Dear Tony, please read MPI-3.1 page 338, lines 36-41. Do these lines resolve your question?
Best regards Rolf ----- Original Message ----- > From: "Main MPI Forum mailing list" <mpi-forum@lists.mpi-forum.org> > To: "Main MPI Forum mailing list" <mpi-forum@lists.mpi-forum.org> > Cc: "Anthony Skjellum" <skjel...@gmail.com> > Sent: Wednesday, October 14, 2020 7:01:54 PM > Subject: [Mpi-forum] Question about MPI_Alloc_mem > Folks, I know we have had this function for a long time, and I've implemented > ports of MPI that actually use it (e.g., with pre-pinned memory). But, I am > trying to understand the logic for why baseptr is passed by value, instead of > by reference. In C, everything is by value, so the last argument in normal C > programs would be void **baseptr. > > The standard has: > int MPI_Alloc_mem(MPI_Aint size, MPI_Info info, void *baseptr); > Now, MPICC/GCC takes this with > void *memory = (void *)0; > int error = MPI_Alloc_mem(1024, MPI_INFO_NULL, &memory); > and you get the memory allocated properly. > What is more, this is incorrect: > int error = MPI_Alloc_mem(1024, MPI_INFO_NULL, memory); > although it compiles fine because that is, indeed, the API. > Why would we have the pointer going in by value, when it is coming out > as an OUT argument? > Isn't this plain wrong? void **baseptr means ---> I am passing you the > address of a void pointer. > Every viable implementation must do *(void **)baseptr = ... > when providing the "malloc'd/special" memory. So... why did we fudge > the C API. Is there some tie-in with the Fortran API? > Thanks in advance, > Tony Skjellum > > > -- > Anthony Skjellum, PhD > [ mailto:skjel...@gmail.com | skjel...@gmail.com ] > Cell: +1-205-807-4968 > > > > _______________________________________________ > mpi-forum mailing list > mpi-forum@lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-forum -- Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseif...@hlrs.de . High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 . University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 . Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner . Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) . _______________________________________________ mpi-forum mailing list mpi-forum@lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpi-forum
