ThreadPool.QueueUserWorkItem 的初階使用－老爹寫程式

沒想到要在 C# 中使用, Thread Pool 這麼簡單.

如下簡單範例, 當然實際的程式不可能這樣, 但這是一個好入門概念.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace ThreadPoo
{
    class ThreadPool1
    {
        static void Main(string[] args)
        {
            System.Threading.WaitCallback waitCallback = new WaitCallback(MyThreadWork);
            ThreadPool.QueueUserWorkItem(waitCallback, "First");
            ThreadPool.QueueUserWorkItem(waitCallback, "Second");
            ThreadPool.QueueUserWorkItem(waitCallback, "Third");
            Console.WriteLine("Main thread exits.");
            Console.ReadKey();
        }

        static void MyThreadWork(object state)
        {
            Console.WriteLine("Begin of {0}", (string)state);
            Thread.Sleep(5000);
            Console.WriteLine("End of {0}", (string)state);
        }
    }
}

輸出結果 :

Main thread exits.
Begin of First
Begin of Third
Begin of Second
End of First
End of Third
End of Second

如果想要使用匿名委派, 也可以這樣寫.

namespace ThreadPoo
{
    class ThreadPool1
    {
        static void Main(string[] args)
        {
            ThreadPool.QueueUserWorkItem(delegate
            {
                Console.WriteLine("Begin of {0}", "First");
                Thread.Sleep(5000);
                Console.WriteLine("End of {0}", "First");
            });
            Console.WriteLine("Main thread exits.");
            Console.ReadKey();
        }
    }
}

如果想要用 Lambda 方式可以改成, 很簡單, 只是一種語法而已.

            ThreadPool.QueueUserWorkItem(callback =>
            {
                Console.WriteLine("Begin of {0}", "First");
                Thread.Sleep(5000);
                Console.WriteLine("End of {0}", "First");
            });

問題來了, 如果 call back function 必須由 caller 傳入一些資訊呢? 可以改成這樣.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace ThreadPoo
{
    public class TaskInfo
    {
        public string Who;
        public TaskInfo(string Value)
        {
            Who = Value;
        }
    }

    class ThreadPool2
    {
        static void Main(string[] args)
        {
            TaskInfo ti = new TaskInfo("Jack");
            ThreadPool.QueueUserWorkItem(new WaitCallback(MyThreadWork), ti);
            Thread.Sleep(1000);
            Console.WriteLine("Main thread exits.");
            Console.ReadKey();
        }

        static void MyThreadWork(object state)
        {
            TaskInfo ti = (TaskInfo)state;
            Console.WriteLine("Begin of {0}", ti.Who);
            Thread.Sleep(5000);
            Console.WriteLine("End of {0}", ti.Who);
        }
    }
}