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

• Microsoft Visual Basic Control Creation, Learning, Professional, and Enterprise Editions for Windows, version 5.0 on the following platform: Win95

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:

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

   ARTICLE-ID: Q171554
   TITLE     : 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.