RFR(S): 8173013: JVMTI tagged object access needs G1 pre-barrier
sangheon.kim at oracle.com
Thu Feb 2 19:11:43 UTC 2017
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.
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,
With this proposed patch, the problem goes away.
Testing: JPRT, some closed tests which use JVMTI and JDI.
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