@Override
  public Object getResult(long timeout, TimeUnit unit)
      throws FunctionException, InterruptedException {
    return rcHolder.getResult(timeout, unit);
  }
Contract of {@link ReplyProcessor21#stillWaiting()} is that it never returns true after
returning false.
geode-core/src/main/java/org/apache/geode/internal/cache/partitioned/PRFunctionStreamingResultCollector.java