RFR: 8215097: Do not create NonJavaThreads before BarrierSet

[Per Liden]

Hi Kim,

On 12/10/18 10:47 PM, Kim Barrett wrote:
[...]
>> But I should also add that ZGC registers its barrier set in the constructor too, before workers are created, so I don't think Kim's patch will cause any problems really. Other collectors typically registers their barrier set in initialize(), which I guess is the root of the bootstrapping issue.
> 
> As noted in the CR, ZGC already does the BarrierSet and thread
> creation in the desired order.  (Observed both by inspection and
> testing.) It was pretty obvious in ZGCs case; the relevant code is
> much nicer than for some of the other GCs.
> 

Ah, sorry, I didn't read the CR before replying. I now see that you had 
checked that ZGC wasn't a problem. So, no objections from me. Thanks!

cheers,
Per