@Override
    protected void flushInMemory(MutableSegment currentActiveMutableSegment) {
      super.flushInMemory(currentActiveMutableSegment);
      flushCounter.incrementAndGet();
      if (!flushByteSizeLessThanSmallAndLargeCellSize) {
        return;
      }

      assertTrue(Thread.currentThread().getName().equals(LARGE_CELL_THREAD_NAME));
      try {
        postCyclicBarrier.await();
      } catch (Throwable e) {
        throw new RuntimeException(e);
      }

    }
After largeCellThread finished flushInMemory method, smallCellThread can add cell to
currentActive . That is to say when largeCellThread called flushInMemory method,
currentActive has no cell.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestHStore.java