Subject: Problem: group descriptors & coherency

From: [email-masked]
Date: Wed, 10 Mar 93 09:12:10 PST

Here's a problem that applies to all proposals.

Groups are dynamic.  

Group ID's must be reusable unless they are very long or we
bound the number of groups that can ever get created.

Every reference to a group ID must be interpreted
in terms of the current definition.

This introduces a coherency problem analogous to shared memory.

There are at least a half-dozen solutions to the coherency problem,
with wide differences in overhead costs and convenience for the user.
Explicit coherency control by the application tends to be cheaper but
less convenient than implicit control.

==> I suggest that each proposal include some mechanism for solving
    the group ID coherency problem, including a discussion of its
    probable costs.

Aside: Coherency of tid's seems like a smaller problem, based on the
assumption that processes will come and go much less often than
groups will be re-formed.  But I'm not sure that we can ignore it.

--Rik