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;
  
  import net.openhft.hashing.LongHashFunction;
  import org.junit.Assert;
  import org.junit.Test;
  
  import java.nio.charset.StandardCharsets;
  import java.util.concurrent.ThreadLocalRandom;
  
  public class KeySegmentDistributionTest {
  
      @Test
      public void keySegmentDistributionTestOneSegment() {
          keySegmentDistributionTest(1000, 1);
      }
  
      @Test
      public void keySegmentDistributionTestPowerOfTwoSegments() {
          keySegmentDistributionTest(1000, 4);
      }
  
      @Test
      public void keySegmentDistributionTestOddSegments() {
          keySegmentDistributionTest(1000, 5);
      }
  
      public void keySegmentDistributionTest(int size, int segments) {
          ChronicleMap<CharSequence, Integer> map = ChronicleMapBuilder
                  .of(CharSequence.class, Integer.class)
                  .actualSegments(segments)
                  // TODO problems with computing proper number of segments/chunks
                  // when I write this without `* 2` I expect not to have ISE "segment is full"...
                  .entries(size * 2)
                  .averageKeySize(10)
                  .create();
  
          byte[] keyBytes = new byte[10];
          ThreadLocalRandom random = ThreadLocalRandom.current();
          for (int i = 0; i < size; i++) {
              random.nextBytes(keyBytes);
              String key = new String(keyBytes, StandardCharsets.US_ASCII);
              long hash = LongHashFunction.xx().hashBytes(StandardCharsets.UTF_8.encode(key));
              int segmentIndex = (((int) hash) & Integer.MAX_VALUE) % segments;
              // Put the segment index as a value to the map
              map.put(key, segmentIndex);
          }
          // The following loop checks that internally hash code and segment index is chosen
          // the same way as we explicitly computed in this test. Since ChMap iteration is segment
          // by segment, we expect to see the sequence of values 0, 0, ... 0, 1, ..1, 2, ..2, 3, ..3
          // or opposite -- 3, 3, ... 3, 2, ..2, 1, ..1, 0, ..0
          int currentSegment = -1;
          boolean ascendingDirection = false;
          for (Integer entrySegment : map.values()) {
              if (currentSegment == -1) {
                  currentSegment = entrySegment;
                  if (currentSegment == 0) {
                      ascendingDirection = true;
                  }
              } else {
                  if (ascendingDirection) {
                      Assert.assertTrue(entrySegment >= currentSegment);
                      currentSegment = entrySegment;
                  } else {
                      // descending iteration direction
                      Assert.assertTrue(entrySegment <= currentSegment);
                      currentSegment = entrySegment;
                  }
              }
          }
      }
  }
  