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。
