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=cut
 
=back
 
=head1 METHODS
 
=over 4
 
=item timeout SECONDS, [ KEY, [, DEFAULT ] ]
 
Set a timer for N seconds to provide "default" value as a value, defaults to
`undef`.  This can be used to ensure that blackboard workflows do not reach a
dead-end if a required value is difficult to obtain.
 
=cut
 
sub timeout {
    my ($self, $seconds, $key, $default) = @_;
 
    $key = [ $key ] unless (ref $key eq "ARRAY");
 
    unless ($self->has($key)) {
        my $guard = AnyEvent->timer(
            after => $seconds,
            cb    => sub {
                unless ($self->has($key)) {
                    $self->put($_ => $default) for @$key;
                }
            }
        );
 
        # Cancel the timer if we find the object first (otherwise this is a NOOP).
        $self->_watch($key, sub { undef $guard });
    }
}
 
=item watch KEYS, WATCHER [, KEYS, WATCHER ]
 
=item watch KEY, WATCHER [, KEYS, WATCHER ]
 
Overrides L<Async::Blackboard> only for the purpose of adding a timeout.