}
  }

  private final class CycleDetectingReentrantReadLock extends ReentrantReadWriteLock.ReadLock {

    @Weak final CycleDetectingReentrantReadWriteLock readWriteLock;

    CycleDetectingReentrantReadLock(CycleDetectingReentrantReadWriteLock readWriteLock) {
      super(readWriteLock);
      this.readWriteLock = readWriteLock;
    }

    @Override
    public void lock() {