zookeeper源码之临时节点管理

Posted 2020-10-22 zhangwanhua

　　配置存储不仅维护了一个树结构，还实现了临时节点的功能，临时节点的生命周期和客户端会话绑定在一起，客户端会话失效，则这个节点就会被自动清除。

　　DataTree内部维护了一个hastable结构，key为sessionid，value为该session创建的临时节点。客户端会话失效，其创建的临时节点都会被删除。

private final Map<Long, HashSet<String>> ephemerals = new ConcurrentHashMap<Long, HashSet<String>>();
    public HashSet<String> getEphemerals(long sessionId) {
        HashSet<String> retv = ephemerals.get(sessionId);
        ...
        HashSet<String> cloned = null;
        synchronized (retv) {
            cloned = (HashSet<String>) retv.clone();
        }
        return cloned;
    }
public String createNode(String path, byte data[], List<ACL> acl,
            long ephemeralOwner, long zxid, long time)
            throws KeeperException.NoNodeException,
            KeeperException.NodeExistsException {
        ...
            if (ephemeralOwner != 0) {
                HashSet<String> list = ephemerals.get(ephemeralOwner);
                if (list == null) {
                    list = new HashSet<String>();
                    ephemerals.put(ephemeralOwner, list);
                }
                synchronized (list) {
                    list.add(path);
                }
            }
        }
        ...
    }
public void deleteNode(String path, long zxid)
            throws KeeperException.NoNodeException {
        ...
        DataNode node = nodes.get(path);
        ...
            long eowner = node.stat.getEphemeralOwner();
            if (eowner != 0) {
                HashSet<String> nodes = ephemerals.get(eowner);
                if (nodes != null) {
                    synchronized (nodes) {
                        nodes.remove(path);
                    }
                }
            }
        ...
    }
void killSession(long session, long zxid) {
        ...
        HashSet<String> list = ephemerals.remove(session);
        if (list != null) {
            for (String path : list) {
                ...
                    deleteNode(path, zxid);
                ...
            }
        }
    }