crawlerStatusList.set(i, Constants.DONE);
                        final String sid = crawlerList.get(i).getCrawlerContext().getSessionId();
                        indexUpdater.addFinishedSessionId(sid);
                        activeCrawlerNum--;
                    }
                }
                ThreadUtil.sleep(crawlingExecutionInterval);
            }

        if (!finishCrawling) {
            if (logger.isInfoEnabled()) {
                logger.info("Stopping all crawler.");
            }
            forceStop();
        }
    }

    public void addFinishedSessionId(final String sessionId) {
        synchronized (finishedSessionIdList) {
            finishedSessionIdList.add(sessionId);
        }
    }

    private void deleteBySessionId(final String sessionId) {