@Override
  public void fragmentCompleting(String fragmentId, State state) {
    int val = 0;
    do {
      // Tez internals may register the same task as completing multiple times.
      val = runningFragmentCount.get();
      if (val == 0) {
        LOG.warn("RunningFragmentCount is already 0. Multiple calls for the same completion.");
        return;
      }
    } while (!runningFragmentCount.compareAndSet(val, val - 1));

    completingFragmentMap.put(fragmentId, new FragmentCompletion(state, clock.getTime()));
  }
A map where fragments live between when the TezTaskRunner2 calls taskSucceeded/Failed, or
 an external caller calls killTask, and when the TaskRunnerCallable comes out of the
 threadpool.
llap-server/src/java/org/apache/hadoop/hive/llap/daemon/impl/TaskExecutorService.java