Re: MFC and threads

There are a couple solutions to this problem.

The choices depend on some performance issues. The simplest one is the following:

typedef struct {
    HANDLE event;
    UINT result;
} QueryParameters;

UINT CMyThread::Query()
   {
    QueryParameters parms;
    parms.event = ::CreateEvent(NULL, TRUE, FALSE, NULL);
    target->PostMessage(UWM_QUERY_WHATEVER, (WPARAM)&parms);
    ::WaitForSingleObject(parms.event, INFINITE);
   ::CloseHandle(parms.event);
    return parms.result;
   }

ON_[REGISTERED_]MESSAGE(UWM_QUERY_WHATEVER, OnQueryWhatever)

LRESULT CMyWindow::OnQueryWhatever(WPARAM wParam, LPARAM)
   {
    QueryParameters * parms = (QueryParameters *)wParam;
    CQueryDialog dlg;
    parms->result = dlg.DoModal();
    ::SetEvent(parms->event);
    return 0;
   }

Note this does something a little strange: it passes the address of a local variable
across a thread boundary. This is normally an erroneous action, but because of the
::WaitForSingleObject, the thread is suspended so the stack address remains valid. (This
is a paradigm used in device drivers for PnP event handling).

Error detection on the WFSO is left as an Exercise For The Reader.
                    joe