while (1) {
      $mtime=(stat($data_file . $$))[9];
      # drop out of the loop if the file hasn't
      # changed in 5 minutes (perhaps longer
      # for a wan connection ?)
      last if (time > $mtime + 300);
  }

##</code><code>##

my $old_mtime = (stat($file))[9];
if (time <= $old_mtime + 300) {
  while (1) {
      sleep 300;
      my $new_mtime=(stat($file))[9];
      last if $old_mtime == $new_mtime;
      $old_mtime = $new_mtime;
  }
}