Question

I’d like to run several services from different .dll’s in a isolated way. Basically, all services are derived from RoleEntryPoint , and I want to load each one in a separated AppDomain and run it there in a different thread.

So far, I can locate the service and get its type:

        String pathToDll = @"C:\....\bin\Debug\ChildWorkerRole.dll"; 
        Assembly assembly = Assembly.LoadFrom(pathToDll);
        Type serviceType = assembly.GetTypes().SingleOrDefault(t => t.BaseType == typeof(RoleEntryPoint));

And also run it in the current AppDomain and Thread:

        RoleEntryPoint myRole2 = (RoleEntryPoint)Activator.CreateInstance(serviceType);
        if (myRole2.OnStart())
            myRole2.Run();

But when I try to run it in a separate in different AppDomain I get an exception:

        AppDomain domain = AppDomain.CreateDomain("MyNewDomain");
        RoleEntryPoint myRole = (RoleEntryPoint)domain.CreateInstanceFromAndUnwrap(pathToDll, serviceType.FullName);
        if (myRole.OnStart())
            myRole.Run();

This exception:

System.Runtime.Serialization.SerializationException was unhandled
  Message=Type 'ChildWorkerRole.WorkerRole' in assembly 'ChildWorkerRole, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' is not marked as serializable.
  Source=mscorlib
  StackTrace:
       at System.AppDomain.CreateInstanceFromAndUnwrap(String assemblyName, String typeName)
.......

The funny thing is that ChildWorkerRole is actually marked with the SerializableAttribute … but may be because RoleEntryPoint is not, it cannot be done.

Any idea or workaround?

thanks!

Answer 1

In order to work with a type in a separate AppDomain, it, and all of the types you directly use, need to be either marked as [Serializable], or you need to derive them from MarshalByRefObject.

If this is not possible, the only real option is to make a proxy class that you can use which does follow the above criteria, and allow it to manage your types internally.