我正在创建一个客户端程序，该程序与通过LAN连接到PC的设备进行通信。
我的程序与设备之间的典型通信如下：
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字表示要跟随的数据大小（D = 13字节）。
我的发送例程如下所示：
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;
}
我的工作线程例程看起来像：
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
最佳答案
正如PerIoData类型的名称所指，每个不完整的I / O请求都需要一个数据结构。从使用PerIoData或WSASend发起异步I / O到使用WSARecv从I / O完成端口检索该请求的完成包之时起，GetQueuedCompletionStatus结构应一直存在。
当您要开始新请求时，应该始终重新初始化您的OVERLAPPED结构。
只要I / O请求已完成，就可以重新使用PerIoData结构。假设您已经从I / O完成端口中检索了pPerIoData，则可以将其重新用于后续请求。只要确保您已重置该结构中的所有适用字段，使其处于适合新I / O请求的状态即可。
编辑以回答后续问题：
答：我会选择continue，因为即使您无法发起其他请求，您也想继续处理I / O事件。如果不使用continue，则将无法再处理I / O完成。在continue之前，您可能需要调用某种错误处理程序。
B.我认为不一定要分配一个“正确”或“错误”的地方，但是请记住，当您在此处分配PerIoData时，实际上您要做的就是重复分配和删除相同的数据一遍又一遍的循环结构。当我使用I / O完成端口编写代码时，我会预先分配一个等价的PerIoData池并重新使用它们。
C.我没有足够的上下文知道答案。显示执行此操作的代码以及断言所在的行，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调用上读取几个字节的效果将不理想。 Winsock通话非常昂贵；要求几个字节的开销很大。我建议您在一个PerIoData中将更大的数据块读入WSARecv缓冲区。然后将大小信息从该缓冲区中拉出，然后开始从该缓冲区中复制数据。如果到达的数据量超出了缓冲区的容量，那么您可以进行其他WSARecv调用，直到读完其余部分为止。