The code for `#stop` has

```ruby
return if clean_up_for_graceful_shutdown
hard_shutdown_in timeout if shutdown
```

In the case where @busy is empty, it will call `terminate` which will `requeue` and call `after (0) {signal(:shutdown)}` which should be what it used to do (except now we're requeuing).

In the case where @busy is not empty and it spins, it'll return false so the code

```ruby
hard_shutdown_in_timeout if shutdown`
```

will get called by `#stop`.