Shenandoah in OpenJDK 17: Sub-millisecond GC pauses

Our primary motivation for the Shenandoah OpenJDK garbage collection (GC) project is to reduce garbage collection pause times. In JDK 12, we released the original Shenandoah garbage collector, which implements concurrent heap evacuation, which solved the major problem of cleaning (potentially large) heaps without stopping the application. This version was eventually backported to JDK 11. In JDK 14, we implemented concurrent class unloading, and in JDK 16, we added concurrent reference processing...