That's ridiculous. You can have 0 of anything. There is absolutely no logical reason why MPI_DATATYPE_NULL should not be valid with count=0. Are you suggesting that one cannot pass buffer=NULL when count=0 either?
Jeff On Tue, Jan 12, 2016 at 6:06 PM, George Bosilca <bosi...@icl.utk.edu> wrote: > As JH mentioned the examples are not normative. The type MPI_DATATYPE_NULL > is not part of the MPI predefined datatypes, and as such is not expected to > be a commited datatype, thus improper for communications (even when the > count is 0). > > George. > > > On Tue, Jan 12, 2016 at 8:25 PM, Jim Edwards <jedwa...@ucar.edu> wrote: > >> 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 >> >> _______________________________________________ >> 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/2016/01/28254.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/2016/01/28255.php > -- Jeff Hammond jeff.scie...@gmail.com http://jeffhammond.github.io/
