@Override
      public void afterWritingBytes() {
        if (!alreadyComeHere) {
          region.get("key");
        }
        alreadyComeHere = true;
      }
A region close is done after flush is over. The close is done in a separate thread and a 3000
ms wait is put to ensure that the separate thread has closed the region
geode-core/src/integrationTest/java/org/apache/geode/internal/cache/ConcurrentFlushingAndRegionOperationsJUnitTest.java