* typically in memory areas not accessible to the other processes.
* As a consequence, the usual use case for this function is to share
* arrays of simple objects such as `double`s or `int`s.
+ *
+ * @note After calling this function, objects on different MPI processes
+ * share a common state. That means that certain operations become
+ * "collective", i.e., they must be called on all participating
+ * processors at the same time. In particular, you can no longer call
+ * resize(), reserve(), or clear() on one MPI process -- you have to do
+ * so on all processes at the same time, because they have to communicate
+ * for these operations. If you do not do so, you will likely get
+ * a deadlock that may be difficult to debug. By extension, this rule of
+ * only collectively resizing extends to this function itself: You can
+ * not call it twice in a row because that implies that first all but the
+ * `root_process` throw away their data, which is not a collective
+ * operation. Generally, these restrictions on what can and can not be
+ * done hint at the correctness of the comments above: You should treat
+ * an AlignedVector on which the current function has been called as
+ * `const`, on which no further operations can be performed until
+ * the destructor is called.
*/
void
replicate_across_communicator(const MPI_Comm & communicator,
{
# ifdef DEAL_II_WITH_MPI
# if DEAL_II_MPI_VERSION_GTE(3, 0)
+
+ // **** Step 0 ****
+ // All but the root process no longer need their data, so release the memory
+ // used to store the previous elements.
+ if (Utilities::MPI::this_mpi_process(communicator) != root_process)
+ {
+ elements.reset();
+ used_elements_end = nullptr;
+ allocated_elements_end = nullptr;
+ }
+
// **** Step 1 ****
// Create communicators for each group of processes that can use
// shared memory areas. Within each of these groups, we don't care about
--- /dev/null
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2012 - 2018 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.
+//
+// ---------------------------------------------------------------------
+
+
+// Test AlignedVector::replicate_across_communicator()
+
+#include <deal.II/base/aligned_vector.h>
+
+#include "../tests.h"
+
+
+void
+test()
+{
+ const MPI_Comm communicator = MPI_COMM_WORLD;
+ const unsigned int root = 1;
+ Assert(root < Utilities::MPI::n_mpi_processes(communicator),
+ ExcInternalError());
+
+ // Create a vector of differing sizes on all processes, but only on
+ // the root process do we put something useful into it
+ AlignedVector<int> avec(
+ Utilities::MPI::this_mpi_process(communicator) == root ? 10 : 5);
+ if (Utilities::MPI::this_mpi_process(communicator) == root)
+ {
+ avec[2] = 2;
+ avec[4] = 4;
+ avec[6] = 6;
+ }
+ else
+ {
+ for (unsigned int i = 0; i < avec.size(); ++i)
+ avec[i] = 100 * Utilities::MPI::this_mpi_process(communicator) + i;
+ }
+
+ // Now replicate this information across all processes
+ avec.replicate_across_communicator(communicator, root);
+
+ // Final step, let every process output what it now has
+ deallog << "On process " << Utilities::MPI::this_mpi_process(communicator)
+ << ": " << std::endl;
+ for (const auto i : avec)
+ deallog << i << ' ';
+ deallog << std::endl;
+}
+
+
+
+int
+main(int argc, char **argv)
+{
+ Utilities::MPI::MPI_InitFinalize mpi_initialization(argc, argv, 1);
+ MPILogInitAll all;
+
+ test();
+}
--- /dev/null
+
+DEAL:0::On process 0:
+DEAL:0::0 0 2 0 4 0 6 0 0 0
+
+DEAL:1::On process 1:
+DEAL:1::0 0 2 0 4 0 6 0 0 0
+
+
+DEAL:2::On process 2:
+DEAL:2::0 0 2 0 4 0 6 0 0 0
+
--- /dev/null
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2012 - 2018 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.
+//
+// ---------------------------------------------------------------------
+
+
+// Test AlignedVector::replicate_across_communicator(). This function
+// puts data into a shared memory area for all MPI processes that are
+// on the same machine. This is a read-write area, and so writing into
+// it becomes visible also to those processes on the same
+// machine. Since we run the test suite only in setups where *all*
+// processes are on the same machine, we know that a change made on
+// one process should be visible on *all*.
+
+#include <deal.II/base/aligned_vector.h>
+
+#include "../tests.h"
+
+
+void
+test()
+{
+ const MPI_Comm communicator = MPI_COMM_WORLD;
+ const unsigned int root = 1;
+ Assert(root < Utilities::MPI::n_mpi_processes(communicator),
+ ExcInternalError());
+
+ // Same as for the _01 test:
+ AlignedVector<int> avec(
+ Utilities::MPI::this_mpi_process(communicator) == root ? 10 : 5);
+ if (Utilities::MPI::this_mpi_process(communicator) == root)
+ {
+ avec[2] = 2;
+ avec[4] = 4;
+ avec[6] = 6;
+ }
+ else
+ {
+ for (unsigned int i = 0; i < avec.size(); ++i)
+ avec[i] = 100 * Utilities::MPI::this_mpi_process(communicator) + i;
+ }
+
+ // Now replicate this information across all processes
+ avec.replicate_across_communicator(communicator, root);
+
+
+ // Now let each process change one element:
+ if (Utilities::MPI::this_mpi_process(communicator) == 0)
+ avec[0] = 42;
+ else if (Utilities::MPI::this_mpi_process(communicator) == 1)
+ avec[1] = 43;
+ else if (Utilities::MPI::this_mpi_process(communicator) == 2)
+ avec[3] = 44;
+
+ // Final step, let every process output what it now has. Every
+ // process should be able to see the changed element, even though
+ // only one changed it.
+ deallog << "On process " << Utilities::MPI::this_mpi_process(communicator)
+ << ": " << std::endl;
+ for (const auto i : avec)
+ deallog << i << ' ';
+ deallog << std::endl;
+}
+
+
+
+int
+main(int argc, char **argv)
+{
+ Utilities::MPI::MPI_InitFinalize mpi_initialization(argc, argv, 1);
+ MPILogInitAll all;
+
+ test();
+}
--- /dev/null
+
+DEAL:0::On process 0:
+DEAL:0::42 43 2 44 4 0 6 0 0 0
+
+DEAL:1::On process 1:
+DEAL:1::42 43 2 44 4 0 6 0 0 0
+
+
+DEAL:2::On process 2:
+DEAL:2::42 43 2 44 4 0 6 0 0 0
+
--- /dev/null
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2012 - 2018 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.
+//
+// ---------------------------------------------------------------------
+
+
+// Test AlignedVector::replicate_across_communicator().
+//
+// Check what happens if we call this function on an empty object.
+
+#include <deal.II/base/aligned_vector.h>
+
+#include "../tests.h"
+
+
+void
+test()
+{
+ const MPI_Comm communicator = MPI_COMM_WORLD;
+ const unsigned int root = 1;
+ Assert(root < Utilities::MPI::n_mpi_processes(communicator),
+ ExcInternalError());
+
+ // Create an empty object and replicate it.
+ AlignedVector<int> avec;
+ avec.replicate_across_communicator(communicator, root);
+
+ deallog << "On process " << Utilities::MPI::this_mpi_process(communicator)
+ << ": " << avec.size() << std::endl;
+}
+
+
+
+int
+main(int argc, char **argv)
+{
+ Utilities::MPI::MPI_InitFinalize mpi_initialization(argc, argv, 1);
+ MPILogInitAll all;
+
+ test();
+}
--- /dev/null
+
+DEAL:0::On process 0: 0
+
+DEAL:1::On process 1: 0
+
+
+DEAL:2::On process 2: 0
+
projects / dealii.git / commitdiff