How to start new process from inside BackgroundWorker?

[rauty]

Hi all,

I have a situation where I'm using BackgroundWorker to run a long process in the background. However, whenever it runs I keep getting the following error:

"TargetInvocationException was unhandled"

The culprit seems to be this guy:

Dim GrainProcess As New Process()

In my DoWork sub I'm calling a sub in another module. The above line is in the middle of that other sub. I'm using Process.Start to run a Matlab executable file (not written by me) that processes an image and spits out a number.

I tried putting the Dim statement outside the sub, but then it just gives me the same error a couple of lines down when I try to set the .StartInfo properties.

Does the "was unhandled" part of the above exception mean that I need to provide some kind of error checking (maybe a try...catch), or does it mean that I'm not allowed to do a Process.Start from within a BackgroundWorker thread?

I'm pretty new to threading in general, so any help would be greatly appreciated. Code examples would be very helpful, since I'm not a programmer by nature and can't always make heads or tails out of what I read in the Microsoft Documentation.

Please also let me know if you need any additional info.

Thanks for your time!

[rauty]

Well, I tried putting the Process.Start routine in a Try...Catch block, but that didn't make any difference. One thing is, when the error occurs, the line

OutputString = Trim(.StandardOutput.ReadToEnd)

is highlighted in light gray, along with the Catch section. Here is all of the code I use to run the executable (from within the BackgroundWorker):

Try
            ' Call MATLAB routine (grain.exe) to calculate grain
            Dim GrainProcess As New Process()
            Dim OutputString As String
            Dim GrainInfo() As String
 
            ReDim Preserve GrainArray(GrainCount)
            ReDim Preserve MatlabLstar(GrainCount)
            ChDir(MatlabDir)
            With GrainProcess
              With .StartInfo
                .UseShellExecute = False
                .RedirectStandardOutput = True
                .RedirectStandardError = True
                .CreateNoWindow = True
                .FileName = "grain.exe"
                .Arguments() = ImgSaveMode & " RawImg.bmp " & ICCfile
              End With
              .Start()
              OutputString = Trim(.StandardOutput.ReadToEnd)
              ' Clean up the output (get rid of spaces, LF, etc.)
              GrainInfo = Split(OutputString, vbLf)
              Array.Copy(GrainInfo, 2, GrainInfo, 1, 1)
              ReDim Preserve GrainInfo(1)
              GrainInfo(1) = Trim(GrainInfo(1))
              GrainArray(GrainCount) = GrainInfo(0)
              MatlabLstar(GrainCount) = GrainInfo(1)
              .WaitForExit()
            End With
          Catch ex As Exception
            MsgBox(ex.Message, MsgBoxStyle.OkOnly + MsgBoxStyle.Exclamation, "Error Accessing grain.exe")
            ex = Nothing
          End Try

See below for a screen capture with highlighted areas:

For some reason I can make calls to functions within a DLL from the BackgroundWorker, but can't start a new process. Any help with this would be greatly appreciated!