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gh-158790: Improve performance for list.insert() and del list[i] free-threaded builds #158791

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gh-158790: Improve performance for list.insert() and del list[i] free-threaded builds #158791

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f4a13b1
gh-158790: Improve performance for list.insert() and del list[i] in f…
hetaozdh Oct 4, 2026
58c3939
gh-158790: Address review comments
hetaozdh Oct 4, 2026
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-10-04-01-40-31.gh-issue-158790.F3kQ7z.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Speed up :meth:`list.insert` and item deletion via :keyword:`del` in free-threaded builds by using :manpage:`memmove(3)`.
21 changes: 19 additions & 2 deletions Objects/listobject.c
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Expand Up @@ -478,10 +478,13 @@ end:;
return ret;
}

static void ptr_wise_atomic_memmove(PyListObject *a, PyObject **dest,
PyObject **src, Py_ssize_t n);

static int
ins1(PyListObject *self, Py_ssize_t where, PyObject *v)
{
Py_ssize_t i, n = Py_SIZE(self);
Py_ssize_t n = Py_SIZE(self);
PyObject **items;
if (v == NULL) {
PyErr_BadInternalCall();
Expand All @@ -500,8 +503,15 @@ ins1(PyListObject *self, Py_ssize_t where, PyObject *v)
if (where > n)
where = n;
items = self->ob_item;
for (i = n; --i >= where; )
#ifdef Py_GIL_DISABLED
if (where < n) {
ptr_wise_atomic_memmove(self, &items[where + 1], &items[where],
n - where);
}
#else
for (Py_ssize_t i = n; --i >= where; )
FT_ATOMIC_STORE_PTR_RELEASE(items[i+1], items[i]);
#endif
FT_ATOMIC_STORE_PTR_RELEASE(items[where], Py_NewRef(v));
return 0;
}
Expand Down Expand Up @@ -1145,9 +1155,16 @@ list_ass_item_lock_held(PyListObject *a, Py_ssize_t i, PyObject *v)
PyObject *tmp = a->ob_item[i];
if (v == NULL) {
Py_ssize_t size = Py_SIZE(a);
#ifdef Py_GIL_DISABLED
if (i < size - 1) {
ptr_wise_atomic_memmove(a, &a->ob_item[i], &a->ob_item[i + 1],
size - 1 - i);
}
#else
for (Py_ssize_t idx = i; idx < size - 1; idx++) {
FT_ATOMIC_STORE_PTR_RELEASE(a->ob_item[idx], a->ob_item[idx + 1]);
}
#endif
Py_SET_SIZE(a, size - 1);
}
else {
Expand Down
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