[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.37 by root, Mon Apr 20 14:34:18 2009 UTC vs.
Revision 1.63 by root, Wed Oct 13 19:49:46 2010 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - the DBI of event loop programming
3		3
4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	loops	5	Qt and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# if you prefer function calls, look at the AE manpage for
		11	# an alternative API.
		12
		13	# file handle or descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub { ... });	14	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
11		15
		16	# one-shot or repeating timers
12	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });	17	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
13	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...	18	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
14		19
15	print AnyEvent->now; # prints current event loop time	20	print AnyEvent->now; # prints current event loop time
16	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.	21	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
17		22
		23	# POSIX signal
18	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });	24	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
19		25
		26	# child process exit
20	my $w = AnyEvent->child (pid => $pid, cb => sub {	27	my $w = AnyEvent->child (pid => $pid, cb => sub {
21	my ($pid, $status) = @_;	28	my ($pid, $status) = @_;
22	...	29	...
23	});	30	});
		31
		32	# called when event loop idle (if applicable)
		33	my $w = AnyEvent->idle (cb => sub { ... });
24		34
25	my $w = AnyEvent->condvar; # stores whether a condition was flagged	35	my $w = AnyEvent->condvar; # stores whether a condition was flagged
26	$w->send; # wake up current and all future recv's	36	$w->send; # wake up current and all future recv's
27	$w->recv; # enters "main loop" till $condvar gets ->send	37	$w->recv; # enters "main loop" till $condvar gets ->send
28	# use a condvar in callback mode:	38	# use a condvar in callback mode:
30		40
31	INTRODUCTION/TUTORIAL	41	INTRODUCTION/TUTORIAL
32	This manpage is mainly a reference manual. If you are interested in a	42	This manpage is mainly a reference manual. If you are interested in a
33	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	43	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
34	manpage.	44	manpage.
		45
		46	SUPPORT
		47	An FAQ document is available as AnyEvent::FAQ.
		48
		49	There also is a mailinglist for discussing all things AnyEvent, and an
		50	IRC channel, too.
		51
		52	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		53	Repository, at <http://anyevent.schmorp.de>, for more info.
35		54
36	WHY YOU SHOULD USE THIS MODULE (OR NOT)	55	WHY YOU SHOULD USE THIS MODULE (OR NOT)
37	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	56	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
38	nowadays. So what is different about AnyEvent?	57	nowadays. So what is different about AnyEvent?
39		58
…		…
54	module users into the same thing by forcing them to use the same event	73	module users into the same thing by forcing them to use the same event
55	model you use.	74	model you use.
56		75
57	For modules like POE or IO::Async (which is a total misnomer as it is	76	For modules like POE or IO::Async (which is a total misnomer as it is
58	actually doing all I/O synchronously...), using them in your module is	77	actually doing all I/O synchronously...), using them in your module is
59	like joining a cult: After you joined, you are dependent on them and you	78	like joining a cult: After you join, you are dependent on them and you
60	cannot use anything else, as they are simply incompatible to everything	79	cannot use anything else, as they are simply incompatible to everything
61	that isn't them. What's worse, all the potential users of your module	80	that isn't them. What's worse, all the potential users of your module
62	are also forced to use the same event loop you use.	81	are also forced to use the same event loop you use.
63		82
64	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	83	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
65	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	84	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
66	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your	85	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
67	module uses one of those, every user of your module has to use it, too.	86	module uses one of those, every user of your module has to use it, too.
68	But if your module uses AnyEvent, it works transparently with all event	87	But if your module uses AnyEvent, it works transparently with all event
69	models it supports (including stuff like IO::Async, as long as those use	88	models it supports (including stuff like IO::Async, as long as those use
70	one of the supported event loops. It is trivial to add new event loops	89	one of the supported event loops. It is easy to add new event loops to
71	to AnyEvent, too, so it is future-proof).	90	AnyEvent, too, so it is future-proof).
72		91
73	In addition to being free of having to use *the one and only true event	92	In addition to being free of having to use *the one and only true event
74	model*, AnyEvent also is free of bloat and policy: with POE or similar	93	model*, AnyEvent also is free of bloat and policy: with POE or similar
75	modules, you get an enormous amount of code and strict rules you have to	94	modules, you get an enormous amount of code and strict rules you have to
76	follow. AnyEvent, on the other hand, is lean and up to the point, by	95	follow. AnyEvent, on the other hand, is lean and to the point, by only
77	only offering the functionality that is necessary, in as thin as a	96	offering the functionality that is necessary, in as thin as a wrapper as
78	wrapper as technically possible.	97	technically possible.
79		98
80	Of course, AnyEvent comes with a big (and fully optional!) toolbox of	99	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
81	useful functionality, such as an asynchronous DNS resolver, 100%	100	useful functionality, such as an asynchronous DNS resolver, 100%
82	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms	101	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
83	such as Windows) and lots of real-world knowledge and workarounds for	102	such as Windows) and lots of real-world knowledge and workarounds for
…		…
86	Now, if you do want lots of policy (this can arguably be somewhat	105	Now, if you do want lots of policy (this can arguably be somewhat
87	useful) and you want to force your users to use the one and only event	106	useful) and you want to force your users to use the one and only event
88	model, you should not use this module.	107	model, you should not use this module.
89		108
90	DESCRIPTION	109	DESCRIPTION
91	AnyEvent provides an identical interface to multiple event loops. This	110	AnyEvent provides a uniform interface to various event loops. This
92	allows module authors to utilise an event loop without forcing module	111	allows module authors to use event loop functionality without forcing
93	users to use the same event loop (as only a single event loop can	112	module users to use a specific event loop implementation (since more
94	coexist peacefully at any one time).	113	than one event loop cannot coexist peacefully).
95		114
96	The interface itself is vaguely similar, but not identical to the Event	115	The interface itself is vaguely similar, but not identical to the Event
97	module.	116	module.
98		117
99	During the first call of any watcher-creation method, the module tries	118	During the first call of any watcher-creation method, the module tries
100	to detect the currently loaded event loop by probing whether one of the	119	to detect the currently loaded event loop by probing whether one of the
101	following modules is already loaded: EV, Event, Glib,	120	following modules is already loaded: EV, AnyEvent::Impl::Perl, Event,
102	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is	121	Glib, Tk, Event::Lib, Qt, POE. The first one found is used. If none are
103	used. If none are found, the module tries to load these modules	122	detected, the module tries to load the first four modules in the order
104	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	123	given; but note that if EV is not available, the pure-perl
105	always succeed) in the order given. The first one that can be	124	AnyEvent::Impl::Perl should always work, so the other two are not
106	successfully loaded will be used. If, after this, still none could be	125	normally tried.
107	found, AnyEvent will fall back to a pure-perl event loop, which is not
108	very efficient, but should work everywhere.
109		126
110	Because AnyEvent first checks for modules that are already loaded,	127	Because AnyEvent first checks for modules that are already loaded,
111	loading an event model explicitly before first using AnyEvent will	128	loading an event model explicitly before first using AnyEvent will
112	likely make that model the default. For example:	129	likely make that model the default. For example:
113		130
…		…
115	use AnyEvent;	132	use AnyEvent;
116		133
117	# .. AnyEvent will likely default to Tk	134	# .. AnyEvent will likely default to Tk
118		135
119	The likely means that, if any module loads another event model and	136	The likely means that, if any module loads another event model and
120	starts using it, all bets are off. Maybe you should tell their authors	137	starts using it, all bets are off - this case should be very rare
121	to use AnyEvent so their modules work together with others seamlessly...	138	though, as very few modules hardcode event loops without announcing this
		139	very loudly.
122		140
123	The pure-perl implementation of AnyEvent is called	141	The pure-perl implementation of AnyEvent is called
124	"AnyEvent::Impl::Perl". Like other event modules you can load it	142	"AnyEvent::Impl::Perl". Like other event modules you can load it
125	explicitly and enjoy the high availability of that event loop :)	143	explicitly and enjoy the high availability of that event loop :)
126		144
…		…
134	callback when the event occurs (of course, only when the event model is	152	callback when the event occurs (of course, only when the event model is
135	in control).	153	in control).
136		154
137	Note that callbacks must not permanently change global variables	155	Note that callbacks must not permanently change global variables
138	potentially in use by the event loop (such as $_ or $[) and that	156	potentially in use by the event loop (such as $_ or $[) and that
139	callbacks must not "die". The former is good programming practise in	157	callbacks must not "die". The former is good programming practice in
140	Perl and the latter stems from the fact that exception handling differs	158	Perl and the latter stems from the fact that exception handling differs
141	widely between event loops.	159	widely between event loops.
142		160
143	To disable the watcher you have to destroy it (e.g. by setting the	161	To disable a watcher you have to destroy it (e.g. by setting the
144	variable you store it in to "undef" or otherwise deleting all references	162	variable you store it in to "undef" or otherwise deleting all references
145	to it).	163	to it).
146		164
147	All watchers are created by calling a method on the "AnyEvent" class.	165	All watchers are created by calling a method on the "AnyEvent" class.
148		166
149	Many watchers either are used with "recursion" (repeating timers for	167	Many watchers either are used with "recursion" (repeating timers for
150	example), or need to refer to their watcher object in other ways.	168	example), or need to refer to their watcher object in other ways.
151		169
152	An any way to achieve that is this pattern:	170	One way to achieve that is this pattern:
153		171
154	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	172	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
155	# you can use $w here, for example to undef it	173	# you can use $w here, for example to undef it
156	undef $w;	174	undef $w;
157	});	175	});
…		…
159	Note that "my $w; $w =" combination. This is necessary because in Perl,	177	Note that "my $w; $w =" combination. This is necessary because in Perl,
160	my variables are only visible after the statement in which they are	178	my variables are only visible after the statement in which they are
161	declared.	179	declared.
162		180
163	I/O WATCHERS	181	I/O WATCHERS
		182	$w = AnyEvent->io (
		183	fh => <filehandle_or_fileno>,
		184	poll => <"r" or "w">,
		185	cb => <callback>,
		186	);
		187
164	You can create an I/O watcher by calling the "AnyEvent->io" method with	188	You can create an I/O watcher by calling the "AnyEvent->io" method with
165	the following mandatory key-value pairs as arguments:	189	the following mandatory key-value pairs as arguments:
166		190
167	"fh" is the Perl file handle (not file descriptor) to watch for	191	"fh" is the Perl file handle (or a naked file descriptor) to watch for
168	events (AnyEvent might or might not keep a reference to this file	192	events (AnyEvent might or might not keep a reference to this file
169	handle). Note that only file handles pointing to things for which	193	handle). Note that only file handles pointing to things for which
170	non-blocking operation makes sense are allowed. This includes sockets,	194	non-blocking operation makes sense are allowed. This includes sockets,
171	most character devices, pipes, fifos and so on, but not for example	195	most character devices, pipes, fifos and so on, but not for example
172	files or block devices.	196	files or block devices.
…		…
182		206
183	The I/O watcher might use the underlying file descriptor or a copy of	207	The I/O watcher might use the underlying file descriptor or a copy of
184	it. You must not close a file handle as long as any watcher is active on	208	it. You must not close a file handle as long as any watcher is active on
185	the underlying file descriptor.	209	the underlying file descriptor.
186		210
187	Some event loops issue spurious readyness notifications, so you should	211	Some event loops issue spurious readiness notifications, so you should
188	always use non-blocking calls when reading/writing from/to your file	212	always use non-blocking calls when reading/writing from/to your file
189	handles.	213	handles.
190		214
191	Example: wait for readability of STDIN, then read a line and disable the	215	Example: wait for readability of STDIN, then read a line and disable the
192	watcher.	216	watcher.
…		…
196	warn "read: $input\n";	220	warn "read: $input\n";
197	undef $w;	221	undef $w;
198	});	222	});
199		223
200	TIME WATCHERS	224	TIME WATCHERS
		225	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		226
		227	$w = AnyEvent->timer (
		228	after => <fractional_seconds>,
		229	interval => <fractional_seconds>,
		230	cb => <callback>,
		231	);
		232
201	You can create a time watcher by calling the "AnyEvent->timer" method	233	You can create a time watcher by calling the "AnyEvent->timer" method
202	with the following mandatory arguments:	234	with the following mandatory arguments:
203		235
204	"after" specifies after how many seconds (fractional values are	236	"after" specifies after how many seconds (fractional values are
205	supported) the callback should be invoked. "cb" is the callback to	237	supported) the callback should be invoked. "cb" is the callback to
…		…
207		239
208	Although the callback might get passed parameters, their value and	240	Although the callback might get passed parameters, their value and
209	presence is undefined and you cannot rely on them. Portable AnyEvent	241	presence is undefined and you cannot rely on them. Portable AnyEvent
210	callbacks cannot use arguments passed to time watcher callbacks.	242	callbacks cannot use arguments passed to time watcher callbacks.
211		243
212	The callback will normally be invoked once only. If you specify another	244	The callback will normally be invoked only once. If you specify another
213	parameter, "interval", as a strictly positive number (> 0), then the	245	parameter, "interval", as a strictly positive number (> 0), then the
214	callback will be invoked regularly at that interval (in fractional	246	callback will be invoked regularly at that interval (in fractional
215	seconds) after the first invocation. If "interval" is specified with a	247	seconds) after the first invocation. If "interval" is specified with a
216	false value, then it is treated as if it were missing.	248	false value, then it is treated as if it were not specified at all.
217		249
218	The callback will be rescheduled before invoking the callback, but no	250	The callback will be rescheduled before invoking the callback, but no
219	attempt is done to avoid timer drift in most backends, so the interval	251	attempt is made to avoid timer drift in most backends, so the interval
220	is only approximate.	252	is only approximate.
221		253
222	Example: fire an event after 7.7 seconds.	254	Example: fire an event after 7.7 seconds.
223		255
224	my $w = AnyEvent->timer (after => 7.7, cb => sub {	256	my $w = AnyEvent->timer (after => 7.7, cb => sub {
…		…
241		273
242	While most event loops expect timers to specified in a relative way,	274	While most event loops expect timers to specified in a relative way,
243	they use absolute time internally. This makes a difference when your	275	they use absolute time internally. This makes a difference when your
244	clock "jumps", for example, when ntp decides to set your clock backwards	276	clock "jumps", for example, when ntp decides to set your clock backwards
245	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is	277	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
246	supposed to fire "after" a second might actually take six years to	278	supposed to fire "after a second" might actually take six years to
247	finally fire.	279	finally fire.
248		280
249	AnyEvent cannot compensate for this. The only event loop that is	281	AnyEvent cannot compensate for this. The only event loop that is
250	conscious about these issues is EV, which offers both relative	282	conscious of these issues is EV, which offers both relative (ev_timer,
251	(ev_timer, based on true relative time) and absolute (ev_periodic, based	283	based on true relative time) and absolute (ev_periodic, based on
252	on wallclock time) timers.	284	wallclock time) timers.
253		285
254	AnyEvent always prefers relative timers, if available, matching the	286	AnyEvent always prefers relative timers, if available, matching the
255	AnyEvent API.	287	AnyEvent API.
256		288
257	AnyEvent has two additional methods that return the "current time":	289	AnyEvent has two additional methods that return the "current time":
…		…
276	*In almost all cases (in all cases if you don't care), this is the	308	*In almost all cases (in all cases if you don't care), this is the
277	function to call when you want to know the current time.*	309	function to call when you want to know the current time.*
278		310
279	This function is also often faster then "AnyEvent->time", and thus	311	This function is also often faster then "AnyEvent->time", and thus
280	the preferred method if you want some timestamp (for example,	312	the preferred method if you want some timestamp (for example,
281	AnyEvent::Handle uses this to update it's activity timeouts).	313	AnyEvent::Handle uses this to update its activity timeouts).
282		314
283	The rest of this section is only of relevance if you try to be very	315	The rest of this section is only of relevance if you try to be very
284	exact with your timing, you can skip it without bad conscience.	316	exact with your timing; you can skip it without a bad conscience.
285		317
286	For a practical example of when these times differ, consider	318	For a practical example of when these times differ, consider
287	Event::Lib and EV and the following set-up:	319	Event::Lib and EV and the following set-up:
288		320
289	The event loop is running and has just invoked one of your callback	321	The event loop is running and has just invoked one of your callbacks
290	at time=500 (assume no other callbacks delay processing). In your	322	at time=500 (assume no other callbacks delay processing). In your
291	callback, you wait a second by executing "sleep 1" (blocking the	323	callback, you wait a second by executing "sleep 1" (blocking the
292	process for a second) and then (at time=501) you create a relative	324	process for a second) and then (at time=501) you create a relative
293	timer that fires after three seconds.	325	timer that fires after three seconds.
294		326
…		…
326	time, which might affect timers and time-outs.	358	time, which might affect timers and time-outs.
327		359
328	When this is the case, you can call this method, which will update	360	When this is the case, you can call this method, which will update
329	the event loop's idea of "current time".	361	the event loop's idea of "current time".
330		362
		363	A typical example would be a script in a web server (e.g.
		364	"mod_perl") - when mod_perl executes the script, then the event loop
		365	will have the wrong idea about the "current time" (being potentially
		366	far in the past, when the script ran the last time). In that case
		367	you should arrange a call to "AnyEvent->now_update" each time the
		368	web server process wakes up again (e.g. at the start of your script,
		369	or in a handler).
		370
331	Note that updating the time might cause some events to be handled.	371	Note that updating the time might cause some events to be handled.
332		372
333	SIGNAL WATCHERS	373	SIGNAL WATCHERS
		374	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		375
334	You can watch for signals using a signal watcher, "signal" is the signal	376	You can watch for signals using a signal watcher, "signal" is the signal
335	name in uppercase and without any "SIG" prefix, "cb" is the Perl	377	name in uppercase and without any "SIG" prefix, "cb" is the Perl
336	callback to be invoked whenever a signal occurs.	378	callback to be invoked whenever a signal occurs.
337		379
338	Although the callback might get passed parameters, their value and	380	Although the callback might get passed parameters, their value and
…		…
343	invocation, and callback invocation will be synchronous. Synchronous	385	invocation, and callback invocation will be synchronous. Synchronous
344	means that it might take a while until the signal gets handled by the	386	means that it might take a while until the signal gets handled by the
345	process, but it is guaranteed not to interrupt any other callbacks.	387	process, but it is guaranteed not to interrupt any other callbacks.
346		388
347	The main advantage of using these watchers is that you can share a	389	The main advantage of using these watchers is that you can share a
348	signal between multiple watchers.	390	signal between multiple watchers, and AnyEvent will ensure that signals
		391	will not interrupt your program at bad times.
349		392
350	This watcher might use %SIG, so programs overwriting those signals	393	This watcher might use %SIG (depending on the event loop used), so
351	directly will likely not work correctly.	394	programs overwriting those signals directly will likely not work
		395	correctly.
352		396
353	Example: exit on SIGINT	397	Example: exit on SIGINT
354		398
355	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	399	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
356		400
		401	Restart Behaviour
		402	While restart behaviour is up to the event loop implementation, most
		403	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		404	pure perl implementation).
		405
		406	Safe/Unsafe Signals
		407	Perl signals can be either "safe" (synchronous to opcode handling) or
		408	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		409	latter might corrupt your memory.
		410
		411	AnyEvent signal handlers are, in addition, synchronous to the event
		412	loop, i.e. they will not interrupt your running perl program but will
		413	only be called as part of the normal event handling (just like timer,
		414	I/O etc. callbacks, too).
		415
		416	Signal Races, Delays and Workarounds
		417	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		418	callbacks to signals in a generic way, which is a pity, as you cannot do
		419	race-free signal handling in perl, requiring C libraries for this.
		420	AnyEvent will try to do its best, which means in some cases, signals
		421	will be delayed. The maximum time a signal might be delayed is specified
		422	in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
		423	can be changed only before the first signal watcher is created, and
		424	should be left alone otherwise. This variable determines how often
		425	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		426	will cause fewer spurious wake-ups, which is better for power and CPU
		427	saving.
		428
		429	All these problems can be avoided by installing the optional
		430	Async::Interrupt module, which works with most event loops. It will not
		431	work with inherently broken event loops such as Event or Event::Lib (and
		432	not with POE currently, as POE does its own workaround with one-second
		433	latency). For those, you just have to suffer the delays.
		434
357	CHILD PROCESS WATCHERS	435	CHILD PROCESS WATCHERS
		436	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		437
358	You can also watch on a child process exit and catch its exit status.	438	You can also watch for a child process exit and catch its exit status.
359		439
360	The child process is specified by the "pid" argument (if set to 0, it	440	The child process is specified by the "pid" argument (on some backends,
361	watches for any child process exit). The watcher will triggered only	441	using 0 watches for any child process exit, on others this will croak).
362	when the child process has finished and an exit status is available, not	442	The watcher will be triggered only when the child process has finished
363	on any trace events (stopped/continued).	443	and an exit status is available, not on any trace events
		444	(stopped/continued).
364		445
365	The callback will be called with the pid and exit status (as returned by	446	The callback will be called with the pid and exit status (as returned by
366	waitpid), so unlike other watcher types, you can rely on child watcher	447	waitpid), so unlike other watcher types, you can rely on child watcher
367	callback arguments.	448	callback arguments.
368		449
…		…
373		454
374	There is a slight catch to child watchers, however: you usually start	455	There is a slight catch to child watchers, however: you usually start
375	them after the child process was created, and this means the process	456	them after the child process was created, and this means the process
376	could have exited already (and no SIGCHLD will be sent anymore).	457	could have exited already (and no SIGCHLD will be sent anymore).
377		458
378	Not all event models handle this correctly (POE doesn't), but even for	459	Not all event models handle this correctly (neither POE nor IO::Async
		460	do, see their AnyEvent::Impl manpages for details), but even for event
379	event models that do handle this correctly, they usually need to be	461	models that do handle this correctly, they usually need to be loaded
380	loaded before the process exits (i.e. before you fork in the first	462	before the process exits (i.e. before you fork in the first place).
381	place).	463	AnyEvent's pure perl event loop handles all cases correctly regardless
		464	of when you start the watcher.
382		465
383	This means you cannot create a child watcher as the very first thing in	466	This means you cannot create a child watcher as the very first thing in
384	an AnyEvent program, you have to create at least one watcher before	467	an AnyEvent program, you have to create at least one watcher before
385	you "fork" the child (alternatively, you can call "AnyEvent::detect").	468	you "fork" the child (alternatively, you can call "AnyEvent::detect").
386		469
		470	As most event loops do not support waiting for child events, they will
		471	be emulated by AnyEvent in most cases, in which the latency and race
		472	problems mentioned in the description of signal watchers apply.
		473
387	Example: fork a process and wait for it	474	Example: fork a process and wait for it
388		475
389	my $done = AnyEvent->condvar;	476	my $done = AnyEvent->condvar;
390		477
391	my $pid = fork or exit 5;	478	my $pid = fork or exit 5;
392		479
393	my $w = AnyEvent->child (	480	my $w = AnyEvent->child (
394	pid => $pid,	481	pid => $pid,
395	cb => sub {	482	cb => sub {
396	my ($pid, $status) = @_;	483	my ($pid, $status) = @_;
397	warn "pid $pid exited with status $status";	484	warn "pid $pid exited with status $status";
398	$done->send;	485	$done->send;
399	},	486	},
400	);	487	);
401		488
402	# do something else, then wait for process exit	489	# do something else, then wait for process exit
403	$done->recv;	490	$done->recv;
404		491
		492	IDLE WATCHERS
		493	$w = AnyEvent->idle (cb => <callback>);
		494
		495	This will repeatedly invoke the callback after the process becomes idle,
		496	until either the watcher is destroyed or new events have been detected.
		497
		498	Idle watchers are useful when there is a need to do something, but it is
		499	not so important (or wise) to do it instantly. The callback will be
		500	invoked only when there is "nothing better to do", which is usually
		501	defined as "all outstanding events have been handled and no new events
		502	have been detected". That means that idle watchers ideally get invoked
		503	when the event loop has just polled for new events but none have been
		504	detected. Instead of blocking to wait for more events, the idle watchers
		505	will be invoked.
		506
		507	Unfortunately, most event loops do not really support idle watchers
		508	(only EV, Event and Glib do it in a usable fashion) - for the rest,
		509	AnyEvent will simply call the callback "from time to time".
		510
		511	Example: read lines from STDIN, but only process them when the program
		512	is otherwise idle:
		513
		514	my @lines; # read data
		515	my $idle_w;
		516	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		517	push @lines, scalar <STDIN>;
		518
		519	# start an idle watcher, if not already done
		520	$idle_w \|\|= AnyEvent->idle (cb => sub {
		521	# handle only one line, when there are lines left
		522	if (my $line = shift @lines) {
		523	print "handled when idle: $line";
		524	} else {
		525	# otherwise disable the idle watcher again
		526	undef $idle_w;
		527	}
		528	});
		529	});
		530
405	CONDITION VARIABLES	531	CONDITION VARIABLES
		532	$cv = AnyEvent->condvar;
		533
		534	$cv->send (<list>);
		535	my @res = $cv->recv;
		536
406	If you are familiar with some event loops you will know that all of them	537	If you are familiar with some event loops you will know that all of them
407	require you to run some blocking "loop", "run" or similar function that	538	require you to run some blocking "loop", "run" or similar function that
408	will actively watch for new events and call your callbacks.	539	will actively watch for new events and call your callbacks.
409		540
410	AnyEvent is different, it expects somebody else to run the event loop	541	AnyEvent is slightly different: it expects somebody else to run the
411	and will only block when necessary (usually when told by the user).	542	event loop and will only block when necessary (usually when told by the
		543	user).
412		544
413	The instrument to do that is called a "condition variable", so called	545	The tool to do that is called a "condition variable", so called because
414	because they represent a condition that must become true.	546	they represent a condition that must become true.
		547
		548	Now is probably a good time to look at the examples further below.
415		549
416	Condition variables can be created by calling the "AnyEvent->condvar"	550	Condition variables can be created by calling the "AnyEvent->condvar"
417	method, usually without arguments. The only argument pair allowed is	551	method, usually without arguments. The only argument pair allowed is
418
419	"cb", which specifies a callback to be called when the condition	552	"cb", which specifies a callback to be called when the condition
420	variable becomes true, with the condition variable as the first argument	553	variable becomes true, with the condition variable as the first argument
421	(but not the results).	554	(but not the results).
422		555
423	After creation, the condition variable is "false" until it becomes	556	After creation, the condition variable is "false" until it becomes
424	"true" by calling the "send" method (or calling the condition variable	557	"true" by calling the "send" method (or calling the condition variable
425	as if it were a callback, read about the caveats in the description for	558	as if it were a callback, read about the caveats in the description for
426	the "->send" method).	559	the "->send" method).
427		560
428	Condition variables are similar to callbacks, except that you can	561	Since condition variables are the most complex part of the AnyEvent API,
429	optionally wait for them. They can also be called merge points - points	562	here are some different mental models of what they are - pick the ones
430	in time where multiple outstanding events have been processed. And yet	563	you can connect to:
431	another way to call them is transactions - each condition variable can	564
432	be used to represent a transaction, which finishes at some point and	565	* Condition variables are like callbacks - you can call them (and pass
433	delivers a result.	566	them instead of callbacks). Unlike callbacks however, you can also
		567	wait for them to be called.
		568
		569	* Condition variables are signals - one side can emit or send them,
		570	the other side can wait for them, or install a handler that is
		571	called when the signal fires.
		572
		573	* Condition variables are like "Merge Points" - points in your program
		574	where you merge multiple independent results/control flows into one.
		575
		576	* Condition variables represent a transaction - functions that start
		577	some kind of transaction can return them, leaving the caller the
		578	choice between waiting in a blocking fashion, or setting a callback.
		579
		580	* Condition variables represent future values, or promises to deliver
		581	some result, long before the result is available.
434		582
435	Condition variables are very useful to signal that something has	583	Condition variables are very useful to signal that something has
436	finished, for example, if you write a module that does asynchronous http	584	finished, for example, if you write a module that does asynchronous http
437	requests, then a condition variable would be the ideal candidate to	585	requests, then a condition variable would be the ideal candidate to
438	signal the availability of results. The user can either act when the	586	signal the availability of results. The user can either act when the
…		…
451		599
452	Condition variables are represented by hash refs in perl, and the keys	600	Condition variables are represented by hash refs in perl, and the keys
453	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy	601	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
454	(it is often useful to build your own transaction class on top of	602	(it is often useful to build your own transaction class on top of
455	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call	603	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
456	it's "new" method in your own "new" method.	604	its "new" method in your own "new" method.
457		605
458	There are two "sides" to a condition variable - the "producer side"	606	There are two "sides" to a condition variable - the "producer side"
459	which eventually calls "-> send", and the "consumer side", which waits	607	which eventually calls "-> send", and the "consumer side", which waits
460	for the send to occur.	608	for the send to occur.
461		609
462	Example: wait for a timer.	610	Example: wait for a timer.
463		611
464	# wait till the result is ready	612	# condition: "wait till the timer is fired"
465	my $result_ready = AnyEvent->condvar;	613	my $timer_fired = AnyEvent->condvar;
466		614
467	# do something such as adding a timer	615	# create the timer - we could wait for, say
468	# or socket watcher the calls $result_ready->send	616	# a handle becomign ready, or even an
469	# when the "result" is ready.	617	# AnyEvent::HTTP request to finish, but
470	# in this case, we simply use a timer:	618	# in this case, we simply use a timer:
471	my $w = AnyEvent->timer (	619	my $w = AnyEvent->timer (
472	after => 1,	620	after => 1,
473	cb => sub { $result_ready->send },	621	cb => sub { $timer_fired->send },
474	);	622	);
475		623
476	# this "blocks" (while handling events) till the callback	624	# this "blocks" (while handling events) till the callback
477	# calls send	625	# calls ->send
478	$result_ready->recv;	626	$timer_fired->recv;
479		627
480	Example: wait for a timer, but take advantage of the fact that condition	628	Example: wait for a timer, but take advantage of the fact that condition
481	variables are also code references.	629	variables are also callable directly.
482		630
483	my $done = AnyEvent->condvar;	631	my $done = AnyEvent->condvar;
484	my $delay = AnyEvent->timer (after => 5, cb => $done);	632	my $delay = AnyEvent->timer (after => 5, cb => $done);
485	$done->recv;	633	$done->recv;
486		634
…		…
492		640
493	...	641	...
494		642
495	my @info = $couchdb->info->recv;	643	my @info = $couchdb->info->recv;
496		644
497	And this is how you would just ste a callback to be called whenever the	645	And this is how you would just set a callback to be called whenever the
498	results are available:	646	results are available:
499		647
500	$couchdb->info->cb (sub {	648	$couchdb->info->cb (sub {
501	my @info = $_[0]->recv;	649	my @info = $_[0]->recv;
502	});	650	});
…		…
517		665
518	Any arguments passed to the "send" call will be returned by all	666	Any arguments passed to the "send" call will be returned by all
519	future "->recv" calls.	667	future "->recv" calls.
520		668
521	Condition variables are overloaded so one can call them directly (as	669	Condition variables are overloaded so one can call them directly (as
522	a code reference). Calling them directly is the same as calling	670	if they were a code reference). Calling them directly is the same as
523	"send". Note, however, that many C-based event loops do not handle	671	calling "send".
524	overloading, so as tempting as it may be, passing a condition
525	variable instead of a callback does not work. Both the pure perl and
526	EV loops support overloading, however, as well as all functions that
527	use perl to invoke a callback (as in AnyEvent::Socket and
528	AnyEvent::DNS for example).
529		672
530	$cv->croak ($error)	673	$cv->croak ($error)
531	Similar to send, but causes all call's to "->recv" to invoke	674	Similar to send, but causes all calls to "->recv" to invoke
532	"Carp::croak" with the given error message/object/scalar.	675	"Carp::croak" with the given error message/object/scalar.
533		676
534	This can be used to signal any errors to the condition variable	677	This can be used to signal any errors to the condition variable
535	user/consumer.	678	user/consumer. Doing it this way instead of calling "croak" directly
		679	delays the error detection, but has the overwhelming advantage that
		680	it diagnoses the error at the place where the result is expected,
		681	and not deep in some event callback with no connection to the actual
		682	code causing the problem.
536		683
537	$cv->begin ([group callback])	684	$cv->begin ([group callback])
538	$cv->end	685	$cv->end
539	These two methods are EXPERIMENTAL and MIGHT CHANGE.
540
541	These two methods can be used to combine many transactions/events	686	These two methods can be used to combine many transactions/events
542	into one. For example, a function that pings many hosts in parallel	687	into one. For example, a function that pings many hosts in parallel
543	might want to use a condition variable for the whole process.	688	might want to use a condition variable for the whole process.
544		689
545	Every call to "->begin" will increment a counter, and every call to	690	Every call to "->begin" will increment a counter, and every call to
546	"->end" will decrement it. If the counter reaches 0 in "->end", the	691	"->end" will decrement it. If the counter reaches 0 in "->end", the
547	(last) callback passed to "begin" will be executed. That callback is	692	(last) callback passed to "begin" will be executed, passing the
548	supposed to call "->send", but that is not required. If no	693	condvar as first argument. That callback is supposed to call
		694	"->send", but that is not required. If no group callback was set,
549	callback was set, "send" will be called without any arguments.	695	"send" will be called without any arguments.
550		696
551	Let's clarify this with the ping example:	697	You can think of "$cv->send" giving you an OR condition (one call
		698	sends), while "$cv->begin" and "$cv->end" giving you an AND
		699	condition (all "begin" calls must be "end"'ed before the condvar
		700	sends).
		701
		702	Let's start with a simple example: you have two I/O watchers (for
		703	example, STDOUT and STDERR for a program), and you want to wait for
		704	both streams to close before activating a condvar:
552		705
553	my $cv = AnyEvent->condvar;	706	my $cv = AnyEvent->condvar;
554		707
		708	$cv->begin; # first watcher
		709	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		710	defined sysread $fh1, my $buf, 4096
		711	or $cv->end;
		712	});
		713
		714	$cv->begin; # second watcher
		715	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		716	defined sysread $fh2, my $buf, 4096
		717	or $cv->end;
		718	});
		719
		720	$cv->recv;
		721
		722	This works because for every event source (EOF on file handle),
		723	there is one call to "begin", so the condvar waits for all calls to
		724	"end" before sending.
		725
		726	The ping example mentioned above is slightly more complicated, as
		727	the there are results to be passwd back, and the number of tasks
		728	that are begun can potentially be zero:
		729
		730	my $cv = AnyEvent->condvar;
		731
555	my %result;	732	my %result;
556	$cv->begin (sub { $cv->send (\%result) });	733	$cv->begin (sub { shift->send (\%result) });
557		734
558	for my $host (@list_of_hosts) {	735	for my $host (@list_of_hosts) {
559	$cv->begin;	736	$cv->begin;
560	ping_host_then_call_callback $host, sub {	737	ping_host_then_call_callback $host, sub {
561	$result{$host} = ...;	738	$result{$host} = ...;
…		…
576	the loop, which serves two important purposes: first, it sets the	753	the loop, which serves two important purposes: first, it sets the
577	callback to be called once the counter reaches 0, and second, it	754	callback to be called once the counter reaches 0, and second, it
578	ensures that "send" is called even when "no" hosts are being pinged	755	ensures that "send" is called even when "no" hosts are being pinged
579	(the loop doesn't execute once).	756	(the loop doesn't execute once).
580		757
581	This is the general pattern when you "fan out" into multiple	758	This is the general pattern when you "fan out" into multiple (but
582	subrequests: use an outer "begin"/"end" pair to set the callback and	759	potentially zero) subrequests: use an outer "begin"/"end" pair to
583	ensure "end" is called at least once, and then, for each subrequest	760	set the callback and ensure "end" is called at least once, and then,
584	you start, call "begin" and for each subrequest you finish, call	761	for each subrequest you start, call "begin" and for each subrequest
585	"end".	762	you finish, call "end".
586		763
587	METHODS FOR CONSUMERS	764	METHODS FOR CONSUMERS
588	These methods should only be used by the consuming side, i.e. the code	765	These methods should only be used by the consuming side, i.e. the code
589	awaits the condition.	766	awaits the condition.
590		767
591	$cv->recv	768	$cv->recv
592	Wait (blocking if necessary) until the "->send" or "->croak" methods	769	Wait (blocking if necessary) until the "->send" or "->croak" methods
593	have been called on c<$cv>, while servicing other watchers normally.	770	have been called on $cv, while servicing other watchers normally.
594		771
595	You can only wait once on a condition - additional calls are valid	772	You can only wait once on a condition - additional calls are valid
596	but will return immediately.	773	but will return immediately.
597		774
598	If an error condition has been set by calling "->croak", then this	775	If an error condition has been set by calling "->croak", then this
599	function will call "croak".	776	function will call "croak".
600		777
601	In list context, all parameters passed to "send" will be returned,	778	In list context, all parameters passed to "send" will be returned,
602	in scalar context only the first one will be returned.	779	in scalar context only the first one will be returned.
603		780
		781	Note that doing a blocking wait in a callback is not supported by
		782	any event loop, that is, recursive invocation of a blocking "->recv"
		783	is not allowed, and the "recv" call will "croak" if such a condition
		784	is detected. This condition can be slightly loosened by using
		785	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		786	thread that doesn't run the event loop itself.
		787
604	Not all event models support a blocking wait - some die in that case	788	Not all event models support a blocking wait - some die in that case
605	(programs might want to do that to stay interactive), so *if you are	789	(programs might want to do that to stay interactive), so *if you are
606	using this from a module, never require a blocking wait*, but let	790	using this from a module, never require a blocking wait*. Instead,
607	the caller decide whether the call will block or not (for example,	791	let the caller decide whether the call will block or not (for
608	by coupling condition variables with some kind of request results	792	example, by coupling condition variables with some kind of request
609	and supporting callbacks so the caller knows that getting the result	793	results and supporting callbacks so the caller knows that getting
610	will not block, while still supporting blocking waits if the caller	794	the result will not block, while still supporting blocking waits if
611	so desires).	795	the caller so desires).
612		796
613	Another reason never to "->recv" in a module is that you cannot
614	sensibly have two "->recv"'s in parallel, as that would require
615	multiple interpreters or coroutines/threads, none of which
616	"AnyEvent" can supply.
617
618	The Coro module, however, can and does supply coroutines and, in
619	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
620	versions and also integrates coroutines into AnyEvent, making
621	blocking "->recv" calls perfectly safe as long as they are done from
622	another coroutine (one that doesn't run the event loop).
623
624	You can ensure that "-recv" never blocks by setting a callback and	797	You can ensure that "->recv" never blocks by setting a callback and
625	only calling "->recv" from within that callback (or at a later	798	only calling "->recv" from within that callback (or at a later
626	time). This will work even when the event loop does not support	799	time). This will work even when the event loop does not support
627	blocking waits otherwise.	800	blocking waits otherwise.
628		801
629	$bool = $cv->ready	802	$bool = $cv->ready
…		…
634	This is a mutator function that returns the callback set and	807	This is a mutator function that returns the callback set and
635	optionally replaces it before doing so.	808	optionally replaces it before doing so.
636		809
637	The callback will be called when the condition becomes "true", i.e.	810	The callback will be called when the condition becomes "true", i.e.
638	when "send" or "croak" are called, with the only argument being the	811	when "send" or "croak" are called, with the only argument being the
639	condition variable itself. Calling "recv" inside the callback or at	812	condition variable itself. If the condition is already true, the
		813	callback is called immediately when it is set. Calling "recv" inside
640	any later time is guaranteed not to block.	814	the callback or at any later time is guaranteed not to block.
		815
		816	SUPPORTED EVENT LOOPS/BACKENDS
		817	The available backend classes are (every class has its own manpage):
		818
		819	Backends that are autoprobed when no other event loop can be found.
		820	EV is the preferred backend when no other event loop seems to be in
		821	use. If EV is not installed, then AnyEvent will fall back to its own
		822	pure-perl implementation, which is available everywhere as it comes
		823	with AnyEvent itself.
		824
		825	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		826	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		827
		828	Backends that are transparently being picked up when they are used.
		829	These will be used if they are already loaded when the first watcher
		830	is created, in which case it is assumed that the application is
		831	using them. This means that AnyEvent will automatically pick the
		832	right backend when the main program loads an event module before
		833	anything starts to create watchers. Nothing special needs to be done
		834	by the main program.
		835
		836	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		837	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		838	AnyEvent::Impl::Tk based on Tk, very broken.
		839	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		840	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		841	AnyEvent::Impl::Irssi used when running within irssi.
		842
		843	Backends with special needs.
		844	Qt requires the Qt::Application to be instantiated first, but will
		845	otherwise be picked up automatically. As long as the main program
		846	instantiates the application before any AnyEvent watchers are
		847	created, everything should just work.
		848
		849	AnyEvent::Impl::Qt based on Qt.
		850
		851	Support for IO::Async can only be partial, as it is too broken and
		852	architecturally limited to even support the AnyEvent API. It also is
		853	the only event loop that needs the loop to be set explicitly, so it
		854	can only be used by a main program knowing about AnyEvent. See
		855	AnyEvent::Impl::IOAsync for the gory details.
		856
		857	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		858
		859	Event loops that are indirectly supported via other backends.
		860	Some event loops can be supported via other modules:
		861
		862	There is no direct support for WxWidgets (Wx) or Prima.
		863
		864	WxWidgets has no support for watching file handles. However, you can
		865	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		866	simply polls 20 times per second, which was considered to be too
		867	horrible to even consider for AnyEvent.
		868
		869	Prima is not supported as nobody seems to be using it, but it has a
		870	POE backend, so it can be supported through POE.
		871
		872	AnyEvent knows about both Prima and Wx, however, and will try to
		873	load POE when detecting them, in the hope that POE will pick them
		874	up, in which case everything will be automatic.
641		875
642	GLOBAL VARIABLES AND FUNCTIONS	876	GLOBAL VARIABLES AND FUNCTIONS
		877	These are not normally required to use AnyEvent, but can be useful to
		878	write AnyEvent extension modules.
		879
643	$AnyEvent::MODEL	880	$AnyEvent::MODEL
644	Contains "undef" until the first watcher is being created. Then it	881	Contains "undef" until the first watcher is being created, before
		882	the backend has been autodetected.
		883
645	contains the event model that is being used, which is the name of	884	Afterwards it contains the event model that is being used, which is
646	the Perl class implementing the model. This class is usually one of	885	the name of the Perl class implementing the model. This class is
647	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	886	usually one of the "AnyEvent::Impl::xxx" modules, but can be any
648	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	887	other class in the case AnyEvent has been extended at runtime (e.g.
649		888	in rxvt-unicode it will be "urxvt::anyevent").
650	The known classes so far are:
651
652	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
653	AnyEvent::Impl::Event based on Event, second best choice.
654	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
655	AnyEvent::Impl::Glib based on Glib, third-best choice.
656	AnyEvent::Impl::Tk based on Tk, very bad choice.
657	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
658	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
659	AnyEvent::Impl::POE based on POE, not generic enough for full support.
660
661	There is no support for WxWidgets, as WxWidgets has no support for
662	watching file handles. However, you can use WxWidgets through the
663	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
664	second, which was considered to be too horrible to even consider for
665	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
666	using it's adaptor.
667
668	AnyEvent knows about Prima and Wx and will try to use POE when
669	autodetecting them.
670		889
671	AnyEvent::detect	890	AnyEvent::detect
672	Returns $AnyEvent::MODEL, forcing autodetection of the event model	891	Returns $AnyEvent::MODEL, forcing autodetection of the event model
673	if necessary. You should only call this function right before you	892	if necessary. You should only call this function right before you
674	would have created an AnyEvent watcher anyway, that is, as late as	893	would have created an AnyEvent watcher anyway, that is, as late as
675	possible at runtime.	894	possible at runtime, and not e.g. during initialisation of your
		895	module.
		896
		897	If you need to do some initialisation before AnyEvent watchers are
		898	created, use "post_detect".
676		899
677	$guard = AnyEvent::post_detect { BLOCK }	900	$guard = AnyEvent::post_detect { BLOCK }
678	Arranges for the code block to be executed as soon as the event	901	Arranges for the code block to be executed as soon as the event
679	model is autodetected (or immediately if this has already happened).	902	model is autodetected (or immediately if that has already happened).
		903
		904	The block will be executed after the actual backend has been
		905	detected ($AnyEvent::MODEL is set), but before any watchers have
		906	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		907	other initialisations - see the sources of AnyEvent::Strict or
		908	AnyEvent::AIO to see how this is used.
		909
		910	The most common usage is to create some global watchers, without
		911	forcing event module detection too early, for example, AnyEvent::AIO
		912	creates and installs the global IO::AIO watcher in a "post_detect"
		913	block to avoid autodetecting the event module at load time.
680		914
681	If called in scalar or list context, then it creates and returns an	915	If called in scalar or list context, then it creates and returns an
682	object that automatically removes the callback again when it is	916	object that automatically removes the callback again when it is
		917	destroyed (or "undef" when the hook was immediately executed). See
683	destroyed. See Coro::BDB for a case where this is useful.	918	AnyEvent::AIO for a case where this is useful.
		919
		920	Example: Create a watcher for the IO::AIO module and store it in
		921	$WATCHER, but do so only do so after the event loop is initialised.
		922
		923	our WATCHER;
		924
		925	my $guard = AnyEvent::post_detect {
		926	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		927	};
		928
		929	# the \|\|= is important in case post_detect immediately runs the block,
		930	# as to not clobber the newly-created watcher. assigning both watcher and
		931	# post_detect guard to the same variable has the advantage of users being
		932	# able to just C<undef $WATCHER> if the watcher causes them grief.
		933
		934	$WATCHER \|\|= $guard;
684		935
685	@AnyEvent::post_detect	936	@AnyEvent::post_detect
686	If there are any code references in this array (you can "push" to it	937	If there are any code references in this array (you can "push" to it
687	before or after loading AnyEvent), then they will called directly	938	before or after loading AnyEvent), then they will be called directly
688	after the event loop has been chosen.	939	after the event loop has been chosen.
689		940
690	You should check $AnyEvent::MODEL before adding to this array,	941	You should check $AnyEvent::MODEL before adding to this array,
691	though: if it contains a true value then the event loop has already	942	though: if it is defined then the event loop has already been
692	been detected, and the array will be ignored.	943	detected, and the array will be ignored.
693		944
694	Best use "AnyEvent::post_detect { BLOCK }" instead.	945	Best use "AnyEvent::post_detect { BLOCK }" when your application
		946	allows it, as it takes care of these details.
		947
		948	This variable is mainly useful for modules that can do something
		949	useful when AnyEvent is used and thus want to know when it is
		950	initialised, but do not need to even load it by default. This array
		951	provides the means to hook into AnyEvent passively, without loading
		952	it.
		953
		954	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		955	together, you could put this into Coro (this is the actual code used
		956	by Coro to accomplish this):
		957
		958	if (defined $AnyEvent::MODEL) {
		959	# AnyEvent already initialised, so load Coro::AnyEvent
		960	require Coro::AnyEvent;
		961	} else {
		962	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		963	# as soon as it is
		964	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		965	}
695		966
696	WHAT TO DO IN A MODULE	967	WHAT TO DO IN A MODULE
697	As a module author, you should "use AnyEvent" and call AnyEvent methods	968	As a module author, you should "use AnyEvent" and call AnyEvent methods
698	freely, but you should not load a specific event module or rely on it.	969	freely, but you should not load a specific event module or rely on it.
699		970
…		…
707	stall the whole program, and the whole point of using events is to stay	978	stall the whole program, and the whole point of using events is to stay
708	interactive.	979	interactive.
709		980
710	It is fine, however, to call "->recv" when the user of your module	981	It is fine, however, to call "->recv" when the user of your module
711	requests it (i.e. if you create a http request object ad have a method	982	requests it (i.e. if you create a http request object ad have a method
712	called "results" that returns the results, it should call "->recv"	983	called "results" that returns the results, it may call "->recv" freely,
713	freely, as the user of your module knows what she is doing. always).	984	as the user of your module knows what she is doing. Always).
714		985
715	WHAT TO DO IN THE MAIN PROGRAM	986	WHAT TO DO IN THE MAIN PROGRAM
716	There will always be a single main program - the only place that should	987	There will always be a single main program - the only place that should
717	dictate which event model to use.	988	dictate which event model to use.
718		989
719	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	990	If the program is not event-based, it need not do anything special, even
720	do anything special (it does not need to be event-based) and let	991	when it depends on a module that uses an AnyEvent. If the program itself
721	AnyEvent decide which implementation to chose if some module relies on	992	uses AnyEvent, but does not care which event loop is used, all it needs
722	it.	993	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		994	available loop implementation.
723		995
724	If the main program relies on a specific event model - for example, in	996	If the main program relies on a specific event model - for example, in
725	Gtk2 programs you have to rely on the Glib module - you should load the	997	Gtk2 programs you have to rely on the Glib module - you should load the
726	event module before loading AnyEvent or any module that uses it:	998	event module before loading AnyEvent or any module that uses it:
727	generally speaking, you should load it as early as possible. The reason	999	generally speaking, you should load it as early as possible. The reason
728	is that modules might create watchers when they are loaded, and AnyEvent	1000	is that modules might create watchers when they are loaded, and AnyEvent
729	will decide on the event model to use as soon as it creates watchers,	1001	will decide on the event model to use as soon as it creates watchers,
730	and it might chose the wrong one unless you load the correct one	1002	and it might choose the wrong one unless you load the correct one
731	yourself.	1003	yourself.
732		1004
733	You can chose to use a pure-perl implementation by loading the	1005	You can chose to use a pure-perl implementation by loading the
734	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1006	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
735	everywhere, but letting AnyEvent chose the model is generally better.	1007	everywhere, but letting AnyEvent chose the model is generally better.
…		…
750	variable somewhere, waiting for it, and sending it when the program	1022	variable somewhere, waiting for it, and sending it when the program
751	should exit cleanly.	1023	should exit cleanly.
752		1024
753	OTHER MODULES	1025	OTHER MODULES
754	The following is a non-exhaustive list of additional modules that use	1026	The following is a non-exhaustive list of additional modules that use
755	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1027	AnyEvent as a client and can therefore be mixed easily with other
756	in the same program. Some of the modules come with AnyEvent, some are	1028	AnyEvent modules and other event loops in the same program. Some of the
757	available via CPAN.	1029	modules come as part of AnyEvent, the others are available via CPAN.
758		1030
759	AnyEvent::Util	1031	AnyEvent::Util
760	Contains various utility functions that replace often-used but	1032	Contains various utility functions that replace often-used blocking
761	blocking functions such as "inet_aton" by event-/callback-based	1033	functions such as "inet_aton" with event/callback-based versions.
762	versions.
763		1034
764	AnyEvent::Socket	1035	AnyEvent::Socket
765	Provides various utility functions for (internet protocol) sockets,	1036	Provides various utility functions for (internet protocol) sockets,
766	addresses and name resolution. Also functions to create non-blocking	1037	addresses and name resolution. Also functions to create non-blocking
767	tcp connections or tcp servers, with IPv6 and SRV record support and	1038	tcp connections or tcp servers, with IPv6 and SRV record support and
768	more.	1039	more.
769		1040
770	AnyEvent::Handle	1041	AnyEvent::Handle
771	Provide read and write buffers, manages watchers for reads and	1042	Provide read and write buffers, manages watchers for reads and
772	writes, supports raw and formatted I/O, I/O queued and fully	1043	writes, supports raw and formatted I/O, I/O queued and fully
773	transparent and non-blocking SSL/TLS.	1044	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
774		1045
775	AnyEvent::DNS	1046	AnyEvent::DNS
776	Provides rich asynchronous DNS resolver capabilities.	1047	Provides rich asynchronous DNS resolver capabilities.
777		1048
		1049	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
		1050	AnyEvent::IGS, AnyEvent::FCP
		1051	Implement event-based interfaces to the protocols of the same name
		1052	(for the curious, IGS is the International Go Server and FCP is the
		1053	Freenet Client Protocol).
		1054
		1055	AnyEvent::Handle::UDP
		1056	Here be danger!
		1057
		1058	As Pauli would put it, "Not only is it not right, it's not even
		1059	wrong!" - there are so many things wrong with AnyEvent::Handle::UDP,
		1060	most notably its use of a stream-based API with a protocol that
		1061	isn't streamable, that the only way to improve it is to delete it.
		1062
		1063	It features data corruption (but typically only under load) and
		1064	general confusion. On top, the author is not only clueless about UDP
		1065	but also fact-resistant - some gems of his understanding: "connect
		1066	doesn't work with UDP", "UDP packets are not IP packets", "UDP only
		1067	has datagrams, not packets", "I don't need to implement proper error
		1068	checking as UDP doesn't support error checking" and so on - he
		1069	doesn't even understand what's wrong with his module when it is
		1070	explained to him.
		1071
778	AnyEvent::HTTP	1072	AnyEvent::DBI
779	A simple-to-use HTTP library that is capable of making a lot of	1073	Executes DBI requests asynchronously in a proxy process for you,
780	concurrent HTTP requests.	1074	notifying you in an event-based way when the operation is finished.
		1075
		1076	AnyEvent::AIO
		1077	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1078	the toolbox of every event programmer. AnyEvent::AIO transparently
		1079	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1080	event-based file I/O, and much more.
781		1081
782	AnyEvent::HTTPD	1082	AnyEvent::HTTPD
783	Provides a simple web application server framework.	1083	A simple embedded webserver.
784		1084
785	AnyEvent::FastPing	1085	AnyEvent::FastPing
786	The fastest ping in the west.	1086	The fastest ping in the west.
787		1087
788	AnyEvent::DBI
789	Executes DBI requests asynchronously in a proxy process.
790
791	AnyEvent::AIO
792	Truly asynchronous I/O, should be in the toolbox of every event
793	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
794	together.
795
796	AnyEvent::BDB
797	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
798	fuses BDB and AnyEvent together.
799
800	AnyEvent::GPSD
801	A non-blocking interface to gpsd, a daemon delivering GPS
802	information.
803
804	AnyEvent::IGS
805	A non-blocking interface to the Internet Go Server protocol (used by
806	App::IGS).
807
808	AnyEvent::IRC
809	AnyEvent based IRC client module family (replacing the older
810	Net::IRC3).
811
812	Net::XMPP2
813	AnyEvent based XMPP (Jabber protocol) module family.
814
815	Net::FCP
816	AnyEvent-based implementation of the Freenet Client Protocol,
817	birthplace of AnyEvent.
818
819	Event::ExecFlow
820	High level API for event-based execution flow control.
821
822	Coro	1088	Coro
823	Has special support for AnyEvent via Coro::AnyEvent.	1089	Has special support for AnyEvent via Coro::AnyEvent.
824		1090
825	IO::Lambda	1091	SIMPLIFIED AE API
826	The lambda approach to I/O - don't ask, look there. Can use	1092	Starting with version 5.0, AnyEvent officially supports a second, much
827	AnyEvent.	1093	simpler, API that is designed to reduce the calling, typing and memory
		1094	overhead by using function call syntax and a fixed number of parameters.
		1095
		1096	See the AE manpage for details.
828		1097
829	ERROR AND EXCEPTION HANDLING	1098	ERROR AND EXCEPTION HANDLING
830	In general, AnyEvent does not do any error handling - it relies on the	1099	In general, AnyEvent does not do any error handling - it relies on the
831	caller to do that if required. The AnyEvent::Strict module (see also the	1100	caller to do that if required. The AnyEvent::Strict module (see also the
832	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	1101	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
842	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1111	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
843	Glib uses "install_exception_handler" and so on.	1112	Glib uses "install_exception_handler" and so on.
844		1113
845	ENVIRONMENT VARIABLES	1114	ENVIRONMENT VARIABLES
846	The following environment variables are used by this module or its	1115	The following environment variables are used by this module or its
847	submodules:	1116	submodules.
		1117
		1118	Note that AnyEvent will remove all environment variables starting with
		1119	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1120	enabled.
848		1121
849	"PERL_ANYEVENT_VERBOSE"	1122	"PERL_ANYEVENT_VERBOSE"
850	By default, AnyEvent will be completely silent except in fatal	1123	By default, AnyEvent will be completely silent except in fatal
851	conditions. You can set this environment variable to make AnyEvent	1124	conditions. You can set this environment variable to make AnyEvent
852	more talkative.	1125	more talkative.
…		…
855	conditions, such as not being able to load the event model specified	1128	conditions, such as not being able to load the event model specified
856	by "PERL_ANYEVENT_MODEL".	1129	by "PERL_ANYEVENT_MODEL".
857		1130
858	When set to 2 or higher, cause AnyEvent to report to STDERR which	1131	When set to 2 or higher, cause AnyEvent to report to STDERR which
859	event model it chooses.	1132	event model it chooses.
		1133
		1134	When set to 8 or higher, then AnyEvent will report extra information
		1135	on which optional modules it loads and how it implements certain
		1136	features.
860		1137
861	"PERL_ANYEVENT_STRICT"	1138	"PERL_ANYEVENT_STRICT"
862	AnyEvent does not do much argument checking by default, as thorough	1139	AnyEvent does not do much argument checking by default, as thorough
863	argument checking is very costly. Setting this variable to a true	1140	argument checking is very costly. Setting this variable to a true
864	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1141	value will cause AnyEvent to load "AnyEvent::Strict" and then to
865	thoroughly check the arguments passed to most method calls. If it	1142	thoroughly check the arguments passed to most method calls. If it
866	finds any problems it will croak.	1143	finds any problems, it will croak.
867		1144
868	In other words, enables "strict" mode.	1145	In other words, enables "strict" mode.
869		1146
870	Unlike "use strict", it is definitely recommended ot keep it off in	1147	Unlike "use strict" (or its modern cousin, "use common::sense", it
871	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment	1148	is definitely recommended to keep it off in production. Keeping
		1149	"PERL_ANYEVENT_STRICT=1" in your environment while developing
872	while developing programs can be very useful, however.	1150	programs can be very useful, however.
873		1151
874	"PERL_ANYEVENT_MODEL"	1152	"PERL_ANYEVENT_MODEL"
875	This can be used to specify the event model to be used by AnyEvent,	1153	This can be used to specify the event model to be used by AnyEvent,
876	before auto detection and -probing kicks in. It must be a string	1154	before auto detection and -probing kicks in. It must be a string
877	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1155	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
918	EDNS0 in its DNS requests.	1196	EDNS0 in its DNS requests.
919		1197
920	"PERL_ANYEVENT_MAX_FORKS"	1198	"PERL_ANYEVENT_MAX_FORKS"
921	The maximum number of child processes that	1199	The maximum number of child processes that
922	"AnyEvent::Util::fork_call" will create in parallel.	1200	"AnyEvent::Util::fork_call" will create in parallel.
		1201
		1202	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1203	The default value for the "max_outstanding" parameter for the
		1204	default DNS resolver - this is the maximum number of parallel DNS
		1205	requests that are sent to the DNS server.
		1206
		1207	"PERL_ANYEVENT_RESOLV_CONF"
		1208	The file to use instead of /etc/resolv.conf (or OS-specific
		1209	configuration) in the default resolver. When set to the empty
		1210	string, no default config will be used.
		1211
		1212	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1213	When neither "ca_file" nor "ca_path" was specified during
		1214	AnyEvent::TLS context creation, and either of these environment
		1215	variables exist, they will be used to specify CA certificate
		1216	locations instead of a system-dependent default.
		1217
		1218	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1219	When these are set to 1, then the respective modules are not loaded.
		1220	Mostly good for testing AnyEvent itself.
923		1221
924	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1222	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
925	This is an advanced topic that you do not normally need to use AnyEvent	1223	This is an advanced topic that you do not normally need to use AnyEvent
926	in a module. This section is only of use to event loop authors who want	1224	in a module. This section is only of use to event loop authors who want
927	to provide AnyEvent compatibility.	1225	to provide AnyEvent compatibility.
…		…
982	warn "read: $input\n"; # output what has been read	1280	warn "read: $input\n"; # output what has been read
983	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1281	$cv->send if $input =~ /^q/i; # quit program if /^q/i
984	},	1282	},
985	);	1283	);
986		1284
987	my $time_watcher; # can only be used once
988
989	sub new_timer {
990	$timer = AnyEvent->timer (after => 1, cb => sub {	1285	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
991	warn "timeout\n"; # print 'timeout' about every second	1286	warn "timeout\n"; # print 'timeout' at most every second
992	&new_timer; # and restart the time
993	});
994	}	1287	});
995
996	new_timer; # create first timer
997		1288
998	$cv->recv; # wait until user enters /^q/i	1289	$cv->recv; # wait until user enters /^q/i
999		1290
1000	REAL-WORLD EXAMPLE	1291	REAL-WORLD EXAMPLE
1001	Consider the Net::FCP module. It features (among others) the following	1292	Consider the Net::FCP module. It features (among others) the following
…		…
1073		1364
1074	The actual code goes further and collects all errors ("die"s,	1365	The actual code goes further and collects all errors ("die"s,
1075	exceptions) that occurred during request processing. The "result" method	1366	exceptions) that occurred during request processing. The "result" method
1076	detects whether an exception as thrown (it is stored inside the $txn	1367	detects whether an exception as thrown (it is stored inside the $txn
1077	object) and just throws the exception, which means connection errors and	1368	object) and just throws the exception, which means connection errors and
1078	other problems get reported tot he code that tries to use the result,	1369	other problems get reported to the code that tries to use the result,
1079	not in a random callback.	1370	not in a random callback.
1080		1371
1081	All of this enables the following usage styles:	1372	All of this enables the following usage styles:
1082		1373
1083	1. Blocking:	1374	1. Blocking:
…		…
1128	through AnyEvent. The benchmark creates a lot of timers (with a zero	1419	through AnyEvent. The benchmark creates a lot of timers (with a zero
1129	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1420	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1130	which it is), lets them fire exactly once and destroys them again.	1421	which it is), lets them fire exactly once and destroys them again.
1131		1422
1132	Source code for this benchmark is found as eg/bench in the AnyEvent	1423	Source code for this benchmark is found as eg/bench in the AnyEvent
1133	distribution.	1424	distribution. It uses the AE interface, which makes a real difference
		1425	for the EV and Perl backends only.
1134		1426
1135	Explanation of the columns	1427	Explanation of the columns
1136	watcher is the number of event watchers created/destroyed. Since	1428	watcher is the number of event watchers created/destroyed. Since
1137	different event models feature vastly different performances, each event	1429	different event models feature vastly different performances, each event
1138	loop was given a number of watchers so that overall runtime is	1430	loop was given a number of watchers so that overall runtime is
…		…
1157	destroy is the time, in microseconds, that it takes to destroy a	1449	destroy is the time, in microseconds, that it takes to destroy a
1158	single watcher.	1450	single watcher.
1159		1451
1160	Results	1452	Results
1161	name watchers bytes create invoke destroy comment	1453	name watchers bytes create invoke destroy comment
1162	EV/EV 400000 224 0.47 0.35 0.27 EV native interface	1454	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1163	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers	1455	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1164	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal	1456	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1165	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation	1457	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1166	Event/Event 16000 517 32.20 31.80 0.81 Event native interface	1458	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1167	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers	1459	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1460	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1461	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1168	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour	1462	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1169	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers	1463	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1170	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event	1464	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1171	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select	1465	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1172		1466
1173	Discussion	1467	Discussion
1174	The benchmark does not measure scalability of the event loop very	1468	The benchmark does not measure scalability of the event loop very
1175	well. For example, a select-based event loop (such as the pure perl one)	1469	well. For example, a select-based event loop (such as the pure perl one)
1176	can never compete with an event loop that uses epoll when the number of	1470	can never compete with an event loop that uses epoll when the number of
…		…
1187	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1481	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1188	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1482	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1189	CPU cycles with POE.	1483	CPU cycles with POE.
1190		1484
1191	"EV" is the sole leader regarding speed and memory use, which are both	1485	"EV" is the sole leader regarding speed and memory use, which are both
1192	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1486	maximal/minimal, respectively. When using the AE API there is zero
		1487	overhead (when going through the AnyEvent API create is about 5-6 times
		1488	slower, with other times being equal, so still uses far less memory than
1193	far less memory than any other event loop and is still faster than Event	1489	any other event loop and is still faster than Event natively).
1194	natively.
1195		1490
1196	The pure perl implementation is hit in a few sweet spots (both the	1491	The pure perl implementation is hit in a few sweet spots (both the
1197	constant timeout and the use of a single fd hit optimisations in the	1492	constant timeout and the use of a single fd hit optimisations in the
1198	perl interpreter and the backend itself). Nevertheless this shows that	1493	perl interpreter and the backend itself). Nevertheless this shows that
1199	it adds very little overhead in itself. Like any select-based backend	1494	it adds very little overhead in itself. Like any select-based backend
…		…
1201	few of them active), of course, but this was not subject of this	1496	few of them active), of course, but this was not subject of this
1202	benchmark.	1497	benchmark.
1203		1498
1204	The "Event" module has a relatively high setup and callback invocation	1499	The "Event" module has a relatively high setup and callback invocation
1205	cost, but overall scores in on the third place.	1500	cost, but overall scores in on the third place.
		1501
		1502	"IO::Async" performs admirably well, about on par with "Event", even
		1503	when using its pure perl backend.
1206		1504
1207	"Glib"'s memory usage is quite a bit higher, but it features a faster	1505	"Glib"'s memory usage is quite a bit higher, but it features a faster
1208	callback invocation and overall ends up in the same class as "Event".	1506	callback invocation and overall ends up in the same class as "Event".
1209	However, Glib scales extremely badly, doubling the number of watchers	1507	However, Glib scales extremely badly, doubling the number of watchers
1210	increases the processing time by more than a factor of four, making it	1508	increases the processing time by more than a factor of four, making it
…		…
1266	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1564	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1267	100 (1%) are active. This mirrors the activity of large servers with	1565	100 (1%) are active. This mirrors the activity of large servers with
1268	many connections, most of which are idle at any one point in time.	1566	many connections, most of which are idle at any one point in time.
1269		1567
1270	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1568	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1271	distribution.	1569	distribution. It uses the AE interface, which makes a real difference
		1570	for the EV and Perl backends only.
1272		1571
1273	Explanation of the columns	1572	Explanation of the columns
1274	sockets is the number of sockets, and twice the number of "servers"	1573	sockets is the number of sockets, and twice the number of "servers"
1275	(as each server has a read and write socket end).	1574	(as each server has a read and write socket end).
1276		1575
…		…
1281	single "request", that is, reading the token from the pipe and	1580	single "request", that is, reading the token from the pipe and
1282	forwarding it to another server. This includes deleting the old timeout	1581	forwarding it to another server. This includes deleting the old timeout
1283	and creating a new one that moves the timeout into the future.	1582	and creating a new one that moves the timeout into the future.
1284		1583
1285	Results	1584	Results
1286	name sockets create request	1585	name sockets create request
1287	EV 20000 69.01 11.16	1586	EV 20000 62.66 7.99
1288	Perl 20000 73.32 35.87	1587	Perl 20000 68.32 32.64
1289	Event 20000 212.62 257.32	1588	IOAsync 20000 174.06 101.15 epoll
1290	Glib 20000 651.16 1896.30	1589	IOAsync 20000 174.67 610.84 poll
		1590	Event 20000 202.69 242.91
		1591	Glib 20000 557.01 1689.52
1291	POE 20000 349.67 12317.24 uses POE::Loop::Event	1592	POE 20000 341.54 12086.32 uses POE::Loop::Event
1292		1593
1293	Discussion	1594	Discussion
1294	This benchmark does measure scalability and overall performance of the	1595	This benchmark does measure scalability and overall performance of the
1295	particular event loop.	1596	particular event loop.
1296		1597
1297	EV is again fastest. Since it is using epoll on my system, the setup	1598	EV is again fastest. Since it is using epoll on my system, the setup
1298	time is relatively high, though.	1599	time is relatively high, though.
1299		1600
1300	Perl surprisingly comes second. It is much faster than the C-based event	1601	Perl surprisingly comes second. It is much faster than the C-based event
1301	loops Event and Glib.	1602	loops Event and Glib.
		1603
		1604	IO::Async performs very well when using its epoll backend, and still
		1605	quite good compared to Glib when using its pure perl backend.
1302		1606
1303	Event suffers from high setup time as well (look at its code and you	1607	Event suffers from high setup time as well (look at its code and you
1304	will understand why). Callback invocation also has a high overhead	1608	will understand why). Callback invocation also has a high overhead
1305	compared to the "$_->() for .."-style loop that the Perl event loop	1609	compared to the "$_->() for .."-style loop that the Perl event loop
1306	uses. Event uses select or poll in basically all documented	1610	uses. Event uses select or poll in basically all documented
…		…
1357		1661
1358	Summary	1662	Summary
1359	* C-based event loops perform very well with small number of watchers,	1663	* C-based event loops perform very well with small number of watchers,
1360	as the management overhead dominates.	1664	as the management overhead dominates.
1361		1665
		1666	THE IO::Lambda BENCHMARK
		1667	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1668	could be misinterpreted to make AnyEvent look bad. In fact, the
		1669	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1670	better (which shouldn't come as a surprise to anybody). As such, the
		1671	benchmark is fine, and mostly shows that the AnyEvent backend from
		1672	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1673	without the extra baggage? To explore this, I wrote the equivalent
		1674	benchmark for AnyEvent.
		1675
		1676	The benchmark itself creates an echo-server, and then, for 500 times,
		1677	connects to the echo server, sends a line, waits for the reply, and then
		1678	creates the next connection. This is a rather bad benchmark, as it
		1679	doesn't test the efficiency of the framework or much non-blocking I/O,
		1680	but it is a benchmark nevertheless.
		1681
		1682	name runtime
		1683	Lambda/select 0.330 sec
		1684	+ optimized 0.122 sec
		1685	Lambda/AnyEvent 0.327 sec
		1686	+ optimized 0.138 sec
		1687	Raw sockets/select 0.077 sec
		1688	POE/select, components 0.662 sec
		1689	POE/select, raw sockets 0.226 sec
		1690	POE/select, optimized 0.404 sec
		1691
		1692	AnyEvent/select/nb 0.085 sec
		1693	AnyEvent/EV/nb 0.068 sec
		1694	+state machine 0.134 sec
		1695
		1696	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1697	benchmarks actually make blocking connects and use 100% blocking I/O,
		1698	defeating the purpose of an event-based solution. All of the newly
		1699	written AnyEvent benchmarks use 100% non-blocking connects (using
		1700	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1701	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1702	connects generally require a lot more bookkeeping and event handling
		1703	than blocking connects (which involve a single syscall only).
		1704
		1705	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1706	offers similar expressive power as POE and IO::Lambda, using
		1707	conventional Perl syntax. This means that both the echo server and the
		1708	client are 100% non-blocking, further placing it at a disadvantage.
		1709
		1710	As you can see, the AnyEvent + EV combination even beats the
		1711	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1712	backend easily beats IO::Lambda and POE.
		1713
		1714	And even the 100% non-blocking version written using the high-level (and
		1715	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1716	higher level ("unoptimised") abstractions by a large margin, even though
		1717	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1718
		1719	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1720	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1721	part of the IO::Lambda distribution and were used without any changes.
		1722
1362	SIGNALS	1723	SIGNALS
1363	AnyEvent currently installs handlers for these signals:	1724	AnyEvent currently installs handlers for these signals:
1364		1725
1365	SIGCHLD	1726	SIGCHLD
1366	A handler for "SIGCHLD" is installed by AnyEvent's child watcher	1727	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1367	emulation for event loops that do not support them natively. Also,	1728	emulation for event loops that do not support them natively. Also,
1368	some event loops install a similar handler.	1729	some event loops install a similar handler.
		1730
		1731	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1732	then AnyEvent will reset it to default, to avoid losing child exit
		1733	statuses.
1369		1734
1370	SIGPIPE	1735	SIGPIPE
1371	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is	1736	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1372	"undef" when AnyEvent gets loaded.	1737	"undef" when AnyEvent gets loaded.
1373		1738
…		…
1381	it is that this way, the handler will be restored to defaults on	1746	it is that this way, the handler will be restored to defaults on
1382	exec.	1747	exec.
1383		1748
1384	Feel free to install your own handler, or reset it to defaults.	1749	Feel free to install your own handler, or reset it to defaults.
1385		1750
		1751	RECOMMENDED/OPTIONAL MODULES
		1752	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1753	its built-in modules) are required to use it.
		1754
		1755	That does not mean that AnyEvent won't take advantage of some additional
		1756	modules if they are installed.
		1757
		1758	This section explains which additional modules will be used, and how
		1759	they affect AnyEvent's operation.
		1760
		1761	Async::Interrupt
		1762	This slightly arcane module is used to implement fast signal
		1763	handling: To my knowledge, there is no way to do completely
		1764	race-free and quick signal handling in pure perl. To ensure that
		1765	signals still get delivered, AnyEvent will start an interval timer
		1766	to wake up perl (and catch the signals) with some delay (default is
		1767	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1768
		1769	If this module is available, then it will be used to implement
		1770	signal catching, which means that signals will not be delayed, and
		1771	the event loop will not be interrupted regularly, which is more
		1772	efficient (and good for battery life on laptops).
		1773
		1774	This affects not just the pure-perl event loop, but also other event
		1775	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1776
		1777	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1778	natively, and either employ their own workarounds (POE) or use
		1779	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1780	Installing Async::Interrupt does nothing for those backends.
		1781
		1782	EV This module isn't really "optional", as it is simply one of the
		1783	backend event loops that AnyEvent can use. However, it is simply the
		1784	best event loop available in terms of features, speed and stability:
		1785	It supports the AnyEvent API optimally, implements all the watcher
		1786	types in XS, does automatic timer adjustments even when no monotonic
		1787	clock is available, can take avdantage of advanced kernel interfaces
		1788	such as "epoll" and "kqueue", and is the fastest backend by far.
		1789	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1790	Glib::EV).
		1791
		1792	If you only use backends that rely on another event loop (e.g.
		1793	"Tk"), then this module will do nothing for you.
		1794
		1795	Guard
		1796	The guard module, when used, will be used to implement
		1797	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1798	uses a lot less memory), but otherwise doesn't affect guard
		1799	operation much. It is purely used for performance.
		1800
		1801	JSON and JSON::XS
		1802	One of these modules is required when you want to read or write JSON
		1803	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		1804	can take advantage of the ultra-high-speed JSON::XS module when it
		1805	is installed.
		1806
		1807	Net::SSLeay
		1808	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1809	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1810	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1811
		1812	Time::HiRes
		1813	This module is part of perl since release 5.008. It will be used
		1814	when the chosen event library does not come with a timing source of
		1815	its own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1816	additionally use it to try to use a monotonic clock for timing
		1817	stability.
		1818
1386	FORK	1819	FORK
1387	Most event libraries are not fork-safe. The ones who are usually are	1820	Most event libraries are not fork-safe. The ones who are usually are
1388	because they rely on inefficient but fork-safe "select" or "poll" calls.	1821	because they rely on inefficient but fork-safe "select" or "poll" calls
1389	Only EV is fully fork-aware.	1822	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		1823	epoll are usually badly thought-out hacks that are incompatible with
		1824	fork in one way or another. Only EV is fully fork-aware and ensures that
		1825	you continue event-processing in both parent and child (or both, if you
		1826	know what you are doing).
		1827
		1828	This means that, in general, you cannot fork and do event processing in
		1829	the child if the event library was initialised before the fork (which
		1830	usually happens when the first AnyEvent watcher is created, or the
		1831	library is loaded).
1390		1832
1391	If you have to fork, you must either do so before creating your first	1833	If you have to fork, you must either do so before creating your first
1392	watcher OR you must not use AnyEvent at all in the child.	1834	watcher OR you must not use AnyEvent at all in the child OR you must do
		1835	something completely out of the scope of AnyEvent.
		1836
		1837	The problem of doing event processing in the parent and the child is
		1838	much more complicated: even for backends that are fork-aware or
		1839	fork-safe, their behaviour is not usually what you want: fork clones all
		1840	watchers, that means all timers, I/O watchers etc. are active in both
		1841	parent and child, which is almost never what you want. USing "exec" to
		1842	start worker children from some kind of manage rprocess is usually
		1843	preferred, because it is much easier and cleaner, at the expense of
		1844	having to have another binary.
1393		1845
1394	SECURITY CONSIDERATIONS	1846	SECURITY CONSIDERATIONS
1395	AnyEvent can be forced to load any event model via	1847	AnyEvent can be forced to load any event model via
1396	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1848	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1397	to execute arbitrary code or directly gain access, it can easily be used	1849	to execute arbitrary code or directly gain access, it can easily be used
…		…
1401		1853
1402	You can make AnyEvent completely ignore this variable by deleting it	1854	You can make AnyEvent completely ignore this variable by deleting it
1403	before the first watcher gets created, e.g. with a "BEGIN" block:	1855	before the first watcher gets created, e.g. with a "BEGIN" block:
1404		1856
1405	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1857	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1406		1858
1407	use AnyEvent;	1859	use AnyEvent;
1408		1860
1409	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1861	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1410	be used to probe what backend is used and gain other information (which	1862	be used to probe what backend is used and gain other information (which
1411	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),	1863	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1412	and $ENV{PERL_ANYEGENT_STRICT}.	1864	and $ENV{PERL_ANYEVENT_STRICT}.
		1865
		1866	Note that AnyEvent will remove all environment variables starting with
		1867	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1868	enabled.
1413		1869
1414	BUGS	1870	BUGS
1415	Perl 5.8 has numerous memleaks that sometimes hit this module and are	1871	Perl 5.8 has numerous memleaks that sometimes hit this module and are
1416	hard to work around. If you suffer from memleaks, first upgrade to Perl	1872	hard to work around. If you suffer from memleaks, first upgrade to Perl
1417	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	1873	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1418	annoying memleaks, such as leaking on "map" and "grep" but it is usually	1874	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1419	not as pronounced).	1875	not as pronounced).
1420		1876
1421	SEE ALSO	1877	SEE ALSO
		1878	Tutorial/Introduction: AnyEvent::Intro.
		1879
		1880	FAQ: AnyEvent::FAQ.
		1881
1422	Utility functions: AnyEvent::Util.	1882	Utility functions: AnyEvent::Util.
1423		1883
1424	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1884	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1425	Event::Lib, Qt, POE.	1885	Event::Lib, Qt, POE.
1426		1886
1427	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1887	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1428	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1888	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1429	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1889	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1890	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
1430		1891
1431	Non-blocking file handles, sockets, TCP clients and servers:	1892	Non-blocking file handles, sockets, TCP clients and servers:
1432	AnyEvent::Handle, AnyEvent::Socket.	1893	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1433		1894
1434	Asynchronous DNS: AnyEvent::DNS.	1895	Asynchronous DNS: AnyEvent::DNS.
1435		1896
1436	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1897	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1437		1898
1438	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1899	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
		1900	AnyEvent::HTTP.
1439		1901
1440	AUTHOR	1902	AUTHOR
1441	Marc Lehmann <schmorp@schmorp.de>	1903	Marc Lehmann <schmorp@schmorp.de>
1442	http://home.schmorp.de/	1904	http://home.schmorp.de/
1443		1905

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Comparing AnyEvent/README (file contents): Revision 1.37 by root, Mon Apr 20 14:34:18 2009 UTC vs. Revision 1.63 by root, Wed Oct 13 19:49:46 2010 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.37 by root, Mon Apr 20 14:34:18 2009 UTC vs.
Revision 1.63 by root, Wed Oct 13 19:49:46 2010 UTC