PRB: Slight Memory Leak Calling VFP COM DLL Repeatedly from VFP

ID: Q197206

The information in this article applies to:
  • Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0

SYMPTOMS

When you repeatedly call a COM DLL created in Visual FoxPro, the memory usage of Visual FoxPro increases slightly.


CAUSE

The memory usage increase between calls to the COM DLL is greater in Visual FoxPro 5.x than in Visual FoxPro 6.0. In Visual FoxPro 5.x, increases of 100K or more are common. In Visual FoxPro 6.0, the memory increases normally range from 4K to 16k.

The problem appears to be related to returning long character strings back from the COM DLL.


MORE INFORMATION

Steps to Reproduce Behavior

The Steps to Reproduce Behavior require that you use a Windows NT computer.

NOTE: If you run this on a different computer (not the one where you built the COM DLL), then you need to register it using Regsvr32.exe.

  1. Create a new project. Name it Test.


  2. Add a new program to the project. Name this Test.prg.


  3. Place the following code in Test.prg and save it: 
    
      DEFINE CLASS ObjectTest AS CUSTOM OLEPUBLIC
         FUNCTION MyGetObject()
            RETURN REPLICATE( "D", 65000 )
         ENDFUNC
      ENDDEFINE


  4. Build the project into a COM DLL.


  5. Create another new program. Name it Dotest.prg. Do not include it in the project.


  6. Place the following code in Dotest.prg and save it: 
    
      x = CreateObject("test.ObjectTest")
      FOR i = 1 TO 10
         x.MyGetObject()
      NEXT i
      x = .NULL.


  7. Keep the Dotest.prg file open in Visual FoxPro.


  8. Open the Windows NT Task Manager. Click the Process tab. Make sure the Mem Usage column is displayed. Find the Visual FoxPro executable file - VFP6.exe or VFP.exe. Note the Mem Usage number.


  9. Run the Dotest.prg program repeatedly by clicking on the Run ToolButton on the Standard toolbar.


RESULT: Note that the Mem Usage number jumps up and then comes back down each time. However, each time it comes back down, it is higher than it was previously. With Visual FoxPro 6.0, it is normally about 4k higher each time. This might vary between 2k and 16k higher. In Visual FoxPro 5.x, the Mem Usage increases by 100k or more each time you run the program.

Additional query words:

Keywords : kbCOMt kbOOP kbVFp500 kbVFp500a kbVFp600
Version : WINDOWS:5.0,5.0a,6.0
Platform : WINDOWS
Issue type : kbprb


Last Reviewed: August 2, 1999
© 2000 Microsoft Corporation. All rights reserved. Terms of Use.