Serial port WaitForMultipleObjects() problem

The call to WaitForMultipleObjects() does not return, it seems the event for the serial port does not get signalled. I was under the impression that sending data to the port will cause the event to be signalled. Am i doing something wrong here?

Code:

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UINT CMyserialportView::ReaderThread(LPVOID p)
{
        TRACE("\nThread ReaderThread() >");

        CSerialParameters* parms = (CSerialParameters *)p;
        OVERLAPPED ovl = {0};
        ovl.hEvent = ::CreateEvent(NULL, TRUE, FALSE, NULL);
        if(ovl.hEvent == NULL)
        { /* failed */
                DWORD err = ::GetLastError();
                parms->m_pWndNotifyee->PostMessage(UWM_READER_SHUTTING_DOWN, (WPARAM)err);
                return 0;
        } /* failed */

        DWORD shutdown;  // reason for shutdown
        HANDLE waiters[2];
        waiters[0] = parms->m_hShutdown;
        waiters[1] = ovl.hEvent;
       
#define MAX_BUFFER_SIZE 100
    BOOL running = TRUE;
    DWORD bytesRead;
    while(running)
      { /* read loop */
        BYTE buffer[MAX_BUFFER_SIZE];
        BOOL ok = ::ReadFile(parms->m_hCom, buffer, MAX_BUFFER_SIZE - 1, &bytesRead, &ovl);
        if(!ok)
        { /* error */
          DWORD err = ::GetLastError();
          if(err != ERROR_IO_PENDING)
          { /* read error */
                                shutdown = err;
                                running = FALSE;
                                continue;
          } /* read error */
         
                  // otherwise, it is ERROR_IO_PENDING
          DWORD result = ::WaitForMultipleObjects(2, waiters, FALSE, INFINITE);
                  //DWORD result = ::WaitForSingleObject(ovl.hEvent, INFINITE);
          switch(result)
          { /* wait */
                                case WAIT_OBJECT_0:  // shutdown
                                        ::CancelIo(parms->m_hCom);
                                        shutdown = ERROR_SUCCESS;  // clean shutdown
                                        running = FALSE;
                                        continue;
                                case WAIT_OBJECT_0 + 1: // I/O complete
                                        ok = ::GetOverlappedResult(parms->m_hCom, &ovl, &bytesRead, TRUE); 
                                        if(!ok)
                                        { /* GetOverlappedResult failed */
                                                DWORD err = ::GetLastError();
                                                running = FALSE;
                                                continue;
                                        } /* GetOverlappedResult failed */
                                        break;
                                default:
                                { /* trouble */
                                        shutdown = ::GetLastError();
                                        ASSERT(FALSE); // failure
                                        running = FALSE;
                                        continue;
                                } /* trouble */
            } /* wait */ 
        } /* error */

        // if we get here, either the ReadFile worked immediately, or we waited for completion
        if(bytesRead == 0)
          continue; // nothing was read
        buffer[bytesRead] = '\0'; // assumes 8-bit characters without embedded NUL
        CString* s = new CString((LPCSTR)buffer);
        parms->m_pWndNotifyee->PostMessage(UWM_DATA_READ, (WPARAM)s);
    } /* read loop */

    parms->m_pWndNotifyee->PostMessage(UWM_READER_SHUTTING_DOWN, (WPARAM)shutdown);
    ::CloseHandle(ovl.hEvent);
    return 0;  // we're gone. You may choose to do something different
} // CMyClass::ReaderThread

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WaitForMultipleObjects waits for all objects, so perhaps it is the other event, parms->m_hShutdown, that is not signalled?

Regards / Z

No i pass in FALSE as one of the parameters which means if one of the parameters is signalled the WaitForMultipleObjects() returns.

bWaitAll
[in] If this parameter is TRUE, the function returns when the state of all objects in the lpHandles array is signaled. If FALSE, the function returns when the state of any one of the objects is set to signaled. In the latter case, the return value indicates the object whose state caused the function to return.

And you did open the com port with FILE_FLAG_OVERLAPPED ?

Regards / Z

This is the OnInitialUpdate() in which i open the serial port and create/start the threads.....

Code:

---

void CMyserialportView::OnInitialUpdate()
{
        CView::OnInitialUpdate();
       
        m_hCom = ::CreateFile(        "\\\\.\\COM2",                // filename
                        GENERIC_READ|GENERIC_WRITE,        // desired access
                        0,                                                        // exclusive
                        NULL,                                                // security irrelevant
                        OPEN_EXISTING,                                // it has to be there
                        FILE_FLAG_OVERLAPPED,                // open asynchronous
                        NULL);                                                // template file
       
        if(m_hCom == NULL)
        {
                AfxMessageBox("Failed to open COM port", 0);
                return;
        }

        // Create writer thread
        m_pSerialWriter = (CSerialWriter*)AfxBeginThread(       
                RUNTIME_CLASS(CSerialWriter),       
                THREAD_PRIORITY_NORMAL,                        // priority
                0,                                                                // default stack size
                CREATE_SUSPENDED);                                // don't run right away

        if(m_pSerialWriter == NULL)
        {
                AfxMessageBox("Could not create writer thread",0);
                return;
        }

        HANDLE m_hShutDown = ::CreateEvent(NULL, TRUE, FALSE, NULL);
        if(m_hShutDown == NULL)
        {
                AfxMessageBox("Could not create shutdown event",0);
                return;
        }

        m_pSerialWriter->m_pParameters = new CSerialParameters(m_hCom, this, m_hShutDown);
        m_pSerialWriter->ResumeThread();

        CString* myS = new CString("010203040506070809A0010203040506070808");
        m_pSerialWriter->PostThreadMessage(UWM_DATA_SEND, (WPARAM)myS, (LPARAM)0);

        // Create reader thread
        AfxBeginThread(ReaderThread, m_pSerialWriter->m_pParameters);

}

---

After opening the port (::CreateFile(...) ) you have to set the DCB (GetCommState/SetCommState) and port TIMEOUTs (GetCommTimeouts/SetCommTimeouts), something like:

Code:

---

// declared in header:            COMMTIMEOUTS m_CommTimeOuts;
        .......
        if(::GetCommTimeouts(m_hCom, &m_CommTimeOuts))
        {
                COMMTIMEOUTS TimeOuts(m_CommTimeOuts);
                //        correct these values
                TimeOuts.ReadIntervalTimeout                = 100;
                TimeOuts.ReadTotalTimeoutConstant        = 100;
                TimeOuts.ReadTotalTimeoutMultiplier        = 10;
                TimeOuts.WriteTotalTimeoutConstant        = 10;
                TimeOuts.WriteTotalTimeoutMultiplier= 100;
                if(::SetCommTimeouts(m_hCom, &TimeOuts))
                {
                      // ready to work with the port to read...

---

Otherwise, your reader thread might hang on waiting for the next character.

If VictorN's suggestion does not help, plz post code for CSerialWriter also