Added a simple btd example

CMakeLists.txt

@@ -719,6 +719,7 @@ set(openPMD_EXAMPLE_NAMES
     13_write_dynamic_configuration
     14_toml_template
     15_compression
+    16_btd_write_parallel
 )
 set(openPMD_PYTHON_EXAMPLE_NAMES
     2_read_serial

examples/16_btd_write_parallel.cpp

@@ -0,0 +1,312 @@
+/* Copyright 2017-2021 Fabian Koller, Axel Huebl
+ *
+ * This file is part of openPMD-api.
+ *
+ * openPMD-api is free software: you can redistribute it and/or modify
+ * it under the terms of of either the GNU General Public License or
+ * the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * openPMD-api is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License and the GNU Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * and the GNU Lesser General Public License along with openPMD-api.
+ * If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <openPMD/openPMD.hpp>
+
+#include <mpi.h>
+
+#include <iostream>
+#include <memory>
+#include <vector> // std::vector
+
+#include <chrono>
+#include <thread>
+
+using std::cout;
+using namespace openPMD;
+
+// Global verbosity flag
+bool m_verbose = false;
+bool m_span = false;
+bool m_barrier_at_flush = false;
+
+auto m_blockX = 32ul;
+auto m_blockY = 64ul;
+auto m_blockZ = 64ul;
+auto m_blockTotal = 4;
+
+/*
+ * assign a rank to work  on a buffer from a snapshot
+ * a snapshot has multiple buffers
+ * at a given time. at most one buffer is active for I/O
+ * and only rank is used to handle a buffer
+ *
+ */
+struct Workload
+{
+    int whichSnapshot;
+    int whichBuffer;
+    int whichWorkRank;
+};
+
+std::vector<int> m_snapshots = {0, 1, 2, 3};
+std::vector<int> m_buffers = {1, 2, 3, 4};
+
+// supposed to be
+// std::vector<std::string> m_common_fields={"B","j", "E"};
+// std::vector<std::string> m_common_comps={"x", "y", "z"};
+// for simplicity
+std::vector<std::string> m_common_fields = {"B"};
+std::vector<std::string> m_common_comps = {"x"};
+
+std::vector<std::string> getBackends()
+{
+    auto variants = getVariants();
+    std::map<std::string, std::string> extensions{
+        {"adios2", "bp"}, {"hdf5", "h5"}};
+    std::vector<std::string> res;
+    for (auto const &pair : variants)
+    {
+        if (pair.second)
+        {
+            auto lookup = extensions.find(pair.first);
+            if (lookup != extensions.end())
+            {
+                std::string extension = lookup->second;
+                res.push_back(std::move(extension));
+            }
+        }
+    }
+    return res;
+}
+
+void setupMeshComp(
+    openPMD::Container<openPMD::Mesh> &meshes, int currRank, const Workload &w)
+{
+    for (auto ff : m_common_fields)
+    {
+        for (auto cc : m_common_comps)
+        {
+            auto mesh_field = meshes[ff];
+            auto curr_mesh_comp = meshes[ff][cc];
+            Datatype datatype = determineDatatype<double>();
+            Extent global_extent = {
+                m_blockX * m_blockTotal, m_blockY, m_blockZ};
+            Dataset dataset = Dataset(datatype, global_extent);
+
+            curr_mesh_comp.resetDataset(dataset);
+            if (m_verbose)
+            {
+                cout << "Rank : " << currRank << " Prepared a Dataset [" << ff
+                     << "/" << cc << "] of size " << dataset.extent[0] << " x "
+                     << dataset.extent[1] << " x " << dataset.extent[2]
+                     << " and Datatype " << dataset.dtype
+                     << " iteration=" << w.whichSnapshot << '\n';
+            }
+        }
+    }
+}
+
+void doFlush(
+    const Workload &w,
+    const std::unique_ptr<openPMD::Series> &series,
+    int currRank)
+{
+
+    if (m_barrier_at_flush)
+    {
+        if (m_verbose)
+            std::cout << " Barrier at doFlush(), rank:" << currRank
+                      << std::endl;
+        MPI_Barrier(MPI_COMM_WORLD);
+    }
+
+    else
+    {
+        if (m_verbose)
+            std::cout << " At doFlush(), rank:" << currRank << std::endl;
+    }
+
+    series->iterations[w.whichSnapshot].seriesFlush(
+        "adios2.engine.preferred_flush_target = \"buffer\"");
+}
+
+void doWork(
+    const Workload &w,
+    const std::unique_ptr<openPMD::Series> &series,
+    int currRank,
+    std::string const &field_name,
+    std::string const &comp_name,
+    double seed)
+{
+
+    bool const first_write_to_iteration =
+        !series->iterations.contains(w.whichSnapshot);
+
+    auto meshes = series->iterations[w.whichSnapshot].meshes;
+
+    // is this the trouble maker?
+    series->iterations[w.whichSnapshot].open();
+
+    if (first_write_to_iteration)
+    {
+        setupMeshComp(meshes, currRank, w);
+    }
+
+    auto mesh_field = meshes[field_name];
+    auto mymesh = mesh_field[comp_name];
+
+    // do work on the assigned rank
+    if (currRank == w.whichWorkRank)
+    {
+        // example shows a 1D domain decomposition in first index
+        Offset chunk_offset = {m_blockX * (m_blockTotal - w.whichBuffer), 0, 0};
+        Extent chunk_extent = {m_blockX, m_blockY, m_blockZ};
+        if (m_verbose)
+        {
+            cout << "Rank: " << currRank << " At snapshot:" << w.whichSnapshot
+                 << " buffer " << w.whichBuffer << "  seed: " << seed;
+            cout << "    box: " << chunk_offset[0] << ", " << chunk_offset[1]
+                 << ", " << chunk_offset[2] << std::endl;
+        }
+
+        // prepare data block value
+        auto value = double(
+            seed + currRank + 0.1 * w.whichSnapshot + 100 * w.whichBuffer);
+        std::vector<double> local_data(
+            size_t(m_blockX) * m_blockY * m_blockZ, value);
+
+        if (!m_span)
+        {
+            mymesh.storeChunkRaw(local_data.data(), chunk_offset, chunk_extent);
+        }
+        else
+        {
+            auto dynamicMemoryView =
+                mymesh.storeChunk<double>(chunk_offset, chunk_extent);
+            std::cout << " span allocation snap:" << w.whichSnapshot << " "
+                      << w.whichBuffer << std::endl;
+            auto spanBuffer = dynamicMemoryView.currentBuffer();
+
+            std::copy(local_data.begin(), local_data.end(), spanBuffer.data());
+        }
+    }
+}
+
+int main(int argc, char *argv[])
+{
+    MPI_Init(&argc, &argv);
+
+    int mpi_size;
+    int mpi_rank;
+
+    MPI_Comm_size(MPI_COMM_WORLD, &mpi_size);
+    MPI_Comm_rank(MPI_COMM_WORLD, &mpi_rank);
+
+    for (int i = 1; i < argc; ++i)
+    {
+        if (std::string(argv[i]) == "-v")
+        {
+            m_verbose = true;
+        }
+        if (std::string(argv[i]) == "-s")
+        {
+            m_span = true;
+        }
+        if (std::string(argv[i]) == "-b")
+        {
+            m_barrier_at_flush = true;
+        }
+    }
+
+    if (0 == mpi_rank)
+    {
+        std::cout << " Configuration: \n\t[verbose] =" << m_verbose
+                  << "\n\t[span] =" << m_span
+                  << "\n\t[barrier_at_flush] =" << m_barrier_at_flush
+                  << std::endl;
+        std::cout << " change with -v -s -b respectively " << std::endl;
+    }
+
+    std::vector<Workload> workOrders;
+    auto maxWorkers = std::min(mpi_size, 4);
+
+    int counter = 0;
+    for (auto snapID : m_snapshots)
+    {
+        for (auto bufferID : m_buffers)
+        {
+            {
+                auto workRank = (counter % maxWorkers);
+                workOrders.push_back(Workload{snapID, bufferID, workRank});
+                counter++;
+            }
+        }
+    }
+
+    if (m_blockTotal < mpi_size)
+        if (0 == mpi_rank)
+            std::cout << " === WARNING: not all buffers in all snapshots will "
+                         "be touched, expecting "
+                      << m_blockTotal
+                      << " ranks to do all work  ==== " << std::endl;
+
+    // std::vector<std::string> exts = {"bp", "h5"};
+    std::vector<std::string> exts = getBackends();
+    for (auto const &ext : exts)
+    {
+        if (0 == mpi_rank)
+            std::cout << "========== I/O with " << ext
+                      << " ========== " << std::endl;
+        try
+        {
+            std::unique_ptr<Series> series = std::make_unique<openPMD::Series>(
+                "../samples/16_btd_%07T." + ext,
+                Access::CREATE,
+                MPI_COMM_WORLD);
+
+            series->setIterationEncoding(openPMD::IterationEncoding::fileBased);
+            series->setMeshesPath("fields");
+
+            double seed = 0.001;
+            for (Workload w : workOrders)
+            {
+                for (auto ff : m_common_fields)
+                {
+                    for (auto cc : m_common_comps)
+                    {
+                        doWork(w, series, mpi_rank, ff, cc, seed);
+                        doFlush(w, series, mpi_rank);
+                        seed += 0.001;
+                        std::this_thread::sleep_for(
+                            std::chrono::milliseconds(1000));
+                    }
+                }
+                // later
+                // doFlush(w, series, mpi_rank);
+            }
+
+            series->close();
+        }
+        catch (const std::exception &e)
+        {
+            if (mpi_rank == 0)
+            {
+                std::cerr << ext
+                          << " Error in workload processing: " << e.what()
+                          << std::endl;
+            }
+        }
+    }
+
+    MPI_Finalize();
+
+    return 0;
+}