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[3.13] gh-149816: Fix race condition in memoryview with free-threading (GH-149858) #149877

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[3.13] gh-149816: Fix race condition in memoryview with free-threading (GH-149858) #149877

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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-05-15-11-31-57.gh-issue-149816.ugN2rx.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix a race condition in :class:`memoryview` with free-threading.
21 changes: 15 additions & 6 deletions Objects/memoryobject.c
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Expand Up @@ -67,6 +67,13 @@ class memoryview "PyMemoryViewObject *" "&PyMemoryView_Type"
releasebufferprocs must NOT decrement view.obj.
*/

#ifdef Py_GIL_DISABLED
#define _FT_ATOMIC_ADD_SSIZE(value, new_value) \
(void)_Py_atomic_add_ssize(&value, new_value)
#else
#define _FT_ATOMIC_ADD_SSIZE(value, new_value) (void)(value += new_value)
#endif


static inline _PyManagedBufferObject *
mbuf_alloc(void)
Expand Down Expand Up @@ -1589,7 +1596,7 @@ memory_getbuf(PyObject *_self, Py_buffer *view, int flags)


view->obj = Py_NewRef(self);
self->exports++;
_FT_ATOMIC_ADD_SSIZE(self->exports, 1);

return 0;
}
Expand All @@ -1598,7 +1605,7 @@ static void
memory_releasebuf(PyObject *_self, Py_buffer *view)
{
PyMemoryViewObject *self = (PyMemoryViewObject *)_self;
self->exports--;
_FT_ATOMIC_ADD_SSIZE(self->exports, -1);
return;
/* PyBuffer_Release() decrements view->obj after this function returns. */
}
Expand Down Expand Up @@ -2337,9 +2344,9 @@ memoryview_hex_impl(PyMemoryViewObject *self, PyObject *sep,
// Prevent 'self' from being freed if computing len(sep) mutates 'self'
// in _Py_strhex_with_sep().
// See: https://github.com/python/cpython/issues/143195.
self->exports++;
_FT_ATOMIC_ADD_SSIZE(self->exports, 1);
PyObject *ret = _Py_strhex_with_sep(src->buf, src->len, sep, bytes_per_sep);
self->exports--;
_FT_ATOMIC_ADD_SSIZE(self->exports, -1);
return ret;
}

Expand Down Expand Up @@ -3081,9 +3088,9 @@ memory_hash(PyObject *_self)
if (view->obj != NULL) {
// Prevent 'self' from being freed when computing the item's hash.
// See https://github.com/python/cpython/issues/142664.
self->exports++;
_FT_ATOMIC_ADD_SSIZE(self->exports, 1);
Py_hash_t h = PyObject_Hash(view->obj);
self->exports--;
_FT_ATOMIC_ADD_SSIZE(self->exports, -1);
if (h == -1) {
/* Keep the original error message */
return -1;
Expand Down Expand Up @@ -3457,3 +3464,5 @@ PyTypeObject PyMemoryView_Type = {
0, /* tp_alloc */
memoryview, /* tp_new */
};

#undef _FT_ATOMIC_ADD_SSIZE
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