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16.6.4 异步远程调用
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16.6.4 异步远程调用
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<h1 id="divCurrentNode" style="color: #b83507; width: 100%; text-align: left; font-size: 12px; padding-left: 2px">当前章节:<a href='100165483.htm'><font color='red'>16.6.4 异步远程调用</font></a></h1>
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<div style='float:left;width:49%'>·<a href='100165480.htm'>16.6.1 配置文件(2)</a></div><div style='float:right;width:49%'>·<a href='100165481.htm'>16.6.2 驻留应用程序</a></div><div style='float:left;width:49%'>·<a href='100165482.htm'>16.6.3 类、接口和Soapsuds</a></div><div style='float:right;width:49%'>·<a href='100165484.htm'>16.6.5 远程调用和事件</a></div><div style='float:left;width:49%'>·<a href='100165485.htm'>16.6.6 调用环境</a></div><div style='float:right;width:49%'>·<a href='100165486.htm'>16.7 小结</a></div></div>
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<div id="text"> <link href="css.css" rel="stylesheet" type="text/css" /><h3 style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 0cm; MARGIN-RIGHT: 0cm; FTEL: 8.15pt"><span lang="EN-US">16.6.4 </span><span style="FONT-FAMILY: 黑体">异步远程</span><span style="FONT-FAMILY: 黑体">调用</span></h3>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">如果服务器的方法要花费一段时间才能完成，同时客户需要做一些不同的工作，就没有必要启动一个单独的线程去进行远程调用。而进行异步调用，方法启动后会立即返回给客户机。在远程对象上可以进行异步的调用，因为在委托的帮助下它们可以在本地对象上调用。使用没有返回值的方法，也可以使用</span><span lang="EN-US">OneWay</span><span style="FONT-FAMILY: 宋体">特性。</span></p>
<h4 style="FTEL: 21.45pt"><span lang="EN-US">1. </span><span style="FONT-FAMILY: 黑体">使用委托和</span><span lang="EN-US">.NET Remoting</span></h4>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">为了实现方法的异步调用，创建一个委托</span><span lang="EN-US">GreetingDelegate</span><span style="FONT-FAMILY: 宋体">，这个委托的参数和返回值与远程对象的</span><span lang="EN-US">Greeting()</span><span style="FONT-FAMILY: 宋体">方法的相同。使用</span><span lang="EN-US">delegate</span><span style="FONT-FAMILY: 宋体">关键字，就可以创建一个派生自</span><span lang="EN-US">MulticastDelegate</span><span style="FONT-FAMILY: 宋体">的类</span><span lang="EN-US">GreetingDelegate</span><span style="FONT-FAMILY: 宋体">。使用</span><span lang="EN-US">ilsasm</span><span style="FONT-FAMILY: 宋体">实用程序，检查程序集，就可以对此进行验证。这个委托类的构造函数的参数是对</span><span lang="EN-US">Greeting()</span><span style="FONT-FAMILY: 宋体">方法的引用。使用委托类的</span><span lang="EN-US">BeginInvoke()</span><span style="FONT-FAMILY: 宋体">方法，可以调用</span><span lang="EN-US">Greeting()</span><span style="FONT-FAMILY: 宋体">。</span><span lang="EN-US">BeginInvoke()</span><span style="FONT-FAMILY: 宋体">的第二个参数是</span><span lang="EN-US">AsyncCallback()</span><span style="FONT-FAMILY: 宋体">实例，该实例定义了方法</span><span lang="EN-US">HelloClient.Callback()</span><span style="FONT-FAMILY: 宋体">，当远程方法完成时，会调用方法</span><span lang="EN-US">HelloClient. Callback()</span><span style="FONT-FAMILY: 宋体">。在</span><span lang="EN-US">Callback()</span><span style="FONT-FAMILY: 宋体">方法中，远程调用是使用</span><span lang="EN-US">EndInvoke()</span><span style="FONT-FAMILY: 宋体">完成的：</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">using System;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">using System.Runtime.Remoting;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">namespace Wrox.ProCSharp.Remoting</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public class HelloClient</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> private delegate String GreetingDelegate(String name);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> private static string greeting;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public static void Main(string[] args)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> RemotingConfiguration.Configure("HelloClient.exe.config");</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Hello obj = new Hello();</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> if (obj == null)</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine("could not locate server");</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> return;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> // synchronous version</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> // string greeting = obj.Greeting("Christian");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> // asynchronous version</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> GreetingDelegate d = new GreetingDelegate(obj.Greeting);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> IAsyncResult ar = d.BeginInvoke("Christian", null, null);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> // do some work and then wait</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> ar.AsyncWaitHandle.WaitOne();</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> if (ar.IsCompleted)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> greeting = d.EndInvoke(ar);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine(greeting);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">在第</span><span lang="EN-US">6</span><span style="FONT-FAMILY: 宋体">章中有事件和委托的详细信息。</span></p>
<h4 style="FTEL: 21.45pt"><span lang="EN-US">2. </span><span style="FONT-FAMILY: 黑体">特性</span><span lang="EN-US">OneWay</span></h4>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">返回值为</span><span lang="EN-US">void</span><span style="FONT-FAMILY: 宋体">，并且只有输入参数的方法由特性</span><span lang="EN-US">OneWay</span><span style="FONT-FAMILY: 宋体">标记。不论客户如何调用方法，特性</span><span lang="EN-US">OneWay(</span><span style="FONT-FAMILY: 宋体">在命名空间</span><span lang="EN-US">System.Runtime.Remoting.Messaging</span><span style="FONT-FAMILY: 宋体">中定义</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">都可以实现方法的自动异步。把方法</span><span lang="EN-US">TakeAWhile()</span><span style="FONT-FAMILY: 宋体">添加到远程对象类</span><span lang="EN-US">RemoteHello</span><span style="FONT-FAMILY: 宋体">中，就可以创建一个</span><span lang="EN-US">fire-and-forget</span><strong><span style="FONT-FAMILY: 宋体">方</span></strong><span style="FONT-FAMILY: 宋体">法。如果客户机通过代理对象调用</span><span lang="EN-US">TakeAWhile() </span><span style="FONT-FAMILY: 宋体">方法，则代理对象会立即返回给客户。在服务器上，方法会在一段时间后完成：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><a ftel="_Toc507815567"><span lang="EN-US"> [OneWay]</span></a></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public void TakeAWhile(int ms)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine("TakeAWhile started");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> System.Threading.Thread.Sleep(ms);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine("TakeAWhile finished");</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> }</span></p></div>
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