private function checkCurlResult($code)
    {
        if ($code != CURLM_OK && $code != CURLM_CALL_MULTI_PERFORM) {
            throw new CurlException(isset($this->multiErrors[$code])
                ? "cURL error: {$code} ({$this->multiErrors[$code][0]}): cURL message: {$this->multiErrors[$code][1]}"
                : 'Unexpected cURL error: ' . $code
            );
        }
    }