* Deletes URL queue data and access result data, and clears the URL filter.
     * @param sessionId The session ID to clean up.
     */
    public void cleanup(final String sessionId) {
        // TODO transaction?
        urlQueueService.delete(sessionId);
        dataService.delete(sessionId);
        urlFilter.clear();
    }

    /**
     * Closes the crawler, releasing resources.

        CrawlerStatus currentStatus = CrawlerStatus.INITIALIZING;
        assertEquals(CrawlerStatus.INITIALIZING, currentStatus);

        // Transition to RUNNING
        currentStatus = CrawlerStatus.RUNNING;
        assertEquals(CrawlerStatus.RUNNING, currentStatus);

        // Transition to DONE
        currentStatus = CrawlerStatus.DONE;
        assertEquals(CrawlerStatus.DONE, currentStatus);

      including but not limited to software source code, documentation
      source, and configuration files.

      "Object" form shall mean any form resulting from mechanical
      transformation or translation of a Source form, including but
      not limited to compiled object code, generated documentation,
      and conversions to other media types.

      "Work" shall mean the work of authorship, whether in Source or

      including but not limited to software source code, documentation
      source, and configuration files.

      "Object" form shall mean any form resulting from mechanical
      transformation or translation of a Source form, including but
      not limited to compiled object code, generated documentation,
      and conversions to other media types.

      "Work" shall mean the work of authorship, whether in Source or