sub close_child_io () {
      Debug "SigCHLD: close iopair[1]";
      local * pipe_catch = sub ($) { Debug "Child already closed";
        $iopair[1] = $iopair[0] = undef; };
      my $tmp = $PathTree::iopair[1];
      $PathTree::iopair[1] = undef;
      $SIG{PIPE}=\&pipe_catch;
      close($tmp);
      $SIG{PIPE}='DEFAULT';
    };