Changing .NET 4 Runtime Activation Policy For Dll Within C++ Code

Question

We've developed a C# 4.0 module that needs to be accessed from an unmanaged C++ program (as well as a Fortran program). The DLL gets loaded correctly and the method is available to the C++ program, but an exception gets thrown when calling the method that points to the C# code. For a visualization:

[Unmanaged C++ / Fortran Projects]  
  -> controller.dll (unmanaged C++ within the C++ project)    
     -> managed_wrapper.dll (managed C++ within the C# project)
        -> C# 4.0 Project

The exception gets thrown when the controller attempts to call the managed C++ (using .NET 4.0 framework).

My suspicions are that the following configuration needs to be applied, as we encountered an error previously when creating a proof of concept:

<configuration>
  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0"/>
  </startup>
</configuration>

I applied it correctly for the aforementioned proof of concept, but that was on a stand-alone console application. Since the unmanaged C++ program is huge and the settings are not universal for every module, I'm unable to create a MyApplication.exe.config file with the above configuration and call it day.

My question is this: Is it possible to apply that configuration to a specific DLL?

Answer 1

From my understanding, this is not possible.

The issue is that, the configuration setting you need to apply (useLegacyV2RuntimeActivationPolicy) is basically saying "for this entire application, no matter what the assembly requests, use CLR 4 instead.

If you could apply it to a single DLL, you'd be violating the goals here - since the goal is to force all assemblies to use CLR 4.

---

Edit:

After further study, there is actually a way to do this in some limited scenarios. I posted about this on my blog, but basically, you can use the CLR Hosting API to get some access to setting this from within a library.