*/
    LockGraphNode getLockGraphNode();

    /**
     * @return {@code true} if the current thread has acquired this lock.
     */
    boolean isAcquiredByCurrentThread();
  }

  /**
   * A {@code LockGraphNode} associated with each lock instance keeps track of the directed edges in
   * the lock acquisition graph.
   */
  private static final class LockGraphNode {