c# - ThreadLocal 性能与使用参数

Question

我目前正在为公式语言实现运行时(即函数集合)。有些公式需要将上下文传递给它们，我创建了一个名为 EvaluationContext 的类，其中包含我需要在运行时访问的所有属性。

使用 ThreadLocal<EvaluationContext>似乎是使此上下文可用于运行时函数的不错选择。另一种选择是将上下文作为参数传递给需要它的函数。

我更喜欢使用 ThreadLocal，但我想知道与通过方法参数传递评估上下文相比是否存在任何性能损失。

Answer 1

我创建了下面的程序，使用参数比使用 ThreadLocal 字段更快。

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace TestThreadLocal
{
  internal class Program
  {
    public class EvaluationContext
    {
      public int A { get; set; }
      public int B { get; set; }
    }

    public static class FormulasRunTime
    {
      public static ThreadLocal<EvaluationContext> Context = new ThreadLocal<EvaluationContext>();

      public static int SomeFunction()
      {
        EvaluationContext ctx = Context.Value;
        return ctx.A + ctx.B;
      }

      public static int SomeFunction(EvaluationContext context)
      {
        return context.A + context.B;
      }
    }



    private static void Main(string[] args)
    {

      Stopwatch stopwatch = Stopwatch.StartNew();
      int N = 10000;
      Task<int>[] tasks = new Task<int>[N];
      int sum = 0;
      for (int i = 0; i < N; i++)
      {
        int x = i;
        tasks[i] = Task.Factory.StartNew(() =>
                                                 {
                                                   //Console.WriteLine("Starting {0}, thread {1}", x, Thread.CurrentThread.ManagedThreadId);
                                                   FormulasRunTime.Context.Value = new EvaluationContext {A = 0, B = x};
                                                   return FormulasRunTime.SomeFunction();
                                                 });
        sum += i;
      }
      Task.WaitAll(tasks);

      Console.WriteLine("Using ThreadLocal: It took {0} millisecs and the sum is {1}", stopwatch.ElapsedMilliseconds, tasks.Sum(t => t.Result));
      Console.WriteLine(sum);
      stopwatch = Stopwatch.StartNew();

      for (int i = 0; i < N; i++)
      {
        int x = i;
        tasks[i] = Task.Factory.StartNew(() =>
        {
          return FormulasRunTime.SomeFunction(new EvaluationContext { A = 0, B = x });
        });

      }
      Task.WaitAll(tasks);

      Console.WriteLine("Using parameter: It took {0} millisecs and the sum is {1}", stopwatch.ElapsedMilliseconds, tasks.Sum(t => t.Result));
      Console.ReadKey();
    }
  }
}