Fix possibility of rare crash during dealloc. Fixes #66

CHANGES.rst

@@ -4,7 +4,8 @@
 4.2.5 (unreleased)
 ------------------
 
-- Nothing changed yet.
+- Fix the possibility of a rare crash in the C extension when
+  deallocating items. See https://github.com/zopefoundation/persistent/issues/66
 
 
 4.2.4.2 (2017-04-23)

persistent/cPersistence.c

@@ -783,6 +783,7 @@ Per__getstate__(cPersistentObject *self)
 static void
 Per_dealloc(cPersistentObject *self)
 {
+    PyObject_GC_UnTrack((PyObject *)self);
     if (self->state >= 0)
     {
         /* If the cache has been cleared, then a non-ghost object

persistent/cPickleCache.c

@@ -891,6 +891,7 @@ cc_init(ccobject *self, PyObject *args, PyObject *kwds)
 static void
 cc_dealloc(ccobject *self)
 {
+    PyObject_GC_UnTrack((PyObject *)self);
     Py_XDECREF(self->data);
     Py_XDECREF(self->jar);
     PyObject_GC_Del(self);