implements CycleDetectingLock {

    // These ReadLock/WriteLock implementations shadow those in the
    // ReentrantReadWriteLock superclass. They are simply wrappers around the
    // internal Sync object, so this is safe since the shadowed locks are never
    // exposed or used.
    private final CycleDetectingReentrantReadLock readLock;
    private final CycleDetectingReentrantWriteLock writeLock;