RFR 8173083: VarHandle usages in LockSupport and ThreadLocalRandom result in circularity issues

[Martin Buchholz]

On Fri, Jan 20, 2017 at 7:58 AM, Paul Sandoz <paul.sandoz at oracle.com> wrote:

>
> I was surprised to see below a change in parentheses that seems to change
> the behavior.
>
>      final long nextSeed() {
>          Thread t; long r; // read and update per-thread seed
> -        SEED.set(t = Thread.currentThread(),
> -                 (r = (long) SEED.get(t)) + GAMMA);
> +        U.putLong(t = Thread.currentThread(), SEED,
> +                  r = U.getLong(t, SEED) + GAMMA);
>          return r;
>      }
>
>
> The update reverted to the previous code:
>
> http://hg.openjdk.java.net/jdk9/dev/jdk/file/7901a13a051c/src/java.base/
> share/classes/java/util/concurrent/ThreadLocalRandom.java
>
> I added the parentheses to bound the cast.
>

It still looks to me like the parenthesis got added to the wrong place (in
the previous changeset!), changing the behavior, and the current reverted
code is correct.