如何防止不确定进度条冻结?

BackgroundWorker

protected void ShowProgress()
{
    if (_progressThread != null)
        return;

        _progressThread = new Thread(() =>
        {
            var progressShell = Program.ViewFactory.CreateDialogShell();
            progressShell.DataContext = new ProgressViewModel(this);
            progressShell.Show();

            Dispatcher.Run();
        });

        _progressThread.SetApartmentState(ApartmentState.STA);
        _progressThread.Start();
}

protected void HideProgress()

{
    if (_progressThread == null)
        return;

    _progressThread.Abort();
    _progressThread = null;
}

        ProgressIndicator.Visibility = System.Windows.Visibility.Visible;            

        ThreadPool.QueueUserWorkItem
        (
            delegate
            {
                // Perform slow action
                Thread.Sleep(5000);

                this.Dispatcher.Invoke(
                    new Action(delegate()
                    {                                    
                            // Insert UI related activity here.
                            // ....
                            ProgressIndicator.Visibility = System.Windows.Visibility.Collapsed;                                                                     
                    }
                    ));
            }
        );