什么是.Net的异步机制(Invoke,BeginInvoke,EndInvoke) - step 2

r囧r小猫 2022-03-29 06:07 180阅读 0赞

现在扩充下上篇文章的类(AsyncTest),提供更多的例子并从中做下简单的对比, 从新的认识下异步的内部机制,下面我们增加一个新的委托

1步,我们添加一个新方法(计算年薪YearlySalary)

public decimal YearlySalary(decimal salary, int monthCount, decimal bonus);

2步,为这个方法增加异步的功能,这样我们仍然使用委托(Delegate)

public delegate decimal SalaryEventHandler(decimal salary, int monthCount, decimal bonus);

经过简单修改后,下面是我们新的AsyncTest类

Code1

1 ![None.gif][] // 我们使用委托来提供.Net的异步机制  
2 ![None.gif][] public delegate string AsyncEventHandler( string name); // 对应Hello 方法  
3 ![None.gif][] public delegate decimal SalaryEventHandler( decimal salary, int monthCount, decimal bonus); // 对应YearlySalary方法  
4 ![None.gif][] public class AsyncTest  
5 ![ExpandedBlockStart.gif][] \{  
6![InBlock.gif][] public string Hello(string name)  
7![ExpandedSubBlockStart.gif][] \{  
8![InBlock.gif][] return "Hello:" + name;  
9![ExpandedSubBlockEnd.gif][] \}  
10![InBlock.gif][]  
11![ExpandedSubBlockStart.gif][] /// <summary>  
12![InBlock.gif][] /// 计算一年的薪水  
13![InBlock.gif][] /// </summary>  
14![InBlock.gif][] /// <param name="salary">月薪</param>  
15![InBlock.gif][] /// <param name="monthCount">一年支付月数量</param>  
16![InBlock.gif][] /// <param name="bonus">奖金</param>  
17![ExpandedSubBlockEnd.gif][] /// <returns></returns>  
18![InBlock.gif][] public decimal YearlySalary(decimal salary, int monthCount, decimal bonus)  
19![ExpandedSubBlockStart.gif][] \{  
20![InBlock.gif][] //添加辅助方法,查看当前的线程ID  
21![InBlock.gif][] Console.WriteLine("Thread ID:\#\{0\}", Thread.CurrentThread.ManagedThreadId);  
22![InBlock.gif][]  
23![InBlock.gif][] return salary \* monthCount + bonus;  
24![ExpandedSubBlockEnd.gif][] \}  
25![ExpandedBlockEnd.gif][]\}

这里用**.NET Reflector 5** 来反编译,之所以用这个,因为比微软的会更加清晰明了.如果想了解这个工具的朋友可查看(http://reflector.red-gate.com/)

![2.1.jpg][]

图1

开始我先对图1中的小图标进行个简单的解释

![2.1.5.jpg][] = 类(Class) ![2.1.2.jpg][] = 类继承的基类 ![2.1.1.jpg][] = sealed(委托)

![2.1.3.jpg][] = 类的构造函数 ![2.1.6.jpg][] = 方法 ![2.1.4.jpg][] = virtual方法

下面我们先比较下**SalaryEventHandler****与** **AsyncEventHandler**委托的异同.

1) **SalaryEventHandler**

public delegate decimal SalaryEventHandler(decimal salary, int monthCount, decimal bonus);

![2.1.7.jpg][]

图2.1

编译器生成的类Code2.1(图2.1)  
Code 2.1

1 ![None.gif][] public sealed class SalaryEventHandler : MulticastDelegate  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] public SalaryEventHandler(object @object, IntPtr method)  
4![ExpandedSubBlockStart.gif][] \{ ![dot.gif][].\}  
5![InBlock.gif][] public virtual IAsyncResult BeginInvoke(decimal salary, int monthCount, decimal bonus,  
AsyncCallback callback, object @object)  
6![ExpandedSubBlockStart.gif][] \{ ![dot.gif][]\}  
7![InBlock.gif][] public virtual decimal EndInvoke(IAsyncResult result)  
8![ExpandedSubBlockStart.gif][] \{ ![dot.gif][]\}  
9![InBlock.gif][] public virtual decimal Invoke(decimal salary, int monthCount, decimal bonus)  
10![ExpandedSubBlockStart.gif][] \{ ![dot.gif][]\}  
11![ExpandedBlockEnd.gif][] \}

2) **AsyncEventHandler**

public delegate string AsyncEventHandler(string name);

![2.1.8.jpg][]

图2.2

编译器生成的类Code2.2(图2.2)

Code2.2

1 ![None.gif][] public sealed class AsyncEventHandler : MulticastDelegate  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] public AsyncEventHandler(object @object, IntPtr method)  
4![ExpandedSubBlockStart.gif][] \{ ![dot.gif][].\}  
5![InBlock.gif][] public virtual IAsyncResult BeginInvoke(string name, AsyncCallback callback, object @object)  
6![ExpandedSubBlockStart.gif][] \{ ![dot.gif][]\}  
7![InBlock.gif][] public virtual string EndInvoke(IAsyncResult result)  
8![ExpandedSubBlockStart.gif][] \{ ![dot.gif][]\}  
9![InBlock.gif][] public virtual string Invoke(string name)  
10![ExpandedSubBlockStart.gif][] \{ ![dot.gif][]\}  
11![ExpandedBlockEnd.gif][] \}

对比两个委托(事实上是一个sealed 的类),都继承于System.MuliticaseDelegate, 三个virtual的 Invoke / BeginInvoke / EndInvoke 方法.

//同步方法

**Invoke :** 参数的个数,类型, 返回值都不相同

//异步方法,作为一组来说明

**BeginInvoke :** 参数的个数和类型不同,返回值相同

**EndInvoke :** 参数相同,返回值不同

这里我们先介绍下 **Invoke**这个方法, 我们用SalaryEventHandler委托为例(直接调用Code 1 的类)

Code 3

1 ![None.gif][] class Program  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] static void Main(string\[\] args)  
4![ExpandedSubBlockStart.gif][] \{  
5![InBlock.gif][] //添加辅助方法,查看当前的线程ID  
6![InBlock.gif][] Console.WriteLine("Main Thread ID:\#\{0\}", Thread.CurrentThread.ManagedThreadId);  
7![InBlock.gif][]  
8![InBlock.gif][] AsyncTest test = new AsyncTest();  
9![InBlock.gif][] //\[1\],我们习惯的调用方式  
10![InBlock.gif][] decimal v1 = test.YearlySalary(100000, 15, 100000);  
11![InBlock.gif][] //使用委托调用  
12![InBlock.gif][] SalaryEventHandler salaryDelegate = test.YearlySalary;  
13![InBlock.gif][] //\[2\],编译器会自动的把\[2\]转变成\[3\]Invoke的调用方式,\[2\]和\[3\]是完全相同的  
14![InBlock.gif][] decimal v2 = salaryDelegate(100000, 15, 100000);  
15![InBlock.gif][] //\[3\]  
16![InBlock.gif][] decimal v3 = salaryDelegate.Invoke(100000, 15, 100000);  
17![InBlock.gif][]  
18![InBlock.gif][] Console.WriteLine("V1:\{0\},V2:\{1\},V3:\{2\}", v1, v2, v3);  
19![InBlock.gif][] Console.ReadLine(); // 让黑屏等待,不会直接关闭..  
20![ExpandedSubBlockEnd.gif][] \}  
21![ExpandedBlockEnd.gif][]\}

输出的结果

![2.2.jpg][]

图3

从结果可以看出,他们是同一个线程调用的(都是\#10).这就说明\[1\],\[2\],\[3\]是同步调用

\[2\],\[3\]对比\[1\], 只不过\[2\],\[3\]是通过委托的方式(其实我们可以说成“通过代理的方式完成”),\[1\]是直接的调用.举一个我们平常生活中例子:买机票，我们到代理点购买机票而不是直接跑到机场购买,就好像我们叫别人帮我们买机票一样,最后到手的机票是一样的, SalaryEventHandler就是我们的代理点.**所以用****”****代理****”****的方式还是直接调用的方式****,****他们提供的参数和返回值必须是一样的****.**

接下来我们开始讲异步机制核心的两个方法**BeginInvoke/EndInvoke,****他们作为一个整体来完成****Invoke****方法的调用****,****不同于****Inoke****方法的是他们是异步执行****(****另外开一个线程执行****)****的**,下面先解释下他们的作用

**BeginInvoke** : 开始一个异步的请求,调用线程池中一个线程来执行  
**EndInvoke** **:** 完成异步的调用, 处理返回值 和 异常错误.

注意: BeginInvoke和EndInvoke必须成对调用.即使不需要返回值，但EndInvoke还是必须调用，否则可能会造成内存泄漏.

我们来对比下 SalaryEventHandler与 AsyncEventHandler委托反编译BeginInoke后的异同.

SalaryEventHandler 委托:

public virtual IAsyncResult BeginInvoke(decimal salary, int monthCount, decimal bonus, AsyncCallback callback, object @object)

AsyncEventHandler 委托:

public virtual IAsyncResult BeginInvoke(string name, AsyncCallback callback, object @object)

可以看出参数的个数和类型是不同的,我们把焦点放到他们的相同点上,

1,返回值是相同的: 返回IAsyncResult 对象(异步的核心). IAsyncResult是什么呢? 简单的说,他存储异步操作的状态信息的一个接口,也可以用他来结束当前异步.具体的可以看下 [http://msdn.microsoft.com/zh-cn/library/system.iasyncresult(VS.80).aspx][http_msdn.microsoft.com_zh-cn_library_system.iasyncresult_VS.80_.aspx]

2,编译器会根据委托的参数个数和类型生成相应的BeginInvoke方法,只有最后两个参数是永远相同的,他提供一个**AsyncCallback** **委托(**public delegate void AsyncCallback(IAsyncResult ar);**)** **和一个 Object** **对象.**

我们再来看看EndInvoke的异同.

SalaryEventHandler 委托:

public virtual decimal EndInvoke(IAsyncResult result)

AsyncEventHandler 委托:

public virtual string EndInvoke(IAsyncResult result)

EndInvoke的参数是一样的, 唯一是在是返回值不同(他们会根据自己委托的返回值类型生成自己的类型)

好,下面我会通过例子来说明**BeginInvoke/EndInvoke**,还是使用SalaryEventHandler委托为例(直接调用Code 1 的类)

.Net Framework 提供了两种方式来使用异步方法

第一种: 通过IAsyncResult 对象

Code 4.1

1 ![None.gif][] class Program  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] static IAsyncResult asyncResult;  
4![InBlock.gif][]  
5![InBlock.gif][] static void Main(string\[\] args)  
6![ExpandedSubBlockStart.gif][] \{  
7![InBlock.gif][]  
8![InBlock.gif][] AsyncTest test = new AsyncTest();  
9![InBlock.gif][] SalaryEventHandler dele = test.YearlySalary;  
10![InBlock.gif][] //异步方法开始执行,返回IAsyncResult(存储异常操作的状态信息) 接口,同时EndInvoke 方法也需要他来作为参数来结束异步调用  
11![InBlock.gif][] asyncResult = dele.BeginInvoke(100000, 15, 100000, null, null);  
12![InBlock.gif][] //获取返回值  
13![InBlock.gif][] decimal val = GetResult();  
14![InBlock.gif][] Console.WriteLine(val);  
15![InBlock.gif][] Console.ReadLine(); // 让黑屏等待,不会直接关闭..  
16![ExpandedSubBlockEnd.gif][] \}  
17![InBlock.gif][]  
18![InBlock.gif][] static decimal GetResult()  
19![ExpandedSubBlockStart.gif][] \{  
20![InBlock.gif][] decimal val = 0;  
21![InBlock.gif][] //获取原始的委托对象:先是获取AsyncResult对象,再根据他的AsyncDelegate属性来调用 当前 的(那一个)委托对象  
22 ![InBlock.gif][] AsyncResult result = (AsyncResult)asyncResult;  
23 ![InBlock.gif][] SalaryEventHandler salDel = (SalaryEventHandler)result.AsyncDelegate;  
24 ![InBlock.gif][]  
25 ![InBlock.gif][] //调用EndInvoke获取返回值  
26 ![InBlock.gif][] val = salDel.EndInvoke(asyncResult);  
27 ![InBlock.gif][]  
28 ![InBlock.gif][] return val;  
29 ![ExpandedSubBlockEnd.gif][] \}  
30 ![ExpandedBlockEnd.gif][]\}

第二种: 通过回调函数. 使用倒数第二个参数**AsyncCallback** **委托(**public delegate void AsyncCallback(IAsyncResult ar);**)** ,建议使用这种方法.

Code 4.2

1 ![None.gif][] class Program  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] static void Main(string\[\] args)  
4![ExpandedSubBlockStart.gif][] \{  
5![InBlock.gif][] AsyncTest test = new AsyncTest();  
6![InBlock.gif][] SalaryEventHandler dele = test.YearlySalary;  
7![InBlock.gif][]  
8![InBlock.gif][] //异步方法开始执行,使用BeginInvoke 倒数第二个参数(AsyncCallback委托对象) ,而不用返回值  
9![InBlock.gif][] dele.BeginInvoke(100000, 15, 100000, GetResultCallBack, null);  
10![InBlock.gif][] //和上面相同的  
11![InBlock.gif][] //AsyncCallback callback = new AsyncCallback(GetResultCallBack);  
12![InBlock.gif][] //dele.BeginInvoke(100000, 15, 100000, callback, null);  
13![InBlock.gif][]  
14![InBlock.gif][] Console.ReadLine(); // 让黑屏等待,不会直接关闭..  
15![ExpandedSubBlockEnd.gif][] \}  
16![InBlock.gif][]  
17![InBlock.gif][] //必须遵循AsyncCallback 委托的定义:返回值为空,一个IAsyncResult对象参数  
18![InBlock.gif][] static void GetResultCallBack(IAsyncResult asyncResult)  
19![ExpandedSubBlockStart.gif][] \{  
20![InBlock.gif][] decimal val = 0;  
21![InBlock.gif][] //获取原始的委托对象  
22![InBlock.gif][] AsyncResult result = (AsyncResult)asyncResult;  
23![InBlock.gif][] SalaryEventHandler salDel = (SalaryEventHandler)result.AsyncDelegate;  
24![InBlock.gif][]  
25![InBlock.gif][] //调用EndInvoke获取返回值  
26![InBlock.gif][] val = salDel.EndInvoke(asyncResult);  
27![InBlock.gif][]  
28![InBlock.gif][] Console.WriteLine(val);  
29![ExpandedSubBlockEnd.gif][] \}  
30![ExpandedBlockEnd.gif][]\}

BeginInvoke最后一个参数是做什么的呢?我把Code 4.2 方法修改下.

Code 4.3

**异步的异常处理**

接下来再讲讲**EndInvoke,**获取最后的返回值之外,他的一个重要的应用在”**引发异常来从异步操作返回异常**”

Code 5

1 ![None.gif][] class Program  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] static void Main(string\[\] args)  
4![ExpandedSubBlockStart.gif][] \{  
5![InBlock.gif][] AsyncTest test = new AsyncTest();  
6![InBlock.gif][] SalaryEventHandler dele = test.YearlySalary;  
7![InBlock.gif][]  
8![InBlock.gif][] dele.BeginInvoke(100000, 15, 100000, GetResultCallBack, null);  
9![InBlock.gif][] Console.ReadLine(); // 让黑屏等待,不会直接关闭..  
10![ExpandedSubBlockEnd.gif][] \}  
11![InBlock.gif][]  
12![InBlock.gif][] static void GetResultCallBack(IAsyncResult asyncResult)  
13![ExpandedSubBlockStart.gif][] \{  
14![InBlock.gif][] decimal val = 0;  
15![InBlock.gif][] //获取原始的委托对象  
16![InBlock.gif][] AsyncResult result = (AsyncResult)asyncResult;  
17![InBlock.gif][] SalaryEventHandler salDel = (SalaryEventHandler)result.AsyncDelegate;  
18![InBlock.gif][] try  
19![ExpandedSubBlockStart.gif][] \{  
20![InBlock.gif][] //如果EndInvoke发生异常,会在EndInvoke得到原始的异常.  
21![InBlock.gif][] val = salDel.EndInvoke(asyncResult);  
22![InBlock.gif][] Console.WriteLine(val);  
23![ExpandedSubBlockEnd.gif][] \}  
24![InBlock.gif][] catch (Exception ex)  
25![ExpandedSubBlockStart.gif][] \{  
26![InBlock.gif][] Console.WriteLine(ex.Message);  
27![ExpandedSubBlockEnd.gif][] \}  
28![ExpandedSubBlockEnd.gif][] \}  
29![ExpandedBlockEnd.gif][]\}  
30 ![None.gif][] public delegate decimal SalaryEventHandler( decimal salary, int monthCount, decimal bonus); // 对应YearlySalary方法  
31 ![None.gif][] public class AsyncTest  
32 ![ExpandedBlockStart.gif][] \{  
33![InBlock.gif][] public decimal YearlySalary(decimal salary, int monthCount, decimal bonus)  
34![ExpandedSubBlockStart.gif][] \{  
35![InBlock.gif][] throw new Exception("error"); //引发异常  
36![InBlock.gif][] return salary \* monthCount + bonus;  
37![ExpandedSubBlockEnd.gif][] \}  
38![ExpandedBlockEnd.gif][]\}

我们主动在YearlySalary方法中引发异常,BeginInvoke开始异步调用的时候捕获到了这个异常,.Net Framework会在EndInvoke得到原始的异常.

说到这里,大家是否可以简单的应用委托来开始自己的异步操作呢? 下面看看我是怎样为我自己的类添加异步的.

第1步, 类的定义,需要遵循.Net Framework 的规则

1)同步和异步是同时并存的

2)从最上面的两个委托**SalaryEventHandler**与 **AsyncEventHandler**生成的BeginInvoke / EndInvoke 对比中看出,我们也来定义我们自己的异步方法,我们遵循微软设计师异步方法设计的规则,Begin+同步方法名 / End+同步方法名

BeginXXX 必须返回IAsyncResult对象,后两位参数必须为AsyncCallback callback, object state,前面的参数和同步方法的参数一样

EndXXX 参数必须为IAsyncResult对象,返回值为同步方法的返回值

Code 6.1

1 ![None.gif][] public class AsyncTest  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] private delegate string AsyncEventHandler(string name);  
4![InBlock.gif][] private AsyncEventHandler \_Async;  
5![InBlock.gif][] public string Hello(string name)  
6![ExpandedSubBlockStart.gif][] \{  
7![InBlock.gif][] return "Hello:" + name;  
8![ExpandedSubBlockEnd.gif][] \}  
9![InBlock.gif][]  
10![InBlock.gif][] //按照.Net Framework的规则 ,编写我们自己的BeginInvoke方法  
11![InBlock.gif][] public virtual IAsyncResult BeginHello(string name, AsyncCallback callback, object state)  
12![ExpandedSubBlockStart.gif][] \{  
13![InBlock.gif][] AsyncEventHandler del = Hello;  
14![InBlock.gif][]  
15![InBlock.gif][] this.\_Async = del;  
16![InBlock.gif][]  
17![InBlock.gif][] return del.BeginInvoke(name, callback, state);  
18![ExpandedSubBlockEnd.gif][] \}  
19![InBlock.gif][] //编写我们自己的EndInvoke方法  
20![InBlock.gif][] public virtual string EndHello(IAsyncResult asyncResult)  
21![ExpandedSubBlockStart.gif][] \{  
22![InBlock.gif][] if (asyncResult == null)  
23![InBlock.gif][] throw new ArgumentNullException("asyncResult");  
24![InBlock.gif][] if (this.\_Async == null)  
25![InBlock.gif][] throw new ArgumentException("\_Async");  
26![InBlock.gif][]  
27![InBlock.gif][] string val = string.Empty;  
28![InBlock.gif][] try  
29![ExpandedSubBlockStart.gif][] \{  
30![InBlock.gif][] val = this.\_Async.EndInvoke(asyncResult);  
31![ExpandedSubBlockEnd.gif][] \}  
32![InBlock.gif][] finally  
33![ExpandedSubBlockStart.gif][] \{  
34![InBlock.gif][] this.\_Async = null;  
35![ExpandedSubBlockEnd.gif][] \}  
36![InBlock.gif][] return val;  
37![ExpandedSubBlockEnd.gif][] \}  
38![ExpandedBlockEnd.gif][]\}

第2步: 调用我们编写的类

Code 6.2

1 ![None.gif][] class Program  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] static void Main(string\[\] args)  
4![ExpandedSubBlockStart.gif][] \{  
5![InBlock.gif][] AsyncTest test = new AsyncTest();  
6![InBlock.gif][] //使用回调函数,就是上面提到的"第二种"  
7![InBlock.gif][] AsyncCallback callback = new AsyncCallback(OnHelloCallback);  
8![InBlock.gif][] test.BeginHello("Andy Huang", callback, test);  
9![InBlock.gif][] //和上面一样  
10![InBlock.gif][] //IAsyncResult result = test.BeginHello("Andy Huang", OnHelloCallback, test);  
11![InBlock.gif][]  
12![InBlock.gif][] Console.ReadLine(); // 让黑屏等待,不会直接关闭..  
13![ExpandedSubBlockEnd.gif][] \}  
14![InBlock.gif][]  
15![InBlock.gif][] static void OnHelloCallback(IAsyncResult asyncResult)  
16![ExpandedSubBlockStart.gif][] \{  
17![InBlock.gif][] //获取额外的参数  
18![InBlock.gif][] AsyncTest obj = (AsyncTest)asyncResult.AsyncState;  
19![InBlock.gif][] string val = obj.EndHello(asyncResult);  
20![InBlock.gif][] Console.WriteLine(val);  
21![ExpandedSubBlockEnd.gif][] \}  
22![ExpandedBlockEnd.gif][]\}

引用自 ：[http://www.cnblogs.com/30ErLi/archive/2010/09/19/1830728.html][http_www.cnblogs.com_30ErLi_archive_2010_09_19_1830728.html]

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[http_msdn.microsoft.com_zh-cn_library_system.iasyncresult_VS.80_.aspx]: http://msdn.microsoft.com/zh-cn/library/system.iasyncresult%28VS.80%29.aspx
[http_www.cnblogs.com_30ErLi_archive_2010_09_19_1830728.html]: http://www.cnblogs.com/30ErLi/archive/2010/09/19/1830728.html