[3.13] gh-119525: Fix deadlock with _PyType_Lookup and the GIL (GH-119527)
#119746
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…onGH-119527) The deadlock only affected the free-threaded build and only occurred when the GIL was enabled at runtime. The `Py_DECREF(old_name)` call might temporarily release the GIL while holding the type seqlock. Another thread may spin trying to acquire the seqlock while holding the GIL. The deadlock occurred roughly 1 in ~1,000 runs of `pool_in_threads.py` from `test_multiprocessing_pool_circular_import`. (cherry picked from commit c22323c) Co-authored-by: Sam Gross <colesbury@gmail.com>
This was referenced May 29, 2024
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The deadlock only affected the free-threaded build and only occurred
when the GIL was enabled at runtime. The
Py_DECREF(old_name)callmight temporarily release the GIL while holding the type seqlock.
Another thread may spin trying to acquire the seqlock while holding the
GIL.
The deadlock occurred roughly 1 in ~1,000 runs of
pool_in_threads.pyfrom
test_multiprocessing_pool_circular_import.(cherry picked from commit c22323c)
Co-authored-by: Sam Gross colesbury@gmail.com