引言

分布式锁是分布式系统的关键组件。本文介绍Redis分布式锁的实现。

一、基础实现

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public class RedisLock {
    private Jedis jedis;
    
    public boolean tryLock(String key, String value, int expireSeconds) {
        String result = jedis.set(key, value, "NX", "EX", expireSeconds);
        return "OK".equals(result);
    }
    
    public void unlock(String key, String value) {
        String script = 
            "if redis.call('get', KEYS[1]) == ARGV[1] then " +
            "    return redis.call('del', KEYS[1]) " +
            "else " +
            "    return 0 " +
            "end";
        jedis.eval(script, Collections.singletonList(key), Collections.singletonList(value));
    }
}

// 使用
String lockKey = "lock:order:123";
String lockValue = UUID.randomUUID().toString();

if (redisLock.tryLock(lockKey, lockValue, 30)) {
    try {
        // 业务逻辑
    } finally {
        redisLock.unlock(lockKey, lockValue);
    }
}

二、Redisson实现

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@Autowired
private RedissonClient redisson;

public void processOrder(Long orderId) {
    RLock lock = redisson.getLock("lock:order:" + orderId);
    
    try {
        // 尝试加锁，最多等待10秒，锁30秒后自动释放
        if (lock.tryLock(10, 30, TimeUnit.SECONDS)) {
            try {
                // 业务逻辑
            } finally {
                lock.unlock();
            }
        }
    } catch (InterruptedException e) {
        Thread.currentThread().interrupt();
    }
}

三、可重入锁

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// Redisson支持可重入
RLock lock = redisson.getLock("myLock");

lock.lock();
try {
    // 可以再次获取锁
    lock.lock();
    try {
        // 业务逻辑
    } finally {
        lock.unlock();
    }
} finally {
    lock.unlock();
}

四、RedLock算法

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// 多个Redis实例
RedissonClient redisson1 = ...;
RedissonClient redisson2 = ...;
RedissonClient redisson3 = ...;

RLock lock1 = redisson1.getLock("myLock");
RLock lock2 = redisson2.getLock("myLock");
RLock lock3 = redisson3.getLock("myLock");

// RedLock
RLock redLock = redisson.getRedLock(lock1, lock2, lock3);

redLock.lock();
try {
    // 业务逻辑
} finally {
    redLock.unlock();
}

总结

Redis分布式锁核心：

  1. SET NX EX：原子性加锁
  2. Lua脚本：原子性解锁
  3. UUID：防止误删
  4. Redisson：完善的分布式锁实现

参考资料