ZooKeeper 开发随笔

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基于 ZooKeeper 实现分布式锁

  • 由于下面使用了 Curator 客户端，因此需要引入相应的依赖
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<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-framework</artifactId>
    <version>5.5.0</version>
</dependency>

<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-recipes</artifactId>
    <version>5.5.0</version>
</dependency>
  • 基于 ZooKeeper 实现分布式锁
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import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.locks.InterProcessLock;
import org.apache.curator.retry.ExponentialBackoffRetry;

public class CuratorDistributedLockExample {
	
    private static final String ZOOKEEPER_CONNECTION_STRING = "localhost:2181";
    private static final String LOCK_PATH = "/zk-lock";

    public static void main(String[] args) throws Exception {
        CuratorFramework client = CuratorFrameworkFactory.newClient(ZOOKEEPER_CONNECTION_STRING, new ExponentialBackoffRetry(1000, 3));
        client.start();

        InterProcessLock lock = new InterProcessMutex(client, LOCK_PATH);
        try {
            // 获取锁
            lock.acquire();
            // 在这里执行需要加锁的业务逻辑
            System.out.println("Lock acquired, do some work here...");
            // 模拟业务逻辑耗时
            Thread.sleep(5000);
        } finally {
            try {
                // 释放锁
                lock.release();
                System.out.println("Lock released.");
            } catch (Exception exception) {
                exception.printStackTrace();
            }
        }

        client.close();
    }
}

在这个示例中，首先创建了 Curator 客户端，然后使用 InterProcessMutex 类创建了一个分布式锁实例。在 try 块中调用 acquire() 方法获取锁，在获取锁后执行需要加锁的业务逻辑，最后在 finally 块中释放锁。Curator 会自动处理加锁、解锁和失败重试等复杂逻辑，简化了分布式锁的使用。

Dubbo 使用 Curator 连接 ZooKeeper 失败

异常日志：

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Caused by: org.apache.zookeeper.KeeperException$UnimplementedException: KeeperErrorCode = Unimplemented for /dubbo/xxx.xxx.service.UserService/providers/dubbo ....

异常分析：ZooKeeper 的版本与 Curator 的版本不兼容所导致，Curator 官网说明如下：

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第一种情况：

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.

第二种情况：

ZooKeeper 3.5.x
    Curator 4.0 has a hard dependency on ZooKeeper 3.5.x
    If you are using ZooKeeper 3.5.x there's nothing additional to do - just use Curator 4.0

ZooKeeper 3.4.x
    Curator 4.0 supports ZooKeeper 3.4.x ensembles in a soft-compatibility mode. To use this mode you must exclude ZooKeeper when adding Curator to your dependency management tool.

解决方法：针对第二种情况，假设各组件的版本分别为 Dubbo (2.7.0)、ZooKeeper (3.4.13)、Curator-Framework (4.0.1)，则需要排除 Curator-Framework (4.0.1) 默认依赖的高版本 ZooKeeper (3.5.x)，然后指定低版本的 ZooKeeper (3.4.x)，Maven 的 POM 写法如下：

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<dependencies>
  <dependency>
  	<groupId>org.apache.zookeeper</groupId>
  	<artifactId>zookeeper</artifactId>
  	<version>3.4.13</version>
  </dependency>

  <dependency>
  	<groupId>org.apache.curator</groupId>
  	<artifactId>curator-framework</artifactId>
  	<version>4.0.1</version>
  	<exclusions>
  		<exclusion>
  			<groupId>org.apache.zookeeper</groupId>
  			<artifactId>zookeeper</artifactId>
  		</exclusion>
  	</exclusions>
  </dependency>

  <dependency>
  	<groupId>org.apache.curator</groupId>
  	<artifactId>curator-recipes</artifactId>
  	<version>4.0.1</version>
  </dependency>
</dependencies>