python · corona10 · Mar 5, 2024 · Mar 2, 2024 · Mar 4, 2024 · Mar 4, 2024
diff --git a/Objects/listobject.c b/Objects/listobject.c
@@ -514,30 +514,33 @@ list_item(PyObject *aa, Py_ssize_t i)
    return item;
 }

-static PyObject *
-list_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh)
+static inline PyObject *
+list_slice_impl(PyListObject *a, Py_ssize_t ilow, Py_ssize_t len)
 {
-    PyListObject *np;
-    PyObject **src, **dest;
-    Py_ssize_t i, len;
-    len = ihigh - ilow;
-    if (len <= 0) {
-        return PyList_New(0);
-    }
-    np = (PyListObject *) list_new_prealloc(len);
-    if (np == NULL)
+    PyListObject *np = (PyListObject *) list_new_prealloc(len);
+    if (np == NULL) {
        return NULL;
-
-    src = a->ob_item + ilow;
-    dest = np->ob_item;
-    for (i = 0; i < len; i++) {
+    }
+    PyObject **src = a->ob_item + ilow;
+    PyObject **dest = np->ob_item;
+    for (Py_ssize_t i = 0; i < len; i++) {
        PyObject *v = src[i];
        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)
+{
+    Py_ssize_t len = ihigh - ilow;
+    if (len <= 0) {
+        return PyList_New(0);
+    }
+    return list_slice_impl(a, ilow, len);
+}
+
 PyObject *
 PyList_GetSlice(PyObject *a, Py_ssize_t ilow, Py_ssize_t ihigh)
 {
@@ -584,13 +587,13 @@ list_concat_lock_held(PyListObject *a, PyListObject *b)
    dest = np->ob_item;
    for (i = 0; i < Py_SIZE(a); i++) {
        PyObject *v = src[i];
-        FT_ATOMIC_STORE_PTR_RELAXED(dest[i], Py_NewRef(v));
+        dest[i] = Py_NewRef(v);
    }
    src = b->ob_item;
    dest = np->ob_item + Py_SIZE(a);
    for (i = 0; i < Py_SIZE(b); i++) {
        PyObject *v = src[i];
-        FT_ATOMIC_STORE_PTR_RELAXED(dest[i], Py_NewRef(v));
+        dest[i] = Py_NewRef(v);
    }
    Py_SET_SIZE(np, size);
    return (PyObject *)np;
@@ -636,15 +639,15 @@ list_repeat_lock_held(PyListObject *a, Py_ssize_t n)
        _Py_RefcntAdd(elem, n);
        PyObject **dest_end = dest + output_size;
        while (dest < dest_end) {
-            FT_ATOMIC_STORE_PTR_RELAXED(*dest++, elem);
+            *dest++ = elem;
        }
    }
    else {
        PyObject **src = a->ob_item;
        PyObject **src_end = src + input_size;
        while (src < src_end) {
            _Py_RefcntAdd(*src, n);
-            FT_ATOMIC_STORE_PTR_RELAXED(*dest++, *src++);
+            *dest++ = *src++;
        }

        _Py_memory_repeat((char *)np->ob_item, sizeof(PyObject *)*output_size,
@@ -718,7 +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
@@ -741,15 +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;
@@ -823,6 +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_impl(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)
 {
@@ -2884,8 +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;
        }
@@ -3085,6 +3106,47 @@ static PySequenceMethods list_as_sequence = {
    list_inplace_repeat,                        /* sq_inplace_repeat */
 };

+static PyObject *
+list_slice_step_lock_held(PyListObject *a, Py_ssize_t start, Py_ssize_t step, Py_ssize_t len)
+{
+    PyObject *obj = list_new_prealloc(len);
+    if (obj == NULL) {
+        return NULL;
+    }
+    PyListObject *np = (PyListObject *)obj;
+    size_t cur;
+    Py_ssize_t i;
+    PyObject **src = a->ob_item;
+    PyObject **dest = np->ob_item;
+    for (cur = start, i = 0; i < len;
+            cur += (size_t)step, i++) {
+        PyObject *v = src[cur];
+        FT_ATOMIC_STORE_PTR_RELAXED(dest[i], Py_NewRef(v));
+    }
+    Py_SET_SIZE(np, len);
+    return (PyObject *)np;
+}
+
+static PyObject *
+list_slice_wrap(PyListObject *aa, Py_ssize_t start, Py_ssize_t stop, Py_ssize_t step)
+{
+    PyObject *res = NULL;
+    PyListObject *a = (PyListObject *)aa;
+    Py_BEGIN_CRITICAL_SECTION(a);
+    Py_ssize_t len = PySlice_AdjustIndices(Py_SIZE(a), &start, &stop, step);
+    if (len <= 0) {
+        res = PyList_New(0);
+    }
+    else if (step == 1) {
+        res = list_slice_impl(a, start, len);
+    }
+    else {
+        res = list_slice_step_lock_held(a, start, step, len);
+    }
+    Py_END_CRITICAL_SECTION();
+    return res;
+}
+
 static PyObject *
 list_subscript(PyObject* _self, PyObject* item)
 {
@@ -3099,38 +3161,11 @@ list_subscript(PyObject* _self, PyObject* item)
        return list_item((PyObject *)self, i);
    }
    else if (PySlice_Check(item)) {
-        Py_ssize_t start, stop, step, slicelength, i;
-        size_t cur;
-        PyObject* result;
-        PyObject* it;
-        PyObject **src, **dest;
-
+        Py_ssize_t start, stop, step;
        if (PySlice_Unpack(item, &start, &stop, &step) < 0) {
            return NULL;
        }
-        slicelength = PySlice_AdjustIndices(Py_SIZE(self), &start, &stop,
-                                            step);
-
-        if (slicelength <= 0) {
-            return PyList_New(0);
-        }
-        else if (step == 1) {
-            return list_slice(self, start, stop);
-        }
-        else {
-            result = list_new_prealloc(slicelength);
-            if (!result) return NULL;
-
-            src = self->ob_item;
-            dest = ((PyListObject *)result)->ob_item;
-            for (cur = start, i = 0; i < slicelength;
-                 cur += (size_t)step, i++) {
-                it = Py_NewRef(src[cur]);
-                dest[i] = it;
-            }
-            Py_SET_SIZE(result, slicelength);
-            return result;
-        }
+        return list_slice_wrap(self, start, stop, step);
    }
    else {
        PyErr_Format(PyExc_TypeError,