Function main

modules/mpi/tutorials/ospMPIDistribTutorialPartialRepl.cpp:47–149

VolumeBrick makeLocalVolume(const int mpiRank, const int mpiWorldSize);

int main(int argc, char **argv)
{
  int mpiThreadCapability = 0;
  MPI_Init_thread(&argc, &argv, MPI_THREAD_MULTIPLE, &mpiThreadCapability);
  if (mpiThreadCapability != MPI_THREAD_MULTIPLE
      && mpiThreadCapability != MPI_THREAD_SERIALIZED) {
    fprintf(stderr,
        "OSPRay requires the MPI runtime to support thread "
        "multiple or thread serialized.\n");
    return 1;
  }

  int mpiRank = 0;
  int mpiWorldSize = 0;
  MPI_Comm_rank(MPI_COMM_WORLD, &mpiRank);
  MPI_Comm_size(MPI_COMM_WORLD, &mpiWorldSize);

  std::cout << "OSPRay rank " << mpiRank << "/" << mpiWorldSize << "\n";

  // load the MPI module, and select the MPI distributed device. Here we
  // do not call ospInit, as we want to explicitly pick the distributed
  // device
  auto OSPRAY_MPI_DISTRIBUTED_GPU =
      utility::getEnvVar<int>("OSPRAY_MPI_DISTRIBUTED_GPU").value_or(0);
  if (OSPRAY_MPI_DISTRIBUTED_GPU) {
    ospLoadModule("mpi_distributed_gpu");
  } else {
    ospLoadModule("mpi_distributed_cpu");
  }

  {
    cpp::Device mpiDevice("mpiDistributed");
    mpiDevice.commit();
    mpiDevice.setCurrent();

    // set an error callback to catch any OSPRay errors and exit the application
    ospDeviceSetErrorCallback(
        mpiDevice.handle(),
        [](void *, OSPError error, const char *errorDetails) {
          std::cerr << "OSPRay error: " << errorDetails << std::endl;
          exit(error);
        },
        nullptr);

    // every two ranks will share a volume brick to render, if we have an
    // odd number of ranks the last one will have its own brick
    const int sharedWorldSize = mpiWorldSize / 2 + mpiWorldSize % 2;

    // all ranks specify the same rendering parameters, with the exception of
    // the data to be rendered, which is distributed among the ranks
    VolumeBrick brick = makeLocalVolume(mpiRank / 2, sharedWorldSize);

    // create the "world" model which will contain all of our geometries
    cpp::World world;
    world.setParam("instance", cpp::CopiedData(brick.instance));

    world.setParam("region", cpp::CopiedData(brick.bounds));
    world.commit();