code: void setStartTime(long startTime) {
      //Making the assumption of passed startTime to be a positive
      //long value explicit.
      if (startTime > 0) {
        this.startTime = startTime;
      } else {
        //Using String utils to get the stack trace.
        LOG.error("Trying to set illegal startTime for task : " + taskid +
            ".Stack trace is : " +
            StringUtils.stringifyException(new Exception()));
      }
    }
docs: Set startTime of the task if start time is greater than zero.
  @param startTime start time