/** @return the {@link LockGraphNode} associated with this lock. */
    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 class LockGraphNode {