Question

I am currently implementing a runtime (i.e. a collection of functions) for a formulas language. Some formulas need a context to be passed to them and I created a class called EvaluationContext which contains all properties I need access to at runtime.

Using ThreadLocal<EvaluationContext> seems like a good option to make this context available to the runtime functions. The other option is to pass the context as a parameter to the functions that need it.

I prefer using ThreadLocal but I was wondering if there is any performance penalty as opposed to passing the evaluation context via method parameters.

Answer 1

I created the program below and it is faster to use parameters rather than the ThreadLocal field.

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();
    }
  }
}