OpenMW/components/misc/objectpool.hpp

#ifndef OPENMW_COMPONENTS_MISC_OBJECTPOOL_H
#define OPENMW_COMPONENTS_MISC_OBJECTPOOL_H

#include <deque>
#include <memory>
#include <vector>

namespace Misc
{
    template <class T>
    class ObjectPool;

    template <class T>
    class ObjectPtrDeleter
    {
    public:
        ObjectPtrDeleter(std::nullptr_t)
            : mPool(nullptr)
        {
        }

        ObjectPtrDeleter(ObjectPool<T>& pool)
            : mPool(&pool)
        {
        }

        void operator()(T* object) const { mPool->recycle(object); }

    private:
        ObjectPool<T>* mPool;
    };

    template <class T>
    struct ObjectPtr final : std::unique_ptr<T, ObjectPtrDeleter<T>>
    {
        using std::unique_ptr<T, ObjectPtrDeleter<T>>::unique_ptr;
        using std::unique_ptr<T, ObjectPtrDeleter<T>>::operator=;

        ObjectPtr()
            : ObjectPtr(nullptr)
        {
        }

        ObjectPtr(std::nullptr_t)
            : std::unique_ptr<T, ObjectPtrDeleter<T>>(nullptr, nullptr)
        {
        }
    };

    template <class T>
    class ObjectPool
    {
        friend class ObjectPtrDeleter<T>;

    public:
        ObjectPool()
            : mObjects(std::make_unique<std::deque<T>>())
        {
        }

        ObjectPtr<T> get()
        {
            T* object;

            if (!mUnused.empty())
            {
                object = mUnused.back();
                mUnused.pop_back();
            }
            else
            {
                mObjects->emplace_back();
                object = &mObjects->back();
            }

            return ObjectPtr<T>(object, ObjectPtrDeleter<T>(*this));
        }

    private:
        std::unique_ptr<std::deque<T>> mObjects;
        std::vector<T*> mUnused;

        void recycle(T* object) { mUnused.push_back(object); }
    };
}

#endif