private readonly CancellationTokenSource s_cts = new CancellationTokenSource();

 public async Task Test()
    {
        Trace.WriteLine("Waiting started.");

        try
        {
            s_cts.CancelAfter(3000);
            await Task.Run(() => Sleep());
        }
        catch (OperationCanceledException ex)
        {
            Trace.WriteLine("Tasks cancelled: timed out.");
        }
        finally
        {
            s_cts.Dispose();
        }

        Trace.WriteLine("Waiting ending.");
    }


    public void Sleep()
    {
        var i = 0;
        while (i < 10)
        {
            Thread.Sleep(1000);
            i += 1;
            Trace.WriteLine(i.ToString());
        }
    }