private void sleepUninterruptibly(int delayMillis) {
    try {
      Thread.sleep(delayMillis);
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
    }
  }
Issues a heartbeat request to the coordinator
@return the corresponding {@link ContainerHeartbeatResponse}.
samza-core/src/main/java/org/apache/samza/container/ContainerHeartbeatClient.java