Example 4.23 of MPI 3.1 (it is hardly a new example, but may have a different number in older versions) demonstrates the use of (buffer=NULL,count=0,type=MPI_DATATYPE_NULL). While examples in the MPI standard are not normative text, this is certainly a valid use of MPI. I can't find a citation where it says explicitly that this is correct, but it follows logically from other text.
The MPICH macro MPIR_ERRTEST_USERBUFFER that is used through the code to test for valid user buffers begins with "if (count > 0..." and thus does concern itself with the type or buffer pointer when count=0. Furthermore, this macro is redundantly protected with a count>0 check when used in MPI_Alltoallw (and other collectives). Best, Jeff On Tue, Jan 12, 2016 at 4:18 PM, Gilles Gouaillardet <gil...@rist.or.jp> wrote: > > Hi Jim, > > can you please confirm my understanding is correct : > > - OpenMPI does *not* accept MPI_DATATYPE_NULL as an input of MPI_Alltoallw > - mpich does accept MPI_DATATYPE_NULL as an input of MPI_Alltoallw *if* the corresponding count *is* zero > - mpich does *not* accept MPI_DATATYPE_NULL as an input of MPI_Alltoallw *if* the corresponding count is *not* zero > > So you are considering as a bug the fact OpenMPI does not accept MPI_DATATYPE_NULL *with* a zero count. > > am i correct ? > > Cheers, > > Gilles > > > On 1/13/2016 8:27 AM, Jim Edwards wrote: > > Hi, > > I am using OpenMPI-1.8.3 built with gcc 4.8.3 > and I am using an MPI_Alltoallw call to perform > an all to some (or some to all) communication. > > In the case in which my task is not sending (or receiving) any data I set the > datatype for that send or recv buffer to MPI_DATATYPE_NULL - this > works fine with other mpi libraries but fails in openmpi. If I set > the datatype to something else say MPI_CHAR - it works fine. I think > that this is a bug in open-mpi - would you agree? > > > > > -- > Jim Edwards > > CESM Software Engineer > National Center for Atmospheric Research > Boulder, CO > > > _______________________________________________ > users mailing list > us...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users > Link to this post: http://www.open-mpi.org/community/lists/users/2016/01/28249.php > > > > _______________________________________________ > users mailing list > us...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users > Link to this post: http://www.open-mpi.org/community/lists/users/2016/01/28250.php -- Jeff Hammond jeff.scie...@gmail.com http://jeffhammond.github.io/
