RFR(XXS) 8222188: Shenandoah: Adjust Shenandoah work gang types

[Aleksey Shipilev]

On 4/9/19 4:13 PM, Zhengyu Gu wrote:
> This is a cleanup in preparation for concurrent class unloading.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8222188
> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8222188/webrev.00/index.html

OK. Changing _safepoint_workers to be GC_Task_threads does not violate correctness?

Nits:

 *) Changeset synopsis is odd?
   "1. cleanup for concurrent class unloading"

 *) Whitespace missing after "*/" at L453 here:

 452   _workers = new ShenandoahWorkGang("Shenandoah GC Threads", _max_workers,
 453                             /* are_GC_task_threads */true,
 454                             /* are_ConcurrentGC_threads */ true);

 *) Better indenting maybe, like this?

   assert(!Thread::current()->is_Worker_thread() &&
              (Thread::current()->is_VM_thread() ||
               Thread::current()->is_ConcurrentGC_thread())

Thanks,
-Aleksey