[8u76] Request for approval: 8140587: Atomic*FieldUpdaters should use Class.isInstance instead of direct class check

[Rob McKenna]

Approved.

	-Rob

On 03/12/15 18:22, Martin Buchholz wrote:
> Both of these changes seem fine to me.
>
> I would prefer the "a" version - this keeps the jdk8u, jdk9, and
> jsr166 CVS versions in sync, so is probably lower risk.  jsr166 CVS
> gets regularly tested against both jdk8u and jdk9.
>
> On Thu, Dec 3, 2015 at 10:14 AM, Aleksey Shipilev
> <aleksey.shipilev at oracle.com> wrote:
>> Hi,
>>
>> This is yet another backport for improving Atomic*FieldUpdaters (A*FU)
>> performance.
>>
>> Bug:
>>    https://bugs.openjdk.java.net/browse/JDK-8140587
>>
>> The rationale for the change is simple: use the intrinsified
>> Class.isInstance instead of doing the direct class checks. This improves
>> C2 performance in some corner cases, and improves C1 performance across
>> most A*FU use cases (but only with C1 fix in JDK-8131782 applied, which
>> is backported separately).
>>
>> Like other A*FU-related patches, thus provides a migration path with the
>> eventual demise of sun.misc.Unsafe. Therefore, I'd like us to consider
>> this in 8u76 to expose users to this improvement earlier than JDK 9 release.
>>
>> I am not a 8u Committer, so if the change is approved, I'd need a sponsor.
>>
>> JDK 9 Changeset:
>>    http://hg.openjdk.java.net/jdk9/dev/jdk/rev/e1a21828acc1
>>
>> JDK 9 Review:
>>
>> http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-July/018473.html
>>
>> This change was in jdk9/dev for a week. The patch DOES NOT apply cleanly
>> over 8u sources, because of the formatting changes present only in jdk9,
>> plus the sun.misc/jdk.internal.misc.Unsafe split, plus some
>> modifier/method shuffling.
>>
>> JDK 9 patch contains a fair amount of formatting/modifier changes as
>> well, so I suggest to copy A*FU classes from jdk9, picking all the minor
>> changes, except for the Unsafe switch -- this would simplify future
>> backports as well:
>>    http://cr.openjdk.java.net/~shade/8140587/webrev.jdk8u-a.01/
>>
>> Alternatively, we can backport the change separately:
>>    http://cr.openjdk.java.net/~shade/8140587/webrev.jdk8u-b.01/
>>
>> With both options, jdk8u builds and runs fine at least on Linux x86_64,
>> and the performance improvement is the same as in JDK 9.
>>
>> Thanks,
>> -Aleksey
>>
>>