内存池完整实现代码及一些思考

为了提高效率和有效的监控内存的实时状态，我们采取了内存池的思想来解决效率与对内存实现监控的问题。

网上查找到了一些方案，根据自己的理解实现了应用。

我们什么时候要调用到内存池，

1，当我们频繁的申请释放同样数据大小的内存空间，我们可以用比动态new更有效方式来管理内存时，我们应该用内存池来提高效率。

2，当我们需要知道内存实时的申请状态，以便于对于服务器内存状态做实时预警时，我们可以用内存池的接口，来给内存增加监控。



实现的特点：

1，内存池内存单元大小可以动态定义，实现多级内存池。

2，申请效率很高，单元测试下是普通new/delete的4倍左右，当然具体性能还应机器类别而异。





MemoryPool.h 的实现


//该内存池理论来自于IBM文章，http://www.ibm.com/developerworks/cn/linux/l-cn-ppp/index6.html
//作者冯宏华，徐莹，程远，汪磊享有论文著作权，由2011-06-06 konyel lin根据相关代码和理论进行优化修改。

#include <string>
#include <malloc.h>
//内存对齐值，可以根据机器取指长度进行设置
#define MEMPOOL_ALIGNMENT 4

#define USHORT unsigned short
#define ULONG unsigned long

struct MemoryBlock
{
USHORT nSize;
USHORT nFree;
USHORT nFirst;
USHORT nDummyAlign1;
MemoryBlock* pNext;
char aData[1];
static void* operator new(size_t,USHORT nTypes, USHORT nUnitSize){
return ::operator new(sizeof(MemoryBlock) + nTypes * nUnitSize);
}
static void operator delete(void *p, size_t){
::operator delete (p);
}
MemoryBlock (USHORT nTypes = 1, USHORT nUnitSize = 0);
~MemoryBlock() {}
};

class MemoryPool
{
private:
MemoryBlock* pBlock;
USHORT nUnitSize;
USHORT nInitSize;
USHORT nGrowSize;
public:
MemoryPool( USHORT nUnitSize,
USHORT nInitSize = 1024,
USHORT nGrowSize = 256 );
~MemoryPool();
void* Alloc();
void Free( void* p );
};




MemoryPool.cpp 的实现


#include "MemoryPool.h"

MemoryPool::MemoryPool( USHORT _nUnitSize,
USHORT _nInitSize, USHORT _nGrowSize )
{
pBlock = NULL;
nInitSize = _nInitSize;
nGrowSize = _nGrowSize;
if ( _nUnitSize > 4 )
nUnitSize = (_nUnitSize + (MEMPOOL_ALIGNMENT-1)) & ~(MEMPOOL_ALIGNMENT-1);
else if ( _nUnitSize <= 2 )
nUnitSize = 2;
else
nUnitSize = 4;
}

void* MemoryPool::Alloc()
{
MemoryBlock* pMyBlock;
if ( !pBlock ){
//第一次调用初始化内存块
pMyBlock =new(nGrowSize, nUnitSize) MemoryBlock(nGrowSize, nUnitSize);
pBlock = pMyBlock;
return (void*)(pMyBlock->aData);
}
pMyBlock = pBlock;
while (pMyBlock && !pMyBlock->nFree )
pMyBlock = pMyBlock->pNext;
if ( pMyBlock ){
printf("get a mem from block/n");
char* pFree = pMyBlock->aData+(pMyBlock->nFirst*nUnitSize);
//aData记录实际的内存单元标识
pMyBlock->nFirst = *((USHORT*)pFree);
pMyBlock->nFree--;
return (void*)pFree;
}
else{
printf("add a new block/n");
if (!nGrowSize)
return NULL;
pMyBlock = new(nGrowSize, nUnitSize) MemoryBlock(nGrowSize, nUnitSize);
if (!pMyBlock )
return NULL;
pMyBlock->pNext = pBlock;
pBlock = pMyBlock;
return (void*)(pMyBlock->aData);
}
}

void MemoryPool::Free( void* pFree ){
MemoryBlock* pMyBlock = pBlock;
MemoryBlock* preMyBlock;
//确定该待回收分配单元（pFree）落在哪一个内存块的指针范围内,大于起始节点，小于终止节点。
while ( ((ULONG)pMyBlock->aData > (ULONG)pFree) ||
((ULONG)pFree >= ((ULONG)pMyBlock->aData + pMyBlock->nSize))){
//不在内存块范围内，则历遍下一个节点
preMyBlock=pMyBlock;
pMyBlock=pMyBlock->pNext;
}
pMyBlock->nFree++;
*((USHORT*)pFree) = pMyBlock->nFirst;
pMyBlock->nFirst = (USHORT)(((ULONG)pFree-(ULONG)(pBlock->aData)) / nUnitSize);
//判断内存块是否全部为自由状态，是则释放整个内存块
if (pMyBlock->nFree*nUnitSize == pMyBlock->nSize ){
preMyBlock->pNext=pMyBlock->pNext;
delete pMyBlock;
}
}

MemoryBlock::MemoryBlock (USHORT nTypes, USHORT nUnitSize)
: nSize (nTypes * nUnitSize),
nFree (nTypes - 1),
nFirst (1),
pNext (0)
{
char * pData = aData;
for (USHORT i = 1; i < nTypes; i++) {
//将内存块的前2个字节用来存放内存单元的标识
*reinterpret_cast<USHORT*>(pData) = i;
pData += nUnitSize;
}
}