private Set<Object> getReferences(final String url) {
        Set<Object> refs = this.refsCache.get(url);
        if (refs == null) {
            refs = new HashSet<Object>();
            final Set<Object> oldRefs = this.refsCache.putIfAbsent(url, refs);
            if (oldRefs != null) {
                refs = oldRefs;
            }
        }
        return refs;
    }
Whether to enable loopback connection for metaq client, default is false.
metamorphosis-client/src/main/java/com/taobao/metamorphosis/client/RemotingClientWrapper.java