C# - mixed assembly (C++/CLI, DirectX native) interplay (32/64bit)

Question

I have a problem related to this question. Two players:

1. C# application
2. Mixed assembly used by 1)

The application has to support anything from Windows XP (32bit) to Windows 7 (32 & 64bit). The assembly is complicated in different ways. It contains managed C++/CLI code and some native C++ classes dancing with native DirectX. It also is linked to a few 32bit native dll's w/o source access (containing C++ classes with import libraries).

Things are working well in 32bit environments (XP and 7 tested) including the 32bit subsystem on Windows 7. Havoc happens, as soon as "Any CPU" is used on 64bit systems in order to build the complete solution. The 32bit assembly is unusable than - but seemingly only in debug mode ("cannot load, wrong format" etc.). It seems to work in release. A 64bit assembly build is prevented by the implicit dependencies to the mentioned 32bit third-party dll's.

Is there any way to provide a real native 64bit application able to use the assembly?

Requirement for the assembly isn't that strict. It could be both - 32 or 64bit - but as said above, should be be usable from the application one way or the other.

Answer 1

You are running into a rock hard limitation in the 64-bit version of Windows, a 64-bit process cannot execute any 32-bit machine code in-process. You certainly have a dependency on machine code when you use C++/CLI and work with DirectX. Although it doesn't sound like you could not execute in 64-bit mode, both C++/CLI and DirectX can be compiled/are available in 64-bit.

This then boils down to a build and deployment issue. You have to build the C++/CLI project(s) in 64-bit mode and deploy only 64-bit components on a 64-bit operating system. The main EXE must be built to AnyCPU. Similarly, on a 32-bit operating system you must build and deploy only the 32-bit compiled version. You solve the build issue by adding the x64 configuration to the solution so you build the 32-bit and 64-bit version separately. You solve the deployment issue by creating two installers.

Since you have to support a 32-bit operating system anyway, the simple solution is to change the Target platform setting on your EXE project to x86. Now everything always runs in 32-bit mode and you don't have to bother with the build and deployment headaches. The only thing you miss out on is the larger virtual memory address space that's available in the 64-bit version.

Answer 2

Forget about the C++/CLI project for a minute.

You have third-party 32-bit DLLs. These CANNOT load in a 64-bit process. So your main application will have to be 32-bit. This restriction has nothing to do with the C++/CLI middleman.

The only way you can make use of these DLLs from a 64-bit application is to load them in a separate (32-bit) process and marshal data back and forth.