RFR: 8194406: Use Atomic::replace_if_null

[Kim Barrett]

> On Jan 3, 2018, at 9:16 AM, coleen.phillimore at oracle.com wrote:
> 
> Looks good.
> Coleen

Thanks.

> 
> On 1/2/18 11:02 PM, Kim Barrett wrote:
>> Please review this change to use Atomic::replace_if_null where
>> applicable.
>> 
>> CR:
>> https://bugs.openjdk.java.net/browse/JDK-8194406
>> 
>> Webrev:
>> http://cr.openjdk.java.net/~kbarrett/8194406/open.00/
>> 
>> Testing:
>> Mach5 hs-tier1,2,3