Combiner functions with priorities

[adferguson]

There is an interest in having HFT combiner functions which support priorities.

basically, the scenario here is:

• we have 10mbps of bandwidth
• user A reserves 10mbps for 2 hours
• after 1 hour, user B comes along and wants to reserve 10mbps for 2 hours

today, PANE says "no, wait your turn" because of the "a promise is a promise" mantra. :-) in the current system, you could design your share tree so that you don't get into this situation if you don't want to (eg, only let user A issue a hint for 10mbps of bandwidth, instead of a reservation).

I think combiner functions with priorities make sense to implement once we have the callbacks in place, since we should notify the application/user anytime PANE breaks a previous promise.