#1009 add serialize method for theLBManager component

problematic types (see members not serialized):
- LBType (ambiguous call)
- LoadModel (pure abstract interface)

src/vt/objgroup/proxy/proxy_objgroup.h

@@ -318,6 +318,11 @@ struct Proxy {
    */
   ProxyElm<ObjT> operator()(NodeType node) const;
 
+  template <typename Serializer>
+  void serialize(Serializer& s) {
+    s | proxy_;
+  }
+
 private:
   ObjGroupProxyType proxy_ = no_obj_group; /**< The raw proxy ID bits */
 };

src/vt/vrt/collection/balance/lb_invoke/lb_manager.h

@@ -252,6 +252,22 @@ struct LBManager : runtime::component::Component<LBManager> {
    */
   std::shared_ptr<LoadModel> getLoadModel() { return model_; }
 
+  template <typename Serializer>
+  void serialize(Serializer& s) {
+    s | num_invocations_
+      | num_release_
+      | cached_phase_
+      // ambiguous: hasNoninSerialize, isEnum
+      //| cached_lb_
+      | destroy_lb_
+      | synced_in_lb_
+      | listeners_
+      | proxy_;
+      // LoadModel is pure abstract interface
+      // | base_model_
+      // | model_;
+  }
+
 protected:
   /**
    * \internal \brief Collectively construct a new load balancer

tests/unit/runtime/test_memory_footprint.nompi.cc

@@ -47,6 +47,7 @@
 #include <checkpoint/checkpoint.h>
 #include "vt/configs/arguments/args.h"
 #include "vt/timetrigger/time_trigger_manager.h"
+#include "vt/vrt/collection/balance/lb_invoke/lb_manager.h"
 
 #include "test_harness.h"
 
@@ -71,4 +72,12 @@ TEST_F(TestMemoryFootprinting, test_time_trigger_manager) {
   fmt::print("getMemoryFootprint: {}\n", size);
 }
 
+TEST_F(TestMemoryFootprinting, test_lb_manager) {
+  vt::vrt::collection::balance::LBManager lb_manager;
+  fmt::print("sizeof instance: {}\n", sizeof(lb_manager));
+
+  auto size = checkpoint::getMemoryFootprint<vt::vrt::collection::balance::LBManager>(lb_manager);
+  fmt::print("getMemoryFootprint: {}\n", size);
+}
+
 }}} /* end namespace vt::tests::unit */