add heavy caching to mapdata api

src/c3nav/mapdata/lastupdate.py

@@ -0,0 +1,33 @@
+import os
+import pickle
+from contextlib import contextmanager
+
+from django.conf import settings
+from django.utils import timezone
+
+last_mapdata_update_filename = os.path.join(settings.DATA_DIR, 'last_mapdata_update')
+last_mapdata_update_decorator_depth = 0
+
+
+def get_last_mapdata_update(default_now=False):
+    try:
+        with open(last_mapdata_update_filename, 'rb') as f:
+            return pickle.load(f)
+    except:
+        return timezone.now() if default_now else None
+
+
+@contextmanager
+def set_last_mapdata_update():
+    global last_mapdata_update_decorator_depth
+    if last_mapdata_update_decorator_depth == 0:
+        try:
+            os.remove(last_mapdata_update_filename)
+        except:
+            pass
+    last_mapdata_update_decorator_depth += 1
+    yield
+    last_mapdata_update_decorator_depth -= 1
+    if last_mapdata_update_decorator_depth == 0:
+        with open(last_mapdata_update_filename, 'wb') as f:
+            pickle.dump(timezone.now(), f)