Greptile Summary

This PR completes DALI's free-threaded Python support by adding py::mod_gil_not_used() to the python_function_plugin pybind11 module — the last DALI extension that lacked this declaration. Without it, importing python_function_plugin (which is transitively always imported) would re-enable the GIL and emit a RuntimeWarning, defeating the purpose of a free-threaded build. The PR also removes the now-unnecessary PYTHON_GIL environment variable plumbing from build/test scripts, adds a test_gil_disabled() sanity test, and expands the free-threading CI test body to include experimental_mode.test_multithreading.

Confidence Score: 5/5

This PR is safe to merge; all changes are correct, minimal, and consistent with the existing pattern in backend_impl.cc.

The core C++ change mirrors a pattern already in production. Script cleanup is straightforward. No P0/P1 issues identified; all remaining observations are P2 or lower and do not block merge.

No files require special attention.

Important Files Changed

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["Python free-threaded build\n(Py_GIL_DISABLED=1)"] --> B["import nvidia.dali"]
    B --> C["backend_impl.cc\nPYBIND11_MODULE(..., py::mod_gil_not_used())"]
    B --> D["python_function_plugin\nPYBIND11_MODULE(..., py::mod_gil_not_used())"]
    C --> E{"GIL re-enabled?"}
    D --> E
    E -- "Before this PR\n(plugin missing declaration)" --> F["⚠️ GIL RE-ENABLED\nRuntimeWarning emitted"]
    E -- "After this PR\n(both declare GIL-not-used)" --> G["✅ GIL stays DISABLED"]
    G --> H["test_gil_disabled()\nassert not sys._is_gil_enabled()"]

_{Reviews (2): Last reviewed commit: "Add a check making sure that DALI doesn'..." | Re-trigger Greptile}

!build

CI MESSAGE: [48400360]: BUILD STARTED

CI MESSAGE: [48400360]: BUILD PASSED