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   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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 org.apache.cassandra.db.commitlog;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.nio.channels.FileChannel;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.util.concurrent.atomic.AtomicLong;
  
  import org.junit.BeforeClass;
  import org.junit.Test;
  
  import net.openhft.chronicle.core.util.ThrowingFunction;
  import org.apache.cassandra.config.Config;
  import org.apache.cassandra.config.DatabaseDescriptor;
  import org.apache.cassandra.io.util.File;
  import org.apache.cassandra.io.util.SimpleCachedBufferPool;
  import org.apache.cassandra.utils.Generators;
  import org.mockito.ArgumentCaptor;
  import org.mockito.internal.creation.MockSettingsImpl;
  import sun.nio.ch.DirectBuffer;
  
  import static org.assertj.core.api.Assertions.assertThat;
  import static org.mockito.ArgumentMatchers.anyLong;
  import static org.mockito.Mockito.doAnswer;
  import static org.mockito.Mockito.doCallRealMethod;
  import static org.mockito.Mockito.doNothing;
  import static org.mockito.Mockito.doReturn;
  import static org.mockito.Mockito.mock;
  import static org.mockito.Mockito.verify;
  import static org.mockito.Mockito.when;
  import static org.quicktheories.QuickTheory.qt;
  
  public class DirectIOSegmentTest
  {
      @BeforeClass
      public static void beforeClass() throws IOException
      {
          File commitLogDir = new File(Files.createTempDirectory("commitLogDir"));
          DatabaseDescriptor.daemonInitialization(() -> {
              Config config = DatabaseDescriptor.loadConfig();
              config.commitlog_directory = commitLogDir.toString();
              return config;
          });
      }
  
      @Test
      public void testFlushBuffer()
      {
          int fsBlockSize = 32;
          int bufSize = 4 * fsBlockSize;
  
          SimpleCachedBufferPool bufferPool = mock(SimpleCachedBufferPool.class);
          AbstractCommitLogSegmentManager manager = mock(AbstractCommitLogSegmentManager.class,
                                                         new MockSettingsImpl<>().useConstructor(CommitLog.instance, DatabaseDescriptor.getCommitLogLocation()));
          doReturn(bufferPool).when(manager).getBufferPool();
          doCallRealMethod().when(manager).getConfiguration();
          when(bufferPool.createBuffer()).thenReturn(ByteBuffer.allocate(bufSize + fsBlockSize));
          doNothing().when(manager).addSize(anyLong());
  
          qt().forAll(Generators.forwardRanges(0, bufSize))
              .checkAssert(startEnd -> {
                  int start = startEnd.lowerEndpoint();
                  int end = startEnd.upperEndpoint();
                  FileChannel channel = mock(FileChannel.class);
                  ThrowingFunction<Path, FileChannel, IOException> channelFactory = path -> channel;
                  ArgumentCaptor<ByteBuffer> bufCap = ArgumentCaptor.forClass(ByteBuffer.class);
                  DirectIOSegment seg = new DirectIOSegment(manager, channelFactory, fsBlockSize);
                  seg.lastSyncedOffset = start;
                  seg.flush(start, end);
                  try
                  {
                      verify(channel).write(bufCap.capture());
                  }
                  catch (IOException e)
                  {
                      throw new RuntimeException(e);
                  }
                  ByteBuffer buf = bufCap.getValue();
  
                  // assert that the entire buffer is written
                  assertThat(buf.position()).isLessThanOrEqualTo(start);
                  assertThat(buf.limit()).isGreaterThanOrEqualTo(end);
  
                  // assert that the buffer is aligned to the fs block size
                  assertThat(buf.position() % fsBlockSize).isZero();
                  assertThat(buf.limit() % fsBlockSize).isZero();
  
                  // assert that the buffer is unnecessarily large
                  assertThat(buf.position()).isGreaterThan(start - fsBlockSize);
                  assertThat(buf.limit()).isLessThan(end + fsBlockSize);
  
                  assertThat(seg.lastWritten).isEqualTo(buf.limit());
              });
      }
  
      @Test
      public void testFlushSize()
      {
          int fsBlockSize = 32;
          int bufSize = 4 * fsBlockSize;
  
          SimpleCachedBufferPool bufferPool = mock(SimpleCachedBufferPool.class);
          AbstractCommitLogSegmentManager manager = mock(AbstractCommitLogSegmentManager.class,
                                                         new MockSettingsImpl<>().useConstructor(CommitLog.instance, DatabaseDescriptor.getCommitLogLocation()));
          doReturn(bufferPool).when(manager).getBufferPool();
          doCallRealMethod().when(manager).getConfiguration();
          when(bufferPool.createBuffer()).thenReturn(ByteBuffer.allocate(bufSize + fsBlockSize));
          doNothing().when(manager).addSize(anyLong());
  
          FileChannel channel = mock(FileChannel.class);
          ThrowingFunction<Path, FileChannel, IOException> channelFactory = path -> channel;
          ArgumentCaptor<ByteBuffer> bufCap = ArgumentCaptor.forClass(ByteBuffer.class);
          DirectIOSegment seg = new DirectIOSegment(manager, channelFactory, fsBlockSize);
  
          AtomicLong size = new AtomicLong();
          doAnswer(i -> size.addAndGet(i.getArgument(0, Long.class))).when(manager).addSize(anyLong());
  
          for (int start = 0; start < bufSize - 1; start++)
          {
              int end = start + 1;
              seg.lastSyncedOffset = start;
              seg.flush(start, end);
              assertThat(size.get()).isGreaterThanOrEqualTo(end);
          }
  
          assertThat(size.get()).isEqualTo(bufSize);
      }
  
      @Test
      public void testBuilder()
      {
          AbstractCommitLogSegmentManager manager = mock(AbstractCommitLogSegmentManager.class,
                                                         new MockSettingsImpl<>().useConstructor(CommitLog.instance, DatabaseDescriptor.getCommitLogLocation()));
          DirectIOSegment.DirectIOSegmentBuilder builder = new DirectIOSegment.DirectIOSegmentBuilder(manager, 4096);
          assertThat(builder.fsBlockSize).isGreaterThan(0);
  
          int segmentSize = Math.max(5 << 20, builder.fsBlockSize * 5);
          DatabaseDescriptor.setCommitLogSegmentSize(segmentSize >> 20);
  
          SimpleCachedBufferPool pool = builder.createBufferPool();
          ByteBuffer buf = pool.createBuffer();
          try
          {
              assertThat(buf.remaining()).isEqualTo(segmentSize);
              assertThat(buf.alignmentOffset(buf.position(), builder.fsBlockSize)).isEqualTo(0);
              assertThat(buf).isInstanceOf(DirectBuffer.class);
              assertThat(((DirectBuffer) buf).attachment()).isNotNull();
          }
          finally
          {
              pool.releaseBuffer(buf);
          }
      }
  }