Zookeeper distributed lock case

I. Overview:

Zookeeper is an open source distributed coordination service that can be used to maintain consistency, order, and naming in distributed systems. Among them, Zookeeper's distributed lock mechanism can be used to implement mutual exclusion access in distributed systems, ensuring simultaneous access to shared resources on multiple nodes.

The implementation principle of Zookeeper distributed lock is based on Zookeeper's temporary ordered nodes and Watcher mechanism. When a node needs to acquire a lock, it will create a temporary ordered node to Zookeeper, and monitor the child nodes of the node through the Watcher mechanism. When the node finds that its own node has the smallest serial number among all nodes, it thinks that it has acquired the lock and can perform access operations on shared resources. When other nodes find that the serial number of their own node is larger than the current maximum serial number, they will give up competing for the lock and wait for the next retry.

To use Zookeeper distributed locks in Spring Boot, you need to configure Zookeeper's connection parameters and basePath first, then inject ZookeeperTemplate and CuratorFramework instances through the annotation @Autowired, and then create distributed lock objects through the DistributedLock class. In the code block that needs to be locked, use the distributedLock.lock() method to acquire the lock, and use the try-with-resources statement block to ensure the release of the lock.

2. Case:

1. You need to use Maven to import the related dependencies of Zookeeper and Spring Boot:

<dependency>  
    <groupId>org.apache.zookeeper</groupId>  
    <artifactId>zookeeper</artifactId>  
    <version>3.7.0</version>  
</dependency>  
  
<dependency>  
    <groupId>org.springframework.boot</groupId>  
    <artifactId>spring-boot-starter-zookeeper</artifactId>  
    <version>2.3.1.RELEASE</version>  
</dependency>

2. Add Zookeeper connection parameters to the configuration file of the Spring Boot application:

spring:  
  zookeeper:  
    connectString: localhost:2181  
    basePath: /my-application

3. Create a distributed lock bean, which can be implemented using ZookeeperTemplate and CuratorLock:

@Configuration  
public class DistributedLockConfig {
    
      
    @Autowired  
    private ZookeeperTemplate zookeeperTemplate;  
  
    @Bean  
    public DistributedLock distributedLock(CuratorFramework client) {
    
      
        return new DistributedLock(client, "/my-lock");  
    }  
}

In the above code, ZookeeperTemplate is a tool class provided by Spring Boot to interact with Zookeeper, and CuratorFramework is a Zookeeper client library provided by Curator.

4. In the code that needs to use distributed locks, distributed locks can be obtained through dependency injection:

@Service  
public class MyService {
    
      
    @Autowired  
    private DistributedLock distributedLock;  
  
    public void doSomething() {
    
      
        try (CloseableLock lock = distributedLock.lock()) {
    
      
            // 在这里执行需要加锁的代码块  
        } catch (Exception e) {
    
      
            // 处理异常情况  
        }  
    }  
}

In the above code, CloseableLock is a closeable distributed lock implementation provided by Curator, which can be used in the try statement block to acquire the lock. If the acquisition of the lock fails, an exception will be thrown and it will enter the catch statement block for processing.

Finally, the functionality of the distributed lock can be tested by running the Spring Boot application. Call the doSomething() method of MyService in multiple instances, and only the instance that successfully acquires the lock can execute the locked code block.