Shulou(Shulou.com)06/03 Report--

This article mainly introduces "how to use Redis lock". In daily operation, I believe many people have doubts about how to use Redis lock. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the doubts about "how to use Redis lock". Next, please follow the editor to study!

1 Local lock

Commonly used locks in JDK, such as synchronize or Lock, can only lock the current process and are only applicable to single architecture services. In distributed multi-service instance scenarios, distributed locks must be used.

2 distributed lock

2.1 principles of distributed locks

Toilet occupancy pit theory

Can go to the same place at the same time to occupy the pit:

To occupy, execute the logic.

Otherwise wait until the lock is released

You can spin by spinning.

"Zhankeng" can go to Redis, DB, any place where all services can access.

2.2 distributed lock evolution

One stage

/ / occupy distributed lock, go to redis to occupy pit Boolean lock = redisTemplate.opsForValue (). SetIfAbsent ("lock", "111"); if (lock) {/ / lock successfully. Execute business Map dataFromDb = getDataFromDb (); redisTemplate. Delete (key: "lock"); / / fH é ti return dataF romDb;} else {/ / failed to lock, try again. Synchronized () / / hibernating 100ms retry / / spin return getCatalogJsonFromDbwithRedisLock ();} follow official account: change Kirin to bug, you can get a copy of Redis actual combat learning notes.

Problem scenario

Setnx occupies the pit, but the business code is abnormal or the program is down during execution, that is, the lock logic is not successfully deleted, resulting in deadlock

Solution: set the automatic expiration of the lock, even if it is not deleted, it will be deleted automatically.

Stage two

/ / 1. Occupy distributed lock, go to redis to occupy pit Boolean lock = redisTemplate.opsForValue (). SetIfAbsent ("lock", "110") if (lock) {/ / lock successfully. Perform business / / sudden power outage / / 2. Set the expiration time redisTemplate.expire ("lock", timeout: 30, TimeUnit.SECONDS); Map dataFromDb = getDataFromDb (); / / remove the lock redisTemplate. Delete (key; "lock"); return dataFromDb;} else {/ / failed to lock. Try again. Synchronized () / / hibernating 100ms retry / / spin mode return getCatalogJsonF romDbWithRedisLock ();}

Problem scenario

Setnx is set up and is about to set expiration time, downtime, and deadlock

Solution: setting expiration time and occupancy must be atomic. Redis supports using the setNxEx command

Stage three

/ / 1. Distributed lock occupancy pit Boolean lock = redisTemplate.opsForValue (). SetIfAbsent ("lock", "110", 300,300, TimeUnit.SECONDS); if (lock) (/ / lock successfully, execute business / / 2. Set the expiration time, which must be used together with locking as an atomic operation / / redisTemplate. Expire ("lock", getDataFromDb 0, TimeUnit.SECONDS); Map dataFromDb = getDataFromDb (); / / remove lock redisTemplate.delete (key: "lock") return dataFromDb;else {/ / failed to lock, retry / hibernate 100ms retry / / spin return getCatalogJsonFromDbithRedislock ()}

Stage four

I've got lockvalue, I've got UUID, but it's expired now! Others get the lock and set a new value, so if deletes someone else's lock! That is, deleting a lock is not an atomic operation.

Map dataFromDb = getDataFromDb (); String lockValue = redisTemplate.opsForValue (). Get ("lock"); if (uuid.equals (lockValue)) {/ / remove my own lock redisTemplate.delete ("lock");}

Problem scenario

If it happens to be the current value, when the lock is about to be deleted, the lock has expired and someone else has successfully set the new value. Then what is deleted is someone else's lock.

Solution

The deletion lock must be atomically guaranteed. Use the redis+Lua script.

Stage five

Make sure that locking / unlocking is atomic.

String script = "if redis.call ('get', KEYS [1]) = ARGV [1] then return redis.call (' del', KEYS [1]) else return 0 end"; follow official account: Kirin changed to bug, you can get a copy of Redis actual combat learning notes.

Ensure the atomicity of locking [placeholder + expiration time] and deleting lock [judge + delete]. The more difficult thing is the automatic renewal of the lock.

At this point, the study on "how to use the Redis lock" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.