CallbackBehaviorAttribute.UseSynchronizationContext Property


Gets or sets a value that specifies whether to use the current synchronization context to choose the thread of execution.

 property bool UseSynchronizationContext { bool get(); void set(bool value); };
public bool UseSynchronizationContext { get; set; }
member this.UseSynchronizationContext : bool with get, set
Public Property UseSynchronizationContext As Boolean

Property Value

true if all calls to the service must run on the thread specified by the SynchronizationContext; otherwise, false. The default value is true.


The following code example shows a CallbackBehaviorAttribute on a callback object that uses the SynchronizationContext object to determine which thread to marshal to, the ValidateMustUnderstand property to enforce message validation, and the IncludeExceptionDetailInFaults property to return exceptions as FaultException objects to the service for debugging purposes.

using System;
using System.ServiceModel;
using System.ServiceModel.Channels;
using System.Threading;

namespace Microsoft.WCF.Documentation
   IncludeExceptionDetailInFaults= true,
  public class Client : SampleDuplexHelloCallback
    AutoResetEvent waitHandle;

    public Client()
      waitHandle = new AutoResetEvent(false);

    public void Run()
      // Picks up configuration from the configuration file.
      SampleDuplexHelloClient wcfClient
        = new SampleDuplexHelloClient(new InstanceContext(this), "WSDualHttpBinding_SampleDuplexHello");
        Console.ForegroundColor = ConsoleColor.White;
        Console.WriteLine("Enter a greeting to send and press ENTER: ");
        Console.Write(">>> ");
        Console.ForegroundColor = ConsoleColor.Green;
        string greeting = Console.ReadLine();
        Console.ForegroundColor = ConsoleColor.White;
        Console.WriteLine("Called service with: \r\n\t" + greeting);
        Console.WriteLine("Execution passes service call and moves to the WaitHandle.");
        Console.ForegroundColor = ConsoleColor.Blue;
        Console.WriteLine("Set was called.");
        Console.Write("Press ");
        Console.ForegroundColor = ConsoleColor.Red;
        Console.ForegroundColor = ConsoleColor.Blue;
        Console.Write(" to exit...");
      catch (TimeoutException timeProblem)
        Console.WriteLine("The service operation timed out. " + timeProblem.Message);
      catch (CommunicationException commProblem)
        Console.WriteLine("There was a communication problem. " + commProblem.Message);
    public static void Main()
      Client client = new Client();

    public void Reply(string response)
      Console.WriteLine("Received output.");
      Console.WriteLine("\r\n\t" + response);

Imports System.ServiceModel
Imports System.ServiceModel.Channels
Imports System.Threading

Namespace Microsoft.WCF.Documentation
  <CallbackBehaviorAttribute(IncludeExceptionDetailInFaults:= True, UseSynchronizationContext:=True, ValidateMustUnderstand:=True)> _
  Public Class Client
      Implements SampleDuplexHelloCallback
    Private waitHandle As AutoResetEvent

    Public Sub New()
      waitHandle = New AutoResetEvent(False)
    End Sub

    Public Sub Run()
      ' Picks up configuration from the configuration file.
      Dim wcfClient As New SampleDuplexHelloClient(New InstanceContext(Me), "WSDualHttpBinding_SampleDuplexHello")
        Console.ForegroundColor = ConsoleColor.White
        Console.WriteLine("Enter a greeting to send and press ENTER: ")
        Console.Write(">>> ")
        Console.ForegroundColor = ConsoleColor.Green
        Dim greeting As String = Console.ReadLine()
        Console.ForegroundColor = ConsoleColor.White
        Console.WriteLine("Called service with: " & Constants.vbCrLf & Constants.vbTab & greeting)
        Console.WriteLine("Execution passes service call and moves to the WaitHandle.")
        Console.ForegroundColor = ConsoleColor.Blue
        Console.WriteLine("Set was called.")
        Console.Write("Press ")
        Console.ForegroundColor = ConsoleColor.Red
        Console.ForegroundColor = ConsoleColor.Blue
        Console.Write(" to exit...")
      Catch timeProblem As TimeoutException
        Console.WriteLine("The service operation timed out. " & timeProblem.Message)
      Catch commProblem As CommunicationException
        Console.WriteLine("There was a communication problem. " & commProblem.Message)
      End Try
    End Sub
    Public Shared Sub Main()
      Dim client As New Client()
    End Sub

    Public Sub Reply(ByVal response As String) Implements SampleDuplexHelloCallback.Reply
      Console.WriteLine("Received output.")
      Console.WriteLine(Constants.vbCrLf & Constants.vbTab & response)
    End Sub
  End Class
End Namespace


Use this property to provide the user interface thread affinity that some applications require. For example, a Windows Forms application may be registered as a singleton service object. In this case, all calls into the service must run on the Windows Forms thread. The default case, in which UseSynchronizationContext is set to true, synchronizes all calls to the service to run on the user interface thread.

Note that the thread used is the current synchronization thread when DuplexChannelFactory<TChannel>.CreateChannel or DuplexClientBase<TChannel>.CreateChannel is called. In the case of an Windows Forms application, this means that these calls should occur after a call to the Application.Run method.

Applies to