Question

I have a job object for long running operations that works like this:

Class LongRunningJob
    Inherits BackgroundWorker

    Protected Overrides Sub OnDoWork(ByVal e As System.ComponentModel.DoWorkEventArgs)
         'do long running job here
    End Sub
End Class

And I invoke this like so:

    Dim job As New LongRunningJob

    'run it
    job.RunWorkerAsync()

This worked fine a year ago, and I moved on to other things. I had to return to this code today, and when I run it now, the OnDoWork override is simply not called. A breakpoint in there isn’t hit, debugging messages aren’t written, the method is simply not called, and no errors are thrown anywhere.

I can’t think what would have changed that could cause this, since it seems like a low level framework thing. The rest of the app loads and runs fine, the main window shows (it’s a WPF app), and button click events fire. It’s just the background thread method that doesn’t fire. What could be going on here?

Answer 1

Well, I figured out how to fix the problem, although I’m not really sure what’s really going on here. If I left the OnDoWork routine empty:

Protected Overrides Sub OnDoWork(ByVal e As System.ComponentModel.DoWorkEventArgs)
     'no code at all
End Sub

it would be called, and if I put basic framework stuff in there, it would also be called. But as soon as I added a line like this:

Dim result = AnotherLibrary.SomeMethod()

the routine would not be called. I looked at the project for AnotherLibrary, which is authored by me as well, looked at the Compile Tab, the Target CPU dropdown and saw that it said x86. I changed it to Any CPU and that fixed the problem. But I’d still like to know what that really means and why it caused this problem.