[cormacrelf]

I agree. Optimistic locking is more akin to an atomic CAS operation than a lock. The usage of the API is the same; if the compare fails, fetch again and retry in a loop. (Incidentally, it doesn’t experience the ABA problem because nobody writes a lower lock_version unless they wait until the field overflows and wraps around… !).

Nobody would call CAS a lock. If your system only uses CAS, it should rightly be called “lock-free”.

[karmakaze]

The point to call Optimistic Locking by its other name Optimistic Concurrency Control (OCC) is a great one and I'll be doing that from now on.

In the spirit of trying to keep this complex subject free of misrepresentation... Compare-and-set (CAS, or alternatively compare-and-swap) is commonly used to implement lock-free algorithms.

A 'spin lock' where a thread uses only CAS in a tight loop and not carrying on until the lock is acquired is indeed a lock and not a kind of non-blocking or lock-free algorithm.