AnyEvent/lib/AnyEvent.pm

=head1 NAME

AnyEvent - provide framework for multiple event loops

Event, Coro, Glib, Tk, Perl - various supported event loops

=head1 SYNOPSIS

   use AnyEvent;

   my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {
      ...
   });

   my $w = AnyEvent->timer (after => $seconds, cb => sub {
      ...
   });

   my $w = AnyEvent->condvar; # stores wether a condition was flagged
   $w->wait; # enters "main loop" till $condvar gets ->broadcast
   $w->broadcast; # wake up current and all future wait's

=head1 DESCRIPTION

L<AnyEvent> provides an identical interface to multiple event loops. This
allows module authors to utilise an event loop without forcing module
users to use the same event loop (as only a single event loop can coexist
peacefully at any one time).

The interface itself is vaguely similar but not identical to the Event
module.

On the first call of any method, the module tries to detect the currently
loaded event loop by probing wether any of the following modules is
loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is
used. If none is found, the module tries to load these modules in the
order given. The first one that could be successfully loaded will be
used. If still none could be found, AnyEvent will fall back to a pure-perl
event loop, which is also not very efficient.

Because AnyEvent first checks for modules that are already loaded, loading
an Event model explicitly before first using AnyEvent will likely make
that model the default. For example:

   use Tk;
   use AnyEvent;

   # .. AnyEvent will likely default to Tk

The pure-perl implementation of AnyEvent is called
C<AnyEvent::Impl::Perl>. Like other event modules you can load it
explicitly.

=head1 WATCHERS

AnyEvent has the central concept of a I<watcher>, which is an object that
stores relevant data for each kind of event you are waiting for, such as
the callback to call, the filehandle to watch, etc.

These watchers are normal Perl objects with normal Perl lifetime. After
creating a watcher it will immediately "watch" for events and invoke
the callback. To disable the watcher you have to destroy it (e.g. by
setting the variable that stores it to C<undef> or otherwise deleting all
references to it).

All watchers are created by calling a method on the C<AnyEvent> class.

=head2 IO WATCHERS

You can create I/O watcher by calling the C<< AnyEvent->io >> method with
the following mandatory arguments:

C<fh> the Perl I<filehandle> (not filedescriptor) to watch for
events. C<poll> must be a string that is either C<r> or C<w>, that creates
a watcher waiting for "r"eadable or "w"ritable events. C<cb> teh callback
to invoke everytime the filehandle becomes ready.

Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on
a socket you can have one r + one w, not any more (limitation comes from
Tk - if you are sure you are not using Tk this limitation is gone).

Filehandles will be kept alive, so as long as the watcher exists, the
filehandle exists, too.

Example:

   # wait for readability of STDIN, then read a line and disable the watcher
   my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
      chomp (my $input = <STDIN>);
      warn "read: $input\n";
      undef $w;
   });

=head2 TIMER WATCHERS

You can create a timer watcher by calling the C<< AnyEvent->timer >>
method with the following mandatory arguments:

C<after> after how many seconds (fractions are supported) should the timer
activate. C<cb> the callback to invoke.

The timer callback will be invoked at most once: if you want a repeating
timer you have to create a new watcher (this is a limitation by both Tk
and Glib).

Example:

   # fire an event after 7.7 seconds
   my $w = AnyEvent->timer (after => 7.7, cb => sub {
      warn "timeout\n";
   });

   # to cancel the timer:
   undef $w

=head2 CONDITION WATCHERS

Condition watchers can be created by calling the C<< AnyEvent->condvar >>
method without any arguments.

A condition watcher watches for a condition - precisely that the C<<
->broadcast >> method has been called.

The watcher has only two methods:

=over 4

=item $cv->wait

Wait (blocking if necessary) until the C<< ->broadcast >> method has been
called on c<$cv>, while servicing other watchers normally.

Not all event models support a blocking wait - some die in that case, so
if you are using this from a module, never require a blocking wait, but
let the caller decide wether the call will block or not (for example,
by coupling condition variables with some kind of request results and
supporting callbacks so the caller knows that getting the result will not
block, while still suppporting blockign waits if the caller so desires).

You can only wait once on a condition - additional calls will return
immediately.

=item $cv->broadcast

Flag the condition as ready - a running C<< ->wait >> and all further
calls to C<wait> will return after this method has been called. If nobody
is waiting the broadcast will be remembered..

Example:

   # wait till the result is ready
   my $result_ready = AnyEvent->condvar;

   # do something such as adding a timer
   # or socket watcher the calls $result_ready->broadcast
   # when the "result" is ready.

   $result_ready->wait;

=back

=head1 GLOBALS

=over 4

=item $AnyEvent::MODEL

Contains C<undef> until the first watcher is being created. Then it
contains the event model that is being used, which is the name of the
Perl class implementing the model. This class is usually one of the
C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).

The known classes so far are:

   AnyEvent::Impl::Coro      based on Coro::Event, best choise.
   AnyEvent::Impl::Event     based on Event, also best choice :)
   AnyEvent::Impl::Glib      based on Glib, second-best choice.
   AnyEvent::Impl::Tk        based on Tk, very bad choice.
   AnyEvent::Impl::Perl      pure-perl implementation, inefficient.

=back

=head1 WHAT TO DO IN A MODULE

As a module author, you should "use AnyEvent" and call AnyEvent methods
freely, but you should not load a specific event module or rely on it.

Be careful when you create watchers in the module body - Anyevent will
decide which event module to use as soon as the first method is called, so
by calling AnyEvent in your module body you force the user of your module
to load the event module first.

=head1 WHAT TO DO IN THE MAIN PROGRAM

There will always be a single main program - the only place that should
dictate which event model to use.

If it doesn't care, it can just "use AnyEvent" and use it itself, or not
do anything special and let AnyEvent decide which implementation to chose.

If the main program relies on a specific event model (for example, in Gtk2
programs you have to rely on either Glib or Glib::Event), you should load
it before loading AnyEvent or any module that uses it, generally, as early
as possible. The reason is that modules might create watchers when they
are loaded, and AnyEvent will decide on the event model to use as soon as
it creates watchers, and it might chose the wrong one unless you load the
correct one yourself.

You can chose to use a rather inefficient pure-perl implementation by
loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is
generally better.

=cut

package AnyEvent;

no warnings;
use strict 'vars';
use Carp;

our $VERSION = '2.0';
our $MODEL;

our $AUTOLOAD;
our @ISA;

our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;

our @REGISTRY;

my @models = (
      [Coro::Event::          => AnyEvent::Impl::Coro::],
      [Event::                => AnyEvent::Impl::Event::],
      [Glib::                 => AnyEvent::Impl::Glib::],
      [Tk::                   => AnyEvent::Impl::Tk::],
      [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
);

our %method = map +($_ => 1), qw(io timer condvar broadcast wait DESTROY);

sub AUTOLOAD {
   $AUTOLOAD =~ s/.*://;

   $method{$AUTOLOAD}
      or croak "$AUTOLOAD: not a valid method for AnyEvent objects";

   unless ($MODEL) {
      # check for already loaded models
      for (@REGISTRY, @models) {
         my ($package, $model) = @$_;
         if (${"$package\::VERSION"} > 0) {
            if (eval "require $model") {
               $MODEL = $model;
               warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;
               last;
            }
         }
      }

      unless ($MODEL) {
         # try to load a model

         for (@REGISTRY, @models) {
            my ($package, $model) = @$_;
            if (eval "require $model") {
               $MODEL = $model;
               warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
               last;
            }
         }

         $MODEL
           or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";
      }
   }

   @ISA = $MODEL;

   my $class = shift;
   $class->$AUTOLOAD (@_);
}

=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE

If you need to support another event library which isn't directly
supported by AnyEvent, you can supply your own interface to it by
pushing, before the first watcher gets created, the package name of
the event module and the package name of the interface to use onto
C<@AnyEvent::REGISTRY>. You can do that before and even without loading
AnyEvent.

Example:

   push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];

This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
package/class when it finds the C<urxvt> package/module is loaded. When
AnyEvent is loaded and asked to find a suitable event model, it will
first check for the presence of urxvt.

The class should prove implementations for all watcher types (see
L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>
(Source code) and so on for actual examples, use C<perldoc -m
AnyEvent::Impl::Glib> to see the sources).

The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
uses the above line as-is. An interface isn't included in AnyEvent
because it doesn't make sense outside the embedded interpreter inside
I<rxvt-unicode>, and it is updated and maintained as part of the
I<rxvt-unicode> distribution.

I<rxvt-unicode> also cheats a bit by not providing blocking access to
condition variables: code blocking while waiting for a condition will
C<die>. This still works with most modules/usages, and blocking calls must
not be in an interactive appliation, so it makes sense.

=head1 ENVIRONMENT VARIABLES

The following environment variables are used by this module:

C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
model gets used.

=head1 EXAMPLE

The following program uses an io watcher to read data from stdin, a timer
to display a message once per second, and a condvar to exit the program
when the user enters quit:

   use AnyEvent;

   my $cv = AnyEvent->condvar;

   my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
      warn "io event <$_[0]>\n";   # will always output <r>
      chomp (my $input = <STDIN>); # read a line
      warn "read: $input\n";       # output what has been read
      $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
   });

   my $time_watcher; # can only be used once

   sub new_timer {
      $timer = AnyEvent->timer (after => 1, cb => sub {
         warn "timeout\n"; # print 'timeout' about every second
         &new_timer; # and restart the time
      });
   }

   new_timer; # create first timer

   $cv->wait; # wait until user enters /^q/i

=head1 REAL-WORLD EXAMPLE

Consider the L<Net::FCP> module. It features (among others) the following
API calls, which are to freenet what HTTP GET requests are to http:

   my $data = $fcp->client_get ($url); # blocks

   my $transaction = $fcp->txn_client_get ($url); # does not block
   $transaction->cb ( sub { ... } ); # set optional result callback
   my $data = $transaction->result; # possibly blocks

The C<client_get> method works like C<LWP::Simple::get>: it requests the
given URL and waits till the data has arrived. It is defined to be:

   sub client_get { $_[0]->txn_client_get ($_[1])->result }

And in fact is automatically generated. This is the blocking API of
L<Net::FCP>, and it works as simple as in any other, similar, module.

More complicated is C<txn_client_get>: It only creates a transaction
(completion, result, ...) object and initiates the transaction.

   my $txn = bless { }, Net::FCP::Txn::;

It also creates a condition variable that is used to signal the completion
of the request:

   $txn->{finished} = AnyAvent->condvar;

It then creates a socket in non-blocking mode.

   socket $txn->{fh}, ...;
   fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
   connect $txn->{fh}, ...
      and !$!{EWOULDBLOCK}
      and !$!{EINPROGRESS}
      and Carp::croak "unable to connect: $!\n";

Then it creates a write-watcher which gets called whenever an error occurs
or the connection succeeds:

   $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });

And returns this transaction object. The C<fh_ready_w> callback gets
called as soon as the event loop detects that the socket is ready for
writing.

The C<fh_ready_w> method makes the socket blocking again, writes the
request data and replaces the watcher by a read watcher (waiting for reply
data). The actual code is more complicated, but that doesn't matter for
this example:

   fcntl $txn->{fh}, F_SETFL, 0;
   syswrite $txn->{fh}, $txn->{request}
      or die "connection or write error";
   $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });

Again, C<fh_ready_r> waits till all data has arrived, and then stores the
result and signals any possible waiters that the request ahs finished:

   sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};

   if (end-of-file or data complete) {
     $txn->{result} = $txn->{buf};
     $txn->{finished}->broadcast;
     $txb->{cb}->($txn) of $txn->{cb}; # also call callback
   }

The C<result> method, finally, just waits for the finished signal (if the
request was already finished, it doesn't wait, of course, and returns the
data:

   $txn->{finished}->wait;
   return $txn->{result};

The actual code goes further and collects all errors (C<die>s, exceptions)
that occured during request processing. The C<result> method detects
wether an exception as thrown (it is stored inside the $txn object)
and just throws the exception, which means connection errors and other
problems get reported tot he code that tries to use the result, not in a
random callback.

All of this enables the following usage styles:

1. Blocking:

   my $data = $fcp->client_get ($url);

2. Blocking, but parallelizing:

   my @datas = map $_->result,
                  map $fcp->txn_client_get ($_),
                     @urls;

Both blocking examples work without the module user having to know
anything about events.

3a. Event-based in a main program, using any support Event module:

   use Event;

   $fcp->txn_client_get ($url)->cb (sub {
      my $txn = shift;
      my $data = $txn->result;
      ...
   });

   Event::loop;

3b. The module user could use AnyEvent, too:

   use AnyEvent;

   my $quit = AnyEvent->condvar;

   $fcp->txn_client_get ($url)->cb (sub {
      ...
      $quit->broadcast;
   });

   $quit->wait;

=head1 SEE ALSO

Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.

Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.

Nontrivial usage example: L<Net::FCP>.

=head1

=cut

1

Revision:	1.16
Committed:	Sun Nov 5 01:08:16 2006 UTC (17 years, 8 months ago) by root
Branch:	MAIN
Changes since 1.15:	+22 -0 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3	root	1.2	AnyEvent - provide framework for multiple event loops
4
5	root	1.14	Event, Coro, Glib, Tk, Perl - various supported event loops
6	root	1.1
7			=head1 SYNOPSIS
8
9	root	1.7	use AnyEvent;
10	root	1.2
11	root	1.14	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {
12	root	1.2	...
13			});
14	root	1.5
15			my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	root	1.2	...
17			});
18
19	root	1.14	my $w = AnyEvent->condvar; # stores wether a condition was flagged
20			$w->wait; # enters "main loop" till $condvar gets ->broadcast
21	root	1.5	$w->broadcast; # wake up current and all future wait's
22
23	root	1.1	=head1 DESCRIPTION
24
25	root	1.2	L<AnyEvent> provides an identical interface to multiple event loops. This
26	root	1.13	allows module authors to utilise an event loop without forcing module
27	root	1.2	users to use the same event loop (as only a single event loop can coexist
28			peacefully at any one time).
29
30			The interface itself is vaguely similar but not identical to the Event
31			module.
32
33			On the first call of any method, the module tries to detect the currently
34			loaded event loop by probing wether any of the following modules is
35			loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is
36			used. If none is found, the module tries to load these modules in the
37			order given. The first one that could be successfully loaded will be
38	root	1.14	used. If still none could be found, AnyEvent will fall back to a pure-perl
39			event loop, which is also not very efficient.
40
41			Because AnyEvent first checks for modules that are already loaded, loading
42			an Event model explicitly before first using AnyEvent will likely make
43			that model the default. For example:
44
45			use Tk;
46			use AnyEvent;
47
48			# .. AnyEvent will likely default to Tk
49
50			The pure-perl implementation of AnyEvent is called
51			C<AnyEvent::Impl::Perl>. Like other event modules you can load it
52			explicitly.
53
54			=head1 WATCHERS
55
56			AnyEvent has the central concept of a I<watcher>, which is an object that
57			stores relevant data for each kind of event you are waiting for, such as
58			the callback to call, the filehandle to watch, etc.
59
60			These watchers are normal Perl objects with normal Perl lifetime. After
61			creating a watcher it will immediately "watch" for events and invoke
62			the callback. To disable the watcher you have to destroy it (e.g. by
63			setting the variable that stores it to C<undef> or otherwise deleting all
64			references to it).
65
66			All watchers are created by calling a method on the C<AnyEvent> class.
67
68			=head2 IO WATCHERS
69
70			You can create I/O watcher by calling the C<< AnyEvent->io >> method with
71			the following mandatory arguments:
72
73			C<fh> the Perl I<filehandle> (not filedescriptor) to watch for
74			events. C<poll> must be a string that is either C<r> or C<w>, that creates
75			a watcher waiting for "r"eadable or "w"ritable events. C<cb> teh callback
76			to invoke everytime the filehandle becomes ready.
77
78			Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on
79			a socket you can have one r + one w, not any more (limitation comes from
80			Tk - if you are sure you are not using Tk this limitation is gone).
81
82			Filehandles will be kept alive, so as long as the watcher exists, the
83			filehandle exists, too.
84
85			Example:
86
87			# wait for readability of STDIN, then read a line and disable the watcher
88			my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
89			chomp (my $input = <STDIN>);
90			warn "read: $input\n";
91			undef $w;
92			});
93
94			=head2 TIMER WATCHERS
95
96			You can create a timer watcher by calling the C<< AnyEvent->timer >>
97			method with the following mandatory arguments:
98
99			C<after> after how many seconds (fractions are supported) should the timer
100			activate. C<cb> the callback to invoke.
101
102			The timer callback will be invoked at most once: if you want a repeating
103			timer you have to create a new watcher (this is a limitation by both Tk
104			and Glib).
105
106			Example:
107
108			# fire an event after 7.7 seconds
109			my $w = AnyEvent->timer (after => 7.7, cb => sub {
110			warn "timeout\n";
111			});
112
113			# to cancel the timer:
114			undef $w
115
116			=head2 CONDITION WATCHERS
117
118			Condition watchers can be created by calling the C<< AnyEvent->condvar >>
119			method without any arguments.
120
121			A condition watcher watches for a condition - precisely that the C<<
122			->broadcast >> method has been called.
123
124			The watcher has only two methods:
125	root	1.2
126	root	1.1	=over 4
127
128	root	1.14	=item $cv->wait
129
130			Wait (blocking if necessary) until the C<< ->broadcast >> method has been
131			called on c<$cv>, while servicing other watchers normally.
132
133			Not all event models support a blocking wait - some die in that case, so
134			if you are using this from a module, never require a blocking wait, but
135			let the caller decide wether the call will block or not (for example,
136			by coupling condition variables with some kind of request results and
137			supporting callbacks so the caller knows that getting the result will not
138			block, while still suppporting blockign waits if the caller so desires).
139
140			You can only wait once on a condition - additional calls will return
141			immediately.
142
143			=item $cv->broadcast
144
145			Flag the condition as ready - a running C<< ->wait >> and all further
146			calls to C<wait> will return after this method has been called. If nobody
147			is waiting the broadcast will be remembered..
148
149			Example:
150
151			# wait till the result is ready
152			my $result_ready = AnyEvent->condvar;
153
154			# do something such as adding a timer
155			# or socket watcher the calls $result_ready->broadcast
156			# when the "result" is ready.
157
158			$result_ready->wait;
159
160			=back
161
162	root	1.16	=head1 GLOBALS
163
164			=over 4
165
166			=item $AnyEvent::MODEL
167
168			Contains C<undef> until the first watcher is being created. Then it
169			contains the event model that is being used, which is the name of the
170			Perl class implementing the model. This class is usually one of the
171			C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
172			AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
173
174			The known classes so far are:
175
176			AnyEvent::Impl::Coro based on Coro::Event, best choise.
177			AnyEvent::Impl::Event based on Event, also best choice :)
178			AnyEvent::Impl::Glib based on Glib, second-best choice.
179			AnyEvent::Impl::Tk based on Tk, very bad choice.
180			AnyEvent::Impl::Perl pure-perl implementation, inefficient.
181
182			=back
183
184	root	1.14	=head1 WHAT TO DO IN A MODULE
185
186			As a module author, you should "use AnyEvent" and call AnyEvent methods
187			freely, but you should not load a specific event module or rely on it.
188
189			Be careful when you create watchers in the module body - Anyevent will
190			decide which event module to use as soon as the first method is called, so
191			by calling AnyEvent in your module body you force the user of your module
192			to load the event module first.
193
194			=head1 WHAT TO DO IN THE MAIN PROGRAM
195
196			There will always be a single main program - the only place that should
197			dictate which event model to use.
198
199			If it doesn't care, it can just "use AnyEvent" and use it itself, or not
200			do anything special and let AnyEvent decide which implementation to chose.
201
202			If the main program relies on a specific event model (for example, in Gtk2
203			programs you have to rely on either Glib or Glib::Event), you should load
204			it before loading AnyEvent or any module that uses it, generally, as early
205			as possible. The reason is that modules might create watchers when they
206			are loaded, and AnyEvent will decide on the event model to use as soon as
207			it creates watchers, and it might chose the wrong one unless you load the
208			correct one yourself.
209
210			You can chose to use a rather inefficient pure-perl implementation by
211			loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is
212			generally better.
213
214	root	1.1	=cut
215
216			package AnyEvent;
217
218	root	1.2	no warnings;
219			use strict 'vars';
220	root	1.1	use Carp;
221
222	root	1.15	our $VERSION = '2.0';
223	root	1.2	our $MODEL;
224	root	1.1
225	root	1.2	our $AUTOLOAD;
226			our @ISA;
227	root	1.1
228	root	1.7	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
229
230	root	1.8	our @REGISTRY;
231
232	root	1.1	my @models = (
233	root	1.14	[Coro::Event:: => AnyEvent::Impl::Coro::],
234			[Event:: => AnyEvent::Impl::Event::],
235			[Glib:: => AnyEvent::Impl::Glib::],
236			[Tk:: => AnyEvent::Impl::Tk::],
237			[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
238	root	1.1	);
239
240	root	1.14	our %method = map +($_ => 1), qw(io timer condvar broadcast wait DESTROY);
241	root	1.3
242	root	1.1	sub AUTOLOAD {
243			$AUTOLOAD =~ s/.*://;
244
245	root	1.3	$method{$AUTOLOAD}
246			or croak "$AUTOLOAD: not a valid method for AnyEvent objects";
247
248	root	1.2	unless ($MODEL) {
249			# check for already loaded models
250	root	1.8	for (@REGISTRY, @models) {
251			my ($package, $model) = @$_;
252	root	1.7	if (${"$package\::VERSION"} > 0) {
253	root	1.8	if (eval "require $model") {
254			$MODEL = $model;
255			warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;
256			last;
257			}
258	root	1.2	}
259	root	1.1	}
260
261	root	1.2	unless ($MODEL) {
262			# try to load a model
263
264	root	1.8	for (@REGISTRY, @models) {
265			my ($package, $model) = @$_;
266			if (eval "require $model") {
267			$MODEL = $model;
268			warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
269			last;
270			}
271	root	1.2	}
272
273			$MODEL
274			or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";
275	root	1.1	}
276			}
277
278	root	1.2	@ISA = $MODEL;
279
280			my $class = shift;
281			$class->$AUTOLOAD (@_);
282	root	1.1	}
283
284	root	1.8	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
285
286			If you need to support another event library which isn't directly
287			supported by AnyEvent, you can supply your own interface to it by
288	root	1.11	pushing, before the first watcher gets created, the package name of
289	root	1.8	the event module and the package name of the interface to use onto
290			C<@AnyEvent::REGISTRY>. You can do that before and even without loading
291			AnyEvent.
292
293			Example:
294
295			push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
296
297	root	1.12	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
298			package/class when it finds the C<urxvt> package/module is loaded. When
299			AnyEvent is loaded and asked to find a suitable event model, it will
300			first check for the presence of urxvt.
301
302			The class should prove implementations for all watcher types (see
303			L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>
304			(Source code) and so on for actual examples, use C<perldoc -m
305			AnyEvent::Impl::Glib> to see the sources).
306	root	1.8
307	root	1.12	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
308			uses the above line as-is. An interface isn't included in AnyEvent
309	root	1.8	because it doesn't make sense outside the embedded interpreter inside
310			I<rxvt-unicode>, and it is updated and maintained as part of the
311			I<rxvt-unicode> distribution.
312
313	root	1.12	I<rxvt-unicode> also cheats a bit by not providing blocking access to
314			condition variables: code blocking while waiting for a condition will
315			C<die>. This still works with most modules/usages, and blocking calls must
316			not be in an interactive appliation, so it makes sense.
317
318	root	1.7	=head1 ENVIRONMENT VARIABLES
319
320			The following environment variables are used by this module:
321
322			C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
323			model gets used.
324
325	root	1.2	=head1 EXAMPLE
326
327			The following program uses an io watcher to read data from stdin, a timer
328			to display a message once per second, and a condvar to exit the program
329			when the user enters quit:
330
331			use AnyEvent;
332
333			my $cv = AnyEvent->condvar;
334
335			my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
336			warn "io event <$_[0]>\n"; # will always output <r>
337			chomp (my $input = <STDIN>); # read a line
338			warn "read: $input\n"; # output what has been read
339			$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
340			});
341
342			my $time_watcher; # can only be used once
343
344			sub new_timer {
345			$timer = AnyEvent->timer (after => 1, cb => sub {
346			warn "timeout\n"; # print 'timeout' about every second
347			&new_timer; # and restart the time
348			});
349			}
350
351			new_timer; # create first timer
352
353			$cv->wait; # wait until user enters /^q/i
354
355	root	1.5	=head1 REAL-WORLD EXAMPLE
356
357			Consider the L<Net::FCP> module. It features (among others) the following
358			API calls, which are to freenet what HTTP GET requests are to http:
359
360			my $data = $fcp->client_get ($url); # blocks
361
362			my $transaction = $fcp->txn_client_get ($url); # does not block
363			$transaction->cb ( sub { ... } ); # set optional result callback
364			my $data = $transaction->result; # possibly blocks
365
366			The C<client_get> method works like C<LWP::Simple::get>: it requests the
367			given URL and waits till the data has arrived. It is defined to be:
368
369			sub client_get { $_[0]->txn_client_get ($_[1])->result }
370
371			And in fact is automatically generated. This is the blocking API of
372			L<Net::FCP>, and it works as simple as in any other, similar, module.
373
374			More complicated is C<txn_client_get>: It only creates a transaction
375			(completion, result, ...) object and initiates the transaction.
376
377			my $txn = bless { }, Net::FCP::Txn::;
378
379			It also creates a condition variable that is used to signal the completion
380			of the request:
381
382			$txn->{finished} = AnyAvent->condvar;
383
384			It then creates a socket in non-blocking mode.
385
386			socket $txn->{fh}, ...;
387			fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
388			connect $txn->{fh}, ...
389			and !$!{EWOULDBLOCK}
390			and !$!{EINPROGRESS}
391			and Carp::croak "unable to connect: $!\n";
392
393	root	1.6	Then it creates a write-watcher which gets called whenever an error occurs
394	root	1.5	or the connection succeeds:
395
396			$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
397
398			And returns this transaction object. The C<fh_ready_w> callback gets
399			called as soon as the event loop detects that the socket is ready for
400			writing.
401
402			The C<fh_ready_w> method makes the socket blocking again, writes the
403			request data and replaces the watcher by a read watcher (waiting for reply
404			data). The actual code is more complicated, but that doesn't matter for
405			this example:
406
407			fcntl $txn->{fh}, F_SETFL, 0;
408			syswrite $txn->{fh}, $txn->{request}
409			or die "connection or write error";
410			$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
411
412			Again, C<fh_ready_r> waits till all data has arrived, and then stores the
413			result and signals any possible waiters that the request ahs finished:
414
415			sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
416
417			if (end-of-file or data complete) {
418			$txn->{result} = $txn->{buf};
419			$txn->{finished}->broadcast;
420	root	1.6	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
421	root	1.5	}
422
423			The C<result> method, finally, just waits for the finished signal (if the
424			request was already finished, it doesn't wait, of course, and returns the
425			data:
426
427			$txn->{finished}->wait;
428	root	1.6	return $txn->{result};
429	root	1.5
430			The actual code goes further and collects all errors (C<die>s, exceptions)
431			that occured during request processing. The C<result> method detects
432			wether an exception as thrown (it is stored inside the $txn object)
433			and just throws the exception, which means connection errors and other
434			problems get reported tot he code that tries to use the result, not in a
435			random callback.
436
437			All of this enables the following usage styles:
438
439			1. Blocking:
440
441			my $data = $fcp->client_get ($url);
442
443			2. Blocking, but parallelizing:
444
445			my @datas = map $_->result,
446			map $fcp->txn_client_get ($_),
447			@urls;
448
449			Both blocking examples work without the module user having to know
450			anything about events.
451
452			3a. Event-based in a main program, using any support Event module:
453
454			use Event;
455
456			$fcp->txn_client_get ($url)->cb (sub {
457			my $txn = shift;
458			my $data = $txn->result;
459			...
460			});
461
462			Event::loop;
463
464			3b. The module user could use AnyEvent, too:
465
466			use AnyEvent;
467
468			my $quit = AnyEvent->condvar;
469
470			$fcp->txn_client_get ($url)->cb (sub {
471			...
472			$quit->broadcast;
473			});
474
475			$quit->wait;
476
477	root	1.2	=head1 SEE ALSO
478
479	root	1.5	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.
480
481			Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.
482
483			Nontrivial usage example: L<Net::FCP>.
484	root	1.2
485			=head1
486
487			=cut
488
489			1
490	root	1.1