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Comparing AnyEvent/README (file contents):
Revision 1.23 by root, Mon May 26 06:04:38 2008 UTC vs.
Revision 1.59 by root, Tue Jan 5 10:45:25 2010 UTC

…		…
1	=> NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - the DBI of event loop programming
3		3
4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	loops	5	Qt and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# file descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		12
		13	# one-shot or repeating timers
		14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		16
		17	print AnyEvent->now; # prints current event loop time
		18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		19
		20	# POSIX signal
		21	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		22
		23	# child process exit
		24	my $w = AnyEvent->child (pid => $pid, cb => sub {
		25	my ($pid, $status) = @_;
11	...	26	...
12	});	27	});
13		28
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	29	# called when event loop idle (if applicable)
15	...	30	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		31
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	32	my $w = AnyEvent->condvar; # stores whether a condition was flagged
19	$w->send; # wake up current and all future recv's	33	$w->send; # wake up current and all future recv's
20	$w->recv; # enters "main loop" till $condvar gets ->send	34	$w->recv; # enters "main loop" till $condvar gets ->send
		35	# use a condvar in callback mode:
		36	$w->cb (sub { $_[0]->recv });
		37
		38	INTRODUCTION/TUTORIAL
		39	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
		41	manpage.
		42
		43	SUPPORT
		44	There is a mailinglist for discussing all things AnyEvent, and an IRC
		45	channel, too.
		46
		47	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		48	Repository, at <http://anyevent.schmorp.de>, for more info.
21		49
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	50	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	51	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	52	nowadays. So what is different about AnyEvent?
25		53
26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	54	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
27	policy* and AnyEvent is small and efficient.	55	policy* and AnyEvent is small and efficient.
28		56
29	First and foremost, AnyEvent is not an event model itself, it only	57	First and foremost, AnyEvent is not an event model itself, it only
30	interfaces to whatever event model the main program happens to use in a	58	interfaces to whatever event model the main program happens to use, in a
31	pragmatic way. For event models and certain classes of immortals alike,	59	pragmatic way. For event models and certain classes of immortals alike,
32	the statement "there can only be one" is a bitter reality: In general,	60	the statement "there can only be one" is a bitter reality: In general,
33	only one event loop can be active at the same time in a process.	61	only one event loop can be active at the same time in a process.
34	AnyEvent helps hiding the differences between those event loops.	62	AnyEvent cannot change this, but it can hide the differences between
		63	those event loops.
35		64
36	The goal of AnyEvent is to offer module authors the ability to do event	65	The goal of AnyEvent is to offer module authors the ability to do event
37	programming (waiting for I/O or timer events) without subscribing to a	66	programming (waiting for I/O or timer events) without subscribing to a
38	religion, a way of living, and most importantly: without forcing your	67	religion, a way of living, and most importantly: without forcing your
39	module users into the same thing by forcing them to use the same event	68	module users into the same thing by forcing them to use the same event
40	model you use.	69	model you use.
41		70
42	For modules like POE or IO::Async (which is a total misnomer as it is	71	For modules like POE or IO::Async (which is a total misnomer as it is
43	actually doing all I/O synchronously...), using them in your module is	72	actually doing all I/O synchronously...), using them in your module is
44	like joining a cult: After you joined, you are dependent on them and you	73	like joining a cult: After you joined, you are dependent on them and you
45	cannot use anything else, as it is simply incompatible to everything	74	cannot use anything else, as they are simply incompatible to everything
46	that isn't itself. What's worse, all the potential users of your module	75	that isn't them. What's worse, all the potential users of your module
47	are also forced to use the same event loop you use.	76	are also forced to use the same event loop you use.
48		77
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	78	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	79	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your	80	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
52	module uses one of those, every user of your module has to use it, too.	81	module uses one of those, every user of your module has to use it, too.
53	But if your module uses AnyEvent, it works transparently with all event	82	But if your module uses AnyEvent, it works transparently with all event
54	models it supports (including stuff like POE and IO::Async, as long as	83	models it supports (including stuff like IO::Async, as long as those use
55	those use one of the supported event loops. It is trivial to add new	84	one of the supported event loops. It is trivial to add new event loops
56	event loops to AnyEvent, too, so it is future-proof).	85	to AnyEvent, too, so it is future-proof).
57		86
58	In addition to being free of having to use *the one and only true event	87	In addition to being free of having to use *the one and only true event
59	model*, AnyEvent also is free of bloat and policy: with POE or similar	88	model*, AnyEvent also is free of bloat and policy: with POE or similar
60	modules, you get an enormous amount of code and strict rules you have to	89	modules, you get an enormous amount of code and strict rules you have to
61	follow. AnyEvent, on the other hand, is lean and up to the point, by	90	follow. AnyEvent, on the other hand, is lean and up to the point, by
62	only offering the functionality that is necessary, in as thin as a	91	only offering the functionality that is necessary, in as thin as a
63	wrapper as technically possible.	92	wrapper as technically possible.
64		93
		94	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
		95	useful functionality, such as an asynchronous DNS resolver, 100%
		96	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		97	such as Windows) and lots of real-world knowledge and workarounds for
		98	platform bugs and differences.
		99
65	Of course, if you want lots of policy (this can arguably be somewhat	100	Now, if you do want lots of policy (this can arguably be somewhat
66	useful) and you want to force your users to use the one and only event	101	useful) and you want to force your users to use the one and only event
67	model, you should not use this module.	102	model, you should not use this module.
68		103
69	DESCRIPTION	104	DESCRIPTION
70	AnyEvent provides an identical interface to multiple event loops. This	105	AnyEvent provides an identical interface to multiple event loops. This
99	starts using it, all bets are off. Maybe you should tell their authors	134	starts using it, all bets are off. Maybe you should tell their authors
100	to use AnyEvent so their modules work together with others seamlessly...	135	to use AnyEvent so their modules work together with others seamlessly...
101		136
102	The pure-perl implementation of AnyEvent is called	137	The pure-perl implementation of AnyEvent is called
103	"AnyEvent::Impl::Perl". Like other event modules you can load it	138	"AnyEvent::Impl::Perl". Like other event modules you can load it
104	explicitly.	139	explicitly and enjoy the high availability of that event loop :)
105		140
106	WATCHERS	141	WATCHERS
107	AnyEvent has the central concept of a watcher, which is an object that	142	AnyEvent has the central concept of a watcher, which is an object that
108	stores relevant data for each kind of event you are waiting for, such as	143	stores relevant data for each kind of event you are waiting for, such as
109	the callback to call, the file handle to watch, etc.	144	the callback to call, the file handle to watch, etc.
…		…
111	These watchers are normal Perl objects with normal Perl lifetime. After	146	These watchers are normal Perl objects with normal Perl lifetime. After
112	creating a watcher it will immediately "watch" for events and invoke the	147	creating a watcher it will immediately "watch" for events and invoke the
113	callback when the event occurs (of course, only when the event model is	148	callback when the event occurs (of course, only when the event model is
114	in control).	149	in control).
115		150
		151	Note that callbacks must not permanently change global variables
		152	potentially in use by the event loop (such as $_ or $[) and that
		153	callbacks must not "die". The former is good programming practise in
		154	Perl and the latter stems from the fact that exception handling differs
		155	widely between event loops.
		156
116	To disable the watcher you have to destroy it (e.g. by setting the	157	To disable the watcher you have to destroy it (e.g. by setting the
117	variable you store it in to "undef" or otherwise deleting all references	158	variable you store it in to "undef" or otherwise deleting all references
118	to it).	159	to it).
119		160
120	All watchers are created by calling a method on the "AnyEvent" class.	161	All watchers are created by calling a method on the "AnyEvent" class.
…		…
122	Many watchers either are used with "recursion" (repeating timers for	163	Many watchers either are used with "recursion" (repeating timers for
123	example), or need to refer to their watcher object in other ways.	164	example), or need to refer to their watcher object in other ways.
124		165
125	An any way to achieve that is this pattern:	166	An any way to achieve that is this pattern:
126		167
127	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	168	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
128	# you can use $w here, for example to undef it	169	# you can use $w here, for example to undef it
129	undef $w;	170	undef $w;
130	});	171	});
131		172
132	Note that "my $w; $w =" combination. This is necessary because in Perl,	173	Note that "my $w; $w =" combination. This is necessary because in Perl,
133	my variables are only visible after the statement in which they are	174	my variables are only visible after the statement in which they are
134	declared.	175	declared.
135		176
136	I/O WATCHERS	177	I/O WATCHERS
		178	$w = AnyEvent->io (
		179	fh => <filehandle_or_fileno>,
		180	poll => <"r" or "w">,
		181	cb => <callback>,
		182	);
		183
137	You can create an I/O watcher by calling the "AnyEvent->io" method with	184	You can create an I/O watcher by calling the "AnyEvent->io" method with
138	the following mandatory key-value pairs as arguments:	185	the following mandatory key-value pairs as arguments:
139		186
140	"fh" the Perl file handle (not file descriptor) to watch for events.	187	"fh" is the Perl file handle (or a naked file descriptor) to watch for
		188	events (AnyEvent might or might not keep a reference to this file
		189	handle). Note that only file handles pointing to things for which
		190	non-blocking operation makes sense are allowed. This includes sockets,
		191	most character devices, pipes, fifos and so on, but not for example
		192	files or block devices.
		193
141	"poll" must be a string that is either "r" or "w", which creates a	194	"poll" must be a string that is either "r" or "w", which creates a
142	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	195	watcher waiting for "r"eadable or "w"ritable events, respectively.
		196
143	is the callback to invoke each time the file handle becomes ready.	197	"cb" is the callback to invoke each time the file handle becomes ready.
144		198
145	Although the callback might get passed parameters, their value and	199	Although the callback might get passed parameters, their value and
146	presence is undefined and you cannot rely on them. Portable AnyEvent	200	presence is undefined and you cannot rely on them. Portable AnyEvent
147	callbacks cannot use arguments passed to I/O watcher callbacks.	201	callbacks cannot use arguments passed to I/O watcher callbacks.
148		202
…		…
152		206
153	Some event loops issue spurious readyness notifications, so you should	207	Some event loops issue spurious readyness notifications, so you should
154	always use non-blocking calls when reading/writing from/to your file	208	always use non-blocking calls when reading/writing from/to your file
155	handles.	209	handles.
156		210
157	Example:
158
159	# wait for readability of STDIN, then read a line and disable the watcher	211	Example: wait for readability of STDIN, then read a line and disable the
		212	watcher.
		213
160	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	214	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
161	chomp (my $input = <STDIN>);	215	chomp (my $input = <STDIN>);
162	warn "read: $input\n";	216	warn "read: $input\n";
163	undef $w;	217	undef $w;
164	});	218	});
165		219
166	TIME WATCHERS	220	TIME WATCHERS
		221	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		222
		223	$w = AnyEvent->timer (
		224	after => <fractional_seconds>,
		225	interval => <fractional_seconds>,
		226	cb => <callback>,
		227	);
		228
167	You can create a time watcher by calling the "AnyEvent->timer" method	229	You can create a time watcher by calling the "AnyEvent->timer" method
168	with the following mandatory arguments:	230	with the following mandatory arguments:
169		231
170	"after" specifies after how many seconds (fractional values are	232	"after" specifies after how many seconds (fractional values are
171	supported) the callback should be invoked. "cb" is the callback to	233	supported) the callback should be invoked. "cb" is the callback to
…		…
173		235
174	Although the callback might get passed parameters, their value and	236	Although the callback might get passed parameters, their value and
175	presence is undefined and you cannot rely on them. Portable AnyEvent	237	presence is undefined and you cannot rely on them. Portable AnyEvent
176	callbacks cannot use arguments passed to time watcher callbacks.	238	callbacks cannot use arguments passed to time watcher callbacks.
177		239
178	The timer callback will be invoked at most once: if you want a repeating	240	The callback will normally be invoked once only. If you specify another
179	timer you have to create a new watcher (this is a limitation by both Tk	241	parameter, "interval", as a strictly positive number (> 0), then the
180	and Glib).	242	callback will be invoked regularly at that interval (in fractional
		243	seconds) after the first invocation. If "interval" is specified with a
		244	false value, then it is treated as if it were missing.
181		245
182	Example:	246	The callback will be rescheduled before invoking the callback, but no
		247	attempt is done to avoid timer drift in most backends, so the interval
		248	is only approximate.
183		249
184	# fire an event after 7.7 seconds	250	Example: fire an event after 7.7 seconds.
		251
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	252	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	253	warn "timeout\n";
187	});	254	});
188		255
189	# to cancel the timer:	256	# to cancel the timer:
190	undef $w;	257	undef $w;
191		258
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	259	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		260
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	261	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		262	warn "timeout\n";
200	};	263	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		264
205	TIMING ISSUES	265	TIMING ISSUES
206	There are two ways to handle timers: based on real time (relative, "fire	266	There are two ways to handle timers: based on real time (relative, "fire
207	in 10 seconds") and based on wallclock time (absolute, "fire at 12	267	in 10 seconds") and based on wallclock time (absolute, "fire at 12
208	o'clock").	268	o'clock").
…		…
220	on wallclock time) timers.	280	on wallclock time) timers.
221		281
222	AnyEvent always prefers relative timers, if available, matching the	282	AnyEvent always prefers relative timers, if available, matching the
223	AnyEvent API.	283	AnyEvent API.
224		284
		285	AnyEvent has two additional methods that return the "current time":
		286
		287	AnyEvent->time
		288	This returns the "current wallclock time" as a fractional number of
		289	seconds since the Epoch (the same thing as "time" or
		290	"Time::HiRes::time" return, and the result is guaranteed to be
		291	compatible with those).
		292
		293	It progresses independently of any event loop processing, i.e. each
		294	call will check the system clock, which usually gets updated
		295	frequently.
		296
		297	AnyEvent->now
		298	This also returns the "current wallclock time", but unlike "time",
		299	above, this value might change only once per event loop iteration,
		300	depending on the event loop (most return the same time as "time",
		301	above). This is the time that AnyEvent's timers get scheduled
		302	against.
		303
		304	*In almost all cases (in all cases if you don't care), this is the
		305	function to call when you want to know the current time.*
		306
		307	This function is also often faster then "AnyEvent->time", and thus
		308	the preferred method if you want some timestamp (for example,
		309	AnyEvent::Handle uses this to update it's activity timeouts).
		310
		311	The rest of this section is only of relevance if you try to be very
		312	exact with your timing, you can skip it without bad conscience.
		313
		314	For a practical example of when these times differ, consider
		315	Event::Lib and EV and the following set-up:
		316
		317	The event loop is running and has just invoked one of your callback
		318	at time=500 (assume no other callbacks delay processing). In your
		319	callback, you wait a second by executing "sleep 1" (blocking the
		320	process for a second) and then (at time=501) you create a relative
		321	timer that fires after three seconds.
		322
		323	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		324	return 501, because that is the current time, and the timer will be
		325	scheduled to fire at time=504 (501 + 3).
		326
		327	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		328	but "AnyEvent->now" returns 500, as that is the time the last event
		329	processing phase started. With EV, your timer gets scheduled to run
		330	at time=503 (500 + 3).
		331
		332	In one sense, Event::Lib is more exact, as it uses the current time
		333	regardless of any delays introduced by event processing. However,
		334	most callbacks do not expect large delays in processing, so this
		335	causes a higher drift (and a lot more system calls to get the
		336	current time).
		337
		338	In another sense, EV is more exact, as your timer will be scheduled
		339	at the same time, regardless of how long event processing actually
		340	took.
		341
		342	In either case, if you care (and in most cases, you don't), then you
		343	can get whatever behaviour you want with any event loop, by taking
		344	the difference between "AnyEvent->time" and "AnyEvent->now" into
		345	account.
		346
		347	AnyEvent->now_update
		348	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		349	current time for each loop iteration (see the discussion of
		350	AnyEvent->now, above).
		351
		352	When a callback runs for a long time (or when the process sleeps),
		353	then this "current" time will differ substantially from the real
		354	time, which might affect timers and time-outs.
		355
		356	When this is the case, you can call this method, which will update
		357	the event loop's idea of "current time".
		358
		359	A typical example would be a script in a web server (e.g.
		360	"mod_perl") - when mod_perl executes the script, then the event loop
		361	will have the wrong idea about the "current time" (being potentially
		362	far in the past, when the script ran the last time). In that case
		363	you should arrange a call to "AnyEvent->now_update" each time the
		364	web server process wakes up again (e.g. at the start of your script,
		365	or in a handler).
		366
		367	Note that updating the time might cause some events to be handled.
		368
225	SIGNAL WATCHERS	369	SIGNAL WATCHERS
		370	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		371
226	You can watch for signals using a signal watcher, "signal" is the signal	372	You can watch for signals using a signal watcher, "signal" is the signal
227	name without any "SIG" prefix, "cb" is the Perl callback to be invoked	373	name in uppercase and without any "SIG" prefix, "cb" is the Perl
228	whenever a signal occurs.	374	callback to be invoked whenever a signal occurs.
229		375
230	Although the callback might get passed parameters, their value and	376	Although the callback might get passed parameters, their value and
231	presence is undefined and you cannot rely on them. Portable AnyEvent	377	presence is undefined and you cannot rely on them. Portable AnyEvent
232	callbacks cannot use arguments passed to signal watcher callbacks.	378	callbacks cannot use arguments passed to signal watcher callbacks.
233		379
…		…
235	invocation, and callback invocation will be synchronous. Synchronous	381	invocation, and callback invocation will be synchronous. Synchronous
236	means that it might take a while until the signal gets handled by the	382	means that it might take a while until the signal gets handled by the
237	process, but it is guaranteed not to interrupt any other callbacks.	383	process, but it is guaranteed not to interrupt any other callbacks.
238		384
239	The main advantage of using these watchers is that you can share a	385	The main advantage of using these watchers is that you can share a
240	signal between multiple watchers.	386	signal between multiple watchers, and AnyEvent will ensure that signals
		387	will not interrupt your program at bad times.
241		388
242	This watcher might use %SIG, so programs overwriting those signals	389	This watcher might use %SIG (depending on the event loop used), so
243	directly will likely not work correctly.	390	programs overwriting those signals directly will likely not work
		391	correctly.
244		392
245	Example: exit on SIGINT	393	Example: exit on SIGINT
246		394
247	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	395	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
248		396
		397	Restart Behaviour
		398	While restart behaviour is up to the event loop implementation, most
		399	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		400	pure perl implementation).
		401
		402	Safe/Unsafe Signals
		403	Perl signals can be either "safe" (synchronous to opcode handling) or
		404	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		405	latter might corrupt your memory.
		406
		407	AnyEvent signal handlers are, in addition, synchronous to the event
		408	loop, i.e. they will not interrupt your running perl program but will
		409	only be called as part of the normal event handling (just like timer,
		410	I/O etc. callbacks, too).
		411
		412	Signal Races, Delays and Workarounds
		413	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		414	callbacks to signals in a generic way, which is a pity, as you cannot do
		415	race-free signal handling in perl, requiring C libraries for this.
		416	AnyEvent will try to do it's best, which means in some cases, signals
		417	will be delayed. The maximum time a signal might be delayed is specified
		418	in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
		419	can be changed only before the first signal watcher is created, and
		420	should be left alone otherwise. This variable determines how often
		421	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		422	will cause fewer spurious wake-ups, which is better for power and CPU
		423	saving.
		424
		425	All these problems can be avoided by installing the optional
		426	Async::Interrupt module, which works with most event loops. It will not
		427	work with inherently broken event loops such as Event or Event::Lib (and
		428	not with POE currently, as POE does it's own workaround with one-second
		429	latency). For those, you just have to suffer the delays.
		430
249	CHILD PROCESS WATCHERS	431	CHILD PROCESS WATCHERS
		432	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		433
250	You can also watch on a child process exit and catch its exit status.	434	You can also watch on a child process exit and catch its exit status.
251		435
252	The child process is specified by the "pid" argument (if set to 0, it	436	The child process is specified by the "pid" argument (one some backends,
253	watches for any child process exit). The watcher will trigger as often	437	using 0 watches for any child process exit, on others this will croak).
254	as status change for the child are received. This works by installing a	438	The watcher will be triggered only when the child process has finished
255	signal handler for "SIGCHLD". The callback will be called with the pid	439	and an exit status is available, not on any trace events
256	and exit status (as returned by waitpid), so unlike other watcher types,	440	(stopped/continued).
257	you can rely on child watcher callback arguments.	441
		442	The callback will be called with the pid and exit status (as returned by
		443	waitpid), so unlike other watcher types, you can rely on child watcher
		444	callback arguments.
		445
		446	This watcher type works by installing a signal handler for "SIGCHLD",
		447	and since it cannot be shared, nothing else should use SIGCHLD or reap
		448	random child processes (waiting for specific child processes, e.g.
		449	inside "system", is just fine).
258		450
259	There is a slight catch to child watchers, however: you usually start	451	There is a slight catch to child watchers, however: you usually start
260	them after the child process was created, and this means the process	452	them after the child process was created, and this means the process
261	could have exited already (and no SIGCHLD will be sent anymore).	453	could have exited already (and no SIGCHLD will be sent anymore).
262		454
263	Not all event models handle this correctly (POE doesn't), but even for	455	Not all event models handle this correctly (neither POE nor IO::Async
		456	do, see their AnyEvent::Impl manpages for details), but even for event
264	event models that do handle this correctly, they usually need to be	457	models that do handle this correctly, they usually need to be loaded
265	loaded before the process exits (i.e. before you fork in the first	458	before the process exits (i.e. before you fork in the first place).
266	place).	459	AnyEvent's pure perl event loop handles all cases correctly regardless
		460	of when you start the watcher.
267		461
268	This means you cannot create a child watcher as the very first thing in	462	This means you cannot create a child watcher as the very first thing in
269	an AnyEvent program, you have to create at least one watcher before	463	an AnyEvent program, you have to create at least one watcher before
270	you "fork" the child (alternatively, you can call "AnyEvent::detect").	464	you "fork" the child (alternatively, you can call "AnyEvent::detect").
271		465
		466	As most event loops do not support waiting for child events, they will
		467	be emulated by AnyEvent in most cases, in which the latency and race
		468	problems mentioned in the description of signal watchers apply.
		469
272	Example: fork a process and wait for it	470	Example: fork a process and wait for it
273		471
274	my $done = AnyEvent->condvar;	472	my $done = AnyEvent->condvar;
275		473
276	my $pid = fork or exit 5;	474	my $pid = fork or exit 5;
277		475
278	my $w = AnyEvent->child (	476	my $w = AnyEvent->child (
279	pid => $pid,	477	pid => $pid,
280	cb => sub {	478	cb => sub {
281	my ($pid, $status) = @_;	479	my ($pid, $status) = @_;
282	warn "pid $pid exited with status $status";	480	warn "pid $pid exited with status $status";
283	$done->send;	481	$done->send;
284	},	482	},
285	);	483	);
286		484
287	# do something else, then wait for process exit	485	# do something else, then wait for process exit
288	$done->recv;	486	$done->recv;
		487
		488	IDLE WATCHERS
		489	$w = AnyEvent->idle (cb => <callback>);
		490
		491	Repeatedly invoke the callback after the process becomes idle, until
		492	either the watcher is destroyed or new events have been detected.
		493
		494	Idle watchers are useful when there is a need to do something, but it is
		495	not so important (or wise) to do it instantly. The callback will be
		496	invoked only when there is "nothing better to do", which is usually
		497	defined as "all outstanding events have been handled and no new events
		498	have been detected". That means that idle watchers ideally get invoked
		499	when the event loop has just polled for new events but none have been
		500	detected. Instead of blocking to wait for more events, the idle watchers
		501	will be invoked.
		502
		503	Unfortunately, most event loops do not really support idle watchers
		504	(only EV, Event and Glib do it in a usable fashion) - for the rest,
		505	AnyEvent will simply call the callback "from time to time".
		506
		507	Example: read lines from STDIN, but only process them when the program
		508	is otherwise idle:
		509
		510	my @lines; # read data
		511	my $idle_w;
		512	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		513	push @lines, scalar <STDIN>;
		514
		515	# start an idle watcher, if not already done
		516	$idle_w \|\|= AnyEvent->idle (cb => sub {
		517	# handle only one line, when there are lines left
		518	if (my $line = shift @lines) {
		519	print "handled when idle: $line";
		520	} else {
		521	# otherwise disable the idle watcher again
		522	undef $idle_w;
		523	}
		524	});
		525	});
289		526
290	CONDITION VARIABLES	527	CONDITION VARIABLES
		528	$cv = AnyEvent->condvar;
		529
		530	$cv->send (<list>);
		531	my @res = $cv->recv;
		532
291	If you are familiar with some event loops you will know that all of them	533	If you are familiar with some event loops you will know that all of them
292	require you to run some blocking "loop", "run" or similar function that	534	require you to run some blocking "loop", "run" or similar function that
293	will actively watch for new events and call your callbacks.	535	will actively watch for new events and call your callbacks.
294		536
295	AnyEvent is different, it expects somebody else to run the event loop	537	AnyEvent is slightly different: it expects somebody else to run the
296	and will only block when necessary (usually when told by the user).	538	event loop and will only block when necessary (usually when told by the
		539	user).
297		540
298	The instrument to do that is called a "condition variable", so called	541	The instrument to do that is called a "condition variable", so called
299	because they represent a condition that must become true.	542	because they represent a condition that must become true.
		543
		544	Now is probably a good time to look at the examples further below.
300		545
301	Condition variables can be created by calling the "AnyEvent->condvar"	546	Condition variables can be created by calling the "AnyEvent->condvar"
302	method, usually without arguments. The only argument pair allowed is	547	method, usually without arguments. The only argument pair allowed is
303	"cb", which specifies a callback to be called when the condition	548	"cb", which specifies a callback to be called when the condition
304	variable becomes true.	549	variable becomes true, with the condition variable as the first argument
		550	(but not the results).
305		551
306	After creation, the condition variable is "false" until it becomes	552	After creation, the condition variable is "false" until it becomes
307	"true" by calling the "send" method (or calling the condition variable	553	"true" by calling the "send" method (or calling the condition variable
308	as if it were a callback, read about the caveats in the description for	554	as if it were a callback, read about the caveats in the description for
309	the "->send" method).	555	the "->send" method).
…		…
311	Condition variables are similar to callbacks, except that you can	557	Condition variables are similar to callbacks, except that you can
312	optionally wait for them. They can also be called merge points - points	558	optionally wait for them. They can also be called merge points - points
313	in time where multiple outstanding events have been processed. And yet	559	in time where multiple outstanding events have been processed. And yet
314	another way to call them is transactions - each condition variable can	560	another way to call them is transactions - each condition variable can
315	be used to represent a transaction, which finishes at some point and	561	be used to represent a transaction, which finishes at some point and
316	delivers a result.	562	delivers a result. And yet some people know them as "futures" - a
		563	promise to compute/deliver something that you can wait for.
317		564
318	Condition variables are very useful to signal that something has	565	Condition variables are very useful to signal that something has
319	finished, for example, if you write a module that does asynchronous http	566	finished, for example, if you write a module that does asynchronous http
320	requests, then a condition variable would be the ideal candidate to	567	requests, then a condition variable would be the ideal candidate to
321	signal the availability of results. The user can either act when the	568	signal the availability of results. The user can either act when the
…		…
355	after => 1,	602	after => 1,
356	cb => sub { $result_ready->send },	603	cb => sub { $result_ready->send },
357	);	604	);
358		605
359	# this "blocks" (while handling events) till the callback	606	# this "blocks" (while handling events) till the callback
360	# calls send	607	# calls ->send
361	$result_ready->recv;	608	$result_ready->recv;
362		609
363	Example: wait for a timer, but take advantage of the fact that condition	610	Example: wait for a timer, but take advantage of the fact that condition
364	variables are also code references.	611	variables are also callable directly.
365		612
366	my $done = AnyEvent->condvar;	613	my $done = AnyEvent->condvar;
367	my $delay = AnyEvent->timer (after => 5, cb => $done);	614	my $delay = AnyEvent->timer (after => 5, cb => $done);
368	$done->recv;	615	$done->recv;
		616
		617	Example: Imagine an API that returns a condvar and doesn't support
		618	callbacks. This is how you make a synchronous call, for example from the
		619	main program:
		620
		621	use AnyEvent::CouchDB;
		622
		623	...
		624
		625	my @info = $couchdb->info->recv;
		626
		627	And this is how you would just set a callback to be called whenever the
		628	results are available:
		629
		630	$couchdb->info->cb (sub {
		631	my @info = $_[0]->recv;
		632	});
369		633
370	METHODS FOR PRODUCERS	634	METHODS FOR PRODUCERS
371	These methods should only be used by the producing side, i.e. the	635	These methods should only be used by the producing side, i.e. the
372	code/module that eventually sends the signal. Note that it is also the	636	code/module that eventually sends the signal. Note that it is also the
373	producer side which creates the condvar in most cases, but it isn't	637	producer side which creates the condvar in most cases, but it isn't
…		…
383		647
384	Any arguments passed to the "send" call will be returned by all	648	Any arguments passed to the "send" call will be returned by all
385	future "->recv" calls.	649	future "->recv" calls.
386		650
387	Condition variables are overloaded so one can call them directly (as	651	Condition variables are overloaded so one can call them directly (as
388	a code reference). Calling them directly is the same as calling	652	if they were a code reference). Calling them directly is the same as
389	"send". Note, however, that many C-based event loops do not handle	653	calling "send".
390	overloading, so as tempting as it may be, passing a condition
391	variable instead of a callback does not work. Both the pure perl and
392	EV loops support overloading, however, as well as all functions that
393	use perl to invoke a callback (as in AnyEvent::Socket and
394	AnyEvent::DNS for example).
395		654
396	$cv->croak ($error)	655	$cv->croak ($error)
397	Similar to send, but causes all call's to "->recv" to invoke	656	Similar to send, but causes all call's to "->recv" to invoke
398	"Carp::croak" with the given error message/object/scalar.	657	"Carp::croak" with the given error message/object/scalar.
399		658
400	This can be used to signal any errors to the condition variable	659	This can be used to signal any errors to the condition variable
401	user/consumer.	660	user/consumer. Doing it this way instead of calling "croak" directly
		661	delays the error detetcion, but has the overwhelmign advantage that
		662	it diagnoses the error at the place where the result is expected,
		663	and not deep in some event clalback without connection to the actual
		664	code causing the problem.
402		665
403	$cv->begin ([group callback])	666	$cv->begin ([group callback])
404	$cv->end	667	$cv->end
405	These two methods are EXPERIMENTAL and MIGHT CHANGE.
406
407	These two methods can be used to combine many transactions/events	668	These two methods can be used to combine many transactions/events
408	into one. For example, a function that pings many hosts in parallel	669	into one. For example, a function that pings many hosts in parallel
409	might want to use a condition variable for the whole process.	670	might want to use a condition variable for the whole process.
410		671
411	Every call to "->begin" will increment a counter, and every call to	672	Every call to "->begin" will increment a counter, and every call to
412	"->end" will decrement it. If the counter reaches 0 in "->end", the	673	"->end" will decrement it. If the counter reaches 0 in "->end", the
413	(last) callback passed to "begin" will be executed. That callback is	674	(last) callback passed to "begin" will be executed, passing the
414	supposed to call "->send", but that is not required. If no	675	condvar as first argument. That callback is supposed to call
		676	"->send", but that is not required. If no group callback was set,
415	callback was set, "send" will be called without any arguments.	677	"send" will be called without any arguments.
416		678
417	Let's clarify this with the ping example:	679	You can think of "$cv->send" giving you an OR condition (one call
		680	sends), while "$cv->begin" and "$cv->end" giving you an AND
		681	condition (all "begin" calls must be "end"'ed before the condvar
		682	sends).
		683
		684	Let's start with a simple example: you have two I/O watchers (for
		685	example, STDOUT and STDERR for a program), and you want to wait for
		686	both streams to close before activating a condvar:
418		687
419	my $cv = AnyEvent->condvar;	688	my $cv = AnyEvent->condvar;
420		689
		690	$cv->begin; # first watcher
		691	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		692	defined sysread $fh1, my $buf, 4096
		693	or $cv->end;
		694	});
		695
		696	$cv->begin; # second watcher
		697	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		698	defined sysread $fh2, my $buf, 4096
		699	or $cv->end;
		700	});
		701
		702	$cv->recv;
		703
		704	This works because for every event source (EOF on file handle),
		705	there is one call to "begin", so the condvar waits for all calls to
		706	"end" before sending.
		707
		708	The ping example mentioned above is slightly more complicated, as
		709	the there are results to be passwd back, and the number of tasks
		710	that are begung can potentially be zero:
		711
		712	my $cv = AnyEvent->condvar;
		713
421	my %result;	714	my %result;
422	$cv->begin (sub { $cv->send (\%result) });	715	$cv->begin (sub { shift->send (\%result) });
423		716
424	for my $host (@list_of_hosts) {	717	for my $host (@list_of_hosts) {
425	$cv->begin;	718	$cv->begin;
426	ping_host_then_call_callback $host, sub {	719	ping_host_then_call_callback $host, sub {
427	$result{$host} = ...;	720	$result{$host} = ...;
…		…
442	the loop, which serves two important purposes: first, it sets the	735	the loop, which serves two important purposes: first, it sets the
443	callback to be called once the counter reaches 0, and second, it	736	callback to be called once the counter reaches 0, and second, it
444	ensures that "send" is called even when "no" hosts are being pinged	737	ensures that "send" is called even when "no" hosts are being pinged
445	(the loop doesn't execute once).	738	(the loop doesn't execute once).
446		739
447	This is the general pattern when you "fan out" into multiple	740	This is the general pattern when you "fan out" into multiple (but
448	subrequests: use an outer "begin"/"end" pair to set the callback and	741	potentially none) subrequests: use an outer "begin"/"end" pair to
449	ensure "end" is called at least once, and then, for each subrequest	742	set the callback and ensure "end" is called at least once, and then,
450	you start, call "begin" and for each subrequest you finish, call	743	for each subrequest you start, call "begin" and for each subrequest
451	"end".	744	you finish, call "end".
452		745
453	METHODS FOR CONSUMERS	746	METHODS FOR CONSUMERS
454	These methods should only be used by the consuming side, i.e. the code	747	These methods should only be used by the consuming side, i.e. the code
455	awaits the condition.	748	awaits the condition.
456		749
…		…
465	function will call "croak".	758	function will call "croak".
466		759
467	In list context, all parameters passed to "send" will be returned,	760	In list context, all parameters passed to "send" will be returned,
468	in scalar context only the first one will be returned.	761	in scalar context only the first one will be returned.
469		762
		763	Note that doing a blocking wait in a callback is not supported by
		764	any event loop, that is, recursive invocation of a blocking "->recv"
		765	is not allowed, and the "recv" call will "croak" if such a condition
		766	is detected. This condition can be slightly loosened by using
		767	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		768	thread that doesn't run the event loop itself.
		769
470	Not all event models support a blocking wait - some die in that case	770	Not all event models support a blocking wait - some die in that case
471	(programs might want to do that to stay interactive), so *if you are	771	(programs might want to do that to stay interactive), so *if you are
472	using this from a module, never require a blocking wait*, but let	772	using this from a module, never require a blocking wait*. Instead,
473	the caller decide whether the call will block or not (for example,	773	let the caller decide whether the call will block or not (for
474	by coupling condition variables with some kind of request results	774	example, by coupling condition variables with some kind of request
475	and supporting callbacks so the caller knows that getting the result	775	results and supporting callbacks so the caller knows that getting
476	will not block, while still supporting blocking waits if the caller	776	the result will not block, while still supporting blocking waits if
477	so desires).	777	the caller so desires).
478
479	Another reason never to "->recv" in a module is that you cannot
480	sensibly have two "->recv"'s in parallel, as that would require
481	multiple interpreters or coroutines/threads, none of which
482	"AnyEvent" can supply.
483
484	The Coro module, however, can and does supply coroutines and, in
485	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
486	versions and also integrates coroutines into AnyEvent, making
487	blocking "->recv" calls perfectly safe as long as they are done from
488	another coroutine (one that doesn't run the event loop).
489		778
490	You can ensure that "-recv" never blocks by setting a callback and	779	You can ensure that "-recv" never blocks by setting a callback and
491	only calling "->recv" from within that callback (or at a later	780	only calling "->recv" from within that callback (or at a later
492	time). This will work even when the event loop does not support	781	time). This will work even when the event loop does not support
493	blocking waits otherwise.	782	blocking waits otherwise.
494		783
495	$bool = $cv->ready	784	$bool = $cv->ready
496	Returns true when the condition is "true", i.e. whether "send" or	785	Returns true when the condition is "true", i.e. whether "send" or
497	"croak" have been called.	786	"croak" have been called.
498		787
499	$cb = $cv->cb ([new callback])	788	$cb = $cv->cb ($cb->($cv))
500	This is a mutator function that returns the callback set and	789	This is a mutator function that returns the callback set and
501	optionally replaces it before doing so.	790	optionally replaces it before doing so.
502		791
503	The callback will be called when the condition becomes "true", i.e.	792	The callback will be called when the condition becomes (or already
504	when "send" or "croak" are called. Calling "recv" inside the	793	was) "true", i.e. when "send" or "croak" are called (or were
505	callback or at any later time is guaranteed not to block.	794	called), with the only argument being the condition variable itself.
		795	Calling "recv" inside the callback or at any later time is
		796	guaranteed not to block.
		797
		798	SUPPORTED EVENT LOOPS/BACKENDS
		799	The available backend classes are (every class has its own manpage):
		800
		801	Backends that are autoprobed when no other event loop can be found.
		802	EV is the preferred backend when no other event loop seems to be in
		803	use. If EV is not installed, then AnyEvent will fall back to its own
		804	pure-perl implementation, which is available everywhere as it comes
		805	with AnyEvent itself.
		806
		807	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		808	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		809
		810	Backends that are transparently being picked up when they are used.
		811	These will be used when they are currently loaded when the first
		812	watcher is created, in which case it is assumed that the application
		813	is using them. This means that AnyEvent will automatically pick the
		814	right backend when the main program loads an event module before
		815	anything starts to create watchers. Nothing special needs to be done
		816	by the main program.
		817
		818	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		819	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		820	AnyEvent::Impl::Tk based on Tk, very broken.
		821	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		822	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		823	AnyEvent::Impl::Irssi used when running within irssi.
		824
		825	Backends with special needs.
		826	Qt requires the Qt::Application to be instantiated first, but will
		827	otherwise be picked up automatically. As long as the main program
		828	instantiates the application before any AnyEvent watchers are
		829	created, everything should just work.
		830
		831	AnyEvent::Impl::Qt based on Qt.
		832
		833	Support for IO::Async can only be partial, as it is too broken and
		834	architecturally limited to even support the AnyEvent API. It also is
		835	the only event loop that needs the loop to be set explicitly, so it
		836	can only be used by a main program knowing about AnyEvent. See
		837	AnyEvent::Impl::Async for the gory details.
		838
		839	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		840
		841	Event loops that are indirectly supported via other backends.
		842	Some event loops can be supported via other modules:
		843
		844	There is no direct support for WxWidgets (Wx) or Prima.
		845
		846	WxWidgets has no support for watching file handles. However, you can
		847	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		848	simply polls 20 times per second, which was considered to be too
		849	horrible to even consider for AnyEvent.
		850
		851	Prima is not supported as nobody seems to be using it, but it has a
		852	POE backend, so it can be supported through POE.
		853
		854	AnyEvent knows about both Prima and Wx, however, and will try to
		855	load POE when detecting them, in the hope that POE will pick them
		856	up, in which case everything will be automatic.
506		857
507	GLOBAL VARIABLES AND FUNCTIONS	858	GLOBAL VARIABLES AND FUNCTIONS
		859	These are not normally required to use AnyEvent, but can be useful to
		860	write AnyEvent extension modules.
		861
508	$AnyEvent::MODEL	862	$AnyEvent::MODEL
509	Contains "undef" until the first watcher is being created. Then it	863	Contains "undef" until the first watcher is being created, before
		864	the backend has been autodetected.
		865
510	contains the event model that is being used, which is the name of	866	Afterwards it contains the event model that is being used, which is
511	the Perl class implementing the model. This class is usually one of	867	the name of the Perl class implementing the model. This class is
512	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	868	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
513	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	869	other class in the case AnyEvent has been extended at runtime (e.g.
514		870	in rxvt-unicode it will be "urxvt::anyevent").
515	The known classes so far are:
516
517	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
518	AnyEvent::Impl::Event based on Event, second best choice.
519	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
520	AnyEvent::Impl::Glib based on Glib, third-best choice.
521	AnyEvent::Impl::Tk based on Tk, very bad choice.
522	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
523	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
524	AnyEvent::Impl::POE based on POE, not generic enough for full support.
525
526	There is no support for WxWidgets, as WxWidgets has no support for
527	watching file handles. However, you can use WxWidgets through the
528	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
529	second, which was considered to be too horrible to even consider for
530	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
531	using it's adaptor.
532
533	AnyEvent knows about Prima and Wx and will try to use POE when
534	autodetecting them.
535		871
536	AnyEvent::detect	872	AnyEvent::detect
537	Returns $AnyEvent::MODEL, forcing autodetection of the event model	873	Returns $AnyEvent::MODEL, forcing autodetection of the event model
538	if necessary. You should only call this function right before you	874	if necessary. You should only call this function right before you
539	would have created an AnyEvent watcher anyway, that is, as late as	875	would have created an AnyEvent watcher anyway, that is, as late as
540	possible at runtime.	876	possible at runtime, and not e.g. while initialising of your module.
		877
		878	If you need to do some initialisation before AnyEvent watchers are
		879	created, use "post_detect".
541		880
542	$guard = AnyEvent::post_detect { BLOCK }	881	$guard = AnyEvent::post_detect { BLOCK }
543	Arranges for the code block to be executed as soon as the event	882	Arranges for the code block to be executed as soon as the event
544	model is autodetected (or immediately if this has already happened).	883	model is autodetected (or immediately if this has already happened).
545		884
		885	The block will be executed after the actual backend has been
		886	detected ($AnyEvent::MODEL is set), but before any watchers have
		887	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		888	other initialisations - see the sources of AnyEvent::Strict or
		889	AnyEvent::AIO to see how this is used.
		890
		891	The most common usage is to create some global watchers, without
		892	forcing event module detection too early, for example, AnyEvent::AIO
		893	creates and installs the global IO::AIO watcher in a "post_detect"
		894	block to avoid autodetecting the event module at load time.
		895
546	If called in scalar or list context, then it creates and returns an	896	If called in scalar or list context, then it creates and returns an
547	object that automatically removes the callback again when it is	897	object that automatically removes the callback again when it is
		898	destroyed (or "undef" when the hook was immediately executed). See
548	destroyed. See Coro::BDB for a case where this is useful.	899	AnyEvent::AIO for a case where this is useful.
		900
		901	Example: Create a watcher for the IO::AIO module and store it in
		902	$WATCHER. Only do so after the event loop is initialised, though.
		903
		904	our WATCHER;
		905
		906	my $guard = AnyEvent::post_detect {
		907	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		908	};
		909
		910	# the \|\|= is important in case post_detect immediately runs the block,
		911	# as to not clobber the newly-created watcher. assigning both watcher and
		912	# post_detect guard to the same variable has the advantage of users being
		913	# able to just C<undef $WATCHER> if the watcher causes them grief.
		914
		915	$WATCHER \|\|= $guard;
549		916
550	@AnyEvent::post_detect	917	@AnyEvent::post_detect
551	If there are any code references in this array (you can "push" to it	918	If there are any code references in this array (you can "push" to it
552	before or after loading AnyEvent), then they will called directly	919	before or after loading AnyEvent), then they will called directly
553	after the event loop has been chosen.	920	after the event loop has been chosen.
554		921
555	You should check $AnyEvent::MODEL before adding to this array,	922	You should check $AnyEvent::MODEL before adding to this array,
556	though: if it contains a true value then the event loop has already	923	though: if it is defined then the event loop has already been
557	been detected, and the array will be ignored.	924	detected, and the array will be ignored.
558		925
559	Best use "AnyEvent::post_detect { BLOCK }" instead.	926	Best use "AnyEvent::post_detect { BLOCK }" when your application
		927	allows it, as it takes care of these details.
		928
		929	This variable is mainly useful for modules that can do something
		930	useful when AnyEvent is used and thus want to know when it is
		931	initialised, but do not need to even load it by default. This array
		932	provides the means to hook into AnyEvent passively, without loading
		933	it.
		934
		935	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		936	together, you could put this into Coro (this is the actual code used
		937	by Coro to accomplish this):
		938
		939	if (defined $AnyEvent::MODEL) {
		940	# AnyEvent already initialised, so load Coro::AnyEvent
		941	require Coro::AnyEvent;
		942	} else {
		943	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		944	# as soon as it is
		945	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		946	}
560		947
561	WHAT TO DO IN A MODULE	948	WHAT TO DO IN A MODULE
562	As a module author, you should "use AnyEvent" and call AnyEvent methods	949	As a module author, you should "use AnyEvent" and call AnyEvent methods
563	freely, but you should not load a specific event module or rely on it.	950	freely, but you should not load a specific event module or rely on it.
564		951
…		…
615	variable somewhere, waiting for it, and sending it when the program	1002	variable somewhere, waiting for it, and sending it when the program
616	should exit cleanly.	1003	should exit cleanly.
617		1004
618	OTHER MODULES	1005	OTHER MODULES
619	The following is a non-exhaustive list of additional modules that use	1006	The following is a non-exhaustive list of additional modules that use
620	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1007	AnyEvent as a client and can therefore be mixed easily with other
621	in the same program. Some of the modules come with AnyEvent, some are	1008	AnyEvent modules and other event loops in the same program. Some of the
622	available via CPAN.	1009	modules come with AnyEvent, most are available via CPAN.
623		1010
624	AnyEvent::Util	1011	AnyEvent::Util
625	Contains various utility functions that replace often-used but	1012	Contains various utility functions that replace often-used but
626	blocking functions such as "inet_aton" by event-/callback-based	1013	blocking functions such as "inet_aton" by event-/callback-based
627	versions.	1014	versions.
628
629	AnyEvent::Handle
630	Provide read and write buffers and manages watchers for reads and
631	writes.
632		1015
633	AnyEvent::Socket	1016	AnyEvent::Socket
634	Provides various utility functions for (internet protocol) sockets,	1017	Provides various utility functions for (internet protocol) sockets,
635	addresses and name resolution. Also functions to create non-blocking	1018	addresses and name resolution. Also functions to create non-blocking
636	tcp connections or tcp servers, with IPv6 and SRV record support and	1019	tcp connections or tcp servers, with IPv6 and SRV record support and
637	more.	1020	more.
638		1021
		1022	AnyEvent::Handle
		1023	Provide read and write buffers, manages watchers for reads and
		1024	writes, supports raw and formatted I/O, I/O queued and fully
		1025	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
		1026
639	AnyEvent::DNS	1027	AnyEvent::DNS
640	Provides rich asynchronous DNS resolver capabilities.	1028	Provides rich asynchronous DNS resolver capabilities.
641		1029
		1030	AnyEvent::HTTP
		1031	A simple-to-use HTTP library that is capable of making a lot of
		1032	concurrent HTTP requests.
		1033
642	AnyEvent::HTTPD	1034	AnyEvent::HTTPD
643	Provides a simple web application server framework.	1035	Provides a simple web application server framework.
644		1036
645	AnyEvent::FastPing	1037	AnyEvent::FastPing
646	The fastest ping in the west.	1038	The fastest ping in the west.
647		1039
		1040	AnyEvent::DBI
		1041	Executes DBI requests asynchronously in a proxy process.
		1042
		1043	AnyEvent::AIO
		1044	Truly asynchronous I/O, should be in the toolbox of every event
		1045	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		1046	together.
		1047
		1048	AnyEvent::BDB
		1049	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		1050	fuses BDB and AnyEvent together.
		1051
		1052	AnyEvent::GPSD
		1053	A non-blocking interface to gpsd, a daemon delivering GPS
		1054	information.
		1055
		1056	AnyEvent::IRC
		1057	AnyEvent based IRC client module family (replacing the older
648	Net::IRC3	1058	Net::IRC3).
649	AnyEvent based IRC client module family.
650		1059
651	Net::XMPP2	1060	AnyEvent::XMPP
652	AnyEvent based XMPP (Jabber protocol) module family.	1061	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		1062	older Net::XMPP2>.
		1063
		1064	AnyEvent::IGS
		1065	A non-blocking interface to the Internet Go Server protocol (used by
		1066	App::IGS).
653		1067
654	Net::FCP	1068	Net::FCP
655	AnyEvent-based implementation of the Freenet Client Protocol,	1069	AnyEvent-based implementation of the Freenet Client Protocol,
656	birthplace of AnyEvent.	1070	birthplace of AnyEvent.
657		1071
…		…
659	High level API for event-based execution flow control.	1073	High level API for event-based execution flow control.
660		1074
661	Coro	1075	Coro
662	Has special support for AnyEvent via Coro::AnyEvent.	1076	Has special support for AnyEvent via Coro::AnyEvent.
663		1077
664	AnyEvent::AIO, IO::AIO	1078	SIMPLIFIED AE API
665	Truly asynchronous I/O, should be in the toolbox of every event	1079	Starting with version 5.0, AnyEvent officially supports a second, much
666	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	1080	simpler, API that is designed to reduce the calling, typing and memory
667	together.	1081	overhead.
668		1082
669	AnyEvent::BDB, BDB	1083	See the AE manpage for details.
670	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
671	fuses IO::AIO and AnyEvent together.
672		1084
673	IO::Lambda	1085	ERROR AND EXCEPTION HANDLING
674	The lambda approach to I/O - don't ask, look there. Can use	1086	In general, AnyEvent does not do any error handling - it relies on the
675	AnyEvent.	1087	caller to do that if required. The AnyEvent::Strict module (see also the
		1088	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1089	checking of all AnyEvent methods, however, which is highly useful during
		1090	development.
676		1091
677	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1092	As for exception handling (i.e. runtime errors and exceptions thrown
678	This is an advanced topic that you do not normally need to use AnyEvent	1093	while executing a callback), this is not only highly event-loop
679	in a module. This section is only of use to event loop authors who want	1094	specific, but also not in any way wrapped by this module, as this is the
680	to provide AnyEvent compatibility.	1095	job of the main program.
681		1096
682	If you need to support another event library which isn't directly	1097	The pure perl event loop simply re-throws the exception (usually within
683	supported by AnyEvent, you can supply your own interface to it by	1098	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
684	pushing, before the first watcher gets created, the package name of the	1099	Glib uses "install_exception_handler" and so on.
685	event module and the package name of the interface to use onto
686	@AnyEvent::REGISTRY. You can do that before and even without loading
687	AnyEvent, so it is reasonably cheap.
688
689	Example:
690
691	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
692
693	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
694	package/class when it finds the "urxvt" package/module is already
695	loaded.
696
697	When AnyEvent is loaded and asked to find a suitable event model, it
698	will first check for the presence of urxvt by trying to "use" the
699	"urxvt::anyevent" module.
700
701	The class should provide implementations for all watcher types. See
702	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
703	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
704	the sources.
705
706	If you don't provide "signal" and "child" watchers than AnyEvent will
707	provide suitable (hopefully) replacements.
708
709	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
710	terminal emulator uses the above line as-is. An interface isn't included
711	in AnyEvent because it doesn't make sense outside the embedded
712	interpreter inside rxvt-unicode, and it is updated and maintained as
713	part of the rxvt-unicode distribution.
714
715	rxvt-unicode also cheats a bit by not providing blocking access to
716	condition variables: code blocking while waiting for a condition will
717	"die". This still works with most modules/usages, and blocking calls
718	must not be done in an interactive application, so it makes sense.
719		1100
720	ENVIRONMENT VARIABLES	1101	ENVIRONMENT VARIABLES
721	The following environment variables are used by this module:	1102	The following environment variables are used by this module or its
		1103	submodules.
		1104
		1105	Note that AnyEvent will remove all environment variables starting with
		1106	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1107	enabled.
722		1108
723	"PERL_ANYEVENT_VERBOSE"	1109	"PERL_ANYEVENT_VERBOSE"
724	By default, AnyEvent will be completely silent except in fatal	1110	By default, AnyEvent will be completely silent except in fatal
725	conditions. You can set this environment variable to make AnyEvent	1111	conditions. You can set this environment variable to make AnyEvent
726	more talkative.	1112	more talkative.
…		…
729	conditions, such as not being able to load the event model specified	1115	conditions, such as not being able to load the event model specified
730	by "PERL_ANYEVENT_MODEL".	1116	by "PERL_ANYEVENT_MODEL".
731		1117
732	When set to 2 or higher, cause AnyEvent to report to STDERR which	1118	When set to 2 or higher, cause AnyEvent to report to STDERR which
733	event model it chooses.	1119	event model it chooses.
		1120
		1121	When set to 8 or higher, then AnyEvent will report extra information
		1122	on which optional modules it loads and how it implements certain
		1123	features.
		1124
		1125	"PERL_ANYEVENT_STRICT"
		1126	AnyEvent does not do much argument checking by default, as thorough
		1127	argument checking is very costly. Setting this variable to a true
		1128	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1129	thoroughly check the arguments passed to most method calls. If it
		1130	finds any problems, it will croak.
		1131
		1132	In other words, enables "strict" mode.
		1133
		1134	Unlike "use strict" (or it's modern cousin, "use common::sense", it
		1135	is definitely recommended to keep it off in production. Keeping
		1136	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1137	programs can be very useful, however.
734		1138
735	"PERL_ANYEVENT_MODEL"	1139	"PERL_ANYEVENT_MODEL"
736	This can be used to specify the event model to be used by AnyEvent,	1140	This can be used to specify the event model to be used by AnyEvent,
737	before auto detection and -probing kicks in. It must be a string	1141	before auto detection and -probing kicks in. It must be a string
738	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1142	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
743	This functionality might change in future versions.	1147	This functionality might change in future versions.
744		1148
745	For example, to force the pure perl model (AnyEvent::Impl::Perl) you	1149	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
746	could start your program like this:	1150	could start your program like this:
747		1151
748	PERL_ANYEVENT_MODEL=Perl perl ...	1152	PERL_ANYEVENT_MODEL=Perl perl ...
749		1153
750	"PERL_ANYEVENT_PROTOCOLS"	1154	"PERL_ANYEVENT_PROTOCOLS"
751	Used by both AnyEvent::DNS and AnyEvent::Socket to determine	1155	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
752	preferences for IPv4 or IPv6. The default is unspecified (and might	1156	preferences for IPv4 or IPv6. The default is unspecified (and might
753	change, or be the result of auto probing).	1157	change, or be the result of auto probing).
…		…
757	mentioned will be used, and preference will be given to protocols	1161	mentioned will be used, and preference will be given to protocols
758	mentioned earlier in the list.	1162	mentioned earlier in the list.
759		1163
760	This variable can effectively be used for denial-of-service attacks	1164	This variable can effectively be used for denial-of-service attacks
761	against local programs (e.g. when setuid), although the impact is	1165	against local programs (e.g. when setuid), although the impact is
762	likely small, as the program has to handle connection errors	1166	likely small, as the program has to handle conenction and other
763	already-	1167	failures anyways.
764		1168
765	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1169	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
766	IPv6, but support both and try to use both.	1170	IPv6, but support both and try to use both.
767	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1171	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
768	resolve or contact IPv6 addresses.	1172	resolve or contact IPv6 addresses.
…		…
775	but some (broken) firewalls drop such DNS packets, which is why it	1179	but some (broken) firewalls drop such DNS packets, which is why it
776	is off by default.	1180	is off by default.
777		1181
778	Setting this variable to 1 will cause AnyEvent::DNS to announce	1182	Setting this variable to 1 will cause AnyEvent::DNS to announce
779	EDNS0 in its DNS requests.	1183	EDNS0 in its DNS requests.
		1184
		1185	"PERL_ANYEVENT_MAX_FORKS"
		1186	The maximum number of child processes that
		1187	"AnyEvent::Util::fork_call" will create in parallel.
		1188
		1189	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1190	The default value for the "max_outstanding" parameter for the
		1191	default DNS resolver - this is the maximum number of parallel DNS
		1192	requests that are sent to the DNS server.
		1193
		1194	"PERL_ANYEVENT_RESOLV_CONF"
		1195	The file to use instead of /etc/resolv.conf (or OS-specific
		1196	configuration) in the default resolver. When set to the empty
		1197	string, no default config will be used.
		1198
		1199	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1200	When neither "ca_file" nor "ca_path" was specified during
		1201	AnyEvent::TLS context creation, and either of these environment
		1202	variables exist, they will be used to specify CA certificate
		1203	locations instead of a system-dependent default.
		1204
		1205	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1206	When these are set to 1, then the respective modules are not loaded.
		1207	Mostly good for testing AnyEvent itself.
		1208
		1209	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1210	This is an advanced topic that you do not normally need to use AnyEvent
		1211	in a module. This section is only of use to event loop authors who want
		1212	to provide AnyEvent compatibility.
		1213
		1214	If you need to support another event library which isn't directly
		1215	supported by AnyEvent, you can supply your own interface to it by
		1216	pushing, before the first watcher gets created, the package name of the
		1217	event module and the package name of the interface to use onto
		1218	@AnyEvent::REGISTRY. You can do that before and even without loading
		1219	AnyEvent, so it is reasonably cheap.
		1220
		1221	Example:
		1222
		1223	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1224
		1225	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
		1226	package/class when it finds the "urxvt" package/module is already
		1227	loaded.
		1228
		1229	When AnyEvent is loaded and asked to find a suitable event model, it
		1230	will first check for the presence of urxvt by trying to "use" the
		1231	"urxvt::anyevent" module.
		1232
		1233	The class should provide implementations for all watcher types. See
		1234	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
		1235	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
		1236	the sources.
		1237
		1238	If you don't provide "signal" and "child" watchers than AnyEvent will
		1239	provide suitable (hopefully) replacements.
		1240
		1241	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
		1242	terminal emulator uses the above line as-is. An interface isn't included
		1243	in AnyEvent because it doesn't make sense outside the embedded
		1244	interpreter inside rxvt-unicode, and it is updated and maintained as
		1245	part of the rxvt-unicode distribution.
		1246
		1247	rxvt-unicode also cheats a bit by not providing blocking access to
		1248	condition variables: code blocking while waiting for a condition will
		1249	"die". This still works with most modules/usages, and blocking calls
		1250	must not be done in an interactive application, so it makes sense.
780		1251
781	EXAMPLE PROGRAM	1252	EXAMPLE PROGRAM
782	The following program uses an I/O watcher to read data from STDIN, a	1253	The following program uses an I/O watcher to read data from STDIN, a
783	timer to display a message once per second, and a condition variable to	1254	timer to display a message once per second, and a condition variable to
784	quit the program when the user enters quit:	1255	quit the program when the user enters quit:
…		…
796	warn "read: $input\n"; # output what has been read	1267	warn "read: $input\n"; # output what has been read
797	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1268	$cv->send if $input =~ /^q/i; # quit program if /^q/i
798	},	1269	},
799	);	1270	);
800		1271
801	my $time_watcher; # can only be used once
802
803	sub new_timer {
804	$timer = AnyEvent->timer (after => 1, cb => sub {	1272	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
805	warn "timeout\n"; # print 'timeout' about every second	1273	warn "timeout\n"; # print 'timeout' at most every second
806	&new_timer; # and restart the time
807	});
808	}	1274	});
809
810	new_timer; # create first timer
811		1275
812	$cv->recv; # wait until user enters /^q/i	1276	$cv->recv; # wait until user enters /^q/i
813		1277
814	REAL-WORLD EXAMPLE	1278	REAL-WORLD EXAMPLE
815	Consider the Net::FCP module. It features (among others) the following	1279	Consider the Net::FCP module. It features (among others) the following
…		…
942	through AnyEvent. The benchmark creates a lot of timers (with a zero	1406	through AnyEvent. The benchmark creates a lot of timers (with a zero
943	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1407	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
944	which it is), lets them fire exactly once and destroys them again.	1408	which it is), lets them fire exactly once and destroys them again.
945		1409
946	Source code for this benchmark is found as eg/bench in the AnyEvent	1410	Source code for this benchmark is found as eg/bench in the AnyEvent
947	distribution.	1411	distribution. It uses the AE interface, which makes a real difference
		1412	for the EV and Perl backends only.
948		1413
949	Explanation of the columns	1414	Explanation of the columns
950	watcher is the number of event watchers created/destroyed. Since	1415	watcher is the number of event watchers created/destroyed. Since
951	different event models feature vastly different performances, each event	1416	different event models feature vastly different performances, each event
952	loop was given a number of watchers so that overall runtime is	1417	loop was given a number of watchers so that overall runtime is
…		…
971	destroy is the time, in microseconds, that it takes to destroy a	1436	destroy is the time, in microseconds, that it takes to destroy a
972	single watcher.	1437	single watcher.
973		1438
974	Results	1439	Results
975	name watchers bytes create invoke destroy comment	1440	name watchers bytes create invoke destroy comment
976	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1441	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
977	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1442	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
978	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1443	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
979	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1444	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
980	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1445	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
981	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1446	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1447	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1448	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
982	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1449	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
983	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1450	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
984	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1451	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
985	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1452	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
986		1453
987	Discussion	1454	Discussion
988	The benchmark does not measure scalability of the event loop very	1455	The benchmark does not measure scalability of the event loop very
989	well. For example, a select-based event loop (such as the pure perl one)	1456	well. For example, a select-based event loop (such as the pure perl one)
990	can never compete with an event loop that uses epoll when the number of	1457	can never compete with an event loop that uses epoll when the number of
…		…
1001	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1468	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1002	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1469	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1003	CPU cycles with POE.	1470	CPU cycles with POE.
1004		1471
1005	"EV" is the sole leader regarding speed and memory use, which are both	1472	"EV" is the sole leader regarding speed and memory use, which are both
1006	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1473	maximal/minimal, respectively. When using the AE API there is zero
		1474	overhead (when going through the AnyEvent API create is about 5-6 times
		1475	slower, with other times being equal, so still uses far less memory than
1007	far less memory than any other event loop and is still faster than Event	1476	any other event loop and is still faster than Event natively).
1008	natively.
1009		1477
1010	The pure perl implementation is hit in a few sweet spots (both the	1478	The pure perl implementation is hit in a few sweet spots (both the
1011	constant timeout and the use of a single fd hit optimisations in the	1479	constant timeout and the use of a single fd hit optimisations in the
1012	perl interpreter and the backend itself). Nevertheless this shows that	1480	perl interpreter and the backend itself). Nevertheless this shows that
1013	it adds very little overhead in itself. Like any select-based backend	1481	it adds very little overhead in itself. Like any select-based backend
…		…
1015	few of them active), of course, but this was not subject of this	1483	few of them active), of course, but this was not subject of this
1016	benchmark.	1484	benchmark.
1017		1485
1018	The "Event" module has a relatively high setup and callback invocation	1486	The "Event" module has a relatively high setup and callback invocation
1019	cost, but overall scores in on the third place.	1487	cost, but overall scores in on the third place.
		1488
		1489	"IO::Async" performs admirably well, about on par with "Event", even
		1490	when using its pure perl backend.
1020		1491
1021	"Glib"'s memory usage is quite a bit higher, but it features a faster	1492	"Glib"'s memory usage is quite a bit higher, but it features a faster
1022	callback invocation and overall ends up in the same class as "Event".	1493	callback invocation and overall ends up in the same class as "Event".
1023	However, Glib scales extremely badly, doubling the number of watchers	1494	However, Glib scales extremely badly, doubling the number of watchers
1024	increases the processing time by more than a factor of four, making it	1495	increases the processing time by more than a factor of four, making it
…		…
1080	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1551	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1081	100 (1%) are active. This mirrors the activity of large servers with	1552	100 (1%) are active. This mirrors the activity of large servers with
1082	many connections, most of which are idle at any one point in time.	1553	many connections, most of which are idle at any one point in time.
1083		1554
1084	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1555	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1085	distribution.	1556	distribution. It uses the AE interface, which makes a real difference
		1557	for the EV and Perl backends only.
1086		1558
1087	Explanation of the columns	1559	Explanation of the columns
1088	sockets is the number of sockets, and twice the number of "servers"	1560	sockets is the number of sockets, and twice the number of "servers"
1089	(as each server has a read and write socket end).	1561	(as each server has a read and write socket end).
1090		1562
…		…
1095	single "request", that is, reading the token from the pipe and	1567	single "request", that is, reading the token from the pipe and
1096	forwarding it to another server. This includes deleting the old timeout	1568	forwarding it to another server. This includes deleting the old timeout
1097	and creating a new one that moves the timeout into the future.	1569	and creating a new one that moves the timeout into the future.
1098		1570
1099	Results	1571	Results
1100	name sockets create request	1572	name sockets create request
1101	EV 20000 69.01 11.16	1573	EV 20000 62.66 7.99
1102	Perl 20000 73.32 35.87	1574	Perl 20000 68.32 32.64
1103	Event 20000 212.62 257.32	1575	IOAsync 20000 174.06 101.15 epoll
1104	Glib 20000 651.16 1896.30	1576	IOAsync 20000 174.67 610.84 poll
		1577	Event 20000 202.69 242.91
		1578	Glib 20000 557.01 1689.52
1105	POE 20000 349.67 12317.24 uses POE::Loop::Event	1579	POE 20000 341.54 12086.32 uses POE::Loop::Event
1106		1580
1107	Discussion	1581	Discussion
1108	This benchmark does measure scalability and overall performance of the	1582	This benchmark does measure scalability and overall performance of the
1109	particular event loop.	1583	particular event loop.
1110		1584
1111	EV is again fastest. Since it is using epoll on my system, the setup	1585	EV is again fastest. Since it is using epoll on my system, the setup
1112	time is relatively high, though.	1586	time is relatively high, though.
1113		1587
1114	Perl surprisingly comes second. It is much faster than the C-based event	1588	Perl surprisingly comes second. It is much faster than the C-based event
1115	loops Event and Glib.	1589	loops Event and Glib.
		1590
		1591	IO::Async performs very well when using its epoll backend, and still
		1592	quite good compared to Glib when using its pure perl backend.
1116		1593
1117	Event suffers from high setup time as well (look at its code and you	1594	Event suffers from high setup time as well (look at its code and you
1118	will understand why). Callback invocation also has a high overhead	1595	will understand why). Callback invocation also has a high overhead
1119	compared to the "$_->() for .."-style loop that the Perl event loop	1596	compared to the "$_->() for .."-style loop that the Perl event loop
1120	uses. Event uses select or poll in basically all documented	1597	uses. Event uses select or poll in basically all documented
…		…
1171		1648
1172	Summary	1649	Summary
1173	* C-based event loops perform very well with small number of watchers,	1650	* C-based event loops perform very well with small number of watchers,
1174	as the management overhead dominates.	1651	as the management overhead dominates.
1175		1652
		1653	THE IO::Lambda BENCHMARK
		1654	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1655	could be misinterpreted to make AnyEvent look bad. In fact, the
		1656	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1657	better (which shouldn't come as a surprise to anybody). As such, the
		1658	benchmark is fine, and mostly shows that the AnyEvent backend from
		1659	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1660	without the extra baggage? To explore this, I wrote the equivalent
		1661	benchmark for AnyEvent.
		1662
		1663	The benchmark itself creates an echo-server, and then, for 500 times,
		1664	connects to the echo server, sends a line, waits for the reply, and then
		1665	creates the next connection. This is a rather bad benchmark, as it
		1666	doesn't test the efficiency of the framework or much non-blocking I/O,
		1667	but it is a benchmark nevertheless.
		1668
		1669	name runtime
		1670	Lambda/select 0.330 sec
		1671	+ optimized 0.122 sec
		1672	Lambda/AnyEvent 0.327 sec
		1673	+ optimized 0.138 sec
		1674	Raw sockets/select 0.077 sec
		1675	POE/select, components 0.662 sec
		1676	POE/select, raw sockets 0.226 sec
		1677	POE/select, optimized 0.404 sec
		1678
		1679	AnyEvent/select/nb 0.085 sec
		1680	AnyEvent/EV/nb 0.068 sec
		1681	+state machine 0.134 sec
		1682
		1683	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1684	benchmarks actually make blocking connects and use 100% blocking I/O,
		1685	defeating the purpose of an event-based solution. All of the newly
		1686	written AnyEvent benchmarks use 100% non-blocking connects (using
		1687	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1688	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1689	connects generally require a lot more bookkeeping and event handling
		1690	than blocking connects (which involve a single syscall only).
		1691
		1692	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1693	offers similar expressive power as POE and IO::Lambda, using
		1694	conventional Perl syntax. This means that both the echo server and the
		1695	client are 100% non-blocking, further placing it at a disadvantage.
		1696
		1697	As you can see, the AnyEvent + EV combination even beats the
		1698	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1699	backend easily beats IO::Lambda and POE.
		1700
		1701	And even the 100% non-blocking version written using the high-level (and
		1702	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1703	higher level ("unoptimised") abstractions by a large margin, even though
		1704	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1705
		1706	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1707	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1708	part of the IO::Lambda distribution and were used without any changes.
		1709
		1710	SIGNALS
		1711	AnyEvent currently installs handlers for these signals:
		1712
		1713	SIGCHLD
		1714	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1715	emulation for event loops that do not support them natively. Also,
		1716	some event loops install a similar handler.
		1717
		1718	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1719	then AnyEvent will reset it to default, to avoid losing child exit
		1720	statuses.
		1721
		1722	SIGPIPE
		1723	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1724	"undef" when AnyEvent gets loaded.
		1725
		1726	The rationale for this is that AnyEvent users usually do not really
		1727	depend on SIGPIPE delivery (which is purely an optimisation for
		1728	shell use, or badly-written programs), but "SIGPIPE" can cause
		1729	spurious and rare program exits as a lot of people do not expect
		1730	"SIGPIPE" when writing to some random socket.
		1731
		1732	The rationale for installing a no-op handler as opposed to ignoring
		1733	it is that this way, the handler will be restored to defaults on
		1734	exec.
		1735
		1736	Feel free to install your own handler, or reset it to defaults.
		1737
		1738	RECOMMENDED/OPTIONAL MODULES
		1739	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1740	it's built-in modules) are required to use it.
		1741
		1742	That does not mean that AnyEvent won't take advantage of some additional
		1743	modules if they are installed.
		1744
		1745	This section explains which additional modules will be used, and how
		1746	they affect AnyEvent's operation.
		1747
		1748	Async::Interrupt
		1749	This slightly arcane module is used to implement fast signal
		1750	handling: To my knowledge, there is no way to do completely
		1751	race-free and quick signal handling in pure perl. To ensure that
		1752	signals still get delivered, AnyEvent will start an interval timer
		1753	to wake up perl (and catch the signals) with some delay (default is
		1754	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1755
		1756	If this module is available, then it will be used to implement
		1757	signal catching, which means that signals will not be delayed, and
		1758	the event loop will not be interrupted regularly, which is more
		1759	efficient (and good for battery life on laptops).
		1760
		1761	This affects not just the pure-perl event loop, but also other event
		1762	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1763
		1764	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1765	natively, and either employ their own workarounds (POE) or use
		1766	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1767	Installing Async::Interrupt does nothing for those backends.
		1768
		1769	EV This module isn't really "optional", as it is simply one of the
		1770	backend event loops that AnyEvent can use. However, it is simply the
		1771	best event loop available in terms of features, speed and stability:
		1772	It supports the AnyEvent API optimally, implements all the watcher
		1773	types in XS, does automatic timer adjustments even when no monotonic
		1774	clock is available, can take avdantage of advanced kernel interfaces
		1775	such as "epoll" and "kqueue", and is the fastest backend by far.
		1776	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1777	Glib::EV).
		1778
		1779	Guard
		1780	The guard module, when used, will be used to implement
		1781	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1782	uses a lot less memory), but otherwise doesn't affect guard
		1783	operation much. It is purely used for performance.
		1784
		1785	JSON and JSON::XS
		1786	One of these modules is required when you want to read or write JSON
		1787	data via AnyEvent::Handle. It is also written in pure-perl, but can
		1788	take advantage of the ultra-high-speed JSON::XS module when it is
		1789	installed.
		1790
		1791	In fact, AnyEvent::Handle will use JSON::XS by default if it is
		1792	installed.
		1793
		1794	Net::SSLeay
		1795	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1796	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1797	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1798
		1799	Time::HiRes
		1800	This module is part of perl since release 5.008. It will be used
		1801	when the chosen event library does not come with a timing source on
		1802	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1803	additionally use it to try to use a monotonic clock for timing
		1804	stability.
		1805
1176	FORK	1806	FORK
1177	Most event libraries are not fork-safe. The ones who are usually are	1807	Most event libraries are not fork-safe. The ones who are usually are
1178	because they rely on inefficient but fork-safe "select" or "poll" calls.	1808	because they rely on inefficient but fork-safe "select" or "poll" calls
1179	Only EV is fully fork-aware.	1809	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		1810	epoll are usually badly thought-out hacks that are incompatible with
		1811	fork in one way or another. Only EV is fully fork-aware and ensures that
		1812	you continue event-processing in both parent and child (or both, if you
		1813	know what you are doing).
		1814
		1815	This means that, in general, you cannot fork and do event processing in
		1816	the child if the event library was initialised before the fork (which
		1817	usually happens when the first AnyEvent watcher is created, or the
		1818	library is loaded).
1180		1819
1181	If you have to fork, you must either do so before creating your first	1820	If you have to fork, you must either do so before creating your first
1182	watcher OR you must not use AnyEvent at all in the child.	1821	watcher OR you must not use AnyEvent at all in the child OR you must do
		1822	something completely out of the scope of AnyEvent.
		1823
		1824	The problem of doing event processing in the parent and the child is
		1825	much more complicated: even for backends that are fork-aware or
		1826	fork-safe, their behaviour is not usually what you want: fork clones all
		1827	watchers, that means all timers, I/O watchers etc. are active in both
		1828	parent and child, which is almost never what you want. USing "exec" to
		1829	start worker children from some kind of manage rprocess is usually
		1830	preferred, because it is much easier and cleaner, at the expense of
		1831	having to have another binary.
1183		1832
1184	SECURITY CONSIDERATIONS	1833	SECURITY CONSIDERATIONS
1185	AnyEvent can be forced to load any event model via	1834	AnyEvent can be forced to load any event model via
1186	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1835	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1187	to execute arbitrary code or directly gain access, it can easily be used	1836	to execute arbitrary code or directly gain access, it can easily be used
…		…
1190	model than specified in the variable.	1839	model than specified in the variable.
1191		1840
1192	You can make AnyEvent completely ignore this variable by deleting it	1841	You can make AnyEvent completely ignore this variable by deleting it
1193	before the first watcher gets created, e.g. with a "BEGIN" block:	1842	before the first watcher gets created, e.g. with a "BEGIN" block:
1194		1843
1195	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1844	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1196		1845
1197	use AnyEvent;	1846	use AnyEvent;
1198		1847
1199	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1848	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1200	be used to probe what backend is used and gain other information (which	1849	be used to probe what backend is used and gain other information (which
1201	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).	1850	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1851	and $ENV{PERL_ANYEVENT_STRICT}.
		1852
		1853	Note that AnyEvent will remove all environment variables starting with
		1854	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1855	enabled.
		1856
		1857	BUGS
		1858	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1859	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1860	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1861	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1862	not as pronounced).
1202		1863
1203	SEE ALSO	1864	SEE ALSO
1204	Utility functions: AnyEvent::Util.	1865	Utility functions: AnyEvent::Util.
1205		1866
1206	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1867	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1207	Event::Lib, Qt, POE.	1868	Event::Lib, Qt, POE.
1208		1869
1209	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1870	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1210	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1871	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1211	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1872	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1873	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
1212		1874
1213	Non-blocking file handles, sockets, TCP clients and servers:	1875	Non-blocking file handles, sockets, TCP clients and servers:
1214	AnyEvent::Handle, AnyEvent::Socket.	1876	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1215		1877
1216	Asynchronous DNS: AnyEvent::DNS.	1878	Asynchronous DNS: AnyEvent::DNS.
1217		1879
1218	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1880	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1219		1881
1220	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1882	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1883	AnyEvent::HTTP.
1221		1884
1222	AUTHOR	1885	AUTHOR
1223	Marc Lehmann <schmorp@schmorp.de>	1886	Marc Lehmann <schmorp@schmorp.de>
1224	http://home.schmorp.de/	1887	http://home.schmorp.de/
1225		1888

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Comparing AnyEvent/README (file contents): Revision 1.23 by root, Mon May 26 06:04:38 2008 UTC vs. Revision 1.59 by root, Tue Jan 5 10:45:25 2010 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.23 by root, Mon May 26 06:04:38 2008 UTC vs.
Revision 1.59 by root, Tue Jan 5 10:45:25 2010 UTC