Use _stop_event consistently across all threads as the way to signal that it should stop. Add thread joins with timeouts to allow the program to exit cleanly

core/live_data_cache.py

@@ -23,6 +23,7 @@ class LiveDataCache:
         self._snapshot_dir = snapshot_dir
         self._disk_cache = diskcache.Cache(str(snapshot_dir))
         self._stop_event = threading.Event()
+        self._snapshot_thread = None
         self._load_snapshot()
         self._start_periodic_snapshot(snapshot_interval_sec)
 
@@ -93,10 +94,16 @@ class LiveDataCache:
             while not self._stop_event.wait(timeout=interval):
                 self.save_snapshot()
 
-        t = threading.Thread(target=loop, name=f"LiveDataCache-Snapshot-{self._snapshot_dir}", daemon=True)
-        t.start()
+        self._snapshot_thread = threading.Thread(
+            target=loop, name=f"LiveDataCache-Snapshot-{self._snapshot_dir}", daemon=True
+        )
+        self._snapshot_thread.start()
 
     def close(self):
         self._stop_event.set()
+        if self._snapshot_thread:
+            self._snapshot_thread.join(timeout=15)
+            if self._snapshot_thread.is_alive():
+                logger.warning(f"LiveDataCache snapshot thread for {self._snapshot_dir} did not exit on time.")
         self.save_snapshot()
         self._disk_cache.close()