实现思路
实现的分布式锁的最常见方式是使用redis分布式锁（redis分布式锁参考我的专栏——分布式锁），基本原理是在各个服务执行到临界区（造作共享资源的代码块）之前，去redis中尝试添加一个带有当前贡献资源标识的redis数据，如果redis中没有该键值，添加成功，代表加锁成功，如果redis中已经存在该键值，添加失败，则加锁失败。
而zookeeper的原理就完全不一样了：
- 首先，每个客户端会去某个指定的znode（一般情况，一类分布式锁都创建在某一个node path下）下创建临时有序节点，所以每个客户端创建出来的临时节点都会按照序列分配序号如/locks/lock_000000001、/locks/lock_000000002、/locks/lock_000000003.......
- 客户端获取到/lock下的子节点，并进行排序，判断排在最前面的节点是否是自己创建的节点，如果是，那么就获取到锁。
- 如果自己创建的节点并不在第一个，则监听前一个节点
- 前一个节点的客户端执行完毕，释放锁之后，就会触发监听，通知到下一个节点的客户端
- 监听客户端重新执行第2步动作，尝试获取锁
基本实现
本文的demo示例仅作为zookeeper分布式锁的原理分析示例！！！
引入zookeeper自带Java客户端
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<dependency>
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<groupId>org.apache.zookeeper
</groupId>
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<artifactId>zookeeper
</artifactId>
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<version>3.7.0
</version>
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</dependency>
编写示例
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package org.leolee.zookeeper.distributedLock;
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import org.apache.zookeeper.*;
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import org.apache.zookeeper.data.Stat;
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-
import java.io.IOException;
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import java.util.Collections;
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import java.util.List;
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import java.util.concurrent.CountDownLatch;
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/**
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* @ClassName MyLock
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* @Description: 分布式锁
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* @Author LeoLee
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* @Date 2021/4/14
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* @Version V1.0
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**/
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public
class MyLock {
-
-
private
static
final String IP =
"127.0.0.1:2181";
-
-
CountDownLatch countDownLatch =
new CountDownLatch(
1);
-
-
ZooKeeper zooKeeper;
-
-
private
static
final String LOCK_ROOT_PATH =
"/locks";
-
-
private
static
final String LOCK_NODE_NAME =
"lock_";
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private String lockPath;
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//连接zookeeper
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public MyLock() {
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try {
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zooKeeper =
new ZooKeeper(IP,
5000,
new Watcher() {
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@Override
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public void process(WatchedEvent watchedEvent) {
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if (watchedEvent.getState().equals(Event.KeeperState.SyncConnected)) {
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System.out.println(
"connect success");
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countDownLatch.countDown();
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}
else
if (watchedEvent.getState().equals(Event.KeeperState.Disconnected)) {
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System.out.println(
"connection break");
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}
else
if (watchedEvent.getState().equals(Event.KeeperState.Expired)) {
-
System.out.println(
"session timeout");
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}
else
if (watchedEvent.getState().equals(Event.KeeperState.AuthFailed)) {
-
System.out.println(
"auth failed");
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}
-
}
-
});
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countDownLatch.await();
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}
catch (IOException e) {
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e.printStackTrace();
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}
catch (InterruptedException e) {
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e.printStackTrace();
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}
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}
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Watcher watcher =
new Watcher() {
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@Override
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public void process(WatchedEvent watchedEvent) {
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//监视的前一个节点被删掉后通知
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if (watchedEvent.getType().equals(Event.EventType.NodeDeleted)) {
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synchronized (watcher) {
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watcher.notifyAll();
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}
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}
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}
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};
-
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/**
-
* 功能描述: <br>
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* 〈〉获取锁
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* @Param: []
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* @Return: void
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* @Author: LeoLee
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* @Date: 2021/4/14 23:00
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*/
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public void acquireLock() throws KeeperException, InterruptedException {
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createLock();
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tryLock();
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}
-
-
private void createLock() throws KeeperException, InterruptedException {
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//判断锁根节点是否存在
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Stat stat = zooKeeper.exists(LOCK_ROOT_PATH,
false);
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if (stat ==
null) {
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zooKeeper.create(LOCK_ROOT_PATH,
new
byte[
0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
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}
-
//创建锁节点（临时有效节点）
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lockPath = zooKeeper.create(LOCK_ROOT_PATH +
"/" + LOCK_NODE_NAME,
new
byte[
0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
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System.out.println(
"lock node create success, lock path:" + lockPath);
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}
-
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private void tryLock() throws KeeperException, InterruptedException {
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List<String> children = zooKeeper.getChildren(LOCK_ROOT_PATH,
false);
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//对子节点进行排序
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Collections.sort(children);
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int index = children.indexOf(lockPath.substring(LOCK_ROOT_PATH.length() +
1));
-
if (index ==
0) {
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System.out.println(
"try lock success");
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return;
-
}
else {
-
//获取上一个节点
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String preNode = children.get(index -
1);
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//对上一个节点进行watch
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Stat preNodeStat = zooKeeper.exists(LOCK_ROOT_PATH +
"/" + preNode, watcher);
-
if (preNodeStat ==
null) {
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acquireLock();
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}
else {
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synchronized (watcher) {
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watcher.wait();
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}
-
}
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}
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}
-
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/**
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* 功能描述: <br>
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* 〈〉释放锁
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* @Param: []
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* @Return: void
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* @Author: LeoLee
-
* @Date: 2021/4/14 23:01
-
*/
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public void releaseLock() throws KeeperException, InterruptedException {
-
//删除临时有序节点
-
zooKeeper.delete(lockPath, -
1);
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System.out.println(
"lock release");
-
zooKeeper.close();
-
}
-
}
转载：https://blog.csdn.net/qq_25805331/article/details/115705694
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