void ensureOpen( int timeout ) throws IOException {
        closeTimeout = 0;
        if( SO_TIMEOUT != 0 ) {
            closeTimeout = Math.max( SO_TIMEOUT, timeout );
        }
        // If socket is still good, the new closeTimeout will
        // be ignored; see tryClose comment.
        if( socket == null ) {
            socket = new DatagramSocket( lport, laddr );