content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.worker.block.io;
  
  import alluxio.metrics.MetricKey;
  import alluxio.metrics.MetricsSystem;
  
  import com.codahale.metrics.Counter;
  import com.google.common.base.Preconditions;
  import com.google.common.io.Closer;
  import io.netty.buffer.ByteBuf;
  
  import java.io.IOException;
  import java.io.RandomAccessFile;
  import java.nio.ByteBuffer;
  import java.nio.channels.FileChannel;
  import java.nio.channels.ReadableByteChannel;
  import javax.annotation.concurrent.NotThreadSafe;
  
  /**
   * This class provides read access to a block data file locally stored in managed storage.
   */
  @NotThreadSafe
  public class LocalFileBlockReader extends BlockReader {
    private static final Counter BLOCKS_READ_LOCAL =
        MetricsSystem.counter(MetricKey.WORKER_BLOCKS_READ_LOCAL.getName());
  
    private final String mFilePath;
    private final RandomAccessFile mLocalFile;
    private final FileChannel mLocalFileChannel;
    private final Closer mCloser = Closer.create();
    private final long mFileSize;
    private boolean mClosed;
    private int mUsageCount = 0;
  
    /**
     * Constructs a Block reader given the file path of the block.
     *
     * @param path file path of the block
     */
    public LocalFileBlockReader(String path) throws IOException {
      mFilePath = Preconditions.checkNotNull(path, "path");
      mLocalFile = mCloser.register(new RandomAccessFile(mFilePath, "r"));
      mFileSize = mLocalFile.length();
      mLocalFileChannel = mCloser.register(mLocalFile.getChannel());
    }
  
    @Override
    public ReadableByteChannel getChannel() {
      return mLocalFileChannel;
    }
  
    @Override
    public long getLength() {
      return mFileSize;
    }
  
    /**
     * increase the file reader usage count.
     */
    public void increaseUsageCount() {
      mUsageCount++;
    }
  
    /**
     * decrease the file reader usage count.
     */
    public void decreaseUsageCount() {
      Preconditions.checkState(mUsageCount > 0);
      mUsageCount--;
    }
  
    /**
     * @return the file reader usage count
     */
    public int getUsageCount() {
      return mUsageCount;
    }
  
    /**
     * @return the file path
     */
    public String getFilePath() {
      return mFilePath;
    }
  
    @Override
    public ByteBuffer read(long offset, long length) throws IOException {
      Preconditions.checkArgument(offset + length <= mFileSize,
          "offset=%s, length=%s, exceeding fileSize=%s", offset, length, mFileSize);
      return mLocalFileChannel.map(FileChannel.MapMode.READ_ONLY, offset, length);
    }
  
    @Override
    public int transferTo(ByteBuf buf) throws IOException {
      return buf.writeBytes(mLocalFileChannel, buf.writableBytes());
    }
  
    @Override
    public void close() throws IOException {
      super.close();
      Preconditions.checkState(mUsageCount == 0);
      if (mClosed) {
        return;
      }
      try {
        mCloser.close();
      } finally {
        mClosed = true;
        BLOCKS_READ_LOCAL.inc();
      }
    }
  
    @Override
    public boolean isClosed() {
      return mClosed;
    }
  
    @Override
    public String getLocation() {
      return mFilePath;
    }
  }
  