public CleanupMapTask(MapMakerInternalMap<?, ?, ?, ?> map) {
      this.mapReference = new WeakReference<>(map);
    }

    @Override
    public void run() {
      MapMakerInternalMap<?, ?, ?, ?> map = mapReference.get();
      if (map == null) {
        throw new CancellationException();
      }

      for (Segment<?, ?, ?, ?> segment : map.segments) {
        segment.runCleanup();
      }