rust / LEVEL 4
THEORY / RETRIEVAL
A load followed by a store is two separate operations and loses concurrent updates. Read-modify-write operations or a compare-exchange loop make the transition conditional on the value that was observed.
Relaxed ordering is enough for an independent statistics counter whose value does not publish other memory. If observing the counter must make other writes visible, the contract needs an acquire/release relationship instead.
CHECKPOINT
02 / IMPLEMENTATION
Implement a lock-free saturating add that returns the new value, never wraps, and preserves concurrent increments. This counter has no synchronization role beyond its number.
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