[Mpi-forum] Question about MPI_Info set on communicators

[Anthony Skjellum]

Jeff, if the value can change over time, is it thread safe?
Tony




Anthony Skjellum, PhD
Professor of Computer Science and Software Engineering
COLSA Professor of Cybersecurity and Information Assurance
Director of the Auburn Cyber Research Center and Lead Cyber Scientist for Auburn
Samuel Ginn College of Engineering
Auburn University
skjellum at auburn.edu or skjellum at gmail.com
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________________________________________
From: mpi-forum <mpi-forum-bounces at lists.mpi-forum.org> on behalf of Jeff Squyres (jsquyres) <jsquyres at cisco.com>
Sent: Monday, February 15, 2016 4:34 PM
To: MPI list
Subject: [Mpi-forum] Question about MPI_Info set on communicators

This question has come up in the Open MPI community:

-----
MPI_Info_set(myinfo, "use_shared_memory", "yes");
MPI_Comm_set_info(comm, myinfo);
MPI_Comm_get_info(comm, myinfo_returned);
// Assume here that there was not enough shared memory available to use shared-memory for
// communication on this comm, so MPI_Info_get() tells us that use_shared_memory is "no".

// ...time passes, and now assume there is more shared-memory available
MPI_Comm_dup_with_info(comm, &newcom);
MPI_comm_get_info(newcom, myinfo_returned);
-----

Should newcom have "use_shared_memory" set to "yes" or "no"?

Arguments for "yes":
- the user originally asked for "yes"
- now there is shared memory available

Arguments for "no":
- the current value for "used_shared_memory" on the parent communicator is "no"

Which should it be?

MPI-3.1 6.4.2 p238 says:

"...Returns in newcomer a new communicator with the same group or groups, same topology, same info hints, any copied cached information, but a new context (see Section 6.7.1)."

So the specific question here is: what exactly does "Same info hints" mean?  The user-specific hint, or the current value of the hint?

--
Jeff Squyres
jsquyres at cisco.com
For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
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