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. Martin 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: [email protected] On 05.11.20, 19:00, "mpiwg-tools on behalf of Joachim Protze via mpiwg-tools" <[email protected] on behalf of [email protected]> 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 variable. Best Joachim -- 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 [email protected] www.itc.rwth-aachen.de