[ViewVC] Diff of: cvs/AnyEvent/lib/AnyEvent.pm

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.42 by root, Mon Apr 7 19:40:12 2008 UTC vs.
Revision 1.104 by root, Wed Apr 30 11:40:22 2008 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	Event, Coro, Glib, Tk, Perl - various supported event loops	5	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
6		6
7	=head1 SYNOPSIS	7	=head1 SYNOPSIS
8		8
9	use AnyEvent;	9	use AnyEvent;
10		10
14		14
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	...	16	...
17	});	17	});
18		18
19	my $w = AnyEvent->condvar; # stores wether a condition was flagged	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	20	$w->wait; # enters "main loop" till $condvar gets ->broadcast
21	$w->broadcast; # wake up current and all future wait's	21	$w->broadcast; # wake up current and all future wait's
22		22
23	=head1 WHY YOU SHOULD USE THIS MODULE	23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		24
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	26	nowadays. So what is different about AnyEvent?
27		27
28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of	28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
29	policy> and AnyEvent is I<small and efficient>.	29	policy> and AnyEvent is I<small and efficient>.
30		30
31	First and foremost, I<AnyEvent is not an event model> itself, it only	31	First and foremost, I<AnyEvent is not an event model> itself, it only
32	interfaces to whatever event model the main program happens to use in a	32	interfaces to whatever event model the main program happens to use in a
33	pragmatic way. For event models and certain classes of immortals alike,	33	pragmatic way. For event models and certain classes of immortals alike,
34	the statement "there can only be one" is a bitter reality, and AnyEvent	34	the statement "there can only be one" is a bitter reality: In general,
35	helps hiding the differences.	35	only one event loop can be active at the same time in a process. AnyEvent
		36	helps hiding the differences between those event loops.
36		37
37	The goal of AnyEvent is to offer module authors the ability to do event	38	The goal of AnyEvent is to offer module authors the ability to do event
38	programming (waiting for I/O or timer events) without subscribing to a	39	programming (waiting for I/O or timer events) without subscribing to a
39	religion, a way of living, and most importantly: without forcing your	40	religion, a way of living, and most importantly: without forcing your
40	module users into the same thing by forcing them to use the same event	41	module users into the same thing by forcing them to use the same event
41	model you use.	42	model you use.
42		43
43	For modules like POE or IO::Async (which is actually doing all I/O	44	For modules like POE or IO::Async (which is a total misnomer as it is
44	I<synchronously>...), using them in your module is like joining a	45	actually doing all I/O I<synchronously>...), using them in your module is
45	cult: After you joined, you are dependent on them and you cannot use	46	like joining a cult: After you joined, you are dependent on them and you
46	anything else, as it is simply incompatible to everything that isn't	47	cannot use anything else, as it is simply incompatible to everything that
47	itself.	48	isn't itself. What's worse, all the potential users of your module are
		49	I<also> forced to use the same event loop you use.
48		50
49	AnyEvent + POE works fine. AnyEvent + Glib works fine. AnyEvent + Tk	51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	works fine etc. etc. but none of these work together with the rest: POE	52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51	+ IO::Async? no go. Tk + Event? no go. If your module uses one of	53	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if
52	those, every user of your module has to use it, too. If your module	54	your module uses one of those, every user of your module has to use it,
53	uses AnyEvent, it works transparently with all event models it supports	55	too. But if your module uses AnyEvent, it works transparently with all
54	(including stuff like POE and IO::Async).	56	event models it supports (including stuff like POE and IO::Async, as long
		57	as those use one of the supported event loops. It is trivial to add new
		58	event loops to AnyEvent, too, so it is future-proof).
55		59
56	In addition of being free of having to use I<the one and only true event	60	In addition to being free of having to use I<the one and only true event
57	model>, AnyEvent also is free of bloat and policy: with POE or similar	61	model>, AnyEvent also is free of bloat and policy: with POE or similar
58	modules, you get an enourmous amount of code and strict rules you have	62	modules, you get an enourmous amount of code and strict rules you have to
59	to follow. AnyEvent, on the other hand, is lean and to the point by only	63	follow. AnyEvent, on the other hand, is lean and up to the point, by only
60	offering the functionality that is useful, in as thin as a wrapper as	64	offering the functionality that is necessary, in as thin as a wrapper as
61	technically possible.	65	technically possible.
62		66
		67	Of course, if you want lots of policy (this can arguably be somewhat
		68	useful) and you want to force your users to use the one and only event
		69	model, you should I<not> use this module.
63		70
64	=head1 DESCRIPTION	71	=head1 DESCRIPTION
65		72
66	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
67	allows module authors to utilise an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
68	users to use the same event loop (as only a single event loop can coexist	75	users to use the same event loop (as only a single event loop can coexist
69	peacefully at any one time).	76	peacefully at any one time).
70		77
71	The interface itself is vaguely similar but not identical to the Event	78	The interface itself is vaguely similar, but not identical to the L<Event>
72	module.	79	module.
73		80
74	On the first call of any method, the module tries to detect the currently	81	During the first call of any watcher-creation method, the module tries
75	loaded event loop by probing wether any of the following modules is	82	to detect the currently loaded event loop by probing whether one of the
76	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,
77	used. If none is found, the module tries to load these modules in the	84	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
78	order given. The first one that could be successfully loaded will be	85	L<POE>. The first one found is used. If none are found, the module tries
79	used. If still none could be found, AnyEvent will fall back to a pure-perl	86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
80	event loop, which is also not very efficient.	87	adaptor should always succeed) in the order given. The first one that can
		88	be successfully loaded will be used. If, after this, still none could be
		89	found, AnyEvent will fall back to a pure-perl event loop, which is not
		90	very efficient, but should work everywhere.
81		91
82	Because AnyEvent first checks for modules that are already loaded, loading	92	Because AnyEvent first checks for modules that are already loaded, loading
83	an Event model explicitly before first using AnyEvent will likely make	93	an event model explicitly before first using AnyEvent will likely make
84	that model the default. For example:	94	that model the default. For example:
85		95
86	use Tk;	96	use Tk;
87	use AnyEvent;	97	use AnyEvent;
88		98
89	# .. AnyEvent will likely default to Tk	99	# .. AnyEvent will likely default to Tk
		100
		101	The I<likely> means that, if any module loads another event model and
		102	starts using it, all bets are off. Maybe you should tell their authors to
		103	use AnyEvent so their modules work together with others seamlessly...
90		104
91	The pure-perl implementation of AnyEvent is called	105	The pure-perl implementation of AnyEvent is called
92	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	106	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
93	explicitly.	107	explicitly.
94		108
…		…
97	AnyEvent has the central concept of a I<watcher>, which is an object that	111	AnyEvent has the central concept of a I<watcher>, which is an object that
98	stores relevant data for each kind of event you are waiting for, such as	112	stores relevant data for each kind of event you are waiting for, such as
99	the callback to call, the filehandle to watch, etc.	113	the callback to call, the filehandle to watch, etc.
100		114
101	These watchers are normal Perl objects with normal Perl lifetime. After	115	These watchers are normal Perl objects with normal Perl lifetime. After
102	creating a watcher it will immediately "watch" for events and invoke	116	creating a watcher it will immediately "watch" for events and invoke the
		117	callback when the event occurs (of course, only when the event model
		118	is in control).
		119
103	the callback. To disable the watcher you have to destroy it (e.g. by	120	To disable the watcher you have to destroy it (e.g. by setting the
104	setting the variable that stores it to C<undef> or otherwise deleting all	121	variable you store it in to C<undef> or otherwise deleting all references
105	references to it).	122	to it).
106		123
107	All watchers are created by calling a method on the C<AnyEvent> class.	124	All watchers are created by calling a method on the C<AnyEvent> class.
108		125
		126	Many watchers either are used with "recursion" (repeating timers for
		127	example), or need to refer to their watcher object in other ways.
		128
		129	An any way to achieve that is this pattern:
		130
		131	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		132	# you can use $w here, for example to undef it
		133	undef $w;
		134	});
		135
		136	Note that C<my $w; $w => combination. This is necessary because in Perl,
		137	my variables are only visible after the statement in which they are
		138	declared.
		139
109	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
110		141
111	You can create I/O watcher by calling the C<< AnyEvent->io >> method with	142	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
112	the following mandatory arguments:	143	with the following mandatory key-value pairs as arguments:
113		144
114	C<fh> the Perl I<filehandle> (not filedescriptor) to watch for	145	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
115	events. C<poll> must be a string that is either C<r> or C<w>, that creates	146	for events. C<poll> must be a string that is either C<r> or C<w>,
116	a watcher waiting for "r"eadable or "w"ritable events. C<cb> the callback	147	which creates a watcher waiting for "r"eadable or "w"ritable events,
117	to invoke everytime the filehandle becomes ready.	148	respectively. C<cb> is the callback to invoke each time the file handle
		149	becomes ready.
118		150
119	Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on	151	Although the callback might get passed parameters, their value and
120	a socket you can have one r + one w, not any more (limitation comes from	152	presence is undefined and you cannot rely on them. Portable AnyEvent
121	Tk - if you are sure you are not using Tk this limitation is gone).	153	callbacks cannot use arguments passed to I/O watcher callbacks.
122		154
123	Filehandles will be kept alive, so as long as the watcher exists, the	155	The I/O watcher might use the underlying file descriptor or a copy of it.
124	filehandle exists, too.	156	You must not close a file handle as long as any watcher is active on the
		157	underlying file descriptor.
		158
		159	Some event loops issue spurious readyness notifications, so you should
		160	always use non-blocking calls when reading/writing from/to your file
		161	handles.
125		162
126	Example:	163	Example:
127		164
128	# wait for readability of STDIN, then read a line and disable the watcher	165	# wait for readability of STDIN, then read a line and disable the watcher
129	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
…		…
135	=head2 TIME WATCHERS	172	=head2 TIME WATCHERS
136		173
137	You can create a time watcher by calling the C<< AnyEvent->timer >>	174	You can create a time watcher by calling the C<< AnyEvent->timer >>
138	method with the following mandatory arguments:	175	method with the following mandatory arguments:
139		176
140	C<after> after how many seconds (fractions are supported) should the timer	177	C<after> specifies after how many seconds (fractional values are
141	activate. C<cb> the callback to invoke.	178	supported) the callback should be invoked. C<cb> is the callback to invoke
		179	in that case.
		180
		181	Although the callback might get passed parameters, their value and
		182	presence is undefined and you cannot rely on them. Portable AnyEvent
		183	callbacks cannot use arguments passed to time watcher callbacks.
142		184
143	The timer callback will be invoked at most once: if you want a repeating	185	The timer callback will be invoked at most once: if you want a repeating
144	timer you have to create a new watcher (this is a limitation by both Tk	186	timer you have to create a new watcher (this is a limitation by both Tk
145	and Glib).	187	and Glib).
146		188
…		…
152	});	194	});
153		195
154	# to cancel the timer:	196	# to cancel the timer:
155	undef $w;	197	undef $w;
156		198
		199	Example 2:
		200
		201	# fire an event after 0.5 seconds, then roughly every second
		202	my $w;
		203
		204	my $cb = sub {
		205	# cancel the old timer while creating a new one
		206	$w = AnyEvent->timer (after => 1, cb => $cb);
		207	};
		208
		209	# start the "loop" by creating the first watcher
		210	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		211
		212	=head3 TIMING ISSUES
		213
		214	There are two ways to handle timers: based on real time (relative, "fire
		215	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		216	o'clock").
		217
		218	While most event loops expect timers to specified in a relative way, they
		219	use absolute time internally. This makes a difference when your clock
		220	"jumps", for example, when ntp decides to set your clock backwards from
		221	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		222	fire "after" a second might actually take six years to finally fire.
		223
		224	AnyEvent cannot compensate for this. The only event loop that is conscious
		225	about these issues is L<EV>, which offers both relative (ev_timer, based
		226	on true relative time) and absolute (ev_periodic, based on wallclock time)
		227	timers.
		228
		229	AnyEvent always prefers relative timers, if available, matching the
		230	AnyEvent API.
		231
		232	=head2 SIGNAL WATCHERS
		233
		234	You can watch for signals using a signal watcher, C<signal> is the signal
		235	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
		236	be invoked whenever a signal occurs.
		237
		238	Although the callback might get passed parameters, their value and
		239	presence is undefined and you cannot rely on them. Portable AnyEvent
		240	callbacks cannot use arguments passed to signal watcher callbacks.
		241
		242	Multiple signal occurances can be clumped together into one callback
		243	invocation, and callback invocation will be synchronous. synchronous means
		244	that it might take a while until the signal gets handled by the process,
		245	but it is guarenteed not to interrupt any other callbacks.
		246
		247	The main advantage of using these watchers is that you can share a signal
		248	between multiple watchers.
		249
		250	This watcher might use C<%SIG>, so programs overwriting those signals
		251	directly will likely not work correctly.
		252
		253	Example: exit on SIGINT
		254
		255	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		256
		257	=head2 CHILD PROCESS WATCHERS
		258
		259	You can also watch on a child process exit and catch its exit status.
		260
		261	The child process is specified by the C<pid> argument (if set to C<0>, it
		262	watches for any child process exit). The watcher will trigger as often
		263	as status change for the child are received. This works by installing a
		264	signal handler for C<SIGCHLD>. The callback will be called with the pid
		265	and exit status (as returned by waitpid), so unlike other watcher types,
		266	you I<can> rely on child watcher callback arguments.
		267
		268	There is a slight catch to child watchers, however: you usually start them
		269	I<after> the child process was created, and this means the process could
		270	have exited already (and no SIGCHLD will be sent anymore).
		271
		272	Not all event models handle this correctly (POE doesn't), but even for
		273	event models that I<do> handle this correctly, they usually need to be
		274	loaded before the process exits (i.e. before you fork in the first place).
		275
		276	This means you cannot create a child watcher as the very first thing in an
		277	AnyEvent program, you I<have> to create at least one watcher before you
		278	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		279
		280	Example: fork a process and wait for it
		281
		282	my $done = AnyEvent->condvar;
		283
		284	AnyEvent::detect; # force event module to be initialised
		285
		286	my $pid = fork or exit 5;
		287
		288	my $w = AnyEvent->child (
		289	pid => $pid,
		290	cb => sub {
		291	my ($pid, $status) = @_;
		292	warn "pid $pid exited with status $status";
		293	$done->broadcast;
		294	},
		295	);
		296
		297	# do something else, then wait for process exit
		298	$done->wait;
		299
157	=head2 CONDITION WATCHERS	300	=head2 CONDITION VARIABLES
158		301
159	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	302	Condition variables can be created by calling the C<< AnyEvent->condvar >>
160	method without any arguments.	303	method without any arguments.
161		304
162	A condition watcher watches for a condition - precisely that the C<<	305	A condition variable waits for a condition - precisely that the C<<
163	->broadcast >> method has been called.	306	->broadcast >> method has been called.
164		307
		308	They are very useful to signal that a condition has been fulfilled, for
		309	example, if you write a module that does asynchronous http requests,
		310	then a condition variable would be the ideal candidate to signal the
		311	availability of results.
		312
		313	You can also use condition variables to block your main program until
		314	an event occurs - for example, you could C<< ->wait >> in your main
		315	program until the user clicks the Quit button in your app, which would C<<
		316	->broadcast >> the "quit" event.
		317
165	Note that condition watchers recurse into the event loop - if you have	318	Note that condition variables recurse into the event loop - if you have
166	two watchers that call C<< ->wait >> in a round-robbin fashion, you	319	two pirces of code that call C<< ->wait >> in a round-robbin fashion, you
167	lose. Therefore, condition watchers are good to export to your caller, but	320	lose. Therefore, condition variables are good to export to your caller, but
168	you should avoid making a blocking wait, at least in callbacks, as this	321	you should avoid making a blocking wait yourself, at least in callbacks,
169	usually asks for trouble.	322	as this asks for trouble.
170		323
171	The watcher has only two methods:	324	This object has two methods:
172		325
173	=over 4	326	=over 4
174		327
175	=item $cv->wait	328	=item $cv->wait
176		329
177	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	330	Wait (blocking if necessary) until the C<< ->broadcast >> method has been
178	called on c<$cv>, while servicing other watchers normally.	331	called on c<$cv>, while servicing other watchers normally.
179		332
180	Not all event models support a blocking wait - some die in that case, so
181	if you are using this from a module, never require a blocking wait, but
182	let the caller decide wether the call will block or not (for example,
183	by coupling condition variables with some kind of request results and
184	supporting callbacks so the caller knows that getting the result will not
185	block, while still suppporting blockign waits if the caller so desires).
186
187	You can only wait once on a condition - additional calls will return	333	You can only wait once on a condition - additional calls will return
188	immediately.	334	immediately.
189		335
		336	Not all event models support a blocking wait - some die in that case
		337	(programs might want to do that to stay interactive), so I<if you are
		338	using this from a module, never require a blocking wait>, but let the
		339	caller decide whether the call will block or not (for example, by coupling
		340	condition variables with some kind of request results and supporting
		341	callbacks so the caller knows that getting the result will not block,
		342	while still suppporting blocking waits if the caller so desires).
		343
		344	Another reason I<never> to C<< ->wait >> in a module is that you cannot
		345	sensibly have two C<< ->wait >>'s in parallel, as that would require
		346	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		347	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
		348	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
		349	from different coroutines, however).
		350
190	=item $cv->broadcast	351	=item $cv->broadcast
191		352
192	Flag the condition as ready - a running C<< ->wait >> and all further	353	Flag the condition as ready - a running C<< ->wait >> and all further
193	calls to C<wait> will return after this method has been called. If nobody	354	calls to C<wait> will (eventually) return after this method has been
194	is waiting the broadcast will be remembered..	355	called. If nobody is waiting the broadcast will be remembered..
		356
		357	=back
195		358
196	Example:	359	Example:
197		360
198	# wait till the result is ready	361	# wait till the result is ready
199	my $result_ready = AnyEvent->condvar;	362	my $result_ready = AnyEvent->condvar;
200		363
201	# do something such as adding a timer	364	# do something such as adding a timer
202	# or socket watcher the calls $result_ready->broadcast	365	# or socket watcher the calls $result_ready->broadcast
203	# when the "result" is ready.	366	# when the "result" is ready.
		367	# in this case, we simply use a timer:
		368	my $w = AnyEvent->timer (
		369	after => 1,
		370	cb => sub { $result_ready->broadcast },
		371	);
204		372
		373	# this "blocks" (while handling events) till the watcher
		374	# calls broadcast
205	$result_ready->wait;	375	$result_ready->wait;
206		376
207	=back	377	=head1 GLOBAL VARIABLES AND FUNCTIONS
208
209	=head2 SIGNAL WATCHERS
210
211	You can listen for signals using a signal watcher, C<signal> is the signal
212	I<name> without any C<SIG> prefix. Multiple signals events can be clumped
213	together into one callback invocation, and callback invocation might or
214	might not be asynchronous.
215
216	These watchers might use C<%SIG>, so programs overwriting those signals
217	directly will likely not work correctly.
218
219	Example: exit on SIGINT
220
221	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
222
223	=head2 CHILD PROCESS WATCHERS
224
225	You can also listen for the status of a child process specified by the
226	C<pid> argument (or any child if the pid argument is 0). The watcher will
227	trigger as often as status change for the child are received. This works
228	by installing a signal handler for C<SIGCHLD>. The callback will be called with
229	the pid and exit status (as returned by waitpid).
230
231	Example: wait for pid 1333
232
233	my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });
234
235	=head1 GLOBALS
236		378
237	=over 4	379	=over 4
238		380
239	=item $AnyEvent::MODEL	381	=item $AnyEvent::MODEL
240		382
…		…
245	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	387	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
246		388
247	The known classes so far are:	389	The known classes so far are:
248		390
249	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.	391	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
250	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).
251	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.	392	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
		393	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
252	AnyEvent::Impl::Event based on Event, also second best choice :)	394	AnyEvent::Impl::Event based on Event, second best choice.
		395	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
253	AnyEvent::Impl::Glib based on Glib, second-best choice.	396	AnyEvent::Impl::Glib based on Glib, third-best choice.
254	AnyEvent::Impl::Tk based on Tk, very bad choice.	397	AnyEvent::Impl::Tk based on Tk, very bad choice.
255	AnyEvent::Impl::Perl pure-perl implementation, inefficient.	398	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		399	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		400	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		401
		402	There is no support for WxWidgets, as WxWidgets has no support for
		403	watching file handles. However, you can use WxWidgets through the
		404	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		405	second, which was considered to be too horrible to even consider for
		406	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		407	it's adaptor.
		408
		409	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		410	autodetecting them.
256		411
257	=item AnyEvent::detect	412	=item AnyEvent::detect
258		413
259	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if	414	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
260	necessary. You should only call this function right before you would have	415	if necessary. You should only call this function right before you would
261	created an AnyEvent watcher anyway, that is, very late at runtime.	416	have created an AnyEvent watcher anyway, that is, as late as possible at
		417	runtime.
262		418
263	=back	419	=back
264		420
265	=head1 WHAT TO DO IN A MODULE	421	=head1 WHAT TO DO IN A MODULE
266		422
267	As a module author, you should "use AnyEvent" and call AnyEvent methods	423	As a module author, you should C<use AnyEvent> and call AnyEvent methods
268	freely, but you should not load a specific event module or rely on it.	424	freely, but you should not load a specific event module or rely on it.
269		425
270	Be careful when you create watchers in the module body - Anyevent will	426	Be careful when you create watchers in the module body - AnyEvent will
271	decide which event module to use as soon as the first method is called, so	427	decide which event module to use as soon as the first method is called, so
272	by calling AnyEvent in your module body you force the user of your module	428	by calling AnyEvent in your module body you force the user of your module
273	to load the event module first.	429	to load the event module first.
274		430
		431	Never call C<< ->wait >> on a condition variable unless you I<know> that
		432	the C<< ->broadcast >> method has been called on it already. This is
		433	because it will stall the whole program, and the whole point of using
		434	events is to stay interactive.
		435
		436	It is fine, however, to call C<< ->wait >> when the user of your module
		437	requests it (i.e. if you create a http request object ad have a method
		438	called C<results> that returns the results, it should call C<< ->wait >>
		439	freely, as the user of your module knows what she is doing. always).
		440
275	=head1 WHAT TO DO IN THE MAIN PROGRAM	441	=head1 WHAT TO DO IN THE MAIN PROGRAM
276		442
277	There will always be a single main program - the only place that should	443	There will always be a single main program - the only place that should
278	dictate which event model to use.	444	dictate which event model to use.
279		445
280	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	446	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
281	do anything special and let AnyEvent decide which implementation to chose.	447	do anything special (it does not need to be event-based) and let AnyEvent
		448	decide which implementation to chose if some module relies on it.
282		449
283	If the main program relies on a specific event model (for example, in Gtk2	450	If the main program relies on a specific event model. For example, in
284	programs you have to rely on either Glib or Glib::Event), you should load	451	Gtk2 programs you have to rely on the Glib module. You should load the
285	it before loading AnyEvent or any module that uses it, generally, as early	452	event module before loading AnyEvent or any module that uses it: generally
286	as possible. The reason is that modules might create watchers when they	453	speaking, you should load it as early as possible. The reason is that
287	are loaded, and AnyEvent will decide on the event model to use as soon as	454	modules might create watchers when they are loaded, and AnyEvent will
288	it creates watchers, and it might chose the wrong one unless you load the	455	decide on the event model to use as soon as it creates watchers, and it
289	correct one yourself.	456	might chose the wrong one unless you load the correct one yourself.
290		457
291	You can chose to use a rather inefficient pure-perl implementation by	458	You can chose to use a rather inefficient pure-perl implementation by
292	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	459	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
293	generally better.	460	behaviour everywhere, but letting AnyEvent chose is generally better.
		461
		462	=head1 OTHER MODULES
		463
		464	The following is a non-exhaustive list of additional modules that use
		465	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		466	in the same program. Some of the modules come with AnyEvent, some are
		467	available via CPAN.
		468
		469	=over 4
		470
		471	=item L<AnyEvent::Util>
		472
		473	Contains various utility functions that replace often-used but blocking
		474	functions such as C<inet_aton> by event-/callback-based versions.
		475
		476	=item L<AnyEvent::Handle>
		477
		478	Provide read and write buffers and manages watchers for reads and writes.
		479
		480	=item L<AnyEvent::Socket>
		481
		482	Provides a means to do non-blocking connects, accepts etc.
		483
		484	=item L<AnyEvent::HTTPD>
		485
		486	Provides a simple web application server framework.
		487
		488	=item L<AnyEvent::DNS>
		489
		490	Provides asynchronous DNS resolver capabilities, beyond what
		491	L<AnyEvent::Util> offers.
		492
		493	=item L<AnyEvent::FastPing>
		494
		495	The fastest ping in the west.
		496
		497	=item L<Net::IRC3>
		498
		499	AnyEvent based IRC client module family.
		500
		501	=item L<Net::XMPP2>
		502
		503	AnyEvent based XMPP (Jabber protocol) module family.
		504
		505	=item L<Net::FCP>
		506
		507	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		508	of AnyEvent.
		509
		510	=item L<Event::ExecFlow>
		511
		512	High level API for event-based execution flow control.
		513
		514	=item L<Coro>
		515
		516	Has special support for AnyEvent.
		517
		518	=item L<IO::Lambda>
		519
		520	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		521
		522	=item L<IO::AIO>
		523
		524	Truly asynchronous I/O, should be in the toolbox of every event
		525	programmer. Can be trivially made to use AnyEvent.
		526
		527	=item L<BDB>
		528
		529	Truly asynchronous Berkeley DB access. Can be trivially made to use
		530	AnyEvent.
		531
		532	=back
294		533
295	=cut	534	=cut
296		535
297	package AnyEvent;	536	package AnyEvent;
298		537
299	no warnings;	538	no warnings;
300	use strict;	539	use strict;
301		540
302	use Carp;	541	use Carp;
303		542
304	our $VERSION = '3.0';	543	our $VERSION = '3.3';
305	our $MODEL;	544	our $MODEL;
306		545
307	our $AUTOLOAD;	546	our $AUTOLOAD;
308	our @ISA;	547	our @ISA;
309		548
…		…
311		550
312	our @REGISTRY;	551	our @REGISTRY;
313		552
314	my @models = (	553	my @models = (
315	[Coro::EV:: => AnyEvent::Impl::CoroEV::],	554	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
		555	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
316	[EV:: => AnyEvent::Impl::EV::],	556	[EV:: => AnyEvent::Impl::EV::],
317	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
318	[Event:: => AnyEvent::Impl::Event::],	557	[Event:: => AnyEvent::Impl::Event::],
		558	[Tk:: => AnyEvent::Impl::Tk::],
		559	[Wx:: => AnyEvent::Impl::POE::],
		560	[Prima:: => AnyEvent::Impl::POE::],
		561	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		562	# everything below here will not be autoprobed as the pureperl backend should work everywhere
319	[Glib:: => AnyEvent::Impl::Glib::],	563	[Glib:: => AnyEvent::Impl::Glib::],
320	[Tk:: => AnyEvent::Impl::Tk::],	564	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
321	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	565	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		566	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
322	);	567	);
323		568
324	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	569	our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);
325		570
326	sub detect() {	571	sub detect() {
327	unless ($MODEL) {	572	unless ($MODEL) {
328	no strict 'refs';	573	no strict 'refs';
329		574
		575	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		576	my $model = "AnyEvent::Impl::$1";
		577	if (eval "require $model") {
		578	$MODEL = $model;
		579	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		580	} else {
		581	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		582	}
		583	}
		584
330	# check for already loaded models	585	# check for already loaded models
		586	unless ($MODEL) {
331	for (@REGISTRY, @models) {	587	for (@REGISTRY, @models) {
332	my ($package, $model) = @$_;	588	my ($package, $model) = @$_;
333	if (${"$package\::VERSION"} > 0) {	589	if (${"$package\::VERSION"} > 0) {
334	if (eval "require $model") {	590	if (eval "require $model") {
335	$MODEL = $model;	591	$MODEL = $model;
336	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	592	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
337	last;	593	last;
		594	}
338	}	595	}
339	}	596	}
340	}
341		597
342	unless ($MODEL) {	598	unless ($MODEL) {
343	# try to load a model	599	# try to load a model
344		600
345	for (@REGISTRY, @models) {	601	for (@REGISTRY, @models) {
346	my ($package, $model) = @$_;	602	my ($package, $model) = @$_;
347	if (eval "require $package"	603	if (eval "require $package"
348	and ${"$package\::VERSION"} > 0	604	and ${"$package\::VERSION"} > 0
349	and eval "require $model") {	605	and eval "require $model") {
350	$MODEL = $model;	606	$MODEL = $model;
351	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	607	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
352	last;	608	last;
		609	}
353	}	610	}
		611
		612	$MODEL
		613	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";
354	}	614	}
355
356	$MODEL
357	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event), Glib or Tk.";
358	}	615	}
359		616
360	unshift @ISA, $MODEL;	617	unshift @ISA, $MODEL;
361	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	618	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
362	}	619	}
…		…
473	undef $CHLD_W unless keys %PID_CB;	730	undef $CHLD_W unless keys %PID_CB;
474	}	731	}
475		732
476	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	733	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
477		734
		735	This is an advanced topic that you do not normally need to use AnyEvent in
		736	a module. This section is only of use to event loop authors who want to
		737	provide AnyEvent compatibility.
		738
478	If you need to support another event library which isn't directly	739	If you need to support another event library which isn't directly
479	supported by AnyEvent, you can supply your own interface to it by	740	supported by AnyEvent, you can supply your own interface to it by
480	pushing, before the first watcher gets created, the package name of	741	pushing, before the first watcher gets created, the package name of
481	the event module and the package name of the interface to use onto	742	the event module and the package name of the interface to use onto
482	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	743	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
483	AnyEvent.	744	AnyEvent, so it is reasonably cheap.
484		745
485	Example:	746	Example:
486		747
487	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	748	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
488		749
489	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	750	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
490	package/class when it finds the C<urxvt> package/module is loaded. When	751	package/class when it finds the C<urxvt> package/module is already loaded.
		752
491	AnyEvent is loaded and asked to find a suitable event model, it will	753	When AnyEvent is loaded and asked to find a suitable event model, it
492	first check for the presence of urxvt.	754	will first check for the presence of urxvt by trying to C<use> the
		755	C<urxvt::anyevent> module.
493		756
494	The class should provide implementations for all watcher types (see	757	The class should provide implementations for all watcher types. See
495	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	758	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
496	(Source code) and so on for actual examples, use C<perldoc -m	759	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
497	AnyEvent::Impl::Glib> to see the sources).	760	see the sources.
498		761
		762	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		763	provide suitable (hopefully) replacements.
		764
499	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	765	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
500	uses the above line as-is. An interface isn't included in AnyEvent	766	terminal emulator uses the above line as-is. An interface isn't included
501	because it doesn't make sense outside the embedded interpreter inside	767	in AnyEvent because it doesn't make sense outside the embedded interpreter
502	I<rxvt-unicode>, and it is updated and maintained as part of the	768	inside I<rxvt-unicode>, and it is updated and maintained as part of the
503	I<rxvt-unicode> distribution.	769	I<rxvt-unicode> distribution.
504		770
505	I<rxvt-unicode> also cheats a bit by not providing blocking access to	771	I<rxvt-unicode> also cheats a bit by not providing blocking access to
506	condition variables: code blocking while waiting for a condition will	772	condition variables: code blocking while waiting for a condition will
507	C<die>. This still works with most modules/usages, and blocking calls must	773	C<die>. This still works with most modules/usages, and blocking calls must
508	not be in an interactive application, so it makes sense.	774	not be done in an interactive application, so it makes sense.
509		775
510	=head1 ENVIRONMENT VARIABLES	776	=head1 ENVIRONMENT VARIABLES
511		777
512	The following environment variables are used by this module:	778	The following environment variables are used by this module:
513		779
514	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	780	=over 4
515	model gets used.
516		781
		782	=item C<PERL_ANYEVENT_VERBOSE>
		783
		784	By default, AnyEvent will be completely silent except in fatal
		785	conditions. You can set this environment variable to make AnyEvent more
		786	talkative.
		787
		788	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		789	conditions, such as not being able to load the event model specified by
		790	C<PERL_ANYEVENT_MODEL>.
		791
		792	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		793	model it chooses.
		794
		795	=item C<PERL_ANYEVENT_MODEL>
		796
		797	This can be used to specify the event model to be used by AnyEvent, before
		798	autodetection and -probing kicks in. It must be a string consisting
		799	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		800	and the resulting module name is loaded and if the load was successful,
		801	used as event model. If it fails to load AnyEvent will proceed with
		802	autodetection and -probing.
		803
		804	This functionality might change in future versions.
		805
		806	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		807	could start your program like this:
		808
		809	PERL_ANYEVENT_MODEL=Perl perl ...
		810
		811	=back
		812
517	=head1 EXAMPLE	813	=head1 EXAMPLE PROGRAM
518		814
519	The following program uses an io watcher to read data from stdin, a timer	815	The following program uses an I/O watcher to read data from STDIN, a timer
520	to display a message once per second, and a condvar to exit the program	816	to display a message once per second, and a condition variable to quit the
521	when the user enters quit:	817	program when the user enters quit:
522		818
523	use AnyEvent;	819	use AnyEvent;
524		820
525	my $cv = AnyEvent->condvar;	821	my $cv = AnyEvent->condvar;
526		822
527	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	823	my $io_watcher = AnyEvent->io (
		824	fh => \*STDIN,
		825	poll => 'r',
		826	cb => sub {
528	warn "io event <$_[0]>\n"; # will always output <r>	827	warn "io event <$_[0]>\n"; # will always output <r>
529	chomp (my $input = <STDIN>); # read a line	828	chomp (my $input = <STDIN>); # read a line
530	warn "read: $input\n"; # output what has been read	829	warn "read: $input\n"; # output what has been read
531	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	830	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
		831	},
532	});	832	);
533		833
534	my $time_watcher; # can only be used once	834	my $time_watcher; # can only be used once
535		835
536	sub new_timer {	836	sub new_timer {
537	$timer = AnyEvent->timer (after => 1, cb => sub {	837	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
619	$txn->{finished}->wait;	919	$txn->{finished}->wait;
620	return $txn->{result};	920	return $txn->{result};
621		921
622	The actual code goes further and collects all errors (C<die>s, exceptions)	922	The actual code goes further and collects all errors (C<die>s, exceptions)
623	that occured during request processing. The C<result> method detects	923	that occured during request processing. The C<result> method detects
624	wether an exception as thrown (it is stored inside the $txn object)	924	whether an exception as thrown (it is stored inside the $txn object)
625	and just throws the exception, which means connection errors and other	925	and just throws the exception, which means connection errors and other
626	problems get reported tot he code that tries to use the result, not in a	926	problems get reported tot he code that tries to use the result, not in a
627	random callback.	927	random callback.
628		928
629	All of this enables the following usage styles:	929	All of this enables the following usage styles:
630		930
631	1. Blocking:	931	1. Blocking:
632		932
633	my $data = $fcp->client_get ($url);	933	my $data = $fcp->client_get ($url);
634		934
635	2. Blocking, but parallelizing:	935	2. Blocking, but running in parallel:
636		936
637	my @datas = map $_->result,	937	my @datas = map $_->result,
638	map $fcp->txn_client_get ($_),	938	map $fcp->txn_client_get ($_),
639	@urls;	939	@urls;
640		940
641	Both blocking examples work without the module user having to know	941	Both blocking examples work without the module user having to know
642	anything about events.	942	anything about events.
643		943
644	3a. Event-based in a main program, using any support Event module:	944	3a. Event-based in a main program, using any supported event module:
645		945
646	use Event;	946	use EV;
647		947
648	$fcp->txn_client_get ($url)->cb (sub {	948	$fcp->txn_client_get ($url)->cb (sub {
649	my $txn = shift;	949	my $txn = shift;
650	my $data = $txn->result;	950	my $data = $txn->result;
651	...	951	...
652	});	952	});
653		953
654	Event::loop;	954	EV::loop;
655		955
656	3b. The module user could use AnyEvent, too:	956	3b. The module user could use AnyEvent, too:
657		957
658	use AnyEvent;	958	use AnyEvent;
659		959
…		…
664	$quit->broadcast;	964	$quit->broadcast;
665	});	965	});
666		966
667	$quit->wait;	967	$quit->wait;
668		968
		969
		970	=head1 BENCHMARKS
		971
		972	To give you an idea of the performance and overheads that AnyEvent adds
		973	over the event loops themselves and to give you an impression of the speed
		974	of various event loops I prepared some benchmarks.
		975
		976	=head2 BENCHMARKING ANYEVENT OVERHEAD
		977
		978	Here is a benchmark of various supported event models used natively and
		979	through anyevent. The benchmark creates a lot of timers (with a zero
		980	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		981	which it is), lets them fire exactly once and destroys them again.
		982
		983	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		984	distribution.
		985
		986	=head3 Explanation of the columns
		987
		988	I<watcher> is the number of event watchers created/destroyed. Since
		989	different event models feature vastly different performances, each event
		990	loop was given a number of watchers so that overall runtime is acceptable
		991	and similar between tested event loop (and keep them from crashing): Glib
		992	would probably take thousands of years if asked to process the same number
		993	of watchers as EV in this benchmark.
		994
		995	I<bytes> is the number of bytes (as measured by the resident set size,
		996	RSS) consumed by each watcher. This method of measuring captures both C
		997	and Perl-based overheads.
		998
		999	I<create> is the time, in microseconds (millionths of seconds), that it
		1000	takes to create a single watcher. The callback is a closure shared between
		1001	all watchers, to avoid adding memory overhead. That means closure creation
		1002	and memory usage is not included in the figures.
		1003
		1004	I<invoke> is the time, in microseconds, used to invoke a simple
		1005	callback. The callback simply counts down a Perl variable and after it was
		1006	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		1007	signal the end of this phase.
		1008
		1009	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1010	watcher.
		1011
		1012	=head3 Results
		1013
		1014	name watchers bytes create invoke destroy comment
		1015	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1016	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1017	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1018	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1019	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1020	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1021	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1022	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1023	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1024	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1025
		1026	=head3 Discussion
		1027
		1028	The benchmark does I<not> measure scalability of the event loop very
		1029	well. For example, a select-based event loop (such as the pure perl one)
		1030	can never compete with an event loop that uses epoll when the number of
		1031	file descriptors grows high. In this benchmark, all events become ready at
		1032	the same time, so select/poll-based implementations get an unnatural speed
		1033	boost.
		1034
		1035	Also, note that the number of watchers usually has a nonlinear effect on
		1036	overall speed, that is, creating twice as many watchers doesn't take twice
		1037	the time - usually it takes longer. This puts event loops tested with a
		1038	higher number of watchers at a disadvantage.
		1039
		1040	To put the range of results into perspective, consider that on the
		1041	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1042	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1043	cycles with POE.
		1044
		1045	C<EV> is the sole leader regarding speed and memory use, which are both
		1046	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1047	far less memory than any other event loop and is still faster than Event
		1048	natively.
		1049
		1050	The pure perl implementation is hit in a few sweet spots (both the
		1051	constant timeout and the use of a single fd hit optimisations in the perl
		1052	interpreter and the backend itself). Nevertheless this shows that it
		1053	adds very little overhead in itself. Like any select-based backend its
		1054	performance becomes really bad with lots of file descriptors (and few of
		1055	them active), of course, but this was not subject of this benchmark.
		1056
		1057	The C<Event> module has a relatively high setup and callback invocation
		1058	cost, but overall scores in on the third place.
		1059
		1060	C<Glib>'s memory usage is quite a bit higher, but it features a
		1061	faster callback invocation and overall ends up in the same class as
		1062	C<Event>. However, Glib scales extremely badly, doubling the number of
		1063	watchers increases the processing time by more than a factor of four,
		1064	making it completely unusable when using larger numbers of watchers
		1065	(note that only a single file descriptor was used in the benchmark, so
		1066	inefficiencies of C<poll> do not account for this).
		1067
		1068	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1069	more than 2000 watchers is a big setback, however, as correctness takes
		1070	precedence over speed. Nevertheless, its performance is surprising, as the
		1071	file descriptor is dup()ed for each watcher. This shows that the dup()
		1072	employed by some adaptors is not a big performance issue (it does incur a
		1073	hidden memory cost inside the kernel which is not reflected in the figures
		1074	above).
		1075
		1076	C<POE>, regardless of underlying event loop (whether using its pure perl
		1077	select-based backend or the Event module, the POE-EV backend couldn't
		1078	be tested because it wasn't working) shows abysmal performance and
		1079	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1080	as EV watchers, and 10 times as much memory as Event (the high memory
		1081	requirements are caused by requiring a session for each watcher). Watcher
		1082	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1083	implementation.
		1084
		1085	The design of the POE adaptor class in AnyEvent can not really account
		1086	for the performance issues, though, as session creation overhead is
		1087	small compared to execution of the state machine, which is coded pretty
		1088	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1089	using multiple sessions is not a good approach, especially regarding
		1090	memory usage, even the author of POE could not come up with a faster
		1091	design).
		1092
		1093	=head3 Summary
		1094
		1095	=over 4
		1096
		1097	=item * Using EV through AnyEvent is faster than any other event loop
		1098	(even when used without AnyEvent), but most event loops have acceptable
		1099	performance with or without AnyEvent.
		1100
		1101	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1102	the actual event loop, only with extremely fast event loops such as EV
		1103	adds AnyEvent significant overhead.
		1104
		1105	=item * You should avoid POE like the plague if you want performance or
		1106	reasonable memory usage.
		1107
		1108	=back
		1109
		1110	=head2 BENCHMARKING THE LARGE SERVER CASE
		1111
		1112	This benchmark atcually benchmarks the event loop itself. It works by
		1113	creating a number of "servers": each server consists of a socketpair, a
		1114	timeout watcher that gets reset on activity (but never fires), and an I/O
		1115	watcher waiting for input on one side of the socket. Each time the socket
		1116	watcher reads a byte it will write that byte to a random other "server".
		1117
		1118	The effect is that there will be a lot of I/O watchers, only part of which
		1119	are active at any one point (so there is a constant number of active
		1120	fds for each loop iterstaion, but which fds these are is random). The
		1121	timeout is reset each time something is read because that reflects how
		1122	most timeouts work (and puts extra pressure on the event loops).
		1123
		1124	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1125	(1%) are active. This mirrors the activity of large servers with many
		1126	connections, most of which are idle at any one point in time.
		1127
		1128	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1129	distribution.
		1130
		1131	=head3 Explanation of the columns
		1132
		1133	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1134	each server has a read and write socket end).
		1135
		1136	I<create> is the time it takes to create a socketpair (which is
		1137	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1138
		1139	I<request>, the most important value, is the time it takes to handle a
		1140	single "request", that is, reading the token from the pipe and forwarding
		1141	it to another server. This includes deleting the old timeout and creating
		1142	a new one that moves the timeout into the future.
		1143
		1144	=head3 Results
		1145
		1146	name sockets create request
		1147	EV 20000 69.01 11.16
		1148	Perl 20000 73.32 35.87
		1149	Event 20000 212.62 257.32
		1150	Glib 20000 651.16 1896.30
		1151	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1152
		1153	=head3 Discussion
		1154
		1155	This benchmark I<does> measure scalability and overall performance of the
		1156	particular event loop.
		1157
		1158	EV is again fastest. Since it is using epoll on my system, the setup time
		1159	is relatively high, though.
		1160
		1161	Perl surprisingly comes second. It is much faster than the C-based event
		1162	loops Event and Glib.
		1163
		1164	Event suffers from high setup time as well (look at its code and you will
		1165	understand why). Callback invocation also has a high overhead compared to
		1166	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1167	uses select or poll in basically all documented configurations.
		1168
		1169	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1170	clearly fails to perform with many filehandles or in busy servers.
		1171
		1172	POE is still completely out of the picture, taking over 1000 times as long
		1173	as EV, and over 100 times as long as the Perl implementation, even though
		1174	it uses a C-based event loop in this case.
		1175
		1176	=head3 Summary
		1177
		1178	=over 4
		1179
		1180	=item * The pure perl implementation performs extremely well.
		1181
		1182	=item * Avoid Glib or POE in large projects where performance matters.
		1183
		1184	=back
		1185
		1186	=head2 BENCHMARKING SMALL SERVERS
		1187
		1188	While event loops should scale (and select-based ones do not...) even to
		1189	large servers, most programs we (or I :) actually write have only a few
		1190	I/O watchers.
		1191
		1192	In this benchmark, I use the same benchmark program as in the large server
		1193	case, but it uses only eight "servers", of which three are active at any
		1194	one time. This should reflect performance for a small server relatively
		1195	well.
		1196
		1197	The columns are identical to the previous table.
		1198
		1199	=head3 Results
		1200
		1201	name sockets create request
		1202	EV 16 20.00 6.54
		1203	Perl 16 25.75 12.62
		1204	Event 16 81.27 35.86
		1205	Glib 16 32.63 15.48
		1206	POE 16 261.87 276.28 uses POE::Loop::Event
		1207
		1208	=head3 Discussion
		1209
		1210	The benchmark tries to test the performance of a typical small
		1211	server. While knowing how various event loops perform is interesting, keep
		1212	in mind that their overhead in this case is usually not as important, due
		1213	to the small absolute number of watchers (that is, you need efficiency and
		1214	speed most when you have lots of watchers, not when you only have a few of
		1215	them).
		1216
		1217	EV is again fastest.
		1218
		1219	Perl again comes second. It is noticably faster than the C-based event
		1220	loops Event and Glib, although the difference is too small to really
		1221	matter.
		1222
		1223	POE also performs much better in this case, but is is still far behind the
		1224	others.
		1225
		1226	=head3 Summary
		1227
		1228	=over 4
		1229
		1230	=item * C-based event loops perform very well with small number of
		1231	watchers, as the management overhead dominates.
		1232
		1233	=back
		1234
		1235
		1236	=head1 FORK
		1237
		1238	Most event libraries are not fork-safe. The ones who are usually are
		1239	because they rely on inefficient but fork-safe C<select> or C<poll>
		1240	calls. Only L<EV> is fully fork-aware.
		1241
		1242	If you have to fork, you must either do so I<before> creating your first
		1243	watcher OR you must not use AnyEvent at all in the child.
		1244
		1245
		1246	=head1 SECURITY CONSIDERATIONS
		1247
		1248	AnyEvent can be forced to load any event model via
		1249	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1250	execute arbitrary code or directly gain access, it can easily be used to
		1251	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1252	will not be active when the program uses a different event model than
		1253	specified in the variable.
		1254
		1255	You can make AnyEvent completely ignore this variable by deleting it
		1256	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1257
		1258	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1259
		1260	use AnyEvent;
		1261
		1262
669	=head1 SEE ALSO	1263	=head1 SEE ALSO
670		1264
671	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1265	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,
		1266	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
		1267	L<Event::Lib>, L<Qt>, L<POE>.
672		1268
		1269	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
673	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1270	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,
		1271	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
		1272	L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.
674		1273
675	Nontrivial usage example: L<Net::FCP>.	1274	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
676		1275
677	=head1	1276
		1277	=head1 AUTHOR
		1278
		1279	Marc Lehmann <schmorp@schmorp.de>
		1280	http://home.schmorp.de/
678		1281
679	=cut	1282	=cut
680		1283
681	1	1284	1
682		1285

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Comparing AnyEvent/lib/AnyEvent.pm (file contents):
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Revision 1.104 by root, Wed Apr 30 11:40:22 2008 UTC