如何从Parallel.ForEach收集返回值？ [英] How do I collect return values from Parallel.ForEach?

问题描述

我正在同时调用慢速网络服务。一切都很棒，直到我意识到我需要从服务中获取一些信息。但是我看不到在哪里找回价值。我无法写入数据库HttpContext。在使用Parallel.ForEach

I'm calling a slow webservice in parallel. Things were great until I realized I need to get some information back from the service. But I don't see where to get the values back. I can't write to the database, HttpContext.Current appears to be null inside of a method called using Parallel.ForEach

的方法中，Current似乎为空，下面是一个示例程序（在您看来，请想象一个缓慢的Web服务而不是字符串连接）

Below is a sample program (in your mind, please imagine a slow web service instead of a string concatenation)

using System;
using System.Threading.Tasks;

class Program
{
    static void Main(string[] args)
    {
        WordMaker m = new WordMaker();
        m.MakeIt();
    }
    public class WordMaker
    {
        public void MakeIt()
        {
            string[] words = { "ack", "ook" };
            ParallelLoopResult result = Parallel.ForEach(words, word => AddB(word));
            Console.WriteLine("Where did my results go?");
            Console.ReadKey();
        }
        public string AddB(string word)
        {
            return "b" + word;
        }
    }

}

推荐答案

您已将其丢弃在这里。

ParallelLoopResult result = Parallel.ForEach(words, word => AddB(word));

您可能想要类似的东西，

You probably want something like,

ParallelLoopResult result = Parallel.ForEach(words, word =>
{
    string result = AddB(word);
    // do something with result
});

如果您想在此末尾进行某种收藏，请考虑使用 System.Collections.Concurrent ，例如 ConcurrentBag

If you want some sort of collection at the end of this, consider using one of the collections under System.Collections.Concurrent, like ConcurrentBag

ConcurrentBag<string> resultCollection = new ConcurrentBag<string>();
ParallelLoopResult result = Parallel.ForEach(words, word =>
{
    resultCollection.Add(AddB(word));
});

// Do something with the result

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