon delivering GPS
936	information.
937
938	AnyEvent::IRC
939	AnyEvent based IRC client module family (replacing the older
940	Net::IRC3).
941
942	AnyEvent::XMPP
943	AnyEvent based XMPP (Jabber protocol) module family (replacing the
944	older Net::XMPP2>.
945
946	AnyEvent::IGS
947	A non-blocking interface to the Internet Go Server protocol (used by
948	App::IGS).
949
950	Net::FCP
951	AnyEvent-based implementation of the Freenet Client Protocol,
952	birthplace of AnyEvent.
953
954	Event::ExecFlow
955	High level API for event-based execution flow control.
956
957	Coro	1164	Coro
958	Has special support for AnyEvent via Coro::AnyEvent.	1165	Has special support for AnyEvent via Coro::AnyEvent, which allows
		1166	you to simply invert the flow control - don't call us, we will call
		1167	you:
		1168
		1169	async {
		1170	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
		1171	print "5 seconds later!\n";
		1172
		1173	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
		1174	my $line = <STDIN>; # works for ttys
		1175
		1176	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
		1177	my ($body, $hdr) = Coro::rouse_wait;
		1178	};
		1179
		1180	SIMPLIFIED AE API
		1181	Starting with version 5.0, AnyEvent officially supports a second, much
		1182	simpler, API that is designed to reduce the calling, typing and memory
		1183	overhead by using function call syntax and a fixed number of parameters.
		1184
		1185	See the AE manpage for details.
959		1186
960	ERROR AND EXCEPTION HANDLING	1187	ERROR AND EXCEPTION HANDLING
961	In general, AnyEvent does not do any error handling - it relies on the	1188	In general, AnyEvent does not do any error handling - it relies on the
962	caller to do that if required. The AnyEvent::Strict module (see also the	1189	caller to do that if required. The AnyEvent::Strict module (see also the
963	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	1190	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
972	The pure perl event loop simply re-throws the exception (usually within	1199	The pure perl event loop simply re-throws the exception (usually within
973	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1200	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
974	Glib uses "install_exception_handler" and so on.	1201	Glib uses "install_exception_handler" and so on.
975		1202
976	ENVIRONMENT VARIABLES	1203	ENVIRONMENT VARIABLES
977	The following environment variables are used by this module or its	1204	AnyEvent supports a number of environment variables that tune the
978	submodules.	1205	runtime behaviour. They are usually evaluated when AnyEvent is loaded,
		1206	initialised, or a submodule that uses them is loaded. Many of them also
		1207	cause AnyEvent to load additional modules - for example,
		1208	"PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
		1209	loaded.
979		1210
980	Note that AnyEvent will remove all environment variables starting with	1211	All the environment variables documented here start with
981	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is	1212	"PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
982	enabled.	1213	Other modules are encouraged (but by no means required) to use
		1214	"PERL_ANYEVENT_SUBMODULE" if they have registered the
		1215	AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
		1216	AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
		1217	should not access env variables starting with "AE_", see below).
		1218
		1219	All variables can also be set via the "AE_" prefix, that is, instead of
		1220	setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
		1221	there is a clash btween anyevent and another program that uses
		1222	"AE_something" you can set the corresponding "PERL_ANYEVENT_something"
		1223	variable to the empty string, as those variables take precedence.
		1224
		1225	When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
		1226	their "PERL_ANYEVENT_xxx" counterpart unless that variable already
		1227	exists. If taint mode is on, then AnyEvent will remove all environment
		1228	variables starting with "PERL_ANYEVENT_" from %ENV (or replace them with
		1229	"undef" or the empty string, if the corresaponding "AE_" variable is
		1230	set).
		1231
		1232	The exact algorithm is currently:
		1233
		1234	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		1235	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		1236	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		1237
		1238	This ensures that child processes will not see the "AE_" variables.
		1239
		1240	The following environment variables are currently known to AnyEvent:
983		1241
984	"PERL_ANYEVENT_VERBOSE"	1242	"PERL_ANYEVENT_VERBOSE"
985	By default, AnyEvent will be completely silent except in fatal	1243	By default, AnyEvent will log messages with loglevel 4 ("error") or
986	conditions. You can set this environment variable to make AnyEvent	1244	higher (see AnyEvent::Log). You can set this environment variable to
987	more talkative.	1245	a numerical loglevel to make AnyEvent more (or less) talkative.
988		1246
		1247	If you want to do more than just set the global logging level you
		1248	should have a look at "PERL_ANYEVENT_LOG", which allows much more
		1249	complex specifications.
		1250
		1251	When set to 0 ("off"), then no messages whatsoever will be logged
		1252	with everything else at defaults.
		1253
989	When set to 1 or higher, causes AnyEvent to warn about unexpected	1254	When set to 5 or higher ("warn"), AnyEvent warns about unexpected
990	conditions, such as not being able to load the event model specified	1255	conditions, such as not being able to load the event model specified
991	by "PERL_ANYEVENT_MODEL".	1256	by "PERL_ANYEVENT_MODEL", or a guard callback throwing an exception
		1257	- this is the minimum recommended level for use during development.
992		1258
993	When set to 2 or higher, cause AnyEvent to report to STDERR which	1259	When set to 7 or higher (info), AnyEvent reports which event model
994	event model it chooses.	1260	it chooses.
		1261
		1262	When set to 8 or higher (debug), then AnyEvent will report extra
		1263	information on which optional modules it loads and how it implements
		1264	certain features.
		1265
		1266	"PERL_ANYEVENT_LOG"
		1267	Accepts rather complex logging specifications. For example, you
		1268	could log all "debug" messages of some module to stderr, warnings
		1269	and above to stderr, and errors and above to syslog, with:
		1270
		1271	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		1272
		1273	For the rather extensive details, see AnyEvent::Log.
		1274
		1275	This variable is evaluated when AnyEvent (or AnyEvent::Log) is
		1276	loaded, so will take effect even before AnyEvent has initialised
		1277	itself.
		1278
		1279	Note that specifying this environment variable causes the
		1280	AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
		1281	does not, so only using the latter saves a few hundred kB of memory
		1282	unless a module explicitly needs the extra features of
		1283	AnyEvent::Log.
995		1284
996	"PERL_ANYEVENT_STRICT"	1285	"PERL_ANYEVENT_STRICT"
997	AnyEvent does not do much argument checking by default, as thorough	1286	AnyEvent does not do much argument checking by default, as thorough
998	argument checking is very costly. Setting this variable to a true	1287	argument checking is very costly. Setting this variable to a true
999	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1288	value will cause AnyEvent to load "AnyEvent::Strict" and then to
1000	thoroughly check the arguments passed to most method calls. If it	1289	thoroughly check the arguments passed to most method calls. If it
1001	finds any problems, it will croak.	1290	finds any problems, it will croak.
1002		1291
1003	In other words, enables "strict" mode.	1292	In other words, enables "strict" mode.
1004		1293
1005	Unlike "use strict", it is definitely recommended to keep it off in	1294	Unlike "use strict" (or its modern cousin, "use common::sense", it
1006	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment	1295	is definitely recommended to keep it off in production. Keeping
		1296	"PERL_ANYEVENT_STRICT=1" in your environment while developing
1007	while developing programs can be very useful, however.	1297	programs can be very useful, however.
		1298
		1299	"PERL_ANYEVENT_DEBUG_SHELL"
		1300	If this env variable is nonempty, then its contents will be
		1301	interpreted by "AnyEvent::Socket::parse_hostport" and
		1302	"AnyEvent::Debug::shell" (after replacing every occurance of $$ by
		1303	the process pid). The shell object is saved in
		1304	$AnyEvent::Debug::SHELL.
		1305
		1306	This happens when the first watcher is created.
		1307
		1308	For example, to bind a debug shell on a unix domain socket in
		1309	/tmp/debug<pid>.sock, you could use this:
		1310
		1311	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		1312	# connect with e.g.: socat readline /tmp/debug123.sock
		1313
		1314	Or to bind to tcp port 4545 on localhost:
		1315
		1316	PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
		1317	# connect with e.g.: telnet localhost 4545
		1318
		1319	Note that creating sockets in /tmp or on localhost is very unsafe on
		1320	multiuser systems.
		1321
		1322	"PERL_ANYEVENT_DEBUG_WRAP"
		1323	Can be set to 0, 1 or 2 and enables wrapping of all watchers for
		1324	debugging purposes. See "AnyEvent::Debug::wrap" for details.
1008		1325
1009	"PERL_ANYEVENT_MODEL"	1326	"PERL_ANYEVENT_MODEL"
1010	This can be used to specify the event model to be used by AnyEvent,	1327	This can be used to specify the event model to be used by AnyEvent,
1011	before auto detection and -probing kicks in. It must be a string	1328	before auto detection and -probing kicks in.
1012	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1329
1013	gets prepended and the resulting module name is loaded and if the	1330	It normally is a string consisting entirely of ASCII letters (e.g.
1014	load was successful, used as event model. If it fails to load	1331	"EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
		1332	the resulting module name is loaded and - if the load was successful
		1333	- used as event model backend. If it fails to load then AnyEvent
1015	AnyEvent will proceed with auto detection and -probing.	1334	will proceed with auto detection and -probing.
1016		1335
1017	This functionality might change in future versions.	1336	If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
		1337	then nothing gets prepended and the module name is used as-is (hint:
		1338	"::" at the end of a string designates a module name and quotes it
		1339	appropriately).
1018		1340
1019	For example, to force the pure perl model (AnyEvent::Impl::Perl) you	1341	For example, to force the pure perl model (AnyEvent::Loop::Perl) you
1020	could start your program like this:	1342	could start your program like this:
1021		1343
1022	PERL_ANYEVENT_MODEL=Perl perl ...	1344	PERL_ANYEVENT_MODEL=Perl perl ...
		1345
		1346	"PERL_ANYEVENT_IO_MODEL"
		1347	The current file I/O model - see AnyEvent::IO for more info.
		1348
		1349	At the moment, only "Perl" (small, pure-perl, synchronous) and
		1350	"IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
		1351	if AnyEvent::AIO can be loaded, otherwise it is "Perl".
1023		1352
1024	"PERL_ANYEVENT_PROTOCOLS"	1353	"PERL_ANYEVENT_PROTOCOLS"
1025	Used by both AnyEvent::DNS and AnyEvent::Socket to determine	1354	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
1026	preferences for IPv4 or IPv6. The default is unspecified (and might	1355	preferences for IPv4 or IPv6. The default is unspecified (and might
1027	change, or be the result of auto probing).	1356	change, or be the result of auto probing).
…		…
1031	mentioned will be used, and preference will be given to protocols	1360	mentioned will be used, and preference will be given to protocols
1032	mentioned earlier in the list.	1361	mentioned earlier in the list.
1033		1362
1034	This variable can effectively be used for denial-of-service attacks	1363	This variable can effectively be used for denial-of-service attacks
1035	against local programs (e.g. when setuid), although the impact is	1364	against local programs (e.g. when setuid), although the impact is
1036	likely small, as the program has to handle conenction and other	1365	likely small, as the program has to handle connection and other
1037	failures anyways.	1366	failures anyways.
1038		1367
1039	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1368	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
1040	IPv6, but support both and try to use both.	1369	IPv6, but support both and try to use both.
1041	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1370	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
1042	resolve or contact IPv6 addresses.	1371	resolve or contact IPv6 addresses.
1043	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but	1372	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
1044	prefer IPv6 over IPv4.	1373	prefer IPv6 over IPv4.
1045		1374
		1375	"PERL_ANYEVENT_HOSTS"
		1376	This variable, if specified, overrides the /etc/hosts file used by
		1377	AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
		1378	read from that file instead.
		1379
1046	"PERL_ANYEVENT_EDNS0"	1380	"PERL_ANYEVENT_EDNS0"
1047	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension	1381	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
1048	for DNS. This extension is generally useful to reduce DNS traffic,	1382	for DNS. This extension is generally useful to reduce DNS traffic,
1049	but some (broken) firewalls drop such DNS packets, which is why it	1383	especially when DNSSEC is involved, but some (broken) firewalls drop
1050	is off by default.	1384	such DNS packets, which is why it is off by default.
1051		1385
1052	Setting this variable to 1 will cause AnyEvent::DNS to announce	1386	Setting this variable to 1 will cause AnyEvent::DNS to announce
1053	EDNS0 in its DNS requests.	1387	EDNS0 in its DNS requests.
1054		1388
1055	"PERL_ANYEVENT_MAX_FORKS"	1389	"PERL_ANYEVENT_MAX_FORKS"
…		…
1059	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"	1393	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
1060	The default value for the "max_outstanding" parameter for the	1394	The default value for the "max_outstanding" parameter for the
1061	default DNS resolver - this is the maximum number of parallel DNS	1395	default DNS resolver - this is the maximum number of parallel DNS
1062	requests that are sent to the DNS server.	1396	requests that are sent to the DNS server.
1063		1397
		1398	"PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
		1399	Perl has inherently racy signal handling (you can basically choose
		1400	between losing signals and memory corruption) - pure perl event
		1401	loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
		1402	available) therefore have to poll regularly to avoid losing signals.
		1403
		1404	Some event loops are racy, but don't poll regularly, and some event
		1405	loops are written in C but are still racy. For those event loops,
		1406	AnyEvent installs a timer that regularly wakes up the event loop.
		1407
		1408	By default, the interval for this timer is 10 seconds, but you can
		1409	override this delay with this environment variable (or by setting
		1410	the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
		1411	watchers).
		1412
		1413	Lower values increase CPU (and energy) usage, higher values can
		1414	introduce long delays when reaping children or waiting for signals.
		1415
		1416	The AnyEvent::Async module, if available, will be used to avoid this
		1417	polling (with most event loops).
		1418
1064	"PERL_ANYEVENT_RESOLV_CONF"	1419	"PERL_ANYEVENT_RESOLV_CONF"
1065	The file to use instead of /etc/resolv.conf (or OS-specific	1420	The absolute path to a resolv.conf-style file to use instead of
1066	configuration) in the default resolver. When set to the empty	1421	/etc/resolv.conf (or the OS-specific configuration) in the default
1067	string, no default config will be used.	1422	resolver, or the empty string to select the default configuration.
1068		1423
1069	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".	1424	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
1070	When neither "ca_file" nor "ca_path" was specified during	1425	When neither "ca_file" nor "ca_path" was specified during
1071	AnyEvent::TLS context creation, and either of these environment	1426	AnyEvent::TLS context creation, and either of these environment
1072	variables exist, they will be used to specify CA certificate	1427	variables are nonempty, they will be used to specify CA certificate
1073	locations instead of a system-dependent default.	1428	locations instead of a system-dependent default.
		1429
		1430	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1431	When these are set to 1, then the respective modules are not loaded.
		1432	Mostly good for testing AnyEvent itself.
1074		1433
1075	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1434	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
1076	This is an advanced topic that you do not normally need to use AnyEvent	1435	This is an advanced topic that you do not normally need to use AnyEvent
1077	in a module. This section is only of use to event loop authors who want	1436	in a module. This section is only of use to event loop authors who want
1078	to provide AnyEvent compatibility.	1437	to provide AnyEvent compatibility.
…		…
1133	warn "read: $input\n"; # output what has been read	1492	warn "read: $input\n"; # output what has been read
1134	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1493	$cv->send if $input =~ /^q/i; # quit program if /^q/i
1135	},	1494	},
1136	);	1495	);
1137		1496
1138	my $time_watcher; # can only be used once
1139
1140	sub new_timer {
1141	$timer = AnyEvent->timer (after => 1, cb => sub {	1497	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
1142	warn "timeout\n"; # print 'timeout' about every second	1498	warn "timeout\n"; # print 'timeout' at most every second
1143	&new_timer; # and restart the time
1144	});
1145	}	1499	});
1146
1147	new_timer; # create first timer
1148		1500
1149	$cv->recv; # wait until user enters /^q/i	1501	$cv->recv; # wait until user enters /^q/i
1150		1502
1151	REAL-WORLD EXAMPLE	1503	REAL-WORLD EXAMPLE
1152	Consider the Net::FCP module. It features (among others) the following	1504	Consider the Net::FCP module. It features (among others) the following
…		…
1224		1576
1225	The actual code goes further and collects all errors ("die"s,	1577	The actual code goes further and collects all errors ("die"s,
1226	exceptions) that occurred during request processing. The "result" method	1578	exceptions) that occurred during request processing. The "result" method
1227	detects whether an exception as thrown (it is stored inside the $txn	1579	detects whether an exception as thrown (it is stored inside the $txn
1228	object) and just throws the exception, which means connection errors and	1580	object) and just throws the exception, which means connection errors and
1229	other problems get reported tot he code that tries to use the result,	1581	other problems get reported to the code that tries to use the result,
1230	not in a random callback.	1582	not in a random callback.
1231		1583
1232	All of this enables the following usage styles:	1584	All of this enables the following usage styles:
1233		1585
1234	1. Blocking:	1586	1. Blocking:
…		…
1279	through AnyEvent. The benchmark creates a lot of timers (with a zero	1631	through AnyEvent. The benchmark creates a lot of timers (with a zero
1280	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1632	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1281	which it is), lets them fire exactly once and destroys them again.	1633	which it is), lets them fire exactly once and destroys them again.
1282		1634
1283	Source code for this benchmark is found as eg/bench in the AnyEvent	1635	Source code for this benchmark is found as eg/bench in the AnyEvent
1284	distribution.	1636	distribution. It uses the AE interface, which makes a real difference
		1637	for the EV and Perl backends only.
1285		1638
1286	Explanation of the columns	1639	Explanation of the columns
1287	watcher is the number of event watchers created/destroyed. Since	1640	watcher is the number of event watchers created/destroyed. Since
1288	different event models feature vastly different performances, each event	1641	different event models feature vastly different performances, each event
1289	loop was given a number of watchers so that overall runtime is	1642	loop was given a number of watchers so that overall runtime is
…		…
1308	destroy is the time, in microseconds, that it takes to destroy a	1661	destroy is the time, in microseconds, that it takes to destroy a
1309	single watcher.	1662	single watcher.
1310		1663
1311	Results	1664	Results
1312	name watchers bytes create invoke destroy comment	1665	name watchers bytes create invoke destroy comment
1313	EV/EV 400000 224 0.47 0.35 0.27 EV native interface	1666	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1314	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers	1667	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1315	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal	1668	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1316	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation	1669	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1317	Event/Event 16000 517 32.20 31.80 0.81 Event native interface	1670	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1318	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers	1671	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
1319	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll	1672	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
1320	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll	1673	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1321	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour	1674	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1322	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers	1675	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1323	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event	1676	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1324	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select	1677	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1325		1678
1326	Discussion	1679	Discussion
1327	The benchmark does not measure scalability of the event loop very	1680	The benchmark does not measure scalability of the event loop very
1328	well. For example, a select-based event loop (such as the pure perl one)	1681	well. For example, a select-based event loop (such as the pure perl one)
1329	can never compete with an event loop that uses epoll when the number of	1682	can never compete with an event loop that uses epoll when the number of
…		…
1340	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1693	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1341	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1694	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1342	CPU cycles with POE.	1695	CPU cycles with POE.
1343		1696
1344	"EV" is the sole leader regarding speed and memory use, which are both	1697	"EV" is the sole leader regarding speed and memory use, which are both
1345	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1698	maximal/minimal, respectively. When using the AE API there is zero
		1699	overhead (when going through the AnyEvent API create is about 5-6 times
		1700	slower, with other times being equal, so still uses far less memory than
1346	far less memory than any other event loop and is still faster than Event	1701	any other event loop and is still faster than Event natively).
1347	natively.
1348		1702
1349	The pure perl implementation is hit in a few sweet spots (both the	1703	The pure perl implementation is hit in a few sweet spots (both the
1350	constant timeout and the use of a single fd hit optimisations in the	1704	constant timeout and the use of a single fd hit optimisations in the
1351	perl interpreter and the backend itself). Nevertheless this shows that	1705	perl interpreter and the backend itself). Nevertheless this shows that
1352	it adds very little overhead in itself. Like any select-based backend	1706	it adds very little overhead in itself. Like any select-based backend
…		…
1398	when used without AnyEvent), but most event loops have acceptable	1752	when used without AnyEvent), but most event loops have acceptable
1399	performance with or without AnyEvent.	1753	performance with or without AnyEvent.
1400		1754
1401	* The overhead AnyEvent adds is usually much smaller than the overhead	1755	* The overhead AnyEvent adds is usually much smaller than the overhead
1402	of the actual event loop, only with extremely fast event loops such	1756	of the actual event loop, only with extremely fast event loops such
1403	as EV adds AnyEvent significant overhead.	1757	as EV does AnyEvent add significant overhead.
1404		1758
1405	* You should avoid POE like the plague if you want performance or	1759	* You should avoid POE like the plague if you want performance or
1406	reasonable memory usage.	1760	reasonable memory usage.
1407		1761
1408	BENCHMARKING THE LARGE SERVER CASE	1762	BENCHMARKING THE LARGE SERVER CASE
…		…
1422	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1776	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1423	100 (1%) are active. This mirrors the activity of large servers with	1777	100 (1%) are active. This mirrors the activity of large servers with
1424	many connections, most of which are idle at any one point in time.	1778	many connections, most of which are idle at any one point in time.
1425		1779
1426	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1780	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1427	distribution.	1781	distribution. It uses the AE interface, which makes a real difference
		1782	for the EV and Perl backends only.
1428		1783
1429	Explanation of the columns	1784	Explanation of the columns
1430	sockets is the number of sockets, and twice the number of "servers"	1785	sockets is the number of sockets, and twice the number of "servers"
1431	(as each server has a read and write socket end).	1786	(as each server has a read and write socket end).
1432		1787
…		…
1438	forwarding it to another server. This includes deleting the old timeout	1793	forwarding it to another server. This includes deleting the old timeout
1439	and creating a new one that moves the timeout into the future.	1794	and creating a new one that moves the timeout into the future.
1440		1795
1441	Results	1796	Results
1442	name sockets create request	1797	name sockets create request
1443	EV 20000 69.01 11.16	1798	EV 20000 62.66 7.99
1444	Perl 20000 73.32 35.87	1799	Perl 20000 68.32 32.64
1445	IOAsync 20000 157.00 98.14 epoll	1800	IOAsync 20000 174.06 101.15 epoll
1446	IOAsync 20000 159.31 616.06 poll	1801	IOAsync 20000 174.67 610.84 poll
1447	Event 20000 212.62 257.32	1802	Event 20000 202.69 242.91
1448	Glib 20000 651.16 1896.30	1803	Glib 20000 557.01 1689.52
1449	POE 20000 349.67 12317.24 uses POE::Loop::Event	1804	POE 20000 341.54 12086.32 uses POE::Loop::Event
1450		1805
1451	Discussion	1806	Discussion
1452	This benchmark does measure scalability and overall performance of the	1807	This benchmark does measure scalability and overall performance of the
1453	particular event loop.	1808	particular event loop.
1454		1809
…		…
1567	As you can see, the AnyEvent + EV combination even beats the	1922	As you can see, the AnyEvent + EV combination even beats the
1568	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl	1923	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
1569	backend easily beats IO::Lambda and POE.	1924	backend easily beats IO::Lambda and POE.
1570		1925
1571	And even the 100% non-blocking version written using the high-level (and	1926	And even the 100% non-blocking version written using the high-level (and
1572	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a	1927	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
1573	large margin, even though it does all of DNS, tcp-connect and socket I/O	1928	higher level ("unoptimised") abstractions by a large margin, even though
1574	in a non-blocking way.	1929	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
1575		1930
1576	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and	1931	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
1577	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are	1932	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
1578	part of the IO::lambda distribution and were used without any changes.	1933	part of the IO::Lambda distribution and were used without any changes.
1579		1934
1580	SIGNALS	1935	SIGNALS
1581	AnyEvent currently installs handlers for these signals:	1936	AnyEvent currently installs handlers for these signals:
1582		1937
1583	SIGCHLD	1938	SIGCHLD
…		…
1603	it is that this way, the handler will be restored to defaults on	1958	it is that this way, the handler will be restored to defaults on
1604	exec.	1959	exec.
1605		1960
1606	Feel free to install your own handler, or reset it to defaults.	1961	Feel free to install your own handler, or reset it to defaults.
1607		1962
		1963	RECOMMENDED/OPTIONAL MODULES
		1964	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1965	its built-in modules) are required to use it.
		1966
		1967	That does not mean that AnyEvent won't take advantage of some additional
		1968	modules if they are installed.
		1969
		1970	This section explains which additional modules will be used, and how
		1971	they affect AnyEvent's operation.
		1972
		1973	Async::Interrupt
		1974	This slightly arcane module is used to implement fast signal
		1975	handling: To my knowledge, there is no way to do completely
		1976	race-free and quick signal handling in pure perl. To ensure that
		1977	signals still get delivered, AnyEvent will start an interval timer
		1978	to wake up perl (and catch the signals) with some delay (default is
		1979	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1980
		1981	If this module is available, then it will be used to implement
		1982	signal catching, which means that signals will not be delayed, and
		1983	the event loop will not be interrupted regularly, which is more
		1984	efficient (and good for battery life on laptops).
		1985
		1986	This affects not just the pure-perl event loop, but also other event
		1987	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1988
		1989	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1990	natively, and either employ their own workarounds (POE) or use
		1991	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1992	Installing Async::Interrupt does nothing for those backends.
		1993
		1994	EV This module isn't really "optional", as it is simply one of the
		1995	backend event loops that AnyEvent can use. However, it is simply the
		1996	best event loop available in terms of features, speed and stability:
		1997	It supports the AnyEvent API optimally, implements all the watcher
		1998	types in XS, does automatic timer adjustments even when no monotonic
		1999	clock is available, can take avdantage of advanced kernel interfaces
		2000	such as "epoll" and "kqueue", and is the fastest backend by far.
		2001	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		2002	Glib::EV).
		2003
		2004	If you only use backends that rely on another event loop (e.g.
		2005	"Tk"), then this module will do nothing for you.
		2006
		2007	Guard
		2008	The guard module, when used, will be used to implement
		2009	"AnyEvent::Util::guard". This speeds up guards considerably (and
		2010	uses a lot less memory), but otherwise doesn't affect guard
		2011	operation much. It is purely used for performance.
		2012
		2013	JSON and JSON::XS
		2014	One of these modules is required when you want to read or write JSON
		2015	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		2016	can take advantage of the ultra-high-speed JSON::XS module when it
		2017	is installed.
		2018
		2019	Net::SSLeay
		2020	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2021	worthwhile: If this module is installed, then AnyEvent::Handle (with
		2022	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		2023
		2024	Time::HiRes
		2025	This module is part of perl since release 5.008. It will be used
		2026	when the chosen event library does not come with a timing source of
		2027	its own. The pure-perl event loop (AnyEvent::Loop) will additionally
		2028	load it to try to use a monotonic clock for timing stability.
		2029
		2030	AnyEvent::AIO (and IO::AIO)
		2031	The default implementation of AnyEvent::IO is to do I/O
		2032	synchronously, stopping programs while they access the disk, which
		2033	is fine for a lot of programs.
		2034
		2035	Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
		2036	switch to a true asynchronous implementation, so event processing
		2037	can continue even while waiting for disk I/O.
		2038
1608	FORK	2039	FORK
1609	Most event libraries are not fork-safe. The ones who are usually are	2040	Most event libraries are not fork-safe. The ones who are usually are
1610	because they rely on inefficient but fork-safe "select" or "poll" calls.	2041	because they rely on inefficient but fork-safe "select" or "poll" calls
1611	Only EV is fully fork-aware.	2042	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		2043	epoll are usually badly thought-out hacks that are incompatible with
		2044	fork in one way or another. Only EV is fully fork-aware and ensures that
		2045	you continue event-processing in both parent and child (or both, if you
		2046	know what you are doing).
		2047
		2048	This means that, in general, you cannot fork and do event processing in
		2049	the child if the event library was initialised before the fork (which
		2050	usually happens when the first AnyEvent watcher is created, or the
		2051	library is loaded).
1612		2052
1613	If you have to fork, you must either do so before creating your first	2053	If you have to fork, you must either do so before creating your first
1614	watcher OR you must not use AnyEvent at all in the child.	2054	watcher OR you must not use AnyEvent at all in the child OR you must do
		2055	something completely out of the scope of AnyEvent (see below).
		2056
		2057	The problem of doing event processing in the parent and the child is
		2058	much more complicated: even for backends that are fork-aware or
		2059	fork-safe, their behaviour is not usually what you want: fork clones all
		2060	watchers, that means all timers, I/O watchers etc. are active in both
		2061	parent and child, which is almost never what you want. Using "exec" to
		2062	start worker children from some kind of manage prrocess is usually
		2063	preferred, because it is much easier and cleaner, at the expense of
		2064	having to have another binary.
		2065
		2066	In addition to logical problems with fork, there are also implementation
		2067	problems. For example, on POSIX systems, you cannot fork at all in Perl
		2068	code if a thread (I am talking of pthreads here) was ever created in the
		2069	process, and this is just the tip of the iceberg. In general, using fork
		2070	from Perl is difficult, and attempting to use fork without an exec to
		2071	implement some kind of parallel processing is almost certainly doomed.
		2072
		2073	To safely fork and exec, you should use a module such as Proc::FastSpawn
		2074	that let's you safely fork and exec new processes.
		2075
		2076	If you want to do multiprocessing using processes, you can look at the
		2077	AnyEvent::Fork module (and some related modules such as
		2078	AnyEvent::Fork::RPC, AnyEvent::Fork::Pool and AnyEvent::Fork::Remote).
		2079	This module allows you to safely create subprocesses without any
		2080	limitations - you can use X11 toolkits or AnyEvent in the children
		2081	created by AnyEvent::Fork safely and without any special precautions.
1615		2082
1616	SECURITY CONSIDERATIONS	2083	SECURITY CONSIDERATIONS
1617	AnyEvent can be forced to load any event model via	2084	AnyEvent can be forced to load any event model via
1618	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	2085	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1619	to execute arbitrary code or directly gain access, it can easily be used	2086	to execute arbitrary code or directly gain access, it can easily be used
…		…
1643	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	2110	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1644	annoying memleaks, such as leaking on "map" and "grep" but it is usually	2111	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1645	not as pronounced).	2112	not as pronounced).
1646		2113
1647	SEE ALSO	2114	SEE ALSO
1648	Utility functions: AnyEvent::Util.	2115	Tutorial/Introduction: AnyEvent::Intro.
1649		2116
1650	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	2117	FAQ: AnyEvent::FAQ.
1651	Event::Lib, Qt, POE.	2118
		2119	Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
		2120	(simply logging).
		2121
		2122	Development/Debugging: AnyEvent::Strict (stricter checking),
		2123	AnyEvent::Debug (interactive shell, watcher tracing).
		2124
		2125	Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
		2126	Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK.
1652		2127
1653	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	2128	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1654	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	2129	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1655	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,	2130	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
1656	AnyEvent::Impl::IOAsync.	2131	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi, AnyEvent::Impl::FLTK.
1657		2132
1658	Non-blocking file handles, sockets, TCP clients and servers:	2133	Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1659	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.	2134	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1660		2135
		2136	Asynchronous File I/O: AnyEvent::IO.
		2137
1661	Asynchronous DNS: AnyEvent::DNS.	2138	Asynchronous DNS: AnyEvent::DNS.
1662		2139
1663	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	2140	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1664		2141
1665	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,	2142	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
1666	AnyEvent::HTTP.	2143	AnyEvent::HTTP.
1667		2144
1668	AUTHOR	2145	AUTHOR
1669	Marc Lehmann <schmorp@schmorp.de>	2146	Marc Lehmann <schmorp@schmorp.de>
1670	http://home.schmorp.de/	2147	http://anyevent.schmorp.de
1671		2148

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Revision 1.45 by root, Fri Jul 17 14:57:03 2009 UTC vs.
Revision 1.73 by root, Fri Sep 5 22:24:12 2014 UTC