Hi Sangheon,
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?
Thanks,
David
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/~stefank/8173013/reproducer/
<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.
Thanks,
Sangheon
