RFR: 8210889: Some service thread cleanups can be starved

[Per Liden]

Nice! Looks good.

/Per

On 09/19/2018 02:46 AM, Kim Barrett wrote:
> Please review this small change to the ServiceThread.  When checking
> for work to be done, rather than immediately doing the first kind of
> work found, instead determine all pending work and then do all known
> pending work.  This avoids the possibility of frequently available
> work early in the sequence of checks from leading to starvation of
> work associated with later checks.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8210889
> 
> Webrev:
> http://cr.openjdk.java.net/~kbarrett/8210889/open.00/
> 
> Testing:
> mach5 tier1-3
>