CIOCPServer的数据结构定义及内存池方案

为了避免频繁的申请释放内存，使用内存池来管理缓冲区对象和客户上下文对象使用的内存。

使用指针保存所有空闲的内存块，形成空闲列表。

申请内存时，这个指针不为NULL，就从空闲列表中取出一个来使用，如果取完，就真正的申请内存。

---

                  1 缓冲区对象               

程序使用CIOCPBuffer来描述per-IO数据，包含IO操作的必要信息，提交时，提交的就是CIOCPBuffer对象

下面是申请缓冲区对象代码：

CIOCPBuffer *CIOCPServer::AllocateBuffer(int nLen){
    CIOCPBuffer *pBuffer = NULL;
    if(nLen>BUFFER_SIZE)
        return NULL;

    ::EnterCriticalSection(&m_FreeBufferListLock);
    if(m_pFreeBufferList == NULL)
    {
        pBuffer=(CIOCPBuffer*)::HeapAlloc(GetProcessHeap(),HEAP_ZERO_MEMORY,sizeof(CIOCPBuffer)+BUFFER_SIZE);
    }
    else
    {
        pBuffer = m_pFreeBufferList;
        m_pFreeBufferList = m_pFreeBufferList->pNext;
        pBuffer->pNext = NULL;
        m_nFreeBufferCount--;
    }
    ::LeaveCriticalSection(&m_FreeBufferListLock);
    if(pBuffer!=NULL)
    {
        pBuffer->buff = (char*)(pBuffer+1);
        pBuffer->nLen = nLen;
    }
    return pBuffer;
}

下面是释放缓冲区对象的代码：

void CIOCPServer::ReleaseBuffer(CIOCPBuffer *pBuffer)
{
    ::EnterCriticalSection(&m_pFreeBufferListLock);
    if(m_nFreeBufferCount<=m_nMaxFreeBuffers)
    {
        memset(pBuffer,0,sizeof(CIOCPBuffer)+BUFFERSIZE);
        pBuffer->pNext = m_pFreeBufferList;
        m_pFreeBufferList = pBuffer;
        m_pFreeBufferCount++;
    }
    else
    {
        ::HeapFree(::GetProcessHeap(),0,pBuffer);
    }
    ::LeaveCriticalSection(&m_pFreeBufferListLock);
}

                  2 客户区上下文对象                    

客户上下文对象便是per-Handle数据，包含了套接字的信息，服务器程序接收到一个新的连接，就为新连接创建客户上下文对象，以记录客户信息。

代码差不多与缓冲区上下文对象差不多，释放的代码如下：

void CIOCPServer::RealeaseContext(CIOCPContext *pContext)
{
    if(pContext->s != INVALID_SOCKET)
        ::closesocket(pContext->s);
    CIOCPBuffer *pNext;
    while(pContext->pOutOfOrderReads !=NULL)
    {
        pNext = pContext->pOutOfOrderReads->pNext;
        ReleaseBuffer(pContext->pOutOfOrderReads);
        pContext->pOutOfOrderReads = pNext;
    }
    ::EnterCriticalSection(&m_pFreeBufferListLock);
    if(m_nFreeBufferCount<=m_nMaxFreeBuffers)
    {
        CRITICAL_SECTION cstmp = pContext->Lock;
        memset(pContext,0,sizeof(CIOCPContext));
        pContext->Lock = cstmp;
        pContext->pNext = m_pFreeContextList;
        m_pFreeContextList = pContext;
        m_nFreeContextCount++;
    }
    else
    {
        ::DeleteCriticalSection(&pContext->Lock);
        ::HeapFree(::GetProcessHeap(),0,pBuffer);
    }
    ::LeaveCriticalSection(&m_pFreeBufferListLock);
}