Re: MPS: Area scanners

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> I remember now why I thought tht scan_bc would work they way I thought,
> so that I could compute a suitable scan end and so on. I read in the MPS
> docs this:
>
>   type mps_area_scan_t
>
>   Warning: Area scanning functions are subject to the same set of
>   restrictions as format scanning functions, described under Cautions.
>
> And Cautions links to a long list containing
>
>   7.3. Cautions
>
>   The MPS guarantees that format methods have exclusive access to the
>   object for the duration of the call. This guarantee may entail
>   suspending arbitrary threads. The methods that manipulate the object
>   must not perform any sort of inter-thread locking or communication.
>
> etc.
>
> Question is of course now, what is with the exclusive access for area
> scanning functions? Is that point a member of the "set of restrictions"?
>
> I can't answer that ATM. Maybe someone else can?

After reading the MPS Guide (Roots, Maintaining consistency, Scanning)
again, I must say I believe that the exclusive access is granted. The
docs everywhere basically equate format scanners and root scanning
functions.

(As an aside, I'm having a hard time imagining how stack scanning, area
scanning would word if that weren't true. It doesn't have to be
barriers, it could also temporarily halt threads.)

I'd be interested in others' opinions!