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ASP.NET创建XML Web服务全接触(10)

[摘要]和XML Web服务异步地通讯  和一个XML Web服务异步通讯遵循被Microsoft.NET Framework其它部分使用的异步设计模式。然而,在你取得那些细节之前,重要的是注意一个XML Web服务不必特意的写来处理用于异步调用的异步请求。你使用Wsdl.exe为你的客户端创建的代理类自...

    

  和XML Web服务异步地通讯

  和一个XML Web服务异步通讯遵循被Microsoft.NET Framework其它部分使用的异步设计模式。然而,在你取得那些细节之前,重要的是注意一个XML Web服务不必特意的写来处理用于异步调用的异步请求。你使用Wsdl.exe为你的客户端创建的代理类自动地创建用于异步调用XML Web服务方法的方法。即使只有一个XML Web服务方法的同步实现也是这样的。

  .NET Framework异步方法调用设计模式

  用于调用异步方法的设计模式,尤其是用于.NET Framework,针对每个同步方法分别有两个异步方法。对每个同步方法,都有一个Begin异步方法和一个End异步方法。Begin方法被客户端调用来开始方法调用。也就是说,客户端指示这个方法来开始处理方法调用,但是立即返回。End方法被客户端调用来取得XML Web服务方法调用执行的处理结果。

  一个客户端如何知道何时调用End方法?.NET Framework定义了两种方法来实现客户端判断其时间。第一种是传送一个回调函数到Begin方法,当方法已经完成处理的时候调用。第二个方法是使用WaitHandle类的一个方法来导致客户端等待方法完成。当一个客户端实现第二个方法,并且调用Begin方法,返回值不是XML Web服务方法指定的数据类型,而是一个实现IAsyncResult接口的类型。IAsyncResult接口包含一个WaitHandle类型的AsyncWaitHandle属性,实现支持等待同步对象变为带有WaitHandle.WaitOne、WaitAny和WaitAll标记的方法。当一个同步对象被标记的时候,它指示等待特定的资源的线程可以访问资源的。如果一个XML Web服务客户端使用wait方法仅仅异步地调用一个XML Web服务方法,那么它可以调用WaitOne来等待XML Web服务方法完成处理。

  重要的是注意不管客户端选择来与XML Web服务异步通讯的两种方法中的哪一种,SOAP消息发送和接收都与同步通信时吻合。也就是说,只有一个SOAP请求和SOAP响应通过网络发送和接收。代理类通过使用一个不同的线程而不是客户端用来调用Begin方法的线程来处理SOAP响应。因此,客户端可以继续执行线程上的其它的工作,而代理类处理接收和操作SOAP响应。

  实现一个产生异步的方法调用的XML Web服务客户端

  用于从使用ASP.NET创建的XML Web服务客户端产生一个到XML Web服务的异步调用的体系结构被嵌入.NET Framework和由Wsdl.exe构造的代理类中。用于异步调用的设计模式被.NET Framework定义,代理类提供和一个XML Web服务异步通信的机制。当一个用于XML Web服务的代理类被使用Wsdl.exe构造的时候,有三个方法分别被创建,用于XML Web服务中的公共XML Web服务方法。下面的表格描述那三个方法。

  代理类中的方法名 描述

  <NameOfWebServiceMethod> 同步发送用于名为<NameOfWebServiceMethod>的XML Web服务方法的消息。

  Begin<NameOfWebServiceMethod> 开始与名为<NameOfWebServiceMethod>的XML Web服务方法的异步消息通信。

  End<NameOfWebServiceMethod> 结束与名为<NameOfWebServiceMethod>的XML Web服务方法的异步消息通信,从XML Web服务方法中取得完成的消息。

  下面的代码示例是一个XML Web服务方法,它可能花费相对长的时间来完成处理。因此,当你应该设置你的XML Web服务客户端来异步地调用XML Web服务方法的时候,它是一个很好的示例。

[C#]
<%@ WebService Language="C#" Class="PrimeFactorizer" %>

using System;
using System.Collections;
using System.Web.Services;

class PrimeFactorizer {

 [WebMethod]
 public long[] Factorize(long factorizableNum){
  ArrayList outList = new ArrayList();
  long i = 0;
  int j;
  try{
   long Check = factorizableNum;

   //Go through every possible integer
   //factor between 2 and factorizableNum / 2.
   //Thus, for 21, check between 2 and 10.
   for (i = 2; i < (factorizableNum / 2); i++){
    while(Check % i == 0){
     outList.Add(i);
     Check = (Check/i);
    }
   }
   //Double-check to see how many prime factors have been added.
   //If none, add 1 and the number.
   j = outList.Count;
   if (j == 0) {
    outList.Add(1);
    outList.Add(factorizableNum);
   }
   j = outList.Count;

   //Return the results and
   //create an array to hold them.
   long[] primeFactor = new long[j];
   for (j = 0; j < outList.Count; j++){
    //Pass the values one by one, making sure
    //to convert them to type ulong.
    primeFactor[j] = Convert.ToInt64(outList[j]);
   }
   return primeFactor;
  }
  catch (Exception) {
   return null;
  }
 }
}

[Visual Basic]
<%@ WebService Class="PrimeFactorizer" Language="VB" %>
Imports System
Imports System.Collections
Imports System.Web.Services

Public Class PrimeFactorizer
<WebMethod> _
Public Function Factorize(factorizableNum As Long) As Long()
 Dim outList As New ArrayList()
 Dim i As Long = 0
 Dim j As Integer
 Try
  Dim Check As Long = factorizableNum

  'Go through every possible integer
  'factor between 2 and factorizableNum / 2.
  'Thus, for 21, check between 2 and 10.
  For i = 2 To CLng(factorizableNum / 2) - 1
   While Check Mod i = 0
    outList.Add(i)
    Check = CLng(Check / i)
   End While
  Next i
  'Double-check to see how many prime factors have been added.
  'If none, add 1 and the number.
  j = outList.Count
  If j = 0 Then
   outList.Add(1)
   outList.Add(factorizableNum)
  End If
  j = outList.Count

  'Return the results and
  'create an array to hold them.
  Dim primeFactor(j - 1) As Long
  For j = 0 To outList.Count - 1
   'Pass the values one by one, making sure
   'to convert them to type ulong.
   primeFactor(j) = CLng(outList(j))
  Next j
  Return primeFactor
 Catch
  Return Nothing
 End Try
End Function
End Class


  下面的代码示例是一个Wsdl.exe生成的代理类的一部分,用于上述XML Web服务方法。注意BeginFactorize和EndFactorize方法,因为它们被用来与Factorize XML Web服务方法异步通信。

public class PrimeFactorizer : System.Web.Services.Protocols.SoapHttpClientProtocol {

 public long[] Factorize(long factorizableNum) {
  object[] results = this.Invoke("Factorize", new object[] { factorizableNum});
   return ((long[])(results[0]));
 }

 public System.IAsyncResult BeginFactorize(long factorizableNum, System.AsyncCallback callback, object  asyncState) {
  return this.BeginInvoke("Factorize", new object[] {
  factorizableNum}, callback, asyncState);
 }

 public long[] EndFactorize(System.IAsyncResult asyncResult) {
  object[] results = this.EndInvoke(asyncResult);
  return ((long[])(results[0]));
 }
}


  有两个方法用来和XML Web服务方法异步通信。下面的代码示例说明了如何与一个XML Web服务方法异步通信,并且使用回调函数来取得XML Web服务方法的结果。

[C#]
using System;
using System.Runtime.Remoting.Messaging;
using MyFactorize;

class TestCallback
{
 public static void Main(){
  long factorizableNum = 12345;
  PrimeFactorizer pf = new PrimeFactorizer();

  //Instantiate an AsyncCallback delegate to use as a parameter
  //in the BeginFactorize method.
  AsyncCallback cb = new AsyncCallback(TestCallback.FactorizeCallback);

  // Begin the Async call to Factorize, passing in our
  // AsyncCalback delegate and a reference
  // to our instance of PrimeFactorizer.
  IAsyncResult ar = pf.BeginFactorize(factorizableNum, cb, pf);

  // Keep track of the time it takes to complete the async call
  // as the call proceeds.
  int start = DateTime.Now.Second;
  int currentSecond = start;
  while (ar.IsCompleted == false){
   if (currentSecond < DateTime.Now.Second) {
    currentSecond = DateTime.Now.Second;
    Console.WriteLine("Seconds Elapsed..." + (currentSecond - start).ToString() );
   }
  }
  // Once the call has completed, you need a method to ensure the
  // thread executing this Main function
  // doesn't complete prior to the call-back function completing.
  Console.Write("Press Enter to quit");
  int quitchar = Console.Read();
 }
 // Set up a call-back function that is invoked by the proxy class
 // when the asynchronous operation completes.
 public static void FactorizeCallback(IAsyncResult ar)
 {
  // You passed in our instance of PrimeFactorizer in the third
  // parameter to BeginFactorize, which is accessible in the
  // AsyncState property.
  PrimeFactorizer pf = (PrimeFactorizer) ar.AsyncState;
  long[] results;

  // Get the completed results.
  results = pf.EndFactorize(ar);

  //Output the results.
  Console.Write("12345 factors into: ");
  int j;
  for (j = 0; j<results.Length;j++){
   if (j == results.Length - 1)
    Console.WriteLine(results[j]);
   else
    Console.Write(results[j] + ", ");
  }
 }
}

[Visual Basic]
Imports System
Imports System.Runtime.Remoting.Messaging
Imports MyFactorize

Public Class TestCallback
Public Shared Sub Main()
Dim factorizableNum As Long = 12345
Dim pf As PrimeFactorizer = new PrimeFactorizer()

'Instantiate an AsyncCallback delegate to use as a parameter
' in the BeginFactorize method.
Dim cb as AsyncCallback
cb = new AsyncCallback(AddressOf TestCallback.FactorizeCallback)

' Begin the Async call to Factorize, passing in the
' AsyncCallback delegate and a reference to our instance
' of PrimeFactorizer.
Dim ar As IAsyncResult = pf.BeginFactorize(factorizableNum, cb, pf)

' Keep track of the time it takes to complete the async call as
' the call proceeds.
Dim start As Integer = DateTime.Now.Second
Dim currentSecond As Integer = start
Do while (ar.IsCompleted = false)
If (currentSecond < DateTime.Now.Second) Then
 currentSecond = DateTime.Now.Second
 Console.WriteLine("Seconds Elapsed..." + (currentSecond - start).ToString() )
End If
Loop

' Once the call has completed, you need a method to ensure the
' thread executing this Main function
' doesn't complete prior to the callback function completing.
Console.Write("Press Enter to quit")
Dim quitchar As Integer = Console.Read()
End Sub

' Set up the call-back function that is invoked by the proxy
' class when the asynchronous operation completes.
Public Shared Sub FactorizeCallback(ar As IAsyncResult)

' You passed in the instance of PrimeFactorizer in the third
' parameter to BeginFactorize, which is accessible in the
' AsyncState property.

Dim pf As PrimeFactorizer = ar.AsyncState
Dim results() as Long

' Get the completed results.
results = pf.EndFactorize(ar)

'Output the results.
Console.Write("12345 factors into: ")
Dim j as Integer
For j = 0 To results.Length - 1
 If j = (results.Length - 1) Then
  Console.WriteLine(results(j) )
 Else
  Console.Write(results(j).ToString + ", ")
 End If
Next j
End Sub
End Class


  下面的代码示例说明了如何与一个XML Web服务方法异步通信,然后使用一个同步对象来等待处理结束。

[C#]
// -----------------------------------------------------------------------// Async Variation 2.
// Asynchronously invoke the Factorize method,
//without specifying a call back.
using System;
using System.Runtime.Remoting.Messaging;
// MyFactorize, is the name of the namespace in which the proxy class is
// a member of for this sample.
using MyFactorize;

class TestCallback
{
 public static void Main(){
  long factorizableNum = 12345;
  PrimeFactorizer pf = new PrimeFactorizer();

  // Begin the Async call to Factorize.
  IAsyncResult ar = pf.BeginFactorize(factorizableNum, null, null);

  // Wait for the asynchronous operation to complete.
  ar.AsyncWaitHandle.WaitOne();

  // Get the completed results.
  long[] results;
  results = pf.EndFactorize(ar);

  //Output the results.
  Console.Write("12345 factors into: ");
  int j;
  for (j = 0; j<results.Length;j++){
   if (j == results.Length - 1)
    Console.WriteLine(results[j]);
   else
    Console.Write(results[j] + ", ");
  }
 }
}

[Visual Basic]
Imports System
Imports System.Runtime.Remoting.Messaging
Imports MyFactorize ' Proxy class namespace

Public Class TestCallback
Public Shared Sub Main()
Dim factorizableNum As Long = 12345
Dim pf As PrimeFactorizer = new PrimeFactorizer()

' Begin the Async call to Factorize.
Dim ar As IAsyncResult = pf.BeginFactorize(factorizableNum, Nothing, Nothing)

' Wait for the asynchronous operation to complete.
ar.AsyncWaitHandle.WaitOne()

' Get the completed results.
Dim results() as Long
results = pf.EndFactorize(ar)

'Output the results.
Console.Write("12345 factors into: ")
Dim j as Integer
For j = 0 To results.Length - 1
 If j = (results.Length - 1) Then
  Console.WriteLine(results(j) )
 Else
  Console.Write(results(j).ToString + ", ")
 End If
Next j
End Sub
End Class


  注意:如果FactorizeCallback是一个需要同步化/线成亲和上下文的上下文绑定类,那么回调被通过上下文分配体系结构来分配。换句话说,相对于它的对这样的上下文的调用者,回调可能异步的执行。在方法标记上有单向修饰词的精确的语义。这指的是任何这样的方法调用可能同步地或异步地执行,相对于调用者,并且在执行控制返回给它的时候,调用者不能产生任何关于完成这样一个调用的假设。
而且,在异步操作完成之前调用EndInvoke将阻塞调用者。使用相同的AsyncResult再次调用它的行为是不确定的。

  Cancel方法是一个在过去一段特定时间之后取消方法处理的请求。注意它是一个客户端的请求,并且最好服务器对此有所承诺。在接收到方法已经被取消的消息之后,客户端就不必做服务器是否已经停止处理的假设了。客户端最好不要破坏资源,例如文件对象,因为服务器可能仍然需要使用它们。IAsyncResult实例的IsCompleted属性在服务器结束它的处理之后将被设置为true,不再使用任何客户端提供的资源。因此,IsCompleted属性设置为true之后,客户端就可以安全的销毁资源了。