docs: public void sendMessageUntilStopCount(int stopCount) {
  
          // always send with valid data.
          for (int i = processedWorkerCount; i < workers.size(); ++i) {
              ActorRef worker = workers.get(i);
              try {
  
                  /**
                   * !!! This is a must; without this sleep; stuck occured at 5K.
                   * AKKA seems cannot handle too much too fast message send out.
                   */
                  Thread.sleep(1L);
  
              } catch (InterruptedException e) {
                  logger.error("sleep exception " + e + " details: ", e);
              }
  
              // send as if the sender is the origin manager; so reply back to
              // origin manager
              worker.tell(OperationWorkerMsgType.PROCESS_REQUEST, originalManager);
  
              processedWorkerCount++;
  
              if (processedWorkerCount > stopCount) {
                  return;
              }
  
              logger.debug("REQ_SENT: {} / {} taskId {}", 
                   processedWorkerCount, requestTotalCount, taskIdTrim);
  
          }// end for loop
      }