RFR 8047737 Move array component mirror to instance of java/lang/Class

[Peter Levart]

On 07/02/2014 02:22 PM, Peter Levart wrote:
> On 07/02/2014 08:26 AM, Mandy Chung wrote:
>>
>> On 6/30/2014 9:51 PM, Christian Thalinger wrote:
>>> On Jun 30, 2014, at 5:50 PM, Coleen Phillimore 
>>> <coleen.phillimore at oracle.com> wrote:
>>>
>>>
>>> On 6/30/14, 3:50 PM, Christian Thalinger wrote:
>>>>>       private Class(ClassLoader loader) {
>>>>>           // Initialize final field for classLoader.  The 
>>>>> initialization value of non-null
>>>>>           // prevents future JIT optimizations from assuming this 
>>>>> final field is null.
>>>>>           classLoader = loader;
>>>>> +        componentType = null;
>>>>>       }
>>>>>
>>>>> Are we worried about the same optimization?
>>>> Hi,  I've decided to make them consistent and add another parameter 
>>>> to the Class constructor.
>>>>
>>>> http://cr.openjdk.java.net/~coleenp/8047737_jdk_2/
>>
>> The jdk change looks okay while I am beginning to think whether we 
>> really want to keep expanding this constructor to deal with this 
>> future JIT optimization (you will be moving more fields out from the 
>> VM to java.lang.Class).
>>
>> There are places in JDK initializing the final fields to null while 
>> the final field value is overridden via native/VM - e.g. System.in, 
>> System.out, etc.  I would prefer reverting the classLoader 
>> constructor change to expanding the constructor for any new field 
>> being added.  Handle it (and other places in JDK) when such JIT 
>> optimization comes.
>>
>> Mandy
>>
>
> What about:
>
>
>     private Class() {
>         classLoader = none();
>         componentType = none();
>         ...
>     }
>
>     private <T> T none() { throw new Error(); }
>
>
> I think this should be resistant to future optimizations.

And you could even remove the special-casing in 
AccessibleObject.setAccessible0() then.

Regards, Peter

>
> Regards, Peter
>