线程池使用

（一）在线程池中调用委托

代码class Program
{
    private delegate string RunOnThreadPool(out int 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("Main: 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("Main: Thread pool worker thread id: {0}", threadId);
        Console.WriteLine(result);

        Thread.Sleep(TimeSpan.FromSeconds(2));
        Console.WriteLine("Main: End.......");
        Console.ReadKey();
    }

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

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

代码分析（见下图）