A Non-intrusive Technique for Interfacing Legacy Fortran Codes with Modern C++ Runtime Systems

Many HPC applications developed over the past two decades have used Fortran and MPI-based parallelization. As the size of today´s HPC resources continues to increase, these codes struggle to efficiently utilize the million-way parallelism of these platforms. Rewriting these codes from scratch to leverage modern programming paradigms would be time-consuming and error-prone. We evaluate a robust approach for interfacing with next-generation C++-based libraries and drivers. We have successfully used this technique to modify the Fortran code DGSWEM (Discontinuous Galerkin Shallow Water Equation Model), allowing it to take advantage of the new parallel runtime system HPX. Our goal was to make as few modifications to the DGSWEM Fortran source code as possible, thereby minimizing the chances of introducing bugs and reducing the amount of re-verification that needed to be done.