code: void refresh(long now) {
      refreshCandidateSpeculativeMaps(now);
      refreshCandidateSpeculativeReduces(now);
      refreshTaskCountsAndWaitTime(TaskType.MAP, now);
      refreshTaskCountsAndWaitTime(TaskType.REDUCE, now);
    }
docs: Refresh speculative task candidates and running tasks. This needs to be
  called periodically to obtain fresh values.