RFR(XS): 8005875: G1: Kitchensink fails with ParallelGCThreads=0

John Cuthbertson john.cuthbertson at oracle.com
Thu Jan 10 00:41:23 UTC 2013

Hi Vitaly,

Thanks for looking over the changes. AFAICT checking if 
_parallel_workers is not null is equivalent to checking that the number 
of parallel marking threads is > 0. I went with the latter check as 
other references to the parallel workers work gang are guarded by it. 
I'm not sure why the code was originally written that way but my guess 
is that, when originally written, the marking threads (like the 
concurrent refinement threads currently) were not in a work gang.



On 1/8/2013 8:37 PM, Vitaly Davidovich wrote:
> Hi John,
> What's the advantage of checking parallel marking thread count > 0 
> rather than checking if parallel workers is not NULL? Is it clearer 
> that way? I'm thinking checking for NULL here (perhaps with a comment 
> on when NULL can happen) may be a bit more robust in case it can be 
> null for some other reason, even if parallel marking thread count is > 0.
> Looks good though.
> Thanks
> Sent from my phone
> On Jan 8, 2013 5:14 PM, "John Cuthbertson" 
> <john.cuthbertson at oracle.com <mailto:john.cuthbertson at oracle.com>> wrote:
>     Hi Everyone,
>     Can I please have a couple of volunteers look over the fix for
>     this CR - the webrev can be found at:
>     http://cr.openjdk.java.net/~johnc/8005875/webrev.0/
>     <http://cr.openjdk.java.net/%7Ejohnc/8005875/webrev.0/>
>     Summary:
>     One of the modules in the Kitchensink test generates a
>     VM_PrintThreads vm operation. The JVM crashes when it tries to
>     print out G1's concurrent marking worker threads when
>     ParallelGCThreads=0 because the work gang has not been created.
>     The fix is to add the same check that's used elsewhere in G1's
>     concurrent marking.
>     Testing:
>     Kitchensink with ParallelGCThreads=0
>     Thanks,
>     JohnC

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