[mpiwg-sessions] more excitement - more nuanced response to issue 435

Pritchard Jr., Howard howardp at lanl.gov
Fri Feb 19 12:13:42 CST 2021

HI All,

Ah this is exciting.  So I spent some time on baking verbiage to add about MPI_Session_finalize non-local behavior.

See the attached cutout from the results pdf.

I’ve added verbiage describing the semantics (copying some wording from MPI_Sendrecv, or at least the flavor) of session finalize in the event that the user has not cleaned up MPI objects associated with the session(s).
It’s a simple easy to understand (I think) model.  Basically session finalize has the semantics of a MPI_Ialltoall for each communicators still associated with the session at finalize, followed by a waitall.  As long as all other processes finalizing their sessions generate in aggregate, a message pattern which matches, no deadlock.  If not,  potential deadlock.  One takeaway from this is that we can’t support arbitrary associations of communicators to sessions in each MPI process when the app doesn’t do its own cleanup so as to make MPI_Session_finalize a local op.

I’ve added some examples and we can add more as we think needed.  May have to change the presentation mechanism however.

I didn’t want to open this as a PR at this point, hence this notification mechanism.



Howard Pritchard
Los Alamos National Laboratory

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