Benchmark keeps running

[Aleksey Shipilev]

On 05/08/2013 07:21 AM, Yann Le Tallec wrote:
> @OutputTimeUnit(TimeUnit.NANOSECONDS)
> public class CAS {
> 
>     @State(Scope.Benchmark)
>     public static class AIState {
>         private final AtomicInteger ai = new AtomicInteger();
>     }
> 
>     @GenerateMicroBenchmark(BenchmarkType.AverageTimePerOp)
>     public int cas(CAS.AIState state) {
>         int i = state.ai.get();
>         while (!state.ai.compareAndSet(i, i + 1)) { }
>         return state.ai.get();
>     }
> }

Your benchmark is probably incorrect, you have to re-read the AI value
in the CAS'ed loop: if you had failed to CAS, that means the current
value is not "i" anymore:

    @GenerateMicroBenchmark(BenchmarkType.AverageTimePerOp)
    public int cas(AIState state) {
        int i;
        while (!state.ai.compareAndSet((i = state.ai.get()), i + 1)) { }
        return state.ai.get();
    }

Otherwise some thread can obviously be stuck. If that is the behavior
you are after, you have to let JMH terminate the loop, see
http://hg.openjdk.java.net/code-tools/jmh/file/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_18_Control.java

-Aleksey.