[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.30 by root, Mon Sep 29 02:08:57 2008 UTC vs.
Revision 1.64 by root, Fri Dec 31 04:50:44 2010 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - the DBI of event loop programming
3		3
4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	loops	5	Qt and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# if you prefer function calls, look at the AE manpage for
		11	# an alternative API.
		12
		13	# file handle or descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub { ... });	14	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
11		15
		16	# one-shot or repeating timers
12	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });	17	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
13	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...	18	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
14		19
15	print AnyEvent->now; # prints current event loop time	20	print AnyEvent->now; # prints current event loop time
16	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.	21	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
17		22
		23	# POSIX signal
18	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });	24	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
19		25
		26	# child process exit
20	my $w = AnyEvent->child (pid => $pid, cb => sub {	27	my $w = AnyEvent->child (pid => $pid, cb => sub {
21	my ($pid, $status) = @_;	28	my ($pid, $status) = @_;
22	...	29	...
23	});	30	});
		31
		32	# called when event loop idle (if applicable)
		33	my $w = AnyEvent->idle (cb => sub { ... });
24		34
25	my $w = AnyEvent->condvar; # stores whether a condition was flagged	35	my $w = AnyEvent->condvar; # stores whether a condition was flagged
26	$w->send; # wake up current and all future recv's	36	$w->send; # wake up current and all future recv's
27	$w->recv; # enters "main loop" till $condvar gets ->send	37	$w->recv; # enters "main loop" till $condvar gets ->send
28	# use a condvar in callback mode:	38	# use a condvar in callback mode:
30		40
31	INTRODUCTION/TUTORIAL	41	INTRODUCTION/TUTORIAL
32	This manpage is mainly a reference manual. If you are interested in a	42	This manpage is mainly a reference manual. If you are interested in a
33	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	43	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
34	manpage.	44	manpage.
		45
		46	SUPPORT
		47	An FAQ document is available as AnyEvent::FAQ.
		48
		49	There also is a mailinglist for discussing all things AnyEvent, and an
		50	IRC channel, too.
		51
		52	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		53	Repository, at <http://anyevent.schmorp.de>, for more info.
35		54
36	WHY YOU SHOULD USE THIS MODULE (OR NOT)	55	WHY YOU SHOULD USE THIS MODULE (OR NOT)
37	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	56	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
38	nowadays. So what is different about AnyEvent?	57	nowadays. So what is different about AnyEvent?
39		58
…		…
54	module users into the same thing by forcing them to use the same event	73	module users into the same thing by forcing them to use the same event
55	model you use.	74	model you use.
56		75
57	For modules like POE or IO::Async (which is a total misnomer as it is	76	For modules like POE or IO::Async (which is a total misnomer as it is
58	actually doing all I/O synchronously...), using them in your module is	77	actually doing all I/O synchronously...), using them in your module is
59	like joining a cult: After you joined, you are dependent on them and you	78	like joining a cult: After you join, you are dependent on them and you
60	cannot use anything else, as they are simply incompatible to everything	79	cannot use anything else, as they are simply incompatible to everything
61	that isn't them. What's worse, all the potential users of your module	80	that isn't them. What's worse, all the potential users of your module
62	are also forced to use the same event loop you use.	81	are also forced to use the same event loop you use.
63		82
64	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	83	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
65	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	84	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
66	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your	85	with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
67	module uses one of those, every user of your module has to use it, too.	86	uses one of those, every user of your module has to use it, too. But if
68	But if your module uses AnyEvent, it works transparently with all event	87	your module uses AnyEvent, it works transparently with all event models
69	models it supports (including stuff like IO::Async, as long as those use	88	it supports (including stuff like IO::Async, as long as those use one of
70	one of the supported event loops. It is trivial to add new event loops	89	the supported event loops. It is easy to add new event loops to
71	to AnyEvent, too, so it is future-proof).	90	AnyEvent, too, so it is future-proof).
72		91
73	In addition to being free of having to use *the one and only true event	92	In addition to being free of having to use *the one and only true event
74	model*, AnyEvent also is free of bloat and policy: with POE or similar	93	model*, AnyEvent also is free of bloat and policy: with POE or similar
75	modules, you get an enormous amount of code and strict rules you have to	94	modules, you get an enormous amount of code and strict rules you have to
76	follow. AnyEvent, on the other hand, is lean and up to the point, by	95	follow. AnyEvent, on the other hand, is lean and to the point, by only
77	only offering the functionality that is necessary, in as thin as a	96	offering the functionality that is necessary, in as thin as a wrapper as
78	wrapper as technically possible.	97	technically possible.
79		98
80	Of course, AnyEvent comes with a big (and fully optional!) toolbox of	99	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
81	useful functionality, such as an asynchronous DNS resolver, 100%	100	useful functionality, such as an asynchronous DNS resolver, 100%
82	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms	101	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
83	such as Windows) and lots of real-world knowledge and workarounds for	102	such as Windows) and lots of real-world knowledge and workarounds for
…		…
86	Now, if you do want lots of policy (this can arguably be somewhat	105	Now, if you do want lots of policy (this can arguably be somewhat
87	useful) and you want to force your users to use the one and only event	106	useful) and you want to force your users to use the one and only event
88	model, you should not use this module.	107	model, you should not use this module.
89		108
90	DESCRIPTION	109	DESCRIPTION
91	AnyEvent provides an identical interface to multiple event loops. This	110	AnyEvent provides a uniform interface to various event loops. This
92	allows module authors to utilise an event loop without forcing module	111	allows module authors to use event loop functionality without forcing
93	users to use the same event loop (as only a single event loop can	112	module users to use a specific event loop implementation (since more
94	coexist peacefully at any one time).	113	than one event loop cannot coexist peacefully).
95		114
96	The interface itself is vaguely similar, but not identical to the Event	115	The interface itself is vaguely similar, but not identical to the Event
97	module.	116	module.
98		117
99	During the first call of any watcher-creation method, the module tries	118	During the first call of any watcher-creation method, the module tries
100	to detect the currently loaded event loop by probing whether one of the	119	to detect the currently loaded event loop by probing whether one of the
101	following modules is already loaded: EV, Event, Glib,	120	following modules is already loaded: EV, AnyEvent::Impl::Perl, Event,
102	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is	121	Glib, Tk, Event::Lib, Qt, POE. The first one found is used. If none are
103	used. If none are found, the module tries to load these modules	122	detected, the module tries to load the first four modules in the order
104	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should	123	given; but note that if EV is not available, the pure-perl
105	always succeed) in the order given. The first one that can be	124	AnyEvent::Impl::Perl should always work, so the other two are not
106	successfully loaded will be used. If, after this, still none could be	125	normally tried.
107	found, AnyEvent will fall back to a pure-perl event loop, which is not
108	very efficient, but should work everywhere.
109		126
110	Because AnyEvent first checks for modules that are already loaded,	127	Because AnyEvent first checks for modules that are already loaded,
111	loading an event model explicitly before first using AnyEvent will	128	loading an event model explicitly before first using AnyEvent will
112	likely make that model the default. For example:	129	likely make that model the default. For example:
113		130
…		…
115	use AnyEvent;	132	use AnyEvent;
116		133
117	# .. AnyEvent will likely default to Tk	134	# .. AnyEvent will likely default to Tk
118		135
119	The likely means that, if any module loads another event model and	136	The likely means that, if any module loads another event model and
120	starts using it, all bets are off. Maybe you should tell their authors	137	starts using it, all bets are off - this case should be very rare
121	to use AnyEvent so their modules work together with others seamlessly...	138	though, as very few modules hardcode event loops without announcing this
		139	very loudly.
122		140
123	The pure-perl implementation of AnyEvent is called	141	The pure-perl implementation of AnyEvent is called
124	"AnyEvent::Impl::Perl". Like other event modules you can load it	142	"AnyEvent::Impl::Perl". Like other event modules you can load it
125	explicitly and enjoy the high availability of that event loop :)	143	explicitly and enjoy the high availability of that event loop :)
126		144
…		…
132	These watchers are normal Perl objects with normal Perl lifetime. After	150	These watchers are normal Perl objects with normal Perl lifetime. After
133	creating a watcher it will immediately "watch" for events and invoke the	151	creating a watcher it will immediately "watch" for events and invoke the
134	callback when the event occurs (of course, only when the event model is	152	callback when the event occurs (of course, only when the event model is
135	in control).	153	in control).
136		154
		155	Note that callbacks must not permanently change global variables
		156	potentially in use by the event loop (such as $_ or $[) and that
		157	callbacks must not "die". The former is good programming practice in
		158	Perl and the latter stems from the fact that exception handling differs
		159	widely between event loops.
		160
137	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
138	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
139	to it).	163	to it).
140		164
141	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.
142		166
143	Many watchers either are used with "recursion" (repeating timers for	167	Many watchers either are used with "recursion" (repeating timers for
144	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.
145		169
146	An any way to achieve that is this pattern:	170	One way to achieve that is this pattern:
147		171
148	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	172	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
149	# you can use $w here, for example to undef it	173	# you can use $w here, for example to undef it
150	undef $w;	174	undef $w;
151	});	175	});
…		…
153	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,
154	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
155	declared.	179	declared.
156		180
157	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
158	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
159	the following mandatory key-value pairs as arguments:	189	the following mandatory key-value pairs as arguments:
160		190
161	"fh" the Perl file handle (not file descriptor) to watch for events	191	"fh" is the Perl file handle (or a naked file descriptor) to watch for
162	(AnyEvent might or might not keep a reference to this file handle).	192	events (AnyEvent might or might not keep a reference to this file
		193	handle). Note that only file handles pointing to things for which
		194	non-blocking operation makes sense are allowed. This includes sockets,
		195	most character devices, pipes, fifos and so on, but not for example
		196	files or block devices.
		197
163	"poll" must be a string that is either "r" or "w", which creates a	198	"poll" must be a string that is either "r" or "w", which creates a
164	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	199	watcher waiting for "r"eadable or "w"ritable events, respectively.
		200
165	is the callback to invoke each time the file handle becomes ready.	201	"cb" is the callback to invoke each time the file handle becomes ready.
166		202
167	Although the callback might get passed parameters, their value and	203	Although the callback might get passed parameters, their value and
168	presence is undefined and you cannot rely on them. Portable AnyEvent	204	presence is undefined and you cannot rely on them. Portable AnyEvent
169	callbacks cannot use arguments passed to I/O watcher callbacks.	205	callbacks cannot use arguments passed to I/O watcher callbacks.
170		206
171	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
172	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
173	the underlying file descriptor.	209	the underlying file descriptor.
174		210
175	Some event loops issue spurious readyness notifications, so you should	211	Some event loops issue spurious readiness notifications, so you should
176	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
177	handles.	213	handles.
178		214
179	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
180	watcher.	216	watcher.
…		…
184	warn "read: $input\n";	220	warn "read: $input\n";
185	undef $w;	221	undef $w;
186	});	222	});
187		223
188	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
189	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
190	with the following mandatory arguments:	234	with the following mandatory arguments:
191		235
192	"after" specifies after how many seconds (fractional values are	236	"after" specifies after how many seconds (fractional values are
193	supported) the callback should be invoked. "cb" is the callback to	237	supported) the callback should be invoked. "cb" is the callback to
…		…
195		239
196	Although the callback might get passed parameters, their value and	240	Although the callback might get passed parameters, their value and
197	presence is undefined and you cannot rely on them. Portable AnyEvent	241	presence is undefined and you cannot rely on them. Portable AnyEvent
198	callbacks cannot use arguments passed to time watcher callbacks.	242	callbacks cannot use arguments passed to time watcher callbacks.
199		243
200	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
201	parameter, "interval", as a strictly positive number (> 0), then the	245	parameter, "interval", as a strictly positive number (> 0), then the
202	callback will be invoked regularly at that interval (in fractional	246	callback will be invoked regularly at that interval (in fractional
203	seconds) after the first invocation. If "interval" is specified with a	247	seconds) after the first invocation. If "interval" is specified with a
204	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.
205		249
206	The callback will be rescheduled before invoking the callback, but no	250	The callback will be rescheduled before invoking the callback, but no
207	attempt is done to avoid timer drift in most backends, so the interval	251	attempt is made to avoid timer drift in most backends, so the interval
208	is only approximate.	252	is only approximate.
209		253
210	Example: fire an event after 7.7 seconds.	254	Example: fire an event after 7.7 seconds.
211		255
212	my $w = AnyEvent->timer (after => 7.7, cb => sub {	256	my $w = AnyEvent->timer (after => 7.7, cb => sub {
…		…
229		273
230	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,
231	they use absolute time internally. This makes a difference when your	275	they use absolute time internally. This makes a difference when your
232	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
233	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
234	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
235	finally fire.	279	finally fire.
236		280
237	AnyEvent cannot compensate for this. The only event loop that is	281	AnyEvent cannot compensate for this. The only event loop that is
238	conscious about these issues is EV, which offers both relative	282	conscious of these issues is EV, which offers both relative (ev_timer,
239	(ev_timer, based on true relative time) and absolute (ev_periodic, based	283	based on true relative time) and absolute (ev_periodic, based on
240	on wallclock time) timers.	284	wallclock time) timers.
241		285
242	AnyEvent always prefers relative timers, if available, matching the	286	AnyEvent always prefers relative timers, if available, matching the
243	AnyEvent API.	287	AnyEvent API.
244		288
245	AnyEvent has two additional methods that return the "current time":	289	AnyEvent has two additional methods that return the "current time":
…		…
264	*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
265	function to call when you want to know the current time.*	309	function to call when you want to know the current time.*
266		310
267	This function is also often faster then "AnyEvent->time", and thus	311	This function is also often faster then "AnyEvent->time", and thus
268	the preferred method if you want some timestamp (for example,	312	the preferred method if you want some timestamp (for example,
269	AnyEvent::Handle uses this to update it's activity timeouts).	313	AnyEvent::Handle uses this to update its activity timeouts).
270		314
271	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
272	exact with your timing, you can skip it without bad conscience.	316	exact with your timing; you can skip it without a bad conscience.
273		317
274	For a practical example of when these times differ, consider	318	For a practical example of when these times differ, consider
275	Event::Lib and EV and the following set-up:	319	Event::Lib and EV and the following set-up:
276		320
277	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
278	at time=500 (assume no other callbacks delay processing). In your	322	at time=500 (assume no other callbacks delay processing). In your
279	callback, you wait a second by executing "sleep 1" (blocking the	323	callback, you wait a second by executing "sleep 1" (blocking the
280	process for a second) and then (at time=501) you create a relative	324	process for a second) and then (at time=501) you create a relative
281	timer that fires after three seconds.	325	timer that fires after three seconds.
282		326
…		…
302	In either case, if you care (and in most cases, you don't), then you	346	In either case, if you care (and in most cases, you don't), then you
303	can get whatever behaviour you want with any event loop, by taking	347	can get whatever behaviour you want with any event loop, by taking
304	the difference between "AnyEvent->time" and "AnyEvent->now" into	348	the difference between "AnyEvent->time" and "AnyEvent->now" into
305	account.	349	account.
306		350
		351	AnyEvent->now_update
		352	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		353	current time for each loop iteration (see the discussion of
		354	AnyEvent->now, above).
		355
		356	When a callback runs for a long time (or when the process sleeps),
		357	then this "current" time will differ substantially from the real
		358	time, which might affect timers and time-outs.
		359
		360	When this is the case, you can call this method, which will update
		361	the event loop's idea of "current time".
		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
		371	Note that updating the time might cause some events to be handled.
		372
307	SIGNAL WATCHERS	373	SIGNAL WATCHERS
		374	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		375
308	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
309	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
310	callback to be invoked whenever a signal occurs.	378	callback to be invoked whenever a signal occurs.
311		379
312	Although the callback might get passed parameters, their value and	380	Although the callback might get passed parameters, their value and
…		…
317	invocation, and callback invocation will be synchronous. Synchronous	385	invocation, and callback invocation will be synchronous. Synchronous
318	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
319	process, but it is guaranteed not to interrupt any other callbacks.	387	process, but it is guaranteed not to interrupt any other callbacks.
320		388
321	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
322	signal between multiple watchers.	390	signal between multiple watchers, and AnyEvent will ensure that signals
		391	will not interrupt your program at bad times.
323		392
324	This watcher might use %SIG, so programs overwriting those signals	393	This watcher might use %SIG (depending on the event loop used), so
325	directly will likely not work correctly.	394	programs overwriting those signals directly will likely not work
		395	correctly.
326		396
327	Example: exit on SIGINT	397	Example: exit on SIGINT
328		398
329	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	399	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
330		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
331	CHILD PROCESS WATCHERS	435	CHILD PROCESS WATCHERS
		436	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		437
332	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.
333		439
334	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,
335	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).
336	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
337	on any trace events (stopped/continued).	443	and an exit status is available, not on any trace events
		444	(stopped/continued).
338		445
339	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
340	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
341	callback arguments.	448	callback arguments.
342		449
…		…
347		454
348	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
349	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
350	could have exited already (and no SIGCHLD will be sent anymore).	457	could have exited already (and no SIGCHLD will be sent anymore).
351		458
352	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
353	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
354	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).
355	place).	463	AnyEvent's pure perl event loop handles all cases correctly regardless
		464	of when you start the watcher.
356		465
357	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
358	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
359	you "fork" the child (alternatively, you can call "AnyEvent::detect").	468	you "fork" the child (alternatively, you can call "AnyEvent::detect").
360		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
361	Example: fork a process and wait for it	474	Example: fork a process and wait for it
362		475
363	my $done = AnyEvent->condvar;	476	my $done = AnyEvent->condvar;
364		477
365	my $pid = fork or exit 5;	478	my $pid = fork or exit 5;
366		479
367	my $w = AnyEvent->child (	480	my $w = AnyEvent->child (
368	pid => $pid,	481	pid => $pid,
369	cb => sub {	482	cb => sub {
370	my ($pid, $status) = @_;	483	my ($pid, $status) = @_;
371	warn "pid $pid exited with status $status";	484	warn "pid $pid exited with status $status";
372	$done->send;	485	$done->send;
373	},	486	},
374	);	487	);
375		488
376	# do something else, then wait for process exit	489	# do something else, then wait for process exit
377	$done->recv;	490	$done->recv;
378		491
		492	IDLE WATCHERS
		493	$w = AnyEvent->idle (cb => <callback>);
		494
		495	This will repeatedly invoke the callback after the process becomes idle,
		496	until either the watcher is destroyed or new events have been detected.
		497
		498	Idle watchers are useful when there is a need to do something, but it is
		499	not so important (or wise) to do it instantly. The callback will be
		500	invoked only when there is "nothing better to do", which is usually
		501	defined as "all outstanding events have been handled and no new events
		502	have been detected". That means that idle watchers ideally get invoked
		503	when the event loop has just polled for new events but none have been
		504	detected. Instead of blocking to wait for more events, the idle watchers
		505	will be invoked.
		506
		507	Unfortunately, most event loops do not really support idle watchers
		508	(only EV, Event and Glib do it in a usable fashion) - for the rest,
		509	AnyEvent will simply call the callback "from time to time".
		510
		511	Example: read lines from STDIN, but only process them when the program
		512	is otherwise idle:
		513
		514	my @lines; # read data
		515	my $idle_w;
		516	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		517	push @lines, scalar <STDIN>;
		518
		519	# start an idle watcher, if not already done
		520	$idle_w \|\|= AnyEvent->idle (cb => sub {
		521	# handle only one line, when there are lines left
		522	if (my $line = shift @lines) {
		523	print "handled when idle: $line";
		524	} else {
		525	# otherwise disable the idle watcher again
		526	undef $idle_w;
		527	}
		528	});
		529	});
		530
379	CONDITION VARIABLES	531	CONDITION VARIABLES
		532	$cv = AnyEvent->condvar;
		533
		534	$cv->send (<list>);
		535	my @res = $cv->recv;
		536
380	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
381	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
382	will actively watch for new events and call your callbacks.	539	will actively watch for new events and call your callbacks.
383		540
384	AnyEvent is different, it expects somebody else to run the event loop	541	AnyEvent is slightly different: it expects somebody else to run the
385	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).
386		544
387	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
388	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.
389		549
390	Condition variables can be created by calling the "AnyEvent->condvar"	550	Condition variables can be created by calling the "AnyEvent->condvar"
391	method, usually without arguments. The only argument pair allowed is	551	method, usually without arguments. The only argument pair allowed is
392
393	"cb", which specifies a callback to be called when the condition	552	"cb", which specifies a callback to be called when the condition
394	variable becomes true, with the condition variable as the first argument	553	variable becomes true, with the condition variable as the first argument
395	(but not the results).	554	(but not the results).
396		555
397	After creation, the condition variable is "false" until it becomes	556	After creation, the condition variable is "false" until it becomes
398	"true" by calling the "send" method (or calling the condition variable	557	"true" by calling the "send" method (or calling the condition variable
399	as if it were a callback, read about the caveats in the description for	558	as if it were a callback, read about the caveats in the description for
400	the "->send" method).	559	the "->send" method).
401		560
402	Condition variables are similar to callbacks, except that you can	561	Since condition variables are the most complex part of the AnyEvent API,
403	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
404	in time where multiple outstanding events have been processed. And yet	563	you can connect to:
405	another way to call them is transactions - each condition variable can	564
406	be used to represent a transaction, which finishes at some point and	565	* Condition variables are like callbacks - you can call them (and pass
407	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.
408		582
409	Condition variables are very useful to signal that something has	583	Condition variables are very useful to signal that something has
410	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
411	requests, then a condition variable would be the ideal candidate to	585	requests, then a condition variable would be the ideal candidate to
412	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
…		…
425		599
426	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
427	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
428	(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
429	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call	603	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
430	it's "new" method in your own "new" method.	604	its "new" method in your own "new" method.
431		605
432	There are two "sides" to a condition variable - the "producer side"	606	There are two "sides" to a condition variable - the "producer side"
433	which eventually calls "-> send", and the "consumer side", which waits	607	which eventually calls "-> send", and the "consumer side", which waits
434	for the send to occur.	608	for the send to occur.
435		609
436	Example: wait for a timer.	610	Example: wait for a timer.
437		611
438	# wait till the result is ready	612	# condition: "wait till the timer is fired"
439	my $result_ready = AnyEvent->condvar;	613	my $timer_fired = AnyEvent->condvar;
440		614
441	# do something such as adding a timer	615	# create the timer - we could wait for, say
442	# or socket watcher the calls $result_ready->send	616	# a handle becomign ready, or even an
443	# when the "result" is ready.	617	# AnyEvent::HTTP request to finish, but
444	# in this case, we simply use a timer:	618	# in this case, we simply use a timer:
445	my $w = AnyEvent->timer (	619	my $w = AnyEvent->timer (
446	after => 1,	620	after => 1,
447	cb => sub { $result_ready->send },	621	cb => sub { $timer_fired->send },
448	);	622	);
449		623
450	# this "blocks" (while handling events) till the callback	624	# this "blocks" (while handling events) till the callback
451	# calls send	625	# calls ->send
452	$result_ready->recv;	626	$timer_fired->recv;
453		627
454	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
455	variables are also code references.	629	variables are also callable directly.
456		630
457	my $done = AnyEvent->condvar;	631	my $done = AnyEvent->condvar;
458	my $delay = AnyEvent->timer (after => 5, cb => $done);	632	my $delay = AnyEvent->timer (after => 5, cb => $done);
459	$done->recv;	633	$done->recv;
460		634
…		…
466		640
467	...	641	...
468		642
469	my @info = $couchdb->info->recv;	643	my @info = $couchdb->info->recv;
470		644
471	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
472	results are available:	646	results are available:
473		647
474	$couchdb->info->cb (sub {	648	$couchdb->info->cb (sub {
475	my @info = $_[0]->recv;	649	my @info = $_[0]->recv;
476	});	650	});
…		…
491		665
492	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
493	future "->recv" calls.	667	future "->recv" calls.
494		668
495	Condition variables are overloaded so one can call them directly (as	669	Condition variables are overloaded so one can call them directly (as
496	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
497	"send". Note, however, that many C-based event loops do not handle	671	calling "send".
498	overloading, so as tempting as it may be, passing a condition
499	variable instead of a callback does not work. Both the pure perl and
500	EV loops support overloading, however, as well as all functions that
501	use perl to invoke a callback (as in AnyEvent::Socket and
502	AnyEvent::DNS for example).
503		672
504	$cv->croak ($error)	673	$cv->croak ($error)
505	Similar to send, but causes all call's to "->recv" to invoke	674	Similar to send, but causes all calls to "->recv" to invoke
506	"Carp::croak" with the given error message/object/scalar.	675	"Carp::croak" with the given error message/object/scalar.
507		676
508	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
509	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.
510		683
511	$cv->begin ([group callback])	684	$cv->begin ([group callback])
512	$cv->end	685	$cv->end
513	These two methods are EXPERIMENTAL and MIGHT CHANGE.
514
515	These two methods can be used to combine many transactions/events	686	These two methods can be used to combine many transactions/events
516	into one. For example, a function that pings many hosts in parallel	687	into one. For example, a function that pings many hosts in parallel
517	might want to use a condition variable for the whole process.	688	might want to use a condition variable for the whole process.
518		689
519	Every call to "->begin" will increment a counter, and every call to	690	Every call to "->begin" will increment a counter, and every call to
520	"->end" will decrement it. If the counter reaches 0 in "->end", the	691	"->end" will decrement it. If the counter reaches 0 in "->end", the
521	(last) callback passed to "begin" will be executed. That callback is	692	(last) callback passed to "begin" will be executed, passing the
522	supposed to call "->send", but that is not required. If no	693	condvar as first argument. That callback is supposed to call
		694	"->send", but that is not required. If no group callback was set,
523	callback was set, "send" will be called without any arguments.	695	"send" will be called without any arguments.
524		696
525	Let's clarify this with the ping example:	697	You can think of "$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:
526		705
527	my $cv = AnyEvent->condvar;	706	my $cv = AnyEvent->condvar;
528		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
529	my %result;	732	my %result;
530	$cv->begin (sub { $cv->send (\%result) });	733	$cv->begin (sub { shift->send (\%result) });
531		734
532	for my $host (@list_of_hosts) {	735	for my $host (@list_of_hosts) {
533	$cv->begin;	736	$cv->begin;
534	ping_host_then_call_callback $host, sub {	737	ping_host_then_call_callback $host, sub {
535	$result{$host} = ...;	738	$result{$host} = ...;
…		…
550	the loop, which serves two important purposes: first, it sets the	753	the loop, which serves two important purposes: first, it sets the
551	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
552	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
553	(the loop doesn't execute once).	756	(the loop doesn't execute once).
554		757
555	This is the general pattern when you "fan out" into multiple	758	This is the general pattern when you "fan out" into multiple (but
556	subrequests: use an outer "begin"/"end" pair to set the callback and	759	potentially zero) subrequests: use an outer "begin"/"end" pair to
557	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,
558	you start, call "begin" and for each subrequest you finish, call	761	for each subrequest you start, call "begin" and for each subrequest
559	"end".	762	you finish, call "end".
560		763
561	METHODS FOR CONSUMERS	764	METHODS FOR CONSUMERS
562	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
563	awaits the condition.	766	awaits the condition.
564		767
565	$cv->recv	768	$cv->recv
566	Wait (blocking if necessary) until the "->send" or "->croak" methods	769	Wait (blocking if necessary) until the "->send" or "->croak" methods
567	have been called on c<$cv>, while servicing other watchers normally.	770	have been called on $cv, while servicing other watchers normally.
568		771
569	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
570	but will return immediately.	773	but will return immediately.
571		774
572	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
573	function will call "croak".	776	function will call "croak".
574		777
575	In list context, all parameters passed to "send" will be returned,	778	In list context, all parameters passed to "send" will be returned,
576	in scalar context only the first one will be returned.	779	in scalar context only the first one will be returned.
577		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
578	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
579	(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
580	using this from a module, never require a blocking wait*, but let	790	using this from a module, never require a blocking wait*. Instead,
581	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
582	by coupling condition variables with some kind of request results	792	example, by coupling condition variables with some kind of request
583	and supporting callbacks so the caller knows that getting the result	793	results and supporting callbacks so the caller knows that getting
584	will not block, while still supporting blocking waits if the caller	794	the result will not block, while still supporting blocking waits if
585	so desires).	795	the caller so desires).
586		796
587	Another reason never to "->recv" in a module is that you cannot
588	sensibly have two "->recv"'s in parallel, as that would require
589	multiple interpreters or coroutines/threads, none of which
590	"AnyEvent" can supply.
591
592	The Coro module, however, can and does supply coroutines and, in
593	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
594	versions and also integrates coroutines into AnyEvent, making
595	blocking "->recv" calls perfectly safe as long as they are done from
596	another coroutine (one that doesn't run the event loop).
597
598	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
599	only calling "->recv" from within that callback (or at a later	798	only calling "->recv" from within that callback (or at a later
600	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
601	blocking waits otherwise.	800	blocking waits otherwise.
602		801
603	$bool = $cv->ready	802	$bool = $cv->ready
…		…
608	This is a mutator function that returns the callback set and	807	This is a mutator function that returns the callback set and
609	optionally replaces it before doing so.	808	optionally replaces it before doing so.
610		809
611	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.
612	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
613	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
614	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	AnyEvent::Impl::IOAsync based on IO::Async.
		843	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		844
		845	Backends with special needs.
		846	Qt requires the Qt::Application to be instantiated first, but will
		847	otherwise be picked up automatically. As long as the main program
		848	instantiates the application before any AnyEvent watchers are
		849	created, everything should just work.
		850
		851	AnyEvent::Impl::Qt based on Qt.
		852
		853	Event loops that are indirectly supported via other backends.
		854	Some event loops can be supported via other modules:
		855
		856	There is no direct support for WxWidgets (Wx) or Prima.
		857
		858	WxWidgets has no support for watching file handles. However, you can
		859	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		860	simply polls 20 times per second, which was considered to be too
		861	horrible to even consider for AnyEvent.
		862
		863	Prima is not supported as nobody seems to be using it, but it has a
		864	POE backend, so it can be supported through POE.
		865
		866	AnyEvent knows about both Prima and Wx, however, and will try to
		867	load POE when detecting them, in the hope that POE will pick them
		868	up, in which case everything will be automatic.
615		869
616	GLOBAL VARIABLES AND FUNCTIONS	870	GLOBAL VARIABLES AND FUNCTIONS
		871	These are not normally required to use AnyEvent, but can be useful to
		872	write AnyEvent extension modules.
		873
617	$AnyEvent::MODEL	874	$AnyEvent::MODEL
618	Contains "undef" until the first watcher is being created. Then it	875	Contains "undef" until the first watcher is being created, before
		876	the backend has been autodetected.
		877
619	contains the event model that is being used, which is the name of	878	Afterwards it contains the event model that is being used, which is
620	the Perl class implementing the model. This class is usually one of	879	the name of the Perl class implementing the model. This class is
621	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	880	usually one of the "AnyEvent::Impl::xxx" modules, but can be any
622	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	881	other class in the case AnyEvent has been extended at runtime (e.g.
623		882	in rxvt-unicode it will be "urxvt::anyevent").
624	The known classes so far are:
625
626	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
627	AnyEvent::Impl::Event based on Event, second best choice.
628	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
629	AnyEvent::Impl::Glib based on Glib, third-best choice.
630	AnyEvent::Impl::Tk based on Tk, very bad choice.
631	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
632	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
633	AnyEvent::Impl::POE based on POE, not generic enough for full support.
634
635	There is no support for WxWidgets, as WxWidgets has no support for
636	watching file handles. However, you can use WxWidgets through the
637	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
638	second, which was considered to be too horrible to even consider for
639	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
640	using it's adaptor.
641
642	AnyEvent knows about Prima and Wx and will try to use POE when
643	autodetecting them.
644		883
645	AnyEvent::detect	884	AnyEvent::detect
646	Returns $AnyEvent::MODEL, forcing autodetection of the event model	885	Returns $AnyEvent::MODEL, forcing autodetection of the event model
647	if necessary. You should only call this function right before you	886	if necessary. You should only call this function right before you
648	would have created an AnyEvent watcher anyway, that is, as late as	887	would have created an AnyEvent watcher anyway, that is, as late as
649	possible at runtime.	888	possible at runtime, and not e.g. during initialisation of your
		889	module.
		890
		891	If you need to do some initialisation before AnyEvent watchers are
		892	created, use "post_detect".
650		893
651	$guard = AnyEvent::post_detect { BLOCK }	894	$guard = AnyEvent::post_detect { BLOCK }
652	Arranges for the code block to be executed as soon as the event	895	Arranges for the code block to be executed as soon as the event
653	model is autodetected (or immediately if this has already happened).	896	model is autodetected (or immediately if that has already happened).
		897
		898	The block will be executed after the actual backend has been
		899	detected ($AnyEvent::MODEL is set), but before any watchers have
		900	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		901	other initialisations - see the sources of AnyEvent::Strict or
		902	AnyEvent::AIO to see how this is used.
		903
		904	The most common usage is to create some global watchers, without
		905	forcing event module detection too early, for example, AnyEvent::AIO
		906	creates and installs the global IO::AIO watcher in a "post_detect"
		907	block to avoid autodetecting the event module at load time.
654		908
655	If called in scalar or list context, then it creates and returns an	909	If called in scalar or list context, then it creates and returns an
656	object that automatically removes the callback again when it is	910	object that automatically removes the callback again when it is
		911	destroyed (or "undef" when the hook was immediately executed). See
657	destroyed. See Coro::BDB for a case where this is useful.	912	AnyEvent::AIO for a case where this is useful.
		913
		914	Example: Create a watcher for the IO::AIO module and store it in
		915	$WATCHER, but do so only do so after the event loop is initialised.
		916
		917	our WATCHER;
		918
		919	my $guard = AnyEvent::post_detect {
		920	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		921	};
		922
		923	# the \|\|= is important in case post_detect immediately runs the block,
		924	# as to not clobber the newly-created watcher. assigning both watcher and
		925	# post_detect guard to the same variable has the advantage of users being
		926	# able to just C<undef $WATCHER> if the watcher causes them grief.
		927
		928	$WATCHER \|\|= $guard;
658		929
659	@AnyEvent::post_detect	930	@AnyEvent::post_detect
660	If there are any code references in this array (you can "push" to it	931	If there are any code references in this array (you can "push" to it
661	before or after loading AnyEvent), then they will called directly	932	before or after loading AnyEvent), then they will be called directly
662	after the event loop has been chosen.	933	after the event loop has been chosen.
663		934
664	You should check $AnyEvent::MODEL before adding to this array,	935	You should check $AnyEvent::MODEL before adding to this array,
665	though: if it contains a true value then the event loop has already	936	though: if it is defined then the event loop has already been
666	been detected, and the array will be ignored.	937	detected, and the array will be ignored.
667		938
668	Best use "AnyEvent::post_detect { BLOCK }" instead.	939	Best use "AnyEvent::post_detect { BLOCK }" when your application
		940	allows it, as it takes care of these details.
		941
		942	This variable is mainly useful for modules that can do something
		943	useful when AnyEvent is used and thus want to know when it is
		944	initialised, but do not need to even load it by default. This array
		945	provides the means to hook into AnyEvent passively, without loading
		946	it.
		947
		948	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		949	together, you could put this into Coro (this is the actual code used
		950	by Coro to accomplish this):
		951
		952	if (defined $AnyEvent::MODEL) {
		953	# AnyEvent already initialised, so load Coro::AnyEvent
		954	require Coro::AnyEvent;
		955	} else {
		956	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		957	# as soon as it is
		958	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		959	}
669		960
670	WHAT TO DO IN A MODULE	961	WHAT TO DO IN A MODULE
671	As a module author, you should "use AnyEvent" and call AnyEvent methods	962	As a module author, you should "use AnyEvent" and call AnyEvent methods
672	freely, but you should not load a specific event module or rely on it.	963	freely, but you should not load a specific event module or rely on it.
673		964
…		…
681	stall the whole program, and the whole point of using events is to stay	972	stall the whole program, and the whole point of using events is to stay
682	interactive.	973	interactive.
683		974
684	It is fine, however, to call "->recv" when the user of your module	975	It is fine, however, to call "->recv" when the user of your module
685	requests it (i.e. if you create a http request object ad have a method	976	requests it (i.e. if you create a http request object ad have a method
686	called "results" that returns the results, it should call "->recv"	977	called "results" that returns the results, it may call "->recv" freely,
687	freely, as the user of your module knows what she is doing. always).	978	as the user of your module knows what she is doing. Always).
688		979
689	WHAT TO DO IN THE MAIN PROGRAM	980	WHAT TO DO IN THE MAIN PROGRAM
690	There will always be a single main program - the only place that should	981	There will always be a single main program - the only place that should
691	dictate which event model to use.	982	dictate which event model to use.
692		983
693	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	984	If the program is not event-based, it need not do anything special, even
694	do anything special (it does not need to be event-based) and let	985	when it depends on a module that uses an AnyEvent. If the program itself
695	AnyEvent decide which implementation to chose if some module relies on	986	uses AnyEvent, but does not care which event loop is used, all it needs
696	it.	987	to do is "use AnyEvent". In either case, AnyEvent will choose the best
		988	available loop implementation.
697		989
698	If the main program relies on a specific event model - for example, in	990	If the main program relies on a specific event model - for example, in
699	Gtk2 programs you have to rely on the Glib module - you should load the	991	Gtk2 programs you have to rely on the Glib module - you should load the
700	event module before loading AnyEvent or any module that uses it:	992	event module before loading AnyEvent or any module that uses it:
701	generally speaking, you should load it as early as possible. The reason	993	generally speaking, you should load it as early as possible. The reason
702	is that modules might create watchers when they are loaded, and AnyEvent	994	is that modules might create watchers when they are loaded, and AnyEvent
703	will decide on the event model to use as soon as it creates watchers,	995	will decide on the event model to use as soon as it creates watchers,
704	and it might chose the wrong one unless you load the correct one	996	and it might choose the wrong one unless you load the correct one
705	yourself.	997	yourself.
706		998
707	You can chose to use a pure-perl implementation by loading the	999	You can chose to use a pure-perl implementation by loading the
708	"AnyEvent::Impl::Perl" module, which gives you similar behaviour	1000	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
709	everywhere, but letting AnyEvent chose the model is generally better.	1001	everywhere, but letting AnyEvent chose the model is generally better.
…		…
724	variable somewhere, waiting for it, and sending it when the program	1016	variable somewhere, waiting for it, and sending it when the program
725	should exit cleanly.	1017	should exit cleanly.
726		1018
727	OTHER MODULES	1019	OTHER MODULES
728	The following is a non-exhaustive list of additional modules that use	1020	The following is a non-exhaustive list of additional modules that use
729	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1021	AnyEvent as a client and can therefore be mixed easily with other
730	in the same program. Some of the modules come with AnyEvent, some are	1022	AnyEvent modules and other event loops in the same program. Some of the
731	available via CPAN.	1023	modules come as part of AnyEvent, the others are available via CPAN.
732		1024
733	AnyEvent::Util	1025	AnyEvent::Util
734	Contains various utility functions that replace often-used but	1026	Contains various utility functions that replace often-used blocking
735	blocking functions such as "inet_aton" by event-/callback-based	1027	functions such as "inet_aton" with event/callback-based versions.
736	versions.
737		1028
738	AnyEvent::Socket	1029	AnyEvent::Socket
739	Provides various utility functions for (internet protocol) sockets,	1030	Provides various utility functions for (internet protocol) sockets,
740	addresses and name resolution. Also functions to create non-blocking	1031	addresses and name resolution. Also functions to create non-blocking
741	tcp connections or tcp servers, with IPv6 and SRV record support and	1032	tcp connections or tcp servers, with IPv6 and SRV record support and
742	more.	1033	more.
743		1034
744	AnyEvent::Handle	1035	AnyEvent::Handle
745	Provide read and write buffers, manages watchers for reads and	1036	Provide read and write buffers, manages watchers for reads and
746	writes, supports raw and formatted I/O, I/O queued and fully	1037	writes, supports raw and formatted I/O, I/O queued and fully
747	transparent and non-blocking SSL/TLS.	1038	transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
748		1039
749	AnyEvent::DNS	1040	AnyEvent::DNS
750	Provides rich asynchronous DNS resolver capabilities.	1041	Provides rich asynchronous DNS resolver capabilities.
751		1042
		1043	AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
		1044	AnyEvent::IGS, AnyEvent::FCP
		1045	Implement event-based interfaces to the protocols of the same name
		1046	(for the curious, IGS is the International Go Server and FCP is the
		1047	Freenet Client Protocol).
		1048
		1049	AnyEvent::Handle::UDP
		1050	Here be danger!
		1051
		1052	As Pauli would put it, "Not only is it not right, it's not even
		1053	wrong!" - there are so many things wrong with AnyEvent::Handle::UDP,
		1054	most notably its use of a stream-based API with a protocol that
		1055	isn't streamable, that the only way to improve it is to delete it.
		1056
		1057	It features data corruption (but typically only under load) and
		1058	general confusion. On top, the author is not only clueless about UDP
		1059	but also fact-resistant - some gems of his understanding: "connect
		1060	doesn't work with UDP", "UDP packets are not IP packets", "UDP only
		1061	has datagrams, not packets", "I don't need to implement proper error
		1062	checking as UDP doesn't support error checking" and so on - he
		1063	doesn't even understand what's wrong with his module when it is
		1064	explained to him.
		1065
752	AnyEvent::HTTP	1066	AnyEvent::DBI
753	A simple-to-use HTTP library that is capable of making a lot of	1067	Executes DBI requests asynchronously in a proxy process for you,
754	concurrent HTTP requests.	1068	notifying you in an event-based way when the operation is finished.
		1069
		1070	AnyEvent::AIO
		1071	Truly asynchronous (as opposed to non-blocking) I/O, should be in
		1072	the toolbox of every event programmer. AnyEvent::AIO transparently
		1073	fuses IO::AIO and AnyEvent together, giving AnyEvent access to
		1074	event-based file I/O, and much more.
755		1075
756	AnyEvent::HTTPD	1076	AnyEvent::HTTPD
757	Provides a simple web application server framework.	1077	A simple embedded webserver.
758		1078
759	AnyEvent::FastPing	1079	AnyEvent::FastPing
760	The fastest ping in the west.	1080	The fastest ping in the west.
761		1081
762	AnyEvent::DBI
763	Executes DBI requests asynchronously in a proxy process.
764
765	AnyEvent::AIO
766	Truly asynchronous I/O, should be in the toolbox of every event
767	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
768	together.
769
770	AnyEvent::BDB
771	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
772	fuses BDB and AnyEvent together.
773
774	AnyEvent::GPSD
775	A non-blocking interface to gpsd, a daemon delivering GPS
776	information.
777
778	AnyEvent::IGS
779	A non-blocking interface to the Internet Go Server protocol (used by
780	App::IGS).
781
782	Net::IRC3
783	AnyEvent based IRC client module family.
784
785	Net::XMPP2
786	AnyEvent based XMPP (Jabber protocol) module family.
787
788	Net::FCP
789	AnyEvent-based implementation of the Freenet Client Protocol,
790	birthplace of AnyEvent.
791
792	Event::ExecFlow
793	High level API for event-based execution flow control.
794
795	Coro	1082	Coro
796	Has special support for AnyEvent via Coro::AnyEvent.	1083	Has special support for AnyEvent via Coro::AnyEvent.
797		1084
798	IO::Lambda	1085	SIMPLIFIED AE API
799	The lambda approach to I/O - don't ask, look there. Can use	1086	Starting with version 5.0, AnyEvent officially supports a second, much
800	AnyEvent.	1087	simpler, API that is designed to reduce the calling, typing and memory
		1088	overhead by using function call syntax and a fixed number of parameters.
		1089
		1090	See the AE manpage for details.
801		1091
802	ERROR AND EXCEPTION HANDLING	1092	ERROR AND EXCEPTION HANDLING
803	In general, AnyEvent does not do any error handling - it relies on the	1093	In general, AnyEvent does not do any error handling - it relies on the
804	caller to do that if required. The AnyEvent::Strict module (see also the	1094	caller to do that if required. The AnyEvent::Strict module (see also the
805	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	1095	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
815	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1105	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
816	Glib uses "install_exception_handler" and so on.	1106	Glib uses "install_exception_handler" and so on.
817		1107
818	ENVIRONMENT VARIABLES	1108	ENVIRONMENT VARIABLES
819	The following environment variables are used by this module or its	1109	The following environment variables are used by this module or its
820	submodules:	1110	submodules.
		1111
		1112	Note that AnyEvent will remove all environment variables starting with
		1113	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1114	enabled.
821		1115
822	"PERL_ANYEVENT_VERBOSE"	1116	"PERL_ANYEVENT_VERBOSE"
823	By default, AnyEvent will be completely silent except in fatal	1117	By default, AnyEvent will be completely silent except in fatal
824	conditions. You can set this environment variable to make AnyEvent	1118	conditions. You can set this environment variable to make AnyEvent
825	more talkative.	1119	more talkative.
…		…
828	conditions, such as not being able to load the event model specified	1122	conditions, such as not being able to load the event model specified
829	by "PERL_ANYEVENT_MODEL".	1123	by "PERL_ANYEVENT_MODEL".
830		1124
831	When set to 2 or higher, cause AnyEvent to report to STDERR which	1125	When set to 2 or higher, cause AnyEvent to report to STDERR which
832	event model it chooses.	1126	event model it chooses.
		1127
		1128	When set to 8 or higher, then AnyEvent will report extra information
		1129	on which optional modules it loads and how it implements certain
		1130	features.
833		1131
834	"PERL_ANYEVENT_STRICT"	1132	"PERL_ANYEVENT_STRICT"
835	AnyEvent does not do much argument checking by default, as thorough	1133	AnyEvent does not do much argument checking by default, as thorough
836	argument checking is very costly. Setting this variable to a true	1134	argument checking is very costly. Setting this variable to a true
837	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1135	value will cause AnyEvent to load "AnyEvent::Strict" and then to
838	thoroughly check the arguments passed to most method calls. If it	1136	thoroughly check the arguments passed to most method calls. If it
839	finds any problems it will croak.	1137	finds any problems, it will croak.
840		1138
841	In other words, enables "strict" mode.	1139	In other words, enables "strict" mode.
842		1140
843	Unlike "use strict", it is definitely recommended ot keep it off in	1141	Unlike "use strict" (or its modern cousin, "use common::sense", it
844	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment	1142	is definitely recommended to keep it off in production. Keeping
		1143	"PERL_ANYEVENT_STRICT=1" in your environment while developing
845	while developing programs can be very useful, however.	1144	programs can be very useful, however.
846		1145
847	"PERL_ANYEVENT_MODEL"	1146	"PERL_ANYEVENT_MODEL"
848	This can be used to specify the event model to be used by AnyEvent,	1147	This can be used to specify the event model to be used by AnyEvent,
849	before auto detection and -probing kicks in. It must be a string	1148	before auto detection and -probing kicks in. It must be a string
850	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1149	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
869	mentioned will be used, and preference will be given to protocols	1168	mentioned will be used, and preference will be given to protocols
870	mentioned earlier in the list.	1169	mentioned earlier in the list.
871		1170
872	This variable can effectively be used for denial-of-service attacks	1171	This variable can effectively be used for denial-of-service attacks
873	against local programs (e.g. when setuid), although the impact is	1172	against local programs (e.g. when setuid), although the impact is
874	likely small, as the program has to handle connection errors	1173	likely small, as the program has to handle conenction and other
875	already-	1174	failures anyways.
876		1175
877	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1176	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
878	IPv6, but support both and try to use both.	1177	IPv6, but support both and try to use both.
879	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1178	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
880	resolve or contact IPv6 addresses.	1179	resolve or contact IPv6 addresses.
…		…
891	EDNS0 in its DNS requests.	1190	EDNS0 in its DNS requests.
892		1191
893	"PERL_ANYEVENT_MAX_FORKS"	1192	"PERL_ANYEVENT_MAX_FORKS"
894	The maximum number of child processes that	1193	The maximum number of child processes that
895	"AnyEvent::Util::fork_call" will create in parallel.	1194	"AnyEvent::Util::fork_call" will create in parallel.
		1195
		1196	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1197	The default value for the "max_outstanding" parameter for the
		1198	default DNS resolver - this is the maximum number of parallel DNS
		1199	requests that are sent to the DNS server.
		1200
		1201	"PERL_ANYEVENT_RESOLV_CONF"
		1202	The file to use instead of /etc/resolv.conf (or OS-specific
		1203	configuration) in the default resolver. When set to the empty
		1204	string, no default config will be used.
		1205
		1206	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1207	When neither "ca_file" nor "ca_path" was specified during
		1208	AnyEvent::TLS context creation, and either of these environment
		1209	variables exist, they will be used to specify CA certificate
		1210	locations instead of a system-dependent default.
		1211
		1212	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1213	When these are set to 1, then the respective modules are not loaded.
		1214	Mostly good for testing AnyEvent itself.
896		1215
897	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1216	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
898	This is an advanced topic that you do not normally need to use AnyEvent	1217	This is an advanced topic that you do not normally need to use AnyEvent
899	in a module. This section is only of use to event loop authors who want	1218	in a module. This section is only of use to event loop authors who want
900	to provide AnyEvent compatibility.	1219	to provide AnyEvent compatibility.
…		…
955	warn "read: $input\n"; # output what has been read	1274	warn "read: $input\n"; # output what has been read
956	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1275	$cv->send if $input =~ /^q/i; # quit program if /^q/i
957	},	1276	},
958	);	1277	);
959		1278
960	my $time_watcher; # can only be used once
961
962	sub new_timer {
963	$timer = AnyEvent->timer (after => 1, cb => sub {	1279	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
964	warn "timeout\n"; # print 'timeout' about every second	1280	warn "timeout\n"; # print 'timeout' at most every second
965	&new_timer; # and restart the time
966	});
967	}	1281	});
968
969	new_timer; # create first timer
970		1282
971	$cv->recv; # wait until user enters /^q/i	1283	$cv->recv; # wait until user enters /^q/i
972		1284
973	REAL-WORLD EXAMPLE	1285	REAL-WORLD EXAMPLE
974	Consider the Net::FCP module. It features (among others) the following	1286	Consider the Net::FCP module. It features (among others) the following
…		…
1046		1358
1047	The actual code goes further and collects all errors ("die"s,	1359	The actual code goes further and collects all errors ("die"s,
1048	exceptions) that occurred during request processing. The "result" method	1360	exceptions) that occurred during request processing. The "result" method
1049	detects whether an exception as thrown (it is stored inside the $txn	1361	detects whether an exception as thrown (it is stored inside the $txn
1050	object) and just throws the exception, which means connection errors and	1362	object) and just throws the exception, which means connection errors and
1051	other problems get reported tot he code that tries to use the result,	1363	other problems get reported to the code that tries to use the result,
1052	not in a random callback.	1364	not in a random callback.
1053		1365
1054	All of this enables the following usage styles:	1366	All of this enables the following usage styles:
1055		1367
1056	1. Blocking:	1368	1. Blocking:
…		…
1101	through AnyEvent. The benchmark creates a lot of timers (with a zero	1413	through AnyEvent. The benchmark creates a lot of timers (with a zero
1102	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1414	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1103	which it is), lets them fire exactly once and destroys them again.	1415	which it is), lets them fire exactly once and destroys them again.
1104		1416
1105	Source code for this benchmark is found as eg/bench in the AnyEvent	1417	Source code for this benchmark is found as eg/bench in the AnyEvent
1106	distribution.	1418	distribution. It uses the AE interface, which makes a real difference
		1419	for the EV and Perl backends only.
1107		1420
1108	Explanation of the columns	1421	Explanation of the columns
1109	watcher is the number of event watchers created/destroyed. Since	1422	watcher is the number of event watchers created/destroyed. Since
1110	different event models feature vastly different performances, each event	1423	different event models feature vastly different performances, each event
1111	loop was given a number of watchers so that overall runtime is	1424	loop was given a number of watchers so that overall runtime is
…		…
1130	destroy is the time, in microseconds, that it takes to destroy a	1443	destroy is the time, in microseconds, that it takes to destroy a
1131	single watcher.	1444	single watcher.
1132		1445
1133	Results	1446	Results
1134	name watchers bytes create invoke destroy comment	1447	name watchers bytes create invoke destroy comment
1135	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1448	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1136	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1449	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1137	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1450	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1138	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1451	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1139	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1452	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1140	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1453	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1454	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1455	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1141	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1456	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1142	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1457	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1143	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1458	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1144	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1459	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1145		1460
1146	Discussion	1461	Discussion
1147	The benchmark does not measure scalability of the event loop very	1462	The benchmark does not measure scalability of the event loop very
1148	well. For example, a select-based event loop (such as the pure perl one)	1463	well. For example, a select-based event loop (such as the pure perl one)
1149	can never compete with an event loop that uses epoll when the number of	1464	can never compete with an event loop that uses epoll when the number of
…		…
1160	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1475	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1161	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1476	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1162	CPU cycles with POE.	1477	CPU cycles with POE.
1163		1478
1164	"EV" is the sole leader regarding speed and memory use, which are both	1479	"EV" is the sole leader regarding speed and memory use, which are both
1165	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1480	maximal/minimal, respectively. When using the AE API there is zero
		1481	overhead (when going through the AnyEvent API create is about 5-6 times
		1482	slower, with other times being equal, so still uses far less memory than
1166	far less memory than any other event loop and is still faster than Event	1483	any other event loop and is still faster than Event natively).
1167	natively.
1168		1484
1169	The pure perl implementation is hit in a few sweet spots (both the	1485	The pure perl implementation is hit in a few sweet spots (both the
1170	constant timeout and the use of a single fd hit optimisations in the	1486	constant timeout and the use of a single fd hit optimisations in the
1171	perl interpreter and the backend itself). Nevertheless this shows that	1487	perl interpreter and the backend itself). Nevertheless this shows that
1172	it adds very little overhead in itself. Like any select-based backend	1488	it adds very little overhead in itself. Like any select-based backend
…		…
1174	few of them active), of course, but this was not subject of this	1490	few of them active), of course, but this was not subject of this
1175	benchmark.	1491	benchmark.
1176		1492
1177	The "Event" module has a relatively high setup and callback invocation	1493	The "Event" module has a relatively high setup and callback invocation
1178	cost, but overall scores in on the third place.	1494	cost, but overall scores in on the third place.
		1495
		1496	"IO::Async" performs admirably well, about on par with "Event", even
		1497	when using its pure perl backend.
1179		1498
1180	"Glib"'s memory usage is quite a bit higher, but it features a faster	1499	"Glib"'s memory usage is quite a bit higher, but it features a faster
1181	callback invocation and overall ends up in the same class as "Event".	1500	callback invocation and overall ends up in the same class as "Event".
1182	However, Glib scales extremely badly, doubling the number of watchers	1501	However, Glib scales extremely badly, doubling the number of watchers
1183	increases the processing time by more than a factor of four, making it	1502	increases the processing time by more than a factor of four, making it
…		…
1239	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1558	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1240	100 (1%) are active. This mirrors the activity of large servers with	1559	100 (1%) are active. This mirrors the activity of large servers with
1241	many connections, most of which are idle at any one point in time.	1560	many connections, most of which are idle at any one point in time.
1242		1561
1243	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1562	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1244	distribution.	1563	distribution. It uses the AE interface, which makes a real difference
		1564	for the EV and Perl backends only.
1245		1565
1246	Explanation of the columns	1566	Explanation of the columns
1247	sockets is the number of sockets, and twice the number of "servers"	1567	sockets is the number of sockets, and twice the number of "servers"
1248	(as each server has a read and write socket end).	1568	(as each server has a read and write socket end).
1249		1569
…		…
1254	single "request", that is, reading the token from the pipe and	1574	single "request", that is, reading the token from the pipe and
1255	forwarding it to another server. This includes deleting the old timeout	1575	forwarding it to another server. This includes deleting the old timeout
1256	and creating a new one that moves the timeout into the future.	1576	and creating a new one that moves the timeout into the future.
1257		1577
1258	Results	1578	Results
1259	name sockets create request	1579	name sockets create request
1260	EV 20000 69.01 11.16	1580	EV 20000 62.66 7.99
1261	Perl 20000 73.32 35.87	1581	Perl 20000 68.32 32.64
1262	Event 20000 212.62 257.32	1582	IOAsync 20000 174.06 101.15 epoll
1263	Glib 20000 651.16 1896.30	1583	IOAsync 20000 174.67 610.84 poll
		1584	Event 20000 202.69 242.91
		1585	Glib 20000 557.01 1689.52
1264	POE 20000 349.67 12317.24 uses POE::Loop::Event	1586	POE 20000 341.54 12086.32 uses POE::Loop::Event
1265		1587
1266	Discussion	1588	Discussion
1267	This benchmark does measure scalability and overall performance of the	1589	This benchmark does measure scalability and overall performance of the
1268	particular event loop.	1590	particular event loop.
1269		1591
1270	EV is again fastest. Since it is using epoll on my system, the setup	1592	EV is again fastest. Since it is using epoll on my system, the setup
1271	time is relatively high, though.	1593	time is relatively high, though.
1272		1594
1273	Perl surprisingly comes second. It is much faster than the C-based event	1595	Perl surprisingly comes second. It is much faster than the C-based event
1274	loops Event and Glib.	1596	loops Event and Glib.
		1597
		1598	IO::Async performs very well when using its epoll backend, and still
		1599	quite good compared to Glib when using its pure perl backend.
1275		1600
1276	Event suffers from high setup time as well (look at its code and you	1601	Event suffers from high setup time as well (look at its code and you
1277	will understand why). Callback invocation also has a high overhead	1602	will understand why). Callback invocation also has a high overhead
1278	compared to the "$_->() for .."-style loop that the Perl event loop	1603	compared to the "$_->() for .."-style loop that the Perl event loop
1279	uses. Event uses select or poll in basically all documented	1604	uses. Event uses select or poll in basically all documented
…		…
1330		1655
1331	Summary	1656	Summary
1332	* C-based event loops perform very well with small number of watchers,	1657	* C-based event loops perform very well with small number of watchers,
1333	as the management overhead dominates.	1658	as the management overhead dominates.
1334		1659
		1660	THE IO::Lambda BENCHMARK
		1661	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1662	could be misinterpreted to make AnyEvent look bad. In fact, the
		1663	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1664	better (which shouldn't come as a surprise to anybody). As such, the
		1665	benchmark is fine, and mostly shows that the AnyEvent backend from
		1666	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1667	without the extra baggage? To explore this, I wrote the equivalent
		1668	benchmark for AnyEvent.
		1669
		1670	The benchmark itself creates an echo-server, and then, for 500 times,
		1671	connects to the echo server, sends a line, waits for the reply, and then
		1672	creates the next connection. This is a rather bad benchmark, as it
		1673	doesn't test the efficiency of the framework or much non-blocking I/O,
		1674	but it is a benchmark nevertheless.
		1675
		1676	name runtime
		1677	Lambda/select 0.330 sec
		1678	+ optimized 0.122 sec
		1679	Lambda/AnyEvent 0.327 sec
		1680	+ optimized 0.138 sec
		1681	Raw sockets/select 0.077 sec
		1682	POE/select, components 0.662 sec
		1683	POE/select, raw sockets 0.226 sec
		1684	POE/select, optimized 0.404 sec
		1685
		1686	AnyEvent/select/nb 0.085 sec
		1687	AnyEvent/EV/nb 0.068 sec
		1688	+state machine 0.134 sec
		1689
		1690	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1691	benchmarks actually make blocking connects and use 100% blocking I/O,
		1692	defeating the purpose of an event-based solution. All of the newly
		1693	written AnyEvent benchmarks use 100% non-blocking connects (using
		1694	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1695	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1696	connects generally require a lot more bookkeeping and event handling
		1697	than blocking connects (which involve a single syscall only).
		1698
		1699	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1700	offers similar expressive power as POE and IO::Lambda, using
		1701	conventional Perl syntax. This means that both the echo server and the
		1702	client are 100% non-blocking, further placing it at a disadvantage.
		1703
		1704	As you can see, the AnyEvent + EV combination even beats the
		1705	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1706	backend easily beats IO::Lambda and POE.
		1707
		1708	And even the 100% non-blocking version written using the high-level (and
		1709	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1710	higher level ("unoptimised") abstractions by a large margin, even though
		1711	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1712
		1713	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1714	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1715	part of the IO::Lambda distribution and were used without any changes.
		1716
		1717	SIGNALS
		1718	AnyEvent currently installs handlers for these signals:
		1719
		1720	SIGCHLD
		1721	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1722	emulation for event loops that do not support them natively. Also,
		1723	some event loops install a similar handler.
		1724
		1725	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1726	then AnyEvent will reset it to default, to avoid losing child exit
		1727	statuses.
		1728
		1729	SIGPIPE
		1730	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1731	"undef" when AnyEvent gets loaded.
		1732
		1733	The rationale for this is that AnyEvent users usually do not really
		1734	depend on SIGPIPE delivery (which is purely an optimisation for
		1735	shell use, or badly-written programs), but "SIGPIPE" can cause
		1736	spurious and rare program exits as a lot of people do not expect
		1737	"SIGPIPE" when writing to some random socket.
		1738
		1739	The rationale for installing a no-op handler as opposed to ignoring
		1740	it is that this way, the handler will be restored to defaults on
		1741	exec.
		1742
		1743	Feel free to install your own handler, or reset it to defaults.
		1744
		1745	RECOMMENDED/OPTIONAL MODULES
		1746	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1747	its built-in modules) are required to use it.
		1748
		1749	That does not mean that AnyEvent won't take advantage of some additional
		1750	modules if they are installed.
		1751
		1752	This section explains which additional modules will be used, and how
		1753	they affect AnyEvent's operation.
		1754
		1755	Async::Interrupt
		1756	This slightly arcane module is used to implement fast signal
		1757	handling: To my knowledge, there is no way to do completely
		1758	race-free and quick signal handling in pure perl. To ensure that
		1759	signals still get delivered, AnyEvent will start an interval timer
		1760	to wake up perl (and catch the signals) with some delay (default is
		1761	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1762
		1763	If this module is available, then it will be used to implement
		1764	signal catching, which means that signals will not be delayed, and
		1765	the event loop will not be interrupted regularly, which is more
		1766	efficient (and good for battery life on laptops).
		1767
		1768	This affects not just the pure-perl event loop, but also other event
		1769	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1770
		1771	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1772	natively, and either employ their own workarounds (POE) or use
		1773	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1774	Installing Async::Interrupt does nothing for those backends.
		1775
		1776	EV This module isn't really "optional", as it is simply one of the
		1777	backend event loops that AnyEvent can use. However, it is simply the
		1778	best event loop available in terms of features, speed and stability:
		1779	It supports the AnyEvent API optimally, implements all the watcher
		1780	types in XS, does automatic timer adjustments even when no monotonic
		1781	clock is available, can take avdantage of advanced kernel interfaces
		1782	such as "epoll" and "kqueue", and is the fastest backend by far.
		1783	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1784	Glib::EV).
		1785
		1786	If you only use backends that rely on another event loop (e.g.
		1787	"Tk"), then this module will do nothing for you.
		1788
		1789	Guard
		1790	The guard module, when used, will be used to implement
		1791	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1792	uses a lot less memory), but otherwise doesn't affect guard
		1793	operation much. It is purely used for performance.
		1794
		1795	JSON and JSON::XS
		1796	One of these modules is required when you want to read or write JSON
		1797	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		1798	can take advantage of the ultra-high-speed JSON::XS module when it
		1799	is installed.
		1800
		1801	Net::SSLeay
		1802	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1803	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1804	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1805
		1806	Time::HiRes
		1807	This module is part of perl since release 5.008. It will be used
		1808	when the chosen event library does not come with a timing source of
		1809	its own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1810	additionally use it to try to use a monotonic clock for timing
		1811	stability.
		1812
1335	FORK	1813	FORK
1336	Most event libraries are not fork-safe. The ones who are usually are	1814	Most event libraries are not fork-safe. The ones who are usually are
1337	because they rely on inefficient but fork-safe "select" or "poll" calls.	1815	because they rely on inefficient but fork-safe "select" or "poll" calls
1338	Only EV is fully fork-aware.	1816	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		1817	epoll are usually badly thought-out hacks that are incompatible with
		1818	fork in one way or another. Only EV is fully fork-aware and ensures that
		1819	you continue event-processing in both parent and child (or both, if you
		1820	know what you are doing).
		1821
		1822	This means that, in general, you cannot fork and do event processing in
		1823	the child if the event library was initialised before the fork (which
		1824	usually happens when the first AnyEvent watcher is created, or the
		1825	library is loaded).
1339		1826
1340	If you have to fork, you must either do so before creating your first	1827	If you have to fork, you must either do so before creating your first
1341	watcher OR you must not use AnyEvent at all in the child.	1828	watcher OR you must not use AnyEvent at all in the child OR you must do
		1829	something completely out of the scope of AnyEvent.
		1830
		1831	The problem of doing event processing in the parent and the child is
		1832	much more complicated: even for backends that are fork-aware or
		1833	fork-safe, their behaviour is not usually what you want: fork clones all
		1834	watchers, that means all timers, I/O watchers etc. are active in both
		1835	parent and child, which is almost never what you want. USing "exec" to
		1836	start worker children from some kind of manage rprocess is usually
		1837	preferred, because it is much easier and cleaner, at the expense of
		1838	having to have another binary.
1342		1839
1343	SECURITY CONSIDERATIONS	1840	SECURITY CONSIDERATIONS
1344	AnyEvent can be forced to load any event model via	1841	AnyEvent can be forced to load any event model via
1345	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1842	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1346	to execute arbitrary code or directly gain access, it can easily be used	1843	to execute arbitrary code or directly gain access, it can easily be used
…		…
1350		1847
1351	You can make AnyEvent completely ignore this variable by deleting it	1848	You can make AnyEvent completely ignore this variable by deleting it
1352	before the first watcher gets created, e.g. with a "BEGIN" block:	1849	before the first watcher gets created, e.g. with a "BEGIN" block:
1353		1850
1354	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1851	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1355		1852
1356	use AnyEvent;	1853	use AnyEvent;
1357		1854
1358	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1855	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1359	be used to probe what backend is used and gain other information (which	1856	be used to probe what backend is used and gain other information (which
1360	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),	1857	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1361	and $ENV{PERL_ANYEGENT_STRICT}.	1858	and $ENV{PERL_ANYEVENT_STRICT}.
		1859
		1860	Note that AnyEvent will remove all environment variables starting with
		1861	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1862	enabled.
1362		1863
1363	BUGS	1864	BUGS
1364	Perl 5.8 has numerous memleaks that sometimes hit this module and are	1865	Perl 5.8 has numerous memleaks that sometimes hit this module and are
1365	hard to work around. If you suffer from memleaks, first upgrade to Perl	1866	hard to work around. If you suffer from memleaks, first upgrade to Perl
1366	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	1867	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1367	annoying mamleaks, such as leaking on "map" and "grep" but it is usually	1868	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1368	not as pronounced).	1869	not as pronounced).
1369		1870
1370	SEE ALSO	1871	SEE ALSO
		1872	Tutorial/Introduction: AnyEvent::Intro.
		1873
		1874	FAQ: AnyEvent::FAQ.
		1875
1371	Utility functions: AnyEvent::Util.	1876	Utility functions: AnyEvent::Util.
1372		1877
1373	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1878	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1374	Event::Lib, Qt, POE.	1879	Event::Lib, Qt, POE.
1375		1880
1376	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1881	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1377	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1882	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1378	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1883	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1884	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
1379		1885
1380	Non-blocking file handles, sockets, TCP clients and servers:	1886	Non-blocking file handles, sockets, TCP clients and servers:
1381	AnyEvent::Handle, AnyEvent::Socket.	1887	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1382		1888
1383	Asynchronous DNS: AnyEvent::DNS.	1889	Asynchronous DNS: AnyEvent::DNS.
1384		1890
1385	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1891	Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1386		1892
1387	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1893	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
		1894	AnyEvent::HTTP.
1388		1895
1389	AUTHOR	1896	AUTHOR
1390	Marc Lehmann <schmorp@schmorp.de>	1897	Marc Lehmann <schmorp@schmorp.de>
1391	http://home.schmorp.de/	1898	http://home.schmorp.de/
1392		1899

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Comparing AnyEvent/README (file contents): Revision 1.30 by root, Mon Sep 29 02:08:57 2008 UTC vs. Revision 1.64 by root, Fri Dec 31 04:50:44 2010 UTC

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Revision 1.30 by root, Mon Sep 29 02:08:57 2008 UTC vs.
Revision 1.64 by root, Fri Dec 31 04:50:44 2010 UTC