We saw before that locks can sometimes be replaced with interlocked operations and we also used such operations to implement custom-made locking. Interlocked operations are also the basis for the optimistic locking pattern, which can be used to implement changes in shared data without using a classical locking mechanism.
Optimistic locking works when a chance of conflict between threads is very low. Like a database transaction mechanism, optimistic locking assumes that there will be no problem and applies required modifications on its own copy of the data (creates a new object, for example). In the second step, optimistic locking tries to commit the change. With one atomic step (usually implemented with an interlocked instruction), the current state is replaced with a new value.
This atomic replacement can, however, fail (if the state was modified...