public Iterator<ReferenceEntry<K, V>> iterator() {
      return new AbstractSequentialIterator<ReferenceEntry<K, V>>(peek()) {
        @CheckForNull
        @Override
        protected ReferenceEntry<K, V> computeNext(ReferenceEntry<K, V> previous) {
          ReferenceEntry<K, V> next = previous.getNextInWriteQueue();
          return (next == head) ? null : next;
        }
      };
    }
  }

  /**