RFR: Restore string table rehashing task in cleanup tasks

[Aleksey Shipilev]

On 06/14/2018 02:00 PM, Zhengyu Gu wrote:
> I wrongly removed string table rehashing task from safeppont cleanup phase, thought it should be
> performed concurrently.
> 
> I believe that StringInternCleanup test failure is due to upstream bug - I filed JDK-8205006
> (https://bugs.openjdk.java.net/browse/JDK-8205006) and temporary disable the test till the bug is
> fixed.
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/restore_stringtable_rehashing/webrev.00/

I think ignoring the test masks the issue. Can we keep the test around, but disable rehashing with
UseShenandoahGC? E.g.:

 // Workaround upstream bug in StringTable rehashing, see JDK-8205006.
 if (StringTable::needs_rehashing() && !UseShenandoahGC) {

This way we have non-broken VM -- with performance hit, but still non-broken?

Thanks,
-Aleksey