.net – 正则表达式的多线程使用

Regex objects can be created on any thread and shared between threads.

我发现,对于性能,最好不要在使用ThreadLocal类时在线程之间共享Regex实例.

请问有人可以解释为什么线程本地实例的运行速度大约快5倍？

以下是结果(在8核机器上)：

Using Regex singleton' returns 3000000 and takes 00:00:01.1005695
   Using thread local Regex' returns 3000000 and takes 00:00:00.2243880

源代码：

using System;
using System.Linq;
using System.Threading;
using System.Text.RegularExpressions;
using System.Diagnostics;

namespace ConsoleApplication1
{
    class Program
    {
        static readonly string str = new string('a',400);
        static readonly Regex re = new Regex("(a{200})(a{200})",RegexOptions.Compiled);

        static void Test(Func<Regex> regexGettingMethod,string methodDesciption)
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            var sum = Enumerable.Repeat(str,1000000).AsParallel().Select(s => regexGettingMethod().Match(s).Groups.Count).Sum();
            sw.Stop();
            Console.WriteLine("'{0}' returns {1} and takes {2}",methodDesciption,sum,sw.Elapsed);
        }

        static void Main(string[] args)
        {
            Test(() => re,"Using Regex singleton");

            var threadLocalRe = new ThreadLocal<Regex>(() => new Regex(re.ToString(),RegexOptions.Compiled));
            Test(() => threadLocalRe.Value,"Using thread local Regex");

            Console.Write("Press any key");
            Console.ReadKey();
        }
    }
}