C / C++ / MFC

for (int i=0; i<number_of_windows; i++)
if (!InitInstance (hInstance, nCmdShow))
{
  return FALSE;
}

for (i=0; i<number_of_windows; i++)
while (GetMessage(&msg, NULL, 0, 0)) 
{
  if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg)) 
  {
    TranslateMessage(&msg);
    DispatchMessage(&msg);
  }
}

LONG lCount=1;

LONG lMan=0;
do
{
  while (GetMessage(&msg, NULL, 0, 0))
  {
    if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
    {
      TranslateMessage(&msg);
      DispatchMessage(&msg);
    }
  }
  InterlockedDecrement(&lCount); // a window has been closed; put a breakpoint here!!!
  InterlockedCompareExchange((void **)&lMan, (PVOID)1,
    (PVOID)lCount); // if lCount==lMan==0 then lMan=1
} while (!lMan);

case IDC_BUTTON:
  InitInstance(hInst, SW_SHOW); // new window
  InterlockedIncrement(&lCount);
  break;