RFR(S): 8173013: JVMTI tagged object access needs G1 pre-barrier
david.holmes at oracle.com
Fri Feb 3 01:20:14 UTC 2017
On 3/02/2017 5:11 AM, sangheon wrote:
> Hi all,
> Could I have some reviews for this change that adds G1 pre-barrier?
> JvmtiTagHashmapEntry has a bare oop member and this is a weak reference.
> So any place that allows this oop to 'escape' needs the G1 pre-barrier.
> JvmtiEnv::GetObjectsWithTags() provides such an escape path.
> For G1, in order to maintain the SATB invariants, reading the referent
> of a weak reference must ensure the referent is marked alive.
> So this proposal includes adding the pre-barrier at
> TagObjectCollector::do_entry(JvmtiTagHashmapEntry* entry) which I see
> the only place interacts(except 'peek' operations) with the bare oop member.
Pardon my GC ignorance but it seems odd to me that this barrier is
inserted immediately before we create a local JNIHandle. Won't the
JNIHandle ensure the object is seen as live?
> As writing stable test could take some more time, Stefan Karlsson and I
> did some tests to provoke this problem.
> ( Stefan Karlsson kindly provided the test,
> <http://cr.openjdk.java.net/%7Estefank/8173013/reproducer/> )
> With this proposed patch, the problem goes away.
> CR: https://bugs.openjdk.java.net/browse/JDK-8173013
> Webrev: http://cr.openjdk.java.net/~sangheki/8173013/webrev.0
> Testing: JPRT, some closed tests which use JVMTI and JDI.
More information about the hotspot-gc-dev