ERROR : Thread was being aborted in c# Windows application

Question

I got below error when I used of thread for called waiting form during a long process.

"An unhandled exception of type 'System.Threading.ThreadAbortException' occurred in System.Windows.Forms.dll

Additional information: Thread was being aborted."

Sometimes my code works well but sometimes this error occurred.

class ProgressCLS
{
    private static Thread th = new Thread(new ThreadStart(showProgressForm));
    public void startProgress()
    {
        th = new Thread(new ThreadStart(showProgressForm));

        th.Start();
    }

    private static void showProgressForm()
    {              
                Waiting sForm = new Waiting();            
                sForm.ShowDialog();
    }

    public void stopProgress()
    {
            th.Abort();
            th = null;          
    }


}

I got this error on showProgressForm() Method on sform.ShowDialog() Line

and the main program I called this class looks like this:

ProgressCLS PC = new ProgressCLS();
PC.startProgress();
TodayDate = txtDate.SelectedDateTime.ToString("yy-MM-dd");
ClearField();
CalculateMSG();
tabControl1.SelectedIndex = 1;
btnShowFolderLocal.Enabled = true;
btnShowFolderTop.Enabled = true;
btnShowDpsFailed.Enabled = true;
btnShowDpsFailed2.Enabled = true;
btnShowFolderTopic.Enabled = true;
ShowMSGButtonClicked = true;
PC.stopProgress();

any Idea?

Answer 1

private static Thread th = new Thread(new ThreadStart(showProgressForm));  
public void startProgress()
{
    th = new Thread(new ThreadStart(showProgressForm));
    th.Start();
}

Not a big deal, but why do you instantiate your thread twice? Not really clean. I think only the one in your ctor is mandatory, because you set th = null when calling stopProgress().

Anyway look at your code, and remember that thread are asynchronous, so:

        ProgressCLS PC = new ProgressCLS();
        PC.startProgress();

It runs your progress form in a dedicated thread (asynchronous, so your code is still running).

    TodayDate = txtDate.SelectedDateTime.ToString("yy-MM-dd");
    ClearField();
    CalculateMSG();
    ...

You perform a serie of process in the main thread (synchrounously, your progress form still running in the background).

        PC.stopProgress();

Whatever the status of your progress form, it is aborted. And as you might have missed from the MSDN documentation, it "Raises a ThreadAbortException in the thread on which it is invoked". Thus to be fair, it is even Strange that your code "sometimes work", because if it hits the th.Abort() line, it should failed.

A few hints here:

• Usually we run UI form in the main Thread, and process in the Background
• With your current design, you may be in trouble if any of you process (ClearField() and CalculateMSG()) have asynchrounous operation.
• You rarely need to explicitely abort a Thread (only if there is an unexpected error). Just close the form when the progress is done, the Gargbage Collector can do the rest.