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[Decided] Free-threaded CPython 3.15t is the only build; make every repo correct on it #158
Description
Decision needed (asked 2026-10-04). Background: AGENTS §12.8 (parallelism from free-threaded CPython), ROADMAP §9, SPEC T-1/T-2, docs/design/threading-and-abi.md.
Why the default stays GIL today: no free-threaded prebuilt for Android or iOS (checked 2026-08-12), so switching splits the threading, lifetime and thread-state design across platforms; free-threaded wheel coverage of C extensions is thin; our own code is not ready (PyType.getInstance cache race, GIL release after init not enabled (C-4), ROADMAP 9.1 open).
Recommendation:
- Keep pythonFreeThreaded=false as the default.
- Make every thisisthepy repo free-threaded-ready: no reliance on GIL atomicity; a required CI job on desktop 3.14t for python-multiplatform, TypedPython and pythonx-*; native extensions declare Py_MOD_GIL_NOT_USED only once proven thread-safe.
- TypedPython free-threaded support as its own stage (see linked issue).
- Binder issues: PyType cache race, GIL release after init, withGIL on JVM virtual threads.
- Investigate building free-threaded CPython for Android and iOS ourselves.
Options: (a) the above; (b) switch desktop default to 3.14t now and accept the platform split; (c) do nothing until upstream mobile prebuilts exist.
Activity
b-re-w commentedon Oct 3, 2026
Decided by the maintainer, 2026-10-04:
Follow-up: AGENTS §12.8, SPEC T-1/T-2/C-4, threading-and-abi.md, gradle.properties default, CPython pins.
[-][Decision] Free-threaded readiness: keep GIL as default, make every repo correct on 3.14t[/-][+][Decided] Free-threaded CPython 3.15t is the only build; make every repo correct on it[/+]