From f63e33717292c9e779d4dee3889f6c6e2eca27fb Mon Sep 17 00:00:00 2001
From: Donghee Nals <donghee.na@python.org>
Date: Sat, 16 Mar 2024 17:20:43 +0900
Subject: [PATCH 1/2] gh-116621: Specialize list.extend for dict items

---
 Objects/listobject.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/Objects/listobject.c b/Objects/listobject.c
index 6f919ce02b3ce2..840feaa3183f76 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -1320,6 +1320,35 @@ list_extend_dict(PyListObject *self, PyDictObject *dict, int which_item)
     return 0;
 }
 
+static int
+list_extend_dictitems(PyListObject *self, PyDictObject *dict)
+{
+    Py_ssize_t m = Py_SIZE(self);
+    Py_ssize_t n = PyDict_GET_SIZE(dict);
+    if (list_resize(self, m + n) < 0) {
+        return -1;
+    }
+
+    // TODO: Don't start a garbage collection cycle when creating tuples
+    PyObject **dest = self->ob_item + m;
+    Py_ssize_t pos = 0;
+    Py_ssize_t i = 0;
+    PyObject *key, *value;
+    while (_PyDict_Next((PyObject *)dict, &pos, &key, &value, NULL)) {
+        PyObject *item = PyTuple_Pack(2, key, value);
+        if (item == NULL) {
+            Py_SET_SIZE(self, m + i);
+            return -1;
+        }
+        FT_ATOMIC_STORE_PTR_RELAXED(*dest, item);
+        dest++;
+        i++;
+    }
+
+    Py_SET_SIZE(self, m + n);
+    return 0;
+}
+
 static int
 _list_extend(PyListObject *self, PyObject *iterable)
 {
@@ -1359,6 +1388,12 @@ _list_extend(PyListObject *self, PyObject *iterable)
         res = list_extend_dict(self, dict, 1 /*values*/);
         Py_END_CRITICAL_SECTION2();
     }
+    else if (Py_IS_TYPE(iterable, &PyDictItems_Type)) {
+        PyDictObject *dict = ((_PyDictViewObject *)iterable)->dv_dict;
+        Py_BEGIN_CRITICAL_SECTION2(self, dict);
+        res = list_extend_dictitems(self, dict);
+        Py_END_CRITICAL_SECTION2();
+    }
     else {
         Py_BEGIN_CRITICAL_SECTION(self);
         res = list_extend_iter_lock_held(self, iterable);

From c764ce8799e031bf3d6e13768e1644f89e886f66 Mon Sep 17 00:00:00 2001
From: Donghee Nals <donghee.na@python.org>
Date: Tue, 19 Mar 2024 09:03:46 +0900
Subject: [PATCH 2/2] Address code review

---
 Objects/listobject.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/Objects/listobject.c b/Objects/listobject.c
index 840feaa3183f76..4cb409cc524f22 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -1289,7 +1289,7 @@ list_extend_set(PyListObject *self, PySetObject *other)
     PyObject **dest = self->ob_item + m;
     while (_PySet_NextEntry((PyObject *)other, &setpos, &key, &hash)) {
         Py_INCREF(key);
-        *dest = key;
+        FT_ATOMIC_STORE_PTR_RELEASE(*dest, key);
         dest++;
     }
     Py_SET_SIZE(self, m + n);
@@ -1312,7 +1312,7 @@ list_extend_dict(PyListObject *self, PyDictObject *dict, int which_item)
     while (_PyDict_Next((PyObject *)dict, &pos, &keyvalue[0], &keyvalue[1], NULL)) {
         PyObject *obj = keyvalue[which_item];
         Py_INCREF(obj);
-        *dest = obj;
+        FT_ATOMIC_STORE_PTR_RELEASE(*dest, obj);
         dest++;
     }
 
@@ -1329,7 +1329,6 @@ list_extend_dictitems(PyListObject *self, PyDictObject *dict)
         return -1;
     }
 
-    // TODO: Don't start a garbage collection cycle when creating tuples
     PyObject **dest = self->ob_item + m;
     Py_ssize_t pos = 0;
     Py_ssize_t i = 0;
@@ -1340,7 +1339,7 @@ list_extend_dictitems(PyListObject *self, PyDictObject *dict)
             Py_SET_SIZE(self, m + i);
             return -1;
         }
-        FT_ATOMIC_STORE_PTR_RELAXED(*dest, item);
+        FT_ATOMIC_STORE_PTR_RELEASE(*dest, item);
         dest++;
         i++;
     }
@@ -1354,7 +1353,6 @@ _list_extend(PyListObject *self, PyObject *iterable)
 {
     // Special case:
     // lists and tuples which can use PySequence_Fast ops
-    // TODO(@corona10): Add more special cases for other types.
     int res = -1;
     if ((PyObject *)self == iterable) {
         Py_BEGIN_CRITICAL_SECTION(self);