shiboken: Make AutoDecRef safe

The well-known Shiboken::AutoDecref construction for
easier refcount handling has a serious flaw.

In Python's object.h, this is called a naive implementation
that can be deadly when deallocating object containers.

This patch uses the same idea as the Python's Py_XSETREF
macro.

Task-number: PYSIDE-15
Change-Id: I7a36713790f35df89736437d236c8f1f58d7be1e
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 3 insertions, 1 deletions

diff --git a/sources/shiboken2/libshiboken/autodecref.h b/sources/shiboken2/libshiboken/autodecref.h
index d3353b1e4..498b1aec4 100644
--- a/sources/shiboken2/libshiboken/autodecref.h
+++ b/sources/shiboken2/libshiboken/autodecref.h
@@ -96,8 +96,10 @@ public:
      */
     void reset(PyObject *other)
     {
-        Py_XDECREF(m_pyObj);
+        // Safely decref m_pyObj. See Py_XSETREF in object.h .
+        PyObject *_py_tmp = m_pyObj;
         m_pyObj = other;
+        Py_XDECREF(_py_tmp);
     }
 private:
     PyObject *m_pyObj;