Deregister any Python-extended prototypes on exit.

When Python exits, remove any Python-extended objects from the
C++ registry.  This avoids crash due to deallocation of Python
objects in the C++ registry with Python already kaput.

Replace the reference counting hack that was used to avoid the crash before.

Author: pavoljuhas

diffpy/srreal/_cleanup.py

@@ -0,0 +1,82 @@
+#!/usr/bin/env python
+##############################################################################
+#
+# diffpy.srreal     Complex Modeling Initiative
+#                   (c) 2016 Brookhaven Science Associates,
+#                   Brookhaven National Laboratory.
+#                   All rights reserved.
+#
+# File coded by:    Pavol Juhas
+#
+# See AUTHORS.txt for a list of people who contributed.
+# See LICENSE.txt for license information.
+#
+##############################################################################
+
+
+"""\
+Cancel registration of Python-extended C++ classes when Python exits.
+
+Note
+----
+Python finishes before the shared library libdiffpy, but the registry of
+class prototypes is implemented in libdiffpy.  Any Python-extended classes
+thus need to be removed from the registry prior to Python exit.
+
+This module is not intended for direct use.  It is used implicitly within
+a call of _registerThisType.
+"""
+
+
+import weakref
+
+
+# Routine to be used from srreal_ext module ----------------------------------
+
+def registerForCleanUp(obj):
+    """Remember to clean up the specified prototype at Python exit.
+
+    Parameters
+    ----------
+    obj : wrapped class that has class registry
+        This is an object being added to the C++ registry of prototypes.
+        If active at Python exit, the associated string type will be
+        removed from the class registry.
+
+    No return value.
+    """
+    _cleanup_handler.add(obj)
+    return
+
+# ----------------------------------------------------------------------------
+
+class _DerivedClassesCleanUpHandler(object):
+
+    def __init__(self):
+        self._references = set()
+        return
+
+
+    def add(self, obj):
+        wr = weakref.ref(obj)
+        self._references.add(wr)
+        return
+
+
+    def __del__(self):
+        while self._references:
+            wr = self._references.pop()
+            obj = wr()
+            if obj is not None:
+                obj._deregisterType(obj.type())
+        return
+
+# end of class _DerivedClassesCleanUpHandler
+
+
+# create singleton instance of the cleanup handler
+_cleanup_handler = _DerivedClassesCleanUpHandler()
+del _DerivedClassesCleanUpHandler
+
+
+# End of file.

srrealmodule/srreal_registry.cpp

@@ -23,6 +23,13 @@ namespace srrealmodule {
 
 using namespace boost::python;
 
+void register_for_cleanup(PyObject* pobj)
+{
+    object obj(borrowed(pobj));
+    object reg = import("diffpy.srreal._cleanup").attr("registerForCleanUp");
+    reg(obj);
+}
+
 
 /// get dictionary of Python-defined docstrings for the cls class.
 object get_registry_docstrings(object& cls)

srrealmodule/srreal_registry.hpp

@@ -24,6 +24,10 @@
 
 namespace srrealmodule {
 
+/// helper for remembering instances of Python-derived class.
+void register_for_cleanup(PyObject*);
+
+
 /// template class for handling Python Wrapper classes in C++ class registry
 template <class T>
 class wrapper_registry_configurator
@@ -55,7 +59,7 @@ class wrapper_registry_configurator
         void setup(TSharedPtr ptr) const
         {
             assert(mcptr && mcptr == ptr.get());
-            ::boost::python::incref(mpyptr);
+            register_for_cleanup(mpyptr);
             mcptr = 0;
             mpyptr = 0;
         }