[MeL/IO] Add generic abstraction layer for parallel and serial file IO

MeshLib/CMakeLists.txt

@@ -14,6 +14,11 @@ append_source_files(SOURCES IO/Legacy)
 append_source_files(SOURCES IO/VtkIO)
 if(OGS_USE_XDMF)
     append_source_files(SOURCES IO/XDMF)
+    if(OGS_USE_PETSC)
+        append_source_files(SOURCES IO/XDMF/mpi)
+    else()
+        append_source_files(SOURCES IO/XDMF/posix)
+    endif()
 endif()
 append_source_files(SOURCES MeshQuality)
 append_source_files(SOURCES Vtk)

MeshLib/IO/XDMF/mpi/partition.cpp

+/**
+ * \file
+ * \author Tobias Meisel
+ * \date   2020-12-08
+ * \brief  Function specific to execution with MPI!!
+ * \copyright Copyright (c) 2012-2020, OpenGeoSys Community
+ * (http://www.opengeosys.org) Distributed under a Modified BSD License. See
+ * accompanying file LICENSE.txt or http://www.opengeosys.org/project/license
+ */
+
+#include <mpi.h>
+
+#include <deque>
+#include <numeric>
+
+#include "../fileIO.h"
+#include "BaseLib/Logging.h"
+
+namespace MeshLib::IO
+{
+bool isFileManager()
+{
+    int mpi_rank;
+    MPI_Comm_rank(MPI_COMM_WORLD, &mpi_rank);
+    return mpi_rank == 0;
+}
+
+std::pair<std::size_t, std::size_t> getPartitionInfo(std::size_t const size)
+{
+    MPI_Comm const mpi_comm = MPI_COMM_WORLD;
+    int mpi_size;
+    int mpi_rank;
+    MPI_Comm_size(mpi_comm, &mpi_size);
+    MPI_Comm_rank(mpi_comm, &mpi_rank);
+
+    std::vector<std::size_t> partition_sizes;
+    partition_sizes.resize(mpi_size);
+
+    MPI_Allgather(&size,
+                  1,
+                  MPI_UNSIGNED_LONG,
+                  partition_sizes.data(),
+                  1,
+                  MPI_UNSIGNED_LONG,
+                  mpi_comm);
+
+    // the first partition's offset is zero, offsets for subsequent
+    // partitions are the accumulated sum of all preceding size (excluding
+    // own size)
+    std::vector<std::size_t> partition_offsets(1, 0);
+    std::partial_sum(partition_sizes.begin(),
+                     partition_sizes.end(),
+                     back_inserter(partition_offsets));
+
+    return {partition_offsets[mpi_rank], partition_offsets.back()};
+}
+}  // namespace MeshLib::IO

MeshLib/IO/XDMF/partition.h

+/**
+ * \file
+ * \author Tobias Meisel
+ * \date   2020-12-08
+ * \brief  Dispatches functions specific to execution plattform (w/o MPI)
+ * \copyright Copyright (c) 2012-2020, OpenGeoSys Community
+ * (http://www.opengeosys.org) Distributed under a Modified BSD License. See
+ * accompanying file LICENSE.txt or http://www.opengeosys.org/project/license
+ */
+
+#pragma once
+
+#include <utility>
+
+namespace MeshLib::IO
+{
+std::pair<std::size_t, std::size_t> getPartitionInfo(std::size_t const size);
+bool isFileManager();
+}  // namespace MeshLib::IO

MeshLib/IO/XDMF/posix/partition.cpp

+#include "../partition.h"
+
+namespace MeshLib::IO
+{
+bool isFileManager()
+{
+    return true;
+}
+
+std::pair<std::size_t, std::size_t> getPartitionInfo(std::size_t const size)
+{
+    return {0, size};
+}
+}  // namespace MeshLib::IO
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