RFR(S): 8194741: Refactor oops in constant pool from CDS to use the Access API

Erik Österlund erik.osterlund at oracle.com
Wed Jan 10 15:38:16 UTC 2018

Hi Coleen,

Thank you for the review. I did consider reusing IN_CONCURRENT_ROOT, but 
thought I'd rather make an explicit one for the archive. The reason is 
that all other concurrent roots are all visited either during a 
safepoint or during concurrent scanning. But these archive roots are 
never scanned by the GC, giving it slightly different semantics that I 
would prefer not to mix.


On 2018-01-10 15:49, coleen.phillimore at oracle.com wrote:
> This looks fine.  I don't see why you couldn't use IN_CONCURRENT_ROOT 
> for them, like the others though.  I like where the barrier ended up 
> though.
> thanks,
> Coleen
> On 1/10/18 9:29 AM, Erik Österlund wrote:
>> Hi,
>> The constant pool may install resolved_references from CDS archives. 
>> This installation might happen during concurrent marking. Therefore, 
>> a new previously known graph is mounted onto the existing Java heap 
>> object graph. Naturally, this makes SATB invariants confused and 
>> therefore requires explicit enqueuing.
>> This patch hooks this into the Access API. While there are different 
>> ways that this could be annotated, I chose to introduce a new 
>> decorator called IN_ARCHIVE_ROOT, which similar to IN_CONCURRENT_ROOT 
>> denotes a kind of special root that needs to be handled differently. 
>> In the G1 case, it results in a SATB enqueue when it is loaded. This 
>> approach made me scratch my head less than various other ideas I had.
>> Webrev:
>> http://cr.openjdk.java.net/~eosterlund/8194741/webrev.00/
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8194741
>> /Erik

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