sg_size_t get_size() { return size_; }
sg_size_t get_used_size() { return used_size_; }
void decr_used_size(sg_size_t size) { used_size_ -= size; }
void incr_used_size(sg_size_t size) { used_size_ += size; }
private:
sg_size_t get_size() { return size_; }
sg_size_t get_used_size() { return used_size_; }
void decr_used_size(sg_size_t size) { used_size_ -= size; }
void incr_used_size(sg_size_t size) { used_size_ += size; }
private: