Docserver: Persist stat cache for versioned file systems

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

+# Copyright 2014 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 All, Future
+
+
+class _RefreshWorkOrder(object):
+  '''A set of tasks that must be completed in a refresh cycle.'''
+  def __init__(self, tasks):
+    self.tasks = set(tasks)
+
+
+class _RefreshTaskCompletion(object):
+  '''Marks the completion of a single named task for some refresh cycle.'''
+  def __init__(self, task):
+    self.task = task
+
+
+def _TaskKey(refresh_id, task):
+  return '%s@%s' % (refresh_id, task)
+
+
+class RefreshTracker(object):
+  '''Manages and tracks the progress of data refresh cycles.'''
+  def __init__(self, object_store_creator):
+    # These object stores should never be created empty since they are strictly
+    # used to persist state across requests.
+    self._work_orders = object_store_creator.Create(_RefreshWorkOrder,
+        start_empty=False)
+    self._task_completions = object_store_creator.Create(_RefreshTaskCompletion,
+        start_empty=False)
+
+  def _GetWorkOrder(self, refresh_id):
+    '''Retrieves the work order for a refresh cycle identified by |id|.'''
+    return self._work_orders.Get(refresh_id)
+
+  def StartRefresh(self, refresh_id, tasks):
+    work_order = _RefreshWorkOrder(tasks)
+    return self._work_orders.Set(refresh_id, work_order)
+
+  def GetRefreshComplete(self, refresh_id):
+    '''Determines if a refresh cycle identified by |id| is complete. Returns
+    a |Future| which resolves to either |True| or |False|.'''
+    def is_work_order_complete(work_order):
+      # If the identified refresh cycle is not known, always return False.
+      if work_order is None:
+        return False
+      return (self._task_completions.GetMulti(
+                _TaskKey(refresh_id, task) for task in work_order.tasks)
+              .Then(lambda tasks: len(tasks) == len(work_order.tasks)))
+    return self._GetWorkOrder(refresh_id).Then(is_work_order_complete)
+
+  def MarkTaskComplete(self, refresh_id, task):
+    return self._task_completions.Set(_TaskKey(refresh_id, task),
+        _RefreshTaskCompletion(task))