Re: [mpi-21] Ballot 4 proposal: fix attribute example 4.13

[Jeff Squyres <jsquyres@xxxxxxxxx>]

Terry and I further noticed that there appears to be another minor  
problem in example 4.13.  So here's an addendum to the proposal:

MPI-2:4.12.7 p59 line 1 reads:

  int *p

But should read

  MPI_Aint *p

Rationale: The value that is set from fortran is an  
INTEGER(kind=MPI_ADDRESS_KIND).  Hence, to dereference it properly,  
the corresponding C pointer type needs to be an (MPI_Aint*), not (int*).


On Feb 7, 2008, at 12:04 PM, Terry Dontje wrote:

> After talking with Jeff and reading the spec further I retract my
> concern because the spec does explicitly cover my concern in the  
> verbage
> above example 4.13.
>
> --td
>
> Terry Dontje wrote:
> > Sorry I didn't send this out sooner but in reading the discussion for
> > the errata item "Interlaguage use of Attributes" I think the below
> > proposal has a potential hole that never was resolved in the mail
> > discussion in:
> > http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-errata/discuss/getattr/
> >
> >
> > The specific hole pointed out by Nick Nevin in the following  
> > paragraph
> > from the email discussion:
> >
> > This might work for predefined attributes where the address can
> > point to the integer value in static storage, but won't work for
> > attributes set by the user in Fortran code.  If you store a pointer
> > to the integer as the attribute it may point to a temporary which
> > might no longer exist when you try and access it later.
> >
> >
> > So I think relying on the address passed in for the attribute as
> > opposed to the value could cause some
> > issues with Fortran.
> >
> > --td
> > Jeff Squyres wrote:
> > > Per
> > > http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-errata/ 
> > > ,
> > > the errata item entitled "Error in Example 4.13 in MPI-2 (Use of
> > > Attributes in C and Fortran)".  I believe that this errata item
> > > supersedes the errata item "Interlanguage use of Attributes".
> > >
> > > See the mail discussing:
> > >
> > > http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-errata/discuss/attrcandf/
> > >
> > >
> > > Proposal:
> > >
> > > Change MPI-2:4.12, p58:36 from:
> > >  IF (val.NE.5) THEN CALL ERROR
> > > to
> > >  IF (val.NE.address_of_i) THEN CALL ERROR
> > >
> > > Rationale:
> > >
> > > MPI-2:4.12 p58:12-13 and 16-18 clearly state that if an attribute is
> > > set by C, retrieving it in Fortran will obtain the address of the
> > > attribute.
> > >
> > > See the mails for more discussion, including an exhaustive list of
> > > what happens for each of the 9 possibilities of setting and getting
> > > attribute values between the different languages.
>
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--
Jeff Squyres
Cisco Systems