RFR (S) 8225357: Rewire ShenandoahHeap::maybe_update_with_forwarded for contending fixups

Roman Kennke rkennke at redhat.com
Thu Jun 6 16:57:29 UTC 2019


Looks good, thanks.
Roman

Am 6. Juni 2019 18:41:43 MESZ schrieb Aleksey Shipilev <shade at redhat.com>:
>RFE:
>  https://bugs.openjdk.java.net/browse/JDK-8225357
>
>Currently the method can return NULL on the path where something else
>is contending over the write.
>In most current cases, that path works correctly, but not when
>something else (for example, inline
>fixup in barrier taken by Java thread) updates the references on their
>own.
>
>Then, the CAS might fail (as it should), and the GC code would think
>that thread is responsible to
>show the object to the marking code. This is risky and would lead to
>bugs. Instead, we would want to
>reply with the most actual reference at all times.
>
>Webrev:
>  http://cr.openjdk.java.net/~shade/8225357/webrev.01/
>
>Testing: hotspot_gc_shenandoah
>
>-- 
>Thanks,
>-Aleksey

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