ZGC: Check that all ZWorkers are initialized during startup

[Per Liden]

Looks good!

/Per

On 06/05/2018 12:27 PM, Stefan Karlsson wrote:
> Hi all,
> 
> Please review this patch to check that all ZWorkers have been properly 
> initialized during startup, and otherwise shutdown the VM.
> 
> http://cr.openjdk.java.net/~stefank/zgc/zPreInitializeZWorker/
> 
> Without this patch ZGC will hang if the diagnostic 
> -XX:+InjectGCWorkerCreationFailure flag is used. It would also be 
> problematic with, for example, ZMarkTerminate, if we didn't get all 
> workers to start.
> 
> Thanks,
> StefanK