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This article mainly explains "what is the implementation principle of redis distributed lock". The content of the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what is the implementation principle of redis distributed lock"?

With the help of the command setnx (key, value) in redis, key is added if it doesn't exist, and nothing can be done if it exists. Multiple clients send setnx commands at the same time, and only one client can succeed and return 1 (true); the other clients return 0 (false).

The operating environment of this tutorial: windows7 system, Redis5.0.10 version, DELL G3 computer.

Implementation of distributed Lock

With the need of business development, after the original single machine deployment system is evolved into a distributed cluster system, because the distributed system is multi-threaded, multi-process and distributed on different machines, this will invalidate the concurrency control lock strategy under the original single machine deployment, and Java API alone can not provide the ability of distributed lock. In order to solve this problem, we need a cross-JVM mutual exclusion mechanism to control the access to shared resources, which is the problem of distributed locking!

The mainstream implementation scheme of distributed lock:

Implementation of distributed Lock based on Database

Based on cache (Redis, etc.)

Based on Zookeeper

Here, we implement distributed locks based on redis.

Basic realization

With the help of the command setnx (key, value) in redis, key is added if it doesn't exist, and nothing can be done if it exists. Multiple clients send setnx commands at the same time, and only one client can succeed and return 1 (true); the other clients return 0 (false).

Mainly use the Redis Setnx command

Sets the specified value for key when the specified key does not exist

If the setting is successful, return 1. Failed to set, 0 is returned

Redis > EXISTS job # job does not exist (integer) 0 redis > SETNX job "programmer" # job setting succeeded (integer) 1 redis > SETNX job "code-farmer" # attempted to overwrite job, failed (integer) 0 redis > GET job # not overwritten "programmer"

Java code

Public void testLock () {/ / execute the setnx command of redis String uuid = UUID.randomUUID () .toString (); Boolean lock = redisTemplate.opsForValue () .setIfAbsent ("lock", uuid, 5, TimeUnit.SECONDS) / / determine whether to get the lock if (lock) {/ / execute the business logic code / /... / / release the lock resource (ensure the atomicity of the acquisition value and delete operation) the LUA script guarantees deletion. Atomicity String script = "if redis.call ('get' KEYS [1]) = ARGV [1] then return redis.call ('del', KEYS [1]) else return 0 end " This.redisTemplate.execute (new DefaultRedisScript (script), Arrays.asList ("lock"), Arrays.asList (uuid)); / / if (StrUtil.equals (uuid,redisTemplate.opsForValue (). Get ("lock")) {/ / redisTemplate.delete ("lock") / /}} else {/ / other request attempted to acquire lock testLock ();}}

To ensure that distributed locks are available, we need to ensure that the lock implementation meets at least the following four conditions:

Repulsion. At any given time, only one client can hold the lock.

There is no deadlock. Even if one client crashes while holding the lock without actively unlocking it, it is guaranteed that other clients will be able to lock it.

The person who unlocks the bell must also tie the bell. Locking and unlocking must be the same client, and the client cannot unlock the lock added by others.

Thank you for reading, the above is the content of "what is the implementation principle of redis distributed lock". After the study of this article, I believe you have a deeper understanding of what the implementation principle of redis distributed lock is, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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