Docserver: Persist stat cache for versioned file systems

chrome/common/extensions/docs/server2/object_store.py

 # Copyright (c) 2012 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.
 
 from future import Future
 
 
 class ObjectStore(object):
   '''A class for caching picklable objects.
   '''
   def Get(self, key):
     '''Gets a |Future| with the value of |key| in the object store, or None
     if |key| is not in the object store.
     '''
     return self.GetMulti((key,)).Then(lambda keys: keys.get(key))
 
   def GetMulti(self, keys):
     '''Gets a |Future| with values mapped to |keys| from the object store, with
     any keys not in the object store omitted.
     '''
     raise NotImplementedError(self.__class__)
 
   def Set(self, key, value):
-    '''Sets key -> value in the object store.
+    '''Sets key -> value in the object store. Returns a |Future| which is
+    resolved once the key's new value has been stored.
     '''
-    self.SetMulti({ key: value })
+    return self.SetMulti({ key: value })
 
   def SetMulti(self, items):
     '''Atomically sets the mapping of keys to values in the object store.
+    Returns a |Future| which is resolved once the new mapping has been stored.
     '''
     raise NotImplementedError(self.__class__)
 
   def Del(self, key):
     '''Deletes a key from the object store.
     '''
     self.DelMulti([key])
 
   def DelMulti(self, keys):
     '''Deletes |keys| from the object store.
     '''
     raise NotImplementedError(self.__class__)