synchronized (urlQueueList) {
            final List<UrlQueueImpl<Long>> targetList = new ArrayList<>();
            for (final UrlQueueImpl<Long> urlQueue : newUrlQueueList) {
                if (isNewUrl(urlQueue, urlQueueList)) {
                    targetList.add(urlQueue);
                }
            }
            urlQueueList.addAll(targetList);
        }

    }

    /**