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

[Yumin Qi]

Ioi,

   As Dan indicates, Symbol now is derivative from SymbolBase, so it 
should be reflected in SA code --- more changes needed.
   The name split is for calculation of size? The only difference is
    jbyte _body[1];

    now it is in Symbol, not in SymbolBase.

    Originally,
    size = sizeof(Symbol)  include sizeof(jbyte) which should be 
excluded if the symbol length > sizeof(jbyte).
    So the should calculation  if no change to Symbol inheritance be:

   size_t sz = heap_word_size(sizeof(Symbol) + (length > sizeof(jbyte) ? length - sizeof(jbyte) : 0));

   Thanks
   Yumin

On 6/21/2013 10:15 AM, Ioi Lam wrote:
> 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_

>> _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
>>
>

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