[petsc-dev] Including petsc.h breaks user code

[Barry Smith]

  Matt,

   I ran with OpenMPI and got exactly the error you’d expect and what they reported "An error occurred in MPI_Type_size”. A simple use of the debugger would reveal where it happened. I suspect that MPICH is more generous when you call MPI_Type_size() with a null type, perhaps it just gives a size of zero.

   I hunted around on the web and could not find a definitive statement of what MPI_Type_size() should do when passed an argument of a null datatype.


   Barry

On Sep 15, 2014, at 4:40 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Sun, Sep 14, 2014 at 8:36 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
>    Pierre,
> 
>      Thanks for reporting this, it is, indeed our bug. In petsclog.h we have macros for the various MPI calls in order to log their usage, for example,
> 
> #define MPI_Scatter(sendbuf,sendcount,sendtype,recvbuf,recvcount,recvtype,root,comm) \
>  ((petsc_scatter_ct++,0) || PetscMPITypeSize(&petsc_recv_len,recvcount,recvtype) || MPI_Scatter(sendbuf,sendcount,sendtype,recvbuf,recvcount,recvtype,root,comm))
> 
> but PetscMPITypeSize() simply called MPI_Type_size() which generated an MPI error for MPI_DATATYPE_NULL
> 
> PETSC_STATIC_INLINE PetscErrorCode PetscMPITypeSize(PetscLogDouble *buff,PetscMPIInt count,MPI_Datatype type)
> {
>   PetscMPIInt mysize; return  (MPI_Type_size(type,&mysize) || ((*buff += (PetscLogDouble) (count*mysize)),0));
> }
> 
> What error did you get? Why did I not get this error when I ran it? I ran with MPICH 3.0.4 since that was the one I had compiled for C++.
> 
>   Matt
>  
> In the branch barry/fix-usage-with-mpidatatypenull I have added a check for this special case and avoid the MPI_Type_size() call. I will put this branch into next and if all tests pass it will be merged into maint and master and be in the next patch release.
> 
>    Thank you for reporting the problem.
> 
>    Barry
> 
> Barry still thinks MPI 1.1 is the height of HPC computing :-(
> 
> 
> 
> On Sep 14, 2014, at 4:16 PM, Pierre Jolivet <jolivet at ann.jussieu.fr> wrote:
> 
> > Hello,
> > Could you please explain to me why the following example is not working properly when <petsc.h> (from master, with OpenMPI 1.8.1) is included ?
> >
> > $ mpicxx in-place.cpp  -I$PETSC_DIR/include -I$PETSC_DIR/$PETSC_ARCH/include -L$PETSC_DIR/$PETSC_ARCH/lib -lpetsc
> > $ mpirun -np 2 ./a.out
> > Done with the scatter !
> > 0 0 0 0 (this line should be filled with 0)
> > 1 1 1 1 (this line should be filled with 1)
> > Done with the gather !
> >
> > $ mpicxx in-place.cpp  -I$PETSC_DIR/include -I$PETSC_DIR/$PETSC_ARCH/include -L$PETSC_DIR/$PETSC_ARCH/lib -lpetsc -DPETSC_BUG
> > $ mpirun -np 2 ./a.out
> > [:3367] *** An error occurred in MPI_Type_size
> > [:3367] *** reported by process [4819779585,140733193388032]
> > [:3367] *** on communicator MPI_COMM_WORLD
> > [:3367] *** MPI_ERR_TYPE: invalid datatype
> > [:3367] *** MPI_ERRORS_ARE_FATAL (processes in this communicator will now abort,
> > [:3367] ***    and potentially your MPI job)
> >
> > Thank you for looking,
> > Pierre
> >
> > <in-place.cpp>
> 
> 
> 
> 
> -- 
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener