ArcMap and BackgroundWorkerThread

I am reading here, I have to stick to STA threads while working inside ArcMap. I used the usual BackgroudnWorker

one and my code was very slow. I am trying to change it so that a worker creates an STA thread internally and runs it for "heavy" stuff.

Now my problem is that after executing the second thread, all my com-objects will be released. I checked if I have some kind of marshal. Calling RelaseComObject or Shutdown, but I don't think it is. Maybe just because the thread that fetched those COM objects is running, the objects are automatically deallocated?

here is my example code:

    private void bckgrndWrkrController_DoWork(object sender, DoWorkEventArgs e)
    {
        BackgroundWorker worker = sender as BackgroundWorker;
        if (worker != null)
        {
            controller.BackgroundWorker = worker;
            Thread thread = new Thread(STAProcessSelection);
            thread.SetApartmentState(ApartmentState.STA);
            thread.Start(e.Argument);
            thread.Join();
            e.Result = processingResult;
            e.Cancel = worker.CancellationPending;
        }
    }

    private void STAProcessSelection(object argument)
    {
        ISelection selection = argument as ISelection;
        if (selection != null)
        {
            processingResult = controller.ProcessSelection(selection);
        }
    }

    private void bckgrndWrkrController_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        if (e.Error != null)
        {
            MessageBox.Show(e.Error.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
        else if (e.Result is bool)
        {
            // Making sure the thread was not cancelled after we got the result
            processingResult = (bool)e.Result && !worker.CancellationPending;
            if (processingResult)
            {
                // Set the datasource of the grid
                bindingSource.DataSource = controller.List;
            }
        }

        // and inform the command we are done
        OnDoneProcessing(EventArgs.Empty);
    }

      

        
        
        
      

    

On line # 22, after calling ProcessSelection, the controller .List [0] contains a valid com object. On line # 11, after the call to thread.Join, the controller.List [0] element already contains a released com object. What am I doing wrong here?