Fix races in txnBuf

filter/txnBuf/context.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package txnBuf
 
 import (
         "golang.org/x/net/context"
 
         ds "github.com/luci/gae/service/datastore"
-        "github.com/luci/gae/service/info"
 )
 
 type key int
 
 var (
-        dsTxnBufParent key
+        dsTxnBufParent   key
+        dsTxnBufHaveLock key = 1
 )
 
 // FilterRDS installs a transaction buffer datastore filter in the context.
 func FilterRDS(c context.Context) context.Context {
         // TODO(riannucci): allow the specification of the set of roots to limit this
         // transaction to, transitively.
         return ds.AddRawFilters(c, func(c context.Context, rds ds.RawInterface) ds.RawInterface {
                 if par, _ := c.Value(dsTxnBufParent).(*txnBufState); par != nil {
-                        return &dsTxnBuf{c, par}
+                        haveLock, _ := c.Value(dsTxnBufHaveLock).(bool)
+                        return &dsTxnBuf{c, par, haveLock}
                 }
-                return &dsBuf{rds, info.Get(c).GetNamespace()}
+                return &dsBuf{rds}
         })
 }
 
 // impossible is a marker function to indicate that the given error is an
 // impossible state, due to conditions outside of the function.
 func impossible(err error) {
         if err != nil {
                 panic(err)
         }
 }
 
 // memoryCorruption is a marker function to indicate that given error is
 // actually due to corrupted memory to make it easier to read the code.
 func memoryCorruption(err error) {
         if err != nil {
                 panic(err)
         }
 }