code: synchronized void setJobPriority(JobID jobId, JobPriority priority) {
      JobInProgress job = jobs.get(jobId);
      if (job != null) {
        synchronized (taskScheduler) {
          JobStatus oldStatus = (JobStatus)job.getStatus().clone();
          job.setPriority(priority);
          JobStatus newStatus = (JobStatus)job.getStatus().clone();
          JobStatusChangeEvent event =
            new JobStatusChangeEvent(job, EventType.PRIORITY_CHANGED, oldStatus,
                                     newStatus);
          updateJobInProgressListeners(event);
        }
      } else {
        LOG.warn("Trying to change the priority of an unknown job: " + jobId);
      }
    }
docs: Change the run-time priority of the given job.
  @param jobId job id
  @param priority new {@link JobPriority} for the job