while(@array) {
  while (@array2) {
    my $item = shift @array2;
    my $result = do_stuff2($item);
    if ($result == 1) {
      push @array, $item
    } elsif ($result == 2) {
      push @array2, $item
    } # else done with item, discard.
  }
  my $item = shift @array;
  my $result = do_stuff($item);
  if ($result == 1) {
    push @array, $item
  } elsif ($result == 2) {
    push @array2, $item
  } # else done with item, discard.
}