FIX: RESTORE SCREEN Causes Memory Leak in Visual FoxPro 5.0

• Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a

SYMPTOMS

Repeatedly calling the SAVE SCREEN TO <memvar> and RESTORE SCREEN FROM <memvar> commands causes the operating system to run low on memory.

In Windows NT 4.0, the following message appears in a window titled "System Process-Out of Virtual Memory":

   Your system is running low on virtual memory. Please close some
   applications. You can then start the System option in the Control Panel
   and choose the Virtual Memory button to create as additional paging file
   or to increase the size of your current paging file.

   Program Error
   There is not enough memory to complete this operation.

   Program Error
   There is not enough memory to complete this operation.

RESOLUTION

As a workaround, place the following two commands before the RESTORE SCREEN FROM command in the code example below:

   ACTIVATE SCREEN
   CLEAR

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been fixed in Visual Studio 97 Service Pack 3.

For more information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q170365
   TITLE     : INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION

The amount of the memory leak with each iteration of the SAVE and RESTORE combination is dependent on screen resolution, size of Visual FoxPro desktop, and color depth. Memory leakage will be some multiple of the product of the _SCREEN.Width and _SCREEN.Height. This can be on a magnitude of megabytes per iteration.

Steps to Reproduce Behavior

WARNING: Running this code causes a low memory situation on the computer. This condition may cause the operating system to become unstable. Close all running applications and save your data before following this procedure. To close all open applications, press CTRL+ALT+Delete to open the NT Task Manager or the Windows 95 Close Program window, and then close all the other applications you have running.

1. Create a program containing the following code:

         ON KEY LABEL f12 CANCEL
         SAVE SCREEN TO s_var
         Y=1
         DO WHILE .T.
         Y=Y+1
         @ 1,1 SAY Y
         RESTORE SCREEN FROM s_var
         ENDDO
   

2. Run the program.