#2 Job cancellation

[Kazuyuki Shudo]

In P3, a job is represented by a peer-group
advertisement (adv) and there is no way to delete such
an advertisement currently.

An advertisement is cached by rendevzous peers and
propagates between them until their expiration time.
Therefore it is very hard to delete all of advs on network.

But it is possible to implement job removal by getting
an adv to represent a removed job in addition to an
existing job. Controller will be able to replace an adv
representing an exisiting job by a newly updated adv
representing a removed job.