/** Returns the previous entry in the write queue. */
  ReferenceEntry<K, V> getPreviousInWriteQueue();

  /** Sets the previous entry in the write queue. */
  void setPreviousInWriteQueue(ReferenceEntry<K, V> previous);

  /** Returns the previous entry in the write queue. */
  ReferenceEntry<K, V> getPreviousInWriteQueue();

  /** Sets the previous entry in the write queue. */
  void setPreviousInWriteQueue(ReferenceEntry<K, V> previous);

    previous.setNextInWriteQueue(next);
    next.setPreviousInWriteQueue(previous);
  }

  // Guarded By Segment.this
  static <K, V> void nullifyWriteOrder(ReferenceEntry<K, V> nulled) {
    ReferenceEntry<K, V> nullEntry = nullEntry();
    nulled.setNextInWriteQueue(nullEntry);
    nulled.setPreviousInWriteQueue(nullEntry);
  }

  /**

    previous.setNextInWriteQueue(next);
    next.setPreviousInWriteQueue(previous);
  }

  // Guarded By Segment.this
  static <K, V> void nullifyWriteOrder(ReferenceEntry<K, V> nulled) {
    ReferenceEntry<K, V> nullEntry = nullEntry();
    nulled.setNextInWriteQueue(nullEntry);
    nulled.setPreviousInWriteQueue(nullEntry);
  }

  /**

    @Override
    public ReferenceEntry<K, V> getPreviousInWriteQueue() {
      return previousWrite;
    }

    @Override
    public void setPreviousInWriteQueue(ReferenceEntry<K, V> previous) {
      this.previousWrite = previous;
    }
  }

  static class DummyValueReference<K, V> implements ValueReference<K, V> {
    private @Nullable V value;

    @Override
    public ReferenceEntry<K, V> getPreviousInWriteQueue() {
      return previousWrite;
    }

    @Override
    public void setPreviousInWriteQueue(ReferenceEntry<K, V> previous) {
      this.previousWrite = previous;
    }
  }

  static class DummyValueReference<K, V> implements ValueReference<K, V> {
    private @Nullable V value;