this.stack = new ArrayDeque<>();
      stack.addLast(expand(root));
    }

    @Override
    @CheckForNull
    protected T computeNext() {
      while (!stack.isEmpty()) {
        PostOrderNode<T> top = stack.getLast();
        if (top.childIterator.hasNext()) {
          T child = top.childIterator.next();
          stack.addLast(expand(child));
        } else {
          stack.removeLast();

  /**
   * Forces the segment containing the given {@code key} to expand (see {@link Segment#expand()}).
   */
  static <K, V> void forceExpandSegment(Cache<K, V> cache, K key) {
    checkNotNull(cache);
    checkNotNull(key);
    LocalCache<K, V> map = toLocalCache(cache);
    int hash = map.hash(key);
    Segment<K, V> segment = map.segmentFor(hash);
    segment.expand();
  }

  /**

          try {
            if (cells == as) { // Expand table unless stale
              Cell[] rs = new Cell[n << 1];
              for (int i = 0; i < n; ++i) rs[i] = as[i];
              cells = rs;
            }
          } finally {
            busy = 0;
          }
          collide = false;
          continue; // Retry with expanded table
        }
        h ^= h << 13; // Rehash

    oldValueRef.clear();
    assertNull(segment.put(key, hash, newValue, true));
    assertEquals(1, segment.count);
    assertSame(newValue, segment.get(key, hash));
  }

  public void testSegmentPut_expand() {
    MapMakerInternalMap<Object, Object, ?, ?> map =
        makeMap(createMapMaker().concurrencyLevel(1).initialCapacity(1));
    Segment<Object, Object, ?, ?> segment = map.segments[0];

    oldValueRef.clear();
    assertNull(segment.put(key, hash, newValue, true));
    assertEquals(1, segment.count);
    assertSame(newValue, segment.get(key, hash));
  }

  public void testSegmentPut_expand() {
    MapMakerInternalMap<Object, Object, ?, ?> map =
        makeMap(createMapMaker().concurrencyLevel(1).initialCapacity(1));
    Segment<Object, Object, ?, ?> segment = map.segments[0];

  /**
   * Forces the segment containing the given {@code key} to expand (see {@link Segment#expand()}).
   */
  static <K, V> void forceExpandSegment(Cache<K, V> cache, K key) {
    checkNotNull(cache);
    checkNotNull(key);
    LocalCache<K, V> map = toLocalCache(cache);
    int hash = map.hash(key);
    Segment<K, V> segment = map.segmentFor(hash);
    segment.expand();
  }

  /**

          try {
            if (cells == as) { // Expand table unless stale
              Cell[] rs = new Cell[n << 1];
              for (int i = 0; i < n; ++i) rs[i] = as[i];
              cells = rs;
            }
          } finally {
            busy = 0;
          }
          collide = false;
          continue; // Retry with expanded table
        }
        h ^= h << 13; // Rehash

          try {
            if (cells == as) { // Expand table unless stale
              Cell[] rs = new Cell[n << 1];
              for (int i = 0; i < n; ++i) rs[i] = as[i];
              cells = rs;
            }
          } finally {
            busy = 0;
          }
          collide = false;
          continue; // Retry with expanded table
        }
        h ^= h << 13; // Rehash

        this.count = newCount; // write-volatile
        return null;
      } finally {
        unlock();
      }
    }

    /** Expands the table if possible. */
    @GuardedBy("this")
    void expand() {
      AtomicReferenceArray<E> oldTable = table;
      int oldCapacity = oldTable.length();
      if (oldCapacity >= MAXIMUM_CAPACITY) {
        return;
      }

    oldValueRef.clear();
    assertNull(segment.put(key, hash, newValue, true));
    assertEquals(1, segment.count);
    assertSame(newValue, segment.get(key, hash));
  }

  public void testSegmentPut_expand() {
    LocalCache<Object, Object> map =
        makeLocalCache(createCacheBuilder().concurrencyLevel(1).initialCapacity(1));
    Segment<Object, Object> segment = map.segments[0];