Indeed, this blanket advice does not apply in situations where shared resources that require mutable access need to be synchronized. If my async HTTP router is serving two requests that are using the same database client to persist changes, that needs to be synchronized. How does one do this without a mutex?
The lifetime/borrow-checking is the mutex. If you've got a database client that must only be used by one caller at a time, make a function that takes the client as &mut.
By acquiring and releasing resources. I’m not intimately familiar with Rust, so I’ll use Go as an example.
Create a one-buffered channel: `make(chan T, 1)`. To acquire, receive from the channel. If the object is in use, the receive will block (goroutine put to sleep) until it’s available. To release, send the acquired object to the channel.
