code: public synchronized void suspended(ServerActivityCallback requestCountListener) {
          this.paused = true;
          listenerUpdater.set(this, requestCountListener);
  
          if (activeRequestCountUpdater.get(this) == 0) {
              if (listenerUpdater.compareAndSet(this, requestCountListener, null)) {
                  requestCountListener.done();
              }
          }
      }
docs: Pause the controller. All existing requests will have a chance to finish, and once all requests are
  finished the provided listener will be invoked.
  <p/>
  While the container is paused no new requests will be accepted.
  
  @param requestCountListener The listener that will be notified when all requests are done