René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Python 3.14 free-threaded support","articleBody":"Tracking issue for free-threaded Python (`Py_GIL_DISABLED`) support. Companion to the umbrella 3.14 tracker #2610.\n\n## Why FT is different from a normal GIL build\n\n- `PyObject_HEAD` is 16 bytes larger; the refcount is split across `ob_ref_local` + `ob_ref_shared` and must be read via `Py_REFCNT` (a real exported symbol on 3.14+).\n- Build detection: `sys._is_gil_enabled()` (added in 3.13) returns `False` on FT.\n- The GIL has been silently serialising every pythonnet static cache, lock-free counter, finalizer-thread interaction, and `Reflection.Emit` use site. All of those need explicit synchronisation under FT.\n\n## Hazards in pythonnet (resolved by PR #2721)\n\n| Area | What broke | How it was fixed |\n|---|---|---|\n| Refcount / ABI | Single-offset read | `Py_REFCNT` P/Invoke + `ObjectHeadOffset = 16` for FT |\n| Type-creation race | Duplicate `cache.Add`; partial-type visibility | Two-cache (`cache` + `_inProgressCache`) under `_cacheCreateLock` |\n| GCHandle in `tp_clear`/`tp_dealloc` | Double-free under main-thread + finalizer-thread race | `Interlocked.Exchange` on the slot |\n| `Reflection.Emit` | Concurrent `DefineType` corrupts IL / throws \"Duplicate type name\" | Lock both `CreateDerivedType` and `DelegateManager.GetDispatcher` |\n| Static collections | Plain `Dictionary`/`HashSet`/`List` thread-safety issues | `ConcurrentDictionary` where possible; `Interlocked`/`Volatile` for single-cell state; locks for nested mutation and ordered list semantics |\n| Finalizer-thread / `Py_Finalize` interaction | Stale `ob_ref_local` reads after teardown crash the process | `Runtime._Py_IsFinalizing()` guards on all decref-from-finalizer paths |\n| Chained `ClassDerived.Finalize` IL | Nested Python-derived classes with `__namespace__` chained through emitted `Finalize` methods, queuing the same `__pyobj__` twice → `PyObject_GC_Del` on freed memory | Skip the base-Finalize chain when the base is itself pythonnet-emitted (`IPythonDerivedType`) |\n\nSee PR #2721 for the per-file detail.\n\n## References\n\n- PR: #2721\n- Umbrella 3.14 tracker: #2610\n- CPython PEP 703: https://peps.python.org/pep-0703/\n- CPython 3.14 free-threading docs: https://docs.python.org/3.14/howto/free-threading-extensions.html\n\n","author":{"url":"https://github.com/greateggsgreg","@type":"Person","name":"greateggsgreg"},"datePublished":"2026-05-09T21:58:25.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/2720/pythonnet/issues/2720"}