线程池示例（摘抄）

using System.Threading;

namespace System
{
    public static class CompileCSCAtRuntime
    {
        private delegate string RunOnThreadPool(out int threadId);

        private static void Callback(IAsyncResult ar)
        {
            Console.WriteLine("Starting a callback...");
            Console.WriteLine("State passed to a callback: {0}", ar.AsyncState);
            Console.WriteLine("Is Thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
            Console.WriteLine("Thread pool worker thread id: {0}", Thread.CurrentThread.ManagedThreadId);
        }

        private static string Test(out int threadId)
        {
            Console.WriteLine("Starting...");
            Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
            Thread.Sleep(TimeSpan.FromSeconds(2));
            threadId = Thread.CurrentThread.ManagedThreadId;
            return string.Format("Thread pool worker thread id was: {0}", threadId);
        }

        static void Main(string[] args)
        {
            int threadId = 0;

            RunOnThreadPool poolDelegate = Test;

            var t = new Thread(() => Test(out threadId));
            t.Start();
            t.Join();

            Console.WriteLine("Thread id: {0}", threadId);

            IAsyncResult r = poolDelegate.BeginInvoke(out threadId, Callback, "a delegate asynchronous call");
            r.AsyncWaitHandle.WaitOne();

            string result = poolDelegate.EndInvoke(out threadId, r);

            Console.WriteLine("Thread pool worker thread id: {0}", threadId);
            Console.WriteLine(result);

            Console.WriteLine("main threadid was: {0}", Thread.CurrentThread.ManagedThreadId);

            Thread.Sleep(TimeSpan.FromSeconds(2));
        }

    }
}

示例来源：《C#多线程编程实战》