I'm currently working on a Multitasking Demo which comes from a Petzold book.

The app takes 99% of CPU usage, which makes it almost impossible to close it down, even causing system instability. Is it possible to restrict CPU usage?

Code:
LRESULT APIENTRY WndProc (HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
     {
     static char   *szChildClass[] = { "Child1", "Child2",
                                       "Child3", "Child4" } ;
     static HWND    hwndChild[4] ;
     static WNDPROC ChildProc[] = { WndProc1, WndProc2,
                                    WndProc3, WndProc4 } ;
     HINSTANCE      hInstance ;
     int            i, cxClient, cyClient ;
     WNDCLASSEX     wndclass ;

     switch (iMsg)
          {
          case WM_CREATE :
               hInstance = (HINSTANCE) GetWindowLong (hwnd, GWL_HINSTANCE) ;

               wndclass.cbSize        = sizeof (wndclass) ;
               wndclass.style         = CS_HREDRAW | CS_VREDRAW ;
               wndclass.cbClsExtra    = 0 ;
               wndclass.cbWndExtra    = 0 ;
               wndclass.hInstance     = hInstance ;
               wndclass.hIcon         = NULL ;
               wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;
               wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
               wndclass.lpszMenuName  = NULL ;
               wndclass.hIconSm       = NULL ;

               for (i = 0 ; i < 4 ; i++)
                    {
                    wndclass.lpfnWndProc   = ChildProc[i] ;
                    wndclass.lpszClassName = szChildClass[i] ;

                    RegisterClassEx (&wndclass) ;

                    hwndChild[i] = CreateWindow (szChildClass[i], NULL,
                          WS_CHILDWINDOW | WS_BORDER | WS_VISIBLE,
                          0, 0, 0, 0, hwnd, (HMENU) i, hInstance, NULL) ;
                    }

               return 0 ;

          case WM_SIZE :
               cxClient = LOWORD (lParam) ;
               cyClient = HIWORD (lParam) ;

               for (i = 0 ; i < 4 ; i++)
                    MoveWindow (hwndChild[i], (i % 2) * cxClient / 2,
                                              (i > 1) * cyClient / 2,
                                cxClient / 2, cyClient / 2, TRUE) ;
               return 0 ;

          case WM_CHAR :
               if (wParam == '\x1B')
                    DestroyWindow (hwnd) ;

               return 0 ;

          case WM_DESTROY :
               PostQuitMessage (0) ;
               return 0 ;
          }
     return DefWindowProc (hwnd, iMsg, wParam, lParam) ;
     }