AsParallel 究竟是如何工作的？

发布于 2024-08-13 13:50:01 字数 668 浏览 9 评论 0原文

对于下面的测试程序来说，它似乎并没有做深蹲。这是因为我正在用一个小列表进行测试吗？

static void Main(string[] args)
{
    List<int> list = 0.UpTo(4);

    Test(list.AsParallel());
    Test(list);
}

private static void Test(IEnumerable<int> input)
{
    var timer = new Stopwatch();
    timer.Start();
    var size = input.Count();
    if (input.Where(IsOdd).Count() != size / 2)
        throw new Exception("Failed to count the odds");

    timer.Stop();
    Console.WriteLine("Tested " + size + " numbers in " + timer.Elapsed.TotalSeconds + " seconds");
}

private static bool IsOdd(int n)
{
    Thread.Sleep(1000);
    return n%2 == 1;
}

两个版本的运行时间均为 4 秒。

原文

It doesn't seem to do squat for the following test program. Is this because I'm testing with a small list?

static void Main(string[] args)
{
    List<int> list = 0.UpTo(4);

    Test(list.AsParallel());
    Test(list);
}

private static void Test(IEnumerable<int> input)
{
    var timer = new Stopwatch();
    timer.Start();
    var size = input.Count();
    if (input.Where(IsOdd).Count() != size / 2)
        throw new Exception("Failed to count the odds");

    timer.Stop();
    Console.WriteLine("Tested " + size + " numbers in " + timer.Elapsed.TotalSeconds + " seconds");
}

private static bool IsOdd(int n)
{
    Thread.Sleep(1000);
    return n%2 == 1;
}

Both versions take 4 seconds to run.

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凯凯我们等你回来 2024-08-20 13:50:01

任务并行库关心序列的静态类型。对于要由 TPL 处理的操作，它应该是 IParallelEnumerable。当您调用 Test 时，您会将集合强制转换回 IEnumerable。因此，编译器会将序列上的 .Where 调用解析为 System.Linq.Enumerable.Where 扩展方法，而不是 TPL 提供的并行版本。

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情深如许 2024-08-20 13:50:01

（更新.NET4，因为这个问题在 Google 搜索 AsParallel() 中排名相当靠前）

只需进行一些更改即可让您的示例按照我想象的方式工作。

更改 List; list = 0.UpTo(4); 到 var list = Enumerable.Range(0, 4);

如果您添加了带有采用 ParallelQuery 签名的函数重载，则您的示例将有效...

    private static void Test(ParallelQuery<int> input)
    {
        var timer = new Stopwatch();
        timer.Start();

        int size = input.Count();
        if (input.Where(IsOdd).Count() != size / 2)
        {
            throw new Exception("Failed to count the odds");
        }
        timer.Stop();

        Console.WriteLine("Tested " + size + " numbers in " + timer.Elapsed.TotalSeconds + " seconds");
    }

或者，您可以使用 LINQ 语法...

    private static void Test(ParallelQuery<int> list)
    {
        var timer = Stopwatch.StartNew();

        if ((from n in list.AsParallel()
             where IsOdd(n)
             select n).Count() != (list.Count() / 2))
        {
            throw new Exception("Failed to count the odds");
        }

        Console.WriteLine("Tested " + list.Count() + " numbers in " + timer.Elapsed.TotalSeconds + " seconds");
    }

希望这对某人有帮助！

(Updating for .NET4 since this question ranks pretty high in a Google search for AsParallel())

Just a few changes will allow your example to work as I imagine you expected.

Change List<int> list = 0.UpTo(4); to var list = Enumerable.Range(0, 4);

Your example would work if you added a function overload with a signature that takes a ParallelQuery...

    private static void Test(ParallelQuery<int> input)
    {
        var timer = new Stopwatch();
        timer.Start();

        int size = input.Count();
        if (input.Where(IsOdd).Count() != size / 2)
        {
            throw new Exception("Failed to count the odds");
        }
        timer.Stop();

        Console.WriteLine("Tested " + size + " numbers in " + timer.Elapsed.TotalSeconds + " seconds");
    }

Alternatively, you could use LINQ syntax....

    private static void Test(ParallelQuery<int> list)
    {
        var timer = Stopwatch.StartNew();

        if ((from n in list.AsParallel()
             where IsOdd(n)
             select n).Count() != (list.Count() / 2))
        {
            throw new Exception("Failed to count the odds");
        }

        Console.WriteLine("Tested " + list.Count() + " numbers in " + timer.Elapsed.TotalSeconds + " seconds");
    }

Hope this helps someone!

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