RFR(s): 8204094: assert(worker_i < _length) failed: Worker 15 is greater than max: 11 at ReferenceProcessorPhaseTimes

[sangheon.kim at oracle.com]

Hi all,

Can I have reviews for this patch that fixes assertion failure at 
ReferenceProcessorPhaseTimes?

This failure only happens when ParallelRefProcEnabled option is set on 
CMS and Parallel GC.
The problem is that we are using more workers than we created a storage 
for workers.
When we create ReferenceProcessorPhaseTimes, we set how many workers 
will be monitored (i.e. prepare an array to save time information). And 
currently we are setting it with ReferenceProcessor queue 
size(ReferenceProcessor::_num_queues). But this is problematic because 
the queue size is continuously updated by 
ReferenceProcessor::set_active_mt_degree() with active workers every GC. 
And the queue size is decided later than ReferenceProcessorPhaseTimes is 
created. So if active workers repeats to increase/decrease, 
ReferenceProcessorPhaseTimes would have smaller than active workers.

This patch is proposing to use maximum queue when create 
ReferenceProcessorPhaseTimes.

CR: https://bugs.openjdk.java.net/browse/JDK-8204094
Webrev: http://cr.openjdk.java.net/~sangheki/8204094/webrev.0
Testing: hs-tier1-5 with/without ParallelRefProcEnabled

Thanks,
Sangheon
------------------------
For example:
1) Set 2 when create ReferenceProcessorPhaseTimes(xx, 2): 
ReferenceProcessor::num_queues() = 2, because previously we had only 2 
active workers.
2) Set 23 for ReferenceProcessor::set_active_mt_degree(23), current 
active workers are increased.
3) Assertion failure as we are using more workers than set from #1.