WPF调用线程（三)线程池初步

当我们频繁的要调用线程来执行任务时，一个好的办法是采用线程池来对线程进行管理，
 “线程池”是可以用来在后台执行多个任务的线程集合。 每个传入请求都将分配给线程池中的一个线程，因此可以异步处理请求，而不会占用主线程，也不会延迟后续请求的处理。一旦池中的某个线程完成任务，它将返回到等待线程队列中，等待被再次使用。 这使应用程序可以避免为每个任务创建新线程的开销。线程还是比较昂贵的。

（you must avoid using threads as much as  possible because they consume a lot of memory and they require time to create, destroy,and manage . Time is also wasted when Windows context switches between threads and when garbage collections occur . However, this discussion should also help you realize that threads must be used sometimes because they allow Windows to be robust and responsive）摘自 CLR via C#

线程池通常具有最大线程数限制。 如果所有线程都繁忙，则额外的任务将放入队列中，直到有线程可用时才能够得到处理。

下面用WPF程序演示线程池基本的使用，运行效果如图：

XAML代码如下：

View Code

后台CS代码：

 1 namespace WpfThreadTest
 2 {
 3     /// <summary>
 4     /// ThreadPoolDemo.xaml 的交互逻辑
 5     /// </summary>
 6     public partial class ThreadPoolDemo : Window
 7     {
 8         public ThreadPoolDemo()
 9         {
10             InitializeComponent();
11             ///设置线程池的最大可用辅助线程数目，最大异步线程数目
12             ThreadPool.SetMaxThreads(100, 10);       
13 
14         }
15 
16         private void button1_Click(object sender, RoutedEventArgs e)
17         {           
18              //调用线程去计算数字，仅供演示
19              ThreadPool.QueueUserWorkItem(new WaitCallback(CountNumber), 1);
20         }
21         private void CountNumber(object state)
22         {
23             int count = int.Parse(state.ToString());
24             while (true)
25             {                
26                 count++;
27                 this.textBlock2.Dispatcher.Invoke(
28                     DispatcherPriority.Normal,
29                     new Action(() =>
30                     {
31                         this.textBlock2.Text = count.ToString();
32                     }));
33                 Thread.Sleep(100);
34             }
35         }
36         /// <summary>
37         /// 测试线程中传递引用对象，以期望获得返回值
38         /// </summary>
39         /// <param name="state"></param>
40         private void ReturnValueMethod(object state)
41         {
42             MyParam myParam = state as MyParam;
43             myParam.MyInt = 100;
44             myParam.MyString = "updated string";            
45         }
46 
47         private void button2_Click(object sender, RoutedEventArgs e)
48         {
49             ///将引用对象传递给线程
50             MyParam myParam = new MyParam() { MyInt = 12, MyString = "test" };
51            
52             ThreadPool.QueueUserWorkItem(new WaitCallback(ReturnValueMethod), myParam);            
53 
54             ///主线程睡眠5ms后，再去读取对象的值
55             ///如果不睡眠，直接读取，可能读不到修改后的值，因为他们处于不同的线程当中
56             ///当主线程去读取时，子线程尚未更改,
57             ///即便如此，也会有读取不到的时候，故此种传值方式并不十分可取，
58             ///具体线程返回值可以参考MSDN http://msdn.microsoft.com/zh-cn/library/wkays279.aspx
59             Thread.Sleep(5);
60             this.textBlock1.Text=string.Format("MyInt:{0},MyString:{1}", myParam.MyInt, myParam.MyString);
61         }
62 
63         private void button3_Click(object sender, RoutedEventArgs e)
64         {
65             ThreadPool.QueueUserWorkItem(new WaitCallback(GetThreadPoolInfo), null);          
66         }
67         private void GetThreadPoolInfo(object state)
68         {
69             while (true)
70             {
71                 int workerThreads = 0;
72                 int completionPortThreads = 0;
73                 ThreadPool.GetAvailableThreads(out workerThreads, out completionPortThreads);
74                 this.textBlock3.Dispatcher.Invoke(DispatcherPriority.SystemIdle, new Action(() =>
75                 {
76                     this.textBlock3.Text =
77                         string.Format("池中可用辅助线程：{0},可用异步 I/O 线程：{1}",
78                         workerThreads, completionPortThreads);
79                 }));
80                 Thread.Sleep(1000);
81             }
82         }
83     }
84     public class MyParam
85     {
86         public int MyInt { get; set; }
87         public string MyString { get; set; }
88     }
89 }