Does dereffing past a RwLockReadGuard immediately drop the guard?

1 
/// The default manager for handling the list of users stored locally. It also allows for user creation, and is used especially
/// for when creating a new user via the registration service
pub struct AccountManagerInner {
    local_nac: NetworkAccount,
    cnacs: HashMap<u64, ClientNetworkAccount>
}


pub struct AccountManager {
    inner: Arc<RwLock<AccountManagerInner>>
}

impl Deref for AccountManager {
    type Target = AccountManagerInner; // How about RwLockReadGuard<'a, AccountManagerInner>?
    fn deref(&self) -> &Self::Target {
        &*self.inner.read() // Deref happens here with the &*
        // If I just return self.inner.read(), then I return a RwLockReadGuard<'a, AccountManagerInner>. But, this doesn't work because we need to pass a reference thereto. The struct gets created and then immediantly dropped, which invalidated the reference
    }
}

Is returning a deref'd RwLockReadGuard<'a, AccountManagerInner> wise? Does dereffing it drop the guard? If not, then how does the program know that a borrow still exists?

2

Yes, the guard will be dropped at the end of the scope, and that reference will be invalidated. You cannot implement Deref to look into RwLock and friends.

1 Like
3

I'm pretty sure this won't compile, for precisely the reasons that the OP is concerned about. Thus, the question is moot.

4

Yeah, I just tried in in the playground and it doesn't compile. Okay. So, if this was a type in your program that you needed distributed throughout, and 99% of the time you were just going to read into it, is there an optimal design pattern that you're aware of for thread-safe multiple access? Or, should I stick with the current design of Arc+RwLock, and then only read and write within the closure that I need to?

5

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