// implements Queue

    @Override
    public boolean offer(ReferenceEntry<K, V> entry) {
      // unlink
      connectWriteOrder(entry.getPreviousInWriteQueue(), entry.getNextInWriteQueue());

      // add to tail
      connectWriteOrder(head.getPreviousInWriteQueue(), entry);
      connectWriteOrder(entry, head);

      return true;
    }

    @CheckForNull
    @Override

    // implements Queue

    @Override
    public boolean offer(ReferenceEntry<K, V> entry) {
      // unlink
      connectWriteOrder(entry.getPreviousInWriteQueue(), entry.getNextInWriteQueue());

      // add to tail
      connectWriteOrder(head.getPreviousInWriteQueue(), entry);
      connectWriteOrder(entry, head);

      return true;
    }

    @CheckForNull
    @Override

        for (ReferenceEntry<?, ?> current : segment.writeQueue) {
          assertTrue(entries.add(current));
          if (prev != null) {
            assertSame(prev, current.getPreviousInWriteQueue());
            assertSame(prev.getNextInWriteQueue(), current);
            assertThat(prev.getWriteTime()).isAtMost(current.getWriteTime());
          }
          Object key = current.getKey();

        for (ReferenceEntry<?, ?> current : segment.writeQueue) {
          assertTrue(entries.add(current));
          if (prev != null) {
            assertSame(prev, current.getPreviousInWriteQueue());
            assertSame(prev.getNextInWriteQueue(), current);
            assertThat(prev.getWriteTime()).isAtMost(current.getWriteTime());
          }
          Object key = current.getKey();

      this.nextWrite = next;
    }

    private ReferenceEntry<K, V> previousWrite = nullEntry();

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

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

      this.nextWrite = next;
    }

    private ReferenceEntry<K, V> previousWrite = nullEntry();

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

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