c# – 即使指定TaskContinuationOptions,任务延续也始终运行

通过阅读Web上的文档和示例,我想我可以使用Task.ContinueWith并指定TaskContinuationOptions.OnlyOnRanToCompletion.

但是,这并不像我预期的那样.

以下代码是在Visual Studio 2012中创建的控制台程序.Net 4.5：

using System;
using System.Threading.Tasks;

namespace TaskContinueTest
{
    class Program
    {
        static void Main(string[] args)
        {
            var jobTask = Task.Factory.StartNew(() => { });

            jobTask.ContinueWith((task, options) =>
            {
                Console.WriteLine("Completed handler. Task status is {0}", task.Status);
            }, TaskContinuationOptions.OnlyOnRanToCompletion);

            jobTask.ContinueWith((task, options) =>
            {
                Console.WriteLine("Faulted handler. Task status is {0}", task.Status);
            }, TaskContinuationOptions.OnlyOnFaulted);

            Console.ReadLine();
        }
    }
}

运行时,我得到输出：

Completed handler. Task status is RanToCompletion
Faulted handler. Task status is RanToCompletion

这是非常令人惊讶的(至少对我而言).为什么两个延期都安排好了？

如果我在jobTask中抛出异常,我会得到相同的行为,但输出现在是：

Completed handler. Task status is Faulted
Faulted handler. Task status is Faulted

所以框架清楚地知道任务的状态,但为什么两个延续仍然安排？

public Task ContinueWith(
    Action<Task, Object> continuationAction,
    Object state
)

你想要的是this overload：

public Task ContinueWith(
    Action<Task> continuationAction,
    TaskContinuationOptions continuationOptions
)

您只需要更改lambda表达式以使用单个参数：

Task.ContinueWith(task => Console.WriteLine(...),
    TaskContinuationOptions.OnlyOnRanToCompletion);