Hash outside the sub routine:
   %hash = (); // for storing drift line
   %printable_data = (); // some data are there
   $terminal = new Term::Screen;
   $screen_height = $terminal->row;
   The thread subroutine:
   sub refresher 
   {
      $terminal->at(0,0);
      $terminal->clreos();
      foreach (keys %printable_data) {
            $term->puts($_);
            .
            .
            .
            if ( $curser_position >= $screen_height )
                {
                  $hash{$key} = $_;
                }
      }
   }