sub spawn {
   ...
   ...
   my $pid = fork;

   unless (defined ($pid)) {
      warn "Cannot fork: $!" if $^W;
      return undef;
   }

   if($pid) {
      # parent
      my $errno;
      ${*$self}{exp_Pid} = $pid;
      close STAT_WTR;
      $self->close_slave();
      $self->set_raw() if $self->raw_pty and isatty($self);

      # now wait for child exec (eof due to close-on-exit)   
      # or exec error
      my $errstatus = sysread(STAT_RDR, $errno, 256);
      die "Cannot sync with child: $!" if not defined    
         $errstatus;
      close STAT_RDR;
      if ($errstatus) {
         $! = $errno+0;
         warn "Cannot exec(@cmd): $!\n" if $^W;
         return undef;
      }
   }
   else {
      # child
      close STAT_RDR;
   
      $self->make_slave_controlling_terminal();
      my $slv = $self->slave()
         or die "Cannot get slave: $!";
   
      $slv->set_raw() if $self->raw_pty;
      close($self);

      close(STDIN);
      open(STDIN,"<&". $slv->fileno())
         or die "Couldn't reopen STDIN for reading, $!\n";

      #
      # ---- execution stops/waits on the call below ----
      #
      close(STDOUT);

      open(STDOUT,">&". $slv->fileno())
         or die "Couldn't reopen STDOUT for writing, $!\n";
      close(STDERR);
      open(STDERR,">&". $slv->fileno())
         or die "Couldn't reopen STDERR for writing, $!\n";
   
      { exec(@cmd) };
      print STAT_WTR $!+0;
      die "Cannot exec(@cmd): $!\n";
   }
}