利用委托实现异步调用

1. 同步调用示例(委托是一个类型安全的,面向对象的指针)

   using System;
   using System.Threading;
   
   namespace Demo
   {
       public delegate int Operate(int x, int y);
   
       public class DelegateAsync
       {
           static int Add(int a, int b)
           {
               Console.WriteLine ("Add() invoked on thread:{0}\n",
                   Thread.CurrentThread.GetHashCode ());
               Thread.Sleep (5000);
               return a + b;
           }
   
           static void Main()
           {
               Console.WriteLine ("Main() invoked on thread:{0}",
                   Thread.CurrentThread.GetHashCode ());
               //Add() call in Synchronouse mode
               Operate op = new Operate (Add);
               int answer = op (10, 20);
               //after Add() executed, the folow goes on.
               Console.Write("After Add() executed, result = {0}",answer);
               Console.ReadKey ();
           }
       }
   }

   剖析代码的继承关系: 代理Operate经历了3次派生(绿色部分),实现了一个构造和3个虚拟函数(黄色部分).

   

2. 异步调用方法:线程异步了,但是主线程等待次线程返回才能获得结果,阻塞在EndInvoke上.

   using System;
   using System.Threading;
   
   namespace Demo
   {
       public delegate int Operate(int x, int y);
   
       public class DelegateAsync
       {
           static int Add(int a, int b)
           {
               Console.WriteLine ("Add() invoked on thread:{0}\n",
                   Thread.CurrentThread.GetHashCode ());
               Thread.Sleep (5000);
               return a + b;
           }
   
           static void Main()
           {
               Console.WriteLine ("Main() invoked on thread:{0}",
                   Thread.CurrentThread.GetHashCode ());
               //Add() call in Synchronouse mode
               Operate op = new Operate (Add);
               IAsyncResult result = op.BeginInvoke(10,20,null,null);
               Console.WriteLine ("Doing more in Main() exected immediately.");
               //the thread susppend on EndInvoke while ‘result‘ is ready!
               int answer = op.EndInvoke (result);
               Console.Write("After Add() executed, result = {0}",answer);
               Console.ReadKey ();
           }
       }
   }

3. 同步调用:如果线程没有返回,不要一直问何时返回,每间隔500ms做该做的事情!!!

   using System;
   using System.Threading;
   
   namespace Demo
   {
       public delegate int Operate(int x, int y);
   
       public class DelegateAsync
       {
           static int Add(int a, int b)
           {
               Console.WriteLine ("Add() invoked on thread:{0}\n",
                   Thread.CurrentThread.GetHashCode ());
               Thread.Sleep (5000);
               return a + b;
           }
   
           static void Main()
           {
               Console.WriteLine ("Main() invoked on thread:{0}\n",
                   Thread.CurrentThread.GetHashCode ());
               //Add() call in Synchronouse mode
               Operate op = new Operate (Add);
               IAsyncResult result = op.BeginInvoke(10,20,null,null);
               //while result is not OK, do it every 500 ms.
               while (!result.AsyncWaitHandle.WaitOne(500,true)) {//result.IsCompleted
                   Console.WriteLine ("Doing more work in Main().");
               }
               int answer = op.EndInvoke (result);
               Console.Write("After Add() executed, result = {0}",answer);
               Console.ReadKey ();
           }
       }
   }

4. 线程回调: 好吧,干脆你返回的时候通知我,我该干啥不耽搁!

   using System;
   using System.Threading;
   
   /// <summary>
   /* Main() invoked on thread:1
   Main() execute no need to wait any more.
   Add() invoked on thread:3
   AddComplete() invoked on thread:3
   Your Addition is complete.
   */
   /// </summary>
   namespace Demo
   {
       public delegate int Operate(int x, int y);
   
       public class DelegateAsync
       {
           static int Add(int a, int b)
           {
               Console.WriteLine ("Add() invoked on thread:{0}",
                   Thread.CurrentThread.GetHashCode ());
               Thread.Sleep (5000);
               return a + b;
           }
   
           static void AddComplete(IAsyncResult ia)
           {
               Console.WriteLine ("AddComplete() invoked on thread:{0}",
                   Thread.CurrentThread.GetHashCode ());
               //Get Result value
               System.Runtime.Remoting.Messaging.AsyncResult ar=
                   (System.Runtime.Remoting.Messaging.AsyncResult)ia;
               Operate op = (Operate)ar.AsyncDelegate;
               Console.WriteLine ("The value is {0}.", op.EndInvoke (ia));
           }
   
           static void Main()
           {
               Console.WriteLine ("Main() invoked on thread:{0}",
                   Thread.CurrentThread.GetHashCode ());
               //Add() call in Synchronouse mode
               Operate op = new Operate (Add);
               IAsyncResult result = op.BeginInvoke (10, 20, new AsyncCallback (AddComplete), null);
               Console.WriteLine ("Main() execute no need to wait any more.");
               Console.ReadKey ();
           }
       }
   }

5. 主线程向次线程传递对象,通知!

   using System;
   using System.Threading;
   
   /// <summary>
   /*

   Main() invoked on thread:1
   Main() execute no need to wait any more.
   Add() invoked on thread:3
   AddComplete() invoked on thread:3
   The value is 30.
   The Main() thread is :1

   */
   /// </summary>
   namespace Demo
   {
       public delegate int Operate(int x, int y);
   
       public class DelegateAsync
       {
           static int Add(int a, int b)
           {
               Console.WriteLine ("Add() invoked on thread:{0}",
                   Thread.CurrentThread.GetHashCode ());
               Thread.Sleep (5000);
               return a + b;
           }
   
           static void AddComplete(IAsyncResult ia)
           {
               Console.WriteLine ("AddComplete() invoked on thread:{0}",
                   Thread.CurrentThread.GetHashCode ());
               //Get Result value
               System.Runtime.Remoting.Messaging.AsyncResult ar=
                   (System.Runtime.Remoting.Messaging.AsyncResult)ia;
               Operate op = (Operate)ar.AsyncDelegate;
               Console.WriteLine ("The value is {0}.", op.EndInvoke (ia));
               Thread thread = (Thread)ia.AsyncState;
               Console.WriteLine ("The Main() thread is :{0}", thread.GetHashCode());
           }
   
           static void Main()
           {
               Console.WriteLine ("Main() invoked on thread:{0}",
                   Thread.CurrentThread.GetHashCode ());
               //Add() call in Synchronouse mode
               Operate op = new Operate (Add);
               IAsyncResult result = op.BeginInvoke (10, 20,
                   new AsyncCallback (AddComplete),Thread.CurrentThread);
               Console.WriteLine ("Main() execute no need to wait any more.");
               Console.ReadKey ();
           }
       }
   }

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