'Starts downloading the scriptors if we haven\'t started already.'

def start(self):

    with self._downloader_thread_lock:
        if (self._downloader_thread is None):
            self._downloader_thread = threading.Thread(name='Descriptor    Query', target=self._download_descriptors, args=(self.retries,))
            self._downloader_thread.setDaemon(True)
            self._downloader_thread.start()
