Forward port from Zope 2.7 branch.

_handle_independent():  Failed to record that a ReadConflictError
was raised for an object with a _p_independent() method that
returned false.

NEWS.txt

@@ -43,6 +43,12 @@ is raised.
 transaction
 -----------
 
+If ReadConflictError was raised by an attempt to load an object with a
+_p_independent() method that returned false, attempting to commit the
+transaction failed to (re)raise ReadConflictError for that object.  Note
+that ZODB intends to prevent committing a transaction in which a
+ReadConflictError occurred; this was an obscure case it missed.
+
 Growing pains:  ZODB 3.1 and 3.2 had a bug wherein Transaction.begin()
 didn't abort the current transaction if the only pending changes were in a
 subtransaction.  In ZODB 3.3, it's intended that transaction managers be

src/ZODB/Connection.py

@@ -229,6 +229,14 @@ class Connection(ExportImport, object):
         self._inv_lock = threading.Lock()
         self._invalidated = d = {}
         self._invalid = d.has_key
+
+        # We intend to prevent committing a transaction in which
+        # ReadConflictError occurs.  _conflicts is the set of oids that
+        # experienced ReadConflictError.  Any time we raise ReadConflictError,
+        # the oid should be added to this set, and we should be sure that the
+        # object is registered.  Because it's registered, Connection.commit()
+        # will raise ReadConflictError again (because the oid is in
+        # _conflicts).
         self._conflicts = {}
 
         # If MVCC is enabled, then _mvcc is True and _txn_time stores
@@ -907,6 +915,7 @@ class Connection(ExportImport, object):
             finally:
                 self._inv_lock.release()
         else:
+            self._conflicts[obj._p_oid] = 1
             self._register(obj)
             raise ReadConflictError(object=obj)
 

src/ZODB/tests/testZODB.py

@@ -286,6 +286,10 @@ class ZODBTests(unittest.TestCase):
         # transaction.
         if shouldFail:
             self.assertRaises(ReadConflictError, lambda: obj.child1)
+            # And since ReadConflictError was raised, attempting to commit
+            # the transaction should re-raise it.  checkNotIndependent()
+            # failed this part of the test for a long time.
+            self.assertRaises(ReadConflictError, tm2.get().commit)
         else:
             # make sure that accessing the object succeeds
             obj.child1