C# Task 取消执行的简单封装

孙兴龙

我让DeepSeek帮我写了一段使用 CancellationTokenSource 取消任务的简单示例如下：

取消任务的简单示例

using System.Threading.Tasks;
using System.Threading;

public async Task Test()
{
    var cts = new CancellationTokenSource();
    var task = Task.Run(() =>
    {
        while (true)
        {
            cts.Token.ThrowIfCancellationRequested();
            Thread.Sleep(200);
        }
    });
    await Task.Delay(1000);
    cts.Cancel();
    try
    {
        await task;
    }
    catch (OperationCanceledException)
    {
        // task is cancelled
    }
    finally
    {
        cts.Dispose();
    }
}

相对于不可取消的普通任务多了很多代码，并且终止任务的方式 ThrowIfCancellationRequested 内部是通过抛出异常实现的

ThrowIfCancellationRequested 内部代码

public void ThrowIfCancellationRequested()
{
    if (IsCancellationRequested)
    {
        throw new OperationCanceledExceptionEx(this);
    }
}

于是我就想自己封装一个简单的包装类，代码如下：

CancelableTask

namespace System.Threading.Tasks
{
    public sealed class CancelableTask : Task
    {
        readonly object cancelLock = new object();
        CancellationTokenSource cts;

        public bool IsCancellationRequested => cts != null && cts.IsCancellationRequested;

        private CancelableTask(Action action, CancellationToken token) : base(action, token) { }

        protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                cts?.Dispose();
            }
            base.Dispose(disposing);
        }

        public void Cancel()
        {
            lock (cancelLock)
            {
                if (!IsCompleted && !IsCancellationRequested)
                {
                    cts.Cancel();
                }
            }
        }

        public static CancelableTask StartNew(Action action)
        {
            var cts = new CancellationTokenSource();
            var task = new CancelableTask(action, cts.Token);
            task.cts = cts;
            task.Start();
            return task;
        }

        public static void Restart(ref CancelableTask task, Action action)
        {
            var oldTask = Interlocked.Exchange(ref task, null);
            oldTask?.Cancel();
            var newTask = StartNew(action);
            Interlocked.Exchange(ref task, newTask);
        }
    }
}

此类公开了 Cancel 用来取消任务，静态的 StartNew 用来创建新实例，以及静态的 Restart 用来取消上个任务并重启任务，
还公开了一个 IsCancellationRequested 属性用来获取是否请求过取消任务，相对于调用 ThrowIfCancellationRequested 抛出异常来终止任务的方式性能更好也更加友好
使用此类重新编写上面的示例就简单很多了

CancelableTask 使用示例

using System.Threading.Tasks;

CancelableTask task;

public async Task Test()
{
    task = CancelableTask.StartNew(() =>
    {
        while (!task.IsCancellationRequested)
        {
            Thread.Sleep(200);
        }
    });
    await Task.Delay(1000);
    task.Cancel();
    await task;
}

来源：https://www.cnblogs.com/BluePointLilac/p/18908951