Assynchronous Cancelation while operation is running

Question

I'm starting a few tests about asynchronous programing in .net and now i'm stuck at trying ti cancel a long operation using cancellationToken.

So I have the following code:

CancellationTokenSource cancelationToken = new CancellationTokenSource();

My buttons to start the operations

    private void button2_Click(object sender, EventArgs e)
    {
        cancelationToken.Cancel(true);
    }

    private void button1_Click(object sender, EventArgs e)
    {
        StartOperation(cancelationToken.Token);
    }

And finally my operations

    private async void StartOperation(CancellationToken cancelToken)
    {
        await GetItensFromDatabase2(cancelToken);
    }

    public static Task<int> GetItensFromDatabase(CancellationToken cancelToken)
    {
        //cancelToken.Register( () => Console.WriteLine("Canceled") );
        return Task.Factory.StartNew<int>(() =>
        {
            int result = 0;

            cancelToken.ThrowIfCancellationRequested();

            result = MyLongOperation();  // Simulates my operation -> I want to cancel while this operation is still running

            return result;

        }, cancelToken);
    }

So, how to cancel MyLongOperation() method ? Is it possible to do ?

Answer 1

It is not possible to cancel in any point, the purpose of CancellationToken is to allow user to cancel the operation, when the long running operation expect that...

while(!finished)
{
     cancelToken.ThrowIfCancellationRequested();
     //Some not cancelable operations
}

Here is more common method of cancelable method

private static void LongRunning(CancellationToken cancelToken)
{
    while (true)
    {
        if(cancelToken.IsCancellationRequested)
        {
            return;
        }
        //Not canceled, continue to work
    }
}

The idea is, that user requests cancellation, but only executor decides when to stop his work. Usually executor do cancellation after reaching some "safe-point"

It is not good experiance to Abort long running operations without asking oppinion, a lot of posts have been written about this.