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在網(wǎng)絡(luò)中為了保證數(shù)據(jù)的實時性，需要對數(shù)據(jù)進(jìn)行異步操作。Java Web Service和J2EE中的異步操作通過java消息機制來完成，消息機制是非常完善的技術(shù)了。而Microsoft的Web Service的異步功能是怎樣完成的呢？怎樣才能達(dá)到j(luò)ava的境地呢？當(dāng)然，Microsoft有自己的一套。
眾所周知，Web Service是靠SOAP協(xié)議進(jìn)行數(shù)據(jù)傳輸?shù)摹６鳶OAP是基于XML技術(shù)之上的。SOAP協(xié)議是連接客戶和服務(wù)器的橋梁。而SOAP協(xié)議本身沒有異步功能，需要在客戶端實現(xiàn)異步調(diào)用。我們以一個簡單的Web Service的例子來說明這一點。
一、MathService.asmx
<%@ WebService Language="C#" Class="MathService" %>
using System;
using System.Web.Services;
[WebService]
public class MathService : WebService {
[WebMethod]
public float Add(float a, float b)
{
return a + b;
}
[WebMethod]
public double Subtract(double a, double b)
{
return a - b;
}
[WebMethod]
public float Multiply(float a, float b)
{
return a * b;
}
[WebMethod]
public float Divide(float a, float b)
{
if (b==0) return -1;
return a / b;
}
}
這是個實現(xiàn)了加，減，乘，除的Web Service，任何客戶端程序都可以調(diào)用它。下面我們用wsdl（微軟公司提供）工具產(chǎn)生一個MathService.asmx 的客戶代理程序：wsdl /n:MyMath http://localhost/mathservice.asmx (假設(shè)MathService.asmx放在IIS服務(wù)器的根目錄) ，產(chǎn)生一個MathService.cs代理程序，默認(rèn)是SOAP協(xié)議。
二、MathService.cs:
namespace MyMath{
using System.Diagnostics;
using System.Xml.Serialization;
using System;
using System.Web.Services.Protocols;
using System.ComponentModel;
using System.Web.Services;
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Web.Services.WebServiceBindingAttribute(Name="MathServiceSoap", Namespace="http://tempuri.org/")]
public class MathService : System.Web.Services.Protocols.SoapHttpClientProtocol {
public MathService() {
this.Url = "http://localhost/mathservice.asmx";
}
[System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://tempuri.org/Add", RequestNamespace="http://tempuri.org/", ResponseNamespace="http://tempuri.org/", Use=System.Web.Services.Description.SoapBindingUse.Literal, ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
public System.Single Add(System.Single a, System.Single b) {
object[] results = this.Invoke("Add", new object[] {
a,
b});
return ((System.Single)(results[0]));
}
public System.IAsyncResult BeginAdd(System.Single a, System.Single b, System.AsyncCallback callback, object asyncState) {
return this.BeginInvoke("Add", new object[] {
a,
b}, callback, asyncState);
}
/// <remarks/>
public System.Single EndAdd(System.IAsyncResult asyncResult) {
object[] results = this.EndInvoke(asyncResult);
return ((System.Single)(results[0]));
}
/// <remarks/>
[System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://tempuri.org/Subtract", RequestNamespace="http://tempuri.org/", ResponseNamespace="http://tempuri.org/", Use=System.Web.Services.Description.SoapBindingUse.Literal, ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
public System.Double Subtract(System.Double a, System.Double b) {
object[] results = this.Invoke("Subtract", new object[] {
a,
b});
return ((System.Double)(results[0]));
}
/// <remarks/>
public System.IAsyncResult BeginSubtract(System.Double a, System.Double b, System.AsyncCallback callback, object asyncState) {
return this.BeginInvoke("Subtract", new object[] {
a,
b}, callback, asyncState);
}
/// <remarks/>
public System.Double EndSubtract(System.IAsyncResult asyncResult) {
object[] results = this.EndInvoke(asyncResult);
return ((System.Double)(results[0]));
}
/// <remarks/>
[System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://tempuri.org/Multiply", RequestNamespace="http://tempuri.org/", ResponseNamespace="http://tempuri.org/", Use=System.Web.Services.Description.SoapBindingUse.Literal, ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
public System.Single Multiply(System.Single a, System.Single b) {
object[] results = this.Invoke("Multiply", new object[] {
a,
b});
return ((System.Single)(results[0]));
}
/// <remarks/>
public System.IAsyncResult BeginMultiply(System.Single a, System.Single b, System.AsyncCallback callback, object asyncState) {
return this.BeginInvoke("Multiply", new object[] {
a,
b}, callback, asyncState);
}
/// <remarks/>
public System.Single EndMultiply(System.IAsyncResult asyncResult) {
object[] results = this.EndInvoke(asyncResult);
return ((System.Single)(results[0]));
}
/// <remarks/>
[System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://tempuri.org/Divide", RequestNamespace="http://tempuri.org/", ResponseNamespace="http://tempuri.org/", Use=System.Web.Services.Description.SoapBindingUse.Literal, ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
public System.Single Divide(System.Single a, System.Single b) {
object[] results = this.Invoke("Divide", new object[] {
a,
b});
return ((System.Single)(results[0]));
}
/// <remarks/>
public System.IAsyncResult BeginDivide(System.Single a, System.Single b, System.AsyncCallback callback, object asyncState) {
return this.BeginInvoke("Divide", new object[] {
a,
b}, callback, asyncState);
}
/// <remarks/>
public System.Single EndDivide(System.IAsyncResult asyncResult) {
object[] results = this.EndInvoke(asyncResult);
return ((System.Single)(results[0]));
}
}
}
之后我們用csc /t:library MathService.cs編譯并產(chǎn)生一個MathService.dll.
現(xiàn)在我們可以寫任何的客戶程序去調(diào)用服務(wù)器上的MathService.asmx。
如：WinForm, C#,ASPX等。
下面我們寫一個test.cs去測試異步調(diào)用：
三、test.cs:
using System;
public class test{
public static void Main(){
MyMath.MathService math = new MyMath.MathService();
IAsyncResult result1 = math.BeginAdd(10,20,null,null);
Object result=math.EndAdd(result1);
Console.WriteLine("result =========="+result);
}
}
我們看到它是先調(diào)用代理MathService.cs中的BeginAdd方法，然后狀態(tài)信息保存在IasyncResult中，直到調(diào)用了EndAdd方法才返回調(diào)用的確切值。本例是遠(yuǎn)端調(diào)用MathService.asmx中的Add方法。
那Microsoft到底怎樣實現(xiàn)客戶端的異步呢？設(shè)計模式又是怎樣的呢？
異步模式所提供的革新之一就是調(diào)用方確定特定調(diào)用是否應(yīng)是異步的。 對于被調(diào)用的對象，沒有必要執(zhí)行附加的編程來用于支持其客戶端的異步行為；在該模式中異步委托提供此功能。公共語言運行庫處理調(diào)用方和被調(diào)用的對象視圖之間的差異。被調(diào)用的對象可以選擇顯式支持異步行為，這或者是因為它可以比一般結(jié)構(gòu)更為有效地實現(xiàn)異步行為，或者是因為它想只支持其調(diào)用方的異步行為。但是，建議這種被調(diào)用的對象遵循公開異步操作的異步設(shè)計模式。
類型安全是異步模式的另一項革新。尤其對于異步委托，針對 .NET 框架和公共語言運行庫的語言編譯器可令映射到規(guī)則 Invoke 方法的開始和結(jié)束操作（例如，BeginInvoke 和 EndInvoke）的方法簽名是類型安全的。這是十分重要的，因為編譯器為異步委托將同步調(diào)用拆分成開始和結(jié)束操作，使其能夠只傳遞有效參數(shù)。
在此模式中所蘊含的基本想法如下所示：
1．調(diào)用方確定特定調(diào)用是否應(yīng)是異步的。
2. 對于被調(diào)用的對象，沒有必要由其客戶端執(zhí)行附加的編程來用于支持異步行為。公共語言運行庫結(jié)構(gòu)應(yīng)該能夠處理調(diào)用方和被調(diào)用的對象視圖之間的差異。
3. 被調(diào)用的對象可以選擇顯式支持異步行為，這或者是因為它可以比一般結(jié)構(gòu)更為有效地實現(xiàn)異步行為，或者是因為它想只支持其調(diào)用方的異步行為。但是，建議這種被調(diào)用的對象遵循公開異步操作的異步設(shè)計模式。
4. 編譯器為 BeginInvoke 和 EndInvoke 以及異步委托生成類型安全方法簽名。
5. .NET 框架提供支持異步編程模型所需的服務(wù)。此類服務(wù)的部分列表示例是：
(1)同步基元，例如監(jiān)視器和閱讀器編寫器鎖定。
(2)線程和線程池。
(3)同步構(gòu)造，例如支持等候?qū)ο蟮娜萜鳌?/p>
(4)向基礎(chǔ)結(jié)構(gòu)片（例如 IMessage 對象和線程池）公開。
該模式將一個同步調(diào)用拆分成各構(gòu)成部分：開始操作、結(jié)束操作和結(jié)果對象。考慮以下示例，在其中可能要用大量時間來完成 Factorize 方法。
public class PrimeFactorizer
{
public bool Factorize(int factorizableNum, ref int primefactor1, ref int primefactor2)
{
// Determine whether factorizableNum is prime.
// If is prime, return true. Otherwise, return false.
// If is prime, place factors in primefactor1 and primefactor2.
}
}
如果遵循異步模式，則類庫編寫器添加 BeginFactorize 和 EndFactorize方法，這兩個方法將同步操作拆分成兩個異步操作：
public class PrimeFactorizer
{
public bool Factorize(
int factorizableNum,
ref int primefactor1,
ref int primefactor2)
{
// Determine whether factorizableNum is prime.
// if is prime, return true; otherwise return false.
// if is prime palce factors in primefactor1 and primefactor2
}
public IAsyncResult BeginFactorize(
int factorizableNum,
ref int primefactor1,
ref int primefactor2,
AsyncCallback callback,
Object state)
{
// Begin the factorizing asynchronously, and return a result object,
}
public bool EndFactorize(
ref int primefactor1,
ref int primefactor2,
IAsyncResult asyncResult
)
{
// End (or complete) the factorizing, and
// return the results,
// and obtain the prime factors.
}
}
服務(wù)器將異步操作拆分成兩個邏輯部分：采用來自客戶端的輸入并調(diào)用異步操作的部分，向客戶端提供異步操作結(jié)果的部分。
除了異步操作所需的輸入外，第一部分還采用在完成異步操作時后要被調(diào)用的 AsyncCallback 委托。第一部分返回一個可等待的對象，該對象實現(xiàn)客戶端使用的 IAsyncResult 接口來確定異步操作的狀態(tài)。
服務(wù)器還利用它返回到客戶端的可等待的對象來維護(hù)與異步操作關(guān)聯(lián)的任何狀態(tài)。通過提供可等待的對象，客戶端使用第二部分獲取異步操作的結(jié)果。
可用于客戶端來啟動異步操作的選項有：
在開始異步調(diào)用時提供回調(diào)委托。
public class Driver1
{
public PrimeFactorizer primeFactorizer;
public void Results(IAsyncResult asyncResult)
{
int primefactor1=0;
int primefactor2=0;
bool prime = primeFactorizer.EndFactorize(
ref primefactor1,
ref primefactor2,
asyncResult);
}
public void Work()
{
int factorizableNum=1000589023,
int primefactor1=0;
int primefactor2=0;
Object state = new Object();
primeFactorizer = new PrimeFactorizer();
AsyncCallback callback = new Callback(this.Results);
IAsyncResult asyncResult = primeFactorizer.BeginFactorize(
factorizableNum,
ref primefactor1,
ref primefactor2,
callback,
state);
}
｝
在開始異步調(diào)用時不提供回調(diào)委托。
public class Driver2
{
public static void Work()
{
int factorizableNum=1000589023,
int primefactor1=0;
int primefactor2=0;
Object state = new Object();
PrimeFactorizer primeFactorizer = new PrimeFactorizer();
AsyncCallback callback = new Callback(this.Results);
IAsyncResult asyncResult = primeFactorizer.BeginFactorize(
factorizableNum,
ref primefactor1,
ref primefactor2,
callback,
state);
bool prime = primeFactorizer.EndFactorize(
ref primefactor1,
ref primefactor2,
asyncResult);
}
}
我們以.Net的一個例子來說明這一點：
AsyncDelegate2.cs
using System;
using System.Threading;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Messaging;
public class Wak
{
public int Pat(int i)
{
Console.WriteLine("Hash: {0} Wak Pat", Thread.CurrentThread.GetHashCode());
return i*2;
}
};
public delegate int WakPatDelegate(int i);// 異步調(diào)用的委派.
public class Simple
{
public static void SomeMethod(IAsyncResult ar)
{
// Obtain value from AsyncState object
int value = Convert.ToInt32(ar.AsyncState);
// Obtain results via EndInvoke
int result = ((WakPatDelegate)((AsyncResult)ar).AsyncDelegate ).EndInvoke(ar);
Console.WriteLine("Simple.SomeMethod (AsyncCallback): Result of {0} in Wak.Pak is {1} ",value, result);
}
public static void Main(String[] args)
{
Console.WriteLine("Thread Simple Context Sample");
Console.WriteLine("");
Console.WriteLine("Make an instance of a context-bound type Wak");
Wak oWak = new Wak();
int value=0;
int result=0;
Console.WriteLine("Make a sync call on the object");
value = 10;
result = oWak.Pat(value);
Console.WriteLine("Result of {0} in Wak.Pak is {1} ",value, result);
Console.WriteLine("Make single Async call on Context-bound object");
WakPatDelegate wpD1 = new WakPatDelegate(oWak.Pat);
value = 20;
IAsyncResult ar1 = wpD1.BeginInvoke(value,null,null);
ar1.AsyncWaitHandle.WaitOne();
result = wpD1.EndInvoke(ar1);
Console.WriteLine("Result of {0} in Wak.Pak is {1} ",value, result);
Console.WriteLine("Make single Async call on Context-bound object - use AsyncCallback and StateObject");
WakPatDelegate wpD2 = new WakPatDelegate(oWak.Pat);
value = 30;
IAsyncResult ar2 = wpD2.BeginInvoke(
value,
new AsyncCallback(Simple.SomeMethod),
value
);
Console.WriteLine("Make multiple Async calls on Context-bound object");
int asyncCalls = 5;
IAsyncResult[] ars = new IAsyncResult[asyncCalls];
WaitHandle[] whs = new WaitHandle[asyncCalls];
int[] values = new int[asyncCalls];
WakPatDelegate wpD3 = new WakPatDelegate(oWak.Pat);
for (int i=0; i < asyncCalls; i++)
{
values[i] = i;
ars[i] = wpD3.BeginInvoke(values[i],null,null);
whs[i] = ars[i].AsyncWaitHandle;
}
WaitHandle.WaitAll(whs,1000, false);
for (int i=0; i < asyncCalls; i++)
{
result = wpD3.EndInvoke(ars[i]);
Console.WriteLine("Result of {0} in Wak.Pak is {1} ",values[i], result);
}
Console.WriteLine("");
Console.WriteLine("Done");
}
}
如果異步調(diào)用成功，將顯示：
Thread Simple Context Sample
Make an instance of a context-bound type Wak
Make a sync call on the object
Hash: 3 Wak Pat
Result of 10 in Wak.Pak is 20
Make single Async call on Context-bound object
Hash: 16 Wak Pat
Result of 20 in Wak.Pak is 40
Make single Async call on Context-bound object - use AsyncCallback and StateObje
ct
Hash: 16 Wak Pat
Make multiple Async calls on Context-bound object
Simple.SomeMethod (AsyncCallback): Result of 30 in Wak.Pak is 60
Hash: 16 Wak Pat
Hash: 16 Wak Pat
Hash: 16 Wak Pat
Hash: 16 Wak Pat
Hash: 16 Wak Pat
Result of 0 in Wak.Pak is 0
Result of 1 in Wak.Pak is 2
Result of 2 in Wak.Pak is 4
Result of 3 in Wak.Pak is 6
Result of 4 in Wak.Pak is 8
Done
原文地址：http://www.ccw.com.cn/htm/center/prog/02_8_23_6.asp