RegionScanner getScanner(long scannerId) {
    RegionScannerHolder rsh = checkQuotaAndGetRegionScannerContext(scannerId);
    return rsh == null ? null : rsh.s;
  }
Returns The outstanding RegionScanner for <code>scannerId</code> or null if none found.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RSRpcServices.java