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

[William Gropp]

Actually, MPICH is incorrect here.  NULL objects are an error unless specifically permitted.

Bill

On Sep 15, 2014, at 1:08 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

> 
>  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
>