mpi.comm.disconnect disconnects itself from a communicator and then
deallocates the communicator so it points to MPI\_COMM\_NULL.
mpi.comm.disconnect(comm=1)a communicator number
1 if success. Otherwise 0.
When members associated with a communicator finish jobs or exit, they have to
call mpi.comm.disconnect to release resource if the communicator was
created from an intercommunicator by mpi.intercomm.merge. If
mpi.comm.free is used instead, mpi.finalize called
by slaves may cause undefined impacts on master who wishes to stay.