使用线程池

简介

创建线程是昂贵的操作，为每一个短暂的异步操作创建线程会产生显著的开销。

在线程池中调用委托

 1 using System;
 2 using System.Threading;
 3 
 4 namespace Chapter3.Recipe1
 5 {
 6     class Program
 7     {
 8         static void Main(string[] args)
 9         {
10             int threadId = 0;
11 
12             RunOnThreadPool poolDelegate = Test;
13 
14             var t = new Thread(() => Test(out threadId));
15             t.Start();
16             t.Join();
17 
18             Console.WriteLine("Thread id: {0}", threadId);
19 
20             //调用BeginInvoke()运行委托，回调函数在异步操作完成后被调用
21             //BeginInvoke()调用后会立即返回,线程池中的工作线程在执行异步操作时，仍允许继续其他工作。
22             IAsyncResult r = poolDelegate.BeginInvoke(out threadId, Callback, "a delegate asynchronous call"); 
23             r.AsyncWaitHandle.WaitOne(); //等待异步操作完成
24             //事实上EndInvoke()会等待异步操作的完成，所以r.AsyncWaitHandle.WaitOne();并不是必要的
25             string result = poolDelegate.EndInvoke(out threadId, r);
26             //异步操作完成后，回调函数会被放置到线程池中，确切的说是一个工作线程中。
27             Console.WriteLine("Thread pool worker thread id: {0}", threadId);
28             Console.WriteLine(result);
29 
30             Thread.Sleep(TimeSpan.FromSeconds(2));
31         }
32 
33         private delegate string RunOnThreadPool(out int threadId);
34 
35         private static void Callback(IAsyncResult ar)//回调函数
36         {
37             Console.WriteLine("Starting a callback...");
38             Console.WriteLine("State passed to a callbak: {0}", ar.AsyncState);
39             Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
40             Console.WriteLine("Thread pool worker thread id: {0}", Thread.CurrentThread.ManagedThreadId);
41         }
42 
43 
44         private static string Test(out int threadId)
45         {
46             Console.WriteLine("Starting...");
47             Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
48             Thread.Sleep(TimeSpan.FromSeconds(2));
49             threadId = Thread.CurrentThread.ManagedThreadId;
50             return string.Format("Thread pool worker thread id was: {0}", threadId);
51         }
52     }
53 }

使用BeginOperationName/EndOperation方法和.NET中的IAsyncResult对象等方式被称为异步编程模型，这样的方法对被称为异步方法。

 向线程池放入异步操作

 1 using System;
 2 using System.Threading;
 3 
 4 namespace Chapter3.Recipe2
 5 {
 6     class Program
 7     {
 8         static void Main(string[] args)
 9         {
10             const int x = 1;
11             const int y = 2;
12             const string lambdaState = "lambda state 2";
13 
14             //使用ThreadPool的静态方法QueueUserWorkItem()将方法放到线程池中
15             ThreadPool.QueueUserWorkItem(AsyncOperation);
16             Thread.Sleep(TimeSpan.FromSeconds(1));
17             //Thread.Sleep()让线程池拥有为新操作重用线程的可能性
18             ThreadPool.QueueUserWorkItem(AsyncOperation, "async state");
19             Thread.Sleep(TimeSpan.FromSeconds(1));
20             //使用lambda表达式方式
21             ThreadPool.QueueUserWorkItem(state => {
22                 Console.WriteLine("Operation state: {0}", state);
23                 Console.WriteLine("Worker thread id: {0}", Thread.CurrentThread.ManagedThreadId);
24                 Thread.Sleep(TimeSpan.FromSeconds(2));
25             }, "lambda state");
26             //使用必报机制
27             ThreadPool.QueueUserWorkItem(_ =>
28             {
29                 Console.WriteLine("Operation state: {0}, {1}", x + y, lambdaState);
30                 Console.WriteLine("Worker thread id: {0}", Thread.CurrentThread.ManagedThreadId);
31                 Thread.Sleep(TimeSpan.FromSeconds(2));
32             }, "lambda state");
33 
34             Thread.Sleep(TimeSpan.FromSeconds(2));
35         }
36 
37         private static void AsyncOperation(object state)
38         {
39             Console.WriteLine("Operation state: {0}", state ?? "(null)");
40             Console.WriteLine("Worker thread id: {0}", Thread.CurrentThread.ManagedThreadId);
41             Thread.Sleep(TimeSpan.FromSeconds(2));
42         }
43     }
44 }