Extensions Docs Server: Internal file system

chrome/common/extensions/docs/server2/memcache_file_system.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 file_system import FileSystem
+from future import Future
+import appengine_memcache as memcache
+
+class MemcacheFileSystem(FileSystem):
+  """FileSystem implementation which memcaches the results of Read.
+  """
+  def __init__(self, file_system, memcache):
+    self._file_system = file_system
+    self._memcache = memcache
+
+  def Stat(self, path):
+    """Stats the directory given, or if a file is given, the file's parent
+    directory.
+    """
+    version = self._memcache.Get(path, memcache.MEMCACHE_FILE_SYSTEM_STAT)
+    if version is None:
+      stat_info = self._file_system.Stat(path)
+      self._memcache.Set(path,
+                         stat_info.version,
+                         memcache.MEMCACHE_FILE_SYSTEM_STAT)
+    else:
+      stat_info = self.StatInfo(version)
+    return stat_info
+
+  def Read(self, paths):
+    """Reads a list of files. If a file is in memcache and it is not out of
+    date, it is returned. Otherwise, the file is retrieved from the file system.
+    """
+    result = {}
+    uncached = []
+    for path in paths:
+      cached_result = self._memcache.Get(path,
+                                         memcache.MEMCACHE_FILE_SYSTEM_READ)
+      if cached_result is None:
+        uncached.append(path)
+        continue
+      data, version = cached_result
+      if self.Stat(path).version > version:
+        self._memcache.Delete(path, memcache.MEMCACHE_FILE_SYSTEM_READ)
+        uncached.append(path)
+        continue
+      result[path] = data
+    new_items = self._file_system.Read(uncached).Get()
+    for item in new_items:
+      version = self.Stat(item).version
+      value = new_items[item]
+      self._memcache.Set(item,
+                         (value, version),
+                         memcache.MEMCACHE_FILE_SYSTEM_READ)
+      result[item] = value
+    return Future(value=result)