Fix possibility of rare crash during dealloc. Fixes #75

BTrees/BTreeTemplate.c

@@ -2277,8 +2277,10 @@ BTree_init(PyObject *self, PyObject *args, PyObject *kwds)
 static void
 BTree_dealloc(BTree *self)
 {
-    if (self->state != cPersistent_GHOST_STATE)
+    PyObject_GC_UnTrack((PyObject *)self);
+    if (self->state != cPersistent_GHOST_STATE) {
         _BTree_clear(self);
+    }
     cPersistenceCAPI->pertype->tp_dealloc((PyObject *)self);
 }
 

BTrees/BucketTemplate.c

@@ -1708,8 +1708,10 @@ Bucket_init(PyObject *self, PyObject *args, PyObject *kwds)
 static void
 bucket_dealloc(Bucket *self)
 {
-    if (self->state != cPersistent_GHOST_STATE)
+    PyObject_GC_UnTrack((PyObject *)self);
+    if (self->state != cPersistent_GHOST_STATE) {
         _bucket_clear(self);
+    }
 
     cPersistenceCAPI->pertype->tp_dealloc((PyObject *)self);
 }

CHANGES.rst

@@ -9,6 +9,9 @@
   BTrees is used but the ``persistent`` C extension is not available.
   Previously this could result in an odd ``AttributeError``. See
   https://github.com/zopefoundation/BTrees/pull/55
+- Fix the possibility of a rare crash in the C extension when
+  deallocating items. See https://github.com/zopefoundation/BTrees/issues/75
+
 
 4.4.1 (2017-01-24)
 ------------------