ScanControllerState destroy() {
      ScanControllerState state = this.state;
      this.state = ScanControllerState.DESTROYED;
      return state;
    }
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