Cache function pointers in global tables by Bromeon · Pull Request #387 · godot-rust/gdext (original) (raw)

🔥 Detailed article here: https://godot-rust.github.io/dev/ffi-optimizations-benchmarking

Instead of repeatedly loading method pointers from Godot for each FFI call (including all the expensive StringName construction), this PR preloads all function pointers at startup. Includes:

• Classes
• Builtin types
• Builtin lifecycle functions (constructors, destructors, conversion methods)
• Global utility functions

This not only improves performance (#11), but also reveals any incompatibilitities or missing methods in Godot immediately. For example, this helped reveal godotengine/godot#80852. On the downside, a single method can prevent gdext from loading (even if that method is not used); however this likely points to an incompatibility that needs to be addressed anyway.

Other changes in this PR include:

• StringCache for caching StringName instances during initialization
• New init API which is easier to use and closer to what Godot provides
  • remove ExtensionLayer, InitHandle

Still missing:

• Classes which are loaded after init-levels (currently only ThemeDB)
• Tests for Editor init-level (our binaries don't boot the editor, so that init-level is skipped in CI)
• Testing of ExtensionLibrary::min_level()
  • Turns out the lower layer callbacks are still called even if Scene is specified as a minimum. What is its use then?
  • Is that even correct? If not, is the new API still suitable (previous API could infer minimum based on registered layer)?

After everything's been done, the codegen crate needs a heavy refactoring. Contributors planning to change that area are recommended to wait a bit.