private static final Logger logger = LogManager.getLogger(Crawler.class);

    /** Thread name for web and file system crawling process. */
    private static final String WEB_FS_CRAWLING_PROCESS = "WebFsCrawler";

    /** Thread name for data store crawling process. */
    private static final String DATA_CRAWLING_PROCESS = "DataStoreCrawler";

    /** Atomic flag indicating whether the crawler is currently running. */