code: private void commitProgress(FileOffset position) {
      if(position==null) {
        return;
      }
      if ( lock!=null && canCommitNow() ) {
        try {
          String pos = position.toString();
          lock.heartbeat(pos);
          LOG.debug("{} Committed progress. {}", spoutId, pos);
          acksSinceLastCommit = 0;
          commitTimeElapsed.set(false);
          setupCommitElapseTimer();
        } catch (IOException e) {
          LOG.error("Unable to commit progress Will retry later. Spout ID = " + spoutId, e);
        }
      }
    }
docs: will commit progress into lock file if commit threshold is reached