public static function socket_send($socket, $data)
    {
        $serialized = serialize($data);
        $hdr = pack('N', strlen($serialized));    // 4 byte length
        $buffer = $hdr . $serialized;
        $total = strlen($buffer);
        while (true) {
            $sent = socket_write($socket, $buffer);
            if ($sent === false) {
                // @todo handle error?
                //$error = socket_strerror(socket_last_error());
                break;
            }
            if ($sent >= $total) {
                break;
            }
            $total -= $sent;
            $buffer = substr($buffer, $sent);
        }
    }