private function executeHandles(&$active, &$mrc, $timeout = 1)
    {
        do {
            $mrc = curl_multi_exec($this->multiHandle, $active);
        } while ($mrc == CURLM_CALL_MULTI_PERFORM && $active);
        $this->checkCurlResult($mrc);

        // @codeCoverageIgnoreStart
        // Select the curl handles until there is any activity on any of the open file descriptors
        // See https://github.com/php/php-src/blob/master/ext/curl/multi.c#L170
        if ($active && $mrc == CURLM_OK && curl_multi_select($this->multiHandle, $timeout) == -1) {
            // Perform a usleep if a previously executed select returned -1
            // @see https://bugs.php.net/bug.php?id=61141
            usleep(100);
        }
        // @codeCoverageIgnoreEnd
    }