Hi Gilles, I think that your conversation with Jeff pretty much covered it but your understanding of my original problem is correct. Thanks for the prompt response and the PR.
On Tue, Jan 12, 2016 at 5:59 PM, Jeff Hammond <jeff.scie...@gmail.com> wrote: > Consider MPI_Get_accumulate with op=MPI_NO_OP, which is used to achieve > atomic Get. Obviously, one does not want to allocate and describe a source > buffer that will not be touched by this. This is a case like MPI_Alltoallw > where (NULL,0,MPI_DATATYPE_NULL) needs to work at participating processes. > > Best, > > Jeff > > On Tue, Jan 12, 2016 at 4:46 PM, Gilles Gouaillardet < > gilles.gouaillar...@gmail.com> wrote: > >> Thanks Jeff, >> >> i could not find anything in the standard that says this is an invalid >> usage ... so i can only agree this is a bug. >> >> fwiw, example 4.23 is working fine with OpenMPI >> but that is a different case : with MPI_Gather and friends, recv stuff >> is irrelevant on non root task. >> in the case of MPI_Alltoallw and friends, no parameter is ignored. >> >> fortunatly, the fix is pretty trivial, so i will make a PR from now >> >> Cheers, >> >> Gilles >> >> >> On Wed, Jan 13, 2016 at 9:37 AM, Jeff Hammond <jeff.scie...@gmail.com> >> wrote: >> > 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/ >> > >> > _______________________________________________ >> > 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/2016/01/28251.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/2016/01/28252.php >> > > > > -- > Jeff Hammond > jeff.scie...@gmail.com > http://jeffhammond.github.io/ > > _______________________________________________ > 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/2016/01/28253.php > -- Jim Edwards CESM Software Engineer National Center for Atmospheric Research Boulder, CO
