::wxSafeYield and WM_NULL

[Victor C.]

After trying to figure out why the following loop never breaks:

 SetEvent(hStopEvent); // thread exits upon this


  DWORD dw;
  HANDLE ahEvent[1] = {hThread};
  while (true)
  {
    dw = MsgWaitForMultipleObjects(1, ahEvent, FALSE, INFINITE,
                                                      QS_ALLINPUT);


    if (dw == WAIT_OBJECT_0)
      break;
    else if (dwRetVal == WAIT_ABANDONED_0)
    {
      break;
    }
    else if (dwRetVal == WAIT_TIMEOUT)
      ::wxSafeYield();                // perhaps needs special handling
    else
      ::wxSafeYield();
  }

I discovere that:

1. MWFMO keeps returning *immediately* on *neither*
    WAIT_OBJECT_0, nor WAIT_ABANDONED_0, nor WAIT_TIMEOUT.
    Instead, it returns on QS_ALLINPUT
2. This, of course, lands on the call to ::wxSafeYield();
3. Stepping through ::wxSafeYield() reveals that it also
    keeps returning *immediately*, after processing WM_NULL.

The problem is... this poor message queue keeps being bombarded with
WM_NULL messages (or is it the same WM_NULL all this time?) and the
result is that this loop never breaks.

Actually, the loop does eventually break (on WAIT_OBJECT_0) - but only
after 5 minutes (which I believe is Windows XP's mechanism to kill
rougue or hung threads).

Any idea what, in the wxWidgets system, could be bombarding the
application's message queue with WM_NULL?

Or, if it doesn't bombard the queue at all, why is WM_NULL never
handled by ::wxSafeYield() ?

I looked at the source code for wxApp::Yield() and noticed that there
is special handling for WM_QUIT. However, I couldn't find anything
special about WM_NULL.

Any ideas or suggestions as to how to solve the mystery?

Thanks,
Victor

P.S. I am using wxMSW-2.6.3 on Windows XP SP2 (VC++ 2005 EE)