{
	package WidgetPool;

	my %widget_state;

	sub init
	{
		@widget_state{ @_ } = (0) x @_;
	}

	sub set_running
	{
		@widget_state{ @_ } = (1) x @_;
	}

	sub replace
	{
		my( $out, $in ) = @_;
		$widget_state{$out} = 0;
		$widget_state{$in} = 1;
	}

	sub is_running
	{
		my( $w ) = @_;
		$widget_state{$w}
	}
}

my @widgets = qw( foo bar baz blort blah plugh xyzzy arfle barfle gloop );
my @running = qw( foo bar baz );

WidgetPool::init( @widgets );
WidgetPool::set_running( @running );

# stand down 'foo', stand up $w:
WidgetPool::is_running('foo') or croak "Um, 'foo' not running.\n";
WidgetPool::replace( 'foo', $w );