Reset ``_cache`` on a connection's ``_reader`` object when resetting the cache

- This change prevent reads from the old cache object, e.g. during Zope2's
  auto-refresh of products. (https://bugs.launchpad.net/zodb/+bug/142667).

NEWS.txt

@@ -4,6 +4,11 @@ Whats new in ZODB 3.8.1
 
 Bugs Fixed:
 
+- (3.8.1) Reset ``_cache`` on a connection's ``_reader`` object when
+  resetting the cache, to prevent reads from the old cache object, e.g.
+  during Zope2's auto-refresh of products.
+  (https://bugs.launchpad.net/zodb/+bug/142667).
+
 - (beta 9) An exception would be raised when an error occured attempting to
   lock a file and logging of said error was enabled.
 

src/ZODB/Connection.py

@@ -1027,7 +1027,7 @@ class Connection(ExportImport, object):
         self._invalidated.clear()
         self._invalidatedCache = False
         cache_size = self._cache.cache_size
-        self._cache = cache = PickleCache(self, cache_size)
+        self._reader._cache = self._cache = PickleCache(self, cache_size)
 
     ##########################################################################
     # Python protocol

src/ZODB/tests/testConnection.py

@@ -140,6 +140,14 @@ class ConnectionDotAdd(unittest.TestCase):
         self.datamgr.tpc_finish(self.transaction)
         self.assert_(obj._p_oid not in self.datamgr._storage._stored)
 
+    def check__resetCacheResetsReader(self):
+        # https://bugs.launchpad.net/zodb/+bug/142667
+        old_cache = self.datamgr._cache
+        self.datamgr._resetCache()
+        new_cache = self.datamgr._cache
+        self.failIf(new_cache is old_cache)
+        self.failUnless(self.datamgr._reader._cache is new_cache)
+
 class UserMethodTests(unittest.TestCase):
 
     # add isn't tested here, because there are a bunch of traditional