@Override
    public RuntimeException generateCancelledException(Throwable e) {
      if (isClosed()) {
        return new CacheClosedException("The disk store is closed", e);
      } else {
        return null;
      }
    }
Need a stopper that only triggers if this DiskRegion has been closed. If we use the
LocalRegion's Stopper then our async writer will not be able to finish flushing on a cache
close.
geode-core/src/main/java/org/apache/geode/internal/cache/DiskStoreImpl.java