[Mpi-forum] Proposal process for a side document for C++ Language Interface for MPI-5.x

Fri Sep 12 12:45:49 CDT 2025

Hi Jeff,

>From recent discussions in the C++/Languages WG, it was apparent that, we could not reach a consensus on a “normative" interface - application/user needs are multifarious, and most users would rather prefer developing their own C++ solutions over MPI to have better control over application logic such as serialization (reflection, explicit buffering, etc.) and managing object lifetimes. OTOH, members agree that having a barebones C++  interface (like the deleted ones?) may help in designing third-party high-level interfaces. So, proposing a new interface or binding would most likely not serve the broader purpose, and compromises that must be baked in due to MPI semantics may thwart modern C++ developers.

So, through a series of prospective side documents, the plan is to capture general guidelines for designing performant C++ interfaces over MPI (expecting several C++ interface implementations over MPI), considering the dissonance between the models.

--

Sayan Ghosh
Computer Scientist
Future Computing Technologies Group
Pacific Northwest National Laboratory
(509)-372-6323 • https://urldefense.us/v3/__https://sg0.github.io__;!!G_uCfscf7eWS!c9LeMozG_yZM54PFqHqEeSabOx1D-x2QdhfuSPa30JtEl5Cm8QDaniu-dxQy9rQZM_FMJp5AiwMd82gVb70IOBqdpX7RimxI$ <https://urldefense.us/v3/__https://sg0.github.io/__;!!G_uCfscf7eWS!c9LeMozG_yZM54PFqHqEeSabOx1D-x2QdhfuSPa30JtEl5Cm8QDaniu-dxQy9rQZM_FMJp5AiwMd82gVb70IOBqdpTsxb2X6$ >

From: mpi-forum <mpi-forum-bounces at lists.mpi-forum.org> on behalf of Jeff Hammond via mpi-forum <mpi-forum at lists.mpi-forum.org>
Date: Friday, September 12, 2025 at 1:16 AM
To: Wes Bland <work at wesbland.com>
Cc: MPI Forum <mpi-forum at lists.mpi-forum.org>, Suggs, Evan <esuggs at tntech.edu>, Uhl, Tim Niklas (SCC) <tim.uhl at kit.edu>, Matthias Schimek <matthias.schimek at kit.edu>
Subject: Re: [Mpi-forum] Proposal process for a side document for C++ Language Interface for MPI-5.x

Check twice before you click! This email originated from outside PNNL.

This Message Is From an External Sender
This message came from outside your organization.

Why do we need a side document?  That would be required if we expect
multiple implementations.  That makes a lot of sense for Memory
Allocation Kinds because we want that capability in all the
implementations, not just MPICH and OMPI but the downstream
derivatives that may implement it distinctly from what the OSS
upstream projects are doing.  I am not convinced that we need more
than one implementation of any C++ interface to MPI.  Do we expect
closed-source vendor implementations?  Is it likely that this
interface will depend on proprietary internals of any implementation?

I contend that, for MPI C++ support, we are better off with the Linux
model of having the open-source implementation be the specification.
I am open to being convinced otherwise.

Jeff

On Tue, Jul 1, 2025 at 5:30 PM Wes Bland via mpi-forum
<mpi-forum at lists.mpi-forum.org> wrote:
>
> Hi Tony, I’ll refer to the procedures doc here: https: //www. mpi-forum. org/docs/other/procedures-36. pdf (*pushes glasses up nose* - Section 2. 2. 5). For side documents, you’ll follow the same procedure as a regular proposal (have a plenary/reading
> ZjQcmQRYFpfptBannerStart
> This Message Is From an External Sender
> This message came from outside your organization.
>
> ZjQcmQRYFpfptBannerEnd
> Hi Tony,
>
> I’ll refer to the procedures doc here: https://urldefense.us/v3/__https://www.mpi-forum.org/docs/other/procedures-36.pdf__;!!G_uCfscf7eWS!Z8jqX_bSy2iiaUh4QR-DabaxiRq5JX6mQXKa_9bV0gLTIIUb6Zhhn0hKzbWk65k9ZddzodXLa2yH_heA5DJk3ztaZ0gVGuA$ (*pushes glasses up nose* - Section 2.2.5).
>
> For side documents, you’ll follow the same procedure as a regular proposal (have a plenary/reading first, then two votes). The only difference is that updates to side docs incrementing the minor version number only have to pass a single vote (like an errata).
>
> Organizationally, we have repositories for each of the side documents in the main MPI Forum GitHub organization so it’s easier for folks to find them. You can find an example with the newer Memory Allocation Kinds side document here: https://urldefense.us/v3/__https://github.com/mpi-forum/mem-alloc__;!!G_uCfscf7eWS!Z8jqX_bSy2iiaUh4QR-DabaxiRq5JX6mQXKa_9bV0gLTIIUb6Zhhn0hKzbWk65k9ZddzodXLa2yH_heA5DJk3ztaWwKnoOY$. I’d be happy to make a repo for you if you’re interested.
>
> I'll put you on the list for the North Carolina meeting. I’m also happy to help schedule a non-voting meeting if you want to get some early feedback during one of our Wednesday time slots.
>
> Thanks,
> Wes
>
> On Jun 26, 2025, at 10:10 AM, Skjellum, Anthony via mpi-forum <mpi-forum at lists.mpi-forum.org> wrote:
>
> This Message Is From an External Sender
> This message came from outside your organization.
> Dear Wesley and Martin, how is a side document proposed to the forum?
>
> We wish to prepare a side document.
>
> Also, here is our recent EuroMPI paper describing the thinking and learning of the subcommittee on C++; we would also like to have a chance to share this at the SC25 BOF.
>
> If we can have plenary time at the next meeting, that would be good.  North Carolina, right?
>
> Here is the EuroMPI paper from Arxiv:
>
> https://urldefense.us/v3/__https://www.arxiv.org/abs/2506.14610__;!!G_uCfscf7eWS!Z8jqX_bSy2iiaUh4QR-DabaxiRq5JX6mQXKa_9bV0gLTIIUb6Zhhn0hKzbWk65k9ZddzodXLa2yH_heA5DJk3ztaJkPlS40$
>
>
> Thanks,
> Tony
>
>
> Anthony Skjellum, PhD
> Professor of Computer Science
> Director, Advanced Scalable Computing,
>               Extreme Networks & Data (ASCEND) Center
> Tennessee Technological University
> email: askjellum at tntech.edu
> cell: +1-205-807-4968
>
>
> _______________________________________________
> mpi-forum mailing list
> mpi-forum at lists.mpi-forum.org
> https://urldefense.us/v3/__https://lists.mpi-forum.org/mailman/listinfo/mpi-forum__;!!G_uCfscf7eWS!Z8jqX_bSy2iiaUh4QR-DabaxiRq5JX6mQXKa_9bV0gLTIIUb6Zhhn0hKzbWk65k9ZddzodXLa2yH_heA5DJk3ztaq6sMe7U$
>
>
> _______________________________________________
> mpi-forum mailing list
> mpi-forum at lists.mpi-forum.org
> https://urldefense.us/v3/__https://lists.mpi-forum.org/mailman/listinfo/mpi-forum__;!!G_uCfscf7eWS!Z8jqX_bSy2iiaUh4QR-DabaxiRq5JX6mQXKa_9bV0gLTIIUb6Zhhn0hKzbWk65k9ZddzodXLa2yH_heA5DJk3ztaq6sMe7U$

--
Jeff Hammond
jeff.science at gmail.com
https://urldefense.us/v3/__http://jeffhammond.github.io/__;!!G_uCfscf7eWS!Z8jqX_bSy2iiaUh4QR-DabaxiRq5JX6mQXKa_9bV0gLTIIUb6Zhhn0hKzbWk65k9ZddzodXLa2yH_heA5DJk3ztaXFqrcRk$

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mpi-forum.org/pipermail/mpi-forum/attachments/20250912/dea8f042/attachment-0001.html>