Create _add_elements_from_sides helper

Author: lindsayad

include/mesh/boundary_info.h

@@ -977,6 +977,14 @@ class BoundaryInfo : public ParallelObject
   _elem_in_requested_subdomains(const Elem * elem,
                                 const std::set<subdomain_id_type> & subdomains_relative_to) const;
 
+  /**
+   * Helper to add boundary elements from given \p sides_id_map
+   */
+  void _add_elements_from_sides(
+      UnstructuredMesh & boundary_mesh,
+      const std::map<std::pair<dof_id_type, unsigned char>, dof_id_type> & side_id_map,
+      bool store_parent_side_ids);
+
   /**
    * A pointer to the Mesh this boundary info pertains to.
    */

src/mesh/boundary_info.C

@@ -573,10 +573,9 @@ void BoundaryInfo::sync (const std::set<boundary_id_type> & requested_boundary_i
   // Add the elements. When syncing a boundary mesh, we also store the
   // parent side ids in addition to the interior_parent pointers,
   // since this information is frequently needed on boundary meshes.
-  this->add_elements(requested_boundary_ids,
-                     boundary_mesh,
-                     subdomains_relative_to,
-                     /*store_parent_side_ids=*/true);
+  this->_add_elements_from_sides(boundary_mesh,
+                                 side_id_map,
+                                 /*store_parent_side_ids=*/true);
 
   // The new elements are currently using the interior mesh's nodes;
   // we want them to use the boundary mesh's nodes instead.
@@ -704,10 +703,10 @@ void BoundaryInfo::add_elements(const std::set<boundary_id_type> & requested_bou
 
 
 
-void BoundaryInfo::add_elements(const std::set<boundary_id_type> & requested_boundary_ids,
-                                UnstructuredMesh & boundary_mesh,
-                                const std::set<subdomain_id_type> & subdomains_relative_to,
-                                bool store_parent_side_ids)
+void BoundaryInfo::_add_elements_from_sides(
+    UnstructuredMesh & boundary_mesh,
+    const std::map<std::pair<dof_id_type, unsigned char>, dof_id_type> & side_id_map,
+    bool store_parent_side_ids)
 {
   LOG_SCOPE("add_elements()", "BoundaryInfo");
 
@@ -728,32 +727,6 @@ void BoundaryInfo::add_elements(const std::set<boundary_id_type> & requested_bou
   // this mesh
   boundary_mesh.set_interior_mesh(*_mesh);
 
-  std::map<std::pair<dof_id_type, unsigned char>, dof_id_type> side_id_map;
-  this->_find_id_maps(requested_boundary_ids,
-                      0,
-                      nullptr,
-                      boundary_mesh.max_elem_id(),
-                      &side_id_map,
-                      subdomains_relative_to);
-
-  // We have to add sides *outside* any element loop, because if
-  // boundary_mesh and _mesh are the same then those additions can
-  // invalidate our element iterators.  So we just use the element
-  // loop to make a list of sides to add.
-  typedef std::vector<std::pair<dof_id_type, unsigned char>>
-    side_container;
-  side_container sides_to_add;
-
-  for (const auto & elem : _mesh->element_ptr_range())
-    {
-      if (!this->_elem_in_requested_subdomains(elem))
-        continue;
-
-      for (auto s : elem->side_index_range())
-        if (this->_side_is_requested(elem, s, requested_boundary_ids))
-          sides_to_add.emplace_back(elem->id(), s);
-    }
-
 #ifdef LIBMESH_ENABLE_UNIQUE_ID
   unique_id_type old_max_unique_id = boundary_mesh.parallel_max_unique_id();
 #endif
@@ -764,20 +737,13 @@ void BoundaryInfo::add_elements(const std::set<boundary_id_type> & requested_bou
   unsigned int parent_side_index_tag = store_parent_side_ids ?
     boundary_mesh.add_elem_integer("parent_side_index") : libMesh::invalid_uint;
 
-  for (const auto & [elem_id, s] : sides_to_add)
+  for (const auto & [elem_side, new_side_id] : side_id_map)
     {
+      const auto [elem_id, s] = elem_side;
       Elem * elem = _mesh->elem_ptr(elem_id);
 
       std::unique_ptr<Elem> side = elem->build_side_ptr(s);
-
       side->processor_id() = elem->processor_id();
-
-      const std::pair<dof_id_type, unsigned char> side_pair(elem_id, s);
-
-      libmesh_assert(side_id_map.count(side_pair));
-
-      const dof_id_type new_side_id = side_id_map[side_pair];
-
       side->set_id(new_side_id);
 
 #ifdef LIBMESH_ENABLE_UNIQUE_ID
@@ -803,7 +769,7 @@ void BoundaryInfo::add_elements(const std::set<boundary_id_type> & requested_bou
 
           libmesh_assert(side_id_map.count(parent_side_pair));
 
-          Elem * side_parent = boundary_mesh.elem_ptr(side_id_map[parent_side_pair]);
+          Elem * side_parent = boundary_mesh.elem_ptr(new_side_id);
 
           libmesh_assert(side_parent);
 
@@ -935,6 +901,25 @@ void BoundaryInfo::add_elements(const std::set<boundary_id_type> & requested_bou
 
 
 
+void BoundaryInfo::add_elements(const std::set<boundary_id_type> & requested_boundary_ids,
+                                UnstructuredMesh & boundary_mesh,
+                                const std::set<subdomain_id_type> & subdomains_relative_to,
+                                bool store_parent_side_ids)
+{
+  std::map<std::pair<dof_id_type, unsigned char>, dof_id_type> side_id_map;
+  // First build side_id_map
+  this->_find_id_maps(requested_boundary_ids,
+                      0,
+                      nullptr,
+                      boundary_mesh.max_elem_id(),
+                      &side_id_map,
+                      subdomains_relative_to);
+  // Then add sides using it
+  this->_add_elements_from_sides(boundary_mesh, side_id_map, store_parent_side_ids);
+}
+
+
+
 void BoundaryInfo::add_node(const dof_id_type node_id,
                             const boundary_id_type id)
 {