code: function setUpdateListener() {
  
    signal.addListener(SIGNAL_KEY, function (err, params) {
  
      exports.update(params.domain, params.collection, function () {
  
        log.debug('The received signal to update the cache. ' + params.collection);
  
        rider.reset(params.collection);
      });
    });
  }
docs: 添加更新信号监听器，当该信号产生时会更新缓存内容