Let's split concurrent root phase into concurrent weak root and concurrent strong root phases. Bug: https://bugs.openjdk.java.net/browse/JDK-8242643 Webrev: http://cr.openjdk.java.net/~zgu/JDK-8242643/webrev.00/index.html Test: hotspot_gc_shenandoah tools/javac Thanks, -Zhengyu