使用.NET 异步编程(2)

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：

usingSystem;

usingSystem.Runtime.Remoting;

publicdelegateboolFactorizingCallback(

intfactorizableNum,

refintprimefactor1,

refintprimefactor2);

//Thisisaclassthatreceivesacallbackwhenthetheresultsareavailable.

publicclassProcessFactorizedNumber

{

privateint_ulNumber;

publicProcessFactorizedNumber(intnumber)

{

_ulNumber=number;

}

//Notethequalifierone-way.

[OneWayAttribute()]

publicvoidFactorizedResults(IAsyncResultar)

{

intfactor1=0,factor2=0;

//ExtractthedelegatefromtheAsyncResult.

FactorizingCallbackfd=

(FactorizingCallback)((AsyncResult)ar).AsyncDelegate;

//Obtaintheresult.

fd.EndInvoke(reffactor1,reffactor2,ar);

//Outputresults.

Console.WriteLine("OnCallBack:Factorsof{0}:{1}{2}",

_ulNumber,factor1,factor2);

}

}

AsynchronousVariation1–call

//TheAsynchronousVariation1call,calls

//theProcessFactorizedNumber.FactorizedResultscallback

//whenthecallcompletes.

publicvoidFactorizeNumber1()

{

//ThefollowingistheClientcode.

PrimeFactorizerpf=newPrimeFactorizer();

FactorizingCallbackfd=newFactorizingCallback(pf.Factorize);

//AsynchronousVariation1

intfactorizableNum=1000589023,temp=0;

//Createaninstanceoftheclasswhichisgoing

//tobecalledwhenthecallcompletes.

ProcessFactorizedNumberfc=newProcessFactorizedNumber(factorizableNum);

//DefinetheAsyncCallbackdelegate.

AsyncCallbackcb=newAsyncCallback(fc.FactorizedResults);

//Youcanstuffanyobjectasthestateobject.

Objectstate=newObject();

//AsynchronouslyinvoketheFactorizemethodonpf.

IAsyncResultar=fd.BeginInvoke(

factorizableNum,

reftemp,

reftemp,

cb,

state);

//

//Dosomeotherusefulwork.

//...

}

AsynchronousVariation2

//AsynchronousVariation2

//Waitsfortheresult.

publicvoidFactorizeNumber2()

{

//ThefollowingistheClientcode.

PrimeFactorizerpf=newPrimeFactorizer();

FactorizingCallbackfd=newFactorizingCallback(pf.Factorize);

//AsynchronousVariation1

intfactorizableNum=1000589023,temp=0;

//Createaninstanceoftheclasswhichisgoing

//tocalledwhenthecallcompletes.

ProcessFactorizedNumberfc=newProcessFactorizedNumber(factorizableNum);

//DefinetheAsyncCallbackdelegate.

AsyncCallbackcb=

newAsyncCallback(fc.FactorizedResults);

//Canstuffanyobjectasthestateobject.

Objectstate=newObject();

//AsynchronouslyinvoketheFactorizemethodonpf.

IAsyncResultar=fd.BeginInvoke(

factorizableNum,

reftemp,

reftemp,

null,

null);

ar.AsyncWaitHandle.WaitOne(10000,false);

if(ar.IsCompleted)

{

intfactor1=0,factor2=0;

//Obtaintheresult.

fd.EndInvoke(reffactor1,reffactor2,ar);

//Outputresults.

Console.WriteLine("Sequencial:Factorsof{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：

publicclassFactorizingCallback:delegate

{

publicboolInvoke(

intfactorizableNum,

refintprimefactor1,

refintprimefactor2);

//Thefollowingcodewassuppliedbythecompiler.

publicIAsyncResultBeginInvoke(

intfactorizableNum,

refintprimefactor1,

refintprimefactor2,

AsyncCallbackcb,

ObjectAsyncState

);

//Thefollowingcodewassuppliedbythecompiler.

publicboolEndInvoke(

refintprimefactor1,

refintprimefactor2,

IAsyncResultar);

}

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。

usingSystem;

usingSystem.Threading;

usingSystem.Runtime.Remoting;

//Createanasynchronousdelegate.

publicdelegateboolFactorizingCallback(

intfactorizableNum,

refintprimefactor1,

refintprimefactor2);

//Createaclassthefactorizersthenumber.

publicclassPrimeFactorizer.

{

publicboolFactorize(

intfactorizableNum,

refintprimefactor1,

refintprimefactor2)

{

primefactor1=1;

primefactor2=factorizableNum;

//Factorizeusingalow-techapproach.

for(inti=2;i<factorizableNum;i++)

{

if(0==(factorizableNum%i))

{

primefactor1=i;

primefactor2=factorizableNum/i;

break;

}

}

if(1==primefactor1)

returnfalse;

else

returntrue;

}

}

//Classthatreceivesacallbackwhenthetheresultsareavailable.

publicclassProcessFactorizedNumber

{

privateint_ulNumber;

publicProcessFactorizedNumber(intnumber)

{

_ulNumber=number;

}

//Notethequalifierisone-way.

[OneWayAttribute()]

publicvoidFactorizedResults(IAsyncResultar)

{

intfactor1=0,factor2=0;

//ExtractthedelegatefromtheAsyncResult.

FactorizingCallbackfd=(FactorizingCallback)((AsyncResult)ar).AsyncDelegate;

//Obtaintheresult.

fd.EndInvoke(reffactor1,reffactor2,ar);

//Outputresults.

Console.WriteLine("OnCallBack:Factorsof{0}:{1}{2}",

_ulNumber,factor1,factor2);

}

}

//ClassthatshowsvariationsofusingAsynchronous

publicclassSimple.

{

//ThefollowingdemonstratestheAsynchronousPatternusingacallback.

publicvoidFactorizeNumber1()

{

//Thefollowingistheclientcode.

PrimeFactorizerpf=newPrimeFactorizer();

FactorizingCallbackfd=newFactorizingCallback(pf.Factorize);

intfactorizableNum=1000589023,temp=0;

//Createaninstanceoftheclasswhichisgoing

//tobecalledwhenthecallcompletes.

ProcessFactorizedNumberfc=newProcessFactorizedNumber(factorizableNum);

//DefinetheAsyncCallbackdelegate.

AsyncCallbackcb=newAsyncCallback(fc.FactorizedResults);

//Youcanstuffanyobjectasthestateobject

Objectstate=newObject();

//AsynchronouslyinvoketheFactorizemethodonpf.

IAsyncResultar=fd.BeginInvoke(

factorizableNum,

reftemp,

reftemp,

cb,

state);

//

//Dosomeotherusefulwork.

//...

}

//ThefollowingdemonstratestheAsynchronousPatternusingaBeginInvoke,followedbywaitingwithatimeout.

publicvoidFactorizeNumber2()

{

//Thefollowingistheclientcode.

PrimeFactorizerpf=newPrimeFactorizer();

FactorizingCallbackfd=newFactorizingCallback(pf.Factorize);

intfactorizableNum=1000589023,temp=0;

//Createaninstanceoftheclasswhichisgoing

//tobecalledwhenthecallcompletes.

ProcessFactorizedNumberfc=newProcessFactorizedNumber(factorizableNum);

//DefinetheAsyncCallbackdelegate.

AsyncCallbackcb=

newAsyncCallback(fc.FactorizedResults);

//Youcanstuffanyobjectasthestateobject.

Objectstate=newObject();

//AsynchronouslyinvoketheFactorizemethodonpf.

IAsyncResultar=fd.BeginInvoke(

factorizableNum,

reftemp,

reftemp,

null,

null);

ar.AsyncWaitHandle.WaitOne(10000,false);

if(ar.IsCompleted)

{

intfactor1=0,factor2=0;

//Obtaintheresult.

fd.EndInvoke(reffactor1,reffactor2,ar);

//Outputresults.

Console.WriteLine("Sequencial:Factorsof{0}:{1}{2}",

factorizableNum,factor1,factor2);

}

}

publicstaticvoidMain(String[]args)

{

Simplesimple=newSimple();

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。