@Override
    public void run() {
      // shutdown executors
      CONTROL_FLOW_EXECUTOR.shutdown();
      UPSTREAM_DATA_FLOW_EXECUTOR.shutdown();
      DOWNSTREAM_DATA_FLOW_EXECUTOR.shutdown();
    }
Downstream Data Flow Executor: execute poll task
iotdb-client/session/src/main/java/org/apache/iotdb/session/subscription/consumer/base/SubscriptionExecutorServiceManager.java