RFR(S): 7099824: G1: we should take the pending list lock before doing the remark pause

[Ramki Ramakrishna]

Hi John, I don't think it would make any performance (latency) 
difference (given how
the reference handler thread takes the lock today). It just seemed
unnecessary, that's all.... OK to take it for all CGC ops, if it helps
keep the code from being messy... your subjective choice (anyone
else have an opinion on code maintainability/robustness here because
of the extra option/attribute in the CGC op c'tor?)

-- ramki

On 10/19/2011 5:09 PM, John Cuthbertson wrote:
> Hi Ramki,
>
> Thanks for the review. Do you think that waiting for the pending list 
> lock will significantly delay cleanups? If so then adding an extra 
> "needs_pll" flag to VM_CGC_Operation is an easy change.
>
> Thanks,
>
> JohnC
>
> On 10/19/11 16:50, Ramki Ramakrishna wrote:
>> Hi John -- This looks good to me, although I didn't see any obvious 
>> reason to make clean up pauses take the
>> PLL lock given they do not mess with the pending list in any manner. 
>> Otherwise looks good to me.
>>
>> -- ramki
>>
>> On 10/17/2011 2:36 PM, John Cuthbertson wrote:
>>> Hi Everyone,
>>>
>>> Can I have a couple of volunteers review these changes? The webrev 
>>> can be found at: http://cr.openjdk.java.net/~johnc/7099824/wevrev.0/
>>>
>>> Summary: During a G1 remark pause, the JVM may enqueue some 
>>> discovered references on to the pending list. Whenever the JVM 
>>> modifies the pending list, it is supposed to synchronize with the 
>>> ReferenceHandler thread and acquire the pending list lock but G1's 
>>> concurrent GC operations were not doing so.
>>>
>>> Testing: the GC test suite with both CMS and G1, and jprt.
>>>
>>> Thanks,
>>>
>>> JohnC
>