Program: 56209
Project: 56209
Buggy source:
/** 
 * Entry point of the thread.
 */
public void go() throws Exception {
  final Channel.Enumerator enumerator=ioManager.createChannelEnumerator();
  List<Channel.ID> channelIDs=new ArrayList<Channel.ID>();
  Collection<MemorySegment> outputSegments=memoryManager.allocate(CombiningUnilateralSortMerger.this.parent,2,ioMemorySize / 2);
  CircularElement element=null;
  while (isRunning() && (element=queues.spill.take()) != SENTINEL) {
    Channel.ID channel=enumerator.next();
    channelIDs.add(channel);
    LOG.debug("String_Node_Str" + channel.toString() + '.');
    ChannelWriter writer=ioManager.createChannelWriter(channel,outputSegments);
    LOG.debug("String_Node_Str" + element.id + '.');
    final BufferSortable<K,V> buffer=element.buffer;
    final CombineValueIterator<V> iter=new CombineValueIterator<V>(buffer);
    final Collector<K,V> collector=new WriterCollector<K,V>(writer);
    int i=0;
    int stop=buffer.size() - 1;
    while (i < stop) {
      int seqStart=i;
      while (i < stop && 0 == buffer.compare(i,i + 1)) {
        i++;
      }
      if (i == seqStart) {
        buffer.writeToChannel(writer,seqStart,1);
      }
 else {
        K key=buffer.getKey(seqStart);
        iter.set(seqStart,i);
        combineStub.combine(key,iter,collector);
      }
      i++;
    }
    if (i == stop) {
      buffer.writeToChannel(writer,stop,1);
    }
    LOG.debug("String_Node_Str" + element.id + "String_Node_Str");
    outputSegments=writer.close();
    element.buffer.reset();
    queues.empty.put(element);
  }
  LOG.debug("String_Node_Str");
  LOG.debug("String_Node_Str");
  memoryManager.release(outputSegments);
  LOG.debug("String_Node_Str");
  while (!queues.empty.isEmpty()) {
    memoryManager.release(queues.empty.take().buffer.unbind());
  }
  while (channelIDs.size() > maxNumFileHandles) {
    channelIDs=mergeChannelList(channelIDs,ioMemorySize);
  }
  if (CombiningUnilateralSortMerger.this.combineLastMerge) {
    KeyGroupedIterator<K,V> iter=new KeyGroupedIterator<K,V>(getMergingIterator(channelIDs,ioMemorySize));
    lazyIterator.setTarget(new CombiningIterator<K,V>(combineStub,iter));
  }
 else {
    lazyIterator.setTarget(getMergingIterator(channelIDs,ioMemorySize));
  }
  LOG.debug("String_Node_Str");
}

Fixed version (ground truth):
/** 
 * Entry point of the thread.
 */
public void go() throws Exception {
  final Channel.Enumerator enumerator=ioManager.createChannelEnumerator();
  List<Channel.ID> channelIDs=new ArrayList<Channel.ID>();
  outputSegments=memoryManager.allocate(CombiningUnilateralSortMerger.this.parent,2,ioMemorySize / 2);
  CircularElement element=null;
  while (isRunning() && (element=queues.spill.take()) != SENTINEL) {
    Channel.ID channel=enumerator.next();
    channelIDs.add(channel);
    LOG.debug("String_Node_Str" + channel.toString() + '.');
    ChannelWriter writer=ioManager.createChannelWriter(channel,outputSegments);
    LOG.debug("String_Node_Str" + element.id + '.');
    final BufferSortable<K,V> buffer=element.buffer;
    final CombineValueIterator<V> iter=new CombineValueIterator<V>(buffer);
    final Collector<K,V> collector=new WriterCollector<K,V>(writer);
    int i=0;
    int stop=buffer.size() - 1;
    while (i < stop) {
      int seqStart=i;
      while (i < stop && 0 == buffer.compare(i,i + 1)) {
        i++;
      }
      if (i == seqStart) {
        buffer.writeToChannel(writer,seqStart,1);
      }
 else {
        K key=buffer.getKey(seqStart);
        iter.set(seqStart,i);
        combineStub.combine(key,iter,collector);
      }
      i++;
    }
    if (i == stop) {
      buffer.writeToChannel(writer,stop,1);
    }
    LOG.debug("String_Node_Str" + element.id + "String_Node_Str");
    outputSegments=writer.close();
    element.buffer.reset();
    queues.empty.put(element);
  }
  LOG.debug("String_Node_Str");
  LOG.debug("String_Node_Str");
  memoryManager.release(outputSegments);
  LOG.debug("String_Node_Str");
  while (!queues.empty.isEmpty()) {
    memoryManager.release(queues.empty.take().buffer.unbind());
  }
  while (channelIDs.size() > maxNumFileHandles) {
    channelIDs=mergeChannelList(channelIDs,ioMemorySize);
  }
  if (CombiningUnilateralSortMerger.this.combineLastMerge) {
    KeyGroupedIterator<K,V> iter=new KeyGroupedIterator<K,V>(getMergingIterator(channelIDs,ioMemorySize));
    lazyIterator.setTarget(new CombiningIterator<K,V>(combineStub,iter));
  }
 else {
    lazyIterator.setTarget(getMergingIterator(channelIDs,ioMemorySize));
  }
  LOG.debug("String_Node_Str");
}