[mpiwg-sessions] World/session model

HOLMES Daniel d.holmes at epcc.ed.ac.uk
Thu Dec 17 12:21:54 CST 2020

Hi Victor,

The phrase “not valid for use as a communicator” is carefully chosen and does *not* mean “can’t even exist”.

If a program uses both the Sessions model and the World model then that program can use MPI_COMM_WORLD within the context of the World Model but must not use it within the context of the Sessions Model.

Thus, there is no conflict between these two statements.

The Chapter Committee will take a look at the reference issue that you point out. Thanks for catching that! It had not been raised by the reviewers of that section during the Release Candidate procedure. We will hopefully be able to address it before the Final Release Meeting (Q1 2021).

Dr Daniel Holmes PhD
Architect (HPC Research)
d.holmes at epcc.ed.ac.uk<mailto:d.holmes at epcc.ed.ac.uk>
Phone: +44 (0) 131 651 3465
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Address: Room 2.09, Bayes Centre, 47 Potterrow, Central Area, Edinburgh, EH8 9BT
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On 17 Dec 2020, at 15:00, Victor Eijkhout <eijkhout at tacc.utexas.edu<mailto:eijkhout at tacc.utexas.edu>> wrote:

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I’m reading the 4.x standard. I noticed the following:

7.2.4 When using the Sessions Model (Section 11.3) for initialization of MPI
re- sources, MPI_COMM_WORLD and MPI_COMM_SELF are not valid for use as
a communica- tor.

11.3 MPI objects derived from the Sessions Model shall not be
intermixed in a single MPI procedure call with MPI objects derived
from the World Model.

Are those two at odds? The first statement seems to imply that in the second
statement objects from the world model can't even exist.


9.1.2 Environmental Inquiries

When using the World Model (Section 11.2),

This is the 3rd time the phrase “when using the World Model” appears, but the first time that the reference is given.

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