RFR: 8187042: Events to show which objects are associated with biased object revocations

[David Holmes]

Thanks robin, these updates seem fine to me.

David

On 14/10/2017 12:56 AM, Robin Westberg wrote:
> Hi again,
> 
> Here’s an updated version that adds a separate event for the 
> self-revocation path. It’s a new event class as it is a bit different 
> from the non-self-revocation path, it does not have any relevant 
> safepoint ID for example.
> 
> Webrev:
> http://cr.openjdk.java.net/~egahlin/8187042_2/
> 
>>>> Third, I would have expected to see more detail in the event such as 
>>>> which thread (id) the object was biased to and which thread revoked 
>>>> the bias. Even perhaps some notion of which instance was involved 
>>>> (though that's harder to shows).
>>> Right, I’ve been looking at capturing which thread the object was 
>>> biased towards, but I was afraid of the possible races there as the 
>>> thread pointer in the mark would have to be saved before executing 
>>> the VM operation. For that to work 100% reliably I suspect it would 
>>> have to be done inside the safepoint.
>>
>> Right the thread holding the bias may not even exist any more! This 
>> may need to utilise the new Thread-SMR work (as a future RFE of 
>> course). :)
> 
> Ah yeah, that may be an effective way of doing it. Another idea 
> suggested by Markus Grönlund was to capture the thread’s id inside the 
> operation and propagate it through an additional field in the VM 
> operation class. But anyway, I’ll file a separate RFE for investigating 
> that improvement.
> 
> Best regards,
> Robin
> 
>>> I will create an updated webrev after looking into adding an event 
>>> for the self-revocation path.
>>
>> Thanks,
>> David
>>
>>> Best regards,
>>> Robin
>