RFR: 8210061: ZGC: Remove STW weak processor mode

[Per Liden]

Hi,

On 08/28/2018 11:58 AM, Erik Österlund wrote:
> Hi,
> 
> ZGC has multiple modes for processing weaks. ZWeakRoots allows treating 
> weaks as strong, and in addition to that, ZConcurrentStringTable, 
> ZConcurrentVMWeakHandles and ZConcurrentJNIWeakGlobalHandles allow 
> certain subsets of weak roots to be processed concurrently or in a 
> pause. Except there is no obvious reason why you would ever opt out of 
> doing it concurrently. So I propose to remove this functionality.
> Part of the motivation is that a concurrent strong root processor is on 
> its way, and all these modes nobody uses leads to pointless complexity.
> 
> Webrev:
> http://cr.openjdk.java.net/~eosterlund/8210061/webrev.00/

Looks good. One thing though, you also want to remove the following stat 
phases, as they are no longer used:

ZSubPhasePauseWeakRootsVMWeakHandles
ZSubPhasePauseWeakRootsJNIWeakHandles
ZSubPhasePauseWeakRootsStringTable

I don't need to see a new webrev.

cheers,
Per

> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8210061
> 
> Thanks,
> /Erik