I’m not sure “what locks it” is a useful question. Locking is a performance and scalability destroying operation in a time when we care about both. Systems that care about both largely avoid locking (including most “lock-free” locks) altogether outside of rare cases, and in such rare cases the logic is simple. Nothing is lost by avoiding locks with good architecture.
In big multi-core systems, I model the handful of locks by the worst-case access frequency for a core to understand contention. In practice, this is often on the order of 100ms, which means the locks are effectively contention-free and the fast path almost always wins.
In big multi-core systems, I model the handful of locks by the worst-case access frequency for a core to understand contention. In practice, this is often on the order of 100ms, which means the locks are effectively contention-free and the fast path almost always wins.