Question

My main thread creates multiple I/O worker threads. I then initiate an I/O request from my main thread by doing:

{
    ...
    IoRequest *pIoRequest = new IoRequest(m_socket);
    pIoRequest->SetBuffer(vecCommandData); // vector of BYTEs
    pIoRequest->SetOperationType(OP_TYPE_SEND);
    WSASend(m_socket, pIoRequest->GetWsaBuffer(), 1, NULL, 0, pIoRequest, NULL);
    ...
}

At some point in one of my I/O worker threads, the request is completed and my IoRequest object’s buffer is filled with valid response data.

DWORD WINAPI WorkerThreadProc(LPVOID lpParameter)
{
    IoCompletionPort *pIocp = reinterpret_cast<IoCompletionPort*>(lpParameter);    
    ...
    while (true)
    {
        BOOL bReturn = pIocp->GetStatus(&ulCompletionKey, &dwNumberOfBytesTransferred, (LPOVERLAPPED*)&pIoRequest);
        ...
        switch (pIoRequest->GetOperationType())
        {
        ...
        case OP_TYPE_RECEIVE_DATA:
            {
                ...
                // the requested I/O operation has completed and pIoRequest's buffer now contains valid response data!
                break;
            } 
        ...
        }
    }

    return 0;
}

How can I place my main thread in an alertable wait state after calling WSASend() and make it receive the response data whenever it’s ready?

Answer 1

In an IOCP server, it’s typically GetQueuedCompletionStatus().