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

Thu Jan 31 13:16:20 CST 2008

Jim

The sense I get from the phrase "the behavior is undefined" is that
defining the behavior is beyond the scope of the standard.

The MPI standard does have some predefined keys and requires an
implementation that supports any predefined key to support it as described
by the standard.  That can lead to one place in the standard saying "the
behavior is undefined" and another saying "here is the definition of the
behavior".

Maybe I am reading more than others into the phrase "the behavior is
undefined" but it does have this strong implication in my mind.

How is this ?

An implementation must support info objects as caches for arbitrary
key, value) pairs, regardless of whether it recognizes the key.
Each function that takes hints in the form of an MPI_Info must
be prepared to ignore any key it does not recognize. This description
of info objects does not attempt to define how a particular function
should react if it recognizes a key but not the associated value.

note:
I also changed MPI function to simply function because with this free form
approach to the info object, it seems to me a third party library that is
intended to work as part of an MPI program may want to use MPI_Info objects
too.  If someone authors a parallel math library and wants the
initialization routine to look like:
   init_pmath( MPI_Info info)
why not?  They should understand that init_pmath must ignore keys it does
not recognize even if i is not an MPI_ routine.

               Dick

Dick Treumann  -  MPI Team/TCEM
IBM Systems & Technology Group
Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
Tele (845) 433-7846         Fax (845) 433-8363

mpi-21-bounces_at_[hidden] wrote on 01/31/2008 09:39:52 AM:

> As you are saying, there are two different classes of errors here.
>
> 1) Keys which are not understood and need to be ignored by functions
> which donâ€™t grok them (â€œJIMS_SECRET_TAGâ€,â€99â€)
> 2) Keys which are understood by a function, but with a value which
> is not (â€œbuffer_sizeâ€, â€œHelloâ€)
>
> I think allowing the second type to have undefined behavior is the
> right thing to do, since itâ€™s the most general.
> If your implementation wants to define the behavior of some out-of-
> range values, thatâ€™s fine and doesnâ€™t make you non-conforming, it
> just means you defined the previously undefined behavior for some
> set of values.
>
> Having that undefined-ness explicit here (in one central place)
> seems to make sense (if only because it may be omitted in one of the
> other places where it should appear).
>
> My addition does not alter the existing change which guarantees case
> 1, itâ€™s only concerned with case 2.
> -- Jim
>
> James Cownie <james.h.cownie_at_[hidden]>
> SSG/DPD/PAT
> Tel: +44 117 9071438
>
> From: mpi-21-bounces_at_[hidden] [mailto:mpi-21-bounces_at_[hidden]]
> On Behalf Of Richard Treumann
> Sent: 31 January 2008 14:20
> To: Mailing list for discussion of MPI 2.1
> Subject: Re: [mpi-21] Ballot 4 - Re: Request for interpretation
>
> Jim -
>
> I was taking the view that the description of what to do for a
> recognized key but dubious value belongs to the function that
> recognizes the specific key. For example if MPI_File_open accepts a
> "buffer_size" hint with range "32K" to "16M" we may want to define
> the behavior of hints that are out of range.
>
> Once we say an info can have arbitrary keys we need to state that
> every info consumer must be prepared to ignore keys it does not
> recognize because we have made unrecognizable keys legitimate.
>
> Dick
> Dick Treumann - MPI Team/TCEM
> IBM Systems & Technology Group
> Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
> Tele (845) 433-7846 Fax (845) 433-8363
>
>
> mpi-21-bounces_at_[hidden] wrote on 01/31/2008 08:43:04 AM:
>
> > However, you have apparently lost the liberty to have undefined
> > behavior which was there in the previous version.
> >
> > Maybe you should keep that, something like
> > An implementation must support info objects as caches for arbitrary
> > (key, value) pairs, regardless of whether it recognizes the keys.
> > Each MPI function which takes hints in the form of an MPI_Info must
> > be prepared to ignore any key it does not recognize. However if a
> > function recognizes a key but not the associated value, then the
> > behavior is undefined.
> > (Modifications in italics)
> > -- Jim
> >
> > James Cownie <james.h.cownie_at_[hidden]>
> > SSG/DPD/PAT
> > Tel: +44 117 9071438
> >
> > From: mpi-21-bounces_at_[hidden] [mailto:mpi-21-bounces_at_[hidden]]
> > On Behalf Of Richard Treumann
> > Sent: 31 January 2008 13:29
> > To: Mailing list for discussion of MPI 2.1
> > Subject: Re: [mpi-21] Ballot 4 - Re: Request for interpretation
> >
> > Your wording works for me Rolf. -- Thanks
> >
> >
> > Dick Treumann - MPI Team/TCEM
> > IBM Systems & Technology Group
> > Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
> > Tele (845) 433-7846 Fax (845) 433-8363
> >
> >
> > mpi-21-bounces_at_[hidden] wrote on 01/31/2008 05:25:46 AM:
> >
> > > I try to summarize all 3 replies in one proposal:
> > >
> > > ___________________________________
> > >
> > > 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.
> > > ___________________________________
> > >
> > > 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)
> > > _______________________________________________
> > > mpi-21 mailing list
> > > mpi-21_at_[hidden]
> > > http://lists.cs.uiuc.edu/mailman/listinfo/mpi-21
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