public void flush() {
      synchronized (this) {
        notify();
      }
    }
Flushes the cache in a thread while scanning. The tests verify that the scan is coherent - e.g.
the returned results are always of the same or later update as the previous results. scan /
compact thread join
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestHRegion.java