On Wed, Feb 10, 2016 at 8:44 AM, Peter Wind <peter.w...@met.no> wrote:
> I agree that in practice the best practice would be to use > Win_shared_query. > > Still I am confused by this part in the documentation: > "The allocated memory is contiguous across process ranks unless the info > key *alloc_shared_noncontig* is specified. Contiguous across process > ranks means that the first address in the memory segment of process i is > consecutive with the last address in the memory segment of process i - 1. > This may enable the user to calculate remote address offsets with local > information only." > > Isn't this an encouragement to use the pointer of Win_allocate_shared > directly? > > No, it is not. Win_allocate_shared only gives you the pointer to the portion of the allocation that is owned by the calling process. If you want to access the whole slab, call Win_shared_query(..,rank=0,..) and use the resulting baseptr. I attempted to modify your code to be more correct, but I don't know enough Fortran to get it right. If you can parse C examples, I'll provide some of those. Jeff > Peter > > ------------------------------ > > I don't know about bulletproof, but Win_shared_query is the *only* valid > way to get the addresses of memory in other processes associated with a > window. > > The default for Win_allocate_shared is contiguous memory, but it can and > likely will be mapped differently into each process, in which case only > relative offsets are transferrable. > > Jeff > > On Wed, Feb 10, 2016 at 4:19 AM, Gilles Gouaillardet < > gilles.gouaillar...@gmail.com> wrote: > >> Peter, >> >> The bulletproof way is to use MPI_Win_shared_query after >> MPI_Win_allocate_shared. >> I do not know if current behavior is a bug or a feature... >> >> Cheers, >> >> Gilles >> >> >> On Wednesday, February 10, 2016, Peter Wind <peter.w...@met.no> wrote: >> >>> Hi, >>> >>> Under fortran, MPI_Win_allocate_shared is called with a window size of >>> zero for some processes. >>> The output pointer is then not valid for these processes (null pointer). >>> Did I understood this wrongly? shouldn't the pointers be contiguous, so >>> that for a zero sized window, the pointer should point to the start of the >>> segment of the next rank? >>> The documentation explicitly specifies "size = 0 is valid". >>> >>> Attached a small code, where rank=0 allocate a window of size zero. All >>> the other ranks get valid pointers, except rank 0. >>> >>> Best regards, >>> Peter >>> _______________________________________________ >>> 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/2016/02/28485.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/2016/02/28493.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/2016/02/28496.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/2016/02/28497.php > -- Jeff Hammond jeff.scie...@gmail.com http://jeffhammond.github.io/
sharetest.f90
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