AtomicInteger getRefs(final long index) {
        AtomicInteger refs = this.refMap.get(index);
        if (refs == null) {
            refs = new AtomicInteger(0);
            final AtomicInteger eRefs = this.refMap.putIfAbsent(index, refs);
            if (eRefs != null) {
                refs = eRefs;
            }
        }
        return refs;
    }
Snapshot storage based on local file storage.

@author boyan (boyan@alibaba-inc.com)
<p>
2018-Mar-13 2:11:30 PM
jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/LocalSnapshotStorage.java