[mpiwg-hybridpm] First draft of Continuations section

[Jeff Hammond]

Regarding Fortran…

In theory, you need ASYNCHRONOUS/VOLATILE attributes on visible state that’s updated out of band.

In practice, MPI implementations have done this with nonblocking send-recv for 25 years and it hasn’t been an issue.

Sent from my iPhone

> On Aug 4, 2021, at 7:36 PM, Joseph Schuchart via mpiwg-hybridpm <mpiwg-hybridpm at lists.mpi-forum.org> wrote:
> 
> Dear all,
> 
> I have written and attached a first draft of the continuations section that I would like to discuss in one of the upcoming meetings. Right now it is embedded at the end Section 3 (Point-to-Point following test and wait etc) where I felt it would fit well, I'm open to other suggestions though.
> 
> There are still some open TODOs that I'd like to discuss. In particular, I'm grappling with the handling of statuses. As suggested during previous discussions, I removed the flag argument to MPI_Continue such that the MPI implementation is allowed to invoke the continuations directly (can be controlled through an info key though). That means that after the call to MPI_Continue there is no good reason to inspect the statuses anymore. However, we may still want the user to provide the status object(s) in order to avoid exposing implementation-internal memory in the callback. But then I am worried that this is a source of error, with users providing pointers to stack memory that goes out of scope before the continuation is invoked.
> 
> Also, I am unsure whether and how this whole mechanism works with Fortran. The python generator happily generates the interface but I have no idea whether that is correct...
> 
> Looking forward to discussing this on the call!
> 
> Cheers
> Joseph
> <mpi40-report-continuations.pdf>
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