hg: shenandoah/jdk9/hotspot: Shortcut reference processing when no work is available

[ashipile at redhat.com]

Changeset: eb9e7bfcd2ec
Author:    shade
Date:      2017-06-06 21:38 +0200
URL:       http://hg.openjdk.java.net/shenandoah/jdk9/hotspot/rev/eb9e7bfcd2ec

Shortcut reference processing when no work is available

! src/share/vm/gc/shared/referenceProcessor.hpp
! src/share/vm/gc/shenandoah/shenandoahConcurrentMark.cpp
! src/share/vm/gc/shenandoah/shenandoahConcurrentMark.hpp