MemoryPool* MemoryService::add_gen(Generation* gen,
                                   const char* name,
                                   bool is_heap,
                                   bool support_usage_threshold) {

  {- -------------------------------------------
  (1) GenerationPool のインスタンスを生成し, _pools_list に登録する.
      ---------------------------------------- -}

      MemoryPool::PoolType type = (is_heap ? MemoryPool::Heap : MemoryPool::NonHeap);
      GenerationPool* pool = new GenerationPool(gen, name, type, support_usage_threshold);
      _pools_list->append(pool);
      return (MemoryPool*) pool;
    }