[mpiwg-hybridpm] Can MPI processes request different threading levels?

[Jeff Hammond]

It is addressed here (in the text for MPI_INIT_THREAD):

Advice to implementors. If provided is not MPI_THREAD_SINGLE then the MPI
library should not invoke C or Fortran library calls that are not thread
safe, e.g., in an environment where malloc is not thread safe, then malloc
should not be used by the MPI library.

Some implementors may want to use different MPI libraries for different
levels of thread support. They can do so using dynamic linking and
selecting which library will be linked when MPI_INIT_THREAD is invoked. If
this is not possible, then optimizations for lower levels of thread support
will occur only when the level of thread support required is specified at
link time.

*Note that required need not be the same value on all processes of
MPI_COMM_WORLD.* (End of advice to implementors.)

Jeff

On Tue, Aug 1, 2023 at 11:47 AM Joachim Jenke via mpiwg-hybridpm <
mpiwg-hybridpm at lists.mpi-forum.org> wrote:
>
> Hello,
>
> I'm not sure whether this is the right group to ask, but it is related
> to hybrid execution :)
>
> Must all MPI processes collectively call MPI_Init or MPI_Init_thread -
> or can some processes call one and other processes call the other
function?
>
> Also, can the processes request different thread-support levels?
>
> Our use case is MPMD execution, where some processes run multi-threaded
> and other single-threaded.
>
> Thanks,
> Joachim
>
>
> --
> Dr. rer. nat. Joachim Jenke
>
> IT Center
> Group: High Performance Computing
> Division: Computational Science and Engineering
> RWTH Aachen University
> Seffenter Weg 23
> D 52074  Aachen (Germany)
> Tel: +49 241 80- 24765
> Fax: +49 241 80-624765
> jenke at itc.rwth-aachen.de
> www.itc.rwth-aachen.de
> _______________________________________________
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--
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/
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