[14] RFR (XS): 8226409: Enable argument profiling for sun.misc.Unsafe.put*/get*

[Vladimir Ivanov]

> Changes are good and trivial.

Thanks, Vladimir.

> But can you explain why do we care about sun.misc.Unsafe in current JDK? 
> All should use jdk.internal.misc.Unsafe.
> May be this issue is good motivation to switch to jdk.internal.misc.Unsafe?

sun.misc.Unsafe is widely used outside JDK and it is listed in JEP 260 
[1] as critical internal API. It is still not encapsulated since 9, 
because there's no supported replacement available yet.

Moreover, jdk.internal.misc.Unsafe is encapsulated from the very 
beginning and shouldn't be used outside of the JDK.

Best regards,
Vladimir Ivanov

[1] http://openjdk.java.net/jeps/260
     JEP 260: Encapsulate Most Internal APIs

> On 7/3/19 2:01 PM, Vladimir Ivanov wrote:
>> http://cr.openjdk.java.net/~vlivanov/8226409/webrev.00/
>> https://bugs.openjdk.java.net/browse/JDK-8226409
>>
>> JDK-8181211 [1] enabled argument profiling for 
>> jdk.internal.misc.Unsafe to recuperate performance regression when 
>> off-heap/on-heap accesses are treated as mixed accesses (due to recent 
>> bug fixes in that area).
>>
>> Profiling data allows to speculatively optimize for on-heap or 
>> off-heap scenario and avoid memory barriers around unsafe accesses 
>> which are mandatory in mixed case.
>>
>> Unfortunately, it doesn't help sun.misc.Unsafe at all.
>>
>> sun.misc.Unsafe delegates to jdk.internal.misc.Unsafe and profiling 
>> data is mostly useless there since it is almost always polluted.
>>
>> Proposed fix is to enable argument profiling for sun.misc.Unsafe as well.
>>
>> Testing: hs-precheckin-comp, tier1-4
>>
>> Thanks!
>>
>> Best regards,
>> Vladimir Ivanov
>>
>> [1] https://bugs.openjdk.java.net/browse/JDK-8181211