建立非同步 XML Web Service 方法

發行項
04/11/2008

若要改善 XML Web Service 方法的效能 (這些方法叫用阻檔其執行緒的長時間執行方法)，您應該考慮將它們公開為非同步 XML Web Service 方法。實作非同步 XML Web Service 方法可讓該執行緒傳回至執行區集區時，執行其他程式碼。如此可使得執行緒集區除了限制的執行緒數目外再多執行一個，加強系統的整體效能和延展性 (Scalability)。

一般來說，XML Web Service 方法會呼叫執行 I/O 作業的方法，是非同步實作的好方法。這類方法的範例包括與其他 XML Web Service 通訊、存取遠端資料庫、執行網路 I/O 和讀取及寫入大型檔案的方法。這些方法全在硬體的執行上花費大量的時間，因此阻斷了執行緒執行 XML Web Service 方法。如果 XML Web Service 方法非同步實作，這個執行緒即可釋放出來以執行其他程式碼。

無論 XML Web Service 方法是否非同步實作，用戶端都可以非同步與其進行通訊。非同步通訊會公開至用 Web 服務描述語言 (WSDL.EXE) 工具所產生的 Proxy 類別內的 .NET 用戶端，即使同步實作 XML Web Service 方法也是一樣。Proxy 類別包含 Begin 和 End 方法，可以用來非同步與每個 XML Web Service 方法通訊。因此，非同步或同步實作 XML Web Service 方法應該根據效能來決定。

**注意 **實作非同步 XML Web Service 方法對用戶端與裝載 XML Web Service 的伺服器之間的 HTTP 連接並沒有影響。HTTP 連接不會關閉也不會共用。

若要實作非同步 XML Web Service 方法

非同步 XML Web Service 方法的實作遵循 .NET Framework 非同步設計模式

將同步的 XML Web Service 方法分隔成兩種方法；每個都具有相同的基底名稱 - 一個從 Begin 開始而另一個從 End 開始。
Begin 方法的參數清單包含所有的 in 和 by reference 參數，因為方法的功能結尾附加了這兩個參數。
- By reference 參數列出為 in 參數。
- 倒數第二個參數必須是 AsyncCallback。AsyncCallback 參數允許用戶端提供委派 (Delegate)，在方法完成時叫用。當非同步 XML Web Service 方法呼叫另一個非同步方法時，這個參數可以傳遞到該方法的倒數第二個參數。
- 最後一個參數是 Object。Object 參數允許呼叫端對方法提供狀態資訊。當非同步 XML Web Service 方法呼叫另一個非同步方法時，這個參數可以傳遞到該方法的最後一個參數。
- 傳回值必須是 IAsyncResult 型別。
下列程式碼範例為 Begin 方法，其具有方法功能專屬的 String 參數。
```
[WebMethod]
public IAsyncResult BeginGetAuthorRoyalties(String Author,
                  AsyncCallback callback, object asyncState) 
[Visual Basic]
<WebMethod()> _
Public Function BeginGetAuthorRoyalties(ByVal Author As String, _
   ByVal callback As AsyncCallback, ByVal asyncState As Object) _
                    As IAsyncResult
```

End 方法的參數清單由 IAsyncResult 組成，其後跟隨方法之功能專屬的任何 out 和 by reference 參數。

傳回值型別與同步 XML Web Service 方法的傳回值型別相同。
By reference 參數列出為 out 參數。

下列程式碼範例為 End 方法，其傳回 AuthorRoyalties 使用者定義型別。

[WebMethod]
public AuthorRoyalties EndGetAuthorRoyalties(IAsyncResult
                                   asyncResult)
[Visual Basic]
<WebMethod()> _
Public Function EndGetAuthorRoyalties(ByVal asyncResult As _
                    IAsyncResult) As AuthorRoyalties

下列程式碼範例是非同步 XML Web Service 方法，可與另一個 XML Web Service 方法進行非同步通訊。

using System;
using System.Web.Services;

[WebService(Namespace="https://www.contoso.com/")]
public class MyService : WebService {
  public RemoteService remoteService;
  public MyService() {
     // Create a new instance of proxy class for 
     // the XML Web service to be called.
     remoteService = new RemoteService();
  }
  // Define the Begin method.
  [WebMethod]
  public IAsyncResult BeginGetAuthorRoyalties(String Author,
                  AsyncCallback callback, object asyncState) {
     // Begin asynchronous communictation with a different XML Web
     // service.
     return remoteService.BeginReturnedStronglyTypedDS(Author,
                         callback,asyncState);
  }
  // Define the End method.
  [WebMethod]
  public AuthorRoyalties EndGetAuthorRoyalties(IAsyncResult
                                   asyncResult) {
   // Return the asynchronous result from the other XML Web service.
   return remoteService.EndReturnedStronglyTypedDS(asyncResult);
  }
}
[Visual Basic]
Imports System.Web.Services
<WebService(Namespace:="https://www.contoso.com/")> _
Public Class MyService
   Inherits WebService
   Public remoteService As RemoteService

   Public Sub New()
      MyBase.New()
      ' Create a new instance of proxy class for 
      ' the XML Web service to be called.
      remoteService = New RemoteService()
   End Sub

   ' Define the Begin method.
   <WebMethod()> _
   Public Function BeginGetAuthorRoyalties(ByVal Author As String, _
   ByVal callback As AsyncCallback, ByVal asyncState As Object) _
                    As IAsyncResult
      ' Begin asynchronous communictation with a different XML Web
      ' service.
      Return remoteService.BeginReturnedStronglyTypedDS(Author, _
                            callback, asyncState)
   End Function
   ' Define the End method.
   <WebMethod()> _
   Public Function EndGetAuthorRoyalties(ByVal asyncResult As _
                    IAsyncResult) As AuthorRoyalties
      ' Return the asynchronous result from the other XML Web service.
      Return remoteService.EndReturnedStronglyTypedDS(asyncResult)
   End Function
End Class

下列程式碼示範在 XML Web Service 方法進行一個以上非同步呼叫且呼叫必須依序執行時，如何鏈結非同步呼叫。BeginGetAuthorRoyalties 方法進行非同步呼叫以決定傳遞的作者是否有效，然後設定名為 AuthorRoyaltiesCallback 的立即回呼 (Callback) 來接收結果。接著該立即回呼會非同步呼叫以取得該作者的版稅 (如果這個作者是有效的)。

using System.Web.Services;
using System.Data;
using System;
// This imports the proxy class for the XML Web services
// that the sample communicates with.
using AsyncWS.localhost;

namespace AsyncWS
{
    [WebService(Namespace="https://www.contoso.com/")]
    public class MyService : System.Web.Services.WebService
    {
        public RemoteService remoteService;
        public MyService()
        {
           remoteService = new RemoteService();
        }

        [WebMethod]
        public IAsyncResult BeginGetAuthorRoyalties(String Author,
               AsyncCallback callback, Object asyncState) 
       {
          // Saves the current state for the call that gets the author's
          // royalties.
          AsyncStateChain state = new AsyncStateChain();
          state.originalState = asyncState;
          state.Author = Author;
          state.originalCallback = callback;

          // Creates an intermediary callback.
          AsyncCallback chainedCallback = new
             AsyncCallback(AuthorRoyaltiesCallback);
          return remoteService.BeginGetAuthors(chainedCallback,state);
       }
       // Intermediate method to handle chaining the 
       // asynchronous calls.
       public void AuthorRoyaltiesCallback(IAsyncResult ar)
       {
          AsyncStateChain state = (AsyncStateChain)ar.AsyncState;
          RemoteService rs = new RemoteService();

          // Gets the result from the call to GetAuthors.
          Authors allAuthors = rs.EndGetAuthors(ar);

          Boolean found = false;
          // Verifies that the requested author is valid.
          int i = 0;
          DataRow row;
          while (i < allAuthors.authors.Rows.Count && !found)
          {
             row = allAuthors.authors.Rows[i];
             if (row["au_lname"].ToString() == state.Author) 
             {
                found = true;
             }
             i++;
          }
          if (found)
          {
             AsyncCallback cb = state.originalCallback;
             // Calls the second XML Web service, because the author is
             // valid.
             rs.BeginReturnedStronglyTypedDS(state.Author,cb,state);
          }
          else
          {
            // Cannot throw the exception in this function or the XML Web
            // service will hang. So, set the state argument to the
            // exception and let the End method of the chained XML Web
            // service check for it.  
            ArgumentException ex = new ArgumentException(
              "Author does not exist.","Author");
            AsyncCallback cb = state.originalCallback;
            // Call the second XML Web service, setting the state to an
            // exception.
            rs.BeginReturnedStronglyTypedDS(state.Author,cb,ex);
          }
       }

       [WebMethod]
       public AuthorRoyalties EndGetAuthorRoyalties(IAsyncResult
                                                    asyncResult) 
       {
        // Check whehter the first XML Web service threw an exception.
        if (asyncResult.AsyncState is ArgumentException)
          throw (ArgumentException) asyncResult.AsyncState;
        else
         return remoteService.EndReturnedStronglyTypedDS(asyncResult);
       }
    }
    // Class to wrap the callback and state for the intermediate
    // asynchronous operation.
    public class AsyncStateChain 
    {
       public AsyncCallback originalCallback;
       public Object originalState;
       public String Author;
    }
}
[Visual Basic]
Imports System.Web.Services
Imports System.Data
Imports System
' This imports the proxy class for the XML Web services
' that the sample communicates with.
Imports AsyncWS_VB.localhost


Namespace AsyncWs

<WebService(Namespace:="https://www.contoso.com/")> _
Public Class MyService
    Inherits WebService
    Public remoteService As remoteService
    Public Sub New()
        MyBase.New()
        remoteService = New localhost.RemoteService()
    End Sub
    ' Defines the Begin method.
    <WebMethod()> _
    Public Function BeginGetAuthorRoyalties(ByVal Author As String, _
    ByVal callback As AsyncCallback, ByVal asyncState As Object) _
                    As IAsyncResult
        ' Saves the current state for the call that gets the author's
        ' royalties.
        Dim state As AsyncStateChain = New AsyncStateChain()
        state.originalState = asyncState
        state.Author = Author
        state.originalCallback = callback

        ' Creates an intermediary callback.
        Dim chainedCallback As AsyncCallback = New AsyncCallback( _
           AddressOf AuthorRoyaltiesCallback)
        ' Begin asynchronous communictation with a different XML Web
        ' service.
        Return remoteService.BeginGetAuthors(chainedCallback, state)
    End Function

    ' Intermediate method to handle chaining the asynchronous calls.
    Public Sub AuthorRoyaltiesCallback(ByVal ar As IAsyncResult)
        Dim state As AsyncStateChain = CType(ar.AsyncState, _
            AsyncStateChain)
        Dim rs As RemoteService = New RemoteService()

        ' Gets the result from the call to GetAuthors.
        Dim allAuthors As Authors = rs.EndGetAuthors(ar)
        Dim found As Boolean = False

        ' Verifies that the requested author is valid.
        Dim i As Integer = 0
        Dim row As DataRow
        While (i < allAuthors.authors.Rows.Count And (Not found))
            row = allAuthors.authors.Rows(i)
            If (row("au_lname").ToString() = state.Author) Then
                found = True
            End If
            i = i + 1
        End While
        If (found) Then
            Dim cb As AsyncCallback = state.originalCallback
            ' Calls the second XML Web service, because the author is
            ' valid.
            rs.BeginReturnedStronglyTypedDS(state.Author, cb, state)
        Else
          ' Cannot throw the exception in this function or the XML Web
          ' service will hang.  So, set the state argument to the
          ' exception and let the End method of the chained XML Web
          ' service check for it.  
            Dim ex As ArgumentException = New ArgumentException( _ 
                "Author does not exist.", "Author")
            Dim cb As AsyncCallback = state.originalCallback
            ' Call the second XML Web service, setting the state to an
            ' exception.
            rs.BeginReturnedStronglyTypedDS(state.Author, cb, ex)
        End If
    End Sub

    ' Define the End method.
    <WebMethod()> _
    Public Function EndGetAuthorRoyalties(ByVal asyncResult As _
            IAsyncResult) As localhost.AuthorRoyalties
        ' Return the asynchronous result from the other XML Web service.
        Return remoteService.EndReturnedStronglyTypedDS(asyncResult)
    End Function

End Class

' Class to wrap the callback and state for the intermediate asynchronous
' operation.
Public Class AsyncStateChain
   Public originalCallback As AsyncCallback
   Public originalState As Object
   Public Author As String
End Class
End Namespace

請參閱

與 XML Web Service 進行非同步通訊 | 包含非同步呼叫 | 使用 ASP.NET 建置 XML Web Service

共用方式為

建立非同步 XML Web Service 方法

請參閱

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