PRB: Petzold's COLORS1 Sample Application Consumes Resources

Last reviewed: July 23, 1997
Article ID: Q85285
3.10 WINDOWS kbprg kbprb kbcode

The information in this article applies to:

  • Microsoft Windows Software Development Kit (SDK) for Windows version 3.1

SYMPTOMS

When the COLORS1 sample application on pages 227-232 of the book "Programming Windows 3" by Charles Petzold (Microsoft Press) is run under Windows 3.1, the amount of free system resources available after the program is complete is less than the amount available before running the program.

CAUSE

The program allocates system resources and does not free them.

RESOLUTION

Make the following modifications to the WndProc function in the COLORS1 sample:

  1. In the code that processes the WM_VSCROLL message, find the following:

          DeleteObject (GetClassWord (hwnd, GCW_HBRBACKGROUND));
          SetClassWord (hwnd, GCW_HBRBACKGROUND,
    
               CreateSolidBrush (RGB (color[0], color[1], color[2])));
    
       Insert the following code in its place:
    
          DeleteObject (SetClassWord (hwnd, GCW_HBRBACKGROUND,
               CreateSolidBrush (RGB (color[0], color[1], color[2]))));
    
    

  2. In the code that processes the WM_DESTROY message, find the following:

          DeleteObject (GetClassWord (hwnd, GCW_HBRBACKGROUND));
    

    Insert the following code in its place:

          DeleteObject (SetClassWord (hwnd, GCW_HBRBACKGROUND,
    
               GetStockObject (WHITE_BRUSH)));
    
    

MORE INFORMATION

In both cases above, the call to DeleteObject fails because the brush is selected into a device context (DC). Each time the user moves one of the scroll bars, the program creates a new brush from the GDI module's heap space. Once the GDI heap reaches its limit of 64 kilobytes, none of the applications running in the system can create GDI objects.

Under the debugging version of Windows 3.1, the following error message is displayed on the debugging terminal each time the erroneous code is executed:

   err COLORS1 GDI: GDI:Attempt to delete object owned by system

The resolution to this situation is to select a different brush into the DC, and then to delete the old brush. Because the SetClassWord function returns the previous value for the specified class word, it is very straightforward to pass the return value from SetClassWord to DeleteObject.


Additional reference words: 3.10
KBCategory: kbprg kbprb kbcode
KBSubcategory: GdiDc
Keywords : kb16bitonly


THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Last reviewed: July 23, 1997
© 1998 Microsoft Corporation. All rights reserved. Terms of Use.