RFR: Added logging for the number of workers used for GC cycles

[Aleksey Shipilev]

On 06/11/2018 05:35 PM, Zhengyu Gu wrote:
> Added logging for the number of workers used for GC cycles.
> 
> Also fixed a few of calls for calculating concurrent workers to use right AdaptiveSizePolicy API.
> However, this is just for correctness, there is not fundamental difference, since Shenandoah always
> setup parallel # = conc # (when parallel # > 1), and AdaptiveSizePolicy basically uses the same
> algorithm to calculate parallel # and conc #.
> 
> We should also look into to tune the sizing settings/algorithm, it looks to me that heap capacity
> factor can easily dominate result. By default, it uses 1 worker for 32M heap space, which only takes
> 256M heap space to max out 8 parallel/concurrent workers. Given the heap size that Shenandoah is
> targeting, it is almost always going to max out parallel/conc workers.
> 
> 
> http://cr.openjdk.java.net/~zgu/shenandoah/calc_conc_workers/webrev/

Can't we put the loggers into ShenandoahWorkerScope constructor itself? I don't think we need "for
XXX" messages all that much, because we can relate that with the other log lines, this simplifies
the whole thing.

Otherwise looks OK.

-Aleksey