[Predator] Add local cache for get command output.

appengine/findit/common/cache_decorator.py

Index: appengine/findit/common/cache_decorator.py
diff --git a/appengine/findit/common/cache_decorator.py b/appengine/findit/common/cache_decorator.py
index 6f1bb1efe42dc866aa7841e4df8eb84db698f26f..9fd67867a42f9af66301c415d1983f6ec9da27fa 100644
--- a/appengine/findit/common/cache_decorator.py
+++ b/appengine/findit/common/cache_decorator.py
@@ -39,11 +39,16 @@ import functools
 import hashlib
 import inspect
 import logging
+import os
 import pickle
+import threading
 import zlib
 
 from google.appengine.api import memcache
 
+_DEFAULT_LOCAL_CACHE_DIR = os.path.join(os.path.expanduser('~'),
+                                        '.culprit_finder', 'local_cache')
+
 
 class Cacher(object):
   """An interface to cache and retrieve data.
@@ -133,6 +138,38 @@ class CompressedMemCacher(Cacher):
     return len(keys_not_set) == 0
 
 
+class LocalCacher(Cacher):
+  """Cacher that uses local files to cache data."""
+
+  lock = threading.Lock()
+
+  def __init__(self, cache_dir=_DEFAULT_LOCAL_CACHE_DIR):

[stgao, 2016/11/02 02:15:07]

Can we avoid the default value, and let client pass it over instead?

[Sharu Jiang, 2016/11/08 01:17:12]

Done.

+    self.cache_dir = cache_dir
+    if not os.path.exists(cache_dir):  # pragma: no cover.
+      os.makedirs(cache_dir)
+
+  def Get(self, key):
+    with LocalCacher.lock:
+      path = os.path.join(self.cache_dir, key)
+      if not os.path.exists(path):
+        return None
+
+      try:
+        with open(path) as f:
+          return pickle.loads(zlib.decompress(f.read()))
+      except Exception as e:  # pragma: no cover.
+        logging.error('Failed loading cache: %s', e)
+        return None
+
+  def Set(self, key, data):  # pylint: disable=W
+    with LocalCacher.lock:
+      try:
+        with open(os.path.join(self.cache_dir, key), 'wb') as f:
+          f.write(zlib.compress(pickle.dumps(data)))
+      except Exception as e:  # pragma: no cover.
+        logging.error('Failed setting cache for key %s: %s', key, e)
+
+
 def _DefaultKeyGenerator(func, args, kwargs):
   """Generates a key from the function and arguments passed to it.