What does “spurious failure” on AtomicInteger weakCompareAndSet mean?

Question

The Java AtomicInteger class has a method -

boolean weakCompareAndSet(int expect,int update)

Its documnentation says:

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Answer 1

A good use-case for weakCompareAndSet is performance counters - no need for ordering, high rate of updates (so ordering hurts on weakly ordered systems), but will not drop counts under high loads (tightly contented perf-counters can drop 99% of all counts, essentially leaving the counters' value relative to un-contended counters random).