[mpi-21] Ballot 4 - Re: Request for interpretation

[Rolf Rabenseifner]

I try to summarize all 3 replies in one proposal:

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Proposal:
MPI 2.0, Sect. 4.10 Info Objects, page 43, line 38-40 read:
   If a function does not recognize a key, 
   it will ignore it, unless otherwise specified.
   If an implementation recognizes a key but does not recognize 
   the format of the corresponding value, the result is undefined.
but should read:
   An implementation must support info objects as caches for arbitrary
   (key, value) pairs, regardless of whether it recognizes the pairs.
   Each MPI function which takes hints in the form of an MPI_Info must
   be prepared to ignore any key it does not recognize.

Add after MPI 2.0, Sect. 4.10 Info Objects, page 44, line 22 a new
paragraph:
   Advice to implementors.
   Although in MPI functions that take hints in form of an MPI_Info
   (e.g., in process creation and management, one-sided communication, 
   or parallel file I/O), an implementation must be prepared to ignore 
   keys that it does not recognize, for the purpose of MPI_INFO_GET_NKEYS, 
   MPI_INFO_GET_NTHKEY, MPI_INFO_GET_VALUELEN, and MPI_INFO_GET, the 
   implementation must retain all (key,value) pairs so that layered 
   functionality can also use the Info object.
   (End of advice to implementors.)
_____________________________
Rationale for this clarification:
  
   The MPI-2.0 text allowed that also MPI_INFO_DELETE, MPI_INFO_SET,
   MPI_INFO_GET, and MPI_INFO_DUP could ignore (key,value) pairs
   that are not recognized in routines in other chapters that
   take hints with info arguments.
   The proposed clarification is necessary when we assume, that 
   layered implementation of parts of the MPI-2 standard should 
   be possible and may use the MPI_Info objects for their needs.
   This was a goal of the MPI-2 Forum and the MPI-2.0 specification.
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Bronis, for me, your wording "an MPI implementation may restrict" was
in conflict with the rest of the advice. I hope the formulation above
is also okay. It is based on the new wording from you and Dick in first 
part of the proposal.

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)