From 79015fbab258296f8b913f390db6481d693df06e Mon Sep 17 00:00:00 2001
From: Marc Fehling <marc.fehling@gmx.net>
Date: Fri, 11 Jan 2019 18:14:45 +0100
Subject: [PATCH] Changed point at which p::d::Tria::pre_distributed_refinement
 is triggered.

---
 source/distributed/tria.cc                    |   4 +-
 .../pre_refinement_signal.cc                  | 134 ++++++++++++++++++
 .../pre_refinement_signal.output              |   3 +
 3 files changed, 139 insertions(+), 2 deletions(-)
 create mode 100644 tests/distributed_grids/pre_refinement_signal.cc
 create mode 100644 tests/distributed_grids/pre_refinement_signal.output

diff --git a/source/distributed/tria.cc b/source/distributed/tria.cc
index fb1eb28f59..edd85a44e0 100644
--- a/source/distributed/tria.cc
+++ b/source/distributed/tria.cc
@@ -3854,12 +3854,12 @@ namespace parallel
             }
         }
 
+      this->prepare_coarsening_and_refinement();
+
       // signal that refinement is going to happen
       this->signals.pre_distributed_refinement();
 
       // now do the work we're supposed to do when we are in charge
-      this->prepare_coarsening_and_refinement();
-
       // make sure all flags are cleared on cells we don't own, since nothing
       // good can come of that if they are still around
       for (typename Triangulation<dim, spacedim>::active_cell_iterator cell =
diff --git a/tests/distributed_grids/pre_refinement_signal.cc b/tests/distributed_grids/pre_refinement_signal.cc
new file mode 100644
index 0000000000..e39dd61dbf
--- /dev/null
+++ b/tests/distributed_grids/pre_refinement_signal.cc
@@ -0,0 +1,134 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2008 - 2019 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// The deal.II library is free software; you can use it, redistribute
+// it, and/or modify it under the terms of the GNU Lesser General
+// Public License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+// The full text of the license can be found in the file LICENSE.md at
+// the top level directory of deal.II.
+//
+// ---------------------------------------------------------------------
+
+
+
+// Tests that functions connected to 'pre_distributed_refinement'
+// signals work on valid 'refine' and 'coarsen' flags
+
+
+#include <deal.II/base/logstream.h>
+
+#include <deal.II/distributed/tria.h>
+
+#include <deal.II/dofs/dof_handler.h>
+
+#include <deal.II/fe/fe_q.h>
+
+#include <deal.II/grid/grid_generator.h>
+
+#include <functional>
+
+#include "../tests.h"
+
+
+// check that cells flagged for coarsening cannot have siblings
+// flagged for refinement
+template <int dim>
+void
+verify_callback(const parallel::distributed::Triangulation<dim> &tria)
+{
+  for (const auto &cell : tria.active_cell_iterators())
+    if (cell->coarsen_flag_set())
+      {
+        const auto parent = cell->parent();
+        for (unsigned int c = 0; c < parent->n_children(); ++c)
+          Assert(parent->child(c)->refine_flag_set() == false,
+                 ExcInternalError());
+      }
+}
+
+
+
+template <int dim>
+void
+test()
+{
+  parallel::distributed::Triangulation<dim> triangulation(
+    MPI_COMM_WORLD, Triangulation<dim>::limit_level_difference_at_vertices);
+  triangulation.signals.pre_distributed_refinement.connect(
+    std::bind(verify_callback<dim>, std::cref(triangulation)));
+
+  GridGenerator::hyper_cube(triangulation);
+  triangulation.refine_global(2);
+
+  DoFHandler<dim> dof_handler(triangulation);
+  FE_Q<dim>       fe(1);
+  dof_handler.distribute_dofs(fe);
+
+  const unsigned int n_refinements[] = {0, 4, 3, 2};
+  for (unsigned int i = 0; i < n_refinements[dim]; ++i)
+    {
+      // refine one-fifth of cells randomly
+      std::vector<bool> flags(triangulation.n_active_cells(), false);
+      for (unsigned int k = 0; k < flags.size() / 5 + 1; ++k)
+        flags[Testing::rand() % flags.size()] = true;
+      // make sure there's at least one that
+      // will be refined
+      flags[0] = true;
+
+      // refine triangulation
+      unsigned int index = 0;
+      for (typename Triangulation<dim>::active_cell_iterator cell =
+             triangulation.begin_active();
+           cell != triangulation.end();
+           ++cell, ++index)
+        if (flags[index])
+          cell->set_refine_flag();
+      AssertThrow(index == triangulation.n_active_cells(), ExcInternalError());
+
+      // flag all other cells for coarsening
+      // (this should ensure that at least
+      // some of them will actually be
+      // coarsened)
+      index = 0;
+      for (typename Triangulation<dim>::active_cell_iterator cell =
+             triangulation.begin_active();
+           cell != triangulation.end();
+           ++cell, ++index)
+        if (!flags[index])
+          cell->set_coarsen_flag();
+
+      triangulation.execute_coarsening_and_refinement();
+    }
+
+  deallog << "OK" << std::endl;
+}
+
+
+int
+main(int argc, char *argv[])
+{
+  Utilities::MPI::MPI_InitFinalize mpi_initialization(argc, argv, 1);
+
+  unsigned int myid = Utilities::MPI::this_mpi_process(MPI_COMM_WORLD);
+  if (myid == 0)
+    {
+      initlog();
+
+      deallog.push("2d");
+      test<2>();
+      deallog.pop();
+
+      deallog.push("3d");
+      test<3>();
+      deallog.pop();
+    }
+  else
+    {
+      test<2>();
+      test<3>();
+    }
+}
diff --git a/tests/distributed_grids/pre_refinement_signal.output b/tests/distributed_grids/pre_refinement_signal.output
new file mode 100644
index 0000000000..25966e9bd0
--- /dev/null
+++ b/tests/distributed_grids/pre_refinement_signal.output
@@ -0,0 +1,3 @@
+
+DEAL:2d::OK
+DEAL:3d::OK
-- 
2.39.5