template<class T, int kPageItems>
class ItemAlloc
{
public:
    struct DataItem
    {
        DataItem* next;
        void* reserve[3];
        T data[kPageItems];
    };
public:
    ItemAlloc() :m_pages(0), first(nullptr), freefirst(nullptr), m_items(0), m_maxitems(0)
    {
        allocPage();
    }
public:
    void* allocPage()
    {
        m_pages++;
        DataItem* tmp = (DataItem *)new char[sizeof(DataItem)];

        //initial
        for (int i = 0; i < kPageItems - 1; i++)
        {
            *(void**)(tmp->data+i) = tmp->data+(i + 1);
        }
        *(void**)&tmp->data[kPageItems - 1] = freefirst;
        tmp->next = first;

        first = tmp;
        freefirst = &tmp->data[0];
        return tmp;
    }

    ~ItemAlloc()
    {
        if (!first)return;
        DataItem* p = first;
        DataItem* next = first->next;
        while (p)
        {
            ::free(p);
            if (!next)break;
            p = next;
            next = p->next;
        }
    }

    T* alloc()
    {
        if (!freefirst)allocPage();
        T* p = freefirst;
        freefirst = (T*)*(void**)p;
        m_items++;
        if(m_items > m_maxitems) m_maxitems++;
        m_ttlitems++;
        return p;
    }
    void destroy(T* p)
    {
        if(p)p->~T();
        free(p);
    }
    void free(void* p )
    {
        m_items--;
        *(void**)p = freefirst;
        freefirst = (T*)p;
    }
public:
    DataItem* first;
    T* freefirst;
public:
    int m_pages;
    int m_items;
    int m_maxitems;
    int m_ttlitems;
};