On 4/8/19 9:36 AM, Roman Kennke wrote: > On 4/7/19 7:18 PM, Roman Kennke wrote: >>> On 4/2/19 10:12 PM, Roman Kennke wrote: >>>>> - No more need for object equals barriers. >>>> >>>> I'm pleased about that. I really hated the AArch64 Shenandoah >>>> CAS! >>> >>> I'm sorry to disappoint you, but the CAS barrier is still needed. >>> The >>> memory location may still legally hold a from-space reference, and >>> comparing that to a to-space reference needs some special care. And >>> yes, ZGC has a similar problem as far as I know. >> >> That's interesting. Could we not simply promote the reference in the >> reference field we're CASing, then do a normal CAS? > > Yes. But it requires two CASes in a row. Don't know if that is better > than our loop, which is rarely even entered (normally the CAS-construct > goes via fast-path with a single CAS).
I think it's better, yes: it's significantly less complex to promote both if needed and then do a normal CAS. -- Andrew Haley Java Platform Lead Engineer Red Hat UK Ltd. <https://www.redhat.com> EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
