@SuppressWarnings("unsafeThreadSchedule")
  public static ScheduledFuture<?> submitHeartbeatWorker(
      final Runnable task, final long heartbeatIntervalMs) {
    CONTROL_FLOW_EXECUTOR.launchIfNeeded();
    return CONTROL_FLOW_EXECUTOR.scheduleWithFixedDelay(
        task,
        generateRandomInitialDelayMs(heartbeatIntervalMs),
        heartbeatIntervalMs,
        TimeUnit.MILLISECONDS);
  }
Downstream Data Flow Executor: execute poll task
iotdb-client/session/src/main/java/org/apache/iotdb/session/subscription/consumer/base/SubscriptionExecutorServiceManager.java