資料庫

唯一索引、排他性
建表核心為業務防重複ID、鎖持有者ID

redis

redis單機是CP

單機不滿足高可用

public class WatchDogDemo
{
    public static final String LOCKKEY = "AAA";
    private static Config config;
    private static Redisson redisson;

    static {
        config = new Config();
        config.useSingleServer().setAddress("redis://"+"192.168.111.147"+":6379").setDatabase(0);
        redisson = (Redisson)Redisson.create(config);
    }

    public static void main(String[] args)
    {
        RLock redissonLock = redisson.getLock(LOCKKEY);
        redissonLock.lock();
        try
        {
            System.out.println("1111");
            //暫停幾秒鐘執行緒
            try { TimeUnit.SECONDS.sleep(25); } catch (InterruptedException e) { e.printStackTrace(); }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
           redissonLock.unlock();
        }
        System.out.println(Thread.currentThread().getName() + " main ------ ends.");
        //暫停幾秒鐘執行緒
        try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); }
        redisson.shutdown();
    }
}
 

redis叢集（主從模式）是AP

存在風險：主節點的資料還沒來得及同步給從節點就掛了

多主模式

N=2X+1個主節點，半數以上拿到鎖才行
redlock==>RedissonRedLock

public class RedLockController {
    public static final String CACHE_KEY_REDLOCK = "ZZYY_REDLOCK";
    @Autowired
    RedissonClient redissonClient1;
    @Autowired
    RedissonClient redissonClient2;
    @Autowired
    RedissonClient redissonClient3;
    @GetMapping(value = "/redlock")
    public void getlock() {
        //CACHE_KEY_REDLOCK為redis 分散式鎖的key
        RLock lock1 = redissonClient1.getLock(CACHE_KEY_REDLOCK);
        RLock lock2 = redissonClient2.getLock(CACHE_KEY_REDLOCK);
        RLock lock3 = redissonClient3.getLock(CACHE_KEY_REDLOCK);
        RedissonRedLock redLock = new RedissonRedLock(lock1, lock2, lock3);
        boolean isLock;
        try {
            //waitTime 鎖的等待時間處理,正常情況下 等5s
            //leaseTime就是redis key的過期時間,正常情況下等5分鐘。
            isLock = redLock.tryLock(5, 300, TimeUnit.SECONDS);
            log.info("執行緒{}，是否拿到鎖：{} ",Thread.currentThread().getName(),isLock);
            if (isLock) {
                //TODO if get lock success, do something;
                //暫停20秒鐘執行緒
                try { TimeUnit.SECONDS.sleep(20); } catch (InterruptedException e) { e.printStackTrace(); }
            }
        } catch (Exception e) {
            log.error("redlock exception ",e);
        } finally {
            // 無論如何, 最後都要解鎖
            redLock.unlock();
            System.out.println(Thread.currentThread().getName()+"\t"+"redLock.unlock()");
        }
    }
}