Merged zagy-lp509801 branch.

Updating blobs in save points could cause spurious "invalidations
out of order" errors.  https://bugs.launchpad.net/zodb/+bug/509801

(Thanks to Christian Zagrodnick for chasing this down.)

src/CHANGES.txt

@@ -8,6 +8,11 @@
 Bugs fixed
 ----------
 
+- Updating blobs in save points could cause spurious "invalidations
+  out of order" errors.  https://bugs.launchpad.net/zodb/+bug/509801
+
+  (Thanks to Christian Zagrodnick for chasing this down.)
+
 - When a demo storage push method was used to create a new demo
   storage and the new storage was closed, the original was
   (incorrectly) closed.

src/ZODB/Connection.py

@@ -328,13 +328,13 @@ class Connection(ExportImport, object):
     def invalidate(self, tid, oids):
         """Notify the Connection that transaction 'tid' invalidated oids."""
         if self.before is not None:
-            # this is an historical connection.  Invalidations are irrelevant.
+            # This is a historical connection.  Invalidations are irrelevant.
             return
         self._inv_lock.acquire()
         try:
             if self._txn_time is None:
                 self._txn_time = tid
-            elif tid < self._txn_time:
+            elif (tid < self._txn_time) and (tid is not None):
                 raise AssertionError("invalidations out of order, %r < %r"
                                      % (tid, self._txn_time))
 
@@ -1121,7 +1121,7 @@ class Connection(ExportImport, object):
                 # that that the next attribute access of its name
                 # unghostify it, which will cause its blob data
                 # to be reattached "cleanly"
-                self.invalidate(s, {oid:True})
+                self.invalidate(None, (oid, ))
             else:
                 s = self._storage.store(oid, serial, data,
                                         '', transaction)

src/ZODB/tests/testblob.py

@@ -563,6 +563,35 @@ def savepoint_isolation():
     >>> db.close()
     """
 
+def savepoint_commits_without_invalidations_out_of_order():
+    """Make sure transactions with blobs can be commited without the
+    invalidations out of order error (LP #509801)
+
+    >>> bs = create_storage()
+    >>> db = DB(bs)
+    >>> tm1 = transaction.TransactionManager()
+    >>> conn1 = db.open(transaction_manager=tm1)
+    >>> conn1.root.b = ZODB.blob.Blob('initial')
+    >>> tm1.commit()
+    >>> conn1.root.b.open('w').write('1')
+    >>> _ = tm1.savepoint()
+
+    >>> tm2 = transaction.TransactionManager()
+    >>> conn2 = db.open(transaction_manager=tm2)
+    >>> conn2.root.b.open('w').write('2')
+    >>> _ = tm1.savepoint()
+    >>> conn1.root.b.open().read()
+    '1'
+    >>> conn2.root.b.open().read()
+    '2'
+    >>> tm2.commit()
+    >>> tm1.commit()  # doctest: +IGNORE_EXCEPTION_DETAIL
+    Traceback (most recent call last):
+        ...
+    ConflictError: database conflict error...
+    >>> db.close()
+    """
+
 def savepoint_cleanup():
     """Make sure savepoint data gets cleaned up.