void setCorePoolSize(final int corePoolSize) {
      if (isShutdown()) {
        synchronized (this) {
          if (isShutdown()) {
            this.corePoolSize = corePoolSize;
            return;
          }
        }
      }

      LOGGER.warn(
          "{} has been launched, set core pool size to {} will be ignored",
          this.name,
          corePoolSize);
    }
Downstream Data Flow Executor: execute poll task
iotdb-client/session/src/main/java/org/apache/iotdb/session/subscription/consumer/base/SubscriptionExecutorServiceManager.java