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reduce communication argList at startup

Merged reduce communication argList at startup
update-argList-mpi-startup into develop
Merged Mark OLESEN requested to merge update-argList-mpi-startup into develop
  1. Apr 23, 2024
    • Mark OLESEN's avatar
      ENH: stricter handling when freeing communicator components · 09377471
      Mark OLESEN authored 
      - previously automatically skipped the first communicator (which was
  assumed to be MPI_COMM_WORLD), but now simply rely on the
  internal pendingMPIFree_ to track which communicators have actually
  been allocated.
      09377471
    • Mark OLESEN's avatar
      ENH: add wrapped accessor for MPI_Comm · 2889dc72
      Mark OLESEN authored 
      - UPstream::Communicator is similar to UPstream::Request to
  wrap/unwrap MPI_Comm. Provides a 'lookup' method to transcribe
  the internal OpenFOAM communicator tracking to the opaque wrapped
  version.

- provide an 'openfoam_mpi.H' interfacing file, which includes
  the <mpi.h> as well as casting routines.

  Example (caution: ugly!)

     MPI_Comm myComm =
         PstreamUtils::Cast::to_mpi
         (
             UPstream::Communicator::lookup(UPstream::worldComm)
         );
      2889dc72
    • Mark OLESEN's avatar
      ENH: reduce communication argList at startup (#3142) · d75c60d8
      Mark OLESEN authored 
      - replace point-to-point transmission of the argList args/options with
  a broadcast. This is sufficient for most cases (without distributed
  roots).

  For "normal" cases (non-distributed roots) this will replace the
  nProcs-1 messages with a single broadcast.

- for cases with distributed roots, distinguish between a single,
  identical root and different roots.  An identical root can also be
  subsequently handled with a broadcast. Different roots will still
  require individual point-to-point communication.

  For cases with distributed roots, it will add the overhead of an
  additional broadcast.
      d75c60d8