I don't have time to look into Serhiy's changes right now but here's a brief summary:

- there's a (I think) *minor* downside in terms of backward compatibility because scheduler._queue won't be updated after cancel() (basically this is the reason why this issue was waiting for Raymond's approval)

- the upside (other than the great speedup) is that I doubt anyone relies on that and scheduler._queue is not supposed to be used in the first place

- tulip's scheduler already provides something very similar to what this patch proposes so no action should be taken on that front


I personally think this should go in but I'd like to hear an OK from Raymond first.