code: def run_next(self):
          
          while 1:
              (op, obj) = self.work_queue.get()
              if op is STOP_SIGNAL:
                  return
              try:
                  (job_id, command_line) = obj
                  try:
                      os.remove(self._job_file(job_id, JOB_FILE_COMMAND_LINE))
                  except Exception:
                      log.exception("Running command but failed to delete - command may rerun on Pulsar boot.")
                  # _run will not do anything if job has been cancelled.
                  self._run(job_id, command_line, background=False)
              except Exception:
                  log.warn("Uncaught exception running job with job_id %s" % job_id)
                  traceback.print_exc()
docs: Run the next item in the queue (a job waiting to run).