[Mpi3-rma] Target displacement sign issue

[Hubert Ritzdorf]

Hi,

Possibly another solution:

(*) Let MPI_AINT_MAX the maximal value of MPI_Aint variable
(*) Let the window_base of a window created by MPI_WIN_CREATE_DYNAMIC
    be MPI_AINT_MAX + 1
(*) Define a new function MPI_Get_address_dynamic returning the
    address of a location relative to MPI_AINT_MAX + 1
(*) Remove the non-negative qualification in the description
    of target_disp in MPI_{Put/Get/Accumulate/...).   

Hubert

> -----Original Message-----
> From: mpi3-rma-bounces at lists.mpi-forum.org [mailto:mpi3-rma-
> bounces at lists.mpi-forum.org] On Behalf Of Hubert Ritzdorf
> Sent: Tuesday, September 04, 2012 7:23 PM
> To: MPI 3.0 Remote Memory Access working group
> Subject: Re: [Mpi3-rma] Target displacement sign issue
> 
> Hi,
> 
> MPI_Get_address returns an MPI_Aint which is signed.(integer).
> 
> C:
> MPI_Aint's may be used in Reduce Operations with Min/Max
> or the application can internally use min/max computations.
> Can anybody guarantee that applications don't perform
> min/max operations on these displacements (which results in different
> results for unsigned and signed variables) or use derived values of these
> displacements in other signed/unsigned significant cases.
> 
> Fortran:
> MPI_BOTTOM is a variable in a common block/module. Thus,
> MPI_Get_address might really return a signed integer (depending on the
> compiler).
> Fortran doesn't have unsigned integers and cannot handle them.
> Thus, the non-negative integer specification for target_disp in
> MPI_{Put/Get/Accumulate/...)
> might be incorrect for Fortran and MPI_Win_Create_dynamic().
> 
> Hubert
> ________________________________________
> From: mpi3-rma-bounces at lists.mpi-forum.org [mpi3-rma-bounces at lists.mpi-
> forum.org] on behalf of Jim Dinan [dinan at mcs.anl.gov]
> Sent: Tuesday, September 04, 2012 5:10 PM
> To: mpi3-rma at lists.mpi-forum.org
> Subject: Re: [Mpi3-rma] Target displacement sign issue
> 
> Hi All,
> 
> This is an important issue that we need to resolve before releasing the
> 3.0 spec.  Please take a look and send feedback.
> 
> Dave has voiced a concern that the implicit type conversion in my
> proposed text below may not be portable.  If anyone has more experience
> with this aspect (signed->unsigned conversion) of C/Fortran/etc type
> systems, please chime in.
> 
>   ~Jim.
> 
> On 8/28/12 2:29 PM, Jim Dinan wrote:
> > Hi All,
> >
> > Here is the suggested change to address this issue.  In the paragraph on
> > page 425, line 1, add the bracketed sentence:
> >
> > In the case of a window created with MPI_WIN_CREATE_DYNAMIC, the
> > target_disp for all RMA functions is the address at the target; i.e.,
> > the effective window_base is MPI_BOTTOM and the disp_unit is one. [Thus,
> > for dynamic windows, the target_disp argument to all RMA functions in
> > interpreted as unsigned.] Users should use MPI_GET_ADDRESS at the target
> > process to determine the address of a target memory location and
> > communicate this address to the origin process.
> >
> >    ~Jim.
> >
> > On 8/28/12 9:46 AM, Jim Dinan wrote:
> >> Hi All,
> >>
> >> Currently, target displacements in put/get/acc/etc are defined to be
> >> non-negative integers of type, MPI_Aint.  MPI_Aint is defined to be a
> >> signed integer.  However, displacements associated with dynamic windows
> >> are addresses (unsigned) and can range into the space of negative
> >> integers.
> >>
> >> It seems like the least impact change would be to add a special case
> >> that the displacement argument will be interpreted as unsigned for
> >> dynamic windows.  Changing the interface to take an 'unsigned MPI_Aint'
> >> would be the most clear (and preserve the existing and intended new
> >> semantics), but would break backward compatibility.
> >>
> >> Interested to hear your thoughts.
> >>
> >>   ~Jim.
> _______________________________________________
> mpi3-rma mailing list
> mpi3-rma at lists.mpi-forum.org
> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
> 
> 
>  Click
> https://www.mailcontrol.com/sr/O6SiJI5AP4bTndxI!oX7Up2F0f+S6NySj!qlvEoKFyZ
> NTFyVkk9WjRzJbmnfHdyw83VGVWKbSfC8ewgPpp7kgg==  to report this email as
> spam.
> 
> _______________________________________________
> mpi3-rma mailing list
> mpi3-rma at lists.mpi-forum.org
> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma