*
   * <p>The benefits of creating our own queue are that (1) we can replace elements in the middle of
   * the queue as part of copyWriteEntry, and (2) the contains method is highly optimized for the
   * current model.
   */
  static final class WriteQueue<K, V> extends AbstractQueue<ReferenceEntry<K, V>> {
    final ReferenceEntry<K, V> head =
        new AbstractReferenceEntry<K, V>() {

          @Override

   *
   * <p>The benefits of creating our own queue are that (1) we can replace elements in the middle of
   * the queue as part of copyWriteEntry, and (2) the contains method is highly optimized for the
   * current model.
   */
  static final class WriteQueue<K, V> extends AbstractQueue<ReferenceEntry<K, V>> {
    final ReferenceEntry<K, V> head =
        new AbstractReferenceEntry<K, V>() {

          @Override