https://github.com/python/cpython/commit/c120cae880759160ac9bc042e4c615aeeb26d7a9
commit: c120cae880759160ac9bc042e4c615aeeb26d7a9
branch: main
author: he_tao <[email protected]>
committer: corona10 <[email protected]>
date: 2026-10-07T21:21:00+09:00
summary:
gh-158790: Improve performance for list.insert() and del list[i] free-threaded
builds (gh-158791)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-10-04-01-40-31.gh-issue-158790.F3kQ7z.rst
M Objects/listobject.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-10-04-01-40-31.gh-issue-158790.F3kQ7z.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-04-01-40-31.gh-issue-158790.F3kQ7z.rst
new file mode 100644
index 00000000000000..b509071e16eea2
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-04-01-40-31.gh-issue-158790.F3kQ7z.rst
@@ -0,0 +1 @@
+Speed up :meth:`list.insert` and item deletion via :keyword:`del` in
free-threaded builds by using :manpage:`memmove(3)`.
diff --git a/Objects/listobject.c b/Objects/listobject.c
index 962ed70aed6b8d..87a669f203589d 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -478,10 +478,43 @@ end:;
return ret;
}
+static void ptr_wise_atomic_memmove(PyListObject *a, PyObject **dest,
+ PyObject **src, Py_ssize_t n);
+
+static inline void
+list_shift_items_right_lock_held(PyListObject *self, Py_ssize_t first,
+ Py_ssize_t last)
+{
+#ifdef Py_GIL_DISABLED
+ ptr_wise_atomic_memmove(self, &self->ob_item[first + 1],
+ &self->ob_item[first], last - first);
+#else
+ PyObject **items = self->ob_item;
+ for (Py_ssize_t i = last; --i >= first; ) {
+ items[i + 1] = items[i];
+ }
+#endif
+}
+
+static inline void
+list_shift_items_left_lock_held(PyListObject *self, Py_ssize_t first,
+ Py_ssize_t last)
+{
+#ifdef Py_GIL_DISABLED
+ ptr_wise_atomic_memmove(self, &self->ob_item[first],
+ &self->ob_item[first + 1], last - first);
+#else
+ PyObject **items = self->ob_item;
+ for (Py_ssize_t i = first; i < last; i++) {
+ items[i] = items[i + 1];
+ }
+#endif
+}
+
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();
@@ -500,8 +533,9 @@ ins1(PyListObject *self, Py_ssize_t where, PyObject *v)
if (where > n)
where = n;
items = self->ob_item;
- for (i = n; --i >= where; )
- FT_ATOMIC_STORE_PTR_RELEASE(items[i+1], items[i]);
+ if (where < n) {
+ list_shift_items_right_lock_held(self, where, n);
+ }
FT_ATOMIC_STORE_PTR_RELEASE(items[where], Py_NewRef(v));
return 0;
}
@@ -1145,8 +1179,8 @@ 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);
- for (Py_ssize_t idx = i; idx < size - 1; idx++) {
- FT_ATOMIC_STORE_PTR_RELEASE(a->ob_item[idx], a->ob_item[idx + 1]);
+ if (i < size - 1) {
+ list_shift_items_left_lock_held(a, i, size - 1);
}
Py_SET_SIZE(a, size - 1);
}
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