This will cause a dead lock if it ever executes as the lock isn't released in this block

Should probably use lock_guard, so that the mutex is unlocked if the reference is dropped

https://en.cppreference.com/w/cpp/thread/lock_guard

I thought the lock is released when the lock object goes out-of-scope, which happens when the function returns. But I may have gotten myself confused – that might only work with lock_guard?

It's dependent on what type you use, we are using a shared_ptr<share_mutex> here.

https://stackoverflow.com/questions/43019598/stdlock-guard-or-stdscoped-lock