<T> List<Future<T>> invokeAll(
        final Collection<? extends Callable<T>> tasks, final long timeoutMs)
        throws InterruptedException {
      if (!isShutdown()) {
        synchronized (this) {
          if (!isShutdown()) {
            return this.executor.invokeAll(tasks, timeoutMs, TimeUnit.MILLISECONDS);
          }
        }
      }

      LOGGER.warn("{} has not been launched, ignore invoke all tasks", this.name);
      return null;
    }
Downstream Data Flow Executor: execute poll task
iotdb-client/session/src/main/java/org/apache/iotdb/session/subscription/consumer/base/SubscriptionExecutorServiceManager.java