如何使用.NET异步编程？

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 paulni@citiz.net。

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