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

[David Holmes]

On 28/07/2020 12:10 am, coleen.phillimore at oracle.com wrote:
> 
> 
> 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.

Sorry I completely fixated on the lock assertion and missed the fact the 
current code still does Atomic::xchg. The new code just internalises 
that in the OopHandle logic. (that will teach me to take too quick a 
look late at night)

Kim and Aleksey already pointed out the only things I was going to point 
out.

Looks good.

Thanks,
David

> 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
>