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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
10	# file descriptor readable	13	# file handle or descriptor readable
11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });	14	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12		15
13	# one-shot or repeating timers	16	# one-shot or repeating timers
14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });	17	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...	18	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
16		19
17	print AnyEvent->now; # prints current event loop time	20	print AnyEvent->now; # prints current event loop time
18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.	21	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
19		22
20	# POSIX signal	23	# POSIX signal
…		…
37		40
38	INTRODUCTION/TUTORIAL	41	INTRODUCTION/TUTORIAL
39	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
40	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
41	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.
42		54
43	WHY YOU SHOULD USE THIS MODULE (OR NOT)	55	WHY YOU SHOULD USE THIS MODULE (OR NOT)
44	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
45	nowadays. So what is different about AnyEvent?	57	nowadays. So what is different about AnyEvent?
46		58
…		…
61	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
62	model you use.	74	model you use.
63		75
64	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
65	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
66	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
67	cannot use anything else, as they are simply incompatible to everything	79	cannot use anything else, as they are simply incompatible to everything
68	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
69	are *also* forced to use the same event loop you use.	81	are *also* forced to use the same event loop you use.
70		82
71	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	83	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
72	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
73	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
74	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.
75	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
76	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
77	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
78	to AnyEvent, too, so it is future-proof).	90	AnyEvent, too, so it is future-proof).
79		91
80	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
81	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
82	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
83	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
84	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
85	wrapper as technically possible.	97	technically possible.
86		98
87	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
88	useful functionality, such as an asynchronous DNS resolver, 100%	100	useful functionality, such as an asynchronous DNS resolver, 100%
89	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
90	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
…		…
93	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
94	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
95	model, you should *not* use this module.	107	model, you should *not* use this module.
96		108
97	DESCRIPTION	109	DESCRIPTION
98	AnyEvent provides an identical interface to multiple event loops. This	110	AnyEvent provides a uniform interface to various event loops. This
99	allows module authors to utilise an event loop without forcing module	111	allows module authors to use event loop functionality without forcing
100	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
101	coexist peacefully at any one time).	113	than one event loop cannot coexist peacefully).
102		114
103	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
104	module.	116	module.
105		117
106	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
107	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
108	following modules is already loaded: EV, Event, Glib,	120	following modules is already loaded: EV, AnyEvent::Impl::Perl, Event,
109	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
110	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
111	(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
112	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
113	successfully loaded will be used. If, after this, still none could be	125	normally tried.
114	found, AnyEvent will fall back to a pure-perl event loop, which is not
115	very efficient, but should work everywhere.
116		126
117	Because AnyEvent first checks for modules that are already loaded,	127	Because AnyEvent first checks for modules that are already loaded,
118	loading an event model explicitly before first using AnyEvent will	128	loading an event model explicitly before first using AnyEvent will
119	likely make that model the default. For example:	129	likely make that model the default. For example:
120		130
…		…
122	use AnyEvent;	132	use AnyEvent;
123		133
124	# .. AnyEvent will likely default to Tk	134	# .. AnyEvent will likely default to Tk
125		135
126	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
127	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
128	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.
129		140
130	The pure-perl implementation of AnyEvent is called	141	The pure-perl implementation of AnyEvent is called
131	"AnyEvent::Impl::Perl". Like other event modules you can load it	142	"AnyEvent::Impl::Perl". Like other event modules you can load it
132	explicitly and enjoy the high availability of that event loop :)	143	explicitly and enjoy the high availability of that event loop :)
133		144
…		…
141	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
142	in control).	153	in control).
143		154
144	Note that callbacks must not permanently change global variables	155	Note that callbacks must not permanently change global variables
145	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
146	callbacks must not "die". The former is good programming practise in	157	callbacks must not "die". The former is good programming practice in
147	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
148	widely between event loops.	159	widely between event loops.
149		160
150	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
151	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
152	to it).	163	to it).
153		164
154	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.
155		166
156	Many watchers either are used with "recursion" (repeating timers for	167	Many watchers either are used with "recursion" (repeating timers for
157	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.
158		169
159	An any way to achieve that is this pattern:	170	One way to achieve that is this pattern:
160		171
161	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	172	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
162	# you can use $w here, for example to undef it	173	# you can use $w here, for example to undef it
163	undef $w;	174	undef $w;
164	});	175	});
…		…
166	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,
167	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
168	declared.	179	declared.
169		180
170	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
171	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
172	the following mandatory key-value pairs as arguments:	189	the following mandatory key-value pairs as arguments:
173		190
174	"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
175	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
176	handle). Note that only file handles pointing to things for which	193	handle). Note that only file handles pointing to things for which
177	non-blocking operation makes sense are allowed. This includes sockets,	194	non-blocking operation makes sense are allowed. This includes sockets,
178	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
179	files or block devices.	196	files or block devices.
…		…
189		206
190	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
191	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
192	the underlying file descriptor.	209	the underlying file descriptor.
193		210
194	Some event loops issue spurious readyness notifications, so you should	211	Some event loops issue spurious readiness notifications, so you should
195	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
196	handles.	213	handles.
197		214
198	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
199	watcher.	216	watcher.
…		…
203	warn "read: $input\n";	220	warn "read: $input\n";
204	undef $w;	221	undef $w;
205	});	222	});
206		223
207	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
208	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
209	with the following mandatory arguments:	234	with the following mandatory arguments:
210		235
211	"after" specifies after how many seconds (fractional values are	236	"after" specifies after how many seconds (fractional values are
212	supported) the callback should be invoked. "cb" is the callback to	237	supported) the callback should be invoked. "cb" is the callback to
…		…
214		239
215	Although the callback might get passed parameters, their value and	240	Although the callback might get passed parameters, their value and
216	presence is undefined and you cannot rely on them. Portable AnyEvent	241	presence is undefined and you cannot rely on them. Portable AnyEvent
217	callbacks cannot use arguments passed to time watcher callbacks.	242	callbacks cannot use arguments passed to time watcher callbacks.
218		243
219	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
220	parameter, "interval", as a strictly positive number (> 0), then the	245	parameter, "interval", as a strictly positive number (> 0), then the
221	callback will be invoked regularly at that interval (in fractional	246	callback will be invoked regularly at that interval (in fractional
222	seconds) after the first invocation. If "interval" is specified with a	247	seconds) after the first invocation. If "interval" is specified with a
223	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.
224		249
225	The callback will be rescheduled before invoking the callback, but no	250	The callback will be rescheduled before invoking the callback, but no
226	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
227	is only approximate.	252	is only approximate.
228		253
229	Example: fire an event after 7.7 seconds.	254	Example: fire an event after 7.7 seconds.
230		255
231	my $w = AnyEvent->timer (after => 7.7, cb => sub {	256	my $w = AnyEvent->timer (after => 7.7, cb => sub {
…		…
248		273
249	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,
250	they use absolute time internally. This makes a difference when your	275	they use absolute time internally. This makes a difference when your
251	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
252	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
253	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
254	finally fire.	279	finally fire.
255		280
256	AnyEvent cannot compensate for this. The only event loop that is	281	AnyEvent cannot compensate for this. The only event loop that is
257	conscious about these issues is EV, which offers both relative	282	conscious of these issues is EV, which offers both relative (ev_timer,
258	(ev_timer, based on true relative time) and absolute (ev_periodic, based	283	based on true relative time) and absolute (ev_periodic, based on
259	on wallclock time) timers.	284	wallclock time) timers.
260		285
261	AnyEvent always prefers relative timers, if available, matching the	286	AnyEvent always prefers relative timers, if available, matching the
262	AnyEvent API.	287	AnyEvent API.
263		288
264	AnyEvent has two additional methods that return the "current time":	289	AnyEvent has two additional methods that return the "current time":
…		…
283	*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
284	function to call when you want to know the current time.*	309	function to call when you want to know the current time.*
285		310
286	This function is also often faster then "AnyEvent->time", and thus	311	This function is also often faster then "AnyEvent->time", and thus
287	the preferred method if you want some timestamp (for example,	312	the preferred method if you want some timestamp (for example,
288	AnyEvent::Handle uses this to update it's activity timeouts).	313	AnyEvent::Handle uses this to update its activity timeouts).
289		314
290	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
291	exact with your timing, you can skip it without bad conscience.	316	exact with your timing; you can skip it without a bad conscience.
292		317
293	For a practical example of when these times differ, consider	318	For a practical example of when these times differ, consider
294	Event::Lib and EV and the following set-up:	319	Event::Lib and EV and the following set-up:
295		320
296	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
297	at time=500 (assume no other callbacks delay processing). In your	322	at time=500 (assume no other callbacks delay processing). In your
298	callback, you wait a second by executing "sleep 1" (blocking the	323	callback, you wait a second by executing "sleep 1" (blocking the
299	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
300	timer that fires after three seconds.	325	timer that fires after three seconds.
301		326
…		…
333	time, which might affect timers and time-outs.	358	time, which might affect timers and time-outs.
334		359
335	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
336	the event loop's idea of "current time".	361	the event loop's idea of "current time".
337		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
338	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.
339		372
340	SIGNAL WATCHERS	373	SIGNAL WATCHERS
		374	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		375
341	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
342	*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
343	callback to be invoked whenever a signal occurs.	378	callback to be invoked whenever a signal occurs.
344		379
345	Although the callback might get passed parameters, their value and	380	Although the callback might get passed parameters, their value and
…		…
350	invocation, and callback invocation will be synchronous. Synchronous	385	invocation, and callback invocation will be synchronous. Synchronous
351	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
352	process, but it is guaranteed not to interrupt any other callbacks.	387	process, but it is guaranteed not to interrupt any other callbacks.
353		388
354	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
355	signal between multiple watchers.	390	signal between multiple watchers, and AnyEvent will ensure that signals
		391	will not interrupt your program at bad times.
356		392
357	This watcher might use %SIG, so programs overwriting those signals	393	This watcher might use %SIG (depending on the event loop used), so
358	directly will likely not work correctly.	394	programs overwriting those signals directly will likely not work
		395	correctly.
359		396
360	Example: exit on SIGINT	397	Example: exit on SIGINT
361		398
362	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	399	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
363		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
364	CHILD PROCESS WATCHERS	435	CHILD PROCESS WATCHERS
		436	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		437
365	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.
366		439
367	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,
368	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).
369	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
370	on any trace events (stopped/continued).	443	and an exit status is available, not on any trace events
		444	(stopped/continued).
371		445
372	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
373	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
374	callback arguments.	448	callback arguments.
375		449
…		…
380		454
381	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
382	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
383	could have exited already (and no SIGCHLD will be sent anymore).	457	could have exited already (and no SIGCHLD will be sent anymore).
384		458
385	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
386	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
387	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).
388	place).	463	AnyEvent's pure perl event loop handles all cases correctly regardless
		464	of when you start the watcher.
389		465
390	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
391	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
392	you "fork" the child (alternatively, you can call "AnyEvent::detect").	468	you "fork" the child (alternatively, you can call "AnyEvent::detect").
393		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
394	Example: fork a process and wait for it	474	Example: fork a process and wait for it
395		475
396	my $done = AnyEvent->condvar;	476	my $done = AnyEvent->condvar;
397		477
398	my $pid = fork or exit 5;	478	my $pid = fork or exit 5;
399		479
400	my $w = AnyEvent->child (	480	my $w = AnyEvent->child (
401	pid => $pid,	481	pid => $pid,
402	cb => sub {	482	cb => sub {
403	my ($pid, $status) = @_;	483	my ($pid, $status) = @_;
404	warn "pid $pid exited with status $status";	484	warn "pid $pid exited with status $status";
405	$done->send;	485	$done->send;
406	},	486	},
407	);	487	);
408		488
409	# do something else, then wait for process exit	489	# do something else, then wait for process exit
410	$done->recv;	490	$done->recv;
411		491
412	IDLE WATCHERS	492	IDLE WATCHERS
413	Sometimes there is a need to do something, but it is not so important to	493	$w = AnyEvent->idle (cb => <callback>);
414	do it instantly, but only when there is nothing better to do. This
415	"nothing better to do" is usually defined to be "no other events need
416	attention by the event loop".
417		494
418	Idle watchers ideally get invoked when the event loop has nothing better	495	This will repeatedly invoke the callback after the process becomes idle,
419	to do, just before it would block the process to wait for new events.	496	until either the watcher is destroyed or new events have been detected.
420	Instead of blocking, the idle watcher is invoked.
421		497
422	Most event loops unfortunately do not really support idle watchers (only	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
423	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent	508	(only EV, Event and Glib do it in a usable fashion) - for the rest,
424	will simply call the callback "from time to time".	509	AnyEvent will simply call the callback "from time to time".
425		510
426	Example: read lines from STDIN, but only process them when the program	511	Example: read lines from STDIN, but only process them when the program
427	is otherwise idle:	512	is otherwise idle:
428		513
429	my @lines; # read data	514	my @lines; # read data
…		…
442	}	527	}
443	});	528	});
444	});	529	});
445		530
446	CONDITION VARIABLES	531	CONDITION VARIABLES
		532	$cv = AnyEvent->condvar;
		533
		534	$cv->send (<list>);
		535	my @res = $cv->recv;
		536
447	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
448	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
449	will actively watch for new events and call your callbacks.	539	will actively watch for new events and call your callbacks.
450		540
451	AnyEvent is different, it expects somebody else to run the event loop	541	AnyEvent is slightly different: it expects somebody else to run the
452	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).
453		544
454	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
455	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.
456		549
457	Condition variables can be created by calling the "AnyEvent->condvar"	550	Condition variables can be created by calling the "AnyEvent->condvar"
458	method, usually without arguments. The only argument pair allowed is	551	method, usually without arguments. The only argument pair allowed is
459
460	"cb", which specifies a callback to be called when the condition	552	"cb", which specifies a callback to be called when the condition
461	variable becomes true, with the condition variable as the first argument	553	variable becomes true, with the condition variable as the first argument
462	(but not the results).	554	(but not the results).
463		555
464	After creation, the condition variable is "false" until it becomes	556	After creation, the condition variable is "false" until it becomes
465	"true" by calling the "send" method (or calling the condition variable	557	"true" by calling the "send" method (or calling the condition variable
466	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
467	the "->send" method).	559	the "->send" method).
468		560
469	Condition variables are similar to callbacks, except that you can	561	Since condition variables are the most complex part of the AnyEvent API,
470	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
471	in time where multiple outstanding events have been processed. And yet	563	you can connect to:
472	another way to call them is transactions - each condition variable can	564
473	be used to represent a transaction, which finishes at some point and	565	* Condition variables are like callbacks - you can call them (and pass
474	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.
475		582
476	Condition variables are very useful to signal that something has	583	Condition variables are very useful to signal that something has
477	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
478	requests, then a condition variable would be the ideal candidate to	585	requests, then a condition variable would be the ideal candidate to
479	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
…		…
492		599
493	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
494	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
495	(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
496	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call	603	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
497	it's "new" method in your own "new" method.	604	its "new" method in your own "new" method.
498		605
499	There are two "sides" to a condition variable - the "producer side"	606	There are two "sides" to a condition variable - the "producer side"
500	which eventually calls "-> send", and the "consumer side", which waits	607	which eventually calls "-> send", and the "consumer side", which waits
501	for the send to occur.	608	for the send to occur.
502		609
503	Example: wait for a timer.	610	Example: wait for a timer.
504		611
505	# wait till the result is ready	612	# condition: "wait till the timer is fired"
506	my $result_ready = AnyEvent->condvar;	613	my $timer_fired = AnyEvent->condvar;
507		614
508	# do something such as adding a timer	615	# create the timer - we could wait for, say
509	# or socket watcher the calls $result_ready->send	616	# a handle becomign ready, or even an
510	# when the "result" is ready.	617	# AnyEvent::HTTP request to finish, but
511	# in this case, we simply use a timer:	618	# in this case, we simply use a timer:
512	my $w = AnyEvent->timer (	619	my $w = AnyEvent->timer (
513	after => 1,	620	after => 1,
514	cb => sub { $result_ready->send },	621	cb => sub { $timer_fired->send },
515	);	622	);
516		623
517	# this "blocks" (while handling events) till the callback	624	# this "blocks" (while handling events) till the callback
518	# calls send	625	# calls ->send
519	$result_ready->recv;	626	$timer_fired->recv;
520		627
521	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
522	variables are also code references.	629	variables are also callable directly.
523		630
524	my $done = AnyEvent->condvar;	631	my $done = AnyEvent->condvar;
525	my $delay = AnyEvent->timer (after => 5, cb => $done);	632	my $delay = AnyEvent->timer (after => 5, cb => $done);
526	$done->recv;	633	$done->recv;
527		634
…		…
533		640
534	...	641	...
535		642
536	my @info = $couchdb->info->recv;	643	my @info = $couchdb->info->recv;
537		644
538	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
539	results are available:	646	results are available:
540		647
541	$couchdb->info->cb (sub {	648	$couchdb->info->cb (sub {
542	my @info = $_[0]->recv;	649	my @info = $_[0]->recv;
543	});	650	});
…		…
558		665
559	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
560	future "->recv" calls.	667	future "->recv" calls.
561		668
562	Condition variables are overloaded so one can call them directly (as	669	Condition variables are overloaded so one can call them directly (as
563	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
564	"send". Note, however, that many C-based event loops do not handle	671	calling "send".
565	overloading, so as tempting as it may be, passing a condition
566	variable instead of a callback does not work. Both the pure perl and
567	EV loops support overloading, however, as well as all functions that
568	use perl to invoke a callback (as in AnyEvent::Socket and
569	AnyEvent::DNS for example).
570		672
571	$cv->croak ($error)	673	$cv->croak ($error)
572	Similar to send, but causes all call's to "->recv" to invoke	674	Similar to send, but causes all calls to "->recv" to invoke
573	"Carp::croak" with the given error message/object/scalar.	675	"Carp::croak" with the given error message/object/scalar.
574		676
575	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
576	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.
577		683
578	$cv->begin ([group callback])	684	$cv->begin ([group callback])
579	$cv->end	685	$cv->end
580	These two methods are EXPERIMENTAL and MIGHT CHANGE.
581
582	These two methods can be used to combine many transactions/events	686	These two methods can be used to combine many transactions/events
583	into one. For example, a function that pings many hosts in parallel	687	into one. For example, a function that pings many hosts in parallel
584	might want to use a condition variable for the whole process.	688	might want to use a condition variable for the whole process.
585		689
586	Every call to "->begin" will increment a counter, and every call to	690	Every call to "->begin" will increment a counter, and every call to
587	"->end" will decrement it. If the counter reaches 0 in "->end", the	691	"->end" will decrement it. If the counter reaches 0 in "->end", the
588	(last) callback passed to "begin" will be executed. That callback is	692	(last) callback passed to "begin" will be executed, passing the
589	*supposed* to call "->send", but that is not required. If no	693	condvar as first argument. That callback is *supposed* to call
		694	"->send", but that is not required. If no group callback was set,
590	callback was set, "send" will be called without any arguments.	695	"send" will be called without any arguments.
591		696
592	Let's clarify this with the ping example:	697	You can think of "$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:
593		705
594	my $cv = AnyEvent->condvar;	706	my $cv = AnyEvent->condvar;
595		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
596	my %result;	732	my %result;
597	$cv->begin (sub { $cv->send (\%result) });	733	$cv->begin (sub { shift->send (\%result) });
598		734
599	for my $host (@list_of_hosts) {	735	for my $host (@list_of_hosts) {
600	$cv->begin;	736	$cv->begin;
601	ping_host_then_call_callback $host, sub {	737	ping_host_then_call_callback $host, sub {
602	$result{$host} = ...;	738	$result{$host} = ...;
…		…
617	the loop, which serves two important purposes: first, it sets the	753	the loop, which serves two important purposes: first, it sets the
618	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
619	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
620	(the loop doesn't execute once).	756	(the loop doesn't execute once).
621		757
622	This is the general pattern when you "fan out" into multiple	758	This is the general pattern when you "fan out" into multiple (but
623	subrequests: use an outer "begin"/"end" pair to set the callback and	759	potentially zero) subrequests: use an outer "begin"/"end" pair to
624	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,
625	you start, call "begin" and for each subrequest you finish, call	761	for each subrequest you start, call "begin" and for each subrequest
626	"end".	762	you finish, call "end".
627		763
628	METHODS FOR CONSUMERS	764	METHODS FOR CONSUMERS
629	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
630	awaits the condition.	766	awaits the condition.
631		767
632	$cv->recv	768	$cv->recv
633	Wait (blocking if necessary) until the "->send" or "->croak" methods	769	Wait (blocking if necessary) until the "->send" or "->croak" methods
634	have been called on c<$cv>, while servicing other watchers normally.	770	have been called on $cv, while servicing other watchers normally.
635		771
636	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
637	but will return immediately.	773	but will return immediately.
638		774
639	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
640	function will call "croak".	776	function will call "croak".
641		777
642	In list context, all parameters passed to "send" will be returned,	778	In list context, all parameters passed to "send" will be returned,
643	in scalar context only the first one will be returned.	779	in scalar context only the first one will be returned.
644		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
645	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
646	(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
647	using this from a module, never require a blocking wait*, but let	790	using this from a module, never require a blocking wait*. Instead,
648	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
649	by coupling condition variables with some kind of request results	792	example, by coupling condition variables with some kind of request
650	and supporting callbacks so the caller knows that getting the result	793	results and supporting callbacks so the caller knows that getting
651	will not block, while still supporting blocking waits if the caller	794	the result will not block, while still supporting blocking waits if
652	so desires).	795	the caller so desires).
653		796
654	Another reason *never* to "->recv" in a module is that you cannot
655	sensibly have two "->recv"'s in parallel, as that would require
656	multiple interpreters or coroutines/threads, none of which
657	"AnyEvent" can supply.
658
659	The Coro module, however, *can* and *does* supply coroutines and, in
660	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
661	versions and also integrates coroutines into AnyEvent, making
662	blocking "->recv" calls perfectly safe as long as they are done from
663	another coroutine (one that doesn't run the event loop).
664
665	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
666	only calling "->recv" from within that callback (or at a later	798	only calling "->recv" from within that callback (or at a later
667	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
668	blocking waits otherwise.	800	blocking waits otherwise.
669		801
670	$bool = $cv->ready	802	$bool = $cv->ready
…		…
675	This is a mutator function that returns the callback set and	807	This is a mutator function that returns the callback set and
676	optionally replaces it before doing so.	808	optionally replaces it before doing so.
677		809
678	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.
679	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
680	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
681	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.
682		875
683	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
684	$AnyEvent::MODEL	880	$AnyEvent::MODEL
685	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
686	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
687	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
688	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
689	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.
690		888	in *rxvt-unicode* it will be "urxvt::anyevent").
691	The known classes so far are:
692
693	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
694	AnyEvent::Impl::Event based on Event, second best choice.
695	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
696	AnyEvent::Impl::Glib based on Glib, third-best choice.
697	AnyEvent::Impl::Tk based on Tk, very bad choice.
698	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
699	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
700	AnyEvent::Impl::POE based on POE, not generic enough for full support.
701
702	There is no support for WxWidgets, as WxWidgets has no support for
703	watching file handles. However, you can use WxWidgets through the
704	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
705	second, which was considered to be too horrible to even consider for
706	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
707	using it's adaptor.
708
709	AnyEvent knows about Prima and Wx and will try to use POE when
710	autodetecting them.
711		889
712	AnyEvent::detect	890	AnyEvent::detect
713	Returns $AnyEvent::MODEL, forcing autodetection of the event model	891	Returns $AnyEvent::MODEL, forcing autodetection of the event model
714	if necessary. You should only call this function right before you	892	if necessary. You should only call this function right before you
715	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
716	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".
717		899
718	$guard = AnyEvent::post_detect { BLOCK }	900	$guard = AnyEvent::post_detect { BLOCK }
719	Arranges for the code block to be executed as soon as the event	901	Arranges for the code block to be executed as soon as the event
720	model is autodetected (or immediately if this has already happened).	902	model is autodetected (or immediately if that has already happened).
		903
		904	The block will be executed *after* the actual backend has been
		905	detected ($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.
721		914
722	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
723	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
724	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;
725		935
726	@AnyEvent::post_detect	936	@AnyEvent::post_detect
727	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
728	before or after loading AnyEvent), then they will called directly	938	before or after loading AnyEvent), then they will be called directly
729	after the event loop has been chosen.	939	after the event loop has been chosen.
730		940
731	You should check $AnyEvent::MODEL before adding to this array,	941	You should check $AnyEvent::MODEL before adding to this array,
732	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
733	been detected, and the array will be ignored.	943	detected, and the array will be ignored.
734		944
735	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	}
736		966
737	WHAT TO DO IN A MODULE	967	WHAT TO DO IN A MODULE
738	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
739	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.
740		970
…		…
748	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
749	interactive.	979	interactive.
750		980
751	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
752	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
753	called "results" that returns the results, it should call "->recv"	983	called "results" that returns the results, it may call "->recv" freely,
754	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).
755		985
756	WHAT TO DO IN THE MAIN PROGRAM	986	WHAT TO DO IN THE MAIN PROGRAM
757	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
758	dictate which event model to use.	988	dictate which event model to use.
759		989
760	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
761	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
762	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
763	it.	993	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		994	available loop implementation.
764		995
765	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
766	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
767	event module before loading AnyEvent or any module that uses it:	998	event module before loading AnyEvent or any module that uses it:
768	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
769	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
770	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,
771	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
772	yourself.	1003	yourself.
773		1004
774	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
775	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1006	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
776	everywhere, but letting AnyEvent chose the model is generally better.	1007	everywhere, but letting AnyEvent chose the model is generally better.
…		…
791	variable somewhere, waiting for it, and sending it when the program	1022	variable somewhere, waiting for it, and sending it when the program
792	should exit cleanly.	1023	should exit cleanly.
793		1024
794	OTHER MODULES	1025	OTHER MODULES
795	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
796	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1027	AnyEvent as a client and can therefore be mixed easily with other
797	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
798	available via CPAN.	1029	modules come as part of AnyEvent, the others are available via CPAN.
799		1030
800	AnyEvent::Util	1031	AnyEvent::Util
801	Contains various utility functions that replace often-used but	1032	Contains various utility functions that replace often-used blocking
802	blocking functions such as "inet_aton" by event-/callback-based	1033	functions such as "inet_aton" with event/callback-based versions.
803	versions.
804		1034
805	AnyEvent::Socket	1035	AnyEvent::Socket
806	Provides various utility functions for (internet protocol) sockets,	1036	Provides various utility functions for (internet protocol) sockets,
807	addresses and name resolution. Also functions to create non-blocking	1037	addresses and name resolution. Also functions to create non-blocking
808	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
809	more.	1039	more.
810		1040
811	AnyEvent::Handle	1041	AnyEvent::Handle
812	Provide read and write buffers, manages watchers for reads and	1042	Provide read and write buffers, manages watchers for reads and
813	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
814	transparent and non-blocking SSL/TLS.	1044	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
815		1045
816	AnyEvent::DNS	1046	AnyEvent::DNS
817	Provides rich asynchronous DNS resolver capabilities.	1047	Provides rich asynchronous DNS resolver capabilities.
818		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
819	AnyEvent::HTTP	1072	AnyEvent::DBI
820	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,
821	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.
822		1081
823	AnyEvent::HTTPD	1082	AnyEvent::HTTPD
824	Provides a simple web application server framework.	1083	A simple embedded webserver.
825		1084
826	AnyEvent::FastPing	1085	AnyEvent::FastPing
827	The fastest ping in the west.	1086	The fastest ping in the west.
828		1087
829	AnyEvent::DBI
830	Executes DBI requests asynchronously in a proxy process.
831
832	AnyEvent::AIO
833	Truly asynchronous I/O, should be in the toolbox of every event
834	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
835	together.
836
837	AnyEvent::BDB
838	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
839	fuses BDB and AnyEvent together.
840
841	AnyEvent::GPSD
842	A non-blocking interface to gpsd, a daemon delivering GPS
843	information.
844
845	AnyEvent::IGS
846	A non-blocking interface to the Internet Go Server protocol (used by
847	App::IGS).
848
849	AnyEvent::IRC
850	AnyEvent based IRC client module family (replacing the older
851	Net::IRC3).
852
853	Net::XMPP2
854	AnyEvent based XMPP (Jabber protocol) module family.
855
856	Net::FCP
857	AnyEvent-based implementation of the Freenet Client Protocol,
858	birthplace of AnyEvent.
859
860	Event::ExecFlow
861	High level API for event-based execution flow control.
862
863	Coro	1088	Coro
864	Has special support for AnyEvent via Coro::AnyEvent.	1089	Has special support for AnyEvent via Coro::AnyEvent.
865		1090
866	IO::Lambda	1091	SIMPLIFIED AE API
867	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
868	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.
869		1097
870	ERROR AND EXCEPTION HANDLING	1098	ERROR AND EXCEPTION HANDLING
871	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
872	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
873	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	1101	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
883	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1111	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
884	Glib uses "install_exception_handler" and so on.	1112	Glib uses "install_exception_handler" and so on.
885		1113
886	ENVIRONMENT VARIABLES	1114	ENVIRONMENT VARIABLES
887	The following environment variables are used by this module or its	1115	The following environment variables are used by this module or its
888	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.
889		1121
890	"PERL_ANYEVENT_VERBOSE"	1122	"PERL_ANYEVENT_VERBOSE"
891	By default, AnyEvent will be completely silent except in fatal	1123	By default, AnyEvent will be completely silent except in fatal
892	conditions. You can set this environment variable to make AnyEvent	1124	conditions. You can set this environment variable to make AnyEvent
893	more talkative.	1125	more talkative.
…		…
896	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
897	by "PERL_ANYEVENT_MODEL".	1129	by "PERL_ANYEVENT_MODEL".
898		1130
899	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
900	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.
901		1137
902	"PERL_ANYEVENT_STRICT"	1138	"PERL_ANYEVENT_STRICT"
903	AnyEvent does not do much argument checking by default, as thorough	1139	AnyEvent does not do much argument checking by default, as thorough
904	argument checking is very costly. Setting this variable to a true	1140	argument checking is very costly. Setting this variable to a true
905	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1141	value will cause AnyEvent to load "AnyEvent::Strict" and then to
906	thoroughly check the arguments passed to most method calls. If it	1142	thoroughly check the arguments passed to most method calls. If it
907	finds any problems it will croak.	1143	finds any problems, it will croak.
908		1144
909	In other words, enables "strict" mode.	1145	In other words, enables "strict" mode.
910		1146
911	Unlike "use strict", it is definitely recommended ot keep it off in	1147	Unlike "use strict" (or its modern cousin, "use common::sense", it
912	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
913	while developing programs can be very useful, however.	1150	programs can be very useful, however.
914		1151
915	"PERL_ANYEVENT_MODEL"	1152	"PERL_ANYEVENT_MODEL"
916	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,
917	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
918	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1155	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
959	EDNS0 in its DNS requests.	1196	EDNS0 in its DNS requests.
960		1197
961	"PERL_ANYEVENT_MAX_FORKS"	1198	"PERL_ANYEVENT_MAX_FORKS"
962	The maximum number of child processes that	1199	The maximum number of child processes that
963	"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.
964		1221
965	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1222	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
966	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
967	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
968	to provide AnyEvent compatibility.	1225	to provide AnyEvent compatibility.
…		…
1023	warn "read: $input\n"; # output what has been read	1280	warn "read: $input\n"; # output what has been read
1024	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1281	$cv->send if $input =~ /^q/i; # quit program if /^q/i
1025	},	1282	},
1026	);	1283	);
1027		1284
1028	my $time_watcher; # can only be used once
1029
1030	sub new_timer {
1031	$timer = AnyEvent->timer (after => 1, cb => sub {	1285	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
1032	warn "timeout\n"; # print 'timeout' about every second	1286	warn "timeout\n"; # print 'timeout' at most every second
1033	&new_timer; # and restart the time
1034	});
1035	}	1287	});
1036
1037	new_timer; # create first timer
1038		1288
1039	$cv->recv; # wait until user enters /^q/i	1289	$cv->recv; # wait until user enters /^q/i
1040		1290
1041	REAL-WORLD EXAMPLE	1291	REAL-WORLD EXAMPLE
1042	Consider the Net::FCP module. It features (among others) the following	1292	Consider the Net::FCP module. It features (among others) the following
…		…
1114		1364
1115	The actual code goes further and collects all errors ("die"s,	1365	The actual code goes further and collects all errors ("die"s,
1116	exceptions) that occurred during request processing. The "result" method	1366	exceptions) that occurred during request processing. The "result" method
1117	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
1118	object) and just throws the exception, which means connection errors and	1368	object) and just throws the exception, which means connection errors and
1119	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,
1120	not in a random callback.	1370	not in a random callback.
1121		1371
1122	All of this enables the following usage styles:	1372	All of this enables the following usage styles:
1123		1373
1124	1. Blocking:	1374	1. Blocking:
…		…
1169	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
1170	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,
1171	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.
1172		1422
1173	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
1174	distribution.	1424	distribution. It uses the AE interface, which makes a real difference
		1425	for the EV and Perl backends only.
1175		1426
1176	Explanation of the columns	1427	Explanation of the columns
1177	*watcher* is the number of event watchers created/destroyed. Since	1428	*watcher* is the number of event watchers created/destroyed. Since
1178	different event models feature vastly different performances, each event	1429	different event models feature vastly different performances, each event
1179	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
…		…
1198	*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
1199	single watcher.	1450	single watcher.
1200		1451
1201	Results	1452	Results
1202	name watchers bytes create invoke destroy comment	1453	name watchers bytes create invoke destroy comment
1203	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
1204	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
1205	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
1206	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
1207	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
1208	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
1209	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
1210	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
1211	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
1212	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
1213		1466
1214	Discussion	1467	Discussion
1215	The benchmark does *not* measure scalability of the event loop very	1468	The benchmark does *not* measure scalability of the event loop very
1216	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)
1217	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
…		…
1228	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1481	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1229	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
1230	CPU cycles with POE.	1483	CPU cycles with POE.
1231		1484
1232	"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
1233	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
1234	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).
1235	natively.
1236		1490
1237	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
1238	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
1239	perl interpreter and the backend itself). Nevertheless this shows that	1493	perl interpreter and the backend itself). Nevertheless this shows that
1240	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
…		…
1242	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
1243	benchmark.	1497	benchmark.
1244		1498
1245	The "Event" module has a relatively high setup and callback invocation	1499	The "Event" module has a relatively high setup and callback invocation
1246	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.
1247		1504
1248	"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
1249	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".
1250	However, Glib scales extremely badly, doubling the number of watchers	1507	However, Glib scales extremely badly, doubling the number of watchers
1251	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
…		…
1307	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
1308	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
1309	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.
1310		1567
1311	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
1312	distribution.	1569	distribution. It uses the AE interface, which makes a real difference
		1570	for the EV and Perl backends only.
1313		1571
1314	Explanation of the columns	1572	Explanation of the columns
1315	*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"
1316	(as each server has a read and write socket end).	1574	(as each server has a read and write socket end).
1317		1575
…		…
1322	single "request", that is, reading the token from the pipe and	1580	single "request", that is, reading the token from the pipe and
1323	forwarding it to another server. This includes deleting the old timeout	1581	forwarding it to another server. This includes deleting the old timeout
1324	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.
1325		1583
1326	Results	1584	Results
1327	name sockets create request	1585	name sockets create request
1328	EV 20000 69.01 11.16	1586	EV 20000 62.66 7.99
1329	Perl 20000 73.32 35.87	1587	Perl 20000 68.32 32.64
1330	Event 20000 212.62 257.32	1588	IOAsync 20000 174.06 101.15 epoll
1331	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
1332	POE 20000 349.67 12317.24 uses POE::Loop::Event	1592	POE 20000 341.54 12086.32 uses POE::Loop::Event
1333		1593
1334	Discussion	1594	Discussion
1335	This benchmark *does* measure scalability and overall performance of the	1595	This benchmark *does* measure scalability and overall performance of the
1336	particular event loop.	1596	particular event loop.
1337		1597
1338	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
1339	time is relatively high, though.	1599	time is relatively high, though.
1340		1600
1341	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
1342	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.
1343		1606
1344	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
1345	will understand why). Callback invocation also has a high overhead	1608	will understand why). Callback invocation also has a high overhead
1346	compared to the "$_->() for .."-style loop that the Perl event loop	1609	compared to the "$_->() for .."-style loop that the Perl event loop
1347	uses. Event uses select or poll in basically all documented	1610	uses. Event uses select or poll in basically all documented
…		…
1398		1661
1399	Summary	1662	Summary
1400	* 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,
1401	as the management overhead dominates.	1664	as the management overhead dominates.
1402		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
1403	SIGNALS	1723	SIGNALS
1404	AnyEvent currently installs handlers for these signals:	1724	AnyEvent currently installs handlers for these signals:
1405		1725
1406	SIGCHLD	1726	SIGCHLD
1407	A handler for "SIGCHLD" is installed by AnyEvent's child watcher	1727	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1408	emulation for event loops that do not support them natively. Also,	1728	emulation for event loops that do not support them natively. Also,
1409	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.
1410		1734
1411	SIGPIPE	1735	SIGPIPE
1412	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
1413	"undef" when AnyEvent gets loaded.	1737	"undef" when AnyEvent gets loaded.
1414		1738
…		…
1422	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
1423	exec.	1747	exec.
1424		1748
1425	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.
1426		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
1427	FORK	1819	FORK
1428	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
1429	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
1430	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).
1431		1832
1432	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
1433	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.
1434		1845
1435	SECURITY CONSIDERATIONS	1846	SECURITY CONSIDERATIONS
1436	AnyEvent can be forced to load any event model via	1847	AnyEvent can be forced to load any event model via
1437	$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
1438	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
…		…
1442		1853
1443	You can make AnyEvent completely ignore this variable by deleting it	1854	You can make AnyEvent completely ignore this variable by deleting it
1444	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:
1445		1856
1446	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1857	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1447		1858
1448	use AnyEvent;	1859	use AnyEvent;
1449		1860
1450	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1861	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1451	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
1452	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),
1453	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.
1454		1869
1455	BUGS	1870	BUGS
1456	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
1457	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
1458	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
1459	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
1460	not as pronounced).	1875	not as pronounced).
1461		1876
1462	SEE ALSO	1877	SEE ALSO
		1878	Tutorial/Introduction: AnyEvent::Intro.
		1879
		1880	FAQ: AnyEvent::FAQ.
		1881
1463	Utility functions: AnyEvent::Util.	1882	Utility functions: AnyEvent::Util.
1464		1883
1465	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,
1466	Event::Lib, Qt, POE.	1885	Event::Lib, Qt, POE.
1467		1886
1468	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1887	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1469	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1888	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1470	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.
1471		1891
1472	Non-blocking file handles, sockets, TCP clients and servers:	1892	Non-blocking file handles, sockets, TCP clients and servers:
1473	AnyEvent::Handle, AnyEvent::Socket.	1893	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1474		1894
1475	Asynchronous DNS: AnyEvent::DNS.	1895	Asynchronous DNS: AnyEvent::DNS.
1476		1896
1477	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1897	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1478		1898
1479	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1899	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
		1900	AnyEvent::HTTP.
1480		1901
1481	AUTHOR	1902	AUTHOR
1482	Marc Lehmann <schmorp@schmorp.de>	1903	Marc Lehmann <schmorp@schmorp.de>
1483	http://home.schmorp.de/	1904	http://home.schmorp.de/
1484		1905

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