From 91000f3ea0dac86e4129c22b75937bec85f64e75 Mon Sep 17 00:00:00 2001
From: lewisgross1296 <ligross@wisc.edu>
Date: Fri, 1 Jul 2022 16:51:39 -0500
Subject: [PATCH] refactored mesh.cpp to allow mesh pointer or filename and
 reduced copied code

---
 include/openmc/mesh.h |  9 ++++++---
 src/mesh.cpp          | 27 ++++++++++++++++++++-------
 2 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/include/openmc/mesh.h b/include/openmc/mesh.h
index 21c58862d9..4d5ebc46ea 100644
--- a/include/openmc/mesh.h
+++ b/include/openmc/mesh.h
@@ -53,7 +53,7 @@ extern vector<unique_ptr<Mesh>> meshes;
 
 #ifdef LIBMESH
 namespace settings {
-// used when creating new libMesh::Mesh instances
+// used when creating new libMesh::MeshBase instances
 extern unique_ptr<libMesh::LibMeshInit> libmesh_init;
 extern const libMesh::Parallel::Communicator* libmesh_comm;
 } // namespace settings
@@ -671,7 +671,8 @@ class LibMesh : public UnstructuredMesh {
 public:
   // Constructors
   LibMesh(pugi::xml_node node);
-  LibMesh(const std::string& filename, double length_multiplier = 1.0);
+  LibMesh(const std::string & filename, double length_multiplier = 1.0);
+  LibMesh(libMesh::MeshBase & input_mesh, double length_multiplier = 1.0);
 
   static const std::string mesh_lib_type;
 
@@ -705,6 +706,7 @@ public:
 
 private:
   void initialize() override;
+  void set_mesh_pointer_from_filename(const std::string& filename);
 
   // Methods
 
@@ -715,7 +717,8 @@ private:
   int get_bin_from_element(const libMesh::Elem* elem) const;
 
   // Data members
-  unique_ptr<libMesh::Mesh> m_; //!< pointer to the libMesh mesh instance
+  unique_ptr<libMesh::MeshBase> unique_m_; //!< pointer to the libMesh MeshBase instance, only used if mesh is created inside OpenMC
+  libMesh::MeshBase * m_; //!< pointer to libMesh MeshBase instance
   vector<unique_ptr<libMesh::PointLocatorBase>>
     pl_; //!< per-thread point locators
   unique_ptr<libMesh::EquationSystems>
diff --git a/src/mesh.cpp b/src/mesh.cpp
index e8f79aa37a..68675b9692 100644
--- a/src/mesh.cpp
+++ b/src/mesh.cpp
@@ -2327,13 +2327,31 @@ LibMesh::LibMesh(pugi::xml_node node) : UnstructuredMesh(node)
   initialize();
 }
 
-LibMesh::LibMesh(const std::string& filename, double length_multiplier)
+// create the mesh from a pointer to a libMesh Mesh
+LibMesh::LibMesh(libMesh::MeshBase & input_mesh, double length_multiplier)
 {
-  filename_ = filename;
+  m_ = &input_mesh;
   set_length_multiplier(length_multiplier);
   initialize();
 }
 
+// create the mesh from an input file
+LibMesh::LibMesh(const std::string& filename, double length_multiplier)
+{
+  set_mesh_pointer_from_filename(filename);
+  set_length_multiplier(length_multiplier);
+  initialize();
+}
+
+void LibMesh::set_mesh_pointer_from_filename(const std::string& filename)
+{
+  filename_ = filename;
+  unique_m_ = make_unique<libMesh::Mesh>(*settings::libmesh_comm, n_dimension_);
+  m_ = unique_m_.get();
+  m_->read(filename_);
+}
+
+// intialize from mesh file
 void LibMesh::initialize()
 {
   if (!settings::libmesh_comm) {
@@ -2344,15 +2362,10 @@ void LibMesh::initialize()
   // assuming that unstructured meshes used in OpenMC are 3D
   n_dimension_ = 3;
 
-  m_ = make_unique<libMesh::Mesh>(*settings::libmesh_comm, n_dimension_);
-  m_->read(filename_);
-
   if (specified_length_multiplier_) {
     libMesh::MeshTools::Modification::scale(*m_, length_multiplier_);
   }
 
-  m_->prepare_for_use();
-
   // ensure that the loaded mesh is 3 dimensional
   if (m_->mesh_dimension() != n_dimension_) {
     fatal_error(fmt::format("Mesh file {} specified for use in an unstructured "