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 ----- Original Message ----- > 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
