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gh-127521: Mark list as "shared" before resizing if necessary (#127524)

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In the free threading build, if a non-owning thread resizes a list,
it must use QSBR to free the old list array because there may be a
concurrent access (without a lock) from the owning thread.

To match the pattern in dictobject.c, we just mark the list as "shared"
before resizing if it's from a non-owning thread and not already marked
as shared.
This commit is contained in:
Sam Gross 2024-12-02 19:38:26 +00:00 • committed by GitHub
parent c4303763da
commit c7dec02de2
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1 changed files with 20 additions and 0 deletions
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20
Objects/listobject.c
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@ -68,6 +68,20 @@ free_list_items(PyObject** items, bool use_qsbr)
#endif
}
static void
ensure_shared_on_resize(PyListObject *self)
{
#ifdef Py_GIL_DISABLED
// Ensure that the list array is freed using QSBR if we are not the
// owning thread.
if (!_Py_IsOwnedByCurrentThread((PyObject *)self) &&
!_PyObject_GC_IS_SHARED(self))
{
_PyObject_GC_SET_SHARED(self);
}
#endif
}
/* Ensure ob_item has room for at least newsize elements, and set
* ob_size to newsize. If newsize > ob_size on entry, the content
* of the new slots at exit is undefined heap trash; it's the caller's
@ -117,6 +131,8 @@ list_resize(PyListObject *self, Py_ssize_t newsize)
if (newsize == 0)
new_allocated = 0;
ensure_shared_on_resize(self);
#ifdef Py_GIL_DISABLED
_PyListArray *array = list_allocate_array(new_allocated);
if (array == NULL) {
@ -804,6 +820,9 @@ list_clear_impl(PyListObject *a, bool is_resize)
Py_XDECREF(items[i]);
}
#ifdef Py_GIL_DISABLED
if (is_resize) {
ensure_shared_on_resize(a);
}
bool use_qsbr = is_resize && _PyObject_GC_IS_SHARED(a);
#else
bool use_qsbr = false;
@ -3069,6 +3088,7 @@ list_sort_impl(PyListObject *self, PyObject *keyfunc, int reverse)
Py_XDECREF(final_ob_item[i]);
}
#ifdef Py_GIL_DISABLED
ensure_shared_on_resize(self);
bool use_qsbr = _PyObject_GC_IS_SHARED(self);
#else
bool use_qsbr = false;