@Override
  public void close() throws IOException {
    long refs = referenceCount.decrementAndGet();
    if (refs == 0) {
      super.close();
    }
  }
Decreases the reference of the underlying reader for the mob file. It's not thread-safe. Use
MobFileCache.closeFile() instead. This underlying reader isn't closed until the reference is 0.
hbase-server/src/main/java/org/apache/hadoop/hbase/mob/CachedMobFile.java