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Revision 1.17 by root, Tue Apr 22 05:12:19 2008 UTC vs.
Revision 1.28 by root, Sat Jul 12 20:45:27 2008 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - provide framework for multiple event loops
3		3
4	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
5	event loops	5	loops
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	14	my $w = AnyEvent->timer (after => $seconds, cb => sub {
15	...	15	...
16	});	16	});
17		17
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	18	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		19	$w->send; # wake up current and all future recv's
19	$w->wait; # enters "main loop" till $condvar gets ->broadcast	20	$w->recv; # enters "main loop" till $condvar gets ->send
20	$w->broadcast; # wake up current and all future wait's	21
		22	INTRODUCTION/TUTORIAL
		23	This manpage is mainly a reference manual. If you are interested in a
		24	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		25	manpage.
21		26
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	27	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	28	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	29	nowadays. So what is different about AnyEvent?
25		30
26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	31	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
27	policy* and AnyEvent is small and efficient.	32	policy* and AnyEvent is small and efficient.
28		33
29	First and foremost, AnyEvent is not an event model itself, it only	34	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	35	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,	36	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,	37	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.	38	only one event loop can be active at the same time in a process.
34	AnyEvent helps hiding the differences between those event loops.	39	AnyEvent cannot change this, but it can hide the differences between
		40	those event loops.
35		41
36	The goal of AnyEvent is to offer module authors the ability to do event	42	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	43	programming (waiting for I/O or timer events) without subscribing to a
38	religion, a way of living, and most importantly: without forcing your	44	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	45	module users into the same thing by forcing them to use the same event
40	model you use.	46	model you use.
41		47
42	For modules like POE or IO::Async (which is a total misnomer as it is	48	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	49	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	50	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	51	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	52	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.	53	are also forced to use the same event loop you use.
48		54
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	55	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	56	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	57	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.	58	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	59	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	60	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	61	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).	62	to AnyEvent, too, so it is future-proof).
57		63
58	In addition to being free of having to use *the one and only true event	64	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	65	model*, AnyEvent also is free of bloat and policy: with POE or similar
60	modules, you get an enourmous amount of code and strict rules you have	66	modules, you get an enormous amount of code and strict rules you have to
61	to follow. AnyEvent, on the other hand, is lean and up to the point, by	67	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	68	only offering the functionality that is necessary, in as thin as a
63	wrapper as technically possible.	69	wrapper as technically possible.
64		70
		71	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
		72	useful functionality, such as an asynchronous DNS resolver, 100%
		73	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		74	such as Windows) and lots of real-world knowledge and workarounds for
		75	platform bugs and differences.
		76
65	Of course, if you want lots of policy (this can arguably be somewhat	77	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	78	useful) and you want to force your users to use the one and only event
67	model, you should not use this module.	79	model, you should not use this module.
68		80
69	DESCRIPTION	81	DESCRIPTION
70	AnyEvent provides an identical interface to multiple event loops. This	82	AnyEvent provides an identical interface to multiple event loops. This
…		…
75	The interface itself is vaguely similar, but not identical to the Event	87	The interface itself is vaguely similar, but not identical to the Event
76	module.	88	module.
77		89
78	During the first call of any watcher-creation method, the module tries	90	During the first call of any watcher-creation method, the module tries
79	to detect the currently loaded event loop by probing whether one of the	91	to detect the currently loaded event loop by probing whether one of the
80	following modules is already loaded: Coro::EV, Coro::Event, EV, Event,	92	following modules is already loaded: EV, Event, Glib,
81	Glib, Tk. The first one found is used. If none are found, the module	93	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82	tries to load these modules in the stated order. The first one that can	94	used. If none are found, the module tries to load these modules
		95	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
		96	always succeed) in the order given. The first one that can be
83	be successfully loaded will be used. If, after this, still none could be	97	successfully loaded will be used. If, after this, still none could be
84	found, AnyEvent will fall back to a pure-perl event loop, which is not	98	found, AnyEvent will fall back to a pure-perl event loop, which is not
85	very efficient, but should work everywhere.	99	very efficient, but should work everywhere.
86		100
87	Because AnyEvent first checks for modules that are already loaded,	101	Because AnyEvent first checks for modules that are already loaded,
88	loading an event model explicitly before first using AnyEvent will	102	loading an event model explicitly before first using AnyEvent will
…		…
97	starts using it, all bets are off. Maybe you should tell their authors	111	starts using it, all bets are off. Maybe you should tell their authors
98	to use AnyEvent so their modules work together with others seamlessly...	112	to use AnyEvent so their modules work together with others seamlessly...
99		113
100	The pure-perl implementation of AnyEvent is called	114	The pure-perl implementation of AnyEvent is called
101	"AnyEvent::Impl::Perl". Like other event modules you can load it	115	"AnyEvent::Impl::Perl". Like other event modules you can load it
102	explicitly.	116	explicitly and enjoy the high availability of that event loop :)
103		117
104	WATCHERS	118	WATCHERS
105	AnyEvent has the central concept of a watcher, which is an object that	119	AnyEvent has the central concept of a watcher, which is an object that
106	stores relevant data for each kind of event you are waiting for, such as	120	stores relevant data for each kind of event you are waiting for, such as
107	the callback to call, the filehandle to watch, etc.	121	the callback to call, the file handle to watch, etc.
108		122
109	These watchers are normal Perl objects with normal Perl lifetime. After	123	These watchers are normal Perl objects with normal Perl lifetime. After
110	creating a watcher it will immediately "watch" for events and invoke the	124	creating a watcher it will immediately "watch" for events and invoke the
111	callback when the event occurs (of course, only when the event model is	125	callback when the event occurs (of course, only when the event model is
112	in control).	126	in control).
…		…
120	Many watchers either are used with "recursion" (repeating timers for	134	Many watchers either are used with "recursion" (repeating timers for
121	example), or need to refer to their watcher object in other ways.	135	example), or need to refer to their watcher object in other ways.
122		136
123	An any way to achieve that is this pattern:	137	An any way to achieve that is this pattern:
124		138
125	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	139	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
126	# you can use $w here, for example to undef it	140	# you can use $w here, for example to undef it
127	undef $w;	141	undef $w;
128	});	142	});
129		143
130	Note that "my $w; $w =" combination. This is necessary because in Perl,	144	Note that "my $w; $w =" combination. This is necessary because in Perl,
131	my variables are only visible after the statement in which they are	145	my variables are only visible after the statement in which they are
132	declared.	146	declared.
133		147
134	IO WATCHERS	148	I/O WATCHERS
135	You can create an I/O watcher by calling the "AnyEvent->io" method with	149	You can create an I/O watcher by calling the "AnyEvent->io" method with
136	the following mandatory key-value pairs as arguments:	150	the following mandatory key-value pairs as arguments:
137		151
138	"fh" the Perl file handle (not file descriptor) to watch for events.	152	"fh" the Perl file handle (not file descriptor) to watch for events
		153	(AnyEvent might or might not keep a reference to this file handle).
139	"poll" must be a string that is either "r" or "w", which creates a	154	"poll" must be a string that is either "r" or "w", which creates a
140	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	155	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
141	is the callback to invoke each time the file handle becomes ready.	156	is the callback to invoke each time the file handle becomes ready.
142		157
143	File handles will be kept alive, so as long as the watcher exists, the	158	Although the callback might get passed parameters, their value and
144	file handle exists, too.	159	presence is undefined and you cannot rely on them. Portable AnyEvent
		160	callbacks cannot use arguments passed to I/O watcher callbacks.
145		161
		162	The I/O watcher might use the underlying file descriptor or a copy of
146	It is not allowed to close a file handle as long as any watcher is	163	it. You must not close a file handle as long as any watcher is active on
147	active on the underlying file descriptor.	164	the underlying file descriptor.
148		165
149	Some event loops issue spurious readyness notifications, so you should	166	Some event loops issue spurious readyness notifications, so you should
150	always use non-blocking calls when reading/writing from/to your file	167	always use non-blocking calls when reading/writing from/to your file
151	handles.	168	handles.
152		169
153	Example:
154
155	# wait for readability of STDIN, then read a line and disable the watcher	170	Example: wait for readability of STDIN, then read a line and disable the
		171	watcher.
		172
156	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	173	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
157	chomp (my $input = <STDIN>);	174	chomp (my $input = <STDIN>);
158	warn "read: $input\n";	175	warn "read: $input\n";
159	undef $w;	176	undef $w;
160	});	177	});
…		…
162	TIME WATCHERS	179	TIME WATCHERS
163	You can create a time watcher by calling the "AnyEvent->timer" method	180	You can create a time watcher by calling the "AnyEvent->timer" method
164	with the following mandatory arguments:	181	with the following mandatory arguments:
165		182
166	"after" specifies after how many seconds (fractional values are	183	"after" specifies after how many seconds (fractional values are
167	supported) should the timer activate. "cb" the callback to invoke in	184	supported) the callback should be invoked. "cb" is the callback to
168	that case.	185	invoke in that case.
169		186
170	The timer callback will be invoked at most once: if you want a repeating	187	Although the callback might get passed parameters, their value and
171	timer you have to create a new watcher (this is a limitation by both Tk	188	presence is undefined and you cannot rely on them. Portable AnyEvent
172	and Glib).	189	callbacks cannot use arguments passed to time watcher callbacks.
173		190
174	Example:	191	The callback will normally be invoked once only. If you specify another
		192	parameter, "interval", as a strictly positive number (> 0), then the
		193	callback will be invoked regularly at that interval (in fractional
		194	seconds) after the first invocation. If "interval" is specified with a
		195	false value, then it is treated as if it were missing.
175		196
		197	The callback will be rescheduled before invoking the callback, but no
		198	attempt is done to avoid timer drift in most backends, so the interval
		199	is only approximate.
		200
176	# fire an event after 7.7 seconds	201	Example: fire an event after 7.7 seconds.
		202
177	my $w = AnyEvent->timer (after => 7.7, cb => sub {	203	my $w = AnyEvent->timer (after => 7.7, cb => sub {
178	warn "timeout\n";	204	warn "timeout\n";
179	});	205	});
180		206
181	# to cancel the timer:	207	# to cancel the timer:
182	undef $w;	208	undef $w;
183		209
184	Example 2:
185
186	# fire an event after 0.5 seconds, then roughly every second	210	Example 2: fire an event after 0.5 seconds, then roughly every second.
187	my $w;
188		211
189	my $cb = sub {
190	# cancel the old timer while creating a new one
191	$w = AnyEvent->timer (after => 1, cb => $cb);	212	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		213	warn "timeout\n";
192	};	214	};
193
194	# start the "loop" by creating the first watcher
195	$w = AnyEvent->timer (after => 0.5, cb => $cb);
196		215
197	TIMING ISSUES	216	TIMING ISSUES
198	There are two ways to handle timers: based on real time (relative, "fire	217	There are two ways to handle timers: based on real time (relative, "fire
199	in 10 seconds") and based on wallclock time (absolute, "fire at 12	218	in 10 seconds") and based on wallclock time (absolute, "fire at 12
200	o'clock").	219	o'clock").
201		220
202	While most event loops expect timers to specified in a relative way,	221	While most event loops expect timers to specified in a relative way,
203	they use absolute time internally. This makes a difference when your	222	they use absolute time internally. This makes a difference when your
204	clock "jumps", for example, when ntp decides to set your clock backwards	223	clock "jumps", for example, when ntp decides to set your clock backwards
205	from the wrong 2014-01-01 to 2008-01-01, a watcher that you created to	224	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
206	fire "after" a second might actually take six years to finally fire.	225	supposed to fire "after" a second might actually take six years to
		226	finally fire.
207		227
208	AnyEvent cannot compensate for this. The only event loop that is	228	AnyEvent cannot compensate for this. The only event loop that is
209	conscious about these issues is EV, which offers both relative	229	conscious about these issues is EV, which offers both relative
210	(ev_timer) and absolute (ev_periodic) timers.	230	(ev_timer, based on true relative time) and absolute (ev_periodic, based
		231	on wallclock time) timers.
211		232
212	AnyEvent always prefers relative timers, if available, matching the	233	AnyEvent always prefers relative timers, if available, matching the
213	AnyEvent API.	234	AnyEvent API.
214		235
		236	AnyEvent has two additional methods that return the "current time":
		237
		238	AnyEvent->time
		239	This returns the "current wallclock time" as a fractional number of
		240	seconds since the Epoch (the same thing as "time" or
		241	"Time::HiRes::time" return, and the result is guaranteed to be
		242	compatible with those).
		243
		244	It progresses independently of any event loop processing, i.e. each
		245	call will check the system clock, which usually gets updated
		246	frequently.
		247
		248	AnyEvent->now
		249	This also returns the "current wallclock time", but unlike "time",
		250	above, this value might change only once per event loop iteration,
		251	depending on the event loop (most return the same time as "time",
		252	above). This is the time that AnyEvent's timers get scheduled
		253	against.
		254
		255	*In almost all cases (in all cases if you don't care), this is the
		256	function to call when you want to know the current time.*
		257
		258	This function is also often faster then "AnyEvent->time", and thus
		259	the preferred method if you want some timestamp (for example,
		260	AnyEvent::Handle uses this to update it's activity timeouts).
		261
		262	The rest of this section is only of relevance if you try to be very
		263	exact with your timing, you can skip it without bad conscience.
		264
		265	For a practical example of when these times differ, consider
		266	Event::Lib and EV and the following set-up:
		267
		268	The event loop is running and has just invoked one of your callback
		269	at time=500 (assume no other callbacks delay processing). In your
		270	callback, you wait a second by executing "sleep 1" (blocking the
		271	process for a second) and then (at time=501) you create a relative
		272	timer that fires after three seconds.
		273
		274	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		275	return 501, because that is the current time, and the timer will be
		276	scheduled to fire at time=504 (501 + 3).
		277
		278	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		279	but "AnyEvent->now" returns 500, as that is the time the last event
		280	processing phase started. With EV, your timer gets scheduled to run
		281	at time=503 (500 + 3).
		282
		283	In one sense, Event::Lib is more exact, as it uses the current time
		284	regardless of any delays introduced by event processing. However,
		285	most callbacks do not expect large delays in processing, so this
		286	causes a higher drift (and a lot more system calls to get the
		287	current time).
		288
		289	In another sense, EV is more exact, as your timer will be scheduled
		290	at the same time, regardless of how long event processing actually
		291	took.
		292
		293	In either case, if you care (and in most cases, you don't), then you
		294	can get whatever behaviour you want with any event loop, by taking
		295	the difference between "AnyEvent->time" and "AnyEvent->now" into
		296	account.
		297
215	SIGNAL WATCHERS	298	SIGNAL WATCHERS
216	You can watch for signals using a signal watcher, "signal" is the signal	299	You can watch for signals using a signal watcher, "signal" is the signal
217	name without any "SIG" prefix, "cb" is the Perl callback to be invoked	300	name in uppercase and without any "SIG" prefix, "cb" is the Perl
218	whenever a signal occurs.	301	callback to be invoked whenever a signal occurs.
219		302
		303	Although the callback might get passed parameters, their value and
		304	presence is undefined and you cannot rely on them. Portable AnyEvent
		305	callbacks cannot use arguments passed to signal watcher callbacks.
		306
220	Multiple signals occurances can be clumped together into one callback	307	Multiple signal occurrences can be clumped together into one callback
221	invocation, and callback invocation will be synchronous. synchronous	308	invocation, and callback invocation will be synchronous. Synchronous
222	means that it might take a while until the signal gets handled by the	309	means that it might take a while until the signal gets handled by the
223	process, but it is guarenteed not to interrupt any other callbacks.	310	process, but it is guaranteed not to interrupt any other callbacks.
224		311
225	The main advantage of using these watchers is that you can share a	312	The main advantage of using these watchers is that you can share a
226	signal between multiple watchers.	313	signal between multiple watchers.
227		314
228	This watcher might use %SIG, so programs overwriting those signals	315	This watcher might use %SIG, so programs overwriting those signals
…		…
237		324
238	The child process is specified by the "pid" argument (if set to 0, it	325	The child process is specified by the "pid" argument (if set to 0, it
239	watches for any child process exit). The watcher will trigger as often	326	watches for any child process exit). The watcher will trigger as often
240	as status change for the child are received. This works by installing a	327	as status change for the child are received. This works by installing a
241	signal handler for "SIGCHLD". The callback will be called with the pid	328	signal handler for "SIGCHLD". The callback will be called with the pid
242	and exit status (as returned by waitpid).	329	and exit status (as returned by waitpid), so unlike other watcher types,
		330	you can rely on child watcher callback arguments.
243		331
244	Example: wait for pid 1333	332	There is a slight catch to child watchers, however: you usually start
		333	them after the child process was created, and this means the process
		334	could have exited already (and no SIGCHLD will be sent anymore).
245		335
		336	Not all event models handle this correctly (POE doesn't), but even for
		337	event models that do handle this correctly, they usually need to be
		338	loaded before the process exits (i.e. before you fork in the first
		339	place).
		340
		341	This means you cannot create a child watcher as the very first thing in
		342	an AnyEvent program, you have to create at least one watcher before
		343	you "fork" the child (alternatively, you can call "AnyEvent::detect").
		344
		345	Example: fork a process and wait for it
		346
		347	my $done = AnyEvent->condvar;
		348
		349	my $pid = fork or exit 5;
		350
246	my $w = AnyEvent->child (	351	my $w = AnyEvent->child (
247	pid => 1333,	352	pid => $pid,
248	cb => sub {	353	cb => sub {
249	my ($pid, $status) = @_;	354	my ($pid, $status) = @_;
250	warn "pid $pid exited with status $status";	355	warn "pid $pid exited with status $status";
		356	$done->send;
251	},	357	},
252	);	358	);
		359
		360	# do something else, then wait for process exit
		361	$done->recv;
253		362
254	CONDITION VARIABLES	363	CONDITION VARIABLES
		364	If you are familiar with some event loops you will know that all of them
		365	require you to run some blocking "loop", "run" or similar function that
		366	will actively watch for new events and call your callbacks.
		367
		368	AnyEvent is different, it expects somebody else to run the event loop
		369	and will only block when necessary (usually when told by the user).
		370
		371	The instrument to do that is called a "condition variable", so called
		372	because they represent a condition that must become true.
		373
255	Condition variables can be created by calling the "AnyEvent->condvar"	374	Condition variables can be created by calling the "AnyEvent->condvar"
256	method without any arguments.	375	method, usually without arguments. The only argument pair allowed is
		376	"cb", which specifies a callback to be called when the condition
		377	variable becomes true.
257		378
258	A condition variable waits for a condition - precisely that the	379	After creation, the condition variable is "false" until it becomes
259	"->broadcast" method has been called.	380	"true" by calling the "send" method (or calling the condition variable
		381	as if it were a callback, read about the caveats in the description for
		382	the "->send" method).
260		383
261	They are very useful to signal that a condition has been fulfilled, for	384	Condition variables are similar to callbacks, except that you can
		385	optionally wait for them. They can also be called merge points - points
		386	in time where multiple outstanding events have been processed. And yet
		387	another way to call them is transactions - each condition variable can
		388	be used to represent a transaction, which finishes at some point and
		389	delivers a result.
		390
		391	Condition variables are very useful to signal that something has
262	example, if you write a module that does asynchronous http requests,	392	finished, for example, if you write a module that does asynchronous http
263	then a condition variable would be the ideal candidate to signal the	393	requests, then a condition variable would be the ideal candidate to
264	availability of results.	394	signal the availability of results. The user can either act when the
		395	callback is called or can synchronously "->recv" for the results.
265		396
266	You can also use condition variables to block your main program until an	397	You can also use them to simulate traditional event loops - for example,
267	event occurs - for example, you could "->wait" in your main program	398	you can block your main program until an event occurs - for example, you
268	until the user clicks the Quit button in your app, which would	399	could "->recv" in your main program until the user clicks the Quit
269	"->broadcast" the "quit" event.	400	button of your app, which would "->send" the "quit" event.
270		401
271	Note that condition variables recurse into the event loop - if you have	402	Note that condition variables recurse into the event loop - if you have
272	two pirces of code that call "->wait" in a round-robbin fashion, you	403	two pieces of code that call "->recv" in a round-robin fashion, you
273	lose. Therefore, condition variables are good to export to your caller,	404	lose. Therefore, condition variables are good to export to your caller,
274	but you should avoid making a blocking wait yourself, at least in	405	but you should avoid making a blocking wait yourself, at least in
275	callbacks, as this asks for trouble.	406	callbacks, as this asks for trouble.
276		407
277	This object has two methods:	408	Condition variables are represented by hash refs in perl, and the keys
		409	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		410	(it is often useful to build your own transaction class on top of
		411	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		412	it's "new" method in your own "new" method.
278		413
279	$cv->wait	414	There are two "sides" to a condition variable - the "producer side"
		415	which eventually calls "-> send", and the "consumer side", which waits
		416	for the send to occur.
		417
		418	Example: wait for a timer.
		419
		420	# wait till the result is ready
		421	my $result_ready = AnyEvent->condvar;
		422
		423	# do something such as adding a timer
		424	# or socket watcher the calls $result_ready->send
		425	# when the "result" is ready.
		426	# in this case, we simply use a timer:
		427	my $w = AnyEvent->timer (
		428	after => 1,
		429	cb => sub { $result_ready->send },
		430	);
		431
		432	# this "blocks" (while handling events) till the callback
		433	# calls send
		434	$result_ready->recv;
		435
		436	Example: wait for a timer, but take advantage of the fact that condition
		437	variables are also code references.
		438
		439	my $done = AnyEvent->condvar;
		440	my $delay = AnyEvent->timer (after => 5, cb => $done);
		441	$done->recv;
		442
		443	METHODS FOR PRODUCERS
		444	These methods should only be used by the producing side, i.e. the
		445	code/module that eventually sends the signal. Note that it is also the
		446	producer side which creates the condvar in most cases, but it isn't
		447	uncommon for the consumer to create it as well.
		448
		449	$cv->send (...)
		450	Flag the condition as ready - a running "->recv" and all further
		451	calls to "recv" will (eventually) return after this method has been
		452	called. If nobody is waiting the send will be remembered.
		453
		454	If a callback has been set on the condition variable, it is called
		455	immediately from within send.
		456
		457	Any arguments passed to the "send" call will be returned by all
		458	future "->recv" calls.
		459
		460	Condition variables are overloaded so one can call them directly (as
		461	a code reference). Calling them directly is the same as calling
		462	"send". Note, however, that many C-based event loops do not handle
		463	overloading, so as tempting as it may be, passing a condition
		464	variable instead of a callback does not work. Both the pure perl and
		465	EV loops support overloading, however, as well as all functions that
		466	use perl to invoke a callback (as in AnyEvent::Socket and
		467	AnyEvent::DNS for example).
		468
		469	$cv->croak ($error)
		470	Similar to send, but causes all call's to "->recv" to invoke
		471	"Carp::croak" with the given error message/object/scalar.
		472
		473	This can be used to signal any errors to the condition variable
		474	user/consumer.
		475
		476	$cv->begin ([group callback])
		477	$cv->end
		478	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		479
		480	These two methods can be used to combine many transactions/events
		481	into one. For example, a function that pings many hosts in parallel
		482	might want to use a condition variable for the whole process.
		483
		484	Every call to "->begin" will increment a counter, and every call to
		485	"->end" will decrement it. If the counter reaches 0 in "->end", the
		486	(last) callback passed to "begin" will be executed. That callback is
		487	supposed to call "->send", but that is not required. If no
		488	callback was set, "send" will be called without any arguments.
		489
		490	Let's clarify this with the ping example:
		491
		492	my $cv = AnyEvent->condvar;
		493
		494	my %result;
		495	$cv->begin (sub { $cv->send (\%result) });
		496
		497	for my $host (@list_of_hosts) {
		498	$cv->begin;
		499	ping_host_then_call_callback $host, sub {
		500	$result{$host} = ...;
		501	$cv->end;
		502	};
		503	}
		504
		505	$cv->end;
		506
		507	This code fragment supposedly pings a number of hosts and calls
		508	"send" after results for all then have have been gathered - in any
		509	order. To achieve this, the code issues a call to "begin" when it
		510	starts each ping request and calls "end" when it has received some
		511	result for it. Since "begin" and "end" only maintain a counter, the
		512	order in which results arrive is not relevant.
		513
		514	There is an additional bracketing call to "begin" and "end" outside
		515	the loop, which serves two important purposes: first, it sets the
		516	callback to be called once the counter reaches 0, and second, it
		517	ensures that "send" is called even when "no" hosts are being pinged
		518	(the loop doesn't execute once).
		519
		520	This is the general pattern when you "fan out" into multiple
		521	subrequests: use an outer "begin"/"end" pair to set the callback and
		522	ensure "end" is called at least once, and then, for each subrequest
		523	you start, call "begin" and for each subrequest you finish, call
		524	"end".
		525
		526	METHODS FOR CONSUMERS
		527	These methods should only be used by the consuming side, i.e. the code
		528	awaits the condition.
		529
		530	$cv->recv
280	Wait (blocking if necessary) until the "->broadcast" method has been	531	Wait (blocking if necessary) until the "->send" or "->croak" methods
281	called on c<$cv>, while servicing other watchers normally.	532	have been called on c<$cv>, while servicing other watchers normally.
282		533
283	You can only wait once on a condition - additional calls will return	534	You can only wait once on a condition - additional calls are valid
284	immediately.	535	but will return immediately.
		536
		537	If an error condition has been set by calling "->croak", then this
		538	function will call "croak".
		539
		540	In list context, all parameters passed to "send" will be returned,
		541	in scalar context only the first one will be returned.
285		542
286	Not all event models support a blocking wait - some die in that case	543	Not all event models support a blocking wait - some die in that case
287	(programs might want to do that to stay interactive), so *if you are	544	(programs might want to do that to stay interactive), so *if you are
288	using this from a module, never require a blocking wait*, but let	545	using this from a module, never require a blocking wait*, but let
289	the caller decide whether the call will block or not (for example,	546	the caller decide whether the call will block or not (for example,
290	by coupling condition variables with some kind of request results	547	by coupling condition variables with some kind of request results
291	and supporting callbacks so the caller knows that getting the result	548	and supporting callbacks so the caller knows that getting the result
292	will not block, while still suppporting blocking waits if the caller	549	will not block, while still supporting blocking waits if the caller
293	so desires).	550	so desires).
294		551
295	Another reason never to "->wait" in a module is that you cannot	552	Another reason never to "->recv" in a module is that you cannot
296	sensibly have two "->wait"'s in parallel, as that would require	553	sensibly have two "->recv"'s in parallel, as that would require
297	multiple interpreters or coroutines/threads, none of which	554	multiple interpreters or coroutines/threads, none of which
298	"AnyEvent" can supply (the coroutine-aware backends	555	"AnyEvent" can supply.
299	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
300	support concurrent "->wait"'s from different coroutines, however).
301		556
302	$cv->broadcast	557	The Coro module, however, can and does supply coroutines and, in
303	Flag the condition as ready - a running "->wait" and all further	558	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
304	calls to "wait" will (eventually) return after this method has been	559	versions and also integrates coroutines into AnyEvent, making
305	called. If nobody is waiting the broadcast will be remembered..	560	blocking "->recv" calls perfectly safe as long as they are done from
		561	another coroutine (one that doesn't run the event loop).
306		562
307	Example:	563	You can ensure that "-recv" never blocks by setting a callback and
		564	only calling "->recv" from within that callback (or at a later
		565	time). This will work even when the event loop does not support
		566	blocking waits otherwise.
308		567
309	# wait till the result is ready	568	$bool = $cv->ready
310	my $result_ready = AnyEvent->condvar;	569	Returns true when the condition is "true", i.e. whether "send" or
		570	"croak" have been called.
311		571
312	# do something such as adding a timer	572	$cb = $cv->cb ([new callback])
313	# or socket watcher the calls $result_ready->broadcast	573	This is a mutator function that returns the callback set and
314	# when the "result" is ready.	574	optionally replaces it before doing so.
315	# in this case, we simply use a timer:
316	my $w = AnyEvent->timer (
317	after => 1,
318	cb => sub { $result_ready->broadcast },
319	);
320		575
321	# this "blocks" (while handling events) till the watcher	576	The callback will be called when the condition becomes "true", i.e.
322	# calls broadcast	577	when "send" or "croak" are called, with the only argument being the
323	$result_ready->wait;	578	condition variable itself. Calling "recv" inside the callback or at
		579	any later time is guaranteed not to block.
324		580
325	GLOBAL VARIABLES AND FUNCTIONS	581	GLOBAL VARIABLES AND FUNCTIONS
326	$AnyEvent::MODEL	582	$AnyEvent::MODEL
327	Contains "undef" until the first watcher is being created. Then it	583	Contains "undef" until the first watcher is being created. Then it
328	contains the event model that is being used, which is the name of	584	contains the event model that is being used, which is the name of
…		…
330	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	586	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
331	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	587	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
332		588
333	The known classes so far are:	589	The known classes so far are:
334		590
335	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
336	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
337	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	591	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
338	AnyEvent::Impl::Event based on Event, also second best choice :)	592	AnyEvent::Impl::Event based on Event, second best choice.
		593	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
339	AnyEvent::Impl::Glib based on Glib, third-best choice.	594	AnyEvent::Impl::Glib based on Glib, third-best choice.
340	AnyEvent::Impl::Tk based on Tk, very bad choice.	595	AnyEvent::Impl::Tk based on Tk, very bad choice.
341	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	596	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		597	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		598	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		599
		600	There is no support for WxWidgets, as WxWidgets has no support for
		601	watching file handles. However, you can use WxWidgets through the
		602	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		603	second, which was considered to be too horrible to even consider for
		604	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
		605	using it's adaptor.
		606
		607	AnyEvent knows about Prima and Wx and will try to use POE when
		608	autodetecting them.
342		609
343	AnyEvent::detect	610	AnyEvent::detect
344	Returns $AnyEvent::MODEL, forcing autodetection of the event model	611	Returns $AnyEvent::MODEL, forcing autodetection of the event model
345	if necessary. You should only call this function right before you	612	if necessary. You should only call this function right before you
346	would have created an AnyEvent watcher anyway, that is, as late as	613	would have created an AnyEvent watcher anyway, that is, as late as
347	possible at runtime.	614	possible at runtime.
348		615
		616	$guard = AnyEvent::post_detect { BLOCK }
		617	Arranges for the code block to be executed as soon as the event
		618	model is autodetected (or immediately if this has already happened).
		619
		620	If called in scalar or list context, then it creates and returns an
		621	object that automatically removes the callback again when it is
		622	destroyed. See Coro::BDB for a case where this is useful.
		623
		624	@AnyEvent::post_detect
		625	If there are any code references in this array (you can "push" to it
		626	before or after loading AnyEvent), then they will called directly
		627	after the event loop has been chosen.
		628
		629	You should check $AnyEvent::MODEL before adding to this array,
		630	though: if it contains a true value then the event loop has already
		631	been detected, and the array will be ignored.
		632
		633	Best use "AnyEvent::post_detect { BLOCK }" instead.
		634
349	WHAT TO DO IN A MODULE	635	WHAT TO DO IN A MODULE
350	As a module author, you should "use AnyEvent" and call AnyEvent methods	636	As a module author, you should "use AnyEvent" and call AnyEvent methods
351	freely, but you should not load a specific event module or rely on it.	637	freely, but you should not load a specific event module or rely on it.
352		638
353	Be careful when you create watchers in the module body - AnyEvent will	639	Be careful when you create watchers in the module body - AnyEvent will
354	decide which event module to use as soon as the first method is called,	640	decide which event module to use as soon as the first method is called,
355	so by calling AnyEvent in your module body you force the user of your	641	so by calling AnyEvent in your module body you force the user of your
356	module to load the event module first.	642	module to load the event module first.
357		643
358	Never call "->wait" on a condition variable unless you know that the	644	Never call "->recv" on a condition variable unless you know that the
359	"->broadcast" method has been called on it already. This is because it	645	"->send" method has been called on it already. This is because it will
360	will stall the whole program, and the whole point of using events is to	646	stall the whole program, and the whole point of using events is to stay
361	stay interactive.	647	interactive.
362		648
363	It is fine, however, to call "->wait" when the user of your module	649	It is fine, however, to call "->recv" when the user of your module
364	requests it (i.e. if you create a http request object ad have a method	650	requests it (i.e. if you create a http request object ad have a method
365	called "results" that returns the results, it should call "->wait"	651	called "results" that returns the results, it should call "->recv"
366	freely, as the user of your module knows what she is doing. always).	652	freely, as the user of your module knows what she is doing. always).
367		653
368	WHAT TO DO IN THE MAIN PROGRAM	654	WHAT TO DO IN THE MAIN PROGRAM
369	There will always be a single main program - the only place that should	655	There will always be a single main program - the only place that should
370	dictate which event model to use.	656	dictate which event model to use.
…		…
372	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	658	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
373	do anything special (it does not need to be event-based) and let	659	do anything special (it does not need to be event-based) and let
374	AnyEvent decide which implementation to chose if some module relies on	660	AnyEvent decide which implementation to chose if some module relies on
375	it.	661	it.
376		662
377	If the main program relies on a specific event model. For example, in	663	If the main program relies on a specific event model - for example, in
378	Gtk2 programs you have to rely on the Glib module. You should load the	664	Gtk2 programs you have to rely on the Glib module - you should load the
379	event module before loading AnyEvent or any module that uses it:	665	event module before loading AnyEvent or any module that uses it:
380	generally speaking, you should load it as early as possible. The reason	666	generally speaking, you should load it as early as possible. The reason
381	is that modules might create watchers when they are loaded, and AnyEvent	667	is that modules might create watchers when they are loaded, and AnyEvent
382	will decide on the event model to use as soon as it creates watchers,	668	will decide on the event model to use as soon as it creates watchers,
383	and it might chose the wrong one unless you load the correct one	669	and it might chose the wrong one unless you load the correct one
384	yourself.	670	yourself.
385		671
386	You can chose to use a rather inefficient pure-perl implementation by	672	You can chose to use a pure-perl implementation by loading the
387	loading the "AnyEvent::Impl::Perl" module, which gives you similar	673	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
388	behaviour everywhere, but letting AnyEvent chose is generally better.	674	everywhere, but letting AnyEvent chose the model is generally better.
		675
		676	MAINLOOP EMULATION
		677	Sometimes (often for short test scripts, or even standalone programs who
		678	only want to use AnyEvent), you do not want to run a specific event
		679	loop.
		680
		681	In that case, you can use a condition variable like this:
		682
		683	AnyEvent->condvar->recv;
		684
		685	This has the effect of entering the event loop and looping forever.
		686
		687	Note that usually your program has some exit condition, in which case it
		688	is better to use the "traditional" approach of storing a condition
		689	variable somewhere, waiting for it, and sending it when the program
		690	should exit cleanly.
		691
		692	OTHER MODULES
		693	The following is a non-exhaustive list of additional modules that use
		694	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		695	in the same program. Some of the modules come with AnyEvent, some are
		696	available via CPAN.
		697
		698	AnyEvent::Util
		699	Contains various utility functions that replace often-used but
		700	blocking functions such as "inet_aton" by event-/callback-based
		701	versions.
		702
		703	AnyEvent::Socket
		704	Provides various utility functions for (internet protocol) sockets,
		705	addresses and name resolution. Also functions to create non-blocking
		706	tcp connections or tcp servers, with IPv6 and SRV record support and
		707	more.
		708
		709	AnyEvent::Handle
		710	Provide read and write buffers, manages watchers for reads and
		711	writes, supports raw and formatted I/O, I/O queued and fully
		712	transparent and non-blocking SSL/TLS.
		713
		714	AnyEvent::DNS
		715	Provides rich asynchronous DNS resolver capabilities.
		716
		717	AnyEvent::HTTP
		718	A simple-to-use HTTP library that is capable of making a lot of
		719	concurrent HTTP requests.
		720
		721	AnyEvent::HTTPD
		722	Provides a simple web application server framework.
		723
		724	AnyEvent::FastPing
		725	The fastest ping in the west.
		726
		727	AnyEvent::DBI
		728	Executes DBI requests asynchronously in a proxy process.
		729
		730	AnyEvent::AIO
		731	Truly asynchronous I/O, should be in the toolbox of every event
		732	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		733	together.
		734
		735	AnyEvent::BDB
		736	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		737	fuses BDB and AnyEvent together.
		738
		739	AnyEvent::GPSD
		740	A non-blocking interface to gpsd, a daemon delivering GPS
		741	information.
		742
		743	AnyEvent::IGS
		744	A non-blocking interface to the Internet Go Server protocol (used by
		745	App::IGS).
		746
		747	Net::IRC3
		748	AnyEvent based IRC client module family.
		749
		750	Net::XMPP2
		751	AnyEvent based XMPP (Jabber protocol) module family.
		752
		753	Net::FCP
		754	AnyEvent-based implementation of the Freenet Client Protocol,
		755	birthplace of AnyEvent.
		756
		757	Event::ExecFlow
		758	High level API for event-based execution flow control.
		759
		760	Coro
		761	Has special support for AnyEvent via Coro::AnyEvent.
		762
		763	IO::Lambda
		764	The lambda approach to I/O - don't ask, look there. Can use
		765	AnyEvent.
389		766
390	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	767	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
391	This is an advanced topic that you do not normally need to use AnyEvent	768	This is an advanced topic that you do not normally need to use AnyEvent
392	in a module. This section is only of use to event loop authors who want	769	in a module. This section is only of use to event loop authors who want
393	to provide AnyEvent compatibility.	770	to provide AnyEvent compatibility.
…		…
431	must not be done in an interactive application, so it makes sense.	808	must not be done in an interactive application, so it makes sense.
432		809
433	ENVIRONMENT VARIABLES	810	ENVIRONMENT VARIABLES
434	The following environment variables are used by this module:	811	The following environment variables are used by this module:
435		812
436	"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, cause AnyEvent to	813	"PERL_ANYEVENT_VERBOSE"
437	report to STDERR which event model it chooses.	814	By default, AnyEvent will be completely silent except in fatal
		815	conditions. You can set this environment variable to make AnyEvent
		816	more talkative.
		817
		818	When set to 1 or higher, causes AnyEvent to warn about unexpected
		819	conditions, such as not being able to load the event model specified
		820	by "PERL_ANYEVENT_MODEL".
		821
		822	When set to 2 or higher, cause AnyEvent to report to STDERR which
		823	event model it chooses.
		824
		825	"PERL_ANYEVENT_STRICT"
		826	AnyEvent does not do much argument checking by default, as thorough
		827	argument checking is very costly. Setting this variable to a true
		828	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		829	thoroughly check the arguments passed to most method calls. If it
		830	finds any problems it will croak.
		831
		832	In other words, enables "strict" mode.
		833
		834	Unlike "use strict" it is definitely recommended ot keep it off in
		835	production.
		836
		837	"PERL_ANYEVENT_MODEL"
		838	This can be used to specify the event model to be used by AnyEvent,
		839	before auto detection and -probing kicks in. It must be a string
		840	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		841	gets prepended and the resulting module name is loaded and if the
		842	load was successful, used as event model. If it fails to load
		843	AnyEvent will proceed with auto detection and -probing.
		844
		845	This functionality might change in future versions.
		846
		847	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		848	could start your program like this:
		849
		850	PERL_ANYEVENT_MODEL=Perl perl ...
		851
		852	"PERL_ANYEVENT_PROTOCOLS"
		853	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		854	preferences for IPv4 or IPv6. The default is unspecified (and might
		855	change, or be the result of auto probing).
		856
		857	Must be set to a comma-separated list of protocols or address
		858	families, current supported: "ipv4" and "ipv6". Only protocols
		859	mentioned will be used, and preference will be given to protocols
		860	mentioned earlier in the list.
		861
		862	This variable can effectively be used for denial-of-service attacks
		863	against local programs (e.g. when setuid), although the impact is
		864	likely small, as the program has to handle connection errors
		865	already-
		866
		867	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		868	IPv6, but support both and try to use both.
		869	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		870	resolve or contact IPv6 addresses.
		871	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		872	prefer IPv6 over IPv4.
		873
		874	"PERL_ANYEVENT_EDNS0"
		875	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		876	for DNS. This extension is generally useful to reduce DNS traffic,
		877	but some (broken) firewalls drop such DNS packets, which is why it
		878	is off by default.
		879
		880	Setting this variable to 1 will cause AnyEvent::DNS to announce
		881	EDNS0 in its DNS requests.
		882
		883	"PERL_ANYEVENT_MAX_FORKS"
		884	The maximum number of child processes that
		885	"AnyEvent::Util::fork_call" will create in parallel.
438		886
439	EXAMPLE PROGRAM	887	EXAMPLE PROGRAM
440	The following program uses an IO watcher to read data from STDIN, a	888	The following program uses an I/O watcher to read data from STDIN, a
441	timer to display a message once per second, and a condition variable to	889	timer to display a message once per second, and a condition variable to
442	quit the program when the user enters quit:	890	quit the program when the user enters quit:
443		891
444	use AnyEvent;	892	use AnyEvent;
445		893
…		…
450	poll => 'r',	898	poll => 'r',
451	cb => sub {	899	cb => sub {
452	warn "io event <$_[0]>\n"; # will always output <r>	900	warn "io event <$_[0]>\n"; # will always output <r>
453	chomp (my $input = <STDIN>); # read a line	901	chomp (my $input = <STDIN>); # read a line
454	warn "read: $input\n"; # output what has been read	902	warn "read: $input\n"; # output what has been read
455	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	903	$cv->send if $input =~ /^q/i; # quit program if /^q/i
456	},	904	},
457	);	905	);
458		906
459	my $time_watcher; # can only be used once	907	my $time_watcher; # can only be used once
460		908
…		…
465	});	913	});
466	}	914	}
467		915
468	new_timer; # create first timer	916	new_timer; # create first timer
469		917
470	$cv->wait; # wait until user enters /^q/i	918	$cv->recv; # wait until user enters /^q/i
471		919
472	REAL-WORLD EXAMPLE	920	REAL-WORLD EXAMPLE
473	Consider the Net::FCP module. It features (among others) the following	921	Consider the Net::FCP module. It features (among others) the following
474	API calls, which are to freenet what HTTP GET requests are to http:	922	API calls, which are to freenet what HTTP GET requests are to http:
475		923
…		…
524	syswrite $txn->{fh}, $txn->{request}	972	syswrite $txn->{fh}, $txn->{request}
525	or die "connection or write error";	973	or die "connection or write error";
526	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	974	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
527		975
528	Again, "fh_ready_r" waits till all data has arrived, and then stores the	976	Again, "fh_ready_r" waits till all data has arrived, and then stores the
529	result and signals any possible waiters that the request ahs finished:	977	result and signals any possible waiters that the request has finished:
530		978
531	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	979	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
532		980
533	if (end-of-file or data complete) {	981	if (end-of-file or data complete) {
534	$txn->{result} = $txn->{buf};	982	$txn->{result} = $txn->{buf};
535	$txn->{finished}->broadcast;	983	$txn->{finished}->send;
536	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	984	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
537	}	985	}
538		986
539	The "result" method, finally, just waits for the finished signal (if the	987	The "result" method, finally, just waits for the finished signal (if the
540	request was already finished, it doesn't wait, of course, and returns	988	request was already finished, it doesn't wait, of course, and returns
541	the data:	989	the data:
542		990
543	$txn->{finished}->wait;	991	$txn->{finished}->recv;
544	return $txn->{result};	992	return $txn->{result};
545		993
546	The actual code goes further and collects all errors ("die"s,	994	The actual code goes further and collects all errors ("die"s,
547	exceptions) that occured during request processing. The "result" method	995	exceptions) that occurred during request processing. The "result" method
548	detects whether an exception as thrown (it is stored inside the $txn	996	detects whether an exception as thrown (it is stored inside the $txn
549	object) and just throws the exception, which means connection errors and	997	object) and just throws the exception, which means connection errors and
550	other problems get reported tot he code that tries to use the result,	998	other problems get reported tot he code that tries to use the result,
551	not in a random callback.	999	not in a random callback.
552		1000
…		…
583		1031
584	my $quit = AnyEvent->condvar;	1032	my $quit = AnyEvent->condvar;
585		1033
586	$fcp->txn_client_get ($url)->cb (sub {	1034	$fcp->txn_client_get ($url)->cb (sub {
587	...	1035	...
588	$quit->broadcast;	1036	$quit->send;
589	});	1037	});
590		1038
591	$quit->wait;	1039	$quit->recv;
		1040
		1041	BENCHMARKS
		1042	To give you an idea of the performance and overheads that AnyEvent adds
		1043	over the event loops themselves and to give you an impression of the
		1044	speed of various event loops I prepared some benchmarks.
		1045
		1046	BENCHMARKING ANYEVENT OVERHEAD
		1047	Here is a benchmark of various supported event models used natively and
		1048	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1049	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1050	which it is), lets them fire exactly once and destroys them again.
		1051
		1052	Source code for this benchmark is found as eg/bench in the AnyEvent
		1053	distribution.
		1054
		1055	Explanation of the columns
		1056	watcher is the number of event watchers created/destroyed. Since
		1057	different event models feature vastly different performances, each event
		1058	loop was given a number of watchers so that overall runtime is
		1059	acceptable and similar between tested event loop (and keep them from
		1060	crashing): Glib would probably take thousands of years if asked to
		1061	process the same number of watchers as EV in this benchmark.
		1062
		1063	bytes is the number of bytes (as measured by the resident set size,
		1064	RSS) consumed by each watcher. This method of measuring captures both C
		1065	and Perl-based overheads.
		1066
		1067	create is the time, in microseconds (millionths of seconds), that it
		1068	takes to create a single watcher. The callback is a closure shared
		1069	between all watchers, to avoid adding memory overhead. That means
		1070	closure creation and memory usage is not included in the figures.
		1071
		1072	invoke is the time, in microseconds, used to invoke a simple callback.
		1073	The callback simply counts down a Perl variable and after it was invoked
		1074	"watcher" times, it would "->send" a condvar once to signal the end of
		1075	this phase.
		1076
		1077	destroy is the time, in microseconds, that it takes to destroy a
		1078	single watcher.
		1079
		1080	Results
		1081	name watchers bytes create invoke destroy comment
		1082	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1083	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1084	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1085	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1086	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1087	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1088	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1089	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1090	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1091	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1092
		1093	Discussion
		1094	The benchmark does not measure scalability of the event loop very
		1095	well. For example, a select-based event loop (such as the pure perl one)
		1096	can never compete with an event loop that uses epoll when the number of
		1097	file descriptors grows high. In this benchmark, all events become ready
		1098	at the same time, so select/poll-based implementations get an unnatural
		1099	speed boost.
		1100
		1101	Also, note that the number of watchers usually has a nonlinear effect on
		1102	overall speed, that is, creating twice as many watchers doesn't take
		1103	twice the time - usually it takes longer. This puts event loops tested
		1104	with a higher number of watchers at a disadvantage.
		1105
		1106	To put the range of results into perspective, consider that on the
		1107	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1108	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
		1109	CPU cycles with POE.
		1110
		1111	"EV" is the sole leader regarding speed and memory use, which are both
		1112	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1113	far less memory than any other event loop and is still faster than Event
		1114	natively.
		1115
		1116	The pure perl implementation is hit in a few sweet spots (both the
		1117	constant timeout and the use of a single fd hit optimisations in the
		1118	perl interpreter and the backend itself). Nevertheless this shows that
		1119	it adds very little overhead in itself. Like any select-based backend
		1120	its performance becomes really bad with lots of file descriptors (and
		1121	few of them active), of course, but this was not subject of this
		1122	benchmark.
		1123
		1124	The "Event" module has a relatively high setup and callback invocation
		1125	cost, but overall scores in on the third place.
		1126
		1127	"Glib"'s memory usage is quite a bit higher, but it features a faster
		1128	callback invocation and overall ends up in the same class as "Event".
		1129	However, Glib scales extremely badly, doubling the number of watchers
		1130	increases the processing time by more than a factor of four, making it
		1131	completely unusable when using larger numbers of watchers (note that
		1132	only a single file descriptor was used in the benchmark, so
		1133	inefficiencies of "poll" do not account for this).
		1134
		1135	The "Tk" adaptor works relatively well. The fact that it crashes with
		1136	more than 2000 watchers is a big setback, however, as correctness takes
		1137	precedence over speed. Nevertheless, its performance is surprising, as
		1138	the file descriptor is dup()ed for each watcher. This shows that the
		1139	dup() employed by some adaptors is not a big performance issue (it does
		1140	incur a hidden memory cost inside the kernel which is not reflected in
		1141	the figures above).
		1142
		1143	"POE", regardless of underlying event loop (whether using its pure perl
		1144	select-based backend or the Event module, the POE-EV backend couldn't be
		1145	tested because it wasn't working) shows abysmal performance and memory
		1146	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
		1147	watchers, and 10 times as much memory as Event (the high memory
		1148	requirements are caused by requiring a session for each watcher).
		1149	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1150	pure perl implementation.
		1151
		1152	The design of the POE adaptor class in AnyEvent can not really account
		1153	for the performance issues, though, as session creation overhead is
		1154	small compared to execution of the state machine, which is coded pretty
		1155	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1156	using multiple sessions is not a good approach, especially regarding
		1157	memory usage, even the author of POE could not come up with a faster
		1158	design).
		1159
		1160	Summary
		1161	* Using EV through AnyEvent is faster than any other event loop (even
		1162	when used without AnyEvent), but most event loops have acceptable
		1163	performance with or without AnyEvent.
		1164
		1165	* The overhead AnyEvent adds is usually much smaller than the overhead
		1166	of the actual event loop, only with extremely fast event loops such
		1167	as EV adds AnyEvent significant overhead.
		1168
		1169	* You should avoid POE like the plague if you want performance or
		1170	reasonable memory usage.
		1171
		1172	BENCHMARKING THE LARGE SERVER CASE
		1173	This benchmark actually benchmarks the event loop itself. It works by
		1174	creating a number of "servers": each server consists of a socket pair, a
		1175	timeout watcher that gets reset on activity (but never fires), and an
		1176	I/O watcher waiting for input on one side of the socket. Each time the
		1177	socket watcher reads a byte it will write that byte to a random other
		1178	"server".
		1179
		1180	The effect is that there will be a lot of I/O watchers, only part of
		1181	which are active at any one point (so there is a constant number of
		1182	active fds for each loop iteration, but which fds these are is random).
		1183	The timeout is reset each time something is read because that reflects
		1184	how most timeouts work (and puts extra pressure on the event loops).
		1185
		1186	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
		1187	100 (1%) are active. This mirrors the activity of large servers with
		1188	many connections, most of which are idle at any one point in time.
		1189
		1190	Source code for this benchmark is found as eg/bench2 in the AnyEvent
		1191	distribution.
		1192
		1193	Explanation of the columns
		1194	sockets is the number of sockets, and twice the number of "servers"
		1195	(as each server has a read and write socket end).
		1196
		1197	create is the time it takes to create a socket pair (which is
		1198	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1199
		1200	request, the most important value, is the time it takes to handle a
		1201	single "request", that is, reading the token from the pipe and
		1202	forwarding it to another server. This includes deleting the old timeout
		1203	and creating a new one that moves the timeout into the future.
		1204
		1205	Results
		1206	name sockets create request
		1207	EV 20000 69.01 11.16
		1208	Perl 20000 73.32 35.87
		1209	Event 20000 212.62 257.32
		1210	Glib 20000 651.16 1896.30
		1211	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1212
		1213	Discussion
		1214	This benchmark does measure scalability and overall performance of the
		1215	particular event loop.
		1216
		1217	EV is again fastest. Since it is using epoll on my system, the setup
		1218	time is relatively high, though.
		1219
		1220	Perl surprisingly comes second. It is much faster than the C-based event
		1221	loops Event and Glib.
		1222
		1223	Event suffers from high setup time as well (look at its code and you
		1224	will understand why). Callback invocation also has a high overhead
		1225	compared to the "$_->() for .."-style loop that the Perl event loop
		1226	uses. Event uses select or poll in basically all documented
		1227	configurations.
		1228
		1229	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1230	clearly fails to perform with many filehandles or in busy servers.
		1231
		1232	POE is still completely out of the picture, taking over 1000 times as
		1233	long as EV, and over 100 times as long as the Perl implementation, even
		1234	though it uses a C-based event loop in this case.
		1235
		1236	Summary
		1237	* The pure perl implementation performs extremely well.
		1238
		1239	* Avoid Glib or POE in large projects where performance matters.
		1240
		1241	BENCHMARKING SMALL SERVERS
		1242	While event loops should scale (and select-based ones do not...) even to
		1243	large servers, most programs we (or I :) actually write have only a few
		1244	I/O watchers.
		1245
		1246	In this benchmark, I use the same benchmark program as in the large
		1247	server case, but it uses only eight "servers", of which three are active
		1248	at any one time. This should reflect performance for a small server
		1249	relatively well.
		1250
		1251	The columns are identical to the previous table.
		1252
		1253	Results
		1254	name sockets create request
		1255	EV 16 20.00 6.54
		1256	Perl 16 25.75 12.62
		1257	Event 16 81.27 35.86
		1258	Glib 16 32.63 15.48
		1259	POE 16 261.87 276.28 uses POE::Loop::Event
		1260
		1261	Discussion
		1262	The benchmark tries to test the performance of a typical small server.
		1263	While knowing how various event loops perform is interesting, keep in
		1264	mind that their overhead in this case is usually not as important, due
		1265	to the small absolute number of watchers (that is, you need efficiency
		1266	and speed most when you have lots of watchers, not when you only have a
		1267	few of them).
		1268
		1269	EV is again fastest.
		1270
		1271	Perl again comes second. It is noticeably faster than the C-based event
		1272	loops Event and Glib, although the difference is too small to really
		1273	matter.
		1274
		1275	POE also performs much better in this case, but is is still far behind
		1276	the others.
		1277
		1278	Summary
		1279	* C-based event loops perform very well with small number of watchers,
		1280	as the management overhead dominates.
		1281
		1282	FORK
		1283	Most event libraries are not fork-safe. The ones who are usually are
		1284	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1285	Only EV is fully fork-aware.
		1286
		1287	If you have to fork, you must either do so before creating your first
		1288	watcher OR you must not use AnyEvent at all in the child.
		1289
		1290	SECURITY CONSIDERATIONS
		1291	AnyEvent can be forced to load any event model via
		1292	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
		1293	to execute arbitrary code or directly gain access, it can easily be used
		1294	to make the program hang or malfunction in subtle ways, as AnyEvent
		1295	watchers will not be active when the program uses a different event
		1296	model than specified in the variable.
		1297
		1298	You can make AnyEvent completely ignore this variable by deleting it
		1299	before the first watcher gets created, e.g. with a "BEGIN" block:
		1300
		1301	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1302
		1303	use AnyEvent;
		1304
		1305	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1306	be used to probe what backend is used and gain other information (which
		1307	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1308	and $ENV{PERL_ANYEGENT_STRICT}.
		1309
		1310	BUGS
		1311	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1312	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1313	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1314	annoying mamleaks, such as leaking on "map" and "grep" but it is usually
		1315	not as pronounced).
592		1316
593	SEE ALSO	1317	SEE ALSO
594	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1318	Utility functions: AnyEvent::Util.
595	Glib::Event, Glib, Coro, Tk.
596		1319
597	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1320	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
598	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1321	Event::Lib, Qt, POE.
		1322
		1323	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
599	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl.	1324	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
		1325	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
600		1326
		1327	Non-blocking file handles, sockets, TCP clients and servers:
		1328	AnyEvent::Handle, AnyEvent::Socket.
		1329
		1330	Asynchronous DNS: AnyEvent::DNS.
		1331
		1332	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1333
601	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1334	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
602		1335
603	AUTHOR	1336	AUTHOR
604	Marc Lehmann <schmorp@schmorp.de>	1337	Marc Lehmann <schmorp@schmorp.de>
605	http://home.schmorp.de/	1338	http://home.schmorp.de/
606		1339

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Revision 1.17 by root, Tue Apr 22 05:12:19 2008 UTC vs.
Revision 1.28 by root, Sat Jul 12 20:45:27 2008 UTC