Mutex with multiple processes Nodejs

I came across reading this article, it basically allows using mutex to avoid race conditions running on a single process. The author states that

> If you are running your application on multiple processes (for instance, by using the cluster module, worker threads or a multi-process runner like pm2) using a mutex within our code is not going to solve race conditions across processes. This is also the case if you are running your application on multiple servers.

I'm pretty sure this is a typical use case for a company running a shopping mall. People can purchase it at the same time and system might let some users still able to purchase although there were no more quantities left.

Can be prevented just running on a single process, but when the server goes on production using pm2, how do people tackle mutex-lock problem with multiple clusters? or is there another way not using pm2?

Mutex is use for prevent multiple process to edit variable at the same time which will cause race condition like in the article.

For your example about shopping mall and general usecase, we normally store number of available item in persistent storage or database because you want to keep number of available item even after the program is closed. If you store value in variable, everything will delete after program is closed. Persistent storage and database have their own locking mechanism which can handle multiple process access value at the same time.

There are also other techniques to handle your example.