[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs.
Revision 1.32 by root, Fri Oct 3 07:19:23 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, Event::Lib, Qt, POE -	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, AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found	102	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82	is used. If none are found, the module tries to load these modules	103	used. If none are found, the module tries to load these modules
83	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	104	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
84	always succeed) in the order given. The first one that can be	105	always succeed) in the order given. The first one that can be
85	successfully loaded will be used. If, after this, still none could be	106	successfully loaded will be used. If, after this, still none could be
86	found, AnyEvent will fall back to a pure-perl event loop, which is not	107	found, AnyEvent will fall back to a pure-perl event loop, which is not
87	very efficient, but should work everywhere.	108	very efficient, but should work everywhere.
…		…
99	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
100	to use AnyEvent so their modules work together with others seamlessly...	121	to use AnyEvent so their modules work together with others seamlessly...
101		122
102	The pure-perl implementation of AnyEvent is called	123	The pure-perl implementation of AnyEvent is called
103	"AnyEvent::Impl::Perl". Like other event modules you can load it	124	"AnyEvent::Impl::Perl". Like other event modules you can load it
104	explicitly.	125	explicitly and enjoy the high availability of that event loop :)
105		126
106	WATCHERS	127	WATCHERS
107	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
108	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
109	the callback to call, the filehandle to watch, etc.	130	the callback to call, the file handle to watch, etc.
110		131
111	These watchers are normal Perl objects with normal Perl lifetime. After	132	These watchers are normal Perl objects with normal Perl lifetime. After
112	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
113	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
114	in control).	135	in control).
…		…
122	Many watchers either are used with "recursion" (repeating timers for	143	Many watchers either are used with "recursion" (repeating timers for
123	example), or need to refer to their watcher object in other ways.	144	example), or need to refer to their watcher object in other ways.
124		145
125	An any way to achieve that is this pattern:	146	An any way to achieve that is this pattern:
126		147
127	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	148	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
128	# you can use $w here, for example to undef it	149	# you can use $w here, for example to undef it
129	undef $w;	150	undef $w;
130	});	151	});
131		152
132	Note that "my $w; $w =" combination. This is necessary because in Perl,	153	Note that "my $w; $w =" combination. This is necessary because in Perl,
133	my variables are only visible after the statement in which they are	154	my variables are only visible after the statement in which they are
134	declared.	155	declared.
135		156
136	I/O WATCHERS	157	I/O WATCHERS
137	You can create an I/O watcher by calling the "AnyEvent->io" method with	158	You can create an I/O watcher by calling the "AnyEvent->io" method with
138	the following mandatory key-value pairs as arguments:	159	the following mandatory key-value pairs as arguments:
139		160
140	"fh" the Perl file handle (not file descriptor) to watch for events.	161	"fh" the Perl file handle (not file descriptor) to watch for events
		162	(AnyEvent might or might not keep a reference to this file handle).
141	"poll" must be a string that is either "r" or "w", which creates a	163	"poll" must be a string that is either "r" or "w", which creates a
142	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	164	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
143	is the callback to invoke each time the file handle becomes ready.	165	is the callback to invoke each time the file handle becomes ready.
144		166
145	Although the callback might get passed parameters, their value and	167	Although the callback might get passed parameters, their value and
…		…
152		174
153	Some event loops issue spurious readyness notifications, so you should	175	Some event loops issue spurious readyness notifications, so you should
154	always use non-blocking calls when reading/writing from/to your file	176	always use non-blocking calls when reading/writing from/to your file
155	handles.	177	handles.
156		178
157	Example:
158
159	# wait for readability of STDIN, then read a line and disable the watcher	179	Example: wait for readability of STDIN, then read a line and disable the
		180	watcher.
		181
160	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	182	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
161	chomp (my $input = <STDIN>);	183	chomp (my $input = <STDIN>);
162	warn "read: $input\n";	184	warn "read: $input\n";
163	undef $w;	185	undef $w;
164	});	186	});
…		…
173		195
174	Although the callback might get passed parameters, their value and	196	Although the callback might get passed parameters, their value and
175	presence is undefined and you cannot rely on them. Portable AnyEvent	197	presence is undefined and you cannot rely on them. Portable AnyEvent
176	callbacks cannot use arguments passed to time watcher callbacks.	198	callbacks cannot use arguments passed to time watcher callbacks.
177		199
178	The timer callback will be invoked at most once: if you want a repeating	200	The callback will normally be invoked once only. If you specify another
179	timer you have to create a new watcher (this is a limitation by both Tk	201	parameter, "interval", as a strictly positive number (> 0), then the
180	and Glib).	202	callback will be invoked regularly at that interval (in fractional
		203	seconds) after the first invocation. If "interval" is specified with a
		204	false value, then it is treated as if it were missing.
181		205
182	Example:	206	The callback will be rescheduled before invoking the callback, but no
		207	attempt is done to avoid timer drift in most backends, so the interval
		208	is only approximate.
183		209
184	# fire an event after 7.7 seconds	210	Example: fire an event after 7.7 seconds.
		211
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	212	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	213	warn "timeout\n";
187	});	214	});
188		215
189	# to cancel the timer:	216	# to cancel the timer:
190	undef $w;	217	undef $w;
191		218
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	219	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		220
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	221	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		222	warn "timeout\n";
200	};	223	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		224
205	TIMING ISSUES	225	TIMING ISSUES
206	There are two ways to handle timers: based on real time (relative, "fire	226	There are two ways to handle timers: based on real time (relative, "fire
207	in 10 seconds") and based on wallclock time (absolute, "fire at 12	227	in 10 seconds") and based on wallclock time (absolute, "fire at 12
208	o'clock").	228	o'clock").
…		…
220	on wallclock time) timers.	240	on wallclock time) timers.
221		241
222	AnyEvent always prefers relative timers, if available, matching the	242	AnyEvent always prefers relative timers, if available, matching the
223	AnyEvent API.	243	AnyEvent API.
224		244
		245	AnyEvent has two additional methods that return the "current time":
		246
		247	AnyEvent->time
		248	This returns the "current wallclock time" as a fractional number of
		249	seconds since the Epoch (the same thing as "time" or
		250	"Time::HiRes::time" return, and the result is guaranteed to be
		251	compatible with those).
		252
		253	It progresses independently of any event loop processing, i.e. each
		254	call will check the system clock, which usually gets updated
		255	frequently.
		256
		257	AnyEvent->now
		258	This also returns the "current wallclock time", but unlike "time",
		259	above, this value might change only once per event loop iteration,
		260	depending on the event loop (most return the same time as "time",
		261	above). This is the time that AnyEvent's timers get scheduled
		262	against.
		263
		264	*In almost all cases (in all cases if you don't care), this is the
		265	function to call when you want to know the current time.*
		266
		267	This function is also often faster then "AnyEvent->time", and thus
		268	the preferred method if you want some timestamp (for example,
		269	AnyEvent::Handle uses this to update it's activity timeouts).
		270
		271	The rest of this section is only of relevance if you try to be very
		272	exact with your timing, you can skip it without bad conscience.
		273
		274	For a practical example of when these times differ, consider
		275	Event::Lib and EV and the following set-up:
		276
		277	The event loop is running and has just invoked one of your callback
		278	at time=500 (assume no other callbacks delay processing). In your
		279	callback, you wait a second by executing "sleep 1" (blocking the
		280	process for a second) and then (at time=501) you create a relative
		281	timer that fires after three seconds.
		282
		283	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		284	return 501, because that is the current time, and the timer will be
		285	scheduled to fire at time=504 (501 + 3).
		286
		287	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		288	but "AnyEvent->now" returns 500, as that is the time the last event
		289	processing phase started. With EV, your timer gets scheduled to run
		290	at time=503 (500 + 3).
		291
		292	In one sense, Event::Lib is more exact, as it uses the current time
		293	regardless of any delays introduced by event processing. However,
		294	most callbacks do not expect large delays in processing, so this
		295	causes a higher drift (and a lot more system calls to get the
		296	current time).
		297
		298	In another sense, EV is more exact, as your timer will be scheduled
		299	at the same time, regardless of how long event processing actually
		300	took.
		301
		302	In either case, if you care (and in most cases, you don't), then you
		303	can get whatever behaviour you want with any event loop, by taking
		304	the difference between "AnyEvent->time" and "AnyEvent->now" into
		305	account.
		306
225	SIGNAL WATCHERS	307	SIGNAL WATCHERS
226	You can watch for signals using a signal watcher, "signal" is the signal	308	You can watch for signals using a signal watcher, "signal" is the signal
227	name without any "SIG" prefix, "cb" is the Perl callback to be invoked	309	name in uppercase and without any "SIG" prefix, "cb" is the Perl
228	whenever a signal occurs.	310	callback to be invoked whenever a signal occurs.
229		311
230	Although the callback might get passed parameters, their value and	312	Although the callback might get passed parameters, their value and
231	presence is undefined and you cannot rely on them. Portable AnyEvent	313	presence is undefined and you cannot rely on them. Portable AnyEvent
232	callbacks cannot use arguments passed to signal watcher callbacks.	314	callbacks cannot use arguments passed to signal watcher callbacks.
233		315
234	Multiple signal occurances can be clumped together into one callback	316	Multiple signal occurrences can be clumped together into one callback
235	invocation, and callback invocation will be synchronous. synchronous	317	invocation, and callback invocation will be synchronous. Synchronous
236	means that it might take a while until the signal gets handled by the	318	means that it might take a while until the signal gets handled by the
237	process, but it is guarenteed not to interrupt any other callbacks.	319	process, but it is guaranteed not to interrupt any other callbacks.
238		320
239	The main advantage of using these watchers is that you can share a	321	The main advantage of using these watchers is that you can share a
240	signal between multiple watchers.	322	signal between multiple watchers.
241		323
242	This watcher might use %SIG, so programs overwriting those signals	324	This watcher might use %SIG, so programs overwriting those signals
…		…
248		330
249	CHILD PROCESS WATCHERS	331	CHILD PROCESS WATCHERS
250	You can also watch on a child process exit and catch its exit status.	332	You can also watch on a child process exit and catch its exit status.
251		333
252	The child process is specified by the "pid" argument (if set to 0, it	334	The child process is specified by the "pid" argument (if set to 0, it
253	watches for any child process exit). The watcher will trigger as often	335	watches for any child process exit). The watcher will triggered only
254	as status change for the child are received. This works by installing a	336	when the child process has finished and an exit status is available, not
255	signal handler for "SIGCHLD". The callback will be called with the pid	337	on any trace events (stopped/continued).
256	and exit status (as returned by waitpid), so unlike other watcher types,	338
257	you can rely on child watcher callback arguments.	339	The callback will be called with the pid and exit status (as returned by
		340	waitpid), so unlike other watcher types, you can rely on child watcher
		341	callback arguments.
		342
		343	This watcher type works by installing a signal handler for "SIGCHLD",
		344	and since it cannot be shared, nothing else should use SIGCHLD or reap
		345	random child processes (waiting for specific child processes, e.g.
		346	inside "system", is just fine).
258		347
259	There is a slight catch to child watchers, however: you usually start	348	There is a slight catch to child watchers, however: you usually start
260	them after the child process was created, and this means the process	349	them after the child process was created, and this means the process
261	could have exited already (and no SIGCHLD will be sent anymore).	350	could have exited already (and no SIGCHLD will be sent anymore).
262		351
…		…
269	an AnyEvent program, you have to create at least one watcher before	358	an AnyEvent program, you have to create at least one watcher before
270	you "fork" the child (alternatively, you can call "AnyEvent::detect").	359	you "fork" the child (alternatively, you can call "AnyEvent::detect").
271		360
272	Example: fork a process and wait for it	361	Example: fork a process and wait for it
273		362
274	my $done = AnyEvent->condvar;	363	my $done = AnyEvent->condvar;
275		364
276	AnyEvent::detect; # force event module to be initialised
277
278	my $pid = fork or exit 5;	365	my $pid = fork or exit 5;
279		366
280	my $w = AnyEvent->child (	367	my $w = AnyEvent->child (
281	pid => $pid,	368	pid => $pid,
282	cb => sub {	369	cb => sub {
283	my ($pid, $status) = @_;	370	my ($pid, $status) = @_;
284	warn "pid $pid exited with status $status";	371	warn "pid $pid exited with status $status";
285	$done->broadcast;	372	$done->send;
286	},	373	},
287	);	374	);
288		375
289	# do something else, then wait for process exit	376	# do something else, then wait for process exit
290	$done->wait;	377	$done->recv;
291		378
292	CONDITION VARIABLES	379	CONDITION VARIABLES
		380	If you are familiar with some event loops you will know that all of them
		381	require you to run some blocking "loop", "run" or similar function that
		382	will actively watch for new events and call your callbacks.
		383
		384	AnyEvent is different, it expects somebody else to run the event loop
		385	and will only block when necessary (usually when told by the user).
		386
		387	The instrument to do that is called a "condition variable", so called
		388	because they represent a condition that must become true.
		389
293	Condition variables can be created by calling the "AnyEvent->condvar"	390	Condition variables can be created by calling the "AnyEvent->condvar"
294	method without any arguments.	391	method, usually without arguments. The only argument pair allowed is
295		392
296	A condition variable waits for a condition - precisely that the	393	"cb", which specifies a callback to be called when the condition
297	"->broadcast" method has been called.	394	variable becomes true, with the condition variable as the first argument
		395	(but not the results).
298		396
299	They are very useful to signal that a condition has been fulfilled, for	397	After creation, the condition variable is "false" until it becomes
		398	"true" by calling the "send" method (or calling the condition variable
		399	as if it were a callback, read about the caveats in the description for
		400	the "->send" method).
		401
		402	Condition variables are similar to callbacks, except that you can
		403	optionally wait for them. They can also be called merge points - points
		404	in time where multiple outstanding events have been processed. And yet
		405	another way to call them is transactions - each condition variable can
		406	be used to represent a transaction, which finishes at some point and
		407	delivers a result.
		408
		409	Condition variables are very useful to signal that something has
300	example, if you write a module that does asynchronous http requests,	410	finished, for example, if you write a module that does asynchronous http
301	then a condition variable would be the ideal candidate to signal the	411	requests, then a condition variable would be the ideal candidate to
302	availability of results.	412	signal the availability of results. The user can either act when the
		413	callback is called or can synchronously "->recv" for the results.
303		414
304	You can also use condition variables to block your main program until an	415	You can also use them to simulate traditional event loops - for example,
305	event occurs - for example, you could "->wait" in your main program	416	you can block your main program until an event occurs - for example, you
306	until the user clicks the Quit button in your app, which would	417	could "->recv" in your main program until the user clicks the Quit
307	"->broadcast" the "quit" event.	418	button of your app, which would "->send" the "quit" event.
308		419
309	Note that condition variables recurse into the event loop - if you have	420	Note that condition variables recurse into the event loop - if you have
310	two pirces of code that call "->wait" in a round-robbin fashion, you	421	two pieces of code that call "->recv" in a round-robin fashion, you
311	lose. Therefore, condition variables are good to export to your caller,	422	lose. Therefore, condition variables are good to export to your caller,
312	but you should avoid making a blocking wait yourself, at least in	423	but you should avoid making a blocking wait yourself, at least in
313	callbacks, as this asks for trouble.	424	callbacks, as this asks for trouble.
314		425
315	This object has two methods:	426	Condition variables are represented by hash refs in perl, and the keys
		427	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		428	(it is often useful to build your own transaction class on top of
		429	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		430	it's "new" method in your own "new" method.
316		431
317	$cv->wait	432	There are two "sides" to a condition variable - the "producer side"
		433	which eventually calls "-> send", and the "consumer side", which waits
		434	for the send to occur.
		435
		436	Example: wait for a timer.
		437
		438	# wait till the result is ready
		439	my $result_ready = AnyEvent->condvar;
		440
		441	# do something such as adding a timer
		442	# or socket watcher the calls $result_ready->send
		443	# when the "result" is ready.
		444	# in this case, we simply use a timer:
		445	my $w = AnyEvent->timer (
		446	after => 1,
		447	cb => sub { $result_ready->send },
		448	);
		449
		450	# this "blocks" (while handling events) till the callback
		451	# calls send
		452	$result_ready->recv;
		453
		454	Example: wait for a timer, but take advantage of the fact that condition
		455	variables are also code references.
		456
		457	my $done = AnyEvent->condvar;
		458	my $delay = AnyEvent->timer (after => 5, cb => $done);
		459	$done->recv;
		460
		461	Example: Imagine an API that returns a condvar and doesn't support
		462	callbacks. This is how you make a synchronous call, for example from the
		463	main program:
		464
		465	use AnyEvent::CouchDB;
		466
		467	...
		468
		469	my @info = $couchdb->info->recv;
		470
		471	And this is how you would just ste a callback to be called whenever the
		472	results are available:
		473
		474	$couchdb->info->cb (sub {
		475	my @info = $_[0]->recv;
		476	});
		477
		478	METHODS FOR PRODUCERS
		479	These methods should only be used by the producing side, i.e. the
		480	code/module that eventually sends the signal. Note that it is also the
		481	producer side which creates the condvar in most cases, but it isn't
		482	uncommon for the consumer to create it as well.
		483
		484	$cv->send (...)
		485	Flag the condition as ready - a running "->recv" and all further
		486	calls to "recv" will (eventually) return after this method has been
		487	called. If nobody is waiting the send will be remembered.
		488
		489	If a callback has been set on the condition variable, it is called
		490	immediately from within send.
		491
		492	Any arguments passed to the "send" call will be returned by all
		493	future "->recv" calls.
		494
		495	Condition variables are overloaded so one can call them directly (as
		496	a code reference). Calling them directly is the same as calling
		497	"send". Note, however, that many C-based event loops do not handle
		498	overloading, so as tempting as it may be, passing a condition
		499	variable instead of a callback does not work. Both the pure perl and
		500	EV loops support overloading, however, as well as all functions that
		501	use perl to invoke a callback (as in AnyEvent::Socket and
		502	AnyEvent::DNS for example).
		503
		504	$cv->croak ($error)
		505	Similar to send, but causes all call's to "->recv" to invoke
		506	"Carp::croak" with the given error message/object/scalar.
		507
		508	This can be used to signal any errors to the condition variable
		509	user/consumer.
		510
		511	$cv->begin ([group callback])
		512	$cv->end
		513	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		514
		515	These two methods can be used to combine many transactions/events
		516	into one. For example, a function that pings many hosts in parallel
		517	might want to use a condition variable for the whole process.
		518
		519	Every call to "->begin" will increment a counter, and every call to
		520	"->end" will decrement it. If the counter reaches 0 in "->end", the
		521	(last) callback passed to "begin" will be executed. That callback is
		522	supposed to call "->send", but that is not required. If no
		523	callback was set, "send" will be called without any arguments.
		524
		525	Let's clarify this with the ping example:
		526
		527	my $cv = AnyEvent->condvar;
		528
		529	my %result;
		530	$cv->begin (sub { $cv->send (\%result) });
		531
		532	for my $host (@list_of_hosts) {
		533	$cv->begin;
		534	ping_host_then_call_callback $host, sub {
		535	$result{$host} = ...;
		536	$cv->end;
		537	};
		538	}
		539
		540	$cv->end;
		541
		542	This code fragment supposedly pings a number of hosts and calls
		543	"send" after results for all then have have been gathered - in any
		544	order. To achieve this, the code issues a call to "begin" when it
		545	starts each ping request and calls "end" when it has received some
		546	result for it. Since "begin" and "end" only maintain a counter, the
		547	order in which results arrive is not relevant.
		548
		549	There is an additional bracketing call to "begin" and "end" outside
		550	the loop, which serves two important purposes: first, it sets the
		551	callback to be called once the counter reaches 0, and second, it
		552	ensures that "send" is called even when "no" hosts are being pinged
		553	(the loop doesn't execute once).
		554
		555	This is the general pattern when you "fan out" into multiple
		556	subrequests: use an outer "begin"/"end" pair to set the callback and
		557	ensure "end" is called at least once, and then, for each subrequest
		558	you start, call "begin" and for each subrequest you finish, call
		559	"end".
		560
		561	METHODS FOR CONSUMERS
		562	These methods should only be used by the consuming side, i.e. the code
		563	awaits the condition.
		564
		565	$cv->recv
318	Wait (blocking if necessary) until the "->broadcast" method has been	566	Wait (blocking if necessary) until the "->send" or "->croak" methods
319	called on c<$cv>, while servicing other watchers normally.	567	have been called on c<$cv>, while servicing other watchers normally.
320		568
321	You can only wait once on a condition - additional calls will return	569	You can only wait once on a condition - additional calls are valid
322	immediately.	570	but will return immediately.
		571
		572	If an error condition has been set by calling "->croak", then this
		573	function will call "croak".
		574
		575	In list context, all parameters passed to "send" will be returned,
		576	in scalar context only the first one will be returned.
323		577
324	Not all event models support a blocking wait - some die in that case	578	Not all event models support a blocking wait - some die in that case
325	(programs might want to do that to stay interactive), so *if you are	579	(programs might want to do that to stay interactive), so *if you are
326	using this from a module, never require a blocking wait*, but let	580	using this from a module, never require a blocking wait*, but let
327	the caller decide whether the call will block or not (for example,	581	the caller decide whether the call will block or not (for example,
328	by coupling condition variables with some kind of request results	582	by coupling condition variables with some kind of request results
329	and supporting callbacks so the caller knows that getting the result	583	and supporting callbacks so the caller knows that getting the result
330	will not block, while still suppporting blocking waits if the caller	584	will not block, while still supporting blocking waits if the caller
331	so desires).	585	so desires).
332		586
333	Another reason never to "->wait" in a module is that you cannot	587	Another reason never to "->recv" in a module is that you cannot
334	sensibly have two "->wait"'s in parallel, as that would require	588	sensibly have two "->recv"'s in parallel, as that would require
335	multiple interpreters or coroutines/threads, none of which	589	multiple interpreters or coroutines/threads, none of which
336	"AnyEvent" can supply (the coroutine-aware backends	590	"AnyEvent" can supply.
337	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
338	support concurrent "->wait"'s from different coroutines, however).
339		591
340	$cv->broadcast	592	The Coro module, however, can and does supply coroutines and, in
341	Flag the condition as ready - a running "->wait" and all further	593	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
342	calls to "wait" will (eventually) return after this method has been	594	versions and also integrates coroutines into AnyEvent, making
343	called. If nobody is waiting the broadcast will be remembered..	595	blocking "->recv" calls perfectly safe as long as they are done from
		596	another coroutine (one that doesn't run the event loop).
344		597
345	Example:	598	You can ensure that "-recv" never blocks by setting a callback and
		599	only calling "->recv" from within that callback (or at a later
		600	time). This will work even when the event loop does not support
		601	blocking waits otherwise.
346		602
347	# wait till the result is ready	603	$bool = $cv->ready
348	my $result_ready = AnyEvent->condvar;	604	Returns true when the condition is "true", i.e. whether "send" or
		605	"croak" have been called.
349		606
350	# do something such as adding a timer	607	$cb = $cv->cb ($cb->($cv))
351	# or socket watcher the calls $result_ready->broadcast	608	This is a mutator function that returns the callback set and
352	# when the "result" is ready.	609	optionally replaces it before doing so.
353	# in this case, we simply use a timer:
354	my $w = AnyEvent->timer (
355	after => 1,
356	cb => sub { $result_ready->broadcast },
357	);
358		610
359	# this "blocks" (while handling events) till the watcher	611	The callback will be called when the condition becomes "true", i.e.
360	# calls broadcast	612	when "send" or "croak" are called, with the only argument being the
361	$result_ready->wait;	613	condition variable itself. Calling "recv" inside the callback or at
		614	any later time is guaranteed not to block.
362		615
363	GLOBAL VARIABLES AND FUNCTIONS	616	GLOBAL VARIABLES AND FUNCTIONS
364	$AnyEvent::MODEL	617	$AnyEvent::MODEL
365	Contains "undef" until the first watcher is being created. Then it	618	Contains "undef" until the first watcher is being created. Then it
366	contains the event model that is being used, which is the name of	619	contains the event model that is being used, which is the name of
…		…
368	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	621	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
369	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	622	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
370		623
371	The known classes so far are:	624	The known classes so far are:
372		625
373	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
374	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
375	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	626	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
376	AnyEvent::Impl::Event based on Event, second best choice.	627	AnyEvent::Impl::Event based on Event, second best choice.
		628	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
377	AnyEvent::Impl::Glib based on Glib, third-best choice.	629	AnyEvent::Impl::Glib based on Glib, third-best choice.
378	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
379	AnyEvent::Impl::Tk based on Tk, very bad choice.	630	AnyEvent::Impl::Tk based on Tk, very bad choice.
380	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).	631	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
381	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	632	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
382	AnyEvent::Impl::POE based on POE, not generic enough for full support.	633	AnyEvent::Impl::POE based on POE, not generic enough for full support.
383		634
…		…
395	Returns $AnyEvent::MODEL, forcing autodetection of the event model	646	Returns $AnyEvent::MODEL, forcing autodetection of the event model
396	if necessary. You should only call this function right before you	647	if necessary. You should only call this function right before you
397	would have created an AnyEvent watcher anyway, that is, as late as	648	would have created an AnyEvent watcher anyway, that is, as late as
398	possible at runtime.	649	possible at runtime.
399		650
		651	$guard = AnyEvent::post_detect { BLOCK }
		652	Arranges for the code block to be executed as soon as the event
		653	model is autodetected (or immediately if this has already happened).
		654
		655	If called in scalar or list context, then it creates and returns an
		656	object that automatically removes the callback again when it is
		657	destroyed. See Coro::BDB for a case where this is useful.
		658
		659	@AnyEvent::post_detect
		660	If there are any code references in this array (you can "push" to it
		661	before or after loading AnyEvent), then they will called directly
		662	after the event loop has been chosen.
		663
		664	You should check $AnyEvent::MODEL before adding to this array,
		665	though: if it contains a true value then the event loop has already
		666	been detected, and the array will be ignored.
		667
		668	Best use "AnyEvent::post_detect { BLOCK }" instead.
		669
400	WHAT TO DO IN A MODULE	670	WHAT TO DO IN A MODULE
401	As a module author, you should "use AnyEvent" and call AnyEvent methods	671	As a module author, you should "use AnyEvent" and call AnyEvent methods
402	freely, but you should not load a specific event module or rely on it.	672	freely, but you should not load a specific event module or rely on it.
403		673
404	Be careful when you create watchers in the module body - AnyEvent will	674	Be careful when you create watchers in the module body - AnyEvent will
405	decide which event module to use as soon as the first method is called,	675	decide which event module to use as soon as the first method is called,
406	so by calling AnyEvent in your module body you force the user of your	676	so by calling AnyEvent in your module body you force the user of your
407	module to load the event module first.	677	module to load the event module first.
408		678
409	Never call "->wait" on a condition variable unless you know that the	679	Never call "->recv" on a condition variable unless you know that the
410	"->broadcast" method has been called on it already. This is because it	680	"->send" method has been called on it already. This is because it will
411	will stall the whole program, and the whole point of using events is to	681	stall the whole program, and the whole point of using events is to stay
412	stay interactive.	682	interactive.
413		683
414	It is fine, however, to call "->wait" when the user of your module	684	It is fine, however, to call "->recv" when the user of your module
415	requests it (i.e. if you create a http request object ad have a method	685	requests it (i.e. if you create a http request object ad have a method
416	called "results" that returns the results, it should call "->wait"	686	called "results" that returns the results, it should call "->recv"
417	freely, as the user of your module knows what she is doing. always).	687	freely, as the user of your module knows what she is doing. always).
418		688
419	WHAT TO DO IN THE MAIN PROGRAM	689	WHAT TO DO IN THE MAIN PROGRAM
420	There will always be a single main program - the only place that should	690	There will always be a single main program - the only place that should
421	dictate which event model to use.	691	dictate which event model to use.
…		…
423	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	693	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
424	do anything special (it does not need to be event-based) and let	694	do anything special (it does not need to be event-based) and let
425	AnyEvent decide which implementation to chose if some module relies on	695	AnyEvent decide which implementation to chose if some module relies on
426	it.	696	it.
427		697
428	If the main program relies on a specific event model. For example, in	698	If the main program relies on a specific event model - for example, in
429	Gtk2 programs you have to rely on the Glib module. You should load the	699	Gtk2 programs you have to rely on the Glib module - you should load the
430	event module before loading AnyEvent or any module that uses it:	700	event module before loading AnyEvent or any module that uses it:
431	generally speaking, you should load it as early as possible. The reason	701	generally speaking, you should load it as early as possible. The reason
432	is that modules might create watchers when they are loaded, and AnyEvent	702	is that modules might create watchers when they are loaded, and AnyEvent
433	will decide on the event model to use as soon as it creates watchers,	703	will decide on the event model to use as soon as it creates watchers,
434	and it might chose the wrong one unless you load the correct one	704	and it might chose the wrong one unless you load the correct one
435	yourself.	705	yourself.
436		706
437	You can chose to use a rather inefficient pure-perl implementation by	707	You can chose to use a pure-perl implementation by loading the
438	loading the "AnyEvent::Impl::Perl" module, which gives you similar	708	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
439	behaviour everywhere, but letting AnyEvent chose is generally better.	709	everywhere, but letting AnyEvent chose the model is generally better.
		710
		711	MAINLOOP EMULATION
		712	Sometimes (often for short test scripts, or even standalone programs who
		713	only want to use AnyEvent), you do not want to run a specific event
		714	loop.
		715
		716	In that case, you can use a condition variable like this:
		717
		718	AnyEvent->condvar->recv;
		719
		720	This has the effect of entering the event loop and looping forever.
		721
		722	Note that usually your program has some exit condition, in which case it
		723	is better to use the "traditional" approach of storing a condition
		724	variable somewhere, waiting for it, and sending it when the program
		725	should exit cleanly.
440		726
441	OTHER MODULES	727	OTHER MODULES
442	The following is a non-exhaustive list of additional modules that use	728	The following is a non-exhaustive list of additional modules that use
443	AnyEvent and can therefore be mixed easily with other AnyEvent modules	729	AnyEvent and can therefore be mixed easily with other AnyEvent modules
444	in the same program. Some of the modules come with AnyEvent, some are	730	in the same program. Some of the modules come with AnyEvent, some are
…		…
447	AnyEvent::Util	733	AnyEvent::Util
448	Contains various utility functions that replace often-used but	734	Contains various utility functions that replace often-used but
449	blocking functions such as "inet_aton" by event-/callback-based	735	blocking functions such as "inet_aton" by event-/callback-based
450	versions.	736	versions.
451		737
		738	AnyEvent::Socket
		739	Provides various utility functions for (internet protocol) sockets,
		740	addresses and name resolution. Also functions to create non-blocking
		741	tcp connections or tcp servers, with IPv6 and SRV record support and
		742	more.
		743
452	AnyEvent::Handle	744	AnyEvent::Handle
453	Provide read and write buffers and manages watchers for reads and	745	Provide read and write buffers, manages watchers for reads and
454	writes.	746	writes, supports raw and formatted I/O, I/O queued and fully
		747	transparent and non-blocking SSL/TLS.
455		748
456	AnyEvent::Socket	749	AnyEvent::DNS
457	Provides a means to do non-blocking connects, accepts etc.	750	Provides rich asynchronous DNS resolver capabilities.
		751
		752	AnyEvent::HTTP
		753	A simple-to-use HTTP library that is capable of making a lot of
		754	concurrent HTTP requests.
458		755
459	AnyEvent::HTTPD	756	AnyEvent::HTTPD
460	Provides a simple web application server framework.	757	Provides a simple web application server framework.
461		758
462	AnyEvent::DNS
463	Provides asynchronous DNS resolver capabilities, beyond what
464	AnyEvent::Util offers.
465
466	AnyEvent::FastPing	759	AnyEvent::FastPing
467	The fastest ping in the west.	760	The fastest ping in the west.
468		761
		762	AnyEvent::DBI
		763	Executes DBI requests asynchronously in a proxy process.
		764
		765	AnyEvent::AIO
		766	Truly asynchronous I/O, should be in the toolbox of every event
		767	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		768	together.
		769
		770	AnyEvent::BDB
		771	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		772	fuses BDB and AnyEvent together.
		773
		774	AnyEvent::GPSD
		775	A non-blocking interface to gpsd, a daemon delivering GPS
		776	information.
		777
		778	AnyEvent::IGS
		779	A non-blocking interface to the Internet Go Server protocol (used by
		780	App::IGS).
		781
		782	AnyEvent::IRC
		783	AnyEvent based IRC client module family (replacing the older
469	Net::IRC3	784	Net::IRC3).
470	AnyEvent based IRC client module family.
471		785
472	Net::XMPP2	786	Net::XMPP2
473	AnyEvent based XMPP (Jabber protocol) module family.	787	AnyEvent based XMPP (Jabber protocol) module family.
474		788
475	Net::FCP	789	Net::FCP
…		…
478		792
479	Event::ExecFlow	793	Event::ExecFlow
480	High level API for event-based execution flow control.	794	High level API for event-based execution flow control.
481		795
482	Coro	796	Coro
483	Has special support for AnyEvent.	797	Has special support for AnyEvent via Coro::AnyEvent.
484		798
485	IO::Lambda	799	IO::Lambda
486	The lambda approach to I/O - don't ask, look there. Can use	800	The lambda approach to I/O - don't ask, look there. Can use
487	AnyEvent.	801	AnyEvent.
488		802
489	IO::AIO	803	ERROR AND EXCEPTION HANDLING
490	Truly asynchronous I/O, should be in the toolbox of every event	804	In general, AnyEvent does not do any error handling - it relies on the
491	programmer. Can be trivially made to use AnyEvent.	805	caller to do that if required. The AnyEvent::Strict module (see also the
		806	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		807	checking of all AnyEvent methods, however, which is highly useful during
		808	development.
492		809
493	BDB Truly asynchronous Berkeley DB access. Can be trivially made to use	810	As for exception handling (i.e. runtime errors and exceptions thrown
494	AnyEvent.	811	while executing a callback), this is not only highly event-loop
		812	specific, but also not in any way wrapped by this module, as this is the
		813	job of the main program.
		814
		815	The pure perl event loop simply re-throws the exception (usually within
		816	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		817	Glib uses "install_exception_handler" and so on.
		818
		819	ENVIRONMENT VARIABLES
		820	The following environment variables are used by this module or its
		821	submodules:
		822
		823	"PERL_ANYEVENT_VERBOSE"
		824	By default, AnyEvent will be completely silent except in fatal
		825	conditions. You can set this environment variable to make AnyEvent
		826	more talkative.
		827
		828	When set to 1 or higher, causes AnyEvent to warn about unexpected
		829	conditions, such as not being able to load the event model specified
		830	by "PERL_ANYEVENT_MODEL".
		831
		832	When set to 2 or higher, cause AnyEvent to report to STDERR which
		833	event model it chooses.
		834
		835	"PERL_ANYEVENT_STRICT"
		836	AnyEvent does not do much argument checking by default, as thorough
		837	argument checking is very costly. Setting this variable to a true
		838	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		839	thoroughly check the arguments passed to most method calls. If it
		840	finds any problems it will croak.
		841
		842	In other words, enables "strict" mode.
		843
		844	Unlike "use strict", it is definitely recommended ot keep it off in
		845	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment
		846	while developing programs can be very useful, however.
		847
		848	"PERL_ANYEVENT_MODEL"
		849	This can be used to specify the event model to be used by AnyEvent,
		850	before auto detection and -probing kicks in. It must be a string
		851	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		852	gets prepended and the resulting module name is loaded and if the
		853	load was successful, used as event model. If it fails to load
		854	AnyEvent will proceed with auto detection and -probing.
		855
		856	This functionality might change in future versions.
		857
		858	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		859	could start your program like this:
		860
		861	PERL_ANYEVENT_MODEL=Perl perl ...
		862
		863	"PERL_ANYEVENT_PROTOCOLS"
		864	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		865	preferences for IPv4 or IPv6. The default is unspecified (and might
		866	change, or be the result of auto probing).
		867
		868	Must be set to a comma-separated list of protocols or address
		869	families, current supported: "ipv4" and "ipv6". Only protocols
		870	mentioned will be used, and preference will be given to protocols
		871	mentioned earlier in the list.
		872
		873	This variable can effectively be used for denial-of-service attacks
		874	against local programs (e.g. when setuid), although the impact is
		875	likely small, as the program has to handle connection errors
		876	already-
		877
		878	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		879	IPv6, but support both and try to use both.
		880	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		881	resolve or contact IPv6 addresses.
		882	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		883	prefer IPv6 over IPv4.
		884
		885	"PERL_ANYEVENT_EDNS0"
		886	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		887	for DNS. This extension is generally useful to reduce DNS traffic,
		888	but some (broken) firewalls drop such DNS packets, which is why it
		889	is off by default.
		890
		891	Setting this variable to 1 will cause AnyEvent::DNS to announce
		892	EDNS0 in its DNS requests.
		893
		894	"PERL_ANYEVENT_MAX_FORKS"
		895	The maximum number of child processes that
		896	"AnyEvent::Util::fork_call" will create in parallel.
495		897
496	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	898	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
497	This is an advanced topic that you do not normally need to use AnyEvent	899	This is an advanced topic that you do not normally need to use AnyEvent
498	in a module. This section is only of use to event loop authors who want	900	in a module. This section is only of use to event loop authors who want
499	to provide AnyEvent compatibility.	901	to provide AnyEvent compatibility.
…		…
533		935
534	rxvt-unicode also cheats a bit by not providing blocking access to	936	rxvt-unicode also cheats a bit by not providing blocking access to
535	condition variables: code blocking while waiting for a condition will	937	condition variables: code blocking while waiting for a condition will
536	"die". This still works with most modules/usages, and blocking calls	938	"die". This still works with most modules/usages, and blocking calls
537	must not be done in an interactive application, so it makes sense.	939	must not be done in an interactive application, so it makes sense.
538
539	ENVIRONMENT VARIABLES
540	The following environment variables are used by this module:
541
542	"PERL_ANYEVENT_VERBOSE"
543	By default, AnyEvent will be completely silent except in fatal
544	conditions. You can set this environment variable to make AnyEvent
545	more talkative.
546
547	When set to 1 or higher, causes AnyEvent to warn about unexpected
548	conditions, such as not being able to load the event model specified
549	by "PERL_ANYEVENT_MODEL".
550
551	When set to 2 or higher, cause AnyEvent to report to STDERR which
552	event model it chooses.
553
554	"PERL_ANYEVENT_MODEL"
555	This can be used to specify the event model to be used by AnyEvent,
556	before autodetection and -probing kicks in. It must be a string
557	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
558	gets prepended and the resulting module name is loaded and if the
559	load was successful, used as event model. If it fails to load
560	AnyEvent will proceed with autodetection and -probing.
561
562	This functionality might change in future versions.
563
564	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
565	could start your program like this:
566
567	PERL_ANYEVENT_MODEL=Perl perl ...
568		940
569	EXAMPLE PROGRAM	941	EXAMPLE PROGRAM
570	The following program uses an I/O watcher to read data from STDIN, a	942	The following program uses an I/O watcher to read data from STDIN, a
571	timer to display a message once per second, and a condition variable to	943	timer to display a message once per second, and a condition variable to
572	quit the program when the user enters quit:	944	quit the program when the user enters quit:
…		…
580	poll => 'r',	952	poll => 'r',
581	cb => sub {	953	cb => sub {
582	warn "io event <$_[0]>\n"; # will always output <r>	954	warn "io event <$_[0]>\n"; # will always output <r>
583	chomp (my $input = <STDIN>); # read a line	955	chomp (my $input = <STDIN>); # read a line
584	warn "read: $input\n"; # output what has been read	956	warn "read: $input\n"; # output what has been read
585	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	957	$cv->send if $input =~ /^q/i; # quit program if /^q/i
586	},	958	},
587	);	959	);
588		960
589	my $time_watcher; # can only be used once	961	my $time_watcher; # can only be used once
590		962
…		…
595	});	967	});
596	}	968	}
597		969
598	new_timer; # create first timer	970	new_timer; # create first timer
599		971
600	$cv->wait; # wait until user enters /^q/i	972	$cv->recv; # wait until user enters /^q/i
601		973
602	REAL-WORLD EXAMPLE	974	REAL-WORLD EXAMPLE
603	Consider the Net::FCP module. It features (among others) the following	975	Consider the Net::FCP module. It features (among others) the following
604	API calls, which are to freenet what HTTP GET requests are to http:	976	API calls, which are to freenet what HTTP GET requests are to http:
605		977
…		…
654	syswrite $txn->{fh}, $txn->{request}	1026	syswrite $txn->{fh}, $txn->{request}
655	or die "connection or write error";	1027	or die "connection or write error";
656	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1028	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
657		1029
658	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1030	Again, "fh_ready_r" waits till all data has arrived, and then stores the
659	result and signals any possible waiters that the request ahs finished:	1031	result and signals any possible waiters that the request has finished:
660		1032
661	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1033	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
662		1034
663	if (end-of-file or data complete) {	1035	if (end-of-file or data complete) {
664	$txn->{result} = $txn->{buf};	1036	$txn->{result} = $txn->{buf};
665	$txn->{finished}->broadcast;	1037	$txn->{finished}->send;
666	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1038	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
667	}	1039	}
668		1040
669	The "result" method, finally, just waits for the finished signal (if the	1041	The "result" method, finally, just waits for the finished signal (if the
670	request was already finished, it doesn't wait, of course, and returns	1042	request was already finished, it doesn't wait, of course, and returns
671	the data:	1043	the data:
672		1044
673	$txn->{finished}->wait;	1045	$txn->{finished}->recv;
674	return $txn->{result};	1046	return $txn->{result};
675		1047
676	The actual code goes further and collects all errors ("die"s,	1048	The actual code goes further and collects all errors ("die"s,
677	exceptions) that occured during request processing. The "result" method	1049	exceptions) that occurred during request processing. The "result" method
678	detects whether an exception as thrown (it is stored inside the $txn	1050	detects whether an exception as thrown (it is stored inside the $txn
679	object) and just throws the exception, which means connection errors and	1051	object) and just throws the exception, which means connection errors and
680	other problems get reported tot he code that tries to use the result,	1052	other problems get reported tot he code that tries to use the result,
681	not in a random callback.	1053	not in a random callback.
682		1054
…		…
713		1085
714	my $quit = AnyEvent->condvar;	1086	my $quit = AnyEvent->condvar;
715		1087
716	$fcp->txn_client_get ($url)->cb (sub {	1088	$fcp->txn_client_get ($url)->cb (sub {
717	...	1089	...
718	$quit->broadcast;	1090	$quit->send;
719	});	1091	});
720		1092
721	$quit->wait;	1093	$quit->recv;
722		1094
723	BENCHMARKS	1095	BENCHMARKS
724	To give you an idea of the performance and overheads that AnyEvent adds	1096	To give you an idea of the performance and overheads that AnyEvent adds
725	over the event loops themselves and to give you an impression of the	1097	over the event loops themselves and to give you an impression of the
726	speed of various event loops I prepared some benchmarks.	1098	speed of various event loops I prepared some benchmarks.
727		1099
728	BENCHMARKING ANYEVENT OVERHEAD	1100	BENCHMARKING ANYEVENT OVERHEAD
729	Here is a benchmark of various supported event models used natively and	1101	Here is a benchmark of various supported event models used natively and
730	through anyevent. The benchmark creates a lot of timers (with a zero	1102	through AnyEvent. The benchmark creates a lot of timers (with a zero
731	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1103	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
732	which it is), lets them fire exactly once and destroys them again.	1104	which it is), lets them fire exactly once and destroys them again.
733		1105
734	Source code for this benchmark is found as eg/bench in the AnyEvent	1106	Source code for this benchmark is found as eg/bench in the AnyEvent
735	distribution.	1107	distribution.
…		…
751	between all watchers, to avoid adding memory overhead. That means	1123	between all watchers, to avoid adding memory overhead. That means
752	closure creation and memory usage is not included in the figures.	1124	closure creation and memory usage is not included in the figures.
753		1125
754	invoke is the time, in microseconds, used to invoke a simple callback.	1126	invoke is the time, in microseconds, used to invoke a simple callback.
755	The callback simply counts down a Perl variable and after it was invoked	1127	The callback simply counts down a Perl variable and after it was invoked
756	"watcher" times, it would "->broadcast" a condvar once to signal the end	1128	"watcher" times, it would "->send" a condvar once to signal the end of
757	of this phase.	1129	this phase.
758		1130
759	destroy is the time, in microseconds, that it takes to destroy a	1131	destroy is the time, in microseconds, that it takes to destroy a
760	single watcher.	1132	single watcher.
761		1133
762	Results	1134	Results
…		…
823	the figures above).	1195	the figures above).
824		1196
825	"POE", regardless of underlying event loop (whether using its pure perl	1197	"POE", regardless of underlying event loop (whether using its pure perl
826	select-based backend or the Event module, the POE-EV backend couldn't be	1198	select-based backend or the Event module, the POE-EV backend couldn't be
827	tested because it wasn't working) shows abysmal performance and memory	1199	tested because it wasn't working) shows abysmal performance and memory
828	usage: Watchers use almost 30 times as much memory as EV watchers, and	1200	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
829	10 times as much memory as Event (the high memory requirements are	1201	watchers, and 10 times as much memory as Event (the high memory
830	caused by requiring a session for each watcher). Watcher invocation	1202	requirements are caused by requiring a session for each watcher).
831	speed is almost 900 times slower than with AnyEvent's pure perl	1203	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1204	pure perl implementation.
		1205
832	implementation. The design of the POE adaptor class in AnyEvent can not	1206	The design of the POE adaptor class in AnyEvent can not really account
833	really account for this, as session creation overhead is small compared	1207	for the performance issues, though, as session creation overhead is
834	to execution of the state machine, which is coded pretty optimally	1208	small compared to execution of the state machine, which is coded pretty
835	within AnyEvent::Impl::POE. POE simply seems to be abysmally slow.	1209	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1210	using multiple sessions is not a good approach, especially regarding
		1211	memory usage, even the author of POE could not come up with a faster
		1212	design).
836		1213
837	Summary	1214	Summary
838	* Using EV through AnyEvent is faster than any other event loop (even	1215	* Using EV through AnyEvent is faster than any other event loop (even
839	when used without AnyEvent), but most event loops have acceptable	1216	when used without AnyEvent), but most event loops have acceptable
840	performance with or without AnyEvent.	1217	performance with or without AnyEvent.
…		…
845		1222
846	* You should avoid POE like the plague if you want performance or	1223	* You should avoid POE like the plague if you want performance or
847	reasonable memory usage.	1224	reasonable memory usage.
848		1225
849	BENCHMARKING THE LARGE SERVER CASE	1226	BENCHMARKING THE LARGE SERVER CASE
850	This benchmark atcually benchmarks the event loop itself. It works by	1227	This benchmark actually benchmarks the event loop itself. It works by
851	creating a number of "servers": each server consists of a socketpair, a	1228	creating a number of "servers": each server consists of a socket pair, a
852	timeout watcher that gets reset on activity (but never fires), and an	1229	timeout watcher that gets reset on activity (but never fires), and an
853	I/O watcher waiting for input on one side of the socket. Each time the	1230	I/O watcher waiting for input on one side of the socket. Each time the
854	socket watcher reads a byte it will write that byte to a random other	1231	socket watcher reads a byte it will write that byte to a random other
855	"server".	1232	"server".
856		1233
857	The effect is that there will be a lot of I/O watchers, only part of	1234	The effect is that there will be a lot of I/O watchers, only part of
858	which are active at any one point (so there is a constant number of	1235	which are active at any one point (so there is a constant number of
859	active fds for each loop iterstaion, but which fds these are is random).	1236	active fds for each loop iteration, but which fds these are is random).
860	The timeout is reset each time something is read because that reflects	1237	The timeout is reset each time something is read because that reflects
861	how most timeouts work (and puts extra pressure on the event loops).	1238	how most timeouts work (and puts extra pressure on the event loops).
862		1239
863	In this benchmark, we use 10000 socketpairs (20000 sockets), of which	1240	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
864	100 (1%) are active. This mirrors the activity of large servers with	1241	100 (1%) are active. This mirrors the activity of large servers with
865	many connections, most of which are idle at any one point in time.	1242	many connections, most of which are idle at any one point in time.
866		1243
867	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1244	Source code for this benchmark is found as eg/bench2 in the AnyEvent
868	distribution.	1245	distribution.
869		1246
870	Explanation of the columns	1247	Explanation of the columns
871	sockets is the number of sockets, and twice the number of "servers"	1248	sockets is the number of sockets, and twice the number of "servers"
872	(as each server has a read and write socket end).	1249	(as each server has a read and write socket end).
873		1250
874	create is the time it takes to create a socketpair (which is	1251	create is the time it takes to create a socket pair (which is
875	nontrivial) and two watchers: an I/O watcher and a timeout watcher.	1252	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
876		1253
877	request, the most important value, is the time it takes to handle a	1254	request, the most important value, is the time it takes to handle a
878	single "request", that is, reading the token from the pipe and	1255	single "request", that is, reading the token from the pipe and
879	forwarding it to another server. This includes deleting the old timeout	1256	forwarding it to another server. This includes deleting the old timeout
…		…
909	POE is still completely out of the picture, taking over 1000 times as	1286	POE is still completely out of the picture, taking over 1000 times as
910	long as EV, and over 100 times as long as the Perl implementation, even	1287	long as EV, and over 100 times as long as the Perl implementation, even
911	though it uses a C-based event loop in this case.	1288	though it uses a C-based event loop in this case.
912		1289
913	Summary	1290	Summary
914	* The pure perl implementation performs extremely well, considering	1291	* The pure perl implementation performs extremely well.
915	that it uses select.
916		1292
917	* Avoid Glib or POE in large projects where performance matters.	1293	* Avoid Glib or POE in large projects where performance matters.
918		1294
919	BENCHMARKING SMALL SERVERS	1295	BENCHMARKING SMALL SERVERS
920	While event loops should scale (and select-based ones do not...) even to	1296	While event loops should scale (and select-based ones do not...) even to
…		…
944	and speed most when you have lots of watchers, not when you only have a	1320	and speed most when you have lots of watchers, not when you only have a
945	few of them).	1321	few of them).
946		1322
947	EV is again fastest.	1323	EV is again fastest.
948		1324
949	Perl again comes second. It is noticably faster than the C-based event	1325	Perl again comes second. It is noticeably faster than the C-based event
950	loops Event and Glib, although the difference is too small to really	1326	loops Event and Glib, although the difference is too small to really
951	matter.	1327	matter.
952		1328
953	POE also performs much better in this case, but is is still far behind	1329	POE also performs much better in this case, but is is still far behind
954	the others.	1330	the others.
955		1331
956	Summary	1332	Summary
957	* C-based event loops perform very well with small number of watchers,	1333	* C-based event loops perform very well with small number of watchers,
958	as the management overhead dominates.	1334	as the management overhead dominates.
959		1335
		1336	SIGNALS
		1337	AnyEvent currently installs handlers for these signals:
		1338
		1339	SIGCHLD
		1340	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1341	emulation for event loops that do not support them natively. Also,
		1342	some event loops install a similar handler.
		1343
		1344	SIGPIPE
		1345	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1346	"undef" when AnyEvent gets loaded.
		1347
		1348	The rationale for this is that AnyEvent users usually do not really
		1349	depend on SIGPIPE delivery (which is purely an optimisation for
		1350	shell use, or badly-written programs), but "SIGPIPE" can cause
		1351	spurious and rare program exits as a lot of people do not expect
		1352	"SIGPIPE" when writing to some random socket.
		1353
		1354	The rationale for installing a no-op handler as opposed to ignoring
		1355	it is that this way, the handler will be restored to defaults on
		1356	exec.
		1357
		1358	Feel free to install your own handler, or reset it to defaults.
		1359
960	FORK	1360	FORK
961	Most event libraries are not fork-safe. The ones who are usually are	1361	Most event libraries are not fork-safe. The ones who are usually are
962	because they are so inefficient. Only EV is fully fork-aware.	1362	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1363	Only EV is fully fork-aware.
963		1364
964	If you have to fork, you must either do so before creating your first	1365	If you have to fork, you must either do so before creating your first
965	watcher OR you must not use AnyEvent at all in the child.	1366	watcher OR you must not use AnyEvent at all in the child.
966		1367
967	SECURITY CONSIDERATIONS	1368	SECURITY CONSIDERATIONS
…		…
973	model than specified in the variable.	1374	model than specified in the variable.
974		1375
975	You can make AnyEvent completely ignore this variable by deleting it	1376	You can make AnyEvent completely ignore this variable by deleting it
976	before the first watcher gets created, e.g. with a "BEGIN" block:	1377	before the first watcher gets created, e.g. with a "BEGIN" block:
977		1378
978	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1379	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
979		1380
980	use AnyEvent;	1381	use AnyEvent;
		1382
		1383	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1384	be used to probe what backend is used and gain other information (which
		1385	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1386	and $ENV{PERL_ANYEGENT_STRICT}.
		1387
		1388	BUGS
		1389	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1390	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1391	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1392	annoying mamleaks, such as leaking on "map" and "grep" but it is usually
		1393	not as pronounced).
981		1394
982	SEE ALSO	1395	SEE ALSO
983	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1396	Utility functions: AnyEvent::Util.
984	Glib::Event, Glib, Coro, Tk, Event::Lib, Qt, POE.
985		1397
986	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1398	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
987	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1399	Event::Lib, Qt, POE.
988	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib,	1400
		1401	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
		1402	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
989	AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1403	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
990		1404
		1405	Non-blocking file handles, sockets, TCP clients and servers:
		1406	AnyEvent::Handle, AnyEvent::Socket.
		1407
		1408	Asynchronous DNS: AnyEvent::DNS.
		1409
		1410	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1411
991	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1412	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
992		1413
993	AUTHOR	1414	AUTHOR
994	Marc Lehmann <schmorp@schmorp.de>	1415	Marc Lehmann <schmorp@schmorp.de>
995	http://home.schmorp.de/	1416	http://home.schmorp.de/
996		1417

Diff Legend

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

Comparing AnyEvent/README (file contents): Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs. Revision 1.32 by root, Fri Oct 3 07:19:23 2008 UTC

Diff Legend

Comparing AnyEvent/README (file contents):
Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs.
Revision 1.32 by root, Fri Oct 3 07:19:23 2008 UTC