RFR (S) 8218151: Simplify JavaThread::thread_state definition

[Kim Barrett]

> On Jan 31, 2019, at 4:13 PM, Aleksey Shipilev <shade at redhat.com> wrote:
> 
> RFE:
>  https://bugs.openjdk.java.net/browse/JDK-8218151
> 
> Fix:
>  http://cr.openjdk.java.net/~shade/8218151/webrev.01/
> 
> The difference in definitions in JavaThread::thread_state in AArch64 and PPC64 is the source of
> frequent build failures when someone tests only x86_64, see the linked issues for a taste. The way
> out of this is to push the #if-s inside the method body, so that definition is always in one place,
> and would not accidentally break the build.
> 
> Testing: Linux {x86_64, x86_32, aarch64, arm32, ppc64el, s390x} builds, Mac OS X {x86_64} build,
> Windows {x86_64} build, jdk-submit (failed windows test and macos build, but I suspect there are
> infra problems, will wait and re-run; see for example mach5-one-shade-JDK-8218151-20190131-1631-233989).
> 
> Thanks,
> -Aleksey

So why are the definitions different, using OrderAccess for PPC64 and
AARCH64, but not for other platforms?  Why not unconditionally use
OrderAccess?  If that's needed for some weakly ordered architectures,
seems like it should be needed for all.  And for TSO the OrderAccess
operations shouldn't introduce any additional overhead.