* </p>
 * <ul>
 *   <li>Before processing a URL ({@link #delayBeforeProcessing()})</li>
 *   <li>After processing a URL ({@link #delayAfterProcessing()})</li>
 *   <li>When there are no URLs in the queue ({@link #delayAtNoUrlInQueue()})</li>
 *   <li>While waiting for new URLs to be added to the queue ({@link #delayForWaitingNewUrl()})</li>
 * </ul>
 *
 * <p>

            ThreadUtil.sleep(delayMillisAfterProcessing);
        }
    }

    /**
     * Delays when no URL is in the queue.
     */
    @Override
    protected void delayAtNoUrlInQueue() {
        if (delayMillisAtNoUrlInQueue > 0) {
            ThreadUtil.sleep(delayMillisAtNoUrlInQueue);
        }
    }

    /**
     * Delays before processing a URL.
     */
    @Override