异步委托
异步委托提供以异步方式调用同步方法的能力。当同步调用一个委托时，调用方法直接对当前线程调用目标方法。如果编译器支持异步委托，则它将生成该调用方法以及 BeginInvoke 和 EndInvoke 方法。如果调用 BeginInvoke 方法，则公共语言运行库将对请求进行排队并立即返回到调用方。将对来自线程池的线程调用该目标方法。提交请求的原始线程自由地继续与目标方法并行执行，该目标方法是对线程池线程运行的。如果已经对 BeginInvoke 指定了回调，当目标方法返回时将调用它。在回调中，使用 EndInvoke 方法来获取返回值和输入/输出参数。如果没有对 BeginInvoke 指定回调，则可以在提交请求的原始线程上使用 EndInvoke。
使用委托
对于异步编程，如果调用方使用一个委托，则该调用方在调用一个方法时必须定义该委托。在以下代码示例中，首先定义该委托，接着创建该委托的实例，然后调用它。下面的示例说明为异步调用 Factorize 方法定义一个模式的调用方： using System; using System.Runtime.Remoting; public delegate bool FactorizingCallback( int factorizableNum, ref int primefactor1, ref int primefactor2); // This is a class that receives a callback when the the results are available. public class ProcessFactorizedNumber { private int _ulNumber; public ProcessFactorizedNumber(int number) { _ulNumber = number; } // Note the qualifier one-way. [OneWayAttribute()] public void FactorizedResults(IAsyncResult ar) { int factor1=0, factor2=0; // Extract the delegate from the AsyncResult. FactorizingCallback fd = (FactorizingCallback) ((AsyncResult)ar).AsyncDelegate; // Obtain the result. fd.EndInvoke(ref factor1, ref factor2, ar); // Output results. Console.WriteLine("On CallBack: Factors of {0} : {1} {2}", _ulNumber, factor1, factor2); } } Asynchronous Variation 1 – call // The Asynchronous Variation 1 call, calls // the ProcessFactorizedNumber.FactorizedResults callback // when the call completes. public void FactorizeNumber1() { // The following is the Client code. PrimeFactorizer pf = new PrimeFactorizer(); FactorizingCallback fd = new FactorizingCallback(pf.Factorize); // Asynchronous Variation 1 int factorizableNum = 1000589023, temp=0; // Create an instance of the class which is going // to be called when the call completes. ProcessFactorizedNumber fc = new ProcessFactorizedNumber(factorizableNum); // Define the AsyncCallback delegate. AsyncCallback cb = new AsyncCallback(fc.FactorizedResults); // You can stuff any object as the state object. Object state = new Object(); // Asynchronously invoke the Factorize method on pf. IAsyncResult ar = fd.BeginInvoke( factorizableNum, ref temp, ref temp, cb, state); // // Do some other useful work. //. . . } Asynchronous Variation 2 // Asynchronous Variation 2 // Waits for the result. public void FactorizeNumber2() { // The following is the Client code. PrimeFactorizer pf = new PrimeFactorizer(); FactorizingCallback fd = new FactorizingCallback(pf.Factorize); // Asynchronous Variation 1 int factorizableNum = 1000589023, temp=0; // Create an instance of the class which is going // to called when the call completes. ProcessFactorizedNumber fc = new ProcessFactorizedNumber(factorizableNum); // Define the AsyncCallback delegate. AsyncCallback cb = new AsyncCallback(fc.FactorizedResults); // Can stuff any object as the state object. Object state = new Object(); // Asynchronously invoke the Factorize method on pf. IAsyncResult ar = fd.BeginInvoke( factorizableNum, ref temp, ref temp, null, null); ar.AsyncWaitHandle.WaitOne(10000, false); if (ar.IsCompleted) { int factor1=0, factor2=0; // Obtain the result. fd.EndInvoke(ref factor1, ref factor2, ar); // Output results. Console.WriteLine("Sequencial : Factors of {0} : {1} {2}", factorizableNum, factor1, factor2); } }
编译器和公共语言运行库支持
当编译器发出 FactorizingCallback 委托类时（在按如下所示分析其定义后），它将使用异步方法签名以及 Invoke 方法生成 BeginInvoke 和 EndInvoke 方法，如以下代码中所示： public class FactorizingCallback : delegate { public bool Invoke( int factorizableNum, ref int primefactor1, ref int primefactor2); // The following code was supplied by the compiler. public IAsyncResult BeginInvoke( int factorizableNum, ref int primefactor1, ref int primefactor2, AsyncCallback cb, Object AsyncState ); // The following code was supplied by the compiler. public bool EndInvoke( ref int primefactor1, ref int primefactor2, IAsyncResult ar); }
编译器提供的委托 BeginInvoke 和 EndInvoke 方法
使用用户指定的委托签名，编译器应发出具有 Invoke、BeginInvoke 和 EndInvoke 方法的委托类。BeginInvoke 和 EndInvoke 方法应被修饰为本机的。因为这些方法被标记为本机的，所以公共语言运行库在类加载时自动提供该实现。加载程序确保它们未被重写。
异步委托编程示例
以下代码通过求解某些数字因子的简单类阐释如何使用 .NET 异步编程。 using System; using System.Threading; using System.Runtime.Remoting; // Create an asynchronous delegate. public delegate bool FactorizingCallback( int factorizableNum, ref int primefactor1, ref int primefactor2); // Create a class the factorizers the number. public class PrimeFactorizer. { public bool Factorize( int factorizableNum, ref int primefactor1, ref int primefactor2) { primefactor1 = 1; primefactor2 = factorizableNum; // Factorize using a low-tech approach. for (int i=2;i<factorizableNum;i++) { if (0 == (factorizableNum % i)) { primefactor1 = i; primefactor2 = factorizableNum / i; break; } } if (1 == primefactor1 ) return false; else return true ; } } // Class that receives a callback when the the results are available. public class ProcessFactorizedNumber { private int _ulNumber; public ProcessFactorizedNumber(int number) { _ulNumber = number; } // Note the qualifier is one-way. [OneWayAttribute()] public void FactorizedResults(IAsyncResult ar) { int factor1=0, factor2=0; // Extract the delegate from the AsyncResult. FactorizingCallback fd = (FactorizingCallback)((AsyncResult)ar).AsyncDelegate; // Obtain the result. fd.EndInvoke(ref factor1, ref factor2, ar); // Output results. Console.WriteLine("On CallBack: Factors of {0} : {1} {2}", _ulNumber, factor1, factor2); } } // Class that shows variations of using Asynchronous public class Simple. { // The following demonstrates the Asynchronous Pattern using a callback. public void FactorizeNumber1() { // The following is the client code. PrimeFactorizer pf = new PrimeFactorizer(); FactorizingCallback fd = new FactorizingCallback(pf.Factorize); int factorizableNum = 1000589023, temp=0; // Create an instance of the class which is going // to be called when the call completes. ProcessFactorizedNumber fc = new ProcessFactorizedNumber(factorizableNum); // Define the AsyncCallback delegate. AsyncCallback cb = new AsyncCallback(fc.FactorizedResults); // You can stuff any object as the state object Object state = new Object(); // Asynchronously invoke the Factorize method on pf. IAsyncResult ar = fd.BeginInvoke( factorizableNum, ref temp, ref temp, cb, state); // // Do some other useful work. //. . . } // The following demonstrates the Asynchronous Pattern using a BeginInvoke, followed by waiting with a timeout. public void FactorizeNumber2() { // The following is the client code. PrimeFactorizer pf = new PrimeFactorizer(); FactorizingCallback fd = new FactorizingCallback(pf.Factorize); int factorizableNum = 1000589023, temp=0; // Create an instance of the class which is going // to be called when the call completes. ProcessFactorizedNumber fc = new ProcessFactorizedNumber(factorizableNum); // Define the AsyncCallback delegate. AsyncCallback cb = new AsyncCallback(fc.FactorizedResults); // You can stuff any object as the state object. Object state = new Object(); // Asynchronously invoke the Factorize method on pf. IAsyncResult ar = fd.BeginInvoke( factorizableNum, ref temp, ref temp, null, null); ar.AsyncWaitHandle.WaitOne(10000, false); if (ar.IsCompleted) { int factor1=0, factor2=0; // Obtain the result. fd.EndInvoke(ref factor1, ref factor2, ar); // Output results. Console.WriteLine("Sequencial : Factors of {0} : {1} {2}", factorizableNum, factor1, factor2); } } public static void Main(String[] args) { Simple simple = new Simple(); simple.FactorizeNumber1(); simple.FactorizeNumber2(); } }
总结
上面是VS.NET中.NET异步编程方面的基本概念和示例代码，整理出来给大家参考一下。有任何建议请MAIL我 [email protected]。
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