線程池（ThreadPool）

線程池使用起來很簡單,但它有一些限制:

• 線程池中的所有線程都是後臺線程。如果進程的所有前臺線程都結束了,所有的後臺線程就會停止。不能把入池的線程改為前臺線程。
• 不能給入池的線程設置優先順序或名稱。
• 對於COM對象,入池的所有線程都是多線程單元線 程。許多COM對象都需要單線程單元線程。
• 入池的線程只能用於時間較短的任務。如果線程要一直運行(如 Word的拼寫檢查器線程),就應使用 Thread類創建一個線程。

代碼示例：

class ThreadPoolDemo
    {
        public static void start()
        {
            int workerThreads, completionPortThreads;
            //設置線程最大值
            ThreadPool.SetMaxThreads(5, 5);
            ////設置線程最小值
            ThreadPool.SetMinThreads(2, 2);
            //檢索線程池在新請求預測中維護的空閑線程數
            ThreadPool.GetMinThreads(out workerThreads, out completionPortThreads);
            Console.WriteLine("workerThreads:" + workerThreads);
            Console.WriteLine("completionPortThreads:" + workerThreads);
            //綁定線程，當有可用線程時執行。
            ThreadPool.QueueUserWorkItem(WaitCallback, "第1個");
            ThreadPool.QueueUserWorkItem(WaitCallback, "第2個");
            ThreadPool.QueueUserWorkItem(WaitCallback, "第3個");
            ThreadPool.QueueUserWorkItem(WaitCallback, "第4個");
            ThreadPool.QueueUserWorkItem(WaitCallback, "第5個");
            ThreadPool.QueueUserWorkItem(WaitCallback, "第6個");
            ThreadPool.QueueUserWorkItem(WaitCallback, "第7個");
            ThreadPool.QueueUserWorkItem(WaitCallback, "第8個");
            ThreadPool.QueueUserWorkItem(WaitCallback, "第9個");
            ThreadPool.QueueUserWorkItem(WaitCallback, "第10個");
        }
        static void WaitCallback(object state)
        {
            Console.WriteLine("線程調用" + state);
            int workerThreads, completionPortThreads;
            //檢測可用線程和io線程數
            ThreadPool.GetAvailableThreads(out workerThreads, out completionPortThreads);
            Console.WriteLine("workerThreads:" + workerThreads);
            Console.WriteLine("completionPortThreads:" + workerThreads);
            Thread.Sleep(2000);
            if ("第2個" == state.ToString())
            {
                Thread.Sleep(6000);
            }
            Console.WriteLine(state + "調用結束");
        }
    }