Static fields in specialized classes

Remi Forax forax at univ-mlv.fr
Wed Oct 15 11:14:05 UTC 2014


On 10/15/2014 12:22 PM, Paul Sandoz wrote:
> On Oct 14, 2014, at 11:45 PM, Brian Goetz <brian.goetz at Oracle.COM> wrote:
>
>>> - care might need to be taken with class initlization, static access
>>> should trigger initialisation before that access occurs but does this
>>> mean both Foo and Foo<int> should be initialized if access occurs
>>> from the latter? (not sure if you already have this aspect covered)
>> I think we have this one covered.  The compiler and specializer cooperate to have this effect.
>>
>> - All declarations of static members (fields and methods, including <clinit>) are stripped out during specialization.  So the static members exist only on the template (base) class.
>>
>> - All references to static members (whether through classes or through instances) are rewritten to directly reference the template class.
>>
>> - Specialized classes acquire a <clinit> that does "LDC template.class", idempotently forcing the template class to be initialized if it is not already.
>>
> I am not sure an LDC is sufficient to guarantee initialization of the template class. See example program below.

No, it doesn't.
LDC do load the class but the VM is not required to trigger the class 
initialisation.

>
> It may be necessary to invoke UNSAFE.ensureClassInitialized after the LDC of the class.
>
> If thats the case we could stuff a global UNSAFE instance in the constant pool when anonymously defining the class (much like direct method handles to fields).

or to call an empty static method generated on purpose by javac.

>
> Paul.

Rémi



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