Rolf, you’ve discovered a problem with the spec… it’s global to attach a buffer, so implicitly associated with ‘world model’ and the communicators derived from MPI_Comm_world … Each session is to be isolated resource wise … so, we have to make a new API when there is no world model . The API would take a session key to align buffer attachment to a session in my opinion. Use of the current api with a session appears erroneous. :-) I am sure it would work in real implementations nonetheless. Tony Anthony Skjellum, PhD 205-807-4968 On Sep 17, 2022, at 8:42 AM, Rolf Rabenseifner via mpiwg-sessions <[email protected]> wrote: Dear sessions-group, is there any information about the usage of MPI_Buffer_attach, MPI_Buffer_detach and MPI_Bsend for applications that use the world model together with (several) sessions. MPI-4.0, the function index entries of MPI_Buffer_attach and the corresponding texts do not give an answer, or do they? Is it allowed or intended that two MPI_Bsend calls with two different communicators derived not from the same session or world may use portions of the same buffer that was attached with MPI_Buffer_attach? Is there any issue or pull request already for this problem prepared? Or slides in previous meetings? Best regards Rolf -- Dr. Rolf Rabenseifner . . . . . . . . . .. . . [email protected] . High Performance Computing Center (HLRS) . . . ++49(0)711/685-65530 . University of Stuttgart . . . . . . www.hlrs.de/people/rabenseifner . Nobelstr. 19, 70569 Stuttgart, Germany _______________________________________________ mpiwg-sessions mailing list [email protected] https://lists.mpi-forum.org/mailman/listinfo/mpiwg-sessions