Prevent NEST from running under mpirun-control if not built with MPI

[heplesser]

If NEST is built without MPI support, invoking NEST with mpirun -np N will create N independent NEST instances. This is a behaviour the user most likely does not desire. When writing to files, there is considerable risk that these instances will write to the same output files simultaneously, creating a mess at best.

Therefore, it would be good if an MPI-free NEST could report an error if it is run from mpirun or similar.

Unfortunately, this discussion on StackOverflow suggest this might not be solvable in general.

I still suggest we explore and close this issue if we conclude that there is no possibility to implement this feature.

[github-actions]

Issue automatically marked stale!

[med-ayssar]

Won't be feasible to check the number of processes (MPI_num) and have a flag HAS_MPI that either set to true or false during the compilation.

During execution and on kernel startup, we can check if MPI_num > 1 and not HAS_MPI => exit with error, else continue execution, or is it a too naive solution?