...
    my $session = get_session_id();
    my $cache   = get_cache_handle();
    $cache->set( $session, [ 0, "" ] );           # no data yet
    my $background = go_background( $session );
    ...
    if( not $background->alive ) {
        if( my $data  = $cache->get( $session ) ){
           return show_results( $data );
        }
    }
    ...



sub get_cache_handle {
  use Cache::FileCache;
  return Cache::FileCache->new
  ...
}