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Comparing AnyEvent/README (file contents):
Revision 1.20 by root, Sat May 10 22:30:28 2008 UTC vs.
Revision 1.54 by root, Tue Sep 1 18:27:46 2009 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 enourmous amount of code and strict rules you have	89	modules, you get an enormous amount of code and strict rules you have to
61	to 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 filehandle to watch, etc.	144	the callback to call, the file handle to watch, etc.
110		145
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	Note that updating the time might cause some events to be handled.
		360
225	SIGNAL WATCHERS	361	SIGNAL WATCHERS
		362	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		363
226	You can watch for signals using a signal watcher, "signal" is the signal	364	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	365	name in uppercase and without any "SIG" prefix, "cb" is the Perl
228	whenever a signal occurs.	366	callback to be invoked whenever a signal occurs.
229		367
230	Although the callback might get passed parameters, their value and	368	Although the callback might get passed parameters, their value and
231	presence is undefined and you cannot rely on them. Portable AnyEvent	369	presence is undefined and you cannot rely on them. Portable AnyEvent
232	callbacks cannot use arguments passed to signal watcher callbacks.	370	callbacks cannot use arguments passed to signal watcher callbacks.
233		371
234	Multiple signal occurances can be clumped together into one callback	372	Multiple signal occurrences can be clumped together into one callback
235	invocation, and callback invocation will be synchronous. synchronous	373	invocation, and callback invocation will be synchronous. Synchronous
236	means that it might take a while until the signal gets handled by the	374	means that it might take a while until the signal gets handled by the
237	process, but it is guarenteed not to interrupt any other callbacks.	375	process, but it is guaranteed not to interrupt any other callbacks.
238		376
239	The main advantage of using these watchers is that you can share a	377	The main advantage of using these watchers is that you can share a
240	signal between multiple watchers.	378	signal between multiple watchers, and AnyEvent will ensure that signals
		379	will not interrupt your program at bad times.
241		380
242	This watcher might use %SIG, so programs overwriting those signals	381	This watcher might use %SIG (depending on the event loop used), so
243	directly will likely not work correctly.	382	programs overwriting those signals directly will likely not work
		383	correctly.
244		384
245	Example: exit on SIGINT	385	Example: exit on SIGINT
246		386
247	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	387	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
248		388
		389	Signal Races, Delays and Workarounds
		390	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		391	callbacks to signals in a generic way, which is a pity, as you cannot do
		392	race-free signal handling in perl, requiring C libraries for this.
		393	AnyEvent will try to do it's best, which means in some cases, signals
		394	will be delayed. The maximum time a signal might be delayed is specified
		395	in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
		396	can be changed only before the first signal watcher is created, and
		397	should be left alone otherwise. This variable determines how often
		398	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		399	will cause fewer spurious wake-ups, which is better for power and CPU
		400	saving.
		401
		402	All these problems can be avoided by installing the optional
		403	Async::Interrupt module, which works with most event loops. It will not
		404	work with inherently broken event loops such as Event or Event::Lib (and
		405	not with POE currently, as POE does it's own workaround with one-second
		406	latency). For those, you just have to suffer the delays.
		407
249	CHILD PROCESS WATCHERS	408	CHILD PROCESS WATCHERS
		409	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		410
250	You can also watch on a child process exit and catch its exit status.	411	You can also watch on a child process exit and catch its exit status.
251		412
252	The child process is specified by the "pid" argument (if set to 0, it	413	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	414	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	415	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	416	and an exit status is available, not on any trace events
256	and exit status (as returned by waitpid), so unlike other watcher types,	417	(stopped/continued).
257	you can rely on child watcher callback arguments.	418
		419	The callback will be called with the pid and exit status (as returned by
		420	waitpid), so unlike other watcher types, you can rely on child watcher
		421	callback arguments.
		422
		423	This watcher type works by installing a signal handler for "SIGCHLD",
		424	and since it cannot be shared, nothing else should use SIGCHLD or reap
		425	random child processes (waiting for specific child processes, e.g.
		426	inside "system", is just fine).
258		427
259	There is a slight catch to child watchers, however: you usually start	428	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	429	them after the child process was created, and this means the process
261	could have exited already (and no SIGCHLD will be sent anymore).	430	could have exited already (and no SIGCHLD will be sent anymore).
262		431
263	Not all event models handle this correctly (POE doesn't), but even for	432	Not all event models handle this correctly (neither POE nor IO::Async
		433	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	434	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	435	before the process exits (i.e. before you fork in the first place).
266	place).	436	AnyEvent's pure perl event loop handles all cases correctly regardless
		437	of when you start the watcher.
267		438
268	This means you cannot create a child watcher as the very first thing in	439	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	440	an AnyEvent program, you have to create at least one watcher before
270	you "fork" the child (alternatively, you can call "AnyEvent::detect").	441	you "fork" the child (alternatively, you can call "AnyEvent::detect").
271		442
		443	As most event loops do not support waiting for child events, they will
		444	be emulated by AnyEvent in most cases, in which the latency and race
		445	problems mentioned in the description of signal watchers apply.
		446
272	Example: fork a process and wait for it	447	Example: fork a process and wait for it
273		448
274	my $done = AnyEvent->condvar;	449	my $done = AnyEvent->condvar;
275		450
276	my $pid = fork or exit 5;	451	my $pid = fork or exit 5;
277		452
278	my $w = AnyEvent->child (	453	my $w = AnyEvent->child (
279	pid => $pid,	454	pid => $pid,
280	cb => sub {	455	cb => sub {
281	my ($pid, $status) = @_;	456	my ($pid, $status) = @_;
282	warn "pid $pid exited with status $status";	457	warn "pid $pid exited with status $status";
283	$done->send;	458	$done->send;
284	},	459	},
285	);	460	);
286		461
287	# do something else, then wait for process exit	462	# do something else, then wait for process exit
288	$done->recv;	463	$done->recv;
		464
		465	IDLE WATCHERS
		466	$w = AnyEvent->idle (cb => <callback>);
		467
		468	Sometimes there is a need to do something, but it is not so important to
		469	do it instantly, but only when there is nothing better to do. This
		470	"nothing better to do" is usually defined to be "no other events need
		471	attention by the event loop".
		472
		473	Idle watchers ideally get invoked when the event loop has nothing better
		474	to do, just before it would block the process to wait for new events.
		475	Instead of blocking, the idle watcher is invoked.
		476
		477	Most event loops unfortunately do not really support idle watchers (only
		478	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		479	will simply call the callback "from time to time".
		480
		481	Example: read lines from STDIN, but only process them when the program
		482	is otherwise idle:
		483
		484	my @lines; # read data
		485	my $idle_w;
		486	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		487	push @lines, scalar <STDIN>;
		488
		489	# start an idle watcher, if not already done
		490	$idle_w \|\|= AnyEvent->idle (cb => sub {
		491	# handle only one line, when there are lines left
		492	if (my $line = shift @lines) {
		493	print "handled when idle: $line";
		494	} else {
		495	# otherwise disable the idle watcher again
		496	undef $idle_w;
		497	}
		498	});
		499	});
289		500
290	CONDITION VARIABLES	501	CONDITION VARIABLES
		502	$cv = AnyEvent->condvar;
		503
		504	$cv->send (<list>);
		505	my @res = $cv->recv;
		506
291	If you are familiar with some event loops you will know that all of them	507	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	508	require you to run some blocking "loop", "run" or similar function that
293	will actively watch for new events and call your callbacks.	509	will actively watch for new events and call your callbacks.
294		510
295	AnyEvent is different, it expects somebody else to run the event loop	511	AnyEvent is slightly different: it expects somebody else to run the
296	and will only block when necessary (usually when told by the user).	512	event loop and will only block when necessary (usually when told by the
		513	user).
297		514
298	The instrument to do that is called a "condition variable", so called	515	The instrument to do that is called a "condition variable", so called
299	because they represent a condition that must become true.	516	because they represent a condition that must become true.
		517
		518	Now is probably a good time to look at the examples further below.
300		519
301	Condition variables can be created by calling the "AnyEvent->condvar"	520	Condition variables can be created by calling the "AnyEvent->condvar"
302	method, usually without arguments. The only argument pair allowed is	521	method, usually without arguments. The only argument pair allowed is
303	"cb", which specifies a callback to be called when the condition	522	"cb", which specifies a callback to be called when the condition
304	variable becomes true.	523	variable becomes true, with the condition variable as the first argument
		524	(but not the results).
305		525
306	After creation, the conditon variable is "false" until it becomes "true"	526	After creation, the condition variable is "false" until it becomes
		527	"true" by calling the "send" method (or calling the condition variable
		528	as if it were a callback, read about the caveats in the description for
307	by calling the "send" method.	529	the "->send" method).
308		530
309	Condition variables are similar to callbacks, except that you can	531	Condition variables are similar to callbacks, except that you can
310	optionally wait for them. They can also be called merge points - points	532	optionally wait for them. They can also be called merge points - points
311	in time where multiple outstandign events have been processed. And yet	533	in time where multiple outstanding events have been processed. And yet
312	another way to call them is transations - each condition variable can be	534	another way to call them is transactions - each condition variable can
313	used to represent a transaction, which finishes at some point and	535	be used to represent a transaction, which finishes at some point and
314	delivers a result.	536	delivers a result. And yet some people know them as "futures" - a
		537	promise to compute/deliver something that you can wait for.
315		538
316	Condition variables are very useful to signal that something has	539	Condition variables are very useful to signal that something has
317	finished, for example, if you write a module that does asynchronous http	540	finished, for example, if you write a module that does asynchronous http
318	requests, then a condition variable would be the ideal candidate to	541	requests, then a condition variable would be the ideal candidate to
319	signal the availability of results. The user can either act when the	542	signal the availability of results. The user can either act when the
…		…
323	you can block your main program until an event occurs - for example, you	546	you can block your main program until an event occurs - for example, you
324	could "->recv" in your main program until the user clicks the Quit	547	could "->recv" in your main program until the user clicks the Quit
325	button of your app, which would "->send" the "quit" event.	548	button of your app, which would "->send" the "quit" event.
326		549
327	Note that condition variables recurse into the event loop - if you have	550	Note that condition variables recurse into the event loop - if you have
328	two pieces of code that call "->recv" in a round-robbin fashion, you	551	two pieces of code that call "->recv" in a round-robin fashion, you
329	lose. Therefore, condition variables are good to export to your caller,	552	lose. Therefore, condition variables are good to export to your caller,
330	but you should avoid making a blocking wait yourself, at least in	553	but you should avoid making a blocking wait yourself, at least in
331	callbacks, as this asks for trouble.	554	callbacks, as this asks for trouble.
332		555
333	Condition variables are represented by hash refs in perl, and the keys	556	Condition variables are represented by hash refs in perl, and the keys
…		…
338		561
339	There are two "sides" to a condition variable - the "producer side"	562	There are two "sides" to a condition variable - the "producer side"
340	which eventually calls "-> send", and the "consumer side", which waits	563	which eventually calls "-> send", and the "consumer side", which waits
341	for the send to occur.	564	for the send to occur.
342		565
343	Example:	566	Example: wait for a timer.
344		567
345	# wait till the result is ready	568	# wait till the result is ready
346	my $result_ready = AnyEvent->condvar;	569	my $result_ready = AnyEvent->condvar;
347		570
348	# do something such as adding a timer	571	# do something such as adding a timer
…		…
353	after => 1,	576	after => 1,
354	cb => sub { $result_ready->send },	577	cb => sub { $result_ready->send },
355	);	578	);
356		579
357	# this "blocks" (while handling events) till the callback	580	# this "blocks" (while handling events) till the callback
358	# calls send	581	# calls ->send
359	$result_ready->recv;	582	$result_ready->recv;
		583
		584	Example: wait for a timer, but take advantage of the fact that condition
		585	variables are also callable directly.
		586
		587	my $done = AnyEvent->condvar;
		588	my $delay = AnyEvent->timer (after => 5, cb => $done);
		589	$done->recv;
		590
		591	Example: Imagine an API that returns a condvar and doesn't support
		592	callbacks. This is how you make a synchronous call, for example from the
		593	main program:
		594
		595	use AnyEvent::CouchDB;
		596
		597	...
		598
		599	my @info = $couchdb->info->recv;
		600
		601	And this is how you would just set a callback to be called whenever the
		602	results are available:
		603
		604	$couchdb->info->cb (sub {
		605	my @info = $_[0]->recv;
		606	});
360		607
361	METHODS FOR PRODUCERS	608	METHODS FOR PRODUCERS
362	These methods should only be used by the producing side, i.e. the	609	These methods should only be used by the producing side, i.e. the
363	code/module that eventually sends the signal. Note that it is also the	610	code/module that eventually sends the signal. Note that it is also the
364	producer side which creates the condvar in most cases, but it isn't	611	producer side which creates the condvar in most cases, but it isn't
…		…
373	immediately from within send.	620	immediately from within send.
374		621
375	Any arguments passed to the "send" call will be returned by all	622	Any arguments passed to the "send" call will be returned by all
376	future "->recv" calls.	623	future "->recv" calls.
377		624
		625	Condition variables are overloaded so one can call them directly (as
		626	if they were a code reference). Calling them directly is the same as
		627	calling "send".
		628
378	$cv->croak ($error)	629	$cv->croak ($error)
379	Similar to send, but causes all call's to "->recv" to invoke	630	Similar to send, but causes all call's to "->recv" to invoke
380	"Carp::croak" with the given error message/object/scalar.	631	"Carp::croak" with the given error message/object/scalar.
381		632
382	This can be used to signal any errors to the condition variable	633	This can be used to signal any errors to the condition variable
383	user/consumer.	634	user/consumer. Doing it this way instead of calling "croak" directly
		635	delays the error detetcion, but has the overwhelmign advantage that
		636	it diagnoses the error at the place where the result is expected,
		637	and not deep in some event clalback without connection to the actual
		638	code causing the problem.
384		639
385	$cv->begin ([group callback])	640	$cv->begin ([group callback])
386	$cv->end	641	$cv->end
387	These two methods are EXPERIMENTAL and MIGHT CHANGE.
388
389	These two methods can be used to combine many transactions/events	642	These two methods can be used to combine many transactions/events
390	into one. For example, a function that pings many hosts in parallel	643	into one. For example, a function that pings many hosts in parallel
391	might want to use a condition variable for the whole process.	644	might want to use a condition variable for the whole process.
392		645
393	Every call to "->begin" will increment a counter, and every call to	646	Every call to "->begin" will increment a counter, and every call to
394	"->end" will decrement it. If the counter reaches 0 in "->end", the	647	"->end" will decrement it. If the counter reaches 0 in "->end", the
395	(last) callback passed to "begin" will be executed. That callback is	648	(last) callback passed to "begin" will be executed, passing the
396	supposed to call "->send", but that is not required. If no	649	condvar as first argument. That callback is supposed to call
		650	"->send", but that is not required. If no group callback was set,
397	callback was set, "send" will be called without any arguments.	651	"send" will be called without any arguments.
398		652
399	Let's clarify this with the ping example:	653	You can think of "$cv->send" giving you an OR condition (one call
		654	sends), while "$cv->begin" and "$cv->end" giving you an AND
		655	condition (all "begin" calls must be "end"'ed before the condvar
		656	sends).
		657
		658	Let's start with a simple example: you have two I/O watchers (for
		659	example, STDOUT and STDERR for a program), and you want to wait for
		660	both streams to close before activating a condvar:
400		661
401	my $cv = AnyEvent->condvar;	662	my $cv = AnyEvent->condvar;
402		663
		664	$cv->begin; # first watcher
		665	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		666	defined sysread $fh1, my $buf, 4096
		667	or $cv->end;
		668	});
		669
		670	$cv->begin; # second watcher
		671	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		672	defined sysread $fh2, my $buf, 4096
		673	or $cv->end;
		674	});
		675
		676	$cv->recv;
		677
		678	This works because for every event source (EOF on file handle),
		679	there is one call to "begin", so the condvar waits for all calls to
		680	"end" before sending.
		681
		682	The ping example mentioned above is slightly more complicated, as
		683	the there are results to be passwd back, and the number of tasks
		684	that are begung can potentially be zero:
		685
		686	my $cv = AnyEvent->condvar;
		687
403	my %result;	688	my %result;
404	$cv->begin (sub { $cv->send (\%result) });	689	$cv->begin (sub { shift->send (\%result) });
405		690
406	for my $host (@list_of_hosts) {	691	for my $host (@list_of_hosts) {
407	$cv->begin;	692	$cv->begin;
408	ping_host_then_call_callback $host, sub {	693	ping_host_then_call_callback $host, sub {
409	$result{$host} = ...;	694	$result{$host} = ...;
…		…
424	the loop, which serves two important purposes: first, it sets the	709	the loop, which serves two important purposes: first, it sets the
425	callback to be called once the counter reaches 0, and second, it	710	callback to be called once the counter reaches 0, and second, it
426	ensures that "send" is called even when "no" hosts are being pinged	711	ensures that "send" is called even when "no" hosts are being pinged
427	(the loop doesn't execute once).	712	(the loop doesn't execute once).
428		713
429	This is the general pattern when you "fan out" into multiple	714	This is the general pattern when you "fan out" into multiple (but
430	subrequests: use an outer "begin"/"end" pair to set the callback and	715	potentially none) subrequests: use an outer "begin"/"end" pair to
431	ensure "end" is called at least once, and then, for each subrequest	716	set the callback and ensure "end" is called at least once, and then,
432	you start, call "begin" and for eahc subrequest you finish, call	717	for each subrequest you start, call "begin" and for each subrequest
433	"end".	718	you finish, call "end".
434		719
435	METHODS FOR CONSUMERS	720	METHODS FOR CONSUMERS
436	These methods should only be used by the consuming side, i.e. the code	721	These methods should only be used by the consuming side, i.e. the code
437	awaits the condition.	722	awaits the condition.
438		723
…		…
447	function will call "croak".	732	function will call "croak".
448		733
449	In list context, all parameters passed to "send" will be returned,	734	In list context, all parameters passed to "send" will be returned,
450	in scalar context only the first one will be returned.	735	in scalar context only the first one will be returned.
451		736
		737	Note that doing a blocking wait in a callback is not supported by
		738	any event loop, that is, recursive invocation of a blocking "->recv"
		739	is not allowed, and the "recv" call will "croak" if such a condition
		740	is detected. This condition can be slightly loosened by using
		741	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		742	thread that doesn't run the event loop itself.
		743
452	Not all event models support a blocking wait - some die in that case	744	Not all event models support a blocking wait - some die in that case
453	(programs might want to do that to stay interactive), so *if you are	745	(programs might want to do that to stay interactive), so *if you are
454	using this from a module, never require a blocking wait*, but let	746	using this from a module, never require a blocking wait*. Instead,
455	the caller decide whether the call will block or not (for example,	747	let the caller decide whether the call will block or not (for
456	by coupling condition variables with some kind of request results	748	example, by coupling condition variables with some kind of request
457	and supporting callbacks so the caller knows that getting the result	749	results and supporting callbacks so the caller knows that getting
458	will not block, while still suppporting blocking waits if the caller	750	the result will not block, while still supporting blocking waits if
459	so desires).	751	the caller so desires).
460
461	Another reason never to "->recv" in a module is that you cannot
462	sensibly have two "->recv"'s in parallel, as that would require
463	multiple interpreters or coroutines/threads, none of which
464	"AnyEvent" can supply.
465
466	The Coro module, however, can and does supply coroutines and, in
467	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
468	versions and also integrates coroutines into AnyEvent, making
469	blocking "->recv" calls perfectly safe as long as they are done from
470	another coroutine (one that doesn't run the event loop).
471		752
472	You can ensure that "-recv" never blocks by setting a callback and	753	You can ensure that "-recv" never blocks by setting a callback and
473	only calling "->recv" from within that callback (or at a later	754	only calling "->recv" from within that callback (or at a later
474	time). This will work even when the event loop does not support	755	time). This will work even when the event loop does not support
475	blocking waits otherwise.	756	blocking waits otherwise.
476		757
477	$bool = $cv->ready	758	$bool = $cv->ready
478	Returns true when the condition is "true", i.e. whether "send" or	759	Returns true when the condition is "true", i.e. whether "send" or
479	"croak" have been called.	760	"croak" have been called.
480		761
481	$cb = $cv->cb ([new callback])	762	$cb = $cv->cb ($cb->($cv))
482	This is a mutator function that returns the callback set and	763	This is a mutator function that returns the callback set and
483	optionally replaces it before doing so.	764	optionally replaces it before doing so.
484		765
485	The callback will be called when the condition becomes "true", i.e.	766	The callback will be called when the condition becomes (or already
486	when "send" or "croak" are called. Calling "recv" inside the	767	was) "true", i.e. when "send" or "croak" are called (or were
487	callback or at any later time is guaranteed not to block.	768	called), with the only argument being the condition variable itself.
		769	Calling "recv" inside the callback or at any later time is
		770	guaranteed not to block.
		771
		772	SUPPORTED EVENT LOOPS/BACKENDS
		773	The available backend classes are (every class has its own manpage):
		774
		775	Backends that are autoprobed when no other event loop can be found.
		776	EV is the preferred backend when no other event loop seems to be in
		777	use. If EV is not installed, then AnyEvent will fall back to its own
		778	pure-perl implementation, which is available everywhere as it comes
		779	with AnyEvent itself.
		780
		781	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		782	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		783
		784	Backends that are transparently being picked up when they are used.
		785	These will be used when they are currently loaded when the first
		786	watcher is created, in which case it is assumed that the application
		787	is using them. This means that AnyEvent will automatically pick the
		788	right backend when the main program loads an event module before
		789	anything starts to create watchers. Nothing special needs to be done
		790	by the main program.
		791
		792	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		793	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		794	AnyEvent::Impl::Tk based on Tk, very broken.
		795	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		796	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		797	AnyEvent::Impl::Irssi used when running within irssi.
		798
		799	Backends with special needs.
		800	Qt requires the Qt::Application to be instantiated first, but will
		801	otherwise be picked up automatically. As long as the main program
		802	instantiates the application before any AnyEvent watchers are
		803	created, everything should just work.
		804
		805	AnyEvent::Impl::Qt based on Qt.
		806
		807	Support for IO::Async can only be partial, as it is too broken and
		808	architecturally limited to even support the AnyEvent API. It also is
		809	the only event loop that needs the loop to be set explicitly, so it
		810	can only be used by a main program knowing about AnyEvent. See
		811	AnyEvent::Impl::Async for the gory details.
		812
		813	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		814
		815	Event loops that are indirectly supported via other backends.
		816	Some event loops can be supported via other modules:
		817
		818	There is no direct support for WxWidgets (Wx) or Prima.
		819
		820	WxWidgets has no support for watching file handles. However, you can
		821	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		822	simply polls 20 times per second, which was considered to be too
		823	horrible to even consider for AnyEvent.
		824
		825	Prima is not supported as nobody seems to be using it, but it has a
		826	POE backend, so it can be supported through POE.
		827
		828	AnyEvent knows about both Prima and Wx, however, and will try to
		829	load POE when detecting them, in the hope that POE will pick them
		830	up, in which case everything will be automatic.
488		831
489	GLOBAL VARIABLES AND FUNCTIONS	832	GLOBAL VARIABLES AND FUNCTIONS
		833	These are not normally required to use AnyEvent, but can be useful to
		834	write AnyEvent extension modules.
		835
490	$AnyEvent::MODEL	836	$AnyEvent::MODEL
491	Contains "undef" until the first watcher is being created. Then it	837	Contains "undef" until the first watcher is being created, before
		838	the backend has been autodetected.
		839
492	contains the event model that is being used, which is the name of	840	Afterwards it contains the event model that is being used, which is
493	the Perl class implementing the model. This class is usually one of	841	the name of the Perl class implementing the model. This class is
494	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	842	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
495	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	843	other class in the case AnyEvent has been extended at runtime (e.g.
496		844	in rxvt-unicode it will be "urxvt::anyevent").
497	The known classes so far are:
498
499	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
500	AnyEvent::Impl::Event based on Event, second best choice.
501	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
502	AnyEvent::Impl::Glib based on Glib, third-best choice.
503	AnyEvent::Impl::Tk based on Tk, very bad choice.
504	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
505	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
506	AnyEvent::Impl::POE based on POE, not generic enough for full support.
507
508	There is no support for WxWidgets, as WxWidgets has no support for
509	watching file handles. However, you can use WxWidgets through the
510	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
511	second, which was considered to be too horrible to even consider for
512	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
513	using it's adaptor.
514
515	AnyEvent knows about Prima and Wx and will try to use POE when
516	autodetecting them.
517		845
518	AnyEvent::detect	846	AnyEvent::detect
519	Returns $AnyEvent::MODEL, forcing autodetection of the event model	847	Returns $AnyEvent::MODEL, forcing autodetection of the event model
520	if necessary. You should only call this function right before you	848	if necessary. You should only call this function right before you
521	would have created an AnyEvent watcher anyway, that is, as late as	849	would have created an AnyEvent watcher anyway, that is, as late as
522	possible at runtime.	850	possible at runtime, and not e.g. while initialising of your module.
		851
		852	If you need to do some initialisation before AnyEvent watchers are
		853	created, use "post_detect".
523		854
524	$guard = AnyEvent::post_detect { BLOCK }	855	$guard = AnyEvent::post_detect { BLOCK }
525	Arranges for the code block to be executed as soon as the event	856	Arranges for the code block to be executed as soon as the event
526	model is autodetected (or immediately if this has already happened).	857	model is autodetected (or immediately if this has already happened).
527		858
		859	The block will be executed after the actual backend has been
		860	detected ($AnyEvent::MODEL is set), but before any watchers have
		861	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		862	other initialisations - see the sources of AnyEvent::Strict or
		863	AnyEvent::AIO to see how this is used.
		864
		865	The most common usage is to create some global watchers, without
		866	forcing event module detection too early, for example, AnyEvent::AIO
		867	creates and installs the global IO::AIO watcher in a "post_detect"
		868	block to avoid autodetecting the event module at load time.
		869
528	If called in scalar or list context, then it creates and returns an	870	If called in scalar or list context, then it creates and returns an
529	object that automatically removes the callback again when it is	871	object that automatically removes the callback again when it is
		872	destroyed (or "undef" when the hook was immediately executed). See
530	destroyed. See Coro::BDB for a case where this is useful.	873	AnyEvent::AIO for a case where this is useful.
		874
		875	Example: Create a watcher for the IO::AIO module and store it in
		876	$WATCHER. Only do so after the event loop is initialised, though.
		877
		878	our WATCHER;
		879
		880	my $guard = AnyEvent::post_detect {
		881	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		882	};
		883
		884	# the \|\|= is important in case post_detect immediately runs the block,
		885	# as to not clobber the newly-created watcher. assigning both watcher and
		886	# post_detect guard to the same variable has the advantage of users being
		887	# able to just C<undef $WATCHER> if the watcher causes them grief.
		888
		889	$WATCHER \|\|= $guard;
531		890
532	@AnyEvent::post_detect	891	@AnyEvent::post_detect
533	If there are any code references in this array (you can "push" to it	892	If there are any code references in this array (you can "push" to it
534	before or after loading AnyEvent), then they will called directly	893	before or after loading AnyEvent), then they will called directly
535	after the event loop has been chosen.	894	after the event loop has been chosen.
536		895
537	You should check $AnyEvent::MODEL before adding to this array,	896	You should check $AnyEvent::MODEL before adding to this array,
538	though: if it contains a true value then the event loop has already	897	though: if it is defined then the event loop has already been
539	been detected, and the array will be ignored.	898	detected, and the array will be ignored.
540		899
541	Best use "AnyEvent::post_detect { BLOCK }" instead.	900	Best use "AnyEvent::post_detect { BLOCK }" when your application
		901	allows it,as it takes care of these details.
		902
		903	This variable is mainly useful for modules that can do something
		904	useful when AnyEvent is used and thus want to know when it is
		905	initialised, but do not need to even load it by default. This array
		906	provides the means to hook into AnyEvent passively, without loading
		907	it.
542		908
543	WHAT TO DO IN A MODULE	909	WHAT TO DO IN A MODULE
544	As a module author, you should "use AnyEvent" and call AnyEvent methods	910	As a module author, you should "use AnyEvent" and call AnyEvent methods
545	freely, but you should not load a specific event module or rely on it.	911	freely, but you should not load a specific event module or rely on it.
546		912
…		…
566	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	932	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
567	do anything special (it does not need to be event-based) and let	933	do anything special (it does not need to be event-based) and let
568	AnyEvent decide which implementation to chose if some module relies on	934	AnyEvent decide which implementation to chose if some module relies on
569	it.	935	it.
570		936
571	If the main program relies on a specific event model. For example, in	937	If the main program relies on a specific event model - for example, in
572	Gtk2 programs you have to rely on the Glib module. You should load the	938	Gtk2 programs you have to rely on the Glib module - you should load the
573	event module before loading AnyEvent or any module that uses it:	939	event module before loading AnyEvent or any module that uses it:
574	generally speaking, you should load it as early as possible. The reason	940	generally speaking, you should load it as early as possible. The reason
575	is that modules might create watchers when they are loaded, and AnyEvent	941	is that modules might create watchers when they are loaded, and AnyEvent
576	will decide on the event model to use as soon as it creates watchers,	942	will decide on the event model to use as soon as it creates watchers,
577	and it might chose the wrong one unless you load the correct one	943	and it might chose the wrong one unless you load the correct one
578	yourself.	944	yourself.
579		945
580	You can chose to use a rather inefficient pure-perl implementation by	946	You can chose to use a pure-perl implementation by loading the
581	loading the "AnyEvent::Impl::Perl" module, which gives you similar	947	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
582	behaviour everywhere, but letting AnyEvent chose is generally better.	948	everywhere, but letting AnyEvent chose the model is generally better.
		949
		950	MAINLOOP EMULATION
		951	Sometimes (often for short test scripts, or even standalone programs who
		952	only want to use AnyEvent), you do not want to run a specific event
		953	loop.
		954
		955	In that case, you can use a condition variable like this:
		956
		957	AnyEvent->condvar->recv;
		958
		959	This has the effect of entering the event loop and looping forever.
		960
		961	Note that usually your program has some exit condition, in which case it
		962	is better to use the "traditional" approach of storing a condition
		963	variable somewhere, waiting for it, and sending it when the program
		964	should exit cleanly.
583		965
584	OTHER MODULES	966	OTHER MODULES
585	The following is a non-exhaustive list of additional modules that use	967	The following is a non-exhaustive list of additional modules that use
586	AnyEvent and can therefore be mixed easily with other AnyEvent modules	968	AnyEvent as a client and can therefore be mixed easily with other
587	in the same program. Some of the modules come with AnyEvent, some are	969	AnyEvent modules and other event loops in the same program. Some of the
588	available via CPAN.	970	modules come with AnyEvent, most are available via CPAN.
589		971
590	AnyEvent::Util	972	AnyEvent::Util
591	Contains various utility functions that replace often-used but	973	Contains various utility functions that replace often-used but
592	blocking functions such as "inet_aton" by event-/callback-based	974	blocking functions such as "inet_aton" by event-/callback-based
593	versions.	975	versions.
594		976
		977	AnyEvent::Socket
		978	Provides various utility functions for (internet protocol) sockets,
		979	addresses and name resolution. Also functions to create non-blocking
		980	tcp connections or tcp servers, with IPv6 and SRV record support and
		981	more.
		982
595	AnyEvent::Handle	983	AnyEvent::Handle
596	Provide read and write buffers and manages watchers for reads and	984	Provide read and write buffers, manages watchers for reads and
597	writes.	985	writes, supports raw and formatted I/O, I/O queued and fully
		986	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
		987
		988	AnyEvent::DNS
		989	Provides rich asynchronous DNS resolver capabilities.
		990
		991	AnyEvent::HTTP
		992	A simple-to-use HTTP library that is capable of making a lot of
		993	concurrent HTTP requests.
598		994
599	AnyEvent::HTTPD	995	AnyEvent::HTTPD
600	Provides a simple web application server framework.	996	Provides a simple web application server framework.
601		997
602	AnyEvent::DNS
603	Provides asynchronous DNS resolver capabilities, beyond what
604	AnyEvent::Util offers.
605
606	AnyEvent::FastPing	998	AnyEvent::FastPing
607	The fastest ping in the west.	999	The fastest ping in the west.
608		1000
		1001	AnyEvent::DBI
		1002	Executes DBI requests asynchronously in a proxy process.
		1003
		1004	AnyEvent::AIO
		1005	Truly asynchronous I/O, should be in the toolbox of every event
		1006	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		1007	together.
		1008
		1009	AnyEvent::BDB
		1010	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		1011	fuses BDB and AnyEvent together.
		1012
		1013	AnyEvent::GPSD
		1014	A non-blocking interface to gpsd, a daemon delivering GPS
		1015	information.
		1016
		1017	AnyEvent::IRC
		1018	AnyEvent based IRC client module family (replacing the older
609	Net::IRC3	1019	Net::IRC3).
610	AnyEvent based IRC client module family.
611		1020
612	Net::XMPP2	1021	AnyEvent::XMPP
613	AnyEvent based XMPP (Jabber protocol) module family.	1022	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		1023	older Net::XMPP2>.
		1024
		1025	AnyEvent::IGS
		1026	A non-blocking interface to the Internet Go Server protocol (used by
		1027	App::IGS).
614		1028
615	Net::FCP	1029	Net::FCP
616	AnyEvent-based implementation of the Freenet Client Protocol,	1030	AnyEvent-based implementation of the Freenet Client Protocol,
617	birthplace of AnyEvent.	1031	birthplace of AnyEvent.
618		1032
…		…
620	High level API for event-based execution flow control.	1034	High level API for event-based execution flow control.
621		1035
622	Coro	1036	Coro
623	Has special support for AnyEvent via Coro::AnyEvent.	1037	Has special support for AnyEvent via Coro::AnyEvent.
624		1038
625	AnyEvent::AIO, IO::AIO	1039	SIMPLIFIED AE API
626	Truly asynchronous I/O, should be in the toolbox of every event	1040	Starting with version 5.0, AnyEvent officially supports a second, much
627	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	1041	simpler, API that is designed to reduce the calling, typing and memory
628	together.	1042	overhead.
629		1043
630	AnyEvent::BDB, BDB	1044	See the AE manpage for details.
631	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
632	fuses IO::AIO and AnyEvent together.
633		1045
634	IO::Lambda	1046	ERROR AND EXCEPTION HANDLING
635	The lambda approach to I/O - don't ask, look there. Can use	1047	In general, AnyEvent does not do any error handling - it relies on the
636	AnyEvent.	1048	caller to do that if required. The AnyEvent::Strict module (see also the
		1049	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1050	checking of all AnyEvent methods, however, which is highly useful during
		1051	development.
		1052
		1053	As for exception handling (i.e. runtime errors and exceptions thrown
		1054	while executing a callback), this is not only highly event-loop
		1055	specific, but also not in any way wrapped by this module, as this is the
		1056	job of the main program.
		1057
		1058	The pure perl event loop simply re-throws the exception (usually within
		1059	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		1060	Glib uses "install_exception_handler" and so on.
		1061
		1062	ENVIRONMENT VARIABLES
		1063	The following environment variables are used by this module or its
		1064	submodules.
		1065
		1066	Note that AnyEvent will remove all environment variables starting with
		1067	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1068	enabled.
		1069
		1070	"PERL_ANYEVENT_VERBOSE"
		1071	By default, AnyEvent will be completely silent except in fatal
		1072	conditions. You can set this environment variable to make AnyEvent
		1073	more talkative.
		1074
		1075	When set to 1 or higher, causes AnyEvent to warn about unexpected
		1076	conditions, such as not being able to load the event model specified
		1077	by "PERL_ANYEVENT_MODEL".
		1078
		1079	When set to 2 or higher, cause AnyEvent to report to STDERR which
		1080	event model it chooses.
		1081
		1082	When set to 8 or higher, then AnyEvent will report extra information
		1083	on which optional modules it loads and how it implements certain
		1084	features.
		1085
		1086	"PERL_ANYEVENT_STRICT"
		1087	AnyEvent does not do much argument checking by default, as thorough
		1088	argument checking is very costly. Setting this variable to a true
		1089	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1090	thoroughly check the arguments passed to most method calls. If it
		1091	finds any problems, it will croak.
		1092
		1093	In other words, enables "strict" mode.
		1094
		1095	Unlike "use strict" (or it's modern cousin, "use common::sense", it
		1096	is definitely recommended to keep it off in production. Keeping
		1097	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1098	programs can be very useful, however.
		1099
		1100	"PERL_ANYEVENT_MODEL"
		1101	This can be used to specify the event model to be used by AnyEvent,
		1102	before auto detection and -probing kicks in. It must be a string
		1103	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		1104	gets prepended and the resulting module name is loaded and if the
		1105	load was successful, used as event model. If it fails to load
		1106	AnyEvent will proceed with auto detection and -probing.
		1107
		1108	This functionality might change in future versions.
		1109
		1110	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		1111	could start your program like this:
		1112
		1113	PERL_ANYEVENT_MODEL=Perl perl ...
		1114
		1115	"PERL_ANYEVENT_PROTOCOLS"
		1116	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		1117	preferences for IPv4 or IPv6. The default is unspecified (and might
		1118	change, or be the result of auto probing).
		1119
		1120	Must be set to a comma-separated list of protocols or address
		1121	families, current supported: "ipv4" and "ipv6". Only protocols
		1122	mentioned will be used, and preference will be given to protocols
		1123	mentioned earlier in the list.
		1124
		1125	This variable can effectively be used for denial-of-service attacks
		1126	against local programs (e.g. when setuid), although the impact is
		1127	likely small, as the program has to handle conenction and other
		1128	failures anyways.
		1129
		1130	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		1131	IPv6, but support both and try to use both.
		1132	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		1133	resolve or contact IPv6 addresses.
		1134	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		1135	prefer IPv6 over IPv4.
		1136
		1137	"PERL_ANYEVENT_EDNS0"
		1138	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		1139	for DNS. This extension is generally useful to reduce DNS traffic,
		1140	but some (broken) firewalls drop such DNS packets, which is why it
		1141	is off by default.
		1142
		1143	Setting this variable to 1 will cause AnyEvent::DNS to announce
		1144	EDNS0 in its DNS requests.
		1145
		1146	"PERL_ANYEVENT_MAX_FORKS"
		1147	The maximum number of child processes that
		1148	"AnyEvent::Util::fork_call" will create in parallel.
		1149
		1150	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1151	The default value for the "max_outstanding" parameter for the
		1152	default DNS resolver - this is the maximum number of parallel DNS
		1153	requests that are sent to the DNS server.
		1154
		1155	"PERL_ANYEVENT_RESOLV_CONF"
		1156	The file to use instead of /etc/resolv.conf (or OS-specific
		1157	configuration) in the default resolver. When set to the empty
		1158	string, no default config will be used.
		1159
		1160	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1161	When neither "ca_file" nor "ca_path" was specified during
		1162	AnyEvent::TLS context creation, and either of these environment
		1163	variables exist, they will be used to specify CA certificate
		1164	locations instead of a system-dependent default.
		1165
		1166	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1167	When these are set to 1, then the respective modules are not loaded.
		1168	Mostly good for testing AnyEvent itself.
637		1169
638	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1170	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
639	This is an advanced topic that you do not normally need to use AnyEvent	1171	This is an advanced topic that you do not normally need to use AnyEvent
640	in a module. This section is only of use to event loop authors who want	1172	in a module. This section is only of use to event loop authors who want
641	to provide AnyEvent compatibility.	1173	to provide AnyEvent compatibility.
…		…
675		1207
676	rxvt-unicode also cheats a bit by not providing blocking access to	1208	rxvt-unicode also cheats a bit by not providing blocking access to
677	condition variables: code blocking while waiting for a condition will	1209	condition variables: code blocking while waiting for a condition will
678	"die". This still works with most modules/usages, and blocking calls	1210	"die". This still works with most modules/usages, and blocking calls
679	must not be done in an interactive application, so it makes sense.	1211	must not be done in an interactive application, so it makes sense.
680
681	ENVIRONMENT VARIABLES
682	The following environment variables are used by this module:
683
684	"PERL_ANYEVENT_VERBOSE"
685	By default, AnyEvent will be completely silent except in fatal
686	conditions. You can set this environment variable to make AnyEvent
687	more talkative.
688
689	When set to 1 or higher, causes AnyEvent to warn about unexpected
690	conditions, such as not being able to load the event model specified
691	by "PERL_ANYEVENT_MODEL".
692
693	When set to 2 or higher, cause AnyEvent to report to STDERR which
694	event model it chooses.
695
696	"PERL_ANYEVENT_MODEL"
697	This can be used to specify the event model to be used by AnyEvent,
698	before autodetection and -probing kicks in. It must be a string
699	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
700	gets prepended and the resulting module name is loaded and if the
701	load was successful, used as event model. If it fails to load
702	AnyEvent will proceed with autodetection and -probing.
703
704	This functionality might change in future versions.
705
706	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
707	could start your program like this:
708
709	PERL_ANYEVENT_MODEL=Perl perl ...
710		1212
711	EXAMPLE PROGRAM	1213	EXAMPLE PROGRAM
712	The following program uses an I/O watcher to read data from STDIN, a	1214	The following program uses an I/O watcher to read data from STDIN, a
713	timer to display a message once per second, and a condition variable to	1215	timer to display a message once per second, and a condition variable to
714	quit the program when the user enters quit:	1216	quit the program when the user enters quit:
…		…
722	poll => 'r',	1224	poll => 'r',
723	cb => sub {	1225	cb => sub {
724	warn "io event <$_[0]>\n"; # will always output <r>	1226	warn "io event <$_[0]>\n"; # will always output <r>
725	chomp (my $input = <STDIN>); # read a line	1227	chomp (my $input = <STDIN>); # read a line
726	warn "read: $input\n"; # output what has been read	1228	warn "read: $input\n"; # output what has been read
727	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1229	$cv->send if $input =~ /^q/i; # quit program if /^q/i
728	},	1230	},
729	);	1231	);
730		1232
731	my $time_watcher; # can only be used once
732
733	sub new_timer {
734	$timer = AnyEvent->timer (after => 1, cb => sub {	1233	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
735	warn "timeout\n"; # print 'timeout' about every second	1234	warn "timeout\n"; # print 'timeout' at most every second
736	&new_timer; # and restart the time
737	});
738	}	1235	});
739		1236
740	new_timer; # create first timer
741
742	$cv->wait; # wait until user enters /^q/i	1237	$cv->recv; # wait until user enters /^q/i
743		1238
744	REAL-WORLD EXAMPLE	1239	REAL-WORLD EXAMPLE
745	Consider the Net::FCP module. It features (among others) the following	1240	Consider the Net::FCP module. It features (among others) the following
746	API calls, which are to freenet what HTTP GET requests are to http:	1241	API calls, which are to freenet what HTTP GET requests are to http:
747		1242
…		…
796	syswrite $txn->{fh}, $txn->{request}	1291	syswrite $txn->{fh}, $txn->{request}
797	or die "connection or write error";	1292	or die "connection or write error";
798	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1293	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
799		1294
800	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1295	Again, "fh_ready_r" waits till all data has arrived, and then stores the
801	result and signals any possible waiters that the request ahs finished:	1296	result and signals any possible waiters that the request has finished:
802		1297
803	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1298	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
804		1299
805	if (end-of-file or data complete) {	1300	if (end-of-file or data complete) {
806	$txn->{result} = $txn->{buf};	1301	$txn->{result} = $txn->{buf};
807	$txn->{finished}->broadcast;	1302	$txn->{finished}->send;
808	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1303	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
809	}	1304	}
810		1305
811	The "result" method, finally, just waits for the finished signal (if the	1306	The "result" method, finally, just waits for the finished signal (if the
812	request was already finished, it doesn't wait, of course, and returns	1307	request was already finished, it doesn't wait, of course, and returns
813	the data:	1308	the data:
814		1309
815	$txn->{finished}->wait;	1310	$txn->{finished}->recv;
816	return $txn->{result};	1311	return $txn->{result};
817		1312
818	The actual code goes further and collects all errors ("die"s,	1313	The actual code goes further and collects all errors ("die"s,
819	exceptions) that occured during request processing. The "result" method	1314	exceptions) that occurred during request processing. The "result" method
820	detects whether an exception as thrown (it is stored inside the $txn	1315	detects whether an exception as thrown (it is stored inside the $txn
821	object) and just throws the exception, which means connection errors and	1316	object) and just throws the exception, which means connection errors and
822	other problems get reported tot he code that tries to use the result,	1317	other problems get reported tot he code that tries to use the result,
823	not in a random callback.	1318	not in a random callback.
824		1319
…		…
855		1350
856	my $quit = AnyEvent->condvar;	1351	my $quit = AnyEvent->condvar;
857		1352
858	$fcp->txn_client_get ($url)->cb (sub {	1353	$fcp->txn_client_get ($url)->cb (sub {
859	...	1354	...
860	$quit->broadcast;	1355	$quit->send;
861	});	1356	});
862		1357
863	$quit->wait;	1358	$quit->recv;
864		1359
865	BENCHMARKS	1360	BENCHMARKS
866	To give you an idea of the performance and overheads that AnyEvent adds	1361	To give you an idea of the performance and overheads that AnyEvent adds
867	over the event loops themselves and to give you an impression of the	1362	over the event loops themselves and to give you an impression of the
868	speed of various event loops I prepared some benchmarks.	1363	speed of various event loops I prepared some benchmarks.
869		1364
870	BENCHMARKING ANYEVENT OVERHEAD	1365	BENCHMARKING ANYEVENT OVERHEAD
871	Here is a benchmark of various supported event models used natively and	1366	Here is a benchmark of various supported event models used natively and
872	through anyevent. The benchmark creates a lot of timers (with a zero	1367	through AnyEvent. The benchmark creates a lot of timers (with a zero
873	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1368	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
874	which it is), lets them fire exactly once and destroys them again.	1369	which it is), lets them fire exactly once and destroys them again.
875		1370
876	Source code for this benchmark is found as eg/bench in the AnyEvent	1371	Source code for this benchmark is found as eg/bench in the AnyEvent
877	distribution.	1372	distribution. It uses the AE interface, which makes a real difference
		1373	for the EV and Perl backends only.
878		1374
879	Explanation of the columns	1375	Explanation of the columns
880	watcher is the number of event watchers created/destroyed. Since	1376	watcher is the number of event watchers created/destroyed. Since
881	different event models feature vastly different performances, each event	1377	different event models feature vastly different performances, each event
882	loop was given a number of watchers so that overall runtime is	1378	loop was given a number of watchers so that overall runtime is
…		…
893	between all watchers, to avoid adding memory overhead. That means	1389	between all watchers, to avoid adding memory overhead. That means
894	closure creation and memory usage is not included in the figures.	1390	closure creation and memory usage is not included in the figures.
895		1391
896	invoke is the time, in microseconds, used to invoke a simple callback.	1392	invoke is the time, in microseconds, used to invoke a simple callback.
897	The callback simply counts down a Perl variable and after it was invoked	1393	The callback simply counts down a Perl variable and after it was invoked
898	"watcher" times, it would "->broadcast" a condvar once to signal the end	1394	"watcher" times, it would "->send" a condvar once to signal the end of
899	of this phase.	1395	this phase.
900		1396
901	destroy is the time, in microseconds, that it takes to destroy a	1397	destroy is the time, in microseconds, that it takes to destroy a
902	single watcher.	1398	single watcher.
903		1399
904	Results	1400	Results
905	name watchers bytes create invoke destroy comment	1401	name watchers bytes create invoke destroy comment
906	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1402	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
907	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1403	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
908	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1404	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
909	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1405	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
910	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1406	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
911	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1407	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1408	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1409	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
912	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1410	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
913	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1411	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
914	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1412	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
915	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1413	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
916		1414
917	Discussion	1415	Discussion
918	The benchmark does not measure scalability of the event loop very	1416	The benchmark does not measure scalability of the event loop very
919	well. For example, a select-based event loop (such as the pure perl one)	1417	well. For example, a select-based event loop (such as the pure perl one)
920	can never compete with an event loop that uses epoll when the number of	1418	can never compete with an event loop that uses epoll when the number of
…		…
931	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1429	benchmark machine, handling an event takes roughly 1600 CPU cycles with
932	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1430	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
933	CPU cycles with POE.	1431	CPU cycles with POE.
934		1432
935	"EV" is the sole leader regarding speed and memory use, which are both	1433	"EV" is the sole leader regarding speed and memory use, which are both
936	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1434	maximal/minimal, respectively. When using the AE API there is zero
		1435	overhead (when going through the AnyEvent API create is about 5-6 times
		1436	slower, with other times being equal, so still uses far less memory than
937	far less memory than any other event loop and is still faster than Event	1437	any other event loop and is still faster than Event natively).
938	natively.
939		1438
940	The pure perl implementation is hit in a few sweet spots (both the	1439	The pure perl implementation is hit in a few sweet spots (both the
941	constant timeout and the use of a single fd hit optimisations in the	1440	constant timeout and the use of a single fd hit optimisations in the
942	perl interpreter and the backend itself). Nevertheless this shows that	1441	perl interpreter and the backend itself). Nevertheless this shows that
943	it adds very little overhead in itself. Like any select-based backend	1442	it adds very little overhead in itself. Like any select-based backend
…		…
945	few of them active), of course, but this was not subject of this	1444	few of them active), of course, but this was not subject of this
946	benchmark.	1445	benchmark.
947		1446
948	The "Event" module has a relatively high setup and callback invocation	1447	The "Event" module has a relatively high setup and callback invocation
949	cost, but overall scores in on the third place.	1448	cost, but overall scores in on the third place.
		1449
		1450	"IO::Async" performs admirably well, about on par with "Event", even
		1451	when using its pure perl backend.
950		1452
951	"Glib"'s memory usage is quite a bit higher, but it features a faster	1453	"Glib"'s memory usage is quite a bit higher, but it features a faster
952	callback invocation and overall ends up in the same class as "Event".	1454	callback invocation and overall ends up in the same class as "Event".
953	However, Glib scales extremely badly, doubling the number of watchers	1455	However, Glib scales extremely badly, doubling the number of watchers
954	increases the processing time by more than a factor of four, making it	1456	increases the processing time by more than a factor of four, making it
…		…
992		1494
993	* You should avoid POE like the plague if you want performance or	1495	* You should avoid POE like the plague if you want performance or
994	reasonable memory usage.	1496	reasonable memory usage.
995		1497
996	BENCHMARKING THE LARGE SERVER CASE	1498	BENCHMARKING THE LARGE SERVER CASE
997	This benchmark atcually benchmarks the event loop itself. It works by	1499	This benchmark actually benchmarks the event loop itself. It works by
998	creating a number of "servers": each server consists of a socketpair, a	1500	creating a number of "servers": each server consists of a socket pair, a
999	timeout watcher that gets reset on activity (but never fires), and an	1501	timeout watcher that gets reset on activity (but never fires), and an
1000	I/O watcher waiting for input on one side of the socket. Each time the	1502	I/O watcher waiting for input on one side of the socket. Each time the
1001	socket watcher reads a byte it will write that byte to a random other	1503	socket watcher reads a byte it will write that byte to a random other
1002	"server".	1504	"server".
1003		1505
1004	The effect is that there will be a lot of I/O watchers, only part of	1506	The effect is that there will be a lot of I/O watchers, only part of
1005	which are active at any one point (so there is a constant number of	1507	which are active at any one point (so there is a constant number of
1006	active fds for each loop iterstaion, but which fds these are is random).	1508	active fds for each loop iteration, but which fds these are is random).
1007	The timeout is reset each time something is read because that reflects	1509	The timeout is reset each time something is read because that reflects
1008	how most timeouts work (and puts extra pressure on the event loops).	1510	how most timeouts work (and puts extra pressure on the event loops).
1009		1511
1010	In this benchmark, we use 10000 socketpairs (20000 sockets), of which	1512	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1011	100 (1%) are active. This mirrors the activity of large servers with	1513	100 (1%) are active. This mirrors the activity of large servers with
1012	many connections, most of which are idle at any one point in time.	1514	many connections, most of which are idle at any one point in time.
1013		1515
1014	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1516	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1015	distribution.	1517	distribution. It uses the AE interface, which makes a real difference
		1518	for the EV and Perl backends only.
1016		1519
1017	Explanation of the columns	1520	Explanation of the columns
1018	sockets is the number of sockets, and twice the number of "servers"	1521	sockets is the number of sockets, and twice the number of "servers"
1019	(as each server has a read and write socket end).	1522	(as each server has a read and write socket end).
1020		1523
1021	create is the time it takes to create a socketpair (which is	1524	create is the time it takes to create a socket pair (which is
1022	nontrivial) and two watchers: an I/O watcher and a timeout watcher.	1525	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
1023		1526
1024	request, the most important value, is the time it takes to handle a	1527	request, the most important value, is the time it takes to handle a
1025	single "request", that is, reading the token from the pipe and	1528	single "request", that is, reading the token from the pipe and
1026	forwarding it to another server. This includes deleting the old timeout	1529	forwarding it to another server. This includes deleting the old timeout
1027	and creating a new one that moves the timeout into the future.	1530	and creating a new one that moves the timeout into the future.
1028		1531
1029	Results	1532	Results
1030	name sockets create request	1533	name sockets create request
1031	EV 20000 69.01 11.16	1534	EV 20000 62.66 7.99
1032	Perl 20000 73.32 35.87	1535	Perl 20000 68.32 32.64
1033	Event 20000 212.62 257.32	1536	IOAsync 20000 174.06 101.15 epoll
1034	Glib 20000 651.16 1896.30	1537	IOAsync 20000 174.67 610.84 poll
		1538	Event 20000 202.69 242.91
		1539	Glib 20000 557.01 1689.52
1035	POE 20000 349.67 12317.24 uses POE::Loop::Event	1540	POE 20000 341.54 12086.32 uses POE::Loop::Event
1036		1541
1037	Discussion	1542	Discussion
1038	This benchmark does measure scalability and overall performance of the	1543	This benchmark does measure scalability and overall performance of the
1039	particular event loop.	1544	particular event loop.
1040		1545
1041	EV is again fastest. Since it is using epoll on my system, the setup	1546	EV is again fastest. Since it is using epoll on my system, the setup
1042	time is relatively high, though.	1547	time is relatively high, though.
1043		1548
1044	Perl surprisingly comes second. It is much faster than the C-based event	1549	Perl surprisingly comes second. It is much faster than the C-based event
1045	loops Event and Glib.	1550	loops Event and Glib.
		1551
		1552	IO::Async performs very well when using its epoll backend, and still
		1553	quite good compared to Glib when using its pure perl backend.
1046		1554
1047	Event suffers from high setup time as well (look at its code and you	1555	Event suffers from high setup time as well (look at its code and you
1048	will understand why). Callback invocation also has a high overhead	1556	will understand why). Callback invocation also has a high overhead
1049	compared to the "$_->() for .."-style loop that the Perl event loop	1557	compared to the "$_->() for .."-style loop that the Perl event loop
1050	uses. Event uses select or poll in basically all documented	1558	uses. Event uses select or poll in basically all documented
…		…
1090	and speed most when you have lots of watchers, not when you only have a	1598	and speed most when you have lots of watchers, not when you only have a
1091	few of them).	1599	few of them).
1092		1600
1093	EV is again fastest.	1601	EV is again fastest.
1094		1602
1095	Perl again comes second. It is noticably faster than the C-based event	1603	Perl again comes second. It is noticeably faster than the C-based event
1096	loops Event and Glib, although the difference is too small to really	1604	loops Event and Glib, although the difference is too small to really
1097	matter.	1605	matter.
1098		1606
1099	POE also performs much better in this case, but is is still far behind	1607	POE also performs much better in this case, but is is still far behind
1100	the others.	1608	the others.
1101		1609
1102	Summary	1610	Summary
1103	* C-based event loops perform very well with small number of watchers,	1611	* C-based event loops perform very well with small number of watchers,
1104	as the management overhead dominates.	1612	as the management overhead dominates.
		1613
		1614	THE IO::Lambda BENCHMARK
		1615	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1616	could be misinterpreted to make AnyEvent look bad. In fact, the
		1617	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1618	better (which shouldn't come as a surprise to anybody). As such, the
		1619	benchmark is fine, and mostly shows that the AnyEvent backend from
		1620	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1621	without the extra baggage? To explore this, I wrote the equivalent
		1622	benchmark for AnyEvent.
		1623
		1624	The benchmark itself creates an echo-server, and then, for 500 times,
		1625	connects to the echo server, sends a line, waits for the reply, and then
		1626	creates the next connection. This is a rather bad benchmark, as it
		1627	doesn't test the efficiency of the framework or much non-blocking I/O,
		1628	but it is a benchmark nevertheless.
		1629
		1630	name runtime
		1631	Lambda/select 0.330 sec
		1632	+ optimized 0.122 sec
		1633	Lambda/AnyEvent 0.327 sec
		1634	+ optimized 0.138 sec
		1635	Raw sockets/select 0.077 sec
		1636	POE/select, components 0.662 sec
		1637	POE/select, raw sockets 0.226 sec
		1638	POE/select, optimized 0.404 sec
		1639
		1640	AnyEvent/select/nb 0.085 sec
		1641	AnyEvent/EV/nb 0.068 sec
		1642	+state machine 0.134 sec
		1643
		1644	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1645	benchmarks actually make blocking connects and use 100% blocking I/O,
		1646	defeating the purpose of an event-based solution. All of the newly
		1647	written AnyEvent benchmarks use 100% non-blocking connects (using
		1648	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1649	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1650	connects generally require a lot more bookkeeping and event handling
		1651	than blocking connects (which involve a single syscall only).
		1652
		1653	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1654	offers similar expressive power as POE and IO::Lambda, using
		1655	conventional Perl syntax. This means that both the echo server and the
		1656	client are 100% non-blocking, further placing it at a disadvantage.
		1657
		1658	As you can see, the AnyEvent + EV combination even beats the
		1659	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1660	backend easily beats IO::Lambda and POE.
		1661
		1662	And even the 100% non-blocking version written using the high-level (and
		1663	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1664	higher level ("unoptimised") abstractions by a large margin, even though
		1665	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1666
		1667	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1668	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1669	part of the IO::Lambda distribution and were used without any changes.
		1670
		1671	SIGNALS
		1672	AnyEvent currently installs handlers for these signals:
		1673
		1674	SIGCHLD
		1675	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1676	emulation for event loops that do not support them natively. Also,
		1677	some event loops install a similar handler.
		1678
		1679	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1680	then AnyEvent will reset it to default, to avoid losing child exit
		1681	statuses.
		1682
		1683	SIGPIPE
		1684	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1685	"undef" when AnyEvent gets loaded.
		1686
		1687	The rationale for this is that AnyEvent users usually do not really
		1688	depend on SIGPIPE delivery (which is purely an optimisation for
		1689	shell use, or badly-written programs), but "SIGPIPE" can cause
		1690	spurious and rare program exits as a lot of people do not expect
		1691	"SIGPIPE" when writing to some random socket.
		1692
		1693	The rationale for installing a no-op handler as opposed to ignoring
		1694	it is that this way, the handler will be restored to defaults on
		1695	exec.
		1696
		1697	Feel free to install your own handler, or reset it to defaults.
		1698
		1699	RECOMMENDED/OPTIONAL MODULES
		1700	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1701	it's built-in modules) are required to use it.
		1702
		1703	That does not mean that AnyEvent won't take advantage of some additional
		1704	modules if they are installed.
		1705
		1706	This section epxlains which additional modules will be used, and how
		1707	they affect AnyEvent's operetion.
		1708
		1709	Async::Interrupt
		1710	This slightly arcane module is used to implement fast signal
		1711	handling: To my knowledge, there is no way to do completely
		1712	race-free and quick signal handling in pure perl. To ensure that
		1713	signals still get delivered, AnyEvent will start an interval timer
		1714	to wake up perl (and catch the signals) with some delay (default is
		1715	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1716
		1717	If this module is available, then it will be used to implement
		1718	signal catching, which means that signals will not be delayed, and
		1719	the event loop will not be interrupted regularly, which is more
		1720	efficient (And good for battery life on laptops).
		1721
		1722	This affects not just the pure-perl event loop, but also other event
		1723	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1724
		1725	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1726	natively, and either employ their own workarounds (POE) or use
		1727	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1728	Installing Async::Interrupt does nothing for those backends.
		1729
		1730	EV This module isn't really "optional", as it is simply one of the
		1731	backend event loops that AnyEvent can use. However, it is simply the
		1732	best event loop available in terms of features, speed and stability:
		1733	It supports the AnyEvent API optimally, implements all the watcher
		1734	types in XS, does automatic timer adjustments even when no monotonic
		1735	clock is available, can take avdantage of advanced kernel interfaces
		1736	such as "epoll" and "kqueue", and is the fastest backend by far.
		1737	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1738	Glib::EV).
		1739
		1740	Guard
		1741	The guard module, when used, will be used to implement
		1742	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1743	uses a lot less memory), but otherwise doesn't affect guard
		1744	operation much. It is purely used for performance.
		1745
		1746	JSON and JSON::XS
		1747	This module is required when you want to read or write JSON data via
		1748	AnyEvent::Handle. It is also written in pure-perl, but can take
		1749	advantage of the ultra-high-speed JSON::XS module when it is
		1750	installed.
		1751
		1752	In fact, AnyEvent::Handle will use JSON::XS by default if it is
		1753	installed.
		1754
		1755	Net::SSLeay
		1756	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1757	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1758	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1759
		1760	Time::HiRes
		1761	This module is part of perl since release 5.008. It will be used
		1762	when the chosen event library does not come with a timing source on
		1763	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1764	additionally use it to try to use a monotonic clock for timing
		1765	stability.
1105		1766
1106	FORK	1767	FORK
1107	Most event libraries are not fork-safe. The ones who are usually are	1768	Most event libraries are not fork-safe. The ones who are usually are
1108	because they rely on inefficient but fork-safe "select" or "poll" calls.	1769	because they rely on inefficient but fork-safe "select" or "poll" calls.
1109	Only EV is fully fork-aware.	1770	Only EV is fully fork-aware.
1110		1771
1111	If you have to fork, you must either do so before creating your first	1772	If you have to fork, you must either do so before creating your first
1112	watcher OR you must not use AnyEvent at all in the child.	1773	watcher OR you must not use AnyEvent at all in the child OR you must do
		1774	something completely out of the scope of AnyEvent.
1113		1775
1114	SECURITY CONSIDERATIONS	1776	SECURITY CONSIDERATIONS
1115	AnyEvent can be forced to load any event model via	1777	AnyEvent can be forced to load any event model via
1116	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1778	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1117	to execute arbitrary code or directly gain access, it can easily be used	1779	to execute arbitrary code or directly gain access, it can easily be used
…		…
1120	model than specified in the variable.	1782	model than specified in the variable.
1121		1783
1122	You can make AnyEvent completely ignore this variable by deleting it	1784	You can make AnyEvent completely ignore this variable by deleting it
1123	before the first watcher gets created, e.g. with a "BEGIN" block:	1785	before the first watcher gets created, e.g. with a "BEGIN" block:
1124		1786
1125	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1787	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1126		1788
1127	use AnyEvent;	1789	use AnyEvent;
1128		1790
1129	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1791	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1130	be used to probe what backend is used and gain other information (which	1792	be used to probe what backend is used and gain other information (which
1131	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).	1793	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1794	and $ENV{PERL_ANYEVENT_STRICT}.
		1795
		1796	Note that AnyEvent will remove all environment variables starting with
		1797	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1798	enabled.
		1799
		1800	BUGS
		1801	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1802	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1803	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1804	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1805	not as pronounced).
1132		1806
1133	SEE ALSO	1807	SEE ALSO
		1808	Utility functions: AnyEvent::Util.
		1809
1134	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1810	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1135	Event::Lib, Qt, POE.	1811	Event::Lib, Qt, POE.
1136		1812
1137	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1813	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1138	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1814	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1139	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1815	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1816	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
		1817
		1818	Non-blocking file handles, sockets, TCP clients and servers:
		1819	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		1820
		1821	Asynchronous DNS: AnyEvent::DNS.
1140		1822
1141	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1823	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1142		1824
1143	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1825	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1826	AnyEvent::HTTP.
1144		1827
1145	AUTHOR	1828	AUTHOR
1146	Marc Lehmann <schmorp@schmorp.de>	1829	Marc Lehmann <schmorp@schmorp.de>
1147	http://home.schmorp.de/	1830	http://home.schmorp.de/
1148		1831

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Comparing AnyEvent/README (file contents): Revision 1.20 by root, Sat May 10 22:30:28 2008 UTC vs. Revision 1.54 by root, Tue Sep 1 18:27:46 2009 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.20 by root, Sat May 10 22:30:28 2008 UTC vs.
Revision 1.54 by root, Tue Sep 1 18:27:46 2009 UTC