[MPIWG Fortran] Type of MPI_Status

Rolf Rabenseifner rabenseifner at hlrs.de
Sun Mar 16 07:47:11 CDT 2014 

Dear Junchao,

I had not the time to go through all details, but I detected two issues:

1. TYPE(MPI_Status) must be declared with BIND(C).
   It is missing in your example below.

2. To declare an equivalent struct in C, i.e., 
   the C type MPI_F08_status, you should use MPI_Fint
   and not int.

See MPI-3.0 p30:24-26 + ticket #415 and Sect. 17.2..5.

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: Saturday, March 15, 2014 10:52:42 PM
> Subject: Re: [MPIWG Fortran] Type of MPI_Status
> 
> 
> 
> 
> Rolf, you are right. Passing MPI%MPI_SOURCE as an argument will cause
> problems. Thanks.
> I list why I wanted to use c_int in MPI_Status. It is amusing.
> Without c_int, the design is something like
> 
> 
> type MPI_Status
> INTEGER :: MPI_SOURCE, MPI_ERROR, MPI_TAG
> ! other fields
> end type MPI_Status
> 
> 
> type(MPI_Status), parameter :: MPI_STATUS_IGNORE = ...
> 
> 
> type c_Status
> INTEGER(c_int) :: MPI_SOURCE, MPI_ERROR, MPI_TAG
> ! other fields
> end type c_Status
> 
> 
> type(c_Status), BIND(C, name="MPIR_C_STATUS_IGNORE") ::
> MPIR_C_STATUS_IGNORE
> 
> 
> ! Declare the C function prototype to bind
> function MPIR_Example_c(len, counts, status) result(ierror) BIND(C,
> name="MPI_Example")
> integer(c_int), intent(in) :: len
> integer(c_int), intent(in) :: counts(len)
> type(c_Status) :: status
> integer(c_int) :: ierror
> end function
> 
> 
> subroutine MPI_Example_f08(len, counts, status, ierror)
> integer, intent(in) :: len
> integer, intent(in) :: counts(len)
> type(MPI_Status) :: status
> integer, optional :: ierror_c
> 
> 
> integer(c_int), intent(in) :: len_c
> integer(c_int), intent(in) :: counts_c(len)
> type(c_Status) :: status_c
> integer(c_int) :: ierror_c
> 
> 
> if (c_int == kind(0) then ! Common case
> if (c_loc(status) == c_loc(MPI_STATUS_IGNORE)) then ! In C
> MPI_Example, it will checks again if status is 'IGNORE'. But we have
> to duplicate the work here due to type difference of
> MPI_STATUS_IGNORE and MPIR_C_STATUS_IGNORE.
> ierror = MPIR_Example_c(len, counts, MPIR_C_STATUS_IGNORE)
> else
> ! ierror = MPIR_Example_c(len, counts, status) ! Compile error since
> type(MPI_Status) mismatches type(c_Status) even c_int = INTEGER
> ierror = MPIR_Example_c(len, counts, status_c)
> status = status_c ! Note that = is overloaded. Can Compiler optimize
> away this copy propogation? probably not.
> endif ! This is bad since MPI_Status and c_Status are indeed the
> same. Even worse if status is an array.
> else
> len_c = len
> counts_c = counts
> if (c_loc(status) == c_loc(MPI_STATUS_IGNORE)) then
> ierror = MPIR_Example_c(len_c, counts_c, MPIR_C_STATUS_IGNORE)
> else
> ierror = MPIR_Example_c(len_c, counts_c, status_c)
> status = status_c
> endif
> endif
> 
> 
> if(present(ierror)) ierror = ierror_c
> end subroutine
> 
> 
> However, if I can use c_int in MPI_Status, then MPI_Status and
> c_Status are the same. I will have
> 
> 
> type MPI_Status
> INTEGER(c_int) :: MPI_SOURCE, MPI_ERROR, MPI_TAG
> ! other fields
> end type MPI_Status
> 
> 
> type(MPI_Status), BIND(C, name="MPI_STATUS_IGNORE") ::
> MPI_STATUS_IGNORE
> 
> 
> function MPIR_Example_c(len, counts, status) result(ierror) BIND(C,
> name="MPI_Example")
> integer(c_int), intent(in) :: len
> integer(c_int), intent(in) :: counts(len)
> type(MPI_Status) :: status ! Now use MPI_Status instead of c_Status
> integer(c_int) :: ierror
> end function
> 
> 
> subroutine MPI_Example_f08(len, counts, status, ierror)
> integer, intent(in) :: len
> integer, intent(in) :: counts(len)
> type(MPI_Status) :: status
> integer, optional :: ierror_c
> 
> 
> integer(c_int), intent(in) :: len_c
> integer(c_int), intent(in) :: counts_c(len)
> integer(c_int) :: ierror_c
> 
> 
> if (c_int == kind(0) then
> ierror = MPIR_Example_c(len, counts, status) ! Zero overhead incurred
> on status.
> else
> len_c = len
> counts_c = counts
> ierror = MPIR_Example_c(len_c, counts_c, status)
> endif
> 
> 
> if(present(ierror)) ierror = ierror_c
> end subroutine
> 
> 
> 
> 
> 
> --Junchao Zhang
> 
> 
> On Sat, Mar 15, 2014 at 7:38 AM, Rolf Rabenseifner <
> rabenseifner at hlrs.de > wrote:
> 
> 
> Dear Junchao,
> 
> As long as you use status%MPI_SOURCE in an expression,
> all is fine.
> 
> If you pass it to an application routine dummy argument
> that is defined as INTEGER and your status%MPI_SOURCE
> is define as INTEGER(C_INT) then you may get compiler
> warnings or errors if size of both INTEGER types is different.
> 
> CALL foo(status%MPI_SOURCE)
> 
> with
> SUBROUTINE foo(rank)
> INTEGER :: rank
> 
> 
> Best regards
> Rolf
> 
> 
> ----- Original Message -----
> > From: "Junchao Zhang" < jczhang at mcs.anl.gov >
> > To: "MPI-WG Fortran working group" mpi-forum.org >
> 
> 
> > Sent: Saturday, March 15, 2014 11:54:38 AM
> > Subject: Re: [MPIWG Fortran] Type of MPI_Status
> > 
> > 
> > 
> > My point is, with the C_INT implementation of MPI_Status, there
> > should be no compilation warnings AND runtime errors, even if
> > INTEGER kind is not c_int, since users can only operate MPI_Status
> > through their public interfaces, in which we take care of data
> > conversion.
> > 
> > 
> > But for other arguments of type INTEGER or array of INTEGERs, I can
> > not change their type. Users pass in an array of INTEGERs, I can
> > not
> > pretend they are c_int and don't do conversion.
> > 
> > 
> > 
> > --Junchao Zhang
> > 
> > 
> > On Sat, Mar 15, 2014 at 3:33 AM, Rolf Rabenseifner <
> > rabenseifner at hlrs.de > wrote:
> > 
> > 
> > Junchao,
> > 
> > With the erratum ticket #415, your implementation
> > with INTEGER(C_INT) is clearly wrong,
> > but who cares as long as an application programmer cannot
> > write an application code that produces compilation errors
> > or warnings or infos due to your wrong implementation
> > of TYPE(MPI_Status).
> > 
> > I do not exactly now the rules about Fortran subroutine
> > prototype and overloading where handing over a INTEGER rank
> > or a INTEGER(C_INT) rank may cause to choose different interfaces.
> > 
> > Maybe that Bill Long should comment on such strange things
> > before you define any field within TYPE(MPI_Status) or
> > any dummy argument in a routine declaration as INTEGER(C_INT)
> > instead of INTEGER as defined in MPI-3.0.
> > 
> > 
> > Best regards
> > Rolf
> > 
> > ----- Original Message -----
> > > From: "Junchao Zhang" < jczhang at mcs.anl.gov >
> > > To: "MPI-WG Fortran working group" mpi-forum.org >
> > 
> > 
> > > Sent: Saturday, March 15, 2014 12:11:35 AM
> > > Subject: Re: [MPIWG Fortran] Type of MPI_Status
> > > 
> > > 
> > > 
> > > Not sure if it is worth discussing. Even if INTEGER and C_INT are
> > > of
> > > different size, I think I can still use C_INT in MPI_Status.
> > > 
> > > 
> > > 
> > > TYPE, BIND(C) :: MPI_Status
> > > INTEGER(C_INT) :: MPI_SOURCE, MPI_TAG, MPI_ERROR
> > > ... ! other fields
> > > END TYPE MPI_Status
> > > 
> > > 
> > > Since MPI_Status is a derived datatype, users access it through
> > > its
> > > public interfaces(i.e., %MPI_SOURCE, ..., MPI_STATUS_SIZE).
> > > As long as MPI_STATUS_SIZE >= sizeof(MPI_STATUS)/sizeof(INTEGER),
> > > who
> > > cares its internals.
> > > 
> > > 
> > > 
> > > 
> > > 
> > > --Junchao Zhang
> > > 
> > > 
> > > On Thu, Mar 13, 2014 at 10:56 AM, Rolf Rabenseifner <
> > > rabenseifner at hlrs.de > wrote:
> > > 
> > > 
> > > Jeff is right.
> > > Bill's theoretical statement is also correct.
> > > 
> > > And ticket#415 is also correct because it resolves an
> > > inconsistency
> > > within the mpi_f08 interface.
> > > 
> > > Strange theoretical discussions are also there for
> > > long Fortran INTEGER may not be identical with some shorter
> > > INTEGER(C_int).
> > > As a side effect also solved by this ticket.
> > > 
> > > 
> > > Rolf
> > > 
> > > ----- Original Message -----
> > > 
> > > > From: "Jeff Hammond" < jeff.science at gmail.com >
> > > > To: "MPI-WG Fortran working group" mpi-forum.org >
> > > > Sent: Thursday, March 13, 2014 4:12:56 PM
> > > > Subject: Re: [MPIWG Fortran] Type of MPI_Status
> > > > 
> > > > MPI should test for interoperability of Fortran's default
> > > > integer
> > > > and
> > > > light the machine room on fire if it is not.
> > > > 
> > > > Jeff
> > > > 
> > > > On Thu, Mar 13, 2014 at 8:58 AM, Bill Long < longb at cray.com >
> > > > wrote:
> > > > > This does raise an earlier issue that it is
> > > 
> > > 
> > > > > possible that Fortran’s default INTEGER is not an
> > > > > interoperable
> > > > > type, and thus the MPI_Status type should not be a BIND(C)
> > > > > type
> > > > > if
> > > > > it has INTEGER components. Having BIND(C) does allow you to
> > > > > declare a C global name MPI_STATUS_IGNORE in Fortran, which
> > > > > solves
> > > > > one problem nicely. I don’t see any advantage to having
> > > > > INTEGER
> > > > > components (as opposed to INTEGER(C_Int), for example). So
> > > > > this
> > > > > seems to represent the worse of the two options.
> > > > > 
> > > > > Cheers,
> > > > > Bill
> > > > > 
> > > > > 
> > > > > 
> > > > > On Mar 13, 2014, at 8:36 AM, Jeff Squyres (jsquyres)
> > > > > < jsquyres at cisco.com > wrote:
> > > > > 
> > > > >> Done. Good catch:
> > > > >> 
> > > > >> https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/415
> > > > >> 
> > > > >> This is a trivial ticket, but if you could make sure it's
> > > > >> ok,
> > > > >> I'll
> > > > >> send it to the mpi-forum list so that it can get added to
> > > > >> the
> > > > >> next meeting's agenda.
> > > > >> 
> > > > >> 
> > > > >> On Mar 13, 2014, at 1:51 AM, Rolf Rabenseifner
> > > > >> < rabenseifner at hlrs.de > wrote:
> > > > >> 
> > > > >>> Jeff and Junchao,
> > > > >>> 
> > > > >>> it is a missing word INTEGER in this part of the sentence
> > > > >>> 
> > > > >>> In whole MPI these three values are in Fortran INTEGER and
> > > > >>> nothing else
> > > > >>> 
> > > > >>> Junchao, thank you for the hint that an erratum is neede
> > > > >>> to prevent from such misinterpretation
> > > > >>> 
> > > > >>> Jeff, please can you file the errata ticket resulting in
> > > > >>> 
> > > > >>> ... containing three public INTEGER fields named ...
> > > > >>> 
> > > > >>> Best regards
> > > > >>> Rolf
> > > > >>> 
> > > > >>> 
> > > > >>> ----- Original Message -----
> > > > >>>> From: "Junchao Zhang" < jczhang at mcs.anl.gov >
> > > > >>>> To: "MPI-WG Fortran working group"
> > > 
> > > 
> > > > >>>> mpi-forum.org >
> > > > >>>> Sent: Thursday, March 13, 2014 4:49:49 AM
> > > > >>>> Subject: [MPIWG Fortran] Type of MPI_Status
> > > > >>>> 
> > > > >>>> 
> > > > >>>> 
> > > > >>>> 
> > > > >>>> Hello,
> > > > >>>> 
> > > > >>>> 
> > > > >>>> p30 of MPI3 says "In Fortran with USE mpi or INCLUDE
> > > > >>>> ’mpif.h’,
> > > > >>>> status
> > > > >>>> is an array of INTEGERs of size MPI_STATUS_SIZE. ..., With
> > > > >>>> Fortran
> > > > >>>> USE mpi_f08, status is defined as the Fortran BIND(C)
> > > > >>>> derived
> > > > >>>> type
> > > > >>>> TYPE(MPI_Status) containing three public fields named
> > > > >>>> MPI_SOURCE
> > > > >>>> ,
> > > > >>>> MPI_TAG , and MPI_ERROR"
> > > > >>>> 
> > > > >>>> In other words, it does't say type of the three public
> > > > >>>> fields
> > > > >>>> must be
> > > > >>>> INTEGER. So, in mpi_f08, can I declare MPI_Status as
> > > > >>>> 
> > > > >>>> 
> > > > >>>> TYPE, BIND(C) :: MPI_Status
> > > > >>>> INTEGER(C_INT) :: MPI_SOURCE, MPI_TAG, MPI_ERROR
> > > > >>>> ... ! other fields
> > > > >>>> END TYPE MPI_Status
> > > > >>>> 
> > > > >>>> 
> > > > >>>> I find it makes MPI_Status binding easier. Since this type
> > > > >>>> is
> > > > >>>> interoperable with C, I do not need to allocate temp
> > > > >>>> variables
> > > > >>>> to do
> > > > >>>> type conversion when INTEGER is not a C_INT.
> > > > >>>> 
> > > > >>>> 
> > > > >>>> 
> > > > >>>> --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)
> > > > >>> _______________________________________________
> > > > >>> 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
> > > > >> For corporate legal information go to:
> > > > >> http://www.cisco.com/web/about/doing_business/legal/cri/
> > > > >> 
> > > > >> _______________________________________________
> > > > >> mpiwg-fortran mailing list
> > > > >> mpiwg-fortran at lists.mpi-forum.org
> > > > >> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
> > > > > 
> > > > > Bill Long
> > > > > longb at cray.com
> > > > > Fortran Technical Suport & voice:
> > > > > 651-605-9024
> > > > > Bioinformatics Software Development fax:
> > > > > 651-605-9142
> > > > > Cray Inc./ Cray Plaza, Suite 210/ 380 Jackson St./ St. Paul,
> > > > > MN
> > > > > 55101
> > > > > 
> > > > > 
> > > > > _______________________________________________
> > > > > mpiwg-fortran mailing list
> > > > > mpiwg-fortran at lists.mpi-forum.org
> > > > > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
> > > > 
> > > > 
> > > > 
> > > > --
> > > > Jeff Hammond
> > > > jeff.science at gmail.com
> > > > _______________________________________________
> > > > 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
> > > 
> > > _______________________________________________
> > > 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
> > 
> > _______________________________________________
> > 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
> 
> _______________________________________________
> 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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