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

Jeff Squyres (jsquyres) jsquyres at cisco.com
Thu Jul 16 14:35:14 CDT 2020

I just filed the issue:

https://github.com/mpi-forum/mpi-issues/issues/298

And a first cut of the MPI-4.x PR:

https://github.com/mpi-forum/mpi-standard/pull/255

I just added a statement in the text on the PR so far.  I need to work with Martin R to get the Pythonization changes.

I'll post back here when we have something for everyone to review.

After that, we'll make a corresponding equivalent-looking PR for MPI-3.x.

On Jul 16, 2020, at 12:07 PM, Rolf Rabenseifner <rabenseifner at hlrs.de<mailto:rabenseifner at hlrs.de>> wrote:

Good idea.

Fortran binding
which could be substituted by
Fortran binding (the following procedure is not available with mpif.h)

And in A.4.12 we could write in front of the two routines also

The following procedure is not available with mpif.h:

I would not use the positive statement "only available in the mpi module",
because the procedure itself is in mpi_f08 and mpi, and only this
specific Interface only in the mpi module.

I would use "with mpif.h" and not use "in mpif.h", because most/all
MPI libraries do not provide procedure interfaces in mpif.h.

Best regards
Rolf

----- Original Message -----
From: "wgropp" <wgropp at illinois.edu<mailto:wgropp at illinois.edu>>
To: "MPI-WG Fortran working group" <mpiwg-fortran at lists.mpi-forum.org<mailto:mpiwg-fortran at lists.mpi-forum.org>>
Cc: "Rolf Rabenseifner" <rabenseifner at hlrs.de<mailto:rabenseifner at hlrs.de>>, "Jeff Squyres" <jsquyres at cisco.com<mailto:jsquyres at cisco.com>>
Sent: Thursday, July 16, 2020 5:17:55 PM
Subject: Re: [MPIWG Fortran] Question about MPI_Status_f2f08() and _f082f()

Adding something to the MPI_Status_f2f08/f082f bindings to specify these are
only for the MPI module is a good idea.

Bill

William Gropp
Director and Chief Scientist, NCSA
Thomas M. Siebel Chair in Computer Science
University of Illinois Urbana-Champaign

On Jul 16, 2020, at 9:19 AM, Jeff Squyres (jsquyres) via mpiwg-fortran
<mpiwg-fortran at lists.mpi-forum.org<mailto:mpiwg-fortran at lists.mpi-forum.org>> wrote:

Thanks Rolf, Hubert, and Bill.  It all makes sense.

Rolf has proposed that we add the following at the end of the sentence on
MPI-3.1 p657 line 11:

(only in the mpi_f08 and mpi modules)

This sounds reasonable to me, but do we need some additional annotation in the
MPI_Status_f2f08 and _f082f bindings to indicate that the all-caps Fortran
binding is only for the mpi module, and not mpif.h?

On Jul 15, 2020, at 3:08 PM, Rolf Rabenseifner via mpiwg-fortran
<mpiwg-fortran at lists.mpi-forum.org<mailto:mpiwg-fortran at lists.mpi-forum.org>> wrote:

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<mailto:mpiwg-fortran at lists.mpi-forum.org>>
To: "MPI-WG Fortran working group" <mpiwg-fortran at lists.mpi-forum.org<mailto:mpiwg-fortran at lists.mpi-forum.org>>
Cc: "Hubert Ritzdorf" <Hubert.Ritzdorf at EMEA.NEC.COM<mailto: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<mailto:mpiwg-fortran at lists.mpi-forum.org>>
Cc: Jeff Squyres (jsquyres) <jsquyres at cisco.com<mailto: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.

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<mailto: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<mailto: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).

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<mailto:jsquyres at cisco.com> ]

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--
Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de<mailto: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<http://www.hlrs.de/people/rabenseifner> .
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--
Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de<mailto: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<http://www.hlrs.de/people/rabenseifner> .
Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) .

--
Jeff Squyres
jsquyres at cisco.com<mailto:jsquyres at cisco.com>

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