RFR: JDK-8212186: JVMTI lacks a few GC barriers/hooks (original) (raw)

Per Liden per.liden at oracle.com
Thu Oct 18 07:13:44 UTC 2018

On 10/17/2018 07:10 PM, Roman Kennke wrote:

Hi Roman,

Looks fantastic. Thanks! BTW, out of curiosity, how do you do the heap walk - scanning or tracing? Tracing. Scanning would require to carry around complete marking info (to be able to avoid holes of dead objects with recycled Klass*), which we don't.

So that makes me wonder why you needed JDK-8211955 (GC abstraction for LAB reserve) and why you insert filler objects at all? Am I missing something?

cheers, Per

Roman

Thanks, /Erik

On 17 Oct 2018, at 11:48, Roman Kennke <rkennke at redhat.com> wrote:

Erik recently pointed out that JvmtiTagHashmapEntry::equals() is lacking on obj-equals-barrier, and that JvmtiTagHashmap::hash() better does ::resolve() the object to a stable value before casting it to a raw address. This lead us to do some more JVMTI testing and we found that we have a little inconsistency with reporting object size too: the VMObjectAlloc callback now reports a different size that GetObjectSize(). This is also fixed by this proposed change: Bug: https://bugs.openjdk.java.net/browse/JDK-8212186 Webrev: http://cr.openjdk.java.net/~rkennke/JDK-8212186/webrev.00/ Testing: hotspot/tier1, nsk/jvmti with Shenandoah Ok? Roman

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