[MPIWG Fortran] F08 and pair types?

Tue Dec 8 14:13:47 CST 2015

We talked about this in detail at the SJC meeting this morning.

1. In MPI 3.1 section 5.9.4 p180, the following types are defined for fortran:

-----
MPI_2REAL
MPI_2DOUBLE_PRECISION
MPI_2INTEGER
-----

The following types are defined for C:

-----
MPI_FLOAT_INT
MPI_DOUBLE_INT
MPI_LONG_INT
MPI_2INT
MPI_SHORT_INT
MPI_LONG_DOUBLE_INT
-----

2. What Jeff Hammond asks is quite reasonable; it seems like we should use the Fortran derived types for MINLOC and MAXLOC functionality.  The old Fortran types (2REAL, 2DOUBLE_PRECISION, 2INTEGER) exist because there were no derived types back in the early 90's.  

I think we can make three proposals (NOTE: we need to cross reference these proposals with the RMA and collective working groups, but I want to get the Fortran stuff correct first):

2a. Change the definition of MPI_INTEGER from

-----
INTEGER FOO(2)
-----

to (please correct my fortran syntax; you all know I have some of it wrong below...)

------
TYPE :: MPI_2INTEGER_TYPE, SEQUENCE
    INTEGER VAL
    INTEGER LOC
END TYPE
-----

Craig assures me that these two Fortran types are exactly the same in memory representation.  Hence, even though we're technically changing the back-end representation of MPI_2INTEGER, we're changing it to an exactly equivalent definition.  Hence, old codes will not break -- we're just updating to use newer Fortran syntax.

Also, create two new types:

-----
TYPE :: MPI_REAL_INTEGER_TYPE, SEQUENCE
    REAL VAL
    INTEGER LOC
END TYPE

TYPE :: MPI_DOUBLE_PRECISION_INTEGER_TYPE, SEQUENCE
    DOUBLE PRECISION VAL
    INTEGER LOC
END TYPE
-----

And MPI datatypes corresponding to these two new types: MPI_REAL_INTEGER, MPI_DOUBLE_PRECISION_INTEGER

Note: with this one old type (2INTEGER) and the 2 new types (REAL_INTEGER and DOUBLE_PRECISION_INTEGER) correspond to the C types MPI_2INT, MPI_FLOAT_INT, MPI_DOUBLE_INT, respectively.

2b. Create three additional new Fortran types to make parity with the remaining C types (MPI_LONG_INT, MPI_SHORT_INT, MPI_LONG_DOUBLE_INT) -- the names below are completely up for negotiation, and may even be longer than 31 characters:

-----
TYPE :: MPI_LONGINTEGER_INTEGER_TYPE, SEQUENCE
    INTEGER(KIND=whatever) VAL
    INTEGER LOC
END TYPE

TYPE :: MPI_SHORTINTEGER_INTEGER_TYPE, SEQUENCE
    INTEGER(KIND=whatever) VAL
    INTEGER LOC
END TYPE

TYPE :: MPI_QUAD_PRECISION_INTEGER_TYPE, SEQUENCE
    DOUBLE PRECISION(KIND=whatever) VAL
    INTEGER LOC
END TYPE
-----

These 3 new Fortran types would then make Fortran support the same types as C.

3. Deprecate the 2 old MPI datatypes that we don't want to encourage use of anymore:

-----
MPI_2REAL
MPI_2DOUBLE_PRECISION
-----

Thoughts?

> On Dec 8, 2015, at 10:31 AM, Rolf Rabenseifner <rabenseifner at hlrs.de> wrote:
> 
> Sorry, but I was too fast with my negative answer.
> Yes, we have both arguments in the reduction
> and therefore it would be simple to add a new
> datatype to the list of allowed datatypes for 
> MIN/MAXLOC in Fortran.
> 
> Deprecation is too expensive and there is no need.
> 
> Rolf
> 
> 
> ----- Original Message -----
>> From: "Rolf Rabenseifner" <rabenseifner at hlrs.de>
>> To: "MPI-WG Fortran working group" <mpiwg-fortran at lists.mpi-forum.org>
>> Sent: Tuesday, December 8, 2015 7:22:45 PM
>> Subject: Re: [MPIWG Fortran] F08 and pair types?
> 
>> I'm sorry, but I expect that deprecation of a language binding
>> is not possible for a feature that is still valid in other languages (here C).
>> 
>> This means, that MINLOC and MAXLOC are as they are defined
>> and there is no reason to deprecate them.
>> They are not wrong and nobody want to pay the maintenance costs
>> for modifying existing applications that use MIN/MAXLOC.
>> 
>> The only way to do it better, is to add a new feature, e.g.,
>> MINLOC_F08 and MAXLOC_F08 which is valid only for the new
>> mpi_f08 module.
>> 
>> Rolf
>> 
>> ----- Original Message -----
>>> From: "Craig Rasmussen" <rasmus at cas.uoregon.edu>
>>> To: "MPI-WG Fortran working group" <mpiwg-fortran at lists.mpi-forum.org>
>>> Sent: Tuesday, December 8, 2015 6:30:37 PM
>>> Subject: Re: [MPIWG Fortran] F08 and pair types?
>> 
>>> The old stuff could be deprecated because all existing compilers that I know of
>>> support user-defined types. I assume that "deprecated" means that it still
>>> exists in libraries for legacy apps but is no longer really defined in the
>>> standard.
>>> 
>>> -craig
>>> 
>>> On Tue, Dec 8, 2015 at 9:19 AM, Craig Rasmusen < rasmus at cas.uoregon.edu > wrote:
>>> 
>>> 
>>> 
>>> Fortran is a modern language? Wut...
>>> 
>>> Actually seems like a simple and good change. For example, could define:
>>> 
>>> MPI_REAL_INT and MPI_INTEGER_INT
>>> 
>>> However, I'm not sure what would be in the structs (user-defined types). I'll
>>> have to ask Squyres what the text following
>>> 
>>> "The datatype MPI_FLOAT_INT is as if defined by the following sequence of
>>> instructions"
>>> 
>>> means.
>>> 
>>> -craig
>>> 
>>> On Mon, Dec 7, 2015 at 4:20 PM, Jeff Hammond < jeff.science at gmail.com > wrote:
>>> 
>>> 
>>> 
>>> I have a reasonable understanding of why the legacy Fortran bindings use 2REAL,
>>> 2DOUBLE_PRECISION and 2INTEGER with {MAX,MIN}LOC reductions.
>>> 
>>> Doesn't modern Fortran provide a way to create struct-like things along the
>>> lines of C, such that more appropriate pair types could be used for these?
>>> 
>>> The relevant text is section 5.9.4 of MPI 3.1.
>>> 
>>> Jeff
>>> 
>>> --
>>> Jeff Hammond
>>> jeff.science at gmail.com
>>> http://jeffhammond.github.io/
>>> 
>>> _______________________________________________
>>> mpiwg-fortran mailing list
>>> mpiwg-fortran at lists.mpi-forum.org
>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>>> 
>>> 
>>> 
>>> _______________________________________________
>>> 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)
>> _______________________________________________
>> 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)
> _______________________________________________
> mpiwg-fortran mailing list
> mpiwg-fortran at lists.mpi-forum.org
> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran

-- 
Jeff Squyres
jsquyres at cisco.com
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