Function spawn_on 

pub fn spawn_on<F>(
    name: &'static str,
    future: F,
    handle: &Handle,
) -> TaskHandle<F::Output> 
where
    F: Future + Send + 'static,
    F::Output: Send + 'static,

Spawn future as a task named name on the runtime behind handle.

Returns without awaiting or waiting on the task, as spawn does, and may be called from outside any runtime.