如何确定CancellationTokenSource的范围？

我使用async/await而不是传统的线程来实现一个长时间运行的任务，该任务将从各种情况下调用，例如桌面/网络/移动设备。这个问题涉及在使用CancellationTokenSource/CancellationToken对象时的设计考虑。考虑下面这段用.NET Core 5编写的代码：

System
System.Collections.Generic
System.Diagnostics
System.IO
System.Threading
System.Threading.Tasks
[STAThread]
private static async Task Main ()
{
    using (var job = new Job())
    //using (var source = new CancellationTokenSource())
    {
        var watch = Stopwatch.StartNew();
        job.OnJobProgress += (sender, e) => { Console.WriteLine (watch.Elapsed); };
        Task.Run (async () => await job.StartAsync());
        //Task.Run (async () => await job.StartAsync (source.Token));
        do
        {
            await Task.Delay (100);
            if ((Console.KeyAvailable) && (Console.ReadKey ().Key == ConsoleKey.Escape))
            {
                //source.Cancel();
                await job.CancelAsync();
                break;
            }
        }
        while (job.Running);
    }
}
public class Job : IDisposable
{
    public EventHandler OnJobProgress;
    private bool _Running = false;
    private readonly object SyncRoot = new object();
    private CancellationTokenSource CancellationTokenSource = new CancellationTokenSource();
    public bool Running => this._Running;
    public async Task StartAsync () => await this.StartAsync(CancellationToken.None);
    public async Task StartAsync (CancellationToken cancellationToken) => await this.ProcessAsync(cancellationToken);
    public void Cancel ()
    {
        this.CancellationTokenSource?.Cancel();
        do { Thread.Sleep (10); } while (this._Running);
    }
    public async Task CancelAsync ()
    {
        this.CancellationTokenSource?.Cancel();
        do { await Task.Delay (10); } while (this._Running);
    }
    private async Task ProcessAsync (CancellationToken cancellationToken)
    {
        lock (this.SyncRoot)
        {
            if (this._Running) { return; }
            else { this._Running = true; }
        }
        do
        {
            await Task.Delay (100);
            this.OnJobProgress?.Invoke (this, new EventArgs());
        }
        while (!cancellationToken.IsCancellationRequested);
        lock (this.SyncRoot)
        {
            this._Running = false;
            this.CancellationTokenSource?.Dispose();
            this.CancellationTokenSource = new CancellationTokenSource();
        }
    }
    public void Dispose () => this.Cancel();
}

请注意Main方法中的三行被注释的代码，以及Cancel和CancelAsync方法。我的直觉告诉我，在Cancel方法中应该有一个锁机制，而不是在Process方法中。根据CancellationToken来自何处，这个实现中是否存在潜在的死锁问题？不知怎么的，我对do/while的阻塞机制不太放心。

欢迎提出任何想法。附加问题：由于CancellationToken是一个readonly struct并且是按值传递的，那么为什么在CancellationTokenSource上调用Cancel会修改CancellationToken.IsCancellationRequested属性？也许这一直是造成困惑的根源。