分布式锁的两种实现方式：redis&zookeeper

红太狼 2022-05-12 14:20 128阅读 0赞

### redis方式 ###

/**
     * 分布式锁的简单实现代码
     */
    public class DistributedLock {
        private final JedisPool jedisPool;
        public DistributedLock(JedisPool jedisPool) {
            this.jedisPool = jedisPool;
        }
    
        /**
         * 加锁
         * @param lockName       锁的key
         * @param acquireTimeout 获取超时时间
         * @param timeout        锁的超时时间
         * @return 锁标识
         */
        public String lockWithTimeout(String lockName, long acquireTimeout, long timeout) {
            Jedis conn = null;
            String retIdentifier = null;
            try {
                // 获取连接
                conn = jedisPool.getResource();
                // 随机生成一个value
                String identifier = UUID.randomUUID().toString();
                // 锁名，即key值
                String lockKey = "lock:" + lockName;
                // 超时时间，上锁后超过此时间则自动释放锁
                int lockExpire = (int) (timeout / 1000);
    
                // 获取锁的超时时间，超过这个时间则放弃获取锁
                long end = System.currentTimeMillis() + acquireTimeout;
                while (System.currentTimeMillis() < end) {
                    if (conn.setnx(lockKey, identifier) == 1) {
                        conn.expire(lockKey, lockExpire);
                        // 返回value值，用于释放锁时间确认
                        retIdentifier = identifier;
                        return retIdentifier;
                    }
                    // 返回-1代表key没有设置超时时间，为key设置一个超时时间
                    if (conn.ttl(lockKey) == -1) {
                        conn.expire(lockKey, lockExpire);
                    }
    
                    try {
                        Thread.sleep(10);
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                    }
                }
            } catch (JedisException e) {
                e.printStackTrace();
            } finally {
                if (conn != null) {
                    conn.close();
                }
            }
            return retIdentifier;
        }
    
        /**
         * 释放锁
         * @param lockName   锁的key
         * @param identifier 释放锁的标识
         * @return
         */
        public boolean releaseLock(String lockName, String identifier) {
            Jedis conn = null;
            String lockKey = "lock:" + lockName;
            boolean retFlag = false;
            try {
                conn = jedisPool.getResource();
                while (true) {
                    // 监视lock，准备开始事务
                    conn.watch(lockKey);
                    // 通过前面返回的value值判断是不是该锁，若是该锁，则删除，释放锁
                    if (identifier.equals(conn.get(lockKey))) {
                        Transaction transaction = conn.multi();
                        transaction.del(lockKey);
                        List<Object> results = transaction.exec();
                        if (results == null) {
                            continue;
                        }
                        retFlag = true;
                    }
                    conn.unwatch();
                    break;
                }
            } catch (JedisException e) {
                e.printStackTrace();
            } finally {
                if (conn != null) {
                    conn.close();
                }
            }
            return retFlag;
        }
    }

引入

<dependency>
        <groupId>redis.clients</groupId>
        <artifactId>jedis</artifactId>
        <version>2.9.0</version>
    </dependency>

*  参考  
    [秒杀类场景分布式锁的实现][Link 1]

### zookeeper方式 ###

zookeeper+curator与redission

https://www.jianshu.com/p/31335efec309  
https://github.com/ghthou/learning-distributed-lock.git  
https://github.com/Mr-LuXiaoHua/dohko-distributed-lock.git

[Link 1]: https://www.jianshu.com/p/2d22df6eccf8