code: synchronized public Collection<TaskTrackerStatus> blacklistedTaskTrackers() {
      Collection<TaskTrackerStatus> blacklistedTrackers =
        new ArrayList<TaskTrackerStatus>();
      synchronized (taskTrackers) {
        for (TaskTracker tt : taskTrackers.values()) {
          TaskTrackerStatus status = tt.getStatus();
          if (faultyTrackers.isBlacklisted(status.getHost())) {
            blacklistedTrackers.add(status);
          }
        }
      }
      return blacklistedTrackers;
    }
docs: lock" is under JobTracker lock to avoid deadlocks.