RFR (XS) 8223570: Shenandoah needs to acquire lock before CLDG::clear_claimed_marks

[Thomas Schatzl]

Hi,

On Wed, 2019-05-08 at 13:39 +0200, Aleksey Shipilev wrote:
> Bug:
>   https://bugs.openjdk.java.net/browse/JDK-8223570
> 
> New assert fails and exposes this legit GC bug. Shenandoah does
> CLDG::clear_claimed_marks in two places, one under the safepoint
> (which is fine for that assert), and another one in concurrent
> thread, which fails.
> 
> Fix:
> [...]

  fix looks good.

Sorry for not thinking about Shenandoah too when reviewing the G1 fix.

Thanks,
  Thomas