import org.apache.hadoop.mapreduce.task.annotation.Checkpointable; //导入依赖的package包/类
@Override
public void cleanUpPartialOutputForTask(TaskAttemptContext context)
    throws IOException {

  // we double check this is never invoked from a non-preemptable subclass.
  // This should never happen, since the invoking codes is checking it too,
  // but it is safer to double check. Errors handling this would produce
  // inconsistent output.

  if (!this.getClass().isAnnotationPresent(Checkpointable.class)) {
    throw new IllegalStateException("Invoking cleanUpPartialOutputForTask() " +
        "from non @Preemptable class");
  }
  FileSystem fs =
    fsFor(getTaskAttemptPath(context), context.getConfiguration());

  LOG.info("cleanUpPartialOutputForTask: removing everything belonging to " +
      context.getTaskAttemptID().getTaskID() + " in: " +
      getCommittedTaskPath(context).getParent());

  final TaskAttemptID taid = context.getTaskAttemptID();
  final TaskID tid = taid.getTaskID();
  Path pCommit = getCommittedTaskPath(context).getParent();
  // remove any committed output
  for (int i = 0; i < taid.getId(); ++i) {
    TaskAttemptID oldId = new TaskAttemptID(tid, i);
    Path pTask = new Path(pCommit, oldId.toString());
    if (fs.exists(pTask) && !fs.delete(pTask, true)) {
      throw new IOException("Failed to delete " + pTask);
    }
  }
}