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Como: implementar uma operação de serviço assíncrona

  • Artigo

Em aplicativos WCF (Windows Communication Foundation), uma operação de serviço pode ser implementada de forma assíncrona ou síncrona sem determinar como o cliente deve chamá-la. Por exemplo, as operações de serviço assíncronas podem ser chamadas de forma síncrona e as operações de serviço síncronas podem ser chamadas de forma assíncrona. Para obter um exemplo que mostra como chamar uma operação de forma assíncrona em um aplicativo cliente, consulte Como chamar operações de serviço de forma assíncrona. Para obter mais informações sobre operações síncronas e assíncronas, consulte Como criar contratos de serviço e Operações síncronas e assíncronas. Este tópico descreve a estrutura básica de uma operação de serviço assíncrona, o código não está concluído. Para obter um exemplo completo do lado do serviço e do lado do cliente, consulte Assíncrono.

Implementar uma operação de serviço assíncrona

  1. Em seu contrato de serviço, declare um par de métodos assíncronos de acordo com as diretrizes de design assíncronas do .NET. O método Begin usa um parâmetro, um objeto de retorno de chamada e um objeto de estado e retorna um System.IAsyncResult e um método correspondente End que usa um System.IAsyncResult e retorna o valor de retorno. Para obter mais informações sobre chamadas assíncronas, consulte Padrões de Design de Programação Assíncrona.

  2. Marque o método Begin do par de métodos assíncronos com o atributo System.ServiceModel.OperationContractAttribute e defina a propriedade OperationContractAttribute.AsyncPattern como true. Por exemplo, o código a seguir executa as etapas 1 e 2.

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

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

        <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

  3. Implemente o par de métodos Begin/End em sua classe de serviço de acordo com as diretrizes de design assíncronas. Por exemplo, o pedaço de código a seguir mostra uma implementação na qual uma cadeia de caracteres é gravada no console nas partes Begin e End da operação de serviço assíncrona e o valor de retorno da operação End é retornado ao cliente. Para obter o exemplo de código completo, consulte a seção Exemplo.

    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;
}

    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

Exemplo

Os exemplos de código a seguir mostram:

  1. Uma interface de contrato de serviço com:

    1. Uma operação síncrona SampleMethod.

    2. Uma operação assíncrona BeginSampleMethod.

    3. Um par de operações assíncronas BeginServiceAsyncMethod/EndServiceAsyncMethod.

  2. Uma implementação de serviço usando um objeto System.IAsyncResult.

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 synchronous 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
  }
}


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 synchronous 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

Confira também