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MPI Environment Management

Initialisation

It is not required to explicitly initialise either the MPI environment via MPI_Init or the BLACS environment via blacs_gridinit. All those operations are automatically done via RAII.

Use the following to get the rank and size of the current BLACS environment if needed.

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

Finalisation

Finalisation is a bit more complex. When several MPI based libraries are used together, each may have its own initialisation and finalisation processes. Then who is in charge of finalising the MPI resources matters. And the order of calling different finalisation functions matters. Unfortunately, with RAII, there is no reliable way to explicitly assign an order such that, for example, blacs_exit is guaranteed to be called before MPI_Finalize.

However, it is possible to tell ezp to skip finalising MPI. To do so, call the following function anywhere in your application.

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

Once this is called, ezp will memorise the setting and call blacs_exit(1) instead of blacs_exit(0) on destruction, the latter not only releases blacs resources but also further calls MPI_Finalize.

By such, you shall manually call MPI_Finalize, or probably let other libraries to finalise the MPI environment for you.