内存池的C++实现。可能还有小bug。欢迎指正

　　阅读: 1009 评论: 2 作者: mini数据库 发表于 2009-04-21 13:52 原文链接

最近在学习c++程序性能优化，读到内存池部分。自己动手写了一个，小小测试了一下应该没有问题。

内存块MemoryBlock声明文件

MemoryPool.cpp
#include "MemoryPool.h"

const USHORT MEMPOOL_ALIGNMENT=2;

MemoryPool::MemoryPool(const USHORT &unit_size, const USHORT &init_size, const USHORT &grow_size)
:m_pFirst(0),
m_nInitSize(init_size),
m_nGrowSize(grow_size)
{
if(unit_size>4)
{
m_nUnitSize = (unit_size + (MEMPOOL_ALIGNMENT-1)) & ~(MEMPOOL_ALIGNMENT-1);
//m_nUnitSize 取整到大于unit_size的最大的MEMPOOL_ALIGNMENT的倍数

.
//令人纠结的注释
}
else if(unit_size>=2)
m_nUnitSize=4;
else
m_nUnitSize=2;
}

void* MemoryPool::Alloc()
{
if(!m_pFirst)//如果是第一次申请
{
MemoryBlock* pmb_first=new (m_nInitSize,m_nUnitSize)MemoryBlock(m_nInitSize,m_nUnitSize);//14日凌晨至此
m_pFirst=pmb_first;
return (void*)pmb_first->m_data;
}
MemoryBlock* pmb_block=m_pFirst;
while(pmb_block&&pmb_block->m_nFree==0)//pmb_block没走到最后并且当前block没有可分配结点
{
pmb_block=pmb_block->m_pNext;//往后走吧。
}
if(pmb_block)//如果找到可分配结点的block
{
char* pfree=pmb_block->m_data+(pmb_block->m_nFirst*m_nUnitSize);
pmb_block->m_nFirst=*((USHORT*)pfree);
pmb_block->m_nFree--;//可分配节点自减
return (void*)pfree;
}
else//如果找不到,此时pmb_block值为0
{
if(m_nGrowSize==NULL)
return NULL;
pmb_block=new (m_nGrowSize,m_nUnitSize)MemoryBlock(m_nGrowSize,m_nUnitSize);
if(!pmb_block)//new不成功
return NULL;
pmb_block->m_pNext=m_pFirst;//把新建的block放到最前吧
m_pFirst=pmb_block;
return (void*)pmb_block->m_data;
}
}

void MemoryPool::Free(void* pfree)
{
if(m_pFirst==NULL)
return;
MemoryBlock* pmb_block=m_pFirst;
MemoryBlock* pmb_preblock=m_pFirst;
while((ULONG)pfree<(ULONG)pmb_block->m_data||
(ULONG)pfree>(ULONG)(pmb_block->m_data+pmb_block->m_nSize))//pfree不在当前block中
{
pmb_preblock=pmb_block;//前一个block块
pmb_block=pmb_block->m_pNext;
if(!pmb_block)
return;
}
pmb_block->m_nFree++;//可分配数目+1
*((USHORT*)pfree)=pmb_block->m_nFirst;
pmb_block->m_nFirst=(USHORT)((ULONG)pfree-(ULONG)pmb_block->m_data)/m_nUnitSize;
if(pmb_block->m_nFree*m_nUnitSize==pmb_block->m_nSize)//如何该链块为空
{
pmb_preblock->m_pNext=pmb_block->m_pNext;
if((ULONG)pmb_preblock==(ULONG)m_pFirst)
m_pFirst=NULL;
delete pmb_block;
}
}

MemoryPool::~MemoryPool(void)
{
if(m_pFirst)
FreeMemoryBlock(m_pFirst);
}

void MemoryPool::FreeMemoryBlock(MemoryBlock *pblock)
{
if(pblock->m_pNext)
FreeMemoryBlock(pblock->m_pNext);
delete pblock;
pblock=NULL;
}

Test.cpp

#include "MemoryPool.h"
#include "time.h"

void performance_old()
{
clock_t start,stop;
start = clock();//开始时间
int i,b=0;
for(i=0;i<=100000;i++)
{
int* p=new int;
}

cout<<"Without MemoryPool:"<<(double) (clock()-start)<<"ms"<<endl;//输出
}

void memory()
{
clock_t start;
start = clock();//开始时间
MemoryPool mp(sizeof(int),10000,500);
int i=0;
for(i=0;i<=100000;i++)
{
int* p=(int*)mp.Alloc();
}

cout<<"Using MemoryPool:"<<(double)(clock()-start)<<"ms";//输出
}
int main()
{
performance_old();
memory();//内存池
system("pause");
return 0;
}


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