Docserver: Make ObjectStore set calls return Futures

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

 # Copyright 2013 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
+from future import All, Future
 from object_store import ObjectStore
 
 
 class CacheChainObjectStore(ObjectStore):
   '''Maintains an in-memory cache along with a chain of other object stores to
   try for the same keys. This is useful for implementing a multi-layered cache.
   The in-memory cache is inbuilt since it's synchronous, but the object store
   interface is asynchronous.
   The rules for the object store chain are:
     - When setting (or deleting) items, all object stores in the hierarcy will
       have that item set.
     - When getting items, the behaviour depends on |start_empty|.
       - If false, each object store is tried in order. The first object
         store to find the item will trickle back up, setting it on all object
         stores higher in the hierarchy.
       - If true, only the first in-memory cache is checked, as though the store
         had been initialized with no content as opposed to the union of its
         delegate stores.
   '''
   def __init__(self, object_stores, start_empty=False):
     self._object_stores = object_stores
     self._start_empty = start_empty
     self._cache = {}
 
   def SetMulti(self, mapping):
     self._cache.update(mapping)
-    for object_store in self._object_stores:
-      object_store.SetMulti(mapping)
+    return All(object_store.SetMulti(mapping)

[Ken Rockot(use gerrit already), 2014/10/23 20:16:18]

Actually we don't want to force callers to Get the returned future in order for
the set 
operation to complete. So I'm re-listifying this to force evaluation of the
generator (and thus force the RPCs to be started).

(I started running the long test cycle after uploading and just discovered this
bug)

[not at google - send to devlin, 2014/10/23 20:18:08]

ah good point. You might want to add a comment for future adventurers.

+               for object_store in self._object_stores)
 
   def GetMulti(self, keys):
     missing_keys = list(keys)
     cached_items = {}
     for key in keys:
       if key in self._cache:
         cached_items[key] = self._cache.get(key)
         missing_keys.remove(key)
     if len(missing_keys) == 0 or self._start_empty:
       return Future(value=cached_items)
@@ skipping 28 matching lines @@
         if updates:
           object_store.SetMulti(updates)
       return cached_items
     return Future(callback=resolve)
 
   def DelMulti(self, keys):
     for k in keys:
       self._cache.pop(k, None)
     for object_store in self._object_stores:
       object_store.DelMulti(keys)