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2018-10-16

ZooKeeper 实现分布式锁

在 Java 中使用 ZooKeeper 实现分布式锁可按以下几步进行:

  1. 下载安装 ZooKeeper 3.4.13，参考 本机安装 ZooKeeper 集群 进行安装单机版 ZooKeeper，有必要的时候再安装集群
  2. 引入 Curator 的依赖，它实现了 ZooKeeper 的分布式锁
  3. Java 测试程序

下载安装

参考 本机安装 ZooKeeper 集群

引入 Curator 的依赖

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compile group: 'org.apache.curator', name: 'curator-recipes', version: '2.12.0'

注意: Curator 和 ZooKeeper 的版本需要对应，否则会报错

Curator 2.x.x: compatible with both ZooKeeper 3.4.x and ZooKeeper 3.5.x

Curator 3.x.x: compatible only with ZooKeeper 3.5.x and includes support for new features such as dynamic reconfiguration, etc.

Java 测试程序

官方文档: http://curator.apache.org/getting-started.html，先演示 Curator 连接 ZooKeeper 并使用分布式锁 InterProcessMutex:

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public static void testDistributedLock() throws Exception {
    // [1] This will create a connection to a ZooKeeper cluster using default values.
    // The only thing that you need to specify is the retry policy. For most cases, you should use:
    CuratorFramework client = CuratorFrameworkFactory.newClient("127.0.0.1:2181", new ExponentialBackoffRetry(10000, 3));

    // [2] The client must be started (and closed when no longer needed).
    client.start();

    InterProcessMutex lock = new InterProcessMutex(client, "/ebag/lock");

    // [3] 获取全局锁
    if (lock.acquire(10, TimeUnit.SECONDS)) {
        try {
            // [4] 业务代码
            System.out.println("Do something");
        } finally {
            // [5] 释放全局锁
            lock.release();
        }
    }

    // [6] Close the client
    client.close();
}

多线程测试分布式锁，结果 sn 是按顺序输出的，说明锁生效了:

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public static void testZooKeeperThread() {
    CuratorFramework client = CuratorFrameworkFactory.newClient("127.0.0.1:2181", new ExponentialBackoffRetry(10000, 3));
    client.start();
    List<Thread> threads = new LinkedList<>();

    for (int i = 0; i < 100; ++i) {
        threads.add(new Thread(new ZooKeeperRunnable(client, "/ebag/lock")));
    }

    for (Thread thread : threads) {
        thread.start();
    }

    // client.close();
}

class ZooKeeperRunnable implements Runnable {
    public static int sn = 0;
    private InterProcessMutex lock;

    public ZooKeeperRunnable(CuratorFramework client, String path) {
        lock = new InterProcessMutex(client, path);
    }

    public void run() {
        try {
            // 获取全局锁
            if (lock.acquire(10, TimeUnit.SECONDS)) {
                try {
                    // Thread.sleep(100);
                    sn++;
                    System.out.println(sn);
                } finally {
                    // 释放全局锁
                    lock.release();
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

提示: 上面的多线程是同一个 JVM 中的，可以很简单的修改为在多个 JVM 中运行，演示真正的分布式锁的效果，共享资源 sn 可以保存到 Redis，数据库等中。

ZooKeeper 常用命令

  • 创建: create path data: create /foo "Hello"
  • 修改: set path data: set /foo "Vox"
  • 获取: get path: get /foo
  • 删除: delete path: delete /foo
  • 查看: ls path: ls /foo