RFR 8227104: Shenandoah: Implementation of ShenandoahReentrantLock

[Roman Kennke]

Why would we want to backport the ShenandoahReentrantLock if it has no
uses? Or will we have uses that we intend to backport? Not quite sure
here why we would want to push any code that's not currently used, and
not push the code plus its usage instead.

Roman


> This is a prerequisite for concurrent nmethod unloading [1]. Currently,
> it has no users, but will be embedded into ShenandoahNMethod.
> 
> I separate the two changes, in case we may want to backport
> ShenandoahNMethod changes.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8227104
> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8227104/webrev.00/
> 
> Test:
>   fastdebug and release builds.
> 
> Thanks,
> 
> -Zhengyu
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8227102