RFR: 8319376: ParallelGC: Forwarded objects found during heap inspection [v4]

[Albert Mingkun Yang]

On Tue, 7 Nov 2023 14:31:49 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> See JBS issue for details.
>> 
>> Testing:
>>  - [x] gc/logging/TestUnifiedLoggingSwitchStress.java -XX:+UseParallelGC
>>  - [x] tier1 -XX:+UseParallelGC
>>  - [ ] tier2 -XX:+UseParallelGC
>>  - [ ] hotspot_gc
>
> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Don't expose forwarded objects during object iteration

src/hotspot/share/gc/parallel/mutableSpace.cpp line 239:

> 237:   while (p < top()) {
> 238:     oop obj = cast_to_oop(p);
> 239:     if (!obj->is_forwarded()) {

Maybe some comment along these lines "When promotion-failure occurs during Young GC, eden/from space is not cleared, so we can encounter objs with "forwarded" markword. They are essentially dead, so skipping them."

src/hotspot/share/gc/parallel/mutableSpace.cpp line 242:

> 240:       cl->do_object(cast_to_oop(p));
> 241:     }
> 242:     p += cast_to_oop(p)->size();

One can use `obj` instead of `cast_to_oop`.

src/hotspot/share/memory/heapInspection.cpp line 216:

> 214: // of running out of space required to create a new entry.
> 215: bool KlassInfoTable::record_instance(const oop obj) {
> 216:   assert(!obj->is_forwarded(), "must not be forwarded");

It'd be good if someone more familiar with this method/class can comment whether this assert makes sense in this context.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16494#discussion_r1385018851
PR Review Comment: https://git.openjdk.org/jdk/pull/16494#discussion_r1385014921
PR Review Comment: https://git.openjdk.org/jdk/pull/16494#discussion_r1385020892