Issue with "integer" arguments in Fortran API for PNetCDF

[John Michalakes]

That would be helpful. But I think putting 32 in the name would be
misleading, since this is only an issue on 64 bit compiles.  (On 32 bit
compiles, MPI_Offset is the same length as a Fortran INTEGER).

John

> -----Original Message-----
> From: William Gropp [mailto:gropp at mcs.anl.gov]
> Sent: Wednesday, October 25, 2006 9:51 AM
> To: john at michalakes.us
> Cc: parallel-netcdf at mcs.anl.gov
> Subject: Re: Issue with "integer" arguments in Fortran API for PNetCDF
>
>
> As the Fortran interfaces are generated with a script, we could
> create an alternate version that was closer to the serial NetCDF
> interface, using a different prefix to avoid confusion (e.g., maybe
> nf32mpi_xxx).  Would that help?  What do others think of that approach?
>
> Bill
>
> On Oct 25, 2006, at 2:06 AM, John Michalakes wrote:
>
> > PS... There is a problem with the pnetcdf.inc file itself.  This file
> > defines INTEGER parameters such as NF_UNLIMITED which may be used as
> > arguments to NFMPI_* routines that are defined as
> > INTEGER(KIND=MPI_OFFSET_KIND). An example is the 3rd argument of:
> >
> > FORTRAN_API int FORT_CALL nfmpi_def_dim_ ( int *v1, char *v2
> > FORT_MIXED_LEN(d2), MPI_Offset *v3, MPI_Fint *v4 FORT_END_LEN(d2) )
> >
> > Since MPI_Offset can be 64-bits if compiled with OBJECT_MODE 64 on
> > the IBM,
> > passing NF_UNLIMITED (32-bits) as the third argument is incorrect.
> >
> > John
> >
> >> -----Original Message-----
> >> From: owner-parallel-netcdf at mcs.anl.gov
> >> [mailto:owner-parallel-netcdf at mcs.anl.gov]On Behalf Of John
> >> Michalakes
> >> Sent: Tuesday, October 24, 2006 3:30 PM
> >> To: parallel-netcdf at mcs.anl.gov
> >> Subject: Issue with "integer" arguments in Fortran API for PNetCDF
> >>
> >>
> >> I'm having a problem adapting parallel NetCDF as an option in the WRF
> >> (Weather Research and Forecast) model I/O API. WRF currently supports
> >> non-parallel NetCDF, and we're now trying to extend the model to
> >> use the new
> >> parallel NetCDF code. Have run into a problem with some of the
> >> arguments in
> >> the API for parallel-NetCDF:
> >>
> >> The original NetCDF Fortran API defines lengths, starts, and
> >> other arguments
> >> as INTEGER. PnetCDF recasts some (but not all) of these arguments as
> >> MPI_Offset. We compile WRF with OBJECT_MODE 64 on the IBMs where
> >> KIND=MPI_OFFSET_KIND works out to 8 bytes. Thus, the calls in WRF
> >> that pass
> >> these arguments as 32-bit INTEGERs from Fortran are causing
> >> PNetCDF to see
> >> garbage in the high four bytes of the dummy argument. For example,
> >> the
> >> length argument to NFMPI_DEF_DIM ends up being 73 + a very-large-
> >> garbage
> >> value instead of 73.
> >>
> >> I was hoping for a relatively quick drop-in of PnetCDF into WRF
> >> I/O API but
> >> this now seems unlikely. There is a large amount of NetCDF
> >> interface code in
> >> WRF that will need to be gone through.  Or I can write a wrapper
> >> lib for all
> >> these routines.
> >>
> >> Has anyone done this already? What's needed is for the wrapper
> >> routine to
> >> accept INTEGER arguments and copy them to INTEGER
> >> (KIND=MPI_OFFSET_KIND) to
> >> be used as arguments to the actual NFMPI_* routines in PNetCDF and
> >> (in the
> >> case of return values) copy them back to INTEGER again.
> >>
> >> Not arguing, but curious: since PNetCDF is supposed to be a parallel
> >> implementation of the NetCDF API, why was the API altered this way
> >> to use
> >> arguments of type MPI_Offset instead of INTEGER? At least for what
> >> I'm
> >> trying to do, it is a significant impediment.
> >>
> >> I really appreciate that parallel NetCDF is being developed. It
> >> is very much
> >> needed, especially now as we try moving to Petascale. Kudos to the
> >> developers.
> >>
> >> John
> >>
> >> -----------------------------------------------------------
> >> John Michalakes, Software Engineer        michalak at ucar.edu
> >> NCAR, MMM Division                   voice: +1 303 497 8199
> >> 3450 Mitchell Lane                     fax: +1 303 497 8181
> >> Boulder, Colorado 80301 U.S.A.        cell: +1 720 209 2320
> >>         http://www.mmm.ucar.edu/individual/michalakes
> >> -----------------------------------------------------------
> >>
> >
>