code: public void recoverFromStopSync(AlluxioURI uri, long mountId) {
      if (mSyncPathStatus.containsKey(uri)) {
        // nothing to recover from, since the syncPathStatus still contains syncPoint
        return;
      }
      try {
        // the init sync thread has been removed, to reestablish sync, we need to sync again
        MountTable.Resolution resolution = mMountTable.resolve(uri);
        startInitSync(uri, resolution);
        launchPollingThread(resolution.getMountId(), SyncInfo.INVALID_TXID);
      } catch (Throwable t) {
        LOG.warn("Recovering from stop syncing failed {}", t);
      }
    }
docs: Recover from a stop sync operation.
  
  @param uri uri to stop sync
  @param mountId mount id of the uri