[Tinyos-devel] issue with ResourceRequested

[Eric Decker]

Thanks for the reply.
The problem is a little more complicated than what I described.  So while I
can think
of ways to get ResourceDefaultOwner to work but by twisting it a bit.

The twist is A isn't on all the time.  When it is, after it has made some
progress and another
contender requests then we want A to give the resource up.

So I can get ResourceDefaultOwner to work, if A isn't on then it immediately
give up
the resource, otherwise it can determine when to give it up.  Not too bad.

But perhaps a more general solution would be along the lines of adding to
the Resource
interface.  I'm playing with Resource.othersWaiting().  This allows A to
take a look when
it wants.

thoughts,

eric


On Fri, Aug 8, 2008 at 11:18 PM, Philip Levis <pal at cs.stanford.edu> wrote:

>
> On Aug 8, 2008, at 10:15 PM, Eric Decker wrote:
>
>  I think I've found a problem with the structure of arbitration and
>> ResourceRequested.
>>
>> The purpose of ResourceRequested is to allow an owning resource user to be
>> informed
>> that other users have requested the resource so that the owner can release
>> it.
>>
>> There appears to be a start up condition that presents a problem.
>>  Consider
>> three users of the resource, A, B, and C.
>>
>> A wants to use the resource, R, but wants to release if B or C request.  A
>> will release
>> and immediately re-request.  That's the plan anyway.
>>
>> Consider, A requests the resource but it hasn't been granted yet.  While
>> A's grant is
>> pending, B and C request.  Then the granting task gives A the resource.
>>  But there
>> currently isn't anyway for A to know that there are outstanding requests
>> and because
>> the requests for B and C came in prior to A actually owning the resource
>> the
>> ResourceRequested signal wasn't signaled.
>>
>> Any thoughts on how to fix this?  The corner case makes it so
>> ResourceRequested
>> isn't as useful as it could be.
>>
>
> ResourceDefaultOwner can be used for this case.
>
> Note that this only allows two levels of priorities, as there's a single
> default owner, usually the power manager. It doesn't allow, for example, A
> always yields to B, B always yields to C. This would require knowing *who*
> requested, though, so being able to tell if there are pending requests would
> be insufficient.
>
> Phil
>



-- 
Eric B. Decker
Senior (over 50 :-) Researcher
Autonomous Systems Lab
Jack Baskin School of Engineering
UCSC
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