@Override
        public RegionScanner call(RegionObserver observer) throws IOException {
          return observer.postScannerOpen(this, scan, getResult());
        }
@param scan the Scan specification
@param s    the scanner
@return the scanner instance to use
@exception IOException Exception
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RegionCoprocessorHost.java