[mpiwg-sessions] MPI_Buffer_attach in the sessions model

Tony Skjellum skjellum at gmail.com
Sat Sep 17 08:17:58 CDT 2022

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.


Anthony Skjellum, PhD

On Sep 17, 2022, at 8:42 AM, Rolf Rabenseifner via mpiwg-sessions <mpiwg-sessions at lists.mpi-forum.org> 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

Dr. Rolf Rabenseifner . . . . . . . . . .. . . rabenseifner at hlrs.de .
High Performance Computing Center (HLRS) . . . ++49(0)711/685-65530 .
University of Stuttgart . . . . . . www.hlrs.de/people/rabenseifner .
Nobelstr. 19, 70569 Stuttgart, Germany
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