.

bigfile/_file_zodb.pyx

@@ -173,7 +173,8 @@ class ZSync:
     """
 
     def on_connection_resync(zsync):
-        print('ZSync.resync %r %r' % (zsync.zconn, zsync.wconn))
+        print('\nZZZSync.resync %r %r' % (zsync.zconn, zsync.wconn))
+        #import traceback; traceback.print_stack()
         zsync.wconn.resync(zconn_at(zsync.zconn))
 
     # TODO zconn dealloc -> wconn.close

lib/zodb.py

@@ -203,6 +203,7 @@ def Connection_onResyncCallback(self, f):
         # NOTE WeakSet does not work for bound methods - they are always created
         # anew for each obj.method access, and thus will go away almost immediately
         self._onResyncCallbacks = WeakSet()
+    self._onResyncCallbacks.add(f)
 
 assert not hasattr(ZODB.Connection.Connection, 'onResyncCallback')
 ZODB.Connection.Connection.onResyncCallback = Connection_onResyncCallback