code: public void shutdown() {
      this.shouldRun = false;
      this.namespaceSliceDUMap.clear();
      if(this.refreshUsed != null) {
        this.refreshUsed.interrupt();
        try {
          this.refreshUsed.join();
          this.refreshUsed = null;
        } catch (InterruptedException ie) {
        }
      }
    }
docs: Shut down the refreshing thread.