SleepJob源代码注释

package org.apache.hadoop.examples;

import java.io.IOException;
import java.io.DataInput;
import java.io.DataOutput;
import java.util.Iterator;
import java.util.Random;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.mapred.lib.NullOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

/**hadoop的 map/reduce例子程序，在mapper 和reducer里休眠指定的时间。
 * Dummy class for testing MR framefork. Sleeps for a defined period 
 * of time in mapper and reducer. Generates fake input for map / reduce 
 * jobs. Note that generated number of input pairs is in the order 
 * of <code>numMappers * mapSleepTime / 100</code>, so the job uses
 * some disk space.
 */
public class SleepJob extends Configured implements Tool,  
             Mapper<IntWritable, IntWritable, IntWritable, NullWritable>,
             Reducer<IntWritable, NullWritable, NullWritable, NullWritable>,
             Partitioner<IntWritable,NullWritable> {

  private long mapSleepDuration = 100; //map休眠的时间（毫秒）
  private long reduceSleepDuration = 100;//reducer休眠的时间（毫秒）
  private int mapSleepCount = 1; //map的数目
  private int reduceSleepCount = 1;//reduce的数目
  private int count = 0;

  public int getPartition(IntWritable k, NullWritable v, int numPartitions) {
    return k.get() % numPartitions;
  }
  
 /*自定义空的split*/
  public static class EmptySplit implements InputSplit {
    public void write(DataOutput out) throws IOException { }
    public void readFields(DataInput in) throws IOException { }
    public long getLength() { return 0L; }
    public String[] getLocations() { return new String[0]; }
  }

/*自定义inputformat*/
  public static class SleepInputFormat extends Configured
      implements InputFormat<IntWritable,IntWritable> {
    public InputSplit[] getSplits(JobConf conf, int numSplits) {
      InputSplit[] ret = new InputSplit[numSplits];
      for (int i = 0; i < numSplits; ++i) {
        ret[i] = new EmptySplit();
      }
      return ret;
    }
    public RecordReader<IntWritable,IntWritable> getRecordReader(
        InputSplit ignored, JobConf conf, Reporter reporter)
        throws IOException {
      final int count = conf.getInt("sleep.job.map.sleep.count", 1);
      if (count < 0) throw new IOException("Invalid map count: " + count);
      final int redcount = conf.getInt("sleep.job.reduce.sleep.count", 1);
      if (redcount < 0)
        throw new IOException("Invalid reduce count: " + redcount);
      final int emitPerMapTask = (redcount * conf.getNumReduceTasks());
    return new RecordReader<IntWritable,IntWritable>() {
        private int records = 0;
        private int emitCount = 0;

        public boolean next(IntWritable key, IntWritable value)
            throws IOException {
          key.set(emitCount);
          int emit = emitPerMapTask / count;
          if ((emitPerMapTask) % count > records) {
            ++emit;
          }
          emitCount += emit;
          value.set(emit);
          return records++ < count;
        }
        public IntWritable createKey() { return new IntWritable(); }
        public IntWritable createValue() { return new IntWritable(); }
        public long getPos() throws IOException { return records; }
        public void close() throws IOException { }
        public float getProgress() throws IOException {
          return records / ((float)count);
        }
      };
    }
  }
/*mapp方法*/
  public void map(IntWritable key, IntWritable value,
      OutputCollector<IntWritable, NullWritable> output, Reporter reporter)
      throws IOException {

    //it is expected that every map processes mapSleepCount number of records. 
    try {
      reporter.setStatus("Sleeping... (" +
          (mapSleepDuration * (mapSleepCount - count)) + ") ms left");
      Thread.sleep(mapSleepDuration); //开始休眠
    }
    catch (InterruptedException ex) {
      throw (IOException)new IOException(
          "Interrupted while sleeping").initCause(ex);
    }
    ++count;
    // output reduceSleepCount * numReduce number of random values, so that
    // each reducer will get reduceSleepCount number of keys.
    int k = key.get();
    for (int i = 0; i < value.get(); ++i) {
      output.collect(new IntWritable(k + i), NullWritable.get());
    }
  }

/*reduce方法*/
  public void reduce(IntWritable key, Iterator<NullWritable> values,
      OutputCollector<NullWritable, NullWritable> output, Reporter reporter)
      throws IOException {
    try {
      reporter.setStatus("Sleeping... (" +
          (reduceSleepDuration * (reduceSleepCount - count)) + ") ms left");
        Thread.sleep(reduceSleepDuration); //休眠时间
      
    }
    catch (InterruptedException ex) {
      throw (IOException)new IOException(
          "Interrupted while sleeping").initCause(ex);
    }
    count++;
  }

/*初始化参数*/
  public void configure(JobConf job) {
    this.mapSleepCount =
      job.getInt("sleep.job.map.sleep.count", mapSleepCount);
    this.reduceSleepCount =
      job.getInt("sleep.job.reduce.sleep.count", reduceSleepCount);
    this.mapSleepDuration =
      job.getLong("sleep.job.map.sleep.time" , 100) / mapSleepCount;
    this.reduceSleepDuration =
      job.getLong("sleep.job.reduce.sleep.time" , 100) / reduceSleepCount;
  }

  public void close() throws IOException {
  }

  public static void main(String[] args) throws Exception{
    int res = ToolRunner.run(new Configuration(), new SleepJob(), args);
    System.exit(res);
  }

/*driver代码*/
  public int run(int numMapper, int numReducer, long mapSleepTime,
      int mapSleepCount, long reduceSleepTime,
      int reduceSleepCount) throws IOException {
    JobConf job = setupJobConf(numMapper, numReducer, mapSleepTime, 
                  mapSleepCount, reduceSleepTime, reduceSleepCount);
    JobClient.runJob(job);
    return 0;
  }

  public JobConf setupJobConf(int numMapper, int numReducer, 
                                long mapSleepTime, int mapSleepCount, 
                                long reduceSleepTime, int reduceSleepCount) {
    JobConf job = new JobConf(getConf(), SleepJob.class);
    job.setNumMapTasks(numMapper);//设置map的数目
    job.setNumReduceTasks(numReducer);//设置reduce数目
    job.setMapperClass(SleepJob.class);//设置map的类
    job.setMapOutputKeyClass(IntWritable.class);//设置map的输出中间结果key类型
    job.setMapOutputValueClass(NullWritable.class);//设置map的输出中间结果value的类型
    job.setReducerClass(SleepJob.class);//设置reduce的类
    job.setOutputFormat(NullOutputFormat.class);//设置输出类型
    job.setInputFormat(SleepInputFormat.class);//设置输入类型
    job.setPartitionerClass(SleepJob.class);//设置partition类型
    job.setSpeculativeExecution(false);//关闭speculativeexcution属性
    job.setJobName("Sleep job");
    FileInputFormat.addInputPath(job, new Path("ignored"));
    job.setLong("sleep.job.map.sleep.time", mapSleepTime);
    job.setLong("sleep.job.reduce.sleep.time", reduceSleepTime);
    job.setInt("sleep.job.map.sleep.count", mapSleepCount);
    job.setInt("sleep.job.reduce.sleep.count", reduceSleepCount);
    return job;
  }

  public int run(String[] args) throws Exception {

    if(args.length < 1) {
      System.err.println("SleepJob [-m numMapper] [-r numReducer]" +
          " [-mt mapSleepTime (msec)] [-rt reduceSleepTime (msec)]" +
          " [-recordt recordSleepTime (msec)]");
      ToolRunner.printGenericCommandUsage(System.err);
      return -1;
    }

    int numMapper = 1, numReducer = 1;
    long mapSleepTime = 100, reduceSleepTime = 100, recSleepTime = 100;
    int mapSleepCount = 1, reduceSleepCount = 1;

    for(int i=0; i < args.length; i++ ) {
      if(args[i].equals("-m")) {
        numMapper = Integer.parseInt(args[++i]);
      }
      else if(args[i].equals("-r")) {
        numReducer = Integer.parseInt(args[++i]);
      }
      else if(args[i].equals("-mt")) {
        mapSleepTime = Long.parseLong(args[++i]);
      }
      else if(args[i].equals("-rt")) {
        reduceSleepTime = Long.parseLong(args[++i]);
      }
      else if (args[i].equals("-recordt")) {
        recSleepTime = Long.parseLong(args[++i]);
      }
    }
    
    // sleep for *SleepTime duration in Task by recSleepTime per record
    mapSleepCount = (int)Math.ceil(mapSleepTime / ((double)recSleepTime));
    reduceSleepCount = (int)Math.ceil(reduceSleepTime / ((double)recSleepTime));
    
    return run(numMapper, numReducer, mapSleepTime, mapSleepCount,
        reduceSleepTime, reduceSleepCount);
  }

}