[Tinyos-devel] Resource.isOwner() can return false information

[Kevin Klues]

The fix has now been checked in.

Kevin

On 8/24/07, Kevin Klues <klueska at gmail.com> wrote:
> Your right.  The problem is having the id set incorrectly between
> pending requests.    The fix you propose will do the trick.
> Alternatively, resId could be set to NO_RES just before posting the
> granted task.  I think your approach is better though, since under
> most circumstances it is unnecessary to actually change the resId
> between a release and granting a pending request.  The state of the
> arbiter prevents it from doing anything funky in the meantime.  Since
> resources are released more often than isOwner() is called, it makes
> sense to add the check on the state of the arbiter in the body of the
> isOwner() command rather than explicitly change the resId everytime a
> resource is released.  Plus, doing a comparison takes less cycles than
> doing an assignment.  Thanks for pointing out this bug.  I'll make the
> change today and check it into cvs.
>
> Kevin
>
> On 8/24/07, Roman Lim <rlim at ee.ethz.ch> wrote:
> > example case:
> > client0 requests resource
> > client1 requests resource
> > client0 gets the resource granted
> > client0 has a loop wherein it:
> >         *releases the resource on a certain condition
> >         *exits the loop, if the resource was released (e.g. isOwner() returns
> > false)
> >
> > in this case, isOwner() will always return 'true' because in the current
> > implementation, 'resId' is changed in a task that will run after the
> > loop of client0 is finished:
> > in the case of SimpleArbiter, 'resId' is only set to NO_RES, if no
> > request is pending upon release. In the other case, 'resId' remains
> > client0, until the granted task gets executed (after that, it changes to
> > client1).
> > in the case of normal Arbiters 'resId' is also only set to the default
> > owner's id, if no request is pending at the time when the resource was
> > released.
> >
> > by my understanding, isOwner() should return false after the command
> > release() has been called.
> >
> > roman
> >
> > Kevin Klues wrote:
> > > Can you give a use case where this actually occurs?  I understand your
> > > concern... as well as your proposed solution,but as it is implemented
> > > now, upon release 'resId' is either set to NO_RES in the case of
> > > SimpleArbiters or the resource is handed over to its default owner in
> > > the case of normal Arbiters.  I'm not sure under what circumstances it
> > > would falsely return TRUE.
> > >
> > > Kevin
> > >
> > > On 8/23/07, Roman Lim <rlim at ee.ethz.ch> wrote:
> > >> Hi
> > >> I just had a case, where I found a call to Resource.isOwner() returning
> > >> TRUE, even when the Resource was just released.
> > >>
> > >> If there is a request pending while releasing the resource, resId does
> > >> not get assigned another id immediately, but only when the granted task
> > >> gets executed. A call to Resource.isOwner() between release and granted
> > >> will therefore return true for the component that just released the
> > >> resource, because isOwner just compares the id of the caller and the
> > >> resId to determine the return value.
> > >>
> > >> I suggest to check the state of the arbiter in the isOwner() command,
> > >> too and return true, if id==resId and state==RES_BUSY.
> > >>
> > >> Roman
> > >> _______________________________________________
> > >> Tinyos-devel mailing list
> > >> Tinyos-devel at Millennium.Berkeley.EDU
> > >> https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-devel
> > >>
> > >
> > >
> >
> >
>
>
> --
> ~Kevin
>


-- 
~Kevin