Jeff probably ran with MPICH. Open MPI's are consistent with our choice of definition for size=0:
query: me=1, them=0, size=0, disp=1, base=0x0 query: me=1, them=1, size=4, disp=1, base=0x1097e30f8 query: me=1, them=2, size=4, disp=1, base=0x1097e30fc query: me=1, them=3, size=4, disp=1, base=0x1097e3100 query: me=2, them=0, size=0, disp=1, base=0x0 query: me=2, them=1, size=4, disp=1, base=0x109fe10f8 query: me=2, them=2, size=4, disp=1, base=0x109fe10fc query: me=2, them=3, size=4, disp=1, base=0x109fe1100 query: me=2, them=PROC_NULL, size=4, disp=1, base=0x109fe10f8 query: me=3, them=0, size=0, disp=1, base=0x0 query: me=3, them=1, size=4, disp=1, base=0x1088f30f8 query: me=3, them=2, size=4, disp=1, base=0x1088f30fc query: me=3, them=3, size=4, disp=1, base=0x1088f3100 query: me=3, them=PROC_NULL, size=4, disp=1, base=0x1088f30f8 query: me=0, them=0, size=0, disp=1, base=0x0 query: me=0, them=1, size=4, disp=1, base=0x105b890f8 query: me=0, them=2, size=4, disp=1, base=0x105b890fc query: me=0, them=3, size=4, disp=1, base=0x105b89100 query: me=0, them=PROC_NULL, size=4, disp=1, base=0x105b890f8 query: me=1, them=PROC_NULL, size=4, disp=1, base=0x1097e30f8 To be portable only use MPI_Win_shared_query and do not rely on the return value of base if you pass size = 0. -Nathan On Thu, Feb 11, 2016 at 08:23:16PM +0000, Peter Wind wrote: > Thanks Jeff, that was an interesting result. The pointers are here well > defined, also for the zero size segment. > However I can't reproduce your output. I still get null pointers (output > below). > (I tried both 1.8.5 and 1.10.2 versions) > What could be the difference? > Peter > mpirun -np 4 a.out > query: me=0, them=0, size=0, disp=1, base=(nil) > query: me=0, them=1, size=4, disp=1, base=0x2aee280030d0 > query: me=0, them=2, size=4, disp=1, base=0x2aee280030d4 > query: me=0, them=3, size=4, disp=1, base=0x2aee280030d8 > query: me=0, them=PROC_NULL, size=4, disp=1, base=0x2aee280030d0 > query: me=1, them=0, size=0, disp=1, base=(nil) > query: me=1, them=1, size=4, disp=1, base=0x2aabbb9ce0d0 > query: me=1, them=2, size=4, disp=1, base=0x2aabbb9ce0d4 > query: me=1, them=3, size=4, disp=1, base=0x2aabbb9ce0d8 > query: me=1, them=PROC_NULL, size=4, disp=1, base=0x2aabbb9ce0d0 > query: me=2, them=0, size=0, disp=1, base=(nil) > query: me=2, them=1, size=4, disp=1, base=0x2b1579dd40d0 > query: me=2, them=2, size=4, disp=1, base=0x2b1579dd40d4 > query: me=2, them=3, size=4, disp=1, base=0x2b1579dd40d8 > query: me=2, them=PROC_NULL, size=4, disp=1, base=0x2b1579dd40d0 > query: me=3, them=0, size=0, disp=1, base=(nil) > query: me=3, them=1, size=4, disp=1, base=0x2ac8d2c350d0 > query: me=3, them=2, size=4, disp=1, base=0x2ac8d2c350d4 > query: me=3, them=3, size=4, disp=1, base=0x2ac8d2c350d8 > query: me=3, them=PROC_NULL, size=4, disp=1, base=0x2ac8d2c350d0 > > ---------------------------------------------------------------------- > > See attached. Output below. Note that the base you get for ranks 0 and > 1 is the same, so you need to use the fact that size=0 at rank=0 to know > not to dereference that pointer and expect to be writing into rank 0's > memory, since you will write into rank 1's. > I would probably add "if (size==0) base=NULL;" for good measure. > Jeff > > $ mpirun -n 4 ./a.out > > query: me=0, them=0, size=0, disp=1, base=0x10bd64000 > > query: me=0, them=1, size=4, disp=1, base=0x10bd64000 > > query: me=0, them=2, size=4, disp=1, base=0x10bd64004 > > query: me=0, them=3, size=4, disp=1, base=0x10bd64008 > > query: me=0, them=PROC_NULL, size=4, disp=1, base=0x10bd64000 > > query: me=1, them=0, size=0, disp=1, base=0x102d3b000 > > query: me=1, them=1, size=4, disp=1, base=0x102d3b000 > > query: me=1, them=2, size=4, disp=1, base=0x102d3b004 > > query: me=1, them=3, size=4, disp=1, base=0x102d3b008 > > query: me=1, them=PROC_NULL, size=4, disp=1, base=0x102d3b000 > > query: me=2, them=0, size=0, disp=1, base=0x10aac1000 > > query: me=2, them=1, size=4, disp=1, base=0x10aac1000 > > query: me=2, them=2, size=4, disp=1, base=0x10aac1004 > > query: me=2, them=3, size=4, disp=1, base=0x10aac1008 > > query: me=2, them=PROC_NULL, size=4, disp=1, base=0x10aac1000 > > query: me=3, them=0, size=0, disp=1, base=0x100fa2000 > > query: me=3, them=1, size=4, disp=1, base=0x100fa2000 > > query: me=3, them=2, size=4, disp=1, base=0x100fa2004 > > query: me=3, them=3, size=4, disp=1, base=0x100fa2008 > > query: me=3, them=PROC_NULL, size=4, disp=1, base=0x100fa2000 > > On Thu, Feb 11, 2016 at 8:55 AM, Jeff Hammond <jeff.scie...@gmail.com> > wrote: > > On Thu, Feb 11, 2016 at 8:46 AM, Nathan Hjelm <hje...@lanl.gov> wrote: > > > > > > On Thu, Feb 11, 2016 at 02:17:40PM +0000, Peter Wind wrote: > > > I would add that the present situation is bound to give > problems for some > > > users. > > > It is natural to divide an array in segments, each process > treating its > > > own segment, but needing to read adjacent segments too. > > > MPI_Win_allocate_shared seems to be designed for this. > > > This will work fine as long as no segment as size zero. It can > also be > > > expected that most testing would be done with all segments > larger than > > > zero. > > > The document adding "size = 0 is valid", would also make people > confident > > > that it will be consistent for that special case too. > > > > Nope, that statement says its ok for a rank to specify that the > local > > shared memory segment is 0 bytes. Nothing more. The standard > > unfortunately does not define what pointer value is returned for a > rank > > that specifies size = 0. Not sure if the RMA working group > intentionally > > left that undefine... Anyway, Open MPI does not appear to be out of > > compliance with the standard here. > > > MPI_Alloc_mem doesn't say what happens if you pass size=0 either. The > RMA working group intentionally tries to maintain consistency with the > rest of the MPI standard whenever possible, so we did not create a new > semantic here. > MPI_Win_shared_query text includes this: > "If all processes in the group attached to the window specified size = > 0, then the call returns size = 0 and a baseptr as if MPI_ALLOC_MEM > was called with size = 0." > > > > > To be safe you should use MPI_Win_shared_query as suggested. You can > > pass MPI_PROC_NULL as the rank to get the pointer for the first > non-zero > > sized segment in the shared memory window. > Indeed! I forgot about that. MPI_Win_shared_query solves this > problem for the user brilliantly. > Jeff > -- > Jeff Hammond > jeff.scie...@gmail.com > http://jeffhammond.github.io/ > > -- > 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/2016/02/28508.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/2016/02/28511.php
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