MPI Environment Management

Initialisation

It is not required to initialise the MPI environment with MPI_Init or the BLACS environment with blacs_gridinit. All of these operations are performed automatically through RAII. The global environment is a singleton obtained from get_env<IT>(). Use it to query the rank and size of the current BLACS environment.

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ezp::get_env<int>().rank();
ezp::get_env<int>().size();

Finalisation

Finalisation is more involved. When several MPI-based libraries are used together, each may manage its own initialisation and finalisation. It then matters who finalises the MPI resources and in what order. With RAII there is no reliable way to enforce an order that guarantees, for example, blacs_exit runs before MPI_Finalize.

It is, however, possible to tell ezp not to finalise MPI. Call the following function anywhere in the application.

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ezp::blacs_env<int>::do_not_manage_mpi();

Once this is called, ezp remembers the setting. On destruction it calls blacs_exit(1) instead of blacs_exit(0). The latter releases the BLACS resources and also calls MPI_Finalize, whereas the former only releases the resources. You are then responsible for calling MPI_Finalize, or for letting another library finalise the MPI environment.