* #aboutToAcquire(CycleDetectingLock)} and {@link #lockStateChanged(CycleDetectingLock)}.
   */
  // This is logically a Set, but an ArrayList is used to minimize the amount
  // of allocation done on lock()/unlock().
  private static final ThreadLocal<ArrayList<LockGraphNode>> acquiredLocks =
      new ThreadLocal<ArrayList<LockGraphNode>>() {
        @Override