RFR: Make object pinning safepoint aware

[Zhengyu Gu]

>>
>>
> Ok, this is strange indeed. The write barrier should ensure we get no 
> cset objects in pinning. The only logical explanation is that evac 
> failed because of OOM (you should see than in hs_err: it will tell you 
> if we are in cancelled state). However, we must still pin the 
> object/region. I guess we must ensure we wait in oom_during_evacuation() 
> until all GC threads settled (we probably do the right thing already), 
> and then carry on pinning the cset object (i.e. we need an exception in 
> the checking code for when evac has been cancelled). Then we'd slide 
> into full-gc where we would handle pinning correctly (unless the region 
> isn't pinned anymore when we get there).

Here this the complete hs_err: 
http://cr.openjdk.java.net/~zgu/shenandoah/obj_pin_safepoint/hs_err_pid17356.log

-Zhengyu

> 
> Roman