The top level comments strategy with queues seems similar, in that it isn't always possible. It requires the queues form a DAG, which is another word for partial ordering. Thus, requiring the locks form a partial ordering doesn't seem like a comparatively excessive restriction.
> doesn't seem like a comparatively excessive restriction
I think there are some applications and algorithms that we just don't know a way to create an ordering for realistically fine-grained locks.
For example airline seat reservation. Someone clicking on seats to reserve them. You can't apply locks in a total order because... you can't read the person's mind on what seat they're going to click next.
