synchronized (mutex) {
        return map(delegate().row(rowKey), mutex);
      }
    }

    @Override
    public Map<R, V> column(@ParametricNullness C columnKey) {
      synchronized (mutex) {
        return map(delegate().column(columnKey), mutex);
      }
    }

    @Override
    public Set<Cell<R, C, V>> cellSet() {
      synchronized (mutex) {