code: public synchronized void done(TaskAttemptID taskid)
    throws IOException {
      TaskInProgress tip = tasks.get(taskid);
      commitResponses.remove(taskid);
      if (tip != null) {
        tip.reportDone();
      } else {
        LOG.warn("Unknown child task done: "+taskid+". Ignored.");
      }
    }
docs: The task is done.