protected function process()
    {
        // Workaround for PHP Bug #61141.
        if (curl_multi_select($this->handle) === -1) {
            usleep(100);
        }

        do {
            $mrc = curl_multi_exec($this->handle, $active);
        } while ($mrc === CURLM_CALL_MULTI_PERFORM);

        return [$mrc, $active];
    }