pub fn spawn_obj_ok(&self, future: FutureObj<'static, ()>) {
        let task = Task {
            future,
            wake_handle: Arc::new(WakeHandle { exec: self.clone(), mutex: UnparkMutex::new() }),
            exec: self.clone(),
        };
        self.state.send(Message::Run(task));
    }
Spawns a future that will be run to completion.

> **Note**: This method is similar to `Spawn::spawn_obj`, except that
>           it is guaranteed to always succeed.
futures-executor/src/thread_pool.rs