BUG: Invalid Page Fault Occurs with More than 34 DDE Channels

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, versions 5.0, 6.0
  on the following platforms: Win95
• Microsoft Visual Basic Standard, Professional, and Enterprise Editions, 32-bit only, for Windows, version 4.0
  on the following platforms: Win95

SYMPTOMS

The following error message is displayed if you attempt to open more than 34 DDE (Dynamic Data Exchange) channels:

VB5 caused an invalid page fault in module KRNL386.EXE at 0002:000033C6

RESOLUTION

Use OLE automation instead of DDE. OLE automation is the current and future support technology at Microsoft. For more information about OLE automation see the following:

• "Programming with Components" in the Visual Basic Programmer's Guide



• OLE Automation: Communicating with Other Applications at http://www.microsoft.com/AccessDev/Articles/comothap.htm


To be safe, you should also reuse connections rather than open additional ones to keep the total number of open connections below 30.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

The number of DDE channels required to reproduce this problem varies by machine and configuration and is not predictable. This behavior occurs in as few as 34 channels to as many as 72 channels.

The next section shows how to create a sample project that demonstrates this behavior. In order to observe the behavior, you need to create an Excel spreadsheet to act as a server.

Create the Excel Spreadsheet

1. Start Excel. Book1 is created by default.



2. Enter a number in the cell R1C1.



3. Save the spreadsheet using the default filename Book1.xls, and then Minimize Excel.

Steps to Reproduce Behavior

1. Start a new Standard EXE project in Visual Basic. Form1 is created by default.



2. Add the CommandButton, Label, and Text Box to Form1. Set the Index property of the Label control to 0.



3. Copy the following code to the Code window of Form1:




      Option Explicit

      Const MAX_CONNECTIONS = 98

      Private Sub Form_Load()
      'Creates a grid composed of labels.

         Dim i As Integer
         Dim n As Integer
         Dim j As Integer
         Dim temptop As Integer
         Dim templeft As Long

         templeft = 120
         temptop = 120

         ' Set initial properties of label used as template for dynamically
         ' created labels.
         Label1(0).BorderStyle = 1
         Label1(0).Caption = ""
         Label1(0).Visible = False
         Label1(0).Move 120, 120, 1200, 300

         ' Size form to handle array of MAX_CONNECTIONS labels and other
         ' controls.
         Me.Height = (Label1(0).Height * 14) + (60 * 15) + 980
         Me.Width = (Label1(0).Width * 7) + (60 * 8) + 200
         Me.Caption = "DDE Connection Limit Test"

         'Set initial properties of Command1.
         Command1.Caption = "Number of DDE connections"
         Command1.Move 1420, Me.Height - 920, 4800, 400
         Command1.Default = True

         'Set initial properties of Text1.
         Text1.Text = ""
         Text1.Move 120, Command1.Top, 1200, Command1.Height

         'Two nested For loops create grid of labels.
         For i = 1 To 14 'Outer loop moves down the form,
            For j = 1 To 7 'inner loop moves across the form.
               n = n + 1 'supplies you with array index.
               Load Label1(n)
               Label1(n).Visible = True
               Label1(n).Top = temptop
               Label1(n).Left = templeft
               templeft = templeft + Label1(0).Width + 60
            Next j
            templeft = 120
            temptop = temptop + Label1(0).Height + 60
         Next i

         Me.Show
         Text1.SetFocus
      End Sub

      Private Sub Command1_Click()
         Dim iValue As Integer
         Dim i As Integer

         'Get the value entered by the user.
         iValue = Val(Text1)

         'Test for invalid value.
         If iValue < 1 Or iValue > MAX_CONNECTIONS Then
            MsgBox "Enter a number between 1 and " & MAX_CONNECTIONS
            Exit Sub
         End If

         'Remove any existing connections and reset all captions.
         For i = 1 To MAX_CONNECTIONS
            Label1(i).LinkMode = vbLinkNone
            Label1(i).Caption = ""
         Next i

         'Start DDE conversations for the chosen number of labels.
         For i = 1 To iValue
            Label1(i).LinkTopic = "EXCEL|Book1.xls"
            Label1(i).LinkItem = "R1C1"
            Label1(i).LinkMode = vbLinkAutomatic
         Next i
      End Sub
 

4. On the Run menu, click Start, or press the F5 key to start the program. In the Text Box, enter a number between 34 and 98 and click the CommandButton. The result is that an Invalid Page Fault occurs.

Additional query words: IPF GPF Crash Dynamic Data Exchange DDE Link

Keywords : kbinterop kbVBp kbVBp400bug kbVBp500bug kbVBp600bug kbGrpVB kbDSupport
Version : WINDOWS:4.0,5.0,6.0
Platform : WINDOWS
Issue type : kbbug