Improve thread safety of _PyList_AsTupleTakeItems

Author: markshannon

Objects/abstract.c

@@ -2038,9 +2038,6 @@ PySequence_DelSlice(PyObject *s, Py_ssize_t i1, Py_ssize_t i2)
 PyObject *
 PySequence_Tuple(PyObject *v)
 {
-    PyObject *it;  /* iter(v) */
-    Py_ssize_t n;             /* guess for result tuple size */
-
     if (v == NULL) {
         return null_error();
     }
@@ -2057,7 +2054,7 @@ PySequence_Tuple(PyObject *v)
         return PyList_AsTuple(v);
 
     /* Get iterator. */
-    it = PyObject_GetIter(v);
+    PyObject *it = PyObject_GetIter(v);
     if (it == NULL)
         return NULL;
 

Objects/listobject.c

@@ -3177,20 +3177,24 @@ PyList_AsTuple(PyObject *v)
 PyObject *
 _PyList_AsTupleTakeItems(PyObject *v)
 {
-    if (v == NULL || !PyList_Check(v)) {
-        PyErr_BadInternalCall();
-        return NULL;
-    }
+    assert(PyList_Check(v));
     PyObject *ret;
     PyListObject *self = (PyListObject *)v;
     if (Py_SIZE(v) == 0) {
         return PyTuple_New(0);
     }
+    Py_ssize_t size;
+    PyObject **items;
     Py_BEGIN_CRITICAL_SECTION(self);
-    Py_ssize_t size = Py_SIZE(v);
+    size = Py_SIZE(v);
+    items = self->ob_item;
     Py_SET_SIZE(v, 0);
-    ret = _PyTuple_FromArraySteal(self->ob_item, size);
+    self->ob_item = NULL;
     Py_END_CRITICAL_SECTION();
+    ret = _PyTuple_FromArraySteal(items, size);
+    if (size) {
+        free_list_items(items, false);
+    }
     return ret;
 }
 

Objects/tupleobject.c

@@ -105,6 +105,7 @@ PyTuple_GetItem(PyObject *op, Py_ssize_t i)
 int
 PyTuple_SetItem(PyObject *op, Py_ssize_t i, PyObject *newitem)
 {
+    assert(newitem != NULL);
     PyObject **p;
     if (!PyTuple_Check(op) || Py_REFCNT(op) != 1) {
         Py_XDECREF(newitem);