Request for approval: 8140483, Atomic*FieldUpdaters final fields should be trusted

[Aleksey Shipilev]

Hi,

There is a simple Hotspot compiler change that improves the
Atomic*FieldUpdater performance by a large margin, and 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.

Bug:
  https://bugs.openjdk.java.net/browse/JDK-8140483

Webrev:
  http://cr.openjdk.java.net/~shade/8140483/webrev.02/

JDK 9 Changeset:
  http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/0835ef4e6232

JDK 9 Review:

http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-October/019549.html

The change was in jdk9/hs-comp for two weeks now, and a few days in
jdk9/jdk9.

The patch applies automatically with a bit of the fuzz. jdk8u builds and
runs fine at least on Linux x86_64, the performance improvement is the
same as in JDK 9.

Thanks,
-Aleksey