How to handle race conditions in distributed programming?

I can't seem to find much online about this. In distributed programming, there are many scenarios where race conditions pose a risk. For example, if I have a chat system where I want to limit the user count in each room to 100. Many concurrent joins may lead to more than 100 users in a single room due to race conditions. The only solution I can think of is to use a distributed lock. However, I feel that there are cleaner ways to address this/these issues. Are there any guides or resources online about this?