refactor to use shared pointer

diff --git a/examples/step-69/step-69.cc b/examples/step-69/step-69.cc
index 8beef68072244264e1b4eca14e492638f178f3be..c201e69daceaa1ba30c8e419195385385daff65e 100644 (file)
--- a/examples/step-69/step-69.cc
+++ b/examples/step-69/step-69.cc
@@ -506,7 +506,6 @@ namespace Step69
     InitialValues<dim>          initial_values;
     TimeStepping<dim>           time_stepping;
     SchlierenPostprocessor<dim> schlieren_postprocessor;
-    DataOut<dim>                data_out;
 
     vector_type output_vector;
 
@@ -2595,21 +2594,6 @@ namespace Step69
       print_head(pcout, "set up time step");
       time_stepping.prepare();
       schlieren_postprocessor.prepare();
-
-      data_out.attach_dof_handler(offline_data.dof_handler);
-
-      constexpr auto problem_dimension =
-        ProblemDescription<dim>::problem_dimension;
-      const auto &component_names = ProblemDescription<dim>::component_names;
-
-      for (unsigned int i = 0; i < problem_dimension; ++i)
-        {
-          output_vector[i].reinit(offline_data.partitioner);
-          data_out.add_data_vector(output_vector[i], component_names[i]);
-        }
-
-      data_out.add_data_vector(schlieren_postprocessor.schlieren,
-                               "schlieren_plot");
     }
 
     // We will store the current time and state in the variable
@@ -2663,7 +2647,7 @@ namespace Step69
     // With either the initial state set up, or an interrupted state
     // restored it is time to enter the main loop:
 
-    output(U, base_name + "-solution", t, output_cycle++);
+    output(U, base_name, t, output_cycle++);
 
     print_head(pcout, "enter main loop");
 
@@ -2697,7 +2681,7 @@ namespace Step69
 
         if (t > output_cycle * output_granularity)
           {
-            output(U, base_name + "-solution", t, output_cycle, true);
+            output(U, base_name, t, output_cycle, true);
             ++output_cycle;
           }
       }
@@ -2705,9 +2689,7 @@ namespace Step69
     // We wait for any remaining background output thread to finish before
     // printing a summary and exiting.
     if (background_thread_state.valid())
-      {
-        background_thread_state.wait();
-      }
+      background_thread_state.wait();
 
     computing_timer.print_summary();
     pcout << timer_output.str() << std::endl;
@@ -2808,7 +2790,14 @@ namespace Step69
       ProblemDescription<dim>::problem_dimension;
 
     // At this point we make a copy of the state vector, run the schlieren
-    // postprocessor, and run DataOut<dim>::build_patches()
+    // postprocessor, and run DataOut<dim>::build_patches() The actual
+    // output code is standard: We create a DataOut instance, attach all
+    // data vectors we want to output and call
+    // DataOut<dim>::build_patches(). There is one twist, however. In order
+    // to perform asynchronous IO on a background thread we create the
+    // DataOut<dim> object as a shared pointer that we pass on to the
+    // worker thread to ensure that once we exit this function and the
+    // worker thread finishes the DataOut<dim> object gets destroyed again.
 
     for (unsigned int i = 0; i < problem_dimension; ++i)
       {
@@ -2818,8 +2807,20 @@ namespace Step69
 
     schlieren_postprocessor.compute_schlieren(output_vector);
 
-    data_out.build_patches(discretization.mapping,
-                           discretization.finite_element.degree - 1);
+    auto data_out = std::make_shared<DataOut<dim>>();
+
+    data_out->attach_dof_handler(offline_data.dof_handler);
+
+    const auto &component_names = ProblemDescription<dim>::component_names;
+
+    for (unsigned int i = 0; i < problem_dimension; ++i)
+      data_out->add_data_vector(output_vector[i], component_names[i]);
+
+    data_out->add_data_vector(schlieren_postprocessor.schlieren,
+                              "schlieren_plot");
+
+    data_out->build_patches(discretization.mapping,
+                            discretization.finite_element.degree - 1);
 
     // Next we create a lambda function for the background thread. We <a
     // href="https://en.cppreference.com/w/cpp/language/lambda">capture</a>
@@ -2827,7 +2828,7 @@ namespace Step69
     // the output function by value so that we have access to them inside
     // the lambda function.
 
-    const auto output_worker = [this, name, t, cycle, checkpoint]() {
+    const auto output_worker = [this, name, t, cycle, checkpoint, data_out]() {
       if (checkpoint)
         {
           // We checkpoint the current state by doing the precise inverse
@@ -2836,10 +2837,10 @@ namespace Step69
 
           const unsigned int i =
             discretization.triangulation.locally_owned_subdomain();
-          std::string name = base_name + "-checkpoint-" +
-                             Utilities::int_to_string(i, 4) + ".archive";
+          std::string filename =
+            name + "-checkpoint-" + Utilities::int_to_string(i, 4) + ".archive";
 
-          std::ofstream file(name, std::ios::binary | std::ios::trunc);
+          std::ofstream file(filename, std::ios::binary | std::ios::trunc);
 
           boost::archive::binary_oarchive oa(file);
           oa << t << cycle;
@@ -2852,9 +2853,10 @@ namespace Step69
                                   cycle,
                                   true,
                                   DataOutBase::VtkFlags::best_speed);
-      data_out.set_flags(flags);
+      data_out->set_flags(flags);
 
-      data_out.write_vtu_with_pvtu_record("", name, cycle, mpi_communicator, 6);
+      data_out->write_vtu_with_pvtu_record(
+        "", name + "-solution", cycle, mpi_communicator, 6);
     };
 
     // If the asynchronous writeback option is set we launch a new