@Override
    public String cancelInProgress() {
      if (destroyed) {
        return "Pool " + PoolImpl.this + " is shut down";
      } else {
        return null;
      }
    }
A cancel criterion that checks only if this pool has been closed. This is necessary because
there are some things that we want to allow even after the cache has started closing.
geode-core/src/main/java/org/apache/geode/cache/client/internal/PoolImpl.java