tokens: If you created your managed object context on the main thread ( or queue ) , you can only use it from there - so any Core Data operation you perform on that context will block the main thread , and in turn the UI .
ner_tags: O O O O O O O O O O O O O B-Data_Structure O O O O O O O O O O O O B-Library I-Library O O O O O O O O O O O O O O O O O O