zk中ReferenceCountedACLCache的作用是什么

这篇文章给大家介绍zk中ReferenceCountedACLCache的作用是什么，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。

作用：完成LIst与Long互相转换，DataNode中acl是一个Long值，并不是ACL列表

空间复杂：内部类AtomicLongWithEquals

属性：

//日志信息private static final Logger LOG = LoggerFactory.getLogger(ReferenceCountedACLCache.class);// long ACL 列表对应关系final Map> longKeyMap = new HashMap>();//  ACL 列表 long对应关系final Map, Long> aclKeyMap = new HashMap, Long>();final Map referenceCounter = new HashMap();private static final long OPEN_UNSAFE_ACL_ID = -1L;/** * these are the number of acls that we have in the datatree */long aclIndex = 0;

方法：

记录引用次数

private static class AtomicLongWithEquals extends AtomicLong {    private static final long serialVersionUID = 3355155896813725462L;    public AtomicLongWithEquals(long i) {        super(i);    }    @Override    public boolean equals(Object o) {        if (this == o) {            return true;        }        if (o == null || getClass() != o.getClass()) {            return false;        }        return equals((AtomicLongWithEquals) o);    }    public boolean equals(AtomicLongWithEquals that) {        return get() == that.get();    }    @Override    public int hashCode() {        return 31 * Long.valueOf(get()).hashCode();    }}添加使用public synchronized void addUsage(Long acl) {    if (acl == OPEN_UNSAFE_ACL_ID) {        return;    }    if (!longKeyMap.containsKey(acl)) {        LOG.info("Ignoring acl " + acl + " as it does not exist in the cache");        return;    }    AtomicLong count = referenceCounter.get(acl);    if (count == null) {        referenceCounter.put(acl, new AtomicLongWithEquals(1));    } else {        count.incrementAndGet();    }}//移除引用public synchronized void removeUsage(Long acl) {    if (acl == OPEN_UNSAFE_ACL_ID) {        return;    }    if (!longKeyMap.containsKey(acl)) {        LOG.info("Ignoring acl " + acl + " as it does not exist in the cache");        return;    }    long newCount = referenceCounter.get(acl).decrementAndGet();    if (newCount <= 0) {        referenceCounter.remove(acl);        aclKeyMap.remove(longKeyMap.get(acl));        longKeyMap.remove(acl);    }}//如果引用计数值小于0，则移除相关信息public synchronized void purgeUnused() {    Iterator> refCountIter = referenceCounter.entrySet().iterator();    while (refCountIter.hasNext()) {        Map.Entry entry = refCountIter.next();        if (entry.getValue().get() <= 0) {            Long acl = entry.getKey();            aclKeyMap.remove(longKeyMap.get(acl));            longKeyMap.remove(acl);            refCountIter.remove();        }    }}

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