[mpiwg-tools] PMPI and sessions init

Martin Schulz schulzm at in.tum.de
Thu Nov 5 17:39:26 CST 2020

Hi Joachim, all,

Yes, I think you are right - we probably didn't think this all the way through on the TelCon: as long as all items are loaded, the interceptions with PMPI should work, no matter when and where MPI calls are made. The only issue would be the load order of a tool vs. a library using MPI_Sessions, which could lead to situations where a tool wouldn't be able to catch the init calls.


PS: what do you mean with the environment variable in this scenario?

Prof. Dr. Martin Schulz, Chair of Computer Architecture and Parallel Systems
Department of Informatics, TU-Munich, Boltzmannstraße 3, D-85748 Garching
Member of the Board of Directors at the Leibniz Supercomputing Centre (LRZ)
Email: schulzm at in.tum.de

On 05.11.20, 19:00, "mpiwg-tools on behalf of Joachim Protze via mpiwg-tools" <mpiwg-tools-bounces at lists.mpi-forum.org on behalf of mpiwg-tools at lists.mpi-forum.org> wrote:

    Hi all,

    if I understood the discussion about MPI_Session_init and PMPI right, I
    don't think there exists an issue.
    By ld-preloading the PMPI tool, the tool can also intercept a call to
    MPI_Session_init, which might come from a library constructor before
    main. Even a function called from the library constructor of a static
    library can be intercepted by a ld-preloaded tool.

    For libraries, which are explicitly loaded by the MPI runtime during
    initialization, this would also work. For others, it depends on the
    ordering of calling the library constructor (might work by chance :).

    This was one of my main motivation of having such an environmental


    Dipl.-Inf. Joachim Protze

    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
    protze at itc.rwth-aachen.de

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