计算机等级考试内存池的C++实现代码
MemoryBlock.h
#pragma once
#define USHORT unsigned short
#define ULONG unsigned long
#include
using namespace std;
//内存块
struct MemoryBlock
{
USHORT m_nSize;//可分配内存总大小
USHORT m_nFree;//可分配内存单元数目
USHORT m_nFirst;//第一个可用的内存单元位置
MemoryBlock* m_pNext;//指向下一个内存块
char m_data[1];
void* operator new(size_t,const USHORT& sum,const USHORT& unit_size)
{
return ::operator new(sizeof(MemoryBlock)+sum*unit_size);//申请一个内存块空间
}
void operator delete(void* del,size_t)
{
::operator delete(del);//删除内存块空间
}
MemoryBlock(const USHORT& sum,const USHORT& unit_size)
:m_nSize(sum*unit_size),m_nFree(sum-1),m_nFirst(1),m_pNext(0)
{
char* pData=m_data;
for(int i=1;i
{
*reinterpret_cast(pData)=i;
pData+=unit_size;
}
}
~MemoryBlock(){}
};
内存池MemoryPool声明文件
MemoryPool.h
#pragma once
#include "MemoryBlock.h"
//内存池 a very good memory manager
class MemoryPool
{
private:
USHORT m_nUnitSize;//一个可分配单元的大小
USHORT m_nInitSize;//第一个可分配空间数目
USHORT m_nGrowSize;//新增的可分配空间数目
MemoryBlock* m_pFirst;//指向第一个内存块
public:
//单元大小，第一个内存块的可分配空间数目，第二个内存块之后的可分配空间数目
MemoryPool(const USHORT& unit_size,const USHORT& init_size=2048,const USHORT& grow_size=1024);
~MemoryPool(void);
void* Alloc();//分配内存
void Free(void* pfree);//回收内存
void FreeMemoryBlock(MemoryBlock *pblock);//销毁
};
内存池MemoryPool实现文件
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