What is the principle of the distributed lock implementation in Redisson?

The Redisson distributed lock is an implementation of distributed lock based on Redis, and its principle is as follows:

  1. Acquire lock: When a thread wants to acquire a lock, it will send a SET command to the Redis server, attempting to set a specific value (such as a UUID) on the specified key, while also setting an expiration time (to prevent deadlock). If the setting is successful, meaning the lock has been obtained, the thread can proceed to execute the business logic.
  2. Retry acquiring the lock: If a thread fails to acquire the lock, it will enter a spinning process, continuously attempting to acquire the lock until successful or until a set timeout is reached.
  3. Release lock: When the business logic is completed or when an exception occurs, the lock needs to be released. The thread will send a DEL command to the Redis server, deleting the specified key and releasing the lock.
  4. Lock Renewal: In order to prevent locks from being automatically released due to prolonged execution time of business logic, Redisson will start a scheduled task after successfully acquiring a lock, periodically renewing the lock by updating its expiration time. Once the business logic is complete, the lock can be released normally if it has not expired yet. If the lock has already expired, manual release is not necessary as the lock has already been automatically released.
  5. Lock expiration detection: Due to the limited expiration time of locks, if the business logic execution time exceeds the lock’s expiration time, the lock may be automatically released. To prevent this scenario, Redisson periodically checks if the lock has expired and releases it immediately if it has.

The advantages of using Redisson distributed locks are their simplicity, high availability, and reliability, which allow for effective concurrency control in distributed environments.

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