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ASP.NET創(chuàng)建XML Web服務(wù)全接觸(10)

[摘要]和XML Web服務(wù)異步地通訊  和一個XML Web服務(wù)異步通訊遵循被Microsoft.NET Framework其它部分使用的異步設(shè)計模式。然而,在你取得那些細節(jié)之前,重要的是注意一個XML Web服務(wù)不必特意的寫來處理用于異步調(diào)用的異步請求。你使用Wsdl.exe為你的客戶端創(chuàng)建的代理類自...

    

  和XML Web服務(wù)異步地通訊

  和一個XML Web服務(wù)異步通訊遵循被Microsoft.NET Framework其它部分使用的異步設(shè)計模式。然而,在你取得那些細節(jié)之前,重要的是注意一個XML Web服務(wù)不必特意的寫來處理用于異步調(diào)用的異步請求。你使用Wsdl.exe為你的客戶端創(chuàng)建的代理類自動地創(chuàng)建用于異步調(diào)用XML Web服務(wù)方法的方法。即使只有一個XML Web服務(wù)方法的同步實現(xiàn)也是這樣的。

  .NET Framework異步方法調(diào)用設(shè)計模式

  用于調(diào)用異步方法的設(shè)計模式,尤其是用于.NET Framework,針對每個同步方法分別有兩個異步方法。對每個同步方法,都有一個Begin異步方法和一個End異步方法。Begin方法被客戶端調(diào)用來開始方法調(diào)用。也就是說,客戶端指示這個方法來開始處理方法調(diào)用,但是立即返回。End方法被客戶端調(diào)用來取得XML Web服務(wù)方法調(diào)用執(zhí)行的處理結(jié)果。

  一個客戶端如何知道何時調(diào)用End方法?.NET Framework定義了兩種方法來實現(xiàn)客戶端判斷其時間。第一種是傳送一個回調(diào)函數(shù)到Begin方法,當(dāng)方法已經(jīng)完成處理的時候調(diào)用。第二個方法是使用WaitHandle類的一個方法來導(dǎo)致客戶端等待方法完成。當(dāng)一個客戶端實現(xiàn)第二個方法,并且調(diào)用Begin方法,返回值不是XML Web服務(wù)方法指定的數(shù)據(jù)類型,而是一個實現(xiàn)IAsyncResult接口的類型。IAsyncResult接口包含一個WaitHandle類型的AsyncWaitHandle屬性,實現(xiàn)支持等待同步對象變?yōu)閹в蠾aitHandle.WaitOne、WaitAny和WaitAll標記的方法。當(dāng)一個同步對象被標記的時候,它指示等待特定的資源的線程可以訪問資源的。如果一個XML Web服務(wù)客戶端使用wait方法僅僅異步地調(diào)用一個XML Web服務(wù)方法,那么它可以調(diào)用WaitOne來等待XML Web服務(wù)方法完成處理。

  重要的是注意不管客戶端選擇來與XML Web服務(wù)異步通訊的兩種方法中的哪一種,SOAP消息發(fā)送和接收都與同步通信時吻合。也就是說,只有一個SOAP請求和SOAP響應(yīng)通過網(wǎng)絡(luò)發(fā)送和接收。代理類通過使用一個不同的線程而不是客戶端用來調(diào)用Begin方法的線程來處理SOAP響應(yīng)。因此,客戶端可以繼續(xù)執(zhí)行線程上的其它的工作,而代理類處理接收和操作SOAP響應(yīng)。

  實現(xiàn)一個產(chǎn)生異步的方法調(diào)用的XML Web服務(wù)客戶端

  用于從使用ASP.NET創(chuàng)建的XML Web服務(wù)客戶端產(chǎn)生一個到XML Web服務(wù)的異步調(diào)用的體系結(jié)構(gòu)被嵌入.NET Framework和由Wsdl.exe構(gòu)造的代理類中。用于異步調(diào)用的設(shè)計模式被.NET Framework定義,代理類提供和一個XML Web服務(wù)異步通信的機制。當(dāng)一個用于XML Web服務(wù)的代理類被使用Wsdl.exe構(gòu)造的時候,有三個方法分別被創(chuàng)建,用于XML Web服務(wù)中的公共XML Web服務(wù)方法。下面的表格描述那三個方法。

  代理類中的方法名 描述

 。糔ameOfWebServiceMethod> 同步發(fā)送用于名為<NameOfWebServiceMethod>的XML Web服務(wù)方法的消息。

  Begin<NameOfWebServiceMethod> 開始與名為<NameOfWebServiceMethod>的XML Web服務(wù)方法的異步消息通信。

  End<NameOfWebServiceMethod> 結(jié)束與名為<NameOfWebServiceMethod>的XML Web服務(wù)方法的異步消息通信,從XML Web服務(wù)方法中取得完成的消息。

  下面的代碼示例是一個XML Web服務(wù)方法,它可能花費相對長的時間來完成處理。因此,當(dāng)你應(yīng)該設(shè)置你的XML Web服務(wù)客戶端來異步地調(diào)用XML Web服務(wù)方法的時候,它是一個很好的示例。

[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


  下面的代碼示例是一個Wsdl.exe生成的代理類的一部分,用于上述XML Web服務(wù)方法。注意BeginFactorize和EndFactorize方法,因為它們被用來與Factorize XML Web服務(wù)方法異步通信。

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]));
 }
}


  有兩個方法用來和XML Web服務(wù)方法異步通信。下面的代碼示例說明了如何與一個XML Web服務(wù)方法異步通信,并且使用回調(diào)函數(shù)來取得XML Web服務(wù)方法的結(jié)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


  下面的代碼示例說明了如何與一個XML Web服務(wù)方法異步通信,然后使用一個同步對象來等待處理結(jié)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是一個需要同步化/線成親和上下文的上下文綁定類,那么回調(diào)被通過上下文分配體系結(jié)構(gòu)來分配。換句話說,相對于它的對這樣的上下文的調(diào)用者,回調(diào)可能異步的執(zhí)行。在方法標記上有單向修飾詞的精確的語義。這指的是任何這樣的方法調(diào)用可能同步地或異步地執(zhí)行,相對于調(diào)用者,并且在執(zhí)行控制返回給它的時候,調(diào)用者不能產(chǎn)生任何關(guān)于完成這樣一個調(diào)用的假設(shè)。
而且,在異步操作完成之前調(diào)用EndInvoke將阻塞調(diào)用者。使用相同的AsyncResult再次調(diào)用它的行為是不確定的。

  Cancel方法是一個在過去一段特定時間之后取消方法處理的請求。注意它是一個客戶端的請求,并且最好服務(wù)器對此有所承諾。在接收到方法已經(jīng)被取消的消息之后,客戶端就不必做服務(wù)器是否已經(jīng)停止處理的假設(shè)了。客戶端最好不要破壞資源,例如文件對象,因為服務(wù)器可能仍然需要使用它們。IAsyncResult實例的IsCompleted屬性在服務(wù)器結(jié)束它的處理之后將被設(shè)置為true,不再使用任何客戶端提供的資源。因此,IsCompleted屬性設(shè)置為true之后,客戶端就可以安全的銷毀資源了。