I usually write imperative code on Java/Spring MVC, but now my team implement project on WebFlux. I tried to research the topic, but I can’t find the answer to the question about locks.

It’s normal when we have code that should always be executed by only one thread, or that has locks by some condition (for example, the code should not be executed concurrently for the same entity). These locks can be distributed, for example, through a Redis. But how is this problem solved in Project Reactor? As far as I understand, it would be a bad idea to use a synchronized block, or ReentrantLock, because they will block threads while we avoid blocking.

It turns out that we need to design the application in such a way that there is no need for locks. Which is not always possible.

Or is there any solution? I will be grateful for any information.