Add async lock for atomic graph database operations

• Introduced graph_db_lock mechanism
• Ensured atomic node/edge merge and insert operation

lightrag/operate.py

@@ -519,6 +519,11 @@ async def extract_entities(
         for k, v in m_edges.items():
             maybe_edges[tuple(sorted(k))].extend(v)
 
+    from .kg.shared_storage import get_graph_db_lock
+    graph_db_lock = get_graph_db_lock(enable_logging = True)
+    
+    # Ensure that nodes and edges are merged and upserted atomically
+    async with graph_db_lock:
         all_entities_data = await asyncio.gather(
             *[
                 _merge_nodes_then_upsert(k, v, knowledge_graph_inst, global_config)