[MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008 interface - issue with the LOGICAL kind

Hubert Ritzdorf Hubert.Ritzdorf at EMEA.NEC.COM
Mon Mar 25 15:28:34 CDT 2013 

I vote for Option 2.

Option 3 is not possible for an errata. This is a severe change in the standard.
Your modification of Option 3 makes the standard more difficult (we have again mixing of 
BIND(C) and non BIND(C) functions) and I can't see a real application advantage.

To your items:
Item 2: You have to perform also additional work in the wrappers
             (for example memory allocation and transformation for sources
              compiled with -i8; additional error checks)
Item 3: Support of PMPI version of Fortran is not really an issue.
Item 4b: The tools have to support routines compiled with mpi.h and old
                objects.

Hubert

________________________________________
From: Bill Long [longb at cray.com]
Sent: Monday, March 25, 2013 7:35 PM
To: Craig Rasmussen
Cc: Rolf Rabenseifner; MPI-3 Fortran working group; Jeff Squyres (jsquyres); Hubert Ritzdorf; Martin Schulz; Tobias Burnus
Subject: Re: [MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran     2008 interface - issue with the LOGICAL kind

On 3/25/13 12:50 PM, Craig Rasmussen wrote:
> My summary of the three options:
>
> 1. Absolute minimal change, remove BIND(C) only for routines with
> LOGICAL arguments.  Tools will need to support underscore name mangling
> forever (even when TS29113 is implemented by compilers) but only on
> routines with LOGICAL arguments.
>
> 2. Remove BIND(C) from all routines.  Tools will need to support
> underscore name mangling for all routines.
>
> 3. Remove BIND(C) from all routines.  Plus allow Fortran implementations
> to substitute the C PMPI interface standard.
>
> Is this a fair summary?
>
> My vote:
>
> I'm strongly in favor of option 3.  It is the only option that allows
> the possibility of underscore name mangling disappearing in the future.
>   I think most (if not all) MPI Fortran implementations will eventually
> evolve to thin wrappers calling the C API.  There are several advantages
> with this implementation:
>      1. The thin wrappers can be put in a module.
>      2. Compilers may be able to inline the wrappers for very efficient
> implementations.
>      3. Fortran implementations are much simpler because they won't have
> to directly support PMPI in Fortran.
>      4. Since the Fortran implementation is substantially less complex,
> the costs associated with testing, supporting, and maintaining a Fortran
> implementation will also be reduced.
>      4. If all MPI implementations eventually choose to call the C API,
> then the tools community eventually will not have to support underscore
> name mangling, thus reducing their costs as well.

I like option 3 as well.  It uses the C interoperability feature in
Fortran the way it was intended/designed.   I would add to the above:

6. You can isolate the issues of Fortran types (compiled with -i8,
meaning of LOGICAL, character arguments with len > 1) into the Fortran
wrappers so that the C library writers do not have to know about these
issues.   Simplifies the maintenance and testing issues for the C
library code.


I would modify option 3 slightly. The implementer might want to write
some routine ONLY in Fortran.  The routines that convert the status
formats between the Fortran and the C forms comes to mind.  In that
case, BIND(C) would be required, and it would specify the C binding name
as the external linker name. This would be needed so that C codes could
call the routine.


Cheers,
Bill


>
> Craig Rasmussen
> CAS Scientific Programmer
> rasmus at cas.uoregon.edu <mailto:rasmus at cas.uoregon.edu>
>
>
>
>
> On Mar 25, 2013, at 10:11 AM, Rolf Rabenseifner wrote:
>
>> We (Jeff, Bill L., Craig, Hubert, Martin, Tobias, and me (Rolf)) had
>> a telecon today and the outcome are following options:
>>
>> Option 1
>> - #364 as it currently is, as a minimal solution for
>>  the LOGICAL problem:
>>    Pro: It is consistent between Fortran and MPI.
>>         I.e., it is the minimal solution that we must do.
>>    Con: It has a mix of BIND(C) and non-BIND(C) routine groups
>>         which is ugly for the future.
>>    Remark: non-BIND(C) will stay there because the callbacks
>>            need non-BIND(C) in the moment and this cannot be
>>            changed in the future by nice new concepts from
>>            the Fortran language standardization.
>>
>> Option 2
>> - #364 plus changing MPI-3.0 page 605 lines 24-30 and
>>  page 605 line 47 - page 606 line 6 by also using non-BIND(C),
>>  but other linker names:
>>   MPI_Send_f08d (in mpi_f08 with TS29113 quality, i.e.,
>>                  buffers are done with C-descriptors and
>>                  not with void* pointers.)
>>   MPI_Send_fd (in the mpi module or mpif.h if
>>                MPI_SUBARRAYS_SUPPORTED=.TRUE. is also done
>>                there, i.e., with the descriptors.)
>>
>>    Pro: It is consistent between Fortran and MPI
>>         and it is consistent within MPI, i.e., all
>>         functionality is done with non-BIND(C) routines.
>>         BIND(C) can be still used internally to
>>         call MPI_Send_cdesc and MPI_Isend_cdesc.
>>         To be fair, implementatiosn will be based mainly
>>         on this TS 29113 feature, but only internally.
>>    Con: No BIND(C) on the official MPI interface.
>>         We urged Fortran to put some features into TS 29113,
>>         but we will not use these features, because they
>>         are not needed on this internal interface.
>>
>> Option 3:
>> - Option 2 plus the following rule:
>>   - The Fortran PMPI interface can be substituted by a
>>     wrapper based sulution that internally calls the full
>>     MPI C interface.
>>   - In this case, the Fortran interface should be hidden
>>     to the tools.
>>   - For the buffer routines with the new cdesc descriptor,
>>     new interfaces are added for the tools people,
>>     e.g., MPI_Send_cdesc and MPI_Isend_cdesc.
>>
>>   Pro: I'm not sure whether there is a real pro?
>>
>>        Bill, can you add the pros, it is your option.
>>
>>   Con: An additional new interface for the tools folk.
>>        It is not backward compatible for users who really
>>        intercept the Fortran MPI interface.
>>
>> My favorite in the moment, i.e. at the starting of
>> the pro-con-discussion: Option 2.
>>
>> Best regards
>> Rolf
>>
>>
>>
>> ----- Original Message -----
>>> From: "Rolf Rabenseifner" <rabenseifner at hlrs.de
>>> <mailto:rabenseifner at hlrs.de>>
>>> To: longb at cray.com <mailto:longb at cray.com>
>>> Cc: "Jeff Squyres (jsquyres)" <jsquyres at cisco.com
>>> <mailto:jsquyres at cisco.com>>, "Craig E Rasmussen"
>>> <rasmus at cas.uoregon.edu <mailto:rasmus at cas.uoregon.edu>>, "Hubert
>>> Ritzdorf"
>>> <Hubert.Ritzdorf at emea.nec.com <mailto:Hubert.Ritzdorf at emea.nec.com>>,
>>> "Martin Schulz" <schulzm at llnl.gov <mailto:schulzm at llnl.gov>>, "Tobias
>>> Burnus" <burnus at net-b.de <mailto:burnus at net-b.de>>
>>> Sent: Monday, March 25, 2013 12:21:39 PM
>>> Subject: Re: [MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008
>>> interface - issue with the LOGICAL kind
>>> Yes, this freedom (1)-(4) in Bill's email is important.
>>>
>>> In our discussion, we forgot one additional reason why we defined
>>> it as it is written in MPI-3.0 Section 17.1.5, page 605:
>>>
>>> - It should be possible to implement the interfaces with
>>> these non-standard Fortran-void-* directives,
>>> and later on,
>>> to substitute this implementation by new ones
>>> that are based on TS 29113.
>>> - When doing this substitution, it should be save for
>>> applications when the application is not re-compiled.
>>> - More than that, it should be possible to combine older
>>> .o files with newly TS 29113 based .o files.
>>> - For this, we decided, that the implementation has to switch
>>> from non-BIND(C) to BIND(C) at least in the MPI_ISEND
>>> routine group when switching to MPI_SUBARRAYS_SUPPORTED==.TRUE.
>>> - The real trick is that the linker name must be changed.
>>> - This all is valid for both, the new mpi_f08 module,
>>> and the old mpi module.
>>>
>>> A second issue in our discussion is always, which changes
>>> we want to do to the mpi_f08 MPI-3.0 user interface.
>>> I want to remember that this user interface is defined
>>> according following rules.
>>> If a user modifies his source to use everywhere mpi_f08,
>>> he/she has to modify:
>>> - He/she has to substitute the "include 'mpif.h'" or "use mpi"
>>> statements by "use mpi_f08".
>>> - He/she has to modify all handle and status declarations.
>>> - In the executable statements, he/she has to substitute all
>>> status(MPI_TAG), status(MPI_SOURCE), status(MPI_ERROR)
>>> accesses into
>>> status%MPI_TAG, status%MPI_SOURCE, status%MPI_ERROR.
>>> - Callback routines need more effort due to the
>>> abstract interface definitions.
>>> This is touched by ticket #364, i.e.,
>>> the MPI-3.0 BIND(C) of callbacks had to be removed.
>>> - Changes in the interfaces are only
>>> -- all handles use the new handle types
>>> and in
>>> -- MPI_User_function,
>>> -- MPI_Datarep_conversion_function,
>>> the buffers are done with TYPE(C_TR), VALUE.
>>>
>>> This should be all.
>>> All other user correct code should directly compile with the new
>>> mpi_f08 module.
>>> We should not change these things, except the necessary
>>> errata in #364.
>>>
>>> I see that we have some freedom only in the area,
>>> what we do internally (together with linker names) and with PMPI,
>>> but not in the user interface.
>>> If we add additional user interfaces (e.g. overloading the LOGICAL
>>> with INTEGER arguments)
>>> we would only make it more complicate.
>>>
>>> Best regards
>>> Rolf
>>>
>>>
>>> ----- Original Message -----
>>>> From: "Bill Long" <longb at cray.com <mailto:longb at cray.com>>
>>>> To: "Rolf Rabenseifner" <rabenseifner at hlrs.de
>>>> <mailto:rabenseifner at hlrs.de>>
>>>> Cc: "Jeff Squyres (jsquyres)" <jsquyres at cisco.com
>>>> <mailto:jsquyres at cisco.com>>, "Craig E
>>>> Rasmussen" <rasmus at cas.uoregon.edu <mailto:rasmus at cas.uoregon.edu>>,
>>>> "Hubert Ritzdorf"
>>>> <Hubert.Ritzdorf at emea.nec.com
>>>> <mailto:Hubert.Ritzdorf at emea.nec.com>>, "Martin Schulz"
>>>> <schulzm at llnl.gov <mailto:schulzm at llnl.gov>>,
>>>> "Tobias Burnus" <burnus at net-b.de <mailto:burnus at net-b.de>>
>>>> Sent: Sunday, March 24, 2013 5:59:38 PM
>>>> Subject: Re: [MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008
>>>> interface - issue with the LOGICAL kind
>>>> This time is OK for me. I'll look for the webex email.
>>>>
>>>> I would like to note that the various options discussed are not
>>>> necessarily "all or nothing" propositions. An implementation could
>>>> use
>>>> the thin wrappers in a module approach to eliminate the bad Fortran
>>>> types problems for most of the MPI routines, but also have some
>>>> routines
>>>> implemented in a different way, such as (1) all in Fortran that is
>>>> callable from C, (2) all in C that is called through an interface
>>>> directly from Fortran, (3) as a fat wrapper in Fortran, or (4) a
>>>> completely replicated routine for the Fortran implementation. There
>>>> is
>>>> no reason that all of the routines have to be the same method - in
>>>> fact
>>>> probably good arguments against that in some cases. We just need to
>>>> have
>>>> the rules such that the tools have some known name to intercept.
>>>> Along
>>>> the lines of "If implementation method X is chosen for routine
>>>> MPI_xxx,
>>>> then these are the linker name requirements:.....".
>>>>
>>>> Cheers,
>>>> Bill
>>>>
>>>>
>>>>
>>>> On 3/23/13 2:11 AM, Rolf Rabenseifner wrote:
>>>>> Dear Jeff, Craig, Bill, Hubert, Martin, and Tobias,
>>>>>
>>>>> I expect that this is the total group that discusses the
>>>>> Fortran LOGICAL etc. problem.
>>>>> We learnt that the solutions also touch the PMPI concept.
>>>>> There was a telecon between Craig, Jeff and Bill with the proposal
>>>>> at the end of this email.
>>>>> I like to understand this proposal and therefore I asked Jeff
>>>>> for explanations. I would like to open this for the whole group.
>>>>>
>>>>>> I have meetings at 9am and 1pm is eastern on Monday. I can talk
>>>>>> any
>>>>>> other time.
>>>>>> Craig prob can't attend because he's 3 hours earlier, but that's
>>>>>> prob ok.
>>>>>
>>>>> Monday March 25,
>>>>>  - 4 PM Central European Time CET
>>>>>  = 11 AM Eastern Daylight Time EST/EDT
>>>>>  = 8 AM Pacific Time
>>>>>
>>>>> I hope these relations are correct. Would this work for you?
>>>>>
>>>>> At least for Jeff and me, because I want to understand
>>>>> what they discussed with their proposal.
>>>>>
>>>>> Jeff, can you set up a webex?
>>>>>
>>>>> Best regards
>>>>> Rolf
>>>>>
>>>>> ----- Original Message -----
>>>>>> From: "Jeff Squyres (jsquyres)" <jsquyres at cisco.com
>>>>>> <mailto:jsquyres at cisco.com>>
>>>>>> To: "Rolf Rabenseifner" <rabenseifner at hlrs.de
>>>>>> <mailto:rabenseifner at hlrs.de>>
>>>>>> Cc: "Craig E Rasmussen" <rasmus at cas.uoregon.edu
>>>>>> <mailto:rasmus at cas.uoregon.edu>>
>>>>>> Sent: Friday, March 22, 2013 8:01:23 PM
>>>>>> Subject: Re: [MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008
>>>>>> interface - issue with the LOGICAL kind
>>>>>> Btw, I'm not sure how this is not the least surprise.
>>>>>>
>>>>>> We can't change the params to not be logical, yes we must still
>>>>>> allow
>>>>>> for calling to c. So the overloaded solution is the only one.
>>>>>>
>>>>>> And the new Integer param signature must have a new bind name so
>>>>>> as
>>>>>> to
>>>>>> did ambiguity it from the one we published in MPI3. See my
>>>>>> previous
>>>>>> mail about this.
>>>>>>
>>>>>> I have meetings at 9am and 1pm is eastern on Monday. I can talk
>>>>>> any
>>>>>> other time.
>>>>>>
>>>>>> Craig prob can't attend because he's 3 hours earlier, but that's
>>>>>> prob
>>>>>> ok.
>>>>>>
>>>>>> Sent from my phone. No type good.
>>>>>>
>>>>>> On Mar 22, 2013, at 8:51 AM, "Rolf Rabenseifner"
>>>>>> <rabenseifner at hlrs.de <mailto:rabenseifner at hlrs.de>> wrote:
>>>>>>
>>>>>>> Jeff,
>>>>>>>
>>>>>>> can I call you by phone?
>>>>>>> I would like to talk to you as the binding responsible and MPI
>>>>>>> chair.
>>>>>>>
>>>>>>>> 2. Replace the current binding names for MPI functions with
>>>>>>>> LOGICAL
>>>>>>>> dummy arguments with a different name and replacing LOGICAL
>>>>>>>> type
>>>>>>>> with
>>>>>>>> default INTEGER arguments. The name must be changed so as to
>>>>>>>> not
>>>>>>> ...
>>>>>>> This is a hard step and far away from "last surprise".
>>>>>>>
>>>>>>> I would like to learn how it came out as a result of your
>>>>>>> telecon,
>>>>>>> before I try to go the next step (e.g. email answer).
>>>>>>>
>>>>>>> Best regards
>>>>>>> Rolf
>>>>>>>
>>>>>>> ----- Original Message -----
>>>>>>>> From: "Craig Rasmussen" <rasmus at cas.uoregon.edu
>>>>>>>> <mailto:rasmus at cas.uoregon.edu>>
>>>>>>>> To: "MPI-3 Fortran working group"
>>>>>>>> <mpi3-fortran at lists.mpi-forum.org
>>>>>>>> <mailto:mpi3-fortran at lists.mpi-forum.org>>
>>>>>>>> Cc: "Hubert Ritzdorf" <Hubert.Ritzdorf at emea.nec.com
>>>>>>>> <mailto:Hubert.Ritzdorf at emea.nec.com>>, "Martin
>>>>>>>> Schulz" <schulzm at llnl.gov <mailto:schulzm at llnl.gov>>
>>>>>>>> Sent: Friday, March 22, 2013 4:29:36 PM
>>>>>>>> Subject: Re: [MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran
>>>>>>>> 2008
>>>>>>>> interface - issue with the LOGICAL kind
>>>>>>>>
>>>>>>>> Bill Long, Jeff Squyres, and I had a phone conversation
>>>>>>>> yesterday
>>>>>>>> and came up with a straw man proposal. We believe it fixes the
>>>>>>>> LOGICAL argument problem while satisfying three major goals:
>>>>>>>>
>>>>>>>> 1. Backwards compatibility.
>>>>>>>> 2. Flexibility so that efficient implementations can be
>>>>>>>> produced
>>>>>>>> on
>>>>>>>>    a variety of hardware.
>>>>>>>> 3. Not dramatically increase the complexity for the tools
>>>>>>>>    community.
>>>>>>>> 4. Ensure that the changes won't be seen by ordinary Fortran
>>>>>>>> MPI
>>>>>>>>    users.
>>>>>>>>
>>>>>>>> The straw man proposal is:
>>>>>>>>
>>>>>>>> 1. Remove the current binding names for MPI functions with
>>>>>>>> LOGICAL
>>>>>>>> dummy arguments (. This must be done because these interfaces
>>>>>>>> break
>>>>>>>> the Fortran standard.
>>>>>>>> 2. Replace the current binding names for MPI functions with
>>>>>>>> LOGICAL
>>>>>>>> dummy arguments with a different name and replacing LOGICAL
>>>>>>>> type
>>>>>>>> with
>>>>>>>> default INTEGER arguments. The name must be changed so as to
>>>>>>>> not
>>>>>>>> conflict with the current name with LOGICAL arguments. For
>>>>>>>> example,
>>>>>>>> the binding name "MPI_Test_f08" will be replaced by
>>>>>>>> "MPI_Test_int_f08"
>>>>>>>> (exact replacement name open for discussion). The Fortran
>>>>>>>> implementation of the function MPI_Test must call
>>>>>>>> MPI_Test_int_f08
>>>>>>>> as soon as possible for the tools implementers.
>>>>>>>> 3. Implementation of the Fortran PMPI calling convention will
>>>>>>>> be
>>>>>>>> made optional (we think it already it). If an MPI implementer
>>>>>>>> doesn't
>>>>>>>> provide the MPI_F08 binding names, then it must call the C MPI
>>>>>>>> implementation in a thin Fortran wrapper so that the tools
>>>>>>>> implementers can intercept the call in C. An MPI implementation
>>>>>>>> shall not provide/call both the MPI_F08 binding name and the C
>>>>>>>> name.
>>>>>>>>
>>>>>>>> Option 2 allows some MPI vendors to implement MPI functions
>>>>>>>> entirely within Fortran (using the MPI_f08 binding names),
>>>>>>>> if this is more efficient.
>>>>>>>>
>>>>>>>> Option 3 allows some MPI implementations to place Fortran
>>>>>>>> wrappers
>>>>>>>> inside modules where they may be inlined by the compiler for
>>>>>>>> efficiency.
>>>>>>>>
>>>>>>>> Craig Rasmussen
>>>>>>>> CAS Scientific Programmer
>>>>>>>> rasmus at cas.uoregon.edu <mailto:rasmus at cas.uoregon.edu>
>>>>>
>>>>
>>>> --
>>>> Bill Long longb at cray.com <mailto:longb at cray.com>
>>>> Fortran Technical Support & voice: 651-605-9024
>>>> Bioinformatics Software Development fax: 651-605-9142
>>>> Cray Inc./Cray Plaza, Suite 210/380 Jackson St./St. Paul, MN 55101
>>>
>>> --
>>> 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)
>>
>> --
>> 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)
>

--
Bill Long                                           longb at cray.com
Fortran Technical Support    &                 voice: 651-605-9024
Bioinformatics Software Development            fax:   651-605-9142
Cray Inc./Cray Plaza, Suite 210/380 Jackson St./St. Paul, MN 55101




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