Object Group Manager

Create object instances across nodes

The object group manager component vt::objgroup::ObjGroupManager, accessed via vt::theObjGroup() allows the creation and management of instances of a group of objects (one per node) that have a collective proxy for performing operations like sends, broadcasts, or reductions across the object group.

Example creating an object group

struct MyObjGroup {
  void handler(int a, int b) {
    auto node = vt::theContext()->getNode();
    fmt::print("{}: MyObjGroup::handler on a={}, b={}\n", node, a, b);
  }
};

int main(int argc, char** argv) {
  vt::initialize(argc, argv);

  const auto this_node = vt::theContext()->getNode();
  const auto num_nodes = vt::theContext()->getNumNodes();

  auto proxy =
    vt::theObjGroup()->makeCollective<MyObjGroup>("examples_hello_world");

  // Create group of odd nodes and multicast to them (from root node)
  vt::theGroup()->newGroupCollective(
    this_node % 2, [proxy, this_node](::vt::GroupType type) {
      if (this_node == 0) {
        proxy.multicast<&MyObjGroup::handler>(type, 122, 244);
      }
    });

  vt::theCollective()->barrier();

  if (this_node == 0) {
    // Send to object 0
    proxy[0].send<&MyObjGroup::handler>(5, 10);
    if (num_nodes > 1) {
      // Send to object 1
      proxy[1].send<&MyObjGroup::handler>(10, 20);
    }

    // Broadcast to all nodes
    proxy.broadcast<&MyObjGroup::handler>(400, 500);

    using namespace ::vt::group::region;

    // Create list of nodes and multicast to them
    List::ListType range;
    for (vt::NodeType node = 0; node < num_nodes; ++node) {
      if (node % 2 == 0) {
        range.push_back(node);
      }
    }

    proxy.multicast<&MyObjGroup::handler>(
      std::make_unique<List>(range), 20, 40
    );
  }
  vt::theCollective()->barrier();

  vt::finalize();

  return 0;
}