Function defer 

pub fn defer<Args, T, F>(f: F, args: Args) -> DeferredFuture<Args, T, F> 
where
    Args: Send + 'static,
    T: Send + 'static,
    F: FnOnce(Args) -> T + Send + 'static,

Defers execution of a blocking function to another thread returning a DeferredFuture, which does nothing until it is awaited.