[Beowulf] no shared state, shared state with explicit locking, shared state without explicit locks

[Mark Hahn]

this question is referring to a thread here:
http://developers.slashdot.org/article.pl?sid=07/10/03/0021253&from=rss

> but I'll bet that those three classifications (no shared state, shared
> state with explicit locking, shared state without explicit locks)

I think there's one big distinction: shared or not shared.  I figured 
the author was talking about functional/dataflow languages which don't
have shared state (including MPI, in a sense) versus languages which 
assume shared memory such as OpenMP.

within the shared-memory approach, explicit locking is pretty clear.
I presume "without explicit locks" just means crude systems like Java's
monitored data types.

IMO, the penitude of parallel packages mainly shows that we don't have 
good answers yet...