rebaseline_server: cache results in long-running ImageDiffDB instance

gm/rebaseline_server/imagediffdb.py

 #!/usr/bin/python
 
 """
 Copyright 2013 Google Inc.
 
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 
 Calulate differences between image pairs, and store them in a database.
 """
@@ skipping 157 matching lines @@
       # write the image files into, rather than having to move them around
       # after skpdiff writes them out.
       shutil.copyfile(rgb_diff_path,
                       os.path.join(storage_root, RGBDIFFS_SUBDIR, basename))
       shutil.copyfile(white_diff_path,
                       os.path.join(storage_root, WHITEDIFFS_SUBDIR, basename))
 
     finally:
       shutil.rmtree(skpdiff_output_dir)
 
+  # TODO(epoger): Use properties instead of getters throughout.
+  # See http://stackoverflow.com/a/6618176
   def get_num_pixels_differing(self):
     """Returns the absolute number of pixels that differ."""
     return self._num_pixels_differing
 
   def get_percent_pixels_differing(self):
     """Returns the percentage of pixels that differ, as a float between
     0 and 100 (inclusive)."""
     return ((float(self._num_pixels_differing) * 100) /
             (self._width * self._height))
 
@@ skipping 26 matching lines @@
     """
     Args:
       storage_root: string; root path within the DB will store all of its stuff
     """
     self._storage_root = storage_root
 
     # Dictionary of DiffRecords, keyed by (expected_image_locator,
     # actual_image_locator) tuples.
     self._diff_dict = {}
 
+  @property
+  def storage_root(self):
+    return self._storage_root
+
   def add_image_pair(self,
                      expected_image_url, expected_image_locator,
                      actual_image_url, actual_image_locator):
     """Download this pair of images (unless we already have them on local disk),
     and prepare a DiffRecord for them.
 
     TODO(epoger): Make this asynchronously download images, rather than blocking
     until the images have been downloaded and processed.
     When we do that, we should probably add a new method that will block
     until all of the images have been downloaded and processed.  Otherwise,
@@ skipping 90 matching lines @@
 
   Args:
     expected_image_locator: locator string pointing at expected image
     actual_image_locator: locator string pointing at actual image
 
   Returns: already-sanitized locator where the diffs between expected and
       actual images can be found
   """
   return "%s-vs-%s" % (_sanitize_locator(expected_image_locator),
                        _sanitize_locator(actual_image_locator))