如何：实现异步服务操作

项目
02/28/2011

在 Windows Communication Foundation (WCF) 应用程序中，服务操作可以按同步方式或异步方式实现，而无需指示客户端如何调用它。例如，异步服务操作可以同步调用，而同步服务操作可以异步调用。有关如何在客户端应用程序中异步调用操作的示例，请参见如何：以异步方式调用 WCF 服务操作。有关同步操作和异步操作的更多信息，请参见设计服务协定和同步和异步操作。本主题介绍异步服务操作的基本结构，代码并不完整。有关服务与客户端方面的完整示例，请参见异步。

按异步方式实现服务操作

在服务协定中，按照 .NET 异步设计准则声明一个异步方法对。Begin 方法采用一个参数、一个回调对象和一个状态对象作为参数，并且返回一个 System.IAsyncResult 和一个匹配的 End 方法，该方法采用一个 System.IAsyncResult 作为参数并将返回值返回。有关异步调用的更多信息，请参见Asynchronous Programming Design Patterns。

使用 System.ServiceModel.OperationContractAttribute 属性 (attribute) 标记该异步方法对的 Begin 方法，并将 System.ServiceModel.OperationContractAttribute.AsyncPattern 属性 (property) 设置为 true。例如，下面的代码执行步骤 1 和 2。

  <OperationContractAttribute(AsyncPattern:=True)> _
  Function BeginServiceAsyncMethod(ByVal msg As String, ByVal callback As AsyncCallback, ByVal asyncState As Object) As IAsyncResult

  ' Note: There is no OperationContractAttribute for the end method.
  Function EndServiceAsyncMethod(ByVal result As IAsyncResult) As String
End Interface

  [OperationContractAttribute(AsyncPattern=true)]
  IAsyncResult BeginServiceAsyncMethod(string msg, AsyncCallback callback, object asyncState);

  // Note: There is no OperationContractAttribute for the end method.
  string EndServiceAsyncMethod(IAsyncResult result);
}

按照异步设计准则在服务类中实现 Begin/End 方法对。例如，下面的代码示例演示一个实现，在此实现中，异步服务操作的 Begin 和 End 部分都向控制台写入一个字符串，并且将 End 操作的返回值返回到客户端。有关完整的代码示例，请参见“示例”部分。

示例

下面的代码示例演示以下各项：

与下列各项之间的服务协定接口：
1. 同步 SampleMethod 操作。
2. 异步 BeginSampleMethod 操作。
3. 异步 BeginServiceAsyncMethod/EndServiceAsyncMethod 操作对。
使用 System.IAsyncResult 对象的服务实现。

Imports System
Imports System.Collections.Generic
Imports System.ServiceModel
Imports System.Text
Imports System.Threading

Namespace Microsoft.WCF.Documentation
  <ServiceContractAttribute(Namespace:="http://microsoft.wcf.documentation")> _
  Public Interface ISampleService

    <OperationContractAttribute> _
    Function SampleMethod(ByVal msg As String) As String

    <OperationContractAttribute(AsyncPattern := True)> _
    Function BeginSampleMethod(ByVal msg As String, ByVal callback As AsyncCallback, ByVal asyncState As Object) As IAsyncResult

    'Note: There is no OperationContractAttribute for the end method.
    Function EndSampleMethod(ByVal result As IAsyncResult) As String

    <OperationContractAttribute(AsyncPattern:=True)> _
    Function BeginServiceAsyncMethod(ByVal msg As String, ByVal callback As AsyncCallback, ByVal asyncState As Object) As IAsyncResult

    ' Note: There is no OperationContractAttribute for the end method.
    Function EndServiceAsyncMethod(ByVal result As IAsyncResult) As String
  End Interface

  Public Class SampleService
      Implements ISampleService
    #Region "ISampleService Members"

    Public Function SampleMethod(ByVal msg As String) As String Implements ISampleService.SampleMethod
      Console.WriteLine("Called synchronous sample method with ""{0}""", msg)
         Return "The sychronous service greets you: " & msg
    End Function

    ' This asynchronously implemented operation is never called because 
    ' there is a synchronous version of the same method.
    Public Function BeginSampleMethod(ByVal msg As String, ByVal callback As AsyncCallback, ByVal asyncState As Object) As IAsyncResult Implements ISampleService.BeginSampleMethod
      Console.WriteLine("BeginSampleMethod called with: " & msg)
      Return New CompletedAsyncResult(Of String)(msg)
    End Function

    Public Function EndSampleMethod(ByVal r As IAsyncResult) As String Implements ISampleService.EndSampleMethod
      Dim result As CompletedAsyncResult(Of String) = TryCast(r, CompletedAsyncResult(Of String))
      Console.WriteLine("EndSampleMethod called with: " & result.Data)
      Return result.Data
    End Function

    Public Function BeginServiceAsyncMethod(ByVal msg As String, ByVal callback As AsyncCallback, ByVal asyncState As Object) As IAsyncResult Implements ISampleService.BeginServiceAsyncMethod
      Console.WriteLine("BeginServiceAsyncMethod called with: ""{0}""", msg)
      Return New CompletedAsyncResult(Of String)(msg)
    End Function

    Public Function EndServiceAsyncMethod(ByVal r As IAsyncResult) As String Implements ISampleService.EndServiceAsyncMethod
      Dim result As CompletedAsyncResult(Of String) = TryCast(r, CompletedAsyncResult(Of String))
      Console.WriteLine("EndServiceAsyncMethod called with: ""{0}""", result.Data)
      Return result.Data
    End Function
    #End Region
  End Class

  ' Simple async result implementation.
  Friend Class CompletedAsyncResult(Of T)
      Implements IAsyncResult
    Private data_Renamed As T

    Public Sub New(ByVal data As T)
        Me.data_Renamed = data
    End Sub

    Public ReadOnly Property Data() As T
        Get
            Return data_Renamed
        End Get
    End Property

    #Region "IAsyncResult Members"
    Public ReadOnly Property AsyncState() As Object Implements IAsyncResult.AsyncState
        Get
            Return CObj(data_Renamed)
        End Get
    End Property

    Public ReadOnly Property AsyncWaitHandle() As WaitHandle Implements IAsyncResult.AsyncWaitHandle
        Get
            Throw New Exception("The method or operation is not implemented.")
        End Get
    End Property

    Public ReadOnly Property CompletedSynchronously() As Boolean Implements IAsyncResult.CompletedSynchronously
        Get
            Return True
        End Get
    End Property

    Public ReadOnly Property IsCompleted() As Boolean Implements IAsyncResult.IsCompleted
        Get
            Return True
        End Get
    End Property
    #End Region
  End Class
End Namespace

using System;
using System.Collections.Generic;
using System.ServiceModel;
using System.Text;
using System.Threading;

namespace Microsoft.WCF.Documentation
{
  [ServiceContractAttribute(Namespace="http://microsoft.wcf.documentation")]
  public interface ISampleService{

    [OperationContractAttribute]
    string SampleMethod(string msg);

    [OperationContractAttribute(AsyncPattern = true)]
    IAsyncResult BeginSampleMethod(string msg, AsyncCallback callback, object asyncState);

    //Note: There is no OperationContractAttribute for the end method.
    string EndSampleMethod(IAsyncResult result);

    [OperationContractAttribute(AsyncPattern=true)]
    IAsyncResult BeginServiceAsyncMethod(string msg, AsyncCallback callback, object asyncState);

    // Note: There is no OperationContractAttribute for the end method.
    string EndServiceAsyncMethod(IAsyncResult result);
  }

  public class SampleService : ISampleService
  {
    #region ISampleService Members

    public string  SampleMethod(string msg)
    {
      Console.WriteLine("Called synchronous sample method with \"{0}\"", msg);
        return "The sychronous service greets you: " + msg;
    }

    // This asynchronously implemented operation is never called because 
    // there is a synchronous version of the same method.
    public IAsyncResult BeginSampleMethod(string msg, AsyncCallback callback, object asyncState)
    {
      Console.WriteLine("BeginSampleMethod called with: " + msg);
      return new CompletedAsyncResult<string>(msg);
    }

    public string EndSampleMethod(IAsyncResult r)
    {
      CompletedAsyncResult<string> result = r as CompletedAsyncResult<string>;
      Console.WriteLine("EndSampleMethod called with: " + result.Data);
      return result.Data;
    }

    public IAsyncResult BeginServiceAsyncMethod(string msg, AsyncCallback callback, object asyncState) 
    {
      Console.WriteLine("BeginServiceAsyncMethod called with: \"{0}\"", msg);
      return new CompletedAsyncResult<string>(msg);
    }

    public string EndServiceAsyncMethod(IAsyncResult r)
    {
      CompletedAsyncResult<string> result = r as CompletedAsyncResult<string>;
      Console.WriteLine("EndServiceAsyncMethod called with: \"{0}\"", result.Data);
      return result.Data;
    }
    #endregion
  }

  // Simple async result implementation.
  class CompletedAsyncResult<T> : IAsyncResult
  {
    T data;

    public CompletedAsyncResult(T data)
    { this.data = data; }

    public T Data
    { get { return data; } }

    #region IAsyncResult Members
    public object AsyncState
    { get { return (object)data; } }

    public WaitHandle AsyncWaitHandle
    { get { throw new Exception("The method or operation is not implemented."); } }

    public bool CompletedSynchronously
    { get { return true; } }

    public bool IsCompleted
    { get { return true; } }
    #endregion
  }
}

另请参见

概念

设计服务协定
 同步和异步操作

通过

如何：实现异步服务操作

按异步方式实现服务操作

示例

另请参见

概念

其他资源