c++ - 如何为 IOCP 构造工作线程逻辑

Question

我正在创建一个客户端程序，它与通过 LAN 连接到我的 PC 的设备进行通信。

我的程序和设备之间典型的通信如下:

Program -> Device   1616000D  08 02 00 00 00 21 11 A1 00 01 22 08 00 // Sender sends data (a specific command to the device) to Receiver
Program <- Device   16160002  80 00 // Receiver sends ACK to sender
Program <- Device   16160005  08 20 00 00 00 // Receiver sends command response to sender
Program -> Device   16160002  80 00 // Sender sends ACK to receiver

第一个字节序列的最后一个十六进制数表示后面的数据大小(D = 13 字节)。

我的发送例程如下:

bool TcpConnection::SendCommand(const Command& rCommand, const std::vector<BYTE>& rvecCommandOptions)
{
    std::vector<BYTE> vecCommandData;
    m_commandBuilder.BuildCommand(rCommand, rvecCommandOptions, vecCommandData);

    if (vecCommandData.empty())
        return false;

    PerIoData *pPerIoData = new PerIoData;
    if (!pPerIoData)
        return false;

    SecureZeroMemory(&(pPerIoData->m_overlapped), sizeof(WSAOVERLAPPED));

    pPerIoData->m_socket = m_socket.Get();
    pPerIoData->m_overlapped.hEvent = WSACreateEvent();
    pPerIoData->m_vecBuffer.assign(vecCommandData.begin(), vecCommandData.end());
    pPerIoData->m_wsaBuf.buf = (CHAR*)(&(pPerIoData->m_vecBuffer[0]));
    pPerIoData->m_wsaBuf.len = pPerIoData->m_vecBuffer.size();
    pPerIoData->m_dwFlags = 0;
    pPerIoData->m_dwNumberOfBytesSent = 0;
    pPerIoData->m_dwNumberOfBytesToSend = pPerIoData->m_wsaBuf.len;
    pPerIoData->m_operationType = OP_TYPE_SEND;

    if (!m_socket.Send(pPerIoData))
        return false;

    return true;
}

我的工作线程例程如下所示:

DWORD WINAPI TcpConnection::WorkerThread(LPVOID lpParameter)
{
    HANDLE hCompletionPort = (HANDLE)lpParameter;
    DWORD dwNumberOfBytesTransferred;
    ULONG ulCompletionKey;
    PerIoData *pPerIoData;

    DWORD dwNumberOfBytesReceived;
    DWORD dwNumberOfBytesSent;
    DWORD dwFlags;

    while (GetQueuedCompletionStatus(hCompletionPort, &dwNumberOfBytesTransferred, &ulCompletionKey, (LPOVERLAPPED*)&pPerIoData, INFINITE)) 
    {
        if (!pPerIoData)
            continue;

        if ((dwNumberOfBytesTransferred == 0) && ((pPerIoData->m_operationType  == OP_TYPE_SEND) || (pPerIoData->m_operationType  == OP_TYPE_RECEIVE)))
        {
            closesocket(pPerIoData->m_socket);
            delete pPerIoData;
            continue;
        }

        if (pPerIoData->m_operationType == OP_TYPE_SEND)
        {
            pPerIoData->m_dwNumberOfBytesSent += dwNumberOfBytesTransferred;
            if (pPerIoData->m_dwNumberOfBytesSent < pPerIoData->m_dwNumberOfBytesToSend)
            {
                pPerIoData->m_wsaBuf.buf = (CHAR*)(&(pPerIoData->m_vecBuffer[pPerIoData->m_dwNumberOfBytesSent]));
                pPerIoData->m_wsaBuf.len = (pPerIoData->m_dwNumberOfBytesToSend - pPerIoData->m_dwNumberOfBytesSent);

                if (WSASend(pPerIoData->m_socket, &(pPerIoData->m_wsaBuf), 1, &dwNumberOfBytesTransferred, 0, &(pPerIoData->m_overlapped), NULL) == 0)
                    continue;

                if (WSAGetLastError() == WSA_IO_PENDING)
                    continue;
            }
            else if (pPerIoData->m_dwNumberOfBytesSent == pPerIoData->m_dwNumberOfBytesToSend)
            {
                delete pPerIoData;
            }

            // Q1. Do I create a new instance of PerIoData here before calling WSARecv() or reuse pPerIoData?

            // QA. If I did do "PerIoData pPerIoData = new PerIoData" here, how do I handle if this momory allocation request has failed?  Should I simply "continue" or "return -1"?

            // QB. Or is this a wrong place to do this memory allocation to achive the typical communication between my program and the device?

            SecureZeroMemory(&(pPerIoData->m_overlapped), sizeof(WSAOVERLAPPED));

            pPerIoData->m_overlapped.hEvent = WSACreateEvent();
            pPerIoData->m_wsaBuf.buf = (CHAR*)(&(pPerIoData->m_vecBuffer[0]));
            pPerIoData->m_wsaBuf.len = pPerIoData->m_vecBuffer.size();
            pPerIoData->m_operationType = OP_TYPE_RECEIVE;

            if (WSARecv(pPerIoData->m_socket, &(pPerIoData->m_wsaBuf), 1, &dwNumberOfBytesReceived, &(pPerIoData->m_dwFlags), &(pPerIoData->m_overlapped), NULL) == 0)
                continue;

            if (WSAGetLastError() == WSA_IO_PENDING)
                continue;
        }
        else if (pPerIoData->m_operationType == OP_TYPE_RECEIVE)
        {
            if ((pPerIoData->m_vecBuffer[0] == 0x16) && (pPerIoData->m_vecBuffer[1] == 0x16))
            {
                // Q2. Do I need to do SecureZeroMemory(&(pPerIoData->m_overlapped), sizeof(WSAOVERLAPPED)); here?

                // Q3. Or do I new PerIoData?

                pPerIoData->m_wsaBuf.buf = (CHAR*)(&(pPerIoData->m_vecBuffer[0]));
                pPerIoData->m_wsaBuf.len = pPerIoData->m_vecBuffer.size();
                pPerIoData->m_operationType = OP_TYPE_RECEIVE;

                // QC. At this point two syn bytes (0x16) are received.  I now need to receive two more bytes of data (000D = 13 bytes) to find out the size of the actual command response data.
                // If I clear my m_vecBuffer here and try to resize its size to two, I get this debug assertion: "vector iterators incompatible" at runtime.  Do you know how I can fix this problem?

                if (WSARecv(pPerIoData->m_socket, &(pPerIoData->m_wsaBuf), 1, &dwNumberOfBytesReceived, &(pPerIoData->m_dwFlags), &(pPerIoData->m_overlapped), NULL) == 0)
                    continue;

                if (WSAGetLastError() == WSA_IO_PENDING)
                    continue;
            }

            // QD. I'm not sure how to structure this if clause for when m_operationType is OP_TYPE_RECEIVE.  I mean how do I distinguish one receive operation for getting two syn bytes from another for getting data size?
            // One way I can think of doing is to create more receive operation types such as OP_TYPE_RECEIVE_DATA_SIZE or OP_TYPE_RECEIVE_DATA?  So you can have something like below.
            // Is this how you would do it?
        }
        //else if (pPerIoData->m_operationType == OP_TYPE_RECEIVE_DATA_SIZE)
        //{
            // Call WSARecv() again to get command response data
        //}
    }

    return 0;
}

请在上面的代码中查看我的问题。

非常感谢

Answer 1

1. 正如您的 PerIoData 类型的名称所指，您需要一个数据结构每个不完整的 I/O 请求。 PerIoData 结构应该从您使用 WSASend 或 WSARecv 启动异步 I/O 到您检索该请求的完成数据包时持续存在使用 GetQueuedCompletionStatus 的 I/O 完成端口。
2. 当您即将开始一个新的请求时，您应该总是重新初始化您的OVERLAPPED结构。
3. 只要 I/O 请求完成，您就可以重新使用 PerIoData 结构。鉴于您已经从 I/O 完成端口检索到 pPerIoData，您可以将其重新用于后续请求。只需确保您已重置该结构中的任何适用字段，使其处于适合新 I/O 请求的状态。

编辑以回答后续问题:

一个。我会continue 因为你想继续处理 I/O 事件，即使你不能发起额外的请求。如果您不continue，那么您将无法处理更多的 I/O 完成。在您继续之前，您可能想要调用某种错误处理程序。

B.我认为分配的位置不一定是“正确”或“错误”，但请记住，当您在那里分配 PerIoData 时，您实际上最终做的是重复分配和删除循环中一遍又一遍地使用相同的数据结构。当我使用 I/O 完成端口编写代码时，我预先分配了一个等同于我的 PerIoData 的池并重新使用它们。

C.我没有足够的上下文来知道答案。显示执行此操作的代码以及断言命中的行，我可能会提供帮助。

D.您可以按照建议将操作类型分解为更细粒度的组件，例如 OP_TYPE_RECEIVE_DATA_SIZE 操作。作为警告，在每个 WSARecv 调用中读取几个字节不会像您希望的那样执行。 Winsock 调用很昂贵；请求几个字节的开销很大。我建议您在一个 WSARecv 中将更大的数据 block 读入您的 PerIoData 缓冲区。然后从该缓冲区中提取大小信息，然后开始从该缓冲区中复制数据。如果到达的数据多于缓冲区无法容纳的数据，那么您可以进行额外的 WSARecv 调用，直到您读完其余数据。