P3 lookup text file being read by all MPI ranks

[ndkeen]

I don't think we should be letting all MPI rank try to read the same P3 lookup text file as it can cause some issues on the filesystems esp at scale (and slow us down).

I implemented a read-on-rank0, broadcast solution to test for E3SM components/eam/src/physics/p3/eam/micro_p3.F90, but having trouble in scream components/eam/src/physics/p3/scream/micro_p3.F90 as I don't have access to same modules. So I wanted to test it was ok before making issue, but might need more attention.

For example, don't immediately have access to:

   use mpishorthand, only: mpir8
   use spmd_utils,   only: mpicom

Perhaps someone has already thought of a better solution anyway?

[ambrad]

This approach might work:

Move this line:

scream/components/eamxx/src/physics/p3/eamxx_p3_process_interface.cpp

Line 252 in 5ad00c2

p3::p3_init(/* write_tables = */ false,

down to just above here:

scream/components/eamxx/src/physics/p3/eamxx_p3_process_interface.cpp

Line 423 in 5ad00c2

P3F::init_kokkos_ice_lookup_tables(lookup_tables.ice_table_vals, lookup_tables.collect_table_vals);

Then call that whole block only on the master rank. Finally, broadcast the table data to the other ranks.

However, the approach will fail if there are C++-affecting side effects in p3_init.