RFR (S) 8009575 (2nd) - Reduce Symbol::_refcount from 4 bytes to 2 bytes

[Ioi Lam]

Hi,

Could anyone review this? Coleen has already reviewed it off-list, so I 
just need one more reviewer.

Thanks
- Ioi

On 06/20/2013 11:20 AM, Ioi Lam wrote:
> Please review my 2nd trial for this bug fix. It's much simplified thanks
> to Coleen's suggestion.
>
> http://cr.openjdk.java.net/~iklam/8009575/symbol_refcount_002/
>
> Bug: Reduce Symbol::_refcount from 4 bytes to 2 bytes
>
> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8009575
>     https://jbs.oracle.com/bugs/browse/JDK-8009575
>
> Summary of fix:
>
>     As noted in the bug report, the main problem is _refcount needs to be
>     atomically incremented, but the smallest unit that Atomic::incr() had
>     supported until now was 32-bit int.
>
>     With Coleen's help, I have created a platform-independent version
>     of Atomic::incr(short*) that's based on Atomic::add(int*, n).
>
>     Essentially, Atomic::incr(short*) can be implemented as
>     Atomic::add(int*, 0x10000), as long as the short occupies the most
>     significant 16 bits of the int. I added the macro ATOMIC_SHORT_PAIR
>     to ensure the proper alignment.
>
>     Also Symbol::size(int) is fixed to calculate the correct space needed
>     for a Symbol. (Same as in the previos webrev --
>     see 
> http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2013-March/006385.html)
>
> Tests:
>
>     JPRT
>     UTE:
>        - vm.tmtools.testlist nsk.sajdi.testlist vm.runtime.testlist
>          vm.quick.testlist vm.parallel_class_loading.testlist
>        - Serviceability Agent tested are included in these lists.
>     MedRec
>
> Thanks
> - Ioi
>