[cap-talk] Capability-based Projects - updated list

[David Hopwood]

Jonathan S. Shapiro wrote:
> On Thu, 2007-08-02 at 10:15 -0700, Mark Miller wrote:
>> On 8/2/07, Jonathan S. Shapiro <shap at eros-os.com> wrote:
>>
>>> Spring is not a capability system.
>>
>> Since the Spring folk seem to claim it is, it would be good to clarify
>> the matter. Could you elaborate? Thanks.
>
> Actually, I don't consider Mach a capability system either.
> 
> One issue is that the unit named by descriptors in both systems is the
> server, not the object implemented by the server.

That doesn't seem to be consistent with section 7 of
<http://research.sun.com/features/tenyears/volcd/papers/Mitchell.pdf>,
which says that a "door" can point to a specific "front object" within
a server. (If that were implemented using an unprotected payload to
identify the front object, then the given example would not work.)

In any case, note that Spring applications did not access descriptors
directly; they only performed object invocations via client stubs. So
if you're correct in saying that descriptors (doors) only pointed to a
server, then this was a very near miss: applications would not have
needed to be changed in order for a door to point to an object instead.

-- 
David Hopwood <david.hopwood at industrial-designers.co.uk>