[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.18 by root, Thu Apr 24 09:13:26 2008 UTC vs.
Revision 1.37 by root, Mon Apr 20 14:34:18 2009 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, Event::Lib, Qt -	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
5	various supported 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 { ... });
		11
		12	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		13	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		14
		15	print AnyEvent->now; # prints current event loop time
		16	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		17
		18	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		19
		20	my $w = AnyEvent->child (pid => $pid, cb => sub {
		21	my ($pid, $status) = @_;
11	...	22	...
12	});	23	});
13		24
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {
15	...
16	});
17
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	25	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		26	$w->send; # wake up current and all future recv's
19	$w->wait; # enters "main loop" till $condvar gets ->broadcast	27	$w->recv; # enters "main loop" till $condvar gets ->send
20	$w->broadcast; # wake up current and all future wait's	28	# use a condvar in callback mode:
		29	$w->cb (sub { $_[0]->recv });
		30
		31	INTRODUCTION/TUTORIAL
		32	This manpage is mainly a reference manual. If you are interested in a
		33	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		34	manpage.
21		35
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	36	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	37	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	38	nowadays. So what is different about AnyEvent?
25		39
26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	40	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
27	policy* and AnyEvent is small and efficient.	41	policy* and AnyEvent is small and efficient.
28		42
29	First and foremost, AnyEvent is not an event model itself, it only	43	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	44	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,	45	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,	46	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.	47	only one event loop can be active at the same time in a process.
34	AnyEvent helps hiding the differences between those event loops.	48	AnyEvent cannot change this, but it can hide the differences between
		49	those event loops.
35		50
36	The goal of AnyEvent is to offer module authors the ability to do event	51	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	52	programming (waiting for I/O or timer events) without subscribing to a
38	religion, a way of living, and most importantly: without forcing your	53	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	54	module users into the same thing by forcing them to use the same event
40	model you use.	55	model you use.
41		56
42	For modules like POE or IO::Async (which is a total misnomer as it is	57	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	58	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	59	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	60	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	61	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.	62	are also forced to use the same event loop you use.
48		63
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	64	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	65	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	66	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.	67	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	68	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	69	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	70	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).	71	to AnyEvent, too, so it is future-proof).
57		72
58	In addition to being free of having to use *the one and only true event	73	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	74	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	75	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	76	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	77	only offering the functionality that is necessary, in as thin as a
63	wrapper as technically possible.	78	wrapper as technically possible.
64		79
		80	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
		81	useful functionality, such as an asynchronous DNS resolver, 100%
		82	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		83	such as Windows) and lots of real-world knowledge and workarounds for
		84	platform bugs and differences.
		85
65	Of course, if you want lots of policy (this can arguably be somewhat	86	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	87	useful) and you want to force your users to use the one and only event
67	model, you should not use this module.	88	model, you should not use this module.
68		89
69	DESCRIPTION	90	DESCRIPTION
70	AnyEvent provides an identical interface to multiple event loops. This	91	AnyEvent provides an identical interface to multiple event loops. This
75	The interface itself is vaguely similar, but not identical to the Event	96	The interface itself is vaguely similar, but not identical to the Event
76	module.	97	module.
77		98
78	During the first call of any watcher-creation method, the module tries	99	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	100	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,	101	following modules is already loaded: EV, Event, Glib,
81	Glib, Tk, Event::Lib, Qt. The first one found is used. If none are	102	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82	found, the module tries to load these modules (excluding Event::Lib and	103	used. If none are found, the module tries to load these modules
83	Qt) in the order given. The first one that can be successfully loaded	104	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
84	will be used. If, after this, still none could be found, AnyEvent will	105	always succeed) in the order given. The first one that can be
85	fall back to a pure-perl event loop, which is not very efficient, but	106	successfully loaded will be used. If, after this, still none could be
86	should work everywhere.	107	found, AnyEvent will fall back to a pure-perl event loop, which is not
		108	very efficient, but should work everywhere.
87		109
88	Because AnyEvent first checks for modules that are already loaded,	110	Because AnyEvent first checks for modules that are already loaded,
89	loading an event model explicitly before first using AnyEvent will	111	loading an event model explicitly before first using AnyEvent will
90	likely make that model the default. For example:	112	likely make that model the default. For example:
91		113
…		…
98	starts using it, all bets are off. Maybe you should tell their authors	120	starts using it, all bets are off. Maybe you should tell their authors
99	to use AnyEvent so their modules work together with others seamlessly...	121	to use AnyEvent so their modules work together with others seamlessly...
100		122
101	The pure-perl implementation of AnyEvent is called	123	The pure-perl implementation of AnyEvent is called
102	"AnyEvent::Impl::Perl". Like other event modules you can load it	124	"AnyEvent::Impl::Perl". Like other event modules you can load it
103	explicitly.	125	explicitly and enjoy the high availability of that event loop :)
104		126
105	WATCHERS	127	WATCHERS
106	AnyEvent has the central concept of a watcher, which is an object that	128	AnyEvent has the central concept of a watcher, which is an object that
107	stores relevant data for each kind of event you are waiting for, such as	129	stores relevant data for each kind of event you are waiting for, such as
108	the callback to call, the filehandle to watch, etc.	130	the callback to call, the file handle to watch, etc.
109		131
110	These watchers are normal Perl objects with normal Perl lifetime. After	132	These watchers are normal Perl objects with normal Perl lifetime. After
111	creating a watcher it will immediately "watch" for events and invoke the	133	creating a watcher it will immediately "watch" for events and invoke the
112	callback when the event occurs (of course, only when the event model is	134	callback when the event occurs (of course, only when the event model is
113	in control).	135	in control).
114		136
		137	Note that callbacks must not permanently change global variables
		138	potentially in use by the event loop (such as $_ or $[) and that
		139	callbacks must not "die". The former is good programming practise in
		140	Perl and the latter stems from the fact that exception handling differs
		141	widely between event loops.
		142
115	To disable the watcher you have to destroy it (e.g. by setting the	143	To disable the watcher you have to destroy it (e.g. by setting the
116	variable you store it in to "undef" or otherwise deleting all references	144	variable you store it in to "undef" or otherwise deleting all references
117	to it).	145	to it).
118		146
119	All watchers are created by calling a method on the "AnyEvent" class.	147	All watchers are created by calling a method on the "AnyEvent" class.
…		…
121	Many watchers either are used with "recursion" (repeating timers for	149	Many watchers either are used with "recursion" (repeating timers for
122	example), or need to refer to their watcher object in other ways.	150	example), or need to refer to their watcher object in other ways.
123		151
124	An any way to achieve that is this pattern:	152	An any way to achieve that is this pattern:
125		153
126	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	154	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
127	# you can use $w here, for example to undef it	155	# you can use $w here, for example to undef it
128	undef $w;	156	undef $w;
129	});	157	});
130		158
131	Note that "my $w; $w =" combination. This is necessary because in Perl,	159	Note that "my $w; $w =" combination. This is necessary because in Perl,
132	my variables are only visible after the statement in which they are	160	my variables are only visible after the statement in which they are
133	declared.	161	declared.
134		162
135	IO WATCHERS	163	I/O WATCHERS
136	You can create an I/O watcher by calling the "AnyEvent->io" method with	164	You can create an I/O watcher by calling the "AnyEvent->io" method with
137	the following mandatory key-value pairs as arguments:	165	the following mandatory key-value pairs as arguments:
138		166
139	"fh" the Perl file handle (not file descriptor) to watch for events.	167	"fh" is the Perl file handle (not file descriptor) to watch for
		168	events (AnyEvent might or might not keep a reference to this file
		169	handle). Note that only file handles pointing to things for which
		170	non-blocking operation makes sense are allowed. This includes sockets,
		171	most character devices, pipes, fifos and so on, but not for example
		172	files or block devices.
		173
140	"poll" must be a string that is either "r" or "w", which creates a	174	"poll" must be a string that is either "r" or "w", which creates a
141	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	175	watcher waiting for "r"eadable or "w"ritable events, respectively.
		176
142	is the callback to invoke each time the file handle becomes ready.	177	"cb" is the callback to invoke each time the file handle becomes ready.
143		178
144	As long as the I/O watcher exists it will keep the file descriptor or a	179	Although the callback might get passed parameters, their value and
145	copy of it alive/open.	180	presence is undefined and you cannot rely on them. Portable AnyEvent
		181	callbacks cannot use arguments passed to I/O watcher callbacks.
146		182
		183	The I/O watcher might use the underlying file descriptor or a copy of
147	It is not allowed to close a file handle as long as any watcher is	184	it. You must not close a file handle as long as any watcher is active on
148	active on the underlying file descriptor.	185	the underlying file descriptor.
149		186
150	Some event loops issue spurious readyness notifications, so you should	187	Some event loops issue spurious readyness notifications, so you should
151	always use non-blocking calls when reading/writing from/to your file	188	always use non-blocking calls when reading/writing from/to your file
152	handles.	189	handles.
153		190
154	Example:
155
156	# wait for readability of STDIN, then read a line and disable the watcher	191	Example: wait for readability of STDIN, then read a line and disable the
		192	watcher.
		193
157	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	194	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
158	chomp (my $input = <STDIN>);	195	chomp (my $input = <STDIN>);
159	warn "read: $input\n";	196	warn "read: $input\n";
160	undef $w;	197	undef $w;
161	});	198	});
…		…
163	TIME WATCHERS	200	TIME WATCHERS
164	You can create a time watcher by calling the "AnyEvent->timer" method	201	You can create a time watcher by calling the "AnyEvent->timer" method
165	with the following mandatory arguments:	202	with the following mandatory arguments:
166		203
167	"after" specifies after how many seconds (fractional values are	204	"after" specifies after how many seconds (fractional values are
168	supported) should the timer activate. "cb" the callback to invoke in	205	supported) the callback should be invoked. "cb" is the callback to
169	that case.	206	invoke in that case.
170		207
171	The timer callback will be invoked at most once: if you want a repeating	208	Although the callback might get passed parameters, their value and
172	timer you have to create a new watcher (this is a limitation by both Tk	209	presence is undefined and you cannot rely on them. Portable AnyEvent
173	and Glib).	210	callbacks cannot use arguments passed to time watcher callbacks.
174		211
175	Example:	212	The callback will normally be invoked once only. If you specify another
		213	parameter, "interval", as a strictly positive number (> 0), then the
		214	callback will be invoked regularly at that interval (in fractional
		215	seconds) after the first invocation. If "interval" is specified with a
		216	false value, then it is treated as if it were missing.
176		217
		218	The callback will be rescheduled before invoking the callback, but no
		219	attempt is done to avoid timer drift in most backends, so the interval
		220	is only approximate.
		221
177	# fire an event after 7.7 seconds	222	Example: fire an event after 7.7 seconds.
		223
178	my $w = AnyEvent->timer (after => 7.7, cb => sub {	224	my $w = AnyEvent->timer (after => 7.7, cb => sub {
179	warn "timeout\n";	225	warn "timeout\n";
180	});	226	});
181		227
182	# to cancel the timer:	228	# to cancel the timer:
183	undef $w;	229	undef $w;
184		230
185	Example 2:
186
187	# fire an event after 0.5 seconds, then roughly every second	231	Example 2: fire an event after 0.5 seconds, then roughly every second.
188	my $w;
189		232
190	my $cb = sub {
191	# cancel the old timer while creating a new one
192	$w = AnyEvent->timer (after => 1, cb => $cb);	233	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		234	warn "timeout\n";
193	};	235	};
194
195	# start the "loop" by creating the first watcher
196	$w = AnyEvent->timer (after => 0.5, cb => $cb);
197		236
198	TIMING ISSUES	237	TIMING ISSUES
199	There are two ways to handle timers: based on real time (relative, "fire	238	There are two ways to handle timers: based on real time (relative, "fire
200	in 10 seconds") and based on wallclock time (absolute, "fire at 12	239	in 10 seconds") and based on wallclock time (absolute, "fire at 12
201	o'clock").	240	o'clock").
…		…
213	on wallclock time) timers.	252	on wallclock time) timers.
214		253
215	AnyEvent always prefers relative timers, if available, matching the	254	AnyEvent always prefers relative timers, if available, matching the
216	AnyEvent API.	255	AnyEvent API.
217		256
		257	AnyEvent has two additional methods that return the "current time":
		258
		259	AnyEvent->time
		260	This returns the "current wallclock time" as a fractional number of
		261	seconds since the Epoch (the same thing as "time" or
		262	"Time::HiRes::time" return, and the result is guaranteed to be
		263	compatible with those).
		264
		265	It progresses independently of any event loop processing, i.e. each
		266	call will check the system clock, which usually gets updated
		267	frequently.
		268
		269	AnyEvent->now
		270	This also returns the "current wallclock time", but unlike "time",
		271	above, this value might change only once per event loop iteration,
		272	depending on the event loop (most return the same time as "time",
		273	above). This is the time that AnyEvent's timers get scheduled
		274	against.
		275
		276	*In almost all cases (in all cases if you don't care), this is the
		277	function to call when you want to know the current time.*
		278
		279	This function is also often faster then "AnyEvent->time", and thus
		280	the preferred method if you want some timestamp (for example,
		281	AnyEvent::Handle uses this to update it's activity timeouts).
		282
		283	The rest of this section is only of relevance if you try to be very
		284	exact with your timing, you can skip it without bad conscience.
		285
		286	For a practical example of when these times differ, consider
		287	Event::Lib and EV and the following set-up:
		288
		289	The event loop is running and has just invoked one of your callback
		290	at time=500 (assume no other callbacks delay processing). In your
		291	callback, you wait a second by executing "sleep 1" (blocking the
		292	process for a second) and then (at time=501) you create a relative
		293	timer that fires after three seconds.
		294
		295	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		296	return 501, because that is the current time, and the timer will be
		297	scheduled to fire at time=504 (501 + 3).
		298
		299	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		300	but "AnyEvent->now" returns 500, as that is the time the last event
		301	processing phase started. With EV, your timer gets scheduled to run
		302	at time=503 (500 + 3).
		303
		304	In one sense, Event::Lib is more exact, as it uses the current time
		305	regardless of any delays introduced by event processing. However,
		306	most callbacks do not expect large delays in processing, so this
		307	causes a higher drift (and a lot more system calls to get the
		308	current time).
		309
		310	In another sense, EV is more exact, as your timer will be scheduled
		311	at the same time, regardless of how long event processing actually
		312	took.
		313
		314	In either case, if you care (and in most cases, you don't), then you
		315	can get whatever behaviour you want with any event loop, by taking
		316	the difference between "AnyEvent->time" and "AnyEvent->now" into
		317	account.
		318
		319	AnyEvent->now_update
		320	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		321	current time for each loop iteration (see the discussion of
		322	AnyEvent->now, above).
		323
		324	When a callback runs for a long time (or when the process sleeps),
		325	then this "current" time will differ substantially from the real
		326	time, which might affect timers and time-outs.
		327
		328	When this is the case, you can call this method, which will update
		329	the event loop's idea of "current time".
		330
		331	Note that updating the time might cause some events to be handled.
		332
218	SIGNAL WATCHERS	333	SIGNAL WATCHERS
219	You can watch for signals using a signal watcher, "signal" is the signal	334	You can watch for signals using a signal watcher, "signal" is the signal
220	name without any "SIG" prefix, "cb" is the Perl callback to be invoked	335	name in uppercase and without any "SIG" prefix, "cb" is the Perl
221	whenever a signal occurs.	336	callback to be invoked whenever a signal occurs.
222		337
		338	Although the callback might get passed parameters, their value and
		339	presence is undefined and you cannot rely on them. Portable AnyEvent
		340	callbacks cannot use arguments passed to signal watcher callbacks.
		341
223	Multiple signal occurances can be clumped together into one callback	342	Multiple signal occurrences can be clumped together into one callback
224	invocation, and callback invocation will be synchronous. synchronous	343	invocation, and callback invocation will be synchronous. Synchronous
225	means that it might take a while until the signal gets handled by the	344	means that it might take a while until the signal gets handled by the
226	process, but it is guarenteed not to interrupt any other callbacks.	345	process, but it is guaranteed not to interrupt any other callbacks.
227		346
228	The main advantage of using these watchers is that you can share a	347	The main advantage of using these watchers is that you can share a
229	signal between multiple watchers.	348	signal between multiple watchers.
230		349
231	This watcher might use %SIG, so programs overwriting those signals	350	This watcher might use %SIG, so programs overwriting those signals
…		…
237		356
238	CHILD PROCESS WATCHERS	357	CHILD PROCESS WATCHERS
239	You can also watch on a child process exit and catch its exit status.	358	You can also watch on a child process exit and catch its exit status.
240		359
241	The child process is specified by the "pid" argument (if set to 0, it	360	The child process is specified by the "pid" argument (if set to 0, it
242	watches for any child process exit). The watcher will trigger as often	361	watches for any child process exit). The watcher will triggered only
243	as status change for the child are received. This works by installing a	362	when the child process has finished and an exit status is available, not
244	signal handler for "SIGCHLD". The callback will be called with the pid	363	on any trace events (stopped/continued).
245	and exit status (as returned by waitpid).
246		364
247	Example: wait for pid 1333	365	The callback will be called with the pid and exit status (as returned by
		366	waitpid), so unlike other watcher types, you can rely on child watcher
		367	callback arguments.
248		368
		369	This watcher type works by installing a signal handler for "SIGCHLD",
		370	and since it cannot be shared, nothing else should use SIGCHLD or reap
		371	random child processes (waiting for specific child processes, e.g.
		372	inside "system", is just fine).
		373
		374	There is a slight catch to child watchers, however: you usually start
		375	them after the child process was created, and this means the process
		376	could have exited already (and no SIGCHLD will be sent anymore).
		377
		378	Not all event models handle this correctly (POE doesn't), but even for
		379	event models that do handle this correctly, they usually need to be
		380	loaded before the process exits (i.e. before you fork in the first
		381	place).
		382
		383	This means you cannot create a child watcher as the very first thing in
		384	an AnyEvent program, you have to create at least one watcher before
		385	you "fork" the child (alternatively, you can call "AnyEvent::detect").
		386
		387	Example: fork a process and wait for it
		388
		389	my $done = AnyEvent->condvar;
		390
		391	my $pid = fork or exit 5;
		392
249	my $w = AnyEvent->child (	393	my $w = AnyEvent->child (
250	pid => 1333,	394	pid => $pid,
251	cb => sub {	395	cb => sub {
252	my ($pid, $status) = @_;	396	my ($pid, $status) = @_;
253	warn "pid $pid exited with status $status";	397	warn "pid $pid exited with status $status";
		398	$done->send;
254	},	399	},
255	);	400	);
		401
		402	# do something else, then wait for process exit
		403	$done->recv;
256		404
257	CONDITION VARIABLES	405	CONDITION VARIABLES
		406	If you are familiar with some event loops you will know that all of them
		407	require you to run some blocking "loop", "run" or similar function that
		408	will actively watch for new events and call your callbacks.
		409
		410	AnyEvent is different, it expects somebody else to run the event loop
		411	and will only block when necessary (usually when told by the user).
		412
		413	The instrument to do that is called a "condition variable", so called
		414	because they represent a condition that must become true.
		415
258	Condition variables can be created by calling the "AnyEvent->condvar"	416	Condition variables can be created by calling the "AnyEvent->condvar"
259	method without any arguments.	417	method, usually without arguments. The only argument pair allowed is
260		418
261	A condition variable waits for a condition - precisely that the	419	"cb", which specifies a callback to be called when the condition
262	"->broadcast" method has been called.	420	variable becomes true, with the condition variable as the first argument
		421	(but not the results).
263		422
264	They are very useful to signal that a condition has been fulfilled, for	423	After creation, the condition variable is "false" until it becomes
		424	"true" by calling the "send" method (or calling the condition variable
		425	as if it were a callback, read about the caveats in the description for
		426	the "->send" method).
		427
		428	Condition variables are similar to callbacks, except that you can
		429	optionally wait for them. They can also be called merge points - points
		430	in time where multiple outstanding events have been processed. And yet
		431	another way to call them is transactions - each condition variable can
		432	be used to represent a transaction, which finishes at some point and
		433	delivers a result.
		434
		435	Condition variables are very useful to signal that something has
265	example, if you write a module that does asynchronous http requests,	436	finished, for example, if you write a module that does asynchronous http
266	then a condition variable would be the ideal candidate to signal the	437	requests, then a condition variable would be the ideal candidate to
267	availability of results.	438	signal the availability of results. The user can either act when the
		439	callback is called or can synchronously "->recv" for the results.
268		440
269	You can also use condition variables to block your main program until an	441	You can also use them to simulate traditional event loops - for example,
270	event occurs - for example, you could "->wait" in your main program	442	you can block your main program until an event occurs - for example, you
271	until the user clicks the Quit button in your app, which would	443	could "->recv" in your main program until the user clicks the Quit
272	"->broadcast" the "quit" event.	444	button of your app, which would "->send" the "quit" event.
273		445
274	Note that condition variables recurse into the event loop - if you have	446	Note that condition variables recurse into the event loop - if you have
275	two pirces of code that call "->wait" in a round-robbin fashion, you	447	two pieces of code that call "->recv" in a round-robin fashion, you
276	lose. Therefore, condition variables are good to export to your caller,	448	lose. Therefore, condition variables are good to export to your caller,
277	but you should avoid making a blocking wait yourself, at least in	449	but you should avoid making a blocking wait yourself, at least in
278	callbacks, as this asks for trouble.	450	callbacks, as this asks for trouble.
279		451
280	This object has two methods:	452	Condition variables are represented by hash refs in perl, and the keys
		453	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		454	(it is often useful to build your own transaction class on top of
		455	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		456	it's "new" method in your own "new" method.
281		457
282	$cv->wait	458	There are two "sides" to a condition variable - the "producer side"
		459	which eventually calls "-> send", and the "consumer side", which waits
		460	for the send to occur.
		461
		462	Example: wait for a timer.
		463
		464	# wait till the result is ready
		465	my $result_ready = AnyEvent->condvar;
		466
		467	# do something such as adding a timer
		468	# or socket watcher the calls $result_ready->send
		469	# when the "result" is ready.
		470	# in this case, we simply use a timer:
		471	my $w = AnyEvent->timer (
		472	after => 1,
		473	cb => sub { $result_ready->send },
		474	);
		475
		476	# this "blocks" (while handling events) till the callback
		477	# calls send
		478	$result_ready->recv;
		479
		480	Example: wait for a timer, but take advantage of the fact that condition
		481	variables are also code references.
		482
		483	my $done = AnyEvent->condvar;
		484	my $delay = AnyEvent->timer (after => 5, cb => $done);
		485	$done->recv;
		486
		487	Example: Imagine an API that returns a condvar and doesn't support
		488	callbacks. This is how you make a synchronous call, for example from the
		489	main program:
		490
		491	use AnyEvent::CouchDB;
		492
		493	...
		494
		495	my @info = $couchdb->info->recv;
		496
		497	And this is how you would just ste a callback to be called whenever the
		498	results are available:
		499
		500	$couchdb->info->cb (sub {
		501	my @info = $_[0]->recv;
		502	});
		503
		504	METHODS FOR PRODUCERS
		505	These methods should only be used by the producing side, i.e. the
		506	code/module that eventually sends the signal. Note that it is also the
		507	producer side which creates the condvar in most cases, but it isn't
		508	uncommon for the consumer to create it as well.
		509
		510	$cv->send (...)
		511	Flag the condition as ready - a running "->recv" and all further
		512	calls to "recv" will (eventually) return after this method has been
		513	called. If nobody is waiting the send will be remembered.
		514
		515	If a callback has been set on the condition variable, it is called
		516	immediately from within send.
		517
		518	Any arguments passed to the "send" call will be returned by all
		519	future "->recv" calls.
		520
		521	Condition variables are overloaded so one can call them directly (as
		522	a code reference). Calling them directly is the same as calling
		523	"send". Note, however, that many C-based event loops do not handle
		524	overloading, so as tempting as it may be, passing a condition
		525	variable instead of a callback does not work. Both the pure perl and
		526	EV loops support overloading, however, as well as all functions that
		527	use perl to invoke a callback (as in AnyEvent::Socket and
		528	AnyEvent::DNS for example).
		529
		530	$cv->croak ($error)
		531	Similar to send, but causes all call's to "->recv" to invoke
		532	"Carp::croak" with the given error message/object/scalar.
		533
		534	This can be used to signal any errors to the condition variable
		535	user/consumer.
		536
		537	$cv->begin ([group callback])
		538	$cv->end
		539	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		540
		541	These two methods can be used to combine many transactions/events
		542	into one. For example, a function that pings many hosts in parallel
		543	might want to use a condition variable for the whole process.
		544
		545	Every call to "->begin" will increment a counter, and every call to
		546	"->end" will decrement it. If the counter reaches 0 in "->end", the
		547	(last) callback passed to "begin" will be executed. That callback is
		548	supposed to call "->send", but that is not required. If no
		549	callback was set, "send" will be called without any arguments.
		550
		551	Let's clarify this with the ping example:
		552
		553	my $cv = AnyEvent->condvar;
		554
		555	my %result;
		556	$cv->begin (sub { $cv->send (\%result) });
		557
		558	for my $host (@list_of_hosts) {
		559	$cv->begin;
		560	ping_host_then_call_callback $host, sub {
		561	$result{$host} = ...;
		562	$cv->end;
		563	};
		564	}
		565
		566	$cv->end;
		567
		568	This code fragment supposedly pings a number of hosts and calls
		569	"send" after results for all then have have been gathered - in any
		570	order. To achieve this, the code issues a call to "begin" when it
		571	starts each ping request and calls "end" when it has received some
		572	result for it. Since "begin" and "end" only maintain a counter, the
		573	order in which results arrive is not relevant.
		574
		575	There is an additional bracketing call to "begin" and "end" outside
		576	the loop, which serves two important purposes: first, it sets the
		577	callback to be called once the counter reaches 0, and second, it
		578	ensures that "send" is called even when "no" hosts are being pinged
		579	(the loop doesn't execute once).
		580
		581	This is the general pattern when you "fan out" into multiple
		582	subrequests: use an outer "begin"/"end" pair to set the callback and
		583	ensure "end" is called at least once, and then, for each subrequest
		584	you start, call "begin" and for each subrequest you finish, call
		585	"end".
		586
		587	METHODS FOR CONSUMERS
		588	These methods should only be used by the consuming side, i.e. the code
		589	awaits the condition.
		590
		591	$cv->recv
283	Wait (blocking if necessary) until the "->broadcast" method has been	592	Wait (blocking if necessary) until the "->send" or "->croak" methods
284	called on c<$cv>, while servicing other watchers normally.	593	have been called on c<$cv>, while servicing other watchers normally.
285		594
286	You can only wait once on a condition - additional calls will return	595	You can only wait once on a condition - additional calls are valid
287	immediately.	596	but will return immediately.
		597
		598	If an error condition has been set by calling "->croak", then this
		599	function will call "croak".
		600
		601	In list context, all parameters passed to "send" will be returned,
		602	in scalar context only the first one will be returned.
288		603
289	Not all event models support a blocking wait - some die in that case	604	Not all event models support a blocking wait - some die in that case
290	(programs might want to do that to stay interactive), so *if you are	605	(programs might want to do that to stay interactive), so *if you are
291	using this from a module, never require a blocking wait*, but let	606	using this from a module, never require a blocking wait*, but let
292	the caller decide whether the call will block or not (for example,	607	the caller decide whether the call will block or not (for example,
293	by coupling condition variables with some kind of request results	608	by coupling condition variables with some kind of request results
294	and supporting callbacks so the caller knows that getting the result	609	and supporting callbacks so the caller knows that getting the result
295	will not block, while still suppporting blocking waits if the caller	610	will not block, while still supporting blocking waits if the caller
296	so desires).	611	so desires).
297		612
298	Another reason never to "->wait" in a module is that you cannot	613	Another reason never to "->recv" in a module is that you cannot
299	sensibly have two "->wait"'s in parallel, as that would require	614	sensibly have two "->recv"'s in parallel, as that would require
300	multiple interpreters or coroutines/threads, none of which	615	multiple interpreters or coroutines/threads, none of which
301	"AnyEvent" can supply (the coroutine-aware backends	616	"AnyEvent" can supply.
302	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
303	support concurrent "->wait"'s from different coroutines, however).
304		617
305	$cv->broadcast	618	The Coro module, however, can and does supply coroutines and, in
306	Flag the condition as ready - a running "->wait" and all further	619	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
307	calls to "wait" will (eventually) return after this method has been	620	versions and also integrates coroutines into AnyEvent, making
308	called. If nobody is waiting the broadcast will be remembered..	621	blocking "->recv" calls perfectly safe as long as they are done from
		622	another coroutine (one that doesn't run the event loop).
309		623
310	Example:	624	You can ensure that "-recv" never blocks by setting a callback and
		625	only calling "->recv" from within that callback (or at a later
		626	time). This will work even when the event loop does not support
		627	blocking waits otherwise.
311		628
312	# wait till the result is ready	629	$bool = $cv->ready
313	my $result_ready = AnyEvent->condvar;	630	Returns true when the condition is "true", i.e. whether "send" or
		631	"croak" have been called.
314		632
315	# do something such as adding a timer	633	$cb = $cv->cb ($cb->($cv))
316	# or socket watcher the calls $result_ready->broadcast	634	This is a mutator function that returns the callback set and
317	# when the "result" is ready.	635	optionally replaces it before doing so.
318	# in this case, we simply use a timer:
319	my $w = AnyEvent->timer (
320	after => 1,
321	cb => sub { $result_ready->broadcast },
322	);
323		636
324	# this "blocks" (while handling events) till the watcher	637	The callback will be called when the condition becomes "true", i.e.
325	# calls broadcast	638	when "send" or "croak" are called, with the only argument being the
326	$result_ready->wait;	639	condition variable itself. Calling "recv" inside the callback or at
		640	any later time is guaranteed not to block.
327		641
328	GLOBAL VARIABLES AND FUNCTIONS	642	GLOBAL VARIABLES AND FUNCTIONS
329	$AnyEvent::MODEL	643	$AnyEvent::MODEL
330	Contains "undef" until the first watcher is being created. Then it	644	Contains "undef" until the first watcher is being created. Then it
331	contains the event model that is being used, which is the name of	645	contains the event model that is being used, which is the name of
…		…
333	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	647	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
334	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	648	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
335		649
336	The known classes so far are:	650	The known classes so far are:
337		651
338	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
339	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
340	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	652	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
341	AnyEvent::Impl::Event based on Event, second best choice.	653	AnyEvent::Impl::Event based on Event, second best choice.
		654	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
342	AnyEvent::Impl::Glib based on Glib, third-best choice.	655	AnyEvent::Impl::Glib based on Glib, third-best choice.
343	AnyEvent::Impl::Tk based on Tk, very bad choice.	656	AnyEvent::Impl::Tk based on Tk, very bad choice.
344	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
345	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).	657	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
346	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	658	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		659	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		660
		661	There is no support for WxWidgets, as WxWidgets has no support for
		662	watching file handles. However, you can use WxWidgets through the
		663	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		664	second, which was considered to be too horrible to even consider for
		665	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
		666	using it's adaptor.
		667
		668	AnyEvent knows about Prima and Wx and will try to use POE when
		669	autodetecting them.
347		670
348	AnyEvent::detect	671	AnyEvent::detect
349	Returns $AnyEvent::MODEL, forcing autodetection of the event model	672	Returns $AnyEvent::MODEL, forcing autodetection of the event model
350	if necessary. You should only call this function right before you	673	if necessary. You should only call this function right before you
351	would have created an AnyEvent watcher anyway, that is, as late as	674	would have created an AnyEvent watcher anyway, that is, as late as
352	possible at runtime.	675	possible at runtime.
353		676
		677	$guard = AnyEvent::post_detect { BLOCK }
		678	Arranges for the code block to be executed as soon as the event
		679	model is autodetected (or immediately if this has already happened).
		680
		681	If called in scalar or list context, then it creates and returns an
		682	object that automatically removes the callback again when it is
		683	destroyed. See Coro::BDB for a case where this is useful.
		684
		685	@AnyEvent::post_detect
		686	If there are any code references in this array (you can "push" to it
		687	before or after loading AnyEvent), then they will called directly
		688	after the event loop has been chosen.
		689
		690	You should check $AnyEvent::MODEL before adding to this array,
		691	though: if it contains a true value then the event loop has already
		692	been detected, and the array will be ignored.
		693
		694	Best use "AnyEvent::post_detect { BLOCK }" instead.
		695
354	WHAT TO DO IN A MODULE	696	WHAT TO DO IN A MODULE
355	As a module author, you should "use AnyEvent" and call AnyEvent methods	697	As a module author, you should "use AnyEvent" and call AnyEvent methods
356	freely, but you should not load a specific event module or rely on it.	698	freely, but you should not load a specific event module or rely on it.
357		699
358	Be careful when you create watchers in the module body - AnyEvent will	700	Be careful when you create watchers in the module body - AnyEvent will
359	decide which event module to use as soon as the first method is called,	701	decide which event module to use as soon as the first method is called,
360	so by calling AnyEvent in your module body you force the user of your	702	so by calling AnyEvent in your module body you force the user of your
361	module to load the event module first.	703	module to load the event module first.
362		704
363	Never call "->wait" on a condition variable unless you know that the	705	Never call "->recv" on a condition variable unless you know that the
364	"->broadcast" method has been called on it already. This is because it	706	"->send" method has been called on it already. This is because it will
365	will stall the whole program, and the whole point of using events is to	707	stall the whole program, and the whole point of using events is to stay
366	stay interactive.	708	interactive.
367		709
368	It is fine, however, to call "->wait" when the user of your module	710	It is fine, however, to call "->recv" when the user of your module
369	requests it (i.e. if you create a http request object ad have a method	711	requests it (i.e. if you create a http request object ad have a method
370	called "results" that returns the results, it should call "->wait"	712	called "results" that returns the results, it should call "->recv"
371	freely, as the user of your module knows what she is doing. always).	713	freely, as the user of your module knows what she is doing. always).
372		714
373	WHAT TO DO IN THE MAIN PROGRAM	715	WHAT TO DO IN THE MAIN PROGRAM
374	There will always be a single main program - the only place that should	716	There will always be a single main program - the only place that should
375	dictate which event model to use.	717	dictate which event model to use.
…		…
377	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	719	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
378	do anything special (it does not need to be event-based) and let	720	do anything special (it does not need to be event-based) and let
379	AnyEvent decide which implementation to chose if some module relies on	721	AnyEvent decide which implementation to chose if some module relies on
380	it.	722	it.
381		723
382	If the main program relies on a specific event model. For example, in	724	If the main program relies on a specific event model - for example, in
383	Gtk2 programs you have to rely on the Glib module. You should load the	725	Gtk2 programs you have to rely on the Glib module - you should load the
384	event module before loading AnyEvent or any module that uses it:	726	event module before loading AnyEvent or any module that uses it:
385	generally speaking, you should load it as early as possible. The reason	727	generally speaking, you should load it as early as possible. The reason
386	is that modules might create watchers when they are loaded, and AnyEvent	728	is that modules might create watchers when they are loaded, and AnyEvent
387	will decide on the event model to use as soon as it creates watchers,	729	will decide on the event model to use as soon as it creates watchers,
388	and it might chose the wrong one unless you load the correct one	730	and it might chose the wrong one unless you load the correct one
389	yourself.	731	yourself.
390		732
391	You can chose to use a rather inefficient pure-perl implementation by	733	You can chose to use a pure-perl implementation by loading the
392	loading the "AnyEvent::Impl::Perl" module, which gives you similar	734	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
393	behaviour everywhere, but letting AnyEvent chose is generally better.	735	everywhere, but letting AnyEvent chose the model is generally better.
		736
		737	MAINLOOP EMULATION
		738	Sometimes (often for short test scripts, or even standalone programs who
		739	only want to use AnyEvent), you do not want to run a specific event
		740	loop.
		741
		742	In that case, you can use a condition variable like this:
		743
		744	AnyEvent->condvar->recv;
		745
		746	This has the effect of entering the event loop and looping forever.
		747
		748	Note that usually your program has some exit condition, in which case it
		749	is better to use the "traditional" approach of storing a condition
		750	variable somewhere, waiting for it, and sending it when the program
		751	should exit cleanly.
		752
		753	OTHER MODULES
		754	The following is a non-exhaustive list of additional modules that use
		755	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		756	in the same program. Some of the modules come with AnyEvent, some are
		757	available via CPAN.
		758
		759	AnyEvent::Util
		760	Contains various utility functions that replace often-used but
		761	blocking functions such as "inet_aton" by event-/callback-based
		762	versions.
		763
		764	AnyEvent::Socket
		765	Provides various utility functions for (internet protocol) sockets,
		766	addresses and name resolution. Also functions to create non-blocking
		767	tcp connections or tcp servers, with IPv6 and SRV record support and
		768	more.
		769
		770	AnyEvent::Handle
		771	Provide read and write buffers, manages watchers for reads and
		772	writes, supports raw and formatted I/O, I/O queued and fully
		773	transparent and non-blocking SSL/TLS.
		774
		775	AnyEvent::DNS
		776	Provides rich asynchronous DNS resolver capabilities.
		777
		778	AnyEvent::HTTP
		779	A simple-to-use HTTP library that is capable of making a lot of
		780	concurrent HTTP requests.
		781
		782	AnyEvent::HTTPD
		783	Provides a simple web application server framework.
		784
		785	AnyEvent::FastPing
		786	The fastest ping in the west.
		787
		788	AnyEvent::DBI
		789	Executes DBI requests asynchronously in a proxy process.
		790
		791	AnyEvent::AIO
		792	Truly asynchronous I/O, should be in the toolbox of every event
		793	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		794	together.
		795
		796	AnyEvent::BDB
		797	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		798	fuses BDB and AnyEvent together.
		799
		800	AnyEvent::GPSD
		801	A non-blocking interface to gpsd, a daemon delivering GPS
		802	information.
		803
		804	AnyEvent::IGS
		805	A non-blocking interface to the Internet Go Server protocol (used by
		806	App::IGS).
		807
		808	AnyEvent::IRC
		809	AnyEvent based IRC client module family (replacing the older
		810	Net::IRC3).
		811
		812	Net::XMPP2
		813	AnyEvent based XMPP (Jabber protocol) module family.
		814
		815	Net::FCP
		816	AnyEvent-based implementation of the Freenet Client Protocol,
		817	birthplace of AnyEvent.
		818
		819	Event::ExecFlow
		820	High level API for event-based execution flow control.
		821
		822	Coro
		823	Has special support for AnyEvent via Coro::AnyEvent.
		824
		825	IO::Lambda
		826	The lambda approach to I/O - don't ask, look there. Can use
		827	AnyEvent.
		828
		829	ERROR AND EXCEPTION HANDLING
		830	In general, AnyEvent does not do any error handling - it relies on the
		831	caller to do that if required. The AnyEvent::Strict module (see also the
		832	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		833	checking of all AnyEvent methods, however, which is highly useful during
		834	development.
		835
		836	As for exception handling (i.e. runtime errors and exceptions thrown
		837	while executing a callback), this is not only highly event-loop
		838	specific, but also not in any way wrapped by this module, as this is the
		839	job of the main program.
		840
		841	The pure perl event loop simply re-throws the exception (usually within
		842	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		843	Glib uses "install_exception_handler" and so on.
		844
		845	ENVIRONMENT VARIABLES
		846	The following environment variables are used by this module or its
		847	submodules:
		848
		849	"PERL_ANYEVENT_VERBOSE"
		850	By default, AnyEvent will be completely silent except in fatal
		851	conditions. You can set this environment variable to make AnyEvent
		852	more talkative.
		853
		854	When set to 1 or higher, causes AnyEvent to warn about unexpected
		855	conditions, such as not being able to load the event model specified
		856	by "PERL_ANYEVENT_MODEL".
		857
		858	When set to 2 or higher, cause AnyEvent to report to STDERR which
		859	event model it chooses.
		860
		861	"PERL_ANYEVENT_STRICT"
		862	AnyEvent does not do much argument checking by default, as thorough
		863	argument checking is very costly. Setting this variable to a true
		864	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		865	thoroughly check the arguments passed to most method calls. If it
		866	finds any problems it will croak.
		867
		868	In other words, enables "strict" mode.
		869
		870	Unlike "use strict", it is definitely recommended ot keep it off in
		871	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment
		872	while developing programs can be very useful, however.
		873
		874	"PERL_ANYEVENT_MODEL"
		875	This can be used to specify the event model to be used by AnyEvent,
		876	before auto detection and -probing kicks in. It must be a string
		877	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		878	gets prepended and the resulting module name is loaded and if the
		879	load was successful, used as event model. If it fails to load
		880	AnyEvent will proceed with auto detection and -probing.
		881
		882	This functionality might change in future versions.
		883
		884	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		885	could start your program like this:
		886
		887	PERL_ANYEVENT_MODEL=Perl perl ...
		888
		889	"PERL_ANYEVENT_PROTOCOLS"
		890	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		891	preferences for IPv4 or IPv6. The default is unspecified (and might
		892	change, or be the result of auto probing).
		893
		894	Must be set to a comma-separated list of protocols or address
		895	families, current supported: "ipv4" and "ipv6". Only protocols
		896	mentioned will be used, and preference will be given to protocols
		897	mentioned earlier in the list.
		898
		899	This variable can effectively be used for denial-of-service attacks
		900	against local programs (e.g. when setuid), although the impact is
		901	likely small, as the program has to handle conenction and other
		902	failures anyways.
		903
		904	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		905	IPv6, but support both and try to use both.
		906	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		907	resolve or contact IPv6 addresses.
		908	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		909	prefer IPv6 over IPv4.
		910
		911	"PERL_ANYEVENT_EDNS0"
		912	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		913	for DNS. This extension is generally useful to reduce DNS traffic,
		914	but some (broken) firewalls drop such DNS packets, which is why it
		915	is off by default.
		916
		917	Setting this variable to 1 will cause AnyEvent::DNS to announce
		918	EDNS0 in its DNS requests.
		919
		920	"PERL_ANYEVENT_MAX_FORKS"
		921	The maximum number of child processes that
		922	"AnyEvent::Util::fork_call" will create in parallel.
394		923
395	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	924	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
396	This is an advanced topic that you do not normally need to use AnyEvent	925	This is an advanced topic that you do not normally need to use AnyEvent
397	in a module. This section is only of use to event loop authors who want	926	in a module. This section is only of use to event loop authors who want
398	to provide AnyEvent compatibility.	927	to provide AnyEvent compatibility.
…		…
433	rxvt-unicode also cheats a bit by not providing blocking access to	962	rxvt-unicode also cheats a bit by not providing blocking access to
434	condition variables: code blocking while waiting for a condition will	963	condition variables: code blocking while waiting for a condition will
435	"die". This still works with most modules/usages, and blocking calls	964	"die". This still works with most modules/usages, and blocking calls
436	must not be done in an interactive application, so it makes sense.	965	must not be done in an interactive application, so it makes sense.
437		966
438	ENVIRONMENT VARIABLES
439	The following environment variables are used by this module:
440
441	"PERL_ANYEVENT_VERBOSE"
442	When set to 2 or higher, cause AnyEvent to report to STDERR which
443	event model it chooses.
444
445	"PERL_ANYEVENT_MODEL"
446	This can be used to specify the event model to be used by AnyEvent,
447	before autodetection and -probing kicks in. It must be a string
448	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
449	gets prepended and the resulting module name is loaded and if the
450	load was successful, used as event model. If it fails to load
451	AnyEvent will proceed with autodetection and -probing.
452
453	This functionality might change in future versions.
454
455	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
456	could start your program like this:
457
458	PERL_ANYEVENT_MODEL=Perl perl ...
459
460	EXAMPLE PROGRAM	967	EXAMPLE PROGRAM
461	The following program uses an IO watcher to read data from STDIN, a	968	The following program uses an I/O watcher to read data from STDIN, a
462	timer to display a message once per second, and a condition variable to	969	timer to display a message once per second, and a condition variable to
463	quit the program when the user enters quit:	970	quit the program when the user enters quit:
464		971
465	use AnyEvent;	972	use AnyEvent;
466		973
…		…
471	poll => 'r',	978	poll => 'r',
472	cb => sub {	979	cb => sub {
473	warn "io event <$_[0]>\n"; # will always output <r>	980	warn "io event <$_[0]>\n"; # will always output <r>
474	chomp (my $input = <STDIN>); # read a line	981	chomp (my $input = <STDIN>); # read a line
475	warn "read: $input\n"; # output what has been read	982	warn "read: $input\n"; # output what has been read
476	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	983	$cv->send if $input =~ /^q/i; # quit program if /^q/i
477	},	984	},
478	);	985	);
479		986
480	my $time_watcher; # can only be used once	987	my $time_watcher; # can only be used once
481		988
…		…
486	});	993	});
487	}	994	}
488		995
489	new_timer; # create first timer	996	new_timer; # create first timer
490		997
491	$cv->wait; # wait until user enters /^q/i	998	$cv->recv; # wait until user enters /^q/i
492		999
493	REAL-WORLD EXAMPLE	1000	REAL-WORLD EXAMPLE
494	Consider the Net::FCP module. It features (among others) the following	1001	Consider the Net::FCP module. It features (among others) the following
495	API calls, which are to freenet what HTTP GET requests are to http:	1002	API calls, which are to freenet what HTTP GET requests are to http:
496		1003
…		…
545	syswrite $txn->{fh}, $txn->{request}	1052	syswrite $txn->{fh}, $txn->{request}
546	or die "connection or write error";	1053	or die "connection or write error";
547	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1054	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
548		1055
549	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1056	Again, "fh_ready_r" waits till all data has arrived, and then stores the
550	result and signals any possible waiters that the request ahs finished:	1057	result and signals any possible waiters that the request has finished:
551		1058
552	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1059	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
553		1060
554	if (end-of-file or data complete) {	1061	if (end-of-file or data complete) {
555	$txn->{result} = $txn->{buf};	1062	$txn->{result} = $txn->{buf};
556	$txn->{finished}->broadcast;	1063	$txn->{finished}->send;
557	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1064	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
558	}	1065	}
559		1066
560	The "result" method, finally, just waits for the finished signal (if the	1067	The "result" method, finally, just waits for the finished signal (if the
561	request was already finished, it doesn't wait, of course, and returns	1068	request was already finished, it doesn't wait, of course, and returns
562	the data:	1069	the data:
563		1070
564	$txn->{finished}->wait;	1071	$txn->{finished}->recv;
565	return $txn->{result};	1072	return $txn->{result};
566		1073
567	The actual code goes further and collects all errors ("die"s,	1074	The actual code goes further and collects all errors ("die"s,
568	exceptions) that occured during request processing. The "result" method	1075	exceptions) that occurred during request processing. The "result" method
569	detects whether an exception as thrown (it is stored inside the $txn	1076	detects whether an exception as thrown (it is stored inside the $txn
570	object) and just throws the exception, which means connection errors and	1077	object) and just throws the exception, which means connection errors and
571	other problems get reported tot he code that tries to use the result,	1078	other problems get reported tot he code that tries to use the result,
572	not in a random callback.	1079	not in a random callback.
573		1080
…		…
604		1111
605	my $quit = AnyEvent->condvar;	1112	my $quit = AnyEvent->condvar;
606		1113
607	$fcp->txn_client_get ($url)->cb (sub {	1114	$fcp->txn_client_get ($url)->cb (sub {
608	...	1115	...
609	$quit->broadcast;	1116	$quit->send;
610	});	1117	});
611		1118
612	$quit->wait;	1119	$quit->recv;
		1120
		1121	BENCHMARKS
		1122	To give you an idea of the performance and overheads that AnyEvent adds
		1123	over the event loops themselves and to give you an impression of the
		1124	speed of various event loops I prepared some benchmarks.
		1125
		1126	BENCHMARKING ANYEVENT OVERHEAD
		1127	Here is a benchmark of various supported event models used natively and
		1128	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1129	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1130	which it is), lets them fire exactly once and destroys them again.
		1131
		1132	Source code for this benchmark is found as eg/bench in the AnyEvent
		1133	distribution.
		1134
		1135	Explanation of the columns
		1136	watcher is the number of event watchers created/destroyed. Since
		1137	different event models feature vastly different performances, each event
		1138	loop was given a number of watchers so that overall runtime is
		1139	acceptable and similar between tested event loop (and keep them from
		1140	crashing): Glib would probably take thousands of years if asked to
		1141	process the same number of watchers as EV in this benchmark.
		1142
		1143	bytes is the number of bytes (as measured by the resident set size,
		1144	RSS) consumed by each watcher. This method of measuring captures both C
		1145	and Perl-based overheads.
		1146
		1147	create is the time, in microseconds (millionths of seconds), that it
		1148	takes to create a single watcher. The callback is a closure shared
		1149	between all watchers, to avoid adding memory overhead. That means
		1150	closure creation and memory usage is not included in the figures.
		1151
		1152	invoke is the time, in microseconds, used to invoke a simple callback.
		1153	The callback simply counts down a Perl variable and after it was invoked
		1154	"watcher" times, it would "->send" a condvar once to signal the end of
		1155	this phase.
		1156
		1157	destroy is the time, in microseconds, that it takes to destroy a
		1158	single watcher.
		1159
		1160	Results
		1161	name watchers bytes create invoke destroy comment
		1162	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1163	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1164	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1165	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1166	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1167	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1168	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1169	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1170	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1171	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1172
		1173	Discussion
		1174	The benchmark does not measure scalability of the event loop very
		1175	well. For example, a select-based event loop (such as the pure perl one)
		1176	can never compete with an event loop that uses epoll when the number of
		1177	file descriptors grows high. In this benchmark, all events become ready
		1178	at the same time, so select/poll-based implementations get an unnatural
		1179	speed boost.
		1180
		1181	Also, note that the number of watchers usually has a nonlinear effect on
		1182	overall speed, that is, creating twice as many watchers doesn't take
		1183	twice the time - usually it takes longer. This puts event loops tested
		1184	with a higher number of watchers at a disadvantage.
		1185
		1186	To put the range of results into perspective, consider that on the
		1187	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1188	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
		1189	CPU cycles with POE.
		1190
		1191	"EV" is the sole leader regarding speed and memory use, which are both
		1192	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1193	far less memory than any other event loop and is still faster than Event
		1194	natively.
		1195
		1196	The pure perl implementation is hit in a few sweet spots (both the
		1197	constant timeout and the use of a single fd hit optimisations in the
		1198	perl interpreter and the backend itself). Nevertheless this shows that
		1199	it adds very little overhead in itself. Like any select-based backend
		1200	its performance becomes really bad with lots of file descriptors (and
		1201	few of them active), of course, but this was not subject of this
		1202	benchmark.
		1203
		1204	The "Event" module has a relatively high setup and callback invocation
		1205	cost, but overall scores in on the third place.
		1206
		1207	"Glib"'s memory usage is quite a bit higher, but it features a faster
		1208	callback invocation and overall ends up in the same class as "Event".
		1209	However, Glib scales extremely badly, doubling the number of watchers
		1210	increases the processing time by more than a factor of four, making it
		1211	completely unusable when using larger numbers of watchers (note that
		1212	only a single file descriptor was used in the benchmark, so
		1213	inefficiencies of "poll" do not account for this).
		1214
		1215	The "Tk" adaptor works relatively well. The fact that it crashes with
		1216	more than 2000 watchers is a big setback, however, as correctness takes
		1217	precedence over speed. Nevertheless, its performance is surprising, as
		1218	the file descriptor is dup()ed for each watcher. This shows that the
		1219	dup() employed by some adaptors is not a big performance issue (it does
		1220	incur a hidden memory cost inside the kernel which is not reflected in
		1221	the figures above).
		1222
		1223	"POE", regardless of underlying event loop (whether using its pure perl
		1224	select-based backend or the Event module, the POE-EV backend couldn't be
		1225	tested because it wasn't working) shows abysmal performance and memory
		1226	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
		1227	watchers, and 10 times as much memory as Event (the high memory
		1228	requirements are caused by requiring a session for each watcher).
		1229	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1230	pure perl implementation.
		1231
		1232	The design of the POE adaptor class in AnyEvent can not really account
		1233	for the performance issues, though, as session creation overhead is
		1234	small compared to execution of the state machine, which is coded pretty
		1235	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1236	using multiple sessions is not a good approach, especially regarding
		1237	memory usage, even the author of POE could not come up with a faster
		1238	design).
		1239
		1240	Summary
		1241	* Using EV through AnyEvent is faster than any other event loop (even
		1242	when used without AnyEvent), but most event loops have acceptable
		1243	performance with or without AnyEvent.
		1244
		1245	* The overhead AnyEvent adds is usually much smaller than the overhead
		1246	of the actual event loop, only with extremely fast event loops such
		1247	as EV adds AnyEvent significant overhead.
		1248
		1249	* You should avoid POE like the plague if you want performance or
		1250	reasonable memory usage.
		1251
		1252	BENCHMARKING THE LARGE SERVER CASE
		1253	This benchmark actually benchmarks the event loop itself. It works by
		1254	creating a number of "servers": each server consists of a socket pair, a
		1255	timeout watcher that gets reset on activity (but never fires), and an
		1256	I/O watcher waiting for input on one side of the socket. Each time the
		1257	socket watcher reads a byte it will write that byte to a random other
		1258	"server".
		1259
		1260	The effect is that there will be a lot of I/O watchers, only part of
		1261	which are active at any one point (so there is a constant number of
		1262	active fds for each loop iteration, but which fds these are is random).
		1263	The timeout is reset each time something is read because that reflects
		1264	how most timeouts work (and puts extra pressure on the event loops).
		1265
		1266	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
		1267	100 (1%) are active. This mirrors the activity of large servers with
		1268	many connections, most of which are idle at any one point in time.
		1269
		1270	Source code for this benchmark is found as eg/bench2 in the AnyEvent
		1271	distribution.
		1272
		1273	Explanation of the columns
		1274	sockets is the number of sockets, and twice the number of "servers"
		1275	(as each server has a read and write socket end).
		1276
		1277	create is the time it takes to create a socket pair (which is
		1278	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1279
		1280	request, the most important value, is the time it takes to handle a
		1281	single "request", that is, reading the token from the pipe and
		1282	forwarding it to another server. This includes deleting the old timeout
		1283	and creating a new one that moves the timeout into the future.
		1284
		1285	Results
		1286	name sockets create request
		1287	EV 20000 69.01 11.16
		1288	Perl 20000 73.32 35.87
		1289	Event 20000 212.62 257.32
		1290	Glib 20000 651.16 1896.30
		1291	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1292
		1293	Discussion
		1294	This benchmark does measure scalability and overall performance of the
		1295	particular event loop.
		1296
		1297	EV is again fastest. Since it is using epoll on my system, the setup
		1298	time is relatively high, though.
		1299
		1300	Perl surprisingly comes second. It is much faster than the C-based event
		1301	loops Event and Glib.
		1302
		1303	Event suffers from high setup time as well (look at its code and you
		1304	will understand why). Callback invocation also has a high overhead
		1305	compared to the "$_->() for .."-style loop that the Perl event loop
		1306	uses. Event uses select or poll in basically all documented
		1307	configurations.
		1308
		1309	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1310	clearly fails to perform with many filehandles or in busy servers.
		1311
		1312	POE is still completely out of the picture, taking over 1000 times as
		1313	long as EV, and over 100 times as long as the Perl implementation, even
		1314	though it uses a C-based event loop in this case.
		1315
		1316	Summary
		1317	* The pure perl implementation performs extremely well.
		1318
		1319	* Avoid Glib or POE in large projects where performance matters.
		1320
		1321	BENCHMARKING SMALL SERVERS
		1322	While event loops should scale (and select-based ones do not...) even to
		1323	large servers, most programs we (or I :) actually write have only a few
		1324	I/O watchers.
		1325
		1326	In this benchmark, I use the same benchmark program as in the large
		1327	server case, but it uses only eight "servers", of which three are active
		1328	at any one time. This should reflect performance for a small server
		1329	relatively well.
		1330
		1331	The columns are identical to the previous table.
		1332
		1333	Results
		1334	name sockets create request
		1335	EV 16 20.00 6.54
		1336	Perl 16 25.75 12.62
		1337	Event 16 81.27 35.86
		1338	Glib 16 32.63 15.48
		1339	POE 16 261.87 276.28 uses POE::Loop::Event
		1340
		1341	Discussion
		1342	The benchmark tries to test the performance of a typical small server.
		1343	While knowing how various event loops perform is interesting, keep in
		1344	mind that their overhead in this case is usually not as important, due
		1345	to the small absolute number of watchers (that is, you need efficiency
		1346	and speed most when you have lots of watchers, not when you only have a
		1347	few of them).
		1348
		1349	EV is again fastest.
		1350
		1351	Perl again comes second. It is noticeably faster than the C-based event
		1352	loops Event and Glib, although the difference is too small to really
		1353	matter.
		1354
		1355	POE also performs much better in this case, but is is still far behind
		1356	the others.
		1357
		1358	Summary
		1359	* C-based event loops perform very well with small number of watchers,
		1360	as the management overhead dominates.
		1361
		1362	SIGNALS
		1363	AnyEvent currently installs handlers for these signals:
		1364
		1365	SIGCHLD
		1366	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1367	emulation for event loops that do not support them natively. Also,
		1368	some event loops install a similar handler.
		1369
		1370	SIGPIPE
		1371	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1372	"undef" when AnyEvent gets loaded.
		1373
		1374	The rationale for this is that AnyEvent users usually do not really
		1375	depend on SIGPIPE delivery (which is purely an optimisation for
		1376	shell use, or badly-written programs), but "SIGPIPE" can cause
		1377	spurious and rare program exits as a lot of people do not expect
		1378	"SIGPIPE" when writing to some random socket.
		1379
		1380	The rationale for installing a no-op handler as opposed to ignoring
		1381	it is that this way, the handler will be restored to defaults on
		1382	exec.
		1383
		1384	Feel free to install your own handler, or reset it to defaults.
613		1385
614	FORK	1386	FORK
615	Most event libraries are not fork-safe. The ones who are usually are	1387	Most event libraries are not fork-safe. The ones who are usually are
616	because they are so inefficient. Only EV is fully fork-aware.	1388	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1389	Only EV is fully fork-aware.
617		1390
618	If you have to fork, you must either do so before creating your first	1391	If you have to fork, you must either do so before creating your first
619	watcher OR you must not use AnyEvent at all in the child.	1392	watcher OR you must not use AnyEvent at all in the child.
620		1393
621	SECURITY CONSIDERATIONS	1394	SECURITY CONSIDERATIONS
…		…
627	model than specified in the variable.	1400	model than specified in the variable.
628		1401
629	You can make AnyEvent completely ignore this variable by deleting it	1402	You can make AnyEvent completely ignore this variable by deleting it
630	before the first watcher gets created, e.g. with a "BEGIN" block:	1403	before the first watcher gets created, e.g. with a "BEGIN" block:
631		1404
632	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1405	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
633		1406
634	use AnyEvent;	1407	use AnyEvent;
		1408
		1409	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1410	be used to probe what backend is used and gain other information (which
		1411	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1412	and $ENV{PERL_ANYEGENT_STRICT}.
		1413
		1414	BUGS
		1415	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1416	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1417	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1418	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1419	not as pronounced).
635		1420
636	SEE ALSO	1421	SEE ALSO
637	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1422	Utility functions: AnyEvent::Util.
638	Glib::Event, Glib, Coro, Tk, Event::Lib, Qt.
639		1423
640	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1424	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
641	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1425	Event::Lib, Qt, POE.
642	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib,
643	AnyEvent::Impl::Qt.
644		1426
		1427	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
		1428	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
		1429	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
		1430
		1431	Non-blocking file handles, sockets, TCP clients and servers:
		1432	AnyEvent::Handle, AnyEvent::Socket.
		1433
		1434	Asynchronous DNS: AnyEvent::DNS.
		1435
		1436	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1437
645	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1438	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
646		1439
647	AUTHOR	1440	AUTHOR
648	Marc Lehmann <schmorp@schmorp.de>	1441	Marc Lehmann <schmorp@schmorp.de>
649	http://home.schmorp.de/	1442	http://home.schmorp.de/
650		1443

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing AnyEvent/README (file contents): Revision 1.18 by root, Thu Apr 24 09:13:26 2008 UTC vs. Revision 1.37 by root, Mon Apr 20 14:34:18 2009 UTC

Diff Legend

Comparing AnyEvent/README (file contents):
Revision 1.18 by root, Thu Apr 24 09:13:26 2008 UTC vs.
Revision 1.37 by root, Mon Apr 20 14:34:18 2009 UTC