Zookeeper：实现“分布式锁”的 Demo

2022-12-02 08:27:40 浏览数 (1)

Zookeeper 能保证数据的强一致性，用户任何时候都可以相信集群中每个节点的数据都是相同的。一个用户创建一个节点作为锁，另一个用户检测该节点，如果存在，代表别的用户已经锁住，如果不存在，则可以创建一个节点，代表拥有一个锁。 ～ 本篇内容包括：Demo 概述、代码实现、测试结果

文章目录
  • 一、Demo 概述
    • 1、关于 zookeeper “命名服务协调”
    • 2、Demo 设计
    • 3、Demo 前提

  • 二、代码实现
    • 1、引用 Maven 依赖
    • 2、ConnectionWatcher 类创建 Zookeeper 连接
    • 3、ActiveKeyValueStore 类读写 Zookeeper 数据
    • 4、ZkLock 类实现分布式锁
  • 三、测试结果

一、Demo 概述

1、关于 zookeeper “命名服务协调”

Zookeeper 能保证数据的强一致性，用户任何时候都可以相信集群中每个节点的数据都是相同的。一个用户创建一个节点作为锁，另一个用户检测该节点，如果存在，代表别的用户已经锁住，如果不存在，则可以创建一个节点，代表拥有一个锁。

2、Demo 设计

分布式锁本质，就是多个资源竞争者对一份资源的排他占有

  • 我们设置多个线程，分别在同一 path 下创建节点
  • 没个线程获取当前 path 下子节点，看最小子节点是否为自身，是则加锁成功（更好的方式是用 Watcher 对前一个地址监控，这里图方便用子节点排序取最小的方式 ）
  • 线程加锁成功后，执行任务，执行完毕后解锁
3、Demo 前提

参考：Mac通过Docker安装Zookeeper集群

二、代码实现

1、引用 Maven 依赖
代码语言：javascript复制
        <!--    选择对应的Zookeeper版本    -->
        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.7.0</version>
        </dependency>
2、ConnectionWatcher 类创建 Zookeeper 连接
代码语言：javascript复制
import java.io.IOException;
import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

public class ConnectionWatcher implements Watcher {

    private final CountDownLatch connectedSignal = new CountDownLatch(1);
    private static final int SESSION_TIMEOUT = 5000;
    protected ZooKeeper zk;


    public void connect(String hosts) throws IOException, InterruptedException {
        zk = new ZooKeeper(hosts, SESSION_TIMEOUT, this);
        connectedSignal.await();
    }

    @Override
    public void process(WatchedEvent event) {
        if (event.getState() == Event.KeeperState.SyncConnected) {
            connectedSignal.countDown();
        }
    }

    public void close() throws InterruptedException {
        zk.close();
    }

}
3、ActiveKeyValueStore 类读写 Zookeeper 数据
代码语言：javascript复制
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.List;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.data.Stat;

public class ActiveKeyValueStore extends ConnectionWatcher {

    private static final Charset CHARSET = StandardCharsets.UTF_8;

    int state = 0;

    /**
     * 写入节点数据
     *
     * @param path  节点地址
     * @param value 数据值
     * @throws InterruptedException 中断异常
     * @throws KeeperException      ZooKeeper异常
     */
    public void write(String path, String value) throws InterruptedException, KeeperException {
        Stat stat = zk.exists(path, false);
        if (stat == null) {
            if (value == null) {
                zk.create(path, null,
                        ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            } else {
                zk.create(path, value.getBytes(CHARSET),
                        ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            }

        } else {
            if (value == null) {
                zk.setData(path, null, -1);
            } else {
                zk.setData(path, value.getBytes(CHARSET), -1);
            }

        }
    }
  
   public boolean lock(String path, String name) throws InterruptedException, KeeperException {
        boolean flag = tryLock(path, name);
        if (flag) {
            state  ;
        }
        return flag;
    }

    public boolean tryLock(String path, String name) throws InterruptedException, KeeperException {

        String lockPath = path   "/"   name;
        zk.create(lockPath, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        List<String> waits = readChildren(path, null);
        Collections.sort(waits);
        if (waits.get(0).equals(name)) {
            return true;
        }
        CountDownLatch latch = new CountDownLatch(1);
        for (int i = 0; i < waits.size(); i  ) {
            String cur = waits.get(i);
            if (!cur.equalsIgnoreCase(name)) {
                continue;
            }
            String prePath = path   "/"   waits.get(i - 1);
            zk.exists(prePath, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    latch.countDown();
                }
            });
            break;
        }
        latch.await();
        return true;
    }

    public boolean unlock(String path, String name) {
        if (state > 1) {
            state--;
            return true;
        }

        String lockPath = path   "/"   name;

        try {
            Stat stat = zk.exists(lockPath, false);
            int version = stat.getVersion();
            zk.delete(lockPath, version);
            state--;
            return true;
        } catch (Exception e) {
            System.out.println("unlock:"   lockPath   " ,exception,");
        }
        return false;
    }

    /**
     * 获取所有子节点
     *
     * @param path    节点地址
     * @param watcher watcher
     * @return 所有子节点
     * @throws InterruptedException 中断异常
     * @throws KeeperException      ZooKeeper异常
     */
    public List<String> readChildren(String path, Watcher watcher) throws InterruptedException, KeeperException {
        List<String> childrens = null;
        if (watcher == null) {
            childrens = zk.getChildren(path, false);
        } else {
            childrens = zk.getChildren(path, watcher, null);
        }
        return childrens;
    }
}
4、ZkLock 类实现分布式锁
代码语言：javascript复制
import lombok.SneakyThrows;
import org.apache.zookeeper.KeeperException;

import java.io.IOException;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

public class ZkLock {


    /**
     * 开启的线程数，模拟多客户端操作
     */
    private static final int CLIENTS_NUM = 3;

    private final ActiveKeyValueStore store;

    public ZkLock(String hosts) throws IOException, InterruptedException {
        //定义一个类
        store = new ActiveKeyValueStore();
        //连接Zookeeper
        store.connect(hosts);
    }

    public static void testLock() {
        //线程计数器控制业务的执行
        final CountDownLatch countDownLatch = new CountDownLatch(CLIENTS_NUM);
        for (int i = 0; i < CLIENTS_NUM; i  ) {
            new Thread() {
                @Override
                public void run() {

                }
            }.start();
        }
        try {
            // 堵塞线程，任务执行完后释放
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }


    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {

        String hosts = "localhost:2181";
        ZkLock zkLock = new ZkLock(hosts);

        // 创建父节点
        zkLock.store.write("/lock4", "父亲节点");
        //
        CountDownLatch latch = new CountDownLatch(CLIENTS_NUM);
        for (int i = 0; i < CLIENTS_NUM; i  ) {

            int finalI = i;
            new Thread() {
                @SneakyThrows
                @Override
                public void run() {

                    String name = "Thread-"   String.valueOf(finalI);
                    zkLock.store.lock("/lock4", name);
                    TimeUnit.SECONDS.sleep(2);
                    System.out.println("线程-"   name   "执行完毕");
                    latch.countDown();
                    zkLock.store.unlock("/lock4", name);


                }
            }.start();
        }
        latch.await();
        System.out.println("end ...");
    }


}

三、测试结果

ZkLock 代码测试结果如下：

代码语言：javascript复制
线程-Thread-0执行完毕
线程-Thread-1执行完毕
线程-Thread-2执行完毕
end ...

通过 ZkLock 打印的信息可以看出，已经成功模拟实现分布式锁

分布式 腾讯云测试服务 zookeeper maven

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