提高C++性能的编程技术 6.1,6.2读书笔记

对于内存池这一块接触都有几年的时间了,看了很多代码也不明白,真是差啊,今天把这本书的代码抄了一遍,代码在Linux下编译有些问题

1.全局函数

关于static_cast在gcc 4.1.2上使用有误

#include <iostream>

class Rational
{
    public:
    Rational (int a = 0, int b = 1) : n(a),d(b) {}

    private:
        int n;
        int d;
};


int main()
{
    Rational *array[1000];

    for (int j = 0; j < 500; j++)
    {
        for (int i = 0; i < 1000; i++)
        {
            array[i] = new Rational(i);
        }
        for (int i = 0; i < 1000; i++)
        {
            delete array[i];
        }
    }
    return 0;
}

2 .专用Rational 内存管理器

1.依然是static_cast的使用

#include <iostream>


class NextOnFreeList
{
    public:
        NextOnFreeList *next;
};

class Rational
{
    public:
    Rational (int a = 0, int b = 1) : n(a),d(b) {}

    inline void *operator new(size_t size);
    inline void operator delete(void *doomed,size_t size);

    static void newMemPool() { expandTheFreeList();}
    static void deleteMemPool();

    private:
        static NextOnFreeList *freeList;
        static void expandTheFreeList();
        enum { EXPANSION_SIZE = 32};

        int n; //numerator
        int d; //denominator
};

inline size_t mymax(size_t a,size_t b) { return a > b ? a: b;}

inline
void* Rational::operator new(size_t size)
{
    if (0 == freeList)
    {
        expandTheFreeList();
    }
    NextOnFreeList *head = freeList;
    freeList = head->next;

    return head;
}

inline
void Rational::operator delete(void* doomed, size_t size)
{
    NextOnFreeList *head = static_cast<NextOnFreeList *> (doomed);

    head->next = freeList;
    freeList = head;
}

void Rational::expandTheFreeList()
{
    size_t size = mymax(sizeof(Rational),sizeof(NextOnFreeList *));

    NextOnFreeList *runner = static_cast<NextOnFreeList *> (static_cast<void *>(new char[size]));

    freeList = runner;
    for (int i = 0; i < EXPANSION_SIZE; i++)
    {
        runner->next = static_cast<NextOnFreeList *> (static_cast<void *>(new char[size]));
        runner = runner->next;
    }
    runner->next = NULL;
}

NextOnFreeList* Rational::freeList = NULL;
int main()
{
    Rational *array[1000];

    for (int j = 0; j < 500; j++)
    {
        for (int i = 0; i < 1000; i++)
        {
            array[i] = new Rational(i);
        }
        for (int i = 0; i < 1000; i++)
        {
            delete array[i];
        }
    }
    return 0;
}

我所使用的系统是虚拟机，经过测试第二个是第一个效率的2倍

使用Tcmalloc的效率提升多少没有实验