I am curious about where and how PHP stores semaphores in context of sharing them within the application.
From what I was able to understand from documentation, they use shared memory.

Since containers were introduced a few years ago the "use semaphores if you want lock shared within a host" no longer works, or at least I would not trust it to be reliable.

So my questions are:
Where exactly are those semaphores?
Will they be shared between fpm and cli?
Will they work inside a container?
Will they work between containers?
Do I need to share a file using volumes or bind mounts between containers to ensure sharing?
Are there any gotchas when using semaphores in modern systems?