Issue #20440: Massive replacing unsafe attribute setting code with special
macro Py_SETREF.
diff --git a/Include/object.h b/Include/object.h
index 4ee1f8e..8fe202d 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -824,6 +824,29 @@
#define Py_XINCREF(op) do { if ((op) == NULL) ; else Py_INCREF(op); } while (0)
#define Py_XDECREF(op) do { if ((op) == NULL) ; else Py_DECREF(op); } while (0)
+/* Safely decref `op` and set `op` to `op2`.
+ *
+ * As in case of Py_CLEAR "the obvious" code can be deadly:
+ *
+ * Py_XDECREF(op);
+ * op = op2;
+ *
+ * The safe way is:
+ *
+ * Py_SETREF(op, op2);
+ *
+ * That arranges to set `op` to `op2` _before_ decref'ing, so that any code
+ * triggered as a side-effect of `op` getting torn down no longer believes
+ * `op` points to a valid object.
+ */
+
+#define Py_SETREF(op, op2) \
+ do { \
+ PyObject *_py_tmp = (PyObject *)(op); \
+ (op) = (op2); \
+ Py_XDECREF(_py_tmp); \
+ } while (0)
+
/*
These are provided as conveniences to Python runtime embedders, so that
they can have object code that is not dependent on Python compilation flags.