Zookeeper分布式共享锁

港控/mmm° 2022-01-21 00:37 192阅读 0赞

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zookeeper实现分布式共享锁逻辑：

1.程序节点启动时到zookeeper上注册一个“短暂+序号”的znode,并监听父节点（详情：Zookeeper：[用客户端对Zookeeper进行操作][Zookeeper]）

2.获取父节点下的所有程序子节点，比较序号大小

3.序号最小的获取到“锁”，去访问资源，访问完后，删除自己的节点，相当于释放锁，并且重新注册一个新的节点

4.其他程序会受到事件通知，则可以去zookeeper上竞争锁

public class DistributedClient \{

// 超时时间

private static final int SESSION\_TIMEOUT = 5000;

// zookeeper server列表

private String hosts = "localhost:4180,localhost:4181,localhost:4182";

private String groupNode = "locks";

private String subNode = "sub";

private ZooKeeper zk;

// 当前client创建的子节点

private String thisPath;

// 当前client等待的子节点

private String waitPath;

private CountDownLatch latch = new CountDownLatch(1);

/\*\*

\* 连接zookeeper

\*/

public void connectZookeeper() throws Exception \{

zk = new ZooKeeper(hosts, SESSION\_TIMEOUT, new Watcher() \{

public void process(WatchedEvent event) \{

try \{

// 连接建立时, 打开latch, 唤醒wait在该latch上的线程

if (event.getState() == KeeperState.SyncConnected) \{

latch.countDown();

// 发生了waitPath的删除事件

if (event.getType() == EventType.NodeDeleted && event.getPath().equals(waitPath)) \{

doSomething();

\} catch (Exception e) \{

e.printStackTrace();

\});

// 等待连接建立

latch.await();

// 创建子节点

thisPath = zk.create("/" + groupNode + "/" + subNode, null, Ids.OPEN\_ACL\_UNSAFE,

CreateMode.EPHEMERAL\_SEQUENTIAL);

// wait一小会, 让结果更清晰一些

Thread.sleep(10);

// 注意, 没有必要监听"/locks"的子节点的变化情况

List<String> childrenNodes = zk.getChildren("/" + groupNode, false);

// 列表中只有一个子节点, 那肯定就是thisPath, 说明client获得锁

if (childrenNodes.size() == 1) \{

doSomething();

\} else \{

String thisNode = thisPath.substring(("/" + groupNode + "/").length());

// 排序

Collections.sort(childrenNodes);

int index = childrenNodes.indexOf(thisNode);

if (index == -1) \{

// never happened

\} else if (index == 0) \{

// inddx == 0, 说明thisNode在列表中最小, 当前client获得锁

doSomething();

\} else \{

// 获得排名比thisPath前1位的节点

this.waitPath = "/" + groupNode + "/" + childrenNodes.get(index - 1);

// 在waitPath上注册监听器, 当waitPath被删除时, zookeeper会回调监听器的process方法

zk.getData(waitPath, true, new Stat());

private void doSomething() throws Exception \{

try \{

System.out.println("gain lock: " + thisPath);

Thread.sleep(2000);

// do something

\} finally \{

System.out.println("finished: " + thisPath);

// 将thisPath删除, 监听thisPath的client将获得通知

// 相当于释放锁

zk.delete(this.thisPath, -1);

public static void main(String\[\] args) throws Exception \{

for (int i = 0; i < 10; i++) \{

new Thread() \{

public void run() \{

try \{

DistributedClient dl = new DistributedClient();

dl.connectZookeeper();

\} catch (Exception e) \{

e.printStackTrace();

\}.start();

Thread.sleep(Long.MAX\_VALUE);

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[Zookeeper]: https://mp.csdn.net/postedit/90906212
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