如何取消正在等待超时的任务而不抛出异常

Question

使用取消标记取消超时（超时结束之前）的任务时，会引发异常。示例：

mytask.start();
bool didTaskRunInTime = mytask.wait(5 mins, _cancelToken);

这意味着我不能像下面这样继续下去。

//was the task cancelled
if (_cancelToken.IsCancelRequested)
{
    // log cancel from user to file etc
}

if (didTaskRunInTime )
{
    int taskResult = myTask.Result;
    // log result to file
}
else if (!_cancelToken.IsCancelRequested)
{
    // Tell user task timed out , log a message etc
}

我必须在 catch 块中完成所有这些操作，并且我的代码看起来很混乱。这样做的正确方法是什么？

Answer 1

您可以使用 Task.WaitAny 调用只是该任务的数组。然后，您可以根据任务的状态采取行动，但方法会返回。示例代码：

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

class Test
{
    static void Main()
    {
        Task sleeper = Task.Factory.StartNew(() => Thread.Sleep(100000));

        int index = Task.WaitAny(new[] { sleeper },
                                 TimeSpan.FromSeconds(0.5));
        Console.WriteLine(index); // Prints -1, timeout

        var cts = new CancellationTokenSource();

        // Just a simple wait of getting a cancellable task
        Task cancellable = sleeper.ContinueWith(ignored => {}, cts.Token);

        // It doesn't matter that we cancel before the wait
        cts.Cancel();

        index = Task.WaitAny(new[] { cancellable },
                             TimeSpan.FromSeconds(0.5));
        Console.WriteLine(index); // 0 - task 0  has completed (ish :)
        Console.WriteLine(cancellable.Status); // Cancelled
    }
}

请注意，如果任务出错，您应该“观察”异常，以避免它在最终确定时发生爆炸:)

Answer 2

尝试使用OperationCanceledException

try
{           
    mytask.start();
    bool didTaskRunInTime = mytask.wait(5 mins, _cancelToken);

    if (didTaskRunInTime )
    {
        int taskResult = myTask.Result;
        //log result to file
    }
    else
    {
        // Tell user task timed out , log a message etc
    }
}
catch (OperationCanceledException ex)
{
    // log cancel from user to file et
}