Add transaction buffer filter.

impl/memory/datastore_data.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 memory
 
 import (
         "bytes"
         "fmt"
         "sync"
@@ skipping 108 matching lines @@
         d.rwlock.RLock()
         defer d.rwlock.RUnlock()
         return d.disableSpecialEntities
 }
 
 func (d *dataStoreData) getQuerySnaps(consistent bool) (idx, head *memStore) {
         d.rwlock.RLock()
         defer d.rwlock.RUnlock()
         if d.snap == nil {
                 // we're 'always consistent'
-                return d.head, d.head
+                snap := d.head.Snapshot()
+                return snap, snap

[iannucci, 2015/09/30 03:03:31]

This was really dumb on my part. `d.head` is the current mutable HEAD state.
getQuerySnaps is supposed to return read-only snapshots.

         }
 
         head = d.head.Snapshot()
         if consistent {
                 idx = head
         } else {
                 idx = d.snap
         }
         return
 }
@@ skipping 409 matching lines @@
 }
 
 func keyBytes(key *ds.Key) []byte {
         return serialize.ToBytes(ds.MkProperty(key))
 }
 
 func rpm(data []byte) (ds.PropertyMap, error) {
         return serialize.ReadPropertyMap(bytes.NewBuffer(data),
                 serialize.WithContext, "", "")
 }