在高效C++編程中看到一個不錯的內存池實現方案，這里共享下，大家看看有什么不足。
代碼很簡單，如下：

template<typename?T>
class?CMemoryPool
{
????public:
????????enum?{?EXPANSION_SIZE?=?32};

????????CMemoryPool(unsigned?int?nItemCount?=?EXPANSION_SIZE)
????????{
????????????ExpandFreeList(nItemCount);
????????}
????????
????????~CMemoryPool()
????????{
????????????//free?all?memory?in?the?list
????????????CMemoryPool<T>*?pNext?=?NULL;
????????????for(pNext?=?m_pFreeList;?pNext?!=?NULL;?pNext?=?m_pFreeList)
????????????{
????????????????m_pFreeList?=?m_pFreeList->m_pFreeList;
????????????????delete?[](char*)pNext;
????????????}
????????}

????????void*?Alloc(unsigned?int?/*size*/)
????????{
????????????if(m_pFreeList?==?NULL)
????????????{
????????????????ExpandFreeList();
????????????}
????????????
????????????//get?free?memory?from?head
????????????CMemoryPool<T>*?pHead?=?m_pFreeList;
????????????m_pFreeList?=?m_pFreeList->m_pFreeList;
????????????return?pHead;
????????}

????????void?Free(void*?p)
????????{
????????????//push?the?free?memory?back?to?list
????????????CMemoryPool<T>*?pHead?=?static_cast<CMemoryPool<T>*>(p);
????????????pHead->m_pFreeList?=?m_pFreeList;
????????????m_pFreeList?=?pHead;
????????}

????protected:
????????//allocate?memory?and?push?to?the?list
????????void?ExpandFreeList(unsigned?nItemCount?=?EXPANSION_SIZE)
????????{
????????????unsigned?int?nSize?=?sizeof(T)?>?sizeof(CMemoryPool<T>*)???sizeof(T)?:?sizeof(CMemoryPool<T>*);
????????????CMemoryPool<T>*?pLastItem?=?static_cast<CMemoryPool<T>*>(static_cast<void*>(new?char[nSize]));
????????????m_pFreeList?=?pLastItem;
????????????for(int?i=0;?i<nItemCount-1;?++i)
????????????{
????????????????pLastItem->m_pFreeList?=?static_cast<CMemoryPool<T>*>(static_cast<void*>(new?char[nSize]));
????????????????pLastItem?=?pLastItem->m_pFreeList;
????????????}

????????????pLastItem->m_pFreeList?=?NULL;
????????}

????private:
????????CMemoryPool<T>*?m_pFreeList;
};

它的實現思想就是每次從List的頭上取內存， 如果取不到則重新分配一定數量； 用完后把內存放回List頭部，這樣的話效率很高，因為每次List上可以取到的話，肯定是空閑的內存。

當然上面的代碼只是針對單線程的，要支持多線程的話也很簡單，外面加一層就可以了，
代碼如下：

class?CCriticalSection
{
public:
????CCriticalSection()
????{
????????InitializeCriticalSection(&m_cs);
????}

????~CCriticalSection()
????{
????????DeleteCriticalSection(&m_cs);
????}

????void?Lock()
????{
????????EnterCriticalSection(&m_cs);?
????}

????void?Unlock()
????{
????????LeaveCriticalSection(&m_cs);
????}

protected:
????CRITICAL_SECTION?m_cs;
};

template<typename?POOLTYPE,?typename?LOCKTYPE>
class?CMTMemoryPool
{
????public:
????????void*?Alloc(unsigned?int?size)
????????{
????????????void*?p?=?NULL;
????????????m_lock.Lock();
????????????p?=?m_pool.Alloc(size);
????????????m_lock.Unlock();

????????????return?p;
????????}

????????void?Free(void*?p)
????????{
????????????m_lock.Lock();
????????????m_pool.Free(p);
????????????m_lock.Unlock();????
????????}

????private:
????????POOLTYPE?m_pool;
????????LOCKTYPE?m_lock;
};

這是我的測試代碼：

#include?<iostream>
#include?<windows.h>

using?namespace?std;

#include?"MemoryPool.h"
#include?"MTMemoryPool.h"

class?CTest
{
public:
????int?m_n;
????int?m_n1;

????void*?operator?new(size_t?size)
????{
????????void*?p?=?s_pool->Alloc(size);
????????return?p;
????}

????void?operator?delete(void*?p,?size_t?size)
????{
????????s_pool->Free(p);
????}

????static?void?NewPool()
????{
????????//s_pool?=?new?CMemoryPool<CTest>;
????????s_pool?=?new?CMTMemoryPool<CMemoryPool<CTest>,?CCriticalSection>;
????}

????static?void?DeletePool()
????{
????????delete?s_pool;
????????s_pool?=?NULL;
????}
????
????//static?CMemoryPool<CTest>*?s_pool;
????static?CMTMemoryPool<CMemoryPool<CTest>,?CCriticalSection>*?s_pool;
};

//CMemoryPool<CTest>*?CTest::s_pool?=?NULL;
CMTMemoryPool<CMemoryPool<CTest>,?CCriticalSection>*?CTest::s_pool?=?NULL;

void?testFun()
{
????int?i;
????const?int?nLoop?=?10;
????const?int?nCount?=?10000;
????
????for(int?j?=?0;?j<nLoop;?++j)
????{
????????typedef?CTest*?LPTest;
????????LPTest?arData[nCount];
????????for(i=0;i?<nCount;?++i)
????????{
????????????arData[i]?=?new?CTest;
????????}

????????for(i=0;i?<nCount;?++i)
????????{
????????????delete?arData[i];
????????}
????}
}

int?main(int?argc,?char*?argv[])
{
????{
????????unsigned?int?dwStartTickCount?=?GetTickCount();

????????CTest::NewPool();

????????testFun();
????????
????????CTest::DeletePool();
????????
????????cout?<<?"total?cost"?<<?GetTickCount()?-?dwStartTickCount?<<?endl;
????}


????system("pause");

????return?0;
}

在我機器上測試結果比系統默認的CRT實現高效N倍。

轉載自:

http://www.cppblog.com/weiym/archive/2012/05/05/173785.html

轉載于:https://blog.51cto.com/7044041/1856098

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