This field is not really necessary in ```NewThreadScheduler``` but essential in ```EventLoopsScheduler``` to support the removal of the task from the ```innerSubscription``` once the task has completed. Besides, a ```ScheduledAction``` is already heavy because the underlying ```ScheduledFutureTask``` keeping all kinds of state information. I can't think of any other way to eliminate this and have the whole thing remain correct from the unsubscription perspective.