From 0a8592912a6c13704177234719e7d97c1ede6e2c Mon Sep 17 00:00:00 2001
From: Marc Fehling <marc.fehling@gmx.net>
Date: Fri, 15 May 2020 00:25:31 +0200
Subject: [PATCH] Bugfix: Cells may not receive any variable size data.

---
 source/distributed/tria.cc                    |  8 +-
 tests/particles/particle_handler_14.cc        | 96 +++++++++++++++++++
 ...handler_14.with_p4est=true.mpirun=2.output |  4 +
 3 files changed, 104 insertions(+), 4 deletions(-)
 create mode 100644 tests/particles/particle_handler_14.cc
 create mode 100644 tests/particles/particle_handler_14.with_p4est=true.mpirun=2.output

diff --git a/source/distributed/tria.cc b/source/distributed/tria.cc
index ff7c033397..f0f395dde4 100644
--- a/source/distributed/tria.cc
+++ b/source/distributed/tria.cc
@@ -1611,16 +1611,16 @@ namespace parallel
       const bool         callback_variable_transfer = (handle % 2 == 0);
       const unsigned int callback_index             = handle / 2;
 
+      // Cells will always receive fixed size data (i.e., CellStatus
+      // information), but not necessarily variable size data (e.g., with a
+      // ParticleHandler a cell might not contain any particle at all).
+      // Thus it is sufficient to check if fixed size data has been received.
       Assert(sizes_fixed_cumulative.size() > 0,
              ExcMessage("No data has been packed!"));
       if (quad_cell_relations.size() > 0)
         {
           Assert(dest_data_fixed.size() > 0,
                  ExcMessage("No data has been received!"));
-
-          if (callback_variable_transfer)
-            Assert(dest_data_variable.size() > 0,
-                   ExcMessage("No data has been received!"));
         }
 
       std::vector<char>::const_iterator dest_data_it;
diff --git a/tests/particles/particle_handler_14.cc b/tests/particles/particle_handler_14.cc
new file mode 100644
index 0000000000..ae31bf7713
--- /dev/null
+++ b/tests/particles/particle_handler_14.cc
@@ -0,0 +1,96 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2020 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.
+//
+// ---------------------------------------------------------------------
+
+
+
+// check variable size data transfer for parallel distributed applications
+// if one cell does not contain any particle at all
+
+
+#include <deal.II/distributed/tria.h>
+
+#include <deal.II/fe/mapping_q.h>
+
+#include <deal.II/grid/grid_generator.h>
+
+#include <deal.II/particles/particle_handler.h>
+
+#include "../tests.h"
+
+template <int dim, int spacedim>
+void
+test()
+{
+  parallel::distributed::Triangulation<dim, spacedim> tr(MPI_COMM_WORLD);
+
+  MappingQ<dim, spacedim> mapping(1);
+
+  // setup triangulation
+  const unsigned int n_cells = 2;
+
+  std::vector<unsigned int> rep(dim, 1);
+  rep[0] = n_cells;
+  Point<dim> p1, p2;
+  for (unsigned int d = 0; d < dim; ++d)
+    {
+      p1[d] = 0;
+      p2[d] = (d == 0) ? n_cells : 1;
+    }
+  GridGenerator::subdivided_hyper_rectangle(tr, rep, p1, p2);
+
+  // setup one particle in first cell
+  Particles::ParticleHandler<dim, spacedim> particle_handler(tr, mapping);
+
+  Particles::Particle<dim, spacedim> particle(Point<spacedim>(),
+                                              Point<dim>(),
+                                              0);
+
+  particle_handler.insert_particle(particle, tr.begin_active());
+  particle_handler.update_cached_numbers();
+
+  // initiate data transfer
+  tr.signals.pre_distributed_repartition.connect([&particle_handler]() {
+    particle_handler.register_store_callback_function();
+  });
+
+  tr.signals.post_distributed_repartition.connect([&particle_handler]() {
+    particle_handler.register_load_callback_function(false);
+  });
+
+  tr.repartition();
+
+  deallog << "OK" << std::endl;
+}
+
+
+
+int
+main(int argc, char *argv[])
+{
+  Utilities::MPI::MPI_InitFinalize mpi_initialization(argc, argv, 1);
+
+  if (Utilities::MPI::this_mpi_process(MPI_COMM_WORLD) == 0)
+    initlog();
+
+  deallog.push("2d/2d");
+  test<2, 2>();
+  deallog.pop();
+  deallog.push("2d/3d");
+  test<2, 3>();
+  deallog.pop();
+  deallog.push("3d/3d");
+  test<3, 3>();
+  deallog.pop();
+}
diff --git a/tests/particles/particle_handler_14.with_p4est=true.mpirun=2.output b/tests/particles/particle_handler_14.with_p4est=true.mpirun=2.output
new file mode 100644
index 0000000000..988eda8574
--- /dev/null
+++ b/tests/particles/particle_handler_14.with_p4est=true.mpirun=2.output
@@ -0,0 +1,4 @@
+
+DEAL:2d/2d::OK
+DEAL:2d/3d::OK
+DEAL:3d/3d::OK
-- 
2.39.5