Refactor of caching & data storage part 1

core/url_data_cache.py

@@ -0,0 +1,23 @@
+import threading
+from datetime import timedelta
+
+from requests_cache import CachedSession
+
+# Cache for "semi-static" data retrieved from a URL. This is a layet of caching in addition to the normal caching of
+# spots, alerts and other data in the DataStore class. Its purpose is to avoid hitting remote endpoints frequently when
+# e.g. restarting Spothole many times during testing.
+_session = CachedSession("cache/semi_static_urls", expire_after=timedelta(days=1),
+                         allowable_codes=(200, 400, 401, 403, 404))
+_lock = threading.Lock()
+
+
+class _ThreadSafeSession:
+    """Wraps CachedSession with a lock to prevent concurrent SQLite access across threads. This allows a single object
+    to be used freely across the application."""
+
+    def get(self, *args, **kwargs):
+        with _lock:
+            return _session.get(*args, **kwargs)
+
+# Global object
+URL_DATA_CACHE = _ThreadSafeSession()