[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 1.47 by root, Mon Jul 20 22:39:57 2009 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - events independent of event loop implementation
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 and POE are various supported
5	various supported event loops	5	event loops.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# file descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		12
		13	# one-shot or repeating timers
		14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		16
		17	print AnyEvent->now; # prints current event loop time
		18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		19
		20	# POSIX signal
		21	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		22
		23	# child process exit
		24	my $w = AnyEvent->child (pid => $pid, cb => sub {
		25	my ($pid, $status) = @_;
11	...	26	...
12	});	27	});
13		28
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	29	# called when event loop idle (if applicable)
15	...	30	my $w = AnyEvent->idle (cb => sub { ... });
16	});
17		31
18	my $w = AnyEvent->condvar; # stores whether a condition was flagged	32	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		33	$w->send; # wake up current and all future recv's
19	$w->wait; # enters "main loop" till $condvar gets ->broadcast	34	$w->recv; # enters "main loop" till $condvar gets ->send
20	$w->broadcast; # wake up current and all future wait's	35	# use a condvar in callback mode:
		36	$w->cb (sub { $_[0]->recv });
		37
		38	INTRODUCTION/TUTORIAL
		39	This manpage is mainly a reference manual. If you are interested in a
		40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
		41	manpage.
		42
		43	SUPPORT
		44	There is a mailinglist for discussing all things AnyEvent, and an IRC
		45	channel, too.
		46
		47	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		48	Respository, at <http://anyevent.schmorp.de>, for more info.
21		49
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	50	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	51	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	52	nowadays. So what is different about AnyEvent?
25		53
26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of	54	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
27	policy* and AnyEvent is small and efficient.	55	policy* and AnyEvent is small and efficient.
28		56
29	First and foremost, AnyEvent is not an event model itself, it only	57	First and foremost, AnyEvent is not an event model itself, it only
30	interfaces to whatever event model the main program happens to use in a	58	interfaces to whatever event model the main program happens to use, in a
31	pragmatic way. For event models and certain classes of immortals alike,	59	pragmatic way. For event models and certain classes of immortals alike,
32	the statement "there can only be one" is a bitter reality: In general,	60	the statement "there can only be one" is a bitter reality: In general,
33	only one event loop can be active at the same time in a process.	61	only one event loop can be active at the same time in a process.
34	AnyEvent helps hiding the differences between those event loops.	62	AnyEvent cannot change this, but it can hide the differences between
		63	those event loops.
35		64
36	The goal of AnyEvent is to offer module authors the ability to do event	65	The goal of AnyEvent is to offer module authors the ability to do event
37	programming (waiting for I/O or timer events) without subscribing to a	66	programming (waiting for I/O or timer events) without subscribing to a
38	religion, a way of living, and most importantly: without forcing your	67	religion, a way of living, and most importantly: without forcing your
39	module users into the same thing by forcing them to use the same event	68	module users into the same thing by forcing them to use the same event
40	model you use.	69	model you use.
41		70
42	For modules like POE or IO::Async (which is a total misnomer as it is	71	For modules like POE or IO::Async (which is a total misnomer as it is
43	actually doing all I/O synchronously...), using them in your module is	72	actually doing all I/O synchronously...), using them in your module is
44	like joining a cult: After you joined, you are dependent on them and you	73	like joining a cult: After you joined, you are dependent on them and you
45	cannot use anything else, as it is simply incompatible to everything	74	cannot use anything else, as they are simply incompatible to everything
46	that isn't itself. What's worse, all the potential users of your module	75	that isn't them. What's worse, all the potential users of your module
47	are also forced to use the same event loop you use.	76	are also forced to use the same event loop you use.
48		77
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	78	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	79	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your	80	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
52	module uses one of those, every user of your module has to use it, too.	81	module uses one of those, every user of your module has to use it, too.
53	But if your module uses AnyEvent, it works transparently with all event	82	But if your module uses AnyEvent, it works transparently with all event
54	models it supports (including stuff like POE and IO::Async, as long as	83	models it supports (including stuff like IO::Async, as long as those use
55	those use one of the supported event loops. It is trivial to add new	84	one of the supported event loops. It is trivial to add new event loops
56	event loops to AnyEvent, too, so it is future-proof).	85	to AnyEvent, too, so it is future-proof).
57		86
58	In addition to being free of having to use *the one and only true event	87	In addition to being free of having to use *the one and only true event
59	model*, AnyEvent also is free of bloat and policy: with POE or similar	88	model*, AnyEvent also is free of bloat and policy: with POE or similar
60	modules, you get an enourmous amount of code and strict rules you have	89	modules, you get an enormous amount of code and strict rules you have to
61	to follow. AnyEvent, on the other hand, is lean and up to the point, by	90	follow. AnyEvent, on the other hand, is lean and up to the point, by
62	only offering the functionality that is necessary, in as thin as a	91	only offering the functionality that is necessary, in as thin as a
63	wrapper as technically possible.	92	wrapper as technically possible.
64		93
		94	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
		95	useful functionality, such as an asynchronous DNS resolver, 100%
		96	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		97	such as Windows) and lots of real-world knowledge and workarounds for
		98	platform bugs and differences.
		99
65	Of course, if you want lots of policy (this can arguably be somewhat	100	Now, if you do want lots of policy (this can arguably be somewhat
66	useful) and you want to force your users to use the one and only event	101	useful) and you want to force your users to use the one and only event
67	model, you should not use this module.	102	model, you should not use this module.
68		103
69	DESCRIPTION	104	DESCRIPTION
70	AnyEvent provides an identical interface to multiple event loops. This	105	AnyEvent provides an identical interface to multiple event loops. This
75	The interface itself is vaguely similar, but not identical to the Event	110	The interface itself is vaguely similar, but not identical to the Event
76	module.	111	module.
77		112
78	During the first call of any watcher-creation method, the module tries	113	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	114	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,	115	following modules is already loaded: EV, Event, Glib,
81	Glib, AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found	116	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	117	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	118	(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	119	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	120	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	121	found, AnyEvent will fall back to a pure-perl event loop, which is not
87	very efficient, but should work everywhere.	122	very efficient, but should work everywhere.
…		…
99	starts using it, all bets are off. Maybe you should tell their authors	134	starts using it, all bets are off. Maybe you should tell their authors
100	to use AnyEvent so their modules work together with others seamlessly...	135	to use AnyEvent so their modules work together with others seamlessly...
101		136
102	The pure-perl implementation of AnyEvent is called	137	The pure-perl implementation of AnyEvent is called
103	"AnyEvent::Impl::Perl". Like other event modules you can load it	138	"AnyEvent::Impl::Perl". Like other event modules you can load it
104	explicitly.	139	explicitly and enjoy the high availability of that event loop :)
105		140
106	WATCHERS	141	WATCHERS
107	AnyEvent has the central concept of a watcher, which is an object that	142	AnyEvent has the central concept of a watcher, which is an object that
108	stores relevant data for each kind of event you are waiting for, such as	143	stores relevant data for each kind of event you are waiting for, such as
109	the callback to call, the filehandle to watch, etc.	144	the callback to call, the file handle to watch, etc.
110		145
111	These watchers are normal Perl objects with normal Perl lifetime. After	146	These watchers are normal Perl objects with normal Perl lifetime. After
112	creating a watcher it will immediately "watch" for events and invoke the	147	creating a watcher it will immediately "watch" for events and invoke the
113	callback when the event occurs (of course, only when the event model is	148	callback when the event occurs (of course, only when the event model is
114	in control).	149	in control).
115		150
		151	Note that callbacks must not permanently change global variables
		152	potentially in use by the event loop (such as $_ or $[) and that
		153	callbacks must not "die". The former is good programming practise in
		154	Perl and the latter stems from the fact that exception handling differs
		155	widely between event loops.
		156
116	To disable the watcher you have to destroy it (e.g. by setting the	157	To disable the watcher you have to destroy it (e.g. by setting the
117	variable you store it in to "undef" or otherwise deleting all references	158	variable you store it in to "undef" or otherwise deleting all references
118	to it).	159	to it).
119		160
120	All watchers are created by calling a method on the "AnyEvent" class.	161	All watchers are created by calling a method on the "AnyEvent" class.
…		…
122	Many watchers either are used with "recursion" (repeating timers for	163	Many watchers either are used with "recursion" (repeating timers for
123	example), or need to refer to their watcher object in other ways.	164	example), or need to refer to their watcher object in other ways.
124		165
125	An any way to achieve that is this pattern:	166	An any way to achieve that is this pattern:
126		167
127	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	168	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
128	# you can use $w here, for example to undef it	169	# you can use $w here, for example to undef it
129	undef $w;	170	undef $w;
130	});	171	});
131		172
132	Note that "my $w; $w =" combination. This is necessary because in Perl,	173	Note that "my $w; $w =" combination. This is necessary because in Perl,
133	my variables are only visible after the statement in which they are	174	my variables are only visible after the statement in which they are
134	declared.	175	declared.
135		176
136	I/O WATCHERS	177	I/O WATCHERS
137	You can create an I/O watcher by calling the "AnyEvent->io" method with	178	You can create an I/O watcher by calling the "AnyEvent->io" method with
138	the following mandatory key-value pairs as arguments:	179	the following mandatory key-value pairs as arguments:
139		180
140	"fh" the Perl file handle (not file descriptor) to watch for events.	181	"fh" is the Perl file handle (or a naked file descriptor) to watch for
		182	events (AnyEvent might or might not keep a reference to this file
		183	handle). Note that only file handles pointing to things for which
		184	non-blocking operation makes sense are allowed. This includes sockets,
		185	most character devices, pipes, fifos and so on, but not for example
		186	files or block devices.
		187
141	"poll" must be a string that is either "r" or "w", which creates a	188	"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"	189	watcher waiting for "r"eadable or "w"ritable events, respectively.
		190
143	is the callback to invoke each time the file handle becomes ready.	191	"cb" is the callback to invoke each time the file handle becomes ready.
144		192
145	Although the callback might get passed parameters, their value and	193	Although the callback might get passed parameters, their value and
146	presence is undefined and you cannot rely on them. Portable AnyEvent	194	presence is undefined and you cannot rely on them. Portable AnyEvent
147	callbacks cannot use arguments passed to I/O watcher callbacks.	195	callbacks cannot use arguments passed to I/O watcher callbacks.
148		196
…		…
152		200
153	Some event loops issue spurious readyness notifications, so you should	201	Some event loops issue spurious readyness notifications, so you should
154	always use non-blocking calls when reading/writing from/to your file	202	always use non-blocking calls when reading/writing from/to your file
155	handles.	203	handles.
156		204
157	Example:
158
159	# wait for readability of STDIN, then read a line and disable the watcher	205	Example: wait for readability of STDIN, then read a line and disable the
		206	watcher.
		207
160	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	208	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
161	chomp (my $input = <STDIN>);	209	chomp (my $input = <STDIN>);
162	warn "read: $input\n";	210	warn "read: $input\n";
163	undef $w;	211	undef $w;
164	});	212	});
…		…
173		221
174	Although the callback might get passed parameters, their value and	222	Although the callback might get passed parameters, their value and
175	presence is undefined and you cannot rely on them. Portable AnyEvent	223	presence is undefined and you cannot rely on them. Portable AnyEvent
176	callbacks cannot use arguments passed to time watcher callbacks.	224	callbacks cannot use arguments passed to time watcher callbacks.
177		225
178	The timer callback will be invoked at most once: if you want a repeating	226	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	227	parameter, "interval", as a strictly positive number (> 0), then the
180	and Glib).	228	callback will be invoked regularly at that interval (in fractional
		229	seconds) after the first invocation. If "interval" is specified with a
		230	false value, then it is treated as if it were missing.
181		231
182	Example:	232	The callback will be rescheduled before invoking the callback, but no
		233	attempt is done to avoid timer drift in most backends, so the interval
		234	is only approximate.
183		235
184	# fire an event after 7.7 seconds	236	Example: fire an event after 7.7 seconds.
		237
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	238	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	239	warn "timeout\n";
187	});	240	});
188		241
189	# to cancel the timer:	242	# to cancel the timer:
190	undef $w;	243	undef $w;
191		244
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	245	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		246
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	247	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		248	warn "timeout\n";
200	};	249	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		250
205	TIMING ISSUES	251	TIMING ISSUES
206	There are two ways to handle timers: based on real time (relative, "fire	252	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	253	in 10 seconds") and based on wallclock time (absolute, "fire at 12
208	o'clock").	254	o'clock").
…		…
220	on wallclock time) timers.	266	on wallclock time) timers.
221		267
222	AnyEvent always prefers relative timers, if available, matching the	268	AnyEvent always prefers relative timers, if available, matching the
223	AnyEvent API.	269	AnyEvent API.
224		270
		271	AnyEvent has two additional methods that return the "current time":
		272
		273	AnyEvent->time
		274	This returns the "current wallclock time" as a fractional number of
		275	seconds since the Epoch (the same thing as "time" or
		276	"Time::HiRes::time" return, and the result is guaranteed to be
		277	compatible with those).
		278
		279	It progresses independently of any event loop processing, i.e. each
		280	call will check the system clock, which usually gets updated
		281	frequently.
		282
		283	AnyEvent->now
		284	This also returns the "current wallclock time", but unlike "time",
		285	above, this value might change only once per event loop iteration,
		286	depending on the event loop (most return the same time as "time",
		287	above). This is the time that AnyEvent's timers get scheduled
		288	against.
		289
		290	*In almost all cases (in all cases if you don't care), this is the
		291	function to call when you want to know the current time.*
		292
		293	This function is also often faster then "AnyEvent->time", and thus
		294	the preferred method if you want some timestamp (for example,
		295	AnyEvent::Handle uses this to update it's activity timeouts).
		296
		297	The rest of this section is only of relevance if you try to be very
		298	exact with your timing, you can skip it without bad conscience.
		299
		300	For a practical example of when these times differ, consider
		301	Event::Lib and EV and the following set-up:
		302
		303	The event loop is running and has just invoked one of your callback
		304	at time=500 (assume no other callbacks delay processing). In your
		305	callback, you wait a second by executing "sleep 1" (blocking the
		306	process for a second) and then (at time=501) you create a relative
		307	timer that fires after three seconds.
		308
		309	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		310	return 501, because that is the current time, and the timer will be
		311	scheduled to fire at time=504 (501 + 3).
		312
		313	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		314	but "AnyEvent->now" returns 500, as that is the time the last event
		315	processing phase started. With EV, your timer gets scheduled to run
		316	at time=503 (500 + 3).
		317
		318	In one sense, Event::Lib is more exact, as it uses the current time
		319	regardless of any delays introduced by event processing. However,
		320	most callbacks do not expect large delays in processing, so this
		321	causes a higher drift (and a lot more system calls to get the
		322	current time).
		323
		324	In another sense, EV is more exact, as your timer will be scheduled
		325	at the same time, regardless of how long event processing actually
		326	took.
		327
		328	In either case, if you care (and in most cases, you don't), then you
		329	can get whatever behaviour you want with any event loop, by taking
		330	the difference between "AnyEvent->time" and "AnyEvent->now" into
		331	account.
		332
		333	AnyEvent->now_update
		334	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		335	current time for each loop iteration (see the discussion of
		336	AnyEvent->now, above).
		337
		338	When a callback runs for a long time (or when the process sleeps),
		339	then this "current" time will differ substantially from the real
		340	time, which might affect timers and time-outs.
		341
		342	When this is the case, you can call this method, which will update
		343	the event loop's idea of "current time".
		344
		345	Note that updating the time might cause some events to be handled.
		346
225	SIGNAL WATCHERS	347	SIGNAL WATCHERS
226	You can watch for signals using a signal watcher, "signal" is the signal	348	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	349	name in uppercase and without any "SIG" prefix, "cb" is the Perl
228	whenever a signal occurs.	350	callback to be invoked whenever a signal occurs.
229		351
230	Although the callback might get passed parameters, their value and	352	Although the callback might get passed parameters, their value and
231	presence is undefined and you cannot rely on them. Portable AnyEvent	353	presence is undefined and you cannot rely on them. Portable AnyEvent
232	callbacks cannot use arguments passed to signal watcher callbacks.	354	callbacks cannot use arguments passed to signal watcher callbacks.
233		355
234	Multiple signal occurances can be clumped together into one callback	356	Multiple signal occurrences can be clumped together into one callback
235	invocation, and callback invocation will be synchronous. synchronous	357	invocation, and callback invocation will be synchronous. Synchronous
236	means that it might take a while until the signal gets handled by the	358	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.	359	process, but it is guaranteed not to interrupt any other callbacks.
238		360
239	The main advantage of using these watchers is that you can share a	361	The main advantage of using these watchers is that you can share a
240	signal between multiple watchers.	362	signal between multiple watchers, and AnyEvent will ensure that signals
		363	will not interrupt your program at bad times.
241		364
242	This watcher might use %SIG, so programs overwriting those signals	365	This watcher might use %SIG (depending on the event loop used), so
243	directly will likely not work correctly.	366	programs overwriting those signals directly will likely not work
		367	correctly.
244		368
245	Example: exit on SIGINT	369	Example: exit on SIGINT
246		370
247	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	371	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		372
		373	Signal Races, Delays and Workarounds
		374	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		375	callbacks to signals in a generic way, which is a pity, as you cannot do
		376	race-free signal handling in perl. AnyEvent will try to do it's best,
		377	but in some cases, signals will be delayed. The maximum time a signal
		378	might be delayed is specified in $AnyEvent::MAX_SIGNAL_LATENCY (default:
		379	10 seconds). This variable can be changed only before the first signal
		380	watcher is created, and should be left alone otherwise. Higher values
		381	will cause fewer spurious wake-ups, which is better for power and CPU
		382	saving. All these problems can be avoided by installing the optional
		383	Async::Interrupt module. This will not work with inherently broken event
		384	loops such as Event or Event::Lib (and not with POE currently, as POE
		385	does it's own workaround with one-second latency). With those, you just
		386	have to suffer the delays.
248		387
249	CHILD PROCESS WATCHERS	388	CHILD PROCESS WATCHERS
250	You can also watch on a child process exit and catch its exit status.	389	You can also watch on a child process exit and catch its exit status.
251		390
252	The child process is specified by the "pid" argument (if set to 0, it	391	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	392	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	393	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	394	on any trace events (stopped/continued).
256	and exit status (as returned by waitpid), so unlike other watcher types,	395
257	you can rely on child watcher callback arguments.	396	The callback will be called with the pid and exit status (as returned by
		397	waitpid), so unlike other watcher types, you can rely on child watcher
		398	callback arguments.
		399
		400	This watcher type works by installing a signal handler for "SIGCHLD",
		401	and since it cannot be shared, nothing else should use SIGCHLD or reap
		402	random child processes (waiting for specific child processes, e.g.
		403	inside "system", is just fine).
258		404
259	There is a slight catch to child watchers, however: you usually start	405	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	406	them after the child process was created, and this means the process
261	could have exited already (and no SIGCHLD will be sent anymore).	407	could have exited already (and no SIGCHLD will be sent anymore).
262		408
263	Not all event models handle this correctly (POE doesn't), but even for	409	Not all event models handle this correctly (neither POE nor IO::Async
		410	do, see their AnyEvent::Impl manpages for details), but even for event
264	event models that do handle this correctly, they usually need to be	411	models that do handle this correctly, they usually need to be loaded
265	loaded before the process exits (i.e. before you fork in the first	412	before the process exits (i.e. before you fork in the first place).
266	place).	413	AnyEvent's pure perl event loop handles all cases correctly regardless
		414	of when you start the watcher.
267		415
268	This means you cannot create a child watcher as the very first thing in	416	This means you cannot create a child watcher as the very first thing in
269	an AnyEvent program, you have to create at least one watcher before	417	an AnyEvent program, you have to create at least one watcher before
270	you "fork" the child (alternatively, you can call "AnyEvent::detect").	418	you "fork" the child (alternatively, you can call "AnyEvent::detect").
271		419
		420	As most event loops do not support waiting for child events, they will
		421	be emulated by AnyEvent in most cases, in which the latency and race
		422	problems mentioned in the description of signal watchers apply.
		423
272	Example: fork a process and wait for it	424	Example: fork a process and wait for it
273		425
274	my $done = AnyEvent->condvar;	426	my $done = AnyEvent->condvar;
275		427
276	AnyEvent::detect; # force event module to be initialised
277
278	my $pid = fork or exit 5;	428	my $pid = fork or exit 5;
279		429
280	my $w = AnyEvent->child (	430	my $w = AnyEvent->child (
281	pid => $pid,	431	pid => $pid,
282	cb => sub {	432	cb => sub {
283	my ($pid, $status) = @_;	433	my ($pid, $status) = @_;
284	warn "pid $pid exited with status $status";	434	warn "pid $pid exited with status $status";
285	$done->broadcast;	435	$done->send;
286	},	436	},
287	);	437	);
288		438
289	# do something else, then wait for process exit	439	# do something else, then wait for process exit
290	$done->wait;	440	$done->recv;
		441
		442	IDLE WATCHERS
		443	Sometimes there is a need to do something, but it is not so important to
		444	do it instantly, but only when there is nothing better to do. This
		445	"nothing better to do" is usually defined to be "no other events need
		446	attention by the event loop".
		447
		448	Idle watchers ideally get invoked when the event loop has nothing better
		449	to do, just before it would block the process to wait for new events.
		450	Instead of blocking, the idle watcher is invoked.
		451
		452	Most event loops unfortunately do not really support idle watchers (only
		453	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		454	will simply call the callback "from time to time".
		455
		456	Example: read lines from STDIN, but only process them when the program
		457	is otherwise idle:
		458
		459	my @lines; # read data
		460	my $idle_w;
		461	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		462	push @lines, scalar <STDIN>;
		463
		464	# start an idle watcher, if not already done
		465	$idle_w \|\|= AnyEvent->idle (cb => sub {
		466	# handle only one line, when there are lines left
		467	if (my $line = shift @lines) {
		468	print "handled when idle: $line";
		469	} else {
		470	# otherwise disable the idle watcher again
		471	undef $idle_w;
		472	}
		473	});
		474	});
291		475
292	CONDITION VARIABLES	476	CONDITION VARIABLES
		477	If you are familiar with some event loops you will know that all of them
		478	require you to run some blocking "loop", "run" or similar function that
		479	will actively watch for new events and call your callbacks.
		480
		481	AnyEvent is slightly different: it expects somebody else to run the
		482	event loop and will only block when necessary (usually when told by the
		483	user).
		484
		485	The instrument to do that is called a "condition variable", so called
		486	because they represent a condition that must become true.
		487
		488	Now is probably a good time to look at the examples further below.
		489
293	Condition variables can be created by calling the "AnyEvent->condvar"	490	Condition variables can be created by calling the "AnyEvent->condvar"
294	method without any arguments.	491	method, usually without arguments. The only argument pair allowed is
		492	"cb", which specifies a callback to be called when the condition
		493	variable becomes true, with the condition variable as the first argument
		494	(but not the results).
295		495
296	A condition variable waits for a condition - precisely that the	496	After creation, the condition variable is "false" until it becomes
297	"->broadcast" method has been called.	497	"true" by calling the "send" method (or calling the condition variable
		498	as if it were a callback, read about the caveats in the description for
		499	the "->send" method).
298		500
299	They are very useful to signal that a condition has been fulfilled, for	501	Condition variables are similar to callbacks, except that you can
		502	optionally wait for them. They can also be called merge points - points
		503	in time where multiple outstanding events have been processed. And yet
		504	another way to call them is transactions - each condition variable can
		505	be used to represent a transaction, which finishes at some point and
		506	delivers a result. And yet some people know them as "futures" - a
		507	promise to compute/deliver something that you can wait for.
		508
		509	Condition variables are very useful to signal that something has
300	example, if you write a module that does asynchronous http requests,	510	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	511	requests, then a condition variable would be the ideal candidate to
302	availability of results.	512	signal the availability of results. The user can either act when the
		513	callback is called or can synchronously "->recv" for the results.
303		514
304	You can also use condition variables to block your main program until an	515	You can also use them to simulate traditional event loops - for example,
305	event occurs - for example, you could "->wait" in your main program	516	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	517	could "->recv" in your main program until the user clicks the Quit
307	"->broadcast" the "quit" event.	518	button of your app, which would "->send" the "quit" event.
308		519
309	Note that condition variables recurse into the event loop - if you have	520	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	521	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,	522	lose. Therefore, condition variables are good to export to your caller,
312	but you should avoid making a blocking wait yourself, at least in	523	but you should avoid making a blocking wait yourself, at least in
313	callbacks, as this asks for trouble.	524	callbacks, as this asks for trouble.
314		525
315	This object has two methods:	526	Condition variables are represented by hash refs in perl, and the keys
		527	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		528	(it is often useful to build your own transaction class on top of
		529	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		530	it's "new" method in your own "new" method.
316		531
317	$cv->wait	532	There are two "sides" to a condition variable - the "producer side"
318	Wait (blocking if necessary) until the "->broadcast" method has been	533	which eventually calls "-> send", and the "consumer side", which waits
319	called on c<$cv>, while servicing other watchers normally.	534	for the send to occur.
320		535
321	You can only wait once on a condition - additional calls will return	536	Example: wait for a timer.
322	immediately.
323
324	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
326	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,
328	by coupling condition variables with some kind of request results
329	and supporting callbacks so the caller knows that getting the result
330	will not block, while still suppporting blocking waits if the caller
331	so desires).
332
333	Another reason never to "->wait" in a module is that you cannot
334	sensibly have two "->wait"'s in parallel, as that would require
335	multiple interpreters or coroutines/threads, none of which
336	"AnyEvent" can supply (the coroutine-aware backends
337	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
338	support concurrent "->wait"'s from different coroutines, however).
339
340	$cv->broadcast
341	Flag the condition as ready - a running "->wait" and all further
342	calls to "wait" will (eventually) return after this method has been
343	called. If nobody is waiting the broadcast will be remembered..
344
345	Example:
346		537
347	# wait till the result is ready	538	# wait till the result is ready
348	my $result_ready = AnyEvent->condvar;	539	my $result_ready = AnyEvent->condvar;
349		540
350	# do something such as adding a timer	541	# do something such as adding a timer
351	# or socket watcher the calls $result_ready->broadcast	542	# or socket watcher the calls $result_ready->send
352	# when the "result" is ready.	543	# when the "result" is ready.
353	# in this case, we simply use a timer:	544	# in this case, we simply use a timer:
354	my $w = AnyEvent->timer (	545	my $w = AnyEvent->timer (
355	after => 1,	546	after => 1,
356	cb => sub { $result_ready->broadcast },	547	cb => sub { $result_ready->send },
357	);	548	);
358		549
359	# this "blocks" (while handling events) till the watcher	550	# this "blocks" (while handling events) till the callback
360	# calls broadcast	551	# calls -<send
361	$result_ready->wait;	552	$result_ready->recv;
		553
		554	Example: wait for a timer, but take advantage of the fact that condition
		555	variables are also callable directly.
		556
		557	my $done = AnyEvent->condvar;
		558	my $delay = AnyEvent->timer (after => 5, cb => $done);
		559	$done->recv;
		560
		561	Example: Imagine an API that returns a condvar and doesn't support
		562	callbacks. This is how you make a synchronous call, for example from the
		563	main program:
		564
		565	use AnyEvent::CouchDB;
		566
		567	...
		568
		569	my @info = $couchdb->info->recv;
		570
		571	And this is how you would just set a callback to be called whenever the
		572	results are available:
		573
		574	$couchdb->info->cb (sub {
		575	my @info = $_[0]->recv;
		576	});
		577
		578	METHODS FOR PRODUCERS
		579	These methods should only be used by the producing side, i.e. the
		580	code/module that eventually sends the signal. Note that it is also the
		581	producer side which creates the condvar in most cases, but it isn't
		582	uncommon for the consumer to create it as well.
		583
		584	$cv->send (...)
		585	Flag the condition as ready - a running "->recv" and all further
		586	calls to "recv" will (eventually) return after this method has been
		587	called. If nobody is waiting the send will be remembered.
		588
		589	If a callback has been set on the condition variable, it is called
		590	immediately from within send.
		591
		592	Any arguments passed to the "send" call will be returned by all
		593	future "->recv" calls.
		594
		595	Condition variables are overloaded so one can call them directly (as
		596	if they were a code reference). Calling them directly is the same as
		597	calling "send".
		598
		599	$cv->croak ($error)
		600	Similar to send, but causes all call's to "->recv" to invoke
		601	"Carp::croak" with the given error message/object/scalar.
		602
		603	This can be used to signal any errors to the condition variable
		604	user/consumer. Doing it this way instead of calling "croak" directly
		605	delays the error detetcion, but has the overwhelmign advantage that
		606	it diagnoses the error at the place where the result is expected,
		607	and not deep in some event clalback without connection to the actual
		608	code causing the problem.
		609
		610	$cv->begin ([group callback])
		611	$cv->end
		612	These two methods can be used to combine many transactions/events
		613	into one. For example, a function that pings many hosts in parallel
		614	might want to use a condition variable for the whole process.
		615
		616	Every call to "->begin" will increment a counter, and every call to
		617	"->end" will decrement it. If the counter reaches 0 in "->end", the
		618	(last) callback passed to "begin" will be executed. That callback is
		619	supposed to call "->send", but that is not required. If no
		620	callback was set, "send" will be called without any arguments.
		621
		622	You can think of "$cv->send" giving you an OR condition (one call
		623	sends), while "$cv->begin" and "$cv->end" giving you an AND
		624	condition (all "begin" calls must be "end"'ed before the condvar
		625	sends).
		626
		627	Let's start with a simple example: you have two I/O watchers (for
		628	example, STDOUT and STDERR for a program), and you want to wait for
		629	both streams to close before activating a condvar:
		630
		631	my $cv = AnyEvent->condvar;
		632
		633	$cv->begin; # first watcher
		634	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		635	defined sysread $fh1, my $buf, 4096
		636	or $cv->end;
		637	});
		638
		639	$cv->begin; # second watcher
		640	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		641	defined sysread $fh2, my $buf, 4096
		642	or $cv->end;
		643	});
		644
		645	$cv->recv;
		646
		647	This works because for every event source (EOF on file handle),
		648	there is one call to "begin", so the condvar waits for all calls to
		649	"end" before sending.
		650
		651	The ping example mentioned above is slightly more complicated, as
		652	the there are results to be passwd back, and the number of tasks
		653	that are begung can potentially be zero:
		654
		655	my $cv = AnyEvent->condvar;
		656
		657	my %result;
		658	$cv->begin (sub { $cv->send (\%result) });
		659
		660	for my $host (@list_of_hosts) {
		661	$cv->begin;
		662	ping_host_then_call_callback $host, sub {
		663	$result{$host} = ...;
		664	$cv->end;
		665	};
		666	}
		667
		668	$cv->end;
		669
		670	This code fragment supposedly pings a number of hosts and calls
		671	"send" after results for all then have have been gathered - in any
		672	order. To achieve this, the code issues a call to "begin" when it
		673	starts each ping request and calls "end" when it has received some
		674	result for it. Since "begin" and "end" only maintain a counter, the
		675	order in which results arrive is not relevant.
		676
		677	There is an additional bracketing call to "begin" and "end" outside
		678	the loop, which serves two important purposes: first, it sets the
		679	callback to be called once the counter reaches 0, and second, it
		680	ensures that "send" is called even when "no" hosts are being pinged
		681	(the loop doesn't execute once).
		682
		683	This is the general pattern when you "fan out" into multiple (but
		684	potentially none) subrequests: use an outer "begin"/"end" pair to
		685	set the callback and ensure "end" is called at least once, and then,
		686	for each subrequest you start, call "begin" and for each subrequest
		687	you finish, call "end".
		688
		689	METHODS FOR CONSUMERS
		690	These methods should only be used by the consuming side, i.e. the code
		691	awaits the condition.
		692
		693	$cv->recv
		694	Wait (blocking if necessary) until the "->send" or "->croak" methods
		695	have been called on c<$cv>, while servicing other watchers normally.
		696
		697	You can only wait once on a condition - additional calls are valid
		698	but will return immediately.
		699
		700	If an error condition has been set by calling "->croak", then this
		701	function will call "croak".
		702
		703	In list context, all parameters passed to "send" will be returned,
		704	in scalar context only the first one will be returned.
		705
		706	Note that doing a blocking wait in a callback is not supported by
		707	any event loop, that is, recursive invocation of a blocking "->recv"
		708	is not allowed, and the "recv" call will "croak" if such a condition
		709	is detected. This condition can be slightly loosened by using
		710	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		711	thread that doesn't run the event loop itself.
		712
		713	Not all event models support a blocking wait - some die in that case
		714	(programs might want to do that to stay interactive), so *if you are
		715	using this from a module, never require a blocking wait*. Instead,
		716	let the caller decide whether the call will block or not (for
		717	example, by coupling condition variables with some kind of request
		718	results and supporting callbacks so the caller knows that getting
		719	the result will not block, while still supporting blocking waits if
		720	the caller so desires).
		721
		722	You can ensure that "-recv" never blocks by setting a callback and
		723	only calling "->recv" from within that callback (or at a later
		724	time). This will work even when the event loop does not support
		725	blocking waits otherwise.
		726
		727	$bool = $cv->ready
		728	Returns true when the condition is "true", i.e. whether "send" or
		729	"croak" have been called.
		730
		731	$cb = $cv->cb ($cb->($cv))
		732	This is a mutator function that returns the callback set and
		733	optionally replaces it before doing so.
		734
		735	The callback will be called when the condition becomes "true", i.e.
		736	when "send" or "croak" are called, with the only argument being the
		737	condition variable itself. Calling "recv" inside the callback or at
		738	any later time is guaranteed not to block.
		739
		740	SUPPORTED EVENT LOOPS/BACKENDS
		741	The available backend classes are (every class has its own manpage):
		742
		743	Backends that are autoprobed when no other event loop can be found.
		744	EV is the preferred backend when no other event loop seems to be in
		745	use. If EV is not installed, then AnyEvent will try Event, and,
		746	failing that, will fall back to its own pure-perl implementation,
		747	which is available everywhere as it comes with AnyEvent itself.
		748
		749	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		750	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		751	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		752
		753	Backends that are transparently being picked up when they are used.
		754	These will be used when they are currently loaded when the first
		755	watcher is created, in which case it is assumed that the application
		756	is using them. This means that AnyEvent will automatically pick the
		757	right backend when the main program loads an event module before
		758	anything starts to create watchers. Nothing special needs to be done
		759	by the main program.
		760
		761	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		762	AnyEvent::Impl::Tk based on Tk, very broken.
		763	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		764	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		765
		766	Backends with special needs.
		767	Qt requires the Qt::Application to be instantiated first, but will
		768	otherwise be picked up automatically. As long as the main program
		769	instantiates the application before any AnyEvent watchers are
		770	created, everything should just work.
		771
		772	AnyEvent::Impl::Qt based on Qt.
		773
		774	Support for IO::Async can only be partial, as it is too broken and
		775	architecturally limited to even support the AnyEvent API. It also is
		776	the only event loop that needs the loop to be set explicitly, so it
		777	can only be used by a main program knowing about AnyEvent. See
		778	AnyEvent::Impl::Async for the gory details.
		779
		780	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		781
		782	Event loops that are indirectly supported via other backends.
		783	Some event loops can be supported via other modules:
		784
		785	There is no direct support for WxWidgets (Wx) or Prima.
		786
		787	WxWidgets has no support for watching file handles. However, you can
		788	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		789	simply polls 20 times per second, which was considered to be too
		790	horrible to even consider for AnyEvent.
		791
		792	Prima is not supported as nobody seems to be using it, but it has a
		793	POE backend, so it can be supported through POE.
		794
		795	AnyEvent knows about both Prima and Wx, however, and will try to
		796	load POE when detecting them, in the hope that POE will pick them
		797	up, in which case everything will be automatic.
362		798
363	GLOBAL VARIABLES AND FUNCTIONS	799	GLOBAL VARIABLES AND FUNCTIONS
		800	These are not normally required to use AnyEvent, but can be useful to
		801	write AnyEvent extension modules.
		802
364	$AnyEvent::MODEL	803	$AnyEvent::MODEL
365	Contains "undef" until the first watcher is being created. Then it	804	Contains "undef" until the first watcher is being created, before
		805	the backend has been autodetected.
		806
366	contains the event model that is being used, which is the name of	807	Afterwards it contains the event model that is being used, which is
367	the Perl class implementing the model. This class is usually one of	808	the name of the Perl class implementing the model. This class is
368	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	809	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
369	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	810	other class in the case AnyEvent has been extended at runtime (e.g.
370		811	in rxvt-unicode it will be "urxvt::anyevent").
371	The known classes so far are:
372
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).
376	AnyEvent::Impl::Event based on Event, second best choice.
377	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.
380	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
381	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
382	AnyEvent::Impl::POE based on POE, not generic enough for full support.
383
384	There is no support for WxWidgets, as WxWidgets has no support for
385	watching file handles. However, you can use WxWidgets through the
386	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
387	second, which was considered to be too horrible to even consider for
388	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
389	using it's adaptor.
390
391	AnyEvent knows about Prima and Wx and will try to use POE when
392	autodetecting them.
393		812
394	AnyEvent::detect	813	AnyEvent::detect
395	Returns $AnyEvent::MODEL, forcing autodetection of the event model	814	Returns $AnyEvent::MODEL, forcing autodetection of the event model
396	if necessary. You should only call this function right before you	815	if necessary. You should only call this function right before you
397	would have created an AnyEvent watcher anyway, that is, as late as	816	would have created an AnyEvent watcher anyway, that is, as late as
398	possible at runtime.	817	possible at runtime, and not e.g. while initialising of your module.
		818
		819	If you need to do some initialisation before AnyEvent watchers are
		820	created, use "post_detect".
		821
		822	$guard = AnyEvent::post_detect { BLOCK }
		823	Arranges for the code block to be executed as soon as the event
		824	model is autodetected (or immediately if this has already happened).
		825
		826	The block will be executed after the actual backend has been
		827	detected ($AnyEvent::MODEL is set), but before any watchers have
		828	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		829	other initialisations - see the sources of AnyEvent::Strict or
		830	AnyEvent::AIO to see how this is used.
		831
		832	The most common usage is to create some global watchers, without
		833	forcing event module detection too early, for example, AnyEvent::AIO
		834	creates and installs the global IO::AIO watcher in a "post_detect"
		835	block to avoid autodetecting the event module at load time.
		836
		837	If called in scalar or list context, then it creates and returns an
		838	object that automatically removes the callback again when it is
		839	destroyed. See Coro::BDB for a case where this is useful.
		840
		841	@AnyEvent::post_detect
		842	If there are any code references in this array (you can "push" to it
		843	before or after loading AnyEvent), then they will called directly
		844	after the event loop has been chosen.
		845
		846	You should check $AnyEvent::MODEL before adding to this array,
		847	though: if it is defined then the event loop has already been
		848	detected, and the array will be ignored.
		849
		850	Best use "AnyEvent::post_detect { BLOCK }" when your application
		851	allows it,as it takes care of these details.
		852
		853	This variable is mainly useful for modules that can do something
		854	useful when AnyEvent is used and thus want to know when it is
		855	initialised, but do not need to even load it by default. This array
		856	provides the means to hook into AnyEvent passively, without loading
		857	it.
399		858
400	WHAT TO DO IN A MODULE	859	WHAT TO DO IN A MODULE
401	As a module author, you should "use AnyEvent" and call AnyEvent methods	860	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.	861	freely, but you should not load a specific event module or rely on it.
403		862
404	Be careful when you create watchers in the module body - AnyEvent will	863	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,	864	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	865	so by calling AnyEvent in your module body you force the user of your
407	module to load the event module first.	866	module to load the event module first.
408		867
409	Never call "->wait" on a condition variable unless you know that the	868	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	869	"->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	870	stall the whole program, and the whole point of using events is to stay
412	stay interactive.	871	interactive.
413		872
414	It is fine, however, to call "->wait" when the user of your module	873	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	874	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"	875	called "results" that returns the results, it should call "->recv"
417	freely, as the user of your module knows what she is doing. always).	876	freely, as the user of your module knows what she is doing. always).
418		877
419	WHAT TO DO IN THE MAIN PROGRAM	878	WHAT TO DO IN THE MAIN PROGRAM
420	There will always be a single main program - the only place that should	879	There will always be a single main program - the only place that should
421	dictate which event model to use.	880	dictate which event model to use.
…		…
423	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	882	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	883	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	884	AnyEvent decide which implementation to chose if some module relies on
426	it.	885	it.
427		886
428	If the main program relies on a specific event model. For example, in	887	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	888	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:	889	event module before loading AnyEvent or any module that uses it:
431	generally speaking, you should load it as early as possible. The reason	890	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	891	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,	892	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	893	and it might chose the wrong one unless you load the correct one
435	yourself.	894	yourself.
436		895
437	You can chose to use a rather inefficient pure-perl implementation by	896	You can chose to use a pure-perl implementation by loading the
438	loading the "AnyEvent::Impl::Perl" module, which gives you similar	897	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
439	behaviour everywhere, but letting AnyEvent chose is generally better.	898	everywhere, but letting AnyEvent chose the model is generally better.
		899
		900	MAINLOOP EMULATION
		901	Sometimes (often for short test scripts, or even standalone programs who
		902	only want to use AnyEvent), you do not want to run a specific event
		903	loop.
		904
		905	In that case, you can use a condition variable like this:
		906
		907	AnyEvent->condvar->recv;
		908
		909	This has the effect of entering the event loop and looping forever.
		910
		911	Note that usually your program has some exit condition, in which case it
		912	is better to use the "traditional" approach of storing a condition
		913	variable somewhere, waiting for it, and sending it when the program
		914	should exit cleanly.
440		915
441	OTHER MODULES	916	OTHER MODULES
442	The following is a non-exhaustive list of additional modules that use	917	The following is a non-exhaustive list of additional modules that use
443	AnyEvent and can therefore be mixed easily with other AnyEvent modules	918	AnyEvent as a client and can therefore be mixed easily with other
444	in the same program. Some of the modules come with AnyEvent, some are	919	AnyEvent modules and other event loops in the same program. Some of the
445	available via CPAN.	920	modules come with AnyEvent, most are available via CPAN.
446		921
447	AnyEvent::Util	922	AnyEvent::Util
448	Contains various utility functions that replace often-used but	923	Contains various utility functions that replace often-used but
449	blocking functions such as "inet_aton" by event-/callback-based	924	blocking functions such as "inet_aton" by event-/callback-based
450	versions.	925	versions.
451		926
		927	AnyEvent::Socket
		928	Provides various utility functions for (internet protocol) sockets,
		929	addresses and name resolution. Also functions to create non-blocking
		930	tcp connections or tcp servers, with IPv6 and SRV record support and
		931	more.
		932
452	AnyEvent::Handle	933	AnyEvent::Handle
453	Provide read and write buffers and manages watchers for reads and	934	Provide read and write buffers, manages watchers for reads and
454	writes.	935	writes, supports raw and formatted I/O, I/O queued and fully
		936	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
455		937
456	AnyEvent::Socket	938	AnyEvent::DNS
457	Provides a means to do non-blocking connects, accepts etc.	939	Provides rich asynchronous DNS resolver capabilities.
		940
		941	AnyEvent::HTTP
		942	A simple-to-use HTTP library that is capable of making a lot of
		943	concurrent HTTP requests.
458		944
459	AnyEvent::HTTPD	945	AnyEvent::HTTPD
460	Provides a simple web application server framework.	946	Provides a simple web application server framework.
461		947
462	AnyEvent::DNS
463	Provides asynchronous DNS resolver capabilities, beyond what
464	AnyEvent::Util offers.
465
466	AnyEvent::FastPing	948	AnyEvent::FastPing
467	The fastest ping in the west.	949	The fastest ping in the west.
468		950
		951	AnyEvent::DBI
		952	Executes DBI requests asynchronously in a proxy process.
		953
		954	AnyEvent::AIO
		955	Truly asynchronous I/O, should be in the toolbox of every event
		956	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		957	together.
		958
		959	AnyEvent::BDB
		960	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
		961	fuses BDB and AnyEvent together.
		962
		963	AnyEvent::GPSD
		964	A non-blocking interface to gpsd, a daemon delivering GPS
		965	information.
		966
		967	AnyEvent::IRC
		968	AnyEvent based IRC client module family (replacing the older
469	Net::IRC3	969	Net::IRC3).
470	AnyEvent based IRC client module family.
471		970
472	Net::XMPP2	971	AnyEvent::XMPP
473	AnyEvent based XMPP (Jabber protocol) module family.	972	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		973	older Net::XMPP2>.
		974
		975	AnyEvent::IGS
		976	A non-blocking interface to the Internet Go Server protocol (used by
		977	App::IGS).
474		978
475	Net::FCP	979	Net::FCP
476	AnyEvent-based implementation of the Freenet Client Protocol,	980	AnyEvent-based implementation of the Freenet Client Protocol,
477	birthplace of AnyEvent.	981	birthplace of AnyEvent.
478		982
479	Event::ExecFlow	983	Event::ExecFlow
480	High level API for event-based execution flow control.	984	High level API for event-based execution flow control.
481		985
482	Coro	986	Coro
483	Has special support for AnyEvent.	987	Has special support for AnyEvent via Coro::AnyEvent.
484		988
485	IO::Lambda	989	ERROR AND EXCEPTION HANDLING
486	The lambda approach to I/O - don't ask, look there. Can use	990	In general, AnyEvent does not do any error handling - it relies on the
487	AnyEvent.	991	caller to do that if required. The AnyEvent::Strict module (see also the
		992	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		993	checking of all AnyEvent methods, however, which is highly useful during
		994	development.
488		995
489	IO::AIO	996	As for exception handling (i.e. runtime errors and exceptions thrown
490	Truly asynchronous I/O, should be in the toolbox of every event	997	while executing a callback), this is not only highly event-loop
491	programmer. Can be trivially made to use AnyEvent.	998	specific, but also not in any way wrapped by this module, as this is the
		999	job of the main program.
492		1000
493	BDB Truly asynchronous Berkeley DB access. Can be trivially made to use	1001	The pure perl event loop simply re-throws the exception (usually within
494	AnyEvent.	1002	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
		1003	Glib uses "install_exception_handler" and so on.
		1004
		1005	ENVIRONMENT VARIABLES
		1006	The following environment variables are used by this module or its
		1007	submodules.
		1008
		1009	Note that AnyEvent will remove all environment variables starting with
		1010	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1011	enabled.
		1012
		1013	"PERL_ANYEVENT_VERBOSE"
		1014	By default, AnyEvent will be completely silent except in fatal
		1015	conditions. You can set this environment variable to make AnyEvent
		1016	more talkative.
		1017
		1018	When set to 1 or higher, causes AnyEvent to warn about unexpected
		1019	conditions, such as not being able to load the event model specified
		1020	by "PERL_ANYEVENT_MODEL".
		1021
		1022	When set to 2 or higher, cause AnyEvent to report to STDERR which
		1023	event model it chooses.
		1024
		1025	When set to 8 or higher, then AnyEvent will report extra information
		1026	on which optional modules it loads and how it implements certain
		1027	features.
		1028
		1029	"PERL_ANYEVENT_STRICT"
		1030	AnyEvent does not do much argument checking by default, as thorough
		1031	argument checking is very costly. Setting this variable to a true
		1032	value will cause AnyEvent to load "AnyEvent::Strict" and then to
		1033	thoroughly check the arguments passed to most method calls. If it
		1034	finds any problems, it will croak.
		1035
		1036	In other words, enables "strict" mode.
		1037
		1038	Unlike "use strict" (or it's modern cousin, "use common::sense", it
		1039	is definitely recommended to keep it off in production. Keeping
		1040	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1041	programs can be very useful, however.
		1042
		1043	"PERL_ANYEVENT_MODEL"
		1044	This can be used to specify the event model to be used by AnyEvent,
		1045	before auto detection and -probing kicks in. It must be a string
		1046	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		1047	gets prepended and the resulting module name is loaded and if the
		1048	load was successful, used as event model. If it fails to load
		1049	AnyEvent will proceed with auto detection and -probing.
		1050
		1051	This functionality might change in future versions.
		1052
		1053	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		1054	could start your program like this:
		1055
		1056	PERL_ANYEVENT_MODEL=Perl perl ...
		1057
		1058	"PERL_ANYEVENT_PROTOCOLS"
		1059	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		1060	preferences for IPv4 or IPv6. The default is unspecified (and might
		1061	change, or be the result of auto probing).
		1062
		1063	Must be set to a comma-separated list of protocols or address
		1064	families, current supported: "ipv4" and "ipv6". Only protocols
		1065	mentioned will be used, and preference will be given to protocols
		1066	mentioned earlier in the list.
		1067
		1068	This variable can effectively be used for denial-of-service attacks
		1069	against local programs (e.g. when setuid), although the impact is
		1070	likely small, as the program has to handle conenction and other
		1071	failures anyways.
		1072
		1073	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		1074	IPv6, but support both and try to use both.
		1075	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		1076	resolve or contact IPv6 addresses.
		1077	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		1078	prefer IPv6 over IPv4.
		1079
		1080	"PERL_ANYEVENT_EDNS0"
		1081	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		1082	for DNS. This extension is generally useful to reduce DNS traffic,
		1083	but some (broken) firewalls drop such DNS packets, which is why it
		1084	is off by default.
		1085
		1086	Setting this variable to 1 will cause AnyEvent::DNS to announce
		1087	EDNS0 in its DNS requests.
		1088
		1089	"PERL_ANYEVENT_MAX_FORKS"
		1090	The maximum number of child processes that
		1091	"AnyEvent::Util::fork_call" will create in parallel.
		1092
		1093	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1094	The default value for the "max_outstanding" parameter for the
		1095	default DNS resolver - this is the maximum number of parallel DNS
		1096	requests that are sent to the DNS server.
		1097
		1098	"PERL_ANYEVENT_RESOLV_CONF"
		1099	The file to use instead of /etc/resolv.conf (or OS-specific
		1100	configuration) in the default resolver. When set to the empty
		1101	string, no default config will be used.
		1102
		1103	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1104	When neither "ca_file" nor "ca_path" was specified during
		1105	AnyEvent::TLS context creation, and either of these environment
		1106	variables exist, they will be used to specify CA certificate
		1107	locations instead of a system-dependent default.
		1108
		1109	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1110	When these are set to 1, then the respective modules are not loaded.
		1111	Mostly good for testing AnyEvent itself.
495		1112
496	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1113	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
497	This is an advanced topic that you do not normally need to use AnyEvent	1114	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	1115	in a module. This section is only of use to event loop authors who want
499	to provide AnyEvent compatibility.	1116	to provide AnyEvent compatibility.
…		…
533		1150
534	rxvt-unicode also cheats a bit by not providing blocking access to	1151	rxvt-unicode also cheats a bit by not providing blocking access to
535	condition variables: code blocking while waiting for a condition will	1152	condition variables: code blocking while waiting for a condition will
536	"die". This still works with most modules/usages, and blocking calls	1153	"die". This still works with most modules/usages, and blocking calls
537	must not be done in an interactive application, so it makes sense.	1154	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		1155
569	EXAMPLE PROGRAM	1156	EXAMPLE PROGRAM
570	The following program uses an I/O watcher to read data from STDIN, a	1157	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	1158	timer to display a message once per second, and a condition variable to
572	quit the program when the user enters quit:	1159	quit the program when the user enters quit:
…		…
580	poll => 'r',	1167	poll => 'r',
581	cb => sub {	1168	cb => sub {
582	warn "io event <$_[0]>\n"; # will always output <r>	1169	warn "io event <$_[0]>\n"; # will always output <r>
583	chomp (my $input = <STDIN>); # read a line	1170	chomp (my $input = <STDIN>); # read a line
584	warn "read: $input\n"; # output what has been read	1171	warn "read: $input\n"; # output what has been read
585	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1172	$cv->send if $input =~ /^q/i; # quit program if /^q/i
586	},	1173	},
587	);	1174	);
588		1175
589	my $time_watcher; # can only be used once	1176	my $time_watcher; # can only be used once
590		1177
…		…
595	});	1182	});
596	}	1183	}
597		1184
598	new_timer; # create first timer	1185	new_timer; # create first timer
599		1186
600	$cv->wait; # wait until user enters /^q/i	1187	$cv->recv; # wait until user enters /^q/i
601		1188
602	REAL-WORLD EXAMPLE	1189	REAL-WORLD EXAMPLE
603	Consider the Net::FCP module. It features (among others) the following	1190	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:	1191	API calls, which are to freenet what HTTP GET requests are to http:
605		1192
…		…
654	syswrite $txn->{fh}, $txn->{request}	1241	syswrite $txn->{fh}, $txn->{request}
655	or die "connection or write error";	1242	or die "connection or write error";
656	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1243	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
657		1244
658	Again, "fh_ready_r" waits till all data has arrived, and then stores the	1245	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:	1246	result and signals any possible waiters that the request has finished:
660		1247
661	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1248	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
662		1249
663	if (end-of-file or data complete) {	1250	if (end-of-file or data complete) {
664	$txn->{result} = $txn->{buf};	1251	$txn->{result} = $txn->{buf};
665	$txn->{finished}->broadcast;	1252	$txn->{finished}->send;
666	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1253	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
667	}	1254	}
668		1255
669	The "result" method, finally, just waits for the finished signal (if the	1256	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	1257	request was already finished, it doesn't wait, of course, and returns
671	the data:	1258	the data:
672		1259
673	$txn->{finished}->wait;	1260	$txn->{finished}->recv;
674	return $txn->{result};	1261	return $txn->{result};
675		1262
676	The actual code goes further and collects all errors ("die"s,	1263	The actual code goes further and collects all errors ("die"s,
677	exceptions) that occured during request processing. The "result" method	1264	exceptions) that occurred during request processing. The "result" method
678	detects whether an exception as thrown (it is stored inside the $txn	1265	detects whether an exception as thrown (it is stored inside the $txn
679	object) and just throws the exception, which means connection errors and	1266	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,	1267	other problems get reported tot he code that tries to use the result,
681	not in a random callback.	1268	not in a random callback.
682		1269
…		…
713		1300
714	my $quit = AnyEvent->condvar;	1301	my $quit = AnyEvent->condvar;
715		1302
716	$fcp->txn_client_get ($url)->cb (sub {	1303	$fcp->txn_client_get ($url)->cb (sub {
717	...	1304	...
718	$quit->broadcast;	1305	$quit->send;
719	});	1306	});
720		1307
721	$quit->wait;	1308	$quit->recv;
722		1309
723	BENCHMARKS	1310	BENCHMARKS
724	To give you an idea of the performance and overheads that AnyEvent adds	1311	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	1312	over the event loops themselves and to give you an impression of the
726	speed of various event loops I prepared some benchmarks.	1313	speed of various event loops I prepared some benchmarks.
727		1314
728	BENCHMARKING ANYEVENT OVERHEAD	1315	BENCHMARKING ANYEVENT OVERHEAD
729	Here is a benchmark of various supported event models used natively and	1316	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	1317	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,	1318	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.	1319	which it is), lets them fire exactly once and destroys them again.
733		1320
734	Source code for this benchmark is found as eg/bench in the AnyEvent	1321	Source code for this benchmark is found as eg/bench in the AnyEvent
735	distribution.	1322	distribution.
…		…
751	between all watchers, to avoid adding memory overhead. That means	1338	between all watchers, to avoid adding memory overhead. That means
752	closure creation and memory usage is not included in the figures.	1339	closure creation and memory usage is not included in the figures.
753		1340
754	invoke is the time, in microseconds, used to invoke a simple callback.	1341	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	1342	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	1343	"watcher" times, it would "->send" a condvar once to signal the end of
757	of this phase.	1344	this phase.
758		1345
759	destroy is the time, in microseconds, that it takes to destroy a	1346	destroy is the time, in microseconds, that it takes to destroy a
760	single watcher.	1347	single watcher.
761		1348
762	Results	1349	Results
763	name watchers bytes create invoke destroy comment	1350	name watchers bytes create invoke destroy comment
764	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1351	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
765	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1352	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
766	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1353	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
767	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1354	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
768	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1355	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
769	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1356	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1357	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1358	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
770	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1359	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
771	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1360	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
772	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1361	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
773	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1362	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
774		1363
775	Discussion	1364	Discussion
776	The benchmark does not measure scalability of the event loop very	1365	The benchmark does not measure scalability of the event loop very
777	well. For example, a select-based event loop (such as the pure perl one)	1366	well. For example, a select-based event loop (such as the pure perl one)
778	can never compete with an event loop that uses epoll when the number of	1367	can never compete with an event loop that uses epoll when the number of
…		…
804	benchmark.	1393	benchmark.
805		1394
806	The "Event" module has a relatively high setup and callback invocation	1395	The "Event" module has a relatively high setup and callback invocation
807	cost, but overall scores in on the third place.	1396	cost, but overall scores in on the third place.
808		1397
		1398	"IO::Async" performs admirably well, about on par with "Event", even
		1399	when using its pure perl backend.
		1400
809	"Glib"'s memory usage is quite a bit higher, but it features a faster	1401	"Glib"'s memory usage is quite a bit higher, but it features a faster
810	callback invocation and overall ends up in the same class as "Event".	1402	callback invocation and overall ends up in the same class as "Event".
811	However, Glib scales extremely badly, doubling the number of watchers	1403	However, Glib scales extremely badly, doubling the number of watchers
812	increases the processing time by more than a factor of four, making it	1404	increases the processing time by more than a factor of four, making it
813	completely unusable when using larger numbers of watchers (note that	1405	completely unusable when using larger numbers of watchers (note that
…		…
823	the figures above).	1415	the figures above).
824		1416
825	"POE", regardless of underlying event loop (whether using its pure perl	1417	"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	1418	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	1419	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	1420	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	1421	watchers, and 10 times as much memory as Event (the high memory
830	caused by requiring a session for each watcher). Watcher invocation	1422	requirements are caused by requiring a session for each watcher).
831	speed is almost 900 times slower than with AnyEvent's pure perl	1423	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1424	pure perl implementation.
		1425
832	implementation. The design of the POE adaptor class in AnyEvent can not	1426	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	1427	for the performance issues, though, as session creation overhead is
834	to execution of the state machine, which is coded pretty optimally	1428	small compared to execution of the state machine, which is coded pretty
835	within AnyEvent::Impl::POE. POE simply seems to be abysmally slow.	1429	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1430	using multiple sessions is not a good approach, especially regarding
		1431	memory usage, even the author of POE could not come up with a faster
		1432	design).
836		1433
837	Summary	1434	Summary
838	* Using EV through AnyEvent is faster than any other event loop (even	1435	* Using EV through AnyEvent is faster than any other event loop (even
839	when used without AnyEvent), but most event loops have acceptable	1436	when used without AnyEvent), but most event loops have acceptable
840	performance with or without AnyEvent.	1437	performance with or without AnyEvent.
…		…
845		1442
846	* You should avoid POE like the plague if you want performance or	1443	* You should avoid POE like the plague if you want performance or
847	reasonable memory usage.	1444	reasonable memory usage.
848		1445
849	BENCHMARKING THE LARGE SERVER CASE	1446	BENCHMARKING THE LARGE SERVER CASE
850	This benchmark atcually benchmarks the event loop itself. It works by	1447	This benchmark actually benchmarks the event loop itself. It works by
851	creating a number of "servers": each server consists of a socketpair, a	1448	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	1449	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	1450	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	1451	socket watcher reads a byte it will write that byte to a random other
855	"server".	1452	"server".
856		1453
857	The effect is that there will be a lot of I/O watchers, only part of	1454	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	1455	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).	1456	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	1457	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).	1458	how most timeouts work (and puts extra pressure on the event loops).
862		1459
863	In this benchmark, we use 10000 socketpairs (20000 sockets), of which	1460	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	1461	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.	1462	many connections, most of which are idle at any one point in time.
866		1463
867	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1464	Source code for this benchmark is found as eg/bench2 in the AnyEvent
868	distribution.	1465	distribution.
869		1466
870	Explanation of the columns	1467	Explanation of the columns
871	sockets is the number of sockets, and twice the number of "servers"	1468	sockets is the number of sockets, and twice the number of "servers"
872	(as each server has a read and write socket end).	1469	(as each server has a read and write socket end).
873		1470
874	create is the time it takes to create a socketpair (which is	1471	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.	1472	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
876		1473
877	request, the most important value, is the time it takes to handle a	1474	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	1475	single "request", that is, reading the token from the pipe and
879	forwarding it to another server. This includes deleting the old timeout	1476	forwarding it to another server. This includes deleting the old timeout
880	and creating a new one that moves the timeout into the future.	1477	and creating a new one that moves the timeout into the future.
881		1478
882	Results	1479	Results
883	name sockets create request	1480	name sockets create request
884	EV 20000 69.01 11.16	1481	EV 20000 69.01 11.16
885	Perl 20000 73.32 35.87	1482	Perl 20000 73.32 35.87
		1483	IOAsync 20000 157.00 98.14 epoll
		1484	IOAsync 20000 159.31 616.06 poll
886	Event 20000 212.62 257.32	1485	Event 20000 212.62 257.32
887	Glib 20000 651.16 1896.30	1486	Glib 20000 651.16 1896.30
888	POE 20000 349.67 12317.24 uses POE::Loop::Event	1487	POE 20000 349.67 12317.24 uses POE::Loop::Event
889		1488
890	Discussion	1489	Discussion
891	This benchmark does measure scalability and overall performance of the	1490	This benchmark does measure scalability and overall performance of the
892	particular event loop.	1491	particular event loop.
893		1492
894	EV is again fastest. Since it is using epoll on my system, the setup	1493	EV is again fastest. Since it is using epoll on my system, the setup
895	time is relatively high, though.	1494	time is relatively high, though.
896		1495
897	Perl surprisingly comes second. It is much faster than the C-based event	1496	Perl surprisingly comes second. It is much faster than the C-based event
898	loops Event and Glib.	1497	loops Event and Glib.
		1498
		1499	IO::Async performs very well when using its epoll backend, and still
		1500	quite good compared to Glib when using its pure perl backend.
899		1501
900	Event suffers from high setup time as well (look at its code and you	1502	Event suffers from high setup time as well (look at its code and you
901	will understand why). Callback invocation also has a high overhead	1503	will understand why). Callback invocation also has a high overhead
902	compared to the "$_->() for .."-style loop that the Perl event loop	1504	compared to the "$_->() for .."-style loop that the Perl event loop
903	uses. Event uses select or poll in basically all documented	1505	uses. Event uses select or poll in basically all documented
…		…
909	POE is still completely out of the picture, taking over 1000 times as	1511	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	1512	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.	1513	though it uses a C-based event loop in this case.
912		1514
913	Summary	1515	Summary
914	* The pure perl implementation performs extremely well, considering	1516	* The pure perl implementation performs extremely well.
915	that it uses select.
916		1517
917	* Avoid Glib or POE in large projects where performance matters.	1518	* Avoid Glib or POE in large projects where performance matters.
918		1519
919	BENCHMARKING SMALL SERVERS	1520	BENCHMARKING SMALL SERVERS
920	While event loops should scale (and select-based ones do not...) even to	1521	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	1545	and speed most when you have lots of watchers, not when you only have a
945	few of them).	1546	few of them).
946		1547
947	EV is again fastest.	1548	EV is again fastest.
948		1549
949	Perl again comes second. It is noticably faster than the C-based event	1550	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	1551	loops Event and Glib, although the difference is too small to really
951	matter.	1552	matter.
952		1553
953	POE also performs much better in this case, but is is still far behind	1554	POE also performs much better in this case, but is is still far behind
954	the others.	1555	the others.
955		1556
956	Summary	1557	Summary
957	* C-based event loops perform very well with small number of watchers,	1558	* C-based event loops perform very well with small number of watchers,
958	as the management overhead dominates.	1559	as the management overhead dominates.
959		1560
		1561	THE IO::Lambda BENCHMARK
		1562	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1563	could be misinterpreted to make AnyEvent look bad. In fact, the
		1564	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1565	better (which shouldn't come as a surprise to anybody). As such, the
		1566	benchmark is fine, and mostly shows that the AnyEvent backend from
		1567	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1568	without the extra baggage? To explore this, I wrote the equivalent
		1569	benchmark for AnyEvent.
		1570
		1571	The benchmark itself creates an echo-server, and then, for 500 times,
		1572	connects to the echo server, sends a line, waits for the reply, and then
		1573	creates the next connection. This is a rather bad benchmark, as it
		1574	doesn't test the efficiency of the framework or much non-blocking I/O,
		1575	but it is a benchmark nevertheless.
		1576
		1577	name runtime
		1578	Lambda/select 0.330 sec
		1579	+ optimized 0.122 sec
		1580	Lambda/AnyEvent 0.327 sec
		1581	+ optimized 0.138 sec
		1582	Raw sockets/select 0.077 sec
		1583	POE/select, components 0.662 sec
		1584	POE/select, raw sockets 0.226 sec
		1585	POE/select, optimized 0.404 sec
		1586
		1587	AnyEvent/select/nb 0.085 sec
		1588	AnyEvent/EV/nb 0.068 sec
		1589	+state machine 0.134 sec
		1590
		1591	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1592	benchmarks actually make blocking connects and use 100% blocking I/O,
		1593	defeating the purpose of an event-based solution. All of the newly
		1594	written AnyEvent benchmarks use 100% non-blocking connects (using
		1595	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1596	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1597	connects generally require a lot more bookkeeping and event handling
		1598	than blocking connects (which involve a single syscall only).
		1599
		1600	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1601	offers similar expressive power as POE and IO::Lambda, using
		1602	conventional Perl syntax. This means that both the echo server and the
		1603	client are 100% non-blocking, further placing it at a disadvantage.
		1604
		1605	As you can see, the AnyEvent + EV combination even beats the
		1606	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1607	backend easily beats IO::Lambda and POE.
		1608
		1609	And even the 100% non-blocking version written using the high-level (and
		1610	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a
		1611	large margin, even though it does all of DNS, tcp-connect and socket I/O
		1612	in a non-blocking way.
		1613
		1614	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1615	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1616	part of the IO::lambda distribution and were used without any changes.
		1617
		1618	SIGNALS
		1619	AnyEvent currently installs handlers for these signals:
		1620
		1621	SIGCHLD
		1622	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1623	emulation for event loops that do not support them natively. Also,
		1624	some event loops install a similar handler.
		1625
		1626	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1627	then AnyEvent will reset it to default, to avoid losing child exit
		1628	statuses.
		1629
		1630	SIGPIPE
		1631	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1632	"undef" when AnyEvent gets loaded.
		1633
		1634	The rationale for this is that AnyEvent users usually do not really
		1635	depend on SIGPIPE delivery (which is purely an optimisation for
		1636	shell use, or badly-written programs), but "SIGPIPE" can cause
		1637	spurious and rare program exits as a lot of people do not expect
		1638	"SIGPIPE" when writing to some random socket.
		1639
		1640	The rationale for installing a no-op handler as opposed to ignoring
		1641	it is that this way, the handler will be restored to defaults on
		1642	exec.
		1643
		1644	Feel free to install your own handler, or reset it to defaults.
		1645
		1646	RECOMMENDED/OPTIONAL MODULES
		1647	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1648	it's built-in modules) are required to use it.
		1649
		1650	That does not mean that AnyEvent won't take advantage of some additional
		1651	modules if they are installed.
		1652
		1653	This section epxlains which additional modules will be used, and how
		1654	they affect AnyEvent's operetion.
		1655
		1656	Async::Interrupt
		1657	This slightly arcane module is used to implement fast signal
		1658	handling: To my knowledge, there is no way to do completely
		1659	race-free and quick signal handling in pure perl. To ensure that
		1660	signals still get delivered, AnyEvent will start an interval timer
		1661	to wake up perl (and catch the signals) with some delay (default is
		1662	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1663
		1664	If this module is available, then it will be used to implement
		1665	signal catching, which means that signals will not be delayed, and
		1666	the event loop will not be interrupted regularly, which is more
		1667	efficient (And good for battery life on laptops).
		1668
		1669	This affects not just the pure-perl event loop, but also other event
		1670	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1671
		1672	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1673	natively, and either employ their own workarounds (POE) or use
		1674	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1675	Installing Async::Interrupt does nothing for those backends.
		1676
		1677	EV This module isn't really "optional", as it is simply one of the
		1678	backend event loops that AnyEvent can use. However, it is simply the
		1679	best event loop available in terms of features, speed and stability:
		1680	It supports the AnyEvent API optimally, implements all the watcher
		1681	types in XS, does automatic timer adjustments even when no monotonic
		1682	clock is available, can take avdantage of advanced kernel interfaces
		1683	such as "epoll" and "kqueue", and is the fastest backend by far.
		1684	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1685	Glib::EV).
		1686
		1687	Guard
		1688	The guard module, when used, will be used to implement
		1689	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1690	uses a lot less memory), but otherwise doesn't affect guard
		1691	operation much. It is purely used for performance.
		1692
		1693	JSON and JSON::XS
		1694	This module is required when you want to read or write JSON data via
		1695	AnyEvent::Handle. It is also written in pure-perl, but can take
		1696	advantage of the ultra-high-speed JSON::XS module when it is
		1697	installed.
		1698
		1699	In fact, AnyEvent::Handle will use JSON::XS by default if it is
		1700	installed.
		1701
		1702	Net::SSLeay
		1703	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1704	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1705	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1706
		1707	Time::HiRes
		1708	This module is part of perl since release 5.008. It will be used
		1709	when the chosen event library does not come with a timing source on
		1710	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1711	additionally use it to try to use a monotonic clock for timing
		1712	stability.
		1713
960	FORK	1714	FORK
961	Most event libraries are not fork-safe. The ones who are usually are	1715	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.	1716	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1717	Only EV is fully fork-aware.
963		1718
964	If you have to fork, you must either do so before creating your first	1719	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.	1720	watcher OR you must not use AnyEvent at all in the child OR you must do
		1721	something completely out of the scope of AnyEvent.
966		1722
967	SECURITY CONSIDERATIONS	1723	SECURITY CONSIDERATIONS
968	AnyEvent can be forced to load any event model via	1724	AnyEvent can be forced to load any event model via
969	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1725	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
970	to execute arbitrary code or directly gain access, it can easily be used	1726	to execute arbitrary code or directly gain access, it can easily be used
…		…
973	model than specified in the variable.	1729	model than specified in the variable.
974		1730
975	You can make AnyEvent completely ignore this variable by deleting it	1731	You can make AnyEvent completely ignore this variable by deleting it
976	before the first watcher gets created, e.g. with a "BEGIN" block:	1732	before the first watcher gets created, e.g. with a "BEGIN" block:
977		1733
978	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1734	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
979		1735
980	use AnyEvent;	1736	use AnyEvent;
		1737
		1738	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1739	be used to probe what backend is used and gain other information (which
		1740	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
		1741	and $ENV{PERL_ANYEVENT_STRICT}.
		1742
		1743	Note that AnyEvent will remove all environment variables starting with
		1744	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1745	enabled.
		1746
		1747	BUGS
		1748	Perl 5.8 has numerous memleaks that sometimes hit this module and are
		1749	hard to work around. If you suffer from memleaks, first upgrade to Perl
		1750	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
		1751	annoying memleaks, such as leaking on "map" and "grep" but it is usually
		1752	not as pronounced).
981		1753
982	SEE ALSO	1754	SEE ALSO
983	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1755	Utility functions: AnyEvent::Util.
984	Glib::Event, Glib, Coro, Tk, Event::Lib, Qt, POE.
985		1756
986	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1757	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
987	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1758	Event::Lib, Qt, POE.
988	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib,	1759
		1760	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
		1761	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
989	AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1762	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1763	AnyEvent::Impl::IOAsync.
990		1764
		1765	Non-blocking file handles, sockets, TCP clients and servers:
		1766	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
		1767
		1768	Asynchronous DNS: AnyEvent::DNS.
		1769
		1770	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1771
991	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1772	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1773	AnyEvent::HTTP.
992		1774
993	AUTHOR	1775	AUTHOR
994	Marc Lehmann <schmorp@schmorp.de>	1776	Marc Lehmann <schmorp@schmorp.de>
995	http://home.schmorp.de/	1777	http://home.schmorp.de/
996		1778

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 1.47 by root, Mon Jul 20 22:39:57 2009 UTC

Diff Legend

Comparing AnyEvent/README (file contents):
Revision 1.19 by root, Mon Apr 28 08:02:14 2008 UTC vs.
Revision 1.47 by root, Mon Jul 20 22:39:57 2009 UTC