为什么我的单线程代码比我的多线程代码快 [英] Why is my single threading code faster than my multithreading code

问题描述

我写了一些简单的代码来从一个 json 字符串中获取一些关键值，但是当我去多线程时，为了让它快速多次获取值，每次都会变慢.我不太确定为什么会发生这种情况，我在想这可能与我的 CPU 有关?添加一个等待函数似乎可以修复它，但它会变得非常缓慢，我没有想法，我不确定是什么导致了它.

I wrote some simple code to grab some key values from a json string, but when i go to multi thread it, to make it quickly grab the value multiple times, it gets slower each time. Im not quite sure why this is happening, i was thinking it might have had something to do with my cpu? Adding a wait function seems to fix it, but makes it go extremely slow, im out of ideas and im not sure as to what is causing it.

输出:

Single Threaded
598
Elapsed=0.558
598
Elapsed=0.121
598
Elapsed=0.127
598
Elapsed=0.127
598
Elapsed=1.167
598
Elapsed=0.122
598
Elapsed=0.124
598
Elapsed=0.145
598
Elapsed=0.146
598
Elapsed=0.12
------------------------------
Multi Threading
598
Elapsed=0.129
598
Elapsed=0.179
598
Elapsed=0.227
598
Elapsed=0.299
598
Elapsed=0.326
598
Elapsed=0.396
598
Elapsed=0.427
598
Elapsed=0.505
598
Elapsed=0.525
598
Elapsed=0.703

private static void Test2() {
        Stopwatch sw = new Stopwatch();
        sw.Start();
        using (WebClient wb = new WebClient()) {
            wb.Proxy = null;
            string data = wb.DownloadString("https://google.com");
            sw.Stop();
            Console.WriteLine("Elapsed={0}", (double)sw.ElapsedMilliseconds / 1000);
        }
    }
    static void Main(string[] args) {

        Console.WriteLine("Single Threaded");

        Test2();
        Test2();
        Test2();
        Test2();
        Test2();
        Test2();
        Test2();
        Test2();
        Test2();
        Test2();

        Console.WriteLine("------------------------------");
        Console.WriteLine("Multi Threading");

        for (int i = 0; i < 10; i++) {
            void Multi() {
                Test2();
            }
            new Thread(Multi).Start();
        }
        Console.Read();
    }

推荐答案

仅供对比；我使用异步代码进行了一些重写.从 OP 代码中重用了很多，我知道有一些旧的东西，但现在让我们保持这样.

Just for comparing; I made a little rewrite using async code. Lot of reuse from OPs code, I know there is some old stuff, but let's keep it like that for now.

单线程:Elapsed=2.688

Single Threaded: Elapsed=2.688

多线程:Elapsed=0.317

Multi Threaded: Elapsed=0.317

AMD 8 核 CPU

AMD 8-Core CPU

public class ThreadingTests
{
    private static async Task Test2()
    {
        await Task.Delay(1); // only here to make method async

        using var wb = new WebClient { Proxy = null };
        var data = wb.DownloadString("https://www.roblox.com/users/inventory/list-json?assetTypeId=41&cursor=&itemsPerPage=100&pageNumber=1&userId=539720021");
        dynamic parsed = JObject.Parse(data);
    }

    [Test]
    public async Task SingleTest()
    {
        Console.WriteLine("Single Threaded");
        var sw = new Stopwatch();
        sw.Start();

        for (var i = 0; i < 10; i++)
        {
            await Test2();
        }
        
        sw.Stop();
        Console.WriteLine("Elapsed={0}", (double)sw.ElapsedMilliseconds / 1000);
    }

    [Test]
    public async Task MultiTest()
    {
        Console.WriteLine("Multi Threaded");
        var sw = new Stopwatch();
        sw.Start();

        var taskList = new List<Task>();
        for (var i = 0; i < 10; i++)
        {
            taskList.Add(Test2());
        }

        await Task.WhenAll(taskList);

        sw.Stop();
        Console.WriteLine("Elapsed={0}", (double)sw.ElapsedMilliseconds / 1000);
    }
}

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