public static <T> List<Future<T>> submitMultiplePollTasks(
      final Collection<? extends Callable<T>> tasks, final long timeoutMs)
      throws InterruptedException {
    DOWNSTREAM_DATA_FLOW_EXECUTOR.launchIfNeeded();
    return DOWNSTREAM_DATA_FLOW_EXECUTOR.invokeAll(tasks, timeoutMs);
  }
Downstream Data Flow Executor: execute poll task
iotdb-client/session/src/main/java/org/apache/iotdb/session/subscription/consumer/base/SubscriptionExecutorServiceManager.java