PDD 25 "Concurrency" - first review

[Allison Randal]

I've finished a first pass through PDD 25 on threading/concurrency. It's 
largely a collection of prior thinking on the subject. Before I start 
kicking it into a more structured form, I'd like to do an initial round 
of discussion. This is your chance to mention anything you hoped or 
expected from Parrot's concurrency models. How do you plan to use 
concurrency, and in what contexts? What's your favorite concurrency 
model and why should we consider using it? How integral a role should 
the new STM play in Parrot's concurrency? Etc.

I've changed the name of the PDD from "Threads" to "Concurrency" 
because: a) the notion of "threads" seems to have taken on mythical 
proportions, so this is a symbolic step toward practicality, and b) 
Parrot has more than one concurrency model, and this PDD will be the 
overview of all them, plus the ways the various models interact.

Allison