[mpi-21] Ballot 4 - User defined datarep - was Re: Question toMPI/IO

[Rajeev Thakur]

>   Then in subsequent calls to the conversion function, 
>   MPI will increment the value in position by the count of items 
>   converted in the previous call, and userbuf is kept unchanged. 

Maybe we should be more clear and say that "the userbuf pointer is left
unchanged"
  
Rajeev

> -----Original Message-----
> From: mpi-21-bounces_at_[hidden] 
> [mailto:mpi-21-bounces_at_[hidden]] On Behalf Of Rolf Rabenseifner
> Sent: Thursday, January 31, 2008 10:49 AM
> To: mpi-21_at_[hidden]
> Subject: [mpi-21] Ballot 4 - User defined datarep - was Re: 
> Question toMPI/IO
> 
> This is a proposal for MPI 2.1, Ballot 4.
> 
> I'm asking especially 
>   Hubert Ritzdorf, Jean-Pierre Prost, John May, Bill Nitzberg,
> the participants of the email-discussion in 1999, to review 
> this proposal.
> 
> This is a follow up to:
>   Interpretation of user defined datarep 
>   in 
> http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-
> errata/index.html
> with mail discussion in
>   
> http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-
> errata/discuss/datarep/
> ___________________________________
> 
> Proposal:
> MPI-2.0 Sect. 9.5.3 User-defined Data Representations, page 254, 
> lines 13-15 read:
>   Then in subsequent calls to the conversion function, 
>   MPI will increment the value in position by the count of items 
>   converted in the previous call.
>  
> but should read:
>   Then in subsequent calls to the conversion function, 
>   MPI will increment the value in position by the count of items 
>   converted in the previous call, and userbuf is kept unchanged. 
>   
> ___________________________________
> Rationale for this clarification:
>   It was not clear, whether the userbuf pointer must also be moved
>   in the subsequent calls. This clarification was already done in 
>   1999 and should already be implemented in existing implementations
>   of user-defined data representations.
> ___________________________________
> Total text page 254 lines 8-15:
>   If MPI cannot allocate a buffer large enough to hold all the 
>   data to be converted from a read operation, it may call the 
>   conversion function repeatedly using the same datatype and 
>   userbuf, and reading successive chunks of data to be converted 
>   in filebuf. For the first call (and in the case when all the data 
>   to be converted fits into filebuf), MPI will call the function 
>   with position set to zero. Data converted during this call will 
>   be stored in the userbuf according to the first count data items 
>   in datatype. Then in subsequent calls to the conversion function, 
>   MPI will increment the value in position by the count of items 
>   converted in the previous call,
>   (new text added:)
>   and userbuf is kept unchanged. 
> ___________________________________
> 
> Best regards
> Rolf
> 
> 
> Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner_at_[hidden]
> 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: Allmandring 30)
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>