private function executeHandles()
    {
        // The first curl_multi_select often times out no matter what, but is usually required for fast transfers
        $selectTimeout = 0.001;
        $active = false;
        do {
            while (($mrc = curl_multi_exec($this->multiHandle, $active)) == CURLM_CALL_MULTI_PERFORM);
            $this->checkCurlResult($mrc);
            $this->processMessages();
            if ($active && curl_multi_select($this->multiHandle, $selectTimeout) === -1) {
                // Perform a usleep if a select returns -1: https://bugs.php.net/bug.php?id=61141
                usleep(150);
            }
            $selectTimeout = $this->selectTimeout;
        } while ($active);
    }