Q176399: PRB: OLE Automation Error - 2147418107 (80010005)
Article: Q176399
Product(s): Microsoft Visual Basic for Windows
Version(s):
Operating System(s):
Keyword(s): kberrmsg kbole kbVBp500 kbVBp600 kbGrpDSVB
Last Modified: 11-JAN-2001
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The information in this article applies to:
- Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0
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SYMPTOMS
========
When a compiled Visual Basic application makes calls to an ActiveX server via a
timer event, the following error may occur:
Run-time error '-2147418107 (80010005)': Automation error
CAUSE
=====
After the first WM_TIMER event is fired, subsequent WM_TIMER events cannot be
processed until the first event is completed. The error message equates to:
It is illegal to call out while inside message filter.
RESOLUTION
==========
Three workarounds have been implemented with success:
Workaround 1
------------
Set a boolean flag in the timer event (see code listed in the Steps to Reproduce
Behavior section below).
1. Select Project .Add Module and add a standard module
2. Type the following code into the module:
Public flag As Boolean
3. Change the Timer1_Timer event code to read as follows:
Private Sub Timer1_Timer()
If Not flag Then
flag = True
RetStr = t.Test(100000)
flag = False
End If
Text1.Text = RetStr
End Sub
By doing this, the timer can't call the server until the previous call is
completed.
Workaround 2
------------
Create the server as a DLL, not an EXE. ActiveX DLLs are in-process servers. An
in-process server would not use Remote Procedure Call engine (RPC). (See the
MORE INFORMATION below.)
Workaround 3
------------
Place error handling in effect to ignore the error:
Private Sub Timer1_Timer()
On Error Resume Next
RetStr = t.Test(100000)
End Sub
STATUS
======
This behavior is by design.
MORE INFORMATION
================
Timers in Microsoft Windows are fired by Windows placing WM_TIMER messages in a
windows message queue. For example, an application receives the first timer's
WM_TIMER message in its window proc. This causes Visual Basic to fire the first
timer's Timer event, which calls the ActiveX server through the Remote Procedure
Call engine (RPC) because ActiveX EXE servers run in a separate process.
While the Visual Basic application is waiting for the RPC call to complete, the
RPC engine allows the Visual Basic application to sit and poll its message
queue. This is allowed primarily for screen redraw (if WM_PAINT messages come in
because the user was switching around windows), so the application can update
its windows while it is waiting for the RPC call to complete.
If, while Visual Basic waits for the first RPC call to complete, it processes a
second WM_TIMER message coming in through the RPC message filter, this causes
Visual Basic to fire the second timer's Timer event, which attempts to call the
ActiveX server again through the RPC engine. However, the RPC engine explicitly
does not allow an application to make an RPC call when it is in the RPC message
filter, so it returns an error that Visual Basic returns to the user.
At the point at which Visual Basic gets the WM_TIMER message, there is no way for
Visual Basic to know whether firing the Timer event will cause an RPC call to be
made. In fact, because ActiveX servers can be transparently remote, there is no
way for Visual Basic to know, when it is calling an object method, whether that
method will be routed through the RPC engine. Thus, there is no way for Visual
Basic to know ahead of time that the RPC engine is going to throw an error.
Steps to Reproduce Behavior
---------------------------
NOTE: The error will not reproduce unless you have compiled the projects.
Server
------
1. Start a new ActiveX EXE project.
2. Change the following properties:
Project Name:TestDelayServer
Class Name: cTestClass
3. Place the following code into cTestClass:
Option Explicit
Public Function Test(Optional delay As Long = 1000) as String
Dim index As Long
Dim Y As String
Dim X As String
Y = "a;lskdjf;laksdjf;lkasjd;flkajsmd;lfkjma;sldkfj;laskdj"
For index = 1 To delay
X = Right(Y, CInt(Len(Y) / 2))
X = ""
Next
Test = "I'm here"
End Function
4. Compile the EXE.
5. Run the EXE to register it.
Client
------
1. Start a new Standard EXE.
2. Select TestDelayServer from the Project - References menu.
3. Insert a Command Button, Timer Control and TextBox Control.
4. Place the following code into Form1's code window:
Option Explicit
Dim t As New TestDelayServer.cTestClass
Dim f As Form
Public RetStr As String
Private Sub Command1_Click()
Set f = New Form1
f.Show
End Sub
Private Sub Form_Load()
Timer1.Interval = 1000
Timer1.Enabled = True
End Sub
Private Sub Timer1_Timer()
RetStr = t.Test(100000)
Text1.Text = RetStr
End Sub
5. Save the project.
6. Compile the EXE.
7. Run the compiled EXE. Note that the Automation error occurs.
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Keywords : kberrmsg kbole kbVBp500 kbVBp600 kbGrpDSVB
Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600
Issue type : kbprb
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