CPU Architecture Independent P/Invoke: Can the DllName or path be “dynamic”?

Question

Is there a way to have the particular DLL referenced by a P/Invoke (DllImport) signature depend on the CPU architecture?

I\'m working on an application that loads a

Answer 1

"If instead of different DLL names it was the same name in different folders, does that open any other options?"

Maybe this would work for you:

public static class NativeMethods
{
  // here we just use "Foo" and at runtime we load "Foo.dll" dynamically
  // from any path on disk depending on the logic you want to implement
  [DllImport("Foo", EntryPoint = "bar")]
  private void bar();

  [DllImport("kernel32")]
  private unsafe static extern void* LoadLibrary(string dllname);

  [DllImport("kernel32")]
  private unsafe static extern void FreeLibrary(void* handle);

  private sealed unsafe class LibraryUnloader
  {
    internal LibraryUnloader(void* handle)
    {
      this.handle = handle;
    }

    ~LibraryUnloader()
    {
      if (handle != null)
        FreeLibrary(handle);
    }

    private void* handle;

  } // LibraryUnloader

  private static readonly LibraryUnloader unloader;

  static NativeMethods()
  {
    string path;

    if (IntPtr.Size == 4)
      path = "path/to/the/32/bit/Foo.dll";
    else
      path = "path/to/the/64/bit/Foo.dll";

    unsafe
    {
      void* handle = LoadLibrary(path);

      if (handle == null)
        throw new DllNotFoundException("unable to find the native Foo library: " + path);

      unloader = new LibraryUnloader(handle);
    }
  }
}

It consists in explicitly loading the native library with its full path before P/Invoke itself tries to load it.

What do you think?