Question

I have a winforms app with a long running task and two buttons.
One button Start and one Stop.

A new task with a cancellation Token starts when I press the start button.
And if I press the Stop button the cancellation Token’s Cancel Method gets called.

I want the UI to be usable during all the time so where do I put the try, catch block for this job. In all the examples I saw they put it around t.Wait();

But if I do that the UI freezes and that is the reason why I used a Task in the first place, to continue using the ui while doing the task. So where to put the try catch block without using Task.Wait.

Start button:

 tokenSource2 = new CancellationTokenSource();
   ct = tokenSource2.Token;
   t = new Task(doStart, ct);
   t.Start();

Stop button:

tokenSource2.Cancel();

Answer 1

You could update doStart to handle the cancellation event and exit the task gracefully so you wouldn’t need to use Wait at all e.g.

public void doStart(CancellationToken token)
{
    while(...)
    {
        ...
        if (token.IsCancellationRequested)
            break;
    }
}

Alternatively, you could wait for the task result on another thread e.g.

Thread.QueueUserWorkItem((state) =>
{
    try
    {
        t.Wait();
    }
    catch(...)
    {
        ...
    }
});