You have to tag a function as async if interacts with anything async and doesn't create an executor itself. Executors have functionality that let you start an a

You have to tag a function as async if interacts with anything async and doesn't create an executor itself. Executors have functionality that let you start an async fn/block in the currently instantiated executor and return immediately. Such a function wouldn't need to be marked async, IIUC. Note that marking a function as async is only syntactic sugar for a function that returns a future.