加速 C# 循环

Question

我正在尝试找到一种快速方法来加快以下for loops 的速度。 （只是有趣的理论）

我有以下程序

using System;
using System.Collections;
using System.Diagnostics;

namespace SpeedTest
{
    class Program
    {
        static void Main(string[] args)
        {
            Stopwatch timer = new Stopwatch();
            timer.Start();

            ArrayList widgets = new ArrayList(50000);

            for (int i = 0; i < widgets.Capacity; i++)
            {
                widgets.Add(new Widget(i));
            }

            string ProcessingMessages = "";

            for (int i = 0; i < widgets.Count; i++)
            {
                Widget widgetToProcess = (Widget)widgets[i];
                ProcessingMessages += widgetToProcess.ProcessWidget();
                ProcessingMessages += "\r\n";
            }

            Console.WriteLine(ProcessingMessages);

            timer.Stop();

            Console.WriteLine(timer.Elapsed);
            Console.ReadLine();
        }
    }

    class Widget
    {
        public Widget()
        {
            this.CreatedDateTime = DateTime.Now;
        }

        public Widget(int ID) : this()
        {
            this.ID = ID;
        }

        public DateTime CreatedDateTime { get; set; }
        public int ID { get; set; }

        public string ProcessWidget()
        {
            int Z = this.ID + this.ID;
            string Message = "Widget ID " + this.ID;
            Message += " was created on ";
            Message += CreatedDateTime.Year + "-" + CreatedDateTime.Month + "-" + CreatedDateTime.Day + ", at ";
            Message += CreatedDateTime.Hour + ":" + CreatedDateTime.Minute + ", with a value of ";
            Message += Z.ToString();
            return Message;
        }
    }
}

我怎样才能加快这些for loops 自身的速度？我知道实现并行性会很有用，例如

for (int i = 0; i < widgets.Count; i += 10)
            {
                Widget widgetToProcess1 = (Widget)widgets[i];
                Widget widgetToProcess2 = (Widget)widgets[i+1];
                Widget widgetToProcess3 = (Widget)widgets[i+2];
                Widget widgetToProcess4 = (Widget)widgets[i+3];
                Widget widgetToProcess5 = (Widget)widgets[i+4];
                Widget widgetToProcess6 = (Widget)widgets[i + 5];
                Widget widgetToProcess7 = (Widget)widgets[i + 6];
                Widget widgetToProcess8 = (Widget)widgets[i + 7];
                Widget widgetToProcess9 = (Widget)widgets[i + 8];
                Widget widgetToProcess10 = (Widget)widgets[i + 9];
                ProcessingMessages += widgetToProcess1.ProcessWidget() + "\r\n" +
                    widgetToProcess2.ProcessWidget() + "\r\n" +
                    widgetToProcess3.ProcessWidget() + "\r\n" +
                    widgetToProcess4.ProcessWidget() + "\r\n" +
                    widgetToProcess5.ProcessWidget() + "\r\n" +
                    widgetToProcess6.ProcessWidget() + "\r\n" +
                    widgetToProcess7.ProcessWidget() + "\r\n" +
                    widgetToProcess8.ProcessWidget() + "\r\n" +
                    widgetToProcess9.ProcessWidget() + "\r\n" +
                    widgetToProcess10.ProcessWidget() + "\r\n";
             }

然而，这都是手动编写的。我正在尝试找到一种方法来动态分解大型任务/数组大小并更快地运行这些块。

在这方面寻找一些简单的想法/概念。或者，如果有比使用for 循环进行此测试更好的选择。

Answer 1

对于初学者来说，你是在一个紧密的循环中进行字符串连接 - 不好，请查看 StringBuilder。

其次，您将在时间安排中包括设置您的测试场景。

第三，目前尚不清楚 for 循环的处理与 ProcessWidget() 方法的成本之间的相对成本是多少。肯定会在此方法中进行任何优化吗？

向下滚动查看ProcessWidget() 方法后，您还将受益于删除所有字符串连接并用一个大的string.Format() 调用或使用StringBuilder 替换。此外，ID 和 CreatedDateTime 看起来像不可变字段，也许值得将它们定义为 readonly 并在构造函数中预先创建字符串描述（如果 ProcessWidget() 可能被多次调用）。

Answer 2

您也可以考虑使用：

widgets.Cast<Widget>().AsParallel().ForAll(widgetToProcess => {...});

这将提高您的进程的性能，从 4 分钟到 30 秒（取决于 CPU 配置）。

Answer 3

您可以通过使用StringBuilder 并将控制台输出移动到 ProcessWidget 调用中，然后将数组填充和处理放入 Parallel.For 总运行时间约为 7 秒

这是修改后的代码：

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

using System.Collections;
using System.Diagnostics;

namespace parallelFor
{
    class Program
    {
        static void Main(string[] args)
        {
            Stopwatch timer = new Stopwatch();
            timer.Start();
            int size = 50000;
            ArrayList widgets = new ArrayList(size);

            Parallel.For(0, size, i =>
            {
                Widget w = new Widget((int)i);
                widgets.Add(w);
                w.ProcessWidget();
            });


            timer.Stop();

            Console.WriteLine(timer.Elapsed);
            Console.ReadLine();
        }
    }

    class Widget
    {
        public Widget()
        {
            this.CreatedDateTime = DateTime.Now;
        }

        public Widget(int ID)
            : this()
        {
            this.ID = ID;
        }

        public DateTime CreatedDateTime { get; set; }
        public int ID { get; set; }

        public void ProcessWidget()
        {
        int Z = this.ID + this.ID;
        string Message = "Widget ID " + this.ID;
        Message += " was created on ";
        Message += CreatedDateTime.Year + "-" + CreatedDateTime.Month + "-" + CreatedDateTime.Day + ", at ";
        Message += CreatedDateTime.Hour + ":" + CreatedDateTime.Minute + ", with a value of ";
        Message += Z.ToString();
        Console.WriteLine(Message);
        }
    }
}