[MPIWG Fortran] Data type of F08 subarray

Tue May 13 14:19:53 CDT 2014

On Tue, May 13, 2014 at 2:00 PM, Bill Long <longb at cray.com> wrote:

>
> On May 13, 2014, at 12:44 PM, Junchao Zhang <jczhang at mcs.anl.gov> wrote:
>
> >
> > On Tue, May 13, 2014 at 11:56 AM, Rolf Rabenseifner <
> rabenseifner at hlrs.de> wrote:
> > > REAL s(100)
> > > MPI_SEND(s (1:100:5) , 3, dtype, ...)
> > > dtype can only be MPI_REAL. In other words, dtype is kind of
> > > redundant here since the type map is actually specified by the
> > > subarray.
>
> Right.  The descriptor for the first argument has a member whose value is
> a type code.  In principal the library could verify this is compatible with
> the data type handle supplied as the third argument, and issue an error if
> not.  Perhaps in a “debug” mode.
>
> >
> > No, if dtype is a vector then it is applied to a virtual
> > contiguous array that consists of s(1), s(6), s(11) …
>
> dtype is not  a vector, is it?  That argument is a scalar of type
> TYPE(MPI_DATATYPE).  At least that is what the interface says.
>

Rolf meant dtype is an MPI datatype created by MPI_Type_vector.  For this
case, I will have two datatypes, one from the MPI_Datatype argument, the
other from the choice buffer itself. It is hard to implement that. Perhaps
it is useless since it obscures the program.

>
> Cheers,
> Bill
>
>
> >
> > That is nasty. Then I will have two data types. I even can not assume
> any relationship between the two types. I have to allocate a scratch buffer
> for the virtual contiguous array in MPI_ISEND etc, do memory copying and
> then free the buffer in MPI_WAIT. I'm not sure one can implement it
> efficiently.
> >
> >
> >
> > ----- Original Message -----
> > > From: "Junchao Zhang" <jczhang at mcs.anl.gov>
> > > To: "MPI-WG Fortran working group" <mpiwg-fortran at lists.mpi-forum.org>
> > > Sent: Tuesday, May 13, 2014 6:23:08 PM
> > > Subject: Re: [MPIWG Fortran] Data type of F08 subarray
> > >
> > >
> > >
> > > Thanks, Rolf. And I feel there is a jump from contiguous subarray to
> > > non-contiguous subarray.
> > >
> > >
> > >
> > > For contiguous subarray, such as
> > >
> > >
> > >
> > >
> > > REAL s(100)
> > >
> > > MPI_SEND(s(2:50), 3, dtype, ...) s only gives the start address.
> > > dtype can be anything, e.g., either a basic type or a derived type
> > > created by MPI_Type_vector() etc.
> > >
> > >
> > >
> > > For non-contiguous subarray, such as
> > >
> > >
> > >
> > > REAL s(100)
> > > MPI_SEND(s (1:100:5) , 3, dtype, ...)
> > > dtype can only be MPI_REAL. In other words, dtype is kind of
> > > redundant here since the type map is actually specified by the
> > > subarray.
> > >
> > >
> > >
> > >
> > >
> > >
> > > --Junchao Zhang
> > >
> > >
> > > On Tue, May 13, 2014 at 10:20 AM, Rolf Rabenseifner <
> > > rabenseifner at hlrs.de > wrote:
> > >
> > >
> > > Dear Junchao,
> > >
> > > MPI-3.0 p25:7-8 describes only communication with language type
> > > of the buffer argument matches to the MPI datatype used
> > > in the datatype argument.
> > > Same p83:36-37.
> > >
> > > Therefore, the answer is no and the compiler cannot detect
> > > a mismatch beteen language buffer specification and
> > > MPI datatype specification.
> > >
> > > I hope my answer could help.
> > >
> > > Best regards
> > > Rolf
> > >
> > >
> > >
> > >
> > > ----- Original Message -----
> > > > From: "Junchao Zhang" < jczhang at mcs.anl.gov >
> > > > To: "MPI-WG Fortran working group" <
> > > > mpiwg-fortran at lists.mpi-forum.org >
> > > > Sent: Tuesday, May 13, 2014 5:08:30 PM
> > > > Subject: [MPIWG Fortran] Data type of F08 subarray
> > > >
> > > >
> > > >
> > > >
> > > > p626 of MPI-3.0 gives such an example
> > > >
> > > >
> > > > REAL s(100), r(100)
> > > > CALL MPI_Isend(s(1:100:5), 3, MPI_REAL, ..., rq, ierror)
> > > >
> > > > All nonblocking MPI functions behave as if the user-specified
> > > > elements of choice buffers are copied to a contiguous scratch
> > > > buffer
> > > > in the MPI runtime environment. All datatype descriptions (in the
> > > > example above, “3, MPI_REAL”) read and store data from and to this
> > > > virtual contiguous scratch buffer ...
> > > >
> > > > Here, data type of s(100) match with MPI_REAL, so everything is
> > > > fine.
> > > > But I want to know if MPI permits mismatched types, for example,
> > > > can
> > > > s(100) be an integer array? If the answer is no, then compilers can
> > > > not detect this error ; if yes, then it is hard to implement that.
> > > > To avoid memory copying to a scratch buffer, I want to use MPI
> > > > datatypes. But if I have two types, one is given by the choice
> > > > buffer itself, the other is given by the MPI_Datatype argument, how
> > > > could I do that?
> > > >
> > > > Any thoughts?
> > > >
> > > > Thanks
> > > >
> > > > --Junchao Zhang
> > > > _______________________________________________
> > > > mpiwg-fortran mailing list
> > > > mpiwg-fortran at lists.mpi-forum.org
> > > > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
> > >
> > > --
> > > Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
> > > High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
> > > University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
> > > Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
> > > Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307)
> > > _______________________________________________
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> > >
> > > _______________________________________________
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> >
> > --
> > Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
> > High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
> > University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
> > Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
> > Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307)
> > _______________________________________________
> > mpiwg-fortran mailing list
> > mpiwg-fortran at lists.mpi-forum.org
> > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
> >
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>
> Bill Long
>       longb at cray.com
> Fortran Technical Suport  &                                  voice:
> 651-605-9024
> Bioinformatics Software Development                     fax:  651-605-9142
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