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gh-127266: avoid data races when updating type slots (gh-131174)

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In the free-threaded build, avoid data races caused by updating type slots
or type flags after the type was initially created.  For those (typically
rare) cases, use the stop-the-world mechanism.  Remove the use of atomics
when reading or writing type flags.  The use of atomics is not sufficient to
avoid races (since flags are sometimes read without a lock and without
atomics) and are no longer required.
This commit is contained in:
Neil Schemenauer 2025-04-28 13:28:44 -07:00 • committed by GitHub
parent 22f0730d40
commit e414a2d81c
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10 changed files with 233 additions and 112 deletions
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12
Include/object.h
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@ -620,6 +620,12 @@ given type object has a specified feature.
#define Py_TPFLAGS_HAVE_FINALIZE (1UL << 0)
#define Py_TPFLAGS_HAVE_VERSION_TAG (1UL << 18)
// Flag values for ob_flags (16 bits available, if SIZEOF_VOID_P > 4).
#define _Py_IMMORTAL_FLAGS (1 << 0)
#define _Py_STATICALLY_ALLOCATED_FLAG (1 << 2)
#if defined(Py_GIL_DISABLED) && defined(Py_DEBUG)
#define _Py_TYPE_REVEALED_FLAG (1 << 3)
#endif
#define Py_CONSTANT_NONE 0
#define Py_CONSTANT_FALSE 1
@ -776,11 +782,7 @@ PyType_HasFeature(PyTypeObject *type, unsigned long feature)
// PyTypeObject is opaque in the limited C API
flags = PyType_GetFlags(type);
#else
# ifdef Py_GIL_DISABLED
flags = _Py_atomic_load_ulong_relaxed(&type->tp_flags);
# else
flags = type->tp_flags;
# endif
flags = type->tp_flags;
#endif
return ((flags & feature) != 0);
}