多线程和加快速度

Question

我有以下代码.我希望在多个线程上启动文件创建.目标是当我在多个线程上创建10个文件时,它将花费更少的时间.据我所知,我需要引入异步调用元素来实现这一点.

我应该在这段代码中做出哪些改变？

using System;
using System.Text;
using System.Threading;
using System.IO;
using System.Diagnostics;

namespace MultiDemo
{
    class MultiDemo
    {
        public static void Main()
        {
            var stopWatch = new Stopwatch();
            stopWatch.Start();
            // Create an instance of the test class.
            var ad = new MultiDemo();

            //Should create 10 files in a loop.
            for (var x = 0; x < 10; x++)
            {
                var y = x;
                int threadId;
                var myThread = new Thread(() => TestMethod("outpFile", y, out threadId));
                myThread.Start();
                myThread.Join();
                //TestMethod("outpFile", y, out threadId);
            }
            stopWatch.Stop();
            Console.WriteLine("Seconds Taken:\t{0}",stopWatch.Elapsed.TotalMilliseconds);
        }

        public static void TestMethod(string fileName, int hifi, out int threadId)
        {
            fileName = fileName + hifi;
            var fs = new FileStream(fileName, FileMode.OpenOrCreate, FileAccess.ReadWrite);
            var sw = new StreamWriter(fs, Encoding.UTF8);
            for (int x = 0; x < 10000; x++)
                {
                    sw.WriteLine(DateTime.Now.ToString());
                }
            sw.Close();
           threadId = Thread.CurrentThread.ManagedThreadId;
            Console.WriteLine("{0}",threadId);
        }
    }
}

现在,如果我评论代码的线程创建部分并且只是在循环中调用testMethod 10次,那么它比线程创建尝试处理的多个线程更快.

Answer 1

你的代码的线程版本正在做额外的工作,所以它的速度慢并不令人惊讶.

当你做类似的事情时:

var myThread = new Thread(() => TestMethod("outpFile", y, out threadId));
myThread.Start();
myThread.Join();

...你正在创建一个线程,让它调用TestMethod,然后等待它完成. 创建和启动线程的额外开销会比TestMethod没有任何线程的调用更慢.

如果您启动所有线程然后等待它们完成,您可能会看到更好的性能,例如:

var workers = new List<Thread>();
for (int i = 0; i < 10; ++i) 
{
   var y = x;
   int threadId;
   var myThread = new Thread(() => TestMethod("outpFile", y, out threadId));
   myThread.Start();
   workers.Add(myThread);
}
foreach (var worker in workers) worker.Join();