Free Threading - Initial Support #15
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…(albeit still static), adding critical w/ free-threading enabled for Py_GIL_DISABLED builds, with critical sections for default_connections
…s whether GIL or free threaded. Tested with pytest-run-parallel: `pytest --parallel-threads=10 --iterations=5`
…hreading starting it earlier
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Per discussion, this PR enables free-threading for DuckDB for 3.14t (or later).
This should be considered highly experimental, since it was tested on release candidate builds of 3.14 and without pyarrow, pandas or polars support.
Background
Python 3.14 is in RC3 with release scheduled for Oct 7, 2025.
Python 3.13 released experimental support for free-threading.
In Python 3.14 free-threaded Python is officially supported
Module State
PEP489 - multi-phase-init calls for module_state to be initialized with each interpreter*. This PR takes a half-step towards that, by consolidating global state into a single static DuckDBPyModuleState. The idea being: it's easier to manage concurrency through a single instance than across instances.
Alternative ideas: DuckDBPyModuleState is not absolutely required. The alternative is to keep the import cache/instance cache/etc and add mutexes or scoped_critical_sections to control access.
* each interpreter refers to support for subinterpreters. Multiple subinterpreters is not supported in this PR for a few reasons, primarily due to the difficulty of attaching the import_cache to all the calls that assume a single global import_cache.
scoped_critical_section
DefaultConnection is synchronized with a py::scoped_critical_section
Since cursors are not thread safe. Segfaults occur in both release & these builds when cursors are used in an unsafe manner.
Testing
A set of threading test cases are added to
tests/fast/threading. These tests should pass in both GIL enabled and free-threaded (no-GIL) builds.