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Q171472: FIX: Toggling PortOpen w/MSCOMM32.OCX Leaks Memory on Win95/98

Article: Q171472
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:
Operating System(s): 
Keyword(s): kbCtrl kbVBp kbVBp500bug kbVS97fix kbVS97sp3fix kbGrpDSVB kbDSupport kbvbp500sp2fix
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Control Creation Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
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SYMPTOMS
========

When using the PortOpen method of the MSCOMM32.OCX control, continuous or
multiple uses of this method will produce a memory drain. The exact amount of
memory and resources lost varies with different port drivers installed.


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 2.

For more information on the Visual Studio 97 Service Pack 2, please see the
following article in the Microsoft Knowledge Base:

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

For a list of the Visual Basic 5.0 bugs that were fixed in the Visual Studio 97
Service Pack 2, please see the following article in the Microsoft Knowledge
Base:

  Q171554 : INFO: Visual Basic 5.0 Fixes in Visual Studio 97 Service Pack 2

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Create a new Standard EXE project.

2. Add an instance of the mscomm32.ocx control to Form1.

3. Add the following code to Form1.

        Sub Form_Load()
          Show
          While True
             MSComm1.Settings = "9600, N, 8, 1"
             MSComm1.PortOpen = True
             x = Timer
             Do While x + 0.25 > Timer
                 DoEvents: DoEvents: DoEvents
             Loop
             MSComm1.PortOpen = False
             x = Timer
             Do While x + 0.25 > Timer
                 DoEvents: DoEvents: DoEvents
             Loop
          Wend
        End Sub
    

4. Run the application by pressing the F5 Key.

After about 100 iterations, memory will be reduced by about 4k.

Additional query words: com port

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Keywords          : kbCtrl kbVBp kbVBp500bug kbVS97fix kbVS97sp3fix kbGrpDSVB kbDSupport kbvbp500sp2fix 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500Search kbVBA500 kbVBA600 kbVB500 kbVB600 kbZNotKeyword3
Version           : WINDOWS:
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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