RFR: 8210045: Allow using a subset of worker threads even when UseDynamicNumberOfGCThreads is false

[Erik Österlund]

Hi Per,

Looks good.

Thanks,
/Erik

On 2018-08-28 09:06, Per Liden wrote:
> When UseDynamicNumberOfGCThreads is not set, AbstractWorkGang requires 
> all worker threads to be used when starting a task. For example, 
> calling update_active_workers(5) on a WorkGang with 10 worker threads 
> results in an failed assert. ZGC does not dynamically re-calculate the 
> number of workers to use each GC cycle (except for the boost-mode), in 
> the way that UseDynamicNumberOfGCThreads suggests. However, it shares 
> a single WorkGang for both STW and concurrent phases, where the 
> concurrent phases typically want to use fewer workers than the STW 
> phases. Today, ZGC is forced to set UseDynamicNumberOfGCThreads to 
> true to avoid the assert in update_active_workers(). I propose that we 
> remove this assert, making AbstractWorkGang slightly more flexible on 
> this point.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8210045
> Webrev: http://cr.openjdk.java.net/~pliden/8210045/webrev.0
>
> /Per