Function async_executor 

pub fn async_executor<C, F, Fut, R>(
    f: F,
) -> Box<dyn Fn(Arc<C>) -> Pin<Box<dyn Future<Output = Box<dyn Any + Send>> + Send>> + Send + Sync>
where
    F: Fn(Arc<C>) -> Fut + Send + Sync + 'static,
    Fut: Future<Output = R> + Send + 'static,
    R: Any + Send + 'static,