content: /*
   * 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.MappedByteBuffer;
  import java.nio.channels.FileChannel;
  import java.nio.file.Path;
  import java.nio.file.StandardOpenOption;
  
  import net.openhft.chronicle.core.util.ThrowingFunction;
  import org.apache.cassandra.config.DatabaseDescriptor;
  import org.apache.cassandra.io.FSWriteError;
  import org.apache.cassandra.io.util.SimpleCachedBufferPool;
  import org.apache.cassandra.utils.NativeLibrary;
  import org.apache.cassandra.utils.SyncUtil;
  import org.apache.cassandra.utils.memory.MemoryUtil;
  
  /*
   * Memory-mapped segment. Maps the destination channel into an appropriately-sized memory-mapped buffer in which the
   * mutation threads write. On sync forces the buffer to disk.
   * If possible, recycles used segment files to avoid reallocating large chunks of disk.
   */
  public class MemoryMappedSegment extends CommitLogSegment
  {
      private final int fd;
  
      /**
       * Constructs a new segment file.
       */
      MemoryMappedSegment(AbstractCommitLogSegmentManager manager, ThrowingFunction<Path, FileChannel, IOException> channelFactory)
      {
          super(manager, channelFactory);
          // mark the initial sync marker as uninitialised
          int firstSync = buffer.position();
          buffer.putInt(firstSync + 0, 0);
          buffer.putInt(firstSync + 4, 0);
          fd = NativeLibrary.getfd(channel);
      }
  
      @Override
      protected ByteBuffer createBuffer()
      {
          try
          {
              MappedByteBuffer mappedFile = channel.map(FileChannel.MapMode.READ_WRITE, 0, DatabaseDescriptor.getCommitLogSegmentSize());
              manager.addSize(DatabaseDescriptor.getCommitLogSegmentSize());
              return mappedFile;
          }
          catch (IOException e)
          {
              throw new FSWriteError(e, logFile);
          }
      }
  
      @Override
      void write(int startMarker, int nextMarker)
      {
          // if there's room in the discard section to write an empty header,
          // zero out the next sync marker so replayer can cleanly exit
          if (nextMarker <= buffer.capacity() - SYNC_MARKER_SIZE)
          {
              buffer.putInt(nextMarker, 0);
              buffer.putInt(nextMarker + 4, 0);
          }
  
          // write previous sync marker to point to next sync marker
          // we don't chain the crcs here to ensure this method is idempotent if it fails
          writeSyncMarker(id, buffer, startMarker, startMarker, nextMarker);
      }
  
      @Override
      protected void flush(int startMarker, int nextMarker)
      {
          try
          {
              SyncUtil.force((MappedByteBuffer) buffer);
          }
          catch (Exception e) // MappedByteBuffer.force() does not declare IOException but can actually throw it
          {
              throw new FSWriteError(e, getPath());
          }
          NativeLibrary.trySkipCache(fd, startMarker, nextMarker, logFile.absolutePath());
      }
  
      @Override
      public long onDiskSize()
      {
          return DatabaseDescriptor.getCommitLogSegmentSize();
      }
  
      @Override
      protected void internalClose()
      {
          MemoryUtil.clean(buffer);
          super.internalClose();
      }
  
      protected static class MemoryMappedSegmentBuilder extends CommitLogSegment.Builder
      {
          public MemoryMappedSegmentBuilder(AbstractCommitLogSegmentManager segmentManager)
          {
              super(segmentManager);
          }
  
          @Override
          public MemoryMappedSegment build()
          {
              return new MemoryMappedSegment(segmentManager,
                                             path ->  FileChannel.open(path, StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE));
          }
  
          @Override
          public SimpleCachedBufferPool createBufferPool()
          {
              return null;
          }
      }
  }
  