code: public void shutdown () {
          synchronized ( this.queueDiscoverers ) {
              for (MBeanDestinationDiscovererScheduler oneDiscovererScheduler : this.queueDiscoverers.values()) {
                  oneDiscovererScheduler.stop();
              }
          }
  
          synchronized ( this.brokerPollerMap ) {
              for ( ActiveMQBrokerPoller onePoller : this.brokerPollerMap.values() ) {
                  onePoller.stop();
              }
          }
  
          this.discovererExecutorService.shutdown();
      }
docs: TBD: make sure nothing new gets added during shutdown