# [MPIWG Fortran] Question about MPI_Status_f2f08() and _f082f()

Rolf Rabenseifner rabenseifner at hlrs.de
Wed Jul 15 14:08:18 CDT 2020

Dear Hubert and Jeff,

> Ø I'm a little curious as to why we conspicuously left it out of mpif.h.

of the operators .NE. and .EQ. for all TYPE(MPI_....).
I'm not sure whether such declaration is allowed outside of a module.

The use of mpif.h was already deprecated, i.e., if somebody
wants to use mpi_f08 stuff in old code, he or she must
first substitute the include mpif.h by use mpi.

> ... But it was never intended that the programmer
> does this transformation within the old Fortran subroutine (and old Fortran 77
> compiler or using Fortran 77 language kind wouldn’t support Type(MPI_Status) in
> mpif.h).

It was intended that you can convert from old INTEGER variable or array
to new TYPE(MPI_...) within source code using the mpi module
or using the mpi_f08 module.

But we excluded mpif.h because it need not to provide compile-time
argument checking and it use is therefore "strongly discouraged".
Why should we add something to this "strongly discouraged" mpif.h
area.

And, to add it in a later version of MPI is simple. To remove it later
is not backward compatible. This may be another reason for not

Best regards
Rolf

----- Original Message -----
> From: "MPI-WG Fortran working group" <mpiwg-fortran at lists.mpi-forum.org>
> To: "MPI-WG Fortran working group" <mpiwg-fortran at lists.mpi-forum.org>
> Cc: "Hubert Ritzdorf" <Hubert.Ritzdorf at EMEA.NEC.COM>
> Sent: Wednesday, July 15, 2020 6:15:58 PM
> Subject: Re: [MPIWG Fortran] Question about MPI_Status_f2f08() and _f082f()

> Ø I'm a little curious as to why we conspicuously left it out of mpif.h.
>
>
>
> When I remember correctly, MPI_Status_f2f08() and _f082f() subroutines were for
> a smooth transition from Fortran 77 to Fortran 08.
>
> I.e. if a programmer has changed some functions from old Fortran to Fortran 08
> and uses other libraries or subroutines which still use the old Fortran status
> as input or output argument, it was possible to transfer the old Fortran status
> within the Fortran 08 subroutine. But it was never intended that the programmer
> does this transformation within the old Fortran subroutine (and old Fortran 77
> compiler or using Fortran 77 language kind wouldn’t support Type(MPI_Status) in
> mpif.h).
>
>
>
> Hubert
>
>
>
>
> From: mpiwg-fortran [mailto:mpiwg-fortran-bounces at lists.mpi-forum.org] On Behalf
> Of Jeff Squyres (jsquyres) via mpiwg-fortran
> Sent: Wednesday, July 15, 2020 5:26 PM
> To: MPI Fortran WG <mpiwg-fortran at lists.mpi-forum.org>
> Cc: Jeff Squyres (jsquyres) <jsquyres at cisco.com>
> Subject: Re: [MPIWG Fortran] Question about MPI_Status_f2f08() and _f082f()
>
>
>
>
>
>
>
>
>
> plus a few more:
>
>
>
>
>
>
>
>
> On your question on TYPE(MPI_Status), TYPE(MPI_Comm), ...:
>
>
> MPI-3.1
>
>
> - page 607 lines 18-24 require these types and the overloaded
>
>
> operators .EQ./.NE. for mpi_f08 module
>
>
> - page 609 lines 34-36 require these types and the overloaded
>
>
> operators .EQ./.NE. for mpi module
>
>
> - there is no such text on page 611-612 on mpif.h
>
>
>
>
>
> And page 802 lines 9-15 also Show that it was never intented to add
>
>
> These types anf routines to old mpif.h.
>
>
>
>
>
> It would be helpful, to add at least on page 657 line 11
>
>
>
>
>
> C, some in both C and Fortran (only in the mpi_f08 and mpi modules).
>
>
>
>
>
> Can you fix this with an one-vote-bug-fix-issue?
>
>
> Because it is not good if the information must be taken from the change-log.
>
>
>
>
>
> ---
>
>
> Summary:
>
>
>
>
>
> Does this mean that TYPE(MPI_Status)
>
>
> [ and the Fortran routines MPI_STATUS_F2F08 and _F082F ]
>
>
> needs to be defined in
>
>
>
>
>
> - mpif.h? NO
>
>
> - and the mpi module? YES
>
>
>
>
>
> Bug-fix needed in MPI-3.1 page 657 line 11: add
>
>
> "(only in the mpi_f08 and mpi modules)" at the end.
>
>
>
>
>
> I hope this helps.
>
>
>
>
>
> Best regards
>
>
> Rolf
>
>
>
>
>
> So I think there's at least a clarification here: the TYPE(MPI_Status) and
> associated functions is -- at a minimum -- supposed to be in the mpi module.
>
>
>
>
>
> I'm a little curious as to why we conspicuously left it out of mpif.h.
>
>
>
>
>
> Bill: this is somewhat counter to the clarification you proposed.
>
>
>
>
>
> Are you ok with this? I think the text in the standard supports what Rolf
> proposes.
>
>
>
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>
>
> On Jul 10, 2020, at 12:11 PM, Jeff Squyres (jsquyres) via mpiwg-fortran < [
> mailto:mpiwg-fortran at lists.mpi-forum.org | mpiwg-fortran at lists.mpi-forum.org ]
> > wrote:
>
>
>
>
>
> On Jul 10, 2020, at 11:18 AM, Bill Long < [ mailto:longb at cray.com |
> longb at cray.com ] > wrote:
>
>
>
>
>
>
> In the “change” section there is this txt:
>
> • Within the mpi_08 Fortran module, the status was defined as TYPE(MPI_Status).
> Additionally, within both the mpi and the mpi_f08 modules, the constants
> MPI_STATUS_SIZE, MPI_SOURCE, MPI_TAG, MPI_ERROR, and TYPE(MPI_Status) are
> defined. New conversion routines were added: MPI_STATUS_F2F08,
> MPI_STATUS_F082F, MPI_Status_c2f08, and MPI_Status_f082c, In mpi.h, the new
> type MPI_F08_status, and the external variables MPI_F08_STATUS_IGNORE and
>
>
> Good point.
>
> Just to be clear, you're referring to the changelog section in MPI-3.1,
> specifically bullet 30 on p802.
>
> That being said:
>
> - the changelog is non-binding ...but it does indicate our intent from that time
> - the changelog text states that the mpi module has TYPE(MPI_Status) -- but it
> does not say it was added to mpif.h
>
>
>
>
>
>
> 1) Why would the F08 status be defined different from the C definition? (If that
> were the case, conversions between f08 and C would be irrelevant).
>
>
> I remember that there was a lot of discussion about this at the time, which is
> what resulted in Figure 17.1.
>
> I know there were discussions about making the F08 and C statuses the same, but
> for some reason we chose not to mandate it. Perhaps we wanted to allow
> implementations to do whatever they wanted...? (e.g., allow Status_c2f08 be a
> no-op if the implementation wanted to, but not mandate it)
>
>
>
>
>
>
> 2) \begin{unpopular} Why are the legacy mpi module and mpif.h still included in
> the spec? These are embarrassingly obsolete. If this was fixed, none of the
> above mentioned conversion routines would be needed. \end(unpopular}
>
>
>
> I would love it if we could ditch -- at a minimum -- mpif.h.
>
> However, there's oodles of legacy code out there that uses it. That's why even
> deprecating it gets shouted down at Forum meetings.
>
> --
> Jeff Squyres
> [ mailto:jsquyres at cisco.com | jsquyres at cisco.com ]
>
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> --
> Jeff Squyres
> [ mailto:jsquyres at cisco.com | jsquyres at cisco.com ]
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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) .