code: @Override
      public void close() {
          // unregister MBeans
          if(stats != null) {
              try {
                  if(this.jmxEnabled)
                      JmxUtils.unregisterMbean(getAggregateMetricName());
              } catch(Exception e) {}
              stats.close();
          }
          factory.close();
          queuedPool.close();
      }
docs: Permanently close the ClientRequestExecutor pool. Resources subsequently
  checked in will be destroyed.