gh-112087: Make list_{count, index, contains} to be thread-safe.

python · corona10 · Feb 6, 2024 · Feb 2, 2024 · Feb 3, 2024 · Feb 5, 2024
commit 4b8ac83521c30577c4b0cfd3f37f43c30703b7d9
diff --git a/Objects/listobject.c b/Objects/listobject.c
@@ -478,18 +478,21 @@ list_length(PyObject *a)
 static int
 list_contains(PyObject *aa, PyObject *el)
 {
-    PyListObject *a = (PyListObject *)aa;
-    PyObject *item;
-    Py_ssize_t i;
-    int cmp;

-    for (i = 0, cmp = 0 ; cmp == 0 && i < Py_SIZE(a); ++i) {
-        item = PyList_GET_ITEM(a, i);
-        Py_INCREF(item);
-        cmp = PyObject_RichCompareBool(item, el, Py_EQ);
+    for (Py_ssize_t i = 0; ; i++) {
+        PyObject *item = PyList_GetItemRef(aa, i);
+        if (item == NULL && PyErr_ExceptionMatches(PyExc_IndexError)) {
+            // out-of-bounds
+            PyErr_Clear();
+            return 0;
+        }
+        int cmp = PyObject_RichCompareBool(item, el, Py_EQ);
        Py_DECREF(item);
+        if (cmp != 0) {
+            return cmp;
+        }
    }
-    return cmp;
+    return 0;
 }

 static PyObject *
@@ -2737,8 +2740,11 @@ list_index_impl(PyListObject *self, PyObject *value, Py_ssize_t start,
            stop = 0;
    }
    for (i = start; i < stop && i < Py_SIZE(self); i++) {
-        PyObject *obj = self->ob_item[i];
-        Py_INCREF(obj);
+        PyObject *obj = PyList_GetItemRef((PyObject *)self, i);
+        if (obj == NULL && PyErr_ExceptionMatches(PyExc_IndexError)) {
+            PyErr_Clear();
+            break;
+        }
        int cmp = PyObject_RichCompareBool(obj, value, Py_EQ);
        Py_DECREF(obj);
        if (cmp > 0)
@@ -2764,15 +2770,17 @@ list_count(PyListObject *self, PyObject *value)
 /*[clinic end generated code: output=b1f5d284205ae714 input=3bdc3a5e6f749565]*/
 {
    Py_ssize_t count = 0;
-    Py_ssize_t i;
-
-    for (i = 0; i < Py_SIZE(self); i++) {
-        PyObject *obj = self->ob_item[i];
+    for (Py_ssize_t i = 0; ; i++) {
+        PyObject *obj = PyList_GetItemRef((PyObject *)self, i);
+        if (obj == NULL && PyErr_ExceptionMatches(PyExc_IndexError)) {
+            PyErr_Clear();
+            break;
+        }
        if (obj == value) {
           count++;
+           Py_DECREF(obj);
           continue;
        }
-        Py_INCREF(obj);
        int cmp = PyObject_RichCompareBool(obj, value, Py_EQ);
        Py_DECREF(obj);
        if (cmp > 0)