C#并行线程代码性能

我一直在测试System.Threading.Parallel和一个线程的性能,我很惊讶地看到并行花费更长的时间完成任务比线程.我确定这是由于我对Parallel的知识有限,我刚刚开始阅读.

我以为我会分享几个片段,如果有人可以指出我的paralle代码运行速度比线程代码慢.还试图运行相同的比较找到素数,发现并行代码完成比线程代码晚.

public class ThreadFactory
{
    int workersCount;
    private List<Thread> threads = new List<Thread>();

    public ThreadFactory(int threadCount,int workCount,Action<int,int,string> action)
    {
        workersCount = threadCount;

        int totalWorkLoad = workCount;
        int workLoad = totalWorkLoad / workersCount;
        int extraLoad = totalWorkLoad % workersCount;

        for (int i = 0; i < workersCount; i++)
        {
            int min,max;
            if (i < (workersCount - 1))
            {
                min = (i * workLoad);
                max = ((i * workLoad) + workLoad - 1);
            }
            else
            {
                min = (i * workLoad);
                max = (i * workLoad) + (workLoad - 1 + extraLoad);
            }
            string name = "Working Thread#" + i; 

            Thread worker = new Thread(() => { action(min,max,name); });
            worker.Name = name;
            threads.Add(worker);
        }
    }

    public void StartWorking()
    {
        foreach (Thread thread in threads)
        {
            thread.Start();
        }

        foreach (Thread thread in threads)
        {
            thread.Join();
        }
    }
}

这是程序：

Stopwatch watch = new Stopwatch();
watch.Start();
int path = 1;

List<int> numbers = new List<int>(Enumerable.Range(0,10000));

if (path == 1)
{
    Parallel.ForEach(numbers,x =>
    {
        Console.WriteLine(x);
        Thread.Sleep(1);

    });
}
else
{
    ThreadFactory workers = new ThreadFactory(10,numbers.Count,(min,text) => {

        for (int i = min; i <= max; i++)
        {
            Console.WriteLine(numbers[i]);
            Thread.Sleep(1);
        }
    });

    workers.StartWorking();
}

watch.Stop();
Console.WriteLine(watch.Elapsed.TotalSeconds.ToString());

Console.ReadLine();

更新：

考虑到锁定：我尝试了以下代码段.同样的结果,Parallel似乎完成得比较慢.

path = 1;
cieling = 10000000;

List<int> numbers = new List<int>();

    if (path == 1)
    {
        Parallel.For(0,cieling,x =>
        {
            lock (numbers)
            {
                numbers.Add(x);    
            }

        });
    }

    else
    {
        ThreadFactory workers = new ThreadFactory(10,text) =>
        {

            for (int i = min; i <= max; i++)
            {
                lock (numbers)
                {
                    numbers.Add(i);    
                }                       

            }
        });

        workers.StartWorking();
    }

更新2：
只是一个快速更新,我的机器有四核处理器.所以Parallel可以有4个内核.

解决方法

我想我可以回答你的问题.首先,你没有写出你的系统有多少核心.如果你正在运行一个双核,只有4个线程将使用Parallel.For工作,而你在线程示例中使用10个线程.更多的线程会更好的工作,因为你正在运行的任务(打印短睡眠)是一个非常短的任务,线程和线程开销是非常大的任务相比,我几乎可以肯定,如果你编写相同的代码没有线程将工作更快.

两种方法的工作原理相同,但是如果您先创建所有线程,则可以将Parallels分配给Parallel.For使用任务池来添加一些移动开销.