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Remoting Example: Asynchronous Remoting

This topic is specific to a legacy technology that is retained for backward compatibility with existing applications and is not recommended for new development. Distributed applications should now be developed using the  Windows Communication Foundation (WCF).

The following sample application demonstrates asynchronous programming in a remoting scenario. The example first creates a synchronous delegate to a remote object and invokes it to illustrate the thread waiting on the return. It then uses asynchronous delegates and a ManualResetEvent object to invoke a remote object method and wait for the response.

This application runs on a single computer or across a network. If you want to run this application over a network, you must replace "localhost" in the client configuration with the name of the remote computer.

.NET Framework remoting does not do authentication or encryption by default. Therefore, it is recommended that you take all necessary steps to make certain of the identity of clients or servers before interacting with them remotely. Because .NET Framework remoting applications require FullTrust permissions to execute, if an unauthorized client were granted access on your server, the client could execute code as though it were fully trusted. Always authenticate your endpoints and encrypt the communication streams, either by hosting your remoted types in Internet Information Services (IIS) or by building a custom channel sink pair to do this work.

To compile this sample

  1. Type the following commands at the command prompt:

    vbc /t:library ServiceClass.vb
    vbc /r:ServiceClass.dll Server.vb
    vbc /r:ServiceClass.dll Client.vb
  2. Open two command prompts that point to the same directory. In one, type server. In the other, type client.


Imports System
Imports System.Runtime.Remoting

Public Class ServiceClass
    Inherits MarshalByRefObject

    Public Sub New()
        Console.WriteLine("ServiceClass created.")
    End Sub

    Public Function VoidCall() As String
        Console.WriteLine("VoidCall called.")
        Return "You are calling the void call on the ServiceClass."
    End Function

    Public Function GetServiceCode() As Integer
        Return Me.GetHashCode()
    End Function

    Public Function TimeConsumingRemoteCall() As String
        Console.WriteLine("TimeConsumingRemoteCall called.")

        For i As Integer = 0 To 20000
            Console.Write("Counting: " & i.ToString() & vbCr)
        Return "This is a time-consuming call."
    End Function
End Class


Imports System
Imports System.Runtime.Remoting

Public Class Server

    Public Shared Sub Main()
        RemotingConfiguration.Configure("server.exe.config", False)
    End Sub

End Class
using System;
using System.Runtime.Remoting;

public class Server
    public static void Main(string[] args)
        RemotingConfiguration.Configure("server.exe.config", false);


<?xml version="1.0" encoding="utf-8" ?>
           type="ServiceClass, ServiceClass"
        <channel ref="http" 
                 port="8080" />


Imports System
Imports System.Runtime.Remoting
Imports System.Runtime.Remoting.Messaging
Imports System.Threading

Public Class Client
    Inherits MarshalByRefObject
    Public Shared e As ManualResetEvent

    ' Declares two delegates, each of which represents 
    ' a function that returns a string. The names are strictly 
    ' for clarity in the code – there is no difference between
    ' the two delegates. (In fact, the same delegate type 
    ' could be used for both synchronous and asynchronous 
    ' calls.)

    Public Delegate Function RemoteSyncDelegate() As String
    Public Delegate Function RemoteAsyncDelegate() As String

    ' This is the call that the AsyncCallback delegate references
    <OneWay()> _
    Public Sub OurRemoteAsyncCallback(ByVal ar As IAsyncResult)
        Dim del As RemoteAsyncDelegate = CType(ar, AsyncResult).AsyncDelegate
        Console.WriteLine(vbLf & "**SUCCESS**: Result of the remote AsyncCallBack: " + del.EndInvoke(ar))

        ' Signal the thread.
    End Sub

    Public Shared Sub Main()
        'IMPORTANT: .NET Framework remoting does not remote
        'static members. This class must be an instance before
        'the callback from the asynchronous invocation can reach this client.
        Dim clientApp As Client = New Client()
    End Sub

    Public Sub Run()
        'Enable this and the e.WaitOne call at the bottom if you 
        'are going to make more than one asynchronous call.

        e = New ManualResetEvent(False)

        Console.WriteLine("Remote synchronous and asynchronous delegates.")
        Console.WriteLine(New String("_", 80))

        ' This is the only thing you must do in a remoting scenario
        ' for either synchronous or asynchronous programming 
        ' configuration.
        RemotingConfiguration.Configure("Client.exe.config", False)

        ' The remaining steps are identical to single-
        ' AppDomain programming.
        Dim obj As ServiceClass = New ServiceClass()

        ' This delegate is a remote synchronous delegate.
        Dim Remotesyncdel As RemoteSyncDelegate = New RemoteSyncDelegate(AddressOf obj.VoidCall)

        ' When invoked, program execution waits until the method returns.
        ' This delegate can be passed to another application domain
        ' to be used as a callback to the obj.VoidCall method.

        ' This delegate is an asynchronous delegate. Two delegates must 
        ' be created. The first is the system-defined AsyncCallback 
        ' delegate, which references the method that the remote type calls 
        ' back when the remote method is done.
        Dim RemoteCallback As AsyncCallback = New AsyncCallback(AddressOf OurRemoteAsyncCallback)

        ' Create the delegate to the remote method you want to use 
        ' asynchronously.
        Dim RemoteDel As RemoteAsyncDelegate = New RemoteAsyncDelegate(AddressOf obj.TimeConsumingRemoteCall)

        ' Start the method call. Note that execution on this 
        ' thread continues immediately without waiting for the return of 
        ' the method call. 
        Dim RemAr As IAsyncResult = RemoteDel.BeginInvoke(RemoteCallback, Nothing)

        ' If you want to stop execution on this thread to 
        ' wait for the return from this specific call, retrieve the 
        '  IAsyncResult returned from the BeginIvoke call, obtain its 
        ' WaitHandle, and pause the thread, such as the next line:
        ' RemAr.AsyncWaitHandle.WaitOne();

        ' To wait in general, if, for example, many asynchronous calls 
        ' have been made and you want notification of any of them, or, 
        ' like this example, because the application domain can be 
        ' recycled before the callback can print the result to the 
        ' console.
        ' e.WaitOne();

        ' This simulates some other work going on in this thread while the 
        ' async call has not returned. 
        Dim count As Integer = 0
        While Not RemAr.IsCompleted
            Console.Write("Not completed: " & count & vbCr)
            count = count + 1
            ' Make sure the callback thread can invoke callback.
        End While

    End Sub
End Class


<?xml version="1.0" encoding="utf-8" ?>
           type="ServiceClass, ServiceClass"

See Also