Question

想法：创建一个Task，打印越来越多的星号。当用户按下Enter时，Task会打印10个星号，然后停止。

代码：

namespace CancellingLongRunningTasks
{
    using System;
    using System.Threading;
    using System.Threading.Tasks;

    class Program
    {
        static void Main()
        {
            var cancellationTokenSource = new CancellationTokenSource();
            var token = cancellationTokenSource.Token;

            Task task = Task.Run(() =>
            {
                int count = 1;
                while (!token.IsCancellationRequested)
                {
                    Console.WriteLine(new string('*', count));
                    Thread.Sleep(1000);
                    count++;
                }
            }, token).ContinueWith(
                parent =>
                {
                    var count = 10;
                    while (count > 0)
                    {
                        Console.WriteLine(new string('*', count));
                        Thread.Sleep(1000);
                        count--;
                    }
                }, TaskContinuationOptions.OnlyOnCanceled);

            Console.WriteLine("Press enter to stop the task.");

            if (Console.ReadLine().Contains(Environment.NewLine))
            {
                cancellationTokenSource.Cancel();
                task.Wait();
            }
        }
    }
}

问题：为什么我的继续执行任务没有执行？

Answer 1

它没有被执行，因为您没有主动取消Task，只检查是否请求取消。使用引发OperationCanceledException的{{3}}并将Task转换为已取消状态，或者只是使用相应的令牌抛出异常：

Task task = Task.Run(() =>
{
      int count = 1;
      while (!token.IsCancellationRequested)
      {
           Console.WriteLine(new string('*', count));
           Thread.Sleep(1000);
           count++;
       }
       token.ThrowIfCancellationRequested();
 }, token)

相当于：

Task task = Task.Run(() =>
{
      int count = 1;
      while (!token.IsCancellationRequested)
      {
           Console.WriteLine(new string('*', count));
           Thread.Sleep(1000);
           count++;
       }
       throw new OperationCanceledException(token);
 }, token)

取消任务时，不执行继续任务

1 个答案: