A Simple Thread Pool Implementation (Part 2)

I said last time I'd compare the performance of my super duper simple implementation against the .NET ThreadPool, so here it is! Here's the test code:

ManualResetEvent evt = new ManualResetEvent(false);
int total = 100000;
int count = 0;
DateTime start = DateTime.Now;
for (int i = 0; i < total; ++i)
{
//  ThreadQueue.QueueUserWorkItem(delegate(object obj)
    ThreadPool.QueueUserWorkItem(delegate(object obj)
    {
        Console.WriteLine(obj);
        if (Interlocked.Increment(ref count) == total)
            evt.Set();
    }, i);
}
evt.WaitOne();

Console.WriteLine("Time: {0}ms", (DateTime.Now - start).TotalMilliseconds);
Console.ReadLine();

Here are the initial tests. My CPU is a Core2Duo clocked at 3.6GHz. I also ran a release build outside of the debugger. I set my ThreadQueue to have 25 worker threads. The results were pretty surprising:
ThreadPool: 1515.6444ms ThreadQueue: 5093.8152ms Well, that's interesting. The .NET ThreadPool whooped my butt! How can that be? Let's dig deeper and find out how many threads actually got used. I used ThreadPool.GetMinThreads and ThreadPool.GetMaxThreads, and I got 2-500 for worker threads, and 2-1000 for completion IO threads. Then, I tracked how many threads were actually used, like this:

Dictionary threads = new Dictionary();
// ...snip
    ThreadPool.QueueUserWorkItem(delegate(object obj)
    {
        Console.WriteLine(obj);
        threads[Thread.CurrentThread.ManagedThreadId] = 0;
        if (Interlocked.Increment(ref count) == total)
            evt.Set();
    }, i);
// ...snip
Console.WriteLine("Threads used: {0}", threads.Count);

Surprisingly, only 2 threads were used. So, I set the number of worker threads of my ThreadQueue to 2. Viola! 1437.5184ms, which is just a little under 100ms faster than the ThreadPool. I guess this shows that more threads does not mean better or faster! For fun I set the number of worker threads to 200 and it took 27906.6072ms! There was clearly a lot of locking overhead here...