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.client.hadoop;
  
  import org.apache.hadoop.conf.Configured;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.io.LongWritable;
  import org.apache.hadoop.io.Text;
  import org.apache.hadoop.mapred.JobConf;
  import org.apache.hadoop.mapred.Mapper;
  import org.apache.hadoop.mapred.OutputCollector;
  import org.apache.hadoop.mapred.Reporter;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.net.InetAddress;
  import javax.annotation.Nullable;
  
  /**
   * Base mapper class for IO operations.
   * <p>
   * Two abstract methods {@link #doIO(Reporter, String, long)} and
   * {@link #collectStats(OutputCollector, String,long, Object)} should be
   * overloaded in derived classes to define the IO operation and the statistics data to be collected
   * by subsequent reducers.
   *
   */
  public abstract class AbstractIOMapper<T> extends Configured implements
      Mapper<Text, LongWritable, Text, Text> {
  
    protected byte[] mBuffer;
    protected int mBufferSize;
    protected FileSystem mFS;
    protected String mHostname;
    protected Closeable mStream;
  
    public AbstractIOMapper() {}
  
    @Override
    public void configure(JobConf conf) {
      setConf(conf);
      try {
        mFS = FileSystem.get(conf);
      } catch (Exception e) {
        throw new RuntimeException("Cannot create file system.", e);
      }
      mBufferSize = conf.getInt("test.io.file.buffer.size", 4096);
      mBuffer = new byte[mBufferSize];
      try {
        mHostname = InetAddress.getLocalHost().getHostName();
      } catch (Exception e) {
        mHostname = "localhost";
      }
    }
  
    @Override
    public void close() throws IOException {}
  
    /**
     * Perform io operation, usually read or write.
     *
     * @param reporter
     * @param name file name
     * @param value offset within the file
     * @return object that is passed as a parameter to
     *         {@link #collectStats(OutputCollector, String,long, Object)}
     */
    abstract T doIO(Reporter reporter, String name, long value) throws IOException;
  
    /**
     * Create an input or output stream based on the specified file. Subclasses should override this
     * method to provide an actual stream.
     *
     * @param name file name
     * @return the stream
     */
    @Nullable
    public Closeable getIOStream(String name) throws IOException {
      return null;
    }
  
    /**
     * Collect stat data to be combined by a subsequent reducer.
     *
     * @param output
     * @param name file name
     * @param execTime IO execution time
     * @param doIOReturnValue value returned by
     *        {@link #doIO(Reporter, String,long)}
     */
    abstract void collectStats(OutputCollector<Text, Text> output, String name, long execTime,
        T doIOReturnValue) throws IOException;
  
    /**
     * Map file name and offset into statistical data.
     * <p>
     * The map task is to get the <tt>key</tt>, which contains the file name, and the <tt>value</tt>,
     * which is the offset within the file.
     *
     * The parameters are passed to the abstract method
     * {@link #doIO(Reporter, String,long)}, which performs the io operation,
     * usually read or write data, and then
     * {@link #collectStats(OutputCollector, String,long, Object)} is called
     * to prepare stat data for a subsequent reducer.
     */
    @Override
    public void map(Text key, LongWritable value, OutputCollector<Text, Text> output,
        Reporter reporter) throws IOException {
      String name = key.toString();
      long longValue = value.get();
  
      reporter.setStatus("starting " + name + " ::host = " + mHostname);
  
      mStream = getIOStream(name);
      T statValue = null;
      long tStart = System.currentTimeMillis();
      try {
        statValue = doIO(reporter, name, longValue);
      } finally {
        if (mStream != null) {
          mStream.close();
        }
      }
      long tEnd = System.currentTimeMillis();
      long execTime = tEnd - tStart;
      collectStats(output, name, execTime, statValue);
  
      reporter.setStatus("finished " + name + " ::host = " + mHostname);
    }
  }
  