[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.23 by root, Mon May 26 06:04:38 2008 UTC vs.
Revision 1.60 by root, Mon Apr 12 02:50:31 2010 UTC

…		…
1	=> NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - the DBI of event loop programming
3		3
4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	loops	5	Qt and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# if you prefer function calls, look at the L<AE> manpage for
		11	# an alternative API.
		12
		13	# file handle or descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	14	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		15
		16	# one-shot or repeating timers
		17	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		18	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		19
		20	print AnyEvent->now; # prints current event loop time
		21	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		22
		23	# POSIX signal
		24	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		25
		26	# child process exit
		27	my $w = AnyEvent->child (pid => $pid, cb => sub {
		28	my ($pid, $status) = @_;
11	...	29	...
12	});	30	});
13		31
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	32	# called when event loop idle (if applicable)
15	...	33	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		34
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	35	my $w = AnyEvent->condvar; # stores whether a condition was flagged
19	$w->send; # wake up current and all future recv's	36	$w->send; # wake up current and all future recv's
20	$w->recv; # enters "main loop" till $condvar gets ->send	37	$w->recv; # enters "main loop" till $condvar gets ->send
		38	# use a condvar in callback mode:
		39	$w->cb (sub { $_[0]->recv });
		40
		41	INTRODUCTION/TUTORIAL
		42	This manpage is mainly a reference manual. If you are interested in a
		43	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		44	manpage.
		45
		46	SUPPORT
		47	There is a mailinglist for discussing all things AnyEvent, and an IRC
		48	channel, too.
		49
		50	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		51	Repository, at <http://anyevent.schmorp.de>, for more info.
21		52
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	53	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	54	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	55	nowadays. So what is different about AnyEvent?
25		56
26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	57	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
27	policy* and AnyEvent is small and efficient.	58	policy* and AnyEvent is small and efficient.
28		59
29	First and foremost, AnyEvent is not an event model itself, it only	60	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	61	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,	62	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,	63	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.	64	only one event loop can be active at the same time in a process.
34	AnyEvent helps hiding the differences between those event loops.	65	AnyEvent cannot change this, but it can hide the differences between
		66	those event loops.
35		67
36	The goal of AnyEvent is to offer module authors the ability to do event	68	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	69	programming (waiting for I/O or timer events) without subscribing to a
38	religion, a way of living, and most importantly: without forcing your	70	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	71	module users into the same thing by forcing them to use the same event
40	model you use.	72	model you use.
41		73
42	For modules like POE or IO::Async (which is a total misnomer as it is	74	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	75	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	76	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	77	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	78	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.	79	are also forced to use the same event loop you use.
48		80
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	81	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	82	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	83	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.	84	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	85	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	86	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	87	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).	88	to AnyEvent, too, so it is future-proof).
57		89
58	In addition to being free of having to use *the one and only true event	90	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	91	model*, AnyEvent also is free of bloat and policy: with POE or similar
60	modules, you get an enormous amount of code and strict rules you have to	92	modules, you get an enormous amount of code and strict rules you have to
61	follow. AnyEvent, on the other hand, is lean and up to the point, by	93	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	94	only offering the functionality that is necessary, in as thin as a
63	wrapper as technically possible.	95	wrapper as technically possible.
64		96
		97	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
		98	useful functionality, such as an asynchronous DNS resolver, 100%
		99	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		100	such as Windows) and lots of real-world knowledge and workarounds for
		101	platform bugs and differences.
		102
65	Of course, if you want lots of policy (this can arguably be somewhat	103	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	104	useful) and you want to force your users to use the one and only event
67	model, you should not use this module.	105	model, you should not use this module.
68		106
69	DESCRIPTION	107	DESCRIPTION
70	AnyEvent provides an identical interface to multiple event loops. This	108	AnyEvent provides an identical interface to multiple event loops. This
99	starts using it, all bets are off. Maybe you should tell their authors	137	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...	138	to use AnyEvent so their modules work together with others seamlessly...
101		139
102	The pure-perl implementation of AnyEvent is called	140	The pure-perl implementation of AnyEvent is called
103	"AnyEvent::Impl::Perl". Like other event modules you can load it	141	"AnyEvent::Impl::Perl". Like other event modules you can load it
104	explicitly.	142	explicitly and enjoy the high availability of that event loop :)
105		143
106	WATCHERS	144	WATCHERS
107	AnyEvent has the central concept of a watcher, which is an object that	145	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	146	stores relevant data for each kind of event you are waiting for, such as
109	the callback to call, the file handle to watch, etc.	147	the callback to call, the file handle to watch, etc.
…		…
111	These watchers are normal Perl objects with normal Perl lifetime. After	149	These watchers are normal Perl objects with normal Perl lifetime. After
112	creating a watcher it will immediately "watch" for events and invoke the	150	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	151	callback when the event occurs (of course, only when the event model is
114	in control).	152	in control).
115		153
		154	Note that callbacks must not permanently change global variables
		155	potentially in use by the event loop (such as $_ or $[) and that
		156	callbacks must not "die". The former is good programming practise in
		157	Perl and the latter stems from the fact that exception handling differs
		158	widely between event loops.
		159
116	To disable the watcher you have to destroy it (e.g. by setting the	160	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	161	variable you store it in to "undef" or otherwise deleting all references
118	to it).	162	to it).
119		163
120	All watchers are created by calling a method on the "AnyEvent" class.	164	All watchers are created by calling a method on the "AnyEvent" class.
…		…
122	Many watchers either are used with "recursion" (repeating timers for	166	Many watchers either are used with "recursion" (repeating timers for
123	example), or need to refer to their watcher object in other ways.	167	example), or need to refer to their watcher object in other ways.
124		168
125	An any way to achieve that is this pattern:	169	An any way to achieve that is this pattern:
126		170
127	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	171	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
128	# you can use $w here, for example to undef it	172	# you can use $w here, for example to undef it
129	undef $w;	173	undef $w;
130	});	174	});
131		175
132	Note that "my $w; $w =" combination. This is necessary because in Perl,	176	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	177	my variables are only visible after the statement in which they are
134	declared.	178	declared.
135		179
136	I/O WATCHERS	180	I/O WATCHERS
		181	$w = AnyEvent->io (
		182	fh => <filehandle_or_fileno>,
		183	poll => <"r" or "w">,
		184	cb => <callback>,
		185	);
		186
137	You can create an I/O watcher by calling the "AnyEvent->io" method with	187	You can create an I/O watcher by calling the "AnyEvent->io" method with
138	the following mandatory key-value pairs as arguments:	188	the following mandatory key-value pairs as arguments:
139		189
140	"fh" the Perl file handle (not file descriptor) to watch for events.	190	"fh" is the Perl file handle (or a naked file descriptor) to watch for
		191	events (AnyEvent might or might not keep a reference to this file
		192	handle). Note that only file handles pointing to things for which
		193	non-blocking operation makes sense are allowed. This includes sockets,
		194	most character devices, pipes, fifos and so on, but not for example
		195	files or block devices.
		196
141	"poll" must be a string that is either "r" or "w", which creates a	197	"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"	198	watcher waiting for "r"eadable or "w"ritable events, respectively.
		199
143	is the callback to invoke each time the file handle becomes ready.	200	"cb" is the callback to invoke each time the file handle becomes ready.
144		201
145	Although the callback might get passed parameters, their value and	202	Although the callback might get passed parameters, their value and
146	presence is undefined and you cannot rely on them. Portable AnyEvent	203	presence is undefined and you cannot rely on them. Portable AnyEvent
147	callbacks cannot use arguments passed to I/O watcher callbacks.	204	callbacks cannot use arguments passed to I/O watcher callbacks.
148		205
…		…
152		209
153	Some event loops issue spurious readyness notifications, so you should	210	Some event loops issue spurious readyness notifications, so you should
154	always use non-blocking calls when reading/writing from/to your file	211	always use non-blocking calls when reading/writing from/to your file
155	handles.	212	handles.
156		213
157	Example:
158
159	# wait for readability of STDIN, then read a line and disable the watcher	214	Example: wait for readability of STDIN, then read a line and disable the
		215	watcher.
		216
160	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	217	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
161	chomp (my $input = <STDIN>);	218	chomp (my $input = <STDIN>);
162	warn "read: $input\n";	219	warn "read: $input\n";
163	undef $w;	220	undef $w;
164	});	221	});
165		222
166	TIME WATCHERS	223	TIME WATCHERS
		224	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		225
		226	$w = AnyEvent->timer (
		227	after => <fractional_seconds>,
		228	interval => <fractional_seconds>,
		229	cb => <callback>,
		230	);
		231
167	You can create a time watcher by calling the "AnyEvent->timer" method	232	You can create a time watcher by calling the "AnyEvent->timer" method
168	with the following mandatory arguments:	233	with the following mandatory arguments:
169		234
170	"after" specifies after how many seconds (fractional values are	235	"after" specifies after how many seconds (fractional values are
171	supported) the callback should be invoked. "cb" is the callback to	236	supported) the callback should be invoked. "cb" is the callback to
…		…
173		238
174	Although the callback might get passed parameters, their value and	239	Although the callback might get passed parameters, their value and
175	presence is undefined and you cannot rely on them. Portable AnyEvent	240	presence is undefined and you cannot rely on them. Portable AnyEvent
176	callbacks cannot use arguments passed to time watcher callbacks.	241	callbacks cannot use arguments passed to time watcher callbacks.
177		242
178	The timer callback will be invoked at most once: if you want a repeating	243	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	244	parameter, "interval", as a strictly positive number (> 0), then the
180	and Glib).	245	callback will be invoked regularly at that interval (in fractional
		246	seconds) after the first invocation. If "interval" is specified with a
		247	false value, then it is treated as if it were missing.
181		248
182	Example:	249	The callback will be rescheduled before invoking the callback, but no
		250	attempt is done to avoid timer drift in most backends, so the interval
		251	is only approximate.
183		252
184	# fire an event after 7.7 seconds	253	Example: fire an event after 7.7 seconds.
		254
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	255	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	256	warn "timeout\n";
187	});	257	});
188		258
189	# to cancel the timer:	259	# to cancel the timer:
190	undef $w;	260	undef $w;
191		261
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	262	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		263
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	264	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		265	warn "timeout\n";
200	};	266	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		267
205	TIMING ISSUES	268	TIMING ISSUES
206	There are two ways to handle timers: based on real time (relative, "fire	269	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	270	in 10 seconds") and based on wallclock time (absolute, "fire at 12
208	o'clock").	271	o'clock").
…		…
220	on wallclock time) timers.	283	on wallclock time) timers.
221		284
222	AnyEvent always prefers relative timers, if available, matching the	285	AnyEvent always prefers relative timers, if available, matching the
223	AnyEvent API.	286	AnyEvent API.
224		287
		288	AnyEvent has two additional methods that return the "current time":
		289
		290	AnyEvent->time
		291	This returns the "current wallclock time" as a fractional number of
		292	seconds since the Epoch (the same thing as "time" or
		293	"Time::HiRes::time" return, and the result is guaranteed to be
		294	compatible with those).
		295
		296	It progresses independently of any event loop processing, i.e. each
		297	call will check the system clock, which usually gets updated
		298	frequently.
		299
		300	AnyEvent->now
		301	This also returns the "current wallclock time", but unlike "time",
		302	above, this value might change only once per event loop iteration,
		303	depending on the event loop (most return the same time as "time",
		304	above). This is the time that AnyEvent's timers get scheduled
		305	against.
		306
		307	*In almost all cases (in all cases if you don't care), this is the
		308	function to call when you want to know the current time.*
		309
		310	This function is also often faster then "AnyEvent->time", and thus
		311	the preferred method if you want some timestamp (for example,
		312	AnyEvent::Handle uses this to update it's activity timeouts).
		313
		314	The rest of this section is only of relevance if you try to be very
		315	exact with your timing, you can skip it without bad conscience.
		316
		317	For a practical example of when these times differ, consider
		318	Event::Lib and EV and the following set-up:
		319
		320	The event loop is running and has just invoked one of your callback
		321	at time=500 (assume no other callbacks delay processing). In your
		322	callback, you wait a second by executing "sleep 1" (blocking the
		323	process for a second) and then (at time=501) you create a relative
		324	timer that fires after three seconds.
		325
		326	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		327	return 501, because that is the current time, and the timer will be
		328	scheduled to fire at time=504 (501 + 3).
		329
		330	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		331	but "AnyEvent->now" returns 500, as that is the time the last event
		332	processing phase started. With EV, your timer gets scheduled to run
		333	at time=503 (500 + 3).
		334
		335	In one sense, Event::Lib is more exact, as it uses the current time
		336	regardless of any delays introduced by event processing. However,
		337	most callbacks do not expect large delays in processing, so this
		338	causes a higher drift (and a lot more system calls to get the
		339	current time).
		340
		341	In another sense, EV is more exact, as your timer will be scheduled
		342	at the same time, regardless of how long event processing actually
		343	took.
		344
		345	In either case, if you care (and in most cases, you don't), then you
		346	can get whatever behaviour you want with any event loop, by taking
		347	the difference between "AnyEvent->time" and "AnyEvent->now" into
		348	account.
		349
		350	AnyEvent->now_update
		351	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		352	current time for each loop iteration (see the discussion of
		353	AnyEvent->now, above).
		354
		355	When a callback runs for a long time (or when the process sleeps),
		356	then this "current" time will differ substantially from the real
		357	time, which might affect timers and time-outs.
		358
		359	When this is the case, you can call this method, which will update
		360	the event loop's idea of "current time".
		361
		362	A typical example would be a script in a web server (e.g.
		363	"mod_perl") - when mod_perl executes the script, then the event loop
		364	will have the wrong idea about the "current time" (being potentially
		365	far in the past, when the script ran the last time). In that case
		366	you should arrange a call to "AnyEvent->now_update" each time the
		367	web server process wakes up again (e.g. at the start of your script,
		368	or in a handler).
		369
		370	Note that updating the time might cause some events to be handled.
		371
225	SIGNAL WATCHERS	372	SIGNAL WATCHERS
		373	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		374
226	You can watch for signals using a signal watcher, "signal" is the signal	375	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	376	name in uppercase and without any "SIG" prefix, "cb" is the Perl
228	whenever a signal occurs.	377	callback to be invoked whenever a signal occurs.
229		378
230	Although the callback might get passed parameters, their value and	379	Although the callback might get passed parameters, their value and
231	presence is undefined and you cannot rely on them. Portable AnyEvent	380	presence is undefined and you cannot rely on them. Portable AnyEvent
232	callbacks cannot use arguments passed to signal watcher callbacks.	381	callbacks cannot use arguments passed to signal watcher callbacks.
233		382
…		…
235	invocation, and callback invocation will be synchronous. Synchronous	384	invocation, and callback invocation will be synchronous. Synchronous
236	means that it might take a while until the signal gets handled by the	385	means that it might take a while until the signal gets handled by the
237	process, but it is guaranteed not to interrupt any other callbacks.	386	process, but it is guaranteed not to interrupt any other callbacks.
238		387
239	The main advantage of using these watchers is that you can share a	388	The main advantage of using these watchers is that you can share a
240	signal between multiple watchers.	389	signal between multiple watchers, and AnyEvent will ensure that signals
		390	will not interrupt your program at bad times.
241		391
242	This watcher might use %SIG, so programs overwriting those signals	392	This watcher might use %SIG (depending on the event loop used), so
243	directly will likely not work correctly.	393	programs overwriting those signals directly will likely not work
		394	correctly.
244		395
245	Example: exit on SIGINT	396	Example: exit on SIGINT
246		397
247	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	398	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
248		399
		400	Restart Behaviour
		401	While restart behaviour is up to the event loop implementation, most
		402	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		403	pure perl implementation).
		404
		405	Safe/Unsafe Signals
		406	Perl signals can be either "safe" (synchronous to opcode handling) or
		407	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		408	latter might corrupt your memory.
		409
		410	AnyEvent signal handlers are, in addition, synchronous to the event
		411	loop, i.e. they will not interrupt your running perl program but will
		412	only be called as part of the normal event handling (just like timer,
		413	I/O etc. callbacks, too).
		414
		415	Signal Races, Delays and Workarounds
		416	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		417	callbacks to signals in a generic way, which is a pity, as you cannot do
		418	race-free signal handling in perl, requiring C libraries for this.
		419	AnyEvent will try to do it's best, which means in some cases, signals
		420	will be delayed. The maximum time a signal might be delayed is specified
		421	in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
		422	can be changed only before the first signal watcher is created, and
		423	should be left alone otherwise. This variable determines how often
		424	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		425	will cause fewer spurious wake-ups, which is better for power and CPU
		426	saving.
		427
		428	All these problems can be avoided by installing the optional
		429	Async::Interrupt module, which works with most event loops. It will not
		430	work with inherently broken event loops such as Event or Event::Lib (and
		431	not with POE currently, as POE does it's own workaround with one-second
		432	latency). For those, you just have to suffer the delays.
		433
249	CHILD PROCESS WATCHERS	434	CHILD PROCESS WATCHERS
		435	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		436
250	You can also watch on a child process exit and catch its exit status.	437	You can also watch on a child process exit and catch its exit status.
251		438
252	The child process is specified by the "pid" argument (if set to 0, it	439	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	440	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	441	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	442	and an exit status is available, not on any trace events
256	and exit status (as returned by waitpid), so unlike other watcher types,	443	(stopped/continued).
257	you can rely on child watcher callback arguments.	444
		445	The callback will be called with the pid and exit status (as returned by
		446	waitpid), so unlike other watcher types, you can rely on child watcher
		447	callback arguments.
		448
		449	This watcher type works by installing a signal handler for "SIGCHLD",
		450	and since it cannot be shared, nothing else should use SIGCHLD or reap
		451	random child processes (waiting for specific child processes, e.g.
		452	inside "system", is just fine).
258		453
259	There is a slight catch to child watchers, however: you usually start	454	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	455	them after the child process was created, and this means the process
261	could have exited already (and no SIGCHLD will be sent anymore).	456	could have exited already (and no SIGCHLD will be sent anymore).
262		457
263	Not all event models handle this correctly (POE doesn't), but even for	458	Not all event models handle this correctly (neither POE nor IO::Async
		459	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	460	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	461	before the process exits (i.e. before you fork in the first place).
266	place).	462	AnyEvent's pure perl event loop handles all cases correctly regardless
		463	of when you start the watcher.
267		464
268	This means you cannot create a child watcher as the very first thing in	465	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	466	an AnyEvent program, you have to create at least one watcher before
270	you "fork" the child (alternatively, you can call "AnyEvent::detect").	467	you "fork" the child (alternatively, you can call "AnyEvent::detect").
271		468
		469	As most event loops do not support waiting for child events, they will
		470	be emulated by AnyEvent in most cases, in which the latency and race
		471	problems mentioned in the description of signal watchers apply.
		472
272	Example: fork a process and wait for it	473	Example: fork a process and wait for it
273		474
274	my $done = AnyEvent->condvar;	475	my $done = AnyEvent->condvar;
275		476
276	my $pid = fork or exit 5;	477	my $pid = fork or exit 5;
277		478
278	my $w = AnyEvent->child (	479	my $w = AnyEvent->child (
279	pid => $pid,	480	pid => $pid,
280	cb => sub {	481	cb => sub {
281	my ($pid, $status) = @_;	482	my ($pid, $status) = @_;
282	warn "pid $pid exited with status $status";	483	warn "pid $pid exited with status $status";
283	$done->send;	484	$done->send;
284	},	485	},
285	);	486	);
286		487
287	# do something else, then wait for process exit	488	# do something else, then wait for process exit
288	$done->recv;	489	$done->recv;
		490
		491	IDLE WATCHERS
		492	$w = AnyEvent->idle (cb => <callback>);
		493
		494	Repeatedly invoke the callback after the process becomes idle, until
		495	either the watcher is destroyed or new events have been detected.
		496
		497	Idle watchers are useful when there is a need to do something, but it is
		498	not so important (or wise) to do it instantly. The callback will be
		499	invoked only when there is "nothing better to do", which is usually
		500	defined as "all outstanding events have been handled and no new events
		501	have been detected". That means that idle watchers ideally get invoked
		502	when the event loop has just polled for new events but none have been
		503	detected. Instead of blocking to wait for more events, the idle watchers
		504	will be invoked.
		505
		506	Unfortunately, most event loops do not really support idle watchers
		507	(only EV, Event and Glib do it in a usable fashion) - for the rest,
		508	AnyEvent will simply call the callback "from time to time".
		509
		510	Example: read lines from STDIN, but only process them when the program
		511	is otherwise idle:
		512
		513	my @lines; # read data
		514	my $idle_w;
		515	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		516	push @lines, scalar <STDIN>;
		517
		518	# start an idle watcher, if not already done
		519	$idle_w \|\|= AnyEvent->idle (cb => sub {
		520	# handle only one line, when there are lines left
		521	if (my $line = shift @lines) {
		522	print "handled when idle: $line";
		523	} else {
		524	# otherwise disable the idle watcher again
		525	undef $idle_w;
		526	}
		527	});
		528	});
289		529
290	CONDITION VARIABLES	530	CONDITION VARIABLES
		531	$cv = AnyEvent->condvar;
		532
		533	$cv->send (<list>);
		534	my @res = $cv->recv;
		535
291	If you are familiar with some event loops you will know that all of them	536	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	537	require you to run some blocking "loop", "run" or similar function that
293	will actively watch for new events and call your callbacks.	538	will actively watch for new events and call your callbacks.
294		539
295	AnyEvent is different, it expects somebody else to run the event loop	540	AnyEvent is slightly different: it expects somebody else to run the
296	and will only block when necessary (usually when told by the user).	541	event loop and will only block when necessary (usually when told by the
		542	user).
297		543
298	The instrument to do that is called a "condition variable", so called	544	The instrument to do that is called a "condition variable", so called
299	because they represent a condition that must become true.	545	because they represent a condition that must become true.
		546
		547	Now is probably a good time to look at the examples further below.
300		548
301	Condition variables can be created by calling the "AnyEvent->condvar"	549	Condition variables can be created by calling the "AnyEvent->condvar"
302	method, usually without arguments. The only argument pair allowed is	550	method, usually without arguments. The only argument pair allowed is
303	"cb", which specifies a callback to be called when the condition	551	"cb", which specifies a callback to be called when the condition
304	variable becomes true.	552	variable becomes true, with the condition variable as the first argument
		553	(but not the results).
305		554
306	After creation, the condition variable is "false" until it becomes	555	After creation, the condition variable is "false" until it becomes
307	"true" by calling the "send" method (or calling the condition variable	556	"true" by calling the "send" method (or calling the condition variable
308	as if it were a callback, read about the caveats in the description for	557	as if it were a callback, read about the caveats in the description for
309	the "->send" method).	558	the "->send" method).
…		…
311	Condition variables are similar to callbacks, except that you can	560	Condition variables are similar to callbacks, except that you can
312	optionally wait for them. They can also be called merge points - points	561	optionally wait for them. They can also be called merge points - points
313	in time where multiple outstanding events have been processed. And yet	562	in time where multiple outstanding events have been processed. And yet
314	another way to call them is transactions - each condition variable can	563	another way to call them is transactions - each condition variable can
315	be used to represent a transaction, which finishes at some point and	564	be used to represent a transaction, which finishes at some point and
316	delivers a result.	565	delivers a result. And yet some people know them as "futures" - a
		566	promise to compute/deliver something that you can wait for.
317		567
318	Condition variables are very useful to signal that something has	568	Condition variables are very useful to signal that something has
319	finished, for example, if you write a module that does asynchronous http	569	finished, for example, if you write a module that does asynchronous http
320	requests, then a condition variable would be the ideal candidate to	570	requests, then a condition variable would be the ideal candidate to
321	signal the availability of results. The user can either act when the	571	signal the availability of results. The user can either act when the
…		…
342	which eventually calls "-> send", and the "consumer side", which waits	592	which eventually calls "-> send", and the "consumer side", which waits
343	for the send to occur.	593	for the send to occur.
344		594
345	Example: wait for a timer.	595	Example: wait for a timer.
346		596
347	# wait till the result is ready	597	# condition: "wait till the timer is fired"
348	my $result_ready = AnyEvent->condvar;	598	my $timer_fired = AnyEvent->condvar;
349		599
350	# do something such as adding a timer	600	# create the timer - we could wait for, say
351	# or socket watcher the calls $result_ready->send	601	# a handle becomign ready, or even an
352	# when the "result" is ready.	602	# AnyEvent::HTTP request to finish, but
353	# in this case, we simply use a timer:	603	# in this case, we simply use a timer:
354	my $w = AnyEvent->timer (	604	my $w = AnyEvent->timer (
355	after => 1,	605	after => 1,
356	cb => sub { $result_ready->send },	606	cb => sub { $timer_fired->send },
357	);	607	);
358		608
359	# this "blocks" (while handling events) till the callback	609	# this "blocks" (while handling events) till the callback
360	# calls send	610	# calls ->send
361	$result_ready->recv;	611	$timer_fired->recv;
362		612
363	Example: wait for a timer, but take advantage of the fact that condition	613	Example: wait for a timer, but take advantage of the fact that condition
364	variables are also code references.	614	variables are also callable directly.
365		615
366	my $done = AnyEvent->condvar;	616	my $done = AnyEvent->condvar;
367	my $delay = AnyEvent->timer (after => 5, cb => $done);	617	my $delay = AnyEvent->timer (after => 5, cb => $done);
368	$done->recv;	618	$done->recv;
		619
		620	Example: Imagine an API that returns a condvar and doesn't support
		621	callbacks. This is how you make a synchronous call, for example from the
		622	main program:
		623
		624	use AnyEvent::CouchDB;
		625
		626	...
		627
		628	my @info = $couchdb->info->recv;
		629
		630	And this is how you would just set a callback to be called whenever the
		631	results are available:
		632
		633	$couchdb->info->cb (sub {
		634	my @info = $_[0]->recv;
		635	});
369		636
370	METHODS FOR PRODUCERS	637	METHODS FOR PRODUCERS
371	These methods should only be used by the producing side, i.e. the	638	These methods should only be used by the producing side, i.e. the
372	code/module that eventually sends the signal. Note that it is also the	639	code/module that eventually sends the signal. Note that it is also the
373	producer side which creates the condvar in most cases, but it isn't	640	producer side which creates the condvar in most cases, but it isn't
…		…
383		650
384	Any arguments passed to the "send" call will be returned by all	651	Any arguments passed to the "send" call will be returned by all
385	future "->recv" calls.	652	future "->recv" calls.
386		653
387	Condition variables are overloaded so one can call them directly (as	654	Condition variables are overloaded so one can call them directly (as
388	a code reference). Calling them directly is the same as calling	655	if they were a code reference). Calling them directly is the same as
389	"send". Note, however, that many C-based event loops do not handle	656	calling "send".
390	overloading, so as tempting as it may be, passing a condition
391	variable instead of a callback does not work. Both the pure perl and
392	EV loops support overloading, however, as well as all functions that
393	use perl to invoke a callback (as in AnyEvent::Socket and
394	AnyEvent::DNS for example).
395		657
396	$cv->croak ($error)	658	$cv->croak ($error)
397	Similar to send, but causes all call's to "->recv" to invoke	659	Similar to send, but causes all call's to "->recv" to invoke
398	"Carp::croak" with the given error message/object/scalar.	660	"Carp::croak" with the given error message/object/scalar.
399		661
400	This can be used to signal any errors to the condition variable	662	This can be used to signal any errors to the condition variable
401	user/consumer.	663	user/consumer. Doing it this way instead of calling "croak" directly
		664	delays the error detetcion, but has the overwhelmign advantage that
		665	it diagnoses the error at the place where the result is expected,
		666	and not deep in some event clalback without connection to the actual
		667	code causing the problem.
402		668
403	$cv->begin ([group callback])	669	$cv->begin ([group callback])
404	$cv->end	670	$cv->end
405	These two methods are EXPERIMENTAL and MIGHT CHANGE.
406
407	These two methods can be used to combine many transactions/events	671	These two methods can be used to combine many transactions/events
408	into one. For example, a function that pings many hosts in parallel	672	into one. For example, a function that pings many hosts in parallel
409	might want to use a condition variable for the whole process.	673	might want to use a condition variable for the whole process.
410		674
411	Every call to "->begin" will increment a counter, and every call to	675	Every call to "->begin" will increment a counter, and every call to
412	"->end" will decrement it. If the counter reaches 0 in "->end", the	676	"->end" will decrement it. If the counter reaches 0 in "->end", the
413	(last) callback passed to "begin" will be executed. That callback is	677	(last) callback passed to "begin" will be executed, passing the
414	supposed to call "->send", but that is not required. If no	678	condvar as first argument. That callback is supposed to call
		679	"->send", but that is not required. If no group callback was set,
415	callback was set, "send" will be called without any arguments.	680	"send" will be called without any arguments.
416		681
417	Let's clarify this with the ping example:	682	You can think of "$cv->send" giving you an OR condition (one call
		683	sends), while "$cv->begin" and "$cv->end" giving you an AND
		684	condition (all "begin" calls must be "end"'ed before the condvar
		685	sends).
		686
		687	Let's start with a simple example: you have two I/O watchers (for
		688	example, STDOUT and STDERR for a program), and you want to wait for
		689	both streams to close before activating a condvar:
418		690
419	my $cv = AnyEvent->condvar;	691	my $cv = AnyEvent->condvar;
420		692
		693	$cv->begin; # first watcher
		694	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		695	defined sysread $fh1, my $buf, 4096
		696	or $cv->end;
		697	});
		698
		699	$cv->begin; # second watcher
		700	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		701	defined sysread $fh2, my $buf, 4096
		702	or $cv->end;
		703	});
		704
		705	$cv->recv;
		706
		707	This works because for every event source (EOF on file handle),
		708	there is one call to "begin", so the condvar waits for all calls to
		709	"end" before sending.
		710
		711	The ping example mentioned above is slightly more complicated, as
		712	the there are results to be passwd back, and the number of tasks
		713	that are begung can potentially be zero:
		714
		715	my $cv = AnyEvent->condvar;
		716
421	my %result;	717	my %result;
422	$cv->begin (sub { $cv->send (\%result) });	718	$cv->begin (sub { shift->send (\%result) });
423		719
424	for my $host (@list_of_hosts) {	720	for my $host (@list_of_hosts) {
425	$cv->begin;	721	$cv->begin;
426	ping_host_then_call_callback $host, sub {	722	ping_host_then_call_callback $host, sub {
427	$result{$host} = ...;	723	$result{$host} = ...;
…		…
442	the loop, which serves two important purposes: first, it sets the	738	the loop, which serves two important purposes: first, it sets the
443	callback to be called once the counter reaches 0, and second, it	739	callback to be called once the counter reaches 0, and second, it
444	ensures that "send" is called even when "no" hosts are being pinged	740	ensures that "send" is called even when "no" hosts are being pinged
445	(the loop doesn't execute once).	741	(the loop doesn't execute once).
446		742
447	This is the general pattern when you "fan out" into multiple	743	This is the general pattern when you "fan out" into multiple (but
448	subrequests: use an outer "begin"/"end" pair to set the callback and	744	potentially none) subrequests: use an outer "begin"/"end" pair to
449	ensure "end" is called at least once, and then, for each subrequest	745	set the callback and ensure "end" is called at least once, and then,
450	you start, call "begin" and for each subrequest you finish, call	746	for each subrequest you start, call "begin" and for each subrequest
451	"end".	747	you finish, call "end".
452		748
453	METHODS FOR CONSUMERS	749	METHODS FOR CONSUMERS
454	These methods should only be used by the consuming side, i.e. the code	750	These methods should only be used by the consuming side, i.e. the code
455	awaits the condition.	751	awaits the condition.
456		752
…		…
465	function will call "croak".	761	function will call "croak".
466		762
467	In list context, all parameters passed to "send" will be returned,	763	In list context, all parameters passed to "send" will be returned,
468	in scalar context only the first one will be returned.	764	in scalar context only the first one will be returned.
469		765
		766	Note that doing a blocking wait in a callback is not supported by
		767	any event loop, that is, recursive invocation of a blocking "->recv"
		768	is not allowed, and the "recv" call will "croak" if such a condition
		769	is detected. This condition can be slightly loosened by using
		770	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		771	thread that doesn't run the event loop itself.
		772
470	Not all event models support a blocking wait - some die in that case	773	Not all event models support a blocking wait - some die in that case
471	(programs might want to do that to stay interactive), so *if you are	774	(programs might want to do that to stay interactive), so *if you are
472	using this from a module, never require a blocking wait*, but let	775	using this from a module, never require a blocking wait*. Instead,
473	the caller decide whether the call will block or not (for example,	776	let the caller decide whether the call will block or not (for
474	by coupling condition variables with some kind of request results	777	example, by coupling condition variables with some kind of request
475	and supporting callbacks so the caller knows that getting the result	778	results and supporting callbacks so the caller knows that getting
476	will not block, while still supporting blocking waits if the caller	779	the result will not block, while still supporting blocking waits if
477	so desires).	780	the caller so desires).
478
479	Another reason never to "->recv" in a module is that you cannot
480	sensibly have two "->recv"'s in parallel, as that would require
481	multiple interpreters or coroutines/threads, none of which
482	"AnyEvent" can supply.
483
484	The Coro module, however, can and does supply coroutines and, in
485	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
486	versions and also integrates coroutines into AnyEvent, making
487	blocking "->recv" calls perfectly safe as long as they are done from
488	another coroutine (one that doesn't run the event loop).
489		781
490	You can ensure that "-recv" never blocks by setting a callback and	782	You can ensure that "-recv" never blocks by setting a callback and
491	only calling "->recv" from within that callback (or at a later	783	only calling "->recv" from within that callback (or at a later
492	time). This will work even when the event loop does not support	784	time). This will work even when the event loop does not support
493	blocking waits otherwise.	785	blocking waits otherwise.
494		786
495	$bool = $cv->ready	787	$bool = $cv->ready
496	Returns true when the condition is "true", i.e. whether "send" or	788	Returns true when the condition is "true", i.e. whether "send" or
497	"croak" have been called.	789	"croak" have been called.
498		790
499	$cb = $cv->cb ([new callback])	791	$cb = $cv->cb ($cb->($cv))
500	This is a mutator function that returns the callback set and	792	This is a mutator function that returns the callback set and
501	optionally replaces it before doing so.	793	optionally replaces it before doing so.
502		794
503	The callback will be called when the condition becomes "true", i.e.	795	The callback will be called when the condition becomes (or already
504	when "send" or "croak" are called. Calling "recv" inside the	796	was) "true", i.e. when "send" or "croak" are called (or were
505	callback or at any later time is guaranteed not to block.	797	called), with the only argument being the condition variable itself.
		798	Calling "recv" inside the callback or at any later time is
		799	guaranteed not to block.
		800
		801	SUPPORTED EVENT LOOPS/BACKENDS
		802	The available backend classes are (every class has its own manpage):
		803
		804	Backends that are autoprobed when no other event loop can be found.
		805	EV is the preferred backend when no other event loop seems to be in
		806	use. If EV is not installed, then AnyEvent will fall back to its own
		807	pure-perl implementation, which is available everywhere as it comes
		808	with AnyEvent itself.
		809
		810	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		811	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		812
		813	Backends that are transparently being picked up when they are used.
		814	These will be used when they are currently loaded when the first
		815	watcher is created, in which case it is assumed that the application
		816	is using them. This means that AnyEvent will automatically pick the
		817	right backend when the main program loads an event module before
		818	anything starts to create watchers. Nothing special needs to be done
		819	by the main program.
		820
		821	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		822	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		823	AnyEvent::Impl::Tk based on Tk, very broken.
		824	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		825	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		826	AnyEvent::Impl::Irssi used when running within irssi.
		827
		828	Backends with special needs.
		829	Qt requires the Qt::Application to be instantiated first, but will
		830	otherwise be picked up automatically. As long as the main program
		831	instantiates the application before any AnyEvent watchers are
		832	created, everything should just work.
		833
		834	AnyEvent::Impl::Qt based on Qt.
		835
		836	Support for IO::Async can only be partial, as it is too broken and
		837	architecturally limited to even support the AnyEvent API. It also is
		838	the only event loop that needs the loop to be set explicitly, so it
		839	can only be used by a main program knowing about AnyEvent. See
		840	AnyEvent::Impl::Async for the gory details.
		841
		842	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		843
		844	Event loops that are indirectly supported via other backends.
		845	Some event loops can be supported via other modules:
		846
		847	There is no direct support for WxWidgets (Wx) or Prima.
		848
		849	WxWidgets has no support for watching file handles. However, you can
		850	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		851	simply polls 20 times per second, which was considered to be too
		852	horrible to even consider for AnyEvent.
		853
		854	Prima is not supported as nobody seems to be using it, but it has a
		855	POE backend, so it can be supported through POE.
		856
		857	AnyEvent knows about both Prima and Wx, however, and will try to
		858	load POE when detecting them, in the hope that POE will pick them
		859	up, in which case everything will be automatic.
506		860
507	GLOBAL VARIABLES AND FUNCTIONS	861	GLOBAL VARIABLES AND FUNCTIONS
		862	These are not normally required to use AnyEvent, but can be useful to
		863	write AnyEvent extension modules.
		864
508	$AnyEvent::MODEL	865	$AnyEvent::MODEL
509	Contains "undef" until the first watcher is being created. Then it	866	Contains "undef" until the first watcher is being created, before
		867	the backend has been autodetected.
		868
510	contains the event model that is being used, which is the name of	869	Afterwards it contains the event model that is being used, which is
511	the Perl class implementing the model. This class is usually one of	870	the name of the Perl class implementing the model. This class is
512	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	871	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
513	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	872	other class in the case AnyEvent has been extended at runtime (e.g.
514		873	in rxvt-unicode it will be "urxvt::anyevent").
515	The known classes so far are:
516
517	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
518	AnyEvent::Impl::Event based on Event, second best choice.
519	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
520	AnyEvent::Impl::Glib based on Glib, third-best choice.
521	AnyEvent::Impl::Tk based on Tk, very bad choice.
522	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
523	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
524	AnyEvent::Impl::POE based on POE, not generic enough for full support.
525
526	There is no support for WxWidgets, as WxWidgets has no support for
527	watching file handles. However, you can use WxWidgets through the
528	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
529	second, which was considered to be too horrible to even consider for
530	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
531	using it's adaptor.
532
533	AnyEvent knows about Prima and Wx and will try to use POE when
534	autodetecting them.
535		874
536	AnyEvent::detect	875	AnyEvent::detect
537	Returns $AnyEvent::MODEL, forcing autodetection of the event model	876	Returns $AnyEvent::MODEL, forcing autodetection of the event model
538	if necessary. You should only call this function right before you	877	if necessary. You should only call this function right before you
539	would have created an AnyEvent watcher anyway, that is, as late as	878	would have created an AnyEvent watcher anyway, that is, as late as
540	possible at runtime.	879	possible at runtime, and not e.g. while initialising of your module.
		880
		881	If you need to do some initialisation before AnyEvent watchers are
		882	created, use "post_detect".
541		883
542	$guard = AnyEvent::post_detect { BLOCK }	884	$guard = AnyEvent::post_detect { BLOCK }
543	Arranges for the code block to be executed as soon as the event	885	Arranges for the code block to be executed as soon as the event
544	model is autodetected (or immediately if this has already happened).	886	model is autodetected (or immediately if this has already happened).
545		887
		888	The block will be executed after the actual backend has been
		889	detected ($AnyEvent::MODEL is set), but before any watchers have
		890	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		891	other initialisations - see the sources of AnyEvent::Strict or
		892	AnyEvent::AIO to see how this is used.
		893
		894	The most common usage is to create some global watchers, without
		895	forcing event module detection too early, for example, AnyEvent::AIO
		896	creates and installs the global IO::AIO watcher in a "post_detect"
		897	block to avoid autodetecting the event module at load time.
		898
546	If called in scalar or list context, then it creates and returns an	899	If called in scalar or list context, then it creates and returns an
547	object that automatically removes the callback again when it is	900	object that automatically removes the callback again when it is
		901	destroyed (or "undef" when the hook was immediately executed). See
548	destroyed. See Coro::BDB for a case where this is useful.	902	AnyEvent::AIO for a case where this is useful.
		903
		904	Example: Create a watcher for the IO::AIO module and store it in
		905	$WATCHER. Only do so after the event loop is initialised, though.
		906
		907	our WATCHER;
		908
		909	my $guard = AnyEvent::post_detect {
		910	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		911	};
		912
		913	# the \|\|= is important in case post_detect immediately runs the block,
		914	# as to not clobber the newly-created watcher. assigning both watcher and
		915	# post_detect guard to the same variable has the advantage of users being
		916	# able to just C<undef $WATCHER> if the watcher causes them grief.
		917
		918	$WATCHER \|\|= $guard;
549		919
550	@AnyEvent::post_detect	920	@AnyEvent::post_detect
551	If there are any code references in this array (you can "push" to it	921	If there are any code references in this array (you can "push" to it
552	before or after loading AnyEvent), then they will called directly	922	before or after loading AnyEvent), then they will called directly
553	after the event loop has been chosen.	923	after the event loop has been chosen.
554		924
555	You should check $AnyEvent::MODEL before adding to this array,	925	You should check $AnyEvent::MODEL before adding to this array,
556	though: if it contains a true value then the event loop has already	926	though: if it is defined then the event loop has already been
557	been detected, and the array will be ignored.	927	detected, and the array will be ignored.
558		928
559	Best use "AnyEvent::post_detect { BLOCK }" instead.	929	Best use "AnyEvent::post_detect { BLOCK }" when your application
		930	allows it, as it takes care of these details.
		931
		932	This variable is mainly useful for modules that can do something
		933	useful when AnyEvent is used and thus want to know when it is
		934	initialised, but do not need to even load it by default. This array
		935	provides the means to hook into AnyEvent passively, without loading
		936	it.
		937
		938	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		939	together, you could put this into Coro (this is the actual code used
		940	by Coro to accomplish this):
		941
		942	if (defined $AnyEvent::MODEL) {
		943	# AnyEvent already initialised, so load Coro::AnyEvent
		944	require Coro::AnyEvent;
		945	} else {
		946	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		947	# as soon as it is
		948	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		949	}
560		950
561	WHAT TO DO IN A MODULE	951	WHAT TO DO IN A MODULE
562	As a module author, you should "use AnyEvent" and call AnyEvent methods	952	As a module author, you should "use AnyEvent" and call AnyEvent methods
563	freely, but you should not load a specific event module or rely on it.	953	freely, but you should not load a specific event module or rely on it.
564		954
…		…
615	variable somewhere, waiting for it, and sending it when the program	1005	variable somewhere, waiting for it, and sending it when the program
616	should exit cleanly.	1006	should exit cleanly.
617		1007
618	OTHER MODULES	1008	OTHER MODULES
619	The following is a non-exhaustive list of additional modules that use	1009	The following is a non-exhaustive list of additional modules that use
620	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1010	AnyEvent as a client and can therefore be mixed easily with other
621	in the same program. Some of the modules come with AnyEvent, some are	1011	AnyEvent modules and other event loops in the same program. Some of the
622	available via CPAN.	1012	modules come with AnyEvent, most are available via CPAN.
623		1013
624	AnyEvent::Util	1014	AnyEvent::Util
625	Contains various utility functions that replace often-used but	1015	Contains various utility functions that replace often-used but
626	blocking functions such as "inet_aton" by event-/callback-based	1016	blocking functions such as "inet_aton" by event-/callback-based
627	versions.	1017	versions.
628
629	AnyEvent::Handle
630	Provide read and write buffers and manages watchers for reads and
631	writes.
632		1018
633	AnyEvent::Socket	1019	AnyEvent::Socket
634	Provides various utility functions for (internet protocol) sockets,	1020	Provides various utility functions for (internet protocol) sockets,
635	addresses and name resolution. Also functions to create non-blocking	1021	addresses and name resolution. Also functions to create non-blocking
636	tcp connections or tcp servers, with IPv6 and SRV record support and	1022	tcp connections or tcp servers, with IPv6 and SRV record support and
637	more.	1023	more.
638		1024
		1025	AnyEvent::Handle
		1026	Provide read and write buffers, manages watchers for reads and
		1027	writes, supports raw and formatted I/O, I/O queued and fully
		1028	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
		1029
639	AnyEvent::DNS	1030	AnyEvent::DNS
640	Provides rich asynchronous DNS resolver capabilities.	1031	Provides rich asynchronous DNS resolver capabilities.
641		1032
		1033	AnyEvent::HTTP
		1034	A simple-to-use HTTP library that is capable of making a lot of
		1035	concurrent HTTP requests.
		1036
642	AnyEvent::HTTPD	1037	AnyEvent::HTTPD
643	Provides a simple web application server framework.	1038	Provides a simple web application server framework.
644		1039
645	AnyEvent::FastPing	1040	AnyEvent::FastPing
646	The fastest ping in the west.	1041	The fastest ping in the west.
647		1042
		1043	AnyEvent::DBI
		1044	Executes DBI requests asynchronously in a proxy process.
		1045
		1046	AnyEvent::AIO
		1047	Truly asynchronous I/O, should be in the toolbox of every event
		1048	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		1049	together.
		1050
		1051	AnyEvent::BDB
		1052	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		1053	fuses BDB and AnyEvent together.
		1054
		1055	AnyEvent::GPSD
		1056	A non-blocking interface to gpsd, a daemon delivering GPS
		1057	information.
		1058
		1059	AnyEvent::IRC
		1060	AnyEvent based IRC client module family (replacing the older
648	Net::IRC3	1061	Net::IRC3).
649	AnyEvent based IRC client module family.
650		1062
651	Net::XMPP2	1063	AnyEvent::XMPP
652	AnyEvent based XMPP (Jabber protocol) module family.	1064	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		1065	older Net::XMPP2>.
		1066
		1067	AnyEvent::IGS
		1068	A non-blocking interface to the Internet Go Server protocol (used by
		1069	App::IGS).
653		1070
654	Net::FCP	1071	Net::FCP
655	AnyEvent-based implementation of the Freenet Client Protocol,	1072	AnyEvent-based implementation of the Freenet Client Protocol,
656	birthplace of AnyEvent.	1073	birthplace of AnyEvent.
657		1074
…		…
659	High level API for event-based execution flow control.	1076	High level API for event-based execution flow control.
660		1077
661	Coro	1078	Coro
662	Has special support for AnyEvent via Coro::AnyEvent.	1079	Has special support for AnyEvent via Coro::AnyEvent.
663		1080
664	AnyEvent::AIO, IO::AIO	1081	SIMPLIFIED AE API
665	Truly asynchronous I/O, should be in the toolbox of every event	1082	Starting with version 5.0, AnyEvent officially supports a second, much
666	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent	1083	simpler, API that is designed to reduce the calling, typing and memory
667	together.	1084	overhead by using function call syntax and a fixed number of parameters.
668		1085
669	AnyEvent::BDB, BDB	1086	See the AE manpage for details.
670	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
671	fuses IO::AIO and AnyEvent together.
672		1087
673	IO::Lambda	1088	ERROR AND EXCEPTION HANDLING
674	The lambda approach to I/O - don't ask, look there. Can use	1089	In general, AnyEvent does not do any error handling - it relies on the
675	AnyEvent.	1090	caller to do that if required. The AnyEvent::Strict module (see also the
		1091	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		1092	checking of all AnyEvent methods, however, which is highly useful during
		1093	development.
676		1094
677	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1095	As for exception handling (i.e. runtime errors and exceptions thrown
678	This is an advanced topic that you do not normally need to use AnyEvent	1096	while executing a callback), this is not only highly event-loop
679	in a module. This section is only of use to event loop authors who want	1097	specific, but also not in any way wrapped by this module, as this is the
680	to provide AnyEvent compatibility.	1098	job of the main program.
681		1099
682	If you need to support another event library which isn't directly	1100	The pure perl event loop simply re-throws the exception (usually within
683	supported by AnyEvent, you can supply your own interface to it by	1101	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
684	pushing, before the first watcher gets created, the package name of the	1102	Glib uses "install_exception_handler" and so on.
685	event module and the package name of the interface to use onto
686	@AnyEvent::REGISTRY. You can do that before and even without loading
687	AnyEvent, so it is reasonably cheap.
688
689	Example:
690
691	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
692
693	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
694	package/class when it finds the "urxvt" package/module is already
695	loaded.
696
697	When AnyEvent is loaded and asked to find a suitable event model, it
698	will first check for the presence of urxvt by trying to "use" the
699	"urxvt::anyevent" module.
700
701	The class should provide implementations for all watcher types. See
702	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
703	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
704	the sources.
705
706	If you don't provide "signal" and "child" watchers than AnyEvent will
707	provide suitable (hopefully) replacements.
708
709	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
710	terminal emulator uses the above line as-is. An interface isn't included
711	in AnyEvent because it doesn't make sense outside the embedded
712	interpreter inside rxvt-unicode, and it is updated and maintained as
713	part of the rxvt-unicode distribution.
714
715	rxvt-unicode also cheats a bit by not providing blocking access to
716	condition variables: code blocking while waiting for a condition will
717	"die". This still works with most modules/usages, and blocking calls
718	must not be done in an interactive application, so it makes sense.
719		1103
720	ENVIRONMENT VARIABLES	1104	ENVIRONMENT VARIABLES
721	The following environment variables are used by this module:	1105	The following environment variables are used by this module or its
		1106	submodules.
		1107
		1108	Note that AnyEvent will remove all environment variables starting with
		1109	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1110	enabled.
722		1111
723	"PERL_ANYEVENT_VERBOSE"	1112	"PERL_ANYEVENT_VERBOSE"
724	By default, AnyEvent will be completely silent except in fatal	1113	By default, AnyEvent will be completely silent except in fatal
725	conditions. You can set this environment variable to make AnyEvent	1114	conditions. You can set this environment variable to make AnyEvent
726	more talkative.	1115	more talkative.
…		…
729	conditions, such as not being able to load the event model specified	1118	conditions, such as not being able to load the event model specified
730	by "PERL_ANYEVENT_MODEL".	1119	by "PERL_ANYEVENT_MODEL".
731		1120
732	When set to 2 or higher, cause AnyEvent to report to STDERR which	1121	When set to 2 or higher, cause AnyEvent to report to STDERR which
733	event model it chooses.	1122	event model it chooses.
		1123
		1124	When set to 8 or higher, then AnyEvent will report extra information
		1125	on which optional modules it loads and how it implements certain
		1126	features.
		1127
		1128	"PERL_ANYEVENT_STRICT"
		1129	AnyEvent does not do much argument checking by default, as thorough
		1130	argument checking is very costly. Setting this variable to a true
		1131	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1132	thoroughly check the arguments passed to most method calls. If it
		1133	finds any problems, it will croak.
		1134
		1135	In other words, enables "strict" mode.
		1136
		1137	Unlike "use strict" (or it's modern cousin, "use common::sense", it
		1138	is definitely recommended to keep it off in production. Keeping
		1139	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1140	programs can be very useful, however.
734		1141
735	"PERL_ANYEVENT_MODEL"	1142	"PERL_ANYEVENT_MODEL"
736	This can be used to specify the event model to be used by AnyEvent,	1143	This can be used to specify the event model to be used by AnyEvent,
737	before auto detection and -probing kicks in. It must be a string	1144	before auto detection and -probing kicks in. It must be a string
738	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1145	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
743	This functionality might change in future versions.	1150	This functionality might change in future versions.
744		1151
745	For example, to force the pure perl model (AnyEvent::Impl::Perl) you	1152	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
746	could start your program like this:	1153	could start your program like this:
747		1154
748	PERL_ANYEVENT_MODEL=Perl perl ...	1155	PERL_ANYEVENT_MODEL=Perl perl ...
749		1156
750	"PERL_ANYEVENT_PROTOCOLS"	1157	"PERL_ANYEVENT_PROTOCOLS"
751	Used by both AnyEvent::DNS and AnyEvent::Socket to determine	1158	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
752	preferences for IPv4 or IPv6. The default is unspecified (and might	1159	preferences for IPv4 or IPv6. The default is unspecified (and might
753	change, or be the result of auto probing).	1160	change, or be the result of auto probing).
…		…
757	mentioned will be used, and preference will be given to protocols	1164	mentioned will be used, and preference will be given to protocols
758	mentioned earlier in the list.	1165	mentioned earlier in the list.
759		1166
760	This variable can effectively be used for denial-of-service attacks	1167	This variable can effectively be used for denial-of-service attacks
761	against local programs (e.g. when setuid), although the impact is	1168	against local programs (e.g. when setuid), although the impact is
762	likely small, as the program has to handle connection errors	1169	likely small, as the program has to handle conenction and other
763	already-	1170	failures anyways.
764		1171
765	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1172	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
766	IPv6, but support both and try to use both.	1173	IPv6, but support both and try to use both.
767	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1174	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
768	resolve or contact IPv6 addresses.	1175	resolve or contact IPv6 addresses.
…		…
775	but some (broken) firewalls drop such DNS packets, which is why it	1182	but some (broken) firewalls drop such DNS packets, which is why it
776	is off by default.	1183	is off by default.
777		1184
778	Setting this variable to 1 will cause AnyEvent::DNS to announce	1185	Setting this variable to 1 will cause AnyEvent::DNS to announce
779	EDNS0 in its DNS requests.	1186	EDNS0 in its DNS requests.
		1187
		1188	"PERL_ANYEVENT_MAX_FORKS"
		1189	The maximum number of child processes that
		1190	"AnyEvent::Util::fork_call" will create in parallel.
		1191
		1192	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1193	The default value for the "max_outstanding" parameter for the
		1194	default DNS resolver - this is the maximum number of parallel DNS
		1195	requests that are sent to the DNS server.
		1196
		1197	"PERL_ANYEVENT_RESOLV_CONF"
		1198	The file to use instead of /etc/resolv.conf (or OS-specific
		1199	configuration) in the default resolver. When set to the empty
		1200	string, no default config will be used.
		1201
		1202	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1203	When neither "ca_file" nor "ca_path" was specified during
		1204	AnyEvent::TLS context creation, and either of these environment
		1205	variables exist, they will be used to specify CA certificate
		1206	locations instead of a system-dependent default.
		1207
		1208	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1209	When these are set to 1, then the respective modules are not loaded.
		1210	Mostly good for testing AnyEvent itself.
		1211
		1212	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1213	This is an advanced topic that you do not normally need to use AnyEvent
		1214	in a module. This section is only of use to event loop authors who want
		1215	to provide AnyEvent compatibility.
		1216
		1217	If you need to support another event library which isn't directly
		1218	supported by AnyEvent, you can supply your own interface to it by
		1219	pushing, before the first watcher gets created, the package name of the
		1220	event module and the package name of the interface to use onto
		1221	@AnyEvent::REGISTRY. You can do that before and even without loading
		1222	AnyEvent, so it is reasonably cheap.
		1223
		1224	Example:
		1225
		1226	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1227
		1228	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
		1229	package/class when it finds the "urxvt" package/module is already
		1230	loaded.
		1231
		1232	When AnyEvent is loaded and asked to find a suitable event model, it
		1233	will first check for the presence of urxvt by trying to "use" the
		1234	"urxvt::anyevent" module.
		1235
		1236	The class should provide implementations for all watcher types. See
		1237	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
		1238	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
		1239	the sources.
		1240
		1241	If you don't provide "signal" and "child" watchers than AnyEvent will
		1242	provide suitable (hopefully) replacements.
		1243
		1244	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
		1245	terminal emulator uses the above line as-is. An interface isn't included
		1246	in AnyEvent because it doesn't make sense outside the embedded
		1247	interpreter inside rxvt-unicode, and it is updated and maintained as
		1248	part of the rxvt-unicode distribution.
		1249
		1250	rxvt-unicode also cheats a bit by not providing blocking access to
		1251	condition variables: code blocking while waiting for a condition will
		1252	"die". This still works with most modules/usages, and blocking calls
		1253	must not be done in an interactive application, so it makes sense.
780		1254
781	EXAMPLE PROGRAM	1255	EXAMPLE PROGRAM
782	The following program uses an I/O watcher to read data from STDIN, a	1256	The following program uses an I/O watcher to read data from STDIN, a
783	timer to display a message once per second, and a condition variable to	1257	timer to display a message once per second, and a condition variable to
784	quit the program when the user enters quit:	1258	quit the program when the user enters quit:
…		…
796	warn "read: $input\n"; # output what has been read	1270	warn "read: $input\n"; # output what has been read
797	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1271	$cv->send if $input =~ /^q/i; # quit program if /^q/i
798	},	1272	},
799	);	1273	);
800		1274
801	my $time_watcher; # can only be used once
802
803	sub new_timer {
804	$timer = AnyEvent->timer (after => 1, cb => sub {	1275	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
805	warn "timeout\n"; # print 'timeout' about every second	1276	warn "timeout\n"; # print 'timeout' at most every second
806	&new_timer; # and restart the time
807	});
808	}	1277	});
809
810	new_timer; # create first timer
811		1278
812	$cv->recv; # wait until user enters /^q/i	1279	$cv->recv; # wait until user enters /^q/i
813		1280
814	REAL-WORLD EXAMPLE	1281	REAL-WORLD EXAMPLE
815	Consider the Net::FCP module. It features (among others) the following	1282	Consider the Net::FCP module. It features (among others) the following
…		…
887		1354
888	The actual code goes further and collects all errors ("die"s,	1355	The actual code goes further and collects all errors ("die"s,
889	exceptions) that occurred during request processing. The "result" method	1356	exceptions) that occurred during request processing. The "result" method
890	detects whether an exception as thrown (it is stored inside the $txn	1357	detects whether an exception as thrown (it is stored inside the $txn
891	object) and just throws the exception, which means connection errors and	1358	object) and just throws the exception, which means connection errors and
892	other problems get reported tot he code that tries to use the result,	1359	other problems get reported to the code that tries to use the result,
893	not in a random callback.	1360	not in a random callback.
894		1361
895	All of this enables the following usage styles:	1362	All of this enables the following usage styles:
896		1363
897	1. Blocking:	1364	1. Blocking:
…		…
942	through AnyEvent. The benchmark creates a lot of timers (with a zero	1409	through AnyEvent. The benchmark creates a lot of timers (with a zero
943	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1410	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
944	which it is), lets them fire exactly once and destroys them again.	1411	which it is), lets them fire exactly once and destroys them again.
945		1412
946	Source code for this benchmark is found as eg/bench in the AnyEvent	1413	Source code for this benchmark is found as eg/bench in the AnyEvent
947	distribution.	1414	distribution. It uses the AE interface, which makes a real difference
		1415	for the EV and Perl backends only.
948		1416
949	Explanation of the columns	1417	Explanation of the columns
950	watcher is the number of event watchers created/destroyed. Since	1418	watcher is the number of event watchers created/destroyed. Since
951	different event models feature vastly different performances, each event	1419	different event models feature vastly different performances, each event
952	loop was given a number of watchers so that overall runtime is	1420	loop was given a number of watchers so that overall runtime is
…		…
971	destroy is the time, in microseconds, that it takes to destroy a	1439	destroy is the time, in microseconds, that it takes to destroy a
972	single watcher.	1440	single watcher.
973		1441
974	Results	1442	Results
975	name watchers bytes create invoke destroy comment	1443	name watchers bytes create invoke destroy comment
976	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1444	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
977	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1445	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
978	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1446	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
979	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1447	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
980	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1448	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
981	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1449	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1450	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1451	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
982	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1452	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
983	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1453	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
984	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1454	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
985	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1455	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
986		1456
987	Discussion	1457	Discussion
988	The benchmark does not measure scalability of the event loop very	1458	The benchmark does not measure scalability of the event loop very
989	well. For example, a select-based event loop (such as the pure perl one)	1459	well. For example, a select-based event loop (such as the pure perl one)
990	can never compete with an event loop that uses epoll when the number of	1460	can never compete with an event loop that uses epoll when the number of
…		…
1001	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1471	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1002	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1472	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1003	CPU cycles with POE.	1473	CPU cycles with POE.
1004		1474
1005	"EV" is the sole leader regarding speed and memory use, which are both	1475	"EV" is the sole leader regarding speed and memory use, which are both
1006	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1476	maximal/minimal, respectively. When using the AE API there is zero
		1477	overhead (when going through the AnyEvent API create is about 5-6 times
		1478	slower, with other times being equal, so still uses far less memory than
1007	far less memory than any other event loop and is still faster than Event	1479	any other event loop and is still faster than Event natively).
1008	natively.
1009		1480
1010	The pure perl implementation is hit in a few sweet spots (both the	1481	The pure perl implementation is hit in a few sweet spots (both the
1011	constant timeout and the use of a single fd hit optimisations in the	1482	constant timeout and the use of a single fd hit optimisations in the
1012	perl interpreter and the backend itself). Nevertheless this shows that	1483	perl interpreter and the backend itself). Nevertheless this shows that
1013	it adds very little overhead in itself. Like any select-based backend	1484	it adds very little overhead in itself. Like any select-based backend
…		…
1015	few of them active), of course, but this was not subject of this	1486	few of them active), of course, but this was not subject of this
1016	benchmark.	1487	benchmark.
1017		1488
1018	The "Event" module has a relatively high setup and callback invocation	1489	The "Event" module has a relatively high setup and callback invocation
1019	cost, but overall scores in on the third place.	1490	cost, but overall scores in on the third place.
		1491
		1492	"IO::Async" performs admirably well, about on par with "Event", even
		1493	when using its pure perl backend.
1020		1494
1021	"Glib"'s memory usage is quite a bit higher, but it features a faster	1495	"Glib"'s memory usage is quite a bit higher, but it features a faster
1022	callback invocation and overall ends up in the same class as "Event".	1496	callback invocation and overall ends up in the same class as "Event".
1023	However, Glib scales extremely badly, doubling the number of watchers	1497	However, Glib scales extremely badly, doubling the number of watchers
1024	increases the processing time by more than a factor of four, making it	1498	increases the processing time by more than a factor of four, making it
…		…
1080	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1554	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1081	100 (1%) are active. This mirrors the activity of large servers with	1555	100 (1%) are active. This mirrors the activity of large servers with
1082	many connections, most of which are idle at any one point in time.	1556	many connections, most of which are idle at any one point in time.
1083		1557
1084	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1558	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1085	distribution.	1559	distribution. It uses the AE interface, which makes a real difference
		1560	for the EV and Perl backends only.
1086		1561
1087	Explanation of the columns	1562	Explanation of the columns
1088	sockets is the number of sockets, and twice the number of "servers"	1563	sockets is the number of sockets, and twice the number of "servers"
1089	(as each server has a read and write socket end).	1564	(as each server has a read and write socket end).
1090		1565
…		…
1095	single "request", that is, reading the token from the pipe and	1570	single "request", that is, reading the token from the pipe and
1096	forwarding it to another server. This includes deleting the old timeout	1571	forwarding it to another server. This includes deleting the old timeout
1097	and creating a new one that moves the timeout into the future.	1572	and creating a new one that moves the timeout into the future.
1098		1573
1099	Results	1574	Results
1100	name sockets create request	1575	name sockets create request
1101	EV 20000 69.01 11.16	1576	EV 20000 62.66 7.99
1102	Perl 20000 73.32 35.87	1577	Perl 20000 68.32 32.64
1103	Event 20000 212.62 257.32	1578	IOAsync 20000 174.06 101.15 epoll
1104	Glib 20000 651.16 1896.30	1579	IOAsync 20000 174.67 610.84 poll
		1580	Event 20000 202.69 242.91
		1581	Glib 20000 557.01 1689.52
1105	POE 20000 349.67 12317.24 uses POE::Loop::Event	1582	POE 20000 341.54 12086.32 uses POE::Loop::Event
1106		1583
1107	Discussion	1584	Discussion
1108	This benchmark does measure scalability and overall performance of the	1585	This benchmark does measure scalability and overall performance of the
1109	particular event loop.	1586	particular event loop.
1110		1587
1111	EV is again fastest. Since it is using epoll on my system, the setup	1588	EV is again fastest. Since it is using epoll on my system, the setup
1112	time is relatively high, though.	1589	time is relatively high, though.
1113		1590
1114	Perl surprisingly comes second. It is much faster than the C-based event	1591	Perl surprisingly comes second. It is much faster than the C-based event
1115	loops Event and Glib.	1592	loops Event and Glib.
		1593
		1594	IO::Async performs very well when using its epoll backend, and still
		1595	quite good compared to Glib when using its pure perl backend.
1116		1596
1117	Event suffers from high setup time as well (look at its code and you	1597	Event suffers from high setup time as well (look at its code and you
1118	will understand why). Callback invocation also has a high overhead	1598	will understand why). Callback invocation also has a high overhead
1119	compared to the "$_->() for .."-style loop that the Perl event loop	1599	compared to the "$_->() for .."-style loop that the Perl event loop
1120	uses. Event uses select or poll in basically all documented	1600	uses. Event uses select or poll in basically all documented
…		…
1171		1651
1172	Summary	1652	Summary
1173	* C-based event loops perform very well with small number of watchers,	1653	* C-based event loops perform very well with small number of watchers,
1174	as the management overhead dominates.	1654	as the management overhead dominates.
1175		1655
		1656	THE IO::Lambda BENCHMARK
		1657	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1658	could be misinterpreted to make AnyEvent look bad. In fact, the
		1659	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1660	better (which shouldn't come as a surprise to anybody). As such, the
		1661	benchmark is fine, and mostly shows that the AnyEvent backend from
		1662	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1663	without the extra baggage? To explore this, I wrote the equivalent
		1664	benchmark for AnyEvent.
		1665
		1666	The benchmark itself creates an echo-server, and then, for 500 times,
		1667	connects to the echo server, sends a line, waits for the reply, and then
		1668	creates the next connection. This is a rather bad benchmark, as it
		1669	doesn't test the efficiency of the framework or much non-blocking I/O,
		1670	but it is a benchmark nevertheless.
		1671
		1672	name runtime
		1673	Lambda/select 0.330 sec
		1674	+ optimized 0.122 sec
		1675	Lambda/AnyEvent 0.327 sec
		1676	+ optimized 0.138 sec
		1677	Raw sockets/select 0.077 sec
		1678	POE/select, components 0.662 sec
		1679	POE/select, raw sockets 0.226 sec
		1680	POE/select, optimized 0.404 sec
		1681
		1682	AnyEvent/select/nb 0.085 sec
		1683	AnyEvent/EV/nb 0.068 sec
		1684	+state machine 0.134 sec
		1685
		1686	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1687	benchmarks actually make blocking connects and use 100% blocking I/O,
		1688	defeating the purpose of an event-based solution. All of the newly
		1689	written AnyEvent benchmarks use 100% non-blocking connects (using
		1690	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1691	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1692	connects generally require a lot more bookkeeping and event handling
		1693	than blocking connects (which involve a single syscall only).
		1694
		1695	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1696	offers similar expressive power as POE and IO::Lambda, using
		1697	conventional Perl syntax. This means that both the echo server and the
		1698	client are 100% non-blocking, further placing it at a disadvantage.
		1699
		1700	As you can see, the AnyEvent + EV combination even beats the
		1701	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1702	backend easily beats IO::Lambda and POE.
		1703
		1704	And even the 100% non-blocking version written using the high-level (and
		1705	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1706	higher level ("unoptimised") abstractions by a large margin, even though
		1707	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1708
		1709	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1710	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1711	part of the IO::Lambda distribution and were used without any changes.
		1712
		1713	SIGNALS
		1714	AnyEvent currently installs handlers for these signals:
		1715
		1716	SIGCHLD
		1717	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1718	emulation for event loops that do not support them natively. Also,
		1719	some event loops install a similar handler.
		1720
		1721	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1722	then AnyEvent will reset it to default, to avoid losing child exit
		1723	statuses.
		1724
		1725	SIGPIPE
		1726	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1727	"undef" when AnyEvent gets loaded.
		1728
		1729	The rationale for this is that AnyEvent users usually do not really
		1730	depend on SIGPIPE delivery (which is purely an optimisation for
		1731	shell use, or badly-written programs), but "SIGPIPE" can cause
		1732	spurious and rare program exits as a lot of people do not expect
		1733	"SIGPIPE" when writing to some random socket.
		1734
		1735	The rationale for installing a no-op handler as opposed to ignoring
		1736	it is that this way, the handler will be restored to defaults on
		1737	exec.
		1738
		1739	Feel free to install your own handler, or reset it to defaults.
		1740
		1741	RECOMMENDED/OPTIONAL MODULES
		1742	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1743	it's built-in modules) are required to use it.
		1744
		1745	That does not mean that AnyEvent won't take advantage of some additional
		1746	modules if they are installed.
		1747
		1748	This section explains which additional modules will be used, and how
		1749	they affect AnyEvent's operation.
		1750
		1751	Async::Interrupt
		1752	This slightly arcane module is used to implement fast signal
		1753	handling: To my knowledge, there is no way to do completely
		1754	race-free and quick signal handling in pure perl. To ensure that
		1755	signals still get delivered, AnyEvent will start an interval timer
		1756	to wake up perl (and catch the signals) with some delay (default is
		1757	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1758
		1759	If this module is available, then it will be used to implement
		1760	signal catching, which means that signals will not be delayed, and
		1761	the event loop will not be interrupted regularly, which is more
		1762	efficient (and good for battery life on laptops).
		1763
		1764	This affects not just the pure-perl event loop, but also other event
		1765	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1766
		1767	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1768	natively, and either employ their own workarounds (POE) or use
		1769	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1770	Installing Async::Interrupt does nothing for those backends.
		1771
		1772	EV This module isn't really "optional", as it is simply one of the
		1773	backend event loops that AnyEvent can use. However, it is simply the
		1774	best event loop available in terms of features, speed and stability:
		1775	It supports the AnyEvent API optimally, implements all the watcher
		1776	types in XS, does automatic timer adjustments even when no monotonic
		1777	clock is available, can take avdantage of advanced kernel interfaces
		1778	such as "epoll" and "kqueue", and is the fastest backend by far.
		1779	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1780	Glib::EV).
		1781
		1782	If you only use backends that rely on another event loop (e.g.
		1783	"Tk"), then this module will do nothing for you.
		1784
		1785	Guard
		1786	The guard module, when used, will be used to implement
		1787	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1788	uses a lot less memory), but otherwise doesn't affect guard
		1789	operation much. It is purely used for performance.
		1790
		1791	JSON and JSON::XS
		1792	One of these modules is required when you want to read or write JSON
		1793	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		1794	can take advantage of the ultra-high-speed JSON::XS module when it
		1795	is installed.
		1796
		1797	Net::SSLeay
		1798	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1799	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1800	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1801
		1802	Time::HiRes
		1803	This module is part of perl since release 5.008. It will be used
		1804	when the chosen event library does not come with a timing source on
		1805	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1806	additionally use it to try to use a monotonic clock for timing
		1807	stability.
		1808
1176	FORK	1809	FORK
1177	Most event libraries are not fork-safe. The ones who are usually are	1810	Most event libraries are not fork-safe. The ones who are usually are
1178	because they rely on inefficient but fork-safe "select" or "poll" calls.	1811	because they rely on inefficient but fork-safe "select" or "poll" calls
1179	Only EV is fully fork-aware.	1812	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		1813	epoll are usually badly thought-out hacks that are incompatible with
		1814	fork in one way or another. Only EV is fully fork-aware and ensures that
		1815	you continue event-processing in both parent and child (or both, if you
		1816	know what you are doing).
		1817
		1818	This means that, in general, you cannot fork and do event processing in
		1819	the child if the event library was initialised before the fork (which
		1820	usually happens when the first AnyEvent watcher is created, or the
		1821	library is loaded).
1180		1822
1181	If you have to fork, you must either do so before creating your first	1823	If you have to fork, you must either do so before creating your first
1182	watcher OR you must not use AnyEvent at all in the child.	1824	watcher OR you must not use AnyEvent at all in the child OR you must do
		1825	something completely out of the scope of AnyEvent.
		1826
		1827	The problem of doing event processing in the parent and the child is
		1828	much more complicated: even for backends that are fork-aware or
		1829	fork-safe, their behaviour is not usually what you want: fork clones all
		1830	watchers, that means all timers, I/O watchers etc. are active in both
		1831	parent and child, which is almost never what you want. USing "exec" to
		1832	start worker children from some kind of manage rprocess is usually
		1833	preferred, because it is much easier and cleaner, at the expense of
		1834	having to have another binary.
1183		1835
1184	SECURITY CONSIDERATIONS	1836	SECURITY CONSIDERATIONS
1185	AnyEvent can be forced to load any event model via	1837	AnyEvent can be forced to load any event model via
1186	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1838	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1187	to execute arbitrary code or directly gain access, it can easily be used	1839	to execute arbitrary code or directly gain access, it can easily be used
…		…
1190	model than specified in the variable.	1842	model than specified in the variable.
1191		1843
1192	You can make AnyEvent completely ignore this variable by deleting it	1844	You can make AnyEvent completely ignore this variable by deleting it
1193	before the first watcher gets created, e.g. with a "BEGIN" block:	1845	before the first watcher gets created, e.g. with a "BEGIN" block:
1194		1846
1195	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1847	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1196		1848
1197	use AnyEvent;	1849	use AnyEvent;
1198		1850
1199	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1851	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1200	be used to probe what backend is used and gain other information (which	1852	be used to probe what backend is used and gain other information (which
1201	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).	1853	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1854	and $ENV{PERL_ANYEVENT_STRICT}.
		1855
		1856	Note that AnyEvent will remove all environment variables starting with
		1857	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1858	enabled.
		1859
		1860	BUGS
		1861	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1862	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1863	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1864	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1865	not as pronounced).
1202		1866
1203	SEE ALSO	1867	SEE ALSO
1204	Utility functions: AnyEvent::Util.	1868	Utility functions: AnyEvent::Util.
1205		1869
1206	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1870	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1207	Event::Lib, Qt, POE.	1871	Event::Lib, Qt, POE.
1208		1872
1209	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1873	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1210	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1874	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1211	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1875	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1876	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
1212		1877
1213	Non-blocking file handles, sockets, TCP clients and servers:	1878	Non-blocking file handles, sockets, TCP clients and servers:
1214	AnyEvent::Handle, AnyEvent::Socket.	1879	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1215		1880
1216	Asynchronous DNS: AnyEvent::DNS.	1881	Asynchronous DNS: AnyEvent::DNS.
1217		1882
1218	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1883	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1219		1884
1220	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1885	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1886	AnyEvent::HTTP.
1221		1887
1222	AUTHOR	1888	AUTHOR
1223	Marc Lehmann <schmorp@schmorp.de>	1889	Marc Lehmann <schmorp@schmorp.de>
1224	http://home.schmorp.de/	1890	http://home.schmorp.de/
1225		1891

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Comparing AnyEvent/README (file contents): Revision 1.23 by root, Mon May 26 06:04:38 2008 UTC vs. Revision 1.60 by root, Mon Apr 12 02:50:31 2010 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.23 by root, Mon May 26 06:04:38 2008 UTC vs.
Revision 1.60 by root, Mon Apr 12 02:50:31 2010 UTC