RFR: 8080869: FlexibleWorkGang initializes _active_workers to more than _total_workers

[Stefan Karlsson]

Hi all,

Please, review this small patch to fix the initialization of 
FlexibleWorkGang::_active_workers.

http://cr.openjdk.java.net/~stefank/8080869/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8080869

 From the bug report:
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This is the FlexibleWorkGang constructor:

   FlexibleWorkGang(const char* name, uint workers,
                    bool are_GC_task_threads,
                    bool  are_ConcurrentGC_threads) :
     WorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads),
     _active_workers(UseDynamicNumberOfGCThreads ? 1U : 
ParallelGCThreads) {}

and the WorkGang constructor:

WorkGang::WorkGang(const char* name,
                    uint        workers,
                    bool        are_GC_task_threads,
                    bool        are_ConcurrentGC_threads) :
   AbstractWorkGang(name, are_GC_task_threads, are_ConcurrentGC_threads) {
   _total_workers = workers;
}

If 'workers' are less than ParallelGCThreads, then _active_workers will 
be set to a value that is greater than _total_workers (unless we run 
with UseDynamicNumberOfGCThreads). Both G1 and CMS typically sets the 
number of concurrent workers to a value below ParallelGCThreads.

This is currently a benign bug, since the GCs will later calculate a new 
value for _active_workers that will never be higher than _total_workers.

However, this bug impedes stricter asserts and should be fixed.
--------------------------------------------------------------------------------

Thanks,
StefanK