Zookeeper(七)分布式锁
获取锁实现思路:
1. 首先创建一个作为锁目录(znode),通常用它来描述锁定的实体,称为:/lock_node
2. 希望获得锁的客户端在锁目录下创建znode,作为锁/lock_node的子节点,并且节点类型为有序临时节点(EPHEMERAL_SEQUENTIAL);
例如:有两个客户端创建znode,分别为/lock_node/lock-1和/lock_node/lock-2
3. 当前客户端调用getChildren(/lock_node)得到锁目录所有子节点,不设置watch,接着获取小于自己(步骤2创建)的兄弟节点
4. 步骤3中获取小于自己的节点不存在 && 最小节点与步骤2中创建的相同,说明当前客户端顺序号最小,获得锁,结束。
5. 客户端监视(watch)相对自己次小的有序临时节点状态
6. 如果监视的次小节点状态发生变化,则跳转到步骤3,继续后续操作,直到退出锁竞争。
public synchronized void unlock() throws RuntimeException { if (!isClosed() && id != null) { // we don't need to retry this operation in the case of failure // as ZK will remove ephemeral files and we don't wanna hang // this process when closing if we cannot reconnect to ZK try { ZooKeeperOperation zopdel = new ZooKeeperOperation() { public boolean execute() throws KeeperException, InterruptedException { // 删除节点 忽略版本 zookeeper.delete(id, -1); return Boolean.TRUE; } }; zopdel.execute(); } catch (InterruptedException e) { LOG.warn("Caught: " + e, e); //set that we have been interrupted. Thread.currentThread().interrupt(); } catch (KeeperException.NoNodeException e) { // do nothing } catch (KeeperException e) { LOG.warn("Caught: " + e, e); throw (RuntimeException) new RuntimeException(e.getMessage()). initCause(e); } finally { if (callback != null) { callback.lockReleased(); } id = null; } } }