public CancelCriterion getCancelCriterion() {
    return stopper;
  }
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