RFR (S) 8250589: Move Universe::_reference_pending_list into OopHandle

[coleen.phillimore at oracle.com]

On 7/27/20 9:24 AM, David Holmes wrote:
> Hi Coleen,
>
> On 27/07/2020 11:05 pm, coleen.phillimore at oracle.com wrote:
>> Summary: Use synchronization to reference the _reference_pending_list 
>> with OopHandle
>
> Why isn't ownership of the Heap_lock sufficient for the 
> synchronization any more?

Multiple GC threads synchronize on this value, when one holds the Heap_lock:

   // Reference pending list manipulation.  Access is protected by
   // Heap_lock.  The getter, setter and predicate require the caller
   // owns the lock.  Swap is used by parallel non-concurrent reference
   // processing threads, where some higher level controller owns
   // Heap_lock, so requires the lock is locked, but not necessarily by
   // the current thread.

The comment is in the header file, explaining this.

Thanks,
Coleen

>
> Thanks,
> David
>
> (and apologies as I'm done for the day so won't see your response till 
> morning.)
>
>> Tested with tier1-6 with 100% passed (no other existing test failures!)
>>
>> open webrev at 
>> http://cr.openjdk.java.net/~coleenp/2020/8250589.01/webrev
>> bug link https://bugs.openjdk.java.net/browse/JDK-8250589
>>
>> Thanks,
>> Coleen