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

ID: Q171472

The information in this article applies to:

Microsoft Visual Basic Control Creation, Learning, Professional, and Enterprise Editions for Windows

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

Create a new Standard EXE project.

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

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

Run the application by pressing the F5 Key.

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

Additional query words: com port kbVS97FixSP3 kbVS97FixSP2 kbVBp500bug kbVB5FixSP2 kbVBp kbDSupport kbdsd kbCrtl

Keywords : kbGrpVB
Version : WINDOWS:
Platform : WINDOWS
Issue type : kbbug