How to use distributed locks in Java to achieve synchronization of distributed systems?

How to use distributed locks in Java to achieve synchronization of distributed systems?

Introduction:
In a distributed system, data conflicts and concurrency problems may occur when multiple nodes access shared resources at the same time. In order to ensure data consistency, we need to use distributed locks to achieve synchronization of distributed systems. Java provides a variety of ways to implement distributed locks. This article will introduce the implementation methods of distributed locks based on ZooKeeper and Redis, with code examples.

1. Distributed lock implementation based on ZooKeeper
ZooKeeper is a distributed coordination service that provides a distributed lock mechanism to solve synchronization problems in distributed systems. The following is a sample code that uses ZooKeeper to implement distributed locks:

import org.apache.zookeeper.*;

import java.io.IOException;
import java.util.Collections;
import java.util.List;

public class ZooKeeperDistributedLock implements Watcher {
    private ZooKeeper zooKeeper;
    private String lockPath;
    private String currentPath;
    private String waitPath;

    public ZooKeeperDistributedLock(String connectString, int sessionTimeout, String lockPath) throws IOException {
        zooKeeper = new ZooKeeper(connectString, sessionTimeout, this);
        this.lockPath = lockPath;
    }

    public void lock() throws KeeperException, InterruptedException {
        if (tryLock()) {
            return;
        }

        while (true) {
            List<String> children = zooKeeper.getChildren(lockPath, false);
            Collections.sort(children);

            int index = children.indexOf(currentPath.substring(lockPath.length() + 1));
            if (index == 0) {
                return;
            }

            waitPath = lockPath + "/" + children.get(index - 1);
            zooKeeper.exists(waitPath, true);
            synchronized (this) {
                wait();
            }
        }
    }

    public void unlock() throws KeeperException, InterruptedException {
        zooKeeper.delete(currentPath, -1);
    }

    private boolean tryLock() throws KeeperException, InterruptedException {
        currentPath = zooKeeper.create(lockPath + "/lock", new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        List<String> children = zooKeeper.getChildren(lockPath, false);
        Collections.sort(children);
        if (currentPath.endsWith(children.get(0))) {
            return true;
        }
        String currentPathName = currentPath.substring(lockPath.length() + 1);
        int index = children.indexOf(currentPathName);
        if (index < 0) {
            throw new IllegalStateException("Node " + currentPathName + " no longer exists.");
        } else {
            waitPath = lockPath + "/" + children.get(index - 1);
            zooKeeper.exists(waitPath, true);
            synchronized (this) {
                wait();
            }
            return false;
        }
    }

    @Override
    public void process(WatchedEvent event) {
        if (waitPath != null && event.getType() == Event.EventType.NodeDeleted && event.getPath().equals(waitPath)) {
            synchronized (this) {
                notifyAll();
            }
        }
    }
}

2. Redis-based distributed lock implementation
Redis is a high-performance key-value storage system that provides some atomic operations To implement distributed locks. The following is a sample code that uses Redis to implement distributed locks:

import redis.clients.jedis.Jedis;

public class RedisDistributedLock {
    private Jedis jedis;
    private String lockKey;
    private String requestId;

    public RedisDistributedLock(String host, int port, String password, String lockKey, String requestId) {
        jedis = new Jedis(host, port);
        jedis.auth(password);
        this.lockKey = lockKey;
        this.requestId = requestId;
    }

    public boolean lock(long expireTimeMillis) {
        String result = jedis.set(lockKey, requestId, "NX", "PX", expireTimeMillis);
        return "OK".equals(result);
    }

    public boolean unlock() {
        Long result = (Long) jedis.eval(
                "if redis.call('get', KEYS[1]) == ARGV[1] then " +
                "return redis.call('del', KEYS[1]) " +
                "else " +
                "return 0 " +
                "end",
                1,
                lockKey,
                requestId);
        return result != null && result == 1;
    }
}

Conclusion:
This article introduces two methods of using distributed locks in Java to achieve synchronization of distributed systems: based on ZooKeeper and Redis . Whether you use ZooKeeper or Redis, you can effectively achieve synchronization of distributed systems and ensure data consistency. In actual projects, choosing an appropriate distributed lock solution must be weighed based on specific needs and performance requirements. I hope this article is helpful to you, thanks for reading!

The above is the detailed content of How to use distributed locks in Java to achieve synchronization of distributed systems?. For more information, please follow other related articles on the PHP Chinese website!