RFR: Remove ShFastSyncRoots

[Aleksey Shipilev]

On 09/26/2018 08:07 PM, Roman Kennke wrote:
> We have a fast synchronizer roots iterator, but it's not really used. It
> used to be useful when we did not have thread-local MonitorInUseLists
> and needed to scan one global list efficiently, but MonitorInUseLists
> provides much more natural parallelization via thread stacks. Also,
> MonitorInUseLists is deprecated and I see no point why anybody would
> disable it. Let's remove the extra cruft:
> 
> http://cr.openjdk.java.net/~rkennke/remove-fast-syncroots/webrev.00/

*) I don't understand the removal of upstream code in src/hotspot/share/runtime/synchronizer.cpp:
ObjectSynchronizer::verifyInUse, block in ::InduceScavenge, etc. We only have
ParallelObjectSynchronizerIterator added:

https://builds.shipilev.net/patch-openjdk-shenandoah-jdk/v99-vs-15094d12a632/src/hotspot/share/runtime/synchronizer.cpp.sdiff.html

Otherwise looks good.

-Aleksey