c# - 并行 Linq : Ordered treatment

Question

我正在学习 70-516 MS 考试的资料，我看到了他们解释说如果我们使用 AsOrdered 方法，我们可以确保在进行并行处理的同时进行有序处理的部分。

但是，运行下面的示例不会按顺序输出结果。

基本上，下面的示例代码从 10 个整数的可枚举集合开始，然后对其进行并行化、排序，最后仅选择 Compute 函数返回偶数的元素进行过滤。 Compute 函数在 1 秒延迟后仅返回输入

private void TestLinqParallel()
    {
        Stopwatch sw = new Stopwatch();
        sw.Start();
        var source = Enumerable.Range(1, 10).AsParallel().AsOrdered();
        var evenNums = from num in source
                       where Compute(num) % 2 == 0
                       select num;
        evenNums.ForAll(ev =>
        {
            Debug.WriteLine(string.Format("{0} on Thread {1}", ev, Thread.CurrentThread.GetHashCode()));

        });
        sw.Stop();
        Debug.WriteLine(string.Format("Done {0}", sw.Elapsed));
    }
    public int Compute(int num)
    {
        Debug.WriteLine(string.Format("Computing {0} on Thread {1}", num, Thread.CurrentThread.GetHashCode()));
        Thread.Sleep(1000);
        return num;
    }

书上说

The results are ordered, at least for the even numbers, which is what the AsOrdered extension method is guaranteeing.

但这是我的结果.. 4 的处理先于 2 的处理

Computing 4 on Thread 11
Computing 3 on Thread 10
Computing 2 on Thread 12
Computing 1 on Thread 6
4 on Thread 11
Computing 7 on Thread 11
Computing 6 on Thread 6
2 on Thread 12
Computing 8 on Thread 12
Computing 5 on Thread 10
Computing 9 on Thread 11
6 on Thread 6
Computing 10 on Thread 6
8 on Thread 12
10 on Thread 6
Done 00:00:03.0561023

有人能帮忙吗？

Answer 1

ForAll 是并行化的。这意味着所有排序保证都超出了窗口，因为您的代码主体是并发执行的。尝试 foreach 循环。