opencog-dev team mailing list archive

["Linas Vepstas" <linasvepstas@xxxxxxxxx>]

2008/9/30 Ben Goertzel <ben@xxxxxxxxxxxx>:
>
> Linas,
>
> But the truth values, attention values, etc. associated with an Atom are not
> immutable ...
>
> so for instance, a MindAgent could add a new Version within a
> CompositeTruthValue
> object associated with an Atom ...

Hmm. Well, if one thread is looking at a truth value while
another is setting it, then, in today's system, there would be
a crash (because the old value is deleted, and
Atom::getTruthValue() returns a reference).

This could be solved by having AtomTruthValue() return
a copy, instead of a reference; but then one pays the
penalty of creating a copy, for each and every access.
(this is "copy-on-read").

By contrast, in a garbage-collected system, the worst that
would happen is that someone is looking at an "old, stale"
truth value; as opposed to crashing.  By the principles
of concurrency, there's "no such thing" as an "old stale
value" in between synchronization primitives.

--linas