code: private List<TaskTrackerAction> getJobsForCleanup(String taskTracker) {
      Set<JobID> jobs = null;
      synchronized (trackerToJobsToCleanup) {
        jobs = trackerToJobsToCleanup.remove(taskTracker);
      }
      if (jobs != null) {
        // prepare the actions list
        List<TaskTrackerAction> killList = new ArrayList<TaskTrackerAction>();
        for (JobID killJobId : jobs) {
          killList.add(new KillJobAction(killJobId));
          LOG.debug(taskTracker + " -> KillJobAction: " + killJobId);
        }
  
        return killList;
      }
      return null;
    }
docs: A tracker wants to know if any job needs cleanup because the job completed.