[cap-talk] Petnames versus E-order with ocaps

[Karp, Alan H]

Charles Landau wrote:
> >
> > A petname is a one-to-one mapping between an object reference and a
> > name binding.
> 
> Forgive me, but I have enough trouble understanding this stuff, and
> this
> seems to be imprecise. This reminds me of the confusion of Alice in
> Wonderland between objects, names, and what things are called. Do you
> mean to say, a petname is a one-to-one mapping between an object
> reference and a name? Which I think is the same as saying, a petname is
> a one-to-one binding of an object reference to a name?
>
Sorry for the poor wording.  I realized it about an hour after clicking Send.  You are correct, as are the other folks who corrected me.
> 
> Those two references have different properties, so they are different
> references, in other words references to different objects. So they
> should have different petnames.
>
In what way are the properties different.  In a single vat, the reference is just a pointer to a local object.

________________________
Alan Karp
Principal Scientist
Virus Safe Computing Initiative
Hewlett-Packard Laboratories
1501 Page Mill Road
Palo Alto, CA 94304
(650) 857-3967, fax (650) 857-7029
http://www.hpl.hp.com/personal/Alan_Karp


> -----Original Message-----
> From: cap-talk-bounces at mail.eros-os.org [mailto:cap-talk-
> bounces at mail.eros-os.org] On Behalf Of Bill Frantz
> Sent: Wednesday, January 28, 2009 2:00 PM
> To: General discussions concerning capability systems.
> Subject: Re: [cap-talk] Petnames versus E-order with ocaps
> 
> alan.karp at hp.com (Karp, Alan H) on Wednesday, January 28, 2009 wrote:
> 
> >E-order guarantees the following property.  If Alice sends a message
> to Carol, and then Alice sends a
> >message to Bob containing a reference to Carol, and Bob uses that
> reference to send a message to
> >Carol, Carol will receive the message from Bob after she receives the
> message from Alice.  (Did I get
> >that right, MarkM?)  That ordering is not guaranteed if Bob sends a
> message to Carol using a reference
> >not obtained from Alice.
> >
> >A petname is a one-to-one mapping between an object reference and a
> name binding.  If Bob has a
> >reference to Carol that he calls foo, a reference to Carol that Bob
> receives from Alice will also be
> >denoted foo.
> >
> >Here's where the versus comes in.  Bob would like to ensure that a
> message he sends to Carol arrives
> >after any messages Alice sent to Carol before she sent Bob a reference
> to Carol.  In a petname system,
> >he can't do that if he had a reference to Carol before Alice sent him
> one.  Is that a problem or a
> >feature?
> 
> I think, in the case of CapTP (the part of the E implementation which
> is
> responsible for transferring capabilities over connections), that the
> reference to Carol Bob receives from Alice will look different from the
> one
> he already has until the three-party handoff completes. Any kind of EQ
> operation on the capabilities will also have to wait for the three-
> party
> handoff. So, Bob will not know they are the same reference until the E
> ordering guarantee has, in fact, been met.
> 
> MarkM?  Kevin?
> 
> Cheers - Bill
> 
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