# §5 — Does it wait on anything?

This is the question that decides whether you need a crate you would otherwise not write.

gpui has its own executor and its own main thread. Anything that blocks — a network call, a slow disk, a child process — has to happen somewhere else and arrive back as a message. Atlas gives you exactly one place for that, and the cost of pretending you do not need it is a UI that freezes on a spinning disk.

## Where now

- No. Everything it needs is already in memory. — turn to §61
- Yes — a network call, a slow disk, a child process — turn to §16