MSScript.ocx Leaks Event Handles in Applications That Repeatedly Create and Destroy Threads (315922)


The information in this article applies to:

  • Microsoft Visual Basic Enterprise Edition for Windows 5.0
  • Microsoft Visual Basic Enterprise Edition for Windows 6.0
  • Microsoft Visual Basic Professional Edition for Windows 5.0
  • Microsoft Visual Basic Professional Edition for Windows 6.0
This article was previously published under Q315922

SYMPTOMS

When you use the Microsoft Script control (MSScript.ocx) in an environment that repeatedly creates and destroys threads, MSScript.ocx leaks event handles. For each thread that is created and destroyed, an event handle is leaked if one or more objects of the Script control are created on that thread.

WORKAROUND

Do not repeatedly create and destroy threads; use a thread pool instead.

STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article. Microsoft is researching this problem and will post more information in this article when the information becomes available.

MORE INFORMATION

Steps to Reproduce Behavior

  1. In Visual Basic, create an ActiveX EXE project named Repro. A default class named Class1 is created by default.
  2. Add a form to the project. Keep the default name Form1.
  3. Add Microsoft Script Control 1.0 to the toolbox, and then add an instance of the control to Form1.
  4. Add the following code to Class1:
    Dim f As New Form1
Private Sub Class_Initialize()
    f.Visible = True
End Sub
Private Sub Class_Terminate()
    Unload f
End Sub
  5. Change the threading model of the project to Thread per Object, and then build the project.
  6. In Visual Basic, create a Standard EXE project. Keep the default name Project1. Form1 is created by default.
  7. Add a command button to Form1, and then add the following code to Form1:
    Dim server As Object
Private Sub Command1_Click()
    Dim o As Object
    Set o = CreateObject("repro.class1")
    Set o = Nothing
End Sub

Private Sub Form_Load()
    Set server = CreateObject("repro.class1")
End Sub

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
    Set server = Nothing
End Sub
  8. Build and run Project1. Notice that two processes, Project1.exe and Repro.exe, are started.
  9. Use Performance Monitor or Task Manager to monitor the handle count for Repro.exe.
  10. Repeatedly click the command button on Form1 of Project1, and then observe the handle count for the Repro.exe process. Notice that each time you click the button, an instance of the control is created and destroyed, and the handle count for Repro.exe increases by 1.
Modification Type:MajorLast Reviewed:6/10/2002
Keywords:kbbug KB315922
©2002 Microsoft Corporation. All rights reserved.