RowLockImpl newReadLock() {
      Lock l = readWriteLock.readLock();
      return getRowLock(l);
    }
Get an exclusive ( write lock ) lock on a given row.
@param row Which row to lock.
@return A locked RowLock. The lock is exclusive and already aqquired.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java