C/C++的內存分配（通過malloc或new）可能需要花費很多時。
更糟糕的是，隨 著時間的流逝，內存（memory）將形成碎片，所以一個應用程序的運行會越來越慢。當它 運行了很長時間和/或執行了很多的內存分配（釋放）操作的時候。特別是，你經常申請 很小的一塊內存，堆（heap）會變成碎片的。
解決方案：你自己的內存池一個（ 可能的）解決方法是內存池（Memory Pool）。
在啟動的時候，一個“內存 池”（Memory Pool）分配一塊很大的內存，並將會將這個大塊（block）分成較小 的塊（smaller chunks）。每次你從內存池申請內存空間時，它會從先前已經分配的塊（ chunks）中得到，而不是從操作系統。最大的優勢在於：
1：非常少（幾沒有） 堆碎片
2： 比通常的內存申請/釋放（比如通過malloc， new等）的方式快另外， 你可以得到以下好處：1：檢查任何一個指針是否在內存池裡2：寫一個“堆轉儲 （Heap-Dump）”到你的硬盤（對事後的調試非常有用）
3： 某種“內 存洩漏檢測（memory-leak detection）”：當你沒有釋放所有以前分配的內存時， 內存池（Memory Pool）會拋出一個斷言（assertion）。
SMemoryChunk.h
#ifndef __SMEMORYCHUNK_H__
#define __SMEMORYCHUNK_H__
typedef unsigned char TByte ;
struct SMemoryChunk
{
TByte *Data; //數據
std::size_t DataSize; //該內存塊的總大小
std::size_t UsedSize; //實際使用的大小
bool IsAllocationChunk;
SMemoryChunk *Next; //指向鏈表中下一個塊的指針。
};
#endif
IMemoryBlock.h
#ifndef __IMEMORYBLOCK_H__
#define __IMEMORYBLOCK_H__
class IMemoryBlock
{
public :
virtual ~IMemoryBlock() {};
virtual void *GetMemory(const std::size_t &sMemorySize) = 0;
virtual void FreeMemory(void *ptrMemoryBlock, const std::size_t &sMemoryBlockSize) = 0;
};
#endif
CMemoryPool.h
#ifndef __CMEMORYPOOL_H__
#define __CMEMORYPOOL_H__
#include "IMemoryBlock.h"
#include "SMemoryChunk.h"
static const std::size_t DEFAULT_MEMORY_POOL_SIZE = 1000;//初始內存池的大小
static const std::size_t DEFAULT_MEMORY_CHUNK_SIZE = 128;//Chunk的大小
static const std::size_t DEFAULT_MEMORY_SIZE_TO_ALLOCATE = DEFAULT_MEMORY_CHUNK_SIZE * 2;
class CMemoryPool : public IMemoryBlock
{
public:
CMemoryPool(const std::size_t &sInitialMemoryPoolSize = DEFAULT_MEMORY_POOL_SIZE,
const std::size_t &sMemoryChunkSize = DEFAULT_MEMORY_CHUNK_SIZE,
const std::size_t &sMinimalMemorySizeToAllocate = DEFAULT_MEMORY_SIZE_TO_ALLOCATE,
bool bSetMemoryData = false
);
virtual ~CMemoryPool();
//從內 存池中申請內存
virtual void* GetMemory(const std::size_t &sMemorySize);
virtual void FreeMemory(void *ptrMemoryBlock, const std::size_t &sMemoryBlockSize);
private:
//申請 內存OS
bool AllocateMemory(const std::size_t &sMemorySize);
void FreeAllAllocatedMemory();
//計算可以分多少塊
unsigned int CalculateNeededChunks(const std::size_t &sMemorySize);
//計算內存池最合適的大小
std::size_t CMemoryPool::CalculateBestMemoryBlockSize(const std::size_t &sRequestedMemoryBlockSize);
//建立鏈表.每個結點Data指針指 向內存池中的內存地址
bool LinkChunksToData(SMemoryChunk* ptrNewChunks, unsigned int uiChunkCount, TByte* ptrNewMemBlock);
//重新計算塊(Chunk)的大小1024--896--768--640--512------------
bool RecalcChunkMemorySize(SMemoryChunk* ptrChunk, unsigned int uiChunkCount);
SMemoryChunk* SetChunkDefaults(SMemoryChunk *ptrChunk);
//搜索鏈表找到一個能夠持有被申請大小的內存塊(Chunk).如果它返回NULL，那麼在內 存池中沒有可用的內存
SMemoryChunk* FindChunkSuitableToHoldMemory (const std::size_t &sMemorySize);
std::size_t MaxValue(const std::size_t &sValueA, const std::size_t &sValueB) const;
void SetMemoryChunkValues(SMemoryChunk *ptrChunk, const std::size_t &sMemBlockSize);
SMemoryChunk* SkipChunks(SMemoryChunk *ptrStartChunk, unsigned int uiChunksToSkip);
private:
SMemoryChunk *m_ptrFirstChunk;
SMemoryChunk *m_ptrLastChunk;
SMemoryChunk *m_ptrCursorChunk;
std::size_t m_sTotalMemoryPoolSize; //內存池的總大小
std::size_t m_sUsedMemoryPoolSize; //以使用內存 的大小
std::size_t m_sFreeMemoryPoolSize; //可用內存的大小
std::size_t m_sMemoryChunkSize; //塊(Chunk)的大小
unsigned int m_uiMemoryChunkCount; //塊(Chunk)的數量
unsigned int m_uiObjectCount;
bool m_bSetMemoryData ;
std::size_t m_sMinimalMemorySizeToAllocate;
};
#endif
CMemoryPool.h
#include "stdafx.h"
#include "CMemorypool.h"
#include
#include
static const int NEW_ALLOCATED_MEMORY_CONTENT = 0xFF ;
CMemoryPool::CMemoryPool (const std::size_t &sInitialMemoryPoolSize,
const std::size_t &sMemoryChunkSize,
const std::size_t &sMinimalMemorySizeToAllocate,
bool bSetMemoryData)
{
m_ptrFirstChunk = NULL;
m_ptrLastChunk = NULL;
m_ptrCursorChunk = NULL;
m_sTotalMemoryPoolSize = 0;
m_sUsedMemoryPoolSize = 0;
m_sFreeMemoryPoolSize = 0;
m_sMemoryChunkSize = sMemoryChunkSize;
m_uiMemoryChunkCount = 0;
m_uiObjectCount = 0;
m_bSetMemoryData = !bSetMemoryData;
m_sMinimalMemorySizeToAllocate = sMinimalMemorySizeToAllocate;
AllocateMemory(sInitialMemoryPoolSize);
}
CMemoryPool::~CMemoryPool ()
{
}
void* CMemoryPool::GetMemory(const std::size_t &sMemorySize)
{
std::size_t sBestMemBlockSize = CalculateBestMemoryBlockSize(sMemorySize);
SMemoryChunk* ptrChunk = NULL;
while(!ptrChunk)
{
ptrChunk = FindChunkSuitableToHoldMemory(sBestMemBlockSize);
//ptrChunk等於 NULL表示內存池內存不夠用
if(!ptrChunk)
{
sBestMemBlockSize = MaxValue(sBestMemBlockSize, CalculateBestMemoryBlockSize(m_sMinimalMemorySizeToAllocate));
//從OS申請更多的內存
AllocateMemory(sBestMemBlockSize);
}
}
//下面是找到可用的塊(Chunk)代碼
m_sUsedMemoryPoolSize += sBestMemBlockSize;
m_sFreeMemoryPoolSize -= sBestMemBlockSize;
m_uiObjectCount++;
//標記該塊(Chunk)已用
SetMemoryChunkValues(ptrChunk, sBestMemBlockSize);
return ((void *) ptrChunk->Data);
}
void CMemoryPool::FreeMemory(void *ptrMemoryBlock, const std::size_t &sMemoryBlockSize)
{
}
bool CMemoryPool::AllocateMemory(const std::size_t &sMemorySize)
{
//計算可以分多少塊(1000 / 128 = 8)
unsigned int uiNeededChunks = CalculateNeededChunks(sMemorySize);
//當內存池的初始 大小為1000字節，塊(Chunk)大小128字節，分8塊還差24字節.怎麼辦?
//解決 方案:多申請24字節
std::size_t sBestMemBlockSize = CalculateBestMemoryBlockSize(sMemorySize);
//向OS申請內存
TByte *ptrNewMemBlock = (TByte*) malloc(sBestMemBlockSize);
//分配一 個結構體SmemoryChunk的數組來管理內存塊
SMemoryChunk *ptrNewChunks = (SMemoryChunk*) malloc((uiNeededChunks * sizeof(SMemoryChunk)));
m_sTotalMemoryPoolSize += sBestMemBlockSize;
m_sFreeMemoryPoolSize += sBestMemBlockSize;
m_uiMemoryChunkCount += uiNeededChunks;
if(m_bSetMemoryData)
{
memset(((void *) ptrNewMemBlock), NEW_ALLOCATED_MEMORY_CONTENT, sBestMemBlockSize);
}
return LinkChunksToData(ptrNewChunks, uiNeededChunks, ptrNewMemBlock);
}
unsigned int CMemoryPool::CalculateNeededChunks(const std::size_t &sMemorySize)
{
float f = (float) (((float)sMemorySize) / ((float)m_sMemoryChunkSize));
return ((unsigned int) ceil(f));
}
std::size_t CMemoryPool::CalculateBestMemoryBlockSize(const std::size_t &sRequestedMemoryBlockSize)
{
unsigned int uiNeededChunks = CalculateNeededChunks(sRequestedMemoryBlockSize);
return std::size_t((uiNeededChunks * m_sMemoryChunkSize));
}
bool CMemoryPool::LinkChunksToData(SMemoryChunk* ptrNewChunks, unsigned int uiChunkCount, TByte* ptrNewMemBlock)
{
SMemoryChunk *ptrNewChunk = NULL;
unsigned int uiMemOffSet = 0;
bool bAllocationChunkAssigned = false ;
for(unsigned int i = 0; i < uiChunkCount; i++)
{
//建立鏈表
if(! m_ptrFirstChunk)
{
m_ptrFirstChunk = SetChunkDefaults(&(ptrNewChunks[0]));
m_ptrLastChunk = m_ptrFirstChunk;
m_ptrCursorChunk = m_ptrFirstChunk;
}
else
{
ptrNewChunk = SetChunkDefaults(&(ptrNewChunks[i]));
m_ptrLastChunk- >Next = ptrNewChunk;
m_ptrLastChunk = ptrNewChunk;
}
//根據塊(Chunk)的大小計算下一塊的內存偏移地址
uiMemOffSet = (i * ((unsigned int) m_sMemoryChunkSize));
//結點 指向內存偏移地址
m_ptrLastChunk->Data = &(ptrNewMemBlock [uiMemOffSet]);
if(!bAllocationChunkAssigned)
{
m_ptrLastChunk->IsAllocationChunk = true;
bAllocationChunkAssigned = true;
}
}
return RecalcChunkMemorySize(m_ptrFirstChunk, m_uiMemoryChunkCount);
}
bool CMemoryPool::RecalcChunkMemorySize(SMemoryChunk *ptrChunk, unsigned int uiChunkCount)
{
unsigned int uiMemOffSet = 0 ;
for (unsigned int i = 0; i < uiChunkCount; i++)
{
if (ptrChunk)
{
uiMemOffSet = (i * ((unsigned int) m_sMemoryChunkSize)) ;
ptrChunk->DataSize = (((unsigned int) m_sTotalMemoryPoolSize) - uiMemOffSet);
ptrChunk = ptrChunk->Next ;
}
else
{
assert(false && "Error : ptrChunk == NULL");
return false;
}
}
return true;
}
SMemoryChunk* CMemoryPool::SetChunkDefaults(SMemoryChunk* ptrChunk)
{
if(ptrChunk)
{
ptrChunk->Data = NULL;
ptrChunk->DataSize = 0;
ptrChunk- >UsedSize = 0;
ptrChunk->IsAllocationChunk = false;
ptrChunk->Next = NULL;
}
return ptrChunk;
}
SMemoryChunk *CMemoryPool::FindChunkSuitableToHoldMemory(const std::size_t &sMemorySize)
{
unsigned int uiChunksToSkip = 0;
bool bContinueSearch = true;
SMemoryChunk *ptrChunk = m_ptrCursorChunk;
for(unsigned int i = 0; i < m_uiMemoryChunkCount; i++)
{
if(ptrChunk)
{
if(ptrChunk == m_ptrLastChunk)
{
ptrChunk = m_ptrFirstChunk;
}
if(ptrChunk->DataSize >= sMemorySize)
{
if(ptrChunk->UsedSize == 0)
{
m_ptrCursorChunk = ptrChunk;
return ptrChunk;
}
}
uiChunksToSkip = CalculateNeededChunks(ptrChunk->UsedSize);
if(uiChunksToSkip == 0) uiChunksToSkip = 1;
ptrChunk = SkipChunks(ptrChunk, uiChunksToSkip);
}
else
{
bContinueSearch = false
}
}
return NULL;
}
std::size_t CMemoryPool::MaxValue(const std::size_t &sValueA, const std::size_t &sValueB) const
{
if(sValueA > sValueB)
{
return sValueA;
}
return sValueB;
}
void CMemoryPool::SetMemoryChunkValues (SMemoryChunk *ptrChunk, const std::size_t &sMemBlockSize)
{
if((ptrChunk))
{
ptrChunk->UsedSize = sMemBlockSize;
}
else
{
assert(false && "Error : Invalid NULL-Pointer passed");
}
}
SMemoryChunk *CMemoryPool::SkipChunks(SMemoryChunk *ptrStartChunk, unsigned int uiChunksToSkip)
{
SMemoryChunk *ptrCurrentChunk = ptrStartChunk;
for(unsigned int i = 0; i < uiChunksToSkip; i++)
{
if(ptrCurrentChunk)
{
ptrCurrentChunk = ptrCurrentChunk->Next;
}
else
{
assert(false && "Error : Chunk == NULL was not expected.");
break ;
}
}
return ptrCurrentChunk;
}
測試方法：
// 111.cpp : 定義控制台應用程序的入口點。
//
#include "stdafx.h"
#include "CMemoryPool.h"
CMemoryPool* g_pMemPool = NULL;
class testMemoryPool
{
public:
testMemoryPool(){
}
void *operator new(std::size_t ObjectSize)
{
return g_pMemPool->GetMemory (ObjectSize) ;
}
private:
char a[25];
bool b;
long c;
};//sizeof(32);
int _tmain(int argc, _TCHAR* argv[])
{
g_pMemPool = new CMemoryPool();
testMemoryPool* test = new testMemoryPool();
return 0;
}
