Unable to build CLTs without MPI

[jared321]

The OpenBT Meson build system contains a use_mpi flag, which allows users to build the CLTs with and without MPI. By default, they are built with MPI parallelization. It does so by controlling appropriately the -D_OPENMPI compiler flag.

When I tried to build without MPI support as part of the v1.2.0 release testing, I got the following errors

../src/brt.cpp:1055:21: error: use of undeclared identifier 'MPI_IN_PLACE'
 1055 |       MPI_Allreduce(MPI_IN_PLACE,&nodenums[i],1,MPI_UNSIGNED,MPI_SUM,MPI_COMM_WORLD);
      |                     ^
../src/brt.cpp:1055:49: error: use of undeclared identifier 'MPI_UNSIGNED'
 1055 |       MPI_Allreduce(MPI_IN_PLACE,&nodenums[i],1,MPI_UNSIGNED,MPI_SUM,MPI_COMM_WORLD);
      |                                                 ^
../src/brt.cpp:1055:62: error: use of undeclared identifier 'MPI_SUM'
 1055 |       MPI_Allreduce(MPI_IN_PLACE,&nodenums[i],1,MPI_UNSIGNED,MPI_SUM,MPI_COMM_WORLD);
      |                                                              ^
../src/brt.cpp:1055:70: error: use of undeclared identifier 'MPI_COMM_WORLD'
 1055 |       MPI_Allreduce(MPI_IN_PLACE,&nodenums[i],1,MPI_UNSIGNED,MPI_SUM,MPI_COMM_WORLD);
      |                                                                      ^
../src/brt.cpp:1093:21: error: use of undeclared identifier 'MPI_IN_PLACE'
 1093 |       MPI_Allreduce(MPI_IN_PLACE,&nodenums[i],1,MPI_UNSIGNED,MPI_SUM,MPI_COMM_WORLD);
      |                     ^
../src/brt.cpp:1093:49: error: use of undeclared identifier 'MPI_UNSIGNED'
 1093 |       MPI_Allreduce(MPI_IN_PLACE,&nodenums[i],1,MPI_UNSIGNED,MPI_SUM,MPI_COMM_WORLD);
      |                                                 ^
../src/brt.cpp:1093:62: error: use of undeclared identifier 'MPI_SUM'
 1093 |       MPI_Allreduce(MPI_IN_PLACE,&nodenums[i],1,MPI_UNSIGNED,MPI_SUM,MPI_COMM_WORLD);
      |                                                              ^
../src/brt.cpp:1093:70: error: use of undeclared identifier 'MPI_COMM_WORLD'
 1093 |       MPI_Allreduce(MPI_IN_PLACE,&nodenums[i],1,MPI_UNSIGNED,MPI_SUM,MPI_COMM_WORLD);
      |                                                                      ^
2 warnings and 8 errors generated.

If this failure is confirmed, should

• MPI configurability be removed so that the CLT are always built with MPI or
• fix the code so that such build errors don't occur?

[mpratola]

Yes, the serial codepath is not working for now (I believe OpenBTmixing was the same situation?). So we should disable the option for now and create an issue to fix the serial codepath and re-enable it at a future point release.