NativeLibrary documentation: Cache result of System.Runtime.InteropServices.DllImportResolver

[badcel]

I found the discussion about updating the docs regarding NativeLibrary in #41180 (comment). As i did not want to hijack the discussion I open this issue to improve the documentation on NativeLibrary.

@jkotas I just wanted to raise the question if it is valid to cache the IntPtr to an assembly in the given resolver of SetDllImportResolver (System.Reflection.Assembly assembly, System.Runtime.InteropServices.DllImportResolver resolver);?

I think this could be an important information in the docs because it is very tempting to cache the found IntPtr of NativeLibrary.TryLoad but it is not clear from the documentation if this is valid in all cases.

Sample code:

private static IntPtr DllImportResolver(string libraryName, Assembly assembly, DllImportSearchPath? searchPath)
{
    if (cache.TryGetValue(libraryName, out var cachedLibHandle))
        return cachedLibHandle;

   if (NativeLibrary.TryLoad(GetOsDependentLibraryName(libraryName), assembly, DllImportSearchPath.LegacyBehavior, out var libHandle))
   {
        cache[libraryName] = libHandle;
        return libHandle;
   }

    return IntPtr.Zero;
}

[jkotas]

It is ok to cache this pointer, as long as your code does not call NativeLibrary.Free on it. The runtime itself does not do any lifetime management with DllImportResolver, it assumes that your code will keep the library loaded long enough.

DllImportSearchPath.LegacyBehavior

Is there a good reason that you ignoring the requested searchPath and hardcoding DllImportSearchPath.LegacyBehavior behavior instead? I think the typical pattern would be to pass the requested searchPath through.

[badcel]

Thank you for your feedback and help. As this could result in some performance gain it would be great seeing it documented.

Regarding the DllImportSearchPath.LegacyBehavior we actually never had taken over the value from the delegate as there are some examples suggesting otherwise. I will try to contact the author. We will test if your suggested change is working for us on all platforms. Thank you very much!