pythongh-112087: Make list_{subscript, ass_slice, slice} to be thread…

…-safe

Objects/listobject.c

@@ -531,23 +531,6 @@ list_slice_lock_held(PyListObject *a, Py_ssize_t ilow, Py_ssize_t len)
     return (PyObject *)np;
 }
 
-static PyObject *
-list_slice_lock_held(PyListObject *a, Py_ssize_t start, Py_ssize_t len)
-{
-    PyListObject *np = (PyListObject *) list_new_prealloc(len);
-    if (np == NULL) {
-        return NULL;
-    }
-    PyObject **src = a->ob_item + start;
-    PyObject **dest = np->ob_item;
-    for (Py_ssize_t i = 0; i < len; i++) {
-        PyObject *v = src[i];
-        FT_ATOMIC_STORE_PTR_RELAXED(dest[i], Py_NewRef(v));
-    }
-    Py_SET_SIZE(np, len);
-    return (PyObject *)np;
-}
-
 static PyObject *
 list_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh)
 {
@@ -738,7 +721,7 @@ list_clear_slot(PyObject *self)
  * guaranteed the call cannot fail.
  */
 static int
-list_ass_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
+list_ass_slice_impl(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
 {
     /* Because [X]DECREF can recursively invoke list operations on
        this list, we must postpone all [X]DECREF activity until
@@ -761,15 +744,6 @@ list_ass_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
     if (v == NULL)
         n = 0;
     else {
-        if (a == b) {
-            /* Special case "a[i:j] = a" -- copy b first */
-            v = list_slice(b, 0, Py_SIZE(b));
-            if (v == NULL)
-                return result;
-            result = list_ass_slice(a, ilow, ihigh, v);
-            Py_DECREF(v);
-            return result;
-        }
         v_as_SF = PySequence_Fast(v, "can only assign an iterable");
         if(v_as_SF == NULL)
             goto Error;
@@ -843,6 +817,34 @@ list_ass_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
 #undef b
 }
 
+static int
+list_ass_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
+{
+    int ret;
+    if (a == (PyListObject *)v) {
+        Py_BEGIN_CRITICAL_SECTION(a);
+        Py_ssize_t n = PyList_GET_SIZE(a);
+        PyObject *copy = list_slice_lock_held(a, 0, n);
+        if (copy == NULL) {
+            return -1;
+        }
+        ret = list_ass_slice_impl(a, ilow, ihigh, copy);
+        Py_DECREF(copy);
+        Py_END_CRITICAL_SECTION();
+    }
+    else if (v != NULL && PyList_CheckExact(v)) {
+        Py_BEGIN_CRITICAL_SECTION2(a, v);
+        ret = list_ass_slice_impl(a, ilow, ihigh, v);
+        Py_END_CRITICAL_SECTION2();
+    }
+    else {
+        Py_BEGIN_CRITICAL_SECTION(a);
+        ret = list_ass_slice_impl(a, ilow, ihigh, v);
+        Py_END_CRITICAL_SECTION();
+    }
+    return ret;
+}
+
 int
 PyList_SetSlice(PyObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
 {
@@ -2904,8 +2906,7 @@ list_remove_impl(PyListObject *self, PyObject *value)
         int cmp = PyObject_RichCompareBool(obj, value, Py_EQ);
         Py_DECREF(obj);
         if (cmp > 0) {
-            if (list_ass_slice(self, i, i+1,
-                               (PyObject *)NULL) == 0)
+            if (list_ass_slice_impl(self, i, i+1, NULL) == 0)
                 Py_RETURN_NONE;
             return NULL;
         }