Microsoft KB Archive/149036

= BUG: Modal Dialog in Terminate Causes Lockup on Windows 95/98 =

Article ID: 149036

Article Last Modified on 10/15/2002

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APPLIES TO


 * Microsoft Visual Basic 4.0 Professional Edition
 * Microsoft Visual Basic 4.0 16-bit Enterprise Edition

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This article was previously published under Q149036



SYMPTOMS
Displaying a modal dialog in the Terminate event of a class module can cause a lockup of the server providing the class and any clients. This happens with the 16-bit version of Visual Basic 4.0 on the Windows 95 and Windows 98 operating systems and can be demonstrated by the ds.vbp and thingtst.vbp samples in the oleserv sample directory.



RESOLUTION
Do not show any modal dialogs in the Terminate event of a class. Showing any modal dialogs, including message boxes, is not recommended in either the Initialize or Terminate events of a class module because it can interfere with the creation and/or termination of objects. Both client and server are halted until the modal dialog is dismissed.



STATUS
Microsoft has confirmed this to be an issue in the Microsoft products listed at the beginning of this article.



Steps to Reproduce Behavior

 * 1) Start two instances of Visual Basic 4.0, 16-bit, on Windows 95. Load the ds.vbp sample located in the \vb4\samples\oleserv directory and click F5 to start the server application.
 * 2) Switch to the other running instance of VB4 16 and load the thingtst.vbp sample, which is also located in the \vb4\samples\oleserv directory. Say yes to the Could not create reference dialog box if it appears. The instance of the thing server running in the IDE has changed the registry so that it is used instead of any previously compiled instances of ds.exe. The references need to be changed in the client so this is taken into account.
 * 3) On the Tools menu, choose References to show the References dialog box. Find the MISSING: Demonstration OLE Server entry and clear it. Close the dialog by clicking OK. Reopen the References dialog and check the Demonstration OLE Server entry.
 * 4) Run the client application and enter a name for the Form Thing. Click OK, then click OK again to dismiss the message box shown in the Initialize event.
 * 5) Click the New Form Thing button to set the old object reference to nothing and create a new instance of the Form Thing class. The Thing Terminate modal dialog box displays, but no longer responds to the mouse. The client and server are locked up at this point. The server can be shut down with the Close Program dialog (CTRL+ALT+DELETE and End Task).

Keywords: kbbug kbpending KB149036

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