Final RFR: 8005232 (JEP-149) Class Instance size reduction

David Holmes david.holmes at
Mon Jan 14 01:04:27 UTC 2013

Thanks everyone, this work has now been committed:

author	dholmes
	Sun Jan 13 19:57:06 2013 -0500 (5 minutes ago)
changeset 6357	1109bfff4e92
parent 6356	7db04ae3378f
8005232: (JEP-149) Class Instance size reduction
Summary: Moved the fields for cached reflection objects into a seperate 
ReflectionData object to reduce dynamic footprint.
Reviewed-by: dholmes, mchung, shade
Contributed-by: Peter Levart <peter.levart at>


On 10/01/2013 4:59 PM, David Holmes wrote:
> Hi Mandy,
> Thanks for the review.
> On 10/01/2013 11:25 AM, Mandy Chung wrote:
>> On 1/6/2013 2:46 PM, David Holmes wrote:
>> This looks good to me. David - besides the footprint performance data,
>> do you observe any performance difference in your performance testing
>> (I think refworkload is what you ran)?
> I added the performance numbers to the bug report:
> No observable performance differences with refworkload.
>> On 01/09/2013 01:19 PM, Aleksey Shipilev wrote:
>>> On 01/09/2013 05:04 PM, Peter Levart wrote:
>>>> Strictly speaking, CAS is actually not needed here. Since we keep
>>>> classRedefinedCount snapshot inside the ReflectionData, any races that
>>>> would install "older" ReflectionData over "newer", would be quickly
>>>> caught at next invocation to reflectionData(). So if there are any
>>>> objections to usage of Unsafe, it can be removed and replaced by simple
>>>> volatile write.
>>> Yes, I think that would be more clear without any adverse impacts on
>>> performance. Also, that better expresses the intent of requiring the
>>> visibility, not the atomicity of cache update.
>> I agree with Alekesey that it'd be simpler and clearer if CAS is replaced
>> with the simple volatile write. But this change will require another
>> round
>> of performance measurement to determine its impact. I'd suggest to follow
>> up this cleanup in a separate bug and changeset.
> I'm not sure about the validity of changing from CAS to a simpe write -
> would need to think more deeply on it. But I agree with Mandy that the
> performance impact would need to be investigated. In the normal case it
> would be faster with no CAS but if there were "collisions" that might
> change. Anyway something to consider for a follow-up.
> Thanks again,
> David
>> Mandy

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