RFR: 8224660: Parallel GC: Use WorkGang (2: MarksFromRootsTask)

[Leo Korinth]

Hi,

Here is the second patch in a proposed patch series of eight that
removes gcTaskManager and uses the WorkGang abstraction instead. I will 
try to put these mails in the same mail thread.

This patch moves the  MarkFromRootsTask, ThreadRootsMarkingTask and
the StealMarkingTask (the last one we already moved in the last patch).
They are all called from the new MarkFromRootsTask.

The RootType enum as well as EnumClaimer, a class that can claim
enumeration values atomically is put in an inline header file. It will
be used in later patches outside psParallelCompact if you wonder about
the header file placement.

Enhancement:
   https://bugs.openjdk.java.net/browse/JDK-8224660

Webrev:
 
http://cr.openjdk.java.net/~lkorinth/workgang/0/_8224660-Parallel-GC-Use-WorkGang-2-MarksFromRootsTask/
   http://cr.openjdk.java.net/~lkorinth/workgang/0/all/

Testing (on the whole patch series):
   mach5 remote-build-and-test --build-profiles 
linux-x64,linux-x64-debug,macosx-x64,solaris-sparcv9,windows-x64 --test 
open/test/hotspot/jtreg/:hotspot_gc -a -XX:+UseParallelGC
   gc test suite

Thanks,
Leo