Hi Ioi,
On 6/09/2019 12:27 pm, Ioi Lam wrote:
https://bugs.openjdk.java.net/browse/JDK-8230674
http://cr.openjdk.java.net/~iklam/jdk14/8230674-heap-dump-exclude-dormant-oops.v01
Please review this small fix:
When CDS is in use, archived objects are memory-mapped into the heap
(currently G1GC only). These objects are partitioned into
"subgraphs". Some of these subgraphs may not be loaded (e.g., those
related to jdk.internal.math.FDBigInteger) at the time a heap dump is
requested. >
When a subgraph is not loaded, some of the objects in this subgraph may
belong to a class that's not yet loaded.
The bug happens when such an "dormant" object is dumped, but its class
is not dumped because the class is not in the system dictionary.
There is already code in DumperSupport::dump_instance() that tries to
handle dormant objects, but it needs to be extended to cover arrays, as well as
and references from non-dormant object/arrays to dormant ones.
I have to confess I did not pay any attention to the CDS archived
objects work, so I don't have a firm grasp of how you have implemented
things. But I'm wondering how can you have a reference to a dormant
object from a non-dormant one? Shouldn't the act of becoming non-dormant
automatically cause the subgraph from that object to also become
non-dormant? Or do you have "read barriers" to perform the changes on
demand?
That aside the code changes seem reasonable, you moved the check out of
DumperSupport::dump_instance and into the higher-level
HeapObjectDumper::do_object so that it catches instances and arrays,
plus you added a check for array elements.
Thanks,
David
Thanks
- Ioi
