C# CancellationToken和CancellationTokenSource的用法详解

    public CancellationToken();//因为是结构体，才有空构造函数，不过没什么作用
    public CancellationToken(bool canceled);

    //静态属性，获取一个空的CancellationToken，这个CancellationToken注册的回调方法不会被触发，作用类似于使用空构造函数得到的CancellationToken
    public static CancellationToken None { get; }
    //表示当前CancellationToken是否可以被取消
    public bool CanBeCanceled { get; }
    //表示当前CancellationToken是否已经是取消状态
    public bool IsCancellationRequested { get; }
    //和CancellationToken关联的WaitHandle对象，CancellationToken注册的回调方法执行时通过这个WaitHandle实现的
    public WaitHandle WaitHandle { get; }

    //往CancellationToken中注册回调
    public CancellationTokenRegistration Register(Action callback);
    public CancellationTokenRegistration Register(Action callback, bool useSynchronizationContext);
    public CancellationTokenRegistration Register([NullableAttribute(new[] { 1, 2 })] Action<object?> callback, object? state);
    public CancellationTokenRegistration Register([NullableAttribute(new[] { 1, 2 })] Action<object?> callback, object? state, bool useSynchronizationContext);
    //当CancellationToken处于取消状态是，抛出System.OperationCanceledException异常
    public void ThrowIfCancellationRequested();

    CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
    var cancellationTokenRegistration = cancellationTokenSource.Token.Register(() =>
    {
        Console.WriteLine("Canceled");//这里将不会执行输出
    });

    //cancellationTokenSource.Cancel();
    //var result = cancellationTokenRegistration.Unregister();//result = false

    var result = cancellationTokenRegistration.Unregister();//result = true
　　 cancellationTokenSource.Cancel();

    CancellationToken cancellationToken = new CancellationToken(true);
    cancellationToken.Register(() =>
    {
        Console.WriteLine("Canceled");//这里会立即执行输出Canceled
    });

    CancellationToken cancellationToken = new CancellationToken(false);
    cancellationToken.Register(() =>
    {
        Console.WriteLine("Canceled");//这里不会立即执行输出
    });

    //表示Token是否已处于取消状态
    public bool IsCancellationRequested { get; }
    //CancellationToken 对象
    public CancellationToken Token { get; }

    //立刻取消
    public void Cancel();
    //立刻取消
    public void Cancel(bool throwOnFirstException);
    //延迟指定时间后取消
    public void CancelAfter(int millisecondsDelay);
    //延迟指定时间后取消
    public void CancelAfter(TimeSpan delay);

    CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
    try
    {
        cancellationTokenSource.Token.Register(() =>
        {
            throw new Exception("1");
        });
        cancellationTokenSource.Token.Register(() =>
        {
            throw new Exception("2");//不会执行
        });

        cancellationTokenSource.Cancel(true);
    }
    catch (Exception ex)
    {
        //ex is System.Exception("1")
    }

    CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
    try
    {
        cancellationTokenSource.Token.Register(() =>
        {
            throw new Exception("1");
        });
        cancellationTokenSource.Token.Register(() =>
        {
            throw new Exception("2");
        });

        cancellationTokenSource.Cancel(false);//相当于cancellationTokenSource.Cancel()
    }
    catch (Exception ex)
    {
        //ex is System.AggregateException:[Exception("2"),Exception("1")]
    }

    CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
    var task = new Task(() =>
    {
        Thread.Sleep(1500);//执行了2秒中代码
        Console.WriteLine("Execute Some Code");
    }, cancellationTokenSource.Token);

    task.Start();//启动，等待调度执行

    //发现不对，可以取消task执行
    cancellationTokenSource.Cancel();
    Thread.Sleep(1000);//等待1秒
    Console.WriteLine("Task状态：" + task.Status);//Canceled

    CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
    var task = new Task(() =>
    {
        Thread.Sleep(1500);//执行了2秒中代码
        cancellationTokenSource.Token.ThrowIfCancellationRequested();
        Console.WriteLine("Execute Some Code");
    }, cancellationTokenSource.Token);

    task.Start();//启动，等待调度执行

    Thread.Sleep(1000);////一段时间后发现不对，可以取消task执行
    cancellationTokenSource.Cancel();
    Thread.Sleep(1000);//等待1秒
    Console.WriteLine("Task状态：" + task.Status);//Canceled

    class Demo
    {
        public void Close(Action callback)
        {
            //关闭
            Thread.Sleep(3000);

            callback?.Invoke();//执行通知
        }
    }

    class Demo
    {
        public event Action Callback;

        public void Close()
        {
            //关闭
            Thread.Sleep(3000);

            Callback?.Invoke();//执行通知
        }
    }

        public CancellationTokenSource Listen()
        {
            CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();

            //循环调度执行
            Task.Run(() =>
            {
                while (true)
                {
                    cancellationTokenSource.Token.ThrowIfCancellationRequested();

                    //循环执行一些操作
                    Thread.Sleep(1000);
                    Console.WriteLine("Run");
                }
            });

            return cancellationTokenSource;
        }