RFR: 8186670: Implement _onSpinWait() intrinsic for AArch64 [v13]

[Evgeny Astigeevich]

On Wed, 20 Oct 2021 16:16:45 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Evgeny Astigeevich has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix formatting and spelling
>
> test/micro/org/openjdk/bench/java/lang/ThreadOnSpinWaitProducerConsumer.java line 47:
> 
>> 45: @State(Scope.Benchmark)
>> 46: public class ThreadOnSpinWaitProducerConsumer {
>> 47:     @Param({"100"})
> 
> This test seems rather artificial and unrealistic to me. You can get improved performance simply by increasing the `spinNum` so that it waits for longer. The way to get some advantage from `onSpinWait` is to have multiple threads racing to update the same thing, e.g. to acquire a lock.

@theRealAph, done

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PR: https://git.openjdk.java.net/jdk/pull/5562