Extractors for parts of state that are under a Mutex

[robryk]

Summary

I think I have another usecase for explicit 'state lifetime in FromRequestParts and would like to know if there's another way of achieving the same.

I have a URL pattern that contains a resource ID. My state is morally equivalent to Arc<Mutex<HashMap<String, Resource>>> with the String corresponding to the resource ID. I would like to have an extractor that extracts "access" to the appropriate Resource.

I can make a wrapper struct ResourceHandle<'a>(&'a mut MappedMutexGuard<'a, Resource>) and could give it a FromRequestParts<my_state> implementation, except that I cannot guarantee that the state will outlive 'a.

An obvious alternative is to replace Resource with Arc<Mutex<Resource>> in my state, and have an extractor for that (which will simply clone the Arc). That is certainly doable (and allows for more concurrency -- the global mutex is held only for the duration of the lookup), but it's somewhat more cumbersome to deal with (each handler has to deal with locking the per-resource mutex).

Is there a way of doing some moral equivalent of the former?

axum version

0.7.5

[jplatte]

If you have a tokio Mutex and want to lock it through an extractor until the handler returns or the guard (extractor) is explicitly dropped, have a look at Mutex::lock_owned. Does that help?