RFR(S): 7120038: G1: ParallelGCThreads==0 is broken

John Cuthbertson john.cuthbertson at oracle.com
Thu Dec 15 18:21:22 UTC 2011

Hi Everyone,

I have a new webrev of these changes based upon feedback from Tony 
Printezis and Jon Masamitsu. It can be found at: 

Changes in this version include:
* Fixed a change in ConcurrentMark::calc_parallel_marking_threads() that 
effectively disabled using a dynamic number of threads.
* Modified the cleaning of the card table (at the end of an evacuation 
pause) to use the current number of active worker threads.

Testing: GC test suite.



On 12/13/11 10:54, John Cuthbertson wrote:
> Hi Everyone,
> While testing the changes for 7119908 I discovered that running G1 
> with ParallelGCThreads=0 is broken. Can I have a couple of volunteers 
> look over the changes fix the issues I discovered? The webrev can be 
> found at: http://cr.openjdk.java.net/~johnc/7120038/webrev.0/.
> Most of the changes are correcting unguarded references to the work 
> gang (which is not created when PGCT==0) and a few assertion failures.
> Note: we do have an open RFE to remove code specific to PGCT==0 as it 
> is not a typical configuration, but until then...
> Testing: GC test suite with/without -XX:ParallelGCThreads=0, 
> Kitchensink, jprt.
> Thanks,
> JohnC

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