C / C++ / MFC

UINT CMyDlg::monitorThread(LPVOID pParam)
{
	DWORD		dwRead;
	DWORD		dwRes;
	BOOL		fWaitingOnRead = FALSE;
	OVERLAPPED	osReader = {0};
	struct PTZCommStruct *pPTZStruct = (struct PTZCommStruct *)pParam;


	// Create the overlapped event.
	osReader.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

	if(osReader.hEvent == NULL)
	{
		// Error creatiing overlapped event, abort.
		DWORD err = ::GetLastError();
		pPTZStruct->pWnd->PostMessage(UWM_READER_SHUTTING_DOWN, (WPARAM)err);
		return 0;
	} 


	while(pPTZStruct->nPTZCommTerminate == 0)
	{
		if(!fWaitingOnRead)
		{
			// Issue read Operation.
			BOOL tmp = ReadFile(m_hPTZCtrlPort, PTZbuffer, MAX_BUFFER_SIZE, &dwRead, &osReader);
			if(!tmp)
			{
				if(GetLastError() != ERROR_IO_PENDING) // read not delayed
				{
					// Error in comms - report!!!
					return 0;
				}
				else
				{
					fWaitingOnRead = TRUE;
				}
			}
			else
			{
				// ***Read the data
				pPTZStruct->pWnd->PostMessage(UWM_DATA_READ);
			}
		}
		else
		{
			dwRes = WaitForSingleObject(osReader.hEvent, READ_TIMEOUT);
			switch(dwRes)
			{
				// Read Completed
			case WAIT_OBJECT_0:
				if(!GetOverlappedResult(m_hPTZCtrlPort, &osReader, &dwRead, FALSE))
				{
					DWORD dwError = GetLastError();
					switch(dwError)
					{
						case ERROR_HANDLE_EOF:
							return 0;
							break;
						case ERROR_IO_PENDING:
							return 0;
							break;
						case ERROR_IO_INCOMPLETE:
							return 0;
							break;
						case ERROR_OPERATION_ABORTED:
							return 0;
							break;
						default:
							// error in comms - report
							Dump1("Serial Read Error %d\r\n", ::GetLastError());
							return 0;
							break;
					}
				}
				else
				{
					// ***Read the Data 
			        pPTZStruct->pWnd->PostMessage(UWM_DATA_READ);
				}
				fWaitingOnRead = FALSE;
				break;

			case WAIT_TIMEOUT:
				// Operation isn't complete yet. fWaitingOnRead flag isn't changed since I'll
				// loop back around, and I don't want to issue another read until the first one finishes.
				//
				break;

			default:
				// Error in the WaitForSigleObject; abort!!!!
				// This indicates a problem with the OVERLAPPED structure's event handle.
				return 0;
				break;

			}
		} 
	}
	return 0;
}