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In Windows Communication Foundation (WCF) applications, a service operation can be implemented asynchronously or synchronously without dictating to the client how to call it. For example, asynchronous service operations can be called synchronously, and synchronous service operations can be called asynchronously. For an example that shows how to call an operation asynchronously in a client application, see How to: Call Service Operations Asynchronously. For more information about synchronous and asynchronous operations, see Designing Service Contracts and Synchronous and Asynchronous Operations. This topic describes the basic structure of an asynchronous service operation, the code is not complete. For a complete example of both the service and client sides, see Asynchronous.
Implement a service operation asynchronously
In your service contract, declare an asynchronous method pair according to the .NET asynchronous design guidelines. The
Beginmethod takes a parameter, a callback object, and a state object, and returns a System.IAsyncResult and a matchingEndmethod that takes a System.IAsyncResult and returns the return value. For more information about asynchronous calls, see Asynchronous Programming Design Patterns.Mark the
Beginmethod of the asynchronous method pair with the System.ServiceModel.OperationContractAttribute attribute and set the OperationContractAttribute.AsyncPattern property totrue. For example, the following code performs steps 1 and 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 StringEnd InterfaceImplement the
Begin/Endmethod pair in your service class according to the asynchronous design guidelines. For example, the following code example shows an implementation in which a string is written to the console in both theBeginandEndportions of the asynchronous service operation, and the return value of theEndoperation is returned to the client. For the complete code example, see the Example section.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 FunctionPublic 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.DataEnd Function
Example
The following code examples show:
A service contract interface with:
A synchronous
SampleMethodoperation.An asynchronous
BeginSampleMethodoperation.An asynchronous
BeginServiceAsyncMethod/EndServiceAsyncMethodoperation pair.
A service implementation using a System.IAsyncResult object.
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.GenericImports System.ServiceModelImports System.TextImports System.ThreadingNamespace 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 ClassEnd NamespaceSee also
- Designing Service Contracts
- Synchronous and Asynchronous Operations
