code: public static void cancelJob(String jobHandle) throws NoSuchObjectException {
      checkNonEmpty(jobHandle, "jobHandle");
      Key key = KeyFactory.createKey(JobRecord.DATA_STORE_KIND, jobHandle);
      JobRecord jobRecord = backEnd.queryJob(key, InflationType.NONE);
      CancelJobTask cancelJobTask = new CancelJobTask(key, jobRecord.getQueueSettings());
      try {
        backEnd.enqueue(cancelJobTask);
      } catch (TaskAlreadyExistsException e) {
        // OK. Some other thread has already enqueued this task.
      }
    }
docs: Sends cancellation request to the root job.
  
  @param jobHandle The handle of a job
  @throws NoSuchObjectException If a JobRecord with the given handle cannot
  be found in the data store.