TPL中的任務排序

Question

如果我有以下代碼

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

namespace ConsoleApplication3
{
    class Program
    {
        static Task<int> GetSuperLargeNumber()
        {
            var main = Task.Factory.StartNew(() =>
                                                 {
                                                     Thread.Sleep(1000);
                                                     return 100;
                                                 });
            var second = main.ContinueWith(x => Console.WriteLine("Second: " + x.Result), TaskContinuationOptions.AttachedToParent);
            var third = main.ContinueWith(x => Console.WriteLine("Third: " + x.Result), TaskContinuationOptions.AttachedToParent);

            return main.ContinueWith(x  =>
                                             {
                                                 Task.WaitAll(second, third);
                                                 return x.Result;
                                             });
        }

        static void Main(string[] args)
        {
            GetSuperLargeNumber().ContinueWith(x => Console.WriteLine("Complete"));

            Console.ReadKey();
        }
    }
}

我希望main首先啟動，然后2個依賴項可以在其后並行啟動，它們分別是第一和第二。 然后，我想返回一個帶有值的future，以便調用者在其上添加延續。 但是，我想確保第二和第三個先運行。 下面的代碼是實現此目標的最佳方法嗎？ 似乎有點笨拙

Answer 1

我對TPL不太熟悉，但這不是ContinueWhenAll目的嗎？

static Task<int> GetSuperLargeNumber()
{
    var main = Task.Factory.StartNew(() =>
                                         {
                                             Thread.Sleep(1000);
                                             return 100;
                                         });
    var second = main.ContinueWith(
        x => Console.WriteLine("Second: " + x.Result),
        TaskContinuationOptions.AttachedToParent);
    var third = main.ContinueWith(
        x => Console.WriteLine("Third: " + x.Result),
        TaskContinuationOptions.AttachedToParent);

    return Task.Factory.ContinueWhenAll(
        new[] { second, third },
        (twotasks) => /* not sure how to get the original result here */);
    }

我不知道如何從完成的second和third （包含在twotasks ）獲取main的結果，但是也許您可以修改它們以傳遞結果。

編輯：或者，正如亞歷克斯指出，使用

Task.Factory.ContinueWhenAll(new[] { main, second, third }, (threetasks) => ...

並從threetasks[0]讀取結果。

Answer 2

這樣就足夠了：

static Task<int> GetSuperLargeNumber()
{
    var main = Task.Factory.StartNew<int>(() =>
    {
        Thread.Sleep(1000);
        return 100;
    });
    var second = main.ContinueWith(x => Console.WriteLine("Second: " + x.Result), TaskContinuationOptions.AttachedToParent);
    var third = main.ContinueWith(x => Console.WriteLine("Third: " + x.Result), TaskContinuationOptions.AttachedToParent);

    Task.WaitAll(second, third);

    return main;
}