@Override
    public ScanResumer suspend() {
      preCheck();
      state = ScanControllerState.SUSPENDED;
      ScanResumerImpl resumer = new ScanResumerImpl();
      this.resumer = resumer;
      return resumer;
    }
Retry caller for scanning a region.
<p>
We will modify the {@link Scan} object passed in directly. The upper layer should store the
reference of this object and use it to open new single region scanners.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncScanSingleRegionRpcRetryingCaller.java