Function build_src_dest

cpp/dolfinx/common/IndexMap.cpp:30–48

@brief Given source ranks (ranks that own indices ghosted by the calling rank), compute ranks that ghost indices owned by the calling rank. @param comm MPI communicator. @param owners List of ranks that own each ghost index. @return (src ranks, destination ranks). Both lists are sorted.

/// @param owners List of ranks that own each ghost index.
/// @return (src ranks, destination ranks). Both lists are sorted.
std::array<std::vector<int>, 2>
build_src_dest(MPI_Comm comm, std::span<const int> owners, int tag)
{
  if (dolfinx::MPI::size(comm) == 1)
  {
    assert(owners.empty());
    return std::array<std::vector<int>, 2>();
  }

  std::vector<int> src(owners.begin(), owners.end());
  std::ranges::sort(src);
  auto [unique_end, range_end] = std::ranges::unique(src);
  src.erase(unique_end, range_end);
  src.shrink_to_fit();
  std::vector<int> dest = dolfinx::MPI::compute_graph_edges_nbx(comm, src, tag);
  std::ranges::sort(dest);

  return {std::move(src), std::move(dest)};
}

/// @brief Helper function that sends ghost indices on a given process
/// to their owning rank, and receives indices owned by this process