code: /*
   * Copyright 2012-2018 Chronicle Map Contributors
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package net.openhft.chronicle.map.example;
  
  import net.openhft.chronicle.core.OS;
  import net.openhft.chronicle.map.ChronicleMap;
  import net.openhft.chronicle.map.ChronicleMapBuilder;
  import net.openhft.chronicle.threads.NamedThreadFactory;
  import net.openhft.chronicle.values.Array;
  import net.openhft.chronicle.values.Values;
  
  import java.io.File;
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Random;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.Future;
  
  interface MyFloats {
      @Array(length = 6)
      public void setValueAt(int index, float f);
  
      public float getValueAt(int index);
  }
  
  /**
   * Created by peter.lawrey on 19/12/14.
   */
  public class LotsOfEntriesMain {
      public static void main(String[] args)
              throws IOException, ExecutionException, InterruptedException {
          workEntries(true);
          workEntries(false);
      }
  
      private static void workEntries(final boolean add)
              throws IOException, ExecutionException, InterruptedException {
          final long entries = 100_000_000;
          File file = new File(OS.getTarget(), "lotsOfEntries.dat");
          final ChronicleMap<CharSequence, MyFloats> map = ChronicleMapBuilder
                  .of(CharSequence.class, MyFloats.class)
                  .entries(entries)
                  // + 2 is average oversize because we append 4-letter "-key" in a loop
                  .averageKeySize((Math.log(1.024) - Math.log(0.024)) * 24 + 2)
                  .createPersistedTo(file);
          int threads = Runtime.getRuntime().availableProcessors();
          ExecutorService es = Executors.newFixedThreadPool(threads,
                  new NamedThreadFactory("test"));
          long block = (entries + threads - 1) / threads;
  
          final long start = System.nanoTime();
          List<Future<?>> futures = new ArrayList<>();
          for (int t = 0; t < threads; t++) {
              final long startI = t * block;
              final long endI = Math.min((t + 1) * block, entries);
              futures.add(es.submit(new Runnable() {
                  @Override
                  public void run() {
                      Random rand = new Random(startI);
                      StringBuilder sb = new StringBuilder();
                      MyFloats mf = Values.newHeapInstance(MyFloats.class);
                      if (add)
                          for (int i = 0; i < 6; i++)
                              mf.setValueAt(i, i);
                      for (long i = startI; i < endI; i++) {
                          sb.setLength(0);
                          int length = (int) (24 / (rand.nextFloat() + 24.0 / 1000));
                          sb.append(i);
                          while (sb.length() < length)
                              sb.append("-key");
                          try {
                              if (add)
                                  map.put(sb, mf);
                              else
                                  map.getUsing(sb, mf);
                          } catch (Exception e) {
                              System.out.println("map.size: " + map.size());
                              throw e;
                          }
                      }
                  }
              }));
          }
          for (Future<?> future : futures) {
              future.get();
          }
          long time = System.nanoTime() - start;
          es.shutdown();
          System.out.printf("Map.size: %,d with a throughput of %.1f million/sec to %s.%n",
                  map.size(), entries * 1e3 / time, add ? "add" : "get");
          map.close();
      }
  }
  