*
     * @param sessionId the crawling session identifier
     * @return list of URL queue entries for processing
     */
    @Override
    protected List<OpenSearchUrlQueue> fetchUrlQueueList(final String sessionId) {
        final CrawlingConfigHelper crawlingConfigHelper = ComponentUtil.getCrawlingConfigHelper();
        final CrawlingConfig crawlingConfig = crawlingConfigHelper.get(sessionId);

            synchronized (queueHolder) {
                urlQueue = waitingQueue.poll();
                if (urlQueue == null) {
                    final List<OpenSearchUrlQueue> urlQueueList = fetchUrlQueueList(sessionId);
                    if (urlQueueList.isEmpty()) {
                        return null;
                    }
                    if (logger.isDebugEnabled()) {