Scheduled action no interrupt

At the end of the run, ScheduledAction unsubscribes itself which triggers a set of cleanup actions, and since it is also the way to cancel a running action, it calls future.cancel(true) as well which interrupts the task in the underlying executor framework. However, on a normal completion path, it is unnecessary to interrupt itself at the end of the run since it will complete anyway, and not to mention, it has some performance implications for short running tasks. The downside is the +4 bytes per ScheduledAction.
What is the cost of a failed CAS compared with a volatile read? 

I'm not arguing that testing isUnsubscribed() is cheap or expensive, just that it's not atomic. We could end up calling unsubscribe twice without the CAS check.