torsten's .NET blog - Why .NET Remoting does not have a RemotingConfiguration.Reset() ?

Tuesday, July 05, 2005

Why .NET Remoting does not have a RemotingConfiguration.Reset() ?

Hopefully the .NET 2.0 bits will support a similar call to reset the remoting infrastructure the clear way without restarting the whole remoting application!

As you may have noticed: there exists a RemotingChannels.UnregisterChannel() method to use to get rid of a old used channel and switch to a new one (registering). But that is not enough to get an application seamlessly work with a new remoting service endpoint: after you really used one of you configured services, you will get an exception if you try to register the service again with a different service endpoint. This is because the RemotingConfigHandler+RemotingConfigInfo method AddWellknownEntry() calls a method named CheckForRedirectedClientType() that cause a CantUseRedirectedTypeForWellKnownService exception. So after I tried a "fix" with managing the calls to the .NET remoting classes within a new separate AppDomain (and unload that on a reset remoting request) that did not work I end up with a hack using Reflection to get around that.

Here is the used code that works for our requirements:

    /// <summary>
    /// This is cool, but it is a HACK. Please validate the code each time
    /// the .NET framework gets updated. There is a little safty included to 
    /// throw a InvalidOperationException if something changed we require to get
    /// it work somehow.
    /// </summary>
    /// <exception cref="InvalidOperationException">
    /// On every failed reflection call or if we do not get any of 
    /// the required FieldInfo objects</exception>
    /// <remarks>
    /// The HACK bases on the fact Remoting informations are cached
    /// in the well hidden sync. Hashtable field "_remoteTypeInfo" after they get used once.
    /// This field you can find within the (internal) class 
    /// RemotingConfigHandler.RemotingConfigInfo. The static RemotingConfigHandler.Info 
    /// field holds a reference to an instance if that class.
    /// To reset we simply initialize that field with a new instance of
    /// a synchronized Hashtable. 
    /// Note: We do only "fix" for Singleton objects, not client activated services.
    /// So to get it "fully" work (complete state reset), you may have to hack
    /// more and other fields.
    /// </remarks>
    private static void Release_NETRemotingResources() {
      bool raiseError = true;  // warn if we switch to a new .NET env where the reflection is maybe not working anymore!
      try {
        //HACK: please verify it after each Service Pack or new version of .NET runtime to be used!
        Type configHandlerType = Type.GetType("System.Runtime.Remoting.RemotingConfigHandler");
        if (configHandlerType != null) {
          FieldInfo infoFI = configHandlerType.GetField("Info", BindingFlags.GetField | BindingFlags.Public | BindingFlags.Static);
          if (infoFI != null) {
            object infoFIRef = infoFI.GetValue(null);  // static, so no object instance to provide
            if (infoFIRef != null) {
              FieldInfo remoteTypeInfoFI = infoFI.FieldType.GetField("_remoteTypeInfo", BindingFlags.Instance | BindingFlags.NonPublic);
              if (remoteTypeInfoFI != null) {
                remoteTypeInfoFI.SetValue(infoFIRef, Hashtable.Synchronized(new Hashtable()));
                raiseError = false;  // all seems to be OK
              }
            }
          }
        }
      } catch (Exception ex) {
        throw new InvalidOperationException("Failed to reset .NET internal remoting state.", ex);
      }
 
      if (raiseError)
        throw new InvalidOperationException("Failed to reset .NET internal remoting state.");
    }