RFR: 8194312: Support parallel and concurrent JNI global handle processing

[Kim Barrett]

> On Jan 8, 2018, at 10:57 PM, serguei.spitsyn at oracle.com wrote:
> Also, this fragment looks strange:
> 
> 354   if (block->is_empty()) {
> 355     log_debug(oopstorage, blocks)("%s: block not empty " PTR_FORMAT, name(), p2i(block));
> 356     --_empty_block_count;
> 357   }
> 
> 
> Should the message tell "block is empty" instead of "block not empty”?

This is logging the transition from empty to non-empty.

I could introduce a bool was_empty flag at line 354 to capture the is_empty state before the allocation,
and then log the transition and update the counter after the allocation, if was_empty is true.  The current
code order is just to remove the need for that extra boolean flag.