/**
 * 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.hadoop.mapred;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.nio.ByteBuffer;
import java.nio.IntBuffer;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.LocalDirAllocator;
import org.apache.hadoop.fs.LocalFileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.DataInputBuffer;
import org.apache.hadoop.io.RawComparator;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.WritableUtils;
import org.apache.hadoop.io.SequenceFile.CompressionType;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.DefaultCodec;
import org.apache.hadoop.io.serializer.Deserializer;
import org.apache.hadoop.io.serializer.SerializationFactory;
import org.apache.hadoop.io.serializer.Serializer;
import org.apache.hadoop.mapred.IFile.Writer;
import org.apache.hadoop.mapred.Merger.Segment;
import org.apache.hadoop.mapred.SortedRanges.SkipRangeIterator;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.map.WrappedMapper;
import org.apache.hadoop.mapreduce.split.JobSplit;
import org.apache.hadoop.mapreduce.split.JobSplit.SplitMetaInfo;
import org.apache.hadoop.mapreduce.split.JobSplit.TaskSplitIndex;
import org.apache.hadoop.mapreduce.split.JobSplit.TaskSplitMetaInfo;
import org.apache.hadoop.mapreduce.task.MapContextImpl;
import org.apache.hadoop.mapreduce.MRConfig;
import org.apache.hadoop.mapreduce.MRJobConfig;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.TaskCounter;
import org.apache.hadoop.util.IndexedSortable;
import org.apache.hadoop.util.IndexedSorter;
import org.apache.hadoop.util.Progress;
import org.apache.hadoop.util.QuickSort;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.hadoop.util.StringUtils;

/** A Map task. */
class MapTask extends Task {
  /**
   * The size of each record in the index file for the map-outputs.
   */
  public static final int MAP_OUTPUT_INDEX_RECORD_LENGTH = 24;

  private TaskSplitIndex splitMetaInfo = new TaskSplitIndex();
  private String splitClass;
  private final static int APPROX_HEADER_LENGTH = 150;

  private static final Log LOG = LogFactory.getLog(MapTask.class.getName());

  private Progress mapPhase;
  private Progress sortPhase;
  
  {   // set phase for this task
    setPhase(TaskStatus.Phase.MAP); 
    getProgress().setStatus("map");
  }

  public MapTask() {
    super();
  }

  public MapTask(String jobFile, TaskAttemptID taskId, 
                 int partition, TaskSplitIndex splitIndex,
                 int numSlotsRequired) {
    super(jobFile, taskId, partition, numSlotsRequired);
    this.splitMetaInfo = splitIndex;
  }

  @Override
  public boolean isMapTask() {
    return true;
  }

  @Override
  public void localizeConfiguration(JobConf conf)
      throws IOException {
    super.localizeConfiguration(conf);
    // split.dta/split.info files are used only by IsolationRunner.
    // Write the split file to the local disk if it is a normal map task (not a
    // job-setup or a job-cleanup task) and if the user wishes to run
    // IsolationRunner either by setting keep.failed.tasks.files to true or by
    // using keep.tasks.files.pattern
    if (supportIsolationRunner(conf) && isMapOrReduce()) {
      // localize the split meta-information 
      Path localSplitMeta =
          new LocalDirAllocator(MRConfig.LOCAL_DIR).getLocalPathForWrite(
              TaskTracker.getLocalSplitMetaFile(conf.getUser(), 
                getJobID().toString(), getTaskID()
                  .toString()), conf);
      LOG.debug("Writing local split to " + localSplitMeta);
      DataOutputStream out = FileSystem.getLocal(conf).create(localSplitMeta);
      splitMetaInfo.write(out);
      out.close();
    }
  }
  
  
  @Override
  public TaskRunner createRunner(TaskTracker tracker, 
      TaskTracker.TaskInProgress tip) {
    return new MapTaskRunner(tip, tracker, this.conf);
  }

  @Override
  public void write(DataOutput out) throws IOException {
    super.write(out);
    if (isMapOrReduce()) {
      splitMetaInfo.write(out);
      splitMetaInfo = null;
    }
  }
  
  @Override
  public void readFields(DataInput in) throws IOException {
    super.readFields(in);
    if (isMapOrReduce()) {
      splitMetaInfo.readFields(in);
    }
  }

  /**
   * This class wraps the user's record reader to update the counters and progress
   * as records are read.
   * @param <K>
   * @param <V>
   */
  class TrackedRecordReader<K, V> 
      implements RecordReader<K,V> {
    private RecordReader<K,V> rawIn;
    private Counters.Counter inputByteCounter;
    private Counters.Counter inputRecordCounter;
    private TaskReporter reporter;
    private long beforePos = -1;
    private long afterPos = -1;
    
    TrackedRecordReader(RecordReader<K,V> raw, TaskReporter reporter) 
      throws IOException{
      rawIn = raw;
      inputRecordCounter = reporter.getCounter(TaskCounter.MAP_INPUT_RECORDS);
      inputByteCounter = reporter.getCounter(
                           FileInputFormat.COUNTER_GROUP,
                           FileInputFormat.BYTES_READ);
      this.reporter = reporter;
    }

    public K createKey() {
      return rawIn.createKey();
    }
      
    public V createValue() {
      return rawIn.createValue();
    }
     
    public synchronized boolean next(K key, V value)
    throws IOException {
      boolean ret = moveToNext(key, value);
      if (ret) {
        incrCounters();
      }
      return ret;
    }
    
    protected void incrCounters() {
      inputRecordCounter.increment(1);
      inputByteCounter.increment(afterPos - beforePos);
    }
     
    protected synchronized boolean moveToNext(K key, V value)
      throws IOException {
      beforePos = getPos();
      boolean ret = rawIn.next(key, value);
      afterPos = getPos();
      reporter.setProgress(getProgress());
      return ret;
    }
    
    public long getPos() throws IOException { return rawIn.getPos(); }
    public void close() throws IOException { rawIn.close(); }
    public float getProgress() throws IOException {
      return rawIn.getProgress();
    }
    TaskReporter getTaskReporter() {
      return reporter;
    }
  }

  /**
   * This class skips the records based on the failed ranges from previous 
   * attempts.
   */
  class SkippingRecordReader<K, V> extends TrackedRecordReader<K,V> {
    private SkipRangeIterator skipIt;
    private SequenceFile.Writer skipWriter;
    private boolean toWriteSkipRecs;
    private TaskUmbilicalProtocol umbilical;
    private Counters.Counter skipRecCounter;
    private long recIndex = -1;
    
    SkippingRecordReader(RecordReader<K,V> raw, TaskUmbilicalProtocol umbilical,
                         TaskReporter reporter) throws IOException{
      super(raw, reporter);
      this.umbilical = umbilical;
      this.skipRecCounter = reporter.getCounter(TaskCounter.MAP_SKIPPED_RECORDS);
      this.toWriteSkipRecs = toWriteSkipRecs() &&  
        SkipBadRecords.getSkipOutputPath(conf)!=null;
      skipIt = getSkipRanges().skipRangeIterator();
    }
    
    public synchronized boolean next(K key, V value)
    throws IOException {
      if(!skipIt.hasNext()) {
        LOG.warn("Further records got skipped.");
        return false;
      }
      boolean ret = moveToNext(key, value);
      long nextRecIndex = skipIt.next();
      long skip = 0;
      while(recIndex<nextRecIndex && ret) {
        if(toWriteSkipRecs) {
          writeSkippedRec(key, value);
        }
      	ret = moveToNext(key, value);
        skip++;
      }
      //close the skip writer once all the ranges are skipped
      if(skip>0 && skipIt.skippedAllRanges() && skipWriter!=null) {
        skipWriter.close();
      }
      skipRecCounter.increment(skip);
      reportNextRecordRange(umbilical, recIndex);
      if (ret) {
        incrCounters();
      }
      return ret;
    }
    
    protected synchronized boolean moveToNext(K key, V value)
    throws IOException {
	    recIndex++;
      return super.moveToNext(key, value);
    }
    
    @SuppressWarnings("unchecked")
    private void writeSkippedRec(K key, V value) throws IOException{
      if(skipWriter==null) {
        Path skipDir = SkipBadRecords.getSkipOutputPath(conf);
        Path skipFile = new Path(skipDir, getTaskID().toString());
        skipWriter = 
          SequenceFile.createWriter(
              skipFile.getFileSystem(conf), conf, skipFile,
              (Class<K>) createKey().getClass(),
              (Class<V>) createValue().getClass(), 
              CompressionType.BLOCK, getTaskReporter());
      }
      skipWriter.append(key, value);
    }
  }

  @Override
  public void run(final JobConf job, final TaskUmbilicalProtocol umbilical)
    throws IOException, ClassNotFoundException, InterruptedException {
    this.umbilical = umbilical;

    if (isMapTask()) {
      mapPhase = getProgress().addPhase("map", 0.667f);
      sortPhase  = getProgress().addPhase("sort", 0.333f);
    }
    TaskReporter reporter = startReporter(umbilical);
 
    boolean useNewApi = job.getUseNewMapper();
    initialize(job, getJobID(), reporter, useNewApi);

    // check if it is a cleanupJobTask
    if (jobCleanup) {
      runJobCleanupTask(umbilical, reporter);
      return;
    }
    if (jobSetup) {
      runJobSetupTask(umbilical, reporter);
      return;
    }
    if (taskCleanup) {
      runTaskCleanupTask(umbilical, reporter);
      return;
    }

    if (useNewApi) {
      runNewMapper(job, splitMetaInfo, umbilical, reporter);
    } else {
      runOldMapper(job, splitMetaInfo, umbilical, reporter);
    }
    done(umbilical, reporter);
  }

 @SuppressWarnings("unchecked")
 private <T> T getSplitDetails(Path file, long offset) 
  throws IOException {
   FileSystem fs = file.getFileSystem(conf);
   FSDataInputStream inFile = fs.open(file);
   inFile.seek(offset);
   String className = Text.readString(inFile);
   Class<T> cls;
   try {
     cls = (Class<T>) conf.getClassByName(className);
   } catch (ClassNotFoundException ce) {
     IOException wrap = new IOException("Split class " + className + 
                                         " not found");
     wrap.initCause(ce);
     throw wrap;
   }
   SerializationFactory factory = new SerializationFactory(conf);
   Deserializer<T> deserializer = 
     (Deserializer<T>) factory.getDeserializer(cls);
   deserializer.open(inFile);
   T split = deserializer.deserialize(null);
   long pos = inFile.getPos();
   getCounters().findCounter(
       TaskCounter.SPLIT_RAW_BYTES).increment(pos - offset);
   inFile.close();
   return split;
 }
  
  @SuppressWarnings("unchecked")
  private <INKEY,INVALUE,OUTKEY,OUTVALUE>
  void runOldMapper(final JobConf job,
                    final TaskSplitIndex splitIndex,
                    final TaskUmbilicalProtocol umbilical,
                    TaskReporter reporter
                    ) throws IOException, InterruptedException,
                             ClassNotFoundException {
    InputSplit inputSplit = getSplitDetails(new Path(splitIndex.getSplitLocation()),
           splitIndex.getStartOffset());

    updateJobWithSplit(job, inputSplit);
    reporter.setInputSplit(inputSplit);

    RecordReader<INKEY,INVALUE> rawIn =                  // open input
      job.getInputFormat().getRecordReader(inputSplit, job, reporter);
    RecordReader<INKEY,INVALUE> in = isSkipping() ? 
        new SkippingRecordReader<INKEY,INVALUE>(rawIn, umbilical, reporter) :
        new TrackedRecordReader<INKEY,INVALUE>(rawIn, reporter);
    job.setBoolean(JobContext.SKIP_RECORDS, isSkipping());


    int numReduceTasks = conf.getNumReduceTasks();
    LOG.info("numReduceTasks: " + numReduceTasks);
    MapOutputCollector collector = null;
    if (numReduceTasks > 0) {
      collector = new MapOutputBuffer(umbilical, job, reporter);
    } else { 
      collector = new DirectMapOutputCollector(umbilical, job, reporter);
    }
    MapRunnable<INKEY,INVALUE,OUTKEY,OUTVALUE> runner =
      ReflectionUtils.newInstance(job.getMapRunnerClass(), job);

    try {
      runner.run(in, new OldOutputCollector(collector, conf), reporter);
      mapPhase.complete();
      setPhase(TaskStatus.Phase.SORT);
      statusUpdate(umbilical);
      collector.flush();
    } finally {
      //close
      in.close();                               // close input
      collector.close();
    }
  }

  /**
   * Update the job with details about the file split
   * @param job the job configuration to update
   * @param inputSplit the file split
   */
  private void updateJobWithSplit(final JobConf job, InputSplit inputSplit) {
    if (inputSplit instanceof FileSplit) {
      FileSplit fileSplit = (FileSplit) inputSplit;
      job.set(JobContext.MAP_INPUT_FILE, fileSplit.getPath().toString());
      job.setLong(JobContext.MAP_INPUT_START, fileSplit.getStart());
      job.setLong(JobContext.MAP_INPUT_PATH, fileSplit.getLength());
    }
  }

  static class NewTrackingRecordReader<K,V> 
    extends org.apache.hadoop.mapreduce.RecordReader<K,V> {
    private final org.apache.hadoop.mapreduce.RecordReader<K,V> real;
    private final org.apache.hadoop.mapreduce.Counter inputRecordCounter;
    private final TaskReporter reporter;
    
    NewTrackingRecordReader(org.apache.hadoop.mapreduce.RecordReader<K,V> real,
                            TaskReporter reporter) {
      this.real = real;
      this.reporter = reporter;
      this.inputRecordCounter = reporter.getCounter(TaskCounter.MAP_INPUT_RECORDS);
    }

    @Override
    public void close() throws IOException {
      real.close();
    }

    @Override
    public K getCurrentKey() throws IOException, InterruptedException {
      return real.getCurrentKey();
    }

    @Override
    public V getCurrentValue() throws IOException, InterruptedException {
      return real.getCurrentValue();
    }

    @Override
    public float getProgress() throws IOException, InterruptedException {
      return real.getProgress();
    }

    @Override
    public void initialize(org.apache.hadoop.mapreduce.InputSplit split,
                           org.apache.hadoop.mapreduce.TaskAttemptContext context
                           ) throws IOException, InterruptedException {
      real.initialize(split, context);
    }

    @Override
    public boolean nextKeyValue() throws IOException, InterruptedException {
      boolean result = real.nextKeyValue();
      if (result) {
        inputRecordCounter.increment(1);
      }
      reporter.setProgress(getProgress());
      return result;
    }
  }

  /**
   * Since the mapred and mapreduce Partitioners don't share a common interface
   * (JobConfigurable is deprecated and a subtype of mapred.Partitioner), the
   * partitioner lives in Old/NewOutputCollector. Note that, for map-only jobs,
   * the configured partitioner should not be called. It's common for
   * partitioners to compute a result mod numReduces, which causes a div0 error
   */
  private static class OldOutputCollector<K,V> implements OutputCollector<K,V> {
    private final Partitioner<K,V> partitioner;
    private final MapOutputCollector<K,V> collector;
    private final int numPartitions;

    @SuppressWarnings("unchecked")
    OldOutputCollector(MapOutputCollector<K,V> collector, JobConf conf) {
      numPartitions = conf.getNumReduceTasks();
      if (numPartitions > 1) {
        partitioner = (Partitioner<K,V>)
          ReflectionUtils.newInstance(conf.getPartitionerClass(), conf);
      } else {
        partitioner = new Partitioner<K,V>() {
          @Override
          public void configure(JobConf job) { }
          @Override
          public int getPartition(K key, V value, int numPartitions) {
            return numPartitions - 1;
          }
        };
      }
      this.collector = collector;
    }

    @Override
    public void collect(K key, V value) throws IOException {
      try {
        collector.collect(key, value,
                          partitioner.getPartition(key, value, numPartitions));
      } catch (InterruptedException ie) {
        Thread.currentThread().interrupt();
        throw new IOException("interrupt exception", ie);
      }
    }
  }

  private class NewDirectOutputCollector<K,V>
  extends org.apache.hadoop.mapreduce.RecordWriter<K,V> {
    private final org.apache.hadoop.mapreduce.RecordWriter out;

    private final TaskReporter reporter;

    private final Counters.Counter mapOutputRecordCounter;
    
    @SuppressWarnings("unchecked")
    NewDirectOutputCollector(MRJobConfig jobContext,
        JobConf job, TaskUmbilicalProtocol umbilical, TaskReporter reporter) 
    throws IOException, ClassNotFoundException, InterruptedException {
      this.reporter = reporter;
      out = outputFormat.getRecordWriter(taskContext);
      mapOutputRecordCounter = 
        reporter.getCounter(TaskCounter.MAP_OUTPUT_RECORDS);
    }

    @Override
    @SuppressWarnings("unchecked")
    public void write(K key, V value) 
    throws IOException, InterruptedException {
      reporter.progress();
      out.write(key, value);
      mapOutputRecordCounter.increment(1);
    }

    @Override
    public void close(TaskAttemptContext context) 
    throws IOException,InterruptedException {
      reporter.progress();
      if (out != null) {
        out.close(context);
      }
    }
  }
  
  private class NewOutputCollector<K,V>
    extends org.apache.hadoop.mapreduce.RecordWriter<K,V> {
    private final MapOutputCollector<K,V> collector;
    private final org.apache.hadoop.mapreduce.Partitioner<K,V> partitioner;
    private final int partitions;

    @SuppressWarnings("unchecked")
    NewOutputCollector(org.apache.hadoop.mapreduce.JobContext jobContext,
                       JobConf job,
                       TaskUmbilicalProtocol umbilical,
                       TaskReporter reporter
                       ) throws IOException, ClassNotFoundException {
      collector = new MapOutputBuffer<K,V>(umbilical, job, reporter);
      partitions = jobContext.getNumReduceTasks();
      if (partitions > 1) {
        partitioner = (org.apache.hadoop.mapreduce.Partitioner<K,V>)
          ReflectionUtils.newInstance(jobContext.getPartitionerClass(), job);
      } else {
        partitioner = new org.apache.hadoop.mapreduce.Partitioner<K,V>() {
          @Override
          public int getPartition(K key, V value, int numPartitions) {
            return partitions - 1;
          }
        };
      }
    }

    @Override
    public void write(K key, V value) throws IOException, InterruptedException {
      collector.collect(key, value,
                        partitioner.getPartition(key, value, partitions));
    }

    @Override
    public void close(TaskAttemptContext context
                      ) throws IOException,InterruptedException {
      try {
        collector.flush();
      } catch (ClassNotFoundException cnf) {
        throw new IOException("can't find class ", cnf);
      }
      collector.close();
    }
  }

  @SuppressWarnings("unchecked")
  private <INKEY,INVALUE,OUTKEY,OUTVALUE>
  void runNewMapper(final JobConf job,
                    final TaskSplitIndex splitIndex,
                    final TaskUmbilicalProtocol umbilical,
                    TaskReporter reporter
                    ) throws IOException, ClassNotFoundException,
                             InterruptedException {
    // make a task context so we can get the classes
    org.apache.hadoop.mapreduce.TaskAttemptContext taskContext =
      new org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl(job, 
                                                                  getTaskID());
    // make a mapper
    org.apache.hadoop.mapreduce.Mapper<INKEY,INVALUE,OUTKEY,OUTVALUE> mapper =
      (org.apache.hadoop.mapreduce.Mapper<INKEY,INVALUE,OUTKEY,OUTVALUE>)
        ReflectionUtils.newInstance(taskContext.getMapperClass(), job);
    // make the input format
    org.apache.hadoop.mapreduce.InputFormat<INKEY,INVALUE> inputFormat =
      (org.apache.hadoop.mapreduce.InputFormat<INKEY,INVALUE>)
        ReflectionUtils.newInstance(taskContext.getInputFormatClass(), job);
    // rebuild the input split
    org.apache.hadoop.mapreduce.InputSplit split = null;
    split = getSplitDetails(new Path(splitIndex.getSplitLocation()),
        splitIndex.getStartOffset());

    org.apache.hadoop.mapreduce.RecordReader<INKEY,INVALUE> input =
      new NewTrackingRecordReader<INKEY,INVALUE>
          (inputFormat.createRecordReader(split, taskContext), reporter);
    
    job.setBoolean(JobContext.SKIP_RECORDS, isSkipping());
    org.apache.hadoop.mapreduce.RecordWriter output = null;
    
    // get an output object
    if (job.getNumReduceTasks() == 0) {
      output = 
        new NewDirectOutputCollector(taskContext, job, umbilical, reporter);
    } else {
      output = new NewOutputCollector(taskContext, job, umbilical, reporter);
    }

    org.apache.hadoop.mapreduce.MapContext<INKEY, INVALUE, OUTKEY, OUTVALUE> 
    mapContext = 
      new MapContextImpl<INKEY, INVALUE, OUTKEY, OUTVALUE>(job, getTaskID(), 
          input, output, 
          committer, 
          reporter, split);

    org.apache.hadoop.mapreduce.Mapper<INKEY,INVALUE,OUTKEY,OUTVALUE>.Context 
        mapperContext = 
          new WrappedMapper<INKEY, INVALUE, OUTKEY, OUTVALUE>().getMapContext(
              mapContext);

    input.initialize(split, mapperContext);
    mapper.run(mapperContext);
    mapPhase.complete();
    setPhase(TaskStatus.Phase.SORT);
    statusUpdate(umbilical);
    input.close();
    output.close(mapperContext);
  }

  interface MapOutputCollector<K, V> {

    public void collect(K key, V value, int partition
                        ) throws IOException, InterruptedException;
    public void close() throws IOException, InterruptedException;
    
    public void flush() throws IOException, InterruptedException, 
                               ClassNotFoundException;
        
  }

  class DirectMapOutputCollector<K, V>
    implements MapOutputCollector<K, V> {
 
    private RecordWriter<K, V> out = null;

    private TaskReporter reporter = null;

    private final Counters.Counter mapOutputRecordCounter;

    @SuppressWarnings("unchecked")
    public DirectMapOutputCollector(TaskUmbilicalProtocol umbilical,
        JobConf job, TaskReporter reporter) throws IOException {
      this.reporter = reporter;
      String finalName = getOutputName(getPartition());
      FileSystem fs = FileSystem.get(job);

      out = job.getOutputFormat().getRecordWriter(fs, job, finalName, reporter);

      mapOutputRecordCounter = reporter.getCounter(TaskCounter.MAP_OUTPUT_RECORDS);
    }

    public void close() throws IOException {
      if (this.out != null) {
        out.close(this.reporter);
      }

    }

    public void flush() throws IOException, InterruptedException, 
                               ClassNotFoundException {
    }

    public void collect(K key, V value, int partition) throws IOException {
      reporter.progress();
      out.write(key, value);
      mapOutputRecordCounter.increment(1);
    }
    
  }

  private class MapOutputBuffer<K extends Object, V extends Object>
      implements MapOutputCollector<K, V>, IndexedSortable {
    final int partitions;
    final JobConf job;
    final TaskReporter reporter;
    final Class<K> keyClass;
    final Class<V> valClass;
    final RawComparator<K> comparator;
    final SerializationFactory serializationFactory;
    final Serializer<K> keySerializer;
    final Serializer<V> valSerializer;
    final CombinerRunner<K,V> combinerRunner;
    final CombineOutputCollector<K, V> combineCollector;

    // Compression for map-outputs
    final CompressionCodec codec;

    // k/v accounting
    final IntBuffer kvmeta; // metadata overlay on backing store
    int kvstart;            // marks origin of spill metadata
    int kvend;              // marks end of spill metadata
    int kvindex;            // marks end of fully serialized records

    int equator;            // marks origin of meta/serialization
    int bufstart;           // marks beginning of spill
    int bufend;             // marks beginning of collectable
    int bufmark;            // marks end of record
    int bufindex;           // marks end of collected
    int bufvoid;            // marks the point where we should stop
                            // reading at the end of the buffer

    byte[] kvbuffer;        // main output buffer
    private final byte[] b0 = new byte[0];

    private static final int INDEX = 0;            // index offset in acct
    private static final int VALSTART = 1;         // val offset in acct
    private static final int KEYSTART = 2;         // key offset in acct
    private static final int PARTITION = 3;        // partition offset in acct
    private static final int NMETA = 4;            // num meta ints
    private static final int METASIZE = NMETA * 4; // size in bytes

    // spill accounting
    final int maxRec;
    final int softLimit;
    boolean spillInProgress;;
    int bufferRemaining;
    volatile Throwable sortSpillException = null;

    int numSpills = 0;
    final int minSpillsForCombine;
    final IndexedSorter sorter;
    final ReentrantLock spillLock = new ReentrantLock();
    final Condition spillDone = spillLock.newCondition();
    final Condition spillReady = spillLock.newCondition();
    final BlockingBuffer bb = new BlockingBuffer();
    volatile boolean spillThreadRunning = false;
    final SpillThread spillThread = new SpillThread();

    final FileSystem rfs;

    // Counters
    final Counters.Counter mapOutputByteCounter;
    final Counters.Counter mapOutputRecordCounter;

    final ArrayList<SpillRecord> indexCacheList =
      new ArrayList<SpillRecord>();
    private int totalIndexCacheMemory;
    private static final int INDEX_CACHE_MEMORY_LIMIT = 1024 * 1024;

    @SuppressWarnings("unchecked")
    public MapOutputBuffer(TaskUmbilicalProtocol umbilical, JobConf job,
                           TaskReporter reporter
                           ) throws IOException, ClassNotFoundException {
      this.job = job;
      this.reporter = reporter;
      partitions = job.getNumReduceTasks();
      rfs = ((LocalFileSystem)FileSystem.getLocal(job)).getRaw();

      //sanity checks
      final float spillper =
        job.getFloat(JobContext.MAP_SORT_SPILL_PERCENT, (float)0.8);
      final int sortmb = job.getInt(JobContext.IO_SORT_MB, 100);
      if (spillper > (float)1.0 || spillper <= (float)0.0) {
        throw new IOException("Invalid \"" + JobContext.MAP_SORT_SPILL_PERCENT +
            "\": " + spillper);
      }
      if ((sortmb & 0x7FF) != sortmb) {
        throw new IOException(
            "Invalid \"" + JobContext.IO_SORT_MB + "\": " + sortmb);
      }
      sorter = ReflectionUtils.newInstance(job.getClass("map.sort.class",
            QuickSort.class, IndexedSorter.class), job);
      // buffers and accounting
      int maxMemUsage = sortmb << 20;
      maxMemUsage -= maxMemUsage % METASIZE;
      kvbuffer = new byte[maxMemUsage];
      bufvoid = kvbuffer.length;
      kvmeta = ByteBuffer.wrap(kvbuffer).asIntBuffer();
      setEquator(0);
      bufstart = bufend = bufindex = equator;
      kvstart = kvend = kvindex;

      maxRec = kvmeta.capacity() / NMETA;
      softLimit = (int)(kvbuffer.length * spillper);
      bufferRemaining = softLimit;
      if (LOG.isInfoEnabled()) {
        LOG.info(JobContext.IO_SORT_MB + ": " + sortmb);
        LOG.info("soft limit at " + softLimit);
        LOG.info("bufstart = " + bufstart + "; bufvoid = " + bufvoid);
        LOG.info("kvstart = " + kvstart + "; length = " + maxRec);
      }

      // k/v serialization
      comparator = job.getOutputKeyComparator();
      keyClass = (Class<K>)job.getMapOutputKeyClass();
      valClass = (Class<V>)job.getMapOutputValueClass();
      serializationFactory = new SerializationFactory(job);
      keySerializer = serializationFactory.getSerializer(keyClass);
      keySerializer.open(bb);
      valSerializer = serializationFactory.getSerializer(valClass);
      valSerializer.open(bb);

      // output counters
      mapOutputByteCounter = reporter.getCounter(TaskCounter.MAP_OUTPUT_BYTES);
      mapOutputRecordCounter =
        reporter.getCounter(TaskCounter.MAP_OUTPUT_RECORDS);

      // compression
      if (job.getCompressMapOutput()) {
        Class<? extends CompressionCodec> codecClass =
          job.getMapOutputCompressorClass(DefaultCodec.class);
        codec = ReflectionUtils.newInstance(codecClass, job);
      } else {
        codec = null;
      }

      // combiner
      final Counters.Counter combineInputCounter =
        reporter.getCounter(TaskCounter.COMBINE_INPUT_RECORDS);
      combinerRunner = CombinerRunner.create(job, getTaskID(), 
                                             combineInputCounter,
                                             reporter, null);
      if (combinerRunner != null) {
        final Counters.Counter combineOutputCounter =
          reporter.getCounter(TaskCounter.COMBINE_OUTPUT_RECORDS);
        combineCollector= new CombineOutputCollector<K,V>(combineOutputCounter);
      } else {
        combineCollector = null;
      }
      spillInProgress = false;
      minSpillsForCombine = job.getInt(JobContext.MAP_COMBINE_MIN_SPILLS, 3);
      spillThread.setDaemon(true);
      spillThread.setName("SpillThread");
      spillLock.lock();
      try {
        spillThread.start();
        while (!spillThreadRunning) {
          spillDone.await();
        }
      } catch (InterruptedException e) {
        throw new IOException("Spill thread failed to initialize", e);
      } finally {
        spillLock.unlock();
      }
      if (sortSpillException != null) {
        throw new IOException("Spill thread failed to initialize",
            sortSpillException);
      }
    }

    /**
     * Serialize the key, value to intermediate storage.
     * When this method returns, kvindex must refer to sufficient unused
     * storage to store one METADATA.
     */
    public synchronized void collect(K key, V value, final int partition
                                     ) throws IOException {
      reporter.progress();
      if (key.getClass() != keyClass) {
        throw new IOException("Type mismatch in key from map: expected "
                              + keyClass.getName() + ", recieved "
                              + key.getClass().getName());
      }
      if (value.getClass() != valClass) {
        throw new IOException("Type mismatch in value from map: expected "
                              + valClass.getName() + ", recieved "
                              + value.getClass().getName());
      }
      if (partition < 0 || partition >= partitions) {
        throw new IOException("Illegal partition for " + key + " (" +
            partition + ")");
      }
      checkSpillException();
      bufferRemaining -= METASIZE;
      if (bufferRemaining <= 0) {
        // start spill if the thread is not running and the soft limit has been
        // reached
        spillLock.lock();
        try {
          do {
            if (!spillInProgress) {
              final int kvbidx = 4 * kvindex;
              final int kvbend = 4 * kvend;
              // serialized, unspilled bytes always lie between kvindex and
              // bufindex, crossing the equator. Note that any void space
              // created by a reset must be included in "used" bytes
              final int bUsed = distanceTo(kvbidx, bufindex);
              final boolean bufsoftlimit = bUsed >= softLimit;
              if ((kvbend + METASIZE) % kvbuffer.length !=
                  equator - (equator % METASIZE)) {
                // spill finished, reclaim space
                resetSpill();
                bufferRemaining = Math.min(
                    distanceTo(bufindex, kvbidx) - 2 * METASIZE,
                    softLimit - bUsed) - METASIZE;
                continue;
              } else if (bufsoftlimit && kvindex != kvend) {
                // spill records, if any collected; check latter, as it may
                // be possible for metadata alignment to hit spill pcnt
                startSpill();
                final int avgRec = (int)
                  (mapOutputByteCounter.getCounter() /
                  mapOutputRecordCounter.getCounter());
                // leave at least half the split buffer for serialization data
                // ensure that kvindex >= bufindex
                final int distkvi = distanceTo(bufindex, kvbidx);
                final int newPos = (bufindex +
                  Math.max(2 * METASIZE - 1,
                          Math.min(distkvi / 2,
                                   distkvi / (METASIZE + avgRec) * METASIZE)))
                  % kvbuffer.length;
                setEquator(newPos);
                bufmark = bufindex = newPos;
                final int serBound = 4 * kvend;
                // bytes remaining before the lock must be held and limits
                // checked is the minimum of three arcs: the metadata space, the
                // serialization space, and the soft limit
                bufferRemaining = Math.min(
                    // metadata max
                    distanceTo(bufend, newPos),
                    Math.min(
                      // serialization max
                      distanceTo(newPos, serBound),
                      // soft limit
                      softLimit)) - 2 * METASIZE;
              }
            }
          } while (false);
        } finally {
          spillLock.unlock();
        }
      }

      try {
        // serialize key bytes into buffer
        int keystart = bufindex;
        keySerializer.serialize(key);
        if (bufindex < keystart) {
          // wrapped the key; must make contiguous
          bb.shiftBufferedKey();
          keystart = 0;
        }
        // serialize value bytes into buffer
        final int valstart = bufindex;
        valSerializer.serialize(value);
        // It's possible for records to have zero length, i.e. the serializer
        // will perform no writes. To ensure that the boundary conditions are
        // checked and that the kvindex invariant is maintained, perform a
        // zero-length write into the buffer. The logic monitoring this could be
        // moved into collect, but this is cleaner and inexpensive. For now, it
        // is acceptable.
        bb.write(b0, 0, 0);

        // the record must be marked after the preceding write, as the metadata
        // for this record are not yet written
        int valend = bb.markRecord();

        mapOutputRecordCounter.increment(1);
        mapOutputByteCounter.increment(
            distanceTo(keystart, valend, bufvoid));

        // write accounting info
        kvmeta.put(kvindex + INDEX, kvindex);
        kvmeta.put(kvindex + PARTITION, partition);
        kvmeta.put(kvindex + KEYSTART, keystart);
        kvmeta.put(kvindex + VALSTART, valstart);
        // advance kvindex
        kvindex = (kvindex - NMETA + kvmeta.capacity()) % kvmeta.capacity();
      } catch (MapBufferTooSmallException e) {
        LOG.info("Record too large for in-memory buffer: " + e.getMessage());
        spillSingleRecord(key, value, partition);
        mapOutputRecordCounter.increment(1);
        return;
      }
    }

    /**
     * Set the point from which meta and serialization data expand. The meta
     * indices are aligned with the buffer, so metadata never spans the ends of
     * the circular buffer.
     */
    private void setEquator(int pos) {
      equator = pos;
      // set index prior to first entry, aligned at meta boundary
      final int aligned = pos - (pos % METASIZE);
      kvindex =
        ((aligned - METASIZE + kvbuffer.length) % kvbuffer.length) / 4;
      if (LOG.isInfoEnabled()) {
        LOG.info("(EQUATOR) " + pos + " kvi " + kvindex +
            "(" + (kvindex * 4) + ")");
      }
    }

    /**
     * The spill is complete, so set the buffer and meta indices to be equal to
     * the new equator to free space for continuing collection. Note that when
     * kvindex == kvend == kvstart, the buffer is empty.
     */
    private void resetSpill() {
      final int e = equator;
      bufstart = bufend = e;
      final int aligned = e - (e % METASIZE);
      // set start/end to point to first meta record
      kvstart = kvend =
        ((aligned - METASIZE + kvbuffer.length) % kvbuffer.length) / 4;
      if (LOG.isInfoEnabled()) {
        LOG.info("(RESET) equator " + e + " kv " + kvstart + "(" +
          (kvstart * 4) + ")" + " kvi " + kvindex + "(" + (kvindex * 4) + ")");
      }
    }

    /**
     * Compute the distance in bytes between two indices in the serialization
     * buffer.
     * @see #distanceTo(int,int,int)
     */
    final int distanceTo(final int i, final int j) {
      return distanceTo(i, j, kvbuffer.length);
    }

    /**
     * Compute the distance between two indices in the circular buffer given the
     * max distance.
     */
    int distanceTo(final int i, final int j, final int mod) {
      return i <= j
        ? j - i
        : mod - i + j;
    }

    /**
     * For the given meta position, return the dereferenced position in the
     * integer array. Each meta block contains several integers describing
     * record data in its serialized form, but the INDEX is not necessarily
     * related to the proximate metadata. The index value at the referenced int
     * position is the start offset of the associated metadata block. So the
     * metadata INDEX at metapos may point to the metadata described by the
     * metadata block at metapos + k, which contains information about that
     * serialized record.
     */
    int offsetFor(int metapos) {
      return kvmeta.get(metapos * NMETA + INDEX);
    }

    /**
     * Compare logical range, st i, j MOD offset capacity.
     * Compare by partition, then by key.
     * @see IndexedSortable#compare
     */
    public int compare(final int mi, final int mj) {
      final int kvi = offsetFor(mi % maxRec);
      final int kvj = offsetFor(mj % maxRec);
      final int kvip = kvmeta.get(kvi + PARTITION);
      final int kvjp = kvmeta.get(kvj + PARTITION);
      // sort by partition
      if (kvip != kvjp) {
        return kvip - kvjp;
      }
      // sort by key
      return comparator.compare(kvbuffer,
          kvmeta.get(kvi + KEYSTART),
          kvmeta.get(kvi + VALSTART) - kvmeta.get(kvi + KEYSTART),
          kvbuffer,
          kvmeta.get(kvj + KEYSTART),
          kvmeta.get(kvj + VALSTART) - kvmeta.get(kvj + KEYSTART));
    }

    /**
     * Swap logical indices st i, j MOD offset capacity.
     * @see IndexedSortable#swap
     */
    public void swap(final int mi, final int mj) {
      final int kvi = (mi % maxRec) * NMETA + INDEX;
      final int kvj = (mj % maxRec) * NMETA + INDEX;
      int tmp = kvmeta.get(kvi);
      kvmeta.put(kvi, kvmeta.get(kvj));
      kvmeta.put(kvj, tmp);
    }

    /**
     * Inner class managing the spill of serialized records to disk.
     */
    protected class BlockingBuffer extends DataOutputStream {

      public BlockingBuffer() {
        super(new Buffer());
      }

      /**
       * Mark end of record. Note that this is required if the buffer is to
       * cut the spill in the proper place.
       */
      public int markRecord() {
        bufmark = bufindex;
        return bufindex;
      }

      /**
       * Set position from last mark to end of writable buffer, then rewrite
       * the data between last mark and kvindex.
       * This handles a special case where the key wraps around the buffer.
       * If the key is to be passed to a RawComparator, then it must be
       * contiguous in the buffer. This recopies the data in the buffer back
       * into itself, but starting at the beginning of the buffer. Note that
       * this method should <b>only</b> be called immediately after detecting
       * this condition. To call it at any other time is undefined and would
       * likely result in data loss or corruption.
       * @see #markRecord()
       */
      protected void shiftBufferedKey() throws IOException {
        // spillLock unnecessary; both kvend and kvindex are current
        int headbytelen = bufvoid - bufmark;
        bufvoid = bufmark;
        final int kvbidx = 4 * kvindex;
        final int kvbend = 4 * kvend;
        final int avail =
          Math.min(distanceTo(0, kvbidx), distanceTo(0, kvbend));
        if (bufindex + headbytelen < avail) {
          System.arraycopy(kvbuffer, 0, kvbuffer, headbytelen, bufindex);
          System.arraycopy(kvbuffer, bufvoid, kvbuffer, 0, headbytelen);
          bufindex += headbytelen;
          bufferRemaining -= kvbuffer.length - bufvoid;
        } else {
          byte[] keytmp = new byte[bufindex];
          System.arraycopy(kvbuffer, 0, keytmp, 0, bufindex);
          bufindex = 0;
          out.write(kvbuffer, bufmark, headbytelen);
          out.write(keytmp);
        }
      }
    }

    public class Buffer extends OutputStream {
      private final byte[] scratch = new byte[1];

      @Override
      public void write(int v)
          throws IOException {
        scratch[0] = (byte)v;
        write(scratch, 0, 1);
      }

      /**
       * Attempt to write a sequence of bytes to the collection buffer.
       * This method will block if the spill thread is running and it
       * cannot write.
       * @throws MapBufferTooSmallException if record is too large to
       *    deserialize into the collection buffer.
       */
      @Override
      public void write(byte b[], int off, int len)
          throws IOException {
        // must always verify the invariant that at least METASIZE bytes are
        // available beyond kvindex, even when len == 0
        bufferRemaining -= len;
        if (bufferRemaining <= 0) {
          // writing these bytes could exhaust available buffer space or fill
          // the buffer to soft limit. check if spill or blocking are necessary
          boolean blockwrite = false;
          spillLock.lock();
          try {
            do {
              checkSpillException();

              final int kvbidx = 4 * kvindex;
              final int kvbend = 4 * kvend;
              // ser distance to key index
              final int distkvi = distanceTo(bufindex, kvbidx);
              // ser distance to spill end index
              final int distkve = distanceTo(bufindex, kvbend);

              // if kvindex is closer than kvend, then a spill is neither in
              // progress nor complete and reset since the lock was held. The
              // write should block only if there is insufficient space to
              // complete the current write, write the metadata for this record,
              // and write the metadata for the next record. If kvend is closer,
              // then the write should block if there is too little space for
              // either the metadata or the current write. Note that collect
              // ensures its metadata requirement with a zero-length write
              blockwrite = distkvi <= distkve
                ? distkvi <= len + 2 * METASIZE
                : distkve <= len || distanceTo(bufend, kvbidx) < 2 * METASIZE;

              if (!spillInProgress) {
                if (blockwrite) {
                  if ((kvbend + METASIZE) % kvbuffer.length !=
                      equator - (equator % METASIZE)) {
                    // spill finished, reclaim space
                    // need to use meta exclusively; zero-len rec & 100% spill
                    // pcnt would fail
                    resetSpill(); // resetSpill doesn't move bufindex, kvindex
                    bufferRemaining = Math.min(
                        distkvi - 2 * METASIZE,
                        softLimit - distanceTo(kvbidx, bufindex)) - len;
                    continue;
                  }
                  // we have records we can spill; only spill if blocked
                  if (kvindex != kvend) {
                    startSpill();
                    // Blocked on this write, waiting for the spill just
                    // initiated to finish. Instead of repositioning the marker
                    // and copying the partial record, we set the record start
                    // to be the new equator
                    setEquator(bufmark);
                  } else {
                    // We have no buffered records, and this record is too large
                    // to write into kvbuffer. We must spill it directly from
                    // collect
                    final int size = distanceTo(bufstart, bufindex) + len;
                    setEquator(0);
                    bufstart = bufend = bufindex = equator;
                    kvstart = kvend = kvindex;
                    bufvoid = kvbuffer.length;
                    throw new MapBufferTooSmallException(size + " bytes");
                  }
                }
              }

              if (blockwrite) {
                // wait for spill
                try {
                  while (spillInProgress) {
                    reporter.progress();
                    spillDone.await();
                  }
                } catch (InterruptedException e) {
                    throw new IOException(
                        "Buffer interrupted while waiting for the writer", e);
                }
              }
            } while (blockwrite);
          } finally {
            spillLock.unlock();
          }
        }
        // here, we know that we have sufficient space to write
        if (bufindex + len > bufvoid) {
          final int gaplen = bufvoid - bufindex;
          System.arraycopy(b, off, kvbuffer, bufindex, gaplen);
          len -= gaplen;
          off += gaplen;
          bufindex = 0;
        }
        System.arraycopy(b, off, kvbuffer, bufindex, len);
        bufindex += len;
      }
    }

    public void flush() throws IOException, ClassNotFoundException,
           InterruptedException {
      LOG.info("Starting flush of map output");
      spillLock.lock();
      try {
        while (spillInProgress) {
          reporter.progress();
          spillDone.await();
        }
        checkSpillException();

        final int kvbend = 4 * kvend;
        if ((kvbend + METASIZE) % kvbuffer.length !=
            equator - (equator % METASIZE)) {
          // spill finished
          resetSpill();
        }
        if (kvindex != kvend) {
          kvend = (kvindex + NMETA) % kvmeta.capacity();
          bufend = bufmark;
          if (LOG.isInfoEnabled()) {
            LOG.info("Spilling map output");
            LOG.info("bufstart = " + bufstart + "; bufend = " + bufmark +
                     "; bufvoid = " + bufvoid);
            LOG.info("kvstart = " + kvstart + "(" + (kvstart * 4) +
                     "); kvend = " + kvend + "(" + (kvend * 4) +
                     "); length = " + (distanceTo(kvend, kvstart,
                           kvmeta.capacity()) + 1) + "/" + maxRec);
          }
          sortAndSpill();
        }
      } catch (InterruptedException e) {
        throw new IOException("Interrupted while waiting for the writer", e);
      } finally {
        spillLock.unlock();
      }
      assert !spillLock.isHeldByCurrentThread();
      // shut down spill thread and wait for it to exit. Since the preceding
      // ensures that it is finished with its work (and sortAndSpill did not
      // throw), we elect to use an interrupt instead of setting a flag.
      // Spilling simultaneously from this thread while the spill thread
      // finishes its work might be both a useful way to extend this and also
      // sufficient motivation for the latter approach.
      try {
        spillThread.interrupt();
        spillThread.join();
      } catch (InterruptedException e) {
        throw new IOException("Spill failed", e);
      }
      // release sort buffer before the merge
      kvbuffer = null;
      mergeParts();
    }

    public void close() { }

    protected class SpillThread extends Thread {

      @Override
      public void run() {
        spillLock.lock();
        spillThreadRunning = true;
        try {
          while (true) {
            spillDone.signal();
            while (!spillInProgress) {
              spillReady.await();
            }
            try {
              spillLock.unlock();
              sortAndSpill();
            } catch (Throwable t) {
              sortSpillException = t;
            } finally {
              spillLock.lock();
              if (bufend < bufstart) {
                bufvoid = kvbuffer.length;
              }
              kvstart = kvend;
              bufstart = bufend;
              spillInProgress = false;
            }
          }
        } catch (InterruptedException e) {
          Thread.currentThread().interrupt();
        } finally {
          spillLock.unlock();
          spillThreadRunning = false;
        }
      }
    }

    private void checkSpillException() throws IOException {
      final Throwable lspillException = sortSpillException;
      if (lspillException != null) {
        if (lspillException instanceof Error) {
          final String logMsg = "Task " + getTaskID() + " failed : " +
            StringUtils.stringifyException(lspillException);
          reportFatalError(getTaskID(), lspillException, logMsg);
        }
        throw new IOException("Spill failed", lspillException);
      }
    }

    private void startSpill() {
      assert !spillInProgress;
      kvend = (kvindex + NMETA) % kvmeta.capacity();
      bufend = bufmark;
      spillInProgress = true;
      if (LOG.isInfoEnabled()) {
        LOG.info("Spilling map output");
        LOG.info("bufstart = " + bufstart + "; bufend = " + bufmark +
                 "; bufvoid = " + bufvoid);
        LOG.info("kvstart = " + kvstart + "(" + (kvstart * 4) +
                 "); kvend = " + kvend + "(" + (kvend * 4) +
                 "); length = " + (distanceTo(kvend, kvstart,
                       kvmeta.capacity()) + 1) + "/" + maxRec);
      }
      spillReady.signal();
    }

    private void sortAndSpill() throws IOException, ClassNotFoundException,
                                       InterruptedException {
      //approximate the length of the output file to be the length of the
      //buffer + header lengths for the partitions
      final long size = (bufend >= bufstart
          ? bufend - bufstart
          : (bufvoid - bufend) + bufstart) +
                  partitions * APPROX_HEADER_LENGTH;
      FSDataOutputStream out = null;
      try {
        // create spill file
        final SpillRecord spillRec = new SpillRecord(partitions);
        final Path filename =
            mapOutputFile.getSpillFileForWrite(numSpills, size);
        out = rfs.create(filename);

        final int mstart = kvend / NMETA;
        final int mend = 1 + // kvend is a valid record
          (kvstart >= kvend
          ? kvstart
          : kvmeta.capacity() + kvstart) / NMETA;
        sorter.sort(MapOutputBuffer.this, mstart, mend, reporter);
        int spindex = mstart;
        final IndexRecord rec = new IndexRecord();
        final InMemValBytes value = new InMemValBytes();
        for (int i = 0; i < partitions; ++i) {
          IFile.Writer<K, V> writer = null;
          try {
            long segmentStart = out.getPos();
            writer = new Writer<K, V>(job, out, keyClass, valClass, codec,
                                      spilledRecordsCounter);
            if (combinerRunner == null) {
              // spill directly
              DataInputBuffer key = new DataInputBuffer();
              while (spindex < mend &&
                  kvmeta.get(offsetFor(spindex % maxRec) + PARTITION) == i) {
                final int kvoff = offsetFor(spindex % maxRec);
                key.reset(kvbuffer, kvmeta.get(kvoff + KEYSTART),
                          (kvmeta.get(kvoff + VALSTART) -
                           kvmeta.get(kvoff + KEYSTART)));
                getVBytesForOffset(kvoff, value);
                writer.append(key, value);
                ++spindex;
              }
            } else {
              int spstart = spindex;
              while (spindex < mend &&
                  kvmeta.get(offsetFor(spindex % maxRec)
                            + PARTITION) == i) {
                ++spindex;
              }
              // Note: we would like to avoid the combiner if we've fewer
              // than some threshold of records for a partition
              if (spstart != spindex) {
                combineCollector.setWriter(writer);
                RawKeyValueIterator kvIter =
                  new MRResultIterator(spstart, spindex);
                combinerRunner.combine(kvIter, combineCollector);
              }
            }

            // close the writer
            writer.close();

            // record offsets
            rec.startOffset = segmentStart;
            rec.rawLength = writer.getRawLength();
            rec.partLength = writer.getCompressedLength();
            spillRec.putIndex(rec, i);

            writer = null;
          } finally {
            if (null != writer) writer.close();
          }
        }

        if (totalIndexCacheMemory >= INDEX_CACHE_MEMORY_LIMIT) {
          // create spill index file
          Path indexFilename =
              mapOutputFile.getSpillIndexFileForWrite(numSpills, partitions
                  * MAP_OUTPUT_INDEX_RECORD_LENGTH);
          spillRec.writeToFile(indexFilename, job);
        } else {
          indexCacheList.add(spillRec);
          totalIndexCacheMemory +=
            spillRec.size() * MAP_OUTPUT_INDEX_RECORD_LENGTH;
        }
        LOG.info("Finished spill " + numSpills);
        ++numSpills;
      } finally {
        if (out != null) out.close();
      }
    }

    /**
     * Handles the degenerate case where serialization fails to fit in
     * the in-memory buffer, so we must spill the record from collect
     * directly to a spill file. Consider this "losing".
     */
    private void spillSingleRecord(final K key, final V value,
                                   int partition) throws IOException {
      long size = kvbuffer.length + partitions * APPROX_HEADER_LENGTH;
      FSDataOutputStream out = null;
      try {
        // create spill file
        final SpillRecord spillRec = new SpillRecord(partitions);
        final Path filename =
            mapOutputFile.getSpillFileForWrite(numSpills, size);
        out = rfs.create(filename);

        // we don't run the combiner for a single record
        IndexRecord rec = new IndexRecord();
        for (int i = 0; i < partitions; ++i) {
          IFile.Writer<K, V> writer = null;
          try {
            long segmentStart = out.getPos();
            // Create a new codec, don't care!
            writer = new IFile.Writer<K,V>(job, out, keyClass, valClass, codec,
                                            spilledRecordsCounter);

            if (i == partition) {
              final long recordStart = out.getPos();
              writer.append(key, value);
              // Note that our map byte count will not be accurate with
              // compression
              mapOutputByteCounter.increment(out.getPos() - recordStart);
            }
            writer.close();

            // record offsets
            rec.startOffset = segmentStart;
            rec.rawLength = writer.getRawLength();
            rec.partLength = writer.getCompressedLength();
            spillRec.putIndex(rec, i);

            writer = null;
          } catch (IOException e) {
            if (null != writer) writer.close();
            throw e;
          }
        }
        if (totalIndexCacheMemory >= INDEX_CACHE_MEMORY_LIMIT) {
          // create spill index file
          Path indexFilename =
              mapOutputFile.getSpillIndexFileForWrite(numSpills, partitions
                  * MAP_OUTPUT_INDEX_RECORD_LENGTH);
          spillRec.writeToFile(indexFilename, job);
        } else {
          indexCacheList.add(spillRec);
          totalIndexCacheMemory +=
            spillRec.size() * MAP_OUTPUT_INDEX_RECORD_LENGTH;
        }
        ++numSpills;
      } finally {
        if (out != null) out.close();
      }
    }

    /**
     * Given an offset, populate vbytes with the associated set of
     * deserialized value bytes. Should only be called during a spill.
     */
    private void getVBytesForOffset(int kvoff, InMemValBytes vbytes) {
      // get the keystart for the next serialized value to be the end
      // of this value. If this is the last value in the buffer, use bufend
      final int nextindex = kvoff == kvend
        ? bufend
        : kvmeta.get(
            (kvoff - NMETA + kvmeta.capacity() + KEYSTART) % kvmeta.capacity());
      // calculate the length of the value
      int vallen = (nextindex >= kvmeta.get(kvoff + VALSTART))
        ? nextindex - kvmeta.get(kvoff + VALSTART)
        : (bufvoid - kvmeta.get(kvoff + VALSTART)) + nextindex;
      vbytes.reset(kvbuffer, kvmeta.get(kvoff + VALSTART), vallen);
    }

    /**
     * Inner class wrapping valuebytes, used for appendRaw.
     */
    protected class InMemValBytes extends DataInputBuffer {
      private byte[] buffer;
      private int start;
      private int length;

      public void reset(byte[] buffer, int start, int length) {
        this.buffer = buffer;
        this.start = start;
        this.length = length;

        if (start + length > bufvoid) {
          this.buffer = new byte[this.length];
          final int taillen = bufvoid - start;
          System.arraycopy(buffer, start, this.buffer, 0, taillen);
          System.arraycopy(buffer, 0, this.buffer, taillen, length-taillen);
          this.start = 0;
        }

        super.reset(this.buffer, this.start, this.length);
      }
    }

    protected class MRResultIterator implements RawKeyValueIterator {
      private final DataInputBuffer keybuf = new DataInputBuffer();
      private final InMemValBytes vbytes = new InMemValBytes();
      private final int end;
      private int current;
      public MRResultIterator(int start, int end) {
        this.end = end;
        current = start - 1;
      }
      public boolean next() throws IOException {
        return ++current < end;
      }
      public DataInputBuffer getKey() throws IOException {
        final int kvoff = offsetFor(current % maxRec);
        keybuf.reset(kvbuffer, kvmeta.get(kvoff + KEYSTART),
            kvmeta.get(kvoff + VALSTART) - kvmeta.get(kvoff + KEYSTART));
        return keybuf;
      }
      public DataInputBuffer getValue() throws IOException {
        getVBytesForOffset(offsetFor(current % maxRec), vbytes);
        return vbytes;
      }
      public Progress getProgress() {
        return null;
      }
      public void close() { }
    }

    private void mergeParts() throws IOException, InterruptedException, 
                                     ClassNotFoundException {
      // get the approximate size of the final output/index files
      long finalOutFileSize = 0;
      long finalIndexFileSize = 0;
      final Path[] filename = new Path[numSpills];
      final TaskAttemptID mapId = getTaskID();

      for(int i = 0; i < numSpills; i++) {
        filename[i] = mapOutputFile.getSpillFile(i);
        finalOutFileSize += rfs.getFileStatus(filename[i]).getLen();
      }
      if (numSpills == 1) { //the spill is the final output
        rfs.rename(filename[0],
            new Path(filename[0].getParent(), "file.out"));
        if (indexCacheList.size() == 0) {
          rfs.rename(mapOutputFile.getSpillIndexFile(0),
              new Path(filename[0].getParent(),"file.out.index"));
        } else {
          indexCacheList.get(0).writeToFile(
                new Path(filename[0].getParent(),"file.out.index"), job);
        }
        return;
      }

      // read in paged indices
      for (int i = indexCacheList.size(); i < numSpills; ++i) {
        Path indexFileName = mapOutputFile.getSpillIndexFile(i);
        indexCacheList.add(new SpillRecord(indexFileName, job));
      }

      //make correction in the length to include the sequence file header
      //lengths for each partition
      finalOutFileSize += partitions * APPROX_HEADER_LENGTH;
      finalIndexFileSize = partitions * MAP_OUTPUT_INDEX_RECORD_LENGTH;
      Path finalOutputFile =
          mapOutputFile.getOutputFileForWrite(finalOutFileSize);
      Path finalIndexFile =
          mapOutputFile.getOutputIndexFileForWrite(finalIndexFileSize);

      //The output stream for the final single output file
      FSDataOutputStream finalOut = rfs.create(finalOutputFile, true, 4096);

      if (numSpills == 0) {
        //create dummy files
        IndexRecord rec = new IndexRecord();
        SpillRecord sr = new SpillRecord(partitions);
        try {
          for (int i = 0; i < partitions; i++) {
            long segmentStart = finalOut.getPos();
            Writer<K, V> writer =
              new Writer<K, V>(job, finalOut, keyClass, valClass, codec, null);
            writer.close();
            rec.startOffset = segmentStart;
            rec.rawLength = writer.getRawLength();
            rec.partLength = writer.getCompressedLength();
            sr.putIndex(rec, i);
          }
          sr.writeToFile(finalIndexFile, job);
        } finally {
          finalOut.close();
        }
        return;
      }
      {
        sortPhase.addPhases(partitions); // Divide sort phase into sub-phases
        Merger.considerFinalMergeForProgress();
        
        IndexRecord rec = new IndexRecord();
        final SpillRecord spillRec = new SpillRecord(partitions);
        for (int parts = 0; parts < partitions; parts++) {
          //create the segments to be merged
          List<Segment<K,V>> segmentList =
            new ArrayList<Segment<K, V>>(numSpills);
          for(int i = 0; i < numSpills; i++) {
            IndexRecord indexRecord = indexCacheList.get(i).getIndex(parts);

            Segment<K,V> s =
              new Segment<K,V>(job, rfs, filename[i], indexRecord.startOffset,
                               indexRecord.partLength, codec, true);
            segmentList.add(i, s);

            if (LOG.isDebugEnabled()) {
              LOG.debug("MapId=" + mapId + " Reducer=" + parts +
                  "Spill =" + i + "(" + indexRecord.startOffset + "," +
                  indexRecord.rawLength + ", " + indexRecord.partLength + ")");
            }
          }

          int mergeFactor = job.getInt(JobContext.IO_SORT_FACTOR, 100);
          // sort the segments only if there are intermediate merges
          boolean sortSegments = segmentList.size() > mergeFactor;
          //merge
          @SuppressWarnings("unchecked")
          RawKeyValueIterator kvIter = Merger.merge(job, rfs,
                         keyClass, valClass, codec,
                         segmentList, mergeFactor,
                         new Path(mapId.toString()),
                         job.getOutputKeyComparator(), reporter, sortSegments,
                         null, spilledRecordsCounter, sortPhase.phase());

          //write merged output to disk
          long segmentStart = finalOut.getPos();
          Writer<K, V> writer =
              new Writer<K, V>(job, finalOut, keyClass, valClass, codec,
                               spilledRecordsCounter);
          if (combinerRunner == null || numSpills < minSpillsForCombine) {
            Merger.writeFile(kvIter, writer, reporter, job);
          } else {
            combineCollector.setWriter(writer);
            combinerRunner.combine(kvIter, combineCollector);
          }

          //close
          writer.close();

          sortPhase.startNextPhase();
          
          // record offsets
          rec.startOffset = segmentStart;
          rec.rawLength = writer.getRawLength();
          rec.partLength = writer.getCompressedLength();
          spillRec.putIndex(rec, parts);
        }
        spillRec.writeToFile(finalIndexFile, job);
        finalOut.close();
        for(int i = 0; i < numSpills; i++) {
          rfs.delete(filename[i],true);
        }
      }
    }

  } // MapOutputBuffer
  
  /**
   * Exception indicating that the allocated sort buffer is insufficient
   * to hold the current record.
   */
  @SuppressWarnings("serial")
  private static class MapBufferTooSmallException extends IOException {
    public MapBufferTooSmallException(String s) {
      super(s);
    }
  }

}